Handbook of Food Nanotechnology: Applications and Approaches [1 ed.] 0128158662, 9780128158661

Table of contents :
Cover
Handbook of Food Nanotechnology: Applications and Approaches
Copyright
Dedication
In the Name of GOD,
Contents
List of contributors
Preface
1 Fundamentals of food nanotechnology
1.1 Introduction
1.2 Application of nanotechnology in food processing
1.2.1 Nanofluid thermal processing of food products
1.2.2 Nanofiltration in the food industry
1.2.3 Nanoadsorbents and nanoporous materials for the food industry
1.2.4 Production of food nanomaterials by specialized equipment
1.3 Application of nanotechnology in food ingredients
1.3.1 Nanoemulsions and nanosized ingredients for food formulations
1.3.2 Green synthesis of metal nanoparticles by plant extracts and biopolymers
1.3.3 Nanoencapsulation of food ingredients
1.3.4 Enhancing the bioavailability of nutrients by nanodelivery systems
1.4 Application of nanotechnology for improving food quality and packaging
1.4.1 Metal nanoparticles as antimicrobial agents in food packaging
1.4.2 Nanobased aptasensors for detection of food contaminants
1.4.3 Nanoparticles/nanofibers for checking adulteration/spoilage of food products
1.4.4 Nanoencapsulated bioactive components for active food packaging
1.4.5 Reinforced nanocomposites for food packaging
1.5 Characterization and safety of food nanomaterials
1.5.1 Characterization and analysis of nanomaterials in foods
1.5.2 Safety and regulatory issues of nanomaterials in foods
1.5.3 Consumer expectations and attitudes towards nanomaterials in foods
1.6 Conclusion and further remarks
References
Section 1: Application of nanotechnology in food processing
2 Nanofluid thermal processing of food products
2.1 Introduction
2.2 Thermophysical properties of nanofluids
2.2.1 Thermal conductivity of nanofluids
2.2.2 Viscosity of nanofluids
2.2.3 Density of nanofluids
2.2.4 Specific heat capacity of nanofluids
2.3 Preparation of nanofluids
2.4 Application of nanofluids in different heat exchangers
2.4.1 Heat transfer enhancement by nanofluids
2.4.2 Pressure drop and pumping power
2.4.3 Thermal performance factor and the effectiveness of heat exchangers
2.4.4 Entropy generation and exergy efficiency
2.4.5 Agglomeration and fouling
2.5 Application of nanofluids in thermal processing of food products
2.6 Conclusion and further remarks
References
3 Nanofiltration in the food industry
Abbreviations
3.1 Introduction
3.2 Generalities of nanofiltration membranes
3.3 Application of nanofiltration in fruit juice and plant extract processing
3.4 Winemaking applications of nanofiltration
3.5 Nanofiltration in dairy processing
3.5.1 Concentration and demineralization of whey
3.5.2 Nanofiltration as an alternative for the concentration and demineralization of ultrafiltration–whey permeate
3.5.3 Lactic acid recovery by nanofiltration
3.6 Nanofiltration in the sugar industry
3.7 Role of nanofiltration in valorization of high-added value compounds from food industry wastewaters
3.8 Concluding remarks
References
4 Nanoadsorbents and nanoporous materials for the food industry
4.1 Introduction
4.2 Adsorption by different nanoadsorbents
4.2.1 Clay minerals
4.2.1.1 Structure of clay minerals
4.2.1.2 Adsorbent clays
4.2.1.3 Modification of montmorillonite
4.2.1.3.1 Organic modification
4.2.1.3.2 Inorganic modification
4.2.2 Activated carbon
4.2.2.1 Crystalline structure of active carbon and its porous structure
4.2.2.2 Porous structure of active carbon
4.2.2.3 Adsorption isotherm equations for active carbon
4.2.2.4 Active carbon applications in the food industry
4.2.3 Zero-valent iron nanoparticles
4.2.3.1 Applications of zero-valent iron nanoparticles in the food industry
4.2.3.2 Safety and toxicity of zero-valent iron nanoparticles
4.2.4 Graphite family: graphene, graphene oxide, and reduced graphene oxide
4.2.4.1 Graphene
4.2.4.2 Graphene oxide
4.2.4.3 Reduced GO
4.2.4.4 Synthesis methods
4.2.4.5 Properties and characterization
4.2.4.6 Functionalization
4.2.4.7 Graphene/ graphene oxide-based nanocomposites
4.2.4.7.1 In situ polymerization
4.2.4.7.2 Solution blending
4.2.4.7.3 Melt mixing
4.2.4.7.4 Layer-by-layer assembly
4.2.4.8 Application of graphene in the food industries
4.2.4.8.1 Applications in the food nanosensors
4.2.4.8.2 Evaluation of food composition
4.2.4.9 Toxicity of graphene and graphene oxide
4.2.4.10 Future trends
4.3 Conclusion
References
Further reading
5 Production of food nanomaterials by specialized equipment
5.1 Introduction
5.2 High-pressure techniques
5.2.1 MicrofluidizerTM homogenization process
5.2.2 High-pressure homogenizer
5.3 Sonication
5.4 Electrohydrodynamic devices
5.4.1 Solution blowing
5.5 Nano spray dryer
5.6 Micro/nanofluidic systems
5.7 Vortex fluidic device
5.8 Ball milling
5.9 Membrane technology
5.10 Conclusions and future perspectives
Acknowledgment(s)
References
Section 2: Application of nanotechnology in food ingredients
6 Nanoemulsions and nanosized ingredients for food formulations
6.1 Introduction
6.2 Nanoemulsions in food processing
6.2.1 Classification of nanoemulsions for food industries
6.2.2 Preparation methods of nanoemulsions
6.2.2.1 High-energy methods
6.2.2.2 Low-energy methods
6.2.2.3 Selection of emulsifier or coemulsifier and compatibility of the food processes
6.2.3 Applications of nanoemulsions and their effect on food
6.2.3.1 Encapsulation of active ingredients
6.2.3.2 Delivery of active ingredients
6.2.3.3 Preservation
6.2.3.4 Improvement of nutritional properties
6.2.3.5 Modifying structural or textural properties
6.2.4 Pickering nanoemulsions and stabilization of emulsified foods
6.3 Polymeric nanoparticles in food processing
6.3.1 Definitions and classification of polymeric nanoparticles
6.3.2 Preparation methods of polymeric nanoparticles
6.3.3 Characterization of polymeric nanoparticles
6.3.4 Mechanism of active delivery by polymeric nanoparticles
6.3.5 Application of polymeric nanoparticles in food processing
6.3.6 Effect of polymeric nanoparticles on physicochemical properties of food during storage
6.4 Nanofibers, nanolaminates, and nanocrystals
6.4.1 Preparation methods
6.4.1.1 Nanofibers
6.4.1.2 Nanolaminates
6.4.1.3 Nanocrystals
6.4.2 Use of nanolaminates in edible coating materials
6.4.3 Physicochemical, textural, and color changes in nanocoated foods
6.4.3.1 Effect of nanocoatings on the physicochemical properties of food
6.4.3.2 Effect of nanocoatings on textural changes
6.4.3.3 Effect of nanocoatings on color changes associated with shelf life
6.4.4 Effect of nanocrystals and other nanosize systems on color and sensorial aspects
6.5 Toxicological and normative regulatory issues of nanoparticles in food processing
6.6 Conclusions and future trends
References
7 Green synthesis of metal nanoparticles by plant extracts and biopolymers
7.1 Introduction
7.2 Metallic nanoparticles and green chemistry
7.2.1 Silver nanoparticles
7.2.2 Gold nanoparticles
7.3 Synthesis of metal nanoparticles using living organisms and biomolecules
7.3.1 Plants and algae
7.3.2 Fungi and yeasts
7.3.3 Other natural compounds
7.4 Applications of green metal nanoparticles
7.5 Conclusion
References
8 Nanoencapsulation of bioactive food ingredients
8.1 Introduction
8.2 A brief overview of bioactive ingredients
8.2.1 Polyphenols
8.2.1.1 Classification and the structure
8.2.1.2 Polyphenols in food
8.2.1.3 Health benefits and stabilities
8.2.2 Carotenoids
8.2.2.1 Classification and the structure
8.2.2.2 Carotenoids in food
8.2.2.3 Health benefits and stabilities
8.2.3 Vitamins
8.2.3.1 Classification and the structure
8.2.3.2 Vitamins in food
8.2.3.3 Health benefits and stabilities
8.2.4 Minerals
8.2.4.1 Classification and the structure
8.2.4.2 Minerals in food
8.2.4.3 Health benefits and stabilities
8.2.5 Essential oils
8.2.5.1 Classification and the structure
8.2.5.2 Essential oils in food
8.2.5.3 Health benefits and stabilities
8.3 Encapsulation methods for nanodelivery of bioactive compounds
8.3.1 Nanoemulsification
8.3.2 Nano spray drying
8.3.3 Coacervation
8.3.4 Nanoliposomes and niosomes
8.3.5 Cubosomes and hexosomes
8.3.6 Solid lipid nanoparticles/nanocarriers
8.3.7 Nanostructured lipid carriers
8.3.8 Complexation/conjugation with proteins
8.3.9 Inclusion complexation within cyclodextrins and amylose nanohelices
8.3.10 Nanoprecipitation (solvent displacement)
8.4 Carrier materials used for nanoencapsulation of bioactive compounds
8.4.1 Proteins
8.4.2 Polysaccharides
8.4.3 Lipids
8.4.4 Cyclodextrins
8.4.5 Surfactants
8.4.6 Combinations of different nanocarrier materials
8.5 Challenges toward nanodelivery of bioactive compounds in functional foods
8.6 Concluding remarks and future direction
References
Further reading
9 Enhancing the bioavailability of nutrients by nanodelivery systems
9.1 Introduction
9.2 Desolvation/nanoprecipitation/solvent displacement
9.3 Complex coacervation
9.4 Layer-by-layer assembly
9.4.1 Spherical nanoparticle formation through layer-by-layer assembly
9.4.2 Nanotubular formation through layer-by-layer assembly
9.5 Nano/microemulsions
9.6 Conclusion
References
Section 3: Application of nanotechnology for improving food quality and packaging
10 Metal nanoparticles as antimicrobial agents in food packaging
10.1 Introduction to polymers/biopolymers in food packaging
10.1.1 Solid-state additives in food packaging
10.1.2 Metal nanoparticles in food packaging
10.2 Nanoscale metal oxides in antimicrobial packaging
10.2.1 Copper oxide-based nanomaterials
10.2.2 Titanium oxide-based nanomaterials
10.2.3 Zinc oxide-based nanomaterials
10.2.4 Magnesium oxide-based nanoparticles
10.2.5 Gold and silver nanoparticles
10.3 Layered nonmetal nanomaterials
10.3.1 Silicon dioxide nanoparticles
10.3.2 Montmorillonite nanoclay
10.4 The influence of metal nanoparticles on different properties of food packaging materials
10.4.1 Barrier properties
10.4.2 Mechanical properties
10.4.3 Thermal properties
10.4.4 Morphology
10.4.5 Reactions/interactions
10.5 Antimicrobial influence of metal nanoparticles in food packaging materials
10.5.1 The impact of metal NPs on G+/− bacteria
10.5.2 Fungi (molds/yeasts)
10.5.3 Parasites/viruses
10.6 Toxicological aspects, safety, and migration of metal nanoparticles into food products
10.6.1 The safety issues of human contact to nanoparticles
10.6.2 Regulation for nanomaterials associated with food contact materials
10.6.2.1 European Community
10.6.2.2 US Food and Drug Administration
10.7 Conclusion and further remarks
Acknowledgment
References
11 Nanobiosensors for food analysis
11.1 Introduction
11.2 Nanomaterials and other related tools used to construct biosensors
11.2.1 Metallic nanoparticles and semiconductor nanomaterials
11.2.2 Carbon nanomaterials
11.2.3 Magnetic nanoparticles
11.3 Bioreceptors
11.3.1 Surface functionalization of nanomaterials with bioreceptors
11.4 Transduction mechanisms
11.5 Electrochemical nanobiosensors for food safety and control
11.5.1 Electrochemical biosensing with integrated nanomaterials and hybrid nanostructures
11.5.1.1 Metallic nanoparticles
11.5.1.2 Carbon and semiconductor nanomaterials
11.5.2 Electrochemical biosensing with nanopore membranes
11.5.3 Field-effect transistor-based biosensors
11.6 Optical nanobiosensors for food safety and control
11.6.1 Colorimetric biosensors
11.6.2 Fluorescent biosensors
11.6.3 Localized surface plasmon resonance-based biosensors
11.6.4 Surface-enhanced Raman scattering-based biosensors
11.7 Nanomechanical biosensors for food safety and control
11.7.1 Scanning probe microscopy-based biosensors
11.7.2 Microcantilever-based biosensors
11.8 Micromotor-based (bio)sensing approaches
11.9 Conclusions and future directions
Acknowledgements
References
12 Nanoparticles/nanofibers for checking adulteration/spoilage of food products
12.1 Introduction
12.2 Metal and metal oxide nanoparticles-based nanosensors
12.2.1 Gold nanoparticles
12.2.2 Silver nanoparticles
12.3 Carbon nanomaterial-based nanosensors
12.3.1 Carbon nanotubes
12.3.2 Graphene and its derivatives
12.3.3 Carbon nanofibers
12.4 Magnetic nanoparticles-based nanosensors
12.5 Nanofiber-based nanosensors
12.6 Conclusion
References
13 Nanoencapsulated bioactive components for active food packaging
Abbreviations
13.1 Introduction
13.2 Bioactive compounds
13.3 Nanoencapsulation of bioactive ingredients
13.4 Different bioactive-loaded nanocarriers applied in active food packaging
13.4.1 Phenolic compounds
13.4.2 Carotenoids
13.4.3 Essential oils
13.4.4 Peptides and antimicrobial agents
13.4.5 Vitamins
13.5 Effects of bioactive-loaded nanocarriers on packaging properties
13.5.1 Effect on antimicrobial properties
13.5.2 Effect on antioxidant properties
13.5.3 Effect on mechanical properties
13.5.4 Effect on barrier properties
13.6 Controlled release and migration of bioactive compounds from active food packaging
13.7 Application of active packaging loaded with nanoencapsulated bioactives in various food products
13.8 Perspective and future trends
References
14 Reinforced nanocomposites for food packaging
14.1 Introduction
14.2 Inorganic nanomaterials used in nanocomposites for food packaging
14.2.1 Oxides used in nanocomposites
14.2.1.1 Zinc oxide
14.2.1.2 Titanium dioxide
14.2.1.3 Silicon dioxide (silica)
14.2.1.4 Other oxides
14.2.2 Nanoclays as polymer reinforcement fillers
14.3 Nanocellulose-based nanocomposites for food packaging
14.3.1 Nanocellulose production from agroindustrial biomass
14.3.1.1 Case study: production of nanocellulose from soybean straw by enzymatic method
14.3.2 Nanocellulose as a reinforcement in biodegradable polymers
14.3.2.1 Nanocellulose–polylactic acid composites
14.3.2.2 Nanocellulose–starch composites
14.3.2.3 Nanocellulose–chitosan composites
14.3.2.4 Nanocellulose–polycaprolactone composites
14.3.2.5 Nanocellulose–alginate composites
14.3.2.6 Nanocellulose composites with proteins
14.4 Other bionanomaterials used as reinforcement fillers in food packaging
14.5 Conclusion and future trends
References
Section 4: Characterization and safety of food nanomaterials
15 Characterization and analysis of nanomaterials in foods
15.1 Introduction
15.2 Morphological and microstructural analysis of nanomaterials in foods
15.2.1 Optical microscopy
15.2.1.1 Bright field microscopy
15.2.1.2 Dark field microscopy
15.2.1.3 Ultramicroscopy
15.2.1.4 Polarizing microscopy
15.2.1.5 Fluorescence microscopy
15.2.1.6 Laser scattering confocal microscopy
15.2.2 Electron microscopy
15.2.2.1 Scanning electron microscopy
15.2.2.2 Transmission electron microscopy
15.2.2.3 Analysis of isolated food nanoparticles by electron microscopy
15.2.2.4 Analysis of nanoparticles by environmental scanning electron microscopy
15.2.3 Atomic force microscopy
15.3 Analysis of particle size and size distribution of nanomaterials in foods
15.3.1 Impacts of nanoparticle shape and size on food quality and safety
15.3.1.1 Size versus stability
15.3.1.2 Size versus appearance
15.3.1.3 Size versus bioavailability
15.3.1.4 Size and shape versus toxicity
15.3.2 Measurement of nanoparticle size by light scattering techniques
15.3.2.1 Static light scattering
15.3.2.2 Dynamic light scattering
15.3.3 Nanoparticle tracking analysis
15.3.4 Small-angle X-ray scattering
15.3.5 Differential centrifugal sedimentation
15.4 Surface charge and zeta potential analysis of nanomaterials in foods
15.4.1 Surface charge of nanomaterials in foods
15.4.2 Measurement of zeta potential (ζ)
15.5 Analysis of crystallinity and phase transition in food nanomaterials
15.5.1 Crystallinity and phase transition in lipid-based nanoparticles
15.5.2 Glass transition temperature (Tg) in polymer-based nanoparticles
15.5.3 Measurement of crystallinity and phase transition in food nanomaterials
15.5.3.1 X-ray diffraction
15.5.3.2 Differential scanning calorimetry
15.6 Mechanical characteristics and analysis techniques of nanomaterials in food
15.6.1 Impacts of mechanical properties of food nanoparticles on food quality
15.6.2 Instrumental mechanical assessment of liquid and soft nanoparticles in food
15.6.2.1 Oscillatory tests; viscoelasticity of food materials
15.6.2.2 Colloidal probe atomic force microscopy
15.6.2.3 Micropipette technique
15.6.2.4 Osmotic pressure method
15.6.2.5 Large deformation measurements
15.7 Future trends
Acknowledgment
References
16 Safety and regulatory issues of nanomaterials in foods
16.1 Introduction
16.2 Nanofood market
16.3 Risk assessment of nanostructures used in foods
16.3.1 Detection and characterization of nanoparticles in foods
16.3.2 Exposure routes to food nanoingredients
16.3.2.1 Dermal exposure
16.3.2.2 Inhalation
16.3.2.3 Ingestion
16.3.3 Toxicological end points and outcomes
16.3.3.1 Toxicity of organic nanoparticles
16.3.3.2 Toxicity of inorganic nanoparticles
16.3.4 Approaches for risk assessment of nanoparticles
16.4 Public perception and concerns
16.5 Regulations in using nanomaterials for foods
16.5.1 Regulatory aspects of nanoparticles
16.5.2 Current legislations
16.5.2.1 The United States
16.5.2.2 Europe
16.5.2.3 Canada
16.5.2.4 Australia and New Zealand
16.5.2.5 NonEU countries (Switzerland, Turkey, and Russia)
16.5.2.6 Asia
16.5.2.7 South Africa
16.5.2.8 South America
16.6 Conclusion
References
Further reading
17 Consumer expectations and attitudes toward nanomaterials in foods
17.1 Nanotechnology application in food industry
17.1.1 Benefits of nanotechnology in food packaging
17.1.2 Potential risks of nanotechnology applications
17.2 Consumer attitudes toward nanotechnology in food
17.2.1 Consumer acceptance of food nanotechnology
17.2.2 Factors affecting consumer acceptance of food nanotechnology
17.2.2.1 General attitudes toward new technology
17.2.2.2 Environmental and health concern
17.2.2.3 Preference for prolonging food shelf life
17.2.2.4 Trust in institution
17.2.2.5 Reliance on governmental regulation
17.3 Case study—consumer preference and information provision in nanopackaged food
17.3.1 Theoretical framework and proposed hypothesis
17.3.2 Research material and methodology
17.3.2.1 Auction experiment
17.3.2.2 Products
17.3.2.3 Participants
17.3.2.4 Auction design
17.3.2.5 Auction procedure
17.3.2.6 Structural equation model
17.3.3 Analysis results
17.3.3.1 Demographics and bidding average
17.3.3.2 Measurement statistics
17.3.3.3 Model estimates
17.3.4 Discussion
17.4 Conclusion and implications
References
Index
Back Cover

Citation preview

Handbook of Food Nanotechnology

Two poems by Rudaki

Mausoleum of Rudaki in the city of Pandzhrudak, Tajikistan Abu¯’Abd Alla¯h Ja’far ibn Muhammad al-Ru¯dhakı¯ (c. 859 c. 940/941), better known as Rudaki (‫)ﺭﻭﺩﮐﯽ‬, and also known˙ as “Adam of Poets” (‫)ﺁﺩﻡﺍﻟﺸﻌﺮﺍ‬, was a Persian poet, regarded as the first great literary genius of the Modern Persian language (father of the Persian poem). Rudaki was born in Rudak (Khorasan), a village located in the Samanid Empire which is now Panjakent, located in Tajikistan. Even though most of his biographers assert that he was completely blind, some early biographers are silent about this, or do not mention him as having been born blind. Rudaki composed poems in the modern Persian alphabet and is considered a founder of classical Persian literature. His poetry contains many of the oldest genres of Persian poetry including the “quatrain”; however, only a small percentage of his extensive poetry has survived. As it seems, Rudaki was a musician, poet and declaimer/reciter, and copyist.

Handbook of Food Nanotechnology Applications and Approaches

Edited by

Seid Mahdi Jafari Department of Food Materials and Process Design Engineering, Faculty of Food Science and Technology, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1650, San Diego, CA 92101, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom Copyright © 2020 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 978-0-12-815866-1 For Information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Charlotte Cockle Acquisitions Editor: Nina Rosa Bandeira Editorial Project Manager: Laura Okidi Production Project Manager: R. Vijay Bharath Cover Designer: Mark Rogers Typeset by MPS Limited, Chennai, India

Dedication To: Professor Mahmoud Hessabi (February 23, 1903 – September 3, 1992): “Father of Academic Physics in Iran”.

Prof. Hessabi was born in Tehran, but was originally from Tafresh (Markazi Province, Iran). His father took his family to Beirut, where he received his primary and secondary education in French and American Schools in Beirut. He graduated in civil engineering in 1922 from the American University of Beirut and then moved to Paris and obtained a bachelor’s degree in electrical engineering from the E´cole Supe´rieure d’E´lectricite´ in 1925. Later he worked as an electrical engineer for the Paris railroad system. In the meantime, he continued his studies in physics at ParisSorbonne University and obtained his doctorate in 1927 and returned to Iran. Prof. Hessabi was fluent in English, French, and Arabic, and a self-taught German speaker. During his career, he held important scientific and cultural positions including the education portfolio in 1951 52 in the government of Mohammad Mosaddeq. He founded many cultural and scientific centers in Iran, such as the Civil Engineering School and the Teacher’s College (1928), the first Iranian Meteorological Station (1931), the first radiology center (1931), University of Tehran (1934), the Telecommunication Center of Asad Abad in Hamedan (1959) and the Geophysical Center of University of Tehran in 1961.

In the Name of GOD, The Compassionate, The Merciful

Contents

List of contributors Preface 1

Fundamentals of food nanotechnology Elham Assadpour, Cristian Dima and Seid Mahdi Jafari 1.1 Introduction 1.2 Application of nanotechnology in food processing 1.3 Application of nanotechnology in food ingredients 1.4 Application of nanotechnology for improving food quality and packaging 1.5 Characterization and safety of food nanomaterials 1.6 Conclusion and further remarks References

Section 1 2

3

Application of nanotechnology in food processing

Nanofluid thermal processing of food products Saeed Salari and Seid Mahdi Jafari 2.1 Introduction 2.2 Thermophysical properties of nanofluids 2.3 Preparation of nanofluids 2.4 Application of nanofluids in different heat exchangers 2.5 Application of nanofluids in thermal processing of food products 2.6 Conclusion and further remarks References Nanofiltration in the food industry Roberto Castro-Mun~oz and Emilia Gontarek Abbreviations 3.1 Introduction 3.2 Generalities of nanofiltration membranes 3.3 Application of nanofiltration in fruit juice and plant extract processing 3.4 Winemaking applications of nanofiltration 3.5 Nanofiltration in dairy processing 3.6 Nanofiltration in the sugar industry

xv xix 1 1 2 8 13 20 25 25

37 39 39 40 44 45 56 58 61 73 73 73 74 77 87 91 94

x

Contents

3.7

Role of nanofiltration in valorization of high-added value compounds from food industry wastewaters 96 3.8 Concluding remarks 99 References 100 4

5

Nanoadsorbents and nanoporous materials for the food industry Sara Arabmofrad, Mahsa Bagheri, Hamid Rajabi and Seid Mahdi Jafari 4.1 Introduction 4.2 Adsorption by different nanoadsorbents 4.3 Conclusion References Further reading

107

Production of food nanomaterials by specialized equipment Ali Sedaghat Doost, Maryam Nikbakht Nasrabadi, Anja Sadˇzak and Paul Van der Meeren 5.1 Introduction 5.2 High-pressure techniques 5.3 Sonication 5.4 Electrohydrodynamic devices 5.5 Nano spray dryer 5.6 Micro/nanofluidic systems 5.7 Vortex fluidic device 5.8 Ball milling 5.9 Membrane technology 5.10 Conclusions and future perspectives Acknowledgment(s) References

161

Section 2 6

107 109 144 145 158

161 162 168 171 177 181 184 186 190 193 193 193

Application of nanotechnology in food ingredients 205

Nanoemulsions and nanosized ingredients for food formulations 207 M.L. Zambrano-Zaragoza, D. Quintanar-Guerrero, N. Mendoza-Mun˜oz and G. Leyva-Go´mez 6.1 Introduction 207 6.2 Nanoemulsions in food processing 209 6.3 Polymeric nanoparticles in food processing 217 6.4 Nanofibers, nanolaminates, and nanocrystals 230 6.5 Toxicological and normative regulatory issues of nanoparticles in food processing 238 6.6 Conclusions and future trends 242 References 244

Contents

7

8

9

Green synthesis of metal nanoparticles by plant extracts and biopolymers Lucas F.B. Nogueira, E´der J. Guidelli, Seid Mahdi Jafari and Ana Paula Ramos 7.1 Introduction 7.2 Metallic nanoparticles and green chemistry 7.3 Synthesis of metal nanoparticles using living organisms and biomolecules 7.4 Applications of green metal nanoparticles 7.5 Conclusion References Nanoencapsulation of bioactive food ingredients Ali Rashidinejad and Seid Mahdi Jafari 8.1 Introduction 8.2 A brief overview of bioactive ingredients 8.3 Encapsulation methods for nanodelivery of bioactive compounds 8.4 Carrier materials used for nanoencapsulation of bioactive compounds 8.5 Challenges toward nanodelivery of bioactive compounds in functional foods 8.6 Concluding remarks and future direction References Further reading Enhancing the bioavailability of nutrients by nanodelivery systems H. Turasan and J.L. Kokini 9.1 Introduction 9.2 Desolvation/nanoprecipitation/solvent displacement 9.3 Complex coacervation 9.4 Layer-by-layer assembly 9.5 Nano/microemulsions 9.6 Conclusion References

xi

257

257 259 263 271 274 274 279 279 280 294 318 325 326 326 344 345 345 346 351 358 365 372 372

Section 3 Application of nanotechnology for improving food quality and packaging 377 10

Metal nanoparticles as antimicrobial agents in food packaging Shima Jafarzadeh, Ali Salehabadi and Seid Mahdi Jafari 10.1 Introduction to polymers/biopolymers in food packaging 10.2 Nanoscale metal oxides in antimicrobial packaging 10.3 Layered nonmetal nanomaterials

379 379 383 390

xii

Contents

10.4

The influence of metal nanoparticles on different properties of food packaging materials 393 10.5 Antimicrobial influence of metal nanoparticles in food packaging materials 400 10.6 Toxicological aspects, safety, and migration of metal nanoparticles into food products 404 10.7 Conclusion and further remarks 405 Acknowledgment 406 References 406 11

Nanobiosensors for food analysis 415 Beatriz Jurado-Sa´nchez, Marı´a Moreno-Guzma´n, Juan V. Perales-Rondon and Alberto Escarpa 11.1 Introduction 415 11.2 Nanomaterials and other related tools used to construct biosensors 415 11.3 Bioreceptors 419 11.4 Transduction mechanisms 422 11.5 Electrochemical nanobiosensors for food safety and control 423 11.6 Optical nanobiosensors for food safety and control 432 11.7 Nanomechanical biosensors for food safety and control 442 11.8 Micromotor-based (bio)sensing approaches 444 11.9 Conclusions and future directions 446 Acknowledgements 446 References 447

12

Nanoparticles/nanofibers for checking adulteration/spoilage of food products Zahra Mohammadi and Seid Mahdi Jafari 12.1 Introduction 12.2 Metal and metal oxide nanoparticles-based nanosensors 12.3 Carbon nanomaterial-based nanosensors 12.4 Magnetic nanoparticles-based nanosensors 12.5 Nanofiber-based nanosensors 12.6 Conclusion References

13

Nanoencapsulated bioactive components for active food packaging Arezou Khezerlou and Seid Mahdi Jafari Abbreviations 13.1 Introduction 13.2 Bioactive compounds 13.3 Nanoencapsulation of bioactive ingredients 13.4 Different bioactive-loaded nanocarriers applied in active food packaging 13.5 Effects of bioactive-loaded nanocarriers on packaging properties

459 459 460 471 481 483 485 486 493 493 493 494 496 497 503

Contents

xiii

13.6

Controlled release and migration of bioactive compounds from active food packaging 513 13.7 Application of active packaging loaded with nanoencapsulated bioactives in various food products 518 13.8 Perspective and future trends 522 References 522 14

Reinforced nanocomposites for food packaging Milena Martelli-Tosi, Bruno Stefani Esposto, Natalia Cristina da Silva, Delia Rita Tapia-Bla´cido and Seid Mahdi Jafari 14.1 Introduction 14.2 Inorganic nanomaterials used in nanocomposites for food packaging 14.3 Nanocellulose-based nanocomposites for food packaging 14.4 Other bionanomaterials used as reinforcement fillers in food packaging 14.5 Conclusion and future trends References

533

533 534 543 560 560 561

Section 4 Characterization and safety of food nanomaterials

575

15

Characterization and analysis of nanomaterials in foods Cristian Dima, Elham Assadpour, Stefan Dima and Seid Mahdi Jafari 15.1 Introduction 15.2 Morphological and microstructural analysis of nanomaterials in foods 15.3 Analysis of particle size and size distribution of nanomaterials in foods 15.4 Surface charge and zeta potential analysis of nanomaterials in foods 15.5 Analysis of crystallinity and phase transition in food nanomaterials 15.6 Mechanical characteristics and analysis techniques of nanomaterials in food 15.7 Future trends Acknowledgment References

577

Safety and regulatory issues of nanomaterials in foods O€ zgu€r Tarhan 16.1 Introduction 16.2 Nanofood market 16.3 Risk assessment of nanostructures used in foods

655

16

577 586 604 617 621 633 639 640 640

655 657 658

xiv

17

Contents

16.4 Public perception and concerns 16.5 Regulations in using nanomaterials for foods 16.6 Conclusion References Further reading

678 680 690 691 703

Consumer expectations and attitudes toward nanomaterials in foods Shuoli Zhao, Chengyan Yue and Jennifer Kuzma 17.1 Nanotechnology application in food industry 17.2 Consumer attitudes toward nanotechnology in food 17.3 Case study—consumer preference and information provision in nanopackaged food 17.4 Conclusion and implications References

705

Index

705 707 710 727 728 735

List of contributors

Sara Arabmofrad Department of Food Materials & Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Elham Assadpour Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Mahsa Bagheri Department of Food Materials & Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Roberto Castro-Mun˜oz Tecnolo´gico de Monterrey, Toluca de Lerdo, Me´xico Natalia Cristina da Silva Departamento de Engenharia de Alimentos, Faculdade de Zootecnia e Engenharia de Alimentos, Universidade de Sa˜o Paulo, Sa˜o Paulo, Brazil Cristian Dima Faculty of Food Science and Engineering, “Dunarea de Jos” University of Galati, Galati, Romania Stefan Dima Faculty of Science and Environment, “Dunarea de Jos” University of Galati, Galati, Romania Alberto Escarpa Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, University of Alcala, Madrid, Spain; Chemical Research Institute “Andre´s M. del Rı´o”, University of Alcala, Madrid, Spain Bruno Stefani Esposto Chemical Department, Faculty of Philosophy, Sciences and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Sa˜o Paulo, Brazil Emilia Gontarek Gdansk University of Technology, Gdansk, Poland E´der J. Guidelli Department of Physics, Faculty of Philosophy, Science and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Ribeira˜o Preto/SP, Brazil Seid Mahdi Jafari Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

xvi

List of contributors

Shima Jafarzadeh Food Biopolymer Research Group, Food Technology Division, School of Industrial Technology, Universiti Sains Malaysia, Minden, Malaysia Beatriz Jurado-Sa´nchez Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, University of Alcala, Madrid, Spain; Chemical Research Institute “Andre´s M. del Rı´o”, University of Alcala, Madrid, Spain Arezou Khezerlou Department of Food Science and Technology, Faculty of Nutrition and Food Sciences, Tabriz University of Medical Sciences, Tabriz, Iran J.L. Kokini Department of Food Science, Purdue University, West Lafayette, IN, United States Jennifer Kuzma School of Public and International Affairs, North Carolina State University, Raleigh, NC, United States G. Leyva-Go´mez Departamento de Farmacia, Facultad de Quı´mica, Universidad Nacional Auto´noma de Me´xico, Mexico City, Mexico Milena Martelli-Tosi Departamento de Engenharia de Alimentos, Faculdade de Zootecnia e Engenharia de Alimentos, Universidade de Sa˜o Paulo, Sa˜o Paulo, Brazil N. Mendoza-Mun˜oz Laboratorio de Farmacia, Facultad de Ciencias Quı´micas, Universidad de Colima, Colima, Mexico Zahra Mohammadi Department of Food Materials & Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Marı´a Moreno-Guzma´n Department of Chemistry in Pharmaceutical Sciences, Analytical Chemistry, Faculty of Pharmacy, Universidad Complutense de Madrid, Madrid, Spain Maryam Nikbakht Nasrabadi Particle and Interfacial Technology Group (PaInT), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Gent, Belgium Lucas F.B. Nogueira Department of Chemistry, Faculty of Philosophy, Science and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Ribeira˜o Preto/SP, Brazil Juan V. Perales-Rondon Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, University of Alcala, Madrid, Spain D. Quintanar-Guerrero Laboratorio de Posgrado en Tecnologı´a Farmace´utica, FESCuautitlan. Universidad Nacional Auto´noma de Me´xico, Cuautitla´n Izcalli, Mexico

List of contributors

xvii

Hamid Rajabi Department of Food Materials & Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Ana Paula Ramos Department of Chemistry, Faculty of Philosophy, Science and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Ribeira˜o Preto/SP, Brazil Ali Rashidinejad Riddet Institute Centre of Research Excellence, Massey University, Palmerston North, New Zealand Anja Sadˇzak Laboratory for Biocolloids and Surface Chemistry, Division of Physical Chemistry, Ruðer Boˇskovi´c Institute, Zagreb, Croatia Saeed Salari Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Ali Salehabadi Environmental Technology Division, School of Industrial Technology, Universiti Sains Malaysia, Minden, Malaysia Ali Sedaghat Doost Particle and Interfacial Technology Group (PaInT), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Gent, Belgium Delia Rita Tapia-Bla´cido Chemical Department, Faculty of Philosophy, Sciences and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Sa˜o Paulo, Brazil ¨ zgu¨r Tarhan Department of Food Engineering, Engineering Faculty, U¸sak O University, U¸sak, Turkey H. Turasan Department of Food Science, Purdue University, West Lafayette, IN, United States Paul Van der Meeren Particle and Interfacial Technology Group (PaInT), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Gent, Belgium Chengyan Yue Department of Applied Economics, Department of Horticultural Science, University of Minnesota, Saint Paul, MN, United States M.L. Zambrano-Zaragoza Laboratorio de Procesos de Transformacio´n y Tecnologı´as Emergentes en Alimentos, FES-Cuautitla´n. Universidad Nacional Auto´noma de Me´xico, Cuautitla´n Izcalli, Mexico Shuoli Zhao Department of Agricultural Economics, University of Kentucky, Lexington, KY, United States

Preface

It has been estimated that by 2020, the global economic impact of nanotechnologies will be at least US$ 3 trillion. The continuously increasing market size of nanotechnology products of the food industry is estimated to reach approximately US$ 15 billion by 2020. Food-grade nanomaterials are used in food processing as food additives and nanostructured ingredients; in the manufacture of smart/active packaging and reinforced nanocomposites; nutraceutical protection and the increase of their bioavailability through various nanocarriers and nanoencapsulation techniques; producing biosensors/nanosensors for the detection of toxins, pathogens, and pesticides and even food spoilage and adulteration; and for improving energy efficiency through applying nanofluids, nanoadsorbents, nanofiltration, etc. Knowing the characteristics and safety of nanomaterials in foods is also an important requirement for food producers because they influence the food quality and safety. That is why, lately, more and more research has been focusing on the development of new techniques for analyzing and controlling nanomaterials and evaluating their toxicological consequences. To address these issues, the Handbook of Food Nanotechnology: Applications and Approaches has been defined and written to present novel applications of nanotechnology in the food area and recent developments in this field. This book covers innovative and applied research in all disciplines of food nanotechnology, from nanostructured ingredients to the characterization, safety, and consumer expectations of food nanomaterials. All chapters emphasize original results relating to experimentation, instrument basics, analysis, and/or the applications of nanoscience and nanotechnology for food purposes. After presenting a brief overview and fundamentals of food nanotechnology in Chapter 1, Fundamentals of Food Nanotechnology, the application of nanotechnology in food processing has been covered in Section 1, including nanofluid thermal processing of food products (Chapter 2: Nanofluid Thermal Processing of Food Products), nanofiltration in the food industry (Chapter 3: Nanofiltration in the Food Industry), nanoadsorbents and nanoporous materials for the food industry (Chapter 4: Nanoadsorbents and Nanoporous Materials for the Food Industry), and production of food nanomaterials by specialized equipment (Chapter 5: Production of Food Nanomaterials by Specialized Equipment). Section 2 has been devoted to the application of nanotechnology in food ingredients, including nanoemulsions and nanosized ingredients for food formulations (Chapter 6: Nanoemulsions and Nanosized Ingredients for Food Formulationst), green synthesis of metal nanoparticles by plant extracts and biopolymers (Chapter 7: Green Synthesis of Metal Nanoparticles by Plant Extracts and Biopolymers), nanoencapsulation of food ingredients (Chapter 8:

xx

Preface

Nanoencapsulation of Bioactive Food Ingredients), and enhancing the bioavailability of nutrients by nanodelivery systems (Chapter 9: Enhancing the Bioavailability of Nutrients by Nanodelivery Systems). Another important application of food nanotechnology, i.e., improving food quality and packaging by nanomaterials has been explained in Section 3, including metal nanoparticles as antimicrobial agents in food packaging (Chapter 10: Metal Nanoparticles as Antimicrobial Agents in Food Packaging), nanobased aptasensors for the detection of food contaminants (Chapter 11: Nanobiosensors for Food Analysis), nanoparticles/nanofibers for checking adulteration/spoilage of food products (Chapter 12: Nanoparticles/ Nanofibers for Checking Adulteration/Spoilage of Food Products), nanoencapsulated bioactive components for active food packaging (Chapter 13: Nanoencapsulated Bioactive Components for Active Food Packaging), and reinforced nanocomposites for food packaging (Chapter 14: Reinforced Nanocomposites for Food Packaging). Finally, Section 4 deals with the characterization and safety of food nanomaterials, such as characterization and analysis of nanomaterials in foods (Chapter 15: Characterization and Analysis of Nanomaterials in Foods), safety and regulatory issues of nanomaterials in foods (Chapter 16: Safety and Regulatory Issues of Nanomaterials in Foods), and consumer expectations and attitudes toward nanomaterials in foods (Chapter 17: Consumer Expectations and Attitudes toward Nanomaterials in Foods). All who are engaged in the production of food ingredients, functional food products, food processing, food microbiology/toxicology, and the food packaging industry worldwide can use this book as either a textbook or a reference that will give the readers a good knowledge of the recent and potential applications of nanotechnology in different fields of the food industry. We hope this book will stimulate further research in this rapidly growing area, and will enable scientists to get familiar with specialized and innovative materials/processes/properties by the emergence of food nanotechnology. I really appreciate the great cooperation of all authors of the chapters for taking time from their busy schedules to contribute to this project. Also, it is necessary to express my sincere thanks to all the editorial staff at Elsevier for their help and support throughout the project. Finally, special acknowledgment goes to my family for their understanding and encouragement during the editing of this great project. Seid Mahdi Jafari November, 2019 Gorgan, Iran

Fundamentals of food nanotechnology

1

Elham Assadpour1, Cristian Dima2 and Seid Mahdi Jafari1 1 Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran, 2Faculty of Food Science and Engineering, “Dunarea de Jos” University of Galati, Galati, Romania

1.1

Introduction

After almost 50 years since its inception, nanotechnology is the science able to revolutionize the main fields of human civilization: industry, culture, and society. The results of research in the field of nanotechnology have led to the development of a new class of materials called “nanomaterials,” whose special properties have led to improvements in the human lifestyle, for example, by diversifying communication systems, improving disease investigation and treatment techniques, and developing food quality and safety (Jafari & McClements, 2017). New concepts have appeared, such as “nanosciences,” “nanomedicine,” and “nanofood,” dealing with the use of nanotechnology principles in ensuring human health on the one hand, and on the other hand the identification of potential risks as a result of deliberate or nondeliberate presence of nanomaterials in foods, drugs, or the environment. Since the term “nanotechnology” was first used by Norio Taniguchi in 1974 to date, important changes have occurred in research directions and strategies (Jeevanandam, Barhoum, Chan, Dufresne, & Danquah, 2018). It has been estimated that by 2020, the global economic impact of nanotechnologies will be at least $3 trillion (Roco, Mirkin, & Hersam, 2011). International organizations have also published relevant standards and guidelines, like the US Food and Drug Administration (USFDA), International Organization for Standardization (ISO), European Food Safety Authority (EFSA), etc., providing the legal framework for the use of nanotechnologies and nanomaterials, in an attempt to define the specific terminology of this new science (Jafari, Katouzian, & Akhavan, 2017). As an example, ISO, by the Technical Committee on Nanotechnologies provided the following definition for nanotechnology: Understanding and control of matter and processes at the nanoscale, typically, but not exclusively, below 100 nanometres in one or more dimensions where the onset of size-dependent phenomena usually enables novel applications, where one nanometer is one thousand millionth of a meter. (6-ISO/TC 229, 2014)

In agreement with the recommendation of the European Commission (EC), a “nanomaterial” is considered to be “a natural, incidental or manufactured material Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00001-7 © 2020 Elsevier Inc. All rights reserved.

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Handbook of Food Nanotechnology

containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions are in the size range 1 100 nm” (EFSA, 2016; Peters, Herrera-Rivera, Bouwmeester, Weigel, & Marvin, 2014). The numerous nanomaterials handled in nanotechnologies should be classified according to various criteria (Table 1.1). The commonest classifications of nanomaterials are based on their origin (natural and synthetic nanomaterials), and their chemical composition (inorganic and organic nanomaterials) (Jeevanandam et al., 2018). Foods contain both natural nanomaterials, like casein micelles in milk or certain organelles found in plant or animal cells (DNA, ribosomes, enzymes, antibodies), and engineered nanomaterials (ENMs), which are deliberately added in order to increase food quality and safety, such as nanoparticle-based delivery systems. Other nanoparticles do not directly enter foods, but may come into contact with foods as a result of their inclusion in packaging or nanosensors. According to the EFSA definition, nanomaterials used in the agrifood sector are as follows: nanostructured materials, nanoparticles and their aggregation at the nanoscale, nanoencapsulates, and nanoproducts. These nanomaterials are used in agriculture as nanocarriers to deliver fertilizers, pesticides, herbicides, and plant growth factors. Nanomaterials used in the food industry are approved by USFDA and the EC and these are acknowledged as Generally Recognized as Safe (GRAS). Thus EFSA inventoried 55 types of nanomaterials used in the agro-sector, out of which the most widely researched have been nanoencapsulates, nanometals (silver, iron, gold, aluminum, etc.), nanometal oxides (titanium dioxide, zinc oxide, silicon dioxide, etc.), nanocomposites, and nanosalts (Peters et al., 2014). Food-grade nanomaterials are used in food processing as food additives, in the manufacture of smart packaging, for nutraceutical protection and the increase of their bioavailability, and in producing biosensors for detection of toxins, pathogens, and pesticides (Dasgupta et al., 2015; He, Deng, & Hwang, 2019). A brief overview of nanotechnology applications in various fields of the food industry is discussed in the following sections and more details and explanations have been provided in the next chapters of this book.

1.2

Application of nanotechnology in food processing

1.2.1 Nanofluid thermal processing of food products Due to the high prices of energy, improving the performance of heat exchangers, and reducing their sizes is of great interest in various industries. In this context, one of the challenges that industries should be dealing with is the low thermal conductivity of conventional heat transfer fluids resulting in the poor transfer of heat (Sheikholeslami & Ganji, 2017). According to the formula of the heat transfer rate by convection (q 5 hAΔT), any improvement in the performance of heat transfer devices can be achieved through extending the surface area of heat transfer,

Table 1.1 Classification of nanomaterials. Classification criterion

NM classes

Characteristics

Examples

Origin (source)

Natural NMs

Are produced in nature through biochemical and biological processes in organisms, insects, plants, animals, and human bodies Are synthesized by physical, chemical, biological, or hybrid methods Are naturally occurring nanomaterials or are produced incidentally as a by-product of industrial processes Are mineral salts, carbon, metal, and metal oxide NPs

Proteins, polysaccharides, DNA, ribosomes, enzymes, antibodies, etc.

Synthetic (engineered) NMs Incidental NMs

Chemical composition

Dimensions

NMs, Nanomaterials.

Inorganic NMs

Organic NMs

Occur through physical and chemical interactions between organic component molecules

Composite NMs

One-dimensional NMs Two-dimensional NMs

Are obtained by combining several organic and inorganic materials All the dimensions of nanomaterial are measured within the nanoscale One dimension is outside the nanoscale Two dimensions are outside the nanoscale

Three-dimensional NMs

All dimensions are outside the nanoscale

Zero-dimensional NMs

Metal-based nanoparticles, polymer-based nanoparticles, etc. Volcanic ash, ocean spray, magnetotactic bacteria, mineral composites, etc. Carbon-based nanomaterials: Nanoparticles of Ca21, Zn21, Mg21, Na1, etc. Nanoparticles of Au, Ag, Al, etc. Nanoparticles of TiO2, SiO2, etc. Lipid-based nanoparticles Protein-based nanoparticles Polysaccharide-based nanoparticles Polymer-based nanoparticles Surfactant-based nanoparticles Conjugated/complexed biopolymers-based nanomaterials Nanoparticles, nanocrystals Nanotubes, nanorods, and nanowires Graphene, nanofilms, nanolayers, and nanocoatings Bulk powders, dispersions of nanoparticles, bundles of nanowires, multinanolayers

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Handbook of Food Nanotechnology

increasing temperature, or augmenting the heat transfer coefficient (HTC). Surface area extension and temperature increase are not favorable because they will give rise to sizable equipment, excessive power consumption, and high operating costs. One of the methods that can be used to increase HTC is the addition of solid metal particles into the conventional heat transfer fluids, such as glycols, water, and engine oil (Salari and Jafari, 2020). The advances in nanotechnology paved the way in producing smaller particles to produce nanofluids. The chief interest in nanofluids has fundamentally been based on the anomalously increased thermal conductivity of the base fluid at low concentrations of nanoparticles (Angayarkanni & Philip, 2015). The method used to prepare a nanofluid is a determining step having a significant role in thermal conductivity improvement prompted by the addition of nanoparticles. The preparation methods of nanofluids are generally categorized as one-step or two-step techniques. In the one-step procedure, nanoparticles are directly synthesized and dispersed inside the fluid through physical vapor deposition (PVD) or liquid chemical methods. However, in the two-step technique, nanoparticles, nanofibers, or nanotubes are first synthesized as nanopowders through methods like inert gas condensation, chemical vapor deposition, mechanical alloying, etc. Then the nanofluids are prepared by dispersion of nanopowders into the base fluid (Li, Zhou, Tung, Schneider, & Xi, 2009). In the food industry, heat exchangers have a wide variety of applications including pasteurization, sterilization, fractionation, distillation, concentration, and any processes involving the heating or cooling of fluids (Shah & Sekuli´c, 2003). It has been shown recently that the use of nanofluids for the optimization of heat exchangers in the food processing plants can be beneficial not only from the technical perspective but also by considering their effect on the quality of food products (Jabbari, Jafari, Dehnad, & Shahidi, 2018; Jafari et al., 2017a). Energy consumption, processing time, and the effectiveness of food processing devices are other critical technical parameters influenced by using nanofluids. It has been demonstrated that by using nanofluids instead of conventional heat transfer fluids, the energy consumption and processing time will be significantly reduced, whereas the effectiveness will be improved considerably (Jafari et al., 2017b; Jafari, Saremnejad, Dehnad, & Rashidi, 2017; Longo, Righetti, & Zilio, 2016). Also, Zhang et al. (2017) showed that ZnO nanofluids intensified the inactivation of E. coli through improving the effectiveness of the sonophotocatalysis method, although the effect of reactive oxygen species (ROS) was more pronounced than that of Zn1 ions in bacterial inactivation. In terms of the food quality, it has been demonstrated that by using nanofluids instead of water in a shell and tube heat exchanger, the quality of tomato and watermelon juices (color, pH, acidity, and total soluble solids) has been preserved better. Besides, degradation of bioactive compounds like vitamin C, total phenolic compounds, and lycopene significantly reduced when the nanofluids were used instead of water. The better performance of nanofluids compared to water in connection with the food quality has been attributed to the effect of nanofluids in reducing the duration of thermal processes (Jafari et al., 2017a; Jafari, Saremnejad, & Dehnad, 2017). More details have been provided in Chapter 2, Nanofluid Thermal Processing of Food Products.

Fundamentals of food nanotechnology

5

1.2.2 Nanofiltration in the food industry Nanofiltration (NF) is a relatively new and complex process among other pressuredriven membrane separation technologies. It depends on various interfacial events that are occurring on the membrane’s surface as well as in its nanopores. The performance and efficiency of NF process are attributed to a combination of different effects such as transport, Donnan, steric, and dielectric properties. NF is usually compared with ultrafiltration (UF) and reverse osmosis (RO); however, NF offers several favorable features such as lower operating pressures, higher fluxes and retentions, and continuous operation with clean in place (CIP) procedure, thus lowering maintenance costs. Due to its characteristics, NF is becoming an attractive process for challenging applications in agrofood processing, involving fractionation, water softening, wastewater treatment, vegetable oil processing, and treatment of products from the dairy, beverage, and sugar industries. It was already reported that NF can replace its other counterparts like RO (Chen et al., 2016; Dey, Linnanen, & Pal, 2012). The potential of NF application in food processing can be found in a number of reports that cover different fields including purification of water and sugar, whey processing, juice clarification and concentration, as well as fractionation (Salehi, 2014; Van Der Bruggen, Vandecasteele, Van Gestel, Doyen, & Leysen, 2003). The growing demand for NF membranes is one of the key emerging trends in the market of membranes for agrofood applications. Ionizable groups which are present on the polymeric NF membranes, acidic or basic, make the membrane surface charged due to their dissociation, which strongly depends on the pH of contacting solution. For this reason, the NF separation mechanism is not based only on size exclusion but also on the Donnan effect. Donnan exclusion postulates that ions that are carrying the same charge as the membrane will be excluded by the membrane (Mohammad et al., 2015). The main drawback of NF application, similar to other membrane processes, is membrane fouling. It is generally originated by the binding, accumulation, or absorption of materials on the membrane surface and throughout the membrane pores. Common foulants are organic and inorganic solutes, colloids, and biological particles (Van der Bruggen, M¨antt¨ari, & Nystro¨m, 2008). Membrane fouling causes deleterious effects such as flux decline (productivity drop), increasing cost (higher energy demand, maintenance), and shorter membrane life span. Therefore for the accomplishment of a fruitful NF process, the selection of suitable structured membrane materials in terms of MWCO (molecular weight cutoff) and surface properties (functional groups, charge, hydrophobicity, roughness) is very important. Today, research is directed to the creation of membranes with improved selectivity, rejection, and fouling resistance using various methods, such as interfacial polymerization, nanomaterials incorporation, UV treatment, electron beam irradiation, plasma treatment, or layer-by-layer assembly. The most popular NF membrane materials are polymers (see Chapter 3: Nanofiltration in the Food Industry), including cellulose acetate, polyamide, polyimide, polysulfone, and polyethersulfone; however, some ceramics are also used in the manufacture of membranes, such as zirconia, titania, silica zirconia, and alumina.

6

Handbook of Food Nanotechnology

There are different configurations of NF membranes such as flat-sheet, spiralwound, and tubular, as well as different process configurations, such as total recycle, batch concentration, feed-and-bleed, and multistage operation. The choice of a specific configuration is based on economic aspects associated with performance and the ease of maintenance. The selection of a specific process configuration depends on the goal and final applications of the membrane. The separation performance of a NF membrane is affected by its chemical composition, temperature, pressure, and interactions between membrane surface and feed components. When dealing with NF in the recovery of high-added value compounds from agrofood wastes, the use of membrane-based processes clearly offers economic savings because such NF membranes are able to provide a treatment, as well as to recover compounds from several agrofood wastewaters. If the industries are encouraged to invest for the implementation of a large-scale recovery process, the recovered solutes can be commercialized somehow. More than this, tight UF and NF membranes can offer environmental benefits due to such narrow pore size membranes providing permeate streams obtained from the fractionation of by-products, where basically the clear permeates contain low organic loads. The increased interest in NF over the past 20 years reveals that with further membrane development research, application of NF in food processing will increase significantly in the coming years. Chapter 3, Nanofiltration in the Food Industry, gives more information regarding the application of NF in the food industry.

1.2.3 Nanoadsorbents and nanoporous materials for the food industry Today, the adsorption procedure has become a practical method for the separation and purification process on an industrial scale. Adsorption process is applied to purify, decolorize, deodorize, and concentrate in order to remove the hazardous products or to recover the valuable products from the wastewater and many other industrial by-products (Cunningham, Al-Sayyed, & Srijaranai, 2018; Xu et al., 2018). Adsorption and biodegradation are the two practical and common strategies for the remediation of wastewaters owing to their simplicity, cost-effectiveness, and high efficiency (Crini & Badot, 2011; Gadd, 2009; Jiuhui, 2008). From an industrial perspective, adsorption is a simple and economically feasible technique which yields high-quality water. Different adsorbents have found their way into industrial applications, like organic resins, zeolites, activated carbon, and commercial activated alumina as interesting materials (Wang & Peng, 2010). In recent years, nanoscience and nanotechnology that is growing very rapidly has opened new horizons in different fields including nanoadsorption; for example, resins, nanoclays, graphene, and metal oxides. Nanoadsorbents have unique characteristics like high surface area, small size, high stability, high reactivity, and can be regenerated many times over (Anjum, Miandad, Waqas, Gehany, & Barakat, 2016; Basheer, 2018; Kecili & Hussain, 2018). The mechanism of adsorption is the adhesion of a solute of a fluid phase

Fundamentals of food nanotechnology

7

(adsorbate molecule) through molecular interaction into the porous surface of an adsorbent material. This phenomenon occurs by two means: (1) physical adsorption or physisorption that takes place by van der Waals forces of the adsorbent and adsorbate; and (2) chemical adsorption or chemisorption that is related to the chemical bonding forces between them (Chiou, 2003). Nanoadsorbents have infinite applications in various industries such as wastewater treatment and water purification in the water and environment industry (Kamal, 2018), production of nanofertilizers in agriculture industry (Rai, Ribeiro, Mattoso, & Duran, 2015), and recovery of some valuable compounds from food and beverage by-products in food industries (Bagheri, Jafari, & Eikani, 2019). Factors affecting adsorption are pH, size and specific surface area of adsorbent, contact time, amount of adsorbent and adsorbate, the presence of competing ions, ionic strength, and stirring speed (Ambashta & Sillanp¨aa¨ , 2010; Ersoz & Barrott, 2012; Kecili & Hussain, 2018; Machado & Bergmann, 2011; Sadegh & Ali, 2019). Freundlich, Langmuir, and BET isotherm models are applied for a description of adsorption. The Langmuir and Freundlich isotherms are able to consider a monolayer absorbent; in contrast, BET surface area can be used to find the capacity of a multilayer adsorbent (Ersoz & Barrott, 2012). Chapter 4, Nanoadsorbents and Nanoporous Materials for the Food Industry, reviews the properties of nanoclay, zero valent iron nanoparticles, active carbon, and graphene oxide as abundant, low-cost, and applicable sources for removal and adsorbing agents in the food industry, as well as discussing their characteristics, classification, adsorption, isotherm, and models, plus their application in the food sector.

1.2.4 Production of food nanomaterials by specialized equipment Food nanomaterials have attracted great interest due to their unique characteristics. Different methods have been proposed for the fabrication of food nanomaterials based on two classifications: top-down and bottom-up approaches (Koshani & Jafari, 2019; Rezaei, Fathi, & Jafari, 2019). Top-down methods are based on the breakage of a system into smaller size scales, for instance, through mechanical size reduction input by applying high energy. On the other hand, bottom-up methods require low energy and the process can be controlled by the intrinsic physicochemical properties. These include solvent demixing, self-emulsification (spontaneous emulsification), and phase inversion assays. Top-down methods usually need specialized equipment, including high-pressure, ultrasonication, electrospinning, spray drying, and ball milling (Prakash, Baskaran, Paramasivam, & Vadivel, 2018). Most of these methods have been currently scaled up and industrialized. The reproducibility and large-scale production are the considerable advantages of high-pressure techniques while a vortex fluidic device (VFD) needs lower cost and it is an environment-friendly technique. However, there are some drawbacks that may limit the utilization and promote the modification of these methods or the development of a new technique.

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Handbook of Food Nanotechnology

Among different approaches that exist to produce the nanoscale systems, techniques which require specialized equipment are described in Chapter 5, Production of Food Nanomaterials by Specialized Equipment; including microfluidization, highpressure homogenization, ultrasonication, micro/nanofluidics, nanospray drying, membrane technology, VFD, ball milling, solution blowing, and electrospinning/ spraying. Despite the fact that some conventional approaches are expensive to scale up or they use high energy, the reproducibility and industrial-scale production make these techniques useful. On the other hand, there is an increasing interest in new methods such as electrospinning, vortex fluidic, or micro/nanofluidics. These methods are not yet industrialized but much research has been conducted on them to study different aspects, that is, optimization of the process. It seems that the novel techniques need an in-depth knowledge to understand the utilization possibility for different food ingredients as variable features such as viscosity, sensitivity to heat, solvent limitation, or size may limit their utilization.

1.3

Application of nanotechnology in food ingredients

Recently, consumers have exhibited a preference for minimally processed products with the most natural additives and ingredients that represent a health benefit, such as enzymes, prebiotics, probiotics, antioxidants, and antimicrobials that occur naturally as soluble extracts or essential oils obtained generally from plants (Li & Nie, 2016; Tamjidi, Shahedi, Varshosaz, & Nasirpour, 2013). This is where nanotechnology allows improvement of the functionality of various ingredients, modifying their solubility, decreasing the concentration of substances, and potentiating their effectiveness or controlling their release (Jafari, Fathi, & Mandala, 2015; Jafari & McClements, 2017). Moreover, nanosized systems interact with food; thus the components must be selected carefully depending on the food, beverage, drink, sausage, etc., in which they will be used.

1.3.1 Nanoemulsions and nanosized ingredients for food formulations Nanoemulsions and nanosized ingredients represent a viable alternative in the development of novel products for including components with specific functions (Abbasi, Samadi, Jafari, Ramezanpour, & Shams-Shargh, 2019; Assadpour & Jafari, 2017; Mohammadi, Jafari, Assadpour, & Faridi Esfanjani, 2016). The ingredients can be incorporated during food processing in order to obtain functional products with adequate organoleptic quality, texture improvement, color homogeneity, and stabilizers, or for the release of active substances during storage, distribution, or consumption. These nanosystems possess a greater surface area, reactivity, solubility, and availability of compounds, and they have the ability to interact with the food components to decrease the physiological and enzymatic reaction, producing

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new products or contributing to the development of sausages, mayonnaise, or other low-fat products (Quintanilla-Carvajal et al., 2010; Rezaei et al., 2019). The preparation of nanosystems requires several considerations in terms of how the ingredients will be used during the processing, rendering it necessary to request the desired function in the formulation, such as the following: stabilizers of food emulsions (sausages, mayonnaise, functional beverages); improvers of texture (ice cream, cheese, pˆate´s); homogenization of color; nutrient bioavailability, and enzymatic, oxidative, or respiratory control in minimally processed products. In addition, it remains important to consider the characteristics of the food in which the nanosized systems will be employed and incompatibilities between ingredients. Moreover, physicochemical properties such as pH, water activity, ion charge, fat content, the superficial ionic charge, and composition in general, as well as the desired function that they fulfill during processing, packaging, storage, and consumption should be noted (Oehlke et al., 2014; Weiss, Takhistov, & McClements, 2006). Different nanometric size systems are currently applied in food formulation, such as nanoemulsions, polymeric nanoparticles, solid lipid nanoparticles, lipid nanocarriers, nanocrystals, nanoliposomes, nanomicelles, noisome, nanofibers, and nanolaminates, as described in Chapter 6, Nanoemulsions and Nanosized Ingredients for Food Formulations. Thus the range of possibilities and choices will always depend on the purpose of their use and their relationship with the sensory quality of the products, in that the latter comprises a decisive part in the purchase selection by the consumer. Nanoemulsions represent one of the systems that have shown the greatest interest for use as ingredients in the food industry, mainly because there are different methods for their preparation, as well as being considered as stable systems for the encapsulation of bioactive substances; also as a good release system that will depend on the conditions in which they are applied. They are used in beverages, juices, dressings, sauces, and ice cream, among many others, and they possess greater stability, in addition to being clear and facilitating the incorporation of water-insoluble ingredients such as vitamin, essential oils, colorants, and flavors (Maswal & Dar, 2014). Nanoemulsions can be used as texture modulators. Depending on oil composition, internal-phase proportion, type and concentration of the stabilizer, and droplet size, nanoemulsions can exhibit different rheological behaviors from that of viscous liquids and viscoelastic solids (Dasgupta & Ranjan, 2018). Polymeric nanoparticles are preferred in the development of new products in which stability, easy incorporation, and compatibility are important, because these encapsulation processes also allow obtaining ingredients in powder form, which facilitates the formulation and processing of foods and beverages. Polymeric nanoparticles possess important characteristics that define the compatibility between the foods and components of nanosized systems. Polymeric nanoparticles have a potential use in beverage and semisolid foods, in which a homogeneous distribution of antioxidant and natural colorants is necessary, considering a sensorial balance in the nucleus of the food. The main physical properties of polymeric nanoparticles

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include modification of viscosity, density, and light dispersion, permitting the development of stable and attractive products for the consumer. However, the physicochemical properties of the food and beverages formulated with nanoparticles as ingredients can vary considerably during storage, depending on the polymer used in the preparation of nanostructures and the composition in terms of pH, soluble solids, proteins, lipids, and water content of the food. Nanocoatings have the purpose of maintaining the physicochemical composition of minimally processed products as long as possible without significant variations. Changes in composition, such as humidity, protein and fat content, pH, and acidity index, are important in products of animal origin, while in the case of vegetable products, there will be important changes in pH, weight loss, leakage loss, titratable acidity, and soluble solids. There are currently some studies that consider the use of different types of coatings incorporated into nanosized systems, where it has been shown that their use considerably reduces physicochemical variations and that changes in pH and ionic strength are associated with the polymer type. More details have been provided in Chapter 6, Nanoemulsions and Nanosized Ingredients for Food Formulations.

1.3.2 Green synthesis of metal nanoparticles by plant extracts and biopolymers Metallic nanoparticles have been employed in many different nanotechnological applications including medical diagnosis, drug/bioactive delivery, wound healing, and sensors. In particular, gold and silver nanoparticles have been industrially applied due to their unique properties. Although many methodologies have been used for the synthesis of metal nanoparticles (MNPs), most of them involve the use of hazardous reactants, evidencing that the development of new green protocols is urgent. To be called green, each step of the procedure should employ both environment-friendly solvents and reagents, as well as reduce energy consumption. In other words, green methods focus on the production of nanoparticles by employing natural compounds as reducing and capping agents and decrease, or ideally eliminate, the use or production of hazardous substances during nanoparticle fabrication and/or application. The design, synthesis, and manipulation of metallic nanoparticles (particles with at least one dimension between 1 and 100 nm) deserves special attention in the nanoscience and nanotechnology field due to the remarkable differences in their electrical, magnetic, catalytic, and optical properties in comparison with the bulk state of the same metal (Sangappa et al., 2019; Vijayan, Joseph, & Mathew, 2018). Novel applications of MNPs have received considerable attention on various fronts due to their enhanced properties that can be tuned by composition and also by their size, distribution, and morphology (Ahmed, Ahmad, Swami, & Ikram, 2016; Khatami, Sharifi, Nobre, Zafarnia, & Aflatoonian, 2018; Sangappa et al., 2019). A set of shapes can be obtained by adjusting the concentration of reacting chemicals and also by controlling the reaction environment (Gade, Gaikwad, Duran, & Rai, 2014). The main

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applications can be found in catalysis, biosensors, cryogenic superconducting materials, cosmetic products, electronic components, composite fibers, and antimicrobial activity (Sangappa et al., 2019; Vijayan et al., 2018). The last two applications are the most important in the food industry (Hoseinnejad, Jafari, & Katouzian, 2018). Different physical and chemical methods have been developed to fabricate these particles at the nanoscale. Among these techniques, the chemical reduction is considered the most advantageous process since it results in the production of large amounts of nanoparticles in short periods of time with good control of the size distribution (Gade et al., 2014; Remya, Abitha, Rajput, Rane, & Dutta, 2017; Sangappa et al., 2019). The reducing agent can be organic or inorganic (Sangappa et al., 2019). However, most of the chemical methods use toxic chemicals (such as hydrazine and sodium borohydride), and frequently yield particles in nonpolar organic solutions and noneco-friendly by-products, which goes in the opposite direction of the green chemistry principles. Moreover, the use of these classical methods restricts the application of MNPs for human purposes, including food packaging and medicine. In addition, these traditional methods utilize excessive power consumption, sophisticated apparatus, and have a high cost (Soshnikova et al., 2018). The green chemistry methods for the synthesis of MNPs include the design and development of energy efficient and eco-friendly reactants, waste, and subproducts (Patra et al., 2015; Soshnikova et al., 2018; Vijayan et al., 2018). As a consequence, the biosynthesis of MNPs deserves attention for modern nanotechnology as it represents a greener approach to develop environment-friendly processes (Gade et al., 2014; Mohanpuria, Rana, & Yadav, 2008). The green synthetic routes are described as simple, efficient, clean, or eco-friendly, since they use bioresources (bacteria, fungi, algae, biopolymers, and plant extracts) that can act as reducing agents as well as stabilizing and capping agents to the synthesized metallic nanoparticles (Bindhu and Umadevi, 2015; Patra et al., 2015; Soshnikova et al., 2018; Umamaheswari, Lakshmanan, & Nagarajan, 2018; Vijayan et al., 2018), as described in Chapter 7, Green Synthesis of Metal Nanoparticles by Plant Extracts and Biopolymers. Moreover, the greener approach requires ambient temperature and pressure, minimum energy consumption, and very low or no-consumption of hazardous materials. They can also be easily scaled up for large-scale nanoparticle synthesis (Ahmed et al., 2016; Patra et al., 2015).

1.3.3 Nanoencapsulation of food ingredients One interesting area of food science in which nanotechnology has been greatly helpful and which is attracting a lot more interest day by day is the nanoencapsulation of bioactive ingredients. This is because the reduction in particle size to the nanoscale range can increase the surface:volume ratio, and subsequently can increase the reactivity of the coating materials and the encapsulated ingredients by many folds due to the substantial change in the mechanical, electrical, and optical properties (Neethirajan & Jayas, 2011). Nanotechnology can significantly improve the aqueous solubility and thermal stability of the bioactive ingredients, as well as

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their oral bioavailability (Huang, Yu, & Ru, 2010; Jafari, Assadpoor, He, & Bhandari, 2008; Rashidinejad, Birch, Sun-Waterhouse, & Everett, 2014). Numerous studies have been published in the area of nanotechnology for the encapsulation of bioactives in foods, and their incorporation into novel functional foods (see Chapter 8: Nanoencapsulation of Bioactive Food Ingredients). Over the last couple of decades, there has been a growing research interest in nanoencapsulation of food ingredients using different techniques and the incorporation of the nanoencapsulated ingredients into various food products, known as “functional foods.” This includes the delivery of a diverse class of bioactive ingredients such as polyphenols, carotenoids, vitamins, minerals, essential oils, and flavors. Many nanoencapsulation methods have been experimented and suggested for such a broad group of bioactive compounds; nanoemulsification, nanospray drying, coacervation, nanoliposomal/niosomal entrapment, complexation of proteins polysaccharides, inclusion complexation, encapsulation within solid lipid nanoparticles/nanostructured lipid carriers, etc. In addition, various nanoencapsulated bioactive compounds have been incorporated into food products, including milk and dairy products, bars, bread, breakfast cereals, meat products, cookies, cakes, juices, oils, and chewing gum. As mentioned, the nanoencapsulation approach provides some potential advantages in improving solubility/dispersibility of the bioactive compounds (particularly, hydrophobic compounds) in food, controlling their release in the gastrointestinal digestive tract, masking their undesirable sensorial properties, improving their chemical stability in food during manufacture and storage, and maintaining their functionality/efficacy in the human body. Chapter 8, Nanoencapsulation of Bioactive Food Ingredients, discusses the novel and conventional techniques that have been used for nanodelivery of the aforementioned bioactive compounds. Furthermore, different nanocarriers (wall materials) and their suitability for nanodelivery of bioactive compounds in food, the challenges associated with nanodelivery of bioactive compounds (e.g., potential toxicity), as well as the possible novel approaches for engineering, modification, and overcoming such challenges of the nanoencapsulation systems have been addressed.

1.3.4 Enhancing the bioavailability of nutrients by nanodelivery systems The delivery of health-promoting nutrients, such as antioxidants, vitamins, probiotics, minerals, and phenolic compounds, with conventional methods has some drawbacks in protecting the bioactives through the harmful environment of the gastrointestinal system, leading to decreased bioavailability and bioaccessibility of bioactives and nutrients (Jafari & McClements, 2017; Sadeghi et al., 2018). Encapsulation of these compounds in advanced nanodelivery systems is more advantageous in terms of increased solubility and protection from oxidation, hydrolysis, and acidity of gastric fluids because the polymers coating the bioactives act as a barrier between the compounds and the outer conditions, increasing the

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stability of the compounds until they reach the more neutral acidity of the intestinal tract where they can get absorbed more effectively (Katouzian & Jafari, 2016; Rafiee, Nejatian, Daeihamed, & Jafari, 2019b; Rezaei et al., 2019). Due to these advantages, many groups have explored ways to encapsulate bioactives in nanodelivery systems. Nanocarriers that carry the bioactives can be fabricated from inorganic compounds and synthetic polymers as well as from biobased polymers and organic compounds (Assadpour & Jafari, 2019a, 2019b). Synthetic polymers often give higher encapsulation efficiencies since their longer chains provide better entanglement and a denser network forming around the encapsulated compounds. However, the risk of accumulation of synthetic wall materials in the body leads researchers to focus on fabricating organic biobased nanodelivery systems from plant or animal sources, such as proteins or carbohydrates. In Chapter 9, Enhancing the Bioavailability of Nutrients by Nanodelivery Systems, recent studies on fabrication of biobased nanodelivery systems to enhance the bioavailability of nutrients and nutraceuticals are summarized. To understand the different nanoparticulation methods and their thermodynamic mechanisms, the studies in Chapter 9, Enhancing the Bioavailability of Nutrients by Nanodelivery Systems, are presented in four categories; nanoprecipitation, complex coacervation, layer-by-layer assembly for spherical and tubular nanoparticles, and micro/nanoemulsification. The effects of fabrication parameters on the morphology, stability, encapsulation efficiency, and the bioavailability of nanoparticles are also discussed in detail to provide a comprehensive understanding of nanodelivery systems to the readers. Different studies show that during nanoparticulation, depending on the method used, many parameters, including the selection of coating polymers, temperature, pH, or salt concentration, can affect the formation of nanoparticles, their stabilities and encapsulation performances, which as a result change the bioaccessibility of the encapsulated bioactive significantly. Correct selection of these parameters is of crucial importance for a successful design of the nanodelivery systems.

1.4

Application of nanotechnology for improving food quality and packaging

1.4.1 Metal nanoparticles as antimicrobial agents in food packaging Recent technological advances have allowed biopolymers to be processed similarly to petroleum-based plastics whether in sheets, by extrusion, spinning, injection molding, or thermoforming (Hashemi Tabatabaei, Jafari, Mirzaei, Mohammadi Nafchi, & Dehnad, 2018). In spite of their excellent barrier properties to oxygen and other gases, biopolymers are poor water vapor barriers and, moreover, their barrier and mechanical properties are dependent on moisture, which is not desirable, especially for the packaging of certain food types. Nanobiocomposites are

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considered as an alternative in biobased food packaging which can help overcome disadvantageous features including low water vapor barrier or weak mechanical properties (Joz Majidi et al., 2019). Nanofillers such as MNPs yield desirable results including mechanical properties improvement, reduction of weight, improvement of technology (e.g., fire resistance), antimicrobial attributes, and higher resistance to water vapor and other gases (Jafarzadeh, 2017). Using nanocomposites makes it possible to create stronger and more durable biopolymers which are environment-friendly and can be successful replacements for petroleum-based polymeric materials used in food packaging (Dehnad, Mirzaei, Emam-Djomeh, Jafari, & Dadashi, 2014; Jafarzadeh et al., 2017). The nanomaterials in food packaging are categorized into nanoparticles, nanofibers, and nanolayers. Some common nanomaterials under investigation include MNPs, metal oxide nanoparticles (MONPs), mixed metal oxide nanoparticles (MMONPs), nanoclay families (NCs), and carbon materials (carbon nanotubes [CNTs], graphene). Nanostructured materials in food packaging can improve the final films properties such as mechanical, chemical, structural, and barriers (O2/ H2O, microbial, bacterial, etc.). These new properties maintain the quality of food. Nanomaterials like layered materials, MONPs, MNPs, and carbohydrate nanocrystals are used in food packaging; however, there are several issues against their safety, which has been discussed in Chapter 10, Metal Nanoparticles as Antimicrobial Agents in Food Packaging. The incorporation of NPs and doped-NPs into the organic phase of packaging materials (i.e., polymers) is governed by their mechanical (high strength and stiffness) and barrier (low permeability) properties. Various explanations have been proposed in order to illustrate the mechanisms of microbicidal activities of nanoparticles. Antimicrobial packaging has received the most considerable attention due to its potential to lengthen lag phase of bacteria, minimize growth rate of microorganisms, and preserve the product safety and quality (Hoseinnejad et al., 2018). There are many parameters signifying the promising future of antimicrobial packaging in the food industry, such as the growing request of consumers for convenient, safe, and fresh foods, along with the demand to package products in a versatile way for storage, transportation, and distribution. Nevertheless, there are demands to gain more information and knowledge about how these systems affect the packaged food from the microbiological, chemical, and physiological aspects (Jafarzadeh, 2017).

1.4.2 Nanobased aptasensors for detection of food contaminants Over the last years, the manufacture of biosensors has focused on the use of nanostructured materials (MNPs, semiconductor materials, carbon nanomaterials) and magnetic nanoparticles as platforms for the multiple probes immobilization toward an improved detection (Tiwari & Tuner, 2014). The adequate definition and “concept” of nanobiosensor has generated controversies among the scientific

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community, but in common terms it can be defined as a nanoscale device that monitors a (bio)chemical event by means of an electronic, optical, or magnetic technology through a compact probe. Such tiny sensing elements can be classified according to the biological recognition mechanism or to the signal transduction mechanism. MNPs are an ideal platform for the controlled immobilization of bioreceptors along with a good retention of their native bioactivities (Katz, Willner, & Wang, 2004). Gold nanoparticles (AuNPs) allow the direct transfer of electrons between, for example, redox proteins and the electrode surfaces, avoiding the use of electron transfer mediators. This can be attributed to the relatively high surface volume ratio of AuNPs, along with high surface energy and the ability to decrease the distance between, for example, proteins and metal particles; acting thus as an electroconductive pathway between prosthetic groups and surface of the electrode (Pingarro´n, Ya´n˜ez-Seden˜o, & Gonza´lez-Corte´s, 2008). In addition, the facile synthesis and functionalization of AuNPs makes them excellent scaffolds for the fabrication of novel chemical and biological sensors (Biju, 2014). There are different strategies for the fabrication of biosensors with AuNPs, as described in Chapter 11, Nanobiosensors for Food Analysis. The most commonly used are electrochemical biosensors, in which the electroactive analyte is oxidized or reduced on the working electrode surface (transducer) and the electron fluxes lead to the generation of a signal. Electrochemical methods are classified into potentiometric, coulometric, voltammetric, and impedimetric biosensors (Wang, 2006). Each technique has its own characteristics, which are able to be used according to the analyte, methodology, and sample. Amperometric biosensors exhibit good sensitivity with excellent linear ranges, and also have successfully commercialized devices. Furthermore, the electrochemical biosensors have advantages such as low cost, simple operation, and a small size; they are disposable and incorporate multiple sensing elements in a single chip-like device. These advantages are possible due to the characteristics of the nanomaterials used to modify the transducer (Pe´rez-Lo´pez & Merkoc¸i, 2011). During the past decade, CNTs have been one of the most extensively used materials in nanobiosensors (Katouzian & Jafari, 2019). They consist of a twodimensional hexagonal lattice of carbon atoms, bent and joined in one direction so as to form a hollow cylinder. Besides these single-wall CNTs (SWCNTs), the name is also used for multiwall (MWCNTs) variants consisting of two or more nested nanotubes (Agu¨´ı, Ya´n˜ez-Seden˜o, & Pingarro´n, 2008). The CNT-based biosensors have the following advantages associated with their unique structures: high sensitivity (because of the high ratio of surface to volume); enabled enzyme immobilization with high biological activity; fast response time due to the ability of this nanomaterial to promote electron transfer in electrochemical reactions and negligible surface passivation. Such characteristics have been exploited to design novel biosensors in a myriad of applications (Balasubramanian & Burghard, 2006; Manso, Mena, Yanez-Sedeno, & Pingarron, 2007; Yang, Chen, Ren, Zhang, & Yang, 2015). There are also different strategies for the fabrication of graphene-based nanobiosensors. Modification is commonly carried out by coating or preparing carbon nanomaterial-

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Handbook of Food Nanotechnology

binder composite electrodes (Carralero, Gonza´lez-Corte´s, Ya´n˜ez-Seden˜o, & Pingarro´n, 2007). Also, a useful and simple way consists of the direct casting of a small volume of a nanomaterial suspension onto the electrode surface (Martı´n, Batalla, Herna´ndez-Ferrer, Martı´nez, & Escarpa, 2015). Electrochemical biosensors are still essential tools for food safety assurance and monitoring. Current advances are aimed to improve the sensitivity, selectivity, and specificity with minimal sample treatment by the incorporation of metallic NPs, mainly gold due to the excellent features for modification with specific receptors such as aptamers. The main targets are bacteria (either whole cells or associated toxins) and mycotoxins. A few applications rely on graphene and CNTs for the same purpose, with only recent but interesting advances using MoS2, which will undoubtedly lead to future developments due to the unique surface properties of such nanomaterials. Another important core is devoted to optical nanobiosensors with either colorimetric or fluorescent detection based mainly on the exploitation of aggregation-disaggregation of AuNPs. In fluorescent detection, dye-labeled specific probes are the preferred choice. As in the case of electrochemical biosensors, bacteria and mycotoxins are the main targets. Readers are referred to Chapter 11, Nanobiosensors for Food Analysis, for more details.

1.4.3 Nanoparticles/nanofibers for checking adulteration/ spoilage of food products For the general public, there has long been concern about food fraud. As the world’s population continues to grow, the provision of healthy and standard food is a major issue in today’s world. The scope of food fraud is wide-ranging from adding anionic detergent and melamine to milk, adding illegal dyes, adding cane and beet invert sugars to the fruit juice, and to mixing horse and duck meat to beef. In fact, food fraud is a source of money, opportunity, and a low-cost, easy way to provide food with great profits. Unfortunately, according to statistics, thousands of people die each year from diseases caused by unhealthy and adulterated foods. On the other hand, contamination and spoilage of food both reduce the quality or safety of food. The identification of adulteration and spoilage to increase food safety has received much attention in recent decades. Common methods include spectroscopy, chromatography, and DNA analysis, which are usually time-consuming and expensive. In other words, the main disadvantage of current methods for assessing food safety such as cell culture and fine instrumentation analysis is the long analysis time from several hours to days and usually there are various pretreatment stages. Nutrient monitoring and screening of adulterants and pathogens are the main issues in food products for the evaluation of food quality and safety. For this purpose, new accurate, rapid, and low-cost detection techniques are growing (Rotariu, Lagarde, JaffrezicRenault, & Bala, 2016). Therefore nanotechnology has proposed nanosensors as faster, cheaper, and more precise methods to authenticate the quality and food safety. Recently, nanosensors based on nanoparticles/nanofibers have been used to detect adulterant and pathogenic materials in food packaging or during the process.

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At the nanoscale, materials exhibit unique properties physically and chemically that do not exhibit them in their original form. The high surface area of nanomaterials allows for very large molecular interactions, which may result in higher sensitivity, faster detection, and fewer samples for analysis. Chapter 12, Nanoparticles/nanofibers for checking adulteration/spoilage of food products, reviews the applications of nanoparticle/nanofiber-based nanosensors for efficient detection of adulteration and spoilage in food products (Mercante, Scagion, Migliorini, Mattoso, & Correa, 2017). These types of nanosensor are highly sophisticated yet precise and sensitive systems capable of detecting and responding to physical and chemical stimuli. The range of performance of these sensors is in nanometers, so they are highly precise and responsive so that they even react to the presence of several atoms in a single gas, thus they offer considerable improvements in speed, selectivity, and sensitivity compared to common chemical and biological methods. Also, the nanosensors whose recognizing part has a biological nature are known as nanobiosensors (Joyner & Kumar, 2015). In general, sensors consist of two essential elements: a receptor and a transducer. The receptor can consist of any organic or inorganic material that interacts with the target analyte or its derivatives. On the other hand, the transducer is an element that converts the recognition event that occurs between the analyte and the receptor into a measurable signal (Yin, Kim, Choi, & Lee, 2013). This signal can come in many forms, including electrical (Adhikari, Govindhan, & Chen, 2015), electrochemical (Rotariu et al., 2016), and optical (Koedrith, Thasiphu, Tuitemwong, Boonprasert, & Tuitemwong, 2014). Hence, nanomaterials including metal and MONPs, CNTs, graphene, and its derivatives, and electrospun nanofibers play an important role in the design of sensors and biosensors to detect contamination, adulteration, and spoilage in foods, as described in more detail in Chapter 12, Nanoparticles/ Nanofibers for Checking Adulteration/Spoilage of Food Products.

1.4.4 Nanoencapsulated bioactive components for active food packaging A package is considered active, when the purpose is inactivation/degradation of undesirable compounds that can decrease the commercial shelf life of food (Lee, 2010; Suppakul, Miltz, Sonneveld, & Bigger, 2003). In general terms, active packaging employs components such as antioxidants and antimicrobials to protect foods from contamination or degradation by creating a barrier to the outside environment, and promoting the product shelf life (Vahedikia, Garavand, Tajeddin, Cacciotti, Jafari, Omidi, et al., 2019; Vermeiren, Devlieghere, de Kruijf, & Debevere, 2000). Active packaging can be produced with the addition of substances like scavengers of oxygen, ethylene, moisture, and carbon dioxide, and release of antimicrobial and antioxidant agents (Fang, Zhao, Warner, & Johnson, 2017). A proposed classification of various active packaging systems are antioxidant and antimicrobial films and coatings, nanofiber packaging scavengers and absorbers (Karam, Jama, Dhulster, & Chihib, 2013).

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Handbook of Food Nanotechnology

Furthermore, consumers’ concerns about multiple disorders related to the use of chemical preservatives have led to an increasing tendency toward the application of natural compounds for food preservation (Huang et al., 2011; Kim, Cadwallader, Kido, & Watanabe, 2013). In this respect, bioactive compounds such as phenolic compounds, carotenoids, essential oils, peptides, and antimicrobial agents have been studied for their use in food protection against microbial and oxidation spoilage, which has been a trending subject in recent years (Hashemi Tabatabaei et al., 2018; Hoseinnejad et al., 2018). Nanoencapsulation technology can be used to generate new food packaging; this method is a useful alternative to protect bioactive compounds while providing their controlled release (Sozer & Kokini, 2009). The effects of nanoencapsulated bioactive compounds in active food packaging on their physicochemical and mechanical properties and also, their application in various food products has been discussed in Chapter 13, Nanoencapsulated Bioactive Components for Active Food Packaging. The controlled release and migration of bioactive ingredients from active packaging to food is also investigated in this chapter. The addition of bioactive compounds to packaging materials with the aim of the release at a controlled rate of antimicrobial entities during storage and distribution results in minimizing or even eliminating undesirable microorganisms and increased storage period (Zhang, Hortal, Dobon, Bermudez, & Lara-Lledo, 2015). Meanwhile, incorporation of bioactive compounds can improve the antibacterial properties of active packaging. Addition of antioxidant or antimicrobial compounds into edible films and coatings could alter their functional properties, such as mechanical and barrier, thus this alters the release and bioactivity of the compounds. Edible films and coatings also could control the release of bioactive ingredients using simple factors like temperature, humidity, changes in pH, and mechanical properties of the matrix. Various factors are effective in determining the release from packaging like molecular form, size, polarity, and weight of bioactive compound. However, additional treatments like cross-linking could be used to modify the structure. The cross-linking could also provide a much better controlled release necessary for active packaging applications. The release of an active compound from a matrix may be controlled by melting, diffusion, degradation, or particle fracture or a combination of them (Quiro´s-Sauceda, Ayala-Zavala, Olivas, & Gonza´lez-Aguilar, 2014). Common approaches to achieve controlled release are blending two or more different polymers (by extrusion compounding process) and multilayer structures (active compound placed into surface layer for direct contact with food) (Chen, Chen, Xu, & Yam, 2018). One of the valid solutions for controlling the release of bioactive compounds in packaging can be nanoencapsulation. Examples of scientific studies on bioactive release from food packaging loaded with different nanocarriers are described in Chapter 13, Nanoencapsulated Bioactive Components for Active Food Packaging.

1.4.5 Reinforced nanocomposites for food packaging Biopackaging is obtained from biodegradable materials including polysaccharides, such as chitosan, starch, and cellulose; proteins including gluten, gelatin, and zein;

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and chemical polymers, for example, polycaprolactones (PCLs), polyvinyl alcohol (PVOH), copolymers (ethylene vinyl alcohol, EVOH), and polylactic acid (PLA) (Arvanitoyannis et al., 1997; Haugaard et al., 2001; Petersen et al., 1999); and polymers such as polyhydrooxyalkanoates (PHAs) and polypeptides produced by natural or genetically modified microorganisms (Lagaron & Sanchez-Garcia, 2008; Reguera et al., 2003). Although this kind of packaging is advantageous, it has some drawbacks when compared to synthetic plastics. Disadvantages include low thermal resistance, excessive brittleness, and insufficient barrier to oxygen and water. Therefore there is great industrial and academic interest in obtaining synthetic and biodegradable materials with enhanced barrier properties and mechanical resistance for current and future food packaging applications (Hashemi Tabatabaei et al., 2018; Vahedikia et al., 2019). In this scenario, nanocomposites are a new class of composites consisting of nanoparticle-filled polymers (Dehnad, Mirzaei et al., 2014; Hoseinnejad et al., 2018). They comprise multiphase materials where at least one of the constituent phases, commonly the nanofiller, has at least one dimension in the nanoscale range (Bandyopadhyay & Ray, 2019). Several nanoparticles have been used to reinforce natural matrices with a view to obtaining nanocomposites, for example, zinc oxide (Emamifar et al., 2010), titanium dioxide (Lian, Zhang, & Zhao, 2016), silica (Hou et al., 2019), nanoclay (Ghelejlu, Esmaiili, & Almasi, 2016), nanocellulose (Dehnad, Emam-Djomeh, Mirzaei, Jafari, & Dadashi, 2014), and chitosan nanoparticles (Hosseinnejad & Jafari, 2016), among others, which elicit improved mechanical, gas and water vapor barrier, and bioactive (antimicrobial activity) properties. These improvements derive from strong interactions between the matrices and the nanoreinforcements: the reinforcing nanoparticles are small (,100 nm), which provide the nanocomposites with a greater surface area than their bulk counterparts, consequently boosting their reactivity (Motaung & Linganiso, 2018) and strengthening them (Zhou, Wang, & Gunasekaran, 2009). Furthermore, the high aspect ratio of nanoparticles and their homogeneous dispersion in the polymer matrix changes the polymer chain molecular mobility and relaxation, thus increasing the nanocomposite mechanical and thermal resistance (Bumbudsanpharoke, Choi, & Ko, 2015). In addition, bonds established between the polymer and nanoparticles decrease the number of sites in the polymer chain that could interact with water molecules, thereby improving the nanocomposite barrier to water (Duncan, 2011; Mihindukulasuriya & Lim, 2014). Chapter 14, Reinforced Nanocomposites for Food Packaging, gives an overview of different types of inorganic and organic nanoparticles that are employed to reinforce polymeric matrices and their effects on the properties of nanocomposites intended for food packaging. Despite the advantages of nanocomposites, nanoparticles production is expensive, demands high-cost industrial facilities, and requires production optimization, which may limit their use in food packaging. Moreover, nanoparticles may interact with food components during processing, storage, or distribution and therefore migrate into food. Hence, commercialization of nanocomposite-based consumer goods and packaging requires evidence of safety regarding nanoparticle release from composite materials during normal use, disposal, and recycling.

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1.5

Handbook of Food Nanotechnology

Characterization and safety of food nanomaterials

The special characteristics of food nanoparticules (particle size, particle distribution, surface area and topography, surface charge, dispersion or aggregation state, composition and purity, hydrophobicity and solubility, chemical reactivity and bioactivity, etc.) bring the following advantages: they provide inclusion of ingredients and nutraceuticals in the food matrices without modifying the physical attributes (color, appearance, texture), and sensorial attributes (taste, smell); they also provide the protection of bioactives against the influence of external factors (temperature, light, oxygen) and the physicochemical factors acting during the passage of food through gastrointestinal tract (pH, ionic strength, enzymes); they provide the controlled release of bioactives, increase the bioavailability of bioactives, etc. (AkbariAlavijeh, Shaddel, & Jafari, 2019; Assadpour & Jafari, 2019a, 2019b, 2019c; Dima & Dima, 2016; Faridi Esfanjani, Jafari, & Assadpour, 2017). Unfortunately, some of these aspects are causes of potential toxicity risks for both inorganic (silver, iron oxide, titanium dioxide, silicon dioxide, and zinc oxide) and organic (lipids, proteins, and carbohydrates) nanoparticles in foods (McClements & Xiaol, 2017; Peters et al., 2014). Although the results regarding safety of food-grade nanoparticles are sometimes contradictory or inconclusive, researchers caution food manufacturers on the concentration and characteristics of nanoparticles in foods. This is because nanoparticle interactions have been found with certain components of the digestive system, suspected of being the potential causes of various diseases (Wani, Masoodi, Jafari, & McClements, 2018). It was shown that certain nanoparticles, such as inorganic ones, caused lymphocyte infiltration, alteration of the intestinal mucus composition, and accumulated in the stomach, small intestine, liver, kidneys, and spleen (Bahadar, Maqbool, Kamal Niaz, & Abdollahi, 2016; Huang, Cambre, & Lee, 2017).

1.5.1 Characterization and analysis of nanomaterials in foods In order to optimize the physicochemical and functional characteristics of foodgrade nanomaterials and to decrease the potential risks of using nanoparticles in foods, it was imperative to control and analyze both free food-grade nanomaterials, and foods prepared with nanoparticle-based delivery systems. That is why the control and analysis of foods manufactured with food nanomaterials and nanoparticlebased delivery systems posed two great challenges that experts in various fields, like materials science, physics, chemistry, mathematics, biology, and medicine, tried to solve. The first challenge refers to the performance of analysis instruments that should measure the physicochemical characteristics of nanometric-scale objects, or evince atom and molecule-level interactions, while another challenge refers to the difficulty of analyzing food-grade nanomaterials present in real food matrices, and in the digestive system or other human tissues and organs. If the initial challenge proved solvable as a result of diversifying and improving analysis devices and techniques, the other challenge is harder to surmount because of the

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complexity of physical and biochemical processes that nanoparticles participate in during the processing, storing, and ingesting of foods containing nanoparticles (Jafari, Esfanjani, Katouzian, & Assadpour, 2017). The characteristics of nanoparticles in a food are in constant change as a result of their interaction with the environment where they are placed, such as chemical interactions (oxidation, hydrolysis), physical interactions (flocculation, swelling, degradation), pH and ionic strength variation, biochemical interactions, and enzymatic processes. The main properties of food nanomaterials and their characterization have been discussed in Chapter 15, Characterization and Analysis of Nanomaterials in Foods, such as structure and morphology, surface area, surface charge, surface hydrophobicity, particle size, mechanical strength, thermal stability, sensory attributes, and their impacts on quality and food safety. Also, the main techniques for analyzing the physical characteristics of food nanomaterials are described in Chapter 15, Characterization and Analysis of Nanomaterials in Foods, for example, microscopic techniques including light microscopy, polarizing microscopy, fluorescence microscopy, confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), environmental SEM (ESEM); light-scattering techniques such as static light scattering (SLC), dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), small-angle X-ray scattering (SAXS), laser Doppler electrophoresis (LDE), X-ray diffraction (XRD); thermal techniques, mainly differential scanning calorimetry (DSC); and techniques for characterization of mechanical properties of nanomaterials including oscillatory tests, colloidal probe AFM, and counterrotating shear method. Almost all scientific papers in specialized literature studying the preparation and behavior of nanomaterials in foods describe at least one analysis technique evincing an importance property of nanoparticles. In general, analytical instruments and specialized analysis techniques are developed for a certain feature, although there are cases when the same feature is analyzed by means of two or more techniques, or the same technique measures several features. According to their functionality and analysis techniques, the features of food-grade nanoparticles are grouped into physical features (surface morphology and structure, size, electric charge, mechanical properties, etc.), chemical characteristics (composition, encapsulation efficiency, biocomponent release, sensorial attributes), and biological features (antibacterial activity).

1.5.2 Safety and regulatory issues of nanomaterials in foods The continuously increasing market size of nanotechnology products of food industry is estimated to reach approximately US$15 billion by 2020 (Naseer et al., 2018). Innovative food products manufactured using nanotechnology tools promise many benefits for consumers and industry. However, diverse nanomaterials ranging from organic to inorganic components might introduce some uncertainties and unforeseen impacts when exposed inadequately in agrifood materials. Potential risks to human health and environment through high exposure level and widespread

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usage lead to serious public and environmental doubts (Amenta et al., 2015). Those issues should be taken into consideration to establish rules and policies for the safe handling and consumption of nanotechnology-based agriculture and food products. The wide use of nanotechnology-based products leads to the high potential of exposure to nanoparticles in different routes. There are three main pathways indicating human exposure to nanomaterials (Jafari, Esfanjani, et al., 2017). Those are dermal exposure occurring through skin in the case of direct contact with the cosmetics and drugs containing nanoparticles, inhalation occurring through volatile materials harboring nanoparticles, and ingestion occurring through uptake of food materials supplemented with nanoparticles. In all three cases, these ultrafine particles can enter into the body, pass the cell barriers and penetrate through tissues and organs, and thus be deposited in various parts of the body. The reaction of the body and possible consequences arising from exposure might be highly dependent on type and physicochemical characteristics of nanoparticles (Wani et al., 2018). Organic nanoparticles based on carbohydrates, proteins, lipids, and vitamins are considered as digestible; however, inorganic ones based on metallic chemicals such as silver, titanium, and silica are considered as indigestible. Current literature contains many in vitro and in vivo research studies tracking possible health consequences due to exposure of nanoingredients in agrifood-related products. Worldwide, countries pay great attention to the regulation of safe production and handling of nanomaterials to be used in the food industry (Jafari, Katouzian, et al., 2017). Legislation, recommendations, and guidances introduced by legal authorities are significant tools to be considered in the assessment of potential risks and safety rules of nanotechnology used in foods (Amenta et al., 2015). The European Commission (EC), European Food Safety Agency (EFSA), Environmental Protection agency (EPA), Organization for Economic Cooperation and Development (OECD), International Standard Organization (ISO), Food and Drug Administration (FDA), World Health Organization (WHO), and Scientific Committees and Agencies are major authorized bodies in Europe and the United States who direct regulatory issues and guidelines related to nanomaterials in foods. Common regulatory procedures indicate identification of nanomaterials through their size, surface characteristics, chemical composition, and stability which are very crucial to determine their possible interactions and persistence in the body, thus providing data for risk assessment. Various analytical methods accompanied with imaging techniques are widely used to detect and identify nanoparticles in foods in order to assess their potential risks or hazards. Additionally, in vitro and in vivo studies provide quite significant data to determine possible responses in the body against nanoparticles. Uncertainties and limited knowledge about the effects of nanoparticles incorporated into foods leading to health and safety concerns might be eliminated by welldefined regulations and legislation globally. That will provide transparency in the manufacture and supply of nanofood products, and thus public acceptance will be supported. In Chapter 16, Safety and Regulatory Issues of Nanomaterials in Foods, risk and hazard assessment, possible exposure routes, toxicological outcomes, and regulations and guidelines for risk evaluation and safety assessment have been discussed.

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In order to support the commercial potential of nanotechnology-derived agrifood products, safe and harmonized approaches should be considered. OECD, ISO, FAO, and WHO have created Codex Alimentarius Commission that is proposing to create international food standards and guidelines (Amenta et al., 2015). A well-defined global regulatory approach should be developed for the safety assessment of nanofoods and transparently supported marketing. Each national government is required to generate rules for the regulation of nanoenabled food products, particularly with international cooperation to establish global security systems to detect nanoparticles present in imported food materials (Bumbudsanpharoke & Ko, 2015). Also, each nation has to implement legislative guidelines to protect health and environment against the uncontrolled use of nanomaterials in food-related products. The lack of knowledge on the health and environmental effects and potential risks with uncertain toxicity levels has effects on public perception and acceptance for the consumption of nanoparticle-containing food products.

1.5.3 Consumer expectations and attitudes towards nanomaterials in foods The applications of nanotechnology are becoming increasingly competent in the food sector with evolutional contributions to food safety from the farm field to the end market, leading to radical changes in the way food is stored, processed, monitored, and consumed (Alehosseini & Jafari, 2019; Cushen, Kerry, Morris, CruzRomero, & Cummins, 2012; Katouzian & Jafari, 2016). During agricultural production, nanomaterials can be used as smart coating for agricultural inputs, such as fertilizer and pesticide, and it facilitates the targeted release of ingredients to achieve precise and efficient soil management (Scrinis & Lyons, 2007; Wani et al., 2019). For food manufacturers, nanomaterials could benefit the market intermediaries and reduce production costs by creating nonfouling surfaces to prevent clogging in processing machines (Tepper et al., 2005). For food functionality, certain nanoparticles could create increased bioavailability with enriched nutrients or introduce different flavors into novel food products (Garavand, Rahaee, Vahedikia, & Jafari, 2019; Koshani & Jafari, 2019). Food safety is a major concern of many consumers (Jafari, Ghanbari, Dehnad, & Ganje, 2018), as described in the previous section. The fast-changing pace of people’s daily diet and food habits has brought increasing threats from foodborne pathogens to human health. With the applications of nanotechnology, promising results have been developed in the area of food packaging (Dehnad, EmamDjomeh, et al., 2014; Hashemi Tabatabaei et al., 2018). Despite the increasing opportunities surrounding nanotechnology applications, there are also concerns due to the potential negative effects (Jafari, Katouzian et al., 2017; Rafiee, Nejatian, Daeihamed, & Jafari, 2019a). One concern about human health is that certain nanomaterials in food could gain access to tissues in the human body, resulting in the accumulation of toxic contaminants and causing unintended effects on human health (Cushen et al., 2012; Oberdo¨rster, Oberdo¨rster, & Oberdo¨rster, 2005). Some studies

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have expressed specific health risks including intracellular damage, pulmonary inflammation, and vascular disease (Brown, Stone, Findlay, MacNee, & Donaldson, 2000; Das, Saxena, & Dwivedi, 2008; Mihindukulasuriya & Lim, 2014). In the meantime, production of nanopackaging will inevitably use nanoparticles on a large scale, which leads to possible particle migration into water, air, and soil to cause undesired consequences to the environment (Silvestre, Duraccio, & Cimmino, 2011). While existing studies indicate that the expected nanoparticle concentrations in the environment are substantially limited and present low-level risk for biological systems (Boxall, Tiede, & Chaudhry, 2007), more research is still needed on how long and in which form will the undesired nanoparticles survive. The development and success of food technologies are shown to be contingent upon societal responses to their applications (Fischer, van Dijk, de Jonge, Rowe, & Frewer, 2012). However, in the case of nanopackaging and nanofood, the public awareness and knowledge are limited, and individuals do not have extensive experience with nanotechnology (Fischer et al., 2012; Lee, Scheufele, & Lewenstein, 2005; Siegrist, Stampfli, Kastenholz, & Keller, 2008). As a consequence, a lack of clear information decreases consumer confidence and compromises the acceptance of new nanoproducts despite their social benefits (Roosen, Bieberstein, Marette, Blanchemanche, & Vandermoere, 2011). Under such situation, it is important to explore consumers’ attitude toward the information on nanopackaging used for food products; and how information from different sources may influence public opinion toward and acceptance of nanotechnology, especially nanopackaging. In addition to the general attitude, studies have also shown that the initial attitude toward nanopackaged food products may change considerably as more detailed information becomes available. Fischer et al. (2012) investigated public reactions when different risk benefit information about nanotechnology’s application in food was provided; their results showed that consumer perceptions changed significantly after provision of the information. Roosen et al. (2011) evaluated the effect of information on consumers’ willingness to pay (WTP) for nanofoods and concluded that information had a significant influence on consumer WTP. Specifically, health information significantly decreased WTP, while societal and environmental information was not as important. The success of new food technology applications are largely determined by consumers’ initial attitudes; for nanotechnology application in food, consumer awareness is still low (Chaudhry et al., 2008; Siegrist et al., 2008), which is similar to genetic modification (GM) technology in its early stage. The majority of consumers are undecided or feel that they do not know enough to form a view. Under such circumstances, the level of comfort or ease of adopting new technology applications plays a significant role in the acceptance of nanotechnology (Silvestre et al., 2011). When it comes to the food industry, consumers’ attitudes are even more sensitive (Cushen et al., 2012). For example, several new food technologies in the past faced reluctant acceptance when they first appeared, such as canned food, pasteurized milk, microwave cooking, and GM food (Miller, Lowrey, & Senjen, 2008). Recent studies show that a similar pattern is occurring in nanotechnology and consumers are hesitant to buy nanofood or nanopackaged food (Siegrist, Cousin, Kastenholz, & Wiek, 2007).

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However, the use of nanotechnology in packaging seems to be more acceptable than the use of nanotechnology in food (Siegrist et al., 2008). Different parameters affecting consumer acceptance of food nanotechnology along with a case study have been presented in Chapter 17, Consumer Expectations and Attitudes Toward Nanomaterials in Foods.

1.6

Conclusion and further remarks

Food-grade nanomaterials are used in food processing as food additives, in the manufacture of smart packaging, in nutraceutical protection and to increase their bioavailability, and in producing biosensors for detection of toxins, pathogens, and pesticides. A brief overview of nanotechnology applications in various fields of the food industry was given in this chapter. Despite the increasing opportunities surrounding nanotechnology applications in the food industry, there are also concerns due to the potential negative effects (Jafari, Katouzian, et al., 2017; Rafiee et al., 2019a). One concern about human health is that certain nanomaterials in food could gain access to tissues in the human body, resulting in the accumulation of toxic contaminants and causing unintended effects to human health. Some studies have expressed specific health risks including intracellular damage, pulmonary inflammation, and vascular diseases. Knowing the characteristics of nanomaterials in foods is an important requirement for food producers because they influence the food quality and safety. That is why, lately, more and more research has been focusing on the development of new techniques for analyzing and controlling nanomaterials. Most analysis techniques apply to isolated nanoparticles or samples whose processing may alter the characteristics of nanoparticles. Due to the complexity of food matrices, it is necessary to improve the techniques of sampling and sample preparation, extraction, and separation of nanoparticles for their analysis. Therefore, an important objective of today’s researchers is the invention of high-performance techniques that ensure a minimal processing of samples or analysis of nanomaterials under the real conditions of the food matrix, of the organs and tissues of the human body in which they accumulate, or of the environment.

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Soshnikova, V., Kim, Y. J., Singh, P., Huo, Y., Markus, J., Ahn, S., et al. (2018). Cardamom fruits as a green resource for facile synthesis of gold and silver nanoparticles and their biological applications. Artificial Cells, Nanomedicine, and Biotechnology, 46(1), 108 117. Sozer, N., & Kokini, J. L. (2009). Nanotechnology and its applications in the food sector. Trends in Biotechnology, 27(2), 82 89. Suppakul, P., Miltz, J., Sonneveld, K., & Bigger, S. W. (2003). Active packaging technologies with an emphasis on antimicrobial packaging and its applications. Journal of Food Science, 68(2), 408 420. Tamjidi, F., Shahedi, M., Varshosaz, J., & Nasirpour, A. (2013). Nanostructured lipid carriers (NLC): A potential delivery system for bioactive food molecules. Innovative Food Science and Emerging Technologies., 19, 29 43. Tepper, et al. (2005). Nanosize electropositive fibrous adsorbent, US Patent No. 6,838,005 B2. Tiwari, A., & Tuner, A. P. F. (2014). Nanotechnology Advanced materials series. USA: Wiley-Scrivener, ISBN: 9781118773932. Umamaheswari, C., Lakshmanan, A., & Nagarajan, N. S. (2018). Green synthesis, characterization and catalytic degradation studies of gold nanoparticles against Congo Red and Methyl Orange. Journal of Photochemistry and Photobiology B: Biology, 178(January), 33 39. Vahedikia, N., Garavand, F., Tajeddin, B., Cacciotti, I., Jafari, S. M., Omidi, T., & Zahedi, Z. (2019). Biodegradable zein film composites reinforced with chitosan nanoparticles and cinnamon essential oil: Physical, mechanical, structural and antimicrobial attributes. Colloids and Surfaces B: Biointerfaces, 177, 25 32. Van der Bruggen, B., M¨antt¨ari, M., & Nystro¨m, M. (2008). Drawbacks of applying nanofiltration and how to avoid them: A review. Separation and Purification Technology, 63 (2), 251 263. Van Der Bruggen, B., Vandecasteele, C., Van Gestel, T., Doyen, W., & Leysen, R. (2003). A review of pressure-driven membrane processes in wastewater treatment and drinking water production. Environmental Progress, 22(1), 46 56. Vermeiren, L., Devlieghere, F., de Kruijf, N., & Debevere, J. (2000). Development in the active packaging of foods. Journal of Food Technology in Africa, 5(1), 6 13. Vijayan, R., Joseph, S., & Mathew, B. (2018). Indigofera tinctoria leaf extract mediated green synthesis of silver and gold nanoparticles and assessment of their anticancer, antimicrobial, antioxidant and catalytic properties. Artificial Cells, Nanomedicine, and Biotechnology, 46(4), 861 871. Wang, J. (2006). Analytical electrochemistry. John Wiley & Sons. Wang, S., & Peng, Y. (2010). Natural zeolites as effective adsorbents in water and wastewater treatment. Chemical Engineering Journal, 156(1), 11 24. Wani, T. A., Masoodi, F. A., Baba, W. N., Ahmad, M., Rahmanian, N., & Jafari, S. M. (2019). Chapter 11—Nanoencapsulation of agrochemicals, fertilizers, and pesticides for improved plant production. In M. Ghorbanpour, & S. H. Wani (Eds.), Advances in phytonanotechnology (pp. 279 298). Academic Press. Wani, T. A., Masoodi, F. A., Jafari, S. M., & McClements, D. J. (2018). Chapter 19—Safety of nanoemulsions and their regulatory status. Nanoemulsions (pp. 613 628). Academic Press. Weiss, J., Takhistov, P., & McClements, D. J. (2006). Functional materials in food nanotechnology. Journal of Food Science, 71, 107 116. Xu, J., Cao, Z., Zhang, Y., Yuan, Z., Lou, Z., Xu, X., & Wang, X. (2018). A review of functionalized carbon nanotubes and graphene for heavy metal adsorption from water: Preparation, application, and mechanism. Chemosphere, 195, 351 364.

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Yang, N., Chen, X., Ren, T., Zhang, P., & Yang, D. (2015). Carbon nanotube based biosensors. Sensors & Actuators, B: Chemical, 207, 690 715. Yin, P. T., Kim, T.-H., Choi, J.-W., & Lee, K.-B. (2013). Prospects for graphene nanoparticle-based hybrid sensors. Physical Chemistry Chemical Physics, 15(31), 12785 12799. Zhang, H., Hortal, M., Dobon, A., Bermudez, J. M., & Lara-Lledo, M. (2015). The effect of active packaging on minimizing food losses: Life cycle assessment (LCA) of essential oil component-enabled packaging for fresh beef. Packaging Technology and Science, 28 (9), 761 774. Zhang, L., Qi, H., Yan, Z., Gu, Y., Sun, W., & Zewde, A. A. (2017). Sonophotocatalytic inactivation of E. coli using ZnO nanofluids and its mechanism. Ultrasonics Sonochemistry, 34, 232 238. Zhou, J. J., Wang, S. Y., & Gunasekaran, S. (2009). Preparation and characterization of whey protein film incorporated with TiO2 nanoparticles. Journal of Food Science, 74(7), 50 56.

Nanofluid thermal processing of food products

2

Saeed Salari and Seid Mahdi Jafari Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

2.1

Introduction

Due to the high price of energy, improving the performance of heat exchangers and reducing their sizes is of great interest in various industries. In this context, one of the challenges that industries should be dealing with is the low thermal conductivity of conventional heat transfer fluids, resulting in the poor transfer of heat (Sheikholeslami & Ganji, 2017). According to the formula of the heat transfer rate by convection (q 5 hAΔT), any improvement in the performance of heat transfer devices can be achieved through extending the surface area of heat transfer, increasing temperature, or augmenting the heat transfer coefficient (HTC). Surface area extension and temperature increase are not favorable because they will give rise to sizable equipment, excessive power consumption, and high operating costs. One of the methods that can be used to increase HTC is the addition of solid metal particles into the conventional heat transfer fluids including glycols, water, engine oil, etc. (Mahbubul, 2019a). The concept of adding metallic particles to improve the thermal properties of fluids stemmed from Maxwell’s work published in 1873, however its practicability has been questioned due to the problems caused by large-scale particles, even at micrometer-size range. These problems were the fast sedimentation of particles, clogging, erosion, and significant pressure drop (Ambreen & Kim, 2018). The advances in nanotechnology paved the way to producing smaller particles to tackle the problems mentioned above. Moreover, the effect of nanoparticles in increasing thermal conductivity of the base fluid is significantly higher than microparticles due to their higher surface to volume ratio. Nanofluids are colloidal suspensions containing particles at nanometer size (Ahmadi, Mirlohi, Alhuyi Nazari, & Ghasempour, 2018; Fan & Wang, 2011; Ganji & Kachapi, 2015). The chief interest in nanofluids has fundamentally been based on the anomalously increased thermal conductivity of the base fluid at the low concentrations of nanoparticles (Angayarkanni & Philip, 2015). Recently, a new application for nanofluids in the food industry has been proposed to increase the efficiency of thermal processing devices, reduce the processing time, protect bioactive compounds against degradation, and improve the quality of food products (Salari and Jafari, 2020). In the current chapter, first an overview of nanofluids, their types, properties, preparation methods, and dispersion Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00002-9 © 2020 Elsevier Inc. All rights reserved.

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stability will be given, and then the bodies of research around their effects on the thermal performance of heat exchangers and their applicability in the food industry will be investigated and discussed further.

2.2

Thermophysical properties of nanofluids

Thermophysical properties are generally referred to any feature or characteristic that defines the heat transfer behavior of a material, and they have an essential role in the calculation of some crucial parameters, such as HTC, pressure drop, and energy efficiency, on which the performance of an industrial heat transfer equipment significantly depends (Mahbubul, 2019b; Masood & Trujillo, 2016). In this section, the thermophysical properties of nanofluids, including thermal conductivity, viscosity, density, and specific heat capacity, will be discussed in detail. Thermophysical properties of some common nanofluids have been summarized in Table 2.1.

2.2.1 Thermal conductivity of nanofluids Thermal conductivity is one of the two thermophysical properties influencing the heat transfer behavior of a fluid alongside the viscosity. Studies showed that by adding nanoparticles, thermal conductivity would be increased. That means the heat transfer will be improved by an increase in thermal conductivity (Ahmadi et al., 2018). The thermal conductivity is dependent on several factors (Fig. 2.1) including the particle size and shape (Essajai, Mzerd, Hassanain, & Qjani, 2019; Kim, Choi, & Kim, 2007; Warrier & Teja, 2011), temperature (Duangthongsuk & Wongwises, 2009; Mintsa, Roy, Nguyen, & Doucet, 2009; Yang & Han, 2006), pH (Xian-Ju & Xin-Fang, 2009), surfactant (Ghadimi & Metselaar, 2013; Li et al., 2008), the volume fraction (Oliveira L.R., de Ribeiro, Reis, Cardoso & Bandarra Filho, 2019; Li & Peterson, 2006), and cluster size of particles (Hong, Hong, & Yang, 2006). Murshed, Leong, and Yang (2005) reported the maximum enhancement in thermal conductivity of TiO2/water nanofluid obtained at a nanoparticle volume fraction of 5%, that was 29.70% and 32.80% for nanoparticle sizes of 15 nm, and 10 nm 3 40 nm, respectively. Hong, Yang, and Choi (2005) observed an 11.5% increase in thermal conductivity of ethylene glycol by adding 0.55% volume fraction of Fe nanoparticles and 18% increase after 50 min sonication. Liu, Lin, Tsai, and Wang (2006) studied the thermal conductivity of Cu/water nanofluids prepared by a chemical reduction method. They observed that the thermal conductivity of water increased by 23.8% after the addition of 0.1 vol.% Cu nanoparticles. Godson, Raja, Lal, and Wongwises (2010) reported that at the temperature of 70 C, by adding 0.3 and 0.9 vol.% of silver nanoparticles into water, the thermal conductivity increases 27% and 80%, respectively. Sen Gupta et al. (2011) showed a 27% increase in the thermal conductivity of water when 0.2% of graphene nanosheets was added. Pang, Jung, Lee, and Kang

Table 2.1 Thermophysical properties of some common nanofluids. Nanofluid

Nanoparticle concentration (%)

Temperature

Thermal conductivity (W/m.K)

Viscosity (MPa/s)

Density (kg/ m3)

Specific heat capacity (J/ kg
K)

References

Al2O3/methanol

0.05 0.25

5 25 C

0.21 0.23

0.70 0.94

791 814

3.72 5.18

Al2O3/water

0 4

0.610 0.682

0.611 0.682

996 1112

4181 3719

MWCNT/water

0.613 0.656 0.107 0.116

SiO2/lithium carbonatepotassium carbonate (62:38) Al2O3-Cu/water

0 1 0 0.5 0 1

Mostafizur, Saidur, Abdul Aziz, and Bhuiyan (2015) Jafari, Jabari, Dehnad, et al. (2017b) Hwang et al. (2007)

0.1

0.62

0.93

Fe3O4/water

0 2

0.602 0.753 0.631 0.870 0.653 0.966

CuO/water

0

23 37 nm

1 10

0.79 1.65 0.54 1.12 0.3 0.89 1.305 0.797 0.546 1.311 1.456 0.804 0.912 0.553 0.620 1.338 2.261 0.827 1.440 0.565 1.131

MWCNT/oil

11 nm

20 C 40 C 60 C 10 C 30 C 50 C 10 C 30 C 50 C 10 C 30 C 50 C

1620 1650 1930 2030

Shin and Banerjee (2011)

1001.3

4176.83

998.5 1094.73 992 1088.4 983.3 1079.83

4182 4111.76 4178 4107.84 4183 4112.74

Suresh, Venkitaraj, Selvakumar, and Chandrasekar (2012) Syam Sundar, Singh, and Sousa (2013) Pastoriza-Gallego, Casanova, Legido, and Pin˜eiro (2011)

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Handbook of Food Nanotechnology

Figure 2.1 Influential factors on nanofluid thermal conductivity.

(2012) reported 10.47% and 14.29% augmentation in thermal conductivity of methanol by adding 0.5 vol.% of Al2O3 and SiO2 nanoparticles, respectively. Sadri et al. (2014) found 22.31% increment in the thermal conductivity of water when 0.5 wt. % multiwalled carbon nanotubes (MWCNTs) and 0.25 wt.% gum Arabic has been added (the temperature and sonication time were 45 C and 40 min, respectively). Akilu, Baheta, Kadirgama, Padmanabhan, and Sharma (2019) researched β-SiC/ ethylene glycol and β-SiC/propylene glycol nanofluids. They found that the maximum enhancement of 14.6% and 4.8% have been obtained in thermal conductivity of ethylene and propylene glycols, respectively, after the addition of β-SiC nanoparticles. Essajai et al. (2019) investigated the thermal conductivity of gold (Au) nanoparticles. They found an increase of 12.58% to 21.43% and 15.3% to 29.6% in thermal conductivity of Argon liquid when spherical and rod-shaped gold nanoparticles with the volume fraction ranging from 0.5% to 3% was added, respectively.

2.2.2 Viscosity of nanofluids Viscosity is another property of nanofluids that is of the same importance as thermal conductivity because of its direct influence on convective heat transfer, pressure drop, and pumping power (Mishra, Mukherjee, Nayak, & Panda, 2014). Adding nanoparticles will enhance the viscosity of base fluids that is regarded as being unfavorable since it counteracts the effects of thermal conductivity on improving the heat transfer performance (Venerus et al., 2010). It has been suggested that for applicability of nanofluids, the increase in viscosity should not be more than four times larger than the increase in thermal conductivity (Prasher, Song, Wang, & Phelan, 2006). Studies have shown that the viscosity of nanofluids is dependent on several factors (Fig. 2.2) such as nanoparticle volume fraction (Kole & Dey, 2011), particle size (Jia-Fei, Zhong-Yang, Ming-Jiang, & Ke-Fa,

Nanofluid thermal processing of food products

43

Figure 2.2 Influential factors on viscosity of nanofluids.

2009), temperature (Nguyen et al., 2007), and the shape and agglomeration of particles (Timofeeva, Routbort, & Singh, 2009). The effect of temperature on viscosity of nanofluids seems to be more pronounced than that of nanoparticle size (Hemmat Esfe, Saedodin, Asadi, & Karimipour, 2015). Namburu, Kulkarni, Misra, and Das (2007) reported that by adding 6.12 vol.% CuO into the ethylene glycol and water mixture (60:40), the viscosity increased around four times. Chandrasekar, Suresh, and Chandra Bose (2010) showed that the viscosity of Al2O3/water nanofluid with 5 vol.% nanoparticle was 2.36 times greater than that of the base fluid. Wang, Wang, Yan, Wang, and Feng (2016) reported that by increasing the volume concentration of Fe2O3 from 0.5% to 5%, the viscosity of nanofluid would be enhanced 22.5% at 293 K. They also showed that the viscosity of Fe2O3/water nanofluid containing 0.5 vol.% would decrease 52.94% by increasing the temperature from 293 to 333K.

2.2.3 Density of nanofluids Density is another crucial thermophysical property of nanofluids due to its similar impact as viscosity on characteristics like Reynolds number, friction factor, pressure drop, and pumping power (Mahbubul, Saidur, & Amalina, 2013; Nabati Shoghl, Jamali, & Keshavarz Moraveji, 2016). By definition, density is ratio of the mass to volume of a material. The factors influencing the density of fluids are chemical composition and soluble components, temperature, and pressure (Scho¨n, 2015). It has been shown that the effect of nanoparticle size on the density of a nanofluid is significant, and as the size of particles decreases, the density will increase ˙ Vallejo, and Lugo (2018) reported (Pastoriza-Gallego et al., 2009). In contrast, Zyła, ˙ et al., 2018). that the effect of nanoparticle size on the density is ignorable (Zyła

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Some studies showed that the concentration of nanoparticles significantly affected the density of nanofluids; however, the influence of temperature on density was of no significance (Chavan & Pise, 2019; Vajjha, Das, & Mahagaonkar, 2009). Sharifpur, Yousefi, and Meyer (2016) discussed that for developing a numerical model to predict the density of a nanofluid precisely, the role of the nanolayer must be considered. The nanolayer is defined as a thin layer located at the interface of suspended particles and the base fluid molecules.

2.2.4 Specific heat capacity of nanofluids Specific heat capacity is the amount of thermal energy a material needs to receive or lose for a change in temperature to occur. For calculating the thermal diffusivity or dynamic thermal conductivity and the Prandtl number, the specific heat capacity of material must be measured. It seems that by increasing the volume fraction of nanoparticles, the specific heat capacity of a nanofluid tends to be decreased (Cabaleiro, Gracia-Ferna´ndez, Legido, & Lugo, 2015; Vajjha & Das, 2009; Zhou & Ni, 2008). Other than the volume fraction of the nanoparticles, the type of the base fluid and the nanoparticle material are two influential factors affecting the specific heat capacity of a nanofluid (Murshed, 2011). A study showed that the addition of 15% MgO, ZnO, and ZrO2 nanoparticles into the ethylene glycol has resulted in 9%, 12%, and 12% reduction, respectively, in the specific heat capacity compared to the base fluid (Cabaleiro et al., 2015). Namburu, Kulkarni, Dandekar, and Das (2007) showed that adding SiO2 with the volume fraction of 10% caused a decrease of 12% in the specific heat capacity of the base fluid, a mixture of ethylene glycol and water with the weight ratio of 60:40. On the contrary, Shin and Banerjee (2011) reported a considerable increase (approximately 25%) in specific heat capacity of the mixture of lithium carbonate and potassium carbonate (62:38) after the addition of SiO2 nanoparticles. They suggested that this increase can be attributed to the high specific surface energy of nanoparticles.

2.3

Preparation of nanofluids

The method used to prepare a nanofluid is a determining step with a significant role in thermal conductivity improvement prompted by the addition of nanoparticles. The preparation methods of nanofluids are generally categorized as one-step or two-step techniques, as shown in Fig. 2.3. In the one-step procedure, nanoparticles are directly synthesized and dispersed inside the fluid through physical vapor deposition (PVD) or liquid chemical methods. However, in the two-step technique, nanoparticles, nanofibers, or nanotubes are first synthesized as nanopowders through methods like inert gas condensation, chemical vapor deposition, mechanical alloying, etc. Then nanofluids are prepared by dispersion of nanopowders into the base fluid (Li, Zhou, Tung, Schneider, & Xi, 2009).

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Figure 2.3 Nanofluid preparation methods.

The two-step method is the one that is widely used in the preparation of nanofluids commercially. The benefits of two-step methods are the large-scale production and possibility of using any fluid to produce nanofluids. The big disadvantage of the two-step method is the agglomeration of nanoparticles (Babita, Sharma, & Gupta, 2016). The advantages of the one-step procedure include the lack of stages, such as drying, storage, transportation, and dispersion of nanopowders, and the reduction of nanoparticle clusterings. The preparation of nanofluids through a one-step method can be done physically or chemically, each of which has its pitfalls. Through a physical technique, nanofluids cannot be produced at large scale, and their preparation cost is high. The downfall of the chemical method is that incomplete reactions and stabilization result in impurities interfering with the impact of nanoparticles on thermal conductivity (Yu & Xie, 2012). One of the main obstacles facing the practical application of nanofluids and influencing their impact on thermal conductivity is the agglomeration of nanoparticles that destabilizes their suspensions. Hwang et al. (2008) investigated different techniques to prolong the stability of carbon black/water and Ag/silicon oil nanofluids. They found that surfactants like SDS and oleic acid can be effective in the preparation of stable nanofluids. Also, they reported that to reduce the aggregation of nanoparticles during the two-step procedure, the performance of the high-pressure homogenizer was far better than the stirrer, the ultrasonic bath, and ultrasonic disruptor. In the one-step method, the modified magnetron sputtering system was shown to be promising in the improvement of nanofluid stability (Hwang et al., 2008).

2.4

Application of nanofluids in different heat exchangers

Heat exchangers are devices making the transfer of heat possible between two or more fluids (Manjunath & Kaushik, 2014). Heat exchangers can be categorized based on different criteria such as the flow arrangement, direct or indirect contact between fluids, construction type, etc. (Zohuri, 2018). In the heat exchangers (all mentioned in this section) where the fluid streams are not in direct contact and there

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is a solid wall in between, the heat transfer rate would be expressed in terms of overall HTC (OHTC). In overall heat transfer, the combination of both conductive and convective transfer of heat is considered (Toledo, Singh, & Kong, 2018). Reynolds number, type, and concentration of nanoparticles are some of the factors significantly affecting the convective HTC (Ravi Kumar et al. 2018; Barzegarian, Moraveji, & Aloueyan, 2016; Sun, Peng, Zuo, Yang, & Li, 2016). The two most common types of heat exchangers widely used in the food industry are the plate and shell and tube heat exchangers (Jafari, Jabari, Dehnad, & Shahidi, 2017b). The first use of plate heat exchangers in industry dates back to 1923, when it was used for the thermal processing of milk. Afterward, the innovative advances in the design of this type of heat exchanger made them suitable for chemical industry applications as well (Kumar, 1984). They are generally made up of some gasketed plates located inside a frame in which fluids flow in the channels and go from one plate to another through ports that are in the corner of the plates. The benefits of using these types of heat exchangers, include simplicity and compactness, low cost, low fouling, easy cleaning, and flexibility (Wang & Sundee´n, 2004). Shell and tube heat exchangers are the most common type after the plate exchangers. They fundamentally consist of three parts, including the front head, the shell, and the rear head. The tubes and baffles are located inside the shell side. The main advantage of the shell and tube heat exchanger, particularly compared to plate heat exchangers, is their ability to be used under high temperature and pressure (Jafari, Jabari, Dehnad, et al., 2017b; Mukherjee, 1998).

2.4.1 Heat transfer enhancement by nanofluids For the purpose of optimizing plate heat exchangers, the effect of using nanofluids on the HTC has been investigated. In a study, Kumar, Tiwari, and Ghosh (2016b) reported a 49% increase in OHTC by adding MWCNTs with the volume concentration of 0.75% in water and 5 mm of spacing between plates has been applied. In another study, the use of Ag/water nanofluids with nanoparticle concentration of 100 ppm resulted in 6.18% to 16.79% increase in OHTC (Behrangzade & Heyhat, 2016). Kumar, Tiwari, and Ghosh (2016a) reported 27% enhancement in OHTC, when ZnO/water nanofluid with the nanoparticle volume fraction of 1% and the chevron angle of β 5 60 /60 was applied. In a study on improving the performance of a brazed plate heat exchanger, Barzegarian et al. (2016) demonstrated that by replacing water with TiO2/water nanofluid, 2.5% 23.7% increase in convective HTC and 1.2% 8.5% increase in OHTC was achieved at nanoparticle concentrations of 0.3% 1.5%. In the context of using hybrid nanofluids to achieve better results in the thermal performance of heat exchangers, Huang, Wu, and Sunden (2016) ran a series of experiments to compare the performance of Al2O3/water nanofluids with that of MWCNT-Al2O3/water hybrid nanofluids in a chevron plate heat exchanger. They found that the enhancement in heat transfer achieved by using the hybrid nanofluids was higher than that achieved by using Al2O3/water nanofluids. Moreover, the

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increase in pressure drop caused by the hybrid nanofluids was a little higher, even in comparison with water (Huang et al., 2016). Said, Rahman, El Haj Assad, and Alami (2019) showed that by using CuO/water nanofluids, the effectiveness of the shell and tube heat exchanger increased, whereas the energy consumption and the overall cost decreased. They also observed 11% and 7% enhancement in convective HTC and OHTC, respectively, when nanofluids have been used. Furthermore, they concluded that as the volume fraction of nanoparticles increases, the stability of nanofluids deteriorates. In contrast, the nanofluid stability improved as the surfactant was added (Said et al., 2019). Shahrul, Mahbubul, Saidur, and Sabri (2016) investigated the effect of using various water-based nanofluids on the performance of a shell and tube heat exchanger. They reported that by using ZnO/water [containing polyvinylpyrrolidone (PVP) surfactant], Al2O3/water, and SiO2/water nanofluids at the volume concentrations of 0.3%, 0.5%, and 0.5%, OHTC was improved 35%, 26%, and 12%, respectively. They also showed that the fluid flow rate affected the heat transfer significantly. By keeping the shell-side volumetric flow rate constant (4 L/m), the highest enhancement in heat transfer was achieved at the tube-side volumetric flow rates of 6, 7, and 7 L/m for ZnO/water, Al2O3/water, and SiO2/water nanofluids, respectively. In the case of constant tube-side volumetric flow rate (4 L/m), the highest heat transfer augmentation was observed at the volumetric flow rate of 8 L/m for each nanofluid flowing on the shell side (Shahrul et al., 2016). Kumar and Sonawane (2016) carried out an experiment evaluating heat transfer behavior of Fe2O3/water and Fe2O3/ethylene glycol nanofluids in a shell and tube heat exchanger. They reported that at the temperature of 80 C and flow rate of 3 L/ m, the Nusselt number increased up to 29% and 14% when the nanoparticle volume concentration of Fe2O3/water and Fe2O3/ethylene glycol nanofluids, respectively, increased to 0.08%. According to their conclusion, the higher enhancement in the Nusselt number in the case of Fe2O3/water is attributed to the higher thermal conductivity of water compared to ethylene glycol (Kumar & Sonawane, 2016). Aghabozorg, Rashidi, and Mohammadi (2016) investigated the effect of Fe2O3CNT/water magnetic nanofluids on HTC under different flow regimes (laminar, transient, and turbulent) in a shell and tube heat exchanger. It was found that by increasing Reynolds number, the HTC increased significantly. For Fe2O3-CNT/ water nanofluids with nanoparticle concentration of 0.1% and when the voltage of 80 V was applied, the HTC increased 13.54%, 23.37%, and 27.69% under laminar (Re 5 1698.927), transient (Re 5 3981.860), and turbulent (Re 5 6070.124) flow regimes. According to their conclusion, the enhancement in HTC by using nanofluids can result in improving the efficiency of heat exchangers, reducing costs and energy consumption, and making it possible to design compact heat exchangers (Aghabozorg et al., 2016). Syam Sundar et al. (2019) showed that by using Fe3O4/water nanofluid with nanoparticle concentration of 0.06%, an increase of 14.7% was observed in the Nusselt number compared to water. The incorporation of wire coil with core rod inserts (p/d 5 1) enhanced the Nusselt number further to 32.03% (Re 5 28,954). They also demonstrated that by applying nanofluids with or without wire coil with

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core rod inserts, the friction factor increased about 1.092 and 1.162 times compared with that of water. They concluded that use of nanofluids and wire coil with core rod inserts are desirable in practical applications, due to their positive interaction effect on the thermal performance of double pipe U-bend heat exchangers. Nevertheless, the friction factor has been increased (Syam Sundar et al., 2019). Poongavanam, Panchabikesan, Murugesan, Duraisamy, and Ramalingam (2019) investigated the effects of using MWCNT/solar glycol nanofluids on heat transfer and pressure drop in a double pipe heat exchanger in which the inner tube was shot peened by a surface modification technique. Gum Arabic was added to improve the dispersion of MWCNTs in the base fluid. They reported that at the nanotube volume concentration of 0.6% and temperature in the range of 30 C 50 C, the enhancement in thermal conductivity was 28.45% 30.59%. Moreover, they demonstrated that any increase in mass flow rate and the concentration of nanotubes increased convective HTC and pressure drop. However, the Reynolds number had an inverse effect on the convective HTC. They also stated that up to a 115% increase in the convective HTC has been observed when the mass flow rate applied was 0.04 kg/s (Poongavanam et al., 2019). Arulprakasajothi, Elangovan, Chandrasekhar, and Suresh (2018) investigated TiO2/water nanofluid effect on the thermal performance of a tubular heat exchanger with conical strip inserts. The nanofluid and conical strip inserts had a synergistic effect on increasing the Nusselt number. At the Re 5 2251, the maximum enhancement in the Nusselt number was achieved at the TiO2 nanoparticle volume fraction of 0.5%. In the case of the conical strip inserts, the highest increase in the Nusselt number was achieved at twist ratios of 3 and 2 for the staggered and nonstaggered inserts, respectively. According to their results, applying conical strip inserts resulted in further intensification of pressure drop (Arulprakasajothi et al., 2018). Hussein (2017) evaluated the influence of aluminum nitride/ethylene glycol hybrid nanofluids on heat transfer performance of a double pipe heat exchanger under laminar flow conditions. He reported a 12.5% rise in friction factor and up to 35% increase in the Nusselt number, concluding that using nanofluids is a promising technique to improve the thermal performance in practical applications. Furthermore, he found that the temperature and volume fraction of nanoparticles had a significant impact on heat transfer and friction factor (Hussein, 2017). Raei, Shahraki, Jamialahmadi, and Peyghambarzadeh (2016); Raei, Shahraki, Jamialahmadi & Peyghambarzadeh (2017) investigated the effect of using γ-Al2O3/ water nanofluids on heat transfer performance in a double-tube heat exchanger under fully developed turbulent flow conditions. They found that at the nanoparticle volume concentration of 0.15%, an increase of 23% and 25% in the HTC and friction factor, respectively, happened in comparison with water. They demonstrated that by increasing the Reynolds number, the HTC was decreased and also their results indicated that at a γ-Al2O3 nanoparticle volume concentration range of 0.05% 0.15%, the effect of concentration on heat transfer was not significant (Raei et al., 2016, 2017). Raei et al. (2016, 2017) reported 19.3% augmentation in OHTC by using γ-Al2O3/water nanofluids at the nanoparticle volume fraction of 0.15%; by increasing the inlet temperature of nanofluids from 45 C to 65 C, the

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average heat transfer rate enhanced up to 53%. Furthermore, they observed OHTC declined by increasing the flow rate in comparison to water, although they stated that based on their experimental results, increasing the nanofluid flow rate had a positive effect on OHTC and heat transfer rate (Raei et al., 2016, 2017). Singh, Singh, and Singla (2016) used baffles and CuO/water nanofluids in an effort to increase the heat transfer performance of a double pipe heat exchanger. They reported an 8% increase in the Nusselt number and 25% increase in the HTC when Cuo/water nanofluids were used at a nanoparticle concentration of 0.2%. After baffles insertion, the Nusselt number and HTC increased further to 12% and 30%, respectively. Naik and Vinod (2018) investigated the heat transfer performance of a shell and helical coil heat exchanger by using non-Newtonian aqueous carboxymethyl cellulose-based nanofluids containing Fe2O3, Al2O3, and CuO nanoparticles. They reported that nanofluids increased the heat transfer significantly, compared to the base fluid. They also showed that OHTC and the Nusselt number were directly dependent on the flow rate of cold water, temperature of nanofluid, and stirrer speed. Their results indicated that in comparison to Fe2O3 and Al2O3 nanofluids, the CuO nanofluid had the best performance regarding the heat transfer enhancement. The negative effect of using nanofluids on stirrer speed was of no significance (Naik & Vinod, 2018). Radkar, Bhanvase, Barai, and Sonawane (2019) evaluated the effect of ZnO/ water nanofluid on convective heat transfer in a helical copper tube heat exchanger. They showed that the thermal conductivity increased at higher nanoparticle concentrations and temperature. They also reported that by using ZnO/ water nanofluids at the volume fraction of 0.5%, an increase of 18.6% was observed in the Nusselt number. Bhanvase, Sayankar, Kapre, Fule, and Sonawane (2018) carried out research evaluating the effect of polyaniline (PANI)/water nanofluids on a vertical helical coiled heat exchanger. They observed that the HTC significantly increased through increasing the nanofiber concentration and flow rate of nanofluids. Their results also indicated that 10.5% and 70% increases were achieved by using nanofluids containing 0.1 and 0.5 vol.% PANI nanofibers, respectively (Bhanvase et al., 2018). Sarafraz and Hormozi (2015) studied the effect of a biologically produced silver/ ethylene glycol water nanofluid on forced convective heat transfer in a countercurrent double pipe heat exchanger. It was reported that 67% increase in HTC was achieved when the silver/ethylene glycol water nanofluid was used with a nanoparticle concentration of 1%. However, their data indicated that the use of nanofluids resulted in an insignificant increase in friction factor and pressure drop (Sarafraz & Hormozi, 2015). Palanisamy and Mukesh Kumar (2019) carried out experiments on the use of MWCNT/water nanofluid in a cone helically coiled heat exchanger under turbulent flow conditions (2200 , De , 4200). They reported that in comparison to water, by using nanofluids at nanoparticle concentrations of 0.1%, 0.3%, and 0.5%, the enhancement in HTC was 14%, 30%, and 41% and the increase in pressure drop was 16%, 30%, and 42%, respectively. Akyu¨rek, Geli¸s, Sahin, ¸ and Manay (2018) conducted experiments on a concentric tube heat exchanger evaluating the effect of Al2O3/water nanofluids with or

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without wire coil turbulators on heat transfer and pressure drop. They reported that addition of nanoparticles at volume fractions ranging from 0.4% to 1.6% into water caused an increase in the Nusselt number in the range of 35.66% to 168.26%. Furthermore, they concluded that nanofluids are more suitable to be used without any turbulator because their results demonstrated that using turbulators led to a significant rise in pressure drop (Akyu¨rek et al., 2018). A study on heat transfer behavior of alumina and fly ash nanofluids in a cocurrent and countercurrent concentric tube heat exchanger was also conducted. The results showed that at nanoparticle concentration of 2% and flow rate of 6.2 L/m, OHTC increased 62% and 6% when fly ash and alumina nanofluids were used as hot working fluids in the cocurrent heat exchanger, respectively. In the countercurrent heat exchanger, by using fly ash and alumina nanofluids, 30% and 9% increase in OHTC was observed at a nanoparticle concentration of 2% and flow rate of 6.7 L/m, respectively (So¨zen, Variyenli, ¨ zdemir, Gu¨ru¨, & Aytac¸, 2016). O Walvekar, Siddiqui, Ong, and Ismail (2016) studied the effect of CNT nanofluids stabilized by gum Arabic on heat transfer in a concentric tube heat exchanger under turbulent flow conditions. They reported an enhancement in the range of 67% and 250% in thermal conductivity when CNT nanofluids were used instead of water at nanoparticle concentrations of 0.051% 0.085% at temperatures from 25 C to 55 C. Therefore their results showed that temperature and concentration of nanoparticles had a strong influence on thermal conductivity. They also found a 7% 202% increase in the convective HTC by using CNT nanofluids at the same concentration and temperature range mentioned above. It has been demonstrated that nanofluids had a higher viscosity and density than water. However, they concluded that the effect of nanofluid viscosity and density in deteriorating the heat transfer performance of heat exchangers through pressure drop escalation is ignorable since its positive impact on the HTC is more pronounced. Also, it was shown that at higher temperatures, viscosity decreased, probably because higher temperature decreased the intramolecular forces between nanoparticles and the base fluid molecules (Walvekar et al., 2016). Khalifa and Banwan (2015) investigated the role of nanoparticle concentration in heat transfer behavior of γ-Al2O3/water nanofluids in a concentric tube heat exchanger under turbulent flow conditions. It was demonstrated that the increase in Reynolds number and nanoparticle concentration resulted in a significant augmentation in the Nusselt number and the HTC. In their study, the maximum and minimum increase in the Nusselt number was 22.8% and 2.5% obtained at Reynolds numbers of 6026 and 2957 and γ-Al2O3 concentration of 1% and 0.25%, respectively (Khalifa & Banwan, 2015). Hosseini et al. (2017) carried out experiments on the heat transfer performance of an annular heat exchanger under turbulent flow conditions when covalently functionalized MWCNT/water nanofluids were used as a working fluid. They reported an augmentation up to 35.89% and 20.15% in convective HTC and the Nusselt number, respectively, by employing nanofluids instead of the base fluid at a Reynolds number of 7944 and nanotube concentration of 0.175 wt.%. They also found 3% increase in friction factor by using nanofluids at the same concentration (Hosseini et al., 2017).

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Arzani, Amiri, Kazi, Chew, and Badarudin (2016) investigated the effect of using covalently functionalized MWCNTs in water nanofluids as a new coolant on heat transfer performance of a horizontal annular heat exchanger. Their results showed a significant increase in thermal conductivity, viscosity and density, and a considerable decrease in specific heat capacity after the addition of nanotubes into water. They reported 22.4% increase in HTC by adding 0.1 wt.% MWCNTs at a Reynolds number of 6807 and input power of 1200 W and 62% increase in pressure drop at the same concentration of MWCNTs, Reynolds number of 4880, and input power of 800 W (Arzani et al., 2016). Arzani et al. (2016) experimentally evaluated the heat transfer performance of graphene nanoplatelets/water ethylene glycol as a new coolant in an annular heat exchanger. They reported a significant increase in thermal conductivity, viscosity, and density, whereas specific heat capacity was decreased markedly by using nanofluids. According to them, the graphene nanoplatelets/water ethylene glycol hybrid nanofluid was a promising coolant due to its positive effect in enhancing the convective HTC, even when its adverse influence on pressure drop is considered (Arzani et al., 2016). Nikkhah (2015) investigated the effect of spherical CuO/water nanofluids as a coolant on the convective boiling HTC in an annular heat exchanger. In his research, two regions in the system were observed. In one part, the convective heat transfer and in the other, the nucleate boiling were dominant. In the convective region, increasing the concentration of nanoparticles led to an increase in HTC, whereas in the nucleate boiling region, the influence of concentration on the HTC was reversed. He demonstrated that spherical CuO/water nanofluid was stable for about 1080 h, when nanoparticle concentration and pH were 0.004% and 10.2, respectively (Nikkhah, 2015).

2.4.2 Pressure drop and pumping power It has been shown that, although the use of MWCNT/water nanofluids resulted in up to 68% augmentation in thermal conductivity, it may adversely affect the performance of plate heat exchangers through intensification of the pressure drop. They suggested that an increase in pressure drop should be controlled and minimized by determining the optimal concentration of the nanomaterial (Sarafraz & Hormozi, 2016). It has been found that at low concentration of nanoparticles, the heat transfer has been enhanced, whereas at higher concentrations due to the counteracting effects of viscosity and pressure drop, the heat transfer has been deteriorated. In a comparison between two water-based nanofluids, one containing MWCNTs and the other containing Al2O3, it was observed that the increase in viscosity was more pronounced in the case of MWCNTs compared to Al2O3 nanoparticles (Huang, Wu, & Sunden, 2015). The increase in pressure drop has been reported by Behrangzade and Heyhat (2016) as well. They demonstrated that using Ag/water nanofluids containing 100 ppm nanoparticles resulted in an increase (1.5%) in pressure drop compared to water, but this increase was negligible. Barzegarian et al. (2016) concluded that the

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increase in pressure drop that occurred because of the use of nanofluids would be negligible if the enhancement in convective HTC was considered. Kumar et al. (2016b) showed that by using nanofluids instead of water, the pressure drop and pumping power increased significantly. Among nanofluids, it was demonstrated that the increase in pressure drop (0.53%) and pumping power (5.56%) was the lowest when MWCNT/water nanofluid was used. Kumar, Tiwari, and Ghosh (2017) also performed a comparative study to evaluate the suitability of ZnO/water and CeO2/water nanofluids as cold fluids in a plate heat exchanger. In their research, both the changes in HTC and viscosity were considered. They found that ZnO/water nanofluid was more suitable than CeO2/water nanofluid, because on one hand, at the volume flow rate of 2 L/m, by using ZnO/water nanofluid the HTC increased up to 12.79% compared with CeO2/water nanofluid, and on the other hand, the increase in viscosity caused by ZnO nanoparticles was significantly lower than that by CeO2 nanoparticles (Kumar et al., 2017). In a study performed by Tiwari, Ghosh, and Sarkar (2015), the optimal nanoparticle concentration for Al2O3/water, TiO2/water, SiO2/water, and CeO2/water nanofluids were measured and reported to be 1%, 0.75%, 1.25%, and 0.75%, respectively. At these optimum concentrations, the maximum improvements in performance index for each nanofluid were 6.5% for Al2O3/water, 5% for TiO2/water, 3% for SiO2/water, and 9.5% for CeO2/water nanofluids. In the case of problems like sedimentation, agglomeration of particles, and the formation of porous layers, the performance of CeO2/water nanofluid was better than the others (Tiwari et al., 2015). In a comparative study on water-based carbon nanofluids at two different nanoparticle concentrations (0.2 and 0.6 wt.%), Teng, Hsiao, and Chung (2019) evaluated the influence of nanofluids on improving the thermal performance of a brazed plate heat exchanger, and concluded that the pumping power should be considered in addition to heat exchange capacity. In their study, heat transfer was enhanced more by applying a higher concentration of nanoparticles. However, the efficiency factor showed that the nanofluid with nanoparticle concentration of 0.2 wt.% was more suitable for practical applications because it needs lower pumping power even in comparison with water (Teng et al., 2019). El-Maghlany, Hanafy, Hassan, and El-Magid (2016) studied the effect of Cu/ water nanofluids as a coolant on heat transfer and pressure drop in a horizontal double-tube counterflow heat exchanger. They found that the addition of Cu nanoparticles (0.03 vol.%) in water resulted in 23.4%, 16.5%, and 36% increase in the NTU, the effectiveness of heat exchanger, and pressure drop, respectively. They also reported that although the rotation of inner tube of heat exchanger alongside the use of nanofluids increased the NTU and effectiveness further to 51.4% and 30.7%, it intensified the pressure drop considerably by raising it to 136%. Wu, Wang, Sunde´n, and Wadso¨ (2016) investigated the effect of using MWCNT/water nanofluids on the thermal and hydraulic performance of a double pipe helically coiled heat exchanger. They showed that the relative thermal conductivity and relative viscosity of MWCNT/water nanofluids with the nanotube volume fraction of 1% were 1.04 and 9.56, respectively. They reported that if the flow rate and pumping power were kept constant, no augmentation in heat transfer was observed by

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using MWCNT/nanofluids (Wu et al., 2016). Sarafraz, Hormozi, and Nikkhah (2016) found that by adding CNTs to water at nanoparticle concentration of 0.3%, thermal conductivity of water increased up to 56% and by using CNT/water, OHTC improved. They reported that thermal performance of countercurrent double pipe heat exchanger was improved by about 44% by using CNT/water nanofluids, although the addition of CNTs into water caused an increase up to 9% and 11% in friction factor and pressure drop, respectively. Hormozi, ZareNezhad, and Allahyar (2016) studied the effect of adding sodium dodecyl sulfate (SDS) and PVP surfactants into alumina silver hybrid nanofluids on their thermal behavior in a helical coil heat exchanger. It was reported that the maximum enhancement in the Nusselt number (about 6.283%) was achieved at a nanocomposite concentration of 0.2 vol.%, SDS concentration of 0.1 wt.%, and Reynolds number of 5100. They found that SDS had a better influence in the case of heat transfer rate and pressure drop compared to PVP. By using 0.1 wt.% SDS, the increase in pressure drop was 60% lower than the increase caused by using 0.4 wt.% PVP (Hormozi et al., 2016)

2.4.3 Thermal performance factor and the effectiveness of heat exchangers Allahyar, Hormozi, and ZareNezhad (2016) performed a comparative study on the effects of Al2O3/water nanofluids and Al2O3-Ag/water hybrid nanofluids on the thermal performance of a coiled heat exchanger. It was revealed that at a Reynold number of 4687 and nanoparticle concentration of 0.4%, an enhancement of about 31.58% and 28.42% in the Nusselt number was achieved by using hybrid and Al2O3/water nanofluids, respectively. Due to the fact that using nanofluids has adverse effects on heat transfer through pressure drop intensification, the thermal performance factor should be considered to evaluate the applicability of nanofluids in practice. The results demonstrated that the maximum thermal performance factor during the experiments was observed when Al2O3-Ag/water hybrid nanofluid was used at a nanoparticle concentration of 0.4% and a Reynolds number of 4687 (Allahyar et al., 2016). Barzegarian, Aloueyan, and Yousefi (2017) investigated the effect of γ-Al2O3/water nanofluids as the hot working fluid on the thermal performance of a horizontal shell and tube heat exchanger under forced circulations. They found that the volume concentration of nanoparticles and Reynolds number had a significant influence on the Nusselt number and OHTC. The increase in friction factor caused by nanofluids was ignorable, and at a nanoparticle volume concentration of 0.3, the thermal performance factor of heat exchanger showed an enhancement of about 21.5%. Qi, Luo, Liu, Fan, and Yan (2019) reported that the use of TiO2/water nanofluids instead of the base fluid resulted in 10.8%, 13.4%, and 14.8% increase in thermal performance and 2.77%, 4.38%, and 6.5% increase in pressure drop at nanoparticle concentrations of 0.1, 0.3, and 0.5 wt.%, respectively. They also showed that by using corrugated tubes in a double-tube heat exchanger, the effect of nanofluids on thermal

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performance can be improved further, although the combination of nanofluids and corrugated tube resulted in the intensification of pressure drop around 51.9% and 40.7% when nanofluids flowed in the tube and shell side of the heat exchanger, respectively. Finally, they proposed that using nanofluids in the shell side of a corrugated double-tube heat exchanger can be more suitable in practice due to its better overall performance index compared to the tube side (Qi et al., 2019). Wang et al. (2019) investigated the thermohydraulic performance of nanofluids flowing in corrugated tubes of a heat exchanger and found that in comparison to water, the heat transfer was enhanced 2.64% to 16.9% and 4.8% to 66.3% by using TiO2/water nanofluid in smooth and corrugated tubes, respectively. Kumar et al. (2017) investigated the heat transfer and friction factor of Fe3O4/ water nanofluids flowing in a double pipe U-bend heat exchanger with and without twisted tape inserts. They showed that by using nanofluids at a nanoparticle volume concentration of 0.06% and Re 5 30,000, the Nusselt number increased 14.76% and 38.75% without and with inserts (H/D 5 10), respectively, in comparison with water. Regarding the friction factor, using nanofluids without and with applying inserts (H/D 5 10) resulted in 1.092 and 1.251 times higher friction factor than water at nanoparticle concentration of 0.06% and Re 5 30,000. They stated that the use of nanofluids and twisted tape inserts are suitable for double pipe heat exchangers due to their effect on improving the effectiveness and NTU of the system (Kumar et al., 2017). Kumar et al. (2017) studied the effect of using Fe3O4/water nanofluids on heat transfer, friction factor, and effectiveness in a double pipe heat exchanger with return bend. Adding Fe3O4 nanoparticles with a volume concentration of 0.06% in water resulted in 14.7% augmentation in heat transfer and increased the NTU, the effectiveness, and friction factor 1.037-, 1.024-, and 1.092-fold, respectively, compared with water. They concluded that, although nanofluids intensified the pressure drop, their impact on heat transfer is more pronounced (Ravi Kumar et al., 2017). Khoshvaght-Aliabadi, Jafari, Sartipzadeh, and Salami (2016) evaluated the influence of utilizing Cu/water nanofluids and vortex-generator insert on the performance of a double-tube heat exchanger. An increase of about 6.8% in heat transfer was observed when Cu/water nanofluid with a nanoparticle volume concentration of 0.2% was employed instead of water. Their results indicated that the performance evaluation criterion was maximized (PEC 5 1.83) when the combination of nanofluids and vortex-generator (ew 5 0.6) was used simultaneously at Reynolds number of 12,200. Prasad, Gupta, and Deepak (2015) reported that by using Al2O3/ water nanofluids at a nanoparticle concentration of 0.3% in a double pipe U-tube heat exchanger with trapezoidal-cut twisted tape inserts (H/D 5 5), the Nusselt number and friction factor increased 34.24% and 1.29 times in comparison with water. Their results showed that nanoparticle concentration had a significant effect on both the Nusselt number and friction factor. They concluded that better results in thermal performance of the heat exchangers could be achieved if both nanofluids and trapezoidal-cut twisted tape inserts are applied simultaneously rather than using them alone (Prasad et al., 2015). Khoshvaght-Aliabadi, Akbari, and Hormozi. (2016) comparatively investigated the effect of using passive techniques, including perforations, winglets, and

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55

nanofluids, on the thermal and hydraulic performance of a wavy plate-fin heat exchanger. It was observed that all the methods were able to increase the heat transfer at the expense of raising pumping power. Despite the adverse effects of passive techniques regarding the pressure drop, the performance of the plate-fin heat exchanger was significantly improved by considering the performance factor. They showed that by using perforations, winglets, 0.1 vol.% α-Al2O3/water nanofluid, and 0.3 vol.% Al2O3/water nanofluid, the performance factor increased by 11.8%, 16.5%, 8.3%, and 10.4%, respectively. Srinivas and Venu Vinod (2016) studied the effect of using water-based Al2O3, CuO, and TiO2 nanofluids on heat transfer in a shell and helical coil heat exchanger. By the addition of CuO nanoparticles with a concentration of 2 wt.%, an increase of around 10.2% was observed in the thermal conductivity of water at the temperature of 50 C. This increment was the highest compared to Al2O3 and TiO2 nanoparticles. Moreover, they found that the heat transfer rate and effectiveness of the heat exchanger were the highest when 2 wt.% CuO nanoparticles were applied. Also, the heat transfer rate was significantly dependent on nanofluid concentration, temperature, and stirrer speed (Srinivas & Venu Vinod, 2016). Hung, Wang, Hsu, and Teng (2017) studied the hybrid carbon/water nanofluid influence on heat exchange capacity, pumping power, and system efficiency factor in an air-cooled heat exchanger. The hybrid carbon was a combination of amorphous carbon, graphene oxide, and graphite-2H. At the nanoparticle volume fraction of 0.02%, flow rate of 2 L/m, and inlet temperature of 35 C, the heat exchange capacity and system efficiency factor were increased about 13% and 11.7%, respectively, compared with water. Furthermore, they showed that at high flow rates the performance of hybrid carbon nanofluids was far better than at lower flow rates. Teng, Hsu, Wang, and Fang (2015) investigated the influence of MWCNT/water nanofluids on heat transfer in an air-cooled heat exchanger. At MWCNT concentration of 0.25%, an increase about 7.77% in heat exchange capacity and 7.53% in efficiency factor was observed at the flow rate of 0.03 L/m and heating power of 70 W. The further increase in concentration did not improve the heat exchange capacity and efficiency factor because of the increase in viscosity.

2.4.4 Entropy generation and exergy efficiency In the case of thermal engineering systems like heat exchangers, two important factors that should not be ignored are entropy generation and exergy efficiency. Entropy generation is a measure indicating the dissipation of useful energy and deterioration in the performance of the device. Exergy, by definition, is the maximum amount of useful work that can be done by a device or system when it is in equilibrium with the surroundings thermodynamically by reversible processes (Cleveland & Morris, 2015; Demirel, 2002). Kumar et al. (2016a) reported that by using ZnO/water nanofluids instead of water in a plate heat exchanger, the entropy generation was decreased and at any concentration of nanoparticles, the entropy generation was minimized by using corrugated plates with chevron angle of β 5 60 /60 . Their results also indicated that an 8.78% and 45% increase in performance index and exergetic efficiency was achieved by using ZnO nanofluids with nanoparticle volume fraction of 1% and

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chevron angle of β 5 60 /60 . In another work, Kumar et al. (2016b) showed that in a plate heat exchanger with plate spacing of 5 mm, 7.56%, 12.58%, 18.66%, 26.70%, 41.45%, 50.26%, and 58.14% increase in exergy efficiency in comparison with water was achieved by employing water-based TiO2, Al2O3, ZnO, CeO2, Cu 1 Al2O3, graphene nanoplates, and MWCNT nanofluids, respectively. Esfahani and Languri (2017) evaluated the thermal performance of a shell and tube heat exchanger by utilizing the graphene oxide/water nanofluids. They found that at 25 C, thermal conductivity of nanofluids was 9% and 20% higher than that of water at nanoparticle volume concentration of 0.01 and 0.1 wt.%, respectively. In the case of exergy, 22% and 109% increases in exergy losses were observed by using water compared to graphene oxide nanofluids containing 0.01 and 0.1 wt.% nanoparticles, respectively. They also showed that the inlet temperature of hot fluids had a significant direct effect on exergy loss. Maddah et al. (2018) studied the effect of Al2O3TiO2 hybrid nanofluids at nanoparticle concentration ranged from 0.2% to 1.5% on exergy efficiency of a double pipe heat exchanger under turbulent conditions (Re 5 3000 12,000). The use of nanofluids resulted in an improvement in exergy efficiency of the heat exchanger in comparison with water as the conventional fluid. They also showed that by increasing the concentration of nanoparticles and the Reynolds number, the exergy efficiency increased significantly. Also, the momentum exchange rate was augmented because of the dispersion and random motion of particles intensifying the pressure drop inside the tubes of heat exchanger (Maddah et al., 2018).

2.4.5 Agglomeration and fouling Hosseinian, Meghdadi Isfahani, and Shirani (2018) studied the effect of mechanical vibrations on the heat transfer enhancement and stability of MWCNT/water nanofluids in a flexible double pipe heat exchanger. Mechanical vibration improved the nanofluid stability by reducing the agglomeration of particles. They also reported that the maximum enhancement in HTC (100%) was achieved at the lowest concentration of nanotubes (0.04%) and the highest level of vibration (9 m/s2). According to the results of their study, firstly because the flow rate limited the effect of vibration and secondly at low flow rates the nanotubes tend to sediment rapidly, the use of vibrations is more suitable for the heat exchangers working at low flow rates. Sarafraz, Nikkhah, Madani, Jafarian, and Hormozi (2017) investigated the effectiveness of vibrations on the mitigation of fouling caused by CuO nanoparticles in a plate heat exchanger. By applying low-frequency vibrations, not only was the fouling reduced, but the HTC was augmented.

2.5

Application of nanofluids in thermal processing of food products

In the food industry, heat exchangers have a wide variety of applications including pasteurization, sterilization, fractionation, distillation, concentration, and any processes

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Figure 2.4 Schematic illustration of heat exchanging system in a food plant: (1) heat exchanger; (2) nanofluid reservoir; (3) food product reservoir; (4) centrifugal pumps; (5) tank containing food products after thermal processing.

involving the heating or cooling of fluids (Shah & Sekuli´c, 2003). It has been shown recently that the use of nanofluids for the optimization of heat exchangers in the food processing plants can be beneficial not only from the technical perspective but also by considering their effect on the quality of food products (Jabbari, Jafari, Dehnad, & Shahidi, 2018; Jafari, Jabari, Dehnad, et al., 2017b). Fig. 2.4 demonstrates the schematic illustration of a heat exchange system in the food sector. Technically, it has been shown that the addition of Al2O3 nanoparticles into water and increasing the concentration of particles will result in a significant increase in thermal conductivity, viscosity, and density, whereas the specific heat capacity will be significantly decreased. In the case of heat transfer characteristics, one study in thermal processing of tomato juice demonstrated that by using Al2O3/ water at nanoparticle concentrations of 2% and 4%, the HTC increased 5.42% and 11.94%, respectively. In another study, it was shown that during thermal processing of watermelon juice, the overall heat transfer enhancement was 5%, 8%, and 13% when Al2O3/water nanofluid was employed at nanoparticle concentrations of 1%, 2%, and 4%, respectively (Jafari, Jabari, Dehnad, et al., 2017b; Jafari, Saremnejad, Dehnad, & Rashidi, 2017). Other studies showed that an increase in the concentration of nanoparticles and Peclet number will result in a significant augmentation in the convective HTC (Tabari & Heris, 2015; Taghizadeh-Tabari, Zeinali Heris, Moradi, & Kahani, 2016). For instance, by increasing the Peclet number from 574 to 1000, the convective HTC enhanced from 903 to 1409 W/m2.K at MWCNTs concentration of 0.35%; by increasing the MWCNTs concentration from 0.25% to 0.55%, the convective HTC

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increased from 878 to 978 W/m2
K at a Peclet number of 574. Moreover, it seems that the use of MWCNT nanofluids as a hot fluid instead of water and under turbulent conditions is a promising technique to improve the heat transfer performance of heat exchangers used in the pasteurization of milk (Tabari & Heris, 2015). Taghizadeh-Tabari et al. (2016) reported that, although adding TiO2 nanoparticles into distilled water and increasing the concentration of nanoparticles intensified the pressure drop, the increase was not significant. Their results indicated that at TiO2 concentration of 0.8%, the increase in pressure drop was 8% compared with water. Energy consumption, processing time, and the effectiveness of food processing devices are other critical technical parameters influenced by using nanofluids. It has been demonstrated that by using nanofluids instead of conventional heat transfer fluids, the energy consumption and processing time will be significantly reduced, whereas the effectiveness will be improved considerably (Jafari, Jabari, Dehnad, et al., 2017b; Jafari, Saremnejad, & Dehnad, 2017; Longo, Righetti, & Zilio, 2016). Also, Zhang et al. (2017) showed that ZnO nanofluids intensified the inactivation of Escherichia coli through improving the effectiveness of sonophotocatalysis method, although the effect of reactive oxygen species (ROS) was more pronounced than that of Zn1 ions in bacterial inactivation. Food quality is generally used to refer to any property of a food product that has a connection with the acceptability of that product based on nutritional value and safety. These properties are related to appearance, texture and flavor, chemical composition, physical characteristics, and microorganisms (Zhong & Wang, 2019). Technical and qualitative aspects of nanofluid effects on heat exchanger performance in a food thermal process has been illustrated in Fig. 2.5. In terms of the food quality, it has been demonstrated that by using nanofluids instead of water in a shell and tube heat exchanger, the quality of tomato and watermelon juices (color, pH, acidity, and total soluble solids) has been preserved better. Besides, degradation of bioactive compounds like vitamin C, total phenolic compounds, and lycopene significantly reduced when the nanofluids were used instead of water. The better performance of nanofluids compared to water in connection with the food quality has been attributed to the effect of nanofluids in reducing the duration of thermal processes (Jafari et al., 2017; Jafari, Jabari, Dehnad, et al., 2017a). The summary of nanofluids use in food thermal processes has been shown in Table 2.2. Jafari and his colleagues suggested that for optimizing the thermal process of tomato juice in a shell and tube heat exchanger and using Al2O3 nanofluids to maximize the quality of food products, the temperature, nanoparticle concentration, and process duration should be set at 70 C, 4%, and 30 s, respectively (Jafari, Jabari, Dehnad, et al., 2017a).

2.6

Conclusion and further remarks

Many efforts have been made so far to increase the efficiency of heat exchanging devices in different industries. Nanofluids are one of the techniques introduced

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Figure 2.5 The effects of nanofluids on heat exchanger performance in the food industry.

recently. The logic behind the utilization of nanofluids was based on this concept that the poor performance of conventional heat transfer fluids like water, ethylene glycol, etc. is a big problem limiting the effectiveness of heat exchangers. Nanofluids are made up of metallic or nonmetallic nanoparticles dispersed in the conventional fluids. This new generation of fluids has shown the potential for increasing thermal conductivity significantly. Thermal conductivity is one of the two crucial factors influencing the overall heat transfer performance of a heat exchanging device. However, nanofluids have some major drawbacks that hinder their use in practice. The most important one is the clustering of particles, resulting in particles sedimentation and suspension destabilization. Thus some techniques have been suggested so far for increasing the stability of particles, including sonication, the use of surfactants, and adjusting pH. Another challenge facing the practical application of nanofluids in industry is to prepare stable and uniform nanofluids at a large scale and low price. The increase in viscosity by adding nanoparticles to the fluids is also considered to be a downside due to its negative effect on pressure drop and pumping power. The application of nanofluids in different heat exchangers showed that the use of these fluids would result in a considerable augmentation of OHTC, the efficiency factor, and the effectiveness of heat exchangers, despite their impact on viscosity

Table 2.2 Summary of the results obtained through the use of nanofluids in food thermal processes. References

Nanofluid\food product

Tabari and Heris (2015)

MWCNT/ water Milk

Taghizadeh-Tabari et al. (2016)

TiO2/water Milk

Jabbari et al. (2018); Jafari, Jabari, Dehnad, et al. (2017b); Jafari et al. (2017a) Jafari et al. (2017); Jafari, Saremnejad, Dehnad, et al. (2017)

Al2O3/water Tomato juice

Al2O3/water Watermelon juice

Nanoparticle concentration

0 0.55% Pe 5 574 0.35% Pe 5 574 0.35% Pe 5 1000 0.25 0.8% Pe 5 574 0.8% Pe 5 574 0.8% Pe 5 1000 2% 4%

2% 4% Water

Heat exchanger type

HTC (W/ m2K)

Plate

801 978 903 1409 778 803

Plate

Shell and tube

Shell and tube

742 803 1060 1251 5.42% m 11.94% m 8% m 13% m

Process time

Energy saving

Retention (at 70 C and 30 s) Vitamin C

Lycopene

TPC

96.2%

73.62

22.2% k 46.3% k

22.3% m 48.76% m

66.27%

24.88% k 51.63% k

25% m

63.7%

46% m

67.04% 61.11%

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and pressure drop. Some researchers concluded that the viscosity increase and pressure drop intensification could be negligible at an optimal concentration of nanoparticles. It has been reported that by using nanofluids, the thermal process duration can be reduced. Also, the extension of heat exchange surface and temperature increase are not needed. As a result, the consumption of energy will be decreased markedly. In the food industry, nanofluids have a great potential to improve the thermal processes both technically and qualitatively. The results showed that by using nanofluids, the thermal processes could be accomplished at a shorter time and lower temperature, leading to better preservation of color, total soluble solids, pH, and bioactive compounds, such as vitamin C, phenolics, and lycopene. In this context, for a clearer vision, more research is needed to be carried out with different products, different heat exchangers applicable in the food sector, and different processes, including concentration, sterilization, pasteurization, etc., under various operating conditions. Also, due to the importance of fouling in the heat transfer equipment and problems it causes in the operation of these devices, more investigations should be performed to understand the influence of nanofluids on fouling.

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El-Maghlany, W. M., Hanafy, A. A., Hassan, A. A., & El-Magid, M. A. (2016). Experimental study of Cu water nanofluid heat transfer and pressure drop in a horizontal double-tube heat exchanger. Experimental Thermal and Fluid Science, 78, 100 111. Available from https://doi.org/10.1016/j.expthermflusci.2016.05.015. Esfahani, M. R., & Languri, E. M. (2017). Exergy analysis of a shell-and-tube heat exchanger using graphene oxide nanofluids. Experimental Thermal and Fluid Science, 83, 100 106. Available from https://doi.org/10.1016/j.expthermflusci.2016.12.004. Essajai, R., Mzerd, A., Hassanain, N., & Qjani, M. (2019). Thermal conductivity enhancement of nanofluids composed of rod-shaped gold nanoparticles: Insights from molecular dynamics. Journal of Molecular Liquids, 293, 111494. Available from https://doi.org/ 10.1016/j.molliq.2019.111494. Fan, J., & Wang, L. (2011). Review of heat conduction in nanofluids. Journal of Heat Transfer, 133(4), 040801. Available from https://doi.org/10.1115/1.4002633. Ganji, D. D., & Kachapi, S. H. H. (2015). Introduction to nanotechnology, nanomechanics, micromechanics, and nanofluid. In Application of nonlinear systems in nanomechanics and nanofluids (pp. 1 11). https://doi.org/10.1016/B978-0-323-35237-6.00001-7. Ghadimi, A., & Metselaar, I. H. (2013). The influence of surfactant and ultrasonic processing on improvement of stability, thermal conductivity and viscosity of titania nanofluid. Experimental Thermal and Fluid Science, 51, 1 9. Available from https://doi.org/ 10.1016/j.expthermflusci.2013.06.001. Godson, L., Raja, B., Lal, D. M., & Wongwises, S. (2010). Experimental investigation on the thermal conductivity and viscosity of silver-deionized water nanofluid. Experimental Heat Transfer, 23(4), 317 332. Available from https://doi.org/10.1080/08916150 903564796. Hemmat Esfe, M., Saedodin, S., Asadi, A., & Karimipour, A. (2015). Thermal conductivity and viscosity of Mg(OH)2-ethylene glycol nanofluids: Finding a critical temperature. Journal of Thermal Analysis and Calorimetry, 120(2), 1145 1149. Available from https://doi.org/10.1007/s10973-015-4417-3. Hong, K. S., Hong, T.-K., & Yang, H.-S. (2006). Thermal conductivity of Fe nanofluids depending on the cluster size of nanoparticles. Applied Physics Letters, 88(3), 031901. Available from https://doi.org/10.1063/1.2166199. Hong, T.-K., Yang, H.-S., & Choi, C. J. (2005). Study of the enhanced thermal conductivity of Fe nanofluids. Journal of Applied Physics, 97(6), 064311. Available from https://doi. org/10.1063/1.1861145. Hormozi, F., ZareNezhad, B., & Allahyar, H. R. (2016). An experimental investigation on the effects of surfactants on the thermal performance of hybrid nanofluids in helical coil heat exchangers. International Communications in Heat and Mass Transfer, 78, 271 276. Available from https://doi.org/10.1016/j.icheatmasstransfer.2016.09.022. Hosseini, M., Sadri, R., Kazi, S. N., Bagheri, S., Zubir, N., Bee Teng, C., & Zaharinie, T. (2017). Experimental study on heat transfer and thermo-physical properties of covalently functionalized carbon nanotubes nanofluids in an annular heat exchanger: A green and novel synthesis. Energy & Fuels, 31(5), 5635 5644. Available from https://doi.org/ 10.1021/acs.energyfuels.6b02928. Hosseinian, A., Meghdadi Isfahani, A. H., & Shirani, E. (2018). Experimental investigation of surface vibration effects on increasing the stability and heat transfer coeffcient of MWCNTs-water nanofluid in a flexible double pipe heat exchanger. Experimental Thermal and Fluid Science, 90, 275 285. Available from https://doi.org/10.1016/j. expthermflusci.2017.09.018.

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Wang, L., Wang, Y., Yan, X., Wang, X., & Feng, B. (2016). Investigation on viscosity of Fe3O4 nanofluid under magnetic field. International Communications in Heat and Mass Transfer, 72, 23 28. Available from https://doi.org/10.1016/j.icheatmasstransfer. 2016.01.013. Warrier, P., & Teja, A. (2011). Effect of particle size on the thermal conductivity of nanofluids containing metallic nanoparticles. Nanoscale Research Letters, 6(1), 247. Available from https://doi.org/10.1186/1556-276X-6-247. Wu, Z., Wang, L., Sunde´n, B., & Wadso¨, L. (2016). Aqueous carbon nanotube nanofluids and their thermal performance in a helical heat exchanger. Applied Thermal Engineering, 96, 364 371. Available from https://doi.org/10.1016/j.applthermaleng.2014.10.096. Xian-Ju, W., & Xin-Fang, L. (2009). Influence of pH on nanofluids’ viscosity and thermal conductivity. Chinese Physics Letters, 26(5), 056601. Available from https://doi.org/ 10.1088/0256-307X/26/5/056601. Yang, B., & Han, Z. H. (2006). Temperature-dependent thermal conductivity of nanorodbased nanofluids. Applied Physics Letters, 89(8), 083111. Available from https://doi.org/ 10.1063/1.2338424. Yu, W., & Xie, H. (2012). A review on nanofluids: Preparation, stability mechanisms, and applications. Journal of Nanomaterials, 2012, 1 17. Available from https://doi.org/ 10.1155/2012/435873. Zhang, L., Qi, H., Yan, Z., Gu, Y., Sun, W., & Zewde, A. A. (2017). Sonophotocatalytic inactivation of E. coli using ZnO nanofluids and its mechanism. Ultrasonics Sonochemistry, 34, 232 238. Available from https://doi.org/10.1016/j.ultsonch.2016.05.045. Zhong, J., & Wang, X. (2019). An introduction to evaluation technologies for food quality. In Evaluation technologies for food quality, 1 3. Available from https://doi.org/ 10.1016/B978-0-12-814217-2.00001-9. Zhou, S.-Q., & Ni, R. (2008). Measurement of the specific heat capacity of water-based Al2O3 nanofluid. Applied Physics Letters, 92(9), 093123. Available from https://doi.org/ 10.1063/1.2890431. Zohuri, B. (2018). Heat exchangers. In Physics of cryogenics (pp. 299 330). https://doi.org/ 10.1016/B978-0-12-814519-7.00012-4 ˙ Zyła, G., Vallejo, J. P., & Lugo, L. (2018). Isobaric heat capacity and density of ethylene glycol based nanofluids containing various nitride nanoparticle types: An experimental study. Journal of Molecular Liquids, 261, 530 539. Available from https://doi.org/ 10.1016/j.molliq.2018.04.012.

Nanofiltration in the food industry

3

Roberto Castro-Mun˜oz1 and Emilia Gontarek2 1 Tecnolo´gico de Monterrey, Toluca de Lerdo, Me´xico, 2Gdansk University of Technology, Gdansk, Poland

Abbreviations MF MWCO NF RO TMP UF VRF

3.1

Microfiltration Molecular weight cutoff Nanofiltration Reverse osmosis Transmembrane pressure Ultrafiltration Volume reduction factor

Introduction

Nanofiltration (NF) is a relatively new and complex process among other pressuredriven membrane separation technologies. It depends on various interfacial events that occur on the membrane surface as well as in its nanopores. The performance and efficiency of NF processes are attributed to a combination of different effects such as transport, Donnan, steric, and dielectric properties. NF is usually compared with ultrafiltration (UF) and reverse osmosis (RO); however, NF offers several favorable features such as lower operating pressures, higher fluxes and retentions, and continuous operation with a clean-in-place (CIP) procedure, thus allowing lower maintenance costs. Due to its characteristics, NF is becoming an attractive process for challenging applications in agrofood processing involving fractionation, water softening, wastewater treatment, vegetable oil processing, and treatment of products from the dairy, beverage, and sugar industries (Salehi, 2014). It was already reported that NF can replace its other counterparts such as RO (Chen, Luo, et al., 2016; Dey, Linnanen, & Pal, 2012). Increasingly, governments of various countries are creating strict regulations regarding the hygiene of food products during their processing. Moreover, special types of foods such as low-fat and low-calorie products require advanced processing and improved separation. For this purpose, NF membranes have a great potential due to their capacity to separate monovalent and multivalent ions as well as organic solutes with different sizes from other species.

Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00003-0 © 2020 Elsevier Inc. All rights reserved.

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Handbook of Food Nanotechnology

The potential of NF application in food processing can be found in a number of literature reports that cover different fields, including purification of water and sugar, whey processing, juice clarification and concentration, as well as fractionation (Salehi, 2014; Van Der Bruggen, Vandecasteele, Van Gestel, Doyen, & Leysen, 2003). The growing demand for NF membranes is one of the key emerging trends in the market of membranes for agrofood applications. The purpose of this chapter is to critically review the recent development of NF membranes in the food industry. It will start with the fundamentals and principles of NF; then, applications of NF in different areas of the agrofood processing industry (i.e., fruit juice, wine, dairy, and sugars; and wastewater valorization) will be presented and discussed with descriptions of their main advantages over conventional methods.

3.2

Generalities of nanofiltration membranes

As with all pressure-driven membrane processes, the membranes act as a selective barrier that separates components of the feed solution under a hydrostatic pressure applied on the feed side. As a result, the feed solution is divided into two new streams: “permeate” that contains all the components that pass through the membrane; and a “retentate” that contains all the components that have been rejected by the membrane. The pore size of membranes used in NF is in the range 0.5
1 nm. These values correspond to the membrane molecular weight cutoff (MWCO) that reaches 200
1000 Da. MWCO describes the minimum molecular weight of a solute that is 90% retained by the membrane. To determine MWCO, the retention of the membrane for components with different molecular weights has to be evaluated and plotted, as shown in Fig. 3.1 (Cheryan, 2018).

Figure 3.1 MWCO determined from the relationship between retention and molecular weight of components (Cheryan, 2018).

Nanofiltration in the food industry

75

The transport mechanism through NF membranes lies between a typical RO (nonporous membranes) solution
diffusion mechanism and a typical UF (porous membranes) size exclusion and charge effect. Generally, the transport of components through a NF membrane can be described by Eq. (3.1), that is divided into two parts: a diffusion component and a convection component (Van der Bruggen & Vandecasteele, 2002), this is based on the transport equation of Spiegler and Kedem: Js 5 2 PΔx

dc 1 ð1 2 σÞJv c dx

(3.1)

where Js and Jv are the flux of solute and water, respectively, P is the solute permeability; Δx is the membrane thickness, σ is the reflection-coefficient, and c is the solute concentration. The first part of the equation refers to the diffusion component, which is independent of pressure, while the second part describes the convection component being proportional to applied pressure. Thus at low pressures, the transport of solutes through the membrane is affected by both components, while at higher pressures, the relative importance of convection in the transport increases. This equation is based on the solution
diffusion model, without any consideration of pore size distribution of the membrane. However, this key parameter strongly contributes to the retention of organic molecules. At this point, the Nernst
Planck equation is the most widely used expression for the modeling of NF processes, which describes the transport of charged solutes: Ji 5 2

ci Ki;d Di; N dμ 1 Ki;c ci V: RT dx

(3.2)

where Ji is the ionic flux, c is the concentration, Ki;c and Ki;d are hindrance factors which take into account the convection and diffusion inside a confined spaceðDiÞ; N is the bulk diffusivity of solute, R is the universal gas constant, μ is electric potential, and V is the solvent velocity. This basic modeling theme and the number of its variations are related to the Nernst
Planck equation (Mohammad et al., 2015). Ionizable groups which are present on the polymeric NF membranes, acidic or basic, make the membrane surface charged due to their dissociation, which strongly depends on the pH of the contacting solution. For this reason, the NF separation mechanism is not based only on size exclusion but also on the Donnan effect. Donnan exclusion postulates that ions which are carrying the same charge as the membrane will be excluded by the membrane (Mohammad et al., 2015). The main drawback of NF application, similarly to other membrane processes, is the membrane fouling. It is generally originated by the binding, accumulation, or absorption of materials on the membrane surface and throughout the membrane pores. Common foulants are organic and inorganic solutes, colloids, and biological particles (Van der Bruggen, M¨antt¨ari, & Nystro¨m, 2008). Membrane fouling causes deleterious effects such as flux decline (productivity drop), cost increasing (higher energy demand, maintenance), and shorter membrane life span. Therefore for the accomplishment of a fruitful NF process, the selection of suitable structured

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Handbook of Food Nanotechnology

Table 3.1 The top 15 polymers used in the preparation and modification of nanofiltration membranes (Oatley-Radcliffe et al., 2017). Abbreviation

Chemical name

Papers

PA TMC PSF PES PIP PEI PI PAN CA PDMS PVA PVDF CHI AA PSS

Polyamide Trimesoyl chloride Polysolfone Polyethersulfone Piperazine Polyethyleneimine Polyimide Polyacronitrile Cellulose acetate Poly(dimethylsiloxane) Polyvinyl alcohol Poly(vinylidene fluoride) Chitosan Acrylic acid Poly(styrene sulfonate)

189 106 105 96 71 58 56 46 33 29 25 25 23 21 19

membrane materials in terms of MWCO and surface properties (functional groups, charge, hydrophobicity, roughness) is very important. Today, research is directed to the creation of membranes with improved selectivity, rejection, and fouling resistance using various methods, such as interfacial polymerization, nanomaterials incorporation, UV treatment, electron beam irradiation, plasma treatment, or layer-by-layer assembly. The most popular NF membrane materials are polymers (see Table 3.1), including cellulose acetate, polyamide, polyimide, polysulfone, and polyethersulfone; however, some ceramics are also used in the manufacture of membranes, such as zirconia, titania, silica
zirconia, and alumina. The top 15 materials used in the fabrication and modification of NF membranes are listed in Table 3.1. The main advantage of ceramic membranes is a higher chemical, structural, and thermal stability, when compared with polymeric membranes. On the other hand, it is possible to create a thin-film composite structure from polymeric materials (for example, polyamides or polyethersulfone) that is characterized with a high selectivity and a high permeability (Van der Bruggen et al., 2008). There are different configurations of NF membranes such as flat-sheet, spiralwound, and tubular, as well as different process configurations, such as total recycle, batch concentration, feed-and-bleed, and multistage operation. The choice of a specific configuration is based on economic aspects associated with performance and the ease of maintenance. The selection of a specific process configuration depends on the goal and final applications of the membrane. The separation performance of a NF membrane is affected by its chemical composition, temperature, pressure, and interactions between membrane surface and feed components. The separation efficiency is generally expressed by the rejection

Nanofiltration in the food industry

77

rate (R) of a given compound, which is given by Eq. (3.3):   Cp R5 12 3 100 Cf

(3.3)

where Cp is the solute concentration in the permeate and Cf the solute concentration in the feed. The values of rejection can vary between 0% (complete pass of the solutes through the NF membrane) and 100% (full rejection of the solutes by the membrane). The fraction of feed that passes through the membrane is called the recovery factor (Δ), and it is denoted with the equation: Δ5

Vp Vf

(3.4)

where Vp and Vf are the volumes of permeate and feed solution, respectively. The recovery factor value ranges from 0 and 1 and for commercial NF membranes, high values are desirable, due to the economic importance of this parameter. Another important parameter in the NF processes is volume reduction factor (VRF), described as the ratio between the initial feed volume and the volume of the resulting retentate: VRF 5

Vf Vp 511 Vr Vr

(3.5)

where Vf, Vp, and Vr are the volume of feed, permeate, and retentate, respectively.

3.3

Application of nanofiltration in fruit juice and plant extract processing

Fruit juices are recognized as important components of the human diet, providing a range of key nutrients. General composition of raw fruit juices includes sugar, acid, salts, aroma compounds, and a range of macromolecules, for example, polysaccharides, proteins, and suspended solids. Currently, the manufacturing process of raw juices and plant extracts is attracting great attention in order to improve their commercial use and length of storage. To produce fruit juices, the application of processes designed for the concentration of biologically active compounds present in the juice and for preservation of the physical, chemical, and biological characteristics of these compounds is very important (Jafari, Jabari, Dehnad, & Shahidi, 2017; Jafari, Saremnejad, & Dehnad, 2017). Conventional methods of fruits concentration, such as thermal evaporation, brings the possibility to obtain significant deterioration in the final juice product (Bhattacharjee, Saxena, & Dutta, 2017). On the other hand, clarification of the fruit

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juices is an important manufacturing step in order to remove macromolecules and to ensure the possibility of longer storage. Traditional processes for the clarification of fruit juices are performed with enzyme treatment followed by the addition of fining agents and conventional filtration; however, this process is time-consuming and can affect the taste of the juice since it is difficult to fully remove the additives. Hence, membrane technology represents a suitable alternative for producing additive-free juices with standard organoleptic quality and natural fresh taste. Compared to traditional methods, membrane processes are energy-saving, selective, and simple to operate (Nunes & Peinemann, 2001). Additionally, one of the important advantages of using membranes in food processing is the low operating temperature, which allows thermolabile compounds to be processed without chemical and physical changes or losses in their nutritional characteristic (Bhattacharjee et al., 2017; Echavarrı´a, Torras, Paga´n, & Ibarz, 2011). According to the recent literature, pressure-driven membrane processes can be successfully applied for juice clarification, concentration, and deacidification, thus replacing traditional processes (see Table 3.2) (Nath, Dave, & Patel, 2018). When compared to UF and MF processes, NF offers new possibilities based on its ability to reject low-molecular-weight constituents ( . 1 kDa), such as bacteria and proteins. In particular, the fractionation of molecules with similar molecular weights occurs through the selection of membranes with suitable MWCOs. The advantages of this process can also be found when compared with RO for juice concentration as NF is less energy-consuming due to lower operating pressures, therefore it allows a better quality preservation of the juices. In juice processing, NF is generally used for concentration and separation of useful bioactive compounds from fruit juices and there is the possibility for it to be applied in the preparation and formulation of functional foods and beverages (Conidi, Drioli, & Cassano, 2018). The potential of NF in the concentration of bioactive compounds in watermelon juice was investigated by Arriola et al. (2014), who used a spiral-wound PVDF membrane module with a MWCO ranging between 150 and 300 Da (HL2521TF, from GE Osmonics). It has been proven that using NF, it is possible to achieve a great level of concentration of bioactive compounds during juice processing. Average permeate fluxes (2.3 L/m2 h) and high rejection rates were obtained for lycopene, flavonoids, and total phenolic content (0.99, 0.96, and 0.65, respectively). The NF process was considered to be an effective alternative for concentrating the main bioactive compounds. Acosta, Vaillant, Pe´rez, and Dornier (2017) studied the possibility to concentrate anthocyanins and ellagitannins from blackberry juice, using NF flat-sheet membranes with MWCO around 200 Da. The results showed that the total retention toward ellagitannin was 100% for each membrane and didn’t depend on the membranes’ structure and composition. However, among all tested membranes, the NF270 polypiperazineamide membrane (from Dow-Filmtec) showed the highest permeate flux and retention of the solutes during the concentration of the main polyphenolic compounds. The authors suggested also the suitability of applying NF270 membrane during deacidification of the juice as sugars were completely retained at high pressures, while the retention of titratable acidity was under 90%.

Table 3.2 Brief summary of various application of nanofiltration (NF) in food processing. Source

Objective

Membrane material and module

Operating parameters

Major findings

References

Apple and pear juice

Juice concentration

PA, tubular and flat-sheet

TMP, 8 and 12 bar; T, 25 C
35 C

Warczok et al. (2004)

Bergamot juice

Polyphenols concentration and purification

PA, spiral-wound

TMP, 6 bar; T, 20 C

The greater decrease in permeate flux was observed in juice solutions comparing to fructose solutions High antioxidant activity that can be interesting for nutraceutical applications

TMP, 5
30 bar; v, 0.3 m/s; T, 30 C

Retention toward ellagitannin didn’t depend on the membranes structure and composition

Acosta et al. (2017)

TMP, 6 bar; T, 25 C 6 1 C TMP, 40 bar Qf, 800 L/h T, 30 C

The retentate fraction showed high antioxidant activity 26.5 3 1023 m3 m22 h after 90 min 100% retention of Vitamin C and antioxidant Improved nutritional and sensorial properties of concentrate

Conidi et al. (2017)

Blackberry juice

Polyphenols concentration

Pomegranate juice Sea buckthorn juice

Polyphenols separation and purification Bioactive compounds concentration

Strawberry juice

Polyphenols concentration

PES, spiral-wound PES, spiral-wound Polypiperazineamide, flat-sheet, PA, flat-sheet composite, flat-sheet PA/PS, flat-sheet Polypiperazineamide/PS, flat-sheet PES, flat-sheet PES, flat-sheet TFC, flat-sheet PA, flat sheet

PVDF

TMP, 6 bar; T, 20 C 6 2 C

Conidi and Cassano (2015)

Vincze et al. (2007)

Arend et al. (2017)

(Continued)

Table 3.2 (Continued) Watermelon juice

Bioactive compounds concentration

PVDF, spiral-wound

Red and white wine

Alcohol reduction

PA, spiral-wound

Red and white must

Sugar reduction

HL (GE Osmonics), spiral-wound, TFC

Red wine

Alcohol removal

NF99 HF (Alfa Laval), flat-sheet, TFC, 200 Da NF99 (Alfa Laval), flatsheet, TFC, 200 Da NF97(Alfa Laval), flatsheet, TFC, 200 Da YMHLSP1905 (GE Osmonics), flat-sheet

Grape white must

Sugar content increasing

PA, spiral-wound

PA, spiral-wound

TMP, 6 bar; v, 1 m/s; T, 25 C 6 2 C TMP,33 bar; Qf, 540 L/h; T, 25 C 6 2 C TMP, 24 bar; Qf, 60 L/h; T, 3 C (white must) TMP, 24 bar; Qf,90 L/h; T, 6 C (red must) TMP, 16 bar; Qf,120 L/h; T, 30 C TMP, 16 bar; Qf, 120 L/h; T, 30 C TMP, 16 bar; Qf, 120 L/h; T, 30 C TMP, 16 bar; Qf,120 L/h; T, 30 C TMP, 40 bar; Qf, 1900 L/h; T, 15 C TMP, 40 bar; Qf, 1900 L/h; T, 15 C

NF is an effective alternative to concentrate the main bioactive compounds

Arriola et al. (2014)

Salgado, Ferna´ndezFerna´ndez, Palacio, Herna´ndez, & Pra´danos (2015) Garcı´a-Martı´n et al. (2010)

Catarino and Mendes (2011)

Versari et al. (2003)

(Continued)

Table 3.2 (Continued) Wine (Verdeca and Bombino nero varieties)

Wine quality improving

PA, spiral-wound

TMP, 39 bar

VinoPro (GE Osmonics), Spiral-wound, salt rejection 98%

TMP, 39 bar

TFC-S4v (Koch Membrane Systems), spiral wound, salt rejection 99% NF270 (Dow-Filmtec), spiral-wound, salt rejection 99.7% PA, spiral-wound

TMP, 39 bar

Milk and whey

Milk and whey protein concentration

Stevia extract

Recovery of stevioside

PA skin over a PS support, flat sheet

Whey

Separation and concentration of lactic acid

DK (GE Osmonics), flatsheet, TFC, 150
300 Da DL (GE Osmonics), flatsheet, TFC, 150
300 Da HL (GE Osmonics), flatsheet, TFC, 150
300 Da CK (GE Osmonics), flatsheet, CA, 200 Da

Pati et al. (2014)

TMP, 39 bar

TMP, 10
20 bar; Qf, 100
200 L/h; T, 30 C
50 C TMP, 7.5, 33 bar; Qf, 100
200 L/h; T, 24 C TMP, 14, 21, 28 bar; T, 37 C

Atra et al. (2005)

Maximum purity and recovery of stevioside was obtained for a particular set of operating conditions

Chhaya, Mondal, Majumdar, and De (2012)

Li et al. (2008)

TMP, 14, 21, 28 bar; T, 37 C TMP, 14, 21, 28 bar; T, 37 C TMP, 14, 21, 28 bar; T, 37 C

(Continued)

Table 3.2 (Continued) PA, flat-sheet, Whey

Separation of lactose

DS-5-DL (GE Osmonics), Spiral-wound, TFC, 150
300 Da

Whey

Removal of lactic acid

Model solutions of sugars

Separation of xylose from glucose

Desal DL (GE Osmonics), flat-sheet, TFC, 150
300 Da Desal HL (GE Osmonics), flat-sheet, TFC, 150
300 Da Desal DK (GE Osmonics), flat-sheet, TFC, 150
300 Da Desal 5- DK (GE Osmonics), flat-sheet, TFC, 150
300 Da Desal-5-DL (GE Osmonics), flat-sheet, TFC, 150
300 Da NF270 (Dow Liquid Separations), flat-sheet, TFC, 150
200 Da

TMP, 14, 21, 28 bar; T, 37 C TMP,5
25 bar; T, 16 C
18 C

TMP, 21 bar; Qf, 174 L/h; T, 25 C, 40 C TMP, 21 bar; Qf, 174 L/h; T, 25 C, 40 C TMP, 21 bar; Qf, 174 L/h; T, 25 C, 40 C TMP, 2
40 bar; v, 0.7
1 m/s; T, 50 C TMP, 2
40 bar; v, 0.7
1 m/s; T, 50 C TMP, 2
40 bar; v, 0.7
1 m/s; T, 50 C

Cuartas-Uribe, AlcainaMiranda, Soriano-Acosta, Mendoza-Roca, Iborra-Clar, & Lora-Garcia (2009) Chandrapala et al. (2016)

Sjo¨man et al. (2007)

(Continued)

Table 3.2 (Continued) Solution of inulin with different polymer sizes

Separation of mono- and disaccharides from inulin

Model carbohydrates solution

Separation of sugars

Model sugar solution

Purification of oligosaccharide

Model sugar solution

Fractionation oligosaccharide

GE (GE Osmonics), spiral-wound, TFC, 1000 Da

TMP, 0
24 bar; T, 50 C

GH (GE Osmonics), spiral-wound, TFC, 2500 Da HPA-600 (Permionics), spiral-wound, PA, 600 Da

TMP, 0
24 bar; T, 50 C TMP, 14 bar

Moreno-Vilet et al. (2014)

NF-CA-50 (Intersep Ltd.), flat-sheet, CA, 50% NaCl rejection DS-5-DL (Osmonics Desal) flat-sheet, TFC, 96% MgSO4 rejection DS-51-HL (Osmonics Desal), flat-sheet, TFC, 96% MgSO4 rejection NF-CA-50 (Intersep Ltd.), flat-sheet, CA, 50% NaCl rejection NFTFC-50 (Intersep Ltd.), flat-sheet, TFC, 50% NaCl rejection

TMP, 6.9
27.6 bar; T, 25 C

Goulas , Kapasakalidis, Sinclair, Rastall, & Grandison (2002)

Patil , Feng, Sewalt, Boom, & Janssen (2015)

TMP, 6.9
27.6 bar; T, 25 C
60 C TMP, 6.9
27.6 bar; T, 25 C TMP, 40 bar

Goulas, Grandison, & Rastall (2003)

TMP, 40 bar

(Continued)

Table 3.2 (Continued) Sugar solutions

Sugar solutions

Separation of galactooligosaccharides mixture

Fractionation of galactooligosaccharides

NF-2 (Sepro Membranes Inc.), spiral-wound, CA, 500
600 Da NF-3 (Sepro Membranes Inc.), spiral-wound, CA, 800
1000 Da NF-1812-50 (DowFilmtec), spiral-wound, PA, 150
300 HBRO-1812-2 (Hebei R. O. Environment Tech. Co.), spiral-wound, CA, 800
1000 Da NP030 (Microdyn-Nadir), flat-sheet, PES, 400 Da Desal-5-DL (GE Osmonics), flat-sheet, PA, 150
300 Da

Model solution of sugars

Purification of oligosaccharides at high concentrations

GE (Desalogics), flatsheet, PA, 1000 Da NP030 (Microdyn-Nadir), flat-sheet, PES, 400 Da NP010 (Microdyn-Nadir), flat-sheet, PES, 1000 Da NFA (Parker), flat-sheet, TFC, 500 Da ATF (Parker), flat-sheet, TFC, 200 Da

TMP, 2
8 bar; T, 25 C

Feng et al. (2009)

TMP, 2
8 bar; T, 25 C
50 C TMP, 2
8 bar; T, 25 C TMP, 2
8 bar; T, 25 C

TMP, 25, 35, 45 bar; T, 5 C, 25 C, 60 C TMP, 25, 35, 45 bar; T, 5 C, 25 C, 60 C

Pruksasri, Nguyen, Haltrich, & Novalin (2015)

TMP, 5
25 bar; T, 53.5 C TMP, 5
40 bar; T, 53.5 C TMP, 5
40 bar; T, 53.5 C

Co´rdova et al. (2016)

TMP, 5
30 bar; T, 53.5 C TMP, 5
30 bar; T, 53.5 C

CA, Cellulose acetate; PA, polyamide; PES, polyethersulfone; PVDF, polyvinylidene fluoride; Qf, feed flow rate; T, temperature; TFC, thin film composite; TMP, transmembrane pressure; v, cross-flow velocity.

Nanofiltration in the food industry

85

Similarly, Arend et al. (2017) successfully applied an NF process to concentrate the bioactive compounds from strawberry juice. For this aim, a PVDF NF membrane with a MWCO of 150
300 Da (from GE Osmonics) was used and two different juices were processed: untreated and microfiltered. The results showed an increase in the total phenolic content and anthocyanin content, independent of the processed juice. The antioxidant activity of the NF concentrates showed an increase of 99% and 51% starting for untreated and microfiltered juice, respectively. According to the global color variation (ΔE ) determination, no color degradation occurred during concentration of phenolic compounds. The results confirmed the possibility of producing beverages with improved nutritional and sensorial properties. In another study, the commercial UF and NF flat-sheet membranes, with different MWCOs, were tested to purify and separate biologically active compounds from sugars in clarified pomegranate juice (Conidi, Cassano, Caiazzo, & Drioli, 2017). Even though all the tested membranes showed high retention of biologically active compounds and the ability to recover fructose and glucose in the permeate stream, the results indicated that the Desal GK membrane represented the best performance in terms of efficiency, productivity, and fouling resistance. The chemical composition of raw and clarified juice and both NF permeate and retentate samples after juice treatment is reported in Table 3.3. According to the analytical results, high rejection ( . 95%) was measured for total antioxidant activity (TAA) and total polyphenols, while the retention for different anthocyanins was in the range of 80.4%
99.5%. Another study reported the possibility to concentrate sea buckthorn juice by membrane separation (Vincze, Ba´nyai-Stefanovits, & Vatai, 2007). Results showed that the solid content of the juice increased three times compared with the initial content using RO and four times using NF for the concentration of raw juice. It was revealed that vitamin C and antioxidant retention was almost 100% for NF and RO, and it was 80% for MF, which can be seen in Fig. 3.2. Many works dedicated to NF membranes have also stated successful employment in the fractionation and concentration of phenolic compounds. For example, Conidi, Cassano, and Drioli (2011) used tubular ceramic membranes in titania with MWCO of 450 and 750 Da (from Inopor GmbH) for the purification and concentration of polyphenols from bergamot juice, as an alternative to conventional methods. The depectinized juice was previously clarified by UF in order to remove the suspended solids. As it turns out the best performance in terms of separation of polyphenolics and sugars was shown by a membrane with MWCO of 450 Da. The high TAA of the retentate revealed the recovery of phenolic compounds, while sugar and organic acids were found in the clear solution of permeate. The comparison between the variation of the TAA in the samples processed by UF and NF membranes can be found in Fig. 3.3. Operating at a TMP of 33 bar and at a temperature of 24 C, a steady-state flux of 18 L/m2 h was reached after 80 minutes starting from an initial permeate flux of about 40 L/m2 h. Authors found the opportunity for a possible application of NF in the essential oil processing industry, due to the successful juice valorization. Similarly, in the next work, the authors used NF for the purification and

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Table 3.3 Biologically active compounds in pomegranate juice samples concentrated by NF. Parameter

Fresh juice

Ultrafiltered juice

NF permeate

NF retentate

TSS ( Brix) Glucose (g/L) Fructose (g/L) TAA (mM Trolox) Total polyphenols (mg GAE/L) Cyanidin-3,5-Odiglucoside (mg/ L) Cyanidin-3-Oglucoside (mg/L) Pelargonidin-3,5-Odglucoside (mg/L) Delphinidin-3-Oglucoside (mg/L)

17.03 6 0.04 12.9 6 0.5 21.2 6 4.0 26.8 6 2.9 2636.0 6 12.8

14 6 0.12 12.5 6 0.5 19.4 6 0.6 26.0 6 2.8 2457.5 6 15.3

5.23 6 0.09 11.7 6 0.5 19.1 6 0.4 1.2 6 0.4 65.2 6 0.7

18.36 6 0.15 12.5 6 0.5 21.2 6 2.4 41.9 6 5.8 3589.0 6 21.2

150.9 6 3.2

136.1 6 5.38

0.5 6 0.01

186.3 6 4.3

57.6 6 2.5

53.7 6 2.1

0.5 6 0.06

70.8 6 2.3

4.6 6 0.9

3.5 6 0.9

0.65 6 0.01

6.2 6 0.3

17.8 6 0.1

14.6 6 0.5

0.16 6 0.09

25.2 6 1.3

Figure 3.2 Vitamin C content in the feed, permeates (P) and in the concentrates (C) obtained through various processes.

concentration of polyphenols from ultrafiltered bergamot juice. In this case, Conidi and Cassano (2015) evaluated the performance of different polymeric spiral-wound membranes. Two polyethersulfone membranes with MWCO of 400 and 1000 Da (NF PES10 and N30 F) and a composite PA/PS membrane with MWCO of 150
250 Da (NF 270) were tested. All selected membranes were characterized by steady-state permeate flux; however, the NF 270 membrane presented the highest value. The experimental results indicated that the chemical nature of the membrane has the main impact on membrane performance. High rejection toward flavonoids (naringin, hesperidin, and neohesperidin) was observed for all selected membranes

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Figure 3.3 Total antioxidant activity in samples of clarified bergamot juice processed by various membranes.

(in the range 85.0%
97.7%). However, the best separation of phenolic compounds from sugars was found in NF PES 10, for which the lowest average rejection toward sugar compounds was 35%. Analyzing the produced retentate fractions, the authors concluded that there is a high antioxidant potential for NF membranes, and thus these can be considered for nutraceutical applications. Warczok, Ferrando, Lo´pez, and Gu¨ell (2004) used flat-sheet NF membranes (MPT-34, from Koch Membrane Systems and Desal-5 DK, from Osmonics) to concentrate apple and pear juice. The experimental part was carried out at low pressures to find an optimum process that led to the highest concentration. Results showed that the decrease in permeate flux was significantly greater in juice solutions than in fructose solutions due to the complex composition of the juice, and irreversible fouling of the membrane. In another work, a possibility to use NF membranes for a coffee extract concentration was studied (Pan, Yan, Zhu, & Li, 2013). Six different membranes widely used in the water treatment industry were tested. The one with the best performance was NF-2 with a pore size of 0.57 nm (SEPRO). During the concentration process, no significant solid loss was found, however, the concentration reached 39% (40 bar, 40 C). Based on this study, it can be concluded that during the NF process, the coffee extract can be concentrated to a certain level and it can be applied to conduct a partial concentration during instant coffee production.

3.4

Winemaking applications of nanofiltration

Wine is an alcoholic beverage produced from the fermentation of grapes, and it is one of the most consumed alcoholic drinks in the world, especially in Mediterranean

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countries. Wine is a complex alcoholic beverage, with an ethanol content higher than 8.5 vol.% and hundreds of organic compounds which are related to its flavor and specific aroma (Ortega-Heras, Gonza´lez-SanJose´, & Beltra´n, 2002). The consumption of red wine leads to the decrease of cardiovascular diseases (Assunc¸a˜o et al., 2007). These special properties are related to the high concentration of polyphenolic compounds. Therefore each wine processing should preserve the original aroma, minimizing the formation of undesired characteristics (i.e., plastic flavor) as in the case of juice processing. Membrane processes are replacing several conventional operations within the winemaking industry. In particular, cross-flow MF is largely used in the wine industry for wine clarification and stabilization as an alternative to the use of fining agents. Other membrane processes, such as NF, RO, electrodialysis (ED), and membrane contactors, have been introduced for tartaric stabilization, reduction of alcohol content in wine, control of the sugar content of must, management of dissolved gases, and reduction of volatile acidity in wine (Cassano, Conidi, & CastroMun˜oz, 2019; Daufin et al., 2001). In previous years, the demand for low-alcohol beverages has risen in several countries as a result of health and social issues. In addition, the alcoholic content has a strong impact on the quality of wine, which is influenced by the volatility of aroma compounds. Several strategies have been developed to partially reduce the alcohol content in wines without lowering the concentration of other compounds involved in wine quality, such as viticultural or prefermentation practices, microbiological techniques (i.e., use of novel yeast strains), postfermentation practices (i.e., blending of high and low wine) (Castro-Mun˜oz, 2019a, 2019b), cryoconcentration, and spinning cone column (SCC) concentration (Schmidtke, Blackman, & Agboola, 2012). These technologies present different drawbacks including high energy, high pressure (such as RO), and high working temperature that entail strong alteration of the aroma profile (Pilipovik & Riverol, 2005). In this way, NF seems to be an alternative technology for obtaining low-alcohol wines. This technology can provide higher alcohol flow rates together with greater permeation rates compared to RO. In addition, such a process can be carried out at low pressures and temperatures, thus preserving the organoleptic characteristics of the original product. For instance, Garcı´a-Martı´n et al. (2010) evaluated the retention characteristics of different NF and tight UF membranes toward glucose and fructose in model mixtures, with the purpose to control the sugar in grape musts. The final objective was indeed to reduce the alcohol content of wine in a traditional range, which could be accepted by the consumer without altering the specific organoleptic balance of the final product. The tested membranes (UF-GH, NF-HL, and NF-DK, all from GE Osmonics) showed different rejections toward fructose and glucose (in the range 80%
90%, and 15%
38% for NF and UF membranes, respectively). A higher rejection of NF membranes toward polyphenols, anthocyanins, and tartaric acid, was reported. Moreover, authors designed a two-step NF process aimed at producing wines with a low amount of alcohols but enriched with low- and high-molecularweight compounds. Regarding this process, the nonfermented must was processed in a first NF step, which was able to produce a solution with a moderate content of sugars. High-molecular-weight compounds (e.g., polyphenols and anthocyanins) were

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Figure 3.4 Graphical drawing of the two-stage nanofiltration (NF) process for the production of low-alcohol wine.

retained by the membrane. The NF permeate was then forwarded to a second NF step in order to concentrate most of the sugars in the retentate. At this point, the purpose was to preserve low-molecular-weight compounds (e.g., ions and tartaric acid) in the permeate. A low sugar content must, enriched in high- and low-molecular-weight compounds was satisfactorily obtained by blending the NF retentate and the NF permeate from the first and second step, respectively (see Fig. 3.4). Additionally, the NF retentate coming from the second step was considered to be suitable for the production of sweet wines, liquors, and in the manufacture of functional foods, aiming at increasing the profitability of overall process. In the same framework, Bonnet and De Vilmorin (2004) evaluated the partial sugar reduction by combining UF and NF membranes, as presented in their patent called REDUX. The proposal used a first UF step producing a clear must with the same sugar concentration of the initial must. The UF retentate was then reincorporated into the must that was being treated. The UF permeate was later

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Figure 3.5 Integrated membrane process used for the production of low sugar content fruit juices.

concentrated by a selective NF membrane with minimal permeability to sugars, resulting in a permeate with a low content of sugars and relatively rich in acids of the initial juice. The twice-filtered NF permeate was finally blended with the UF retentate (see Fig. 3.5). More recently, Labanda, Vichi, Llorens, and Lo´pez-Tamames (2009) evaluated the reduction of the ethanol content of a white model wine by using RO and NF membranes. Such an approach basically applied the permeation of aroma compounds during the concentration process. Among the investigated membranes, the UB70 (from Toray) displayed the highest permeability to model wine and the lowest solute rejection values. In a different concept, NF membranes are also able to increase the sugar concentration of must, for when grape must does not contain enough potential alcohol content. At this point, traditional techniques to increase the natural alcohol content of wine comprise the treatment of grape must with additional components, like sugars or ethanol. The incorporation of concentrated must is also an alternative, however, it could influence the quality of wine, while the addition of rectified must concentrate causes a dilution effect. NF membranes can allow an increase in sugar contents in wine without additional nongrape components at room temperature, thus preserving the heat-sensitive substances and volatile compounds, and thus resulting in a minimal negative effect on the marked character of the wine (Banvolgyi, Kiss, Bekassy-Molnar, & Vatai, 2006). Versari, Ferrarini, Parpinello, and Galassi (2003) evaluated the performance of two different NF membranes to increase the sugar content of grape must within wine production. NF membranes provided a higher rejection toward sugars (around 77%
97%) and lower rejection toward malic acid (around 2%
14%). The nanofiltered grape must showed a physicochemical composition like the initial grape must, with minimal changes on malic and tartaric acid content. This is crucial to preserve the quality of the wines; a preservation of the total polyphenols content was

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observed too. The efficiency of different RO and NF membranes, for the concentration of must from different grape varieties, was also documented by Pati, La Notte, Clodoveo, Cicco, and Esti (2014). Both membrane technologies contributed to obtaining a high-quality wine, in terms of total polyphenols, sugars, color intensity, and acidity.

3.5

Nanofiltration in dairy processing

In the dairy industry, NF is primarily used for particular applications, such as partial demineralization of whey, lactose-free milk, or volume reduction of whey (Kumar et al., 2013). NF has found its industrial worldwide use in the dairy industry to desalt whey, mother liquors, and brines (Pouliot, 2008). This is due to NF membranes, based on their intermediate selectivity between UF and RO membranes, representing an interesting alternative to ion exchange and ED if moderate demineralization is required. This technology simultaneously demineralizes whey at the same time as concentrating, contributing savings in terms of cost, time, and water disposal. NF has also been proposed for the removal of salt from salty whey (reaching up to 84%), the partial removal of acid from acid whey (about 42%), and the concentration of whey protein (up to 20%
22% of dry matter) allowing the reduction of minerals by 20%
50%. Furthermore, additional applications of NF membranes in the dairy industry involve the concentration and demineralization of UF
whey permeate containing the desired lactose, the concentration of milk in yogurt manufacture (as an alternative to vacuum evaporation), and the selective demineralization of yogurt.

3.5.1 Concentration and demineralization of whey It is well-known that whey is normally considered as a by-product of the cheesemaking and casein industry. Whey generally contains low solids content (up to 5%
6%) and high biological oxygen demand (BOD5 5 30
50 g/L), making its final disposal complicated and costly (Carvalho, Prazeres, & Rivas, 2013; Prazeres, Carvalho, & Rivas, 2012). For many years, whey was considered a food processing waste material, finding its main reuse in animal feed (postdrying) and partly as a fertilizer. Nevertheless, over recent decades, there was a clear interest in the valorization of whey to produce commercial products like whey proteins due to their nutritional, biological, and functional properties (Daufin et al., 2001). Of course, a further processing of whey to yield valuable products contributes to reduce environmental pollution; in the meantime, it also provides the dairy industry an added economic profit based on the possible sale of the processed products. When dealing with the traditional process of whey demineralization, whey is indeed concentrated by evaporation, or RO, followed by demineralization of the concentrated whey using ED and/or ion-exchange (Chen, Eschbach, Weeks, Gras, & Kentish, 2016). These processes are widely carried out at the industrial scale, but they need high investment and cleaning costs due to the high volume of effluent that

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needs to be treated. As previously mentioned, NF technology allows concentration (of about 20%
22%) and partial demineralization of the whey which can be done in one step (between 25% and 60% or 90% with DF). Specially, according to the selectivity of the membranes, most monovalent ions, organic acids, and some of the lactose can permeate through the NF membrane (Daufin et al., 2001). Some other advantages of NF can be identified compared to conventional processes, such as reduction of overall costs, the low energy consumption, and tastier products with better properties and viscosities (Bidhendi & Nasrabadi, 2006). In addition, the amount of effluent is greatly reduced if compared with other demineralization processes. Based on these advantages, NF is being promoted to replace the traditional processes for the concentration and desalination of whey. For instance, Magueijo et al. (2005) evaluated the performance of two different NF membranes (NFT50 from Alfa-Laval and HR-95-PP from DDS) in plate and frame configurations for the separation of valuable components from a by-product of “Serpa” cheese and curd production. In particular, the NF process was applied to fractionate cheese whey into retentate (a lactose-rich fraction) and a permeate (water with a high salt content). In the case of NFT750 membrane, it allowed recovery of approximately 80% of the water, displaying a significant reduction of the wastewater organic load, and a higher concentration (up to five times) of whey nutrients. Nguyen, Reynolds, and Vigneswaran (2003) also analyzed the use of NF membranes to concentrate the solid content of cottage cheese whey. The pretreated whey (using decanting, heating to 65 C, and filtering through a cheese bag of 5 μm) was then treated through a NF setup fitted with a plate-and-frame membrane (XP-45, from APV Company). A large pilot plant unit equipped with two spiral-wound membrane modules (Desal 5, from Osmonics) was also used. Finally, the process allowed the concentration of cottage cheese whey (from 7 to 26  Brix on the large plant unit by increasing the operating pressure in three steps from 20 bar up to 34 bar) while removing about three-quarters of the sodium and potassium salts and some acid. The retentate fraction (enriched in fat, proteins, and lactose) was potentially considered in the dairy industry for the production of ice-cream and yoghurt. Pan, Song, Wang, and Cao (2011) concentrated and demineralized simultaneously an acidified whey using a spiral-wound NF membrane (TFC 2540 SR2, based aromatic polyimide membrane from Koch membrane Systems). It was found that the desalination of whey was mainly affected by the pH of the feed solution. The best desalination rate was achieved at the isoelectric point of whey (pH 5 4.60).

3.5.2 Nanofiltration as an alternative for the concentration and demineralization of ultrafiltration
whey permeate NF has also been successfully applied for the demineralization of UF
whey permeate streams to produce lactose, minimization of volume prior to disposal, and production of water for other process streams. The benefits of using NF, as an alternative to evaporation, is the reduction of concentration costs, the removal of ions that affect the crystallization step, reduction of postcrystallization lactose

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processing costs, and higher lactose yields (Cassano et al., 2019). In previously proposed processes for lactose production, UF is primarily used to concentrate proteins from whey powder production, followed by a NF step for demineralization and lactose concentration, and a final crystallization (or spray-drying) step for lactose production. Atra, Vatai, Bekassy-Molnar, and Balint (2005) applied UF technology for milk and whey protein concentration, followed by the lactose concentration of the UF permeate by means of NF. Two flat-sheet commercial UF membranes (MWCO 6
8 and 15
20 kDa, both from Zoltek Rt Mavibran) and a spiral-wound NF membrane (MWCO 400 Da, from Millipore), were employed. The UF of fresh milk and whey allowed the production of whey protein concentrates with a protein content of 12%
14% and 8%
10%, respectively, that could be used in cheese production improving its nutritional value. The UF permeate, containing about 0.1%
0.5% and 5% of proteins and lactose, respectively, was then processed with NF process. A concentrated solution containing higher than 25% of lactose resulted. By choosing the optimal operating parameters (temperature of 30 C and VRF 5), the lactose yield was higher than 90%. In this way, the NF retentate can be reused in the sweets industry, while the permeate stream, containing only 0.1%
0.3% of lactose, was considered for further purposes such as cleaning and irrigation.

3.5.3 Lactic acid recovery by nanofiltration Lactic acid is a natural organic acid, which is widely used in the food industry as an acidulant and preservative (Lee, 1997). It is also used in the production of pharmaceutical, cosmetic, and biotechnological products (Datta & Henry, 2006). Lactic acid can be produced either by chemical synthesis or by fermentation. Typically, the conventional process for fermentative production of lactic acid is a batch process having low productivity and high capital and operating costs due to the additional separation and purification steps. Such steps are needed to reach the quality grade requirements for food grade. Specially, the traditional downstream purification implies different steps including filtration, acidification, neutralization, crystallization, adsorption, evaporation, and ion exchange, to mention just a few. Certainly, these methodologies are time-consuming, energy-intensive, and require expensive chemicals, representing 50% of the production costs and the generation of waste. Some conventional and emerging techniques have been proposed to recover lactic acid from fermentation broths, including extraction, adsorption, and membrane separation (Dı´az-Montes & Castro-Mun˜oz, 2019). Membrane-based separation has been extensively used in lactic acid separation (Wang, Li, Fan, & Xing, 2013). In fact, NF in downstream processing can replace the multiple purification steps by using a single step. An integrated membrane process of NF and RO was designed by Li, Shahbazi, Williams, and Wan (2008) for the separation and concentration of lactic acid from cheese whey fermentation broth. The process consisted a preliminary NF step in order to separate lactose and cells from lactic acid in the fermentation broth; afterward, this was followed by RO processing of the NF permeate. Five different commercial NF membranes were

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studied for this purpose. Among the selected membranes, the membrane, based on a thin-film composite membrane with an approximate MWCO of 400 Da, was the most efficient with almost 97% lactose retention. For this membrane, the permeation rates were of about 33 L/m2 h (at 37 C, 21 bar). At the end, NF permeate, containing mainly lactic acid and water, was then processed by means of two different RO membranes (DS 11 AG and ADF from GE Osmonics), to concentrate lactic acid. The ADF membrane presented a complete rejection of lactic acid and thus the permeate was only water. The comparison of the performance of three flat-sheet NF membranes (thin-film composite membranes DK, DL, and HL from GE Osmonics) in the processing of cream cheese acid was performed by Chandrapala et al. (2016). The separation efficiency of NF membranes toward lactose, lactic acid, proteins, and minerals was also evaluated operating in a DF configuration. In this regard, the target was to assay the removal of lactic acid and some minerals from proteins and lactose. In the case of HL membrane, it showed higher permeate fluxes in both NF and DF configuration. At a specific temperature (40 C) and pH 5 3, this membrane provided the highest permeate transmission for lactic acid (about 50%) and a lactose retention of 93%. The obtained insights revealed that NF is a good candidate process in the valorization of acid whey allowing the production of spray-dried whey powders, which can be importantly used in different food ingredient applications. It is important to mention that this approach is accompanied by the reduction of waste disposal costs and, in addition to this, there is a positive environmental impact currently related to the acid whey production. More recently, Be´das et al. (2017) proposed a semiindustrial NF plant using two commercial spiral-wound membranes (NF245
3840/30FF with a MWCO of 200 Da, from Dow-Filmtec) to demineralize and concentrate lactic acid whey prior to vacuum evaporation and spray drying processes. The NF process contributed to improve the dryability of NF concentrate, while the hygroscopicity of obtained lactic acid powder was also improved without affecting its particle size. Furthermore, NF also contributes to minimize the overall industrial energy cost of the lactic acid powder production process compared to traditional methodologies.

3.6

Nanofiltration in the sugar industry

The concentration and purification processes are nowadays important in the production of sugars. Traditional processes are used in this field, including evaporation, crystallization, and ion-exchange chromatography. However, it is well-documented that these processes are energy intensive leading to high operating costs, environmental issues, and low product yields in large-scale applications. At this point, membrane technology can support the development of sustainable processes. For instance, NF is a promising industrial-scale technique for sugar purification and concentration from natural carbohydrate solutions, giving considerable economic advantages over

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traditional processes, including chromatography and vacuum distillation, since it requires a lower energy consumption (Feng, Chang, Wang, & Ma, 2009). Despite the low differences among the molar mass of monosaccharides and di-/ trisaccharides, NF can selectively separate them with interesting yields, for example, glucose from sucrose, as well as glucose from lactose, or even from raffinose (Pontalier, Ismail, & Ghoul, 1997). Several reports document the ability of NF membranes to separate xylose from glucose, which is relevant in the industrial purification of xylose for xylitol production. For instance, Sjo¨man, M¨antt¨ari, Nystro¨m, Koivikko, and Heikkil¨a (2007) used three different NF membranes (Desal-5 DK, Desal-5, DL 270), with a MWCO in the range 150
300 Da, for the treatment of solutions composed of xylose and glucose in different mass ratios and total monosaccharide concentrations. The selected membranes provided comparable fractionation results. Molecular sieving was found to be the primary mechanism implied in the separation of these uncharged molecules. The retention of monosaccharides was mainly affected by the permeate flux. Xylose retentions were lower than glucose; such differences were minimized by increasing the permeate flux. All selected membranes exhibited a xylose separation factor over two and the most favorable xylose separation from glucose was reached with a concentrated monosaccharide mixture at a high pressure. According to the experimental results, NF technology leads to improving the yield and may partially replace chromatographic procedures in xylose production. Bandini and Nataloni (2015) have recently evaluated the recovery of dextrose from crystallization mother liquor, which is a main by-product coming from dextrose manufacturing. The recovery processes employed commercial NF membranes, such as Desal-DK, Desal-DL, K-SR2, and K-MPS34, which were tested to obtain a high purity dextrose ( . 95%). According to the membranes’ intrinsic properties, they showed different separation efficiencies; with Desal-DL membrane being the only one that met the industrial requirements for process application. Such a membrane provided dextrose purity in the permeate stream of higher than 97% NF also represents a competitive alternative to traditional technologies for the purification of disaccharides or monosaccharides (Catarino, Minhalma, Beal, Mateus, & de Pinho, 2008). For example, Xu, Wang, and Zeng (2005) proposed NF membranes to purify maltitol from a complex mixture containing maltitol syrup, sorbitol, multisugar alcohol, and some other components. NF has been also an effective method for purifying xylooligosaccharides (XOs), which are compounds of interest according to their specific health benefits. Actually, NF was used for the removal of impurities from raw XOs syrups, like monosaccharides (mainly xylose and arabinose), salts, and organic acids, which may cause off-flavors and raise safety risks (Mellal et al., 2008). Moreno-Vilet, Bonnin-Paris, Bostyn, Ruiz-Cabrera, and Moscosa-Santilla´n (2014) analyzed the potential of NF for the purification of inulin-type fructans from model solutions containing low-molecular-weight sugars (e.g., glucose, fructose, and sucrose). A pilot-scale NF unit was implemented with a spiral-wound membrane (HPA-600, MWCO 600 Da, hydrophilized polyamide material), and thus used for cross-flow experiments. A specific membrane provided a suitable separation of

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inulin, while removing low-molecular-weight carbohydrates. Response surface analysis (P , .05) revealed inulin rejection values over 90%. Today, the food industry has remarkably shown an increased interest in oligosaccharides such as fructooligosaccharides and galactooligosaccharides due to their prebiotic properties that are beneficial to the consumers’ health. NF seems to be an interesting approach for the purification and concentration of oligosaccharide mixtures as an alternative to chromatographic techniques (Lo´pez Leiva & Guzman, 1995).

3.7

Role of nanofiltration in valorization of high-added value compounds from food industry wastewaters

It is well-known that pressure-driven membrane processes, such as microfiltration (MF), UF, and NF, are not only focused on organic matter removal, but also on the separation and recovery of valuable solutes from agrofood processing by-products (Castro-Mun˜oz, 2018a, 2018b). Using NF, depending on the MWCO of the membranes, the recovery of smaller molecules (e.g., phenolic compounds and sugars) can be achieved, in which solvent and supercritical fluid extraction procedures are usually used (Galanakis, 2013). To date, different food industry wastewaters have been used as sources of valuable compounds, such as artichoke (Cassano, Conidi, Figueroa, & Mun˜oz, 2015; Conidi, Cassano, & Garcia-Castello, 2014), olive mill (Cassano, Conidi, Giorno, & Drioli, 2013; Conidi, Mazzei, Cassano, & Giorno, 2014; Rahmanian, Jafari, & Galanakis, 2014), and nixtamalization wastewaters (Castro-Mun˜oz, 2019a, 2019b; Castro-Mun˜oz, Barraga´n-Huerta, & Ya´n˜ez-Ferna´ndez, 2016; Castro-Mun˜oz & Ya´n˜ez-Ferna´ndez, 2015), to mention just a few. Of course, the separation efficiency of these membrane methodologies depends on a number of factors, such as the physicochemical composition of the bulk solution (e.g., type, weight, polarity, solute charge), operating parameters (e.g., feed flow rate, TMP, temperature, permeate flux), and certain membrane characteristics (e.g., membrane material, configuration of membrane separation module, pore size) (Castro-Mun˜oz, Ya´n˜ez-Ferna´ndez, & Fı´la, 2016). Finally, for the purification and concentration of target compounds, resin adsorption, and chromatography are the most sought-after methods, for which NF technology also meets the requirements. All these technologies have been well-documented and established, while they are generally assumed as safe since they have been used in different sectors of the food processing industry for several decades. To date, there are available many literature surveys (reviews and book chapters) from the research community showing the successful recovery of high-added value compounds using pressure-driven membrane processes, especially NF. Table 3.4 reports some of the most recent publications in this field, which can be consulted by the readers to gain a better understanding and detailed inputs about the recovery task. Through consulting these publications, it can be noticed that these processes are able to offer high recovery rates for several high-added value compounds; for

Table 3.4 Selected publications about the recovery of high-added value compounds from agrofood processing wastewaters by means of NF and tight UF membranes. Publication title

Brief overview

References

Current role of membrane technology: from the treatment of agro-industrial by-products up to the valorization of valuable compounds

This review provides a wide understanding of the current framework for membrane technology in this field. Thereby, the utilization of aqueous wastes from industries for the high-added value solute recovery is denoted. This work reports a critical literature review of the main agrofood by-products treated by membrane technologies for the recovery of nutraceuticals. Particular attention is paid to experimental results reported for the recovery of polyphenols and their derivatives of different molecular weight. This review provides a critical overview of the influence of these parameters on the recovery of phenolic compounds from agrofood by-products by using tight UF and NF membranes. This chapter highlights the potential of membrane operations as an alternative to other conventional separation techniques in the recovery of phenolic compounds from olive mill wastewaters. The chapter provides a complete overview concerning their implementation for the recovery of high-added value compounds from different food waste streams and extracts. The review highlights the outcomes about the separation mechanisms dominating during UF (from 100 to 1 kDa) of different feed solutions aiming the recovery of target macromolecules and micromolecules.

Castro-Mun˜oz, Barraga´nHuerta, Fı´la, Denis, and Ruby-Figueroa (2018)

Phenolic compounds recovered from agro-food byproducts using membrane technologies: An overview

Nanofiltration and tight ultrafiltration membranes for the recovery of polyphenols from agro-food byproducts Recovery of polyphenols from olive mill wastewaters by membrane operations

Recovery of high-added-value compounds from food waste by membrane technology Separation of functional macromolecules and micromolecules: From ultrafiltration to the border of nanofiltration

Castro-Mun˜oz, Ya´n˜ezFerna´ndez, et al. (2016)

Cassano, Conidi, RubyFigueroa, and CastroMun˜oz (2018) Cassano, Conidi, Galanakis, and Castro-Mun˜oz (2016)

Galanakis, Castro-Mun˜oz, Cassano, and Conidi (2016) Galanakis (2015)

(Continued)

Table 3.4 (Continued) Publication title

Brief overview

References

Separation, fractionation and concentration of highadded-value compounds from agro-food by-products through membrane-based technologies

This chapter describes the current applications and compelling overview the fractionation and recovery of high-added value compounds by means of membrane-based technologies. This review analyzes and discusses the recovery of biologically active compounds in relation to separation processes, molecule properties, membrane characteristics, and key factors affecting the performance of such technologies. This short communication addresses the role of membrane separation processes for recovering valuable phenolic compounds from winemaking by-products. This chapter devotes to the MF, UF and NF processes for the recovery of compounds from grape processing by-products.

Castro-Mun˜oz (2018a, 2018b)

This review classifies the main food waste sources and highadded value ingredients prior to exploring the recovery stages, conventional and emerging technologies applied from the raw material to the final product. This short communication addresses challenges and opportunities for the production of nutraceuticals from agricultural by-products using different emerging technologies.

Galanakis (2012)

Membrane-based technologies for meeting the recovery of biologically active compounds from foods and their by-products

Membrane processing: natural antioxidants from winemaking by-products Membrane technologies for the separation of compounds recovered from grape processing byproducts Recovery of high-added-value components from food wastes: conventional, emerging technologies and commercialized applications Emerging technologies for the production of nutraceuticals from agricultural by-products: a viewpoint of opportunities and challenges

Castro-Mun˜oz, Conidi, and Cassano (2018)

Crespo and Brazinha (2010)

Galanakis (2017)

Galanakis (2013)

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instance, MF technology can recover from 47% up to B100% of specific compounds (e.g., anthocyanins, glutamine, isoproline, proline, betanin, isobetanin, sugars, galacturonic acid, and some phenolic compounds), all these in permeate streams. On the other hand, UF technology, depending on its membranes’ MWCO, is able to provide recovery rates between 44% and 99% of those compounds, which can be expected to be contained in permeate samples; however, some of these compounds can start to be rejected by the membranes (commonly through tight UF), and thus partially recovered in the retentate. Importantly, such tight UF membranes are considered as the barrier to NF technology. NF membranes lead to passing practically water: this allows the concentration of the compounds in retentate from 50% up to 99%. It is worth noting that such NF and tight UF membranes can provide permeate streams which may meet the drinking water parameters, that is, the drinking water quality standards (turbidity: ,1 NTU, colorless; total dissolved solids: ,600 mg/L). Thereby, such permeate streams can be reused in the food processing industries as process water or within cleaning procedures (Cassano et al., 2013; Castro-Mun˜oz & Yan˜ez-Fernandez, 2015). Finally, the application of membrane technology and its role in waste management represent an economical and environmentally sustainable approach. In the near future, it is quite possible that governments will establish the use of approaches such as those described herein in order to reduce water and environmental pollution.

3.8

Concluding remarks

Over the course of this chapter, a complete overview of the potential and wellestablished applications of NF in the food processing have been reviewed and discussed. Relevant results on laboratory- and pilot-scale units have proven that NF membranes meet the requirements of the “green food processing” strategy. Specific case studies in different areas of food processing (such as fruit juice, wine and must, dairy, sugars, and food waste valorization) promote the key advantages of NF membranes over traditional technologies according to their intrinsic properties in terms of the high degree of selectivity, minimal thermal damage of the treated solutions, reduction of energetic consumption, and environmental impact. When dealing with NF in the recovery of high-added value compounds from agrofood wastes, the use of membrane-based processes clearly offers economic savings because such NF membranes are able to provide a treatment, as well as to recover compounds from several agrofood wastewaters. If the industries are encouraged to invest for the implementation of large-scale recovery process, the recovered solutes can be commercialized somehow. More than this, tight UF and NF membranes can offer environmental benefits due to such narrow pore size membranes providing permeate streams obtained from the fractionation of by-products, where basically the clear permeates contain low organic loads. The increased interest in NF over the past 20 years reveals that with further membrane development research, the application of NF in food processing will increase significantly in the coming years.

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Nanoadsorbents and nanoporous materials for the food industry

4

Sara Arabmofrad, Mahsa Bagheri, Hamid Rajabi and Seid Mahdi Jafari Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

4.1

Introduction

Today, the adsorption procedure has become a practical method for the separation and purification process on an industrial scale. The adsorption process is applied to purify, decolorize, deodorize, and concentrate in order to remove the hazardous products or to recover the valuable products from wastewater and many other industrial by-products (Cunningham, Al-Sayyed, & Srijaranai, 2018; Xu et al., 2018). Adsorption and biodegradation are the two practical and common strategies for the remediation of wastewater owing to their simplicity, cost-effectiveness, and high efficiency (Crini & Badot, 2011; Gadd, 2009; Jiuhui, 2008). From an industrial perspective, adsorption is a simple technique and economically feasible which yields high-quality water. Generally, active carbon is an effective adsorbent for the removal of a variety of contaminants, such as aromatic compounds, dyes, phenolics, and heavy metals (Da˛browski, Podko´scielny, Hubicki, & Barczak, 2005). In addition, other adsorbents have found their way into industrial applications like organic resins, zeolites, graphene, and commercial activated alumina as interesting materials (Wang & Peng, 2010). Nevertheless, the mentioned systems are rather expensive for use on a pilot scale and cannot be applied as viable options in different parts of the world. Accordingly, industry has focused on low-cost, efficient, and green adsorbents for pollution removal (Ali, Hamad, Hussein, & Malash, 2016; Kooh, Dahri, & Lim, 2018; Sartape et al., 2017). In the last decade, a dramatic advancement has been made in the adsorption process and methods to remove contaminants from industrial effluents. In recent years, nanoscience and nanotechnology, which is growing very rapidly, has opened new horizons in different fields including nanoadsorption, for example, resins, nanoclays, graphene, and metal oxides. Nanoadsorbents have unique characteristics like high surface area, small size, high stability, high reactivity, and can be regenerated many times over (Anjum, Miandad, Waqas, Gehany, & Barakat, 2016; Basheer, 2018; Kecili & Hussain, 2018). The mechanism of adsorption is the adhesion of a solute of a fluid phase (adsorbate molecule) through molecular interaction onto the porous surface of an adsorbent material (Fig. 4.1). This phenomenon occurs by two means: (1) physical adsorption or physisorption that takes place by van der Waals forces of the adsorbent and adsorbate, or (2) chemical adsorption or Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00004-2 © 2020 Elsevier Inc. All rights reserved.

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Figure 4.1 Two types of adsorption: physical and chemical interaction between surface of adsorbent and adsorbate. Source: Reproduced with permission from Kalebaila, K. J. Maseka, K., & Mbulo, M. (2018). Selected adsorbents for removal of contaminants from wastewater: Towards engineering clay minerals. Open Journal of Applied Sciences, 8, 355
369.

chemisorption that is related to chemical bonding forces between them (Chiou, 2003). Factors affecting adsorption are pH, size and specific surface area of adsorbent, contact time, amount of adsorbent and adsorbate, the presence of competing ions, ionic strength, and stirring speed (Ambashta & Sillanp¨aa¨ , 2010; Ersoz & Barrott, 2012; Kecili & Hussain, 2018; Machado & Bergmann, 2011; Sadegh & Ali, 2019). Freundlich, Langmuir, and BET isotherm models are applied for the description of adsorption. The Langmuir and Freundlich isotherms are able to consider a monolayer absorbent; in contrast, BET surface area can be used to find the capacity of a multilayer adsorbent (Ersoz & Barrott, 2012). Nanoadsorbents have numerous applications in various industries, such as wastewater treatment and water purification in the water and environment industry (Kamal, 2018), production of nanofertilizers in the agriculture industry (Rai, Ribeiro, Mattoso, & Duran, 2015), and recovery of some valuable compounds from food and beverage by-products in food industries (Bagheri, Jafari, & Eikani, 2019). The industrial sector today generates high levels of wastewater discharge containing various contaminants, chemically and biologically. During the last 30 years, these polluting agents has captured the attention of people (Khalaf, 2016). Due to the everdecreasing water resources, the higher cost of wastewater treatment has become a fundamental issue, particularly in the food sector containing both chemical and biological pollutants. The most practical means for the treatment of industrial wastewater include biodegradation, precipitation, solvent extraction, electrochemical techniques, and phytoremediation (Bagheri et al., 2019; Burakov et al., 2018; Miklos et al., 2018). This chapter reviews the properties of nanoclay, zero-valent iron nanoparticles, active carbon, and graphene oxide (GO) as abundant, low-cost, and applicable sources for the removal and adsorbing agents in the food industry as well as discussing their characteristics, classification, adsorption isotherms, and models, plus their application in the food sector.

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Adsorption by different nanoadsorbents

4.2.1 Clay minerals Many studies have been conducted on various applications of clay minerals in food, agriculture, environment cleanup, animal feed, and pharmaceutical formulation (Zhu & Njuguna, 2014). Clay minerals have found food industrial applications such as emulsion stabilizing, bleaching earth for oil purification, food and beverage packaging, and food additives (Bumbudsanpharoke & Ko, 2019; Moronta, 2004).

4.2.1.1 Structure of clay minerals Clay minerals are phyllosilicate minerals with a small particle size characterized by a structure with siloxane tetrahedral
central alumina octahedral sheet combinations (Xi, 2006). Actually there are two units in the fundamental structure of clays: tetrahedron and octahedron. In each tetrahedron, Si41 in the center is surrounded by four O22 at the corners. Then they share oxygen with each other to form a tetrahedral sheet. Similarly, a metal cation is at the center and six O22 are in the corners. Fig. 4.2A shows two kinds of clay structural units. Oxygen is shared by a series of octahedrons to form octahedral sheet (Alamgir, 2016; Obaje, Omada, & Dambatta, 2013; Selim, 2013). There are two types of octahedral sheets in clay minerals. Octahedrals that have a divalent cation such as Mg21 and Fe21 in the center form a trioctahedral sheet. If the center of an octahedral is occupied by a trivalent metal such as Al31 and Fe31, it is called a dioctahedral (Xi, 2006). The properties of clay refer to the kind of arrangement of atoms and ions, chemical structure, and kind of bands that exist between its layers (Barton, 2002). Clays have different potential applications depending upon their basic features. Clay minerals are classified into three groups on the features of layer type as follows (Barton, 2002; Landoulsi, 2013; Ombaka, 2016): (1) 1:1 clays where each layer consists of one silica tetrahedral sheet that is joined with an aluminum octahedral layer (e.g., kaolinite and serpentine); (2) the silicate unit layer of another type consists of one octahedral layer which is sandwiched between two tetrahedral layers and is called 2:1 clay (e.g., smectite, vermiculite, and mica), as shown in Fig. 4.2B; (3) the structure of 2:1:1 clay contains two octahedral and two tetrahedral sheets (e.g., chlorite), as depicted in Fig. 4.2C (Dayal & Varma, 2017; Kodama & Grim, 2018). Table 4.1 shows the classification of clay minerals based on the abovementioned features. Also the negative charge, surface area, and interlayer space of clay minerals prepared by Barton (2002) and Brady (1990) are summarized in Table 4.2.

4.2.1.2 Adsorbent clays Clay minerals are classified into three main groups by their ion exchange property: nonionic, cationic and anionic. Nonionic clays have any ion exchange capacity and include chlorite, illite, talc, serpenite, kaolinite, and pyrophyllite. Cationic clays such as vermivulite and smectite have cation exchange capacity (CEC) (Choy & Park, 2004; Wilson, 1987). The smectite group, which is known as cationic clay

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(Continued)

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Table 4.1 Classification of clay minerals. Layer type

Group

Subgroup

Species

1:1 (T.O)

Kaolin
serpentine

Kaolinites

Kaolinte, dickite, nacrite, halloysite Chrysolite, lizardite, amesite Pyrophyllite, talc Montmorillonite, bentonite, laponite, sepiolite, nontronite, beidellite Saponite, hectorite, sauconite Dioct. vermiculite, Trioct. vermiculite Muscovite, paragonite Phlogopite, biotite Margarite

Serpentines 2:1 (T.O.T)

Pyrophyllite
talc Smectite

Dioctahedralsmectites

Trioctahedralsmectites Vermiculite Mica Brittle mica

2:1:1 (T.O.T.O)

Chlorite

Dioctahedral vermiculite Trioctahedral vermiculite Dioctahedral vermiculite Trioctahedral vermiculite Dioctahedral brittle micas Trioctahedral brittle micas Dioctahedral chlorites Trioctahedral chlorites

Seybertite, xanthophyllite, brandisite

Pennine, dinochlore, prochlorite

L

Reproduced with permission from Bergaya, F., & Lagaly, G. (2013). Handbook of clay science (Vol. 5). Newnes; Farihahusnah, H. (2013). Acid activation of bleaching earth for crude palm oil treatment/Farihahusnah Hussin. University of Malaya; Johnston, C. T. (2018). Clay mineral-water interactions. In C. T. J. R. Schoonheydt & F. Bergaya (Eds.), Developments in clay science (Vol. 9) (pp. 89
124); Kotal, M., & Bhowmick, A. K. (2015). Polymer nanocomposites from modified clays: Recent advances and challenges. Progress in Polymer Science, 51, 127
187.

Figure 4.2 (A) Clay structural units; tetrahedral and octahedral. (B) Detail structure of MMT (2:1 clay mineral). (C) Schematic structure of some T.O, T.O.T, and T.O.T.O clay minerals and their thickness. Source: Reproduced with permission from (A) Jordan, A. (2014). Lightening the clay (II). Obtenido de Soil System Sciences. ,http://blogs.egu.eu.; (B) Nuruzzaman, M., Rahman, M. M., Liu, Y., & Naidu, R. (2016). Nanoencapsulation, nano-guard for pesticides: A new window for safe application. Journal of Agricultural and Food Chemistry, 64(7), 1447
1483 and Bhattacharyya, K. G., & Gupta, S. S. (2008). Adsorption of a few heavy metals on natural and modified kaolinite and montmorillonite: A review. Advances in Colloid and Interface Science, 140(2), 114
131; and (C) Reproduced and modified with permission from Claverie, M., Garcia, J., Prevost, T., Brendle´, J., & Limousy, L. (2019). Inorganic and hybrid (organic
inorganic) Lamellar materials for heavy metals and radionuclides capture in energy wastes management—A review. Materials, 12(9), 1399.

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Table 4.2 Properties of clay mineral groups. Group

Kaolin
serpentine

Smectite

Vermiculite

Mica

Chlorite

Net negative charge (cmolkg) Surface area (mV) Interlayer space (C. Su and Puls)

2
5

80
120

100
180

15
40

15
40

10
37 0.7

600
800 1
2

550
700 1
1.5

70
100 1

70
100 1.4

Reproduced with permission from Barton, C. (2002). Clay minerals. In: R. Lal (Ed.), Encyclopedia of soil science (pp. 187
192). New York: Marcel Dekker; Brady, N. (1990). Soil colloids: Their nature and practical significance. In The nature and properties of soils. (15th ed., pp. 177
212). New York: Macmillan Publishing Co.

(2:1 clay mineral), is used as an absorbent due to its critical properties such as vast CEC, high specific surface area, and swelling ability (Xi, 2006). Among all the smectite groups, montmorillonite (MMT) is the most important dioctahedral clay in adsorption because of its unique properties, such as more CEC compared with other members of smectite group, low cost, nontoxicity, as well as other useful properties (Barton, 2002; Reddy et al., 2019; Zhang & Cresswell, 2016). In general, work on clays for the removal of dyes, phenol, heavy metals, pesticides, herbicides, pathogens, and mycotoxin from wastewater has continuously increased in recent decades. Because of their low cost, natural availability, and environment-friendliness, clays are well-known for removing pollutants from wastewater (Shahadat & Isamil, 2018). MMT, the main component of bentonite, is one of the clay minerals that belongs to the smectite group known as 2:1 phyllosilicat minerals. There are electrostatic and van der Waals forces between the interlayer spacing or galleries of the MMT layers (Bertuoli, Piazza, Scienza, & Zattera, 2014). Exchangeable cations such as Na1 and Ca21 exchanging with Al31 in the octahedral layer generate negative charges on the layers because of the positive charge deficiency, while Al13 being replaced with Si14 does not change the crystal structure (Brigatti, Galan, & Theng, 2013; Zhu et al., 2016). These replacements in tetrahedral and octahedral sheets are called isomorphous substitution and the type of cation that exists between layers influences the physical and chemical characteristics of MMT (Johnston, 2018), as shown in Fig. 4.3. The other charge that is produced by edges of MMT causes its surface activity and is pH-dependent (Eslinger & Pevear, 1988; Ghadiri, Chrzanowski, & Rohanizadeh, 2015). Water and polar molecules have great affinity toward the interlayer spacing of MMT due to hydrophilic features (Bertuoli et al., 2014; Soo-Ling, Abdullah, Bee, Sin, & Rahmat, 2018). Furthermore, cationic compounds are adsorbed on the surface of MMT via the electrostatic attraction and positive charge of the surface (Leodopoulos, Doulia, & Gimouhopoulos, 2015; Wibulswas, 2004).

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Figure 4.3 Schematic view of negative charges that are caused by isomorphic substitutions (A) and layer edges (B). Source: Reproduced with permission from Claverie, M., Garcia, J., Prevost, T., Brendle´, J., & Limousy, L. (2019). Inorganic and hybrid (organic
inorganic) Lamellar materials for heavy metals and radionuclides capture in energy wastes management—A review. Materials, 12(9), 1399.

4.2.1.3 Modification of montmorillonite Due to the unique features and adsorptive properties of MMT, such as large porous surface area, nontoxic, high CEC, and high swelling, it is the most commonly used clay in adsorption (de Paiva, Morales, & Valenzuela Dı´az, 2008; Yuan, Theng, Churchman, & Gates, 2013). On the other hand, the negative charge and hydrophilic characteristics of MMT surface make it ineffective in the adsorption of anionic, hydrophobic, and nonpolar compounds (Obi Chidi, 2018). Furthermore, there have been various attempts to achieve better qualities for MMT by modification. Modifiers are divided into two groups including organic and inorganic (Feng et al., 2017; Xiang Ying, 2007).

4.2.1.3.1 Organic modification This modification allows the intercalation of cationic surfactants such as quaternary ammonium compounds inside the interlayer space of sorbent through ion exchange and the adsorption of them on the surface of MMT (Ghadiri et al., 2015). Organic modification provides an expansion of the basal spacing of MMT layers by a cation end and increases the exchange capacity (Jayrajsinh, Shankar, Agrawal, & Bakre,

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2017). Among the organic modifiers, quaternary alkyl ammonium, especially alkyl ammonium salts, have been extensively used to prepare organoclays (Yin, Zhang, Wu, Tan, & Meng, 2015). MMT modified by quaternary alkyl ammonium salts not only has hydrophobic properties but also has a greater interlayer space compared with raw MMT (Bergaya & Lagaly, 2001; Bertuoli et al., 2014; de Paiva et al., 2008; Pavlidou & Papaspyrides, 2008), as revealed in Fig. 4.4A. In recent years, there have been many articles on modification of MMT with several kinds of quaternary alkyl ammonium salts. He, Ma, Zhu, Yuan, and Qing (2010) modified MMT with different CEC based on several kinds of quaternary alkyl ammonium salts with different alkyl chain numbers and chain length. The comparison of organo MMTs showed that surfactant loading, increase of chain number, and the size of alkyl chain length leads to higher basal spacing. The authors explained that CEC of MMT has little effect on basal spacing, however, the amount of surfactant depends on CEC of MMT. Arrangement patterns of organic surfactants between the layers of MMT depend on the layer charge of MMT, the length of the alkyl chain and the concentration of surfactants. As illustrated in Fig. 4.4B, the chains of alkyl ammonium ions lie parallel to the silicate layers as monolayer (basal spacing about 1.37 nm), bilayer (basal spacing about 1.77 nm), and pseudotrimolecular layers (about 2.17 nm) and the interlayer separation is determined by the thickness of one, two, and three alkyl chains, respectively. Also when chain axes and silicate intersect, they form paraffin-type layers (basal spacing .2.2 nm). Generally, for preparation of modified MMT, cationic surfactants are used that form a monolayer (de Paiva et al., 2008; Lagaly, 1986; Lagaly & De´kany, 2005; Ltifi, Ayari, Chehimi, & Ayadi, 2018; Xi, 2006; Zhao, Choo, Bhatt, Burns, & Bate, 2017).

4.2.1.3.2 Inorganic modification Inorganic modified MMT is prepared by using inorganic additives. Acid modification is the most commonly used way for inorganic modification via cation exchange reaction (Feng et al., 2017). As depicted in Fig. 4.5, in the acid activation process, the proton of the mineral acid attacks the interlayer of MMT and liberates octahedral ions (Al 1 3 , Mg 1 2 , Fe 1 2 ) (Foletto, Volzone, & Porto, 2003; Taylor & Jenkins, 1988). By using acid treatment, some properties of MMT such as specific surface area and porosity are improved (Makhoukhi, Didi, Villemin, & Azzouz, 2009). In addition, an increase in the interlayer space results in MMT having exchangeable cations with soluble salts of acid-modified MMT, which is modified by mineral acids; they are used for bleaching earth in the processing of edible oils (Breen, 1991; Falaras, Kovanis, Lezou, & Seiragakis, 1999; Madejova´, Bujda´k, Janek, & Komadel, 1998). This results in increased porosity, specific surface area, and cationic exchange which cause more adsorption capacity of metals, phosphatides, and oil (Valenzuela Dı´az & Santos, 2001). Generally for the production of acid-modified MMT, it is activated with sulfuric acid or hydrochloric acid (Kheok & Lim, 1982). Mukasa-Tebandeke, Wasajja-Tebandeke, Schumann, and Lugolobi (2016) studied the adsorption effect of acid-modified MMT activated with sulfuric and

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Figure 4.4 (A) Conceptual sketch of organo montmorillonite. (B) The arrangements of alkyl ammonium ions in the interlayer space of MMT with increasing loading level. Source: Reproduced with permission from (A) Zhao, Q., Choo, H., Bhatt, A., Burns, S. E., & Bate, B. (2017). Review of the fundamental geochemical and physical behaviors of organoclays in barrier applications. Applied Clay Science, 142, 2
20; (B) Olad, A. (2011). Polymer/clay nanocomposites. In Advances in diverse industrial applications of nanocomposites.

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Figure 4.5 Clay activation by acid attack. Source: Reproduced with permission from Komadel, P. (2016). Acid activated clays: Materials in continuous demand. Applied Clay Science, 131, 84
99.

hydrochloric acids on bleaching of cotton and sunflower oil. Their results showed overall performance of hydrochloric acid-modified MMT was higher than sulfuric acid-modified MMT. Also dilute acid-modified MMT had a better overall performance compared with concentrated acid-modified MMT.

4.2.2 Activated carbon Activated carbon is the most practical type of processed amorphous carbon-based agent. Indeed, it has a microcrystalline structure, a highly developed porosity, and an extended interparticulate surface area. The preparation process includes two steps: the carbonization process at the temperature ,800 C using inert environment conditions and the activation of carbonized yield. Accordingly, all carboncontaining materials have the potential to be converted into activated carbon, although the properties of the final products may vary according to the employed raw material, nature of the activating material, and the process conditions (Frı´as et al., 2018; Mitra, 2018).

4.2.2.1 Crystalline structure of active carbon and its porous structure Active carbons bear a microcrystalline architecture which is formed during the carbonization process. This structure is different from the graphite composition considering the interlayer spacing, which is 0.335 nm for graphite and 0.34
0.35 nm for active carbon. Moreover, the microcrystalline layers are less-ordered in active carbons. The term turbostratic was proposed by Biscoe and Warren to describe this composition. The presence of heteroatoms like oxygen and hydrogen is the reason for this disorder in structure. Franklin classified active carbons based on their graphitizing capability. During the carbonization process, nongraphitizing carbons form powerful bonds between

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the randomly oriented crystalline structures leading to the formation of rigid fixed bodies. The final charcoals present a developed microporous structure which is stable even during high thermal processing. Regarding polyvinylidene chloride (PVDC) charcoal, which is a nongraphitizing carbon, nearly 65% of the carbon is ˚ . PVDC charcoal ordered in the layers of graphite with a mean diameter of 16 A does not graphitize even at extreme temperatures of 3000 C. Generation of a nongraphitizing composition containing powerful cross-links is improved via associated oxygens or by insufficiency of hydrogen in the raw compound. Considering PVC charcoal as a graphitizing carbon, Franklin reported that the initial crystallines had little tendency for the cross-linking process at the starting point of carbonization process. The obtained charcoal was weak and exhibited a less porous structure, whereas the crystallites possessed higher numbers of graphitic layers set parallel to each other. The graphitization ability is closely related to the variety of orientation of crystallines in the two types of carbons.

4.2.2.2 Porous structure of active carbon The random orientation of microcrystallines in active carbons in addition to the powerful cross-linking between them demonstrates a well-developed porous composition. Generally, they have a low density and depict a low degree of graphitization. During the activation process, the porous structure is developed and the spaces between the initial crystallites are eliminated. Besides, the pore size distribution as well as the structure is determined by the nature of the raw compound and the carbonization process the material has gone through. Disorganized carbon is also removed by the activation process and the crystallites are exposed to the activating materials resulting in the generation of a microporous structure. Later in the reaction, larger pores are formed due to the burnout of the walls between the neighboring pores. Hence, transitional porosity and macroporosity are enhanced and the micropore volume is decreased. Dubinin et al. (1949) reported that when the degree of burn-off is ,50%, a microporous active carbon is obtained and when the burnoff degree is between 50%
75%, a mixed porous structure is present, demonstrating all kinds of pores (Dubinin et al., 1949). Generally, active carbons have an organized internal surface which is usually distinguished by their polydisperse capillary composition with pores of different sizes and shapes. Several methods are developed to identify the shapes of pores; these shapes include V-shaped, regular slit-shaped, and ink-bottle shaped, in addition to other shapes (Oschatz et al., 2017; Sethia & Sayari, 2016). Normally, the calculations for the pore radii are done based on the shapes of ink-bottles and nonintersecting cylindrical capillaries. Pores of active carbons range from less than a nanometer to thousands of nanometers. A method of classification of the pores was introduced by Dubinin which has now been adopted by the International Union of Pure and Applied Chemistry (IUPAC). The classification is based on the width (w), which indicates the distance between the walls of the pore bearing a slit shape. The pores are classified into three groups: micropores, mesopores, and macropores. The effective radii of the

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micropores are ,2 nm. Adsorption in these pores takes place via volume filling. Moreover, the adsorption energy in these pores is considerably higher compared with mesopores due to the overlapping of adsorption forces from the across the walls of the micropores. The pore volume is in the range of 0.15
0.70 cm3/g. Dubinin also reported that for some types of active carbons, the microporous composition is divided into two overlapping microporous shapes with the radii of 0.6
0.7 and 0.7
1.6 nm regarding supermicropores (Dubinin, 1979). Mesopores also known as transitional pores possess a volume between 0.1 and 0.2 cm3/g. The surface area of these pores only consists of 5% of the total surface area of the whole carbon. Nevertheless, it is possible to develop activated carbons with higher mesoporisity using specific techniques. The volume of the mesopores reaches 0.65 cm3/g and their surface area is around 200 m2/g. These pores are identified by capillary condensation of the adsorbent along with the development of liquefied adsorbate. The adsorption isotherm demonstrates the hysteresis loops in which the adsorption stops at the relative vapor pressure of 0.4 bar. Moreover, these pores are conduits leading the molecules of adsorbate to the micropore cavity. The pores are generally recognized by electron microscopy or via adsorption
desorption isotherms. Macropores do not have a significant impact on the adsorption process owing to their small contribution to the surface area of the adsorbate, which does not go beyond 0.5 m2/g. They have roles as transportation channels for the adsorbate molecules to the micro- and mesopores. All pores comprise walls and thus include two types of surfaces: internal or microporous surfaces, characterized by Smi and the external surface Se. The former indicates the walls with the area of several hundred square meters per gram, related by Eq. (4.1): smi 5

2 3 10W L

(4.1)

Here, Smi denotes the surface area in m2/g, W indicates the volume in cm3/g, and L is the accessible pore width within the scale of nanometers. Owing to the very small size of L, the area of micropores is significantly larger than mesopores and macropores. The second surface (Se) making up the walls of meso and macropores in addition to the edges and external-facing sheets is relatively small and fluctuates between 10 and 200 m2/g for many active carbons. The variation seen between Smi and Se lies in the volume of adsorption energy (Gong, Li, Luo, Fu, & Pan, 2017; Stoeckli, Perret, & Mena, 1980). The pore width has an inverse relationship with the energetic effect. Upon adsorption in micropores at low relative pressures, the BET procedure is not capable of elucidating the initial stages of the adsorption isotherm (Kim et al., 2018; Zhao et al., 2016).

4.2.2.3 Adsorption isotherm equations for active carbon The adsorption equations are used for the presentation of equilibrium states of an adsorption system. They hand in useful information for the adsorbate, adsorbent,

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and the adsorption operation as well. They determine the surface area of the adsorbent, the volume of the pores, and their size distribution. A series of adsorption isotherm equations are introduced. Among them the useful ones include the Langmuir, the Freundlich, the Temkin, the Brunauer
Emmett
Teller (BET), and the Dubinin equations. Among these equations, the BET and Dubinin equations are the most useful for the interpretation of physical adsorption of gaseous materials on the porous carbon materials (Afonso, Gales, & Mendes, 2016; Inglezakis, Fyrillas, & Park, 2019; Roque-Malherbe, 2018). Generally, three viable theoretical approaches exist for deriving adsorption isotherms: The kinetic mode The statistical mode The thermodynamic mode

Considering the kinetic mode, the equilibration condition reveals that the adsorption and desorption rates are equal. Therefore the two rates can be obtained in an isothermal equation. For the statistical mode, the equilibrium constant is introduced by the partition functions of vacant spots, adsorbed materials, and the gaseous molecules (Santos & Boaventura, 2016; Shayesteh, Rahbar-Kelishami, & Norouzbeigi, 2016). The most common isotherm adsorption equations used for the experimental results are Langmuir isotherm, BET isotherm, and Freundlich and Temkin isotherms. For a complete explanation of these isotherm equations and their related formula, the readers are referred to the book Activated Carbon Adsorption (Bansal & Goyal, 2005).

4.2.2.4 Active carbon applications in the food industry Activated carbon is employed for numerous applications in the food and drinking water industry (Goher et al., 2015; McCleaf et al., 2017). It is also used for the adsorption of phenolic compounds in the wastewater of food plants (Karri, Sahu, & Jayakumar, 2017; Zhang, Huo, & Liu, 2016). Herein, some of the recent examples of the related studies for the adsorption of phenolic compounds and wastewater treatment of food plants are highlighted. Aliakbarian, Casazza, and Perego (2015) investigated the adsorption of olive wastewater phenolics. By using the optimum conditions of 8 g activated carbon per 100 mL of solution, maximum adsorption capacity was reached. Moreover, the pseudo-second-order model was chosen as the most suitable for kinetic results, and in terms of the sorption system the Langmuir isotherm was the best model. To sum up, activated carbon was able to fully recover the polyphenols and carbohydrate of olive mill wastewater plant which could be further applied to generate bioethanol and polyphenols applicable in different sectors (Aliakbarian et al., 2015). Lo´pez et al. (2019) developed a new technique to produce activated carbon. They extracted caffeine and chlorogenic acid from spent coffee grounds. The generated activated carbon obtained via the carbonization process had the maximum adsorption capacity of methylene blue (qm) between 411 and 813 mg/g (Lo´pez et al., 2019). In another interesting research activity, anaerobic digestion of food

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waste in reactors was accelerated by the synergistic effect of activated carbon and trace elements. Thereby, propionic acid was consumed faster leading to the higher production of methane. Also, the addition of activated carbon enhanced the growth rate of both archaea and syntrophic bacteria. Finally, the microbial examinations revealed that hydrogenotrophic methanogens were the prevalent strains (CapsonTojo et al., 2018). Kaveeshwar et al. (2018) developed activated carbon derived from pecan shell with a high surface area of (1500 m2/g) and pore volume (0.7 cm3/g) and it revealed a maximum adsorption capacity for Fe(II) during 90 minutes at the temperature of 30 C. The adsorption isotherm was best described by a pseudo-second-order model (Kaveeshwar et al., 2018). In another study, Yangui and Abderrabba (2018) applied activated carbon with a layer of milk proteins for the recovery of olive mill wastewater polyphenols. Interestingly, this green method increased the adsorption capacity as the overall efficiency for the entire phenols was 75.4% in addition to the high rate of 90.6% for hydroxytyrosol. The extracted polyphenols were further investigated for their radical scavenging power and they demonstrated high antioxidant activity through the DPPH assay (Yangui & Abderrabba, 2018). Hettiarachchi and Rajapakse (2018) implemented tea industry waste activated carbon as a green material for the removal of methylene blue from wastewater. The activating agent was phosphoric acid and the adsorption process was described by Freundlich and Langmuir models. Overall, the Langmuir model gave satisfactory results and the maximum adsorption (q0) obtained for adsorption of methylene blue onto the activated carbon was 303.3 mg/g (Hettiarachchi & Rajapakse, 2018).

4.2.3 Zero-valent iron nanoparticles Zero-valent iron nanoparticles (nZVI) can be produced by different methods. Initially, physical procedures were applied, such as grinding, abrasion, and lithography (Li, Yan, & Zhang, 2009). The popular preparation methods at present include nucleation from solution or gas and annealing at high temperatures (Shan, Yan, Tyagi, Surampalli, & Zhang, 2009). There are also chemical methods used for the production of nZVI. They can be obtained by using NaBH4 as a reducing agent in the reaction below (Wang & Zhang, 1997). 2 0 FeðH2 OÞ31 6 1 3BH4 1 3H2 O ! Fe k 1 3BðOHÞ3 1 10:5H2

(4.2)

Another procedure for the generation of nZVI is the reduction of goethite (α-FeOOH) or hemothite (α-Fe2O3) at high temperatures and decomposition of iron pentacarbonyl in argon gas or organic solutions (Sun, Li, Zhang, & Wang, 2007). Chemical reduction is the most common means to produce nZVI owing to its simplicity and its production of a homogenous network (Jamei, Khosravi, & Anvaripour, 2013).

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The production methods are still being developed at the present time and the main attention is focused on the reduction of costs. Different methods plus their advantages and disadvantages are summarized in Table 4.3.

4.2.3.1 Applications of zero-valent iron nanoparticles in the food industry nZVI has been proved to be effective in the removal of contaminants on the lab scale (Fan et al., 2019; Kang, Yoon, Lee, Kim, & Chang, 2018; Mehrabi et al., 2019). However, for practical applications of nZVI in the removal of contaminants, it is necessary to perform experiments using real circumstances in order to be more realistic and tangible. Moreover, the safety aspects, limitations, and other possibilities should also be considered prior to the implementation of nZVI. The benefits of using nZVI in the environmental treatment include the purification of groundwater and wastewater treatment which is necessary for all the processing sectors. The limitation of using nZVI includes insufficient mobility in the ecosystem. Research conducted by Elliott and Zhang (2001) demonstrated that only 1.5% of nZVI subjected to the groundwater gets to the point of remediation at the depth of 6 m (Elliott & Zhang, 2001). On the other hand, by enhancing the mobility of nZVI, the chance of random propagation in the environment increases, which is undesirable (Saleh et al., 2008). Another facet of the issue is the availability and cost of implementing nZVI on an industrial scale. Lots of companies are currently producing nZVI on an industrial scale, as summarized in Table 4.4. The total cost of nZVI technology depends on several factors, including the type of product, needed amount, transportation cost, etc. Also, the costs of laboratory and experiment fields should be considered plus the pilot experiment on the contaminated spot (Lowry & Phenrat, 2019). Furthermore, migration of nZVI particles is related to the properties of the underground water as well as the number of water resources (Stefaniuk, Oleszczuk, & Ok, 2016). A pilot study is necessary for determining the amount of suspension, mobility of nZVI, and time during which the nanoparticles are still active, plus a preliminary estimate of the reduction of contaminants. Later, remediation work is undertaken, which consists of the stages below: (1) Installation of injection and monitoring wells; (2) examination of the samples from the underground wells; (3) dosing of nZVI considering the factors of the medium like pH, temperature and so on; and (4) analysis of the effectiveness of operation after exposure to nZVI (Zhang, 2003). The examination of other factors is also necessary for determining the effect of nZVI, such as content of oxygen, nitrate, and sulfates (Cundy, Hopkinson, & Whitby, 2008; Su & Puls, 2004). In additions, the size of remediation as well as the remediation zone are important factors regarding the effect of nZVI. A pilot study explored the use of nZVI in the summer of 2000 in Trenton, United States. In short, the employment of TCE, PCE, VC, chloroform, and 2.5 kg of modified Pd/nZVI resulted in the reduction of chloroorganisms to the rate of 96.5% (Elliott & Zhang, 2001). Ordinary nZVI was

Table 4.3 Reported procedures for the synthesis of zero-valent iron nanoparticles. Method

Description

Advantage

Disadvantage

Diameter (C. Su and Puls)

Surface area (m2/g)

References

Lithography and grinding

Break down bulk iron materials

Cheap method

N.A

N.A

Shan et al. (2009)

Precision milling method

The rotatory chamber with steel beads

10
50

39

Shan et al. (2009)

Chemical reduction

Reduction of the iron salts using reducing agent

Elimination of toxic reagents, low energy consumption, and short processing time Simple application

1
100

33.5

Wang and Zhang (1997)

Carbothermal reduction

Fe21 are reduced to nZVI at elevated temperatures with the use of thermal energy in the presence of gaseous reducing agents

Limited control over particle size distribution and morphology Limited control over particle size distribution and morphology The application of toxic reducing agent Now well known

20
150

130 (C was used as a matrix and created Fe0/ C had better properties)

Hoch et al. (2008)

Cheap reducing agent including H2, CO2, and CO

Ultrasound method

Application of ultrasound waves and reducing agent

Electrochemical method

Reduction of the iron salt in the presence of the electrodes and electricity Biosynthesis of nanoparticles using plant extracts

Green synthesis

Generation of small nanoparticles Inexpensive method Replacing toxic reducing agent

Use of toxic reducing agent Tendency to form nZVI clusters Irregular shape

10

34
42

Jamei et al. (2013)

1
20

25.4

20
120

5.8

Chen, Hsu, and Li (2004) Kuang, Wang, Chen, Megharaj, and Naidu (2013)

nZVI, Zero-valent iron nanoparticles. Reprinted with permission from Stefaniuk, M., Oleszczuk, P., & Ok, Y. S. (2016). Review on nano zerovalent iron (nZVI): From synthesis to environmental applications. Chemical Engineering Journal, 287, 618
632.

Table 4.4 Companies active in the production of zero-valent iron nanoparticles. Company

Location

Type of nanoparticle

Size

Surface area (m2/g)

Cost

Nano iron

Czech Republic

nZVI powder

20
100 nm

20
25

Toda Kogyo Corp

Japan

RNIP (mainly iron oxides)

100 nm

23

Polyflon

USA, Florida Germany

nZVI powder

100
200 nm

37
58

120 euro/kg (powder) 25
65 euro (suspension) 25
33 (powder euro/kg) N.A

nZVI powder (contain traces of other metals) mZVI suspension nZVI powder nZVI powder

0
80 μm

N.A

1.2 euro/kg

2 μm 25 nm 20 nm 40
60 nm 60
80 nm 25 nm

N.A N.A 40
60 6
13 7 40
60

N.A 144 $/100 g 337 $/100 g 244 $/100 g 215 $/100 g 330 $/100 g

nZVI suspension

Gotthart Maier Metallpulver GmbH Tokyo ink mfg. Co. Ltd M Knano Sky spring Nanomaterials

Nanostructured Amorphous Materials, Inc

Japan Canada USA, Houston USA, Houston

nZVI powder

nZVI, Zero-valent iron nanoparticles. Reproduced with permission from Stefaniuk, M., Oleszczuk, P., & Ok, Y. S. (2016). Review on nano zerovalent iron (nZVI): From synthesis to environmental applications. Chemical Engineering Journal, 287, 618
632.

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applied in the removal of Cu21 from the industrial wastewater (Li, Wang, Yan, & Zhang, 2014). Also, the modified nZVI revealed a high rate of elimination of chloroorganic materials (He, Zhao, & Paul, 2010; Wei et al., 2010). Recently, nZVI was used for the removal of chloroorganic compounds principally from groundwater (Li, Xu, Xiao, Qian, & Song, 2019; Ren et al., 2019). Most of the pilot and full-scale studies have been conducted in North America (Bardos et al., 2014). The applied nZVI particles were 40% nonmodified, 32% bimetallic, and 16% emulsified NZVI, respectively. Also, the concentration of the prepared suspension was 8 g/L (Jiang et al., 2018; Li, Wang, Liang, & Zhang, 2017). In Europe, nZVI was first applied for the full-scale removal of chloroorganic contaminants in Germany (Bornheim). The area was contaminated by the aerospace industry and the area contaminated was several square kilometers. First, the area was remediated by steam extraction means which did not give satisfactory results at a cost of 1 million euros. Then, the decontamination procedure was changed to the application of nZVI and surprisingly 90% of the contaminants were eliminated with a lower cost and during a short period of time (Mueller et al., 2012). The next country in Europe which applied this technology for the remediation of contaminants was the Czech Republic. Horice and Pisencna injected 300 kg of nZVI in 82 injection wells in which the elimination of contaminants ranged from 60% to 90% (Mueller et al., 2012). It is also reported that food industrial wastes can be employed to produce nZVI (Machado, Grosso, Nouws, Albergaria, & DelerueMatos, 2014).

4.2.3.2 Safety and toxicity of zero-valent iron nanoparticles The larger specific surface area of nZVI has attracted the attention of industry stakeholders and scholars, particularly for their application in the food sector. nZVIs are also employed for the remediation of toxic materials (heavy metals, organic dyes, etc.) from contaminated water (Li, Elliott, & Zhang, 2006; Stefaniuk et al., 2016). In recent years, experiments have been undertaken in order to investigate the possible hazardous effects of nZVI on organisms and some of the related results are discussed below. Green algal cells were exposed to different concentrations of nZVI ranging from 1.11 to 71.6 mM. A cell enumeration method was applied to determine the number of living cells using the microscope. The results demonstrated that chemically synthesized nZVIs induce more susceptible damage on cells compared to the biologically developed nZVIs (Bhuvaneshwari et al., 2017). Also, these authors tested the toxicity of nZVI on Daphnia, which is a small planktonic crustacea. Interestingly, after 48 hours of the nZVI interaction with living cells, Daphnia revealed a higher number of damaged cells compared to algal cells, which underlines the irrelevance of hierarchical superiority. In a nutshell, the introduced materials containing nZVI, GO, and active carbon, in addition to their composites, are normally applied as adsorbents, nanosensors, and packaging materials in the food sector, however their possible toxicity should

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be further examined through in vitro and in vivo assays to guarantee their application in the food industry.

4.2.4 Graphite family: graphene, graphene oxide, and reduced graphene oxide Graphite is a carbon material used as a precursor for the synthesis of a new generation of carbonaceous forms including GO, reduced GO, and graphene. The changes to graphite during the production of these forms resulted in a series of new physicochemical properties regarding water dispersibility, surface area increase, and improved structural features. The type and intensity of changes remaining in graphite after the production process are a function of various factors including oxidizing agent type and concentration, process temperature and duration, and the source of graphite. Graphite, graphite oxide, GO, reduced GO, and graphene all have the same basic structure of the abundant constituent element, that is, carbon. Generally, the differences between these forms come from the physicochemical and structural deviations from pure graphite, caused by a variety of reactions applied on graphite, such as the action of chemical agents and subsequent physical treatments. In the past few years, graphene has been applied in different sectors owing to its superior characteristics. Graphene applications have found their way into the field of food quality and safety (Sundramoorthy, Kumar, & Gunasekaran, 2018). It is important to evaluate the quality of foods before they enter the market; since pesticides and herbicides are commonly used for the improvement of agricultural products and these may remain in the food chain and be a possible threat to the consumers (Damalas & Eleftherohorinos, 2011). Furthermore, processed foods contain preservatives and colorants along with other additives that are used to enhance the overall quality of food products as well as their shelf life. With this in mind, promising analytical techniques are required for quick and precise information about food products. Graphene is a practical and cost-efficient sorbent for several compounds like phenols, cocaine, adenosine, and squalene that is preferred over other sorbents in terms of sorption capacity, recovery of extracted compounds, cost of production, and simple application (Huang & Lee, 2012). In the upcoming sections the synthesis methods, as well as the properties and applications of graphene and its derivatives in the food sector, are explored in detail.

4.2.4.1 Graphene During the last decades, many studies have been run in order to achieve singlelayer graphene. Without exaggeration, graphene is the most important member of the graphite family due to its unique and extraordinary physicochemical properties. Graphene is a two-dimensional (2D) structure in a sheet form which was first discovered by Novoselov and coworkers (Geim & Novoselov, 2010). The carbon atoms in graphene sit next to each other in a sp2-sp3 hybridization forming a 2D configuration (Fig. 4.6A). The scientific importance of graphene and its role in the

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Figure 4.6 (A) Structural model of graphene; (B) structural model of GO; (C) the reduction reaction of GO toward production of reduced GO through omitting oxygenated functional groups.

development of novel industrial processes is very high. Witness to this claim is that Geim and Novoselovin received Nobel Prize of physics in 2010 for their pioneering research regarding grapheme (Torres, 2017). This amazing carbonaceous material has gained significant attention in various different fields of study as consequence of its thermal features (5000 W/mK conductivity), structural characteristics (B2600 m2/g and Young’s modulus of B1 Tpa), and excellent electron mobility (250,000 cm2/Vs). The reason behind these unusual traits is the flowability of π bands in graphene nanosheets which

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occurs due to the presence of semifull p-orbitals (Papageorgiou, Kinloch, & Young, 2017).

4.2.4.2 Graphene oxide When the production of a carbonaceous body with the ability to make a stable dispersion in a polar solution is required, the name of “graphene oxide” is raised. This process is initiated by exposing graphite to two groups of agents, acid and alkali, which results in the insertion of oxygenated functional groups (OFGs) on graphite sheets, thus turning it to graphite oxide. This is followed by application of a mechanical process such as ultrasound or severe stirring, which increases the d-spacing between layers, forming GO. Epoxy, hydroxyl, carboxyl, and carbonyl are the main OFGs of GO. It is proclaimed that the basal plane of GO is decorated via epoxy and hydroxyl while carboxyl and carbonyl are located at the edges of GO (Yang, Li, & Zeng, 2018), as shown in Fig. 4.6B. The siting of OFGs on both the basal plane and edge of GO nanosheets give it the ability to form very stable dispersions in a polar solvent. On the other hand, the presence of these groups gives researchers the opportunity to modify the physicochemical properties of GO by adding specified compounds such as polymers. From the first production of GO by Brodie in 1859, many researchers have focused on improving both the synthesizing procedure and quality of the final product. Generally, in the process of producing GO from graphite, a variety of oxidizing agents are applied in order to insert the OFGs on the graphite nanosheets and increase the interlayer spacing of the sheets (Dreyer, Park, Bielawski, & Ruoff, 2010). From the environmental point of view, researchers have been trying to decrease the amount of these agents as well as apply safer/lower risk oxidizing agents in order to restrict the production of toxic/explosive gases. In the case of GO quality, attempts are underway to design a production process to increase its dispersibility in a polar medium by increasing the density of OFGs, and decrease the structural defects (Marcano et al., 2010).

4.2.4.3 Reduced GO The process in which the OFGs of GO are omitted, via action of the reducer agents or application of the heating operation, is named the reduction process. This results in transforming GO to reduced GO (rGO), as depicted in Fig. 4.6C. The reduction process of GO is conducted through two main approaches of chemical and thermal reduction (Fig. 4.7A). In some works, the reduction process is designed based on the application of both thermal and chemical routes (De Silva, Huang, Joshi, & Yoshimura, 2017). The reducer agents in the chemical reduction of GO are of both chemical and natural sources, including hydrazine (Ferna´ndez-Merino et al., 2010), sodium borohydride (Gao, Alemany, Ci, & Ajayan, 2009), ascorbic acid (Ferna´ndez-Merino et al., 2010), sodium hydroxide (Chua & Pumera, 2014), potassium hydroxide (Chen, Zhou, & Wu, 2014), sodium citrate (Chen et al., 2011), pyrogallol (Ferna´ndez-Merino et al., 2010),

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Figure 4.7 (A) The reduction procedures of graphene oxide; (B) the reduction mechanisms of graphene oxide.

hydroiodic acid (Moon, Lee, Ruoff, & Lee, 2010), uric acid (Choi, Kim, Han, Kim, & Gurunathan, 2016), sugars (Zhu, Guo, Fang, & Dong, 2010), amino acids (Gao et al., 2010), and tea polyphenols (Liu et al., 2018). The reduction process should be conducted with some crucial considerations taken into account. The two main reactions involved are the removal of OFGs and restoration of structural defects. The first reaction determines the kind of OFGs that can be eliminated and the repair of the location that the OFGs were removed to become a large range conjugated structure. In the case of structural restoration, two processes—severe thermal operation and CVD/epitaxial growth —can be applied (Pei & Cheng, 2012). The reduction mechanisms are shown in Fig. 4.7B.

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4.2.4.4 Synthesis methods Various procedures have been proposed for the synthesis of graphene materials (Table 4.5) including chemical vapor deposition (CVD) (Shen et al., 2018), epitaxial growth (Xu et al., 2017), microchemical exfoliation (Pogacean et al., 2019) arc discharge method (Łabe˛d´z, Lange, Bystrzejewski, & Huczko, 2015), and unzipping of carbon nanotubes (CNTs) (Li, Liao, Wang, & Chiang, 2016), in addition to the chemical and electrochemical modes (Bhuyan, Uddin, Islam, Bipasha, & Hossain, 2016; Liu et al., 2016). Chemical techniques include strong oxidation of graphite followed by reduction to graphene via reducing agents. Among these methods, the exfoliation-based procedures including mechanical, liquid phase, and electrochemical exfoliation, although CVD and chemical reduction of GO are more common, as summarized in Fig. 4.8. In a study, Kumar et al. (2013) prepared nitrogen-doped graphene by using the microwave plasma CVD method. Another interesting technique is the electrophoretic deposition (EPD) applied to the synthesis of graphene nanosheets. Accordingly, Chen, Zhang, Yu, and Ma (2010) deposited graphene sheets on nickel foams using this method. Moreover, Ata, Wojtal, and Zhitomirsky (2016) developed graphene using the EPD procedure and aluminon as a film-forming and organic charging material. Graphene could be also developed by a direct current arc
discharge method by the availability of hydrogen at atmospheric pressure using graphite rods as electrodes for the means of deposition (Guo et al., 2013). Laser pyrolysis technology is another means to synthesize multilayer graphene in the presence of dilution gas (Gavrila-Florescu, Sandu, Dutu, Morjan, & Birjega, 2013). Among these methods, CVD is considered to be the most efficient procedure for the production of graphene, nevertheless each technique has its own advantages and disadvantages (Table 4.6). The well-known routes of Brodie, Staudenmaier, and Hummers are the main procedures to oxidize graphite in order to produce GO. A brief description of each procedure along with their advantages/disadvantages is shown in Table 4.7. Different procedures have been developed to rectify the disadvantages of these methods, resulting in the introduction of the popular methods of modified and improved Hummers. The production of GO is considered to be the main precursor in terms of synthesizing reduced GO and graphene. So, the methods by which the graphite oxide is prepared have a very important role in achieving GO, reduced GO, and graphene with appropriate physicochemical characteristics.

4.2.4.5 Properties and characterization In order to confirm the formation of GO, reduced GO, and graphene, some instrumental analyses have already been developed. The data that these methods provide is very important for the determination and prediction of physicochemical and structural properties of final products. Accordingly, the kind, relative fraction, and the distribution pattern of OFGs, the interlayer distance between nanosheets, the

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Table 4.5 A brief description of graphene synthesis methods. Graphene synthesis method

Brief description

References

Chemical vapor deposition (CVD)

CVD is designed based on heating of a stream of carbon-containing gas in the presence of hydrogen gas and a substrate of metal foil. Exposure to temperature of B1000 C brings about decomposition of carbon-containig gas followed by carbon deposition on substrate. The reaction is terminated through cooling the system, followed by collecting the graphene from the surface of metal foil. LPE is initiated by dispersing the graphite/carbon nanotube in appropriate solvent followed by ultrasonication or high-shear mixing and terminated by separating the single layer graphene via centrifugation or sedimentation. CHE as a top-down method is set up based on increasing the interlayer spacing of graphite, resulting in graphene intercalated body followed by layering of this body through employing flash heating or ultrasonication. MCE as a top-down route is based on applying an external force on graphite in order to break the van der Waals forces between carbonaceous nanosheet, bringing about production of mono atoms in layer of carbon. A wide range of procedures such as scotch tap, ultrasonication, and electrical field have been used to produce graphene by this approach. The two approaches of thermal and chemical reduction are applied individually or in combination to remove oxygenated functional groups of graphene oxide. The crucial factors determining the characteristics of final product are the process temperature, process atmosphere, and oxidizing agent properties. EPG as a thermal approach is conducted through applying the temperature of 1000 C
1500 C in vaccum to a substrate of silicon carbid (SiC), resulted in decomposing of carbid toward rearrangmenting of carbon atoms and removing of noncarbon ones. Eventually, the graphene is formed in the surface of Si by annealing.

Guermoune et al. (2011)

Liquid phase exfoliation (LPE)

Chemical exfoliation (CHE)

Mechanical exfoliation (MCE)

Reduction of graphene oxide

Epitaxial growth (EPG)

Bhuyan et al. (2016)

Bhuyan et al. (2016)

Bhuyan et al. (2016)

De Silva et al. (2017)

Tan, Wang, and Guo (2018)

Figure 4.8 Graphene synthesis methods.

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Table 4.6 Pros and cons of techniques used for graphene production. Method

Advantages

Disadvantages

Mechanical exfoliation

Cost-efficient and straightforward No need for special equipment SiO2 thickness is tuned for better contrast Most even films (of any method) Large-scale area Simple upscaling Versatile handling of the suspension Quick process

Uneven films Difficult procedure (not suitable for large-scale production)

Epitaxial growth Graphene oxide

Difficult control of morphology and adsorption energy High-temperature process Fragile stability of the colloidal dispersion Reduction to graphene is just partial

Reproduced with permission from Soldano, C., Mahmood, A., & Dujardin, E. (2010). Production, properties and potential of graphene. Carbon, 48(8), 2127
2150.

morphology and diameter of individual nanosheets, and the density, porosity, surface area, and pore characteristics (volume, diameter, and size distribution) are achievable via these instrumental analyses, as summarized in Table 4.8. ˚ with a powerful bond in a particular The length of bond in C-C is about 1.42 A layer but weak bonding between layers. Also, the specific surface area of an individual graphene sheet is about 2630 m2/g (Ke & Wang, 2016). Graphene and its composite compounds exhibit extraordinary conductivity properties and therefore it is applied as a semiconductor. Some of the prominent characteristics of graphene are listed below: High Young’s modulus B1000 GPa Moisture barrier Electrical conductivity akin to Cu Density four times lower than Cu Thermal conductivity five times greater than Cu Lower density than steel and 50 times more powerful than steel

4.2.4.6 Functionalization A variety of materials such as nanoparticles, polymers/biopolymers, organic and inorganic compounds are employed for the modification of the carbonaceous family via the two main approaches of covalent and noncovalent functionalization (Fig. 4.9). Figuring out the meaning of the word “functionalization” is important for the perception of this process. Generally, the process in which one or more new features are added to a chemical compound or some of its characteristics are changed/modified through covalent or noncovalent bonding with a molecule/polymer/ biopolymer/nanoparticle, is named functionalization. In the case of graphene,

Table 4.7 The main procedures of graphene oxide synthesis. Method

Oxidizing agents

Brief description

Advantages/disadvantages

References

Brodie

Potassium chlorate Nitric acid

Mixing oxidizing agents with graphite at 60  C, followed by washing with water and aquous HCl.

Brodie (1859)

Staudenmaier

Potassium chlorate or sodium chlorate Nitric acid Sulfuric acid Sulfuric acid Sodium nitrate Potassium permanganate

Mixing oxidizing agents of Brodie method as well as concentrated H2SO4 with graphite at ambient temperature, followed by washing with water.

Disadvantages: Toxic/explosive for producing ClO2 gas. Structural defects of final product Scant dispersibility and infirm acidity of final product Disadvantages: Toxic/explosive for producing ClO2 gas Prolongation of process

Advantages: Nontoxic Increases the density of oxygenated functional groups as a result of increasing oxidation level Disadvantages: Prolongation of process for forming graphite oxide as well as its separation and purification

Hummers and Offeman (1958)

Hummers

Mixing concentrated sulfuric acid, sodium nitrate and potassium permanganate with graphite at 35 C
98 C, followed by washing with warm water

Staudenmaier (1898)

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Table 4.8 Instrumental methods for analysis of carbonaceous materials. Instrument analysis

Aims

References

Fourier-transform infrared spectroscopy

Determination of the functional groups of carbonaceous material, usually over a spectral range of 400 2 4000 cm21 Assessment of the surface composition Evaluation ofchange of the functional groups of graphene oxide during the oxidation process Assessment of the atomic structure Determination of the number of layers, wrinkle, folds, and three-dimensional structure of graphene sheets HR-TEM can directly picture the honeycomb lattice along with structural disorder in graphene oxide. Evaluation of surface morphology and surface topography of carbonaceous material Assessment of the structure of the carbonaceous material Determination of the interlayer spacing before and after treatment of graphite and graphene oxide Determination of the degree of bond hybridization in mixed sp2/sp3 bonded carbon Evaluation of specific bonding configurations of functional atoms Assessment of degree of alignment of the graphitic crystal structures within graphene oxide Determination of the structural properties and quality toward imperfection and (dis)ordered structures

Rajabi, Jafari, Rajabzadeh, Sarfarazi, and Sedaghati (2019)

X-ray photoelectron spectroscopy

Transmission electron microscopy and highresolution Transmission electron microscopy (HRTEM)

Scanning electron microscopy and field emission scanning electron microscopy X-Ray diffraction

X-ray absorption near-edge spectroscopy

Raman spectroscopy

Yang et al. (2009)

Ersan, Apul, Perreault, and Karanfil (2017)

Stankovich et al. (2006)

Bandara, Esparza, and Wu (2017)

Zhao, Liu, and Li (2015)

Jiang et al. (2016)

(Continued)

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Table 4.8 (Continued) Instrument analysis

Aims

References

Scanning tunneling microscopy

Evaluation of the morphology Determination of defective areas Determination of the thickness, number of layers, topography, sheet dimension and roughness of individual nanosheets Tracking of the structural changes during thermal processing Studying the structural characteristics toward determination the oxygenated functional groups Tracking of the structural changes come into graphene oxide after oxidation of graphite Quantifying surface area and pore characteristics (total pore volume, pore diameter and pore size distribution) Determination of thermal stability and decomposition temperature of the carbonaceous materials Assessment of the thermal transitions Evaluation of the surface charge of specified carbonaceous solution or zeta potential (ζ potential) at different pH Assessment of swelling properties and water uptake of the carbonaceous materials Evaluation of the electrical conductivity

Zhao et al. (2015)

Atomic force microscopy

Scanning transmission electron microscopy Solid-state nuclear magnetic resonance

UV-Visible spectroscopy

Physisorption analysis

Thermogravimetric analysis

Differential scanning calorimetry Surface charge analysis

Equilibrium swelling analysis

Electrical characterization

Rozada et al. (2015)

Zhu et al. (2012)

Zhao et al. (2015)

Wang, Shen, Yao, and Park (2009)

Ersan et al. (2017)

Sabzevari et al. (2018)

Bandara et al. (2017) Sabzevari et al. (2018)

Sabzevari et al. (2018) Zaaba et al. (2017)

reduced GO, or GO, the covalent functionalization is targeting aromatic domains while the noncovalent approach is employing the aliphatic domains. The changes are introduced in graphite during the oxidation process, resulting from the transition of sp2 to sp3 hybridization; on the one hand, they bring about a

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Figure 4.9 (A) Noncovalent-based, and (B) covalent-based functionalization approaches of graphene, reduced GO and GO.

series of structural defects in GO, while providing appropriate conditions for noncovalent functionalization. The covalent functionalization, in fact, is a chemical conjugation. Organic functionalities are covalently attached to graphene sheets through two main approaches: attack of functionalities on aromatic bond (sp2 region) of graphene, and the role-playing of OFGs in GO for bonding with functionalities. On the other hand, the noncovalent functionalization as a physical route is a function of both surface properties of carbonaceous compounds as well as the characteristics of added functional groups (Fig. 4.10). Dispersing graphene in a special medium is the main goal of functionalization due to the necessity of forming a dispersion in the process of composites synthesis (Georgakilas et al., 2012). The surface manipulation of graphene via functionalization is an efficient method for its application in different fields such as the electronic and food industries.

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Figure 4.10 Molecular models of sp2 hybridized graphene. Source: Reproduced with permission from Terrones, M., Martı´n, O., Gonza´lez, M., Pozuelo, J., Serrano, B., Cabanelas, J. C., . . . & Baselga, J. (2011). Interphases in graphene polymerbased nanocomposites: Achievements and challenges. Advanced Materials, 23(44), 5302
5310.

4.2.4.7 Graphene/ graphene oxide-based nanocomposites As mentioned before, preparation of carbonaceous composites results in stable dispersions to allow adequate interaction with polymers. It is worth mentioning that the characteristics of a carbonaceous
polymer composite are a function of the weight ratio of the compounds as well as the affinity between them (Papageorgiou et al., 2017). Different routes of covalent and noncovalent approaches are applied in order to assemble the nanocomposites, as described below.

4.2.4.7.1 In situ polymerization The process of in situ polymerization is conducted through premixing of graphene with monomers (one type or more) followed by polymerization, causing the polymer and graphene to disperse well through strong interactions. The most important limitation of this procedure is the viscosity increase as the polymerization reaction progresses. In the case of GO, the presence of OFGs results in an increase in the possible bonds with polymer, forming a composite of optimum characteristics. In situ polymerization is used to produce nanocomposites through both covalent and noncovalent approaches.

4.2.4.7.2 Solution blending This method is based on mixing both a carbonaceous suspension and a polymer solution through applying magnetic stirring or sonication. Direct addition of a

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polymer into a carbonaceous suspension will be achievable if the polymer and solvent are compatible in terms of solubility. The resulting network can be turned into a nanocomposite via removing solvent by adding a precipitating agent or by casting the mixture followed by drying. It is declared that the nanocomposites produced via casting method have a tendency to agglomeration, causing the composite properties to be affected adversely. Different polymers have been used to form composites with GO, such as chitosan (Huang, Peng, & Yang, 2018; Rajesh, Sujanthi, Kumar, & Venkatesan, 2015), polyethyleneimine (Li, Chen, & Shi, 2019; Zhao et al., 2018), polyethylene glycol (Baek, Baek, Kim, Jun, & Kim, 2018), poly(vinyl alcohol) (Liu et al., 2018), Arabic gum (Silvestri et al., 2019), welan gum (Yu et al., 2015), poly(amidoamine) (Rafi, Samiey, & Cheng, 2018), zeolitic imidazolate frameworks (Kumar, Jayaramulu, Maji, & Rao, 2013), poly(methyl methacrylate) (Pham, Dang, Hur, Kim, & Chung, 2012), and poly(acrylamide) (Song, Wang, Wang, Shao, & Wang, 2015; Yang, Bolling, Priolo, & Grunlan, 2013).

4.2.4.7.3 Melt mixing As its name implies, this process is conducted through heating the polymer to the melting point followed by adding graphene powder and it is terminated by extruder mixing. The nanocomposite produced with this method has the ultimate extent of dispersion. On the other hand, the temperature at which the polymer melts may have negative effects on the demolition and fracture of graphene nanosheets. The latter especially occurs when complete comingling of the mixture components necessitates applying high shear mixing. Despite the shortcomings of this method in terms of lower degree of dispersion than other methods, its ability to produce exemplary composite as well as its scalability make it popular in the synthesis of graphene-based composites.

4.2.4.7.4 Layer-by-layer assembly Layer-by-layer (LbL) deposition, creates a tenuous film in which the properties can easily be engineered by changing and controlling the deposition succession process. The process variables that have a crucial effect on LbL are reaction medium properties (pH, temperature, and ionic strength) and the possible interactions (electrostatic, covalent, and noncovalent bonding). The latter is especially important when GO is aimed in the LbL assembly, due to its OFGs providing appropriate conditions for electrostatic and hydrogen bonding throughout the LbL deposition.

4.2.4.8 Application of graphene in the food industries The ultimate features of the graphite family allow its members to be applicable in a wide variety of fields, either in the laboratory or at an industrial scale. Water treatment, sensing instruments, batteries, and supercapacitors are some of their applications. Food processing, being a large industry, on the one hand, consumes a large amount of agricultural crops as raw materials, whilst on the other, produces a huge volume of wastewater during the production process. The assessment of raw materials regarding contamination with agricultural pesticides, quality control, and

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packaging of final products as well as wastewater treatment are areas in which the graphite family have a significant role to play. Due to the importance of accessibility to water sources with hygienic requirements, many strategies have been developed. In this regard, due to their enumerated properties the graphite family has been applied for water treatment. Different combinations of polymers with the graphite family with different properties, such as high surface area, the presence of OFGs, and suchlike, have been used to form composites aimed at the removal of contaminants from water. Accordingly, GO, reduced GO, and graphene have been used to form composites with various polymers, including chitosan (Li, Song, Cui, Jiao, & Zhou, 2018; Ocan˜a-Gonza´lez, Ferna´ndez-Torres, Bello-Lo´pez, & Ramos-Paya´n, 2016; Sabzevari, Cree, & Wilson, 2018), polypyrole (Wang et al., 2017), agar gum (Chen et al., 2017), welan gum (Yu et al., 2015), and poly (ethylene glycol dimethacrylate) (Luo, Cheng, Ma, Feng, & Li, 2011). The properties of the graphite family bring about the efficient removal of multiple contaminants, including heavy metals and color, making them a valuable part of the water treatment industry. It is declared that GO coated with modified chitosan hydrogel is an effective adsorbent of catechin through magnetic solid-phase extraction with an adsorption capacity of 27 mg/g (Sereshti, Samadi, Asgari, & Karimi, 2015). Mahpishanian, Sereshti, and Baghdadi (2015) synthesized GO with phenylethylamin to separate pesticides from fruits, vegetables, and water samples. These researchers concluded that the delocalized π-electron system brought about effective bonding of pesticides with nanoadsorbents. The gas barrier properties of graphenic-based film allow its application in the field of food packaging. These nanocomposites have potential application in food preservation in the form of coatings or films. The graphite family, when incorporated with biopolymers such as chitosan, can improve the technological features of chitosan. On the other hand, the antimicrobial activity of graphenic materials can increase the shelf life of food products (Grande et al., 2017). The nanocomposite of GO-chitosan has the ability to inactivate both E. coli and B. subtilis (Grande et al., 2017). The films made from reduced GO are claimed to have the barrier ability over He, H2, water vapor, NaCl salt, and HF acid (Su et al., 2014). Also, it is declared that the composite of GO
PEI synthesized via LbL methods onto a PET film shows low O2 permeability and prominent H2/CO2 selectivity (Yang et al., 2013). Goh et al. (2016) developed a packaging film for food applications comprising poly(lactic acid)
graphene. This film signifcantly improved the shelf life of edible oils and potato chips; about an eightfold extension was observed compared with control sample.

4.2.4.8.1 Applications in the food nanosensors Today, biosensors are increasingly being used in different fields of technology, especially in the food and pharmaceutical sectors. In a recent study, Chekin et al. (2016) developed an electrochemical label-free immunosensor for ultrasensitive detection of gliadin which demonstrated a great progression in the field of food science. The produced sensor takes advantage of the porous structure of reduced GO

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functionalized by the covalent bonds with antigliadin antibodies and the application of 1-pyrenecarboxylic acid as the cross-linker agent. In short, a decrease of the shown current by a differential pulse voltammetry (DPV) revealed the presence of gliadin in the food network at the limit of 1.2 ng/mL over 1.2
34 ng/mL. This constructed sensor offers the possibility of surface regeneration (Chekin et al., 2016). In another study, Li and coworkers fabricated a laminar composite membrane composed of GO with water permeability of 7.70 LMH/bar and a molecular weight cutoff of 1243 Da. It exhibited good stability with both polar and nonpolar solvents. The rejection of orange II sodium salt, safranin O, solvent blue 35, and Rhodamine B were 56.60%, 86.52%, 4.39%, and 66.95%, respectively. Moreover, some bioactive food and pharmaceutical ingredients including tetracycline, rifampicin, roxithromycin, spiramycin, vitamin B12, and lecithin were applied to test the separation capability of the developed membrane. It was demonstrated that it can effectively retain the molecules with a rejection rate of 65.80%, 82.67%, 84.27%, 92.21%, 95.34%, and 98.44%, respectively. Finally, the integrity and separation activity of the membrane was confirmed through several 7-day tests of vitamin B12 in isopropanol (Li, Cui, Japip, Thong, & Chung, 2018). Furthermore, Sac¸macı, Sac¸macı, and Ko¨k (2018) proposed a novel method based on the magnetic dispersive solid-phase extraction (MDSPE) along with the Zetasizer for determination of As(III)/As(V) in water and food networks. The best determination methods in the conditions were different nanocomposite quantities, pH of the sample, type of the applied solution, sample and desorption solution volumes. Overall, the GO/Fe3O4@GSH nanocomposite revealed a wrinkled structure and considerable dispersibility in water and therefore it was considered to be an ideal candidate for the determination of As(III)/As(V) based on Zetasizer measurement and MDSPE. It also presented selective speciation toward arsenite (Sac¸macı et al., 2018).

4.2.4.8.2 Evaluation of food composition The risk of high cholesterol in blood is a major concern globally, especially for urban
industrial lifestyles. Several foods are recognized for their high cholesterol content, such as egg yolk, animal brain, dairy products, etc. Therefore the development of a precise system seems necessary for the determination of cholesterol content in food products. For instance, Cao, Zhang, Chai, and Yuan (2013) developed a biosensor consisting of a TiO2
graphene
Pt
Pd complex coated with AuNPs for the detection of cholesterol (0.017 μM) in foods. Glucose is a crucial energy source and its concentration in blood portrays the energy status of the body (Tonon, Lanfray, Castel, Vaudry, & Morin, 2013). From a clinical viewpoint, it is important to measure the glucose concentration in biological samples and foods. In a study, highly crystalline manganese (II, III) oxide (Mn3O4) was deposited on a three-dimensional graphene foam (3DGF) for determination of glucose as a nonenzymatic developed biosensor. With this nanocomposite, glucose was detected in the range of 0.1
8 mM with the considerable sensitivity of 360 μA mM/cm2 (Si, Dong, Chen, & Kim, 2013). Generally, for the retention of biological activity of glucose oxidase on the electrode surface, the immobilization

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on a biocompatible compound is necessary and therefore a graphene
AuNP film was implemented. Glucose was detected in the range of 0.02
2.26 mmol/L (Cao et al., 2013), as shown in Fig. 4.11A and B. ß-Lactoglobulin (BLG) comprises 10% of the total proteins in bovine milk and is the most allergenic compound, especially to children (Høst, 2002). An aminefunctionalized graphene surface was linked to anti-BLG antibodies with the help of glutaraldehyde for measuring the level of BLG. With the availability of [Fe (CN)6]32/42 in an aqueous solution, the peak current of [Fe(CN)6]3
/4
decreased linearly at higher levels of BLG (from 1 pg/mL to 100 ng/mL) owing to the formation of an antibody
antigen complex on the electrode surface (Eissa, Tlili, L’Hocine, & Zourob, 2012). In another study conducted by Chen and coworkers, a redox-active AuNP/poly(o-phenylenediamine)/graphene hybrid (AuNP-PG) was fabricated via π-π stacking interactions between GNsh and the aromatic poly(o-phenylenediamine). The developed film was employed for labeling and detection of horseradish peroxidase (HRP) and antibodies, respectively. By performing a sandwich immunoassay, the target compound (carcinoembryonic antigen, CEA) was determined quantitatively. Accordingly, a broad range of (0.005
80 ng/mL) for CEA with a low LOD of 5 pg/mL was detected. Also, Chen et al. reported that CEA antibodies can conjugate on the surface of AgNP
poly(ophenylenediamine)
magnetic Fe3O4NPs via SH/NH2 functional groups (Chen, Gao, Cui, Chen, & Tang, 2013; Chen et al., 2012). Electrochemical immunoassay of a-fetoprotein (AFP, as a model biomarker) was explored via immobilizing antiAFP antibody on an Au-functionalized graphene surface. Next, HRPanti-AFP (HRP-anti-AFP) conjugates were also immobilized on the AuNP surface (Fig. 4.11C). A wide range was displayed (0.1
200 ng/mL) with an LOD of 0.05 nm/mL for AFP (Chen et al., 2011).

4.2.4.9 Toxicity of graphene and graphene oxide Graphene and GO are applied in different sectors due to their interesting features. Yet, the toxicity of graphene and GO is still questionable, especially in food contact materials. In a study the toxicity of GO was tracked in vivo using external labeling means. The results demonstrated that PEGylated nano-GO (nGO-PEG) had effective tumor passive targeting due to the high permeability and retention impacts of malignant tumors. Nevertheless, the fluorescent labeling has numerous intrinsic limitations including photobleaching and therefore is not an ideal means to identify the long-term behavior of graphene in living cells. In another study, it was reported that GO can trigger extensive pulmonary thromboembolism in mice (Singh et al., 2011). Also, Schinwald, Murphy, Jones, MacNee, and Donaldson (2012) realized that graphene layers with a diameter of up to 25 μm would induce inflammation in the lungs of mice. Moreover, when GO is injected directly into the lungs of mice, ROS generation takes place in the mitochondria and apoptosis occurs which leads to severe lung damage. Besides, the mentioned scholars tested the lung injury in mice treated with aggregated graphene as well as dispersed graphene. As a result,

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Figure 4.11 (A) Amperometric responses of the (GOD
graphene
AuNPs) 5/GCE at 0.6 V upon successive additions of glucose to air-saturated PBS (pH 7.0) with stirring. Inset: calibration curve between current and glucose. (B) The Lineweaver
Burk plots for the (GOD
graphene
AuNPs)5/GCE with glucose as a substrate. (C) Electrochemical immunosensor and one-step measurement protocol for detection of a-fetoprotein. Source: Adapted with permission from (A and B) Cao, X., Ye, Y., Li, Y., Xu, X., Yu, J., & Liu, S. (2013). Self-assembled glucose oxidase/graphene/gold ternary nanocomposites for direct electrochemistry and electrocatalysis. Journal of Electroanalytical Chemistry, 697, 10
14; (C) Reproduced with permission from Chen, H., Zhang, B., Cui, Y., Liu, B., Chen, G., & Tang, D. (2011). One-step electrochemical immunoassay of biomarker based on nanogold-functionalized graphene sensing platform. Analytical Methods, 3(7), 1615
1621.

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aggregated graphene caused patchy fibrosis in mice, whereas dispersed graphene induced no obvious fibrosis in mice. In a recent study, Yan, Hu, Chen, and Lin (2019) tested the release behavior of graphene
polyethylene composite films in different food simulants. It was further characterized via TEM and UV spectrophotometry. The final results revealed that graphene-released materials mostly occur at interfaces rather than from the internal part of the composite films. The maximum release content of graphene was 1.6 mg/ kg. They noted that the toxicity of graphene is closely related to its pattern, size, content, and exposure time as well (Yan et al., 2019).

4.2.4.10 Future trends The ongoing research in the field of graphene and graphene derivatives has contributed to the fabrication of miniaturized electronic and electrochemical devices for the safety assurance and quality of food products. Nevertheless, fabrication of individual single-layer graphene is not beneficial as the production method (CVD) yields a limited quantity and is not cost-effective, and thus residual oxygen groups are added on the surface of graphene layers, yielding large quantities of reduced GO. Considering the environmental aspect, the prevalent GO production technique (modified Hummers method) will generate large amounts of acid waste and the applied reagents used for the fabrication are hazardous and may even lead to explosions if tests are not done cautiously (Kim, Abdala, & Macosko, 2010). Moreover, the morphology and physical properties of reduced GO are influenced by the synthesis method and the performance of the synthesized sensor is affected by the production method. Overall, it is crucial to search for synthesis methods that produce a large amount of single-layer graphene inexpensively and that may be suitable for commercialization. Graphene presents flexible, transparent, biocompatible, and thermal stability attributes and thus it is a valuable candidate for application in the food packaging and labeling materials. One important challenge for application in the food sector is the safety aspect of GO. If it is used in food contact materials, it is in direct contact with foodstuff, and therefore more research should be undertaken in this field to determine the possible toxicity and safety of GO for food applications.

4.3

Conclusion

With population growth around the world, recycling processes are necessary for survival, such as water for drinking and agriculture purposes. Polyphenols are valuable compounds which are wasted in food processing plant effluents which can be further recovered from the processing plants. Therefore cheap, efficient, and highthroughput materials will enable industrial scale adsorption for the removal or recovery of the wastewater and plant effluents which is a win
win solution for both the industry and the environment. Activated carbon, MMT, GO, and nanozerovalent iron particles were explored in detail in this chapter to signify their

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importance for application individually, as well as in their composites, for better adsorption processes in different sectors, including the food processing activities. The latest research and pilot-scale activities have revealed the high potential for their application for adsorption purposes as they are cheap and straightforward. The last point is the safety and toxicity of the described adsorbents which should be further clarified by in vitro and in vivo studies, as the current studies are not yet sufficient to declare their safety, especially if they are to be applied in food processing plants or even in food contact materials.

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353. Wang, C.-B., & Zhang, W.-X. (1997). Synthesizing nanoscale iron particles for rapid and complete dechlorination of TCE and PCBs. Environmental Science & Technology, 31 (7), 2154
2156. Wang, G., Shen, X., Yao, J., & Park, J. (2009). Graphene nanosheets for enhanced lithium storage in lithium ion batteries. Carbon, 47(8), 2049
2053. Wang, S., & Peng, Y. (2010). Natural zeolites as effective adsorbents in water and wastewater treatment. Chemical Engineering Journal, 156(1), 11
24. Wang, Y., Yang, J., Wang, L., Du, K., Yin, Q., & Yin, Q. (2017). Polypyrrole/graphene/polyaniline ternary nanocomposite with high thermoelectric power factor. ACS Applied Materials & Interfaces, 9(23), 20124
20131. Wei, Y.-T., Wu, S.-C., Chou, C.-M., Che, C.-H., Tsai, S.-M., & Lien, H.-L. (2010). Influence of nanoscale zero-valent iron on geochemical properties of groundwater and vinyl chloride degradation: A field case study. Water Research, 44(1), 131
140. Wibulswas, R. (2004). Batch and fixed bed sorption of methylene blue on precursor and QACs modified montmorillonite. Separation and Purification Technology, 39(1
2), 3
12. Wilson, M. J. (1987). A handbook of determinative methods in clay mineralogy, Chapman and Hall. Xi, Y. (2006). Synthesis, characterisation and application of organoclays. Unpublished PhD Thesis, Queensland University of Technology. Xiang Ying, L. Q. (2007). Montmorillonite modification method and application status. Journal of Beijing Institute of Graphic Communication, 15(4), 30
33.

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Xu, J., Cao, Z., Zhang, Y., Yuan, Z., Lou, Z., Xu, X., & Wang, X. (2018). A review of functionalized carbon nanotubes and graphene for heavy metal adsorption from water: Preparation, application, and mechanism. Chemosphere, 195, 351
364. Xu, X., Zhang, Z., Dong, J., Yi, D., Niu, J., Wu, M., . . . Zhou, J. (2017). Ultrafast epitaxial growth of metre-sized single-crystal graphene on industrial Cu foil. Science Bulletin, 62 (15), 1074
1080. Yan, J.-W., Hu, C., Chen, K., & Lin, Q.-B. (2019). Release of graphene from graphenepolyethylene composite films into food simulants. Food Packaging and Shelf Life, 20, 100310. Yang, D., Velamakanni, A., Bozoklu, G., Park, S., Stoller, M., Piner, R. D., . . . Ventrice, C. A., Jr (2009). Chemical analysis of graphene oxide films after heat and chemical treatments by X-ray photoelectron and micro-Raman spectroscopy. Carbon, 47(1), 145
152. Yang, H., Li, J.-S., & Zeng, X. (2018). Correlation between molecular structure and interfacial properties of edge or basal plane modified graphene oxide. ACS Applied Nano Materials, 1(6), 2763
2773. Yang, Y. H., Bolling, L., Priolo, M. A., & Grunlan, J. C. (2013). Super gas barrier and selectivity of graphene oxide-polymer multilayer thin films. Advanced Materials, 25(4), 503
508. Yangui, A., & Abderrabba, M. (2018). Towards a high yield recovery of polyphenols from olive mill wastewater on activated carbon coated with milk proteins: Experimental design and antioxidant activity. Food Chemistry, 262, 102
109. Yin, Q., Zhang, Z., Wu, S., Tan, J., & Meng, K. (2015). Preparation and characterization of novel cationic
nonionic organo-montmorillonite. Materials Express, 5(3), 180
190. Yu, M., Song, A., Xu, G., Xin, X., Shen, J., Zhang, H., & Song, Z. (2015). 3D welan gum
graphene oxide composite hydrogels with efficient dye adsorption capacity. RSC Advances, 5(92), 75589
75599. Yuan, G., Theng, B., Churchman, J., & Gates, W. (2013). Clays and clay minerals for pollution control. In Developments in clay science, vol. 5 (pp. 587-644). Elsevier. Zaaba, N., Foo, K., Hashim, U., Tan, S., Liu, W.-W., & Voon, C. (2017). Synthesis of graphene oxide using modified hummers method: Solvent influence. Procedia Engineering, 184, 469
477. Zhang, D., Huo, P., & Liu, W. (2016). Behavior of phenol adsorption on thermal modified activated carbon. Chinese Journal of Chemical Engineering, 24(4), 446
452. Zhang, W.-X. (2003). Nanoscale iron particles for environmental remediation: An overview. Journal of Nanoparticle Research, 5(3
4), 323
332. Zhang, X., & Cresswell, M. (2016). Chapter 7—Alternative inorganic systems for controlled release applications. In X. Zhang, & M. Cresswell (Eds.), Inorganic controlled release technology (pp. 189
219). Boston: Butterworth-Heinemann. Zhao, J., Liu, L., & Li, F. (2015). Graphene oxide: Physics and applications (Vol. 1). Springer. Zhao, Q., Choo, H., Bhatt, A., Burns, S. E., & Bate, B. (2017). Review of the fundamental geochemical and physical behaviors of organoclays in barrier applications. Applied Clay Science, 142, 2
20. Zhao, R., Kong, W., Sun, M., Yang, Y., Liu, W., Lv, M., . . . Hao, R. (2018). Highly stable graphene-based nanocomposite (GO
PEI
Ag) with broad-spectrum, long-term antimicrobial activity and antibiofilm effects. ACS Applied Materials & Interfaces, 10 (21), 17617
17629.

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Zhao, S., Yan, T., Wang, H., Zhang, J., Shi, L., & Zhang, D. (2016). Creating 3D hierarchical carbon architectures with micro-, meso-, and macropores via a simple self-blowing strategy for a flow-through deionization capacitor. ACS Applied Materials & Interfaces, 8 (28), 18027
18035. Zhu, C., Guo, S., Fang, Y., & Dong, S. (2010). Reducing sugar: New functional molecules for the green synthesis of graphene nanosheets. ACS Nano, 4(4), 2429
2437. Zhu, H., & Njuguna, J. (2014). 7—Nanolayered silicates/clay minerals: Uses and effects on health. In J. Njuguna, K. Pielichowski, & H. Zhu (Eds.), Health and environmental safety of nanomaterials (pp. 133
146). Woodhead Publishing. Zhu, R., Chen, Q., Zhou, Q., Xi, Y., Zhu, J., & He, H. (2016). Adsorbents based on montmorillonite for contaminant removal from water: A review. Applied Clay Science, 123, 239
258. Zhu, Y., Li, X., Cai, Q., Sun, Z., Casillas, G., Jose-Yacaman, M., . . . Tour, J. M. (2012). Quantitative analysis of structure and bandgap changes in graphene oxide nanoribbons during thermal annealing. Journal of the American Chemical Society, 134(28), 11774
11780.

Further reading Ambrosi, A., & Pumera, M. (2016). Electrochemically exfoliated graphene and graphene oxide for energy storage and electrochemistry applications. Chemistry
A European Journal, 22(1), 153
159. Cao, X., Ye, Y., Li, Y., Xu, X., Yu, J., & Liu, S. (2013). Self-assembled glucose oxidase/graphene/gold ternary nanocomposites for direct electrochemistry and electrocatalysis. Journal of Electroanalytical Chemistry, 697, 10
14. Crini, G., Morin-Crini, N., Fatin-Rouge, N., Deon, S., & Fievet, P. (2017). Metal removal from aqueous media by polymer-assisted ultrafiltration with chitosan. Arabian Journal of Chemistry, 10, S3826
S3839. Dai, L. (2012). Functionalization of graphene for efficient energy conversion and storage. Accounts of Chemical Research, 46(1), 31
42. Duncan, T. V. (2011). Applications of nanotechnology in food packaging and food safety: Barrier materials, antimicrobials and sensors. Journal of Colloid and Interface Science, 363(1), 1
24. Hoseinnejad, M., Jafari, S. M., & Katouzian, I. (2018). Inorganic and metal nanoparticles and their antimicrobial activity in food packaging applications. Critical Reviews in Microbiology, 44(2), 161
181. Hosseinnejad, M., & Jafari, S. M. (2016). Evaluation of different factors affecting antimicrobial properties of chitosan. International Journal of Biological Macromolecules, 85, 467
475. Iupac, J. (1972). Colloid interface chem. Pure and Applied Chemistry, 31, 578. Krishnamoorthy, K., Veerapandian, M., Yun, K., & Kim, S.-J. (2013). The chemical and structural analysis of graphene oxide with different degrees of oxidation. Carbon, 53, 38
49. Park, Y., Ayoko, G. A., & Frost, R. L. (2011). Application of organoclays for the adsorption of recalcitrant organic molecules from aqueous media. Journal of Colloid and Interface Science, 354(1), 292
305.

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Pe´rez-Lo´pez, B., & Merkoc¸i, A. (2011). Nanomaterials based biosensors for food analysis applications. Trends in Food Science & Technology, 22(11), 625
639. Priac, A., Morin-Crini, N., Druart, C., Gavoille, S., Bradu, C., Lagarrigue, C., . . . Crini, G. (2017). Alkylphenol and alkylphenol polyethoxylates in water and wastewater: A review of options for their elimination. Arabian Journal of Chemistry, 10, S3749
S3773. Sundramoorthy, A. K., & Gunasekaran, S. (2014). Applications of graphene in quality assurance and safety of food. TrAC Trends in Analytical Chemistry, 60, 36
53.

Production of food nanomaterials by specialized equipment

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ˇ 2 and Ali Sedaghat Doost1, Maryam Nikbakht Nasrabadi1, Anja Sadzak Paul Van der Meeren1 1 Particle and Interfacial Technology Group (PaInT), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Gent, Belgium, 2 Laboratory for Biocolloids and Surface Chemistry, Division of Physical Chemistry, Ruðer Boˇskovi´c Institute, Zagreb, Croatia

5.1

Introduction

The size of a component in food materials is one of the most vital factors with a powerful contribution to the physicochemical properties of the system. Nanotechnology refers to the production of nanomaterials, that is, usually possess a particle size between 10 and 1000 nm. The nanoscale size of these materials have the potential to enhance the bioavailability and improve the controlled release due to their small size (Jafari & McClements, 2017). Nanosized delivery systems remain to be considered as one of the most promising technologies. These systems have many advantages due to their small size and changes in their mechanical, electrical, and optical properties (Assadpour & Jafari, 2019c). One of the advantages is their increased surface-to-volume ratio, which improves their reactivity and provides an efficient absorption through cells, controlled release, and accurate targeting of bioactive compounds (Prakash, Baskaran, Paramasivam, & Vadivel, 2018). The solubility and thermal stability of encapsulated bioactive compounds can also be enhanced and they can be protected against natural and processing effects, including chemical, enzymatic, and physical instability during processing. Moreover, the incorporation of nanosize delivery systems in food applications can improve their sensory attributes, such as texture, flavor retention, coloring strength, and technological properties such as processibility, and stability during shelf life (Ferreira & Nunes, 2019; Prakash et al., 2018). Different methods have been proposed for the fabrication of food nanomaterials based on two classifications: top-down and bottom-up approaches (Koshani & Jafari, 2019; Rezaei, Fathi, & Jafari, 2019). Top-down methods are based on the breakage of a system into smaller size scales, for instance, through mechanical size reduction input by applying high energy. On the other hand, bottom-up methods require low energy and the process can be controlled by the intrinsic physicochemical properties. These include solvent demixing, self-emulsification (spontaneous emulsification), and phase inversion assays. Top-down methods usually need specialized equipment, Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00005-4 © 2020 Elsevier Inc. All rights reserved.

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including high-pressure, ultrasonication, electrospinning, spray drying, and ball milling (Prakash et al., 2018). Most of these methods have been currently scaled up and industrialized. The reproducibility and large-scale production are the considerable advantages of high-pressure techniques while a vortex fluidic device (VFD) needs lower cost and is an environment-friendly technique. However, there are some drawbacks that may limit their utilization and promote the modification of these methods or the development of a new technique. The preparation technique can indeed exert a considerable influence on the physicochemical stability as well as desired functionality of the produced materials. For instance, despite the fact that temperature of the mixture during sonication can be controlled to some extent, the chemical degradation can be induced, specially if the mixture contains a volatile compound, because of the high pressure and temperature of the cavitation effect (Salvia-Trujillo, Rojas-Grau¨, Soliva-Fortuny, & Martı´n-Belloso, 2014). Another drawback of some of these techniques is high energy consumption, which makes it an expensive processing step for industry. Additionally, the scaling up and infrastructure required for these techniques are also rather dear. In this chapter, the basic principles of techniques that need specialized equipment for the production of food nanomaterials are introduced as well as their advantages and disadvantages.

5.2

High-pressure techniques

5.2.1 MicrofluidizerTM homogenization process Microfluidic processing has been used for the size reduction of emulsions (Bai & McClements, 2016), nanodispersions, liposomes (Guldiken, Gibis, Boyacioglu, Capanoglu, & Weiss, 2018), and for preparing nanomaterials (Ganesan, Karthivashan, Park, Kim, & Choi, 2018). Microfluidizer technology can be used as a high-energy approach for the fabrication of nanoemulsions (Villalobos-Castillejos et al., 2018). Basically, a Microfluidizer consists of three main constituents, an intensifier pump, an air motor, and an interaction chamber, as shown in Fig. 5.1. For emulsification applications, a coarse emulsion is initially prepared by mixing the oil phase and aqueous phase containing an emulsifier using a high-shear mixer. After that, this premix emulsion is fed into an interaction chamber in the Microfluidizer by force. Two streams of coarse emulsion flow at high velocities through channels with small diameter to the direction of an impingement area. The two streams of premix emulsion bump into each other and generate rigorous turbulent forces, including cavitation, turbulence, and shear, resulting in the size reduction of oil droplets (Jafari, He, & Bhandari, 2007a). A significant advantage of Microfluidizer homogenization process is the large-scale production with higher reproducibility (Ganesan et al., 2018). It has been reported that microfluidizer homogenization process is more efficient and more successful in the fabrication of emulsions with small droplet sizes than other homogenizers, such as high-pressure jet and rotor-stator devices (Silverson) (Perrier-Cornet, Marie, & Gervais, 2005). In contrast, Alliod, Almouazen, Nemer, Fessi, and Charcosset (2019) reported that

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Figure 5.1 Schematic representation of a microfluidizer (redrafted from MicrofluidicsM110S manual).

nanoemulsions produced by microfluidizer processor showed a higher chemical degradation of all-trans retinoic acid compared to other emulsification processes, for example, ultrasound and premix membrane emulsification. Moreover, microfluidizer processed nanoemulsions were unstable at a fourfold droplet size enhancement under stress conditions. As the coarse emulsions are forced into the microfluidizer through a reservoir with one inlet, conventional microfluidizer are called single-channel devices which have some limitations. One of their limitations is the necessity of a high-shear mixer to fabricate the coarse emulsion which needs extra devices, cost, and time. Furthermore, several cycles of homogenization passes for the coarse emulsion through the chamber are often required (Jafari, He, & Bhandari, 2007a, 2007b). Another limitation of conventional microfluidizers is that due to the requirement of rinsing before the main preparation, some extent of the premix emulsion is wasted, hence, decreasing the yield. Moreover, the content of used oil is limited since increasing the oil level results in higher viscosities which may become an obstacle to be forced through the device. Thus dual-channel microfluidizer has been designed for the efficient fabrication of nanoemulsions in which the oil phase and aqueous phase are separately fed into the device. The advantages of this method in comparison to its conventional single-channel counterpart are lower consumption of time, cost, energy, and labor since the additional step of preparing a coarse preemulsion with another equipment is omitted, and one cycle of homogenization could be enough for some cases. Moreover, the separate entry of the oil and water phase provides the opportunity of there being no requirement to feed a premix

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coarse emulsion, thus there is no limitation for the content of the used oil. Therefore concentrated nanoemulsions with high oil contents can be produced; thus boosting its application in food and nutraceutical fields (Ganesan et al., 2018; Bai & Mcclements, 2016). The pressure of microfluidizer processor, number of homogenization cycles, oil content, and emulsifier content are the most important process parameters that influence the performance of this apparatus for the fabrication of nanoemulsions (Jafari et al., 2007a; Sedaghat Doost, Devlieghere, Dirckx, & Van Der Meeren, 2018a). By increasing the microfluidizer processor pressure, droplet size of nanoemulsions decreases, as was observed by Uluata, Decker, and Mcclements (2016). Bai and McClements (2016) reported that droplet size of nanoemulsions stabilized by polysorbate 80 was linearly log
log related to the homogenization pressure. It has been also suggested in the literature that by increasing the number of passes through the homogenizer as well as an enhancement in surfactant content decreased the droplet size of nanoemulsions (Sedaghat Doost, Devlieghere, et al., 2018a; Uluata et al., 2016). Lv et al. (2018) observed that by increasing the vitamin E content in the carrier oil (corn oil), droplet size of the quillaja saponin stabilized nanoemulsions, which were fabricated by a dual-channel microfluidizer, increased. This droplet size increase was triggered by the enhancement in viscosity of the oil phase. Consequently, these plant-based nanoemulsions creamed faster and showed lower physical stability during storage. The incorporation of bioactive compounds into microfluidizer processed nanoemulsions is able to improve their efficiency and bioavailability in addition to increasing their physical and chemical stability, which is due to their smaller droplet size. For example, in a study conducted by Raviadaran, Chandran, Shin, and Manickam (2018), curcumin-loaded nanoemulsions were developed applying microfluidizer technology for increasing the bioavailability of curcumin. Luo et al. (2017) also showed that the water dispersibility and chemical stability of β-carotene could be improved by its incorporation into microfluidizer processed nanoemulsions. In order to increase the functionality and bioavailability of essential oils, microfluidizer technology has been used in different studies to prepare oil-in-water nanoemulsions (Sedaghat Doost, Sinnaeve, De Neve, & Van Der Meeren, 2017; Sedaghat Doost, Dewettinck, Devlieghere, & Van Der Meeren, 2018b; Sedaghat Doost, Stevens, Claeys, & Van Der Meeren, 2019c). In addition to conventional nanoemulsions, Pickering nanoemulsions with a high stability against coalescence can be fabricated using microfluidizer homogenization process (Schro¨der, Sprakel, Schroe¨n, Spaen, & Berton-Carabin, 2018). The disadvantages of the microfluidizer homogenization approach for the fabrication of nanoemulsions are the high-energy input requirement, and its wasting since the emulsification only consumes 0.1% of the input energy, and the remaining part is wasted as thermal energy. Furthermore, several passes are required to obtain more monodispersed droplets as not all droplets are exposed to an equal shear stress because of their different positions in the interaction chamber. Also, the generated heat during the process limits its application for heat-labile materials (Alliod et al., 2019).

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Microfluidizer homogenization process can be used for the development of solid lipid nanoparticles (SLNs) without the disadvantages of other fabrication methods, such as high-speed homogenization, spray drying, hot homogenization, cold homogenization, ultrasonication, and supercritical technology, which are partitioning of the lipids, weaker stability, and higher consumption of organic solvents (Katouzian, Faridi Esfanjani, Jafari, & Akhavan, 2017). Due to the abovementioned disadvantages, the development of novel SLNs is limited. Microfluidizer homogenization approach provides the opportunity to produce SLNs with considerably small particle sizes, which boosts their application as a delivery system (Rafiee & Jafari, 2018; Rostamabadi, Falsafi, & Jafari, 2019a). For example, Helgason, Salminen, Kristbergsson, Mcclements, and Weiss (2015) fabricated transparent SLNs ranging from 36 to 136 nm by cooling 10 wt% octadecane and 1
5 wt% sodium dodecyl sulfate (SDS) nanoemulsions homogenized using microfluidizer processor (5000
28,500 psi) which are applicable in clear beverages and juices or other transparent food products. Also, the produced SLNs by microfluidizer homogenization process provide higher encapsulation efficiencies for incorporated bioactive compounds. Moreover, the microfluidizer processed SLNs provide higher stability and bioaccessibility for the encapsulated compounds because of their small particle size (Arora, Kuhad, Kaur, & Chopra, 2015; Singh, Khullar, Kakkar, & Kaur, 2016). Nanoliposomes have also been developed using microfluidizer technology with a small particle size, high encapsulation efficiency, and sustained release of bioactive components (Faridi Esfanjani, Assadpour, & Jafari, 2018; Yousefi, Ehsani, & Jafari, 2019). It has been said that the incorporation of bioactive components into microfluidizer processed nanoliposomes with small size (60
100 nm) provided higher stability and bioaccessibility, and controlled release of tea polyphenols than ultrasonication and high-pressure homogenization (Zou, Liu, et al., 2014a; Zou, Peng, et al., 2014b). Guldiken et al. (2018) also developed black carrot extractloaded nanoliposomes as an antioxidant agent with a particle size ,50 nm using this method. Microfluidizer homogenization process can be further used for the deagglomeration of nanoparticle clusters. This method was used by Gavi, Kubicki, ¨ zcan-Ta¸skın (2018) for completely breaking up silica nanoparticle Padron, and O clusters into submicron aggregates with a size of 150 nm through erosion; additionally, the effect of particle content and viscosity of continuous phase on the deagglomeration of clusters was investigated. More passes or a higher power intensity were required for samples with a higher particle content or the viscosity of a continuous phase.

5.2.2 High-pressure homogenizer High-pressure (HP) homogenization is a type of top-down high-energy technique which fabricates nanoparticles (Riegger, Kowalski, Hilfert, Tovar, & Bach, 2018), ˇ nanoemulsions (Agarwal et al., 2019; Jasmina, DZAna, Alisa, Edina, & Ognjenka, 2017), and nanodispersions (Tan et al., 2016b) by producing powerful disruptive forces including shear stress, cavitation, and turbulent flow. The created disruptive

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force due to the intense energy can disrupt larger particles and oil droplets into the nanosize range, as shown in Fig. 5.2 (Agarwal et al., 2019). The standard range of hydrostatic pressures [i.e., which is generally used for HP homogenization (HPH)] is 150
200 MPa; whereas 350
400 MPa is applied for ultra-HP homogenization using intensifier technology (Singha, Bhattacharya, & Basu, 2016). The requirements of an HPH are an HP positive displacement pump and a restriction assembly. Depending on the type of pump, and the kind and number of restrictions, their designs could be different. The HP can be transferred to the fluid using piston-type pumps. The liquid is withdrawn to the pump by its suction valve; then, it is pushed to the pump depletion valve and the homogenizing valve by a forward stroke of the piston. The restriction assembly is another part of an HPH which exists in three types: adjustable valve, nozzle, and microchannels. The relative distribution of shear, turbulence, impact, and cavitation varies categorically in the HPH based on the type of restriction assembly. The nozzle type is usually a better option among other valves since tunable valves may generate higher variations in different batches (Singha et al., 2016). HPHs can be used as a highly efficient nanoemulsification method by flowing the two liquid phases (i.e., including surfactants and co-surfactants) through the small orifice of a piston homogenizer, called the homogenizing valve, nozzle, or microchannel, under a high pressure (500
5000 psi) (Li, Wu, et al., 2018b; Xu, Mukherjee, & Chang, 2018). These authors used HP homogenization for the production of nanoemulsions based on soy protein and reported that HP homogenization improved the functionality of the protein as an emulsifier. It has been reported that the structural changes of the protein after exposure to HP homogenization could improve its functional properties (Sedaghat Doost, Nikbakht Nasrabadi, Wu, A’yun, & Van Der Meeren, 2019b). Several hydrophobic bioactive compounds, such as curcumin (Ma et al., 2017), essential oils including pepper oil (Galva˜o, Vicente, & Sobral, 2018), carotenoids such as β-carotene (Borba et al., 2019), jackfruit extract (Artocarpus heterophyllus Lam) (Ruiz-Montan˜ez, Ragazzo-Sanchez, Picart-Palmade, Caldero´n-Santoyo, & Chevalier-Lucia, 2017), vitamin E (Ozturk, Argin, Ozilgen, & Mcclements, 2015), and kenaf seed oil (Cheong & Nyam, 2016) have been incorporated into HPhomogenized nanoemulsions. Similar to other high-energy methods, the parameters that affect the obtained droplet size are energy intensity, holding time of the energy input, interfacial tension, the difference between viscosity of the phases, type and level of the emulsifier, and emulsifier-to-oil ratio (Karthik, Ezhilarasi, & Anandharamakrishnan, 2017; Xu et al., 2018). The influence of emulsifier type on the droplet size of HPhomogenized nanoemulsions has been previously investigated. Ozturk et al. (2015) reported that whey protein isolate performed better as an emulsifier at low concentrations in producing smaller droplets than Arabic gum for stabilizing vitamin Efortified nanoemulsions applying HP-homogenization. By increasing the emulsifier content, homogenization time, or energy input, the droplet size of fabricated nanoemulsions could be decreased (Li, Wu, et al., 2018b). Silva, Cerqueira, and Vicente (2015) reported that an enhancement in the homogenizing pressure decreased the

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Figure 5.2 A simple homogenization valve. Source: Reproduced with permission from Dos Santos Aguilar, J. G., Cristianini, M., & Sato, H. H. (2018). Modification of enzymes by use of high-pressure homogenization. Food Research International, 109, 120
125.

droplet size of nanoemulsions stabilized by different surfactants (polysorbate 20, SDS, and DTAB) from 177 to 128 nm. It was also observed that an enhancement in the surfactant level triggered a decrease in the droplet size. Cheong and Nyam (2016) investigated the effect of homogenization pressure in the range of 16,000
28,000 psi and number of homogenization cycles (three to five cycles) on the droplet size and stability of kenaf seed oil nanoemulsions stabilized with sodium caseinate, Tween 20, and β-cyclodextrin complexes. It was observed that increasing the homogenizing pressure and number of passes yielded a smaller nanoemulsion droplet size and a higher stability. The fabricated nanoemulsions had a droplet size of 122 nm, a span of 0.147, and a surface charge of 246.6 mV through the optimum HP-homogenization conditions of 28,000 psi for four cycles. Another effective parameter is the level of oil phase and its ratio in comparison to the emulsifier. An enhancement in the level of oil phase increased the droplet size of HP-homogenized nanoemulsions incorporating curcumin (Ma et al., 2017). Contrary to these results, Silva et al. (2015) reported that by increasing the portion of oil in comparison to water in nanoemulsions stabilized with nonionic surfactants, the droplet size decreased from 341 to 171 nm. HPHs can be used for the fabrication of lipid-based nanoparticles such as SLNs and NLCs (Akhavan, Assadpour, Katouzian, & Jafari, 2018). HP homogenization associated with hot and cold approaches is one of the most common methods for the fabrication of these lipid-based particles since it provides the opportunity to scale up the production without any requirement for using organic solvents

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(Akhavan et al., 2018). The hot HP homogenization is the dissolvation of bioactive compounds and the melted lipid in a hot emulsifier solution with the same temperature followed by a prehomogenization using a high-speed stirrer and then passing through a HPH. The cold HP homogenization is defined by dispersing the bioactive component in the lipid melt, and their mix is then cooled. The resulting solid is subsequently ground to prepare solid microparticles which are dispersed in a cold emulsifier solution and exposed to HP homogenization (Mu¨ller, Radtke, & Wissing, 2002). Different bioactive compounds have been incorporated into lipid-based nanoparticles which were produced using HP-homogenization. For instance, citral into glyceryl monostearate SLNs based on polysorbate 80 and Span 80 (Tian, Lu, Li, & Hu, 2018). Biopolymer-based particles were also fabricated using HP homogenization (Rostamabadi, Falsafi, & Jafari, 2019b; Taheri & Jafari, 2019). Starch nanoparticles were produced through HP homogenization associated with miniemulsion crosslinking (Ding, Zheng, Zhang, & Kan, 2016, Shi, Li, Wang, Li, & Adhikari, 2011). In another study, Riegger et al. (2018), by using one to seven passes of HP homogenization at 40 MPa, fabricated chitosan nanoparticles in the size range of 125
250 nm. Nanodispersions can also be prepared using HP-homogenization. High-pressure valve homogenization was used for the formation of lutein nanodispersions based on polysorbate 80 and compared with their fabricated counterparts of the solvent displacement method by Tan et al. (2016b). It was observed that the particle size and polydispersity index (PDI) were not significantly different for both methods, while lutein retention was better in the nanodispersion formed via the solvent displacement technique. The disadvantage of HP-homogenization like other high-energy methods is its high energy consumption which limits the large-scale application in industry. Moreover, the increase in temperature during the process can be harmful to heatsensitive compounds. Nevertheless, this is the most common method for the preparation of nanoemulsions (Jasmina et al., 2017).

5.3

Sonication

Sonication is an effective method to prepare various nanomaterials (Gharibzahedi & Jafari, 2018). This method has also been used for different food applications, such as microbial inactivation in liquid food products (Knorr, Zenker, Heinz, & Lee, 2004; Piyasena, Mohareb, & Mckellar, 2003) or extraction (Vilkhu, Mawson, Simons, & Bates, 2008). Ultrasound or power ultrasound is a term for the sonic waves, also known as acoustic waves, which have higher frequencies than those sounds audible to the human ear (higher than 16 kHz). Based on the frequency and intensity ranges, there are two ultrasound processes: low and high intensity. Lowintensity (high-frequency) ultrasound has hardly any destructive effects when passing through the medium due to its low power (Jamalabadi, Saremnezhad, Bahrami, & Jafari, 2019). On the other hand, high-intensity (low-frequency) ultrasound can be used for destruction purposes, including depolymerization of macromolecules,

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breaking down particles and aggregates to the nanometer size range, emulsification (homogenization), deflocculating droplets, and extracting bioactive compounds from diverse matrices (Jalili, Jafari, Emam-Djomeh, Malekjani, & Farzaneh, 2018). Cavitation phenomena induced through this method have the ability to stimulate several chemical reactions. Cavitation is the phenomenon that is induced by highintensity sonic waves in the range of 16 kHz
100 MHz through the mass of liquid and is determined by the sequential creation of millions of vapor microbubbles or microcavities in the liquid. When these bubbles are nonlinearly collapsed or burst, the concentrated energy within these bubbles is released very rapidly, resulting in hotspots, turbulence, and free radicals, which can be generated in the cold fluid in a short period of time (Suslick & Price, 1999). A conventional ultrasonication setup consists of different parts, including the electrical supply, a piezoelectric transducer, and an emitter which is typically in the form of a titanium horn (probes) or bath (Suslick & Price, 1999). Nanoparticles based on different food-grade biopolymers have been fabricated via sonication (Koshani & Jafari, 2019). The generated physical forces, such as shear forces, which are formed by microstreaming and normal impingement from the water jets at the interfaces of solid and liquid result in the biopolymers breaking down into nanometric range particles or aggregates. Gilca, Popa, and Crestini (2015) prepared lignin nanoparticles by ultrasonication. Ultrasonication can not only be used for the fabrication of nanoparticles from biopolymers but can also improve their functional properties and boost their application. Zhang, Pan et al. (2018b) reported that ultrasound treatment was able to unfold the conformation of rice bran protein resulting in the exposure of its interior functional groups, which improved its solubility, emulsifying, and foaming properties. Jiang et al. (2019) combined pH-shifting and sonication to prepare and functionalize pea protein nanoaggregates for the fabrication of nanoemulsions and nanocomplexes as nanocarriers for cholecalciferol (vitamin D3). It has been suggested that ultrasoundtreated pea proteins had an improved antioxidant capacity and provided a higher bioavailability for D3. The association of ultrasonication with low hydrostatic pressure and low heat, is called manothermosonication (MTS) and is able to increase the cavitation activity. It can be used for the fabrication and modification of protein nanoparticles. Yildiz, Andrade, Engeseth, and Feng (2017) fabricated and functionalized spherical shaped soy protein nanoparticles with a size of 27 6 1 nm using this process in combination with pH-shifting. Their results revealed that the MTS process enhanced the solubility, emulsifying properties, surface hydrophobicity, and antioxidant activity of the soy protein. The fabricated nanoparticles also showed the ability to stabilize canola oil-in-water nanoemulsions during 21 days of storage. The ultrasonication process can also be used as an aid for decreasing particle size in other particle fabrication methods. For example, in a study conducted by Feng, Zheng, Luan, Shao, and Sun (2019), ultrasonication was used to further decrease the size of antisolvent precipitated zein nanoparticles. Moreover, the surface charge, encapsulation efficiency, and encapsulation capacity for stigmasterol incorporation of zein nanodispersions significantly increased after exposure to the ultrasonication treatment. Ultrasonication can also be used as a postformation

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Figure 5.3 Schematic illustration of ultrasonication to produce nanoemulsions. Source: From Cheaburu-Yilmaz, C. N., Karasulu, H. Y., & Yilmaz, O. (2019). Chapter 13— Nanoscaled dispersed systems used in drug-delivery applications. In Vasile, C. (Ed.), Polymeric nanomaterials in nanotherapeutics. Elsevier.

process in the final step of liposomal preparation for reducing the number of bilayers which helps to fabricate smaller liposomes (Pimentel-Moral et al., 2018). Sonication has been used for the fabrication of nanoemulsions as well (Gharibzahedi & Jafari, 2018). The advantages of this method include lower consumption of energy and surfactant, smaller droplet size and size distribution, and higher stability among other high-energy emulsification methods such as HP homogenization and microfluidization. This process also needs less maintenance and handling time compared to other mechanical methods (Li et al., 2019). Ultrasonication can form nanoemulsions by breaking down the mixture of oil and water, increasing the diffusion rate, and dispersing the aggregates by cavitation (Peshkovsky, Peshkovsky, & Bystryak, 2013). This process is schematically represented in Fig. 5.3. It has been reported that ultrasonication was 18 times more energy-efficient in the fabrication of nanoemulsions in comparison to microfluidization (Kumar, Kaur, Uppal, & Mehta, 2017). The properties of fabricated nanoemulsions (i.e., droplet size, optical and rheological stability) depend on the applied emulsification technologies, their process variables, and emulsifier types (Li et al., 2019). The main effective process variables in nanoemulsification through ultrasonication are the sonication time and intensity (Salvia-Trujillo, Soliva-Fortuny, Rojas-Grau¨, Mcclements, & Martı´nBelloso, 2017). By increasing the sonication time, power level, and emulsifier concentration, the droplet size decreased (Sedaghat Doost, Van Camp, Dewettinck, & Van Der Meeren, 2019d). Tan et al. (2016a) also investigated the effect of

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ultrasonic parameters including presonication ultrasonic intensity, sonication time, and temperature for the formulation of a valproic acid-loaded nanoemulsion stabilized by lecithin and Tween 80 with response surface methodology (RSM). Their results displayed that the relation between ultrasonic intensity and time had the most impact on the size of nanoemulsions. The increase of ultrasonic intensity decreased the Span. Sedaghat Doost, Van Camp, et al. (2019d) identified the ultrasonication time and intensity as the most effective variables for the droplet size of nanoemulsions (i.e., fabricated for encapsulation of thymol as a major compound of some essential oils with antimicrobial and antioxidant activity) (Sedaghat Doost, Nikbakht Nasrabadi, Kassozi, et al., 2019a). However, Mehmood, Ahmed, Ahmad, Ahmad, and Sandhu (2018) observed that the most effective parameter on the droplet size of β-carotene nanoemulsions obtained by ultrasonication was the emulsifier content, rather than sonication time and oil content. Using sonication for the fabrication of nanomaterials may have some drawbacks. One of these drawbacks is the temperature increase (in some cases up to 80 C) due to the hotspots produced during bubble implosion and high-shear rates, which may result in deterioration of components susceptible to heat. Moreover, degradation of lipids due to the hydrolysis or oxidation of triglycerides can occur (Salvia-Trujillo et al., 2017). Free radicals released in acoustic cavitation during the process can also increase the rate of oxidation (Chemat, Grondin, Sing, & Smadja, 2004). Another limitation of industrial application of ultrasonication in the fabrication of nanomaterials is the migration probability of metal ions or metal particles from the sonication probe into the product as a result of the cavitational abrasion which causes contamination for the food-grade labeled products (Freitas, Hielscher, Merkle, & Gander, 2006).

5.4

Electrohydrodynamic devices

Electrospinning is a novel and popular top-down method for the fabrication of nanomaterials in the form of nanofibers with dimensions in the range of 40
2000 nm from a wide variety of starting materials with different applications (Reneker & Chun, 1996; Sedaghat Doost, Nikbakht Nasrabadi, Wu, et al., 2019b). The term “electrospinning” was coined in 1994, although this technique was used for the first time by Anton (1934). There has been considerable attention in this method due to it being cost-effective, scalable, and straightforward (Schiffman & Schauer, 2008). The basic requirements (Fig. 5.4) for this process are a high-power voltage supply, which is connected to a capillary tube containing a polymeric solution with a needle or pipette, and a collector or target, connected through electrical wires (Rostami, Yousefi, Khezerlou, Aman mohammadi, & Jafari, 2019). The capillary tube can be simply a syringe connected to a pump while the collector could be a copper plate (Schiffman & Schauer, 2007a, 2007b), or an aluminum foil, plate, or rotating drum (Chew, Wen, Yim, & Leong, 2005). By applying a high voltage, a pendant droplet of the solution is altered into a conical shape with an angle of 33.5 degrees called a Taylor cone due to the

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Figure 5.4 The basic setup for electrospinning (Hu et al., 2014).

generated electric field between the tip of the syringe needle of the capillary tube and the target, located at a short distance from each other (Taylor, 1969; Yarin, Koombhongse, & Reneker, 2001). This is because the created electric field reduces the surface tension of the polymer solution, resulting in the creation of a Taylor cone at the tip of syringe needle. When the voltage exceeds a critical value a straight jet is released from the cone and reaches the collector. At this voltage level, the electrostatic repulsion is higher than the surface tension between solution droplets resulting in their stretching at the needle tip and being throwing out onto the collector. Dry micro- or nanosized electrospun fibers can be collected from the collector in the form of nonwoven mats due to solvent evaporation during the process (Kakoria & Sinha-Ray, 2018; Schiffman & Schauer, 2008). The electrospinning process can be influenced by several parameters (Jafari, 2017). Some of these are related to the used components, including their molecular weight (MW), MW distribution, solubility, and glass transition temperature; while some others are related to their solution properties such as concentration, viscosity, viscoelasticity, surface tension, electrical conductivity, and solvent quality, which are not independent of each other. The solution feed rate, field strength, applied voltage, geometry of electrodes and their materials, spinning distance, and vapor pressure of the solvent are effective process parameters. The selection of electrospinnable biopolymer is a critical parameter (Rostami et al., 2019). Biopolymers with too high or too low MWs are hard to electrospin. For example, Pirzada, Farias, Chu, and Khan (2019) observed that both native high-MW (B2 3 106 Da) and hydrolyzed low-MW (B1.6 3 104 Da) guar gums were not electrospinnable at the applied conditions. Therefore they used a blend to tune the MW. It is also important to note that polymers with higher MWs need a lower concentration in the solution since they are able to deliver a sufficient number of polymer entanglements and appropriate solution viscosity even at low concentrations (Go´mez-Mascaraque, Sanchez, & Lo´pez-Rubio, 2016). The content of the polymer in the solution is also an important parameter in the electrospinning process. Higher concentrations of biopolymer result in higher viscosities of the solution because of the intensive overlap of polymer chains, which

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resists the thinning of solution jet; thus yielding larger fibers. The viscosity of solution by itself should be optimized since at too low values, droplets are formed instead of the Taylor cone, while at too high values, the ejection of polymer solution jets and the fiber formation become difficult (Bhardwaj & Kundu, 2010). Surface tension is an effective parameter on the size and morphology of electrospun nanofibers, especially when low concentrations of polymers or polymers with lower MWs are used. The greater the surface tension of the solution is, the higher the electric field required for the electrospinning. At too high surface tensions, the jet is unstable and may spray out in the form of droplets instead of fibers (Sunil, 2017). The surface tension of polymer solutions can be tuned by the addition of surfactants, ionic salts, or electrolytes. These additives have the ability to decrease the surface tension or enhance the net charge density of the solution. SDS, dodecyl trimethyl ammonium bromide (DTAB), and Triton X-100 (TX-100) were added to a lignin solution to reduce the surface tension of the spinning dopes to obtain smooth, beadles, and small nanofibers (Fang, Yang, Yuan, Charlton, & Sun, 2017). The electrical conductivity of the solution is another important parameter that is related to the solvent used and the polymer used. Solutions with a lower electrical conductivity yield fibers with larger diameters due to their shorter stretching of the electrified jet (Bhardwaj & Kundu, 2010). The spinnability of a WPI-maltodextrin blend was observed to be more successful in comparison to an SPI-maltodextrin blend due to its lower electrical conductivity (Kutzli, Gibis, Baier, & Weiss, 2019). Fonseca et al. (2019) performed starch phosphorylation to increase the charge density by producing electrostatic charges, which helped it to become electrospinnable. The use of additives such as salts and surfactants can also be effective to modify the electrical conductivity of solutions. Salts provide migrating ions which transport charges in the solution and due to the increase in charge density result in higher conductivities (Sunil, 2017). It has been suggested by many researchers that by increasing the voltage, which usually varies between 6 and 30 kV, more larger fibers are electropsun due to the increase in polymer ejection power. On the other hand, some reports revealed that the increased voltage resulted in more electrostatic repulsive forces on the fluid jet, leading to more stretching of the solution. The polymer solution flow rate, which usually varies between 0.01 and 1 mL/h, is another effective process parameter. An increase in polymer flow rate yields larger fibers with larger pore size with more beads since, at higher flow rates, there is not enough time for the fibers to dry during their travel to the collector. The length of the gap between tip of the needle and collector, which generally varies between 10 and 30 cm, is also important and should be optimized because it determines the time for solvent evaporation and fiber drying before reaching the collector and it is decisive for the number of formed beads in the fiber structure. A larger distance, which means a larger flight time and more stretching, usually produces thinner fibers with less beaded structures. Therefore, a too-large distance causes less stretching of fibers and an increase of their diameter because of the reduction in electrostatic forces and an effective voltage drop. On the other hand, a smaller distance yields beaded structure fibers due to a too strong electrostatic field and jet instability (Katouzian & Jafari, 2019; Taheri & Jafari, 2019).

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Electrospun nanofibers can be used in different fields and applications including drug delivery, tissue engineering, wound dressing materials, filtration and wastewater treatment, fuel cells, and biosensing. In the food industry, nanofibers fabricated from biopolymers can be used for the design of new food ingredients and food additives, delivery systems of bioactive compounds with sustained release, food novel packaging materials, edible food coatings, and food sensors, as they are nontoxic, edible, and biocompatible. The three-dimensional open porous structure of electrospun nanofibers, which is associated with a high specific surface area, enables mass transfer and effective delivery suitable for delivering food bioactive agents with controlled release (Neo, Ray, & Perera, 2018). Since the electrospinning process is a nonthermal process, it is appropriate for the encapsulation of biological components that are susceptible to high temperatures. Moreira et al. (2019) suggested that the thermal stability of phycocyanin, an antioxidant agent extracted from Spirulina microalga, increased after encapsulation by LEB 18/poly(ethylene oxide) (PEO) nanofibers. In addition to the use of electrospun fibers from proteins and polysaccharides as a biomaterial for food packaging, this method also opens a promising route for adding active properties such as antimicrobial (Deng, Kang, Liu, Feng, & Zhang, 2017; Kuntzler, Costa, & Morais, 2018a; Kuntzler, De almeida, Costa, & De Morais, 2018b), antioxidant (Li, Wang, et al., 2018a), and biosensing activities (Moreira, Terra, Costa, & Morais, 2018, Neo et al., 2018). For the encapsulation of bioactive agents, different approaches of electrospinning including blend, coaxial, and emulsion electrospinning and surface modification of the electrospun fiber mats have been used (Faridi Esfanjani & Jafari, 2016; Rostamabadi et al., 2019b). Blend electrospinning, as the most common encapsulation approach, is the direct addition of bioactive agent into the biopolymeric solution. In this method, both the bioactive agent and the biopolymer are dissolved in one solvent. By solidifying the solution jet during the process, the active agent is encapsulated within the polymeric fibers. This method of electrospinning is straightforward and simple, although it is not suitable for the encapsulation of sensitive bioactive compounds including proteins, enzymes, and cells. This is because using organic solutions and mechanical stirring, homogenization, or ultrasonication for blending can cause conformational changes or destroy their biological integrity. Coaxial electrospinning (i.e., with the same setup as conventional electrospinning except having a core
shell syringe) has been developed to prepare core and shell fibers which are sufficient for the delivery of food bioactive components not soluble in organic solvents. In this process, the polymer and the bioactive component are separately dissolved in their proper solvents and separately ejected through two confocal nozzles as the shell and core solutions, respectively. In this method, the sensitive bioactive agent is concentrated in the core of fibers providing effective protection. Emulsion electrospinning is another method in which the active agent is surrounded by emulsifiers or surfactants and impregnated into a polymeric carrier, whereby a controlled encapsulation process with sustained release is achieved. Hydrophilic and hydrophobic compounds, including carotenoids, polyphenols,

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vitamins, enzymes, peptides, oils, essential oils, flavors, and probiotics, can be encapsulated using this method with W/O and O/W emulsions, respectively. This method of electrospinning fabricates core and shell nanofibers using only a single nozzle. Another advantage of this method is minimizing the need for organic solvents which makes it appropriate for food applications (Zhang, Feng, & Zhang, 2018a). The electrospinning equipment and nanofibers are moving forward to commercialization and scaling up to industrialization. Fabricating nanofibers using the electrospinning method, as well as solution bowling, are among the other techniques for nanofiber production (such as drawing, template synthesis, self-assembly, and phase separation), that can be used on an industrial scale (Leidy & Maria Ximena, 2019). Donaldson Co., Inc. in the United States in the early 1980s introduced the first commercial products of submicron sized fibers, mainly for air filtration applications. The scaling-up process is still largely an issue. The issues which should be of concern are large volume processing, accuracy and reproducibility, safety and environmental attributes (Persano, Camposeo, Tekmen, & Pisignano, 2013). Moreover, the electrospinning of food-grade biopolymers is difficult since their high-molecularweight distribution and their complex chemical structure interfere with the entanglement necessary for spinnability (Kutzli et al., 2019). The throughput of electrospinning is also one of its general limitations. This problem can be solved with a novel method known as solution blowing (Section 5.4.1) which belongs to the group of melt blowing processes in which a polymer in a molten state is extruded through a spinneret (Kakoria & Sinha-Ray, 2018). Therefore the solution blowing method is suitable for biopolymers which are sensitive to degradation or denaturation after exposure to high temperatures while melting. Electrospraying, like electrospinning, is an electrohydrodynamic technique that has gained increased interest from food technologists. Electrospraying, first described in 1914 (Zeleny, 1914), requires a setup that is similar to electrospinning. However, in electrospraying small droplets are scattered to the target rather than fibers due to the lower viscosity of the feed solution. Therefore instead of micro- or nanosized fibers, particles are fabricated with a particle size in the range of a few nanometers to 100 μm. Polymer chain entanglement, polymer MW, and the evaporation rate of polymer
solvent are the effective parameters for the formation of particles in this process. Polymer chain entanglement, which is determined by the polymer concentration, is a key factor in the electrohydrodynamic process. A solution with higher biopolymer concentrations would be suitable for electrospinning rather than electrospraying due to its higher chain entanglement and higher viscosity (Niu, Shao, Luo, & Sun, 2020). The polymer MW was reported to affect the concentration, viscosity, surface tension, and conductivity in the case of chitosan solutions, which subsequently influenced the morphology and size of electrosprayed nanoparticles. The lowest chitosan MW (25 kDa) allowed the highest solution concentration and the highest productivity of nanocapsules for the encapsulation of epigallocatechin gallate (EGCG) (Go´mez-Mascaraque et al., 2016). Coaxial electrospraying can be used for the fabrication of multilayer encapsulation structures with food-grade materials as

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delivery systems for both hydrophilic and hydrophobic active agents with improved encapsulation efficiency in food applications (Go´mez-Mascaraque, Tordera, Fabra, Martı´nez-Sanz, & Lopez-Rubio, 2019). EGCG as a model hydrophilic component and α-linolenic acid (ALA) as a model hydrophobic agent were encapsulated in zein and gelatin coaxially electrosprayed capsules and compared with uniaxially electrosprayed particles. The coaxial ones showed a higher encapsulation efficiency and enhanced bioactivity protection in thermal degradation assays (for ALA), as well as enhanced antioxidant activity after in vitro digestion (for EGCG).

5.4.1 Solution blowing Solution blowing is a process for fabricating fibers with a size range of nanometers to micrometers. This process is similar to electrospinning although a high-velocity gas flow is applied instead of an electric field (Fig. 5.5). In this method, the polymer solution in the nozzle is pressed out through the orifices by compressed air which is obtained from a high-speed air supply, and dragged out by a high-velocity gas flow. Therefore a coaxial die is required, consisting of a core nozzle for the polymer solution flow and a shell nozzle for the high-speed air flow. Fibers can be collected on the collector after the evaporation of solvent. The fiber production rate and the diameter of the fabricated fibers are larger in comparison to electrospinning (Kakoria & Sinha-Ray, 2018). The air flow rate, nozzle dimensions, collecting distance, viscoelasticity of the polymer solution, and ambient temperature are the key parameters that play an important role in controlling the solution blowing process. By increasing the air pressure and temperature, the fiber diameter is decreased. The

Figure 5.5 Solution blow spinning (Zhuang et al., 2012).

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advantage of this technique is its capability to blend biopolymers and its scalability (Kolbasov et al., 2015). In a study by Kolbasov et al. (2015), nanofibers with the size of 0.5 and 1.5 μm were fabricated by this method from soy protein isolate solutions containing chitosan, lignin, sodium alginate, or zein, in the range of 900
1600 cm2 in 10 seconds with a solid weight of 5.1 g by using nozzles of 0.002 inch (internal diameter). Blowing-assisted electrospinning or electroblowing is the association of solution blowing and electrospinning. The aerodynamic stretching is associated with the electrostatic force since the nozzle is connected to a high-voltage power supply, resulting in the additional stretching of the polymer jets. This method can solve the limitation of polymer solutions with extremely high viscosities which are hard to be successfully electrospun (Wang et al., 2005).

5.5

Nano spray dryer

Spray drying is a continuous and intensive nanomaterial manufacturing approach. This technique has been used for the preparation of micro/nanocapsules, controlled release particles, composite microparticles, nanoparticles, SLNs, and liposomes. In this method, the stream of a liquid is transformed into dried particles with a onestep process via spraying in a chamber with a stream of hot air or inert gas, which can be fully automatically controlled (Assadpour & Jafari, 2019a, Masters, 1985). A common spray dryer setup comprises several components, including a feed solution container, feed pump, spray nozzle, drying chamber, exhaust filter, cyclone, and collector. Briefly, the feed solution is pumped and then atomized through a nozzle to the drying chamber in which the atomized droplets are exposed to the hot air or inert gas (e.g., nitrogen). By passing the drying chamber, energy-mass transfer occurs at the dynamic droplet surface and eventually the dried powder is separated from the drying air via a cyclone (Assadpour & Jafari, 2019a; Masters, 1985). The main purpose of the atomization process is enhancing the surface area over which heat and mass transfer occur. Different types of atomizers can be used, such as rotary, hydraulic (pressure), pneumatic, or ultrasonic nozzles, which determines the type of pump used. Moreover, the viscosity of feed solution can also affect this selection. For instance, when rotary atomizers or bifluid nozzles are applied, lowpressure pumps are suitable, while high-pressure pumps must be used for pressure nozzles. After going through the nozzle, the atomized droplets are dispersed into the drying chamber with a usual height to diameter ratio of 5:1 (tall) or 2:1 (small) to expose to the drying hot air. There are different flow directions of the drying air including cocurrent, countercurrent, or mixed flow. The cocurrent type is the most common flow type, especially for heat-sensitive components. In this type of flow, atomized droplets and the drying air (150 C
220 C) follow a similar route and the produced powder is exposed to a neither high nor low temperature (50 C
80 C) (Shishir and Chen, 2017). The drying air increases the temperature of atomized droplets, which results in the evaporation of the solvent (water). At the end of the

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drying chamber separation devices (e.g., scrapping devices including vibratory devices, mechanical brushes, and/or compressed air) are embedded for powder recovery. Since scrappers can have adverse effects on the phase behavior of dried dispersions due to the generated stress, cyclones may be used instead. The tangential entry of the gas
solid mixture into the cyclone body generates a circular flow, whereby the centrifugal force triggers the separation of the two phases. Therefore the particles in the air/gas, which is passing through the cyclone, get deposited on the cyclone walls due to the centrifugal force. Finally, the particles settle down due to the gravitational force to the bottom of the cyclone and are collected in the collector. Another type of collector generally used for nano spray dryers with ultrasonic atomizers and with the ability to collect even nanosized particles is the electrostatic particle collector. This device consists of two electrodes: a star electrode and a tubular particle gathering electrode, which are defined as a cathode and an anode, respectively. As a result of the high voltage between them, particles are collected on the surface of the tubular electrode due to their electrostatic deposition (Arpagaus, John, Collenberg, & Ru¨tti, 2017; Arpagaus, Collenberg, Ru¨tti, Assadpour, & Jafari, 2018), as shown in Fig. 5.6.

Figure 5.6 Different parts of a nano spray dryer apparatus Source: From Arpagaus, C., Collenberg, A., Ru¨ttib, D., Assadpour, E., Jafari, S. (2018). Nano spray drying for encapsulation of pharmaceuticals. International Journal of Pharmaceutics, 546 (1
2), 194
214.

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The morphology (size, shape, structure, and surface attributes) of obtained particles depends on the material characteristics, feed solution variables such as feed concentration, solution dynamics of the feed, viscosity, bioactive component/polymer ratio, type and concentration of the carrier agent, and process parameters including inlet temperature, feed rate, drying air/gas flow rate, atomization variables (type of atomizer, speed of atomizer, pressure of atomizer), and outlet temperature (Assadpour & Jafari, 2019a; Shishir & Chen, 2017). Higher inlet temperatures increase the rate of drying, which result in lower residual moisture in the final particles. Moreover, the applied temperature determines the particle size of dried powders. Larger particles are fabricated at higher inlet temperatures due to the faster water evaporation without time for the shrinkage of spheres. Furthermore, at higher temperatures, the bulk density of powder will be decreased since the larger particles are more porous. Atomization is considered to be the most important part of the spray-drying process. Thus it is called the heart of spray drying, since the quality and characteristics of the process and produced particles depend on this feature. The purpose of atomization is to convert the feed stream into fine droplets to increase the surface area, preparing the opportunity for effective and sufficient drying. Higher atomization speeds result in a higher drying rate and a lower residual moisture content. BeckBroichsitter, Strehlow, and Kissel (2015) reported that reducing the spray rate resulted in a decreased particle size and increased Span. Higher atomizer pressures provide smaller particles with a larger surface area. It has also been reported that adding surfactants can be effective in modifying the morphology of spray-dried particles (Moghbeli, Jafari, Maghsoudlou, & Dehnad, 2019). Adding surfactants forms a smooth spherical surface on the dried particles due to their ability to tune the surface-to-viscous forces inside the droplets (Arpagaus et al., 2017). Abdel-Mageed et al. (2019) reported that Tween 80 could be effective in controlling the morphology of spray-dried nanoparticles containing α-amylase. Spray drying has been used for the nanoencapsulation of different types of food bioactive components, such as probiotics (Gong et al., 2019; Su et al., 2018), flavors (Prasad reddy, Padma ishwarya, & Anandharamakrishnan, 2019), PUFA-rich oils (Prasad Reddy et al., 2019), essential fatty acids (Chang and Nickerson, 2018), vitamins (Jafari, Masoudi, & Bahrami, 2019a; Jafari, Vakili, & Dehnad, 2019b; Penalva et al., 2015), antioxidants (Ferreira Nogueira, Matta Fakhouri, & De Oliveira, 2019; Khanji et al., 2018; Kritchenkov et al., 2019), antimicrobial agents (Hu, Gerhard, Upadhyaya, Venkitanarayanan, & Luo, 2016; Wang, Oussama Khelissa, Chihib, Dumas, & Gharsallaoui, 2019), enzymes (Abdel-Mageed et al., 2019), peptides (Sarabandi et al., 2019), and natural food colorants (De Boer, Imhof, & Velikov, 2019; Fang et al., 2017). Spray drying is a favorable technique for bioactive components since it transforms a liquid feed into a powder form which is easier to handle, store, transport, and has higher stability (Veneranda et al., 2018). This method can be directly used for the encapsulation of hydrophilic and indirectly for the encapsulation of hydrophobic compounds after emulsification with a high encapsulation efficiency. Carbohydrates, proteins, lipids and waxes, polymers, surfactants, emulsifiers, and stabilizers can be used as wall material in

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the feed solution (Jafari, Assadpoor, He, & Bhandari, 2008). Using different emulsifiers for stabilizing the prepared emulsions containing hydrophobic bioactive agents before spray drying can be effective in modifying the properties of the final dried particles. Nano spray drying, which is realized by the Bu¨chi Nano Spray Dryer B-90, is a novel technique for the production of nanoscale particles that can be used for drug and nutraceuticals delivery (Li, Anton, Arpagaus, Belleteix, & Vandamme, 2010). Some modifications should be performed on the setup of conventional spray dryers to prepare a nano spray dryer, as depicted in Fig. 5.6. Commonly, ultrasound nozzles are used, and a proper collector, such as an electrostatic particle collector, is also required since conventional cyclones do not have the ability to collect particles with the size ,2 μm (Arpagaus et al., 2017; Arpagaus et al., 2018). The major advantages of a nano spray dryer over conventional ones are the smaller required sample quantities (minimum 2 mL, compared with 30 mL for the conventional ones), lower maximum drying temperature (i.e., 120 C, compared with 220 C for the traditional ones), higher yield, and smaller particle sizes. However, these nano spray dryers have a lower scale-up capability compared to traditional spray driers due to their limited vibrating mesh technology and their use of an electrical particle collector (Arpagaus et al., 2017). Prasad Reddy et al. (2019) prepared roasted coffee bean oil with whey protein as wall material by both nano and conventional spray drying and their results showed that the nano spray-dried capsules were approximately 11-fold smaller than microencapsulates with more uniform particle size distribution and smoother, and more spherical morphology. In another study, zein
sodium caseinate
pectin complex nanoparticles were prepared by Veneranda et al. (2018) for the nanoencapsulation of eugenol using nano spray drying. These nanoparticles loaded with eugenol were spherical and had a small size distribution with a size of 140 nm. The encapsulation of nutraceuticals and bioactive compounds using spray drying protects them and their active performance against environmental stress conditions with high encapsulation efficiencies. Khanji et al. (2018) reported that encapsulation of curcumin in casein micelle powder produced by spray drying protected its antioxidant activity. Kyriakoudi and Tsimidou (2018) also nanoencapsulated saffron extract in maltodextrin wall using a Bu¨chi B-90 nano spray dryer to improve the thermal and in vitro gastrointestinal stability of saffron apocarotenoids. It has also been shown that encapsulation of nutraceuticals by spray drying improves their bioavailability. Penalva et al. (2015) reported that folic acid encapsulation in casein nanoparticles (150 nm), prepared by nano spray drying, promoted its oral bioavailability in male adult rats. There are some reports on food applications of spray-dried particles incorporated with bioactive components. For instance, Moncada et al. (2015) directly incorporated the nano spray-dried sodium chloride in cheese cracker production and compared its sensory and antimicrobial properties with two other salt sizes. The cheese cracker with nanosized salt on its surface had a significantly higher preferred saltiness and significantly lower yeast counts. Thus using nano spray-dried salt can be helpful in decreasing sodium consumption in this kind of product.

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The first industrial uses of spray drying in milk and detergent manufacturing were reported to be in the 1920s while its application has spread to various types of food products, including egg products, beverages, vegetable proteins, fruit and vegetable extracts, carbohydrates, tea extracts, and yogurt (Masters, 1985). One of the limitations of spray drying, especially in the case of applying conventional atomizers, is the large particle size distribution, high electric energy consumption, and blockage of the nozzle. Another limitation of spray drying is using high temperatures which can have adverse effects on sensitive components such as PUFA-rich oils, lycopene, β-carotene, anthocyanins, vitamin C, colors, and flavors (Assadpour & Jafari, 2019a, 2019b, 2019c). Living bacterial agents such as lactic acid bacteria and probiotics can also be damaged due to the exposure to high temperatures even for short times and the reduction in water content. Therefore there is an increasing interest in the association of other methods with spray drying, such as ultrasoundassisted spray drying (i.e., nano spray dryer), vacuum spray drying (Islam et al., 2017), ultrasound-assisted vacuum spray drying (Liu, Zhu, Bai, You, & Yan, 2019), and dehumidified air spray drying (Jedli´nska et al., 2019). Vacuum spray drying is the combination of vacuum drying and spray drying which applies low temperatures for drying as the process is done under vacuum. Therefore this technique is suitable for materials that are labile to heat (Shishir & Chen, 2017). Dehumidified air spray drying is a modification of conventional spray drying that has better performance in decreasing the stickiness limitations and improving the powder collection by connecting a dehumidified air drying system to its chamber via the air inlet. The recovered powder in this method contains a lower moisture level and higher bulk density compared with the conventional method. Moreover, because of the lower outlet temperature and moisture content of the drying air, the produced particles have a smooth surface.

5.6

Micro/nanofluidic systems

The microfluidic technique was originally developed in the 1950s and first used in different chromatographic systems (Golay, 1957). Later on, this technique was used for capillary electrophoresis to improve the separation process. After the 1990s, the use of microfluidic systems was boosted and they were further studied by several researchers (Khan, Serra, Anton, & Vandamme, 2015). The microfluidic and nanofluidic methods (i.e., particularly focused on nanosized productions) are modern low-energy and bottom-up technologies for the fabrication of nanomaterials. Interestingly, these methods have also been used for the manufacture of nanocarriers as drug delivery systems. However, their application for the nanoencapsulation of food nutraceuticals and bioactive components still requires further research and comprehensive study (Ran et al., 2017; Zhang, Liu, Zhang, & Santos, 2019). A microfluidic device has coaxial assemblies of a series of rigid glass capillaries with dimensions of 10
100 μm which are resistant to chemicals. Also, they have a 3D geometry that enables the production of different types of nanomaterials (e.g., nanoemulsions, nanoparticles, and nanoliposomes) (Balbino, Serafin, Radaic, De

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jesus, & Lucimara, 2017; Joshi et al., 2016). Moreover, these channels work with significantly small amounts of samples due to their small dimensions. Other advantages of this method are the low energy consumption and low cost of the whole system, in addition to the use of low amounts of sample and ingredients. Finally, this is a rapid technique that provides the opportunity to develop in vitro evaluations. The specific size of channels makes it possible to fabricate sophisticated nanoparticles with specific sizes and narrow size distributions. Also, nano- to microseconds of mixing, reaction and self-assembly, real-time monitoring or imaging, and direct scale-up, are some favorable properties of this method (Assadpour & Jafari, 2019b; Zhang et al., 2019). The laminar flow in this method (i.e., small Reynolds number) is continuous and controllable. As an emulsification technique, this method does not require high energy inputs, thus it provides a mild process. Besides, there are no temperature fluctuations, making this method suitable for the encapsulation of heat-labile compounds and live microorganisms such as prebiotics and yeasts (Feng & Lee, 2019). There are several different types of microfluidic devices, including terrace-like, T-junction, flow-focusing, capillary-based, coflow, cross-flow, and flow-focusing devices (Fig. 5.7). Among them, channel-based and capillary-based devices are the most common. Microchannel-based devices are manufactured through different microfabrication processes such as micr-milling, micromachining, lithography, and mold replication, by applying varied materials (e.g., metal, glass, silicon, or polymer). However, capillary-based systems are usually fabricated from low-cost commercially available parts in less time with the same efficiency as microchannelbased devices (Khan, Serra, Anton, & Vandamme, 2013). Therefore fabrication and the use of capillary-based systems are more time and cost-efficient. Additionally, they can be applied under aggressive chemical conditions. However, it is more difficult to handle and to be paralleled to achieve larger yields in comparison with microchannel-based counterparts. The microfluidic process is achieved by mixing two phases: (1) continuous, and (2) dispersed phases. The miscibility of these two phases determines the type of final product. The mixing of miscible fluids enables chemical reactions and can be used for the production of nanoparticles while mixing two immiscible fluids

Figure 5.7 Different types of microfluidic devices: (A) T-junction; (B) flow focusing; (C) capillary-based; (D) cross-flow; (E) flow focusing. CP, continuous phase; DP, dispersed phase (Khan et al., 2015).

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provides the formation of droplets (Feng & Lee, 2019). The control over the microfluidic process is usually conducted by adjusting the flow rate of both continuous and dispersed phases which can also determine the characteristics of fabricated nanostructures. The terrace geometry of microfluidic devices is another effective parameter. Y-junction, T-junction, and flow focusing are three types of terrace geometry that provide different shear rates determining the size and properties of final product. Among the mentioned geometries, T-junction geometry provides the highest shear rate which generates emulsions with a smaller droplet size distribution. In addition to the terraced geometry, its angle is also an important factor in the mixing efficacy at the joint of two microchannels where the two phases meet (Feng & Lee, 2019; Zhang et al., 2019). The microfluidic devices have been used as a novel technology for the fabrication of nanoparticles. Biopolymeric particles are usually fabricated through a nanoprecipitation effect and by an antisolvent process. In this process, the stream of biopolymer solution is merged with the stream of antisolvent solution where the two microchannels meet; whereby, the diffusion of solvents results in achieving equilibrium in the concentrations of solvent and antisolvent. At this point, the biopolymer-based nanoparticles are formed with precise control over size and characteristics (Feng & Lee, 2019). It has been reported by Abstiens and Goepferich (2019) that the microfluidic nanoprecipitation results in smaller nanoparticles with monodisperse size distribution in comparison to the bulk nanoprecipitation method. The type and rate of flow are the most effective factors on the size and properties of final nanoparticles. For example, turbulent flows result in larger particle size distributions due to its chaotic condition and various shear rate distribution. However, laminar flows can form more homogenous particles. Microfluidics provides the opportunity of preparing Janus particles in a simpler and more accurate way compared with other conventional methods. Two different polymers within two channels are merged at the junction to fabricate Janus particles, which consist of two distinct segments that are chemically and physically amphiphilic or bipolar (Zhang, Grzybowski, & Granick, 2017). Different biopolymers have been used for the fabrication of nanoparticles using microfluidic techniques, including chitosan (Pessoa, Sipoli, & De La Torre, 2017), polylactic acid (Othman, Vladisavljevi´c, Hemaka bandulasena, & Nagy, 2015), and zein (Olenskyj, Feng, & Lee, 2017). Electrostatic complexes can also be prepared using microfluidic devices. For instance, β-lactoglobulin/gum Arabic complexes were assembled using this new technique by Amine, Boire, Davy, Marquis, and Renard (2017). SLNs can also be produced using this method with particle sizes significantly smaller than those of biopolymeric nanoparticles. For example, Chen et al. (2016) fabricated SLNs using this method with a final particle size of 27 nm. Food nutraceuticals and bioactive compounds can be encapsulated within the self-assembled nanostructures using the microfluidic technique as a novel nanoencapsulation method. Joshi et al. (2016) simultaneously encapsulated both watersoluble and water-insoluble drugs using microfluidic fabricated nanoliposomes with a final particle size ranging between 90
300 nm. The microfluidic devices can be used for the fabrication of nanoemulsions by injecting the dispersed phase into

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another immiscible or partially immiscible liquid phase. Due to the competition between shear stress imposed by the flow of continuous phase and the interfacial force at the junction where the two phases meet, droplets are exposed to shear stress while their droplet size is reduced (Khan et al., 2015; Shaddel, Akbari-Alavijeh, & Jafari, 2019). Also, the spontaneous emulsification process (i.e., mechanism of emulsification) uses a microfluidic system based on Laplace pressure differences in the dispersed phase on the terrace and in the channel. Usually, the microfluidic device is used for further reduction in the droplet size of premixed emulsions (Feng & Lee, 2019). A limitation of this method is the low production per hour due to the low capacity of channels. This issue can be solved by parallelizing droplet generators (Khan et al., 2013; Khan et al., 2015). For scaling up the microfluidic process, the best option for terraced geometry is the Y-junction due to its control over the droplet size (Feng & Lee, 2019). Another limitation for the application of this technique in the field of food industry is the heterogeneity of food ingredients which may result in clogging of the microfluidic channels. This problem can be solved by an autocleaning system; nevertheless, it requires an additional cost (Feng & Lee, 2019).

5.7

Vortex fluidic device

The VFD is a relatively new processing platform used in thin-film microfluidics and thin-film flow chemistry. The processing efficiency of VFD is improving. Thus it is applicable in many fields of scientific research and industry, including the synthesis of small molecules, processing in pharmaceutical industry, and manipulating single-cell organisms. Some of the problems of traditional batch approaches include limited mixing and heat transfer, both of which are solved in VFD (Yasmin, Chen, Stubbs, & Raston, 2013). The VFD consists of a rotating glass tube tilted at an angle θ relative to the horizontal position (Fig. 5.8). The movement of tube causes the liquid inside to accelerate upwards and form Stewartson/Ekman layers on the sides, whereby the rotation causes the formation of a dynamic film (Kumari et al., 2016). VFD can operate in confined mode and continuous flow mode. The confined mode is used when the volume of reactants is finite. The speed, which can be controlled within 1 rpm, has to be sufficient to ensure that a vortex is maintained to the base of tube, but the liquid must not fall out of the tube. Alternatively, in the continuous flow mode, liquid is continuously delivered to the base or a specific point in a tube, while the products are collected from the top. The conversion rate is affected by the residence time of liquid in the tube. The thickness of the film depends on the volume of liquid in the tube (which under continuous flow depends on the flow rate), the speed of rotation, and angle θ. For a fixed tilt angle and rotational speed, the residence time can be expressed as the ratio of fluid volume retained in the device to the incoming fluid flow rate. The optimization of parameters is crucial for the successful use of VFD since even small alterations can have significant consequences for the final result. For instance, Britton and Raston (2014) used the VFD for room-temperature, catalyst-

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Figure 5.8 Schematic representation of the vortex fluidic device (Sitepu et al., 2018).

free conversion of sunflower oil to biodiesel. They found that the percentage of conversion dropped from 100% to 80% when the flow rate increased from 1 to 5 mL/min. Furthermore, Sitepu et al. (2018) used the VFD to transesterificate wet microalgae biomass to biodiesel and reported an increase in the conversion efficiency from 30% to 90% when the speed of rotation increased from 4000 to 8000 rpm. Also, in the confined mode, when using the base catalyst, the conversion efficiency dropped for rotation speed ,6000 rpm. Generally, VFD shows the optimal performance for the rotation speed from 2000 to 9000 rpm and tilt angles Θ . 0 , whereby a tilt angle of 45 degrees is most commonly used. Jones and Raston (2017) reported that, for a specific speed along the tube, film thickness decreases towards the exit and also decreases with speed, with an average thickness 530 μm at 6000 rpm and 294 μm at 8000 rpm. The possibility of controlling the reactivity and selectivity, as well as the ability of simple and efficient preparation of complex molecules resulted in various chemical transformations being performed using the VFD. Britton, Meneghini, Raston, and Weiss (2016) demonstrated the acceleration of enzymatic catalysis for four enzymes using the VFD and established a method to make biocatalysis more practical. Vimalanathan et al. (2017) reported a surfactant-free, one-step method for the controlled growth of stable nanotubules of fullerene C60 within the VFD as a thinfilm microfluidic platform, avoiding the incorporation of solvent molecules. The VFD tube surface can be easily altered to increase the efficiency of micromixing or covalent attachment. Furthermore, it is possible to control the surface contact angle in order to change the fluid’s viscous drag. Incorporation of field effects is also achievable, including light sources and lasers. Besides the fact that the product

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characteristics can be modified by changing the processing parameters, the main advantages of VFD lie in its low environmental impact and low cost. A possible limitation of VFD is the use of highly viscous liquids in continuous flow mode, where clogging of the system can happen. In food technology, encapsulation of fish oil using VFD has been researched. He, Joseph, Luo, and Raston (2019) studied the nanoencapsulation of fish oil in the presence of phospholipids. They also compared the results obtained using VFD with those obtained by conventional homogenization. It was reported that the diameter of encapsulated particles changed significantly; spheroidal particles from 50 to 250 nm in diameter were generated in the VFD, while conventional homogenization yielded particles with diameters ranging from 2 to 4 μm. Smaller particles could potentially exhibit better absorption of fish oil. Additional benefits of VFD include elimination of organic solvents and a smaller number of processing steps. Furthermore, the applicability of a VFD thin-film microfluidic platform for enzymatic hydrolysis, pasteurization, and encapsulation was explored (He et al., 2019). It was found that the processing time of enzymatic hydrolysis shortens from about 2
3 hours to 20 minutes when using the VFD. Additionally, usage of VFD reduced the processing time of standard pasteurization of raw milk from 30 minutes to 10 minutes. VFD was also effective in reducing the size of curcumin particles encapsulated with fish oil and sucrose monolaurate from approximately 1000 nm to ,100 nm, while avoiding the need for expensive homogenization equipment. Although the VFD is just starting to be used in food processing, these preliminary results show that it has a great potential in the food industry.

5.8

Ball milling

A ball mill is a type of grinder which belongs to the group of tumbling mills, which are divided into a few categories, with respect to the type of grinding media and feed particle size. Besides ball mills, there are pebble mills, autogenous mills, rod mills, and tube mills, which work on the same principle. Tumbling mills consist of a hollow rotating cylinder, which is usually horizontal but it can also be tilted at a small angle. The length of cylinder is usually 1 to 1.5 times the cylinder diameter and contains the grinding media and the particles that need to be broken. As it rotates, the mass inside the mill initially moves up the wall of cylinder and acquires potential energy. When the force of gravity surpasses the friction and centrifugal forces, it falls into the “toe” of the mill, as potential energy becomes kinetic. This type of movement causes collisions between the grinding media and the mill wall, as well as between the grinding media themselves. The ultimate result is the grinding of particles that are caught in those collisions. There are two general types of movements that occur during the grinding process in a mill. Cataracting is a process in which grinding balls rise higher inside the cylinder and detach from the interior walls, describing an approximately parabolic trajectory. Cascading implies rolling of the balls one on top of another without falling (Fig. 5.9). When a ball mill is working, those movements are combined and they

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Figure 5.9 Schematic representation of the working principle of a ball milling process.

are determined by the friction, centrifugal, and gravitational forces, as well as the mutual effect of the lining of mill and the grinding bodies. The resultant of the gravitational and centrifugal forces cause the occurrence of a centrifugal force field. The center of this field is at a distance of Y 5 g/ω2 above the mill axis. When that distance is equal to the radius of the mill shell, the gravitational and centrifugal forces are in equilibrium at the top of the mill shell. At this point, the peripheral speed of the mill is so great that instead of falling, the grinding balls adhere to the mill shell and stay on the perimeter of the mill for a complete revolution, thus causing no further grinding, and the mill starts acting like a centrifuge. This speed is called the critical speed (nc) and is equal to: 42:3 nc 5 pffiffiffiffi rpm D where D is the inside diameter in meters. The operational speed (expressed in rpm) is usually given as a percentage of the critical speed. Although there are instances in which ball mills have been successfully operated at speeds ranging from 60% to 90% of their critical speed, it is a common practice to run the mills at speeds between 65% and 80% of their critical speed. A cascading movement (Fig. 5.10) occurs always, while a cataracting movement depends on the grinding body charge and a friction coefficient, which can be influenced by the shape of liner plates (Bellopede, Clerici, Marini, & Zanetti, 2009). Cascading causes finer grinding than

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Figure 5.10 Cascading (A) and cataracting movement (B) in a rotary cylinder (Bellopede et al., 2009).

cataracting, which is why the mill charge should be bigger for coarser grinding. Ball mills are more applicable for cataracting purposes since the weight effect is well accomplished by spherical bodies. Some parameters need to be considered to get the best possible results. One is the sample to media ratio, which is critical because too much powder will limit the milling efficiency due to the poor media
media contact, resulting in less effective tumbling. Furthermore, the rotation speed must be well adjusted. If it is too fast, the centrifugal force will cause the grinding balls to stick to the sides of a mill. On the other hand, if it is too slow, the balls will only roll around the bottom since there will not be sufficient force to lift them. The right choice of the grinding media is crucial when designing an experiment. Among the materials used as grinding balls, ceramic or steel balls are the most common. The balls should be denser and their size should considerably exceed that of the largest pieces of the sample to be ground. They must be durable enough to grind the particles for a significant amount of time but not so tough that they cause damage to the tumbler. Possible interactions of grinding media and the sample have to be considered too. For example, iron can react with corrosive substances, so ceramic or stainless steel grinding media need to be used. Flammable samples can become explosive as they become smaller. This can be circumvented by selecting balls made from ceramic or lead, which don’t produce sparks on impact, and by filling the cylinder with inert gas, which prevents explosive reactions with air. The main advantage of ball milling is the low cost of installation and grinding media (Takacs, 2002). It is applicable for a variety of materials, with a possibility of open as well as closed circuit grinding. Ball mills can produce powders with average particle sizes ,1 μm. Also, ball mills are powerful tools in mechanochemistry where the procedure usually offers one-pot, solvent-free reaction routes with large yields, making it environment-friendly. The milling process can be carried out using dry or wet samples, making this procedure possible for a wide variety of materials. Wet milling requires additional caution because the liquid medium must

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be removed when the process is complete which can cause the formation of agglomerates. A possible disadvantage is the fact that the final product may be contaminated from the wear of grinding balls or the container. To prevent that, the grinding media and container can be coated with hard-wearing ceramic materials such as zirconia. If only the grinding balls are coated, a polymer container must be used. Also, after the completion of the milling process, the sample must be withdrawn. Although there are methods for efficient draining of the mill, it is common that the material remains sticking on the cylinder wall and the surface of grinding balls. These residues can be washed out, and a part of the sample can be lost. Planetary ball mill (Fig. 5.11) is a special type of ball mill which consists of two or more jars mounted on a disc; sometimes called the sun wheel. The jars are rotating at an angular velocity w around their axis, opposite to the disc movement (ratio 22:1 or 21:1), which subjects the grinding balls in the jars to centrifugal and Coriolis forces, and ultimately results in a reduction of particle size. Compared with common ball mills, planetary ball mills are smaller in size and are mainly used in laboratories for grinding sample materials since this alternative offers a higher degree of energy to create finer or more homogenous size distributions. Recently, a great deal of interest for particle size reduction has emerged in the field of food science and biotechnology (Chen, Zhang, Bhandari, & Yang, 2018). That is mainly due to the altered physical and chemical characteristics of compounds when their size is sufficiently reduced. A smaller size of particles means that they have a larger surface area which causes better water absorption and solubility. Kim, Suzuki, Hagiwara, Yamaji, and Takai (2001) used ball milling to

Figure 5.11 Schematic representation of a planetary ball mill (Chauruka et al., 2015).

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convert native potato starch to the relaxed glassy state at ambient temperature and to induce its transition from the glassy to rubbery state. They showed that the process of ball milling can accelerate enthalpy relaxation and provide an alternative way to make glassy starches of different states. He et al. (2014) studied the physicochemical properties of maize starch subjected to ball milling. It was found that after ball milling, the surface morphology of starch granules is altered compared to their native state, which causes an increase in their surface area. Furthermore, the transparency and cold-water solubility of starch increased as well. Those results are consistent with the ones obtained by Huang, Xie, Chen, Lu, and Tong (2008). Besides maize starch, they also studied cassava starch and concluded that the gelatinization temperature and enthalpy of gelatinization decrease after ball milling, while their apparent amylose content, cold-water solubility, and transparency increase. When compared to milled maize starch, milled cassava starch showed a lower amylose content and a greater cold-water solubility and transparency. Ball milling increased the amorphous regions of starch granules and decreased their crystalline regions. In addition to starch, the effect of milling on the physicochemical properties was investigated using the peels of root and tuber crops, including yam (Dioscorea alata L.), taro (Colocasia esculenta L.), and sweet potato (Ipomea batatas L.) (Huang, Chen, & Wang, 2010). The ball milling process resulted in a redistribution of fiber components from insoluble to soluble, decreased the bulk density, and increased the solubility and water-holding capacity of the micronized peels.

5.9

Membrane technology

Membrane technology has been widely used as both a processing and a separation method in the food industry. Generally, this technology is used as an alternative to conventional techniques or as an advanced technology for processing foods and production of new ingredients (Dhineshkumar and Ramasamy, 2017). Membranes are semipermeable barriers that allow the separation of certain species by a combination of sieving and diffusion mechanisms into two fractions: (1) filtrate or permeate (i.e., fraction passing through the membrane), and (2) concentrate or retentate (fraction retained by the membrane). Depending on the driving force, there are mainly two types of membrane technologies used in the food industry. Membranes can be based on a pressure-driven process, in which the main driving force for separation is transmembrane pressure to overcome natural osmotic pressure (Dhineshkumar & Ramasamy, 2017; Kotsanopoulos & Arvanitoyannis, 2015). These pressure-driven membrane processes include microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. Conversely, electrodialysis (ED) enables separation based on an electrical potential difference as a driving force. Depending on the specific applications, membrane materials can be hydrophilic or hydrophobic. They could be made of various organic and inorganic materials, providing different properties as a function of the desired separation process. Polymeric membranes are extensively used in the food industry and can be found in

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a wide range of pore sizes (Dhineshkumar & Ramasamy, 2017). Compared to the inorganic membranes (e.g., ceramic membranes with different metal oxides coatings as active layers), polymeric membranes are significantly cheaper and offer high packing densities. Nevertheless, polymeric membranes are not as mechanically resistant as their inorganic counterparts. They can only work at certain ranges of temperatures, pH, and transmembrane pressures. Inorganic membranes are mainly applied in more extreme industrial conditions but they are considerably expensive. Membranes are packed in membrane modules of different types: plate-andframe, tubular, hollow-fiber, spiral-wound, or membrane cassettes. These modules differ in price and packing density (Dhineshkumar & Ramasamy, 2017). Hollowfiber and spiral-wound modules have the largest packing density, while plate-andframe and tubular modules have the lowest packing density. One of the main advantages of membrane technology in the food industry is its green technology approach. Briefly, membrane technology aims to reduce the negative ecological impact of the processes in the food industry. Membrane technology is also considered as a cold process since it does not increase the temperature during process, which allows the natural taste of food products to be preserved (Dhineshkumar & Ramasamy, 2017; Tr¨aga˚rdh, 1991). In the food industry, one of the most common uses of membrane technology is in the dairy industry. For instance, milk consists of a wide variety of particles of different charges and sizes which enables the use of membranes for an efficient selective separation (Ahmad & Ahmed, 2014). Additional use of membrane technology includes the preparation of food nanomaterials. Membrane emulsification can be used for the fabrication of nanoemulsions whereby the dispersed phase is converted into fine droplets after passing by force under pressure through the membrane into the continuous phase containing surfactant. The small droplets are surrounded immediately after formation by surfactants present in the continuous phase. The characteristics of dispersed and continuous phases can have noticeable influences on the droplet size of membrane emulsified nanoemulsions as well as the properties of the membrane such as its pore size, pore size distribution, pore shape, and hydrophobicity and the type and concentration of surfactant (Charcosset, 2016; Vladisavljevi´c, 2018). The properties of dispersed phase such as its viscosity play an important role in the membrane emulsification process since it should be passed through the pores of the membrane. In the case of dispersed phases with high viscosities, the process faces trouble. A premix membrane emulsification technique could be an alternative in such situations since the initial coarse emulsion has a lower viscosity in comparison with the dispersed phase, makes the process easier (Charcosset, 2016; Gehrmann & Bunjes, 2017). For example, Alliod et al. (2018) used premix membrane emulsification for the fabrication of nanoemulsions, which were stable for 9 months with an average droplet size of 260 nm. By increasing the pore size, droplet size of the final produced nanoemulsions increases. Narrow pore-size distribution membranes result in monodispersed nanoemulsions. It has been reported that the distance between pores of the membrane also has an effect on the properties of fabricated nanoemulsions. The membranes with higher porosity yield nanoemulsions

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Figure 5.12 Schematic illustration of membrane emulsification (A) and membrane mixing (B) (Charcosset, 2016).

with a higher risk of droplet coalescence since the pores are placed close to each other. The type and content of surfactant are also parameters with an effect on the droplet size. Different types of nanoemulsions have been fabricated using this method applying various membranes. For instance, oil-in-water nanoemulsions are emulsified using hydrophilic membranes and water-in-oil nanoemulsions are fabricated using hydrophobic counterparts. Multiple emulsions including water-in-oil-inwater and oil-in-water-in-oil can also be prepared by the membrane emulsification method (Charcosset, 2016; Vladisavljevi´c, 2018). The membrane mixing method is another technique (Fig. 5.12b) which has been reported for the preparation of different colloidal systems such as nanocapsules, nanoparticles, nanoliposomes, and SLNs with a high efficiency by introducing one solution into another. It has been found that nanoemulsions can also be prepared using the membrane mixing method in addition to the membrane emulsification method. In this method, in contrast to the membrane emulsification, there may be a reaction between the two solutions (Charcosset, 2016). Yedomon, Fessi, and Charcosset (2013) prepared nanoscale bovine serum albumin particles (139 nm) with a narrow particle size distribution using the membrane mixing method associated with antisolvent method. This protein was first dissolved in ethanol and then passed through the membrane. For the preparation of nanoliposomes using the membrane technique, at first large-size liposomes are formed in the dispersed phase and then their mixture is passed through the membrane pores. This method is called the membrane extrusion method, which is a straightforward, efficient, and reproducible method for the preparation of nanoliposomes with a high encapsulation efficiency. The properties of formed nanoliposomes depend on the pore size of the membrane as well as the used pressure and temperature during the process. The membrane mixing method can also be used for the direct preparation of nanoliposomes, which is based on the ethanol injection method, whereby the bioactive component and the lipids are passed through a membrane under pressure generated by a pump after being dissolved in ethanol. The process of fabricating SLNs is the same as emulsions using membrane technology, while in the preparation of SLNs, the lipid is heated at a temperature higher than its melting point before passing through the membrane. The advantage of preparing SLNs using the membrane method is the possibility of tuning their size by adjusting the process parameters. Moreover, scaling up can be achieved easily by using membranes with a larger surface area.

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Conclusions and future perspectives

Food nanomaterials have attracted great interest due to their unique characteristics. Among the different approaches that exist to produce the nanoscale systems, techniques which require specialized equipment were briefly highlighted in this chapter. Despite the fact that some conventional approaches are expensive to scale up or they use high energy, the reproducibility and industrial-scale production make them useful. On the other hand, there is an increasing interest for new methods such as electrospinning, vortex fluidic, or micro/nanofluidic devices. These methods are not yet industrialized but much of the research has been conducted on them studying different aspects, i.e., optimization of the process. It seems that the novel techniques need in-depth knowledge to understand the utilization possibilities for different food ingredients as variable features, such as viscosity, sensitivity to heat, solvent compatibility, or size, may limit their utilization.

Acknowledgment(s) We would like to thank Dr. Leonardo Gutierrez from PaInT group at Ghent university for his kind help regarding membrane technology.

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415. Rostami, M., Yousefi, M., Khezerlou, A., Aman mohammadi, M., & Jafari, S. M. (2019). Application of different biopolymers for nanoencapsulation of antioxidants via electrohydrodynamic processes. Food Hydrocolloids, 97, 105170. Ruiz-Montan˜ez, G., Ragazzo-Sanchez, J. A., Picart-Palmade, L., Caldero´n-Santoyo, M., & Chevalier-Lucia, D. (2017). Optimization of nanoemulsions processed by high-pressure homogenization to protect a bioactive extract of jackfruit (Artocarpus heterophyllus Lam). Innovative Food Science & Emerging Technologies, 40, 35
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Salvia-Trujillo, L., Soliva-Fortuny, R., Rojas-Grau¨, M. A., Mcclements, D. J., & Martı´nBelloso, O. (2017). Edible nanoemulsions as carriers of active ingredients: A review. Annual Review of Food Science and Technology, 8, 439
466. Sarabandi, K., Jafari, S. M., Mohammadi, M., Akbarbaglu, Z., Pezeshki, A., & Khakbaz heshmati, M. (2019). Production of reconstitutable nanoliposomes loaded with flaxseed protein hydrolysates: Stability and characterization. Food Hydrocolloids, 96, 442
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987. Zou, L.-Q., Liu, W., Liu, W.-L., Liang, R.-H., Li, T., Liu, C.-M., . . . . . . Liu, Z. (2014a). Characterization and bioavailability of tea polyphenol nanoliposome prepared by combining an ethanol injection method with dynamic high-pressure microfluidization. Journal of Agricultural and Food Chemistry, 62, 934
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M.L. Zambrano-Zaragoza1, D. Quintanar-Guerrero2, N. Mendoza-Mun˜oz3 and G. Leyva-Go´mez4 1 Laboratorio de Procesos de Transformacio´n y Tecnologı´as Emergentes en Alimentos, FES-Cuautitla´n. Universidad Nacional Auto´noma de Me´xico, Cuautitla´n Izcalli, Mexico, 2 Laboratorio de Posgrado en Tecnologı´a Farmace´utica, FES-Cuautitlan. Universidad Nacional Auto´noma de Me´xico, Cuautitla´n Izcalli, Mexico, 3Laboratorio de Farmacia, Facultad de Ciencias Quı´micas, Universidad de Colima, Colima, Mexico, 4Departamento de Farmacia, Facultad de Quı´mica, Universidad Nacional Auto´noma de Me´xico, Mexico City, Mexico

6.1

Introduction

Nanoemulsions and nanosized ingredients represent a viable alternative in the development of novel products for including components with specific functions (Abbasi, Samadi, Jafari, Ramezanpour, & Shams-Shargh, 2019; Assadpour & Jafari, 2017; Mohammadi, Jafari, Assadpour, & Faridi Esfanjani, 2016). The ingredients can be incorporated during food processing in order to obtain functional products with adequate organoleptic quality, texture improvement, color homogeneity, and stabilizers, or for the release of active substances during storage, distribution, or consumption. These nanosystems possess a greater surface area, reactivity, solubility, and availability of compounds, and they have the ability to interact with the food components to decrease the physiological and enzymatic reactions, producing new products or contributing to the development of sausages, mayonnaise, or other low-fat products (Quintanilla-Carvajal et al., 2010; Rezaei, Fathi, & Jafari, 2019). Recently, consumers have exhibited a preference for minimally processed products with the most natural additives and ingredients that represent a health benefit, such as enzymes, prebiotics, probiotics, antioxidants, and antimicrobials that occur naturally as soluble extracts or essential oils obtained generally from plants (Li & Nie, 2016; Tamjidi, Shahedi, Varshosaz, & Nasirpour, 2013). This is where nanotechnology allows improvement of the functionality of various ingredients, modifying their solubility, decreasing the concentration of substances, and potentiating their effectiveness or controlling their release (Jafari & McClements, 2017; Jafari, Fathi, & Mandala, 2015). Moreover, nanosized systems interact with food; thus the components must be selected carefully depending on the food, beverage, drink, sausage, etc., in which they will be used.

Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00006-6 © 2020 Elsevier Inc. All rights reserved.

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The preparation of nanosystems requires several considerations in terms of which the ingredients will be used during the processing, rendering it necessary to request the desired function in the formulation, such as the following: stabilizers of food emulsions (sausages, mayonnaise, functional beverages); improvers of texture (ice cream, cheese, pˆate´s); homogenization of color; nutrient bioavailability, and enzymatic, oxidative, or respiratory control in minimally processed products. In addition, it remains important to consider the characteristics of the food in which the nanosized systems will be employed and incompatibilities between ingredients. Moreover, physicochemical properties such as pH, water activity, ion charge, fat content, the superficial ionic charge, and composition in general, as well as the desired function that they fulfill during processing, packaging, storage, and consumption should be noted (Oehlke et al., 2014; Weiss, Takhistov, & McClements, 2006). Preparation of nanostructured systems involves the use of surfactants that allow two immiscible phases to be stabilized for as long as possible; they play an important role in the interactions and these must be taken into account during the formulation of food. The interaction with the food as well as the release of the functional components will depend on its functional groups, hence its surface charge. In this chapter, we will consider that all nanosized systems should be incorporated directly into the food formulation as an ingredient; therefore all of the substances utilized should be generally recognized as safe (GRAS). Different nanometric size systems are currently applied in food formulation, such as nanoemulsions, polymeric nanoparticles, solid lipid nanoparticles (SLNs), lipid nanocarriers, nanocrystals, nanoliposomes, nanomicelles, noisome, nanofibers, and nanolaminates. Thus the range of possibilities and choices will always depend on the purpose of their use and their relationship with the sensory quality of the products, in that the latter comprises a decisive part in the purchase selection by the consumer. Nanoemulsions and Pickering nanoemulsions are the systems most studied for their incorporation into food formulations. Due to their characteristics and functionality, these are used for increasing the stability of juices, drinks, sauces, dressings, and ice cream (Oehlke et al., 2014; Thiruvengadam, Rajakumar, & Chung, 2018). The main ingredients used as stabilizers for their preparation are as follows: polyelectrolytic molecules such as amphiphilic proteins; peptides; hydrocolloids such as modified starches (oxidized, acid, alkaline, etc.); chitosan, pectin, and alginate, and/ or synthetic stabilizers such as polysorbates, sorbitan esters, and polyoxyethylenes (Hu, Bae, Fleming, Lee, & Luo, 2019; Pe´rez-Masia´ et al., 2015; ZambranoZaragoza & Quintanar-Guerrero, 2019). The substances usually desired for incorporation are essential oils with an antioxidant and/or antimicrobial potential effect, vitamins, polyphenols, and enzymes, to mention some. In addition, the solid particles most commonly used in Pickering nanoemulsions for use in food and beverages are silica, while polymeric nanoparticles are the second type of systems used in food formulation and are preferred for the incorporation of functional ingredients for thermal protection during processing and for the controlled release of substances during storage.

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6.2

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Nanoemulsions in food processing

Nanoemulsions represent one of the systems that have shown the greatest interest for use as ingredients in the food industry, mainly because there are different methods for their preparation, as well as being considered as stable systems for the encapsulation of bioactive substances. Also, their performance as a good release system will depend on the conditions in which they are applied.

6.2.1 Classification of nanoemulsions for food industries An emulsion is a lyophobic colloidal system composed of two immiscible liquids, in which one of the liquids is dispersed homogeneously in the other liquid in the form of spherical globules (Feng, Chen, Wu, Jafari, & McClements, 2018; Hosseini, Jafari, Mirzaei, Asghari, & Akhavan, 2015). Globule size in emulsions has served as a criterion for classification: macroemulsions are considered when globule sizes are within the range of 1.0 100 μm, while nanoemulsions are systems with globules between 20 and 500 nm, and microemulsions possess droplet sizes between 2 and 100 nm (McClements & Rao, 2011). It can be observed that there is an overlap in globule size; however, there are marked differences in the characteristics of different types of emulsions. For example, macroemulsions and nanoemulsions are thermodynamically unstable, while microemulsions are stable (Mehrnia, Jafari, Makhmal-Zadeh, & Maghsoudlou, 2016, 2017). Another difference exists in terms of their appearance; macroemulsions are turbid or opaque, and nanoemulsions are translucent or opalescent with bluish appearance, due to the Tyndall effect, while microemulsions have a transparent aspect. Table 6.1 describes some other properties of the different types of emulsions. Emulsions can be classified according to the number of phases and by which phase is dispersed into the other. Binary (double) emulsions are the most commonly used in industry applications. Water-in-oil (W/O) and oil-in-water (O/W) are the two types of double emulsions that can be prepared (Faridi Esfanjani, Jafari, & Assadpour, 2017; Gharehbeglou, Jafari, Hamishekar, Homayouni, & Mirzaei, 2019); in fact, multiple emulsions are complex systems in which both W/O and O/ Table 6.1 Characteristics and properties of different types of emulsions. Emulsion type

Diameter range

Thermodynamic stability

Cremation rate

Surfactant concentration required for stabilization

Macroemulsion Nanoemulsion

1.0 100 μm

Unstable

High

Low/medium

20 500 nm

Metastable

Free to high

Microemulsion

,100 nm

Stable

Very low or zero Zero

High

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W emulsions are present at the same time. Nanoemulsions can also be prepared as binary or multiple systems, and O/W nanoemulsions are those most used in food applications due to their textural and functional properties. Nanoemulsions in food technology can be classified according to their desired role. In this regard, they can be categorized as follows: (1) encapsulation of active ingredients; (2) delivery of active ingredients; (3) preservation; (4) improvement of nutritional properties; and (5) modification of structural or textural properties.

6.2.2 Preparation methods of nanoemulsions Nanoemulsions, for their formation, require that energy be supplied to the system. The amount of input energy necessary for the preparation of nanoemulsions is directly related to the increase in surface area due to the creation of the new globules and interfacial tension (McClements & Jafari 2018b; Shamsara, Jafari, & Muhidinov, 2017). In practice, the energy will always be greater than that calculated from the expansion values of the surface area and surface tension because it does not take into consideration the effects of energy dissipation by the dispersing phase (e.g., heat or momentum) or other effects such as coalescence (Gharibzahedi & Jafari, 2018; McClements & Jafari, 2018a). According to the theory of emulsification, dispersion of the droplets in the dispersed phase requires the supply of shear forces (deforming inertial forces) sufficiently large in magnitude to overcome the intrinsic cohesive forces of the fluid to be dispersed (Jafari, He, & Bhandari, 2006, 2007b, 2007c). In the case of nanoemulsions, in addition to the latter, we must consider the effects of curvature, Laplace pressure ΔP (the pressure difference between the inside and outside of the drop), which is responsible for maintaining the spherical shape of the droplet, and, in the case of nanoemulsions, the greater amount of energy (stress) required to deform and break the small drops (Santana, Perrechil, & Cunha, 2013). The preparation methods of nanoemulsions have been classified as high energy and low energy, according to the mechanism of the energy delivery to the system to be emulsified.

6.2.2.1 High-energy methods In high-energy methods, the fluid is exposed to high shear forces or pressure differences in order to achieve disruption of the droplets. It is common to use mechanical stirrers equipped with suitable propelers, high-speed devices such as rotor-stator systems, high-pressure homogenizers, membrane systems, or ultrasonic devices (Jafari, Assadpoor, He, & Bhandari, 2008). These methods permit a simple industrial scaling up, and it is possible to produce emulsions with globule size with a narrow distribution (Villalobos-Castillejos et al., 2018). The main drawbacks are the use of relatively high concentrations of surfactants and the low efficiency in terms of energy dissipation: only 0.1% is effective for droplet breaking, whereas 99.9% is dissipated as heat during the homogenization process (Tadros, Izquierdo, Esquena, & Solans, 2004).

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6.2.2.2 Low-energy methods These methods are based on the inherent physicochemical properties of the surfactants for the formation of nanoemulsions. The processes unlike those of highenergy methods, occur under laminar flow and are directed by the chemical potential of the system. There are two main methods reported for the preparation of nanoemulsions by low-energy: spontaneous emulsification and phase inversion. In spontaneous emulsification, the latter is performed at the moment of contact of the two phases without the need for external forces (Mehrnia et al., 2016). In this, the physicochemical characteristics of the surfactant play a critical role in the formation of the emulsion. It has been described that the driving force in spontaneous emulsification comprises the rapid diffusion of the surfactant and/or solvent from the dispersed phase to the continuous phase. In some cases, water-miscible solvents (for O/W nanoemulsions) are used to facilitate the diffusion of the solvent and/or surfactant; through this methodology, it is possible to obtain the Ouzo effect (Botet, 2012). The use of partially miscible solvents has also been reported, and adaptations of the emulsification diffusion method have been proposed that allow obtaining food-grade nanoemulsions and nanocapsules (Mitri et al., 2012; ZambranoZaragoza, Mercado-Silva, Gutie´rrez-Cortez, Castan˜o-Tostado, & QuintanarGuerrero, 2011). On the other hand, in the phase inversion approach, changes in temperature (phase inversion temperature, PIT) or composition (phase inversion composition, PIC) drives the formation of nanoemulsions. In these techniques, change in surfactant curvature is produced as the emulsion switches from negative to positive (to form O/W emulsions) or vice versa (to form W/O emulsions) (Solans & Sole´, 2012). As is clear, in the PIT technique, a change in temperature induces spontaneous inversion of the curvature of the surfactant. Only high temperaturesensitive surfactants can be used in this technique, for example, polyoxyethylenetype nonionic surfactants. Finally, in the PIC technique, one of the components (water or oil) is added progressively to an isotropic mixture of the other component (water or oil/surfactant). As in PIT, surfactant spontaneous- curvature changes from negative to zero, lamellar, or bicontinuous structures are formed at zero curvature and when the transition composition exceeds the structures with zero curvature separated into metastable nanosize droplets (Solans & Sole´, 2012).

6.2.2.3 Selection of emulsifier or coemulsifier and compatibility of the food processes Emulsifiers are mandatory for inclusion in the formulation of nanoemulsions. If emulsifiers are not included, the nanoemulsion will rapidly break down due to the high surface area. Stabilizers or emulsifiers during emulsion improve kinetic stability and extend the food shelf life. Selection of the emulsifiers is a crucial step in the design of a nanoemulsion; in addition to contributing stability to the emulsion, the emulsifier also exerts an enormous effect on the functionality, structure, and texture of many foods (Jafari, He, & Bhandari, 2007a; McClements and Jafari, 2018b). Therefore their compatibility should be evaluated. In fact, a goal during the

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formulation of a nanoemulsion is to reduce the concentration of emulsifiers in order to reduce the cost, not to alter the taste, and not to be worried about safety concerns. Emulsifiers can be classified as follows: (1) surfactants; (2) protective colloids or hydrocolloids; and (3) finely divided particles. Several factors should be kept in mind to select the appropriate emulsifier type in the formulation of a nanoemulsion. For example, surfactants (small amphiphilic molecules) are sensitive to changes in pH, ionic strength, and temperature. To illustrate this, if a polyoxyethylene nonionic surfactant (Tweens or Spans) is utilized during the formation of a nanoemulsion, the processing temperature is crucial, due to the phase-inversion temperature behavior; if the temperature is increased, an emulsion with reduced droplet size is expected, and this has implications in stability and texture (Saberi, Fang, & McClements, 2013). Surfactants can be used for both high-energy and low-energy methods; however, in this latter method, very low interfacial tensions are necessary to facilitate the spontaneous emulsification. Under this condition, the surfactant alone is not sufficient to reduce the surface tension; in this case, a cosurfactant is added to the formulation to achieve the reduction. The most common cosurfactants in food-grade nanoemulsions are short- and medium-chain alcohols such as ethanol or cosolvents such as polyols like propylene glycol, glycerol, and sorbitol. Another aspect to consider is the origin of the emulsifier. Currently, natural emulsifiers are preferred over semisynthetic or synthetic ones. Natural emulsifiers, such as proteins derived from plants or milk, have been employed as effective surfactants during the formulation of nanoemulsions (Assadpour, Maghsoudlou, Jafari, Ghorbani, & Aalami, 2016; Gharehbeglou et al., 2019; Shamsara et al., 2015). Proteins comprise an excellent option because they have a high nutritional value and are GRAS. These proteins include soybean protein isolate, whey protein isolate, β-lactoglobulin (β-lg), and casein. The formulator should take into account that nanoemulsions require a high percentage of emulsifiers in the formulation; consequently, the emulsifier can modify the sensorial and textural properties of the food. For example, protective colloids or hydrocolloids are lyophilic macromolecules that can act as stabilizer or emulsifiers; in food technology, those most utilized are gums such as Arabic, guar, or xanthan, modified starches, modified celluloses, some types of pectin, and some galactomannans (Yousefi & Jafari, 2019). Protective colloids are good stabilizers to a greater degree than good emulsifiers (Dickinson, 2009). Their use in the stabilization of O/ W nanoemulsions is based on the steric repulsion effect at the interface and to the thickening of the aqueous phase, reducing the velocity of creaming. The use of protective colloids for stabilization is intrinsically bound to the modification of the textural properties of the food due to the protective colloids also acting as structuring/ thickening/gelling agents.

6.2.3 Applications of nanoemulsions and their effect on food Food nanoemulsions represent one of the most commonly used colloidal systems as ingredients in food formulation during food processing. These are used in

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beverages, juices, dressings, sauces, and ice cream, among many others, and they possess great stability, in addition to being clear and facilitating the incorporation of water-insoluble ingredients such as vitamin, essential oils, colorants, and flavors (Maswal & Dar, 2014). As mentioned in Section 6.2.1, nanoemulsions are used in foods to improve the performance of the formulations ingredients. This includes some functionalities that are described here.

6.2.3.1 Encapsulation of active ingredients The encapsulation of substances into nanoemulsions can adhere to the protection or solubilization of actives (Akhavan, Assadpour, Katouzian, & Jafari, 2018; Rafiee & Jafari, 2018). For example, in liquid foods such as beverages, it is common to use encapsulated food components such as oil-soluble flavors, vitamins, colorants, preservatives, and other bioactives in order to protect the active ingredients against degradation derived from external factors such as oxygen, light, or others (Joung et al., 2016; Kim, Ha, Choi, & Ko, 2014; Qian, Decker, Xiao, & McClements, 2012a). In line with the same example, in beverages, sometimes flavors or functional active ingredients can affect their clarity. Nanoemulsions are very attractive because they can solubilize and produce products with high stability and clarity. Other applications of encapsulation include masking the unpleasant taste or smell of some substances, increasing the bioavailability of some active ingredients or decreasing the evaporation of food aroma (Salem & Ezzat, 2018). More details have been provided in Chapter 8, Nanoencapsulation of Bioactive Food Ingredients.

6.2.3.2 Delivery of active ingredients Nanoemulsions are excellent carriers of both lipophilic/hydrophilic active compounds in food (Faridi Esfanjani, Assadpour, & Jafari, 2018; Rostamabadi, Falsafi, & Jafari, 2019a). Nanoemulsions are well tolerated orally and can deliver the active ingredients in a controlled manner, improving the nutritional value of some active substances in food. As in pharmaceutical products, nanoemulsions can improve the absorption of highly nutritional compounds, controlling the active release profile (RP) (Jafari, Paximada, Mandala, Assadpour, & Mehrnia, 2017b). The full details are discussed in Chapter 9, Enhancing the Bioavailability of Nutrients by Nanodelivery Systems.

6.2.3.3 Preservation Nanoemulsions are used for surface treatment in minimally processed foods. At present, many ingredients are of natural origin, such as essentials oils with antioxidant and antimicrobial properties. Considering the minimal sensory changes, the concentrations required are low, with the same or better effectiveness than the substance alone. This is because the interactions are increased, reaching the specific sites or interacting better with the food or with its structures and tissues (ZambranoZaragoza et al., 2018). Another point to take into account is the fact that essential oils contain terpenes, terpenoids, phenols, esters, and oxides, among other

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compounds. Also noteworthy is that they are, in addition, antiseptic or known for their antioxidant effects, resulting in interactions with food. Therefore the sensory perception will be modified. These components interact with cellular structures in foods such as meat, cereals, fruits, and vegetables. Together with the surfactant used in the stabilization of nanoemulsions, these promote modifications in the ionic charge and pH, which in turn will destabilize the nanoemulsions, thereby inducing the content to come in contact with the food and contributing to preservation (Prakash, Baskaran, Paramasivam, & Vadivel, 2018; Rezaei et al., 2019; Roy & Guha, 2018). Another field of application for nanoemulsions is as an edible coating for food preservation (Prakash et al., 2018). Nanoemulsions based on antimicrobial compounds such as essential oils have recently been explored as systems of preservation (Jamali, Assadpour, & Jafari, 2019; Yousefi, Ehsani, & Jafari, 2019); nanoemulsions have proven to be more effective against bacteria than conventional emulsions due to their reduced droplet size, providing an extensive covering area on the surface of the food (Acevedo-Fani, Soliva-Fortuny, & Martı´n-Belloso, 2017). Additionally, antimicrobial substances formulated in nanoemulsions can have a long lifetime due to the reduced degradation, increasing their bactericidal effect. To cite an example, Sessa, Ferrari, and Donsı` (2015) tested the functionality of different essential oil-loaded nanoemulsions (lemon, mandarin, oregano, or clove essential oils) incorporated into a chitosan matrix as preservation systems in leafy vegetables, specifically rucola leaf; the edible nanoemulsions provided a 3- to 7day increase in the shelf life in comparison to that of the untreated leaf. Another example is the application of an α-tocopherol nanoemulsion as a coating in a nopal mucilage matrix, applied on the surface of a fresh-cut apple. It was found that this system increased the storage time up to 21 days, decreasing the loss of texture and inhibiting the enzymatic browning. This was attributed to the antioxidant action of α-tocopherol, which diminishes polyphenol oxidase and pectin methylesterase activity. Also, the mucilage matrix may contribute to decreasing the oxygen absorption rate in the tissue and interacts with pectic substances, favoring the maintenance of texture (Zambrano-Zaragoza, Gutie´rrez-Cortez, et al., 2014a; ZambranoZaragoza, Mercado-Silv et al., 2014b).

6.2.3.4 Improvement of nutritional properties Nanoemulsions are suitable for improving the digestibility and bioavailability of nutrients. One example of the model molecules is the carotenoids; they exhibit poor water-solubility and low bioavailability, and their incorporation into many foods is a challenge at present (Rostamabadi et al., 2019a). The impact of the carrier oil and droplet size on the in vitro bioaccessibility of β-carotene nanoemulsions has been studied by Qian, Decker, Xiao, and McClements (2012b) and Salvia-Trujillo, Qian, Martı´n-Belloso, and McClements (2013). The reduction in the size of droplets leads to the increase in bioaccessibility, whereas the carrier oil also plays an important role in the bioaccessibility, formation, and size of mixed micelles (salt bile, free fatty acids). The latter are related to the composition of the carrier oil that makes

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up the nanoemulsions, illustrating the importance of starting materials. In another type of compound, the ability of nanoemulsions to increase bioaccessibility has been demonstrated; for example, vitamins, minerals, plant extracts, polyphenols, omega-3 fatty acids, phytosterols, and tocopherols. Some concerns with respect to the increase in toxicity due to the formulations of nutrients in nanoemulsions are also involved in the debate, and the increase in absorption and repeated intake according to some research could be a risk for the consumers (Addepalli et al., 2017).

6.2.3.5 Modifying structural or textural properties Nanoemulsions can be used as texture modulators. Depending on oil composition, internal-phase proportion, type and concentration of the stabilizer, and droplet size, nanoemulsions can exhibit different rheological behaviors from those of viscous liquids in viscoelastic solids (Dasgupta & Ranjan, 2018). For example, nanoemulsions have been employed to formulate low-fat foods such as mayonnaise and ice cream without sacrificing their texture, but offering a healthier option to consumers (Silva, Cerqueira, & Vicente, 2012). Low-fat nanoemulsions represent a formulation challenge because, due to their reduced oil content, they should be structured with emulsifiers or binders/fillers to increase viscosity. Pickering emulsions have been an excellent option for formulating highly stable low-fat nanoemulsions because the solid particles used for stabilization can act as thickening agents. Nanoemulsions are also utilized as ingredients in foods that are spreads, such as pˆate´s, sausages, dips, and other low-fat products. It has been shown that these help to avoid protein instability, due mainly to oxidation of polyunsaturated fatty acids, and in maintaining or improving the texture and sensorial quality of products, such as quercetin nanoemulsions (0.3 g/L) prepared by inversion of phases, in which Tween 80 or Brijs 30 were used as surfactants, revealing that nanoemulsions prepared with Tweens 80 as surfactant had a 63% inhibition of lipooxidation. It has also been highlighted that sensory changes with the use of nanoemulsions are minimal, while the use of free quercetin demonstrated evident changes in the flavor of the pˆate´ (de Carli, Moraes-Lovison, & Pinho, 2018). Another area where nanoemulsions are considered is in the conservation of margarines, creams, and in the formulation of beverages and juices, where it is important to consider the manufacture of functional foods. Table 6.2 presents some examples of nanoemulsion applications in food and beverage formulation. The main effect in food processing or storage is mentioned, highlighting the emulsifier type that, due to this, plays an important role for incorporation of nanoingredients. In some cases, the use of a natural surfactant is preferred; however, in others, the use of synthetic surfactants manages to maintain charges and can achieve the absorption of lipid compounds more easily (Chen et al., 2018).

Table 6.2 Effect of nanoemulsions as ingredients in food processing and shelf life. Food ingredient in nanoemulsions

Surfactant

Potential use/ application in food formulation

Function

Effect on food preservation

Quercetin (0.3 g/L)

Tween 80 Brij 30 Gypensides natural stabilizer (1%) Tween 20 Tween 80 and Span 20 (10%)

Incorporated into yogurt as stabilizer

Modified rheological behavior and stability of pˆate´ Low fat sausages, dressings and other emulsified foods Modifying viscosity

Maintenance of texture and sensorial quality de Carli et al. (2018)

Astaxanthin (2%) more antioxidant potential of β-carotene ϒ-oryzanol (0.1%) in 3% fish oil

Inhibition of lipid oxidation in spreadable pˆate´ Gypensides had lower fat digestion than Tween 20

Soy lecithin and medium-chain triglycerides (1:1) Poly-sorbate 80 oil phase and glycerol aqueous phase Tween 20 (0.3 0.7 mg/mL)

Ingredient (0.05/100 g) of nanoemulsion in hake hamburger Ice cream

Increasing shelf life

Beverages

Lycopene concentration optimization

Oregano essential oil

Curcumin/sunflower oil

Lycopene (0.015 0.085 mg/ mL)

Stability and sensorial acceptance

Thermal treatment and protection of astaxanthin, controls release of anti-oxidant Chen et al. (2018)

ϒ-oryzanol/fish oil increasing the water- holding capacity and stabilizes the yogurt Zhong, Yang, Cao, Liu, and Qin (2018) Decreasing the bacterial growth rate with incorporation of nanoemulsion and minimal sensorial changes Asensio, Quiroga, Huang, Nepote, and Grosso (2019) Viscosity modifier. Good acceptability at 50% of nanoemulsion and higher stability Borrin, Georges, Brito-Oliveira, Moraes, and Pinho (2018) Beverage stability, between 17 and 39 days depend of lycopene concentration Kim et al. (2014)

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6.2.4 Pickering nanoemulsions and stabilization of emulsified foods Pickering emulsions are stabilized by solid particles (nanosizes), and they have garnered increasing interest in recent years in food technology due to their high stability and because their use is possible as food-compatible emulsifiers such as nanosize GRAS substances as stabilizers, rather than as surfactants (Shaddel, Akbari-Alavijeh, & Jafari, 2019). The main challenge during the formulation of Pickering emulsions is to find or synthesize the solid particles with the appropriate wetting behavior. Similar to the rule of Bancroft, the rule of Finkle determines what type of emulsion (O/W or W/O) will result, depending on the wetting angle of the solid particle: if the wetting angle of the particle is .90 degrees, the particle has preference for the aqueous phase and curves the interphase into the formation of O/W emulsions, whereas if the wetting angle is ,90 degrees, W/O emulsions are formed. However, if particles possess wetting angles of ,30 degrees or .150 degrees, from the energy point of view, these particles would not create stable emulsions (Binks & Clint, 2002; Hunter, Pugh, Franks, & Jameson, 2008) There are various classes of particles that can be employed as Pickering emulsion stabilizers in food applications, including minerals, polysaccharides, fat crystals, synthetic polymers, and proteins (Linke & Drusch, 2018; Xiao, Li, & Huang, 2016). Some of the most used Pickering stabilizers in food emulsions and foams are starch granules (native or with chemical modification) (Rostamabadi, Falsafi, & Jafari, 2019b). Starch is considered a GRAS ingredient, it is biodegradable, thus sustainable, and it is inexpensive. Several examples have been developed from different starch sources: rice, maize, wheat, amaranth, and quinoa (Leal-Castan˜eda et al., 2018; Li, Li, Sun, & Yang, 2013; Rayner, Timgren, Sjo¨o¨, & Dejmek, 2012; Song et al., 2015; Tan et al., 2012; Timgren, Rayner, Sjo¨o¨, & Dejmek, 2011). Despite the great advances in the development of food-grade Pickering emulsions, there are very limited examples of nanoemulsions: the main limitation is the particle size of the stabilizer, which should be considerably smaller than the droplet size to cover the surface. For example, if the nanoemulsion has a droplet size of 100 nm, the size of the stabilizer particles should be ,10 nm in order to contribute enough particles at the interphase. Efforts in the development of Pickering nanoemulsions should be concentrated onto synthesized GRAS nanoparticles of less than 100 nm, and food-grade minerals, lipids, and polymeric nanocrystals profile themselves as promising candidates.

6.3

Polymeric nanoparticles in food processing

6.3.1 Definitions and classification of polymeric nanoparticles Over the last decade, research on nanomaterials for food processing and packaging applications has increased significantly. Thus nanoencapsulation can solve key food

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challenges, such as the following: (1) masking flavors; (2) preventing degradation (e.g., oxidation) due to processing conditions such as mechanical stresses, heat, pressure, or chemical changes; (3) improving stability (thermodynamic and kinetic) of different compounds, facilitating their application; (4) increasing solubility and enhancing bioavailability due to the higher surface area; (5) controlling the release of active ingredients (e.g., micronutrients, antimicrobial compounds, antioxidants, vitamins, phytosterols); and (6) potentiating spatial ubication in specific food targets, etc. Although there is not a universal nanoencapsulation system, polymeric nanoparticles represent the most studied and promising model of a nanomaterial in the food field (Brandelli, Brum, & dos Santos, 2017; dos Santos, Andrade, de, Flˆores, & Rios, 2018; Sarkar, Irshaan, Sivapratha, & Choudhary, 2016; Squillaro, Cimini, Peluso, Giordano, & Melone, 2018). These systems have attracted the interest of the food sector as emerging applications that could provide innovative solutions for the challenges previously mentioned (Abaee, Mohammadian, & Jafari, 2017; Katouzian & Jafari, 2019; Taheri & Jafari, 2019). For example, it is possible to produce active edible coatings when active molecules are encapsulated in polymeric nanoparticles. In these formulations, the compound may be delivered or have its delivery extended or controlled, to create an on-demand microenvironment that improves the properties of foods (e.g., increasing shelf life or nutrimental value). Edible coatings are packing systems that are highly predisposed to incorporate polymeric nanoparticles, due to the chemical compatibility of the nanoparticle matrix or shell and the composition of edible coating support. This ensures that the compounds will be well-dispersed over the surface of treated food (Sarkar et al., 2016; Zambrano-Zaragoza and Quintanar-guerrero, 2019). Polymeric nanoparticles are spherical colloidal structures containing bioactive molecules and macromolecular materials that measure between 10 and 1000 nm, typically 100 600 nm in diameter. Two types of polymeric nanoparticles can be described in terms of morphology and architecture: nanospheres and nanocapsules (Faridi Esfanjani & Jafari, 2016). Nanospheres are formed by a solid polymeric matrix, while nanocapsules are composed of an oil core surrounded by a polymeric membrane (Fig. 6.1A and B). In the case of nanospheres, the food-active molecule to be trapped can be adsorbed onto the surface or molecularly dispersed within the matrix. With nanocapsules, in contrast, the bioactive ingredient can be retained in an aqueous or oily core surrounded by a single thin polymeric wall (Galindo-Pe´rez, Quintanar-Guerrero, Cornejo-Villegas, & Zambrano-Zaragoza, 2018; MendozaMunoz, Quintanar-Guerrero, & Allemann, 2012; Zambrano-Zaragoza et al., 2018). Currently, polymeric nanocapsules comprise the nanostructures most utilized in food development, due to their stability during storage, high efficiency in encapsulating active molecules, their central cavity avoiding direct contact of the active molecule with the external environment, and/or chemical reactions reducing toxicity. They also have easy, large-scale preparation, and allow controlled release and/ or localization of the active molecules in specific regions of the food system, enhancing optimal bioactivity (dos Santos et al., 2018; Zambrano-Zaragoza & Quintanar-Guerrero, 2019).

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6.3.2 Preparation methods of polymeric nanoparticles In general, “milling” techniques are useful for preparing nanocrystals or other food pure nanomaterials of a material block, but not for submicronic systems with active delivery properties. Several techniques starting from “solutions” have been described in patents and research papers, beginning in the 1980s. These are reported as more suitable for obtaining polymeric nanoparticles for food purposes (Quintanar-Guerrero, De La, Zambrano-Zaragoza, Gutie´rrez-Cortez, & MendozaMun˜oz, 2012). They can be classified into the following: (1) in situ polymerization of dispersed monomers (for example, interfacial polymerization), and (2) dispersion of preformed polymers. Typically, methods based on preformed polymers are preferred due to their ease of implementation and lower potential toxicity. Thus polymeric nanoparticles prepared by polymerization can contain by-products that are not completely biocompatible, residues such as remaining monomers, oligomers, and catalysts that can be toxic, and the unlikelihood of cross-reactions with the bioactive ingredient. Five methods with their modalities are reported to obtain polymeric nanoparticles from preformed polymers with food applications: (1) solvent displacement or nanoprecipitation; (2) coacervation including ionic gelation; (3) solvent evaporation including double emulsion; (4) emulsification diffusion and emulsification diffusion by direct solvent displacement, and (5) salting-out (Hu et al., 2019). Fig. 6.2 summarizes the processing steps of each method. Except for coacervation, all of these techniques are similar in that they involve an organic solution (typically the solvent phase), containing the nanoparticle components, and an aqueous solution (typically the nonsolvent phase), containing stabilizers that will constitute the dispersion

Figure 6.1 Schematic representation of nanoparticles. (A) nonocapsules, release mechanism by partitioning process and (B) nanospheres, release mechanism by diffusion and/or erosion.

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medium. These form an emulsion as a prior step to the formation of nanoparticle dispersion. Also, these methods require purification (e.g., reduced pressure, ultracentrifugation, dialysis, or cross-flow filtration) and drying operations (e.g., spray drying or freeze drying) to obtain a powder amenable to administration. One of the main problems with these techniques is the poor encapsulation of water-soluble materials, which separate from the organic phase into a continuous aqueous phase. A double emulsion (water/oil/water) technique can be employed to overcome this drawback (Mendoza-Munoz et al., 2012; Pin˜o´n-Segundo, Mendoza-Mun˜oz, & Quintanar-Guerrero, 2012). Coacervation is a conventional chemical method used to form food microparticles, and at present, to prepare nanoparticles. Polymer solutions tend toward dehydration and phase separation by means of changes in conditions, such as the addition of an electrolyte (ionic gelation), pH, temperature, the addition of a nonsolvent, etc., producing polymer droplets in suspension. If this system is left to undergo separation, two liquid phases are observed: one concentrated colloidal phase, and another highly diluted phase. However, if the process is performed including a bioactive molecule and the particles are recovered before coacervation occurs, nanoparticles are obtained. A modality of coacervation is when two or more macromolecules opposite in charge are present. Coacervation is driven by electrostatic interactive forces (anion cation interactions), this is referred to as complex coacervation, as shown in Fig. 6.3 (Brandelli et al., 2017; Zambrano-Zaragoza & Quintanar-guerrero, 2019). Nano spray drying is a recent mechanical technique also used to prepare polymeric nanoparticles for food purposes (Arpagaus, Collenberg, Ru¨tti, Assadpour, & Jafari, 2018). Spray drying is the transformation of feed from a fluid state into a dried particulate form by spraying the feed into a hot, drying medium. To obtain nanoscale particle modifications in the conventional spray dryer, the equipment requires the following modifications (Assadpour & Jafari, 2019): (1) the atomizer (a piezoelectric-driven vibrating mesh atomizer is mounted to produce nanosize feed droplets); (2) the spray chamber (with vertical configuration to provide laminar air flow); and (3) product collection (by an electrostatic precipitator), depicted in Fig. 6.4. For this method, smooth-spherical particle morphology with particle diameters within the nanoscale range and homogeneous size distribution (SD) are obtained (Pe´rez-Masia´ et al., 2015; Prasad Reddy, Padma Ishwarya, & Anandharamakrishnan, 2019). The selection of a preparation technique needs to consider several aspects, such as the type of food application, the physicochemical characteristics of the bioactive to be encapsulated, food regulatory restrictions, and the desired physicochemical and morphological parameters of the polymeric nanoparticles (size, surface charge, hydrophilicity, controlled release time, etc.) (Mendoza-Munoz et al., 2012). Nonbiodegradable as well as biodegradable polymers from synthetic or natural sources have been widely investigated for different food applications, including coating, encapsulation, and packing. Their selection plays a key role in the most significant characteristics of the polymeric nanoparticles related to the active compound, for example, in the entrapment/encapsulation efficiency (EE) of active

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Figure 6.2 Schematic representation of nanoparticle preparation methods from preformed polymers.

compound, release rate, degradation process, and protective ability, to name just a few. Because of their biocompatibility, biodegradable polymers are preferred for food applications, because they can be degraded into acceptable biocompatible products by chemical or enzymatic processes, they are free of immunogenicity, and their physicochemical properties are predictable and reproducible. The most common biodegradable polymers are poly(alpha-hydroxy acids), poly (anhydrides), poly(ortho esters), poly(amino acids), chitosan, and alginates (Barbosa, Costa Lima, & Reis, 2019; dos Santos et al., 2018; Quintanar-Guerrero

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Figure 6.3 Schematic representation of coacervation processes: (A) simple without active substance; (B) simple with active substance and (C) complex with active substance.

et al., 2012). It is noteworthy that all of the materials involved in a nanoencapsulation process need to be GRAS. Choice of the coating material depends on the physical properties and functionality of the encapsulated material. Probably of greatest importance in this regard is the selection of solvents with minimal toxicity and food acceptability. This is an important issue in terms of considering a potential risk for human health and undesirable adverse effects on organoleptic food properties. Regardless of the polymeric nanoparticles drying process, the residual solvent needs to fall within acceptable food limits (Mendoza-Mun˜oz, Alcala´-Alcala´, & QuintanarGuerrero, 2016; Pin˜o´n-Segundo et al., 2012; Zambrano-Zaragoza & QuintanarGuerrero, 2019).

6.3.3 Characterization of polymeric nanoparticles Polymeric nanoparticles can be used as dispersion or dry powder. In general, their characterization can include all types of conventionally measured properties such as organoleptic and textural characteristics, composition, rheology, densities, pH, water content, etc. Other techniques such as Fourier-transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR), Raman spectroscopy (RS), and X-rays are performed to confirm a possible formation mechanism (e.g., ionic gelation), surface modification, or chemical cross-linking among functional groups (Ferna´ndez, Gonza´lez, & Parada, 2018; Hu et al., 2019). However, these properties are not sufficient to obtain real information of nanosystem behavior (e.g., stability and release behavior) and to acquire a better overall understanding of the relationship between food structures and polymeric nanoparticles (e.g., food application and product formulation). Thus more informative techniques based on nanometric

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Figure 6.4 Schematic representation of nanospray-dry process.

analysis are required to define polymeric nanoparticle properties (Jafari & Esfanjani, 2017). Some common specific properties to be characterized are as follows: 1. MD, SD, and polydispersity index (PDI). These are the first properties evaluated in a polymeric nanoparticle after preparation to confirm submicronic size, dispersion homogeneity, and surface area. Particle-size parameters allow the selection of an adequate preparation method and are tools to optimize the preparative variables. During storage, an increase in particle size suggests physical instability (e.g., particle aggregation or bioactive crystallization). A narrow SD corresponds to particle uniformity in suspension. In contrast, PDI values higher than 0.5 indicate broad distribution and a distribution between 0.1 and 0.25 demonstrates a narrow SD. The PDI is estimated considering the particle mean size, the refractive index of the solvent, the measurement angle, and the variance of the distribution. Various commercial equipment based on different principles is available to determine mean diameter (MD) and SD, such as laser diffraction (LD), Dynamic light scattering (DLS) or quasielastic light scattering (QELS), surface area analysis (Bruneaur Emmett Teller, BET), and X-ray diffraction peak broadening. The most used among these is DLS or QELS, which permits the description of mean size, particle-SD, and polydispersity in a simple and rapid manner. The method consists of particle interaction with light (e.g., laser beam), generally at an observation angle of 90 degrees, and the calculation model is generally based on the equivalent sphere principle (dos Santos et al., 2018). 2. Zeta potential (Ψz). Ψz is the method most frequently utilized to determine the surface charge of particles in dispersion. Ψz is a criterion to predict particle stability in suspension. This parameter is influenced by nanoparticle composition (e.g., polymer type) and the materials (e.g., stabilizers and electrolytes) in the dispersion medium. Ψz may also be applied to investigate whether a food bioactive ingredient is trapped in the polymeric nanoparticle or only adsorbed on its surface, and whether the components of the food substrate affect the surface charge. The actual technique to evaluate Ψz is based on the electrophoretic mobility that corresponds to the boundary of the surrounding liquid layer attached to the moving particles in the medium. Values higher than 30 mV (in absolute value) promote high stability and prevent particle aggregation (dos Santos et al., 2018).

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3. Morphology. Direct visualization of polymeric nanoparticles enables the confirmation of particle size and statistical distribution, and also can show the form, architecture, surface characteristics, porosity, etc. Observation of nanostructures requires the use of techniques based on wavelengths (e.g., electron beams and lasers) much smaller than those of the photons (optical microscopy). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) are the techniques-of-choice to analyze the morphology of polymeric nanoparticles. SEM shows their surface in three dimensions after coating the sample with a metal (e.g., gold), whereas TEM reveals ultrastructure as well as wall thickness for nanocapsules and polymer porosity for nanospheres (Jafari, Esfanjani, Katouzian, & Assadpour, 2017). TEM analysis of nanoparticles is generally performed after the freeze-fracture of nanoparticles (Hu et al., 2019). 4. Loading capacity (LC), EE, and RP. The main purpose of a polymeric nanoparticle is to function as a platform that contains the bioactive in sufficient quantities to render it in effective amounts on the food substrate, while LC, EE, and RP are the parameters to evaluate this function. LC is the amount of the active ingredient loaded per unit weight of nanosized system indicating the mass percentage of the nanoparticle that is due to the encapsulated active ingredient [%LC 5 (Entrapped active/nanoparticle weight) 3 100]. EE is the percentage of active ingredient that is successfully entrapped within the nanoparticles [%EE 5 (bioactive added 2 bioactive unentrapped)/bioactive added 3 100]. Both are variable parameters dependent upon the physicochemical properties of the bioactive ingredient, fabrication process, and type of polymer and stabilizers used. Specifically, for nanocapsules, entrapment within the core is related to the solubility of active ingredient in the oily phase. If, during optimization, LC and EE are high, the quantity of active in nanoparticles required for a specific effect on a food can be reduced. LC and EE can be measured after preparation and separation of polymeric nanoparticles from the continuous phase. Some typical separation techniques include ultracentrifugation, size exclusion chromatography, ultrafiltration, or tangential filtration and dialysis. The quantification technique is linked to the chemical structure of active ingredient and UV-visible spectrometry, HPLC, and U-HPLC are frequently used (dos Santos et al., 2018; Uskokovic & Stevanovic, 2009). The RP provides critical information concerning the polymeric nanoparticles used to assess product safety and efficacy (Ganje, Jafari, Tamadon, Niakosari, & Maghsoudlou, 2019). This parameter also provides details on the release mechanism and kinetics, enabling a rational and scientific approach to product development. Release studies on food can be performed under different conditions (temperature, pH of the dissolution medium, stirring, containers, etc.) depending on the food properties, the process involved, and storage temperatures (dos Santos et al., 2018). The RP of polymeric nanoparticles is currently evaluated employing methods such as sample and separate (SS), continuous flow (CF), and dialysis membrane (DM), and novel techniques such as voltammetry and turbidimetry. Currently, the method most used is dialysis, which consists of the formation of a dialysis bag with a clip through which nanoparticles are added with release media and the bag is subsequently sealed. This sack is placed in a vessel containing sufficient release media to maintain sink conditions and agitated to minimize unstirred water-layer effects. Samples are taken with a replacement of fresh media at periodic intervals and the active ingredient is quantified by an analytical method to build the slope’s released amount (Mt) versus time (t) (Pereira, Soares, Monteiro, Gomes, & Pintado, 2018). 5. Stability of polymeric nanoparticles. The stability can be performed determining the mean size and/or visible organoleptic changes under different conditions and time intervals. Recently, different equipment (e.g., Turbiscan) based on multiple light scattering (MLS) has been proposed to detect the destabilization phenomena of diluted and concentrated

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dispersions at a very early stage (Gonza´lez-Reza, Quintanar-Guerrero, Del Real-Lo´pez, Pin˜on-Segundo, & Zambrano-Zaragoza, 2018b). MLS equipment detects the intensity of both transmitted and backscattered light over the whole cell height. These intensities permit direct monitoring of local physical heterogeneities with vertical resolution down to 20 μm. Thus nascent destabilization phenomena can be detected and monitored over time at different intervals (Mengual, Meunier, Cayre´, Puech, & Snabre, 1999).

6.3.4 Mechanism of active delivery by polymeric nanoparticles One important tool for designing a food-active formulation and as an experimental verification of a release mechanism is to predict the release of active ingredient as a function of time using mathematical models (Assadpour, Jafari, & Maghsoudlou, 2017; dos Santos et al., 2018). Thus to identify a particular release mechanism, it is necessary to obtain experimental data of statistical significance and to find the mathematical model with best correlation on considering the physical characteristics of the system and the properties of the release system; in this case of the food environment and the characteristics of nanoparticles (Siepmann & Peppas, 2011). In the food field, there are few studies that address this issue. Release models are generally based on diffusion equations. Diffusion is highly dependent on the properties of the material that constitutes the release platform and the morphology and architecture of the system. In the case of encapsulated active molecules in biodegradable polymers, release depends on polymer type, structure (nanosphers or nancapsules), quantity of active loading, and loading method. Considering the large specific area of polymeric nanoparticles, it is expected that the release rate will be more rapid than that of other food-release systems (e.g., microparticles or coatings). Thus polymeric nanoparticles are not recommended for long active-RPs. Although the architecture of nanospheres and nanocapsules can correspond to matrix and capsular systems, respectively (Fig. 6.1A and B), their release mechanism does not correlate with these models. In general, when the active ingredient is absorbed on the surface of nanoparticles, release is practically immediate when the system comes into contact with the food media by a simple partitioning process. When the active ingredient is encapsulated within the nanosphere matrix, diffusion into the surrounding food environment prevails. When the nanosphere is formed by a biodegradable polymer, diffusion and erosion will be involved (Sarkar et al., 2017) (see Fig. 6.1B, box below). Korsmeyer Peppas semiempirical model can be employed to determine the release mechanism (Fickian or non-Fickian) and release type (time dependence, tn): Mt =MN 5 k 3 tn

(6.1)

where Mt/MN is the fraction of bioactive released at time t, k is the kinetic rate constant, and n is the release exponent characterizing the different release mechanisms. In their logarithmic form:
log Mt =MN 5 nlogt 1 logk

(6.2)

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The exponential n can be obtained from the slope of the graphics of log (Mt/ MN) versus log t. Then, when n 5 0.5, release kinetics follow Fickian diffusion. The Higuchi equation can be applied in this case, suggesting matrix-like behavior. For n , 0.5, the release mechanism is non-Fickian, meaning that both diffusion and degradation occurred together. For 0.5 , n . 1.0 refers to an anomalous transport mechanism. Finally, a value of n 5 1.0 correlates with zero-order kinetics (Biswal & Saha, 2019). In contrast, the release of active ingredient from nanocapsules with an oily core is related to instantaneous partition processes found within immiscible phases if the food is rich in water, or dissolution if the food is of a lipophilic nature. The membrane wall of nanocapsules practically does not control the release; thus zero-order kinetics are not observed (see Fig. 6.1A, box below). Our group has found that nanocapsules incorporated into coatings fit better to the Higuchi model (ZambranoZaragoza, Quintanar-Guerrero, Del Real, Pin˜on-Segundo, & Zambrano-Zaragoza, 2017). The Higuchi equation was utilized to quantify active release from thin ointment films, containing a finely dispersed active ingredient into perfect sink conditions. Based on a pseudo-steady approach, direct proportionality between the cumulative amount of the active ingredient released and the square root of time (Mt 5 KHt1/2) can be demonstrated in a physically realistic meaning. Thus when the nanocapsules are dispersed in a coating film, the release behavior is explained as a matrix system similar to that obtained with the Higuchi model (Siepmann & Peppas, 2011). Bioactive leakage from nanocapsules has been reduced by additional coatings (e.g., PEG, phospholipids). Recently, polymer nanocomposites, hybrid nanoparticles, and stimuli-response polymeric nanoparticles have been proposed for new functional food applications (e.g., antibacterial packaging and oral bioactive delivery) (Gonza´lez, Olmos, Lorente, Ve´laz, & Gonza´lez-Benito, 2018; Wang, Bae, Lee, & Luo, 2018).

6.3.5 Application of polymeric nanoparticles in food processing Polymeric nanoparticles possess many advantages in relation to other nanosized systems. Using polymers makes it possible to achieve higher efficiency of encapsulation, LC, and the controlled release of functional ingredients. In addition, thermolabile, light, and oxygen-sensitive substances can be used during processing, the selection of polymers used, being important in the preparation of these nanoparticles. It is possible to have polymers with high glass transition temperatures, as in the case of polysaccharide matrices, which allow the achievement of stable ingredients during thermal processing, and subsequently, the release of substances during storage because of the modification of structural polymers by mechanisms of erosion, degradation, or solubilization due to moisture content, pH, and ionic charge. These exert beneficial effects that promote the increased shelf life of food products (Ubbink, 2016). It is also possible that, at the time of application in the food matrix, polymeric nanoparticles decrease their ionic charge, destabilizing the system and modifying the Ψz, thus releasing the total content. Therefore it is

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important to consider the superficial charges for better control of release in the functional ingredient (Cano-Sarmiento et al., 2018). Another important aspect to consider in nanoparticle preparation for use as an ingredient in food processing is the pH and ionic strength, since modification of the latter results in structural changes in the components of food or of the phase separation, in yogurts, beverages, and fruit concentrates. In addition, kinetics of release are dependent on pH, soluble solids, and temperature (Gonza´lez-Reza et al., 2018b). Some studies consider the preparation of nanoparticles using anionic and cationic polysaccharides in the release kinetics of curcumin, using fucoidan as an anionic polysaccharide and chitosan as a cationic polysaccharide, observing variations in Ψz due to the fucoidan:chitosan ratio and showing that Ψz was negative at pH 5 7 and 7.4, with values of 218 and 214 mV, respectively, while at pH 5 6, zeta potential was minimal and negative equal to 24 mV. This was due to the deionization of ammonium ions, which gives rise to a rapid disintegration of the biopolymer and rapid release of curcumin, while at pH 5 4 and 7, there was a slower release of curcumin in comparison with nonencapsulated systems, being useful in release control in the digestive tract and in food with different pH values (Barbosa et al., 2019). However, according to the pH of foods, it would also be important to take this into account for the release of substances during storage or the release of flavors or aromas during consumption of the product. Many hydrocolloids are employed as natural polymers to prepare nanocapsules, because their nanometric size increases their capacity to absorb water, serving as texture modifiers, thickeners, and gelling agents, among others (Li & Nie, 2016). Other major possibilities that demonstrate polymeric nanoparticles as ingredients for food formulation include greater thermal resistance; inorganic materials can be utilized, such as nanoclays. In addition, these materials also allow for better release control due to the increase of nanostructure tortuosity (Trbojevich & Ferna´ndez, 2016). Lipophilic antioxidant encapsulation is also important to decrease the oxidation of oils; the latter would quickly lose their antioxidant capacity because, in general, they are sensitive to oxygen, light, pressure, temperature, and other processing conditions, such as the use of biodegradable natural polymers or synthetic polymers for trapping or encapsulating ingredients in nanosize, limiting the loss of active ingredients during processing. In addition, it is possible to have controlled release during storage. Thus in the preparation of ethyl cellulose nanoparticles with ϒ-oryzanol (a mixture of sterols and ferulic acid) stabilized with polyvinyl alcohol, an increase was found in load capacity, and greater thermal resistance and better control release were also achieved. Therefore on being more stable, it is possible to use this in beverages and oil stabilization, even when the oils are heated for frying and the oil remains at high temperatures (Ghaderi, Ghanbarzadeh, Mohammadhassani, & Hamishehkar, 2014). Epigallocatechin gallate, a powerful antioxidant, was nanoencapsulated in a mixture of zein/chitosan to achieve controlled release in food systems, showing that electrostatic interactions and hydrogen bonds are responsible for nanoparticle formation; the interaction of nanoparticles among nanosystems improved EE (65 80%), with Ψz positive from 21.2 at 34.9 mV, an important consideration in

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the release of antioxidant substances into food products. Therefore epigallocatechin gallate nanoencapsulated in zein/chitosan can be used for the protection of foods rich in fats, such as ice cream and margarines (Liang et al., 2017). Polymeric nanoparticles are important in encapsulation of colorants since, at present, natural colorants are preferred by the consumer (Mahdavee Khazaei, Jafari, Ghorbani, & Hemmati Kakhki, 2014; Mahdavi, Jafari, Ghorbani, & Assadpoor, 2014). These are sensitive to light, oxygen, temperature, pH, and ionic strength. The use of polymers and the nanosize structure entertains great advantages in the preparation of systems loaded with coloring substances, such as carotenoids, flavonoids, anthocyanins, and other natural pigments. Polymeric nanoparticles represent an option for protecting colorants during processing, reconstituting the natural color lost during processing and, especially, for the development of attractive products (Almeida et al., 2018; Gonza´lez-Reza et al., 2018). Encapsulation of colorants also has the objective of increasing solubility and facilitating incorporation into food matrices. Colorant nanoencapsulation increases the solubility of these and facilitates their incorporation into food matrices. Among the colors that have been most nanoencapsulated in polymeric structures, we find the carotenoids, in that these are widely employed in the dairy industry, in the preparation of functional beverages, and in the development of products with health benefits (Gonza´lez-Reza et al., 2018b; Rao & McClements, 2012; Rostamabadi et al., 2019a).

6.3.6 Effect of polymeric nanoparticles on physicochemical properties of food during storage Polymeric nanoparticles are preferred in the development of new products in which stability, easy incorporation, and compatibility are important, because these encapsulation processes also allow obtaining ingredients in powder form, which facilitates the formulation and processing of foods and beverages. Polymeric nanoparticles possess important characteristics that define the compatibility between the foods and components of nanosize systems. Thus the Ψz and pH effects, as well as the surface composition of the food, must be taken into account in order to allow for adhesion and chemical compatibility with polymeric nanoparticles and the release of active ingredient (Liang et al., 2017; Weiss et al., 2006). Food products are developed at different pH values, solid content, and water activity; therefore a large number of polymeric nanoparticles can respond to the pH, surface charge, osmolarity, and water content. For example, in the nanoencapsulation of epigallocatechin gallate with zein/chitosan utilized to release this antioxidant into food, changes in antioxidant capacity in relation to zein amount (72 288 mg) were evaluated, revealing that a high concentration had a positive Ψz between 21 and 35 mV. However, this has a limit, since, at a concentration of 288 mg, Ψz decreased slightly, finding that Ψz is also influenced by the concentration of epigallocatechin gallate; when increased to 8 mg, the Ψz decreased, in turn decreasing the rate of release of the active ingredient into the food. Therefore physicochemical analysis suggested that electrostatic interaction was the main factor in nanoparticle

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preparation, and this will be a relevant factor when it is incorporated into a food (Liang et al., 2017). Polymeric nanoparticles have a potential use in beverage and semisolid foods, in which a homogeneous distribution of antioxidant and natural colorants is necessary, considering a sensorial balance in the nucleus of the food. The main physical properties of polymeric nanoparticles include modification of viscosity, density, and light dispersion, permitting the development of stable and attractive products for the consumer. However, the physicochemical properties of the food and beverages formulated with nanoparticles as ingredients can vary considerably during storage, depending on the polymer used in the preparation of nanostructures and the composition in terms of pH, soluble solids, proteins, lipids, and water content of the food. For example, when poly-ε-caprolactone, a biodegradable synthetic polymer, was employed, a slight acidification of the product was observed, due to polymer degradation, which in turn can contribute to the modification of other components in the food, producing color degradation (Gonza´lez-Reza et al., 2018b). The physicochemical properties of beverages and other functional foods are affected by the type of polymer used in the preparation of nanoparticles, such as polysaccharides, proteins, and their modified structures, as well as synthetic biodegradable polymers. When proteins are utilized, it is necessary to consider different parameters, which will exert an influence on the stability of nanostructures, therefore on the matrix of food that is applied. In this way, the factors to be considered include functional groups, molecular mass, pH, dissolution grade, and cross-linking of food, as well as sensitivity to the temperature during storage time, since these properties will exert an influence on the strength of nanoparticles and the release of functional ingredients in such a way that beneficial changes in the food are produced for maintaining viscosity, color, and general food stability (Saxena, Sachin, Bohidar, & Verma, 2005). Modifications associated with proteins such as casein, gelatin and zein, are widely used in nanoparticles, such as in the shell or matrix during nanoencapsulation of food ingredients, that interact with lipids, proteins, carbohydrates, and other components of foods, producing stability only for some time. This is because the stabilization of these systems are functions of the hydrogen and amino bridges, which are clearly modified by the effect of pH, temperature, and water content. Therefore the physicochemical changes expected during storage will comprise the phase precipitation and separation, syneresis, color changes, and the loss of sensorial quality. The majority of studies carried out have focused on the simulated stabilization of polymeric nanoparticles. Thus it will be necessary to conduct studies on potential nanoparticle food interactions in relation to final application and function during storage. Polysaccharides represent other polymers that are employed in the preparation of nanoparticles. The most likely interactions with food will be hydrogen bonds, with the hydroxyl group (Kilburn, Claude, Schweizer, Alam, & Ubbink, 2005), the factor that will exert the greatest effect on the behavior of incorporated nanoparticles, as ingredients in the nuclei of food. Water will cause changes in viscosity, and thus in the rheological behavior of the food, increasing the release of substances during the storage step.

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Nanofibers, nanolaminates, and nanocrystals

6.4.1 Preparation methods 6.4.1.1 Nanofibers Nanofibers are traditionally produced by electrospinning, a technique used since 1934 for the manufacture of continuous fibers [mainly of polymers, but also with ceramic compounds (Dai, 2016)] with a diameter of nano- to micrometers. A controlled mesh deriving from the nanosize usually offers better mechanical properties, and the high surface area allows the adhesion or release of active ingredients with unique properties (Torres-Giner, 2011). Electrospinning for nanofibers is based on an electrical charge for drawing fibers from a conductive liquid (Rezaei, Nasirpour, & Fathi, 2015). The voltage is gradually increased and, when a sufficient electric charge is achieved on the tip of the syringe and the conductive liquid, the force of electrostatic repulsion exceeds the force of surface tension (Dai, 2016). Then, the droplet is stretched, with a critical point reached where the repulsion force exceeds the surface tension, and a liquid propulsion is released from the surface, creating a conical shape: the Taylor cone. The jet tip is directed toward the opposite electrode where the collector is located. The jet dries during the propulsion (Rezaei et al., 2015). There is a strong relationship among the parameters of the electric field, physical and chemical conditions of the polymer, and the conductive liquid. Fig. 6.5 shows the electrospinning process used to obtain nanofibers. It is possible to obtain different diameters, lengths, morphologies, and framework types. Some of the polymers widely used in food include poly-ε-caprolactone, poly(L-lactic acid), polyvinyl pyrrolidone, cellulose acetate, casein, soy protein, chitosan, and collagen (Rostami, Yousefi, Khezerlou, Aman Mohammadi, & Jafari, 2019). The main applications in the food area are the packaging and encapsulation of active ingredients. In packaging materials, applications consist of the release of antimicrobial compounds, in some cases for antioxidant applications (Torres-Giner, 2011), and the use nanofibers for enzyme immobilization for a reaction surface with food ingredients. This method permits increased stability and higher activity. At present, there are instruments for industrial production of nanofibers that permit obtaining fibers with a length of up to 1.6 m and a capacity of 40 million square meters of coated material annually in a single production line (Torres-Giner, 2011).

6.4.1.2 Nanolaminates Nanolaminates for food applications are usually produced as thin polymer films formed by the alternating physisorption of polyanions and polycations, by means of the layer-by-layer (LbL) technique. The incorporation of nanolaminates allows nearly precise control of the thickness of the multilayer (nm), which is easily moldable to any food surface, and one of its greatest attractions is the incorporation of active ingredients (Arnon-Rips & Poverenov, 2018). Nanolaminates fabricated by means of the LbL technique require an electrically charged surface and involve immersion in different polyelectrolyte solutions, followed by a wash after each deposition. For this

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reason, the multilayer formation of nanolaminates by LbL is driven by electrostatic interactions, which are the main driving forces (Klitzing, 2006). This sequential follow-up has been commonly observed in several reports on food physisorption and where the Ψz changes sign and magnitude. Inversion of the electric charge in some substrates is not necessary, and slight changes in the Ψz may be sufficient for the formation of the multilayer (Klitzing, 2006). The formation of each layer will depend on the interaction of two polyelectrolytes. In consecutive layers, the substrate layer in turn will depend on the previous interaction. For example, in a nanolaminate LbL comprising alginate chitosan alginate chitosan alginate, the interaction of first and second alginate layer will entertain a different potential. A classic method of nanolaminate deposition on a fruit is that followed by Medeiros et al. in the edible coating of pectin/chitosan mangoes. The mango was washed with water and left to dry. After this, the mango was immersed in pectin solution (pH 5 7.0) for 15 minutes, rinsed with distilled water with pH 5 7, and dried with a nitrogen flow. Afterward, the same mango was immersed in the chitosan solution at pH 5 3 for 15 minutes, rinsed with distilled water with pH 5 3, and dried with nitrogen flow (Bartolomeu, Pinheiro, Carneiro-Da-Cunha, & Vicente, 2012). Generally, the number of nanolaminates deposited is five.

6.4.1.3 Nanocrystals Nanocrystals are nanosize active ingredient particles that are stabilized by surfactants, polymers, or a mixture of both (Lin, Huang, & Dufresne, 2012). This concept implies a dispersed system of crystalline or partially crystalline particles (Habibi, Lucia, & Rojas, 2010). When there is a change from a crystalline into an amorphous state, the final formulation, these are denominated amorphous nanoparticles. Sometimes the change into the amorphous and the nanosize state can be combined to favor the process of dissolving active ingredients (Patel, Sharma, & Mehta, 2018). The nanocrystal concept also refers to a system with high bioactive loading (nearly 100%), unlike other nanoencapsulated systems in which the active

Figure 6.5 Electrospinning to produce nanofibers. A high voltage is applied to a polymer solution, the conductive fluid is directed toward the opposite electrode, and it is along the pathway that this solidifies, creating fibers of nanometric size.

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ingredient depends on the composition of the main matrix. Another advantage of nanocrystals is the increase in apparent saturation solubility, a property dependent on size. Nanocrystals, like other colloidal systems, have a high Gibb’s free energy; therefore the addition of stabilizers that possess a charge repulsion mechanism or steric phenomena is necessary (Patel et al., 2018). Nanocrystals can be produced in two ways; bottom-up and top-down. The bottom-up method is based on particles obtained from a molecular solution into nanoparticle size; taking advantage of the classical precipitation process, the active ingredient dissolved in a solvent is added to a nonsolvent (Malamatari, Taylor, Malamataris, Douroumis, & Kachrimanis, 2018). Some variants of the classical method may include sonication, ultrasound, multiinlet vortex, supercritical fluids, and evaporative precipitation. Some of the main parameters studied are type of solvent, type of nonsolvent, proportion of both solutions, proportion of the bioactive, type and concentration of stabilizer, type and speed of agitation, and reactor, among others. With the bottom-up method, there is greater control in the size of nanocrystals and in particle-SD, while with top-down methods, the process starts with large-size crystals that decrease to a small size. The most common methods include wet-milling, microfluidization, and highpressure homogenization (Malamatari et al., 2018). In the latter two, a stabilizing agent is used to maintain the size of the nanocrystals. Energy consumption is greater by means of this modality, and less control is observed in the size and distribution, however, high bioactive loading is obtained.

6.4.2 Use of nanolaminates in edible coating materials Edible coatings are intended to maximize sensorial parameters and shelf life by control of moisture transfer, gas exchange, or oxidation processes (Dhall, 2013). Edible coatings have a long history in food with the participation of wax coatings to control the transpiration of water in lemons and oranges. Edible coatings must withstand the internal changes of the food and maintain resistance against various environmental parameters such as temperature and humidity. One of the most attractive applications of edible coatings is the possible incorporation of various active ingredients into the coating (Vahedikia et al., 2019). Some examples can be antimicrobials, antioxidants, nutraceuticals, antibrowning agents, colorants, and flavors (Dhall, 2013). Edible coatings are traditionally made up of polysaccharides (cellulose, starch, gums, and chitosan), proteins (casein, whey protein, collagen, gelatin, keratin, wheat gluten, soy protein, peanut protein, corn-zein, and cotton seed protein), lipids (waxes, oils, fatty acids, monoglycerides, resins, and preparations with emulsions), or combinations of these or derivatized products (Dhall, 2013). Lipid composition is the most attractive of these due to the hydrophobic nature of lipids and their greater ability to regulate water loss. Edible coatings are usually applied to some fresh fruits and vegetables, while for meat, these are generally in the packaging material. Edible coatings are also represented as edible nanolaminates, constructed as very thin coatings of food-grade materials such as polysaccharides, proteins, or combinations with lipids. Nanolaminates used as edible coatings are generally prepared by

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means of LbL procedures, as described in the previous section. The addition of multiple layers is controlled by opposing electrical charges from a defined substrate, and with different repetitions of the immersion of substrate into coating solutions. The LbL procedure is also referred to as an electrodeposition technique (Fig. 6.6) that allows for adequate adhesion onto hydrophilic surfaces, offering minimal processing of fruits and vegetables. As noted for edible coatings, it is possible to incorporate active ingredients into the thin layers (Shit & Shah, 2014), even combining different active ingredients into each layer. For example, in an ideal case, among the multilayers, proceeding from the center to the outside, we would first find an antibrowning layer, and after this, the antioxidant, antimicrobial, colorant, and flavoring layers. Acevedo-Fani, SolivaFortuny, and Martı´n-Belloso (2018) prepared LbL folic acid-loaded nanolaminated films from an alginate/chitosan composition. These authors used PET sheets and positively charged quartz slides. After this, LbL buildup was performed by immersion in an anionic alginate solution. The washes were required for better adhesion of the next thin layer; subsequently, formation of the nanolaminate was continued by immersion in cationic chitosan solutions. A total of 20 layers were deposited on the initial substrate. Some critical factors included wash times, immersion times, and concentrations of the anionic and cationic solutions. In this study, the authors added hydrophilic active ingredients through the postdiffusion method. It is expected that, by means of this procedure, the folic acid is loaded within the nanolaminates by diffusion and immobilization in the binding sites inside the structure. The authors demonstrated an incorporation of 70 μg folic acid for each cm2. With this procedure, folic acid maintained its adequate stability under exposure to UV light exposure. In another study, Brasil, Gomes, Puerta-Gomez, Castell-Perez, and Moreira (2012) prepared an edible nanolaminate coating of chitosan/pectin with trans-cinnamaldehyde as an antimicrobial encapsulated in β-cyclodextrin. The preparation was applied onto fresh-cut papaya. Prepared in this fashion, papaya accrued greater acceptance by the food-tasting panelists and was characterized by maintaining its color and texture. Edible coatings by means of nanolaminating extended the shelf life of fresh-cut papaya up to 15 days at 4 C; without the coating, the shelf life was ,7 days. Interestingly, the authors mention the influence of fruit packaging on the functionality of edible nanolaminate coating. While nanolamination confers adequate protection, traditional robust packaging is always a guarantee of additional protection; in this study, it was demonstrated by the use of Ziploc packaging (Brasil et al., 2012). On the other hand, Medeiros et al. (2014) prepared an edible nanolaminated coating of alginate/lysozyme on “Coalho” cheese shelf life. The nanolaminate was obtained by LbL methodology, and five alternate layers of alginate and lysozyme were deposited onto the “Coalho” cheese. To monitor the mechanism of basic formation of nanolaminates by the attraction of electrical charges, control of the pH was an important factor in the procedure. The authors confirmed deposition of nanolaminates by UV-vis spectroscopy, contact angle, morphology by SEM, and gas barrier properties. The shelf life of cheese was prolonged by the combined factors of gas barrier and antibacterial action (Medeiros et al., 2014).

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In the same manner, Chiou et al. (2018) prepared edible nanolaminate coatings by means of an LbL technique of chitosan/alginate applied to fruit bars enriched with ascorbic acid. The fruit conserved a high content of ascorbic acid, antioxidant capacity, firmness, and fungal-growth prevention for 6 additional days, and high shelf life. Nanolamination did not prevent the browning phenomenon. Interestingly, the authors evaluated the performance of two types of chitosan according to their sources of origin: animal and vegetable. The results revealed that there were no important differences according to the chitosan type in the performance of nanolaminate. On the other hand, Bartolomeu et al. (2012) obtained pectin/chitosan nanolaminates by means of LbL for application on “Tommy Atkins” mangoes. The authors noted that a basic tool for determining the formation of the nanomultilayer was the change in contact angle. The novel edible coating produced conservation of up to 45 days with adequate sensory properties. As in other studies, the authors of this research employed the in vitro method of nanolaminate deposition onto a transparent PET film that was first aminolyzed/charged to evaluate water vapor, oxygen, and carbon dioxide permeabilities. Afterward, the aminolyzed PET was positively charged with HCl to attach pectin, then washed, and chitosan was subsequently applied. A total of five nanolaminates were deposited. In general, the nanolaminate reduced gas flow, mass loss, and total soluble solids, and presented higher titratable acidity (Bartolomeu et al., 2012). In a similar manner, Salas-Me´ndez et al. (2019) prepared edible nanolaminate coatings with antimicrobial applications by means of Flourensia cernua extract loaded to extend the shelf life of tomato. The authors applied five alternating films of alginate/chitosan nanolaminates. Formation of the coating was also demonstrated by the changes in contact angle. In general, the tomato controlled gas exchange, reduced weight loss, and extended shelf life (Salas-Me´ndez et al., 2019).

Figure 6.6 Edible coating by nanolaminates, a multilayer addition maintained by electric charges with a controlled thickness.

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6.4.3 Physicochemical, textural, and color changes in nanocoated foods Due to the increase in the demand for minimally processed foods and preferably those with health benefits, in recent years there has been a great interest in the development of edible coatings. The functionality of these coatings has clearly been improved when nanolaminated coatings are utilized in order to preserve the microbiological, physicochemical, and sensory quality of fresh foods such as fruits, vegetables, and ready-to-eat products, as well as meat and fish. Generally, nanocoating considers the use of lipophilics or hydrophilics of natural origin with a function as antimicrobials and antioxidants, which depends on the nanocoating-food interaction to fulfill the function of efficient food preservation. The functionality of these nanostructures incorporated into the polysaccharide or the protein matrix is attributable to their homogeneous distribution on the food surface, regulating gas exchange, and the release of compounds trapped inside the matrix. This has been shown in nanocoatings prepared with SLNs supported by xanthan gum, demonstrating that these contribute to reducing physiological weight loss as well as to textural changes by decreasing the activity of pectin methylesterases. In addition, they exerted an effect on phenol metabolism, in that they clearly modified the maturation process. Another effect of nanocoatings is their distribution in the pericarp, similar to the distribution of natural waxes in the fresh product, demonstrating the functionality of these when used in the nanometric size (Garcı´a-Betanzos et al., 2017). It is important to highlight that for the physicochemical modifications to the food, the use of the nanosize systems used for coatings must take into consideration the following: (1) type of oil and interaction with the product; (2) amount of oil employed in the nanostructured system; (3) type of surfactant used; (4) oil used as dissolvent of active substance; (5) pH at which it will be applied; (6) antimicrobial activity of coating including all components; and (7) degree of processing. All of these are associated with physicochemical, textural, and color changes. Next, a brief summary will be presented on the effect of edible nanocoatings applied as functional ingredients during minimal treatments carried out on fruits, meats, and cheeses, with the purpose of highlighting their effectiveness in the increase of shelf life. We will describe the effect of nanosize systems on the physicochemical, textural, and color parameters in these foods.

6.4.3.1 Effect of nanocoatings on the physicochemical properties of food Nanocoatings have the purpose of maintaining the physicochemical composition of minimally processed products as long as possible without significant variations. Changes in composition, such as humidity, protein and fat content, pH, and acidity index, are important in products of animal origin, while in the case of vegetable products, there will be important changes in pH, weight loss, leakage loss, titratable acidity, and soluble solids. There are currently some studies that consider the use of different types of coatings incorporated into nanosize systems, where it has

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been shown that their use considerably reduces physicochemical variations and that changes in pH and ionic strength are associated with the polymer type. Nanoemulsions are the systems most used in the preparation of edible coatings. The apple has been one of the models used to evaluate these coatings, and it has been found that apples manage to significantly reduce cellular oxidative stress, contributing to the maintenance of its physicochemical characteristics (Salvia-Trujillo, Soliva-Fortuny, Rojas-Grau¨, McClements, & Martı´n-Belloso, 2017; ZambranoZaragoza, Gutie´rrez-Cortez, et al., 2014a; Zambrano-Zaragoza, Mercado-Silv et al., 2014b). Nanoemulsions have been used in chicken, meat, and cheese preservation as edible coatings, considering the antioxidant capacity of essential oils and the possibility of decreasing the concentration of these when used as nanoingredients and increases in superficial area. The latter reveals that the type of stabilizer, superficial charge, or the film-forming dispersion are important factors to take into account (Abdou, Galhoum, & Mohamed, 2018; Zambrano-Zaragoza et al., 2018). Other nanosize systems that have been used in the preparation of coatings include SLNs, which have exhibited a different effect on the physicochemical properties, depending on their concentration in the coating. In the conservation of freshcut guava, SLNs prepared with candeuba wax were employed, demonstrating that, at 50 g/L of nanoparticle dispersion, there is a control in the changes of pH and  Bx (Gonza´lez-Reza, Pe´rez-Olivier, Miranda-Linares, & Zambrano-Zaragoza, 2018a). SLNs have been utilized in the conservation of tomatoes to decrease their ripening rate and to increase their shelf life for 26 days at 12 C, which clearly reduced the changes in pH,  Bx, and weight loss (Miranda-Linares, Escamilla-Rendo´n, Del Real-Lo´pez, Gonza´lez-Reza, & Zambrano-Zaragoza, 2018). Polymeric nanoparticles have also been used in edible coatings for the conservation of fresh-cut fruits and vegetables, fish, meat, and other minimally processed foods. The natural polymers that have been employed are mainly chitosan, alginate, and synthetic polymers such as ethyl cellulose and poly-ε-caprolactone. Their effects on physicochemical properties depend on particle size, composition, and antimicrobial and antioxidant capacity. For example, in coatings based on chitosan nanoparticles, analyzing the effect of particle sizes between 400 and 800 nm on tomatoes stored under refrigeration determined that weight loss was lower in emulsified chitosan than in the chitosan nanoparticulate edible coating. However, there were no statistically significant differences in the trend or behavior (Mustafa, Ali, & Manickam, 2013).

6.4.3.2 Effect of nanocoatings on textural changes Many changes associated with the quality of foods are related to textural changes, including enzymatic, microbial, and respiratory activity and/or oxygen absorption, which produce drastic changes in palatability, firmness, shear, and compression resistance. An alternative that aids in preserving textural parameters for as long as possible are edible coatings. Many polysaccharides and proteins have been tested as a base for coatings, demonstrating that these are effective as ingredients of film-forming dispersion to preserve the texture of foods (Shit & Shah, 2014; Yilmaz et al., 2016).

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However, in recent years, nanosize systems have been an alternative sought to add active substances with an antioxidant and antimicrobial capacity for foods with a positive effect on texture. Control of texture during storage is dependent on polymers used in nanoparticle coating formation since these have different action modes in the function of tissue and origin of food. Chitosan can be polymerized by endogenous enzymes that could include the participation of hydrophobic interactions, hydrogen bonding, and electrostatic interactions (Wang et al., 2015). Table 6.3 summarizes some applications of nanosize systems in foods and the effect on texture of products.

6.4.3.3 Effect of nanocoatings on color changes associated with shelf life Color represents one of the most important factors for the acceptance of a food. It is for this reason that the effect of nanosize systems has been studied in terms of color changes during the storage of different foods. With regard to nanoemulsions and nanocapsules incorporated into polymeric matrices, one of the first studies with nanoemulsions applied to the conservation of fresh-cut fruits was the application of α-tocopherol nanoemulsions incorporated into nopal mucilage matrix. In this study, the effect of lipophilic antioxidant on inhibition of browning index was investigated in relation to the polyphenol oxidase activity in the fresh-cut apple. It revealed that this treatment was effective in the inhibition of browning, increasing the apple shelf life by 21 days at 4 C. In this case, particle size exerted a significant effect, which was attributable to interaction with cellular components being more effective at a smaller particle size (Zambrano-Zaragoza, Gutie´rrez-Cortez, et al., 2014a; Zambrano-Zaragoza, MercadoSilv et al., 2014b). In another study carried out on fresh-cut “Fuji” apple, the use of lemongrass essential oil in the emulsion and nanoemulsion within the sodium alginate matrix showed that luminosity decreased during refrigerated storage. This did not occur with apples coated only with sodium alginate, which was attributed to the fact that phenolic compounds of the essential oil are substrates for the polyphenol oxidase activity. In addition, it was considered that there is an increase in the permeability of the cell membrane due to the presence of volatile compounds in the essential oil that promote modification in the cell cytoplasm, allowing the interaction of phenols and enzymes (Yilmaz et al., 2016). It is noteworthy that there are many studies to be carried out in order to ascertain the minimal inhibitory concentration for limiting browning and color changes in fruits due to the effect of polyphenols and enzymes, as well as the effect of polymer type employed as matrix or as a coating in nanoemulsions.

6.4.4 Effect of nanocrystals and other nanosize systems on color and sensorial aspects In recent years, there has been a growing interest in the use of nanocrystals and other nanosize systems as ingredients in food processing, mainly those in which their rheological behavior is important or in which their spreadable properties play a relevant role in the sensorial acceptance of the product (Lin et al., 2012). Nanocrystals prepared from hydrocolloids that possess a great capacity for

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absorbing water have been used in the stabilization of Pickering emulsions; however, it is necessary to consider the changes in the crystallinity of starch depending on the pH, ionic strength, and nanocrystal concentration. In a study in which nanocrystals were prepared with a waxy starch, it was shown that an increase in the nanocrystal concentration was favorable for the formation of stable and gel-like Pickering emulsions, with stronger stiffness at a pH between 5 and 10, these being more susceptible to the concentration of NaCl, although not achieving stable emulsions (Yang et al., 2018). Nanocrystals have been useful in the development of low-fat products, where the sensory effect depends both on taste and textural perception at the moment of product consumption; these physical properties are in turn related with the viscosity associated with fluidity and smoothness. It is then possible to mention that hydrocolloids can replace some fat in mayonnaise, dips, and dressings, being dependent on the molecular characteristics and their influence on bulk physicochemical properties such as thickening, gelling, dilution grade, and light transmission (Dickinson, 2009; Li & Nie, 2016). Cellulose and native starch or their modification are abundant, biocompatible, biodegradable, and nontoxic. Nanocrystals are prepared from starch or cellulose and these have the ability to increase the viscosity of aqueous dispersion; however, it is necessary to take into account the content of fat in the food formulation, since its presence modifies the water-retention capacity of starch, modifies the form of the hydrated molecules, and forms a gel (Choi & Kerr, 2003). The proportion of nanocrystals employed as ingredients in the replacement of fat and the origin of starch or cellulosic materials are factors that are important to study. It has been shown that the concentration of nanocrystals used to reduce fat between 25% and 75% using concentrations of 10%, 12%, and 14% of corn starch nanocrystals decreased the particle size in relation to the concentration. This is attributable to the water present binding to the surface of nanocrystals with Ψz between 218, 24, and 31.9 mV to form the hydrogen bonds, and a higher nanocrystal concentration improving the food emulsion stability, and thus no creaming. In addition, based on the rheological properties, the addition of corn starch nanocrystals formed a gel-like network that trapped the oil droplets, revealing an electrostatic repulsion that produced stability during 6 months (Javidi, Razavi, & Mohammad Amini, 2019).

6.5

Toxicological and normative regulatory issues of nanoparticles in food processing

Nanoparticles as ingredients for food can exhibit different chemical or physical properties, or biological effects compared with larger-scale counterparts. The high surface area exposed increases the reactivity of functional groups, which is associated with a high degree of particle interpenetration into tissues. Dimensiondependent properties in food are usually reflected as more protective food-

Table 6.3 Effect of nanosize systems on color, textural properties, and shelf life of foods. Nanosize system

Polymer used/ active

Nanoemulsion

Food application

Textural effect

Color effect

Shelf life increasing

Leaf vegetable

Nanocoating diminish the firmness loss at Minor firmness loss with extract in nanolaminate (35 % vs 57% without coating) Minimal hardness decrease (235 205 g) when nanoparticles are used compared with control (239 105 g)

No significant effect

Increase from 3 at 7 day with nanocoating rucola leaf Sessa et al. (2015)

More stable redness

Nanolaminate with extract treatment, extend shelf life for 15 days at 0 C Salas-Me´ndez et al. (2019)

Nanolaminate coating

Flourencia cernua extract

Tomato fruit

Nanoparticles

Chitosan

Whiteleg shrimp

Nanocapsules

Polyε-caprolactone/ α-tocopherol

Fresh-cut “Red delicious” apple

10 days of storage at 4 C Wang et al. (2015)

Nanocapsules and nanocapsules/ xanthan gum shown best color control with ΔE , 5

From 12 days without coating to 21 days of storage at 4 C GalindoPe´rez, Quintanar-Guerrero, MercadoSilva, Real-Sandoval, and Zambrano-Zaragoza (2015), Zambrano-Zaragoza, Gutie´rrezCortez, et al. (2014a), Zambrano-Zaragoza, Mercado-Silv et al. (2014b)

(Continued)

Table 6.3 (Continued) Nanosize system

Polymer used/ active

Food application

Textural effect

Nanoparticles

Alginate/agmontmorillonite

Fresh-cut carrot

Nanolaminate

Alginate/lysozyme

“Coalho” Cheese

Nanocrystals

Cellulose

Shelled walnuts

Nanocapsules

β-carotene/polyε-caprolactone

Fresh-cut melon

The application of nanocoating helped conserve firmness (only 9.9% decrease)

Solid lipid nanoparticles (SLNs)

Carnauba wax/ xanthan gum

Fresh-cut guava

Less firmness loss with 5 g/ L of SLNs (35 %)

Increase of storage time with less weight loss

Color effect

Changes in transmittance minor in coating cheese Best color retention for coated walnuts The best retention of color was from the fresh-cut melon with nanocapsules/ xanthan gum with intensity (4.03%). Browning index reduction with 5 g/L of SLN

Shelf life increasing Shelf life prediction of 69.9 days respect fresh-cut carrot without edible coating Costa, Conte, Buonocore, Lavorgna, and Del Nobile (2012) 20 days with less growth of mesophilic and psychotropic microbial counts and best visual aspect Medeiros et al. (2014) Accelerated shelf life test. 30 days of storage at 40 C Fotie, Limbo, and Piergiovanni (2018) 21 days of storage at 4 C ZambranoZaragoza et al. (2017)

18 days of storage at 4 C Gonza´lezReza et al. (2018a)

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packaging materials (Thiruvengadam et al., 2018) and improved delivery of a functional ingredient or a nutrient in food (FDA, 2014). For a considerable time period, regulatory entities such as the FDA have paid more attention to nanomaterials within the range of 1 100 nm. However, there is sufficient evidence in various areas of science that properties dependent on aggregation size are not restricted to the 100-nm limit. Therefore the new recommendations found in FDA documents explore the “possibility” of novel and different material properties depending on an aggregation size of up to 1000 nm. Even more so, some statements from the FDA’s “Guide to Industry” suggest a better understanding of the interaction of physical and chemical characteristics with biological effects. When toxicological aspects are addressed in the food area, a greatest risk associated with nanomaterials derives from the possibility that they are ingested with food (Wani, Masoodi, Jafari, & McClements, 2018). Consequently, after nanomaterials enter the human body, they could exert some adverse effects. Of course, it is true that a fraction of new materials will enter the human body and that they depend on their proximity with food, even in the case of packaging materials. The next sentence. described in “Guidance for Industry, Considering Whether an FDARegulated Product Involves the Application of Nanotechnology” (FDA, 2014), draws attention to the flexible and nonspecific nature of the following statement: “The use of the word should in Agency guidance documents means that something is suggested or recommended, but not required” (FDA, 2014). Therefore all the assertions on the requirements are subject to each particular case. At present, there is no specific establishment of limits in the concentration of nanomaterials, types of permitted nanomaterials, and the function of surface phenomena in the types of nanomaterials present in foods, interaction of nanomaterials with food components, biodistribution, biotransformation, and bioelimination. This advance in official regulations is limited by the progress in the knowledge of basic science and by the economic regulatory policies of the food market. The presence of nanoparticles in a food can comprise intentional alterations, deriving from food-handling processes, food components, or contaminants (Bajpai et al., 2018). It is evident that the manipulation of ingredients toward nanoparticles will “result in new properties not seen in traditionally manufactured food substances.” Essential considerations for the manufacturer should consist at least of particle size, particle SD (PDI value), Ψz, batch-to-batch reproducibility, estimation of surfactant residues on the surface of nanoparticles if applicable, interactions among materials, and interactions with proteins, biodegradation, and possible accumulation in tissues. The first point of interaction of nanoparticles with the biological systems is, naturally, the surface. There are multiple conformations of the surface: the matrix of nanomaterial; surfactants for stabilization; a mixture of both; a surface with one or more layers of organic or inorganic waste (Jain, Ranjan, Dasgupta, & Ramalingam, 2018); or a protein corona. Interaction can even take place with accumulated nanomaterials to reduce surface free energy. Formation of the corona, deposition of one or more layers of proteins on the surface of nanomaterial, is nearly unpredictable because it depends on the biological composition of the food and physiological state of the person.

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One of the main mechanisms of nanomaterial cytotoxicity is through the induction of reactive oxygen species (ROS). The presence of ROS is related to possible inflammatory responses due to the presence of a xenobiotic, generation via peroxisomes, or to by-products of the mitochondrial electron transport chain. Pairs of highly reactive electrons on the surface can also favor the production of ROS (Jain et al., 2018). There are different models in vitro, ex vivo, and in vivo to know the possible reactions of nanomaterials that are present or in contact with food. The in vitro models include simulations and predictions of surface reactivity in terms of energy, ROS evaluation, inflammatory processes, viability, and cell proliferation in different cell lines. Ex vivo models include permeation pathways and kinetics in tissues such as skin, lung, liver, kidney, and brain, while in vivo models comprise those of biodistribution and biotransformation. A correlation of different models at different levels usually provides useful information.

6.6

Conclusions and future trends

There are many important aspects to consider in the development and application of nanoemulsions and nanosize systems, being necessary to consider the method of preparation as well as the materials and conditions required. There are important factors related to the type and concentration of surfactants employed, such as the amount of compound, the superficial charge that stabilizes the colloidal system, and compatibility with the food in which it will be used as an ingredient, in addition to monitoring the need for and stages at which it must be released to enhance the expected effect in relation to the product characteristics. It is also necessary to take into account the preservation of food during storage, or its bioavailability at the moment of being consumed. The superficial charge of the nanosize system and the way that these remain stable once prepared, as well as the food composition and the potential interactions are some other significant parameters. When nanosystems are incorporated as ingredients into foods and beverages, the Ψz with absolute values of .30 mV is preferred; other factors that must be considered are the degree of dilution to be carried out, the way that it is incorporated, and the viscosity, pH, ionic strength, thermal resistance, and interaction with food components. The use of nanosize systems as ingredients is also important in order to analyze the function that is desired. Thus nanoemulsions are preferred in the formulation of beverages, juices, fruit pulp, sauces, and ice cream, while polymeric nanoparticles are preferred in thermal processes in order to confer thermal resistance to components such as flavorings, colorants, vitamins, essential oils, and other thermolabile substances utilized as ingredients in food processing. Nanocoatings provide protection against O2, light, temperature, and humidity, being possible to employ the LbL technique, polymeric nanoparticles, nanoemulsions, and other geometries. In all cases, it is necessary to consider the surface treatment or the composition of minimally processed food. Finally, nanocrystals have been employed for the stabilization of Pickering emulsions and have demonstrated a positive effect on the control

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of rheological behavior of emulsified foods and in spreads such as pˆate´s, margarines, and dips, modifying the sensorial effect with beneficial results. According to the analyses, the nanosize systems have been used as ingredients in food processing and preservation, as antioxidant and antimicrobial natural substances, and as essential oils, colorants, and vitamins. This shows that they interact with the cell metabolism of fresh-cut fruit and vegetables, as well as controlling lipid oxidation reactions in meats and their products. This thereby reduces the action of enzymes and microorganisms present, such as polyphenol oxidases and pectin methylesterases in vegetables, and causes the decrease of microorganisms and enzymes responsible for color changes in meat and their products. In meats, the principal essential oils utilized are rosemary, oregano, thyme, clove, and cinnamon, which decrease tissue degradation due to microbial growth, and for their antioxidant capacity, which decrease the diffusion of oxygen. With the use of nanosize systems, it has been shown that the amount of active ingredients utilized in food formulation and processing is lower, due to minor losses of the volatilization of aromatic components. The latter, in turn, is beneficial, since there is a minimal sensory change in the products. In addition, there has been good progress in the development of novel products with sensory characteristics that appear on chewing the product. Some studies have been conducted on the release kinetics of different components such as essential oils, polyphenols, and other plant extracts with antioxidant and antimicrobial effects. However, due to the monitoring of volatile residuals during product storage, it remains necessary to investigate the effect of interaction of nanosize food systems and the factors that contribute to maintaining the stability of these for as long as possible. The selection of the correct polymer in the formation of polymeric nanoparticles is another important point to consider in the preparation of nanosize systems for use as an ingredient in food processing and preservation, as well as the matrix polymer in the nanocoating and its function on the surface of products. Cellular internalization analyzes the mechanisms that promote its conservative effect and the changes in signaling that give rise to the expression of enzymes and the degradation of components in food. In addition, there must be a continuation of investigation into the potential uses of multilayer and multicomponent nanostructured systems that contribute to strengthening the efficiency of controlled release for different types of food in response to changes in pH, ionic strength, and even tissue modification during the diffusion process, which promote the functionality of nanoingredients. Nanoemulsions and nanosize systems will be useful tools in the extension of shelf life of food and beverages, and in the development of novel functional products, this will potentially permit their use to reduce costs concerning thermolabile components and their reconstitution due to processing, and also, on considering the effective protector of the substances and therefore their protection during storage and consumption, thereby maintaining the effectiveness of the nanoingredient incorporated into the food or beverages.

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nanoemulsions. Food Chemistry, 141, 1475 1480. Available from https://doi.org/ 10.1016/j.foodchem.2013.03.050. Salvia-Trujillo, L., Soliva-Fortuny, R., Rojas-Grau¨, M. A., McClements, D. J., & Martı´nBelloso, O. (2017). Edible nanoemulsions as carriers of active ingredients: A review. Annual Review of Food Science and Technology, 8, 439 466. Available from https:// doi.org/10.1146/annurev-food-030216-025908. Santana, R. C., Perrechil, F. A., & Cunha, R. L. (2013). High- and low-energy emulsifications for food applications: A focus on process. Parameters: Journal of the US Army War College, 107 122. Available from https://doi.org/10.1007/s12393-013-9065-4. Sarkar, P., Choudhary, R., Panigrahi, S., Syed, I., Sivapratha, S., & Dhumal, C. V. (2017). Nano-inspired systems in food technology and packaging. Environmental Chemistry Letters, 15, 607 622. Available from https://doi.org/10.1007/s10311-017-0649-8. Sarkar, P., Irshaan, S., Sivapratha, S., & Choudhary, R. (2016). Nanotechnology in food processing and packaging. Nanoscience in Food and Agriculture, 185 227. Available from https://doi.org/10.1007/978-3-319-39303-2_7. Saxena, A., Sachin, K., Bohidar, H. B., & Verma, A. K. (2005). Effect of molecular weight heterogeneity on drug encapsulation efficiency of gelatin nano-particles. Colloids Surfaces B Biointerfaces, 45, 42 48. Available from https://doi.org/10.1016/j.colsurfb.2005.07.005. Sessa, M., Ferrari, G., & Donsı`, F. (2015). Novel edible coating containing essential oil nanoemulsions to prolong the shelf life of vegetable products. Chemical Engineering Transactions, 43, 55 60. Available from https://doi.org/10.3303/CET1543010. Shaddel, R., Akbari-Alavijeh, S., & Jafari, S. M. (2019). Chapter Five Encapsulation of food ingredients by Pickering nanoemulsions. In S. M. Jafari (Ed.), Lipid-based nanostructures for food encapsulation purposes (pp. 151 176). Academic Press. Available from https://doi.org/10.1016/B978-0-12-815673-5.00005-2. Shamsara, O., Jafari, S. M., & Muhidinov, Z. K. (2017). Fabrication, characterization and stability of oil in water nano-emulsions produced by apricot gum-pectin complexes. International Journal of Biological Macromolecules, 103, 1285 1293. Available from https://doi.org/10.1016/j.ijbiomac.2017.05.164. Shamsara, O., Muhidinov, Z. K., Jafari, S. M., Bobokalonov, J., Jonmurodov, A., Taghvaei, M., & Kumpugdee-Vollrath, M. (2015). Effect of ultrasonication, pH and heating on stability of apricot gum-lactoglobuline two layer nanoemulsions. International Journal of Biological Macromolecules, 81, 1019 1025. Available from https://doi.org/10.1016/j. ijbiomac.2015.09.056. Shit, S. C., & Shah, P. M. (2014). Edible polymers: Challenges and opportunities. Journal of Polymer Science, 2014, 1 13. Available from https://doi.org/10.1155/2014/427259. Siepmann, J., & Peppas, N. A. (2011). Higuchi equation: Derivation, applications, use and misuse. International Journal of Pharmaceutics, 418, 6 12. Available from https://doi. org/10.1016/j.ijpharm.2011.03.051. ˆ ., & Vicente, A. A. (2012). Nanoemulsions for food applicaSilva, H. D., Cerqueira, M. A tions: Development and characterization. Food and Bioprocess Technology, 5, 854 867. Available from https://doi.org/10.1007/s11947-011-0683-7. Solans, C., & Sole´, I. (2012). Nano-emulsions: Formation by low-energy methods. Current Opinion in Colloid & Interface Science, 17, 246 254. Available from https://doi.org/ 10.1016/j.cocis.2012.07.003. Song, X., Pei, Y., Qiao, M., Ma, F., Ren, H., & Zhao, Q. (2015). Preparation and characterizations of Pickering emulsions stabilized by hydrophobic starch particles. Food Hydrocolloids, 45, 256 263. Available from https://doi.org/10.1016/J.FOODHYD.2014.12.007.

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Squillaro, T., Cimini, A., Peluso, G., Giordano, A., & Melone, M. A. B. (2018). Nanodelivery systems for encapsulation of dietary polyphenols: An experimental approach for neurodegenerative diseases and brain tumors. Biochemical Pharmacology, 154, 303 317. Available from https://doi.org/10.1016/j.bcp.2018.05.016. Tadros, T., Izquierdo, P., Esquena, J., & Solans, C. (2004). Formation and stability of nanoemulsions. Advances in Colloid and Interface Science, 108 109, 303 318. Available from https://doi.org/10.1016/J.CIS.2003.10.023. Taheri, A., & Jafari, S. M. (2019). Gum-based nanocarriers for the protection and delivery of food bioactive compounds. Advances in Colloid and Interface Science, 269, 277 295. Available from https://doi.org/10.1016/j.cis.2019.04.009. Tamjidi, F., Shahedi, M., Varshosaz, J., & Nasirpour, A. (2013). Nanostructured lipid carriers (NLC): A potential delivery system for bioactive food molecules. Innovative Food Science and Emerging Technologies, 19, 29 43. Available from https://doi.org/10.1016/ J.IFSET.2013.03.002. Tan, Y., Xu, K., Liu, C., Li, Y., Lu, C., & Wang, P. (2012). Fabrication of starch-based nanospheres to stabilize pickering emulsion. Carbohydrate Polymers, 88, 1358 1363. Available from https://doi.org/10.1016/J.CARBPOL.2012.02.018. Thiruvengadam, M., Rajakumar, G., & Chung, I. M. (2018). Nanotechnology: Current uses and future applications in the food industry. 3 Biotech, 8, 1 13. Available from https:// doi.org/10.1007/s13205-018-1104-7. Timgren, A., Rayner, M., Sjo¨o¨, M., & Dejmek, P. (2011). Starch particles for food based Pickering emulsions. Procedia Food Science, 1, 95 103. Available from https://doi.org/ 10.1016/J.PROFOO.2011.09.016. Trbojevich, R. A., Ferna´ndez, A. (2016). Synthesis and properties of metal[-based nanoparticles with potential applications in food-contact materials. In Aliofkhazraei, M. (eds.), Handbook of nanoparticles. Cham: Springer. https://doi.org/10.1007/978-3-319-15338-4. Torres-Giner, S. (2011). Electrospun nanofibers for food packaging applications. In Multifunctional and nanoreinforced polymers for food packaging (pp. 108 125). Woodhead Publishing. https://doi.org/10.1533/9780857092786.1.108. Ubbink, J. (2016). Structural and thermodynamic aspects of plasticization and antiplasticization in glassy encapsulation and biostabilization matrices. Advanced Drug Delivery Reviews, 100, 10 26. Available from https://doi.org/10.1016/j.addr.2015.12.019. Uskokovic, D., & Stevanovic, M. (2009). Poly(lactide-co-glycolide)-based micro and nanoparticles for the controlled drug delivery of vitamins. Current Nanoscience., 5, 1 14. Available from https://doi.org/10.2174/157341309787314566. Vahedikia, N., Garavand, F., Tajeddin, B., Cacciotti, I., Jafari, S. M., Omidi, T., & Zahedi, Z. (2019). Biodegradable zein film composites reinforced with chitosan nanoparticles and cinnamon essential oil: Physical, mechanical, structural and antimicrobial attributes. Colloids and Surfaces B: Biointerfaces, 177, 25 32. Available from https://doi.org/ 10.1016/j.colsurfb.2019.01.045. Villalobos-Castillejos, F., Granillo-Guerrero, V. G., Leyva-Daniel, D. E., AlamillaBeltra´n, L., Gutie´rrez-Lo´pez, G. F., Monroy-Villagrana, A., & Jafari, S. M. (2018). Chapter 8—Fabrication of nanoemulsions by microfluidization. Nanoemulsions (pp. 207 232). Academic Press. Available from https://doi.org/10.1016/B978-0-12811838-2.00008-4. Wang, T., Bae, M., Lee, J. Y., & Luo, Y. (2018). Solid lipid-polymer hybrid nanoparticles prepared with natural biomaterials: A new platform for oral delivery of lipophilic bioactives. Food Hydrocolloids, 84, 581 592. Available from https://doi.org/10.1016/j. foodhyd.2018.06.041.

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Wang, Y., Liu, L., Zhou, J., Ruan, X., Lin, J., & Fu, L. (2015). Effect of chitosan nanoparticle coatings on the quality changes of postharvest whiteleg shrimp, litopenaeus vannamei, during storage at 4 C. Food Bioprocess Technology, 8, 907 915. Available from https://doi.org/10.1007/s11947-014-1458-8. Wani, T. A., Masoodi, F. A., Jafari, S. M., & McClements, D. J. (2018). Chapter 19—Safety of nanoemulsions and their regulatory status. Nanoemulsions (pp. 613 628). Academic Press. Available from https://doi.org/10.1016/B978-0-12-811838-2.00019-9. Weiss, J., Takhistov, P., & McClements, D. J. (2006). Functional materials in food nanotechnology. Journal of Food Science, 71, 107 116. Available from https://doi.org/10.1111/ j.1750-3841.2006.00195.x. Xiao, J., Li, Y., & Huang, Q. (2016). Trends in Food Science & Technology Recent advances on food-grade particles stabilized Pickering emulsions: Fabrication, characterization and research trends. Trends in Food Science and Technology, 55, 48 60. Available from https://doi.org/10.1016/j.tifs.2016.05.010. Yang, T., Zheng, J., Zheng, B. S., Liu, F., Wang, S., & Tang, C. H. (2018). High internal phase emulsions stabilized by starch nanocrystals. Food Hydrocolloids, 82, 230 238. Available from https://doi.org/10.1016/j.foodhyd.2018.04.006. Yilmaz, A., Bozkurt, F., Cicek, P. K., Dertli, E., Durak, M. Z., & Yilmaz, M. T. (2016). A novel antifungal surface-coating application to limit postharvest decay on coated apples: Molecular, thermal and morphological properties of electrospun zein nanofiber mats loaded with curcumin. Innovative Food Science and Emerging Technologies, 37, 74 83. Available from https://doi.org/10.1016/J.IFSET.2016.08.008. Yousefi, M., Ehsani, A., & Jafari, S. M. (2019). Lipid-based nano delivery of antimicrobials to control food-borne bacteria. Advances in Colloid and Interface Science, 270, 263 277. Available from https://doi.org/10.1016/j.cis.2019.07.005. Yousefi, M., & Jafari, S. M. (2019). Recent advances in application of different hydrocolloids in dairy products to improve their techno-functional properties. Trends in Food Science & Technology (Elmsford, N.Y.), 88, 468 483. Available from https://doi.org/ 10.1016/j.tifs.2019.04.015. Zambrano-Zaragoza, M. L., Gonza´lez-Reza, R., Mendoza-Mun˜oz, N., Miranda-Linares, V., Bernal-Couoh, T. F., Mendoza-Elvira, S., & Quintanar-Guerrero, D. (2018). Nanosystems in edible coatings: A novel strategy for food preservation. International Journal of Molecular Sciences, 19. Available from https://doi.org/10.3390/ijms19030705. Zambrano-Zaragoza, M. L., Gutie´rrez-Cortez, E., Del Real, A., Gonza´lez-Reza, R. M., Galindo-Pe´rez, M. J., & Quintanar-Guerrero, D. (2014a). Fresh-cut red delicious apples coating using tocopherol/mucilage nanoemulsion: Effect of coating on polyphenol oxidase and pectin methylesterase activities. Food Research International, 62, 974 983. Available from https://doi.org/10.1016/j.foodres.2014.05.011. Zambrano-Zaragoza, M. L., Mercado-Silva, E., Del Real, L. A., Gutie´rrez-Cortez, E., Cornejo-Villegas, M. A., & Quintanar-Guerrero, D. (2014b). The effect of nanocoatings with α-tocopherol and xanthan gum on shelf-life and browning index of freshcut “red Delicious” apples. Innovative Food Science and Emerging Technologies, 22, 188 196. Available from https://doi.org/10.1016/j.ifset.2013.09.008. Zambrano-Zaragoza, M. L., Mercado-Silva, E., Gutie´rrez-Cortez, E., Castan˜o-Tostado, E., & Quintanar-Guerrero, D. (2011). Optimization of nanocapsules preparation by the emulsion-diffusion method for food applications. LWT—Food Science and Technology, 44, 1362 1368. Available from https://doi.org/10.1016/j.lwt.2010.10.004. Zambrano-Zaragoza, M. L., & Quintanar-Guerrero, D. (2019). Novel techniques for extrusion, agglomeration, encapsulation, gelation, and coating of foods. In P. Ferranti, E.

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Berry, & A. Jock (Eds.), Encyclopedia of food security and sustainability (pp. 379 392). Amsterdam: Elsevier. Zambrano-Zaragoza, M. L., Quintanar-Guerrero, D., Del Real, A., Pin˜on-Segundo, E., & Zambrano-Zaragoza, J. F. (2017). The release kinetics of β-carotene nanocapsules/ xanthan gum coating and quality changes in fresh-cut melon (cantaloupe). Carbohydrate Polymers, 157. Available from https://doi.org/10.1016/j.carbpol.2016.11.075. Zhong, J., Yang, R., Cao, X., Liu, X., & Qin, X. (2018). Improved physicochemical properties of yogurt fortified with fish oil/γ-oryzanol by nanoemulsion technology. Molecules (Basel, Switzerland), 23. Available from https://doi.org/10.3390/molecules23010056.

Green synthesis of metal nanoparticles by plant extracts and biopolymers

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Lucas F.B. Nogueira1, E´der J. Guidelli2, Seid Mahdi Jafari3 and Ana Paula Ramos1 1 Department of Chemistry, Faculty of Philosophy, Science and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Ribeira˜o Preto/SP, Brazil, 2Department of Physics, Faculty of Philosophy, Science and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Ribeira˜o Preto/ SP, Brazil, 3Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

7.1

Introduction

The development of green chemistry aims to reduce (or eliminate) the use, or generation, of hazardous substances in the synthesis, manufacture, and application of chemical products, reactions, materials, and processes (Garavand, Rahaee, Vahedikia, & Jafari, 2019). To be called green, each step of the procedure, or reaction, should have at least three green components: environment-friendly solvents and reagents/catalysts, and reduced energy consumption. Green chemistry is focused on a set of principles initially proposed by Anastas and Eghbali (2010). These principles are well interconnected in order to direct the methodologies, choice of chemical reactants, and development of analytical methodologies aiming to prevent and reduce the environment damage, as depicted in Fig. 7.1. These principles are briefly as follows: 1. Prevention of waste. The first principle is focused on reducing the amount of waste generated in the production process. It can be achieved by changing solvents or reusing the waste produced in the best possible way: It is better to prevent waste than to treat or clean up waste after it has been created. 2. Atom economy. The second principle is closely related to the previous one. The atom economy, first proposed by Barry Trost (Li & Trost, 2008), suggests that synthetic routes should be designed in order to maximize the incorporation of higher amount of atoms used in the process into the final product. The optimized utilization or inclusion in the final product will lead to waste reduction. 3. Less hazardous chemical synthesis. Synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment. For example, a desirable green solvent should be natural, nontoxic, cheap, and readily available.

Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00007-8 © 2020 Elsevier Inc. All rights reserved.

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Figure 7.1 The 12 principles of green chemistry are interconnected in order to avoid and prevent environmental damage. 4. Designing safer chemicals. Closely related to the third principle, the fourth principle aims at the development of synthetic methods for the use and synthesis of substances that have little or no toxicity to human health and the environment. Replacing harmful chemicals with enzymes makes many industrial processes cleaner. 5. Safer solvents and auxiliaries. This principle recommends, whenever it is possible, the reduction of the use of auxiliary chemical substances (e.g., solvents, separating agents, etc.) during the synthetic processes. When used, they should be harmless. The choice of suitable substitutions for organic solvents can be based on worker safety, the process, and the environment. 6. Design for energy efficiency. A fundamental requirement of any chemical process or synthesis is the minimized use of energy. Mild reaction condition are preferable for green synthesis. 7. Use of renewable feedstocks. Using renewable raw materials is the main point of the seventh principle of green chemistry. This reduces the need to throw away the waste materials. Based on this, production of biodegradable plastic materials is a current trend in green chemistry. 8. Derivative reduction. The reduction of unnecessary derivatization (group blocking, protection/elimination protection, temporary physicochemical modification) of chemical reactions and processes in such steps require additional reactants and can generate waste. 9. Catalysis. The use of biodegradable catalysts protects the environment and reduces the use of energy in chemical reactions and processes as predicted in the sixth principle of green chemistry.

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10. Design for degradation. Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment. 11. Real-time analysis for pollution prevention. The chemical processes and reactions must be monitored in real-time, aiming at preventing the formation of pollutants. This principle supports the development of analytical methodologies able to supply this function. 12. Inherently safer chemistry for accident prevention. This principle advocates for reducing the use of harmful and dangerous substances in chemical reactions and processes in order to avoid adverse effects and accidents (explosion, fire, etc.).

7.2

Metallic nanoparticles and green chemistry

The design, synthesis, and manipulation of metallic nanoparticles (particles with at least one dimension between 1 and 100 nm) deserves special attention in the nanoscience and nanotechnology field due to the remarkable differences in their electrical, magnetic, catalytic, and optical properties in comparison with the bulk state of the same metal (Sangappa et al., 2019; Vijayan, Joseph, & Mathew, 2018). Novel applications of metal nanoparticles have received considerable attention on various fronts due to their enhanced properties that can be tuned by composition and also by their size, distribution, and morphology (Ahmed, Ahmad, Swami, & Ikram, 2016; Khatami, Sharifi, Nobre, Zafarnia, & Aflatoonian, 2018; Sangappa et al., 2019). A set of shapes can be obtained by adjusting the concentration of reacting chemicals and also by controlling the reaction environment (Gade, Gaikwad, Duran, & Rai, 2014). The main applications can be found in catalysis, biosensors, cryogenic superconducting materials, cosmetic products, electronic components, composite fibers, and antimicrobial activity (Sangappa et al., 2019; Vijayan et al., 2018). The last two applications are the most important in the food industry (Hoseinnejad, Jafari, & Katouzian, 2018). Different physical and chemical methods have been developed to fabricate these particles at the nanoscale. Among these techniques, the chemical reduction is considered the most advantageous process since it results in the production of large amounts of nanoparticles in short periods of time with good control of the size distribution (Gade et al., 2014; Remya, Abitha, Rajput, Rane, & Dutta, 2017; Sangappa et al., 2019). The reducing agent can be organic or inorganic (Sangappa et al., 2019). However, most of the chemical methods use toxic chemicals (such as hydrazine and sodium borohydride), and frequently yield particles in nonpolar organic solutions and nonecofriendly by-products, which goes in the opposite direction of the green chemistry principles. Moreover, the use of these classical methods restricts the application of metal nanoparticles for human purposes including food packaging and medicine. In addition, these traditional methods utilize excessive power consumption, have a high cost, and require sophisticated apparatus (Soshnikova et al., 2018). The green chemistry methods for the synthesis of metal nanoparticles include the design and development of energy efficient and eco-friendly reactants, waste,

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and subproducts (Patra et al., 2015; Soshnikova et al., 2018; Vijayan et al., 2018). As a consequence, the biosynthesis of metal nanoparticles deserves attention in modern nanotechnology as it represents a greener approach to develop environment-friendly processes (Gade et al., 2014; Mohanpuria, Rana, & Yadav, 2008). Several advantages of green synthesis over conventional methods were described by Patra et al. (2015). The green synthetic routes are described as simple, efficient, clean, or eco-friendly, since they use bioresources (bacteria, fungi, algae, and plant extracts) that can act as reducing agents as well as stabilizing and capping agents to the synthesized metallic nanoparticles (Bindhu & Umadevi, 2015; Patra et al., 2015; Soshnikova et al., 2018; Umamaheswari, Lakshmanan, & Nagarajan, 2018; Vijayan et al., 2018), as schematically represented in Fig. 7.2. Moreover, the greener approach requires ambient temperature and pressure, minimum energy consumption and very low or no-consumption of hazardous materials. They can also be easily scaled up for large-scale nanoparticle synthesis (Ahmed et al., 2016; Patra et al., 2015). The excellent physical and chemical properties of nanoparticles made of a noble metal, including silver, gold, and platinum, make them the most promising for commercial and industrial application (Kumar, Smita, Cumbal, & Debut, 2017; Vijayan et al., 2018). Also, the different colors exhibited by the colloidal dispersion of these metal nanoparticles, depending on the shape, size, and the tendency of aggregation, improves their industrial interest (Ahmed et al., 2016). The green synthesis of metallic nanoparticles can be thermodynamically described as the formation of colloidal solid/liquid dispersions by using the changes in the concentration of atoms in solution with time due to the nucleation and growth steps. The size of nanoparticles is critically controlled by the nucleation and growth rates. In turn, the nucleation step depends on the supersaturation concentration that must be higher than the solubility of the compound. Sun (2013) has described the process by changes in the atomic concentration as a function of time (Fig. 7.3). The number of nuclei formed in the colloidal dispersion will be higher if the

Figure 7.2 An important advantage of the green routes for nanoparticle synthesis is the possibility of using the molecules as reducing as well as capping agents for the stabilization of colloidal dispersions containing the greener nanoparticles.

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Figure 7.3 The rates of nucleation and growth will dictate the number of nuclei formed in the colloidal dispersion, and so the size of nanoparticles. Source: Reprinted with permission from Sun, Y. (2013). Controlled synthesis of colloidal silver nanoparticles in organic solutions: Empirical rules for nucleation engineering. Chemical Society Reviews, 42(7), 2497
2511. https://doi.org/10.1039/C2CS35289C.

supersaturation concentration is quickly reached. So, a lower number of atoms will be available for the growth step leading to the formation of small-sized nanoparticles. The supersaturation can be quickly reached by the rapid mixing of reactants and also by controlling the concentration of atoms.

7.2.1 Silver nanoparticles Remarkable properties, including chemical stability, good conductivity, and catalytic and antimicrobial activity make silver the most studied and applied noble metal for the fabrication of nanoparticles (Bindhu & Umadevi, 2015; Khatami et al., 2018; Kumar et al., 2017). Synthesis of silver nanoparticles is of much interest to the scientific community since the addition of these particles critically changes the properties of materials, making them suitable for wound healing/dressings, composite fibers, cryogenic superconducting materials, cosmetic products, food industry, topical creams, antiseptic sprays, and electronic components (Bindhu & Umadevi, 2015; Khatami et al., 2018; Kumar et al., 2017). The use of biological compounds and microorganisms including bacteria, fungi, and plant extracts (e.g., leaf, bark, root, and stem) for the production of silver nanoparticles has been described (Ahmed et al., 2016; Bindhu & Umadevi, 2015). The antioxidant or reducing properties of these naturally found reactants are responsible for the reduction of ions into their corresponding metallic nanoparticles. Different

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compounds can be responsible for the reduction of Ag1 ions depending upon the organism/extract used (Srikar, Giri, Pal, Mishra, & Upadhyay, 2016). In general, the presence of any one (or more) of a large number of organic compounds, including carbohydrates, fats, proteins, amino acids, polysaccharides, enzymes, tannins, phenolics, saponins, vitamins, flavonoids, terpenoids, and alkaloids, contributes by donating electrons for the reduction of Ag1 ions into Ag0 in biological entities (Ahmed et al., 2016; Srikar et al., 2016). The difficulty of growth, culture maintenance, and inoculums size standardization make the biosynthesis of silver nanoparticles by microorganisms difficult and more expensive when compared to the use of plant extracts and polysaccharides as reducing and capping agents (Srikar et al., 2016). The efficiency of green methodologies can be evaluated by following the changes in coloration of the dispersion of nanoparticles from colorless to yellow and, then, to a slight brownish
yellow color. It is also important to evaluate the size-stability and aggregation state of nanoparticles. The color changes are assigned to the surface plasmon resonance (SPR) phenomenon. A peak in the range of 300
500 nm in the UV
Vis spectrum of silver nanoparticles is attributed to SPR. The presence of a single SPR peak is related to the formation of uniformly spherical nanoparticles, while the appearance of two or more absorption peaks is due to the irregular shape of nanoparticles (Rolim, Pelegrino, et al., 2019). A red shift in the SPR peak is observed with an increase in nanoparticle size, whereas a blue shift is observed with a decrease in size. The majority of the studies on green routes have reported the fabrication of spherical nanoparticles with a face-centered cubic (fcc) crystalline structure as the best in terms of their application in different fields (Srikar et al., 2016). However, green approaches may also lead to nanoparticles with other shapes and other crystalline structures, as briefly described in the next sections of this chapter.

7.2.2 Gold nanoparticles Among the noble metal nanoparticles, gold nanoparticles have also attracted attention in the field of scientific and technological applications due to their unique properties including catalytic, magnetic, and optical response, and antimicrobial activity (Umamaheswari et al., 2018). However, because of the elevated cost, they are not often employed for further studies, and silver nanoparticles are preferred. Due to unusual optoelectronic and physicochemical properties, ease of synthesis, characterization, and surface modification in the nanoscale range, gold nanoparticles are extensively used in the biomedical field as medicinal agents for the theragnostic applications of several diseases such as diabetes, Parkinson’s, and Alzheimer’s (Patra et al., 2015). In the food industry, gold nanoparticles synthesized using ginger rhizome extract as reducing agents have been applied against bacterial food pathogens (Velmurugan et al., 2014). Therefore due to the relevant potential applications of gold nanoparticles, the design and development of the most efficient, economically cheap, and environmentally safe methods has been considered extremely relevant (Patra et al., 2015).

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The presence of the characteristic single SPR peak around 532 nm in the UV
Vis spectrum also allows the characterization of colloidal gold dispersions by following color changes. Besides the changes in the coloration of the solution from colorless to red, techniques such as transmission electron microscopy (TEM) and X-ray diffraction (XRD) have been used to evaluate the efficiency of green methodologies, characterizing the biosynthesized nanoparticles obtained using eco-friendly approaches.

7.3

Synthesis of metal nanoparticles using living organisms and biomolecules

7.3.1 Plants and algae Plant extracts have been considered to be the best platform for the synthesis of metallic nanoparticles via green routes, being free from toxic chemicals. The extracts can also act as natural capping agents (Fig. 7.2). Moreover, these chemically complex structures can be bioactive, resulting in functionalized particles in one-step synthesis (Ahmed et al., 2016). According to the literature, it is established that both low- (12
22 kDa) and high- (B150 kDa) molecular-weight proteins, depending upon the nature of plant as well as the source of the leaf, play a major role in the reduction of metal ions into metallic nanoparticles (Patra et al., 2015). The general method used to prepare the plant extracts involves the selection and collection of the part of the plant of interest, followed by exhaustive washing processes to remove both epiphytes and necrotic plants. Subsequently, it is shade-dried for 10
15 days and then shredded until it becomes powder (Rahmanian, Jafari, & Wani, 2015; Sarfarazi, Jafari, & Rajabzadeh, 2015). Finally, the powder is dispersed in water and boiled to obtain the infusion, which is completely filtered until no insoluble material appears in the final plant extract. At the end, a few milliliters of plant extracts are added to the solution containing the ions that must be reduced for the production of metallic nanoparticles of interest (Ahmed et al., 2016). This procedure is commonly used in the biosynthesis of silver and gold nanoparticles, so that the reduction of ions can be monitored by measuring the UV
Vis spectrum of the colloidal dispersions (Ahmed et al., 2016). Silver nanoparticles with antibacterial properties were synthesized using olive leaf extract (Khalil, Ismail, El-Baghdady, & Mohamed, 2014). In the study of Bindhu and Umadevi (2015), silver nanoparticles were synthesized using beetroot extract, an excellent source of folate and a good source of manganese and betaines, as the reducing agent. The reduction of silver (Ag1) ions to silver nanoparticles (Ag0) was evaluated by UV
Vis, and the appearance of a symmetric SPR peak at 438 nm confirmed, after 7 h of reaction, the complete reduction of silver ions (Bindhu & Umadevi, 2015). XRD and TEM analyses revealed the formation of fcc nanoparticles with a spherical shape and mean size of 15 nm. These nanoparticles displayed pronounced antibacterial activity against different clinically important pathogenic microorganisms and also exhibited good catalytic activity.

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Kumar et al. (2017) reported an eco-friendly and low-cost method for the synthesis of silver nanoparticles using Andean blackberry fruit extract. The formation of these metallic nanoparticles was observed in a relatively short period of time after Ag1 came in contact with the fruit extract. These biosynthesized metal nanoparticles showed efficient antioxidant efficacy against 1,1-diphenyl-2-picrylhydrazyl. The waste grass extract and silver nitrate solution can be also used for nanoparticle synthesis at ambient conditions (Khatami et al., 2018). The authors reported spherical
oblate nanoparticles with antimicrobial activity against the bacteria Pseudomonas aeruginosa and Acinetobacter baumannii and the fungus Fusarium solani. Another plant extract which has been exploited for silver nanoparticle biosynthesis is green tea (Camellia sinensis). In the study by Rolim, Pelegrino, et al. (2019), the presence of the characteristic SPR peak at 410 nm confirmed the formation of silver nanoparticles. The average size was approximately 3.9
4.2 nm, smaller when compared to other green methodologies. Green tea contains polyphenolic compounds, which are ionized in the extract allowing the transfer of an electron to Ag1, resulting in the formation of nanoparticles and oxidation of polyphenols to quinone. In addition, polyphenols act as capping agents and as antioxidants, increasing the stability of nanoparticles. In terms of application, these biogenic nanoparticles showed antibacterial effect toward Escherichia coli, P. aeruginosa, and Salmonella enterica. Following these first results, Rolim, Pieretti, et al. (2019) incorporated these Ag nanoparticles into polymeric solid films, resulting in a homogeneously distributed material that exhibits a potent antibacterial effect against Gram-positive and Gram-negative bacterial strains. Guidelli, Ramos, Zaniquelli, and Baffa (2011) used rubber latex extracted from Hevea brasiliensis to synthesize colloidal silver nanoparticles with spherical shape and diameters ranging from 2 to 100 nm via an easy green method (Fig. 7.4). The size of the particles was controlled by tuning the AgNO3 content in the starting solution. The rubber latex membranes can also act as matrices for the controlled delivery of silver nanoparticles (Guidelli, Kinoshita, Ramos, & Baffa, 2013). In some studies, the authors have taken advantage of a unique methodology to test the green synthesis for more than one type of metallic nanoparticle preparation. For example, Patra et al. (2015) synthesized gold and silver nanoparticles using Butea monosperma leaf extract, an Ayurvedic herb popular in India due to its antimicrobial activity. The chemicals present in the extract act as both reducing and stabilizing agents. The green synthesis of gold and silver nanoparticles was carried out using HAuCl4 and AgNO3, respectively, in the presence of extract, and after 24 h the formation of noble metal nanoparticles was monitored by UV
Vis spectroscopy. The presence of characteristic SPR peaks, along with the presence of red and yellow coloration, suggests the formation of stable gold and silver nanoparticles. Soshnikova et al. (2018) also described the biosynthesis of gold and silver nanoparticles using plant extracts. In this study, an aqueous extract of dried fruits of Amomum villosum, also known as cardamom fruits, was used as reducing agent. Gold nanoparticles were formed after 3 s of reaction at room temperature, whereas silver nanoparticles formed after 1 h of reaction at 80 C. In regard to the application of nanoparticles, the authors

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Figure 7.4 TEM micrographs of silver nanoparticles using different initial concentration of AgNO3 (A) 0.5 mmol/L; (B) 2 mmol/L; (C)
(F) 4 mmol/L. Source: Reprinted with permission from Guidelli, E. J., Ramos, A. P., Zaniquelli, M. E. D., & Baffa, O. (2011). Green synthesis of colloidal silver nanoparticles using natural rubber latex extracted from Hevea brasiliensis. Spectrochimica Acta: Part A, Molecular and Biomolecular Spectroscopy, 82(1), 140
145. https://doi.org/10.1016/j.saa.2011.07.024.

attested their antioxidant and catalytic potential by the free radical scavenging activity against 2,2-diphenyl-1-picrylhydrzyl and reduction of methylene blue. In addition, they also showed that silver nanoparticles have antibacterial properties against pathogenic E. coli and Staphylococcus aureus. Vijayan et al. (2018) also developed a green synthesis to fabricate gold and silver nanoparticles using Indigofera tinctoria leaf extract. Different from the other studies we have described herein, the authors used the microwave-assisted technology to accelerate the biosynthesis process, maintain the green reaction conditions, and obtain a better yield of product. After 60 s of microwave irradiation, spherical silver nanoparticles with an average particle size of 16.46 nm were obtained. For the green synthesis of gold nanoparticles, the reaction medium changed its color to violet from light yellow solution within 30 s under microwave irradiation. Nanoparticles with average particle size of 19.73 nm and different morphologies

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including spherical, triangular, and hexagonal were obtained. The authors also evaluated the remarkable antimicrobial, antioxidant, and catalytic activities displayed by the gold and silver nanoparticles synthesized using the Indigofera tinctoria leaf extract. Algae extracts have also been exploited for the green synthesis of noble metal nanoparticles. Gonza´lez-Ballesteros, Prado-Lo´pez, Rodrı´guez-Gonza´lez, Lastra, and Rodrı´guez-Argu¨elles (2017) reported an eco-friendly, fast, and one-pot synthetic route for the synthesis of gold nanoparticles using brown macroalgae Cystoseira baccata extracts. In this study, the authors observed the formation of spherical Au nanoparticles with a mean diameter of 8.4 6 2.2 nm after only 100 s of reaction in the extract. The extract acted as a protective agent able to keep the particles apart, avoiding aggregation and coalescence. Table 7.1 summarizes the main plants and algae extracts used for the green synthesis of Au and Ag nanoparticles. The presence of polyphenolic/alcoholic compounds, aldehydes/ketones, and proteins in the plant extract favors the reduction of Au31 (in HAuCl4) to Au0 (gold nanoparticle) and Ag1 (AgNO3) to Ag0 (silver nanoparticles) based on the standard reduction potentials (Patra et al., 2015). Depending on the noble metal nanoparticles to be synthesized, different concentrations of extract must be used.

Table 7.1 Main studies involving plants and algae extracts for the green synthesis of Au and Ag nanoparticles. Greener reducing agent

Nanoparticles

References

Indigofera tinctoria leaf extract Wast-grass Cardamom fruits

Gold and silver

Vijayan et al. (2018)

Silver Gold and silver Silver

Khatami et al. (2018) Soshnikova et al. (2018)

Silver Silver and gold

Rolim, Pelegrino, et al. (2019) Velmurugan et al. (2014)

Silver Silver Gold

Khalil et al. (2014) Guidelli et al. (2011, 2013) Gonza´lez-Ballesteros et al. (2017)

Silver Silver

Zepon et al. (2018), Roy et al. (2019) Shameli et al. (2012, 2014), Alsammarraie et al. (2018), Naksuriya et al. (2014), Shishodia et al. (2007)

Blackberry fruit extract Green tea extract Zingiber officinale root extract Olive leaf extract Rubber latex Algae Cystoseira baccata Carrageenan Curcumin

Kumar et al. (2017)

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7.3.2 Fungi and yeasts Among the green methods used to synthesize metallic nanoparticles, the microbemediated method is not industrially recommended due to the requirements of highly aseptic conditions and the highly expensive maintenance (Ahmed et al., 2016). Microorganisms typically live under comfortable conditions of temperature, pressure, and acidity (Gade et al., 2014). For these reasons, the use of plant extracts for the green synthesis of metal nanoparticles has been highlighted as more advantageous compared to microorganisms (Ahmed et al., 2016; Soshnikova et al., 2018). However, the academic importance of these methodologies has been described in the literature. Among the microorganisms used, it has been highlighted that fungi present some advantages compared to bacterial systems: they are easy to culture in bulk, the downstream processing and handling of biomass is relatively simple, and they produce enzyme extracellularly (Gade et al., 2014). Thus fungi have been widely used for rapid, high-yield, and eco-friendly biosynthesis of metal nanoparticles (Gade et al., 2014). In terms of the biosynthetic process in the presence of fungi and yeasts, the reduction of metal ions from an inorganic salt to metallic nanoparticles occurs with the direct interaction with fungi (Gade et al., 2014). In this sense, the use of fungal systems allows nanoparticles to be synthesized extracellularly directly in the aqueous medium, resulting in a biotransformation-based approach with a better commercial viability (Gade et al., 2014). As an example of this green approach, the study by Gade et al. (2014) describes the production of silver nanoparticles using fungal filtrate from Phoma glomerata (MTCC-2210), grown aerobically in a potato dextrose broth. It was verified that the mixture between AgNO3 and the fungal filtrate led to rapid synthesis after exposure to bright sunlight. In the dark it took nearly 24 h for complete reduction. TEM analysis evidenced the synthesis of polydispersed spherical silver nanoparticles with mean size of 19 nm. Based on these results, the authors have proposed a three-step mechanism for the synthesis of spherical silver nanoparticles by P. glomerata: (1) activation by photosensitization of aromatic compounds in the fungal filtrate on exposure to bright sunlight; (2) nucleation promoted by the photosensitized aromatic compounds or proteins as capping agents to initiate the synthesis of spherical nanoparticles; and (3) actual synthesis by reduction of silver ions to form silver nanoparticles, involving electron donation either by inorganic nitrate or by photosensitized aromatic compounds from fungal filtrate.

7.3.3 Other natural compounds In the previous sections, we have described the reduction of inorganic ions for the production of metallic nanoparticles by the action of certain chemical compounds, which are present in the composition of plants extracts and algae, such as in those secreted by organisms such as fungi, yeasts, and bacteria. Some researchers have also developed eco-friendly methodologies based on the potential reduction of other naturally found compounds, such as carbohydrates, proteins, flavonoids, amino acids, and vitamins, isolated from living organisms.

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As an example, the study by Zepon, Marques, da Silva Paula, Dal Pont Morisso, and Kanis (2018) describes a facile, green, and scalable method to produce silver nanoparticles using kappa-carrageenan, a high-molecular-weight sulfate polysaccharide obtained from certain species of red seaweeds. The hydrogel formed by the polysaccharide chains in the presence of water facilitates the interaction between Ag1 and the available negatively charged functional groups, allowing in situ reduction. Based on UV analysis and changes in the kappa-carrageenan hydrogel from colorless to yellow, the authors confirmed the fast synthesis of spherical silver nanoparticles. The authors also evaluated the silver release from the hydrogel. It was attested a controlled and continuous release for up to 48 h at concentrations able to prevent bacterial growth of Staphylococcus aureus and P. aeruginosa. In the study of Sangappa et al. (2019), anisotropic silver nanoparticles were synthesized using silk fibroin obtained from Bombyx mori silk, using AgNO3 after irradiation under UV-B light for 5 h. TEM images demonstrated that this biogenic synthesis route is suitable to produce silver nanoparticles of different shapes (mainly spherical and nanorod) with an average particle diameter of 31 nm. The nanorod-shaped silver nanoparticles showed enhanced antibacterial activity only against some human pathogenic Gram-negative bacteria (Escherichia coli and P. aeruginosa), compared with spherical-shaped silver nanoparticles, at lower concentration; Candida albicans, a fungus, was sensitive to these biogenic silver nanoparticles at higher concentration. Umamaheswari et al. (2018) developed a novel and greener method for the synthesis of gold nanoparticles (AuNPs) using 5,7-dihydroxy-6-metoxy-30 ,40 -methylenedioxyisoflavone or Dalspinin (isoflavonoid), isolated from the roots of Dalbergia coromandeliana as reducing and capping agent. The biosynthesis was performed by slow addition of ethanolic solution of Dalspinin into the HAuCl4 aqueous solution for 10 min. The reaction mixture changed from yellow to wine red, which confirmed the redox reaction between Dalspinin and Au31, with an SPR peak around 532 nm, assigned to the formation of stable gold nanoparticles. The potential mechanism described in this study was the keto-enol tautomerism of the isoflavonoid, in which the enol form freely liberates reactive hydrogen responsible by the conversion of Au31 to Au0. The hydroxyl and carbonyl groups present at the isoflavonoid structure first bind to Au31 to form gold complexes, which are reduced further to Au0 seed particles, resulting in the formation of clusters, which act as nucleation centers for the reduction of the remaining metal ions. In the study by Roy, Shankar, and Rhim (2019), silver nanoparticles were synthesized by a green method using melanin, a high-molecular-weight black and brown biopolymeric pigment produced by a wide variety of organisms, as a reducing and capping agent. This eco-friendly and green approach consists of the vigorous mixture of AgNO3 with melanin dispersed in a potassium hydroxide aqueous solution at 100 C for 1 h. The authors reported the formation of spherical silver nanoparticles with diameters in the range of 10
50 nm. These nanoparticles were incorporated into carrageenan hydrogel to prepare antimicrobial nanocomposite membranes. The neat carrageenan film did not exhibit antibacterial activity, but silver nanoparticles incorporated in nanocomposite films dramatically reduced cell

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viability of both Escherichia coli and Listeria monocytogenes. The results indicated that nanoparticles were more effective against Gram-negative than Gram-positive bacteria. Roy et al., as well as in the study of Sangappa et al. (2019), associated this result to the differences between the cell wall structure of Gram-positive and Gram-negative bacteria. As a conclusion of this study, the authors emphasized that the nanocomposite membranes with strong antimicrobial activity showed potential application as active food packaging to ensure food safety and extend the shelf life of packaged foods. Chitosan also plays an important role in the green synthesis of metal nanoparticles (Wongpreecha, Polpanich, Suteewong, Kaewsaneha, & Tangboriboonrat, 2018; Zain, Stapley, & Shama, 2014; Di Carlo et al., 2012; Venkatesham, Ayodhya, Madhusudhan, Babu, & Veerabhadram, 2014). This natural polysaccharide contains a large number of amino and hydroxyl functional groups and is considered as a nontoxic, biodegradable, biocompatible, and environment-friendly material (Hosseinnejad & Jafari, 2016). In the procedures used for nanomaterials synthesis, chitosan may act as both reducing and capping agent, and sometimes requires the use of an autoclave for achieving temperatures above 100 C. Wongpreecha et al. (2018) observed that increasing the reaction temperature and pressure enhances the formation of AgNPs in the presence of chitosan. The zeta potential values were above 130 mV at pH values of 2
10, leading to particles that were stable for up to 6 months. Venkatesham et al. (2014) noticed that the reduction capacity of chitosan increased with reaction time, suggesting that upon increasing autoclaving time, more hydroxyl groups were converted to carbonyl groups by air oxidation, which in turn reduces the silver ions. Furthermore, the infrared spectrum of silver nanoparticle stabilized in chitosan indicated the attachment of silver to nitrogen atoms in chitosan. Chitosan may also be used as a ligand by employing additional reducing agents. Zain et al. (2014) reduced silver ions with ascorbic acid in the presence of chitosan and microwave heating and observed that nanoparticle size was increased by augmenting the concentration of silver ions and decreasing the chitosan concentration, probably due to the lower ligand concentration. Zeta potential values were positive for all nanoparticles, further revealing the bonding of chitosan at the nanoparticle surface. Colloidal gold nanoparticles stabilized in a chitosan matrix have also been prepared by reducing the gold ions with organic acids such as acetic, malonic, and oxalic acid (Di Carlo et al., 2012). The authors demonstrated that the morphology of the resulting metal nanoparticles varies according to the reduction rate characteristic of each acid. The gold
chitosan nanocomposites presented a high selectivity and sensitivity for caffeic acid sensing. Huang and Yang (2004) employed chitosan and heparin in order to produce positively and negatively charged gold and silver nanoparticles. The results suggested that the formation of gold and silver nanoparticles occurred inside polysaccharide nanotemplates. Moreover, the morphology and size distribution of metal nanoparticles changed with the concentration of both the polysaccharides and the precursor metal salts evidencing the ability of this synthetic route to tune size, morphology, and surface charge of metal nanoparticles using natural compounds.

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While chitosan is used for the green synthesis of positively charged metal nanoparticles, curcumin is usually the choice for those willing to add antimicrobial or anticancer properties to these nanomaterials (Alsammarraie, Wang, Zhou, Mustapha, & Lin, 2018; Nadagouda et al., 2014; Shameli et al., 2012, 2014). Curcumin is a natural diphenolic yellow/orange pigment extracted from the dried rhizome of turmeric Curcuma longa, possessing a series of biological properties such as antibacterial, antifungal, antiviral, antioxidant, and antiinflammatory activities (Naksuriya, Okonogi, Schiffelers, & Hennink, 2014; Shishodia, Chaturvedi, & Aggarwal, 2007; Rafiee, Nejatian, Daeihamed, & Jafari, 2019). Shameli et al. (2012) produced small silver nanoparticles of approximately 6 nm through a simple and green route using Curcuma longa tuber-powder extracts as a reducing and stabilizing agent. The nanoparticles were obtained after 24 h incubation in aqueous silver nitrate solution and curcuma extract. The solution was kept at room temperature in the dark to avoid any photochemical reactions. Using a similar protocol, Alsammarraie et al. (2018) observed that after 24 h of reaction the color of solution changed from yellow, indicating the formation of spherical silver nanoparticles (Fig. 7.5). These nanoparticles presented high antimicrobial activities against two food-borne pathogens, evidencing the potential of this green methodology for applications in agricultural and food industries. Khoury, Abiad, Kassaify, and Patra (2015) reported a green protocol to produce monodisperse and stable curcumin
silver nanoparticle conjugates. Monodispersity was achieved by adding glycerol to the reaction medium and stability was improved by using polyvinylpyrolidone as a capping agent. Nadagouda et al. (2014) have shown that, although turmeric powder is not soluble in water, when dispersed with

Figure 7.5 TEM images of biosynthesized silver nanoparticles at different magnifications (A); size distribution (B). Source: Reprinted with permission from Alsammarraie, F. K., Wang, W., Zhou, P., Mustapha, A., & Lin, M. 2018. Green synthesis of silver nanoparticles using turmeric extracts and investigation of their antibacterial activities. Colloids and Surfaces B: Biointerfaces, 171, 398
405. https://doi.org/10.1016/j.colsurfb.2018.07.059.

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silver and gold salts, it produces metal nanoparticles of smaller sizes compared with other plant extracts. Furthermore, the gold nanoparticle formation was slower (required days) compared with silver nanoparticles. Table 7.2 depicts a summary of the main greener reducing agents used for the green synthesis of silver and gold nanoparticles.

7.4

Applications of green metal nanoparticles

Metal nanoparticles are largely employed for the development of new technologies in physics, chemistry, and biology. Silver nanoparticles obtained from green synthesis keep their remarkable properties, which has resulted in their incorporation into more than 200 consumer products, including clothing, medicines, and cosmetics (Ahmed et al., 2016). When produced by green methodologies, they are especially useful for biomedical applications, due to their potentially lower toxicity. Silver nanoparticles, for instance, are employed due to the antibacterial, antifungal, and antiviral properties of silver (Morones et al., 2005). Silver nanoparticles display broad bactericidal spectrum and antiviral properties and are effective against Gramnegative, such as E. coli, V. cholera, P. aeruginosa, and S. typhus, and oral bacteria, such as S. mutans, and Gram-positive S. aureus bacteria (Cheng et al., 2012; da Silva et al., 2019; Dos Santos et al., 2014; Morones et al., 2005). The toxicity of silver nanoparticles is related to the production of reactive oxygen species (ROS), which causes oxidative stress, inflammation, and consequent damage to the proteins, cell membrane, and DNA. Table 7.2 The main nonplant reducing agents used for the green synthesis of metallic nanoparticles. Greener reducing agent

Nanoparticles

References

Silk fibroin Fungi Phoma glomerata Flavonoids Melanin Chitosan

Silver Silver

Sangappa et al. (2019) Gade et al. (2014)

Gold Silver Silver, gold, copper

Ascorbic acid

Silver and copper Gold

Srikar et al. (2016), Umamaheswari et al. (2018) Roy et al. (2019) Wongpreecha et al. (2018), Zain et al. (2014), Di Carlo et al. (2012), Venkatesham et al. (2014); Huang and Yang (2004) Zain et al. (2014)

Acetic, malonic, and oxalic acids Heparin Alanine

Silver and gold Gold

Di Carlo et al. (2012) Huang and Yang (2004) Guidelli et al. (2012)

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In this sense, silver nanoparticles produced using the natural biopolymer gum kondagogu (Cochlospermum gossypium) as a reducing and stabilizing agent had significant antibacterial action on both Gram classes of bacteria (Kora, Sashidhar, & Arunachalam, 2010). As silver nanoparticles are encapsulated with functional group-rich gum, they can be easily integrated for several environmental and biomedical applications. Another study employed Zingiber officinale root extract as a reducing and capping agent for silver and gold nanoparticles. In this case, the particles showed moderate antibacterial activity against bacterial food pathogens (Velmurugan et al., 2014). The biosynthesis of silver nanoparticles using Vitex negundo L. extracts revealed antimicrobial activity against Gram-positive and Gram-negative bacteria (Zargar et al., 2011). Ibrahim (2015) also reported that silver nanoparticles produced using banana peel extract showed effective antibacterial activity against representative pathogens of bacteria and yeast. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for several microorganisms were determined. Furthermore, the synthesized nanoparticles showed synergistic effects with levofloxacin antibiotic, evidencing a 1.16
1.32fold enhancement of the antimicrobial activity. Therefore it is clear that the antimicrobial properties of these metal nanoparticles are highly dependent on the biomolecules and natural compounds employed as capping agent. A combination of silver nanoparticles and biomolecules has also been employed to promote angiogenesis while reducing inflammation due to their antibacterial and antifungal activities. It is well-known that natural latex from different species is able to produce tissue replacement and regeneration (de Siqueira Rodrigues Fleury Rosa et al., 2019; Kumar, Rajendran, Houreld, & Abrahamse, 2018). In this sense, Almeida et al. (2019) investigated the cytotoxic and genotoxic effects of biocomposites of Hancornia speciosa latex (HSB) with different concentrations of silver nanoparticles, using the Allium cepa assay. HSB was employed only as capping agent but was able to generate no cytotoxic effect in all the concentrations studied. A genotoxic effect was observed in HSB
silver at the highest silver nanoparticle concentrations, however, not at the lower concentrations. Thus the addition of these particles at the lowest concentration (0.1 wt.%) can improve the pharmacological activity of HSB without causing a toxic effect on vegetal cells. Therefore an HSB
silver biomembrane combines angiogenic, antiinflammatory, and antibacterial properties and can be considered a potential new biomaterial for wound healing. These green metal nanoparticles can also be employed for sensing of several chemical and biochemical species. Pandey, Goswami, and Nanda (2013) reported an eco-friendly method for the synthesis of gold nanoparticles using guar gum (GG). This GG
gold nanocomposite was used as an optical sensor for the detection of aqueous ammonia based on SPR, revealing high reproducibility and sensitivity (with a detection limit of 1 ppb) and response times of B10 s. Sensing of heavy metal ions in aqueous solution is very important for controlling environmental pollution, and many green approaches have been developed to this end. For instance, colorimetric sensing of Hg21, Pb21, and Mn12 ions was reported using l-tyrosinestabilized silver and gold nanoparticles in aqueous medium (Annadhasan,

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Muthukumarasamyvel, Sankar Babu, & Rajendiran, 2014). Silver nanoparticles are highly sensitive to Hg21 and Mn21 ions with the detection limit as low as 16 nM for both ions, whereas gold nanoparticles are sensitive only to Hg21 and Pb21 ions with a detection limit as low as 53 and 16 nM, respectively. Silver nanoparticles produced with Citrus limon (Cl-1) and Citrus limetta (Cl-2) were also employed for colorimetric Hg21 sensing, revealing the potential use of C. limon stabilizedparticles to selectively sense hazardous Hg21 ion in water at micromolar concentrations and in a wide pH range (3.2
8.5). Tagad et al. (2013) produced silver nanoparticles by using locust bean gum (LBG) polysaccharide to detect hydrogen peroxide (H2O2) in a low-cost portable optical fiber-based sensor. The system was able to detect H2O2 concentration as low as 0.01 mM. Besides as chemical sensors, silver nanoparticles produced by a green method have also been used to improve ionizing radiation detection (Guidelli, Ramos, Zaniquelli, Nicolucci, & Baffa, 2012). Silver nanoparticles were produced by the thermal treatment of silver nitrate aqueous solutions with DL-alanine. Alanine is an essential amino acid that is responsible for molecular biosynthesis and is also largely employed as an ionizing radiation sensor. It is possible to detect the presence of free radicals produced by exposure of alanine to X- and γ-rays, for instance. Due to their high atomic number, metal nanoparticles are used to increase the interaction of ionizing radiation with the sensitive volume of detectors. However, since most of the synthetic routes for production of nanoparticles employ a large amount of polymers for passivation of particles and avoidance of agglomeration, a mixture of alanine and nanoparticles would contain a significant quantity of polymer, which in turn would diminish the sensitivity of dosimeters. Therefore alanine was employed as both reducing and capping agent for the green synthesis of silver nanoparticles. Particles with an average size of 7.5 nm, fcc crystalline structure, narrow size distribution, and spherical shape were obtained. Infrared spectroscopy suggested the interaction between silver ions present at the surface of nanoparticles and the amine group of DL-alanine molecule, favoring the reduction of silver ions and providing the stability of the colloid. The biohybrid nanocomposite was used as a radiation dosimeter. The samples containing nanoparticles exhibited increased sensitivity and reduced energy dependence compared with pure DL-alanine, contributing to the construction of small-sized dosimeters. Bindhu and Umadevi (2015) prepared silver nanoparticles using beetroot extract as reducing agent and applied these particles as catalysts. The particles exhibited faster catalytic activity through the reduction of 4-nitrophenol to 4-aminophenol by NaBH4. The authors also highlighted that 4-aminophenol is the intermediate in industrial synthesis of paracetamol and dyes and it was also used in analgesic and antipyretic drugs, photodevelopers, and rubber antioxidant. In addition, this catalytic process was also considered an effective method for the removal of 4nitrophenol, a carcinogenic, mutagenic, and cyto- and embryonic-toxic compound. Due to the high kinetic barrier between the mutually repelling negative ions 4nitrophenol and BH42 , it is suggested that aromatic compounds having an 2 NO2 group are inert to the reduction of NaBH4 (Bindhu & Umadevi, 2015). Thus it was assumed that the electrons are transferred from BH42 ions to the nitro group of 4-

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nitrophenol, resulting in the reduction of this compound to 4-aminophenol, when the silver catalytic surface adsorbed both BH42 and 4-nitrophenol. Vijayan et al. (2018) also demonstrated that gold and silver nanoparticles show excellent catalytic activities toward the reduction of nitroanilines, because the presence of these noble metal nanoparticles overcomes the kinetic barrier in the reduction reactions of o/pniroanilines by NaBH4, through facilitating the electron transfer from donor BH42 to accepter nitroanilines.

7.5

Conclusion

The green synthesis of metallic nanoparticles is of utmost importance for the academy and industry. Nanoparticles with different morphologies, size, and concentration can be obtained using relatively simple methodologies. Due to the environmental importance of green routes, use of microorganisms is expensive and laborious, which makes the use of plants extracts and natural compounds, like polysaccharides, the best option to produce greener particles on a large scale. The properties of these metal nanoparticles are highly dependent on the biomolecules and natural compounds employed as reducing and/or capping agents, allowing for their application in different fields of science and technology.

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334. Available from https://doi.org/10.1016/j.saa.2018.11.050. Alsammarraie, F. K., Wang, W., Zhou, P., Mustapha, A., & Lin, M. (2018). Green synthesis of silver nanoparticles using turmeric extracts and investigation of their antibacterial activities. Colloids and Surfaces B: Biointerfaces, 171, 398
405. Available from https://doi.org/10.1016/j.colsurfb.2018.07.059. Anastas, P., & Eghbali, N. (2010). Green chemistry: Principles and practice. Chemical Society Reviews, 39(1), 301
312. Available from https://doi.org/10.1039/B918763B. Annadhasan, M., Muthukumarasamyvel, T., Sankar Babu, V. R., & Rajendiran, N. (2014). Green synthesized silver and gold nanoparticles for colorimetric detection of Hg 2 1 , Pb 2 1 , and Mn 2 1 in aqueous medium. ACS Sustainable Chemistry & Engineering, 2 (4), 887
896. Available from https://doi.org/10.1021/sc400500z. Bindhu, M. R., & Umadevi, M. (2015). Antibacterial and catalytic activities of green synthesized silver nanoparticles. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 135, 373
378. Available from https://doi.org/10.1016/j.saa.2014.07.045.

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Cheng, L., Weir, M. D., Xu, H. H. K., Antonucci, J. M., Kraigsley, A. M., Lin, N. J., . . . Zhou, X. (2012). Antibacterial amorphous calcium phosphate nanocomposites with a quaternary ammonium dimethacrylate and silver nanoparticles. Dental Materials, 28(5), 561
572. Available from https://doi.org/10.1016/j.dental.2012.01.005. da Silva, G. D., Guidelli, E. J., de Queiroz-Fernandes, G. M., Chaves, M. R. M., Baffa, O., & Kinoshita, A. (2019). Silver nanoparticles in building materials for environment protection against microorganisms. International Journal of Environmental Science and Technology, 16(3), 1239
1248. Available from https://doi.org/10.1007/s13762-0181773-0. de Siqueira Rodrigues Fleury Rosa, S., Fleury Rosa, M. F., Moutinho Fonseca, M. A., da Silva Luz, G. V., Domı´nguez Avila, C. F., Duarte Domı´nguez, A. G., . . . Richter, V. B. (2019). Evidence in practice of tissue healing with latex biomembrane: Integrative review. Journal of Diabetes Research, 2019, 1
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chitosan nanocomposites for caffeic acid sensing. Langmuir, 28(12), 5471
5479. Available from https://doi.org/10.1021/la204924d. Dos Santos, C. A., Seckler, M. M., Ingle, A. P., Gupta, I., Galdiero, S., Galdiero, M., . . . Rai, M. (2014). Silver nanoparticles: Therapeutical uses, toxicity, and safety issues. Journal of Pharmaceutical Sciences, 103(7), 1931
1944. Available from https://doi.org/ 10.1002/jps.24001. Gade, A., Gaikwad, S., Duran, N., & Rai, M. (2014). Green synthesis of silver nanoparticles by Phoma glomerata. Micron, 59, 52
59. Available from https://doi.org/10.1016/j. micron.2013.12.005. Garavand, F., Rahaee, S., Vahedikia, N., & Jafari, S. M. (2019). Different techniques for extraction and micro/nanoencapsulation of saffron bioactive ingredients. Trends in Food Science & Technology, 89, 26
44. Available from https://doi.org/10.1016/j. tifs.2019.05.005. Gonza´lez-Ballesteros, N., Prado-Lo´pez, S., Rodrı´guez-Gonza´lez, J. B., Lastra, M., & Rodrı´guez-Argu¨elles, M. C. (2017). Green synthesis of gold nanoparticles using brown algae Cystoseira baccata: Its activity in colon cancer cells. Colloids and Surfaces B: Biointerfaces, 153, 190
198. Available from https://doi.org/10.1016/j. colsurfb.2017.02.020. Guidelli, E´. J., Kinoshita, A., Ramos, A. P., & Baffa, O. (2013). Silver Nanoparticles delivery system based on natural rubber latex membranes. Journal of Nanoparticle Research, 15 (4), 1536. Available from https://doi.org/10.1007/s11051-013-1536-2. Guidelli, E. J., Ramos, A. P., Zaniquelli, M. E. D., & Baffa, O. (2011). Green synthesis of colloidal silver nanoparticles using natural rubber latex extracted from Hevea brasiliensis. Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy, 82(1), 140
145. Available from https://doi.org/10.1016/j.saa.2011.07.024. Guidelli, E. J., Ramos, A. P., Zaniquelli, M. E. D., Nicolucci, P., & Baffa, O. (2012). Synthesis and characterization of gold/alanine nanocomposites with potential properties for medical application as radiation sensors. ACS Applied Materials & Interfaces, 4(11), 5844
5851. Available from https://doi.org/10.1021/am3014899. Hosseinnejad, M., & Jafari, S. M. (2016). Evaluation of different factors affecting antimicrobial properties of chitosan. International Journal of Biological Macromolecules, 85, 467
475. Available from https://doi.org/10.1016/j.ijbiomac.2016.01.022. Hoseinnejad, M., Jafari, S. M., & Katouzian, I. (2018). Inorganic and metal nanoparticles and their antimicrobial activity in food packaging applications. Critical Reviews in

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181. Available from https://doi.org/10.1080/ 1040841X.2017.1332001. Huang, H., & Yang, X. (2004). Synthesis of polysaccharide-stabilized gold and silver nanoparticles: A green method. Carbohydrate Research, 339(15), 2627
2631. Available from https://doi.org/10.1016/j.carres.2004.08.005. Ibrahim, H. M. M. (2015). Green synthesis and characterization of silver nanoparticles using banana peel extract and their antimicrobial activity against representative microorganisms. Journal of Radiation Research and Applied Sciences, 8(3), 265
275. Available from https://doi.org/10.1016/j.jrras.2015.01.007. Khalil, M. M. H., Ismail, E. H., El-Baghdady, K. Z., & Mohamed, D. (2014). Green synthesis of silver nanoparticles using olive leaf extract and its antibacterial activity. Arabian Journal of Chemistry, 7(6), 1131
1139. Available from https://doi.org/10.1016/j. arabjc.2013.04.007. Khatami, M., Sharifi, I., Nobre, M. A. L., Zafarnia, N., & Aflatoonian, M. R. (2018). Wastegrass-mediated green synthesis of silver nanoparticles and evaluation of their anticancer, antifungal and antibacterial activity. Green Chemistry Letters and Reviews, 11(2), 125
134. Available from https://doi.org/10.1080/17518253.2018.1444797. Khoury, E. E., Abiad, M., Kassaify, Z. G., & Patra, D. (2015). Green synthesis of curcumin conjugated nanosilver for the applications in nucleic acid sensing and anti-bacterial activity. Colloids and Surfaces B: Biointerfaces, 127, 274
280. Available from https:// doi.org/10.1016/j.colsurfb.2015.01.050. Kora, A. J., Sashidhar, R. B., & Arunachalam, J. (2010). Gum kondagogu (Cochlospermum gossypium): A template for the green synthesis and stabilization of silver nanoparticles with antibacterial application. Carbohydrate Polymers, 82(3), 670
679. Available from https://doi.org/10.1016/j.carbpol.2010.05.034. Kumar, B., Smita, K., Cumbal, L., & Debut, A. (2017). Green synthesis of silver nanoparticles using andean blackberry fruit extract. Saudi Journal of Biological Sciences, 24(1), 45
50. Available from https://doi.org/10.1016/j.sjbs.2015.09.006. Kumar, S. S. D., Rajendran, N. K., Houreld, N. N., & Abrahamse, H. (2018). Recent advances on silver nanoparticle and biopolymer-based biomaterials for wound healing applications. International Journal of Biological Macromolecules, 115, 165
175. Available from https://doi.org/10.1016/j.ijbiomac.2018.04.003. Li, C.-J., & Trost, B. M. (2008). Green chemistry for chemical synthesis. Proceedings of the National Academy of Sciences, 105(36), 13197
13202. Available from https://doi.org/ 10.1073/pnas.0804348105. Mohanpuria, P., Rana, N. K., & Yadav, S. K. (2008). Biosynthesis of nanoparticles: Technological concepts and future applications. Journal of Nanoparticle Research, 10 (3), 507
517. Available from https://doi.org/10.1007/s11051-007-9275-x. Morones, J. R., Elechiguerra, J. L., Camacho, A., Holt, K., Kouri, J. B., Ramı´rez, J. T., & Yacaman, M. J. (2005). The bactericidal effect of silver nanoparticles. Nanotechnology, 16(10), 2346
2353. Available from https://doi.org/10.1088/0957-4484/16/10/059. Nadagouda, M. N., Iyanna, N., Lalley, J., Han, C., Dionysiou, D. D., & Varma, R. S. (2014). Synthesis of silver and gold nanoparticles using antioxidants from blackberry, blueberry, pomegranate, and turmeric extracts. ACS Sustainable Chemistry & Engineering, 2(7), 1717
1723. Available from https://doi.org/10.1021/sc500237k. Naksuriya, O., Okonogi, S., Schiffelers, R. M., & Hennink, W. E. (2014). Curcumin nanoformulations: A review of pharmaceutical properties and preclinical studies and clinical data related to cancer treatment. Biomaterials, 35(10), 3365
3383. Available from https://doi.org/10.1016/j.biomaterials.2013.12.090.

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Pandey, S., Goswami, G. K., & Nanda, K. K. (2013). Green synthesis of polysaccharide/gold nanoparticle nanocomposite: An efficient ammonia sensor. Carbohydrate Polymers, 94 (1), 229
234. Available from https://doi.org/10.1016/j.carbpol.2013.01.009. Patra, S., Mukherjee, S., Barui, A. K., Ganguly, A., Sreedhar, B., & Patra, C. R. (2015). Green synthesis, characterization of gold and silver nanoparticles and their potential application for cancer therapeutics. Materials Science and Engineering: C, 53, 298
309. Available from https://doi.org/10.1016/j.msec.2015.04.048. Rafiee, Z., Nejatian, M., Daeihamed, M., & Jafari, S. M. (2019). Application of curcuminloaded nanocarriers for food, drug and cosmetic purposes. Trends in Food Science & Technology, 88, 445
458. Available from https://doi.org/10.1016/j.tifs.2019.04.017. Rahmanian, N., Jafari, S. M., & Wani, T. A. (2015). Bioactive profile, dehydration, extraction and application of the bioactive components of olive leaves. Trends in Food Science and Technology, 42, 150
172. Available from https://doi.org/10.1016/j. tifs.2014.12.009. Remya, V. R., Abitha, V. K., Rajput, P. S., Rane, A. V., & Dutta, A. (2017). Silver nanoparticles green synthesis: A mini review. Chemistry International, 3(32), 165
171. Rolim, W. R., Pelegrino, M. T., de Arau´jo Lima, B., Ferraz, L. S., Costa, F. N., Bernardes, J. S., . . . Seabra, A. B. (2019). Green tea extract mediated biogenic synthesis of silver nanoparticles: Characterization, cytotoxicity evaluation and antibacterial activity. Applied Surface Science, 463, 66
74. Available from https://doi.org/10.1016/j. apsusc.2018.08.203. Rolim, W. R., Pieretti, J. C., Reno´, D. L. S., Lima, B. A., Nascimento, M. H. M., Ambrosio, F. N., . . . Seabra, A. B. (2019). Antimicrobial activity and cytotoxicity to tumor cells of nitric oxide donor and silver nanoparticles containing PVA/PEG films for topical applications. ACS Applied Materials & Interfaces, 11(6), 6589
6604. Available from https:// doi.org/10.1021/acsami.8b19021. Roy, S., Shankar, S., & Rhim, J.-W. (2019). Melanin-mediated synthesis of silver nanoparticle and its use for the preparation of carrageenan-based antibacterial films. Food Hydrocolloids, 88, 237
246. Available from https://doi.org/10.1016/j.foodhyd.2018.10.013. Sangappa, Y., Latha, S., Asha, S., Sindhu, P., Parushuram, N., Shilpa, M., . . . . . . Narayana, B. (2019). Synthesis of anisotropic silver nanoparticles using silk fibroin: Characterization and antimicrobial properties. Materials Research Innovations, 23(2), 79
85. Available from https://doi.org/10.1080/14328917.2017.1383680. Sarfarazi, M., Jafari, S. M., & Rajabzadeh, G. (2015). Extraction optimization of saffron nutraceuticals through response surface methodology. Food Analytical Methods, 8, 2273
2285. Available from https://doi.org/10.1007/s12161-014-9995-3. Shameli, K., Ahmad, M., Shabanzadeh, P., Zamanian, A., Sangpour, P., Abdollahi, Y., & Mohsen, Z. (2012). Green biosynthesis of silver nanoparticles using Curcuma longa tuber powder. International Journal of Nanomedicine, 7, 5603. Available from https:// doi.org/10.2147/IJN.S36786. Shameli, K., Ahmad, M. B., Shabanzadeh, P., Al-Mulla, E. A. J., Zamanian, A., Abdollahi, Y., . . . Haroun, R. Z. (2014). Effect of Curcuma longa tuber powder extract on size of silver nanoparticles prepared by green method. Research on Chemical Intermediates, 40 (3), 1313
1325. Available from https://doi.org/10.1007/s11164-013-1040-4. Shishodia, S., Chaturvedi, M. M., & Aggarwal, B. B. (2007). Role of curcumin in cancer therapy. Current Problems in Cancer, 31(4), 243
305. Available from https://doi.org/ 10.1016/j.currproblcancer.2007.04.001. Soshnikova, V., Kim, Y. J., Singh, P., Huo, Y., Markus, J., Ahn, S., Castro-Aceituno, V., et al. (2018). Cardamom fruits as a green resource for facile synthesis of gold and silver

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nanoparticles and their biological applications. Artificial Cells, Nanomedicine, and Biotechnology, 46(1), 108
117. Available from https://doi.org/10.1080/21691401. 2017.1296849. Srikar, S. K., Giri, D. D., Pal, D. B., Mishra, P. K., & Upadhyay, S. N. (2016). Green synthesis of silver nanoparticles: A review. Green and Sustainable Chemistry, 06(01), 34
56. Available from https://doi.org/10.4236/gsc.2016.61004. Sun, Y. (2013). Controlled synthesis of colloidal silver nanoparticles in organic solutions: Empirical rules for nucleation engineering. Chemical Society Reviews., 42(7), 2497
2511. Available from https://doi.org/10.1039/C2CS35289C. Tagad, C. K., Dugasani, S. R., Aiyer, R., Park, S., Kulkarni, A., & Sabharwal, S. (2013). Green synthesis of silver nanoparticles and their application for the development of optical fiber based hydrogen peroxide sensor. Sensors and Actuators B: Chemical, 183, 144
149. Available from https://doi.org/10.1016/j.snb.2013.03.106. Umamaheswari, C., Lakshmanan, A., & Nagarajan, N. S. (2018). Green synthesis, characterization and catalytic degradation studies of gold nanoparticles against congo red and methyl orange. Journal of Photochemistry and Photobiology B: Biology, 178, 33
39. Available from https://doi.org/10.1016/j.jphotobiol.2017.10.017. Velmurugan, P., Anbalagan, K., Manosathyadevan, M., Lee, K. J., Cho, M., Lee, S. M., . . . Oh, B. T. (2014). Green synthesis of silver and gold nanoparticles using zingiber officinale root extract and antibacterial activity of silver nanoparticles against food pathogens. Bioprocess and Biosystems Engineering, 37(10), 1935
1943. Available from https://doi. org/10.1007/s00449-014-1169-6. Venkatesham, M., Ayodhya, D., Madhusudhan, A., Babu, N. V., & Veerabhadram, G. (2014). A Novel green one-step synthesis of silver nanoparticles using chitosan: Catalytic activity and antimicrobial studies. Applied Nanoscience, 4(1), 113
119. Available from https://doi.org/10.1007/s13204-012-0180-y. Vijayan, R., Joseph, S., & Mathew, B. (2018). Indigofera tinctoria leaf extract mediated green synthesis of silver and gold nanoparticles and assessment of their anticancer, antimicrobial, antioxidant and catalytic properties. Artificial Cells, Nanomedicine, and Biotechnology, 46(4), 861
871. Available from https://doi.org/10.1080/ 21691401.2017.1345930. Wongpreecha, J., Polpanich, D., Suteewong, T., Kaewsaneha, C., & Tangboriboonrat, P. (2018). One-pot, large-scale green synthesis of silver nanoparticles-chitosan with enhanced antibacterial activity and low cytotoxicity. Carbohydrate Polymers, 199, 641
648. Available from https://doi.org/10.1016/j.carbpol.2018.07.039. Zain, N. M., Stapley, A. G. F., & Shama, G. (2014). Green synthesis of silver and copper nanoparticles using ascorbic acid and chitosan for antimicrobial applications. Carbohydrate Polymers, 112, 195
202. Available from https://doi.org/10.1016/j. carbpol.2014.05.081. Zargar, M., Hamid, A. A., Bakar, F. A., Shamsudin, M. N., Shameli, K., Jahanshiri, F., & Farahani, F. (2011). Green synthesis and antibacterial effect of silver nanoparticles using Vitex Negundo L. Molecules, 16(8), 6667
6676. Available from https://doi.org/10.3390/ molecules16086667. Zepon, K. M., Marques, M. S., da Silva Paula, M. M., Dal Pont Morisso, F., & Kanis, L. A. (2018). Facile, green and scalable method to produce carrageenan-based hydrogel containing in situ synthesized AgNPs for application as wound dressing. International Journal of Biological Macromolecules, 113(1), 51
58. Available from https://doi.org/ 10.1016/j.ijbiomac.2018.02.096.

Nanoencapsulation of bioactive food ingredients

8

Ali Rashidinejad1 and Seid Mahdi Jafari2 1 Riddet Institute Centre of Research Excellence, Massey University, Palmerston North, New Zealand, 2Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

8.1

Introduction

Thanks to the power of nature that has created the building blocks of life in the nanoscale (e.g., DNA, sugars, peptides, amino acids, hormones), the human is inspired to engineer such nanomaterials for the purpose of health benefits and well-being. The concept of “nanostructures” was perhaps first proposed in 1959 by Richard Feynman, and later in 1974 the term “nanotechnology” was introduced by Nario Taniguchi in order to manipulate submicron particles. Generally speaking, the term “nano” can refer to a magnitude of 1029 m (Quintanilla-Carvajal et al., 2010), and the term “nanotechnology” refers to the design, characterization, production, and application of any structure, system, and/or device that controls the shape and size of the particles at the nanoscale (Bawa, Bawa, Maebius, Flynn, & Wei, 2005). In the last few decades, this technology has received great attention and has emerged as one of the most promising tools in scientific research, including in the food industry, where it can deal with the manufacture and application of materials with sizes ,1000 nm (Sanguansri & Augustin, 2006). Nanotechnology has revolutionized the entire food industry from the manufacture of food products and corresponding ingredients to their applications and consumption. The improvements in different properties of food, such as sensory attributes (texture, color, taste, etc.), processability, stability during storage (shelf life), and more specifically, the functionality and efficacy of the food components have led to a great number of new and innovative products. In particular, one interesting area of food science in which nanotechnology has been greatly helpful and which is attracting increasing interest day by day is the nanoencapsulation of bioactive ingredients. This is because the reduction in particle size to the nanoscale range can increase the surface:volume ratio, and subsequently can increase the reactivity of the coating materials and the encapsulated ingredients by many folds due to the substantial change in the mechanical, electrical, and optical properties (Neethirajan & Jayas, 2011). Nanotechnology can significantly improve the aqueous solubility and thermal stability of the bioactive ingredients, as well as their oral bioavailability (Huang, Yu, & Ru, 2010; Jafari, Assadpoor, He, & Bhandari, 2008b; Rashidinejad, Birch, SunWaterhouse, & Everett, 2014). Although numerous studies have been published in the Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00008-X © 2020 Elsevier Inc. All rights reserved.

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area of nanotechnology for the encapsulation of bioactives in foods (Arpagaus, Collenberg, Ru¨tti, Assadpour, & Jafari, 2018; Assadpour & Jafari, 2019a, 2019b; Bao et al., 2019; Capriotti, Cavaliere, & Piovesana, 2019; Fathi, Martin, & McClements, 2014; Rashidinejad, Birch, & Everett, 2016; Shen, Zhang, McClements, & Park, 2019; Shishir, Xie, Sun, Zheng, & Chen, 2018; Wen, Al Gailani, Yin, & Rashidinejad, 2018; Zou, Xie, Zhu, & McClements, 2019), there still remains a need for a comprehensive focus on nanoencapsulation of bioactive compounds and their incorporation into novel functional foods. Therefore, the main aim of this chapter is to discuss the various aspects of nanoencapsulation techniques (specifically in terms of food bioactive ingredients), their applications and advantages, as well as the corresponding flaws and variations. To begin with, various bioactive ingredients that have been encapsulated and delivered using nanotechnology are explained.

8.2

A brief overview of bioactive ingredients

8.2.1 Polyphenols Polyphenols, which are also known as polyhydroxyphenols, polyphenolic compounds, or phenolic compounds, are the most abundant antioxidants and accordingly are an integral part of the human diet. By far, polyphenols are the most noticeable bioactive compounds in the area of nanoencapsulation of food bioactives (Assadpour, Jafari, & Esfanjani, 2017; Faridi Esfanjani & Jafari, 2016). These materials are abundantly found in fruits, herbs, and vegetables and include a structural class of mainly natural and organic chemical compounds. These compounds are categorized by the presence of phenol structural units, each presenting various and unique chemical, physical, and biological properties, originating from the variation in the number and properties of these phenol structures. Generally speaking, phenols (also known as polyhydroxyphenols) constitute a class of aromatic compounds from organic sources, similar to alcohols, having at least one hydroxyl group attached to an aromatic benzene ring (Xiao, Ni, Kai, & Chen, 2013). Accordingly, polyphenols are defined as compounds containing more than one phenolic hydroxyl group. These natural compounds are generally found as esters or glycosides in natural sources (i.e., plants) and can be counted as secondary metabolites (El Gharras, 2009).

8.2.1.1 Classification and the structure In general, more than 8000 types of polyphenols have been reported, each varying in terms of their chemical structures (Bravo, 1998), existing within a wide group ranging from simple molecules (phenolic acids) to highly polymerized compounds (tannins). There are two main metabolic mechanisms known by which polyphenols are produced. These include the shikimate pathway and the acetate pathway (Harborne, 1990). Polyphenols can occur in conjugated forms and via hydroxyl groups can link to one or more sugar residues (monosaccharides, disaccharides, and oligosaccharides) (Bravo, 1998; Cutrim & Cortez, 2018). There can also be a direct

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linkage of an aromatic carbon atom to the sugar units, or even linkage with other molecules such as organic and carboxylic acids, amines, lipids, and even other phenols (El Gharras, 2009; Spencer et al., 1988). Polyphenols can be classified according to different criteria, but the most common method of classifying these natural compounds is based on the number of carbons. According to one of the basic methods (Harborne & Simmonds, 1964), polyphenols can be classified into many different groups, as presented in Table 8.1, or they can be categorized depending on the number of the phenolic rings in the structure and/or the structural elements that bind these rings together, as shown in Table 8.2 (Manach, Scalbert, Morand, Re´me´sy, & Jime´nez, 2004; Vermerris & Nicholson, 2006). Flavonoids are considered to be the most important group of polyphenols and include more than 5000 compounds (Harborne, 1993). According to the type of heterocyclic moieties involved, these compounds (i.e., flavonoids) can also be subdivided into six main subcategories including flavanones, flavonols, flavones, isoflavones, flavanols (catechins and proanthocyanidins), and anthocyanidins (Manach, Williamson, Morand, Scalbert, & Re´me´sy, 2005). They share a common structure containing two aromatic rings (rings A and B), which are bound together with three carbon atoms forming an oxygenated heterocycle, considered as ring C (Manach et al., 2004). Perhaps the most common and scientifically studied groups of flavonoids are flavanols (sometimes referred to as flavan-3-ols). These include a derivative of flavans and they have received much research attention recently owing to their well-known health benefits. Flavanols include, but are not limited to, catechin (monomer), epicatechin (isomer), epicatechin gallate, epigallocatechin, epigallocatechin gallate (EGCG), theaflavins, thearubigins, and proanthocyanidins (also known as condensed tannins) (Faridi Esfanjani, Assadpour, & Jafari, 2018).

8.2.1.2 Polyphenols in food Polyphenols are reported to be abundant and near-ubiquitous in most plant foods, including vegetables, fruits, legumes, cereals, nuts, and cocoa, as well as beverages originating from some plants (e.g., tea and coffee). Table 8.3 lists the composition of polyphenols in various plant foods and beverages, reported by Bravo (1998). Obviously, different polyphenols may be found in different plant foods. For instance, fruits such as apricots, grapes, apples, pears, plums, nectarines, blackberries, cranberries, red raspberries, blackcurrants, cherries, and broad beans are rich sources of flavanols (Arts, van de Putte, & Hollman, 2000a; Bandyopadhyay, Chakraborty, & Raychaudhuri, 2007; de Pascual-Teresa, Gutie´rrez-Ferna´ndez, Rivas-Gonzalo, & Santos-Buelga, 1998; Nile & Park, 2014). In addition, the type of the flavanols found in various plant foods is also different. Catechin and epicatechin, for example, are the substantial flavanols found in fruits, whereas epigallocatechin and EGCG exist more in some seeds of leguminous plants, grapes, and predominantly in tea, and specifically green tea (Arts et al., 2000a; Arts, van de Putte, & Hollman, 2000b). Green tea, which originates from the tea plant Camellia sinensis, is the richest source of catechins, especially of the most potent catechin in terms of antioxidant activity (i.e., EGCG); depending upon the conditions of

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Table 8.1 Polyphenol classification on the basis of the number of carbons (Rashidinejad, 2015). Number of carbons in phenolic compound

Related category

Examples

C6 C6 C1

Simple phenolics Phenolic acids and related compounds

C6 C2

C18 C30 C6 C1 C6 C6 C2 C6 C6 C3 C6 (C6 C3)2

Acetophenones and phenylacetic acids Coumarins, isocoumarins cinnamic acids, phenylpropenes, cinnamyl aldehydes, cinnamyl alcohols Naftoquinones 1. Coumarins, isocoumarins, and chromones 2. Chalcones, aurones, dihydrochalcones 3. Flavans 4. Flavones 5. Flavanones 6. Flavanonols 7. Anthocyanidins 8. Anthocyanins Betacyanins Biflavonyls Benzophenones, xanthones Stilbenes Flavonoids Lignans and neolignans

(C6 C3)n

Lignin

Resorcinol, phloroglucinol p-Hydroxybenzoic acid, gallic acid, protocathechuic acid, salicylic acid, and vanillic acid 2-Hydroxyacetophenone and 2hydroxyphenyl acetic acid Cinnamic acid, caffeic acid, pcoumaric acid, ferulic acid, 5hydroxyferulic acid, and sinapic acid Juglone, alkannin, lapachol Umbelliferone and bergenin Butein and phloridzin Kaemferol, hydroxyflavone, quercetin, hydroxyflavone, and myricetin Pelargonidin, Cyanidin, peonidin, delphinidin, petunidin, and Leucodelphinidin Petanin Betanidin, indicaxanthin Ginkgetin Benzophenone, xanthone Resveratrol, piceatannol Flavone, isoflavan, neoflavonoids Pinoresinol, podophyllotoxin, and steganacin Coniferaldehyde, paracoumaryl alcohol, and coniferyl alcohol Tannic acid

C6 C3

C6 C4 C15

Tannins

extraction in preparing the beverage, every infusion of green tea can contain up to 200 mg of catechins (Lakenbrink, Lapczynski, Maiwald, & Engelhardt, 2000). One very important aspect of polyphenols in regard to their presence in the human diet is that they contribute to the sensory qualities of plant foods, in addition to their particular contribution to nutrition. In fact, it is known that the majority of the bitterness and astringency of plants and plant-associated food and beverages

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Table 8.2 The basic structure of the main flavonoids (Rashidinejad, 2015). Flavonoid compound

Basic structure

Chalcone

Aurone

Flavone

Flavonol

Flavanone

Flavan-3-ols (catechins)

Flavandiol

Anthocyianidin

(Continued)

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Table 8.2 (Continued) Flavonoid compound

Basic structure

Isoflavonoid

Neoflavonoid

Proanthocyanidins (condensed tannins)

comes from the polyphenols present in that food or beverage (Lesschaeve & Noble, 2005). Polyphenols (in particular, anthocyanins) are also responsible for the color of fruit and vegetables and derived products (Pe´rez-Magarin˜o & Gonzalez-San Jose, 2006). Oxidation (both enzymatic and nonenzymatic) of polyphenols during both processing and storage can result in some degree of color and flavor undesirability in the corresponding food products. One good example is tea, where the antioxidant activity and phenolic content of green tea, which is a nonfermented product, are much higher than fermented black tea (van het Hof, Kivits, Weststrate, & Tijburg, 1998). This is because of the effect that fermentation has on converting the monomer catechins, with high antioxidant activity, into more complex and condensed phenolic compounds, namely theaflavins (dimers) and thearubigins (polymers) (Johnson, Bryant, & Huntley, 2012).

8.2.1.3 Health benefits and stabilities It is well known that the versatile health benefits of fruit and vegetables are partly attributed to the constituent polyphenols present in these foods, and they, along with tea and coffee, are considered as the main dietary sources of polyphenolic compounds for humans on a daily consumption basis. There have been several epidemiological studies confirming the health-promoting effects of polyphenols because of the

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Table 8.3 The phenolic contents of various plant foods. Food/beverage Cereals (mg/100 g DMa) Barley Corn Millet Oats Rice Sorghum Wheat Legumes (mg/100 g DM) Black gram Chickpeas Cowpeas Common beans Green gram Pigeon pea Nuts (% DM) Betel nuts Cashew nuts Peanuts Pecan nuts Vegetables (mg/100 g FM) Brussels sprouts Cabbage Leek

Total polyphenols

1200 1500 30.9 590 1060 8.7 8.6 170 10,260 22 40

540 1200 78 230 175 590 34 280 440 800 380 1710 26 33 33.7 0.04 8 14

6 15 25 20 40

Onion Parsley

100 2025 55 180

Celery Fruits (mg/100 g FM) Apple Apricot Blackcurrant

94 27 298 30 43 140 1200

Food/beverage Fruits (mg/100 g FMb) Blueberry Cherry Cowberry Cranberry Gooseberry Grape Grapefruit Orange Peach Pear Plum Raspberry Red currant Strawberry Tomato Fruit juices (mg/L) Apple juice Orange juice Beverages Tea leaves (% DM) Green Black Tea, cup (mg/ 200 mL) Coffee beans (% DM) Coffee, cup (mg/ 150 mL) Cacao beans(% DM) Wine (mg/L) White Red Beer (mg/L)

Total polyphenols

135 280 60 90 128 77 247 22 75 50 490 50 50 100 10 15 2 25 4 225 37 429 17 20 38 218 85 130 2 16 370 7100

20 35 22 33 150 210 0.2 10 200 550 12 18 200 300 1000 4000 60 100

a

DM, dry matter. FM, fresh matter. Source: Modified from Bravo, L. (1998). Polyphenols: Chemistry, dietary sources, metabolism, and nutritional significance. Nutrition Reviews, 56(11), 317 333.

b

consumption of foods rich in these natural compounds. In particular, their effect on the reduction risk of chronic diseases, such as cancer, cardiovascular diseases, and diabetes, through preventing the impairment caused by oxidative stress in certain

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biomolecules (e.g., nucleic acids and proteins) has received extensive and growing research and medical attention (Chang, Alasalvar, & Shahidi, 2016; Chen et al., 2019b; Cilla et al., 2009; Fraga, Croft, Kennedy, & Toma´s-Barbera´n, 2019; Jiang & Xiong, 2016; Wichansawakun & Buttar, 2019; Zhang & Tsao, 2016). Some mechanisms have been proposed by which flavonoids or other phenolic compounds may help prevent diseases such as different types of cancers; however, further research is required, such as randomized clinical trials and in vitro chemical studies, to provide clarification about the nature of the effect and the interactions between phenolic compounds and other dietary constitutes. Some specific mechanisms for the reaction of polyphenols in the body include their interaction with enzymes, transcription factors, and some receptors. A “specific mechanism” means that, unlike a general mechanism in which chemical features are shared by most of the phenolic compounds (the phenol group is the key factor), a particular chemical group of a polyphenolic compound is a key factor of the mechanism (Fraga, Galleano, Verstraeten, & Oteiza, 2010). Interactions with proteins that result in a biological effect (depending upon the protein function) are examples of specific mechanisms. This kind of action depends upon modification of enzymatic activities, transcription factors binding to particular sites in DNA and, receptor ligand binding. However, under specific circumstances, the interaction between proteins and polyphenols might also be considered as a general mechanism. A good example of this is an interaction between polyphenols and proline-rich proteins, which starts with an initial hydrophobic association between aromatic phenolic rings and proline residues of the protein, forming small-sized aggregates, and ultimately protein precipitation (PoncetLegrand, Gautier, Cheynier, & Imberty, 2007). Although polyphenols show antioxidant activity in vitro, it is subsequent metabolism and absorption in the digestive tract which governs biological characteristics, including antioxidant activity (Tarko, Duda-Chodak, & Zajac, 2013). Only the fraction of the polyphenols released from the food matrix during digestion (in the small and/or large intestine) is considered part of the digesta. Food polyphenols in their native form mainly exist as polymers, esters, and glycosides which cannot be absorbed as such, and therefore need to be hydrolyzed by endogenous enzymes and/or microflora enzymes in the digestive tract (Williamson, Day, Plumb, & Couteau, 2000). It has been determined that about 48% and 42% of polyphenols can be digested in the small and the large intestines, respectively. The nature of the food matrix itself (e.g., the presence of fat in the case of hydrophobic polyphenols) may also affect the bioavailability of polyphenols as they can react with some constituents in the food matrix (Manach et al., 2004). Some other factors, such as pH, the gastrointestinal environment, and the presence of bile salts significantly affect the metabolism and bioavailability of polyphenols (Manach et al., 2004). Therefore, protection (e.g., nanoencapsulation) of polyphenols against the harsh environmental factors as well the environment of the upper part of the gastrointestinal tract (GIT) may improve their bioavailability. In addition, such an approach may also increase the solubility of most of the hydrophobic flavonoids, as well as reducing their interaction with food components when incorporated into functional foods, and decreasing undesirable sensorial properties (Rashidinejad, Loveday, Jameson, Hindmarsh, & Singh, 2019).

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8.2.2 Carotenoids Carotenoids (or tetraterpenoids), are the chemical organic compounds (pigments) with yellow, orange, and red color produced mostly by plants (they can also be produced by algae, bacteria, and fungi) (Milani, Basirnejad, Shahbazi, & Bolhassani, 2017). These pigments, when absorbed in the diet of animals (exclusively, carnivorous), can be stored in their fatty tissues and in general, it is known that the absorption of carotenoid compounds is enhanced when they are consumed with a significant amount of fat in a meal. It is also known that some processes such as cooking can increase the bioavailability of certain carotenoids in the case of foods such as vegetables (Saini, Nile, & Park, 2015).

8.2.2.1 Classification and the structure Carotenoids are categorized into two different classes; xanthophylls and carotenes (Rostamabadi, Falsafi, & Jafari, 2019a). The first group (xanthophylls) contains oxygen, while the second group (carotenes) contains no oxygen and carotenoids in this class are purely hydrocarbons. Carotenoids that contain unsubstituted β-ionone rings (e.g., α-carotene, β-carotene, β-cryptoxanthin, and γ-carotene) present vitamin A activity, meaning that their conversion to retinol is possible (Milani et al., 2017). There are two key roles for carotenoids known in plants and algae, including absorption of light energy for use in photosynthesis and protection of chlorophyll from photodamage (Yabuzaki, 2017). All of the carotenoids derive from tetraterpenes, indicating that they are produced from molecules of isoprene and contain 40 carbons.

8.2.2.2 Carotenoids in food Carotenoids such as β-carotene are responsible for the orange yellow colors of fruit and vegetables such as pumpkins, carrots, sweet potato, and winter squash. Among the common foods, the highest amount of carotene, which is measured in retinol activity equivalents (provitamin A equivalents), is found in dried carrots (per 100-g serving) (Strøm, 2011). Some fruits such as watermelon, melon, orange, and grapefruit are considered as rich sources of lycopene. The highest concentration of lycopene is known to be in Vietnamese gac fruit (Tran, Parks, Roach, Golding, & Nguyen, 2016). Substantial amounts of β-carotene can also be found in leafy greens such as kale, spinach, collard greens, and turnip greens. The most abundant carotenoid in plants is xanthophyll lutein. Due to the masking presence of chlorophyll, lutein and the other carotenoid pigments are often not obvious in mature leaves of the plants, and when chlorophyll is absent (e.g., autumn foliage), the distinctive colors of yellow and orange of the carotenoids become predominant. The same reason is also applied in the case of ripe fruit, where carotenoid colors often predominate, after being unmasked by the absence/disappearance of green chlorophyll (Bernstein et al., 2016).

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8.2.2.3 Health benefits and stabilities Humans and animals in general are not capable of synthesizing carotenoids, and therefore, they must obtain these chemical compounds through their diet. There have been several studies to review the epidemiological effects of carotenoids and to examine the correlations between the consumption of these materials in food and the potential clinical outcomes. For example, Vieira et al. (2015) reported a protective effect against lung cancer when the diets rich in fruit and vegetables (some rich sources of carotenoids) were consumed. Another review studying the correlations between carotenoids and prevention of prostate cancer concluded that evidence is lacking to confirm that such an effect is exclusively due to carotenoid intake per se, although several studies reported positive correlations between diets rich in carotenoids and reduced risk of prostate cancer (Soares, Teodoro, Lotsch, Granjeiro, & Borojevic, 2015). Van Ryswyk, Villeneuve, Johnson, and Group (2016) found no conflicting results in several reviewed investigations concerning the dietary consumption of carotenoids and the risk of breast cancer. In regard to Parkinson’s disease, for example, a systematic review found no significant correlation between the consumption of carotenoids/vitamin A-rich foods and the risk of this disease (Takeda et al., 2014). An important role of carotenoids is in the formation and maintenance of the dark brown pigment melanin, the important pigment that is found in skin, hair, and eyes, and plays a vital role in absorbing high-energy light and protecting such organs of the body from intracellular damage. In this regard, some positive effects of high-carotenoid diets have been reported on the color, texture, strength, clarity, and elasticity of the skin (Foo, Rhodes, & Simmons, 2017; Roma´nska-Gocka, Wo´zniak, Kaczmarek-Skamira, & Zegarska, 2016; Schagen, Zampeli, Makrantonaki, & Zouboulis, 2012). Since carotenoids are lipophilic (soluble in oil and organic solvents), they can be isomerized by heat, light, and acid, and present spectral changes with different reagents. Due to a large number of the conjugated double bonds, carotenoids are easily oxidized by different environmental factors. This reaction results in the loss of color of the foods containing carotenoids, which is an indication of the instability of carotenoids (Milani et al., 2017; Yabuzaki, 2017). Therefore, nanoencapsulation can be an appropriate approach in order to protect different carotenoids against different environmental factors that result in the chemical instability of these compounds.

8.2.3 Vitamins Vitamins are the organic molecules and essential micronutrients needed (although in small quantities) for the proper functioning of different organisms and their metabolism (Tomas & Jafari, 2018). Such essential micronutrients cannot be synthesized by the organisms themselves (although in some species can be synthesized, but such synthesis is usually in insufficient quantities), and must be obtained via the diet. It is notable that most vitamins may not be necessarily single molecules, but can be groups of associated molecules called vitamers (Basu & Dickerson, 1996).

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8.2.3.1 Classification and the structure Vitamins are categorized into water- and fat-soluble groups. Generally speaking, there are 13 vitamins known in humans. These include four fat-soluble vitamins (i.e., A, D, E, and K) and nine water-soluble vitamins (i.e., vitamin C and eight vitamins in the B group). In the case of water-soluble vitamins, due to their high dissolution rate, largely, they are excreted from the body through urine. Therefore the urinary output is a strong predictor of the consumption or deficiency of water-soluble vitamins (Fukuwatari & Shibata, 2008). Thus, as these vitamins are not stored in the body at significant quantities, consistent consumption of them through the diet is required (Asif, 2016). Fat-soluble vitamins, on the other hand, can be stored and accumulated in the body. With the help of lipids (fats), these vitamins are absorbed through the intestinal tract (Katouzian & Jafari, 2016). It is notable that while the accumulation of the fat-soluble vitamins means less-frequent intake of them through the diet, such accumulation in the cases of some (e.g., vitamins A and D) can result in dangerous hypervitaminosis (Maqbool & Stallings, 2008).

8.2.3.2 Vitamins in food Apart from vitamin K, which can be synthesized by some microorganisms (especially, in the gut flora), and one form of vitamin D, which is produced in skin cells after the exposure to a certain wavelength of ultraviolet light (in sunlight), vitamins are sourced from the diet. In humans, some vitamins can be synthesized from precursors consumed in the daily diet. Some examples are the synthesis of vitamin A from β-carotene, and niacin from the amino acid tryptophan (Yates, Schlicker, & Suitor, 1998). Vitamins can be found in both animal and plant sources; whole grains, fruits, vegetables, legumes, different types of meat, dairy products, oils, nuts, and seeds. In fact, many common foods are rich sources of various vitamins, meaning that it is easy to meet the daily requirements just by proper consumption of typical everyday meals. Obviously, some foods are richer sources of some specific type of vitamins. For instance, vitamin B12 is mostly found in animal products such as red meat, fish, eggs, and dairy, while other vitamins in the B group can be found in various fruit and vegetables. Vitamin C is mostly found in citrus fruit, broccoli, chili, bell peppers, potatoes, spinach, tomatoes, strawberries, Brussels sprouts, and the like. Beef, liver, fish, shrimp/ prawns, eggs, fortified milk, carrots, sweet potatoes, pumpkins, spinach, and mangoes are rich sources of vitamin A. Vitamin D is mostly present in products such as fortified milk and fatty fish. Vegetable oils, leafy green vegetables, nuts and seeds, and whole grains are considered as the richest sources of vitamin E, and vitamin K can be mainly found in foods such as eggs, milk, cabbage, broccoli, spinach, and kale.

8.2.3.3 Health benefits and stabilities The role of vitamins in the growth and development of all living organisms is well known. After the growth and development of the human body have been completed, the healthy maintenance of all cells/tissues and organs remains dependent on vitamins as one class of the essential nutrients. Vitamins are required for numerous

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applications and mechanisms in the human body and each of them plays some vital role(s) in this regard. By the help of vitamins, a multicellular life can efficiently use chemical energy originating from the food eaten, and can process other nutrients including carbohydrates, proteins, and fats, which are necessary for the cellular respiration (Tolonen, 1990; Zmijewski, 2019). The stability of different vitamins in the environment is dependent on the presence of several physical and chemical factors such as temperature, light, pressure, pH, and humidity. For example, exposure to a high content of moisture and hot temperatures during storage may significantly increase the degradation rate of most of the vitamins due to triggering the chemical reactions (e.g., oxidation). Clearly, the susceptibility to degradation by chemical and physical factors is different in the case of various individual vitamins (Ottaway, 1993). Lower stability of vitamins means lower bioavailability, as the bioavailability of vitamins can be substantially decreased by the breakdown of their structure. In this regard, nanoencapsulation can be a promising approach for protecting vitamins against destructive environmental factors during processing, storage, and delivery, as well as their targeted delivery inside the digestive tract (Boisselier, Liang, Dalko-Csiba, Ruiz, & Astruc, 2010; Katouzian & Jafari, 2016).

8.2.4 Minerals Minerals are necessary for different functions in the body, including building bones and teeth, controlling body fluids (both intracellular and intercellular), and conversion of the food into energy through complex processes (Nosratpour & Jafari, 2018). Living organisms, such as the human body, cannot synthesize minerals biochemically, but plants get them from the soil so that the source of the majority of the minerals in a human diet is the plants and animals eaten in the daily diet, besides the drinking water (Grusak & DellaPenna, 1999).

8.2.4.1 Classification and the structure As a general concept in food and nutrition, the term “mineral” refers to a chemical element that is essential for living organisms to perform the necessary functions for life (Zoroddu et al., 2019). Nonetheless, this term usually does not include oxygen, hydrogen, carbon, and nitrogen, the four main structural elements in the human body (by weight, they constitute up to 96% of the weight of the human body). Minerals are classified into major minerals (or macrominerals) and minor minerals (or trace elements). The first group (major minerals) includes calcium, phosphorus, potassium, sodium, and magnesium; whereas, the trace elements (minor minerals) in the human body comprise sulfur, iron, manganese, chlorine, copper, cobalt, zinc, molybdenum, iodine, and selenium (Berdanier, Dwyer, & Feldman, 2007).

8.2.4.2 Minerals in food Minerals required for the human body are mainly supplied through foods rich in the specific mineral of interest (e.g., calcium in dairy foods) or are added to the normal

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food (e.g., salt fortified with iodine, orange juice fortified with calcium, and bread fortified with iron) (Gharibzahedi & Jafari, 2017a, 2017b). The common forms of minerals added as dietary supplements to the food are either in combination with other nutrients (e.g., vitamins), or as a single element in different forms (e.g., calcium in the form of calcium carbonate and calcium citrate, iron in the form of ferrous sulfate and iron bis-glycinate, and magnesium in the form of magnesium oxide). It is known that all the body’s chemical element requirements can be met by the regular diet, and supplements should only be used in the case of recognized deficiencies (Berdanier et al., 2007; Tolonen, 1990). Every common food can be a source of several major and trace minerals. For example, foods rich in major minerals such as calcium and iron are milk and dairy foods, different types of meat (including seafood), eggs, fortified cereals, different fruit and vegetables (especially, leafy greens), herbs, dark chocolate, seeds, and nuts. Magnesium is mainly found in spinach, whole grains, legumes, seeds, nuts, peanut butter, and avocado. Table salt (sodium chloride) is the main source of sodium, while this element also exists in milk and dairy products, sea vegetables, and spinach. Red meat, dairy foods, fish, poultry, bread, oats, and rice are the main sources of phosphorus. At the same time, the aforementioned food products are rich sources of different trace minerals as well (Bartl & Bartl, 2019; Gharibzahedi & Jafari, 2017a, 2017b; Weaver et al., 2016).

8.2.4.3 Health benefits and stabilities Just like other essential nutrients, minerals help the human body to grow, develop, and maintain its health. The body uses different minerals to perform numerous various functions, from using minerals as building blocks for the strong healthy bones to transmitting nerve impulses at the cellular and intracellular levels. Some minerals are used as precursors of some other essential materials in the body, such as hormones. Thus, different major and trace minerals can play different functions in the body. Calcium, for example, as the top macromineral, is the essential material for bones and teeth, as well as helping with many chemical reactions in the body. Iron is required for the transport of oxygen from the lungs to the rest of your body, and it helps with the formation of hemoglobin and oxygen transfer throughout the body. Potassium is a vital element when it comes to the functions of the muscles and nervous system. Zinc is important for the development and functioning of the immune system, in addition to its important role concerning cell growth (Bartl & Bartl, 2019; Garcia-Casal, Pen˜a-Rosas, & Giyose, 2017; Gharibzahedi & Jafari, 2017a, 2017b; Tolonen, 1990; Weaver, 2017). Although minerals are generally more resistant to the environmental factors (e.g., during manufacturing processes and storage) than other bioactive compounds such as vitamins, still chemical changes happen when they are exposed to air, heat, and/or light. Minerals such as iron, copper, and zinc can also be affected by factors such as moisture. Under different conditions, they may also react with other food components (e.g., proteins and carbohydrates). The stability of various forms of different minerals depends on various factors such as the nature of the food, particle size, and the extent of the exposure to environmental factors. Instability of some of the minerals, such as

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iron, can result in off-flavors and undesirable colors or odors. Therefore, by using nanoencapsulation technology, minerals can be potentially protected and used as additive food bioactives to the functional foods without interference with the food matrix and with increased stability under processing, storage, and digestion wherein (Dias, Botrel, Fernandes, & Borges, 2017; Ray, Raychaudhuri, & Chakraborty, 2016; Yang, Zhou, Sun, Gao, & Xu, 2015).

8.2.5 Essential oils Essential oils are concentrated hydrophobic liquids from plants, which contain some volatile chemical compounds (easily evaporated at normal temperatures). These liquids are also known with some other names such as volatile oils, aetherolea, ethereal oils, or simply called the oil of the plant they are extracted from (e.g., rosemary oil, lavender oil) (Hyldgaard, Mygind, & Meyer, 2012). The term “essential” should not be confused with “indispensable” or “nutritionally required,” but it means that the oil contains the “essence of” the specific plant’s fragrance. Essential oils are usually extracted by common processes such as distillation, solvent extraction, cold pressing, expression, absolute oil extraction, resin wax embedding, and tapping, and in the food industry, they are used for flavoring food and drinks. The majority of the common essential oils have been considered as Generally Recognized as Safe (GRAS) by the Food and Drug Administration (FDA) (Preedy, 2015).

8.2.5.1 Classification and the structure Perhaps the most common method for the classification of essential oils is according to their application: G

G

G

G

essential oils used in soap, perfumery, and cosmetic industry; essential oils used in the food and beverages industry (e.g., as flavorings, preservatives, and additives); and essential oils used in agroindustrial proposes (e.g., antifungal and insecticidal) essential oils used in the medical industry.

In addition, other classifications according to the geographical origin and botanical sources might be also possible. These types of classifications are diverse and out of the scope of this chapter. In terms of structure, various essential oils contain complex chemical structures, as there could be hundreds of various aromatic compounds present in every essential oil from a specific plant extract. For example, essential oils from sources such as orange, lemon, spearmint, eucalyptus, and menthe have completely different chemical structures. In addition, the basic structure of essential oils from a specific source may also change due to the extraction method (Hashemi, Khaneghah, & de Souza Sant’Ana, 2017). The chemical structures of the most common monoterpenes from different essential oils are presented in Fig. 8.1A. Also Fig. 8.1B presents the structures of various sesquiterpenes found in essential oils (Hashemi et al., 2017).

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Figure 8.1 (A) The basic chemical structures of the most common monoterpenes from different essential oils. (B) The chemical structures of various sesquiterpenes found in different essential oils. Source: Redrawn from Hashemi, S. M. B., Khaneghah, A. M., & de Souza Sant’Ana, A. (2017). Essential oils in food processing: Chemistry, safety and applications. John Wiley & Sons.

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8.2.5.2 Essential oils in food As mentioned in the previous section (Section 8.2.5.1), the variety of different food sources results in a very wide range of essential oils with complex chemical structures due to different aromatic compounds. Different foods including fruits, vegetables, herbs, spices, flowers, etc. have been known for various essential oils. Oranges, lemons, carrots, onions, garlic, capsicum, cinnamon, clover, basil, parsley, cacao, rosemary, spearmint, anise, bay leaves, cloves, ginger, saffron, tea, thyme, turmeric, vanilla, etc. all been known for their specific and unique essential oils, which mostly have been commercialized and are being used in the food products. In relation to their food applications, although essential oils have been used throughout history in various food products as preservatives, they were not regulated until the 20th century, when the FDA reported that essential oils can be considered as GRAS (Preedy, 2015).

8.2.5.3 Health benefits and stabilities The antioxidant, antiinflammatory, and antitumoral activities of essential oils have resulted in a very important market in both nutraceuticals and food industry. There is a significant body of literature reporting on the prevention of various diseases due to the intake of essential oils from different sources (Bao et al., 2019; Blowman, Magalha˜es, Lemos, Cabral, & Pires, 2018; Jamil et al., 2016; Lacatusu et al., 2015). Linalool, geraniol, and menthol have been reported to be some of the most effective compounds in the essential oils, containing the highest range of antibacterial and antifungal activities (Hashemi et al., 2017; Tan, Chua, Ram, & Kuppusamy, 2016). It is well known that almost all of the essential oils are highly volatile. In addition, they are prone to oxidation due to the exposure to oxygen, light, and heat. In this regard, there have been numerous studies to protect such essential compounds from the aforementioned factors during food processing and storage. It has been reported that essential oils can be well preserved by encapsulation and their bioactivity can be improved when they are encapsulated in different forms (Donsi & Ferrari, 2016; Rao, Chen, & McClements, 2019; Wen et al., 2016).

8.3

Encapsulation methods for nanodelivery of bioactive compounds

The protection of bioactive compounds against environmental factors during the process and storage of the food, as well as during gastrointestinal digestion, can be achieved by nanoencapsulation technologies. To date, nanoencapsulation remains one of the most promising approaches for this purpose, which is due to the capability of entrapping various bioactive compounds using several mechanisms (Ezhilarasi, Karthik, Chhanwal, & Anandharamakrishnan, 2013). Nanoencapsulation of bioactive ingredients is a feasible approach for targeted site-specific delivery of these materials and their efficient absorption through cells in the digestive system (Jafari &

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McClements, 2017). Some examples of the research on various nanoencapsulation techniques for delivery of various bioactive compounds are presented in Table 8.4. While this area of research has been fast progressing during the last couple of decades, investigations in the field of applying bioactive-loaded nanocarriers for the manufacture of corresponding food products have been somehow limited (Assadpour & Jafari, 2019a, 2019b). In the following sections, we focus on the various nanoencapsulation methods, which have been used for nanodelivery of a wide range of food bioactive ingredients. In this scope, the current state of knowledge, recent trends and advantages, and possible limitations of each technique are discussed. Based on the development of nanomaterials/nanoparticles and the approach used to entrap/encapsulate bioactive compounds, nanoencapsulation techniques are classified into either top-down or bottom-up approaches (Ezhilarasi et al., 2013; Pattekari et al., 2011). A top-down approach allows size reduction and structure shaping of the particles using the application of precise tools (e.g., emulsification technique). On the other hand, in the case of a bottom-up approach, the intrinsic properties such as selfassembly and self-organization of the molecules/materials are utilized for manufacturing the nanoparticles (e.g., coacervation, inclusion complexation, and liposomal encapsulation). Obviously, such properties can be influenced by several environmental factors such as temperature, pH, ionic strength, and concentration (Augustin & Sanguansri, 2009).

8.3.1 Nanoemulsification Nanoemulsions are one of the most applicable carriers for bioactive ingredients in aqueous solutions (Jafari, Paximada, Mandala, Assadpour, & Mehrnia, 2017). Emulsification can be used as either the primary method of encapsulation, or secondary and even tertiary method combined with some other methods. Nanoemulsions include both oil-in-water (O/W) and water-in-oil (W/O) emulsions, as well as double and multilayer emulsions. Nanoemulsions are generally colloidal dispersions composed of two immiscible liquids, where one liquid is dispersed in the other. The size of the manufactured droplets using the nanoemulsion technique is in the range of 50 500 nm (Sanguansri & Augustin, 2006). Emulsification technology has a great potential for the delivery of high concentrations of lipophilic (oil-soluble) bioactives such as fatty acids, essential oils, carotenoids, and plant sterols. Lipophilic bioactives can be encapsulated in O/W emulsions, while W/O emulsions are a suitable method for encapsulation of watersoluble food active agents (Zuidam & Shimoni, 2010). After manufacture, nanoemulsions can be directly incorporated into the corresponding food products or dried using drying techniques (e.g., spray drying and freeze drying) and be used as dry powders. One of the advantages of nanoemulsions for the delivery of bioactive ingredients is their high kinetic stability. Resulting from their small droplet sizes (Solans, Izquierdo, Nolla, Azemar, & Garcia-Celma, 2005), it plays a very important role in the retention of surface oil content of the emulsified product (Jafari, Assadpoor, Bhandari, & He, 2008a). However, the emulsification method requires the use of high-energy processes

Table 8.4 Some examples of nanoencapsulation technologies used for delivery of various bioactive ingredients. Nanoencapsulation technique

Important raw materials (wall materials/emulsifiers)

Bioactive compounds

Bioactive class

Size of carrier (nm)

Purposes of encapsulation

References

Nanoemulsions

Gelatin and chitosan

Tocopherol, cinnamaldehyde, and garlic oil

Vitamins, essential oils

110 150

Pe´rez-Co´rdoba et al. (2018)

Medium chain triglyceride, soy lecithin

Turmeric extract

Curcuminoids

163 nm

Whey protein concentrate/pectin

Curcumin

Curcuminoids

150 300 nm

Folic acid

Vitamins

500 nm

Maltodextrin; emulsifiers: modified starch (Hi-Cap 100) Tween 40

D-Limonene

Essential oils

543 1292 nm

Increase physical stability and minimizing the potentially detrimental sensorial effects Increase aqueous solubility, decrease oxidation, and improve immiscibility with food components Enhancement of the bioaccumulation of curcumin in C. elegans Increasing chemical stability and facilitating delivery Protecting the droplets from recoalescence

Flax seed oil

Fatty acids

135 nm

Kentish et al. (2008)

Tween 80, Span 80, and sodium dodecyl sulfate Tween 20

Sunflower oil

Fatty acids

40 nm

Optimizing operating conditions to prevent the droplet from coalescence and cavitational bubble cloud formation Optimizing the conditions to produce nanoemulsion

Curcumin

Curcuminoids

79 618 nm

OSA starch, chitosan, and lambdacarrageenan

MCT

Fatty acids

130 nm

Enhancing the antiinflammation activity Improving the stability for use in food or pharmaceutical industry

Park et al. (2019)

Shen et al. (2019)

Assadpour, Jafari, and Maghsoudlou (2017) Jafari, He, and Bhandari (2007b)

Leong, Wooster, Kentish, and Ashokkumar (2009) Wang et al. (2008) Preetz, Ru¨be, Reiche, Hause, and M¨ader (2008)

Coacervation

Tween 20, Tween 40, Tween 60, and Tween 80 Tween 20

β-Carotene

Carotenoids

132 184 nm

β-Carotene

Carotenoids

121 177 nm

Marine lecithin

Salmon oil

Fatty acids

160 207 nm

Zein, chitosan

Resveratrol

Polyphenols

556 631 nm

Gelatin, maltodextrin and tannins; emulsifiers: Tween 60; other material: glutaraldehyde Gelatin, acacia, and hydrolysable tannins; emulsifiers: hydroxyethyl, cellulose; other material: glutaraldehyde Gelatin, acacia, and tannins; emulsifiers: Tween 60; other material: glutaraldehyde Chitosan, poly (ethyleneglycol-ranpropyleneglycol); other material: sodium tripolyphosphate

Capsaicin

Polyphenols

100 nm

Capsaicin

Polyphenols

300 600 nm

Improving the efficiency and delaying the release property

Xing et al. (2005)

Capsaicin

Polyphenols

100 nm

Masking its pungent odor and improving the stability

Jincheng et al. (2010)

BSA

Proteins

200 580 nm

Controlling the release

Gan and Wang (2007)

Improving physical stability and commercial application Improving the stability Increasing the oxidative stability Improve the stability and bioavailability Masking the pungent odor, giving biocompatibility and biodegradation

Yuan, Gao, Zhao, and Mao (2008a) Yuan, Gao, Mao, and Zhao (2008b) Belhaj, Arab-Tehrany, and Linder (2010) Ren et al. (2019) Wang et al. (2008)

(Continued)

Table 8.4 (Continued) Nanoencapsulation technique

Important raw materials (wall materials/emulsifiers)

Bioactive compounds

Bioactive class

Size of carrier (nm)

Purposes of encapsulation

References

Liposomes/niosomes

Rice bran phospholipids

Quercetin

Polyphenols

157 nm

Improve solubility and bioavailability

Tween 80

α-tocopherol and γ-oryzanol in cold-pressed rice bran oil

200 nm

Improve controlled release and stability

Rodriguez, Almeda, Vidallon, and Reyes (2019) Huynh Mai et al. (2020)

Phosphatidylcholine, pectin Soy lecithin

Vitamin C

Vitamins

130 nm

Increasing chemical stability

Zhou et al. (2014)

Green tea catechins, green tea extract

Polyphenols

153 175 nm

Rashidinejad et al. (2016), Rashidinejad et al. (2014)

Soy phosphatidylcholine

Vitamin C

Vitamins

100 nm

Soy lecithin

Resorcinol

Soy lecithin

Curcumin

Decreasing astringency, increasing stability, improving stability, decreasing interactions with other compounds in food Improving stability under light or heating conditions Increasing water solubility and physical instability Increasing chemical stability

β-Lactoglobulin and low methoxyl pectin

DHA (docosahexaenoic acid)

Zimet and Livney (2009)

α- and β-cyclodextrin

Linoleic acid

Formation of transparent solution, improve the colloidal stability, protection against degradation and useful for enrichment of acid drinks Improving the thermal stability

Inclusion complexation

160 170 nm Curcuminoids

114 nm

100 nm

Fatty acids

236 nm

Yang et al. (2012)

Yang et al. (2012) Hasan, Elkhoury, Kahn, Arab-Tehrany, and Linder (2019)

H˘ad˘arug˘a et al. (2006)

Nanoprecipitation/ nanocomplexation

Monomethoxy poly (ethylene glycol)poly(3-caprolactone) micelles Poly(lactide-coglycolide); emulsifiers: polyethylene glycol5000 Ethyl cellulose and methyl celluolose

Curcumin

Curcuminoids

27 nm

Improving the solubility

Gou et al. (2011)

Curcumin

Curcuminoids

81 nm

Anand et al. (2010)

Curcumin

Curcuminoids

117 218 nm

Poly(D,L-lactic acid) and poly(D,L-lacticcoglycolic acid); emulsifiers: gelatin or Tween 20 Poly(ethylene oxide)-4methoxycinnamoyl phthaloylchitosan, poly(vinylalcoholco-vinyl-4methoxycinnamate), Poly(vinylalcohol), and ethyl cellulose Zein/pectin Sodium caseinate and pectin

β-carotene

Carotenoids

80 nm

Improving the bioavailability, bioactivity, encapsulation efficiency and enhancing the cellular uptake Improving oral bioavailability and sustainability Improving physical, chemical stability and bioavailability

300 320 nm

Improving the solubility and bioavailability

Tachaprutinun, Udomsup, Luadthong, and Wanichwech arungruang (2009)

235 nm 215 nm

Increasing chemical stability Sustained release under simulated intestinal conditions

Huang et al. (2017) Luo et al. (2015)

Astaxanthin

Resveratrol Rutin

Polyphenols Polyphenols

Suwannateep et al. (2011) Ribeiro, Chu, Ichikawa, and Nakajima (2008)

(Continued)

Table 8.4 (Continued) Nanoencapsulation technique

Important raw materials (wall materials/emulsifiers)

Bioactive compounds

Bioactive class

Size of carrier (nm)

Purposes of encapsulation

References

Emulsification solvent evaporation

Chitosan cross-linked with tripolyphosphate; emulsifiers: Span 80 and Tween 80; other materials: acetic acid and ethanol Hydroxyl propyl methyl cellulose and polyvinyl pyrrolidone; emulsifiers: Dα-Tocopheryl polyethylene glycol 1000 succinate, Tween 80, Tween 20, cremophor-RH 40, pluronic-F68, pluronic-F127 Poly-D,L-lactide and polyvinyl alcohol

Curcumin

Polyphenols

254 415 nm

For controlled release

Sowasod, Charinpanitkul, and Tanthapanichakoon (2008)

Curcumin

Curcuminoids

100 nm

Enhance absorption and prolong the rapid clearance of curcumin

Dandekar et al. (2010)

Quercetin

Polyphenols

170 nm

Poly(methyl methacrylate) and polyvinyl alcohol

Coenzyme Q10

Coenzymes

40 260 nm

Kumari, Yadav, Pakade, Singh, and Yadav (2010) Kwon et al. (2002)

Tween 20; other materials: hexane, isopropyl alcohol, ethanol, and acetone

Phytosterol

Sterols

50 282 nm

Improving the controlled release and encapsulation efficiency Improving the reproducibility, stability and target drug loading yield Optimize the operating conditions and reduce phytosterol loss

Leong et al. (2011)

Spray drying

Tween 20

α-Tocopherol

Vitamins

90 120 nm

Sodium caseinate

Astaxanthin

Carotenoids

115 163 nm

Tween 20

β-Carotene

Carotenoids

9 280 nm

Poly(D,L-lactide-coglycolide) and polyvinyl alcohol; other materials: chloroform and ethanol Sodium caseinate/pectin

Curcumin

Curcuminoids

45 nm

Curcumin

Curcuminoids

300 330 nm

Carbohydrate matrix and maltodextrin; other materials: acetone

Catechin (H)

Polyphenols

80 nm

Modified n-octenyl succinate-starch; other materials: ethyl acetate Maltodextrin; emulsifiers: Hi-Cap, whey protein concentrate, and Tween 20

β-carotene

Carotenoids

D-limonene

Essential oils

300 600 nm (droplet size); 12 μm (particle size) 0.2 1.2 μm (emulsion droplet size); 21 53 μm (dried particle size)

Minimizing the recoalescence, improve the physical stability and solubility Optimizing the processing condition and improving bioavailability Improving the physical stability Increase chemical stability

Cheong, Tan, Man, and Misran (2008)

Improving the encapsulation efficiency, physical stability, and sustained release in simulated gastrointestinal conditions Increasing chemical stability, protecting from oxidation and incorporation into beverages Improving dispersibility, coloring strength and bioavailability

Wang, Ma, Lei, and Luo (2016)

Increasing the retention, stability during process

Jafari, He, and Bhandari (2007a)

Anarjan, Mirhosseini, Baharin, and Tan (2011) Silva et al. (2011) Mukerjee and Vishwanatha (2009)

Heyang, Fei, Jiang, Yaping, and Lin (2009)

de Paz et al. (2012)

(Continued)

Table 8.4 (Continued) Nanoencapsulation technique

Self-assembly complexation (pH-driven)

Important raw materials (wall materials/emulsifiers)

Bioactive compounds

Bioactive class

Size of carrier (nm)

Purposes of encapsulation

References

Maltodextrin; emulsifiers: modified starch (Hi-Cap)/whey protein concentrate Casein

Fish oil

Fatty acids

Curcuminoids

Sodium caseinate, pectin Soybean polysaccharide (SOYAFIBE-S Serie)

Rutin

Polyphenols

210 nm

Curcumin

Curcuminoids

200 300 nm

Minimizing the unencapsulated oil at the surface and maximizing encapsulation efficiency Decreasing sensitivity to degradation under environmental conditions Increasing water solubility and improving stability Increasing water solubility and bioactivity

Jafari et al. (2008a)

Curcumin

0.21 5.9 μm (droplet size); 25 41 μm (particle size) 104 nm

Pan et al. (2014)

Luo, Pan, and Zhong (2015) Pan, Chen, Baek, and Zhong (2018)

Source: Upgraded and modified from Ezhilarasi, P., Karthik, P., Chhanwal, N., & Anandharamakrishnan, C. (2013). Nanoencapsulation techniques for food bioactive components: A review. Food and Bioprocess Technology, 6(3), 628 647.

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(e.g., high-shear mixing/stirring, high-pressure homogenization, microfluidization, and ultrasonication) for the formation of nanoparticles (Jafari, Assadpoor, He, & Bhandari, 2008), because nanoemulsions by nature are nonequilibrium systems and cannot be formed spontaneously (Ezhilarasi et al., 2013). Apart from the smaller particle size, nanoemulsion systems possess transparent optical properties, and improved bioavailability of the encapsulated active ingredients. Although different size ranges (from 10 to 500 nm) have been reported for nanoemulsions (McClements, 2012; Wulff-Pe´rez, Torcello-Go´mez, Ga´lvez-Ruı´z, & Martı´n-Rodrı´guez, 2009), generally, nanoemulsions with a droplet size bigger than 200 nm are preferred for food applications (Lohith Kumar & Sarkar, 2018). One of the other important features of emulsification technique is controlled release of bioactive compounds using different properties (e.g., composition, structure, thickness, charge, rheology, chemical reactivity, permeability, and environmental responsiveness) of the coating/wall materials in the case of multilayer emulsions (Decher & Schlenoff, 2003; McClements, 2015). Multilayer and multiple emulsions also allow coencapsulation of both lipophilic and hydrophilic bioactive components, where lipophilic bioactives are entrapped within the oil droplets and hydrophilic compounds can be entrapped within the aqueous phase of the coatings that surround the oil droplets (Gharehbeglou, Jafari, Hamishekar, Homayouni, & Mirzaei, 2019). The release of the entrapped bioactive ingredients within the two different phases of a multilayer/multiple emulsion can be retained in the response to a specific environmental trigger (e.g., pH, temperature, enzyme activity, ionic strength) (McClements, 2010a). The schematic process for the fabrication of multilayer emulsions is presented in Fig. 8.2 (McClements, 2015).

Figure 8.2 Schematic process for the fabrication of multilayer emulsions used for encapsulation of bioactive compounds. Source: Modified from McClements, D. J. (2015). Encapsulation, protection, and release of hydrophilic active components: Potential and limitations of colloidal delivery systems. Advances in Colloid and Interface Science, 219, 27 53.

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Multilayer emulsions have already been used for nanoencapsulation of lipophilic flavor compounds, carotenoids, ω-3 fatty acids, and lipophilic vitamins, in order to improve the physicochemical stability of such bioactive ingredients (Anal, Shrestha, & Sadiq, 2018; Koubaa, Nikmaram, Roohinejad, Rafati, & Greiner, 2018; McClements, 2010b). Several food-grade ingredients are readily available for fabrication of multilayer emulsions utilizing conventional processing operations such as mixing, sonication, and homogenization. However, the choice of such ingredients and preparation methods is very critical in the food industry and must be carefully controlled, due to the possible challenges in regard to food safely, flocculation (instability), and scale-up for commercial applications.

8.3.2 Nano spray drying Spraying a solution/suspension containing bioactive materials along with the wall materials into a hot drying medium is one of the fastest and most efficient ways to nanoencapsulate such materials. This process transforms the feed (solution) into a dried powder, with uniformly spherical-shaped particles, which can be conveniently stored, transported, and utilized (Masters, 1985). Spray drying can also be used as a secondary method of encapsulation in combination with other methods such as emulsification and liposomes. In fact, the incessant production of dry powders makes spray drying one of the most frequently used techniques for the industrial process of the encapsulation of bioactive ingredients (Assadpour and Jafari, 2019a, 2019b; Kuriakose & Anandharamakrishnan, 2010). Furthermore, being a common and convenient method of drying in the food industry, it is a well-established technique for encapsulation of a wide range of food ingredients (e.g., polyphenols, vitamins, minerals, flavors, colors, essential oils) to protect them against surrounding environmental conditions and extend their shelf life stability during storage (Pillai, Prabhasankar, Jena, & Anandharamakrishnan, 2012). However, when it comes to nanoencapsulation, spray drying is only capable of producing a nanostructured powder form by drying a suspension of colloidal nanoparticles. In the case of food bioactive ingredients with specific sensitivities or processing requirements (e.g., aromatic compounds, essential oils, and vitamins), modification of spray drying conditions can be accompanied. For example, process parameters, feed formulation, and final powder properties can be adjusted according to the specific needs (Assadpour and Jafari, 2019a). There remain some challenges with regard to the nanoencapsulation of bioactive ingredients using spray drying. These include difficulties concerning the achievement of a high encapsulation yield with the highest encapsulation efficiency, characterization of spray-dried powders containing different encapsulated bioactive ingredients, and in some cases, production of big particles due to agglomeration and precipitation issues (depending on the type of the bioactive ingredient and the corresponding wall material). Such possible issues have resulted in the recent innovation in spray drying encapsulation of bioactive ingredients such as the design and introduction of the nanospray dryers, with similar principles to the conventional spray dryers (Arpagaus et al., 2018; Li, Anton, Arpagaus, Belleteix, & Vandamme, 2010). Nonetheless, the size and

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morphology of the particles obtained from the spray drying process greatly depends on other processes and techniques used for the preparation and treatment of the solutions/ dispersions prior to spray drying. That means it is possible to control the particle size and morphology of the manufactured dried particles by varying process parameters and formulations (Anandharamakrishnan, Rielly, & Stapley, 2008; Cochereau, Nicolai, Chassenieux, & Silva, 2019).

8.3.3 Coacervation During the coacervation process, phase separation of a polyelectrolyte (or a mixture of polyelectrolytes) from a solution happens (Ghasemi, Jafari, Assadpour, & Khomeiri, 2017). As the next phase, deposition of the newly formed coacervate phase surrounds the bioactive ingredient. In order to increase the robustness of the formed coacervate, a hydrocolloid shell can be cross-linked using a suitable chemical or enzymatic cross-linker such as transglutaminase or glutaraldehyde (Zuidam & Shimoni, 2010). Depending on the number of polymers used for the coacervation process, it can be named as “simple” coacervation, where only one type of polymer is used, and “complex” coacervation, where two or more types of polymers are used (Ezhilarasi et al., 2013). The power of the interactions between the biopolymers and the characteristics of the coacervates formed greatly depend on the properties of the biopolymer(s) (e.g., molar mass, net charge, and flexibility), concentration of the biopolymer(s), pH, ionic strength, and the ratio of the biopolymers, in the case of complex coacervation (De Kruif, Weinbreck, & de Vries, 2004; Turgeon, Schmidt, & Sanchez, 2007). The formation of a complex during the coacervation process is a result of different interactions between biopolymers of opposite charges: electrostatic, hydrophobic, and hydrogen bonding (Sing, 2017). Specific characteristics such as a very high loading (up to 99%) and the possibilities of controlled release of the encapsulated bioactive ingredients make coacervation a distinctive and promising encapsulation technique for the protection and smart delivery of bioactive ingredients (Gouin, 2004). While coacervation, in general, produces large particles, it can successfully be used as a technique for nanoencapsulation of bioactives as well (Rajabi, Jafari, Rajabzadeh, Sarfarazi, & Sedaghati, 2019). For example, Wang, Chen, and Xu (2008) used simple coacervation for encapsulation of capsaicin utilizing gelatin as the wall material and its cross-linking with glutaraldehyde, obtaining nanocapsules with a size of 100 nm. In an earlier study (Xing, Cheng, Yi, & Ma, 2005), the nanocapsules (size range of 300 600 nm) of the same bioactive compound (i.e., capsaicin) were also manufactured using the same wall material (i.e., gelatin) but using complex coacervation. The nanoencapsulation of capsaicin was also demonstrated by Jincheng, Xiaoyu, and Sihao (2010). The size of capsules was in the range of 100 600 nm, where it depended on the drying techniques (vacuum drying and freeze drying), as well as the wall material used (gelatin, gum of acacia, and chitosan). The major concern around using coacervation technology for nanoencapsulation of bioactive ingredients is the commercialization and legislation of the final

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products or the functional foods that the coacervates are incorporated into. This is due to the fact that glutaraldehyde, which is widely used for cross-linking, is not allowed as a food ingredient in some countries (Gerrard & Brown, 2002) so it must be carefully used according to the country’s legislation. Nonetheless, there are some other suitable and food-grade cross-linkers (e.g., glutaric acid) which can be used in the food industry (Gouin, 2004; Mitra, Sailakshmi, & Gnanamani, 2014).

8.3.4 Nanoliposomes and niosomes As the vesicular delivery systems, both liposomes and niosomes have had major impacts on the delivery of food bioactive ingredients in the recent years, in addition to their significant impact on the delivery of these material in cosmetics, pharmaceutics, and farming industries during the last three decades (Akbarzadeh et al., 2013; Rashidinejad, 2015; Rashidinejad et al., 2014; Wen et al., 2018: Rashidinejad, Birch, & Everett, 2016). Such a method of bioactive delivery is gaining more research interest due to the ability of liposomes and niosomes that can safely administer both hydrophilic and lipophilic compounds into the human body in a targeted and sustained release manner (Wen et al., 2018). These delivery systems can convey the aforementioned roles over a longer period, while they can also increase the bioavailability of encapsulated ingredients (Ghorbanzade, Jafari, Akhavan, & Hadavi, 2017; Tavakoli, Hosseini, Jafari, & Katouzian, 2018). They are also suitable candidates when coencapsulation of lipophilic and hydrophilic bioactives is sought. Liposomes and niosomes are sealed spherical structures with a size range of nanometer to micrometer suspended in a solution (Akbarzadeh et al., 2013). These spherical vesicles are composed of a bilayer of amphiphilic molecules, capable of enclosing the surrounding solution in the center, as shown in Fig. 8.3. Liposomal delivery systems were created prior to the niosomal systems. In fact, the advancements in liposomal delivery systems, greatly contributed to the development of niosomal delivery systems. The difference between liposomes and niosomes is that niosomes utilize nonionic surfactants instead of phospholipids, which are used for the manufacture of liposomes (Choi & Maibach, 2005). Nonetheless, both phospholipids and nonionic surfactants contain amphiphilic properties associated with an ether, amide, or ester bond (Marianecci et al., 2014). Both encapsulation systems (i.e., liposomes and niosomes) have been used frequently and successfully for encapsulation of several bioactive ingredients and their incorporation into food (see Table 8.4). These include encapsulation of polyphenols, flavorings, vitamins, and others (Capriotti et al., 2019; Chen et al., 2019a; Choi & Maibach, 2005; Moghassemi & Hadjizadeh, 2014; Rashidinejad et al., 2014; Rashidinejad, John, Sun-Waterhouse, & Everett, 2016; Tiwari & Takhistov, 2012; Wen et al., 2018; Yoshida et al., 1992). Liposomal or niosomal encapsulation can decrease degradation of bioactives during processing, storage, and digestion, as well as decreasing toxicity of some of these compounds. At the same time, it can increase the circulation of bioactives in the body, deliver higher concentrations of the encapsulated compounds to the target site, and lead to greater bioactivity of these compounds (Capriotti et al., 2019; Moghassemi & Hadjizadeh, 2014; Wen et al., 2018). It has also been known that liposomal-based delivery systems can improve the functionality of

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Figure 8.3 (A) Structure of liposomes and niosomes. (B) Different types of liposomes which can be formed from phospholipid bilayers. Source: (A) Modified from Wen, J., Al Gailani, M., Yin, N., & Rashidinejad, A. (2018). Liposomes and niosomes. In Emulsion-based systems for delivery of food active compounds: Formation, application, health and safety (pp. 263 292). (B) Modified from McClements, D. J. (2015). Encapsulation, protection, and release of hydrophilic active components: Potential and limitations of colloidal delivery systems. Advances in Colloid and Interface Science, 219, 27 53.

enzymes in cheese ripening and the removal of lactose from various dairy products (El Soda & Pandian, 1991; Kim, Chung, Lee, Choi, & Kim, 1999; Singh, Thompson, Liu, & Corredig, 2012). It has been reported that niosomes are great delivery systems in regard to protecting bioactive ingredients from acidic and enzymatic degradation throughout the GIT, as well as under acidic conditions of some food products (e.g., beverages) (Aditya et al., 2015; Yoshida et al., 1992). As for liposomes, the surface charge of niosomes can be altered for engineering bioavailability and bioaccessibility of the encapsulated bioactive compound (Aditya, Espinosa, & Norton, 2017). The assembly of phospholipids or nonionic surfactants, as presented in Fig. 8.3, cannot occur spontaneously, but only when the corresponding physical and chemical forces acting on the system are thermodynamically favorable (Marianecci et al.,

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2014). That means there is always a need for sufficient kinetic energy (from an external source) to be introduced into the system in order to reach the desired thermodynamic state for creating liposomes and niosomes. The required energy is usually a combination of pressure, shaking, heat, ultrasound, etc. However, when applying such applications, extra care needs to be taken for applying the optimum energy level to not denature the encapsulated bioactive ingredient (Khan & Irchhaiya, 2016). The bilayers existing in the structure of a liposome or niosome are often referred to as lamellae, which are able to form more than one bilayer within the same vesicle (McClements, 2015). In this regard, the vesicles of liposomes and niosomes are generally classified into unilamellar vesicles (ULVs; only one bilayer) and multilamellar vesicles (MLVs; more than one bilayer) (Akbarzadeh et al., 2013; Marianecci et al., 2014). The unilamellar vesicles themselves can be classified into large unilamellar vesicles (LUVs; larger than 100 nm) and small unilamellar vesicles (SUVs; with a diameter within the range of 20 100 nm) (Akbarzadeh et al., 2013; Marianecci et al., 2014; Wen et al., 2018). The most important fabrication methods for liposomal/niosomal delivery systems for bioactive ingredients include solvent evaporation/rehydration, solvent displacement, surfactant displacement, and homogenization (McClements, 2015). One of the advantages of liposomal/niosomal delivery systems for encapsulation of bioactive ingredients is that the release characteristics of the encapsulated compound can be modified to promote its release at the desired site of action (Rashidi & Khosravi-Darani, 2011). However, the interactions between the encapsulated bioactive ingredient and the structure of vesicle itself as well as the constituents and surrounding media may lead to varied results, meaning that there is optimization required for each delivery system used for encapsulation of each bioactive ingredient (Yi, Meyer, & Frankel, 1997). Furthermore, as mentioned earlier, liposomes and niosomes are able to coencapsulate two different bioactive ingredients with different polarity (i.e., one hydrophilic and one hydrophobic) within the same vesicle ˇ (Chen et al., 2019a; Ingebrigtsen, Skalko-Basnet, Jacobsen, & Holsæter, 2017). Another important reason that both liposomes and niosomes are competent systems for delivering bioactive ingredients is due to the low cytotoxicity, biocompatibility, biodegradability, and various controlled and targeted mechanisms (Khan & Irchhaiya, 2016; Wen et al., 2018). Nevertheless, the toxicity of liposomes in the human body to date remains a debate (Hossen et al., 2019). In addition, the use of an organic solvent in several of the production methods can hinder or inactivate several bioactive compounds (Paini et al., 2015). The cost and scale-up can also be a problem for the application of liposomal and niosomal systems in the food industry (Sarabandi et al., 2019); however, recently there have been a few cost-effective, fast, and industrially relevant methods developed without the need for organic solvents (Khan & Irchhaiya, 2016; Rashidinejad et al., 2014, 2016). Another crucial challenge for the commercial application of liposomes is the leakage of the encapsulated bioactive ingredient during long-term storage. Such leakage has been reported to be significant in the case of bioactives such as ascorbic acid (Wechtersbach, Ulrih, & Cigi´c, 2012) and resveratrol (Isailovi´c et al., 2013). Decreasing the permeability of bilayer membranes and coating the membranes with

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some specific biopolymers may be possible solutions for the leakage problem associated with liposomes (Thompson, Haisman, & Singh, 2006; Zhou et al., 2014). Compared with liposomes, fewer reports are available on the use of niosomes for the delivery of bioactive ingredients. Tavano, Muzzalupo, Picci, and de Cindio (2014) developed some niosomal formulations for coencapsulation of bioactives including gallic acid, ascorbic acid, quercetin, and curcumin, and evaluated the physicochemical properties of the systems, besides the antioxidant properties and release behavior of the encapsulated bioactives. It was found that the coencapsulations of gallic acid curcumin and ascorbic acid quercetin had a significant effect on the physicochemical properties. The encapsulation efficiencies for different bioactives respected the formulations containing the single antioxidants, and niosomal encapsulation improved the release behavior of the encapsulated antioxidants as well as their enhanced antioxidant activity and radical scavenging (Tavano et al., 2014). In another investigation, catechin and EGCG were encapsulated in fabricated niosomes (Song et al., 2014). The findings demonstrated that the cellular uptake and transport (intestinal Caco-2 cells) of the niosomal encapsulated catechins were significantly higher than unentrapped counterparts, resulting in enhanced bioaccessibility and bioavailability (Song et al., 2014). A modified form of niosomes is known as “bilosomes,” where bile salts (e.g., sodium cholate, deoxycholic acid, deoxycholate, and taurocholate) are used along with surfactants in order to create the globular concentric bilayer structures (Aditya et al., 2017). Bilosomes are highly stable under the conditions of the GIT and foodgrade bile salts are widely available (Singh et al., 2004). However, the use of bilosomes in the field of bioactive delivery has yet to be explored. Another progress is improving the stability of nanoliposomes by using biopolymers via coating such as chitosan. For example, Zariwala et al. (2018) reported that the addition of O-palmitoyl chitosan to the liposomal encapsulation of iron created robust nanoliposomal vesicles with substantial improvements in mucoadhesive and absorption enhancing properties, when compared with uncoated liposomes.

8.3.5 Cubosomes and hexosomes The self-assembly of polar amphiphilic lipids, which own a very low aqueous solubility, can result in lyotropic liquid crystalline phases in the presence of excess water (Kaasgaard & Drummond, 2006). Depending upon the nature and structure of the lipids, the conditions of the solution, and the presence of additives, the structures formed can be lamellar (e.g., liposomes; discussed in Section 8.3.4), reverse bicontinuous cubic phase (cubosomes), and reversed hexagonal (hexosomes). Cubosomes (also known as the bicontinuous cubic phases) are highly stable nanoparticles, which can be suitable candidates for delivery of various bioactive ingredients. They are “bicontinuous”, because they contain two distinct hydrophilic regions separated by the bilayer. The bicontinuous lipid cubic phases in the structure of cubosomes contains a single lipid bilayer where a continuous periodic membrane lattice structure is formed with pores formed by two interwoven water channels (Duttagupta, Chaudhary, Jadhav, & Kadam, 2016). These nanoparticles are formed from the lipid cubic phase while a

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polymer-based outer corona is used for their stabilization (Barriga, Holme, & Stevens, 2019; Duttagupta et al., 2016). Cubosomes, which are highly stable under various physiological conditions, can be engineered in terms of the pore sizes or inclusion of bioactives (Barriga et al., 2019). Concerning the delivery of bioactives, cubosomes possess the properties of liposomes and niosomes; however, one advantage of cubosomes over liposomes/niosomes is that the specific structure of cubosomes provides a significantly higher membrane surface area, making them capable of capturing/solubilizing higher loads of both hydrophobic and hydrophilic (as well as amphiphilic compounds) bioactive molecules. This property of cubosomes leads to an equilibrium nanostructure (Barriga et al., 2019). As shown in Fig. 8.4A, different compounds can be entrapped/encapsulated inside the same structure of cubosomes.

Figure 8.4 (A) A schematic structure of cubosomes with the capability of the delivery of different bioactive compounds. (B) Schematic presentation of hexosomes. Source: (A) Modified from Karami, Z., & Hamidi, M. (2016). Cubosomes: Remarkable drug delivery potential. Drug Discovery Today, 21(5), 789 801. (B) Redrawn from Amar-Yuli, I., Libster, D., Aserin, A., & Garti, N. (2009). Solubilization of food bioactives within lyotropic liquid crystalline mesophases. Current Opinion in Colloid & Interface Science, 14(1), 21 32.

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Cubosomes can be manufactured under biological conditions using biocompatible lipids, giving them an advantage for the delivery of bioactive compounds to be incorporated into foods. Cubosomes have recently become an active research topic in the field of drug delivery. This is due to their unique structure that lends itself well to the controlled release applications. Nevertheless, although cubosomes have been produced for more than two decades (Gustafsson, Ljusberg-Wahren, Almgren, & Larsson, 1996; Lindstro¨m, Ljusberg-Wahren, Larsson, & Borgstro¨m, 1981), their application for the delivery of bioactive ingredients in the food industry is very new. The fabrication and use of cubosomes require knowledge of surfactants and the aqueous phase behavior. The surfactant that is most commonly used for formation of cubosomes is glycerol monoolein, which is considered to be an inexpensive food-grade ingredient (Spicer, 2005). In a recent study by Ou et al. (2018), Achyranthes bidentata polysaccharides (ABPs), which are used in Chinese herbal medicine as an immunomodulator, were encapsulated in cubosomes and the characteristics and stability of the nanoparticles were assessed. The encapsulation efficiency was reported to be 72.59 and their in vitro stability was confirmed up to 25 days (Ou et al., 2018). Another example is the encapsulation of gambogenic acid (GNA) in cubosomes by Luo et al. (2015), where physicochemical properties, cellular uptake, in vitro cytotoxicity, and in vivo pharmacokinetics of GNA-loaded cubosomes were investigated. It was reported that GNA-cubosomes were spherical or ellipsoidal monocellular in shape and had a particle size in the range of 150 250 nm. Compared with a GNA solution, the cubosomes containing GNA exhibited markedly extended inhibitory activity in SMMC-7721 cells, in addition to the time-dependent increases in intracellular uptake (Luo et al., 2015). Taken together, the capability of cubosomes to encapsulate hydrophobic, hydrophilic, and even amphiphilic ingredients, as well as other advantages such as simplicity of preparation, bioadhesiveness, and biodegradability, give these novel delivery systems a unique property that can be used in the delivery and controlled released of various bioactive ingredients (Huynh Mai, Thanh Diep, Le, & Nguyen, 2020; Spicer, 2005). Unsaturated monoglycerides (in particular GMO and PHYT), are used for the formation of cubosomes as self-assembled organizations. The production of cubosomes can be done via either top-down or bottom-up approaches. Cubosomes for the delivery of bioactive ingredients can have a particle size in the range of 10 500 nm and pore size of about 5 10 nm (Duttagupta et al., 2016; Karami & Hamidi, 2016). Hexosomes are the reverse hexagonal phases containing hexagonally closepacked infinite water layers (Fig. 8.4B), which are covered by surfactants monolayer (Amar-Yuli, Libster, Aserin, & Garti, 2009; Hirlekar, Jain, Patel, Garse, & Kadam, 2010). Like cubosomes, due to their unique structural properties, hexosomes can be the potential alternative delivery systems for various bioactive compounds. Bioactive ingredients can be either lodged within the aqueous domains of the hexosomal structure or directly coupled to the lipid hydrophobic moieties, which are radially oriented outwards from the center of the water rods. Such encapsulation/entrapment of bioactive ingredients can lead to the improvement in their solubility (especially, poorly water-soluble hydrophobic bioactives) (Boyd,

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Whittaker, Khoo, & Davey, 2006). Encapsulation of bioactives in hexosomes can be a delivery approach with high loading capacity. In addition, large molecules such as peptides and proteins can also be delivered using hexosomes. Like cubosomes, hexosomes can also be fabricated using amphiphiles such as glyceryl monooleate (GMO), phytanyl glycerate (PG), phytantriol (PHY), and olyeyl glycerate (OG) (Hirlekar et al., 2010). Since hexosomes are generally formed at higher temperatures (about 60 C or higher), to form stable phases of hexosomes at ambient temperature, nonpolar additives such as oleic acid, triacylglycerol (tricaprylin), tetradecane, and vitamin E acetate are added (Dong, Larson, Hanley, & Boyd, 2006). Therefore, if hexosomes are used for encapsulation of bioactive ingredients to be incorporated into food, the use of food-grade amphiphiles and additives is inevitable. So far, it does not appear that hexosomes have attracted much interest for new potential applications in the food industry, but great attention has been noted in the area of pharmaceutical technology. Thus, the research in the field of cubosomes as potential delivery systems for food bioactive ingredients is still in its infancy with a limited number of studies focusing on the potential applications, particularly with respect to sustained release of these ingredients in the digestive tract (Jafari, 2017).

8.3.6 Solid lipid nanoparticles/nanocarriers Solidified lipid nanoparticles are delivery systems that can physically entrap bioactive ingredients inside their structure and protect them from the surrounding aqueous environment (Yousefi, Ehsani, & Jafari, 2019). These particles are generally prepared from the food-grade triglycerides or waxes with high-melting-point (e.g., hydrogenated palm oil, tallow, beeswax, butterfat, carnauba wax, candelilla wax) (Mellema, 2007; Mellema, Van Benthum, Boer, Von Harras, & Visser, 2006). In terms of morphology, solid lipid nanoparticles/nanocarriers (SLNs) are mostly spheroid with a size of a few micrometers to a few millimeters based on the fabrication method. In the case of hydrophilic bioactives, the delivery systems can be simply made by dispersing the bioactive throughout the molten fat phase (either as fine solid particles or dissolved within water droplets) prior to solidification. Hydrophilic bioactives, on the other hand, can be entrapped inside SLNs by dissolving in water first, followed by making a W/O emulsion and forming the solid fat particles (Katouzian, Faridi Esfanjani, Jafari, & Akhavan, 2017). Some examples of food bioactives encapsulated using SLNs are EGCG (Shtay, Keppler, Schrader, & Schwarz, 2019), β-carotene (Mehrad, Ravanfar, Licker, Regenstein, & Abbaspourrad, 2018), vitamin B2 (Couto, Alvarez, & Temelli, 2017), vitamin B12 (Genc¸, Kutlu, & Gu¨ney, 2015), peppermint essential oil (Yang & Ciftci, 2016), rosmarinic acid (Madureira et al., 2015), resveratrol (Pandita, Kumar, Poonia, & Lather, 2014), and α-tocopherol (de Carvalho et al., 2013). It is possible to make small particles (as small as 100 nm) using homogenization or high-shear processes or even low-energy methods such as phase inversion temperature and spontaneous emulsification (McClements). The fabrication of the emulsions should be carried out at a temperature above the melting point of the fat. Cooling step for crystallizing the fat and formation of the solid particles can be

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done using methods such as spray chilling and using various types of atomizers (Oxley, 2012). However, there are a few challenges in regard to the development of successful delivery systems based on SLNs to be used in the food industry. The incorporation of solid fat particles containing bioactive ingredients into functional foods increases the viscosity of the foods, depending on the concentration of the solid fat and the size of the particles. It is also very beneficial if the particles are in the nanosized range as the larger particles ( . 20 μm) can be detected by the human tongue, indicating a product with an undesirable “sandy” texture (Mellema, 2007). The large particles may also rapidly sediment in the food, depending on their density and solid fat content. Another critical challenge is that solid fat particles are highly nonpolar on the surface, which makes them prone to aggregation due to the possible hydrophobic attraction. Thus, it is generally required to coat SLNs with a layer of hydrophilic material before their actual incorporation into aqueous liquids. Water-soluble surfactants or the polymer with the ability to adsorb to the surfaces of the solid lipid particles can be used as coatings for solid lipid particles. The other challenge is related to the leakage of hydrophilic bioactives out of solid particles during storage. This has been reported with the appreciable fractions of bioactives such as citric acid and sodium chloride encapsulated within solid particles made of wax spheres after a few weeks storage (Mellema, 2007; Mellema, Van Benthum, Boer, Von Harras, & Visser, 2006). It was also reported that there was a significant increase in the rate of leakage as the particle size decreased, meaning that nanoparticles would show a greater leakage compared to the bigger particles. This is unfortunate as big particles would show the undesirable sensorial effects and one would implement nanoencapsulation to avoid such undesirable properties of the food (Mellema, 2007; Mellema et al., 2006). Lastly, limited loading capacity is also an important drawback that limits the use of SLNs for encapsulation of food bioactive compounds.

8.3.7 Nanostructured lipid carriers Some of the drawbacks of SLNs have been resolved by the development of nanostructured lipid carriers (NLCs) as delivery systems containing both solid and liquid lipids in their core matrix (Koshani & Jafari, 2019; Rafiee & Jafari, 2018). These carriers have shown some advantages for the delivery of bioactives in the pharmaceutical industry over the conventional delivery systems. Such advantages include increased solubility and enhanced bioavailability of the encapsulated bioactives, enhanced storage stability, improved permeability, and prolonged halflife (Fang, Al-Suwayeh, & Fang, 2013). NLCs have attracted a lot of attention in the field of pharmaceuticals in recent years, so they might be an alternative delivery system for the incorporation of various bioactive compounds in functional foods as well. In the last section (Section 8.3.6), some challenges of SLNs were mentioned and it was indicated that NLCs were developed in order to overcome some of those challenges associated with NLCs. In contrast to SLNs being produced from solid lipids, NLCs are manufactured by controlling the mixing of solid lipids with liquid oils, resulting in their special nanostructures, which can

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entrap various bioactives within their structure with improved loading and release properties (Mu¨ller, Radtke, & Wissing, 2002). The comparison of NLCs with SLCs and the comparison of these two with the structure of nanoemulsions are shown in Fig. 8.5. The manufacture of lipid particles from solid lipids results in a matrix that tends to form a relatively perfect crystal lattice, meaning that there is limited space for the accommodation of bioactive ingredients. Conversely, the use of a blend of solid lipids and liquid oils (like what is applied in the case of NLCs) results in the formation of a perfect crystal with required space for the accommodation of the bioactive to be encapsulated in the particle matrix (Fig. 8.5) (Fang et al., 2013; Katouzian et al., 2017). Like SLNs, NLCs have the potential to be employed for encapsulation of bioactive ingredients in the food industry owing to their beneficial properties such as simplicity, low cost, and scale-up capability. Nevertheless, NLCs have been mostly applied in the pharmaceutical industries and their application in the food sector is very new, meaning that there is still a lot to be discovered in this field of their utilization and commercialization in the near future. Some examples of food bioactives that have been encapsulated using NLCs during the recent years include phytosterols (Santos et al., 2019), cardamom essential oil (Keivani Nahr, Ghanbarzadeh, Hamishehkar, & Samadi Kafil, 2018), green tea extract (Manea, Vasile, & Meghea, 2014), rutin (Chanburee & Tiyaboonchai, 2017), vitamin C (Jain et al., 2016), quercetin (Ni, Sun, Zhao, & Xia, 2015), curcumin (Chanburee & Tiyaboonchai, 2017), α-lipoic acid (Wang, Tang, Zhou, & Xia, 2014), and β-carotene (Hejri, Khosravi, Gharanjig, & Hejazi, 2013).

Figure 8.5 The compression of the structure of nanostructured lipid carriers with solid lipid nanoparticles and nanoemulsions. Source: Redrawn from Katouzian, I., Faridi Esfanjani, A., Jafari, S. M., & Akhavan, S. (2017). Formulation and application of a new generation of lipid nano-carriers for the food bioactive ingredients. Trends in Food Science & Technology, 68, 14 25.

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8.3.8 Complexation/conjugation with proteins The interactions between bioactive ingredients and biopolymers such as proteins can sometimes be utilized as a means of delivery for these ingredients. For instance, polyphenolic compounds can form complexes with dietary proteins (Rashidinejad, Birch, Sun-Waterhouse, & Everett, 2017; Rawel, Frey, Meidtner, Kroll, & Schweigert, 2006; Szejtli & Szente, 2005). The principle of this delivery method is based on the relatively large number of functional groups that proteins possess. Under certain environmental conditions (e.g., temperature, pH, ionic concentration, molecular weight, biopolymer flexibility, biopolymer charge density, concentration of both biopolymer and bioactive, pressure, shearing), such functional groups become charged, so such changes can be used for complexation of bioactives and their delivery (Aditya et al., 2017). Fabrication of protein bioactive complexes by electrostatic complexation can be generally achieved through the simultaneous dissolution of the bioactive and biopolymer (in the solvent), mixing of bioactive with the polymer(s) in the required ratio and at the optimum conditions, and in most cases, acidification of the original solution. The latest step (i.e., acidification) can influence the size of the formed complexes (Aditya et al., 2017). Acidification can be implemented prior to or post mixing of the two different materials, known as preblending and postblending acidifications, respectively. Postblending acidification is reported to produce smaller complexes (Be´die´, Turgeon, & Makhlouf, 2008). Nonetheless, the size of the formed particles may also be reduced by subjecting the solutions to processes such as high-shear mixing or sonication (Kurukji, Norton, & Spyropoulos, 2016). This method has been used for the delivery of bioactive ingredients such as polyphenols, vitamins, and minerals. For instance, vitamin B9 has been successfully encapsulated in coacervates of two oppositely charged milk proteins including β-lactoglobulin and lactoferrin (Chapeau et al., 2015). In another example, catechin has been complexed with chitosan, which resulted in a significant decrease in the degradation of this polyphenolic compound within the small intestine (Zhang & Kosaraju, 2007). It is notable that the complexes formed using only electrostatic interactions can be dissociated or degraded under different environmental conditions such as pH, temperature, and ionic strength. Such sensitivity can be used for designing the targeted delivery of bioactive compounds and their controlled release at different places within the GIT. Since the majority of the complexations between bioactives and proteins occur at the acidic conditions, they will be intact within the gastric environment. Therefore, they can be utilized to deliver the complexed bioactives to the upper parts of the gastrointestinal tract, where under alkaline conditions they dissociate and the bioactives are released (Jones, Lesmes, Dubin, & McClements, 2010). Other methods of complexations include the formation of complexes by heat denaturation of globular proteins (e.g., whey proteins) and the following step of electrostatic complexation (Jones et al., 2010; Wagoner & Foegeding, 2017), as well as pH-driven complexation to create colloidally stable nanoparticles (Luo, Pan, & Zhong, 2015; Pan, Luo, Gan, Baek, & Zhong, 2014). Overall, delivery of

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bioactive ingredients via complexation with proteins may come with several advantages for certain commercial applications. These include the flexibility in terms of changing the composition, structure, dimensions, and environmental responsiveness of protein particles in order to design the release of encapsulated bioactive ingredients using triggers such as pH and temperature (McClements, 2015). Furthermore, there are possible associative interactions (e.g., electrostatic complexation and covalent conjugation) between proteins and polysaccharides due to the opposite electrical charges affected by environmental conditions (Hu & Huang, 2013). The encapsulation of various bioactive compounds using a combination of proteins and polysaccharides has been recently reported, where both electrostatic complexation and covalent conjugation between proteins and polysaccharides have been utilized (Huang et al., 2017; Kuhn, e Silva, Netto, & da Cunha, 2019; Papoutsis et al., 2018; Pe´rezCo´rdoba et al., 2018; Shen et al., 2019; Wei & Huang, 2019).

8.3.9 Inclusion complexation within cyclodextrins and amylose nanohelices Inclusion complexation is a method for delivery of various bioactive ingredients, where the supramolecular association of the encapsulated ingredient (as a ligand) into a cavity-bearing substrate (shell material) occurs (Gharibzahedi & Jafari, 2017a, 2017b). This is possible via van der Waals forces, hydrogen bonding, or an entropy-driven hydrophobic effect (Ezhilarasi et al., 2013). The unique structure of cyclodextrins makes them the best candidate for supramolecular self-assembly of bioactive compounds—they contain a specific truncated cone structure with a hydrophilic outer surface and a lipophilic inner cavity (Dalmora & Oliveira, 1999). Although inclusion complexation can be an efficient method of nanoencapsulation for the delivery of bioactive ingredients, the molecular entities with suitable molecular-level cavities, which can be used for encapsulation purpose in the food industry, are rarely available. Nevertheless, this technique has been used for encapsulation of bioactives such as linoleic acid in α- and β-cyclodextrins (α- and β-CD) with a yield of about 74% 88% reported (H˘ad˘arug˘a et al., 2006). It has also been used for encapsulation of usnic acid in β-CD, DHA (docosahexaenoic acid) in β-lactoglobulin (along with low methoxyl pectin), and catechins in β-CD (Krishnaswamy, Orsat, & Thangavel, 2012; Lira et al., 2009; Zimet & Livney, 2009). The inclusion complexation technique is more efficient and applicable in the case of encapsulation of volatile organic molecules such as some vitamins and most of the essential oils (to preserve aromas), where it can also mask the unpleasant odors and flavors. Inclusion complexation can result in the encapsulated products with high yield and encapsulation efficiency, as well as a higher stability of the core component. The challenge is that only a few particular molecular compounds are suitable to be used as the coating materials for encapsulation of bioactive compounds, mainly, β-CD and β-lactoglobulin. However, another option is the encapsulation of bioactives in amylose inclusion complexes (Ganje, Jafari, Tamadon, Niakosari, & Maghsoudlou, 2019; Rostamabadi,

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Falsafi, & Jafari, 2019b). This is possible as the amylose helices arrange to form a crystalline structure, which is known as the “V-type” (Kong, Bhosale, & Ziegler, 2018). This method has recently been used for the encapsulation of α-lipoic acid (Li, Kim, Reddy, Lee, & Lim, 2019), β-carotene (Kong et al., 2018), ascorbyl palmitate (Kong & Ziegler, 2014), and genistein (Cohen, Orlova, Kovalev, Ungar, & Shimoni, 2008) for stability and controlled release purposes. In the case of the encapsulation of the lipophilic bioactives such as β-carotene, some amphiphilic materials (e.g., various surfactants) can be used in order to improve the solubility of the bioactives, and accordingly to increase the accessibility of the amylose hydrophobic helical core to the bioactive compound(s) to be entrapped/encapsulated (Kong et al., 2018).

8.3.10 Nanoprecipitation (solvent displacement) The nanoprecipitation (also known as solvent displacement or desolvation) method is in fact, a process of the spontaneous emulsification of the organic internal phase, which contains the dissolved polymer, bioactive, and organic solvent, into the aqueous external phase. By this technique, the precipitation of a polymer from an organic solution and the diffusion of the organic solvent in the aqueous medium occurs (Galindo-Rodriguez, Allemann, Fessi, & Doelker, 2004), forming nanoparticles in the shape of both nanocapsules and nanospheres. A schematic process of nanoparticle formation using nanoprecipitation technique is given in Fig. 8.6 (Barreras-Urbina et al., 2016). Biodegradable polymers such as polylactide-co-glycolide (PLGA), eudragit, polyalkylcyanoacrylate (PACA), polylactide (PLA), and polycaprolactone (PCL) are commonly used in the solvent displacement method (Pinto Reis, Neufeld, Ribeiro, & Veiga, 2006). During the process of nanoprecipitation, the polar particles readily solubilize in the aqueous medium, whereas the nonpolar particles tend to interact with other nonpolar particles resulting in the formation of nanoaggregates. Thus nanoparticles can possess different charges (positive, negative, or neutral), depending on the wall materials used, as well as the environmental conditions (Joye, Davidov-Pardo, & McClements, 2014). Anand et al. (2010) encapsulated curcumin in PLGA and obtained the particles with a mean diameter of about 81 nm. In another study (Suwannateep et al., 2011), curcumin was also encapsulated in a monopolymeric carrier made from ethyl cellulose and a dipolymeric carrier (ECMC) using the same method, where the nanoparticles with a mean diameter of 281 and 117 nm, respectively, were achieved. One of the main advantages of the nanoprecipitation method is its capability in the formation of nanocapsules of around 100 nm and smaller, making it a very useful and efficient nanoencapsulation technology for the delivery of food bioactive ingredients with high encapsulation efficiency. Additionally, the manufactured nanocapsules tend to exhibit reliable stability against degradation, and present a sustained release, as well as increased cellular uptake and bioavailability during in vivo studies (Ezhilarasi et al., 2013). The challenges, on the other hand, are the dependence of the nanoprecipitation technique on a suitable drying technique (often freeze drying) and the use of only polymer-based wall materials (e.g., PEG and PLGA). Further challenges are the selection of the appropriate solvent and

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Figure 8.6 Formation of nanoparticles using the nanoprecipitation technique. Source: Redrawn from Barreras-Urbina, C. G., Ramı´rez-Wong, B., Lo´pez-Ahumada, G. A., Burruel-Ibarra, S. E., Martı´nez-Cruz, O., Tapia-Herna´ndez, J. A., & Rodrı´guez Fe´lix, F. (2016). Nano- and micro-particles by nanoprecipitation: Possible application in the food and agricultural industries. International Journal of Food Properties, 19(9), 1912 1923.

nonsolvent phases depending on the bioactive ingredient to be encapsulated, as well as the selection of only food-grade polymers and solvents, where the usefulness of the technique is limited to water-miscible solvents (Markwalter, Pagels, Wilson, Ristroph, & Prud’homme, 2019).

8.4

Carrier materials used for nanoencapsulation of bioactive compounds

The selection of the carriers (wall/coating materials) for nanoencapsulation of bioactive ingredients in the food industry mainly depends on the method of encapsulation as well as the physicochemical properties of the bioactive ingredient to be encapsulated (Rostami, Yousefi, Khezerlou, Aman Mohammadi, & Jafari, 2019; Taheri & Jafari, 2019). However, there are some other critical factors to consider

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when selecting the wall material for a specific bioactive to be encapsulated via a specific method. These include stability and behavior of the delivery system within the food matrix during processing and storage as well as the release profile of the bioactive ingredient during the digestion process, which is also influenced by some other factors such as pH, temperature, time, enzymatic activity, and osmotic force. Thus, the composition of nanocarriers for encapsulation of bioactive ingredients is the principle responsible for the functional properties that the nanocapsules exhibit either within the food or in the gastrointestinal tract. Nanocarriers can be selected from a wide variety of both natural and synthetic polymers, but they must be foodgrade and GRAS, in order to be used for encapsulation of food bioactive materials. An ideal carrier material to be used for nanoencapsulation of bioactive ingredients and in order to be incorporated into functional foods should exhibit specific properties as follows (Shah, Mir, & Bashir, 2018): G

G

G

G

G

G

G

G

G

chemical nonreactivity with the bioactive ingredient during processing and storage; the ability to provide maximum protection (against environmental conditions) to the bioactive ingredient; the ability to disperse or emulsify within the food matrix; stability (both physical and chemical) in the food matrix during the storage; proper rheological properties when used at high concentration; the ability to prevent the leakage of the bioactive within the food structure during processing and storage; the ability to entirely release the bioactive ingredient at the targeted site within the digestive tract; when required, solubility in food-grade solvents (e.g., water, ethanol); and cost-effectiveness for use in the food industry.

Below the most frequently used encapsulating materials for bioactive compounds are discussed.

8.4.1 Proteins Proteins, the polymers of amino acids, possess some very principal functional properties, such as solubility, thickening, gelling, foaming, emulsifying, water holding capacity, and surface activity, that make them very suitable candidates for the delivery of bioactive ingredients (Katouzian & Jafari, 2019). Further, proteins are GRAS materials and have high nutritional importance (Shishir et al., 2018). The functional properties of proteins are representatives of their molecular characteristics, including molecular weight, polarity, hydrophobicity, conformation, flexibility, and interactions, meaning that knowledge of this information is very critical in regard to nanoencapsulation of bioactive ingredients (McClements, Decker, Park, & Weiss, 2009). The molecular features of proteins, in turn, are determined by the number, type, and sequence of their building blocks of monomers. Obviously, monomers have different properties depending on their polarity, chemical reactivity, dimensions, and interactions. Along these lines, it is notable that each biopolymer, such as a specific protein, comprises a large number of monomers (20 20,000), with a possible rotation around the links in the chain. That indicates that proteins can

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potentially take up numerous various configurations in the corresponding solutions, which is an advantage for the delivery of food bioactive ingredients. Biopolymers such as proteins implement a well-defined conformation in order to minimize the free energy of the system. On the other hand, most foods are nonequilibrium systems. Thus, proteins may be trapped in a metastable state, due to the presence of large activation energy which prevents these biopolymers from reaching their most thermodynamically stable state (McClements et al., 2009; Mittal, 2019). Generally speaking, there are three broad categories known for the configurations of biopolymers such as proteins: globular, rod-like, and random coil, with rigid compact structures, rigid extended structures (helical), and highly dynamic and flexible structures, respectively. However, many biopolymers contain more than one type of conformation (Damodaran, 2017). Another important aspect of proteins is that they can undergo transitions, due to the significant changes in the environmental conditions (e.g., pH, temperature, ionic strength, and solvent composition). Such transitions can occur from one conformation state (the original and stable state) to another or from one aggregation state to another. Such ability of proteins to conform and interact plays a key role in their ability to carry bioactive compounds in various delivery systems (McClements et al., 2009). Albumin, collagen, gelatin, α-lactoalbumin, β-lactoglobulin, caseins, soy proteins, gluten, zein, and even potato proteins are some examples of natural protein polymers that have been used for the formulation and manufacture of nanodelivery systems for food bioactive ingredients (Fang & Bhandari, 2010; Pan et al., 2014; Rashidinejad et al, 2016; Reineccius, 2019; Reis, Neufeld, Ribeiro, & Veiga, 2006). In this regard, during the last couple of decades, there has been substantial growth in the use of dietary proteins for the development of food nanocarriers for various bioactives ingredients. Apart from the aforementioned advantages of proteins concerning nanoencapsulation of bioactive ingredients, proteins are also excellent emulsifiers, which is a very important property in the case of delivery systems such as emulsification, as well as the systems that require the formation of an emulsion as a first step in the process (e.g., spray drying and coacervation) (Reineccius, 2019). In addition, the new and increasing consumer demand for more protein in the daily diet adds value to the use of proteins as wall materials for the nanoencapsulation of bioactive materials (Reineccius, 2019; Shishir et al., 2018). One of the most important functional properties of proteins is their possession of gelation ability, which has been of significant interest for the manufacture of delivery systems for bioactive ingredients (de Souza Simo˜es et al., 2017). Generally, there are two main steps involved in the gelation process of a protein; partial unfolding/denaturation of the globular structure, and intermolecular aggregation of the protein structure (Abaee, Mohammadian, & Jafari, 2017). The denaturation step can be induced by factors such as temperature (main factor), change in net charge, the addition of chemicals or electrolytes, partial enzymatic hydrolysis, and electrical field increase in hydrostatic pressure. Thus, the alteration of each of these factors in the presence of bioactive ingredients may lead to a delivery method for encapsulation/entrapment of these materials (Ramos et al., 2014). While proteins are advantageous to be used as wall materials in some cases and secondary wall materials in the case of most of the nanoencapsulation systems, in

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some delivery systems such as in coacervation they find even broader usage. This is because both positively charged and negatively charged food polymers are required to form a complex coacervation in the particle wall (Esfahani, Jafari, Jafarpour, & Dehnad, 2019). In fact, proteins are the common components of coacervates, since there are not many alternatives to proteins (apart from chitosan) that can be the right option as the positively charged polymer (Reineccius, 2019). Likewise, the use of proteins in spray drying is widely accepted. However, most proteins can only be safely used for the nonflavoring bioactive ingredients, because some flavoring bioactives react with most dietary proteins and can negatively affect the flavor of the final product. In addition, as proteins contain high viscosity, this can limit the level of infeed solids going into a spray dryer (Charve & Reineccius, 2009). Finally, it can be noted that the protein-based nanodelivery systems can be formed from a single protein or from a mixture of different proteins.

8.4.2 Polysaccharides Polysaccharides are abundantly found polymers obtained from natural sources, and mostly through low-cost processing procedures (de Souza Simo˜es et al., 2017). These polymeric carbohydrate molecules consist of monosaccharide units linked by glycosidic linkages. Like proteins, polysaccharides possess several functional properties such as solubility, emulsification capability, nontoxicity, biodegradability, bioadhesibility, water retention capacity, digestibility, and gelation, which are influenced by the chemical differences in the polymeric chain; that is, the type, number, sequence, and linkage of the comprising monosaccharides (Ramos et al., 2014; Sirisha & Campus, 2015). In regard to delivery of bioactive ingredients, in particular, bioadhesibility of polysaccharides is of particular relevance, because such a property contributes to an increase in the residence time of the encapsulated bioactive ingredient in the gastrointestinal tract (Livney, 2010). Bioadhesibility is a result of the intrinsic hydrophilic groups existing in the polysaccharides (e.g., carbonyl, hydroxyl, and amine). These functional groups can enable the formation of noncovalent binding with biological tissue, resulting in extended absorption rates of the encapsulated bioactive compounds (Lee, Park, & Robinson, 2000; Nitta & Numata, 2013). In terms of their application in the nanodelivery systems for encapsulation of bioactive ingredients, according to their origin, polysaccharides can be systematized into four different categories: G

G

G

G

plant-based polysaccharides (e.g., gums, pectin, starch, and cellulose); animal-based polysaccharides (e.g., chitosan); algae-based polysaccharides (e.g., alginate and carrageenan); and and lastly, microbial-based polysaccharides (e.g., xanthan gum and dextran) (Fathi et al., 2014; Sirisha & Campus, 2015).

Chitosan, various gums (i.e., xanthan gum), alginate, and carrageenan are the most widely used polysaccharides in the manufacture of nanodelivery systems for food bioactive ingredients. As a hydrophilic linear polysaccharide, chitosan is able to improve the permeability of the cell membrane, thus increasing the

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bioavailability of the encapsulated bioactive compounds due to enhancing the residence time in the gastrointestinal tract (Nitta & Numata, 2013). Owing to the thermal stability of most polysaccharides, the delivery systems based on these biopolymers can be suitable protective carriers for labile food bioactives during food processes, where high temperatures are applied and lipid- and protein-based delivery systems cannot be used due to melting and denaturation, respectively (Fathi et al., 2014). Therefore, the surrounding environmental conditions have a substantial influence on the selection of an appropriate polysaccharidebased wall material to be used for nanoencapsulation of specific bioactive ingredients. Correspondingly, the knowledge about the physical and electrical properties of polysaccharide wall materials and their susceptibility to chemical and enzymatic reactions is highly important (Matalanis, Jones, & McClements, 2011). Polysaccharides may also be recognized by their electrostatic interactions based on their intrinsic charge. Thus, according to the base materials, they can be classified as neutral polysaccharides (e.g., amylose, amylopectin, guar gum, and cellulose), anionic polysaccharides (e.g., gums, alginates, carrageenans, and gellan), and cationic polysaccharides (e.g., chitosan) (Thakur & Thakur, 2016). Anionic polysaccharides have no charge at the pH below their pKa value, but they tend to be negatively charged at pH above their pKa value. Cationic polysaccharides, on the other hand, require no charge at pH above their pKa value, while they are positively charged at the pH below their pKa value (Matalanis et al., 2011). A single polysaccharide or a combination of polysaccharides may be used as the wall material for nanoencapsulation of various bioactive ingredients, depending on the delivery method as well as the properties of the bioactive(s) to be encapsulated.

8.4.3 Lipids Various lipids (fats in solid form or oils in liquid form), as natural biodegradable and food-grade ingredients, are used for the nanoencapsulation of various bioactives. Fats and oils are divided into either polar lipids (e.g., phospholipids and monoglycerides) or nonpolar lipids (e.g., triacylglycerol and cholesterol) (Ðorðevi´c et al., 2016). The microstructural characteristics, colloidal stability, and rheological properties of lipids are representative of their physicochemical properties. For example, the melting point and moisture barrier properties of lipids can be substantially affected by a decrease in the length of their hydrocarbon chain, or an increase in the unsaturation degree of the fatty acid chains (Augustin & Hemar, 2009). Nanoliposomes, nanoemulsions, NLCs, and SLNs are the most common lipid-based nanoencapsulation systems for food bioactive ingredients (Rafiee & Jafari, 2018; Rostamabadi et al., 2019a; Yousefi et al., 2019). The selection of a lipid to be used as the wall material for the specific bioactive ingredient depends on the solubility of that bioactive ingredient, and whether it can be dissolved/entrapped within the oil phase or the aqueous phase (Assadpour & Jafari, 2019c). Lipid-based nanodelivery systems have extensive applications in the food industry owing to their excellent functional properties such as stability during process and storage, high encapsulation efficiency, and controlled and targeted release of the bioactive ingredients (Shishir et al., 2018). Polar lipids, in

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particular, phospholipids, contain suitable surface activity, and they are biocompatible and suitable for the protection, stabilization, and controlled release of food bioactive ingredients (Ðorðevi´c et al., 2016). These compounds (i.e., phospholipids) possess natural amphiphilic properties that allow self-assembly, wettability, and emulsifying capability, enabling them to encapsulate both hydrophobic and hydrophilic bioactive ingredients (Rashidinejad et al., 2014; Zhao, Temelli, Curtis, & Chen, 2017). Lipid-based delivery systems have also been known to enhance the bioavailability of hydrophobic bioactive compounds, as well as decreasing their potential toxicity (de Souza Simo˜es et al., 2017).

8.4.4 Cyclodextrins Cyclic oligosaccharides, also known as cyclodextrins, are obtained by the enzymatic modification of starch and are truncated cone-shaped molecules. These oligosaccharides contain a hydrophobic cavity inside the molecule and a hydrophilic external surface (Duchˆene & Bochot, 2016). These characteristics of cyclic oligosaccharides allow the formation of molecular inclusion complexes with hydrophobic bioactive molecules and improve the molecular solubility (Duchˆene & Bochot, 2016). The absorption of cyclodextrins does not occur in the upper part of the gastrointestinal tract, instead, they are metabolized in the colon by the help of the microflora (Szente & Szejtli, 2004), which can be an advantage for the delivery of some of the bioactive compounds that are mostly absorbed through the large intestine. The most common cyclodextrins in nature consist of six, seven, and eight glucopyranose units, referred as α-, β-, and γ-cyclodextrins, respectively. Among these, β-cyclodextrin is extensively used for the encapsulation of food bioactive ingredients due to its cost-effectiveness (Duchˆene & Bochot, 2016). Nonetheless, this form of cyclodextrin (i.e., β-cyclodextrin) possesses low water solubility. This has resulted in the use of some of its derivatives, including 2-hydroxypropyltedβ-cyclodextrin, low methylated-β-cyclodextrin, and randomly methylated-β-cyclodextrin, with enhanced water solubility (Kfoury, Landy, Auezova, Greige-Gerges, & Fourmentin, 2014). Cyclodextrins are considered to be beneficial for the delivery of bioactive ingredients due to their specific abilities to protect lipophilic components against oxidation and thermal degradation, solubilize various hydrophobic bioactives, stabilize various bioactive ingredients such as flavors, vitamins, and essential oils, and to mask unpleasant odors and tastes. On top of all, cyclodextrins are also able to address the controlled release in the case of some bioactive compounds (Astray, Gonzalez-Barreiro, Mejuto, Rial-Otero, & Simal-Gandara, 2009; Kfoury, H˘ad˘arug˘a, H˘ad˘arug˘a, & Fourmentin, 2016).

8.4.5 Surfactants Surfactants are surface-active molecules containing a hydrophilic group (the head) which is attached to a lipophilic group as the tail (Hammer, 2019; Rosen & Kunjappu, 2004). Therefore, the properties of the head and tail determine the functional performance of a surfactant. The head group of a particular surfactant can be anionic, cationic, zwitterionic, or nonionic (Hammer, 2019). The surfactants used in

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the food industry are mostly nonionic (e.g., Tweens, monoglycerides, and Spans), but they can also be anionic (e.g., DATEM, CITREM), or zwitterionic. Each surfactant type contains its own and unique functional properties, which are the result of its unique molecular structure as well as the physicochemical properties of the surrounding environment (McClements & Jafari, 2018a). In the general sense, surfactants can be any material that influences the interfacial surface tension of a system; however, in practice, surfactants can be used as emulsifiers, dispersants, wetting agents, and foaming agents (McClements et al., 2009). In the area of delivery of functionality (in this case, delivery of bioactive ingredients), some surfactants, especially nonionic surfactants, are used as wall materials for encapsulation of food bioactive compounds (McClements & Jafari, 2018b). If the concentrations of a surfactant in a system (solution) is low, it can exist as a monomer, since the attractive forces operating between the surfactant molecules are overweighed by the entropy of mixing (McClements et al., 2009; Rosen & Kunjappu, 2004). However, when the surfactant concentration increases, the spontaneous aggregation of the surfactant into a variety of thermodynamically stable structures occurs. These aggregates are known as association colloids, and include structures such as vesicles, micelles, bilayers, and reverse micelles (Fig. 8.7) (McClements et al., 2009). The hydrophobic effect is the driving force for the formation of such structures of surfactants. This results in the decrease of the thermodynamically unfavorable contact between the tails (nonpolar group) of the molecules and the surrounding water molecules. When the concentration of the surfactants in the solution increases, they may be organized into different liquid crystalline structures (e.g., lamellar, hexagonal, and

Figure 8.7 Schematic representation of the major structures of association colloids formed by surfactants. Source: Modified from McClements, D. J., Decker, E. A., Park, Y., & Weiss, J. (2009). Structural design principles for delivery of bioactive components in nutraceuticals and functional foods. Critical Reviews in Food Science and Nutrition, 49(6), 577 606.

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reversed hexagonal phases), depending on their molecular geometry. The molecular geometry of surfactants is dependent on their chemical structure, temperature, and solution composition (Attwood, 2012). Therefore, these structures of surfactants have been employed as nanodelivery systems for food bioactive ingredients based on the structure and properties of surfactants, most of which are based on the spontaneous selfassembly of surfactant molecules in aqueous solution (Flanagan & Singh, 2006; Mezzenga, Schurtenberger, Burbidge, & Michel, 2005).

8.4.6 Combinations of different nanocarrier materials Depending on the sensitivity/lability of the bioactive ingredients to be encapsulated, the reason for encapsulation (see Table 8.4), the application of the delivery system in the functional foods, and the release profile of the encapsulated bioactive in the GIT, a combination of different wall materials may also be employed in order to take advantage of a system with added properties. Such a combination can improve the properties of nanodelivery systems in terms of encapsulation efficiency and thermal, mechanical, and barrier stabilities, as well as the bioavailability of the incorporated bioactives, if compared with the delivery systems made using a single wall material (Fang & Bhandari, 2011). Perhaps the most widely reported combination of wall materials for encapsulation of bioactive ingredients is the combination of proteins and polysaccharides (Arroyo-Maya & McClements, 2015; Duval, Chung, & McClements, 2015; Luo, Zhang, Whent, Yu, & Wang, 2011). The reason for this combination is utilizing functional properties of proteins such as high nutritional properties, high gelation capacity, and the ability to be hydrolyzed by digestive proteases, in combination with the specific properties of polysaccharides such as stability under harsh gastric conditions and their high bioadhesiveness (Mizrahy & Peer, 2012).

8.5

Challenges toward nanodelivery of bioactive compounds in functional foods

Although the incorporation of nanoencapsulated bioactive materials into functional foods has been shown to be a promising approach for the delivery of such health-promoting compounds to the human body, there still remain some substantial challenges to address before the functional products are fully developed and available for the people in the community. First, the incorporation of bioactive compounds into foods should not result in undesirable changes in the sensorial properties of the food. While nanoencapsulation is able to provide adequate protection against the release of the bioactives into food matrix, the breakdown of the capsule structure and the consequent release of the encapsulated material into the food matrix (during both processing and storage) can still happen to a certain degree, which, in turn and depending on the food matrix, can negatively affect the taste, color, odor, and correspondingly, the acceptability of the end product. Second, even if the encapsulated bioactives have no undesirable effect on the properties of the

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food, to claim the functionality/efficacy of a bioactive compound incorporated into a specific food, there exist some strict regulatory challenges and guidelines to deal with. Be that as it may, such regulations are currently not clear in some countries, and in some cases, they are even not in place yet. Third, the toxicity of some of the bioactive materials over a certain dosage (i.e., the enhanced levels of absorption of a certain bioactive compound after nanoencapsulation), as well as the toxicity of the fabricated nanoparticles (even those made of food-grade materials) is still under question. Therefore, further scientific research is required to establish the guidelines around the safety levels of encapsulated bioactive ingredients. In this regard, a greater understanding of the digestion and metabolism of the fabricated nanoparticles and their subsequent penetration through biological barriers is greatly required to safeguard the development of nanocarriers for the incorporation of bioactive materials for use in the functional foods.

8.6

Concluding remarks and future direction

During the last couple of decades, a lot of interest has been generated in the development of functional foods containing nanoencapsulated bioactive materials, due to the increasing knowledge on the link between dietary habits and human health. The advances in the new technologies introduced to the food industry have also contributed to this fast-growing area of research. Various delivery systems for the delivery of a wide range of bioactive ingredients have been developed and some have been successfully incorporated into a few types of functional foods. This is considered to have promising potential for improving the efficiency of bioactive compounds with their positive effects on human health. Certainly, the future improvements in processing/ manufacturing technologies in the area of nanoencapsulation will lead to new and perhaps more promising nanodelivery systems, which in turn will result in increasing the efficacy of bioactives in functional foods. Bioavailability, bioaccessibility, and the target delivery of the encapsulated bioactive compounds will be specifically the major areas of research on such delivery systems. Nevertheless, there are still several important challenges to be addressed before the functional foods containing nanoencapsulated bioactives are at the reach of the consumers. These include, but are not limited to, consumer’s acceptability, safety/toxicity (i.e., establishing optimal intake levels) of both bioactive compounds and nanocapsules, and regulations. Although some of these challenges may be responded to by the advances in the current technologies in the near future, the problems about regulations and lack of clear guidelines need serious attention from the corresponding authorities.

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Further reading Gan, Q., & Wang, T. (2007). Chitosan nanoparticle as protein delivery carrier—systematic examination of fabrication conditions for efficient loading and release. Colloids and Surfaces B: Biointerfaces, 59(1), 24 34. McClements, D. (2014). Nanoparticle-and microparticle-based delivery systems: Encapsulation, protection and release of active components. Boca Raton, FL: CRC Press. Silva, H. D., Cerqueira, M. A., Souza, B. W. S., Ribeiro, C., Avides, M. C., Quintas, M. A. C., . . . . . . Vicente, A. A. (2011). Nanoemulsions of β-carotene using a highenergy emulsification evaporation technique. Journal of Food Engineering, 102(2), 130 135.

Enhancing the bioavailability of nutrients by nanodelivery systems

9

H. Turasan and J.L. Kokini Department of Food Science, Purdue University, West Lafayette, IN, United States

9.1

Introduction

The delivery of health-promoting nutrients, such as antioxidants, vitamins, probiotics, minerals, and phenolic compounds, with conventional methods has some drawbacks in protecting the bioactives through the harmful environment of the gastrointestinal system, leading to decreased bioavailability and bioaccessibility of bioactives and nutrients (Jafari & McClements, 2017; Sadeghi et al., 2018). Encapsulation of these compounds in advanced nanodelivery systems is more advantageous in terms of increased solubility and protection from oxidation, hydrolysis, and acidity of gastric fluids because the polymers coating the bioactives act as a barrier between the compounds and the outer conditions, increasing the stability of the compounds until they reach the more neutral acidity of the intestinal tract where they can get absorbed more effectively (Katouzian & Jafari, 2016; Rafiee, Nejatian, Daeihamed, & Jafari, 2019; Rezaei, Fathi, & Jafari, 2019). Due to these advantages, many groups explore ways to encapsulate bioactives in nanodelivery systems. Nanocarriers that carry the bioactives can be fabricated from inorganic compounds and synthetic polymers as well as from biobased polymers and organic compounds (Assadpour & Jafari, 2019a, 2019b). Synthetic polymers often give higher encapsulation efficiencies since their longer chains provide better entanglement and a denser network forming around the encapsulated compounds. However, the risk of accumulation of synthetic wall materials in the body leads researchers to focus on fabricating organic biobased nanodelivery systems from plant or animal sources, such as proteins or carbohydrates. There are many ways to fabricate nanodelivery systems to encapsulate bioactives and drugs. Based on the principle of nanoparticulation, these methods can be classified under four main categories: nanoprecipitation, also known as desolvation or solvent displacement method; complex coacervation; layer-by-layer assembly; and nanoemulsification. In this chapter, nanodelivery systems fabricated from these different techniques will be summarized by reviewing recent studies. Also, the main focus of this chapter will be on biobased nanodelivery systems.

Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00009-1 © 2020 Elsevier Inc. All rights reserved.

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Desolvation/nanoprecipitation/solvent displacement

The desolvation method is one of the most preferred methods for the nanoparticulation of polymers because of its ease and rapidity. In this technique, two miscible solvents are required, one of which is a good solvent for the polymer to be nanoparticulated, and the other one should be a poor solvent (nonsolvent) for the polymer. When the polymercontaining good solvent is mixed with the poor solvent, the lack of solubility of the polymer in this new mixture forces polymer molecules to nucleate and aggregate, leading to nanoparticle formation (Faridi Esfanjani & Jafari, 2016; Taheri & Jafari, 2019). This particle formation is often instantaneous and in the presence of bioactive compounds an effective encapsulation can be achieved. Depending on the polymer, solvents, conditions of the solutions, such as temperature and pH, and other parameters like mixing rate and ratios of the solvents to each other, the formation of nanoparticles as well as their bioactive encapsulation efficiencies may change. In this section, recent studies on the nanoparticulation of biopolymers using the desolvation method to encapsulate bioactive compounds are discussed. For the encapsulation of resveratrol, zein/pectin core shell nanoparticles were formed using the desolvation method (Huang et al., 2017). First, zein nanoparticles were formed using aqueous ethanol solution as the good solvent and water as the poor solvent for zein. For the encapsulation, resveratrol was added to the zein ethanol solution prior to nanoparticulation. The solution containing resveratrol-loaded zein nanoparticles was then mixed into a pectin solution at pH 5 4. Pectin concentration was varied to analyze the stability of zein dispersion at the presence of pectin. In the absence of pectin, zein nanoparticle dispersion was highly stable (78 nm particle diameter), due to the electrostatic repulsion between zein nanoparticles at pH 5 4. At low pectin concentrations (,0.02% w/v), extensive nanoparticle aggregation was observed, which precipitated to the bottom of solution. This is due to the instant transition of particle zeta potentials from 141 mV to 29 mV, which eliminated the repulsion force between nanoparticles. As the pectin concentration was increased, zeta potentials of the pectin covering zein nanoparticles decreased to 233 mV and the solution became stable again with an increase in particle diameter (around 200 nm). Increasing resveratrol concentration did not significantly affect the particle sizes or the polydispersity index (PDI) of the particles; however, particle yield (%) and the loading efficiency (%) significantly decreased. DPPH (2,2diphenyl-1-picrylhydrazyl) and ABTS (2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) scavenging capacity and Fe31 reducing power of encapsulated resveratrol in nanoparticles were significantly higher than those of free resveratrol. Anticarcinogenic activity of encapsulated resveratrol was tested on hepatocarcinoma cancer cells, and regardless of the encapsulated resveratrol concentration, inhibition of cancer cells was significantly higher for encapsulated resveratrol. These results show the improved antioxidant and anticancer activity of resveratrol when it was encapsulated in zein/pectin nanoparticles. The stability of resveratrol-loaded zein/pectin nanoparticles against pH, salt, and temperature was tested in another study (Huang et al., 2019). At a pH range of 2 7, zein/pectin nanoparticles were

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stable against aggregation without a significant change in particle diameters. Increasing NaCl concentration did not significantly affect the nanoparticle stability up to 50 mM, beyond which aggregation of nanoparticles were seen, due to the weakening electrostatic interaction between pectin and zein molecules and the screening effect of salt ions. Heating the nanoparticle suspensions at 80 C for 1 h did not affect the particle stability, showing the effectiveness of the pectin coating against heat stability (Hu & McClements, 2015). Bioaccessibility of encapsulated resveratrol was also measured after simulated gastrointestinal tract (GIT) environment exposure. Solubility of encapsulated resveratrol was significantly improved in GIT conditions compared to free resveratrol and a resveratrol physical mixture with zein/pectin nanoparticles. At the end of intestinal digestion, the release of encapsulated resveratrol was also significantly higher than free resveratrol and the resveratrol mixture (Fig. 9.1). Curcumin, another polyphenol that has many health benefits including antioxidant and antiinflammatory properties, was encapsulated in bovine serum albumin (BSA) nanoparticles (Sadeghi et al., 2014). Particles were fabricated using a desolvation method, where water was used as the good solvent, and pure ethanol, pure acetone, and their mixtures at two ratios (70:30 and 50:50 ethanol:acetone) were tested as the poor solvent. The highest nanoparticulation efficiency of 99% was achieved when acetone was used as the poor solvent at a desolvating solution/polymer solution ratio of 3. Poor solvent consisting of 50:50 ethanol:acetone gave a higher nanoparticulation efficiency than a 70:30 ratio, regardless of the desolvating solution/polymer solution ratios. When ethanol alone was used as the poor solvent, nanoparticulation efficiencies ranged between 92% 95% for different desolvating solution/polymer solution ratios. In general, increasing the desolvating solution/ polymer solution ratio increased the nanoparticulation yield. Using ethanol alone as the poor solvent led to the smallest nanoparticles, while using acetone alone resulted in the largest nanoparticles. In the case of ethanol/acetone mixtures, the 50:50 ethanol:acetone solvent gave a higher number of smaller nanoparticles than the 70:30 ethanol:acetone mixture. For the encapsulation of water-insoluble and ethanol-soluble curcumin, curcumin was added into the ethanol solution. Increasing curcumin concentration from 0 to 2.5 curcumin:BSA molar ratio increased the nanoparticle sizes from about 113 126 nm, however, the highest encapsulation efficiency was not obtained at the highest curcumin concentration. Instead, the highest encapsulation efficiency was observed when the curcumin:BSA molar ratio was 1.5. Glutaraldehyde cross-linking resulted in smaller particle formation, higher PDI and higher stability. Release of curcumin from BSA nanoparticles was measured and compared to those of free curcumin dissolved in ethanol and a physical mixture of BSA and curcumin. The results showed that a more controlled release was achieved when curcumin was encapsulated in BSA nanoparticles (Fig. 9.2). The effects of different desolvating agents on the nanoparticulation efficiencies were also tested for ovalbumin (OVA) nanoparticles and α-lactalbumin (α-LA) nanoparticles (Etorki, Gao, Sadeghi, Maldonado-Mejia, & Kokini, 2016). In addition to ethanol and acetone, methanol was also tested as another poor solvent for these water-soluble proteins, and it led to the smallest particles for both OVA and α-LA, possibly due to its

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Figure 9.1 Bioaccessibility of encapsulated resveratrol in zein/pectin nanoparticles, free resveratrol, and a physical mixture of resveratrol with zein/pectin nanoparticles after simulated gastrointestinal tract exposure. Source: Data from Huang, X., Liu, Y., Zou, Y., Liang, X., Peng, Y., McClements, D. J., & Hu, K. (2019). Encapsulation of resveratrol in zein/pectin core-shell nanoparticles: Stability, bioaccessibility, and antioxidant capacity after simulated gastrointestinal digestion. Food Hydrocolloids, 93, 261 269. Reproduced with permission of Elsevier.

shortest aliphatic chains among the three tested solvents and highest polarity. In general, OVA nanoparticles were smaller than α-LA nanoparticles, with particle sizes ranging between 60 and 160 nm for OVA nanoparticles and between 150 and 230 nm for α-LA nanoparticles. Unlike BSA nanoparticles (Sadeghi et al., 2014), OVA and α-LA nanoparticles were not affected by the desolvating solution/polymer solution ratio significantly. However, similar to BSA nanoparticles, glutaraldehyde cross-linking also increased the stability of OVA and α-LA nanoparticles significantly. These improving stabilities of protein nanoparticles with glutaraldehyde cross-linking can be attributed to the newly forming bridges between protein molecules with glutaraldehyde. In another study, the effects of glutaraldehyde cross-linking on zein films were shown and the

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Figure 9.2 In vitro release profiles of curcumin (A), and images of solutions (B). Source: Data from Sadeghi, R., Moosavi-Movahedi, A. A., Emam-Jomeh, Z., Kalbasi, A., Razavi, S. H., Karimi, M., & Kokini, J. (2014). The effect of different desolvating agents on BSA nanoparticle properties and encapsulation of curcumin. Journal of Nanoparticle Research, 16(9), 2565. Reproduced with permission from Springer Nature.

number of cross-links forming per zein molecule with increasing glutaraldehyde concentration were calculated (Turasan, Barber, Malm, & Kokini, 2018). A chemical mechanism was also proposed to show the binding sites of proteins with glutaraldehyde, proving the formation of tighter junction points with cross-linking. In the case of BSA, OVA, and α-LA nanoparticles, similar tighter junctions occurring with glutaraldehyde are possibly leading to higher particle stabilities (Etorki et al., 2016; Sadeghi et al., 2014). Addition of different components, such as surfactants or reducing agents, or changing the fabrication parameters, such as the mixing speed, can also affect the nanoparticulation of biopolymers using the nanoprecipitation technique. Effects of these parameters, along with the addition of salt, changing pH and temperature were tested on gliadin nanoparticulation (Sadeghi et al., 2018). Encapsulation efficiency of gliadin nanoparticles was also tested using curcumin as the model bioactive compound. Since gliadin is a water-insoluble protein, water was used as the poor solvent and 62% ethanol as the good solvent. The effect of pH on zeta potential of gliadin nanoparticles was analyzed; an increasing pH from 2 to 5 was found to increase the zeta potentials to a maximum of 23 mV. Further increasing the pH to 9 decreased the zeta potentials to 225 mV, making them negatively charged. The isoelectric point of gliadin nanoparticles was seen at pH 5 6.1. At the highest (pH 5 5) and lowest (pH 5 9) zeta potentials, the nanoparticles were in their most stable conditions, due to the high repulsion forces between the positively and negatively charged gliadin nanoparticles, respectively. When the water:ethanol ratio was increased from 4:1 to 10:1 (v/v), smaller nanoparticles were obtained (235 nm), possibly due to the lower amount of polymer molecules in the solvent mixture. The size of gliadin nanoparticles increased at higher mixing speeds. Increasing NaCl concentration also increased the size of nanoparticles, due to the higher screening

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effect of salt ions on the charged gliadin nanoparticles, which led to aggregation and larger particles. Pluronic F68 was added as the surfactant, which decreased the size of nanoparticles from 275 to 245 nm. The size of nanoparticles also decreased when the temperature was increased to 60 C (340 nm) from 40 C (240 nm) or when two reducing agents, dithiothreitol (DTT) and 2-Mercaptoethanol, were added. Encapsulating curcumin in gliadin nanoparticles significantly increased their sizes from 296 to 378 nm. The curcumin encapsulation efficiency was calculated as 68%. Clofazimine, a lipophilic antibiotic used in the treatment of infants against cryptosporidiosis, has been nanoparticulated using flash nanoprecipitation technique in the presence of three surface stabilizers: hypromellose acetate succinate (HPMCAS), lecithin, and zein (Zhang et al., 2017). For the nanoparticulation of clofazimine in the presence of HPMCAS or lecithin, a confined impinging jet mixer was used, where acetone and tetrahydrofuran were selected as good solvents, respectively, and water was used as the poor solvent. For nanoparticulation with zein as the surfactant, a multiinlet vortex mixer was used, since clofazimine was not soluble in the solvent for zein (aqueous ethanol). For zein-stabilized nanoparticles, sodium caseinate was also used as the second stabilizer. HPMCAS-stabilized clofazimine nanoparticles had sizes ranging between 70 to 100 nm, very low PDI values, and zeta potentials ranging between 225 and 229 mV. Among three HPMCAS types (different substitution ratios of succinyl and acetyl groups) (HPMCAS 126, 716, and 912), HPMCAS 126 provided the highest stability for 6 h (Fig. 9.3). Lecithin-stabilized nanoparticles had an average diameter of 175 nm and a PDI of 0.16, but after 3 h, the particles became too large (Fig. 9.3). This instability was attributed to the smaller molecular weight of lecithin than HPMCAS, which could not create a thick enough layer on the drug particles. Zein-stabilized

Figure 9.3 Size stability of clofazimine nanoparticles stabilized with HPMCAS 126 (black K), HPMCAS 716 (red ¢), HPMCAS 912 (blue ’), lecithin (green 3 ), and zein (brown V).Data from Zhang, Y., Feng, J., McManus, S. A., Lu, H. D., Ristroph, K. D., Cho, E. J., . . . Prud’homme, R. K. (2017). Design and Solidification of FastReleasing Clofazimine Nanoparticles for Treatment of Cryptosporidiosis. Molecular Pharmaceutics, 14(10), 3480 3488. https://doi.org/10.1021/acs.molpharmaceut.7b00521. Reproduced with permissions from ACS.

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clofazimine nanoparticles had larger sizes than HPMCAS and lecithin nanoparticles with an average of 240 nm, and higher stability than lecithin-stabilized nanoparticles, such that in 6 h, their sizes only slightly increased to an average of 262 nm (Fig. 9.3). Lyophilization and spray drying were tested as two drying methods to see their effects on redispersion of nanoparticles. When HPMCAS and lecithinstabilized nanoparticles were freeze-dried, redispersed nanoparticle sizes were significantly larger (micron-sized) than before. Freeze-dried zein-stabilized nanoparticles were easily redispersible with no significant changes in their sizes. Spray drying gave similar results, such that HPMCAS and lecithin-stabilized nanoparticles led to micron-sized particles after redispersion, while zein-stabilized particles were in nanoscale. The highest encapsulation efficiencies (98.7%) were obtained with both HPMCAS and lecithin-stabilized nanoparticles, while zein-stabilized nanoparticles gave an encapsulation efficiency of 92%. The bioavailability of clofazimine was measured by the dissolution rate of nanoparticles in GIT conditions. HPMCAS and lecithin-stabilized nanoparticles increased the solubility of water-insoluble clofazimine nearly 50 times. Zein-stabilized nanoparticles showed 80 times and 72 times higher solubility than free clofazimine when they were freeze-dried and spray-dried, respectively.

9.3

Complex coacervation

In coacervation, two oppositely charged polyelectrolytes form a complex mainly through the ionic attraction between them (Esfahani, Jafari, Jafarpour, & Dehnad, 2019; Rajabi, Jafari, Rajabzadeh, Sarfarazi, & Sedaghati, 2019). When the solutions of two polyelectrolytes are mixed, the complex coacervates that form can either precipitate or can remain as suspended nanoparticles in solution (Maldonado, Sadeghi, & Kokini, 2017; Piacentini, 2016). Besides the strong electrostatic attraction between the polyelectrolytes, other weaker bonds, such as hydrogen bonds or hydrophobic interactions, can also help the formation of coacervates (Ghasemi, Jafari, Assadpour, & Khomeiri, 2018). Complex coacervates can form either micron-sized or nanosized nanoparticles, which are often used to encapsulate bioactive components and drugs, since they can improve the solubility of encapsulated compounds, prevent the encapsulated material against the acidic environment of stomach, and increase bioavailability of these compounds (Ghasemi, Jafari, Assadpour, & Khomeiri, 2018). Complex coacervation of proteins provide additional advantages since through pH modification, zeta potentials of proteins can easily be tuned to maximize the interaction between polyelectrolytes. In addition, proteins have very high or very low zeta potentials in acidic pH, and this prevents the coacervates from dissociating in the stomach, protecting the encapsulated drug (Assadpour, Jafari, & Maghsoudlou, 2017; Raei, Shahidi, Farhoodi, Jafari, & Rafe, 2017). Besides the choice of polyelectrolytes, coacervation conditions, such as the solvents or the ratios of polyelectrolytes, play an important role in the stability of complex and encapsulation efficiency of the bioactive compounds (Jafari, 2017).

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The majority of the complex coacervations occur between a protein and a polysaccharide (de Kruif, Weinbreck, & de Vries, 2004; Maldonado et al., 2017), but there are also examples of complex coacervation between two proteins (Milanovi´c, Petrovi´c, Sovilj, & Katona, 2014), two polysaccharides (Deka, Deka, Bora, Jha, & Kakati, 2016), a protein and a synthetic polymer (Kaibara, Okazaki, Bohidar, & Dubin, 2000), or a polypeptide and a polyacid (Mu¨ller, Reihs, & Ouyang, 2005). It has been the main focus of many leading labs to understand the thermodynamic mechanism of complex coacervation and the parameters that affect the formation of these complexes. Huang’s group looked at the effects of salt concentration and the initial protein to polysaccharide ratio on the complex coacervation of BSA and pectin by measuring the turbidity and rheological properties of the solutions (Ru, Wang, Lee, Ding, & Huang, 2012). They used turbidity as an indicator for the formation or dissociation of the BSA/pectin coacervates and observed that as the pH of BSA/pectin mixture was decreased from 7, at pH 5 4.7 turbidity increased sharply to almost 100% and formed a plateau until pH value of 3, after which a sharp decrease was observed until pH 5 1.7 (Fig. 9.4). The high turbidity between pH values of 3.0 to 4.5 indicate good attraction between the polyelectrolytes and complex formation due to the negative charges of pectins and positive charges of BSA molecules between these pH values. At lower pH values, due to the loss of strong negative charges of pectins, complex coacervations dissociated into soluble complexes.

Figure 9.4 Turbidity of bovine serum albumin/pectin mixture solution as a function of decreasing pH (salt concentration 0.1 M, BSA/pectin ratio 5 5). Source: Data from Ru, Q., Wang, Y., Lee, J., Ding, Y., & Huang, Q. (2012). Turbidity and rheological properties of bovine serum albumin/pectin coacervates: Effect of salt concentration and initial protein/polysaccharide ratio. Carbohydrate Polymers, 88(3), 838 846. Reproduced with permission from Elsevier.

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Increasing NaCl concentration from 0.01 to 0.4 M shifted the onset pH for turbidity from a pH of almost 5 to 3.5, due to the hindrance of BSA and pectin charges caused by salt ions (Ru et al., 2012). Increasing NaCl concentration also weakened the network formation between BSA and pectin molecules evident from the decreasing G’ values at higher salt concentrations. Increasing BSA to pectin mass ratio promoted complex coacervation, such that an increase of ratio from 1:1 to 10:1 led to tighter coacervate network formation. The maximum attraction between BSA and pectin molecules were at a BSA/pectin ratio of 10:1, evident from the highest shear modulus, indicating equal charge densities between the polyelectrolytes. A further increase in BSA/pectin ratio (20:1) decreased the network strength between the polyelectrolytes, evident from lower G’ values. The same group also investigated a study on the effects of protein selfassociation on a complex coacervation between three proteins, BSA with two isomers of β-lactoglobulin (BLGA and BLGB) and a polysaccharide (pectin) (Li & Huang, 2013). Coarse-grained Monte Carlo simulation was used to explore the proneness of three proteins to the formation of coacervates with pectin. Through the simulation, the positively charged, negatively charged, and hydrophobic sites on the proteins were predicted. Both isomers of β-lactoglobulin had a higher probability to form a coacervate with pectins than BSA with a broader pH range. Due to its extra additional negative titratable residue, BLGA had a stronger self-association proneness than BLGB and was predicted to form a stronger complex coacervate with pectins because of higher electrostatic interactions. Complex coacervation mechanisms between branched poly(ethyleneimine) (PEI) and poly(D,L-glutamic acid) (PGlu) or poly(D,L-aspartic acid) (PAsp) have also been investigated using turbidity and rheological measurements and isothermal titration calorimetry (ITC) (Priftis, Megley, Laugel, & Tirrell, 2013). In complex coacervates of both PEI/PGlu and PEI/PAsp, the highest turbidity values were measured at a polyacid:polybase ratio of 31:69% for all total polymer concentrations and molecular weights of polyelectrolytes and even when no salt was added to the system. This was due to the maximum number of available charged sites of polyelectrolytes at this ratio. At very low (,15 mol% base) or very high ( . 88 mol% base) acid:base ratios, coacervation formation was not seen due to the redissolution of polyelectrolytes. Turbidity also increased at higher total polymer concentrations, suggesting more complex coacervate formation, due to the increasing number of available interaction sites between polyelectrolytes with increasing polyelectrolyte molecules. Increasing salt concentration from 0 to 80 mM of NaCl increased the turbidity and coacervate formation, but further increase of the salt concentration to 1200 mM NaCl, resulted in a lower turbidity, due to the screening effect of salt ions on the charged sites of polyelectrolytes. When higher molecular weight polyelectrolytes were used, turbidity of the solutions and the critical salt concentrations increased. This was considered to be because of the increasing cooperativity of the interpolymer interactions with increasing molecular weight and the smaller entropy of the complex. Temperatures between 20 and 40 C did not significantly affect the turbidity and complex formation when no salt was introduced to the system, since the electrostatic attraction between polyelectrolytes was too strong to be affected by

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these low temperatures. However, in the presence of salt, a higher temperature decreased the turbidity, since the salt molecules weakened and screened the electrostatic attraction between polyelectrolytes, so even a slight change in temperature was effective in the dissociation of the coacervates. ITC results revealed that regardless of the conditions of complex coacervation, such as temperature, salt concentration, total polymer amount, the interaction of polyelectrolytes was endothermic and the dissolution of coacervates were exothermic. Also, a complex coacervation reaction was found to be an entropy-driven reaction. A 10-fold increase in total polymer concentration increased the heat change by sevenfold during coacervate formation. Increasing molecular weights and salt concentrations also slightly increased the reaction enthalpy change, separately. Viscosity of the mixtures decreased as the acid:base ratio was changed from 31:69% to 17:83%, consistent with the highest coacervate formation at 31:69% ratio (Fig. 9.5). Increasing the salt concentration also decreased the viscosity of solutions, since the screening effect of salt ions weakened the attraction between polyelectrolytes and increased the water content, which resulted in a lower viscosity (Fig. 9.5). The effect of addition order of polyelectrolytes on complex coacervation was also investigated using sodium alginate and chitosan (Yilmaz, Maldonado, Turasan, & Kokini, 2019). Zeta potential measurements of sodium alginate and chitosan at varying pH values showed that while sodium alginate was always negatively charged throughout a pH range of 3.5 9, chitosan was positively charged between pH 5 3.5 8 and negatively charged between pH 5 8 9. The maximum difference between zeta potentials of sodium alginate and chitosan was seen at pH 5 4, which was selected as the optimum pH to form coacervates. ITC measurements were conducted to understand the thermodynamics of complex coacervation, and the overall enthalpy of reaction was found to be 23207 kJ/mol when sodium alginate was added into chitosan, and 21683 kJ/mol when chitosan was added into sodium alginate. This difference between the order of additions shows that the interaction between polyelectrolytes is stronger when sodium alginate was added into chitosan. Sodium addition to chitosan also showed a higher entropy change suggesting a complex coacervation with a higher order. Particle size measurements revealed that this stronger interaction between polyelectrolytes when sodium alginate was added into chitosan also results in smaller coacervates. Molar charge ratios also affected the particle size of coacervates (Table 9.1). In the case where sodium alginate was added into chitosan, the enthalpy of reaction and zeta potential of coacervates transitioned more abruptly than when chitosan was added into alginate. In both orders of addition, as the electrical neutrality was reached, the particle size of coacervates increased. When sodium alginate was added into chitosan, initially high positive molar charge ratio due to excess chitosan molecules decreased. Similarly, when chitosan was added into sodium alginate, the initially high negative charge ratio decreased. However, particles had smaller sizes when sodium alginate was added into chitosan (Table 9.1). Choosing the correct design parameters for forming complex coacervates is important to successfully encapsulate bioactive compounds and drugs in these micro- and nanoparticles. Curcumin was encapsulated in complex coacervation of

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Figure 9.5 Viscosity of poly(ethyleneimine) and poly(D, L-glutamic acid) complex coacervates at different acid:base ratios (A), and viscosity of poly(ethyleneimine) and poly (D, L-aspartic acid) coacervates with increasing salt concentration. Source: Data from Priftis, D., Megley, K., Laugel, N., & Tirrell, M. (2013). Complex coacervation of poly(ethylene-imine)/polypeptide aqueous solutions: Thermodynamic and rheological characterization. Journal of Colloid and Interface Science, 398, 39 50. Reproduced with permission from Elsevier.

BSA and poly-D-lysine (PDL) (Maldonado et al., 2017). First, fabrication parameters, such as the molecular weight of PDL, salt concentration, mass and molar charge ratios of BSA and PDL, and cross-linker amount, were varied and their effects on coacervates were investigated. Zeta potential measurements of both polyelectrolytes showed that isoelectric point of BSA was pH 5 5, below which it was positively charged and above, it was negatively charged (Fig. 9.6). The two types of PDL (high- and low-molecular-weight) had positive zeta potentials between the tested pH range (pH 5 4 11). For optimizing the coacervation of BSA/PDL and to maximize the electrostatic attraction between these polyelectrolytes, pH 5 7 was chosen as the fabrication pH for both BSA/low-molecular-weight (LMW) PDL and

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Table 9.1 Particle size (PS)(a), zeta potential (ZP) (b), and polydispersity index (PDI) (c) of sodium alginate/chitosan complex coacervates with different order of additions and molar charge ratios. Order of addition

Molar charge ratio

PSa (nm)

ZPb (mV)

PDIc

Sodium alginate into chitosan

0.01

287 6 38

38.8 6 4

0.34 6 0.04

0.05 0.10 0.20 0.30 0.40 0.50 0.75 0.80 0.85 0.90 1.00 1.15 1.25 1.25

253 6 29 267 6 39 243 6 17 254 6 39 253 6 13 270 6 22 316 6 16 510 6 64 1178 6 71 1383 6 107 4970 6 993 2436 6 112 2211 6 508 727 6 166

35.1 6 6.1 40.9 6 2.7 35.5 6 6.2 35.9 6 6.4 38.3 6 3.4 37.1 6 2 32.3 6 6 32.5 6 4.8 30.1 6 6.2 27.6 6 2.7 214.3 6 7.7 223.7 6 4.2 227.7 6 3.2 34.3 6 2.6

0.3 6 0.01 0.32 6 0.04 0.28 6 0.05 0.37 6 0.05 0.26 6 0.03 0.22 6 0.03 0.28 6 0.01 0.71 6 0.09 0.93 6 0.12 1 6 0.01 0.92 6 0.14 0.55 6 0.26 0.62 6 0.12 0.4 6 0.08

1.17 1.11 1.00 0.87 0.80 0.75 0.60 0.50 0.40 0.33 0.25 0.20 0.10 0.05

1209 6 135 792 6 196 821 6 138 855 6 187 1094 6 137 1000 6 164 513 6 20 477 6 17 439 6 39 465 6 40 537 6 36 638 6 89 1045 6 125 1504 6 258

35.6 6 1.7 33.3 6 1.7 32.6 6 5.3 31 6 3.4 30.5 6 3.6 23.1 6 5.7 224.5 6 1.3 233.8 6 1.7 236.7 6 1.9 238.4 6 2.3 239.8 6 1.6 238.2 6 3.7 241.2 6 2.6 234.9 6 4.5

0.33 6 0.04 0.42 6 0.06 0.34 6 0.05 0.47 6 0.05 0.35 6 0.05 0.31 6 0.03 0.38 6 0.03 0.39 6 0.19 0.39 6 0.05 0.38 6 0.05 0.35 6 0.05 0.42 6 0.03 0.46 6 0.005 0.32 6 0.09

Chitosan into sodium alginate

Source: Data from Yilmaz, T., Maldonado, L., Turasan, H., & Kokini, J. (2019). Thermodynamic mechanism of particulation of sodium alginate and chitosan polyelectrolyte complexes as a function of charge ratio and order of addition. Journal of Food Engineering, 254, 42 50. Reproduced with permission from Elsevier.

BSA/high-molecular-weight (HMW) PDL coacervates. Particle size measurements showed that for both coacervates, the smallest particles were obtained at pH 5 7, confirming the highest electrostatic attraction between polyelectrolytes at this pH. While BSA/LMW PDL coacervates showed spherical morphology, BSA/HMW PDL coacervates had nonspherical shapes (Maldonado et al., 2017). Mass and molar charge ratios of the polyelectrolytes were also effective in particle sizes, such

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Figure 9.6 Zeta potentials of bovine serum albumin, high molecular weight poly-D-lysine, and low molecular weight poly-D-lysine with varying pH values. Source: Data from Maldonado, L., Sadeghi, R., & Kokini, J. (2017). Nanoparticulation of bovine serum albumin and poly-d-lysine through complex coacervation and encapsulation of curcumin. Colloids and Surfaces B: Biointerfaces, 159, 759 769. Reproduced with permission from Elsevier.

that, for LMW PDL, at a BSA:PDL mass ratio of 2, which also corresponded to a molar charge ratio [n2/n1] of 0.08, the smallest complex coacervates were fabricated. For HMW PDL/BSA coacervates, these ratios were 2.5 BSA:PDL mass ratio and molar charge ratio [n2/n1] of 0.1. In general, coacervates fabricated with LMW PDL were smaller than those fabricated with HMW PDL. The effect of ionic strength was tested with increasing NaCl concentration. Smaller coacervates were fabricated with the addition of salt into the system for both polyelectrolyte pairs, with LMW PDL/BSA particles having smaller sizes than HMW PDL/BSA coacervates. The smallest particles for LMW PDL/BSA combination with a particle size of about 210 nm were achieved at a salt concentration of 0.1 M, while the smallest particles of HMW PDL/BSA coacervates had a particle size of 270 nm at 0.4 M

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salt concentration. Addition of glutaraldehyde as cross-linker generally increased the stability of coacervates during a period of 21 days, however HMW PDL/BSA coacervates got larger during storage with cross-linking when they were prepared at a BSA:PDL mass ratio of 3. Curcumin was encapsulated in LMW PDL/BSA nanoparticles. Higher curcumin concentration increased the particle sizes, where the largest nanoparticles were obtained at a curcumin:BSA ratio of 10. Highest curcumin encapsulation efficiency of 60% was also achieved at this curcumin:BSA ratio. Complex coacervates of gum Arabic and gelatin were used for the encapsulation of black raspberry anthocyanins (Shaddel et al., 2018). Before the coacervation process, double emulsions (water in oil in water (W/O/W)) of black raspberry anthocyanins were prepared. First, W/O emulsions of anthocyanins were prepared in soybean oil and then the emulsions were further emulsified in gelatin solutions (W/ O/W). With the addition of gum Arabic to the system, complex coacervation was formed between gum Arabic molecules and gelatin molecules. These coacervates had spherical shapes and smooth surfaces, which showed the successful coacervation of double emulsions. The concentrations of black raspberry extract or the polyelectrolytes did not affect the morphology of particles. The double emulsions before the coacervation process had particle sizes ranging between 26 63 μm, and after coacervation this range increased to 35 80 μm, with the addition of gum Arabic. The solubility of black raspberry extract significantly decreased with encapsulation, showing the stability of black raspberry extract in the microparticles and its controlled release in water. Raspberry extract-loaded coacervates had negative zeta potentials due to the carboxylic acid groups of gum Arabic. The highest loading capacity was reached when gelatin and gum Arabic concentrations were 7.5% and when the core material was added at a ratio of 1:1:1 (gum Arabic:gelatin:black raspberry extract). Encapsulated anthocyanins had a higher stability when they were stored at 7 C than at 37 C. Highest stability was reached for the samples prepared with 5% gum Arabic and gelatin concentrations and when the core material ratio was 1:1:1 (gum Arabic:gelatin:black raspberry extract).

9.4

Layer-by-layer assembly

Layer-by-layer (LbL) deposition also benefits from the electrostatic attraction between oppositely charged polyelectrolytes. Micro- or nanoscale particles are formed with the help of a solid material which is used as the initial charged support layer and is often dissolved after the formation of LbL particles (Sadeghi et al., 2018). The first polyelectrolyte that is oppositely charged with the solid template is forming the first layer on the solid template; when the second polyelectrolyte that is oppositely charged with the first polyelectrolyte and similarly charged with the solid template is introduced to the system, it forms a second layer on the first polyelectrolyte, forming the first bilayer of the system (Fig. 9.7). As the deposition of polyelectrolytes is repeated, more bilayers can be formed until the necessary thickness is reached. The shape of LbL assemblies can either be spherical or tubular,

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with the use of spherical or cylindrical solid or membrane templates. In the case of spherical LbL particles, bioactive compounds and drugs can be encapsulated either in the core of particles after the solid template has been removed, or between the layers during polyelectrolyte depositions (Bastarrachea, Denis-Rohr, & Goddard, 2015). For the cylindrical-shaped LbL particles, bioactives can be loaded to the inner space of nano- or microtubes.

9.4.1 Spherical nanoparticle formation through layer-by-layer assembly Curcumin was encapsulated in hollow and solid spherical LbL nanoparticles fabricated from the most abundant protein of sorghum, kafirin, to improve its solubility in GIT (Li et al., 2019). First, solid particles were fabricated with the desolvation method using ethanol and water as the solvent and nonsolvent. For fabricating the hollow kafirin particles, sodium carbonate molecules were used as the spherical solid templates. Adding kafirin solution into sodium carbonate solution allowed kafirin molecules to form the first layer on the sodium carbonate cores, which were then removed from the core of kafirin particles by adding this solution into water, leaving coreless hollow kafirin nanoparticles. Ethanol-soluble curcumin was initially mixed with kafirin solution for both solid and hollow nanoparticles. LbL assembly of two polyelectrolytes, dextran sulfate and chitosan, were done on the loaded kafirin nanoparticles to provide additional wall materials to the system and increase encapsulation efficiency. First, dextran sulfate molecules that are negatively charged at pH 5 4 were deposited on kafirin nanoparticles, which are positively charged at this pH. The electrostatic attraction between dextran sulfate and kafirin helped to form the first layer. Then, positively charged chitosan solution was added to the system and the first bilayer of polyelectrolytes were formed. Deposition of dextran sulfate and chitosan were repeated once more to achieve double bilayer formation (Fig. 9.8). All the kafirin nanoparticles that were not LbL-assembled, including solid and hollow unloaded and loaded kafirin nanoparticles, had highly negative zeta potentials between 240 to 250 mV, with curcumin-loaded solid and hollow nanoparticles slightly higher than free ones. These zeta potentials show that all these nanoparticles have good electrostatic repulsion between them, which keep the nanoparticles stable in solution. Curcumin loading did not affect the size of either solid or hollow kafirin nanoparticles. In LbL-assembled nanoparticles, the zeta potential

Figure 9.7 Layer-by-layer assembly of polyelectrolytes on a solid template.

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Figure 9.8 Transmission electron microscopy images of solid and hollow kafirin nanoparticles: (A) nonloaded hollow; (B) nonloaded solid; (C) curcumin loaded hollow; (D) curcumin loaded solid; (E) curcumin loaded LbL-assembled hollow; and (F) curcumin loaded LbL-assembled solid kafirin nanoparticles. Source: Data from Li, X., Maldonado, L., Malmr, M., Rouf, T. B., Hua, Y., & Kokini, J. (2019). Development of hollow kafirin-based nanoparticles fabricated through layer-by-layer assembly as delivery vehicles for curcumin. Food Hydrocolloids, 96, 93 101. Reproduced with permission from Elsevier.

and size of particles changed as the layers were deposited (Fig. 9.9A). When the first layer of dextran sulfate was deposited, a negative zeta potential of

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approximately 225 mV was observed, which then turned into 125 mV with the addition of the first chitosan layer. With the addition of the second bilayer, the same zeta potential jump was seen. Addition of bilayers also increased the particle size from 60 70 nm to around 200 nm. LbL-assembled solid kafirin nanoparticles had lower encapsulation efficiencies than LbL-assembled hollow kafirin nanoparticles for every curcumin/kafirin ratio (Fig. 9.9B). Decreasing curcumin/kafirin ratio increased the encapsulation efficiency for both LbL solid and hollow kafirin nanoparticles, where the highest numbers reached 95%. The dissolution of curcumin in GIT increased significantly when it was encapsulated in kafirin nanoparticles, compared to native curcumin. LbL-assembled solid kafirin nanoparticles showed the highest curcumin release, followed by LbL-assembled hollow kafirin nanoparticles. Microparticles fabricated with LbL assembly of chitosan and sodium alginate were used to encapsulate thyme essential oil (Zhang et al., 2019). First, thyme essential oil was emulsified in aqueous solutions containing Span 80 and Tween 80 emulsifiers. Then to form the first layer around thyme oil droplets in water, chitosan solutions prepared in acetic acid were dropwisely added to the thyme oil emulsion. The second layer was formed similarly by adding sodium alginate solution dropwise into the mixture and these steps were repeated to form bilayers of chitosan/sodium alginate. Encapsulating thyme oil in LbL nanoparticles significantly reduced its release rate. At the end of 60day storage, nonencapsulated free thyme oil was released four and two times faster than encapsulated thyme oil at 4 C and 25 C, respectively. Also, the release rates of free thyme oil and encapsulated thyme oil were higher at 25 C compared to 4 C, possibly due to the faster Brownian motion of oil molecules at 25 C than 4 C which triggers thyme oil volatility; more and more oil is lost during storage. The release profiles of

Figure 9.9 (A) Particle size and zeta potential of LbL-assembled kafirin nanotubes loaded with curcumin. Layer numbers indicate the deposition of dextran sulfate and chitosan layers to form 2 bilayers. (B) Encapsulation efficiency of LbL solid (sNPs) and hollow (hNPs) kafirin nanoparticles. Source: Data from Li, X., Maldonado, L., Malmr, M., Rouf, T. B., Hua, Y., & Kokini, J. (2019). Development of hollow kafirin-based nanoparticles fabricated through layer-by-layer assembly as delivery vehicles for curcumin. Food Hydrocolloids, 96, 93 101. Reproduced with permission from Elsevier.

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thyme oil in LbL nanoparticles having, one, two, and three bilayers of chitosan/sodium alginate at 100 C showed that while the unencapsulated thyme oil was almost completely released at the end of 5 h, only 48.84%, 28.38%, and 19.3% thyme oil was released from LbL particles having one, two, and three bilayers, respectively, confirming the effect of bilayer numbers on the protection of volatile thyme oil (Fig. 9.10). pH of the release medium was also effective on the release profile of thyme oil from LbL particles. While only a small amount (,5%) of thyme oil was released from LbL particles at pH 5 2 in the first 90 min, at pH values of 4, 6, 8, and 10, these rates were around 20%, 32%, 50%, and 64%, respectively. After 90 min, the release rates of thyme oil remained stable for all pH values. Thyme oil-loaded LbL particles showed excellent inhibitory effect against three strains of bacteria, Staphylococcus aureus, Bacillus subtilis, and Escherichia coli. Out of three thyme oil-loaded LbL particle concentrations, 15 mg/mL showed the highest inhibitory effect on all three strains. Due to the slower release profiles of thyme oil when it was encapsulated in LbL particles, loaded LbL particles were found to be more effective than free thyme oil in the longer time periods. Inhibition of S. aureus in milk, shown as an example of a real-life food sample, was also successfully done with thyme oil-loaded LbL particles.

9.4.2 Nanotubular formation through layer-by-layer assembly Two polyelectrolytes, BSA and poly-D-lysine (PDL) were used to form biobased LbL-assembled nanotubes for the encapsulation and delivery of curcumin (Sadeghi

Figure 9.10 Release profiles of free thyme oil (denoted with 0), encapsulated thyme oil in signle bilayer (denoted with 2), double bilayers (denoted with 4), and triple bilayers (denoted with 6) of chitosan/sodium alginate. Source: Data from Zhang, Z., Zhang, S., Su, R., Xiong, D., Feng, W., & Chen, J. (2019). Controlled release mechanism and antibacterial effect of layer-by-layer self-assembly thyme oil microcapsule. Journal of Food Science, 84(6), 1427 1438. Reproduced with permission from John Wiley and Sons.

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et al., 2013). First, to provide the maximum attraction between polyelectrolytes, the effect of pH on the zeta potentials of BSA and PDL was explored. The highest zeta potential difference between positively charged PDL and negatively charged BSA molecules was found at pH 5 7.4 and the nanotubes were fabricated at this pH. A negatively charged track-etched polycarbonate membrane with cylindrical holes was used as the solid template. The outermost layer of the LbL nanotubes were fabricated with PDL, since there is an attraction between positively charged PDL molecules and the negatively charged template. After forming the first layer by running the PDL solution through the membrane, BSA solution was passed through the membrane to form the second layer. This procedure was repeated two and three times to form double and triple bilayers of PDL/BSA. After the desired number of bilayers were formed, the membrane was dissolved in N,N-dimethylformamide solution and the LbL nanotubes were freeze-dried. Morphology assessments showed that single-bilayered nanotubes were not stable enough to maintain their nanotubular structures. While double-bilayered nanotubes had better structures than singlebilayered nanotubes, triple-bilayered nanotubes were the most durable nanotubes and maintained their tubular structures. Each bilayer had a thickness of 20.3 nm, and the length of nanotubes were 9 μm. For encapsulation, curcumin was either added to the aqueous ethanol solution of BSA before LbL assembly or the dried nanotubes were mixed with curcumin solution after LbL assembly. Preaddition of curcumin into BSA solution only allowed double bilayers to form since it created thicker wall materials and the polyelectrolyte solutions could not be passed through the template membrane to form the third layer. These nanotubes also had distorted structures. Postloading of curcumin to the inner space of triple-bilayered LbL nanotubes resulted in a stronger structure and a higher encapsulation efficiency (45%) which was obtained after 2 h mixing. In another study, the optimal window of LbL nanotube fabrication parameters was established using BSA and sodium alginate as the model polyelectrolytes, where the LbL nanotubes were fabricated using the same polycarbonate template method (Maldonado & Kokini, 2018). The zeta potential measurements with varying pH showed that the optimal pH window for the formation of LbL nanotubes is 3.5 4, where BSA is positively charged and sodium alginate is negatively charged. The effect of polyelectrolyte concentrations on the formation of nanotubes were also explored. While at dilute polymer concentrations nanotubes were thinner, at high concentrations no nanotubes were formed, but there were clusters. Nanotubes with good structures were formed when the BSA concentration was 0.8 mg/mL and sodium alginate concentration was 0.6 mg/mL. The diameters of nanotubes were varied (200, 400, 600, and 800 nm) by varying the pore size of template. All pore sizes led to nanotubes with good structures, and as expected, LbL nanotubes fabricated with larger diameter templates had thicker walls (Fig. 9.11). 1 mL/min flow rate was decided as the optimal flow rate for fabricating nanotubes, since lower or higher flow rates did not lead to nanotubes with good shapes due to high accumulation and not enough residence time, respectively. Two other polyelectrolyte pairs were also tested to form LbL nanotubes for the delivery of curcumin: chitosan (CHI)/α-lactalbumin (LAC) and BSA/κ-carrageenan

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(CAR) (Maldonado, Chough, Bonilla, Kim, & Kokini, 2019). Similar to the previous study, the pH of solutions was optimized to provide the maximum attraction between polyelectrolyte pairs. The highest zeta potential differences of CHI/LAC and BSA/CAR were obtained at pH 5 7 and pH 5 4, respectively. ITC was used to understand the mechanism of interactions between polyelectrolyte pairs. While both interactions were exothermic, the overall enthalpy of interaction was 26.14 kJ/g for BSA/CAR and 20.494 kJ/g for CHI/LAC. Both reactions were found to be driven by coulombic interactions. The effect of different pore sizes on the formation of nanotubes were also tested for these polyelectrolyte pairs using 400, 600, and 800 nm templates. While 400 nm pores allowed only four bilayers to form for both polyelectrolyte pairs, five bilayers were successfully deposited with 600 and 800 nm templates. Despite the same number of bilayers, BSA/CAR nanotubes had thinner walls (60 with 400 nm template, 67 with 600 nm template, and 76 with

Figure 9.11 Bovine serum albumin/sodium alginate LbL nanotubes fabricated using polycarbonate template with 200 nm (A), 400 nm (B), 600 nm (C), and 800 nm (D) pore sizes. Source: Data from Maldonado, L., & Kokini, J. (2018). An optimal window for the fabrication of edible polyelectrolyte complex nanotubes (EPCNs) from bovine serum albumin (BSA) and sodium alginate. Food Hydrocolloids, 77, 336 346. Reproduced with permission from Elsevier.

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800 nm template) than CHI/LAC nanotubes (81 with 400 nm template, 97 with 600 nm template, and 118 with 800 nm template). The mechanical properties of nanotubes were also tested using atomic force microscopy (AFM). For both polyelectrolyte pairs, nanotubes fabricated with 400 nm pore sized templates had higher Young’s moduli than those fabricated with 600 or 800 nm templates. This was due to the more compact structures of 400 nmsized nanotubes which also had less hollow space inside them, leading to higher resilience. BSA/CAR nanotubes had higher Young’s moduli than CAR/LAC nanotubes, due to the higher attraction between BSA and CAR molecules, evident from their greater zeta potential difference. However, CHI/LAC nanotubes were more stable in PBS solutions (pH 5 7), since the molecules of these polyelectrolyte pairs are oppositely charged at this pH and BSA/CAR molecules are not. Curcumin encapsulation efficiency and loading capacity of BSA/CAR nanotubes were 46.7% and 0.175 mg/mg nanotube, respectively, which were higher than CHI/LAC nanotubes (encapsulation efficiency of 36.9% and loading capacity of 0.14 mg/mg nanotube). The release profiles of curcumin from the nanotubes were tested in PBS solution at pH 5 7. As expected, the weaker interaction between BSA and CAR molecules at this pH led to a faster and a complete (100%) curcumin release from the nanotubes within the first 24 h. For CHI/LAC nanotubes, a complete curcumin release was seen after 48 h. HeLa cells were used to assess the cytotoxicity of unloaded and curcumin-loaded nanotubes for both polyelectrolyte pairs. As expected, nonloaded nanotubes did not show any toxicity on the cells, since they did not contain any curcumin. For curcumin-loaded LbL nanotubes, while there was no difference between the cytotoxicity of polyelectrolyte pairs, at higher curcumin concentration, an increasing cytotoxicity was observed. The highest cytotoxicity and lowest cell viability were seen at a curcumin concentration of 60 μg/mL for both nanotubes. A comparison between encapsulated curcumin and free curcumin showed that encapsulated curcumin in LbL nanotubes showed a higher cytotoxicity for HeLa cells, revealing that nanodelivery of curcumin in LbL nanotubes increased the water solubility of curcumin and its bioaccessibility.

9.5

Nano/microemulsions

Emulsification is another nanodelivery technique used to encapsulate bioactive compounds (Jafari, Paximada, Mandala, Assadpour, & Mehrnia, 2017). It is a simple technique which provides a good protection against environmental factors, such as light, and stability to the encapsulated compound (Montes, Villasen˜or, & Rı´os, 2019). In emulsification, a colloidal system is formed between two immiscible liquids, where one of the liquids is dispersed in the forms of small droplets in the other liquid (McClements & Jafari, 2018). For food and biobased nanodelivery systems, the two phases are often oil and water, and either water-in-oil (W/O) or oilin-water (O/W) systems can be prepared, depending on the solubility of encapsulated compound. To provide additional protection, double emulsions can be

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prepared by further emulsifying the O/W or W/O emulsions in oil and water, respectively (Assadpour, Maghsoudlou, Jafari, Ghorbani, & Aalami, 2016; Esfanjani, Jafari, Assadpoor, & Mohammadi, 2015). In encapsulation through emulsification, parameters like types and ratio of the two phases, types of surfactant, pH, and temperature play significant roles in the encapsulation efficiency, morphology, droplet size and stability of the systems (Akhavan, Assadpour, Katouzian, & Jafari, 2018). These parameters also affect the bioaccessibility of encapsulated compounds. In this section, recent studies on the delivery of bioactive compounds encapsulated in micro/nanoemulsions are summarized, and the effects of fabrication parameters on the final product are discussed. Anthocyanins, which are used as colorants in cosmetic or food industries, were encapsulated in W/O emulsions to reduce their susceptibility to chemical degradation to prevent color loss (Liu, Tan, Zhou, Muriel Mundo, & McClements, 2019). The anthocyanins were first emulsified in a W/O system, which consisted of 20% aqueous phase and 80% corn oil, using polyglycerol polyricinoleate (PGPR) as the hydrophobic emulsifier. Anthocyanins were dispersed in the aqueous phase. Then, this emulsion was double emulsified in a W/O/W system, by dispersing the first emulsion in water at a 20:80 (first emulsion:water) ratio, using Quillaja saponin as the hydrophilic emulsifier. The effect of pH on the color of anthocyanins was measured by changing the pH of the external water phase and storing these emulsions at 20 C. Also, the location of anthocyanins was varied as either in the internal water phase or external water phase. In general, pH changes from 7 to 3 and then back to 7 had more impact on the color of emulsions when anthocyanins were encapsulated in the external water phase, suggesting that emulsification provides a better color protection to anthocyanins when they are internally encapsulated (Fig. 9.12). Also, color change was irreversible after pH modifications for both internally and externally encapsulated anthocyanins. While the similar pH modifications slightly lowered the particle size of control emulsions (no anthocyanins) and the emulsion when anthocyanins were externally encapsulated, it increased the particle size of internally encapsulated anthocyanin emulsions. The shrinkage of external and control emulsions was due to the water leakage from the water inside the W/O droplets, and the enlargement of internal emulsions was due to water uptake from the external water phase, possibly due to osmotic pressure difference created with the presence of anthocyanins. Changing the pH from 7 to 3 made the zeta potential of emulsion droplets less negatively charged, regardless of the location of anthocyanins. When the pH was set back to 7, zeta potentials also changed back to their original values. Release rates of anthocyanins showed that anthocyanins’ diffusion through the oil phase is dependent on the concentration difference between the aqueous phases, and this movement can be controlled by pH and temperature change. At higher temperature (20 C), inward and outward diffusion of anthocyanins were faster compared to at 4 C. Also, at pH 5 3 diffusion of anthocyanins was significantly less compared to at pH 5 7, possibly due to the lower solubility of anthocyanins in oil at pH 5 3. Cinnamon oil encapsulation in an O/W system was also done to enhance its water-dispersibility and antimicrobial activity (Chuesiang et al., 2019). Phase

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Figure 9.12 Effect of pH on the color of water-in-oil-in-water emulsions of anthocyanins dissolved in internal or external water phase: (A) a represents redness-greenness, (B) b represents yellowness-blueness, (C) C represents chroma, (D) digital photographs of samples. Source: Data from Liu, J., Tan, Y., Zhou, H., Muriel Mundo, J. L., & McClements, D. J. (2019). Protection of anthocyanin-rich extract from pH-induced color changes using waterin-oil-in-water emulsions. Journal of Food Engineering, 254, 1 9. Reproduced with permission from Elsevier.

inversion temperature (PIT) method was used to fabricate the emulsions. First, Tween 80 and water were added to the mixture of cinnamon oil and medium chain triglyceride at different ratios and stirred for 30 min. Then the temperature was increased to a range of 67 90 C for various cinnamon oil ratios, to reach temperatures that are 15 C above the PIT. Following the heating step, mixtures were initially cooled down to their PIT, and then to 4 C with rapid water dilution. Nanoemulsions with 40% cinnamon oil and 60% medium chain triglyceride had the smallest droplets with mean droplet size of 101 nm, the lowest PDI values (0.17) and highest stability over a 31-day storage period. Nanoemulsions prepared with higher or lower cinnamon oil ratios had larger droplets and higher PDI. Antimicrobial properties of emulsified cinnamon oil were tested on four strains of bacteria (E. coli, S. Typhimurium, S. aureus, and V. parahaemolyticus) and their effects were compared to free cinnamon oil. All emulsions with different cinnamon oil ratios had inhibitory effects on all four strains, with the exception of 10% cinnamon oil, which only inhibited the growth of V. parahaemolyticus. Minimum

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inhibitory concentrations (MIC) of nanoemulsions were considerably higher than free cinnamon oil and reached minimum values at around 40% 50% cinnamon oil concentration in oil phase, indicating the maximum antimicrobial effect at this concentration. To reduce the caloriefic content of foods, digestible fats in food products are being replaced with indigestible fats, which as a side effect might also reduce the bioaccessibility of some nutrients. The effect of using indigestible oil on the bioaccessibility of vitamin D was tested by emulsifying vitamin D3 in O/W nanoemulsions whose oil phases consisted of digestible oil (corn oil), indigestible oil (mineral oil), or a mixture of digestible and indigestible oil (Tan, Liu, Zhou, Mundo, & McClements, 2019). Also, the nanoemulsions of digestible and indigestible oils were mixed after emulsification and tested as a fourth combination. The emulsions were tested in three parts of simulated GIT environment: mouth phase, stomach phase, and small intestinal phase. The initial particle size and zeta potential measurements showed that nanoemulsion droplets in all four combinations had similar diameters ranging from 0.136 to 0.169 μm with zeta potentials between 249 and 246 mV, indicating good stability. Exposure to mouth phase did not significantly affect the particle size of these nanoemulsion combinations, except for a few flocculations. Stomach phase, on the other hand, increased the particle diameters of all, such that the mean diameters of droplet became 22.7, 18.9, 17.9, and 19.7 μm for digestible oil, indigestible oil, oil mixture, and emulsion mixture emulsions, respectively. This increase was due to intense oil droplet flocculation occurring with significant pH reduction. Also, the remaining mucin residues from the mouth phase possibly created bridges between droplets, leading to flocculation. Stomach phase also made the zeta potentials less negative, ranging between 21.7 and 20.9 mV. In the small intestine phase, flocculations disappeared significantly, but the particle size ranges were still wider than the mouth range. Indigestible oil containing emulsions had larger droplets compared to digestible oil emulsion as expected, since they were not digested in the small intestines and remained intact. Also, micelle formations were observed in the samples containing digestible oil, possibly forming due to the hydrolysis of triglycerides in corn oil, which formed free fatty acids and monoglycerides. These free acids and monoglycerides then merged with endogenous bile acids and phospholipid in the intestine phase fluid and created micelles. Bioaccessibility of vitamin D3, measured after small intestine phase, was the highest for nanoemulsions prepared with only digestible oil, followed by oil mixture and emulsion mixture, which were not significantly different than each other. The lowest bioaccessibility was observed for nanoemulsions prepared with indigestible oil (Fig. 9.13). 14 days of storage did not lower the bioaccessibility of vitamin D3 in any of the emulsions, indicating good stability. The same group also investigated the effect of digestible oil type on the bioaccessibility of vitamin D3 by testing corn oil, fish oil, and flaxseed oil (Schoener, Zhang, Lv, Weiss, & McClements, 2019). A plant-based protein, pea protein, was used as the emulsifier and the effect of its concentration on the emulsions was tested. Increasing pea protein concentration initially decreased the droplet size of emulsions significantly and then created a plateau in droplet size around 0.7%

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Figure 9.13 Bioaccessibility of vitamin D3 encapsulated in nanoemulsions prepared with digestible oil, indigestible oil, oil mixture, and emulsion mixture. Source: Data from Tan, Y., Liu, J., Zhou, H., Mundo, J. M., & McClements, D. J. (2019). Impact of an indigestible oil phase (mineral oil) on the bioaccessibility of vitamin D-3 encapsulated in whey protein-stabilized nanoemulsions. Food Research International, 120, 264 274. Reproduced with permission from Elsevier.

concentration. The smallest droplet sizes of 340 nm were reached at 2% pea protein concentration. The vitamin D3 loaded nanoemulsions were similarly tested in the three phases of GIT: mouth, stomach, and small intestine phase, and the emulsions were evaluated with confocal microscopy (Fig. 9.14). Similar to the previous study, initial particle sizes of the emulsions slightly increased in the mouth phase, due to flocculations. In stomach phase, flocculations significantly increased for all three emulsions due to the aggregation of pea protein-coated droplets at acidic pH values. In the small intestine, flocculations became fewer due to the increase of pH, but some remained, due to digestion of oils and formation of micelles. Bioaccessibility of vitamin D3 was significantly higher in nanoemulsions prepared with corn oil than with flaxseed oil or fish oil, possibly due to the higher monounsaturated content of corn oil, which allows better digestion and higher bioaccessibility. Oleuropein, a polyphenol that is in olive leaves and has antioxidant, antiinflammatory, antidiabetic, antiatherogenic and anticarcinogenic properties, was encapsulated in a double emulsion (W/O/W) using pectin and whey protein concentrate (WPC) (Gharehbeglou, Jafari, Homayouni, Hamishekar, & Mirzaei, 2019). The first W/O emulsion was prepared by dissolving an aqueous solution of oleuropein in soybean oil using Span 80 as the emulsifier. Then, this emulsion was further emulsified in an aqueous solution of pectin and WPC. Twelve different formulations were tested to encapsulate oleuropein, by varying the emulsifier content, pectin and WPC content, and ratio of first W/O emulsion (inner phase) to the double emulsion

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Figure 9.14 Confocal microscopy images of vitamin D3 loaded nanoemulsions prepared with corn oil, flaxseed oil, and fish oil at different phases of gastrointestinal tract digestion. Source: Data from Schoener, A. L., Zhang, R., Lv, S., Weiss, J., & McClements, D. J. (2019). Fabrication of plant-based vitamin D-3-fortified nanoemulsions: Influence of carrier oil type on vitamin bioaccessibility. Food & Function, 10(4), 1826 1835. Reproduced with permission from Royal Society of Chemistry.

(outer phase). Also, the effect of pH was tested on the emulsification. The smallest droplets, with a 250-nm droplet size, were achieved at pH 5 6 when emulsifier concentration was 9%, pectin concentration was 2%, WPC concentration was 10%, ratio of inner phase to outer phase was 0.2, when oleuropein concentration was 260 μg/mL. Higher inner phase/outer phase ratio and WPC and pectin concentrations increased the emulsion droplet sizes. Varying the WPC was found to affect the droplet sizes more than pectin concentrations. Low pH values (2 and 4) caused attraction between the WPC and pectin molecules, leading to coacervation, and at high pH values larger droplet sizes were observed. The optimization of the double emulsification of oleuropein was determined using the response surface methodology (RSM) method, and the optimum emulsion was obtained when 8.74% Span 80, 8% WPC, 1.97% pectin, 0.25 ratio of inner phase/outer phase, and a pH value of 6.12 was used. The encapsulation efficiency of optimum emulsion was calculated as 90.68%. Release of oleuropein from the emulsion with the optimum formulation was calculated as 42% after 28 days of storage, which was also confirmed with HPLC measurements. For the delivery of resveratrol, an oil-soluble polyphenol that is found in grape skins, O/W emulsions were prepared using grape seed oil and orange oil as the oil

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phase and Tween 80 as the surfactant (Davidov-Pardo & McClements, 2015). Effects of orange oil/grape seed oil ratio, surfactant/emulsion ratio, emulsification method on the droplet size, PDI, encapsulation efficiency, and UV stability of the emulsions were investigated. Decreasing orange oil/grape seed oil ratio from 10:0 to 5:5, decreased both the droplet diameters and the PDI of the emulsions significantly, where the lowest droplet diameters were around 100 nm with a PDI of almost 0.22 (Fig. 9.15). A further decrease in this ratio, however, caused micronsized droplets to form, possibly due to a higher Ostwald ripening rate of the emulsions when the grape seed oil, which contains flavor oils, ratio was increased significantly. Increasing surfactant ratio similarly decreased both the particle sizes and the PDI up to 7%, beyond which the droplet diameters kept decreasing while the PDI of the emulsions increased (Fig. 9.15). The sudden increase in the PDI was due to the bimodal size distribution of the emulsions at higher surfactant ratios, where some gel-like clumps began to be seen. The effect of temperature on the solubility of resveratrol in the oil phase was tested at 5, 20, and 37 C for a 150 μg/mL grape seed extract concentration (resveratrol containing extract). The equilibrium solubilities were similar for 5 C (115%) and 20 C (112%), but was significantly higher for 37 C (131%). A comparison between low-energy emulsification (with magnetic stirring) and high-energy emulsification (microfluidization) showed that with microfluidization, a droplet diameter of 99 nm can be reduced to 45 nm. The highest encapsulation efficiency of 92% was also reached using microfluidization at a surfactant/emulsion ratio of 0.1, followed by 89% for low-energy emulsification at a surfactant/emulsion ratio of 0.1, and 82% for low-energy emulsification at a surfactant/emulsion ratio of 0.05. These three emulsion formulations were also significantly better at protecting resveratrol against UV light compared to free resveratrol. Nanoemulsions prepared with low-energy emulsification at a surfactant/emulsion

Figure 9.15 Effects of orange oil/grape seed oil ratio (A) and surfactant/emulsion ratio (B) on droplet diameter and polydispersity index of emulsions. Source: Data from Davidov-Pardo, G., & McClements, D. J. (2015). Nutraceutical delivery systems: Resveratrol encapsulation in grape seed oil nanoemulsions formed by spontaneous emulsification. Food Chemistry, 167, 205 212. Reproduced with permission from Elsevier.

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ratio of 0.05 provided the best UV light protection, due to its large droplet size and higher turbidity.

9.6

Conclusion

This chapter has introduced different nanoparticulation methods that are used as nanodelivery systems for bioactive compounds and nutraceuticals. The main purpose of encapsulating bioactives in nanoparticles is to enhance their solubility and bioaccessibility, provide additional protection against the harsh gastrointestinal tract conditions, and to have a more controlled release. Collectively, the studies summarized in this chapter show that during nanoparticulation, depending on the method used, many parameters, including the selection of coating polymers, temperature, pH, or salt concentration, can affect the formation of nanoparticles, their stabilities, and encapsulation performances, which can result in changing the bioaccessibility of the encapsulated bioactive significantly. The correct selection of these parameters is of crucial importance for the successful design of a nanodelivery system.

References Akhavan, S., Assadpour, E., Katouzian, I., & Jafari, S. M. (2018). Lipid nano scale cargos for the protection and delivery of food bioactive ingredients and nutraceuticals. Trends in Food Science & Technology, 74, 132 146. Assadpour, E., & Jafari, S. M. (2019a). Chapter 3 Nanoencapsulation: Techniques and developments for food applications. In A. Lo´pez Rubio, M. J. Fabra Rovira, M. Martı´nez Sanz, & L. G. Go´mez-Mascaraque (Eds.), Nanomaterials for food applications (pp. 35 61). Elsevier. Assadpour, E., & Jafari, S. M. (2019b). A systematic review on nanoencapsulation of food bioactive ingredients and nutraceuticals by various nanocarriers. Critical Reviews in Food Science and Nutrition, 1 47. Assadpour, E., Jafari, S.-M., & Maghsoudlou, Y. (2017). Evaluation of folic acid release from spray dried powder particles of pectin-whey protein nano-capsules. International Journal of Biological Macromolecules, 95, 238 247. Assadpour, E., Maghsoudlou, Y., Jafari, S.-M., Ghorbani, M., & Aalami, M. (2016). Evaluation of folic acid nano-encapsulation by double emulsions. Food and Bioprocess Technology, 9(12), 2024 2032. Bastarrachea, L. J., Denis-Rohr, A., & Goddard, J. M. (2015). Antimicrobial food equipment coatings: Applications and challenges. Annual Review of Food Science and Technology, 6(1), 97 118. Chuesiang, P., Siripatrawan, U., Sanguandeekul, R., Yang, J. S., McClements, D. J., & McLandsborough, L. (2019). Antimicrobial activity and chemical stability of cinnamon oil in oil-in-water nanoemulsions fabricated using the phase inversion temperature method. LWT, 110, 190 196.

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Davidov-Pardo, G., & McClements, D. J. (2015). Nutraceutical delivery systems: Resveratrol encapsulation in grape seed oil nanoemulsions formed by spontaneous emulsification. Food Chemistry, 167, 205 212. de Kruif, C. G., Weinbreck, F., & de Vries, R. (2004). Complex coacervation of proteins and anionic polysaccharides. Current Opinion in Colloid & Interface Science, 9(5), 340 349. Deka, C., Deka, D., Bora, M. M., Jha, D. K., & Kakati, D. K. (2016). Synthesis of peppermint oil-loaded chitosan/alginate polyelectrolyte complexes and study of their antibacterial activity. Journal of Drug Delivery Science and Technology, 35, 314 322. Esfanjani, A. F., Jafari, S. M., Assadpoor, E., & Mohammadi, A. (2015). Nano-encapsulation of saffron extract through double-layered multiple emulsions of pectin and whey protein concentrate. Journal of Food Engineering, 165, 149 155. Esfahani, R., Jafari, S. M., Jafarpour, A., & Dehnad, D. (2019). Loading of fish oil into nanocarriers prepared through gelatin-gum Arabic complexation. Food Hydrocolloids, 90, 291 298. Etorki, A. M., Gao, M., Sadeghi, R., Maldonado-Mejia, L. F., & Kokini, J. L. (2016). Effects of desolvating agent types, ratios, and temperature on size and nanostructure of nanoparticles from α-lactalbumin and ovalbumin. Journal of Food Science, 81(10), E2511 E2520. Faridi Esfanjani, A., & Jafari, S. M. (2016). Biopolymer nano-particles and natural nanocarriers for nano-encapsulation of phenolic compounds. Colloids and Surfaces B: Biointerfaces, 146, 532 543. Gharehbeglou, P., Jafari, S. M., Homayouni, A., Hamishekar, H., & Mirzaei, H. (2019). Fabrication of double W1/O/W2 nano-emulsions loaded with oleuropein in the internal phase (W1) and evaluation of their release rate. Food Hydrocolloids, 89, 44 55. Ghasemi, S., Jafari, S. M., Assadpour, E., & Khomeiri, M. (2017). Production of pectin-whey protein nano-complexes as carriers of orange peel oil. Carbohydrate Polymers, 177 (Suppl. C), 369 377. Ghasemi, S., Jafari, S. M., Assadpour, E., & Khomeiri, M. (2018). Nanoencapsulation of dlimonene within nanocarriers produced by pectin-whey protein complexes. Food Hydrocolloids, 77, 152 162. Hu, K., & McClements, D. J. (2015). Fabrication of biopolymer nanoparticles by antisolvent precipitation and electrostatic deposition: Zein-alginate core/shell nanoparticles. Food Hydrocolloids, 44, 101 108. Huang, X., Dai, Y., Cai, J., Zhong, N., Xiao, H., McClements, D. J., & Hu, K. (2017). Resveratrol encapsulation in core-shell biopolymer nanoparticles: Impact on antioxidant and anticancer activities. Food Hydrocolloids, 64, 157 165. Huang, X., Liu, Y., Zou, Y., Liang, X., Peng, Y., McClements, D. J., & Hu, K. (2019). Encapsulation of resveratrol in zein/pectin core-shell nanoparticles: Stability, bioaccessibility, and antioxidant capacity after simulated gastrointestinal digestion. Food Hydrocolloids, 93, 261 269. Jafari, S. M. (2017). 1—An overview of nanoencapsulation techniques and their classification. Nanoencapsulation technologies for the food and nutraceutical industries (pp. 1 34). Academic Press. Jafari, S. M., & McClements, D. J. (2017). Nanotechnology approaches for increasing nutrient bioavailability. In Advances in food and nutrition research (Vol. 81, pp. 1 30). Cambridge, MA: Academic Press, Elsevier.

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Jafari, S. M., Paximada, P., Mandala, I., Assadpour, E., & Mehrnia, M. A. (2017). 2 Encapsulation by nanoemulsions. Nanoencapsulation technologies for the food and nutraceutical industries (pp. 36 73). Academic Press. Kaibara, K., Okazaki, T., Bohidar, H. B., & Dubin, P. L. (2000). pH-induced coacervation in complexes of bovine serum albumin and cationic polyelectrolytes. Biomacromolecules, 1(1), 100 107. Katouzian, I., & Jafari, S. M. (2016). Nano-encapsulation as a promising approach for targeted delivery and controlled release of vitamins. Trends in Food Science & Technology, 53, 34 48. Li, Y., & Huang, Q. (2013). Influence of protein self-association on complex coacervation with polysaccharide: A Monte Carlo study. The Journal of Physical Chemistry B, 117 (9), 2615 2624. Li, X., Maldonado, L., Malmr, M., Rouf, T. B., Hua, Y., & Kokini, J. (2019). Development of hollow kafirin-based nanoparticles fabricated through layer-by-layer assembly as delivery vehicles for curcumin. Food Hydrocolloids, 96, 93 101. Liu, J., Tan, Y., Zhou, H., Muriel Mundo, J. L., & McClements, D. J. (2019). Protection of anthocyanin-rich extract from pH-induced color changes using water-in-oil-in-water emulsions. Journal of Food Engineering, 254, 1 9. Maldonado, L., & Kokini, J. (2018). An optimal window for the fabrication of edible polyelectrolyte complex nanotubes (EPCNs) from bovine serum albumin (BSA) and sodium alginate. Food Hydrocolloids, 77, 336 346. Maldonado, L., Chough, S., Bonilla, J., Kim, K. H., & Kokini, J. (2019). Mechanism of fabrication and nano-mechanical properties of α-lactalbumin/chitosan and BSA/κ-carrageenan nanotubes through layer-by-layer assembly for curcumin encapsulation and determination of in vitro cytotoxicity. Food Hydrocolloids, 93, 293 307. Maldonado, L., Sadeghi, R., & Kokini, J. (2017). Nanoparticulation of bovine serum albumin and poly-d-lysine through complex coacervation and encapsulation of curcumin. Colloids and Surfaces B: Biointerfaces, 159, 759 769. McClements, D. J., & Jafari, S. M. (2018). Chapter 1 General aspects of nanoemulsions and their formulation. In S. M. Jafari, & D. J. McClements (Eds.), Nanoemulsions (pp. 3 20). Academic Press. Milanovi´c, J., Petrovi´c, L., Sovilj, V., & Katona, J. (2014). Complex coacervation in gelatin/ sodium caseinate mixtures. Food Hydrocolloids, 37, 196 202. ´ . (2019). Analytical control of nanodelivery lipidMontes, C., Villasen˜or, M. J., & Rı´os, A based systems for encapsulation of nutraceuticals: Achievements and challenges. Trends in Food Science & Technology, 90, 47 62. Mu¨ller, M., Reihs, T., & Ouyang, W. (2005). Needlelike and spherical polyelectrolyte complex nanoparticles of poly(l-lysine) and copolymers of maleic acid. Langmuir, 21(1), 465 469. Piacentini, E. (2016). Coacervation. In E. Drioli, & L. Giorno (Eds.), Encyclopedia of membranes (pp. 422 424). Springer. Priftis, D., Megley, K., Laugel, N., & Tirrell, M. (2013). Complex coacervation of poly(ethylene-imine)/polypeptide aqueous solutions: Thermodynamic and rheological characterization. Journal of Colloid and Interface Science, 398, 39 50. Raei, M., Shahidi, F., Farhoodi, M., Jafari, S. M., & Rafe, A. (2017). Application of whey protein-pectin nano-complex carriers for loading of lactoferrin. International Journal of Biological Macromolecules, 105(Part 1), 281 291.

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Rafiee, Z., Nejatian, M., Daeihamed, M., & Jafari, S. M. (2019). Application of different nanocarriers for encapsulation of curcumin. Critical Reviews in Food Science and Nutrition, 1 77. Rajabi, H., Jafari, S. M., Rajabzadeh, G., Sarfarazi, M., & Sedaghati, S. (2019). Chitosangum Arabic complex nanocarriers for encapsulation of saffron bioactive components. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 578, 123644. Rezaei, A., Fathi, M., & Jafari, S. M. (2019). Nanoencapsulation of hydrophobic and lowsoluble food bioactive compounds within different nanocarriers. Food Hydrocolloids, 88, 146 162. Ru, Q., Wang, Y., Lee, J., Ding, Y., & Huang, Q. (2012). Turbidity and rheological properties of bovine serum albumin/pectin coacervates: Effect of salt concentration and initial protein/polysaccharide ratio. Carbohydrate Polymers, 88(3), 838 846. Sadeghi, R., Chuacharoen, T., Sabliov, C., Moraru, C., Karimi, M., & Kokini, J. (2018). Chapter 2: Advances in nanotechnology of food materials for food and non-food applications. Handbook of food engineering (3rd ed., pp. 153 224). CRC Press. Sadeghi, R., Kalbasi, A., Emam-jomeh, Z., Razavi, S. H., Kokini, J., & Moosavi-Movahedi, A. A. (2013). Biocompatible nanotubes as potential carrier for curcumin as a model bioactive compound. Journal of Nanoparticle Research, 15(11), 1931. Sadeghi, R., Moosavi-Movahedi, A. A., Emam-jomeh, Z., Kalbasi, A., Razavi, S. H., Karimi, M., & Kokini, J. (2014). The effect of different desolvating agents on BSA nanoparticle properties and encapsulation of curcumin. Journal of Nanoparticle Research, 16(9), 2565. Schoener, A. L., Zhang, R., Lv, S., Weiss, J., & McClements, D. J. (2019). Fabrication of plant-based vitamin D-3-fortified nanoemulsions: Influence of carrier oil type on vitamin bioaccessibility. Food & Function, 10(4), 1826 1835. Shaddel, R., Hesari, J., Azadmard-Damirchi, S., Hamishehkar, H., Fathi-Achachlouei, B., & Huang, Q. (2018). Use of gelatin and gum Arabic for encapsulation of black raspberry anthocyanins by complex coacervation. International Journal of Biological Macromolecules, 107, 1800 1810. Taheri, A., & Jafari, S. M. (2019). Gum-based nanocarriers for the protection and delivery of food bioactive compounds. Advances in Colloid and Interface Science, 269, 277 295. Tan, Y., Liu, J., Zhou, H., Mundo, J. M., & McClements, D. J. (2019). Impact of an indigestible oil phase (mineral oil) on the bioaccessibility of vitamin D-3 encapsulated in whey protein-stabilized nanoemulsions. Food Research International, 120, 264 274. Turasan, H., Barber, E. A., Malm, M., & Kokini, J. L. (2018). Mechanical and spectroscopic characterization of crosslinked zein films cast from solutions of acetic acid leading to a new mechanism for the crosslinking of oleic acid plasticized zein films. Food Research International, 108, 357 367. Yilmaz, T., Maldonado, L., Turasan, H., & Kokini, J. (2019). Thermodynamic mechanism of particulation of sodium alginate and chitosan polyelectrolyte complexes as a function of charge ratio and order of addition. Journal of Food Engineering, 254, 42 50. Zhang, Y., Feng, J., McManus, S. A., Lu, H. D., Ristroph, K. D., Cho, E. J., . . . Prud’homme, R. K. (2017). Design and solidification of fast-releasing clofazimine nanoparticles for treatment of cryptosporidiosis. Molecular Pharmaceutics, 14(10), 3480 3488. Zhang, Z., Zhang, S., Su, R., Xiong, D., Feng, W., & Chen, J. (2019). Controlled release mechanism and antibacterial effect of layer-by-layer self-assembly thyme oil microcapsule. Journal of Food Science, 84(6), 1427 1438.

Metal nanoparticles as antimicrobial agents in food packaging

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Shima Jafarzadeh1, Ali Salehabadi2 and Seid Mahdi Jafari3 1 Food Biopolymer Research Group, Food Technology Division, School of Industrial Technology, Universiti Sains Malaysia, Minden, Malaysia, 2Environmental Technology Division, School of Industrial Technology, Universiti Sains Malaysia, Minden, Malaysia, 3 Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

10.1

Introduction to polymers/biopolymers in food packaging

In the polymer area, the main application is food packaging. The versatility and facile production of food packaging have made polymers, which are usually in the film form or rigid shape, an acceptable replacement for conventional matters like metals and glass (Dehnad, Emam-Djomeh, Mirzaei, Jafari, & Dadashi, 2014a; Tajik et al., 2013). The process of food packaging comprises preparing food safely for the purpose of transporting, distributing, storing, and retailing. Currently, the consumption of most food products, which are transported from a distant manufacturer, transcends the production date (Raei & Jafari, 2013). This makes the issue of preventing the deterioration a critical topic in the domain of food packaging. The primary purpose of food packaging is to preserve the food safety and quality from the time of its production to consumption (Pilevar, Bahrami, Beikzadeh, Hosseini, & Jafari, 2019). Foods are considered to be perishable matters vulnerable to chemical, mechanical, biological, and physical deterioration at the stages of storage and distribution (Jafarzadeh, 2017). Packaging material has a direct connection with the safety of food; therefore if the packaging materials do not provide a proper barrier, food content could be contaminated with microorganisms, and then become harmful. However, microbial contamination can also arise if the packaging material does not prevent permeation of moisture or O2. Such a situation provides a platform for microorganisms that are innocuous in the absence of moisture or O2 to grow and present a risk to the consumer (Dehnad, Mirzaei, Emam-Djomeh, Jafari, & Dadashi, 2014b; Jafarzadeh, 2017). As in the case of microbial deterioration, enzymatic reactions are also favored by water content and ease of O2 infiltration into a package entailing deteriorations in food (Vahedikia et al., 2019). Food quality is also affected by chemical Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00010-8 © 2020 Elsevier Inc. All rights reserved.

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and physical reactions within the packaging. There are a number of possible deteriorative chemical reactions that adversely affect the quality of food especially favored by transferred O2 and water vapor. Lipid oxidation (autoxidation) initiated by molecular O2, nonenzymatic browning, color changes related to the presence or absence of O2, and reactions of vitamins or proteins with O2 decrease the nutritional value of packaged food. Chemical changes of food also result in physical changes, thus deteriorating the food quality, for example, softening, caking especially in powder products, toughening, emulsion breakdown, swelling/shrinkage, and crushing/breakage, that can be altered by controlling water uptake as well as protecting from physical impacts. The mechanical properties of the packaging materials are also important (Jafari et al., 2015; Khanzadi et al., 2015). A proper packaging material must be durable, flexible, and strong in order to protect the packaging contains. Materials used in food packaging should have the following features: toughness, low cost, flexibility, lightness, resistance to impacts, inertness, easy fabrication, prevention of water vapor and oxygen transmission, high wet-strength (Jafarzadeh, 2017). Polyethylene (PE) and polypropylene (PP) are famous polymeric packaging materials having these properties; they have been widely used in the food industry for a long time—around 50 years. But, in the last decade, environmental issues have been seriously considered in selecting food packaging materials; therefore in addition to the given properties of an ideal food packaging, environmental effects should be considered in the packaging process. In contrast to their economic value and the growing use of polymers, plastic materials are not sustainable and reusable. Concerning the waste of packaging materials, landfill is still one of the important issues. Besides landfills, incineration or combustion is applied in order to manage waste. In order to avoid this problem, the idea of biobased food packaging has been presented. Biobased (biopolymer) packaging refers to a special kind of packaging consisting of reusable biological raw materials, which are derived from agricultural origins. Recent technological advances have allowed biopolymers to be processed similarly to petroleum-based plastics whether in sheets, by extrusion, spinning, injection molding, or thermoforming (Hashemi Tabatabaei, Jafari, Mirzaei, Mohammadi Nafchi, & Dehnad, 2018). In spite of their excellent barrier properties to oxygen and other gases, biopolymers are poor water-vapor barriers and, moreover, their barrier and mechanical properties are dependent on moisture, which is not desirable, especially for the packaging of certain food types. Nanobiocomposites are considered as alternatives in biobased food packaging which can help overcome disadvantageous features including low water-vapor barrier or weak mechanical properties (Joz Majidi et al., 2019). Nanofillers, such as metal nanoparticles, yield desirable results including mechanical properties improvement, reduction of weight, improvement of technology (e.g., fire resistance), antimicrobial attributes, and higher resistance to water vapor and other gases (Jafarzadeh, 2017). Using nanocomposites makes it possible to create stronger and more durable biopolymers which are environment-friendly and can be successful replacements for petroleum-based polymeric materials used in food packaging (Dehnad et al., 2014b; Jafarzadeh et al., 2017).

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10.1.1 Solid-state additives in food packaging To improve the packaging properties, food quality, and safety, various solid compounds have been suggested for embedding into the polymeric matrices. Their action is essential in reducing some of the main food contamination causes, such as dehydration, rancidity, senescence, color loss/change, microbial proliferation, gas buildup, nutrient losses, and off-odors (Lo´pez-Go´mez et al., 2009). Using antimicrobial agents in a packaging material could lengthen the shelf life of packaged foods by minimizing the growth rate of spoilage microorganisms and extending the lag phase. An antimicrobial packaging system is created using antimicrobial fillers in packaging films directly, coating the packaging films with antimicrobial agents, and generating packaging materials from polymers which have natural antimicrobial features; then the agent is slowly released on top of the food surfaces. This helps to retain a sufficient concentration of the agent to efficiently prevent microbial growth during the product shelf life. Antimicrobial agents can be used in packaging materials in combination with base polymers prior to production (compression molding or extrusion) of the film (Jafarzadeh, 2017). Numerous parts of the plants like leaves, flowers, seed, peel, husk, and roots are known to contain essential pharmacological and biological compounds with antiallergic, antioxidant, antibiotic, and antimicrobial properties and can be used as an alternative to synthetic antimicrobial agents. The mechanism of natural antimicrobial agents is considered to be the disturbance of the active transport mechanisms, cytoplasmic membrane, electron flow, disrupting the proton motive force, and coagulation of cell composition. Natural antimicrobial agents derived from medicinal plants have a great popularity in the food industries. They could be integrated into food packaging in order to prevent microbial reaction. Edible films with natural antimicrobial properties can preferably prolong the shelf life and safety of foods. These active films prevent the growing of pathogenic and spoilage microorganisms as a result of their lag phase extension and/or their growth rate reduction (Vahedikia et al., 2019). Moreover, antimicrobial incorporation in the matrix of packaging materials could decrease the growth of bacteria on the food product, preserve the food by inhibiting the postcontamination, as well as reducing the microbial growth on nonsterilized foods. Antimicrobial packaging systems include dissolving bioactive agents in the formulation of packaging, adding an antimicrobial nanoparticle in the package, using antimicrobial macromolecules with film forming properties, edible matrices, or covering the surface of packaging material with bioactive agents.

10.1.2 Metal nanoparticles in food packaging The advent of nanotechnology has involved the food packaging industries in order to overcome the challenges of food and environment. The application of nanomaterials in food packaging is briefly shown in Fig. 10.1. The nanomaterials in food packaging are categorized into nanoparticles, nanofibers, and nanolayers. Some common nanomaterials under investigation include metal nanoparticles (MNPs), metal oxide nanoparticles (MONPs), mixed metal oxide nanoparticles (MMONPs), nanoclay families (NCs), and carbon materials

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Figure 10.1 Application of nanomaterials in food packaging.

Figure 10.2 Polymer/nanoparticle nanocomposites formation.

[carbon nanotubes (CNTs), graphene]. Nanostructured materials in food packaging can improve the final films’ properties such as mechanical, chemical, structural, and barrier properties (O2/H2O, microbial, bacterial, etc.). These new properties maintain the quality of food. Nanomaterials like layered materials, MONPs, MNPs, and carbohydrate nanocrystals are used in food packaging; however, there are several issues regarding their safety, which will be discussed later in this chapter. The incorporation of NPs and doped-NPs into the organic phase of packaging materials (i.e., polymers) is governed by their mechanical (high strength and stiffness) and barrier (low permeability) properties. Fig. 10.2 represents the incorporation process of nanomaterials in a typical polymeric matrix. Various explanations have been proposed in order to illustrate the mechanisms of microbicidal activities of nanoparticles (Fig. 10.3). The most important pathways can be summarized in the following sequences: G

G

G

G

Penetration of cell membrane ! anchoring and penetration to the bacterial cell ! cell membrane permeability and structural change ! cell death (Singh, Smitha, & Singh, 2014). Modification of essential proteins ! interaction of NPs with proteins ! bioreactivity (Diaz, Care, & Sunna, 2018) ! formation of dynamic NP-protein corona ! inflammation, accumulation, and degradation (Saptarshi, Duschl, & Lopata, 2013). Interference with cell signaling ! dephosphorylating of the peptide substrates by NPs ! signal transduction ! inhibition of bacterial growth Incorporation into the DNA bases ! interaction with sulfur and phosphorus of DNA soft base ! destruction of DNA ! cell death.

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Figure 10.3 Proposed antibacterial activities of nanoparticles.

G

G

G

Inhibition of enzyme activity ! binding of NPs around the enzyme active sites ! blocking access of substrate ! inactivation of enzymes (Lira et al., 2019). Inhibition of peptidoglycan cell wall synthesis ! attaching to the cell wall ! inhibiting peptidoglycan synthesis ! autolytic inactivation of enzymes (Sarkar, Yarlagadda, Ghosh, & Haldar, 2017). Oxidative stress: reactive oxygen species (ROS) can potentially damage biological responses resulting in oxidative stress phenomenon (Sarangapani et al., 2019). Imbalance between ROS and a biological partner has the ability to readily detoxify the reactive intermediates (Singh et al., 2014).

10.2

Nanoscale metal oxides in antimicrobial packaging

Metal oxides (MOs) and mixed MO (MMOs) are the most recent studied materials in food packaging. Much research has been focused on nanotechnology applications of silver-NPs and/or nanoclay [especially montmorillonite (MMT)]. However, owing to the structural and morphological features of MOs and MMOs, these materials can also be used as promising nanoparticles in a typical composite profile. It remains a difficult task to synthesize suitable MMOs with appropriate physicochemical properties, which account for the strong interaction with polymer matrix. M1 and M21 ions (MxO: x 5 1, 2, 3, . . .) tend to form oxides, where the metal has oxidation number I, II, or III, and can be classified as (Atkins, Overton, Rourke, Weller, & Armstrong, 2006): G

G

G

M2O with a rutile or antifluorite structure. MO with a rock salt structure. M2O3 oxides.

The MOs are made by defects which vary from one structure to another. The extent of the vacancies (defects) corresponds to the nature of the MOs, and also the

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Figure 10.4 Most common metal ions/oxides in food packaging.

variation of partial pressure of oxygen above a MO, which causes continuous change in the lattice parameter and the equilibrium composition. Several d-blockMOs, often n-type semiconducting MOs, including ZnO, CuO, TiO2, MgO, etc. are antimicrobially active. Their activities can be due to their tiny variations in both stoichiometry and O-atom defects. MONPs have been added to polymers—either petroleum-based or biobased—in order to produce nanocomposites with superior properties, and intrinsic antimicrobial effects. However, migration of NPs from packaging films is of concern because of their potential toxicity in the human body and the environment. Various nanoscale MOs and structural-based NPs (like clay) are used in packaging in order to improve thermal stability, barrier, and mechanical properties, as well as their possible antimicrobial activity. Fig. 10.4 shows the most abundant metal ions in food packaging. In this section, relevant developments in the area of MO-reinforced polymeric nanocomposites in food packaging will be discussed, including copper (Cu), titanium (Ti), zinc (Zn), and magnesium (Mg) oxides. In addition, silver (Ag) and gold (Au) nanoparticles, along with single/double silicate nanolayers will also be discussed, due to their multifunctional abilities in the food packaging industries. With the advent of modern packaging technologies, involving MONPs and biopolymers, the term “active packaging,” has been evolved. Active packaging is protection of the food through mechanisms activated by internal or external factors, and intelligent packaging (Garcia, Shin, & Kim, 2018a). Why active packaging? It exhibits a controllable and autoantimicrobial activity by the direct contact between the MONPs and the microbial cells. This process extends continuously by the release of antimicrobial agents such as metal cations (Zn21, Ag1, Cu21, Ti41, etc.) and maybe ROS.

10.2.1 Copper oxide-based nanomaterials Copper nanoparticles (CuNPs) and copper oxide nanoparticles (CuONPs) are two main classes of the materials in food packaging. However, CuONP is one of the most extensively studied MOs in industrial food packaging, owing to its antimicrobial activity reducing the growth of bacteria, viruses, and fungi (Kuswandi & Moradi, 2019). The CuONPs interact with the cell membrane due to their enormous surface ´ vila-Lo´pez, Lue´vanoarea. Nanosized CuO can be synthesized via sonochemical (A Hipo´lito, & Torres-Martı´nez, 2019), microwave (Karunakaran, Manikandan, & Gomathisankar, 2013), autocombustion (Kamble & Mote, 2019), electrochemical

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(Jadhav, Gaikwad, Nimse, & Rajbhoj, 2011), thermal decomposition (Ibrahim et al., 2018), and other methods. Copper is one of the essential elements in bioorganisms for metabolism and electron transport. A high level of copper can cause a harmful effect on the growth of bacterial cells. The mechanisms of CuO for limitation of cell growth are divided into four pathways: 1. 2. 3. 4.

Inactivation of enzymes Exchange of essential ions Attacking protein functional groups, generation of H2O2 free radicals Breaking the integrity of plasma membrane.

In packaging systems, antimicrobial activity of Cu21-incorporated poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-co-3HV) (Castro Mayorga, Fabra Rovira, Cabedo Mas, Sa´nchez Moragas, & Lagaro´n Cabello, 2018), chitosan (Almasi, Jafarzadeh, & Mehryar, 2018), cellulose (Muthulakshmi et al., 2019), and agar (Roy & Rhim, 2019) have been examined. In almost in biopackaging systems, antibacterial activity of CuONPs against both Gram-positive (G 1 ) and Gram-negative (G 2 ) bacteria is reported. However, a synergistic effect is observed in some polymeric systems like CuO and chitosan nanofibers (CHNFs) (Almasi et al., 2018). It is renowned that the morphology, size, surface area, structure, and variation in oxidation states govern antimicrobial activity of MO like CuO. In addition, doping/ coupling CuO with other active materials (including MOs, M) can potentially affect the final properties of packaging films. The nanohybrid systems like Cu/CuONPs, CuONPs/AgNPs, etc. can impart enhanced antimicrobial, optical, and O2/H2O barrier properties with biocidal activity against G 1 / 2 bacteria.

10.2.2 Titanium oxide-based nanomaterials Titanium dioxide (TiO2) is the most abundant subgroup of titanium-based materials available for food applications, nutraceuticals, and supplements. TiO2 is a white pigment, odorless, and opacifying agent, which was originally classified as a carcinogenic material for inhalation to humans by the International Agency for Research on Cancer (IARC) (Guseva Canu, Fraize-Frontier, Michel, & Charles, 2019). Here we mean food-grade titanium dioxide. TiO2-NPs, among the most explored materials, have a good thermostability and inertia, which can further modify the properties of biodegradable films. In addition, TiO2-NP in food grade is reasonably cheap, nontoxic, and photostable, with antimicrobial activity. TiO2 has three main polymorphs: anatase, rutile, and brookite. Wet chemistry methods are the best synthetic routes for preparation of TiO2-NPs, since the size of particles can be controlled and colloidal suspensions can be obtained (Bodaghi et al., 2013). The starting materials for synthesis of TiO2-NPs are TiCl4, titanium isopropoxide, or titanyl sulfate-based precursors. TiO2 NP-incorporated polymer matrices impart several properties into the final product (nanocomposites) like photocatalytic activity, strong bactericidal activity, and mechanical, thermal, and physical properties (Table 10.1). The polymers can be

Table 10.1 Various TiO2/polymer nanocomposites and their respective properties. Host polymer/TiO2

Method of preparation

Properties/activity

Target microbial site

References

Chitosan

Solvent casting

Photochemical

E. coli, Salmonella S. aureus Listeria monocytogenes 

Zhang et al. (2017)

Starch Kefiran

Photochemical

Antioxidant Ethylene scavenging Antimicrobial pH-sensitive Photoproducible Photodegradable Photoproducible

HDPE

Blown film extrusion

Photocatalytic Microbiological

Guar gum

Solvent casting

Soybean polysaccharides

Solvent casting

UV, light, oxygen barrier Antimicrobial Antimicrobial

Pseudomonas E. coli Lactic acid bacteria L. monocytogenes, Salmonella enterica sv typhimurium

Wheat gluten/nanocellulose

Solvent casting

Antimicrobial

Pectin/TiO2

Solgel

Insulation Antimicrobial



S. aureus Pseudomonas aeruginosa E. coli Saccharomyces cerevisiae G 2 bacteria E. coli, G 1 bacteria S. aureus E. coli

Goudarzi and ShahabiGhahfarrokhi (2018a) Goudarzi and ShahabiGhahfarrokhi (2018b) Gumiero et al. (2013)

Arfat, Ejaz, Jacob, and Ahmed (2017) Salarbashi, Tafaghodi, and Bazzaz (2018) El-Wakil, Hassan, Abou-Zeid, and Dufresne (2015) Neˇsi´c et al. (2018)

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biobased, such as chitosan, starch, and polylactic acid (PLA), or synthetic like highdensity polyethylene (HDPE). Incorporation of TiO2-NPs promotes the compatibility of food packaging films. The impact of TiO2-NPs on the antimicrobial properties of packaging polymers can be attributed to the biocidal action of TiO2-NPs against bacteria (Huang, Mei, Chen, & Wang, 2018). UV-A activated TiO2 embedded biodegradable polymer films were prepared by Xie and Hung (2018). They reported that with UV-A light illumination at a light intensity of 1.30 6 0.15 mW/cm2 for 2 h there was a reduction in bactericidal activity of 1.69 log CFU/mL. Photocatalytic activities of TiO2 can be affirmed theoretically, since the N(III) atom on the imidazole ring—for example in photoactive sensitizers—is adsorbed on the Ti(V) atom; and the largest/ stable adsorption energy can be achieved. This explains the photocatalytic degradation of ornidazole by TiO2 and reveals the microscopic nature of catalytic degradation (Tan et al., 2019). Among several antimicrobial mechanisms, the destabilization of cytoplasmic membrane and permeabilization of cell membrane are more acceptable (Maness et al., 1999). Titanium ions attach to the interior of the bacterial cell and prevent the synthesis of proteins and nucleic acids. In the second mechanism, autolytic enzymes in the bacterial cell act as an activator for bacterial death. In addition, a contact zone with pathogens also influences the inhibition of their growth.

10.2.3 Zinc oxide-based nanomaterials Bacterial spoilage is adjusted by quorum sensing (QS), that is, the regulation of gene expression in response to fluctuations in cell-population density (Miller & Bassler, 2001). QS controls biofilm formation in food pathogens. The biofilms formed on food surfaces act as carriers of bacterial contamination. MONPs like zinc oxide (ZnO) can inhibit the growth of bacteria (Al-Shabib et al., 2016). Nanosized ZnO is a novel class of antimicrobial solid-state agents for nextgeneration food preservatives materials. ZnO is an inorganic semiconductor with a bandgap of B3.3 eV. Many applications of ZnO have been reported, including pharmaceutical, cosmetic, food, rubber, commodity chemical, painting, ceramic, and glass industries. ZnO has been approved as a generally recognized as safe (GRAS) material by the US Food and Drug Administration (FDA) and listed as a food additive (Espitia et al., 2012). ZnO exists in three crystal structures: wurtzite, zinc blende, and rock salt. The wurtzite structure is thermodynamically more stable compared to the other structures. ZnONPs are synthesized using various physicochemical and biological methods (Kumar, Boro, Ray, Mukherjee, & Dutta, 2019). Industrial production of ZnONPs is based on mechanochemical processing (MCP) and physical vapor synthesis (PVS), while wet chemistry methods like coprecipitation (Ubani & Ibrahim, 2019), microwave (Salah et al., 2019), thermal decomposition (Alp et al., 2018), solgel (Delice, Isik, & Gasanly, 2019; Khan et al., 2016), and hydrothermal (Kumaresan, Ramamurthi, Ramesh Babu, Sethuraman, & Moorthy Babu, 2017) methods can also be used.

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Figure 10.5 Mechanisms of antimicrobial activities of ZnO nanoparticles.

ZnONPs are considered promising materials owing to their photocatalytic and antimicrobial activities. It is reported that the photocatalytic activity of ZnONPs is governed by their morphology; they can change from spherical NPs to microsized hexagonal nanorods/nanodisks (Salah et al., 2019). For instance, 94% photocatalytic activity of ZnO nanodiscs is obtained at B120 min against RhB dye with a rate constant and correlation coefficient of 0.02332 min21 and 0.99509, respectively (Kumaresan et al., 2017). ZnONPs can take advantage of their improved properties with respect to their chemical composition, crystalline structure, morphology, specific surface area, and surface functional chemical groups. As mentioned before, ZnONPs have a wide spectrum of antimicrobial activity with a low propensity to induce resistance (Reyes-Torres et al., 2019). Though the exact mechanism of the reaction/interaction of most of the NPs is still unknown, the antimicrobial activity of NPs can be proposed on the basis of electrostatic interaction, release of antimicrobial ions, and formation of ROS (Fig. 10.5).

10.2.4 Magnesium oxide-based nanoparticles Magnesium oxide (MgO) is a naturally occurring colorless, crystalline mineral with a high melting point that is used in various industries due to its large-scale production. MgO has a high thermal conductivity coupled with a low electrical conductivity. In recent years, the strong antimicrobial activity of MgO with a high stability, compared

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with organic antimicrobial agents, has been an interesting field of research. This combination of properties leads to its use as a multifunctional solid material. In the United States and Europe [EU-approved food additive (E number 530)], MgONPbased packaging has replaced many construction materials in food packaging, as they are impermeable to gas, thermally stable, flexible, and recyclable, with antimicrobial activity. MgONPs can be synthesized via laser ablation, hydrothermal, solgel, wet chemical reaction, microemulsion, microwave-assisted, and ultrasound-assisted methods (Mirtalebi, Almasi, & Alizadeh Khaledabad, 2019). Incorporation of MgNPs into biodegradable polymers such as PLA, PCL, and PHB results in nanocomposite formation with improved properties and antimicrobial features. Pure PLA can be degraded slowly to carbon dioxide, methane, and water in the environment. Upon addition of MgONPs into the above polymers, an industrial level of nanocomposites can be formed with improved mechanical, barrier, optical, thermal, and antibacterial/microbial properties. For example, Swaroop and Shukla (2019) reported improved tensile strength (TS) and plasticity by over 22% and 146%, respectively, for the PLA/MgONP nanocomposite films containing 2 wt.% MgO. In this nanocomposite, the oxygen and water vapor barrier properties also improves by nearly 65% and 57%, respectively, compared with the sample with 1 wt.% MgONPs. They also expressed the antimicrobial properties of this film, where in the presence of 1 wt.% MgONPs, around 44% of E. coli bacteria were killed after 24 h treatment.

10.2.5 Gold and silver nanoparticles Gold (Au) and silver (Ag) are the most noble metals owing to their lack of reactivity (Atkins et al., 2006). Au and Ag NPs are synthesized and used extensively in biomedical applications. However, gold(III) oxides and silver oxide have not been reported in food packaging due to disease diagnostics, and their instability. For example, the heat of formation (ΔHf) for Au2O3 is around 119.3 kJ/mol. This implies that Au2O3 is unstable (Tsai et al., 2003). In vitro investigations of both AgNPs and AuNPs show inhibition of microbial activities via two popular proposed mechanisms, that is, free metal ion toxicity and oxidative stress via a well-known ROS on the surface of AuNPs (Jagadish, Shiralgi, Chandrashekar, Dhananjaya, & Srikantaswamy, 2018). Ag and AuNPs are valuable in the development of antibacterial agents due to their nontoxicity, high ability for functionalization, polyvalent effects, ease of detection, and photothermal activity. In a real experiment, it was observed that Ag and AuNPs can attach to the bacterial membrane, where they cause membrane potential modification, a decreases in adenosine triphosphate level, and inhibition of tRNA binding to the ribosome (Ahmad, Hafeez, Bashir, Rauf, & Mujeeb-urRehman, 2017). The antibacterial and antifungal activities of AuNPs against Micrococcus luteus, S. aureus, P. aeruginosa, E. coli, Aspergillus fumigates, and Aspergillus niger have been reported (Hoseinnejad, Jafari, & Katouzian, 2018; Pagno et al., 2015; Rizvi et al., 2018; Thirumurugan, Ramachandran, & Gowri, 2013). It has been reported that AuNPs are more active on G 1 bacteria than G 2 .

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This is due to the facile internalization into the G 2 site (Cui et al., 2012). On the other hand, the biocidal properties of AuNPs can be due to the roughness and the extent of dispersion on/in the medium. AuNPs are safe for mammalian cells, compared to other MNPs, due to their independent antimicrobial mechanism-based ROS. Moreover, the potential of AuNPs for functionalization makes them ideal NPs against microbial activities. The production and utilization of AgNPs in food packaging was one of the first uses in order to protect food against foodborne diseases (Garcia, Shin, & Kim, 2018b). Due to their broad-spectrum inhibitory activities, AgNPs are known as an effective antimicrobial agent in packaging. Incorporation of AgNPs into the polymer matrix can affect gas permeability and antibacterial activity. Silver salts, like AgNO3, also exhibit an inhibition effect against microbial species. AgNO3 can inhibit the growth of multiple pathogens. Various morphologies of AgNPs, silver nanoclusters (AgNC), and silver-based alloy materials show different antimicrobial activities. The AgNPs-embedded cellulose nanofibrils showed an average size of 10.72 6 4.96 nm and a surface plasmon resonance (SPR) absorption peak at 397 nm (Yu, Wang, Kong, Lin, & Mustapha, 2019). Silver ions can be released from the composite films in the first 24 h. This nanocomposite has inhibition effects against E. coli and Listeria monocytogenes, and thus could potentially be used as an antimicrobial agent in active food packaging.

10.3

Layered nonmetal nanomaterials

Layered nanomaterials have a 2D morphology, which can form sheet, flake, disk, or platelet-like structures. There are a strong electrostatic, hydrogen, and van der Waals attractive forces of layered nanomaterials like layered silicates; therefore the laminar structure cannot be formed in nature (Salehabadi, Bakar, & Bakar, 2014). Hence, they tend to stack by forming larger layers of agglomerates to form tactoids. Graphene, clay, and silica are some examples of this class of material. The layered materials are currently the most relevant for the production of polymer nanocomposites (Tan, Salehabadi, Mohd Isa, Abu Bakar, & Abu Bakar, 2016). Nanoclay and silica are two famous fillers with unique structural properties, well-known chemistry, low cost, and legal approval as food additives by the EFSA (European Food Safety Authority) and as GRAS substances by FDA. Due to their structural features, the modification of layered silicate can improve their properties, or induce a new performance. In this section, silica (SiO2) and montmorillonite (MMT) nanolayers will be discussed with respect to their antimicrobial properties in food packaging.

10.3.1 Silicon dioxide nanoparticles Silicon is a metalloid and the most abundant solid element on Earth, which is found in the form of silica (SiO2) and silicate. SiO2 is the major raw material in many food industries for developing nonstick coatings for jars, bottles, and bags. Like

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Figure 10.6 O2/H2O barrier effect of SiO2 nanoparticles incorporated into polymer matrix.

other MO, SiO2 is known to be a promoter (a compound that enhances catalyst activity). The activities of SiO2-NPs are related to their average particle size, biocompatibility, high surface area, stability, low toxicity, low thermal conductivity, and supreme insulation. Silica, generally after modification with organic matters, can play important roles either as a reinforcing agent or as an antimicrobial agent in food packaging films. Tetraethoxysilane, 3-isocyanatopropyltriethoxysilane, and aminopropyltrietoxysilane are examples of modified SiO2. Polymer/SiO2 nanocomposites are reported to exhibit enhanced water and gas barrier properties as well as mechanical strength compared to the pure polymers. In the most reported articles in food packaging, SiO2-NPs are used individually as a reinforcing agent, while in combination with other materials (organic and inorganic) antimicrobial properties were revealed. For example, a combination of SiO2/ Ag, SiO2/TiO2/Ag, SiO2Al2O3, CoFe2O4/SiO2/Ag, and silicacarbonsilver (SiO2/C/Ag) nanosystems incorporated into polymer matrices are reported as CO2 and O2 regulators, ethylene scavengers, and microbial growth inhibitors. Therefore the combination of nanomaterials containing SiO2 can be a good strategy for nanopackaging development. Fig. 10.6 represents the schematic of O2/H2O barrier effects of typical polymer-based nanocomposites containing loaded SiO2-NPs.

10.3.2 Montmorillonite nanoclay “Clay minerals” is in fact a term originally used by sedimentologists and soil scientists for hydrous-layered magnesium or aluminasilicate and some geoorganic polymers. In many of these minerals, various metallic cations, such as lithium, magnesium, and aluminum act as a proxy, wholly or in part, for the magnesium, aluminum, or silicon, respectively, with alkali metal and alkaline earth metal cations present as exchangeable cations (Salehabadi, 2014). Each magnesium or aluminosilicate is composed of two types of sheets, octahedral and tetrahedral. Table 10.2 indicates the classification of clay minerals according to the structure of silicate layers. The clay of preference is montmorillonite (MMT) with micro/nanosized particles formed by stacks of three-layer sandwiches: a layer of Mg or Al oxides between the silicate layers. These sandwiches of 0.96 nm thickness and an average diameter of about 100500 nm are the desired reinforcing entities for polymeric nanohybrids

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Table 10.2 Various structures of clay (Salehabadi, 2014).

and nanocomposites. The chemical constitution of a MMT unit cell offers three types of reactive sites: anions on the silicate surface, hydroxyl (2OH) groups, and (few) cations on the narrow edges. The basal spacing of such a structure takes a value between 1 and 2 nm (Salehabadi, 2014). Small polar organic molecules and H2O can be absorbed by the cations, exchanged, and may intercalate. The extent of interaction can be varied from intercalation to complete expansion. Fig. 10.7 illustrates the mechanism of interaction between TOT clay and polymer. In packaging systems, MMT is used generally in combination with other organicinorganic materials, in order to enhance MMT properties in a typical polymeric matrix. These combinations lead to the formation of new materials with a huge structure, which can interact/react with polymers, and/or enhance thermomechanical and antimicrobial properties. Following are some examples of the nanocomposites based on MMT, NPs, and at least one polymer: G

Chitosan/MMT/CuO: it is a nanocomposite which is antimicrobially active. It has more than 99% mortality against G 1 bacteria (E. coli, P. aeruginosa) and G-bacteria (S. aureus, B. cereus). Incorporation of 1 wt.% MMT/CuO into chitosan enhances mechanical and antibacterial properties, while depressing both water solubility and UV transition with the lowest effect on the transparency of films (Nouri, Yaraki, Ghorbanpour, Agarwal, & Gupta, 2018).

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Figure 10.7 Interaction profile of silicate layers and polymer chains.

G

G

G

HDPE/MMT/Zn: Zn/MMT intercalates with melt mixed in HDPE to form nanocomposites. The nanocomposites exhibit excellent antimicrobial and antifungal activity with mild hemotoxic and cytotoxic behavior. The nanocomposites demonstrate complete hemocompatibility and cytocompatibility (Roy, Joshi, & Butola, 2019). Cellulose/MMT/Ag: biogenic synthesis of AgNPs in MMT using Curcuma longa tuber aqueous extract as both reducing and capping agent in cellulose leads to the formation of nanocomposites with enhanced tensile properties, UV blocking, oxygen barrier capability, antioxidant, antimicrobial, and antifungal activities (Dairi, Ferfera-Harrar, Ramos, & Garrigo´s, 2019). Ethylene vinyl acetate/MMT/ZnO-Fe: this nanocomposite is a transparent/flexible smart film, which is appropriate for active packaging. The film exhibits remarkable antibacterial and antioxidant activity (Eskandarabadi et al., 2019).

10.4

The influence of metal nanoparticles on different properties of food packaging materials

To protect the foods against moisture, oxygen, pathogenic microorganisms, dust, light, and a variation of other damaging or unsafe materials, the packaging should also be harmless under its intended conditions of procedure, inert, inexpensive to produce, lightweight, easy to dispose or reuse, able to tolerate extreme conditions during processing or filling, impermeable to a host of environmental storage and shipping conditions, and prevent physical and mechanical abuse. A large number of commercial food packaging materials are produced using nondegradable materials, which increase environmental and ecological contamination as well as using petroleum derivatives for their production. The utilization of bionanocomposites for food packaging does not just secure the food and expand its shelf life but can likewise

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Figure 10.8 General requirements for polymers in food packaging.

be viewed as more environmentally friendly since it diminishes the necessity to utilize plastics as packaging materials; but the currently available biodegradable films show weak mechanical and barrier properties that need to be improved before they can replace conventional packaging and consequently help to control the world’s waste issues. Hence, the essential motivation behind nanopackaging is to make a longer shelf life by getting improved barrier properties of food packaging in order to diminish gas and moisture transfer and UV light exposure and increase the mechanical, thermal, and antimicrobial properties. Fig. 10.8 demonstrates the main requirements for food packaging materials.

10.4.1 Barrier properties The barrier properties of food packaging are critical and they must have appropriate mass exchange properties for their utilization. Since the food value and quality losses may happen due to exchange of gases, smell, flavor, moisture, aroma, or change in color to and from the surrounding area, therefore barrier properties in food packaging can have an important role. Inappropriate packaging may lead to moisture losses, weight reduction, and shrinkage in vegetables and fruits during long-term storage (Olivas & Barbosa-Ca´novas, 2005). For example, with permeation of moisture, potato chips become spongy; in multistage foods, quality might be reduced when moisture transfers from one component of the food onto another, such as from the soggy filling of a pie to its dry layer. Also, unfavorable gas movements can cause quality issues. For instance when there is excessive amount of oxygen dissemination from the environment into the oil-containing food products such as nuts, they might experience oxidative rancidity, causing loss of value, quality, nutritional content, and decay of aroma, flavor, smell, texture, and change of color, which in the end leads to the decrease of food value, quality, and shelf life (Wihodo & Moraru, 2013). In this way, monitoring of mass movement in food packaging systems is important to maintain food quality and value. Composite materials are those that include at least two phases, one as the continuous phase and the other as the scatter phase. Regularly the continuous phase is a polymer/biopolymer matrix and the scatter phase is the

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Figure 10.9 (A) Neat polymer; (B) polymers loaded with nanoparticles.

filler, such as nanoparticles. In general, nanocomposites refers to those comprising a single or mixture of polymers with at least one organic or inorganic filler (,100 nm). Fig. 10.9 shows how nanoparticles improve the barrier properties compared with a pure polymer material. There are several interdependent factors affecting a polymer’s permeability to oxygen and water vapor, such as structural properties and polarity of polymeric side chains, properties of hydrogen bonding, polydispersity and molecular weight, the level of cross-linking or branching, method of processing, synthesis techniques, and level of crystallinity (Jafarzadeh, 2017). The presence of other migrants can complicate film permeability. The permeability of polymeric materials to gases could be measured via the diffusion rate of adsorbed gas molecules through the matrix and also adsorption rate of gas molecules into the matrix at the polymer/atmosphere boundary. The rate of adsorption generally depends on the formation rate of holes of free volume in the polymer, which are created by the thermal movement of the polymer chains or at random. On the other hand, jumps of molecular gas to neighboring (empty) holes creates diffusion. Hence, the polymer film permeability is usually estimated through the sizes of free volume holes, level of polymer movement, interaction between polymer and polymer, and interactions between polymer and gas. It should be pointed out that the external properties (e.g., pressure and temperature) and intrinsic polymer chemistry affect these variables. Finally, the film thickness has its own effect on the total rate of gas diffusion. Adding nanosized fillers into the matrix of polymer affects the homogeneous polymer film barrier properties in two unique ways. The first way is to make a tortuous path for the diffusion of gas. Gas molecules must move around filler materials and are not able to find a straight perpendicular path to the surface of film because of the impermeability of the filler materials. The result is that, as Fig. 10.9 shows, gas diffusion has a longer mean path through the film in the presence of fillers. This tortuous path enables manufacturers to create effective thickness in films and to consume a small degree of polymers at the same time (Jafarzadeh, 2017). The next mechanism is to create changes at the interfacial areas within the polymer matrix itself. In case of a desirable interaction between polymer and nanoparticle, polymer strands, which are placed close to each nanoparticle, could be relatively immobilized. As a result, gas molecules moving around the interfacial areas will have poor hopping rates between changed density or free volume holes and/or hole size (Choudalakis & Gotsis, 2009).

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In addition, solubility or diffusivity of the permeants are affected by surfactants or other additives, which are employed into the film matrix. The interfacial regions play a significant role in polymer matrices (e.g., polyolefins) with a highly native gas permeability. Moreover, NPs could act as heterogeneous crystal nucleation agents in the polymer matrix and increase crystallinity which can considerably reduce the rate of passage of contaminants; consequently, a polymer filled with NPs demonstrates a superior barrier property because of the higher degree of crystallinity since crystals are impermeable and prevent the migration process. Also crystals are stiffer than amorphous areas, therefore it is feasible to assume that the transfer properties of films are inhibited positively. Fig. 10.9 displays the “tortuous pathway” made by adding nanoplatelets into a film polymer matrix. Where a film is made only of polymer, the diffusing gas can only travel through a perpendicular pathway to the orientation of the film. However, regarding a nanocomposite, diffusing gases have to move around impermeable platelets/particles and over interfacial areas with a variety of permeability properties other than those of the virgin polymer. Thus the tortuous pathway makes the mean gas diffusion take longer and at the same time increases the shelf life of perishable foods (Jafarzadeh, 2017).

10.4.2 Mechanical properties Mechanical properties of food packaging including deformability, TS, elongation at break (EAB), and elastic modulus (EM), which are critical, since food-packaging materials must keep up their integrity during storage, distribution, and handling. The maximum stress that the film can withstand while being stretched or pulled before failing or breaking is known as TS and EM, which indicates the flexibility and intrinsic stiffness of the films, respectively (Jafarzadeh, 2017). The mechanical properties of biopolymer films depend both on their composition and on the environmental conditions. For instance, the addition of plasticizers causes a higher mobility of polymer chains, which leads to expanded elongation and diminished TS of the plasticized films. Embedding of different additives, such as cross-linking materials or lipids, can improve film strength and extensibility (Vieira, da Silva, dos Santos, & Beppu, 2011). Moreover, humidity and moisture of the environment influences the mechanical properties of polymer/biopolymer films. For example, hydrophilic films absorb humidity more promptly at higher moisture levels, consequently enhancing the plasticizing impact of water, which subsequently decreases the TS and increases the extendibility of the films. In addition, the contact between polymer/biopolymer packaging materials and packaged product can likewise influence the functioning of packaging films. In recent years, the incorporation of NPs has turned into a well-known way to improve the properties of different films, since the utilization of NPs typically gives them improved mechanical properties (Cho & Rhee, 2002). This result is due to the increased surface interaction between the matrix and NPs with a high surface area, as well as the hydrogen bond formation between them. EAB has a reverse relation to TS in most cases, and YM is directly related to TS. Furthermore, the mechanical

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properties of films are closely associated with the density and distribution of the intra- and intermolecular interactions between polymer chains in the film matrix.

10.4.3 Thermal properties Thermal analysis methods have been proven to define suitable processing conditions, application, and polymer chain structures. The thermal profiles of polymers can be investigated by thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC) (Gabbott, 2008). TGA describes the relation between the weight change and temperature. The amount of mass decreased versus temperature, or time, in a controlled atmosphere can provide information about thermal and oxidative stabilities of materials. Based on TGA thermogram, the composition of materials can also be identified. Using TGA, the mass loss/mass gain due to decomposition, oxidation, or loss of volatiles can be examined. It is a useful technique for measuring the polymeric materials like thermoplastics, films, fibers, etc. In industries, TGA measurements can be used to select materials for end-use applications, either by product performance or/and product quality. DSC is a thermal technique to obtain a wealth of information about materials, including polymers, and organicinorganic composites/hybrids. The energy changes during continuous heating and cooling can be obtained from DSC measurements. This enables the scientists to find the transition temperatures, like glass transition temperature (Tg), melting temperature (Tm), and crystallization temperature (Tc). In addition, this quantitative thermal analyzer can provide detailed information regarding the degree of crystallinity. Melting is an endothermic process, that is, the sample absorbs energy. Integrating the peak area gives the heat of fusion (ΔHf). Crystallization of the polymer, which is a process of partial alignment of molecular chains, occurs upon cooling, mechanical stretching, or solvent evaporation. Crystallization can affect optomechanical, thermomechanical, and chemical properties of the polymers (Billmeyer, 2007). The degree of crystallinity can be estimated using Eq. 10.1:  %X 5

ΔHm ΔHref

 3 100

(10.1)

where ΔHm is determined after thermal procedure I of nonisothermal DSC curve, and ΔHref is the reference melting enthalpy of 100% crystalline polymers. For example, the X-factor of pure polyhydroxybutyrate (PHB) is reported to be around 82%. Upon adding MMT, the crystallinity decreases from 19% (1 wt.% MMT) to zero (5 wt.% MMT), as shown in Fig. 10.10. The distance between dispersed platelets (here MMT) is long, therefore the additional nucleation sites can be created. There is a direct relation between MMT loading (concentration) and crystallinity. In a high concentration of MMT, the platelets can retard crystallization, acting as a physical hindrance (Salehabadi, 2014).

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Figure 10.10 DSC thermograms of PHB and various PHB/MMT nanohybrids at 20 C/min: (A) first and (B) second heating rate (Salehabadi, 2014).

10.4.4 Morphology The microstructural properties of food packaging can directly affect the barrier and mechanical properties, which are highly dependent on the manufacturing procedure, film preparation formulation, and agglomeration or scattering of NPs in the matrix (Jafarzadeh, Alias, Ariffin, & Mahmud, 2018). Utilizing atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) could demonstrate the morphology characteristics of NPs and films. For example, the result of SEM can exhibit that valleys and ridges are found within the cross-section of films, which may be associated with increasingly ductile material. In addition, smooth microstructures are demonstrative of a progressively brittle, glassy, and weak material (Hernandez-Izquierdo & Krochta, 2008). A smooth and uniform microstructure could likewise show homogeneity of the made film. Then again, the impressive properties of polymer nanocomposites are ascribed to great interfacial properties between polymer matrix and NPs, such as interaction/adhesion at interface and interfacial area (Zare, Rhee, & Park, 2017). Higher interfacial properties result in the development of another phase known as interphase around NPs, which is not quite the same as either the polymer matrix and NPs, demonstrating the benefit of nanocomposites compared to conventional microcomposites (Esbati & Irani, 2018). However, the high surface region of NPs and the powerful attractive interactions between particles bring about the conglomeration/agglomeration (Fig. 10.11). The strong and dense collectives of NPs signify the aggregation, but the freely joined particles demonstrate the agglomeration, which might be broken by mechanical pressure. The agglomeration of NPs diminishes the potential improvement of mechanical properties in nanocomposites, because of the restriction of the interfacial region. Therefore the most important challenge in the fabrication of nanocomposites includes the achievement of tiny and small size NPs and their great scattering in the matrix. Since the agglomerated nanoparticles usually make a negative impact on the mechanical properties of polymer nanocomposites, therefore it is fundamental to overcome the attractive forces

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Figure 10.11 Schematic illustration of agglomeration of nanorods in polymer nanocomposites.

between NPs that are creating the aggregation/agglomeration, rather than disturbing the structure of the nanoparticles.

10.4.5 Reactions/interactions A reaction profile converts one or more chemical substances into other chemical substances with new properties, while interaction is the phenomenon that occurs between molecules without changing their chemical identity. In nanocomposite technology, it is critical to ensure the extent of interaction (exfoliation, intercalation) and the level of reaction. The interaction is something related to the structure and composition of the materials. The famous techniques for identification of interactions are X-ray techniques like X-ray photoelectron spectroscopy (XPS) and Xray diffraction analysis (XRD). The reaction profile of nanocomposites can be tracked by spectroscopic techniques like Fourier-transform infrared spectroscopy (FTIR). Solid-state materials including nanomaterials and (semi)crystalline polymers have lattice structures with unique fingerprints. Using XRD, the crystallinity of polymers/MO/MMO and their respective crystalline phases can be recognized (Hemmati, Jafari, Kashaninejad, & Barani Motlagh, 2018). It is a primary technique to identify the degree of crystallinity, microstructure; for example, crystallite size, which can be determined using variants of the Scherrer equation, and orientation (through the Hermans orientation function). In polymeric materials, the positions and intensities of peaks are used for identifying the materials. Standard XRD reference patterns for various materials have been collected/reported by the Joint Committee on Powder Diffraction Standards (JCPDS). In packaging systems, especially in the case of bionanocomposites containing MONPs, FTIR and XRD are used in order to detect the potential intermolecular reaction and interaction among various components. The complete interaction profile (exfoliated structure) in a typical nanocomposite affects the mechanical properties of the sample (Salehabadi et al., 2014). Practically, in a bionanocomposite film of agar incorporated with ZnONPs as an active packaging material for shelf life extension of green grapes, the XRD and FTIR profiles exhibited the pure crystal structure of ZnONPs without any impurities (Fig. 10.12). In addition, in their respective FTIR profiles, the stretching vibration of 2 NH2, 2 OH, and 2 CH3 are

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Figure 10.12 (A) XRD pattern of ZnO nanoparticles, and (B) FTIR spectra of agar, and agar/ZNO nanocomposites (Kumar et al., 2019).

related to the agar, while the intensity of FTIR peaks for the agar/ZnO nanocomposites are reduced compared with the pristine agar (Kumar et al., 2019).

10.5

Antimicrobial influence of metal nanoparticles in food packaging materials

Antimicrobial packaging has received the most attention due to its potential to lengthen the lag phase of bacteria, minimize the growth rate of microorganisms, and preserve product safety and quality (Hoseinnejad et al., 2018). There are many parameters signifying the promising future of antimicrobial packaging in the food industry, such as the growing requests by consumers for convenient, safe, and fresh foods, along with the demand to package products in a versatile way for storage, transportation, and distribution. Nevertheless, it is necessary to gain more information and knowledge about how these systems affect the packaged food from microbiological, chemical, and physiological aspects (Jafarzadeh, 2017). Numerous kinds of antimicrobial packaging are available, such as antimicrobial biopolymers/polymers whose surfaces are coated with antimicrobial agents, mixtures of nonvolatile and volatile antimicrobial agents directly fixed to the biopolymer/polymer, and biopolymers holding antimicrobial agents by covalent linkages ¨ zgen, 2010). Nevertheless, the development of effective and novel antimicrobial (O agents appears to be very important, and should be a solution to overcome some food packaging challenges like the short shelf life of some food products. The antimicrobial activity of metals such as Zn, Cu, Ag, Au, and Ti, each having different properties, potencies, and spectra of activity, has been known and applied for centuries, as described in previous sections. In vitro research has demonstrated that metal NPs prevented the growth of several microbial species. The size of NPs and type of materials used for preparing NPs were the two main parameters that influenced the result of antimicrobial

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Figure 10.13 Mechanisms of antimicrobial activities exerted by metal nanoparticles.

effectiveness (Auyeung et al., 2017). Certainly, at the nanometer size, the surface to volume ratio is markedly increased, which in turn improves some properties of the particles (Oves et al., 2013). There are a number of mechanisms which can clarify the antimicrobial action of NPs, however there are two particularly popular proposals: (1) free metal ion toxicity emerging from disintegration of the metals from the surface of NPs; and (2) oxidative stress via the generation of ROS on the surfaces of NPs (He, Liu, Mustapha, & Lin, 2011). Fig. 10.13 demonstrates the distinctive proposed antimicrobial mechanisms of nanometals. In addition, physicochemical and morphological characteristics of metal NPs have been demonstrated to have an impact on their antimicrobial action. It is realized that the small size of NPs has the strongest bactericidal impact. The positive surface charge of metal NPs helps their binding to the negatively charged surface of microbes, which can also result in an improved bactericidal impact. The shape of NPs likewise affects their antimicrobial activity (Auyeung et al., 2017).

10.5.1 The impact of metal NPs on G 1 / 2 bacteria Generally, a major public health problem may be associated with both G 1 / 2 bacteria. The new antibacterial agents can be developed by recent advances in nanobiotechnology area, especially the ability to prepare the specific shape and size of MONPs. By changing the size of NPs, especially at the nanometer scale, their properties can be altered. For instance, the antibacterial activity of ZnO on S. aureus and E. coli can be improved by reducing the particle size. As H2O2 generation is associate with the ZnO surface area, increasing the volume/surface area ratio through particle size reduction will increase the reactivity of the ZnO surface at nanometer size. Thus ROS is more on a larger surface area of ZnO and, consequently, antibacterial activity is greater at smaller NPs (Jones et al., 2008). Furthermore, a greater toxic effect of smaller particles has been reported. Adams et al. (2006) suggested other factors, such as the concentration of microorganism, particle morphology, surface chemistry, and light intensity, as potential reasons of this toxicity.

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Figure 10.14 Membrane structure of Gram-positive and Gram-negative bacteria.

In general, it is believed that the antimicrobial activity of metal NPs mainly depends on the cell wall structure of G 1 / 2 bacteria. The G 1 bacteria are composed of a thick cell wall structure with multilayers of peptidoglycan, while G bacteria are composed of a complex cell wall structure with a thin peptidoglycan layer surrounded by an outer membrane (Paisoonsin, Pornsunthorntawee, & Rujiravanit, 2013). The NPs directly bind with the outer cell wall of G 1 bacteria, which contain plenty of pores allowing easy penetration of NPs into the cells, and thus causing leakage of intracellular contents leading to cell death. But in the case of G bacteria, the NPs bind initially with the bacterial outer cell membrane which contains lipoprotein, lipopolysaccharide, and phospholipids that may reduce the attachment of NPs (Jafarzadeh, 2017), as shown in Fig. 10.14. This observation indicates that the resistance/tolerance of the G 2 strain against such nanomaterials is higher than for the G 1 bacterial strains. As such, the sensitivity of G 1 bacterial strains to nanomaterials is higher in comparison to G 2 strains.

10.5.2 Fungi (molds/yeasts) In recent years, the ability of severe fungal infections to release mycotoxins, which are toxic to humans and animals, has resulted in health concerns. Molds are a large and taxonomically diverse group of filamentous fungi and are able to grow on a variety of rotten organic matter, foods, surfaces, and in any human place. A nonaesthetic appearance and an unpleasant odor are the consequence of their growth (Li & Yang, 2004). Furthermore, specific strains release spores and toxins to the environment and cause allergy sensitivities and other diseases, such as cancer. Considerable economic loss is caused by the growth of fungal pathogens during the postharvest stage (e.g., handling of fruits) of food products (Spadaro, Garibaldi, &

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Gullino, 2004). Severe postharvest fruit diseases including gray and blue molds can be caused by Penicillium expansum and Botrytis cinerea even by using the most advanced postharvest technologies (Spadaro et al., 2004). B. cinerea is one of the most important causes of disease in table grapes, while P. expansum causes the rot of stored apples and pears (Caban˜as, Abarca, Bragulat, & Caban˜es, 2009). In addition, P. expansum is the main producer of a mycotoxin, patulin, which is commonly found in rotting apples. Patulin is limited to 50 mg/L in apple juice by the FDA (Moake, Padilla-Zakour, & Worobo, 2005). Manufacturing firms produce different antifungal compounds to restrict fungal proliferation of food. However, controlling fungal growth is difficult, as fungi have become resistant to many conventional fungicides. To overcome this resistance, it is necessary to replace the current control strategies with novel antifungal agents. Recently, NPs such as Cu, Ti, Zn, Au, and Ag have received attention due to their unique chemical and physical properties and powerful antifungal activities. Due to a high surface area-to-mass ratio, NPs are highly reactive and have been successfully used because of their chemical, electrical, and optical properties, which differ from their normal attributes at the macroscale. Cu, Zn, and Ag NPs are potential antifungal agents and they have shown antifungal activity against fungal strains such as P. expansum, S. cerevisiae, T. beigelii, and C. albicans (He et al., 2011).

10.5.3 Parasites/viruses Viruses, as the major causes of human death and disease, have become a big challenge for biotechnological, food, pharmaceutical, and medical fields. The development of vaccines and medicines to fight against viruses has received special attention. The quick adaptation in the current host and switching to a new host are the characteristics of these infectious agents and this is the major bottleneck in treatment. Although antiviral therapy has improved tremendously, recent medicines and treatments are not able to completely control viral diseases. As such, a quick development of novel antiviral agents is needed. Modifying and improving the effectiveness of existing antiviral compounds is another priority of researchers. Nanotechnology provides a platform to develop and modify the properties of metals through reducing them into NPs, which have plenty of applications in different areas. The researchers are continuously looking to find an effective nanotechnological solution to treat viral infections, and metal NPs could be a promising strategy (Rai et al., 2016). Viruses and other microbes are interacted with NPs due to their unique properties and small size. The metal NPs of zinc, gold, silver, titanium, magnesium, and copper have demonstrated bactericidal characteristics at the nanolevel and they have potential antiviral activities against various types of viruses. These NPs have multivalent interactions with cell membrane receptors and viral surface components, which block viral entry into the cells. Metal NPs are considered to be very effective antiviral agents which act either outside the host by blocking the entry of viral particles or inside by inhibiting viral replication (Singh & Nalwa, 2011).

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Toxicological aspects, safety, and migration of metal nanoparticles into food products

Safety issue is the main concern of using nanopackaging material for food packaging purposes, as additives and plastics can migrate into the packaged food during storage time and processing treatments. The rate of migration depends on the mechanical stress and temperature. The migration of NPs and plastics can change the organoleptic properties of food. Furthermore, as some of these compounds have toxic properties, if the migration rate is higher than legislated values, it can cause health problems. During the development of any materials that have contact with food, it is important to investigate the migration potential of undesirable or harmful substances to the product. The migration test refers to the determination of the release of substances from an article or material either into a food simulant or food (Commission, 2011). After a contact period, the migration test is carried out through identification/ quantification by an analytical technique, such as chromatography or spectroscopy.

10.6.1 The safety issues of human contact to nanoparticles In the food industry, purposely added NPs into the foods are the main exposure sources. Movement of NPs to food from nanocomposite packages is the indirect exposure source. The people who are working in nanocomposites manufacturing firms are directly exposed to NPs, which may cause health issues through skin contact or inhalation. According to scientific evidence, free NPs can cause oxidative reactions and inflammation due to their ability to cross cellular barriers (Maisanaba et al., 2015). However, more study is needed into the extent to which NPs migrate from the nanocomposite packages into the foods, how NPs will act after they enter to the body, how different organs, from mouth to final gastrointestinal tract, absorb them, and the response of the body to them (Wani, Masoodi Jafari, & McClements, 2018). Different parameters including size, morphology, and toxicity of NPs, the rate of NP migration, and the extent to which the human body absorbs them will affect the possible health risks associated with oral ingestion (Cushen, Kerry, Morris, Cruz-Romero, & Cummins, 2012). For example, Han, Yu, Li, and Wang (2011) stated that the small-sized NPs are more dangerous for human health in comparison to the large ones, as they can easily be distributed throughout the organs and the body; also their absorption rate is higher. The packaging toxicology of migrated NPs can be evaluated by in vivo and in vitro procedures. In vitro toxicological assays are applied to comprehend the basal cytotoxicity and toxicity mechanisms of NPs. Rodent and human cell lines, which are obtained from intestine and liver, are the most favored experimental models. The most frequently used tests for investigating basal cytotoxicity are lactate dehydrogenase release assay, cell counting, neutral red uptake, live-dead assay, protein content, alarm blue assay, and tryan blue dye exclusion. Observation of the changes in rodent and human cell lines is the most frequently used way for investigating toxicity mechanisms such as cell necrosis, DNA damage, inflammation

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response, and the use of basal biomarkers including glutathione content and ROS. Ames test, comet assay, and micronucleus assay are the most common assays for investigating genotoxicity. In vivo methods investigate macrotoxic, and subchronic/ chronic exposure or histopathological effects by exposing rodents to the target substance (Maisanaba et al., 2015).

10.6.2 Regulation for nanomaterials associated with food contact materials 10.6.2.1 European Community According to the European Community (EC), nanoscale materials can be utilized only when they are authorized plus cited in the descriptions of Annex I of the rules. Carbon black, amorphous silicon dioxide (SiO2), and titanium nitride (TiN) are recorded in Annex I. In this category, the particle size must be lower or near 100 nm. Besides, in the case of a functional barrier (FB)—FB is a multilayer structure used to prevent the movement of materials from outer layer to the food—nonauthorized materials might be used. The nonauthorized materials must follow the rules; 1. They must not be reprotoxic/mutagenic/carcinogenic 2. Their migration must be below a given detection limit (“EU GMP Annex 1: Manufacture of Sterile Medicinal Products—revision November 2008—ECA Academy,” 2008).

10.6.2.2 US Food and Drug Administration The FDA in the United State is responsible for guaranteeing the security of food contact materials. According to the Commissioner of Food and Drugs (2007), nanotechnology has quite been accepted once dealing with nanotechnology-based products. In order to help the industry, the FDA has published numerous report documents relevant to the issues of nanotechnology, in order to provide; (1) a synopsis of the state of the science for biological interactions of nanoscale materials; (2) analysis and recommendations for science issues; and (3) analysis and recommendations for regulatory policy issues. The FDA provides all reports based on the material sizes (1100 nm), or material properties as well as phenomena that are relevant to the material’s external measurements. The FDA mentions an initial safety evaluation for industries: “Food Ingredients and Food Contact Materials made at nanoscale” (U.S. Department of Health and Human Services, 2014). The FDA only recommends a case-by-case approach regarding security for the final product and its predicted application.

10.7

Conclusion and further remarks

Nanoscale materials including metal NPs and MONPs can be used as antimicrobial additives to packaging systems. They are capable of inhibiting the bacterial cell walls to combat bacterial infections. The approval of new hybrid materials containing

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modified layered materials such as MMT/MOs can enhance additional imparted properties to the final packaging product (film). Although some of the recent examples on nanoscale MOs and hybrid-containing MOs are yet to go beyond the laboratory, the results bear much promise. Biopolymers, owing to their structural deficiencies, can be engineered using MOs nanomaterials, in order to overcome their deficiencies. These bionanocomposites in food packaging—sometimes called active packaging— can be efficient against both Gram-negative and Gram-positive bacteria. Due to the effect food and food packaging on human health and the environmental concerns, systematic management and research are recommended as follows: G

G

G

Synthesis and utilization of nanoscale MMOs in food packaging, instead of MNPs and MONPs. In situ preparation of binanocomposites instead of in vitro addition of NPs into the polymer matrix. Utilization of natural by-products like tropical peels or seeds, with antimicrobial performance instead of new production of synthetic materials.

A global convergence for safety assessment of nanoscale food ingredients and food contact substances is also recommended.

Acknowledgment The authors would like to appreciate Universiti Sains Malaysia for supporting this work in the form of postdoctoral and teaching fellows.

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Maness, P.-C., Smolinski, S., Blake, D. M., Huang, Z., Wolfrum, E. J., & Jacoby, W. A. (1999). Bactericidal activity of photocatalytic TiO2 reaction: Toward an understanding of its killing mechanism. Applied and Environmental Microbiology. Miller, M. B., & Bassler, B. L. (2001). Quorum sensing in bacteria. Annual Review of Microbiology., 55, 165199. Available from https://doi.org/10.1146/annurev. micro.55.1.165. Mirtalebi, S. S., Almasi, H., & Alizadeh Khaledabad, M. (2019). Physical, morphological, antimicrobial and release properties of novel MgO-bacterial cellulose nanohybrids prepared by in-situ and ex-situ methods. International Journal of Biological Macromolecules., 128, 848857. Available from https://doi.org/10.1016/J.IJBIOMAC.2019.02.007. Moake, M. M., Padilla-Zakour, O. I., & Worobo, R. W. (2005). Comprehensive review of patulin control methods in foods. Comprehensive Reviews in Food Science and Food Safety, 4, 821. Muthulakshmi, L., Varada Rajalu, A., Kaliaraj, G. S., Siengchin, S., Parameswaranpillai, J., & Saraswathi, R. (2019). Preparation of cellulose/copper nanoparticles bionanocomposite films using a bioflocculant polymer as reducing agent for antibacterial and anticorrosion applications. Composites Part B: Engineering, 175, 107177. Available from https://doi.org/10.1016/J.COMPOSITESB.2019.107177. ˇ Nedeljkovi´c, J., Smirnova, I., & Neˇsi´c, A., Gordi´c, M., Davidovi´c, S., Radovanovi´c, Z., Gurikov, P. (2018). Pectin-based nanocomposite aerogels for potential insulated food packaging application. Carbohydrate Polymers, 195, 128135. Available from https:// doi.org/10.1016/J.CARBPOL.2018.04.076. Nouri, A., Yaraki, M. T., Ghorbanpour, M., Agarwal, S., & Gupta, V. K. (2018). Enhanced antibacterial effect of chitosan film using Montmorillonite/CuO nanocomposite. International Journal of Biological Macromolecules, 109, 12191231. Available from https://doi.org/10.1016/J.IJBIOMAC.2017.11.119. Olivas, G. I., & Barbosa-Ca´novas, G. V. (2005). Edible coatings for fresh-cut fruits. Critical Reviews in Food Science and Nutrition., 45, 657670. Oves, M., Khan, M. S., Zaidi, A., Ahmed, A. S., Ahmed, F., Ahmad, E., . . . Azam, A. (2013). Antibacterial and cytotoxic efficacy of extracellular silver nanoparticles biofabricated from chromium reducing novel OS4 strain of Stenotrophomonas maltophilia. PLoS One, 8, e59140. ¨ zgen, C. (2010). Isolation of antimicrobial molecules from agricultural biomass and utilizaO tion in xylan-based biodegradable films. Middle East Techical University. Pagno, C. H., Costa, T. M. H., de Menezes, E. W., Benvenutti, E. V., Hertz, P. F., Matte, C. R., . . . Flˆores, S. H. (2015). Development of active biofilms of quinoa (Chenopodium quinoa W.) starch containing gold nanoparticles and evaluation of antimicrobial activity. Food Chemistry., 173, 755762. Available from https://doi.org/10.1016/J. FOODCHEM.2014.10.068. Paisoonsin, S., Pornsunthorntawee, O., & Rujiravanit, R. (2013). Preparation and characterization of ZnO-deposited DBD plasma-treated PP packaging film with antibacterial activities. Applied Surface Science., 273, 824835. Pilevar, Z., Bahrami, A., Beikzadeh, S., Hosseini, H., & Jafari, S. M. (2019). Migration of styrene monomer from polystyrene packaging materials into foods: Characterization and safety evaluation. Trends in Food Science & Technology, 91, 248261. Available from https://doi.org/10.1016/j.tifs.2019.07.020. Raei, M., & Jafari, S. (2013). Influence of modified atmospheric conditions and different packaging materials on pistachio (Pistacia vera L.) oil quality. Latin American Applied Research, 43, 4346.

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Rai, M., Deshmukh, S. D., Ingle, A. P., Gupta, I. R., Galdiero, M., & Galdiero, S. (2016). Metal nanoparticles: The protective nanoshield against virus infection. Critical Reviews in Microbiology, 42, 4656. ´ . M., Pe´rez-Dı´az, M. A., Reyes-Torres, M. A., Mendoza-Mendoza, E., Miranda-Herna´ndez, A Lo´pez-Carrizales, M., Peralta-Rodrı´guez, R. D., . . . Martinez-Gutierrez, F. (2019). Synthesis of CuO and ZnO nanoparticles by a novel green route: Antimicrobial activity, cytotoxic effects and their synergism with ampicillin. Ceramic International.. Available from https://doi.org/10.1016/J.CERAMINT.2019.08.171. Rizvi, S. M. D., Hussain, T., Ahmed, A. B. F., Alshammari, T. M., Moin, A., Ahmed, M. Q., . . . Ashraf, G. M. (2018). Gold nanoparticles: A plausible tool to combat neurological bacterial infections in humans. Biomedicine & Pharmacotherapy., 107, 718. Available from https://doi.org/10.1016/J.BIOPHA.2018.07.130. Roy, A., Joshi, M., & Butola, B. S. (2019). Preparation and antimicrobial assessment of zincmontmorillonite intercalates based HDPE nanocomposites: A cost-effective and safe bioactive plastic. Journal of Cleaner Production., 212, 15181525. Available from https://doi.org/10.1016/J.JCLEPRO.2018.11.235. Roy, S., & Rhim, J.-W. (2019). Melanin-mediated synthesis of copper oxide nanoparticles and preparation of functional Agar/CuO np nanocomposite films. Journal of Nanomaterials, 2019, 110. Available from https://doi.org/10.1155/2019/2840517. Salah, N., AL-Shawafi, W. M., Alshahrie, A., Baghdadi, N., Soliman, Y. M., & Memic, A. (2019). Size controlled, antimicrobial ZnO nanostructures produced by the microwave assisted route. Materials Science and Engineering C, 99, 11641173. Available from https://doi.org/10.1016/J.MSEC.2019.02.077. Salarbashi, D., Tafaghodi, M., & Bazzaz, B. S. F. (2018). Soluble soybean polysaccharide/ TiO2 bionanocomposite film for food application. Carbohydrate Polymers, 186, 384393. Available from https://doi.org/10.1016/J.CARBPOL.2017.12.081. Salehabadi, A. (2014). Effect of organomodified nanoclay in poly (3-hydroxybutyrate) (PHB)-, epoxidized natural rubber (ENR-50) and PHB/ENR-50 blend nanocomposites. Universiti Sains Malaysia. Salehabadi, A., Bakar, M., & Bakar, N. (2014). Effect of organo-modified nanoclay on the thermal and bulk structural properties of poly(3-hydroxybutyrate)-epoxidized natural rubber blends: Formation of multi-components biobased nanohybrids, . Materials (Basel) (7, pp. 45084523). . Available from https://doi.org/10.3390/ma7064508. Saptarshi, S. R., Duschl, A., & Lopata, A. L. (2013). Interaction of nanoparticles with proteins: Relation to bio-reactivity of the nanoparticle. Journal of Nanobiotechnology, 11, 26. Available from https://doi.org/10.1186/1477-3155-11-26. Sarangapani, C., Ziuzina, D., Behan, P., Boehm, D., Gilmore, B. F., Cullen, P. J., & Bourke, P. (2019). Degradation kinetics of cold plasma-treated antibiotics and their antimicrobial activity. Science Reports, 9, 3955. Available from https://doi.org/10.1038/s41598-01940352-9. Sarkar, P., Yarlagadda, V., Ghosh, C., & Haldar, J. (2017). A review on cell wall synthesis inhibitors with an emphasis on glycopeptide antibiotics. MedChemComm, 8, 516. Available from https://doi.org/10.1039/C6MD00585C. Singh, R., & Nalwa, H. S. (2011). Medical applications of nanoparticles in biological imaging, cell labeling, antimicrobial agents, and anticancer nanodrugs. Journal of Biomedical Nanotechnology., 7, 489503. Singh, R., Smitha, M. S., & Singh, S. P. (2014). The role of nanotechnology in combating multi-drug resistant bacteria. Journal of Nanoscience and Nanotechnology., 14, 47454756. Available from https://doi.org/10.1166/jnn.2014.9527.

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Spadaro, D., Garibaldi, A., & Gullino, M. L. (2004). Control of Penicillium expansum and Botrytis cinerea on apple combining a biocontrol agent with hot water dipping and acibenzolar-S-methyl, baking soda, or ethanol application. Postharvest Biology and Technology, 33, 141151. Swaroop, C., & Shukla, M. (2019). Development of blown polylactic acid-MgO nanocomposite films for food packaging. Composites Part A: Applied Science and Manufacturing, 124, 105482. Available from https://doi.org/10.1016/J.COMPOSITESA. 2019.105482. Tajik, S., Maghsoudlou, Y., Khodaiyan, F., Jafari, S. M., Ghasemlou, M., & Aalami, M. (2013). Soluble soybean polysaccharide: A new carbohydrate to make a biodegradable film for sustainable green packaging. Carbohydrate Polymers, 97, 817824. Available from https://doi.org/10.1016/j.carbpol.2013.05.037. Tan, R., Lv, Z., Tang, J., Wang, Y., Guo, J., & Li, L. (2019). Theoretical study of the adsorption characteristics and the environmental influence of ornidazole on the surface of photocatalyst TiO2. Science Reports, 9, 10891. Available from https://doi.org/10.1038/ s41598-019-47379-y. Tan, W. L., Salehabadi, A., Mohd Isa, M. H., Abu Bakar, M., & Abu Bakar, N. H. H. (2016). Synthesis and physicochemical characterization of organomodified halloysite/ epoxidized natural rubber nanocomposites: A potential flame-resistant adhesive. Journal of Materials Science, 51, 11211132. Available from https://doi.org/10.1007/s10853015-9443-9. Thirumurugan, A., Ramachandran, S., & Gowri, S. (2013). Combined effect of bacteriocin with gold nanoparticles against food spoiling bacteria-an approach for food packaging material preparation. International Food Research Journal. Tsai, H., Hu, E., Perng, K., Chen, M., Wu, J.-C., & Chang, Y.-S. (2003). Instability of gold oxide Au2O3. Surface Science, 537, L447L450. Available from https://doi.org/ 10.1016/S0039-6028(03)00640-X. U.S. Department of Health and Human Services. (2014). Guidance for industry. Ubani, C. A., & Ibrahim, M. A. (2019). Complementary processing methods for ZnO nanoparticles. Materials Today: Proceedings, 7, 646654. Available from https://doi.org/ 10.1016/J.MATPR.2018.12.056. Vahedikia, N., Garavand, F., Tajeddin, B., Cacciotti, I., Jafari, S. M., Omidi, T., & Zahedi, Z. (2019). Biodegradable zein film composites reinforced with chitosan nanoparticles and cinnamon essential oil: Physical, mechanical, structural and antimicrobial attributes. Colloids and Surfaces B: Biointerfaces, 177, 2532. Available from https://doi.org/ 10.1016/j.colsurfb.2019.01.045. Vieira, M. G. A., da Silva, M. A., dos Santos, L. O., & Beppu, M. M. (2011). Natural-based plasticizers and biopolymer films: A review. European Polymer Journal, 47, 254263. Wani, T. A., Masoodi, F. A., Jafari, S. M., & McClements, D. J. (2018). Chapter 19—Safety of nanoemulsions and their regulatory status. Nanoemulsions (pp. 613628). Academic Press. Available from https://doi.org/10.1016/B978-0-12-811838-2.00019-9. Wihodo, M., & Moraru, C. I. (2013). Physical and chemical methods used to enhance the structure and mechanical properties of protein films: A review. Journal of Food Engineering, 114, 292302. Xie, J., & Hung, Y.-C. (2018). UV-A activated TiO2 embedded biodegradable polymer film for antimicrobial food packaging application. LWT—Food Science Technology, 96, 307314. Available from https://doi.org/10.1016/J.LWT.2018.05.050. Yu, Z., Wang, W., Kong, F., Lin, M., & Mustapha, A. (2019). Cellulose nanofibril/silver nanoparticle composite as an active food packaging system and its toxicity to human

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colon cells. International Journal of Biological Macromolecules, 129, 887894. Available from https://doi.org/10.1016/J.IJBIOMAC.2019.02.084. Zare, Y., Rhee, K. Y., & Park, S.-J. (2017). Predictions of micromechanics models for interfacial/interphase parameters in polymer/metal nanocomposites. International Journal of Adhesion and Adhesives., 79, 111116. Zhang, X., Xiao, G., Wang, Y., Zhao, Y., Su, H., & Tan, T. (2017). Preparation of chitosanTiO2 composite film with efficient antimicrobial activities under visible light for food packaging applications. Carbohydrate Polymers, 169, 101107. Available from https:// doi.org/10.1016/j.carbpol.2017.03.073.

Nanobiosensors for food analysis

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Beatriz Jurado-Sa´nchez1,2, Marı´a Moreno-Guzma´n3, Juan V. Perales-Rondon1 and Alberto Escarpa1,2 1 Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, University of Alcala, Madrid, Spain, 2Chemical Research Institute “Andre´s M. del Rı´o”, University of Alcala, Madrid, Spain, 3Department of Chemistry in Pharmaceutical Sciences, Analytical Chemistry, Faculty of Pharmacy, Universidad Complutense de Madrid, Madrid, Spain

11.1

Introduction

According to the International Union of Pure and Applied Chemistry (IUPAC), a biosensor can be defined as a self-contained integrated device that can provide analytical information using a recognition element, which is retained in direct spatial contact with a transduction element (The´venot, Toth, Durst, & Wilson, 2001). The adequate definition and “concept” of a nanobiosensor has generated controversies among the scientific community, but in common terms it can be defined as a nanoscale device that monitors a (bio)chemical event by means of electronic, optical, or magnetic technology through a compact probe. Such tiny sensing elements can be classified according to the biological recognition mechanism or to the signal transduction mechanism. Fig. 11.1 summarizes the different components involved in the design of nanobiosensors. Also, Table 11.1 classifies the types of nanobiosensors according to the transduction mechanism, along with their advantages and disadvantages.

11.2

Nanomaterials and other related tools used to construct biosensors

Nanostructured materials offer unique physical and chemical properties due to a larger surface area compared to bulk materials, among other relevant properties (electrical, optical, magnetics) conferred by their nanometric dimensions (Bagheri, Jafari, & Eikani, 2019; Joz Majidi et al., 2019). Such nanometer dimensions result in an increased sensing surface and strong binding properties, resulting in improved sensitivity and selectivity (Luz, Iost, & Crespilho, 2013). Over recent years, the manufacture of biosensors has focused on the use of nanostructured materials (metal nanoparticles, semiconductor materials, carbon nanomaterials) and magnetic Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00011-X © 2020 Elsevier Inc. All rights reserved.

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Figure 11.1 Schematic of a nanobiosensor showing the recognition, reporting, and transducing elements. Source: Adapted and reprinted with permission from Zhang, S., Geryak, R., Geldmeier, J., Kim, S., & Tsukruk, V. V. (2017). Synthesis, assembly, and applications of hybrid nanostructures for biosensing. Chemical Reviews, 117, 12942
13038. Copyright 2017 American Chemical Society.

nanoparticles as platforms for the immobilization of multiple probes for improved detection (Tiwari & Turner, 2014).

11.2.1 Metallic nanoparticles and semiconductor nanomaterials Metal nanoparticles (NPs) are an ideal platform for the controlled immobilization of bioreceptors, along with a good retention of their native bioactivities (Katz, Willner, & Wang, 2004). Gold NPs (AuNPs) allow the direct transfer of electrons between, for example, redox proteins and the electrode surface, avoiding the use of electron transfer mediators. This can be attributed to the relatively high surface to volume ratio of AuNPs, along with their high surface energy and ability to decrease the distance between proteins and metal particles. Thus they act as an electroconductive pathway between prosthetic groups and the surface of the electrode (Pingarro´n, Ya´n˜ez-Seden˜o, & Gonza´lez-Corte´s, 2008). In addition, the facile synthesis and functionalization of AuNPs means they are excellent scaffolds for the fabrication of novel chemical and biological sensors (Biju, 2014). There are different strategies for the fabrication of biosensors with AuNPs. For example,

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Table 11.1 Types of nanobiosensors according to the transduction mechanism and comparison. Transduction mechanism

Type

Advantages

Disadvantages

Electrochemical

Amperometric Potentiometric Impedimetric Conductometric Field-effect transistors

Limited shelf life (single use) Narrow linear range Relatively high cost

Optical

Colorimetric Fluorescent Surface plasmon resonance Raman-SERS Piezoelectric Magnetoelastic Microcantilever

High sensitivity High selectivity One-step target detection Disposability Portability Versatility Versatility Easy-to-use Portability High sensitivity High sensitivity High selectivity

High cost Low availability

Nanomechanical

Limited portability Moderate selectivity

immobilization of tyrosinase by cross-linking onto AuNPs-modified glassy carbon electrodes (GCE) has been applied for the detection of phenolic compounds with good analytical performance (Sanz, Mena, Gonza´lez-Corte´s, Yanez-Sedeno, & Pingarro´n, 2005). Peroxidase biosensors based on enzyme immobilization on AuNPs via self-assembled monolayers (SAMs) allow for detection without the aid of an electron mediator (Yi, Huang-Xian, & Hong-Yuan, 2000). A composite paste electrode combining synergistically the ability of AuNPs to adsorb proteins with the electrocatalytic behavior of carbon nanotubes (CNTs) was used for the determination of cortisol and androsterone hormones (Moreno-Guzma´n, Agu¨´ı, GonzalezCortes, Yanez-Sedeno, & Pingarron, 2013). In addition, in a bienzymatic biosensor for electrochemical detection of D-aminoacids (DAAs) biomarkers, higher loading of enzymes was observed after increasing the amount of electrodeposited AuNPs in CNT-based electrodes by activation of the carboxylate moieties with EDC/sulfoNHS chemistry (Moreno-Guzma´n et al., 2017). On the other hand, AuNPs or silver NPs (AgNPs) exhibit size-tunable plasmon absorbance bands in the UV-Vis region. Numerous studies have been published based on color changes corresponding to dispersed and aggregated NPs. In the literature, there are very interesting works reported on the labeling of biomaterials and staining of biological tissues by metal particles as a means to image and visualize biological processes (Vilela, Gonza´lez, & Escarpa, 2012). Similarly, semiconductor NPs exhibit size-dependent tunable optical properties. Quantum dots (QDs) are nanoscale semiconductor crystalline clusters with unique optical properties and abroad excitation range that are advantageous for the development of biosensors. They have a broad continuous absorption spectrum, at

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wavelengths extending from the ultraviolet to the visible range, depending on particle size (Pe´rez-Lo´pez & Merkoc¸i, 2011). Thus, QDs allow the performance of multiplexed optical bioanalysis due to their inherent advantages such as high sensitivity and specificity, low cost, size-dependent emission wavelength, and fast analyte detection (Frasco & Chaniotakis, 2009).

11.2.2 Carbon nanomaterials Carbon can form a wide variety of structures with fundamentally different properties, also known as carbon allotropes. Thus nanotubes of carbon (CNTs), fullerenes, and graphene have attracted significant research interest due to their outstanding properties. During the past decade, CNTs have been one of the most extensively used materials in nanobiosensors (Katouzian & Jafari, 2019). They consist of a two-dimensional hexagonal lattice of carbon atoms, bent and joined in one direction so as to form a hollow cylinder. In addition to these single-wall CNT (SWCNTs), there are also multiwall (MWCNTs) variants consisting of two or more nested nanotubes (Agu¨´ı, Ya´n˜ez-Seden˜o, & Pingarro´n, 2008). The CNT-based biosensors have the following advantages associated with their unique structures: high sensitivity (because of the high ratio of surface to volume); enabled enzyme immobilization with high biological activity; fast response time due to the ability of this nanomaterial to promote electron transfer in electrochemical reactions; and negligible surface passivation. Such characteristics have been exploited to design novel biosensors in a myriad of applications (Balasubramanian & Burghard, 2006; Manso, Mena, Yanez-Sedeno, & Pingarron, 2007; Yang, Chen, Ren, Zhang, & Yang, 2015). CNTmodified electrodes have also been used in electrochemical detection systems for liquid chromatography and capillary electrophoresis (Chailapakul et al., 2008). Moreover, chemical modification of CNTs is an effective way to increase biosensors selectivity, which has been exploited, for example, for DNA detection. In this case, the DNA probes are covalently bonded to a polymer that is anchored noncovalently to the CNT walls (Eda & Chhowalla, 2009). Carbon nanohorns (CNHs) are carbon nanostructures with a diameter of 2 2 5 nm, a length of 40 2 50 nm, and conical-shaped tips. Several thousand CNHs assemble to form quasispheroidal aggregates shaped like a dahlia flower. The unique structure of CNHs, which contain a large number of oxygenated moieties, allow for their modification with biomolecules. This superior behavior has been shown in a disposable immunosensor for the determination of fibrinogen (Ojeda et al., 2014). Graphene, another type of two-dimensional (2D) nanomaterial, possesses outstanding properties, such as high electrical conductivities, large surface area, and superior mechanical strength. Its large surface area (2630 m2/g for single-layer graphene) and the presence of edges rich in oxygenated species, such as epoxides, carboxyls, hydroxyls, and alcohols, make graphene oxide (GO) more water-soluble and highly biocompatible, enhancing the absorption and desorption of molecules (Justino, Gomes, Freitas, Duarte, & Rocha-Santos, 2017; Martin & Escarpa, 2014). Graphene possesses several advantages as compared to other carbon nanomaterials.

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For example, the atomic thickness of graphene and its extremely high area/volume ratio make it highly sensitive. In addition, graphene can be easily connected to biomolecules by π
π stacking between ring structures of the nucleotide bases and the hexagonal cells of graphene (Morales-Narva´ez & Merkoc¸i, 2012). There are different strategies for the fabrication of graphene-based nanobiosensors. Modification is commonly carried out by coating or preparing carbon nanomaterial
binder composite electrodes (Carralero, Gonza´lez-Corte´s, Ya´n˜ez-Seden˜o, & Pingarro´n, 2007). Also, a useful and simple method consists of the direct casting of a small volume of a nanomaterial suspension onto the electrode surface (Martı´n, Batalla, Herna´ndezFerrer, Martı´nez, & Escarpa, 2015). In another example, the carbon nanomaterial is filtered using a Teflon membrane, in which the carbon nanomaterial acts as a unique conductive material (Garcı´a-Carmona, Moreno-Guzma´n, Sierra, Gonza´lez, & Escarpa, 2018).

11.2.3 Magnetic nanoparticles Magnetic NPs or magnetic beads (MBs) constitute an example of another interesting tool for nanobiosensor developments. They allow for the immobilization of a high loading of molecules along with higher reaction kinetics, thus greatly reducing the reaction times. This can be attributed to the excellent properties of MBs, such as high surface area, easy manipulation by a magnet, and minimization of matrix effects. Moreover, this strategy allows the measurements to be carried out with a small volume of solution, increasing the concentration of reagents on the transducer surface to achieve lower detection limits (Centi, Laschi, & Mascini, 2007; MorenoGuzma´n et al., 2010). MBs are commercially available with different surface functionalities, and have been applied in a myriad of nanobiosensors. The main advantage of using this type of particle is the proper orientation of the antibody binding sites. The coupling of antibodies onto MBs has been achieved through the specific affinity to protein G or A for the Fc part of the antibody (Ab) molecules (Jodra, Lo´pez, & Escarpa, 2015).

11.3

Bioreceptors

Bioreceptors are biological molecular species, such as enzymes, antibodies (Abs), aptamers, proteins, whole cells, and nucleic acids. The function of these bioreceptors is to selectively recognize the analyte in complex matrices, avoiding potential interferences (Viswanathan, Radecka, & Radecki, 2009). The first biosensor relied on the use of enzymes that convert a reactant molecule into products. Clark and Lyons first proposed the initial concept of glucose enzyme electrodes in 1962, using glucose oxidase (GOx) (Clark & Lyons, 1962). Another example is present in immune systems in which antigens interact with Abs. By this specific interaction, Abs and antigens can be exploited as means for diagnostic testing. Some types of Abs can be developed as polyclonal Abs, monoclonal Abs, recombinant Abs, and

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single-domain Abs, also known as nanobodies. Nanobodies can be obtained by recombinant technologies to isolate the variable region or from a particular family of camelids (e.g., dromedaries, llamas, alpacas), or produced by bacteria. The latter ones have become a good alternative to monoclonal Abs, due to their different characteristics, such as lower cost, renaturation, high solubility, stability, and resistance (Campuzano et al., 2014). Enzymes immunoassays, where the Abs are labeled with enzymes, for example, horseradish peroxidase (HRP), alkaline phosphatase (ALP), or GOx, are the most commonly used in electrochemical and optical detection schemes, offering several potential advantages in clinical, medical, biotechnological, food, and environmental applications. The most common configuration is the enzyme-linked immunosorbent assay (ELISA), where one of the species (Ab or antigen) is immobilized onto a solid support and makes use of an enzyme as a tracer of changes provoked in the antigen
Ab complex. One good advantage of employing an enzyme as the tracer is the possibility of amplifying the signal (Lequin, 2005). In the last years, the ELISA test has found applications in the food industry for detecting potential food allergens because of the flexibility in format assay (competitive, sandwich or direct) and its suitability for high-throughput and multianalyte detection (Van Hengel, 2007). The recognition of DNA sequences is essential to control and detect molecular structures. The use of single DNA/RNA chains or synthetic oligonucleotides, called aptamers, is a highly interesting approach. DNA biosensors employ DNA probes for selective molecular recognition, which is subsequently transformed into a signal using the transducer. Aptamers are small chain (40
100 bases) synthetic oligonucleotides that can specifically recognize and bind to ions, whole cells, toxins, peptides, or proteins (Song, Wang, Li, Fan, & Zhao, 2008). Aptamer-based detection methods have attracted significant interest because of their high selectivity and affinity toward their biorecognition elements in biosensor applications. Moreover, aptamers have higher chemical and thermal stability, less variability, and lower cost compared to Abs, and highly reproducible binding features (Lian, He, Wang, & Tong, 2015). Other classes are cell-based biosensors, which combine living cells and sensors or transducers for cellular physiological parameter detection, pharmaceutical analysis, and environmental toxicity tests. They are characterized by a rapid response, excellent selectivity, and sensitive analysis for in situ monitoring with cells; but the common problem of how to prolong the cells’ lifetime still remains as the main challenge (Liu et al., 2014; Wang et al., 2005).

11.3.1 Surface functionalization of nanomaterials with bioreceptors The choice of immobilization technique must promote a stable bond between transductor and the bioreceptor, without interfering with the biological activity of the system. Moreover, high sensitivity can be met by guaranteeing a high density of active biological recognition elements on the sensing surface. Thus the crucial step

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for obtaining an optimal sensor is the immobilization of biomolecules (Tedeschi, Domenici, Ahluwalia, Baldini, & Mencaglia, 2003). Preliminary techniques to develop biosensors involve the entrapment of a biomolecule onto membranes or the electrochemical cross-linking of a polymer in the presence of an enzyme. The entrapment of the biomolecule behind a membrane has proven to be a simple and rapid process, which only requires a direct contact between the two units. Usually, it is used for the immobilization of living cells or the cross-linking of enzymes or proteins. In general, entrapment and adsorption immobilization methods typically perturb the enzyme much less than chemical immobilization and consequently offers retention of the enzyme properties resembling those in solution (Bailey & Ollis, 1976). Even so, the choice of semipermeable membrane or the best polymer may have a significant effect on the sensitivity and background of the resulting signal (Scouten, Luong, & Brown, 1995). In general, chemical immobilization methods (biomolecule attachment onto the matrix by covalent bonds, cross-linking between biomolecule and matrix, and biomolecule cross-linking by multifunctional reagents) tend to reduce the activity of the biomolecule, since the covalent bonds may perturb the biomolecule’s native structure. Yet, such covalent linkages provide a strong stable biomolecular attachment. Usually, a long-term immobilized biomolecule with a lower initial activity is preferable to that of a high level of initial activity but with short-term retention of activity (Dura´n, Rosa, D’annibale, & Gianfreda, 2002). In recent years, electrode modification with nanomaterials, such as metal NPs or carbon materials, has become a convenient approach to increase the overall performance of nanobiosensors. For example, they can be used for enzyme immobilization and further improve electron transfer between the redox center of the enzyme, decreasing the response times and leading to a higher sensitivity (Kumar & Alexis, 2019; Kumar, 2007). Colloidal solutions of metal and semiconductor NPs can act here as small conduction centers on electrodes that adsorb redox enzymes, facilitating the transfer of electrons without any loss of biological activity (Biju, 2014). There are four basic methods of biomolecular immobilization: physical or chemical adsorption, SAMs, and comodification with an electrode component matrix. Physical adsorption consists of reducing the metal NPs with a negatively charged ligand (citrate). As enzymes contain positively charged amino acid residues, electrostatic interaction with a negatively charged surface allows for their immobilization by immersing the modified electrode in solution. This method is fast and simple, but the orientation is probably aleatory (Hanefeld, Gardossi, & Magner, 2009). On the other hand, chemisorption is achieved between the 2 SH groups of cysteine residues that can form covalent bonds with the gold surface. Brogan et al. demonstrated that fragments of Ab (F(Ab0 )) can be directly immobilized onto Au via Au-SH-FAb bonding to produce immunosurfaces that have higher antigenbinding amounts than surfaces produced by nonspecific random adsorption (Brogan, Wolfe, Jones, & Schoenfisch, 2003). SAMs is a simple method for the controlled immobilization of AuNPs and enzymes onto electrodes; AuNPs can be easily modified with surface functional groups (2NH2, or 2 SH) that provide the functional groups for subsequent covalent immobilization of the enzyme. Yang

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et al. utilized SAM-modified electrodes to immobilize GOx (Yang, Wang, Zhao, Sun, & Sun, 2006). The last strategy is the coimmobilization of AuNPs and enzyme into a composite material. Moreno-Guzma´n et al. prepared a nanocomposite electrode material constituted of AuNPs, MWCNTs, and n-octylpyridinium hexafluorophosphate ionic liquid for the determination of cortisol and androsterone hormones (Moreno-Guzma´n et al., 2013). Immobilization of biomolecules on carbon materials has been carried out by physical adsorption, cross-linking, covalence, and embedding. Physically adsorption of enzymes onto carbon nanomaterials depends on critical variables such as temperature, ionic strength, pH, and substrate concentration. Moreover, the adhesion strength between enzyme and electrode substrate surface is fragile, hence the average lifetime of the electrode is shorter. For addressing this issue, some new methods have been developed such as enzyme incorporation into a nanocomposite material (Carralero et al., 2007; Tsai & Tsai, 2009). Chemical cross-linking involving covalent attachment via a linker molecule (e.g., glutaraldehyde) results in a much stronger attachment than physical adsorption with higher enzymatic activity (Carpani, Scavetta, & Tonelli, 2008). Embedding usually involves the ends, sidewalls, or defects which result from the oxidative acid pretreatment of carbon materials and are rich in bound carboxylic groups. The covalent bond is produced between 2 NH2 groups of the biomolecules and 2 COOH groups of the carbon nanomaterials. These links are typically based on carboxylate chemistry via amidation and esterification (Ojeda et al., 2014).

11.4

Transduction mechanisms

As specified in Table 11.1, there is a myriad of biosensors relying on different transduction mechanisms. The most commonly used are electrochemical biosensors, in which the electroactive analyte is oxidized or reduced on the working electrode surface (transducer) and the electron fluxes lead to the generation of a signal. Electrochemical methods are classified in potentiometric, coulometric, voltammetric, and impedimetric biosensors (Wang, 2006a). Each technique has its own characteristics, and each is used according to the analyte, methodology, and sample. Amperometric biosensors exhibit good sensitivity with excellent linear ranges, and also have successfully commercialized devices. Furthermore, the electrochemical biosensors have advantages such as low cost, simple operation, and a small size; they are disposable and incorporate multiple sensing elements in a single chip-like device. These advantages are possible due to the characteristics of the nanomaterials used to modify the transducer (Pe´rez-Lo´pez & Merkoc¸i, 2011). Moreover, that inherent miniaturization property can become a good partner for microfluidic and lab-on-a-chip systems (Escarpa, 2014). The introduction of nanomaterials into electrochemical biosensors conveys advantages such as decreases overpotentials of important electrochemical reactions, guarantees the reversibility of some redox reactions, or gets new labeling opportunities including multidetection capabilities

(Wang, 2006b). All these features make electroanalysis an ideal tool for food quality and food safety analysis. Fluorescence is another physical process used for designing sensors (Jodra et al., 2015). Optical techniques for pathogen detections are fluorescence, surface plasmon resonance (SPR), colorimetry, among others. These techniques monitor the changes of optical signal that occur between a functionalized nanomaterial and a pathogen, toxin, or bacteria (Homola et al., 2002; Kumar, 2007). SPR is the basis of many standard tools for measuring adsorption of material onto planar metal (typically gold or silver) surfaces or onto the surface of metal NPs. Because a SPR sensor records the shift of resonant wavelength as a function of time, it can be used to quantify the amount of captured analyte. The SPR can be scaled up to detect many analytes simultaneously and has the advantage of providing real-time and label-free detections for direct and continuous monitoring of bioanalytes (Taylor et al., 2006). Fluorescent approaches are also attractive for a myriad of biosensing applications. Certain nanomaterials (such as carbon nanomaterials) can play an important role in the development of nanobiosensors, because they act as active quenching elements. Nanomaterials such as metallic NPs and QDs have very good optical properties, allowing low levels of detection and reduced interference of other compounds in complex samples. QDs have proven to be excellent optical labels for improving the sensitivity of optical transducer surfaces of biosensors (Frasco & Chaniotakis, 2009; Pe´rez-Lo´pez & Merkoc¸i, 2011).

11.5

Electrochemical nanobiosensors for food safety and control

As excellent reviews have covered the past progress in the field of electrochemical nanobiosensors (Cosnier, 1999; Pumera, Sa´nchez, Ichinose, & Tang, 2007; Ronkainen, Halsall, & Heineman, 2010; Windmiller & Wang, 2013; Zhang, Geryak, Geldmeier, Kim, & Tsukruk, 2017), herein we will only present selected examples, from modern electrochemical biosensors, integrating state-of-the-art nanostructures to field-effect transistors (FET) biosensors. Table 11.2 summarizes the main characteristics of different types of electrochemical biosensors for food analysis, in terms of nanomaterial used, bioreceptors (if any), and analytical characteristic.

11.5.1 Electrochemical biosensing with integrated nanomaterials and hybrid nanostructures 11.5.1.1 Metallic nanoparticles Metal NPs offer considerable promise for enhanced electrochemical detection. In nanobiosensors, they can act as platforms for enhanced bioreceptor immobilization or as tags to the indirect monitoring of a target analyte via electrochemical

Table 11.2 Summary of electrochemical nanobiosensors for food analysis. Nanomaterial

Bioreceptor

Analyte

Detection

LOD

References

Staphylococcal Enterotoxin B Pseudomonas aeruginosa endotoxin Ochratoxin A

DPV

0.21 fM

DPV

0.51 3 10210 μg/ mL

Mousavi Nodoushan et al. (2019) Chen et al. (2019)

DPV

0.5 pg/mL

Wang et al. (2019)

Malathion Histamine Tyramine Staphylococcus aureus

DPV CV Amperometry ASV

0.5 ng/L 1.25 pg/mL 0.71 μM 1.0 cfu/mL

Nanomaterials and hybrid nanostructures Au nanourchins/GO

Aptamer

AuNPs/Fc/liposome




AuNPs AuNPs AuNPs AuNPs AgNPs

AptamerDNA Aptamer Antibody Enzyme Aptamer

Iridium oxide nanoparticles CdS QDs SnO2-SiC and AuNPs rGO


Antibody Antibody Aptamer

Ochratoxin A Sulfonamide antibiotic Acrylamide Salmonella enterica

ASV ASV CV DPV

5.7 ng/kg 0.11 μg/kg 46 ng/kg 101 cfu/mL

rGO/MWCNTs

Aptamer

EIS

25 cfu/mL

rGO

Enzyme

Amperometry

rGO/polypyrrole/pyrrolepropylic acid nanocomposite MWCNTs/polypyrrole/AuNPs

Antibody

Salmonella ATCC 50761 Sterigmatocystin/ Aflatoxin B1 Aflatoxin B1

Xu et al. (2019) Dong et al. (2017) da Silva et al. (2019) Abbaspour et al. (2015) Rivas et al. (2015) Valera et al. (2013) Wu et al. (2019) Muniandy et al. (2017) Jia et al. (2015)

EIS

2.3 3 1029 mol/ L 10 fg/mL

Diaz Nieto et al. (2019) Wang et al. (2015)

CV

30 cfu/mL

Guner et al. (2017)

Antibody

Escherichia coli O157:H7

MWCNTs MoS2/AuNPs

Antibody Antibody

Aflatoxin B1 Monosodium glutamate

EIS CV

0.03 ng/mL 0.03 μM

Yu et al. (2015) Devi et al. (2019)

Alumina Alumina

Antibody Antibody

CV EIS

22 cfu/mL 102 cfu/mL

Cheng et al. (2011) Tian et al. (2016)

Alumina Alumina/magnetic nanoparticles

Antibody Antibody

E. coli E. coli O157:H7 S. aureus E. coli O157:H7 Histamine

EIS EIS

84 cfu/mL 3 nM

Joung et al. (2013) Ye et al. (2016)

Antibody Antibody

Plum pox virus Iron

Conductivity Conductivity

180 pg/mL 0.05 ng/mL

Berto et al. (2019) Camara-Martos et al. (2016)

Nanopore membranes

Field-effect transistors Gold Single-walled carbon nanotubes

ASV, Anodic square wave voltammetry; cfu, colony-forming unit; CV, cyclic voltammetry; DPV, differential pulse voltammetry; EIS, electronic impedance spectroscopy; LOD, limit of detection.

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detection. Among them, AuNPs are promising nanostructure reporters for performing electrochemical biomolecular detection. For example, a screen-printed electrode (SPE) modified with rGO and gold nanourchins has been used as platform for the immobilization of a single-stranded DNA probe (ssDNA) for the specific detection of Staphylococcal enterotoxin B in milk, meat, and serum samples (Mousavi Nodoushan, Nasirizadeh, Amani, Halabian, & Imani Fooladi, 2019). Specific detachment of the aptamer probe upon the presence of analyte results in a decrease in the peak current of differential pulse voltammetry (DPV) in a concentrationdependent manner. A wide linear range from 5.0 to 500.0 fM was achieved, with a detection limit of 0.21 fM. The authors demonstrated the superior performance of the aptasensor over a commercial ELISA kit. Chen et al. have recently reported on a three-dimensional AuNPs/ferrocene/liposome cluster multifunctional probe (GFLC) for molecular recognition, signal amplification, and output. The nanosensor/nanoprobe was applied in the electrochemical sensing of Pseudomonas aeruginosa endotoxin (lipopolysaccharide) in soft drinks. Multifunctional GFLC can be linked onto a phenylboronic acid (PBA)-modified electrode. Under the presence of galactose oxidase, specific oxidation of 60 -OH in galactose residue of the endotoxin into the corresponding aldehyde group results in the generation of dihydroxyl groups positioned in the cis-form, which coordinate with the boronic acid group of PBA to generate membered ring esters, thus triggering the capture of the target under acidic conditions. In the absence of endotoxin, no binding occurs, resulting in a drastic decrease in the peak current (Chen et al., 2019). Aptamer-conjugated AgNPs have been used for Staphylococcus aureus detection. The strategy relies on the immobilization of a biotinylated primary anti-S. aureus aptamer on streptavidincoated MBs, followed by bacterial capture. Next, a secondary anti-S. aureus aptamer was conjugated to silver NPs (Apt-AgNP) that sensitively reports the detection of target. In the presence of the target bacterium, a sandwich complex is formed, and the electrochemical signal of AgNPs is followed through anodic stripping voltammetry (ASV). Good performance was observed for the determination of such bacteria in water samples, with a detection limit of 1.0 cfu/mL (Abbaspour, Norouz-Sarvestani, Noori, & Soltani, 2015). Ochratoxin A (OTA) is an important food contaminant derived from fungi. Recently, a hairpin aptamer (HA) was used as the OTA recognition element for immobilization into a gold electrode. AuNPs labeled double report DNA were symmetrically hybridized with HA simultaneously. The DPV response of AuNPs was significantly amplified via multiple signal amplification strategy. In the presence of OTA, specific detachment of the double report DNA results in a decrease in the electrochemical response. Linear ranges from 1 pg/mL to 1 ng/mL were achieved (Wang et al., 2019). Excellent detection limits were also achieved with an iridium oxide nanoparticle-based aptasensor for OTA detection (14 pM; 5.7 ng/kg) in wine samples. In this case, detection was carried out by electrochemical impedance spectroscopy (Rivas et al., 2015). For more details, see Fig. 11.2A. Pesticide control in foodstuffs is also essential to protect consumers from serious health effects. NPs offer a convenient approach for the amplification of electrochemical detection for ultrasensitive detection. For example, an AuNP-based

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427

Figure 11.2 Electrochemical (bio)sensors with integrated nanomaterials and hybrid nanostructures for food analysis. (A) Schematic illustration of the fabrication steps and working principle of an impedimetric aptasensor for OTA detection based on iridium oxide nanoparticles. Left, shows the Rct values for the selectivity of the impedimetric OTA aptasensor against ZEA for different toxin concentrations. (B) Schematic of the fabrication of an impedimetric Salmonella aptasensor using a GC electrode modified with a rGO and CNTs composite. Right, shows the Nyquist plots of the rGO-MWCNT-aptamer-modified electrode corresponding to different concentrations of Salmonella (from 1 to 6: 0, 7.5 3 101, 7.5 3 102, 7.5 3 103, 7.5 3 104, 7.5 3 105 cfu/mL) in 0.1 mol/L KCl solution containing 5 mmol/L K3[Fe(CN)6] and K4[Fe(CN)6]. Source: (A) Reprinted with permission from Rivas, L., Mayorga-Martinez, C. C., QuesadaGonzalez, D., Zamora-Galvez, A., De La Escosura-Muniz, A., & Merkoci, A. (2015). Labelfree impedimetric aptasensor for ochratoxin-A detection using iridium oxide nanoparticles. Analytical Chemistry, 87, 5167
5172. Copyright 2015 American Chemical Society. (B) Reprinted with permission from Jia, F., Duan, N., Wu, S., Dai, R., Wang, Z., & Li, X. (2015). Impedimetric Salmonella aptasensor using a glassy carbon electrode modified with an electrodeposited composite consisting of reduced graphene oxide and carbon nanotubes. Microchimica Acta, 183, 337
344. Copyright 2015 Springer.

immunosensor for chlorpyrifos detection exhibited a high sensitivity and stable response within the range of 1 fM to 1 μM with a detection limit up to 10 fM. The AuNPs greatly enhanced the electrical conductivity and overall response of the nanosensor for chlorpyrifos detection in apple, cabbage, and

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pomegranate samples (Talan et al., 2018). Recently, Xu et al. described a dualsignal aptasensor based on polydopamine-AuNPs and exonuclease I (Exo I) for malathion detection in cauliflower and cabbage. Specific interaction between malathion and its aptamer forced the aptamer to detach from the electrode surface and induced the capture probe to form a hairpin structure on the electrode surface. Both aptamers were previously labeled with ferrocene methanol (Fc) or thionine (Tn), allowing for dual-signal current readout in both the signal-on of Fc and the signaloff of Tn. A linear range from 0.5 to 600 ng/L was obtained (Xu et al., 2019). CdS QDs-mediated detection of sulfonamide antibiotic in honey samples is also a convenient approach for the control of such important pollutants. Capture probes consist of MBs functionalized with specific Abs labeled with CdS NPs. After the immunochemical reaction, CdS QDs were dissolved and the metal ions released are reduced at the electrode and measured by ASV. The use of MBs minimizes the matrix effect allowing a detectability (LOD) of 0.11 μg/kg to be reached (Valera, Muriano, Pividori, Sa´nchez-Baeza, & Marco, 2013). Biogenic amines can be present in food due to cooking or food spoilage during extended storage, reaching the food chain and causing toxic effects in human and animals. For example, acrylamide can be present in fried foods due to the Maillard reaction between reducing sugars and asparagine. Potential toxicity effects led to the development of several electrochemical biosensors (Asnaashari, Kenari, Farahmandfar, Abnous, & Taghdisi, 2019; Pundir, Yadav, & Chhillar, 2019). Thus SnO2-SiC hollow sphere nanochains and AuNPs were used as a platform on a GC electrode for the immobilization of acrylamide antigen. Polyclonal Ab specific for acrylamide was conjugated with gold (Au-Ab1) along with HRP-labeled secondary Ab (Au-HRP). Acrylamide present in the sample competed with coating antigen for binding with Au-Ab1. After washing, Au-HRP was added to capture the Au-Ab1, and the electrical signal was obtained by the addition of hydroquinone and hydrogen peroxide. Good sensitivity with a LOD of 46 ng/kg was achieved for food and water samples (Wu et al., 2019). Histamine is a biogenic amine associated with marine food poisoning, which is typically formed by decarboxylation of histidine by bacteria. The US Food and Drug Administration (FDA) has established a maximum allowable level of 50 mg/ kg for this contaminant. Higher levels can cause adverse health effects such as allergic reactions and serious disorders. NP-based electrochemical biosensors hold considerable promise as a convenient approach for histamine control in foodstuffs (Yadav, Nair, Sai, & Satija, 2019). A portable electrochemical immunosensor based on a film of Prussian blue chitosan-AuNPs on a SPE exhibited excellent analytical properties with a LOD of 1.25 pg/mL in fish samples. The detection relies on a typical competitive assay, where histamine antigen competes with free histamine to combine with the HRP-labeled histamine-Ab. Subsequently, the electrochemical signal is generated by introducing hydroquinone and hydrogen peroxide (Dong et al., 2017). Tyramine is one of the well-known biogenic amines produced by decarboxylation of the amino acid tyrosine, due to microbial activity, commonly found in fermented foods and beverages. Such compound acts as a sympathomimetic amine which releases norepinephrine from sympathetic amine nerve endings,

Nanobiosensors for food analysis

429

thus it can cause serious intoxication effects when ingested in large quantities. Immobilization of tyrosinase on an AuNP-modified GC electrode is a convenient approach for the detection of tyramine in dairy products and fermented drinks with the LOD of 0.71 μM (da Silva, Ghica, Ajayi, Iwuoha, & Brett, 2019).

11.5.1.2 Carbon and semiconductor nanomaterials Because of their better electron transfer, carbon nanomaterials have been extensively used in electrochemical detection (Vasilescu, Hayat, Ga´spa´r, & Marty, 2018; Wen et al., 2018). In nanobiosensors, their main role is to increase the active surface area of sensors for the immobilization of higher loading of capture probes, further enhancing the electrochemical signal. rGO has emerged as a promising nanomaterial for reliable detection of pathogenic bacteria due to its exceptional electron transfer ability and large surface to volume ratio, among other properties. Thus a rGO
azophloxine nanocomposite aptasensor has been developed for Salmonella enterica serovar detection in chicken. A linear range of detection from 108 to 101 cfu/mL and a LOD of 101 cfu/mL were obtained (Muniandy et al., 2017). Similarly, a Salmonella ATCC 50761 impedance biosensor has been constructed by electrochemical immobilization of rGO/carboxy-modified MWCNT composites on the surface of a GC electrode, followed by covalent attachment of a specific aptamer (see Fig. 11.2B). The method was applied to the analysis of chicken samples (Jia et al., 2015). An electrochemical immunosensor based on a polypyrrole/AuNPs/MWCNT composite modified with anti-E. coli O157:H7 monoclonal Ab was used for the detection of such biothreat in food samples. A linear range from 3 3 101 to 3 3 107 cfu/mL was obtained (Guner, Cevik, Senel, & Alpsoy, 2017). GO represents also a promising material for mycotoxin detection. For example, a GC electrode modified with a composite of soybean peroxidase enzyme and rGO has been used as an early warning system to detect aflatoxin B1 (AFB1). The biosensor relies on the amperometric detection of sterigmatocystin in corn samples inoculated with Aspergillus flavus fungus, which is an aflatoxin producer. Considering that sterigmatocystin is a precursor of AFB1, its decrease over time was related to the production of such toxin (Diaz Nieto et al., 2019). Direct detection has been performed by using a rGO/polypyrrole/pyrrolepropylic acid nanocomposite modified with a specific Ab, within the range of 10 fg/mL to 10 pg/mL (Wang, Hu, Xiong, Xu, & Ming Li, 2015). Apart from rGO, MWCNTs have been used as a convenient platform for the immobilization of specific Abs in the impedimetric detection of AFB1 in olive oil samples, with a LOD of 0.03 ng/mL. The presence of CNTs guarantees fast electron transfer for signal enhancement (Yu et al., 2015). Compared with the use of metallic NPs and carbon nanomaterials for the fabrication of electrochemical biosensors for food analysis, application of dichalcogenides for such purpose is still in its early infancy, with only a few but impressive reports described in the literature. For example, a MoS2@Au nanocomposite has been used to develop an amperometric immunosensor for the detection of monosodium

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glutamate. The nanocomposite was used as the conductive matrix and for antiglutamate-Ab immobilization. Limits of detection and quantification of 0.03 and 0.1 μM, respectively, were obtained in the determination of such preservative in canned soups (Devi et al., 2019). Very recently, a hybrid nanocomposite consisting of carbon black and molybdenum disulfide (MoS2) was applied to the detection of oleuropein and hydroxytyrosol in extra virgin olive oil with a detection limit of 0.1
1 μM, respectively. The incorporation of MoS2 prevents biofouling for enhanced electrochemical detection (Rojas et al., 2019).

11.5.2 Electrochemical biosensing with nanopore membranes Nanopore membranes can be combined with electrolyte cells, and then the passage of biomolecules in solution can be induced through the hole by applying a biased voltage across the membrane. Further impedance monitoring allows detection to be performed by monitoring the dwell time of the biotarget in the hole. These membranes are based on nanomaterials such as silicon nanowires, boron nitride, MoS2, or graphene structures. Yet, most of the nanopore membrane-based biosensors have been applied for the detection of clinical biomarkers, with only a few studies reported on food analysis (Lemay, 2009; Kant, Yu, Priest, Shapter, & Losic, 2014). Label-free electrochemical detection of E. coli cells has been achieved with a nanoporous alumina membrane
modified electrode. The sensing mechanism relies on the blocking of nanochannels upon the formation of immune complexes at the nanoporous membrane. The resulting obstacle to diffusive mass transfer of a redox probe in the analysis solution to the underlying platinum electrode reduces the Faradaic signal response of the biosensor, measured using cyclic voltammetry. The biosensor gives a low LOD of 22 cfu/mL and is specific toward E. coli with minimal cross-reactivity to two other staphylococci-type pathogenic bacteria (Cheng, Lau, Chow, & Toh, 2011). A schematic of the sensing principle is depicted in Fig. 11.3A. Similarly, a nonbiofouling polyethylene glycol
based microfluidic chip integrated with functionalized nanoporous alumina membrane has been applied for simultaneous electrochemical detection of E. coli O157:H7 and S. aureus with high specificity and low cross-binding of nontarget bacteria (Tian, Lyu, Shi, Tan, & Yang, 2016). Following a similar concept, the commercial nanopore alumina membrane was modified with hyaluronic acid and applied for the impedimetric detection of E. coli O157:H7 in whole milk with a LOD of 83.7 cfu/mL (Joung et al., 2013). Ye et al. developed an impedimetric biosensor based on a biofunctionalized nanoporous alumina membrane and 10 nm antihistamine Ab-modified MBs. Once in the membrane, MBs interact with the antihistamine Ab, resulting in blocking of the pores, which is further amplified due to a relatively large size of the MBs. The rate of impedance change is found to be linearly increased as a function of the logarithmic concentration of histamine in the range of 5 nM to 10 μM with a LOD value of 3 nM. The developed method was useful for histamine detection in fish samples (Ye et al., 2016).

Figure 11.3 (A) Nanoporous membrane-based biosensor for Escherichia coli detection and sensing principle. (B) MoS2-based FET biosensor device. The dielectric layer covering the MoS2 channel is functionalized with receptors for specifically capturing the target biomolecules. The charged biomolecules, after being captured, induce a gating effect, modulating the device current. Bottom, shows different optical images of the device. Source: (A) Reprinted with permission from Cheng, M. S., Lau, S. H., Chow, V. T., & Toh, C. S. (2011). Membrane-based electrochemical nanobiosensor for Escherichia coli detection and analysis of cells viability. Environmental Science & Technology, 45, 6453
6459. Copyright 2011 American Chemical Society. (B) Reprinted with permission from Sarkar, D., Liu, W., Xie, X., Anselmo, A. C., Mitragotri, S., & Banerjee, K. (2014). MoS2 field-effect transistor for next-generation label-free biosensors. ACS Nano, 8, 3992
4003. Copyright 2014 American Chemical Society.

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11.5.3 Field-effect transistor-based biosensors Biofunctionalized FETs exhibit high sensitivity and label-free detection features which along with rapid response promote them being widely explored as biomolecular sensing devices. Semiconducting nanostructures (Si nanowires, graphene, MoS2) are used to promote a gating effect by capturing charged target molecules using specific organic ligand receptors. Channel conductance change or tunneling current variation are used to monitor such changes. The field is still in its early infancy, yet FET is a very promising technology with potentially high sensitivity, low fabrication cost, and sophisticated multiplex capabilities, which is particularly attractive for food analysis (Shen, Li, & Li, 2014; Chen, Li, & Chen, 2011). A label-free FET biosensing system has been proposed for the detection of a buckwheat allergenic protein, by surfactant-induced signal amplification. The coupling with an anionic surfactant (sodium dodecyl sulfate) enhanced the net charge of protein, increasing the voltage and generating a shift which can be correlated with the analyte concentration. The successful operation of biosensors was demonstrated by the analysis of buckwheat, wheat, soy, and egg extracts (Hideshima et al., 2018). Also, a bioelectronic biosensor has been developed for early monitoring and control of plum pox virus (PPV), a pathogen responsible for Sharka disease affecting stone fruit trees. A gold gate electrode was functionalized with anti-PPV polyclonal Ab. Specific binding of the target virus produces a change in the drain current/transconductance which can be related to the concentration. The LOD was estimated to be 180 pg/mL, with a linear range from 5 ng/mL to 50 μg/mL (Berto et al., 2019). In a more realistic approach, Ca´mara-Martos et al. reported on FETs biosensors for iron(III) detection in wine. A CNT network acts as the conductor channel, whereas a transferrin Ab with two specific high-affinity iron(III) binding sites was used for the immunoreaction/capture (Camara-Martos et al., 2016). The unique properties of 2D nanomaterials (molybdenum disulfide) with such a high surface area and enhanced conductivity have been exploited to construct a FET biosensor, which offers extremely high sensitivity as a pH sensor and for specific proteins (from 196 even to 100 femtomolar concentration). A schematic of the sensor is depicted in Fig. 11.3B (Sarkar et al., 2014).

11.6

Optical nanobiosensors for food safety and control

An optical biosensor is a compact analytical device containing a biorecognition sensing element integrated with an optical transducer system, which relies on either infrared (IR), visible (VIS), or ultraviolet (UV) radiation (Farka, Juˇr´ık, Kova´rˇ, Trnkova´, & Skla´dal, 2017; Wang & Duncan, 2017; Zaera, 2012). They can be classified as a function of the nature of transduction mechanisms on which they are based, for instance, absorbance, scattering, diffraction, reflectance, refraction, and luminescence. Among the many optical detection methods, historically, fluorometric and colorimetric ones were the most used in combination with biosensors, mainly because of the high sensitivity in comparison to other optical methods, and

Nanobiosensors for food analysis

433

the ease to follow a color change with a naked-eye observation. However, more recently, localized SPR (LSPR) and surface-enhanced Raman scattering (SERS) have found to be very useful in the development of nanobiosensors. Table 11.3 summarizes the main characteristics of different types of optical nanobiosensors for food analysis.

11.6.1 Colorimetric biosensors In principle, colorimetric nanobiosensors present a change in color when an analyte is in contact with the recognition active site. Quantifying the color changes could be achieved by UV-Vis spectrophotometry, or in the case of substrate-based colorimetric assays, via digital photography and image analysis software (Wang & Duncan, 2017). Colorimetric nanobiosensors should contain an optical active site, which is responsible for the transduction of signal and a probe active site which leads to a suitable molecular recognition. In the case of biosensors, the modification of a biomolecule with a suitable chromophore is the typical construction employed (Li, Askim, & Suslick, 2018). Metal NPs present a specific intense absorption due to the collective movement of the conduction band electrons under excitation with electromagnetic radiation. These localized electron movements produce a high absorption and scattering in the UV-Vis region, which makes metal NPs perfect candidates for the colorimetric detections. For instance, Huang et al. developed a sensitive aptasensor to determine chloroamphenicol (CAP) in milk samples by colorimetric detection (Huang et al., 2019). The authors prepared the optical nanoprobe by functionalization of AuNPs with the complementary oligonucleotide against aptamer and high-content hemin/ G-quadruplex DNAzyme. The assay consisted of the incubation of nanoprobe and CAP at a constructed aptamer
MB biosensing platform; due to the competitive biorecognition reaction, the nanoprobes related to CAP amounts were quantitatively captured onto the MBs surface. Based on the catalytic reaction of peroxidasemimicking DNAzyme, a colored solution was produced. An excellent LOD (0.13 pg/mL), with high selectivity and specificity to CAP, was achieved. Ma et al. developed a novel colorimetric biosensor for the detection of Salmonella typhimurium by combining magnetic NPs with AuNPs (Ma, Song, Xia, Jiang, & Wang, 2017). Both sets of NPs were modified by capture (onto magnetic NPs) and probe DNA (onto AuNPs) which have a partially complementary sequence to the S. typhimurium DNA. A rapid enrichment of the target DNA to magnetic NPs was achieved. With the addition of S. typhimurium target DNA sequences, the sandwich-like structures were formed via the DNA hybridization recognition effect, yielding a change in the color due to changes in the AuNPs dispersion, which could be registered by a UV-Vis spectrometer. Mirkin et al. were the pioneers in the use of the colorimetric detection approach of polynucleotides by LSPR coupling between AuNPs (Elghanian, Storhoff, Mucic, Letsinger, & Mirkin, 1997) (this method will be explained in detail in Section 11.6.3), but new developments in this field have been achieved. Chen et al. developed a colorimetric biosensor to detect Hg21 (Chen et al., 2014) by using

Table 11.3 Summary of optical nanobiosensors for food analysis. Nanomaterial

Bioreceptor

Analyte

Optical detection

LOD

References

AuNPs and MNPs AuNPs and MNPs AuNPs

Aptamer

Chloroamphenicol

0.13 pg/mL

Partially complementary DNA sequence to the S. typhimurium Oligonucleotides

Salmonella typhimurium Hg21

AuNPs

Aptamer

Streptomycin

AuNPs

Aptamer

Chloramphenicol

AuNPs

DNA

miRNA-215

AgNPs




Sugar

Colorimetric (UV-vis) Colorimetric (UV-vis) Colorimetric (UV-vis) Colorimetric (UV-vis) Colorimetric (UV-vis) Naked-eye detection Colorimetric (UV-vis)

Ag2S QDs

Antibody

Cryptosporidium parvum

Near IR emission

10 oocysts/mL

AuNPs

Aptamer

Kanamycin

Fluorescence

321 pM

Fe3O4@SiO2 NPs

Antibody

Fluorescence

3 cfu/mL

CdTe QDs

Antibody

Escherichia coli O157:H7 Ochratoxin A

Fluorescence

0.05 pg/mL

AgNPs

Antibody

Ochratoxin A

Fluorescence

0.06 ng/mL

Huang et al. (2019) (Ma et al. (2017) Chen et al. (2014) Emrani et al. (2016) Abnous et al. (2016) Gao et al. (2014) Della Pelle et al. (2019) Srinivasan et al. (2014) Ramezani et al. (2016) Hu et al. (2016) Huang et al. (2016) Jiang et al. (2017)

0.8 pM 50 nM 73.1 nM 451 pM 60 pM


GQDs

Aptamer

Ochratoxin A

Fluorescence

13 pg/mL

Optical waveguide chip

Antibody

Fluorescence

AuNPs

Antibody

Aflatoxin M1 (AFM1) and Melanine Staphylococcal enterotoxin A

AFM 1 0.045 ng/mL Melanine 13.37 ng/ mL 5 ng/mL

MIP/Au nanodisks




Salivary mouth proteins

Colorimetric (LSPR)

1
140 μmol/L astringency range

AuNPs

Aptamer


Fiber optic functionalized AuNPs Au@AgNPs

Aptamer

S. typhimurium

Colorimetric (LSPR) Colorimetric (LSPR) Colorimetric (LSPR)

104 cfu/mL

AuNPs

Salmonella typhimurium Melamine

Aptamer

Chloramphenicol

SERS

0.19 pg/mL

Aptamer

Aflatoxin B1

SERS

0.4 fg/mL

Antibody

Amantadine

SERS

0.005 ng/mL

Aptamer

Microcystin-LR

SERS

0.002 ng/mL

Antibody

E. coli O157:H7

SERS

10 cfu/mL

AuNPs/Au nanodisks Au nanoflowers (NFs) AuNPs AuNPs/magnetic NPs

Colorimetric (LSPR)

33 nM 128 cfu/mL

Wang et al. (2017) Guo et al. (2016) Ben Haddada et al. (2017) Guerreiro et al. (2017) Oh et al. (2017) Mishra et al. (2017) Xu et al. (2018) Yan et al. (2016) Li et al. (2017) Ma et al. (2018) He et al. (2019) Cho et al. (2015)

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thymine
Hg21
thymine interaction. AuNPs modified by oligonucleotide sequences bind to Hg21 ions, resulting in a strong aggregation of AuNPs, with the subsequent color change. In another representative example, streptomycin was detected by using a colorimetric aptasensor through dsDNA and AuNPs combination. At the beginning, a dye-labeled complementary strand dsDNA remains stable when streptomycin is absent, leading to the aggregation of AuNPs by addition of NaCl and provoking a change in the color of solution from red to blue. As streptomycin is added, the aptamer binds to streptomycin and the dye-labeled complementary strand leaves the aptamer and adsorbs on the surface of AuNPs. This adsorption promotes well-dispersed AuNPs, resulting in a red color. This method allows the detection of streptomycin with a LOD of 73.1 nM (Emrani et al., 2016). Abnous and coworkers developed a colorimetric sandwich aptasensor for sensitive and selective detection of CAP, based on an indirect competitive enzyme-free assay using AuNPs, biotin, and streptavidin. When no CAP is added, a sandwich structure of aptasensor is formed, leading to the observation of a sharp red color. In contrast, when the target is present, functionalized AuNPs cannot bind properly, resulting in a pale red color. A limit of detection as low as 451 pM can be obtained with the constructed optical-based aptasensor (Abnous, Danesh, Ramezani, Emrani, & Taghdisi, 2016). Another interesting approach consists of the modification of AuNPs with a DNA residue to be used in a lateral flow nucleic acid biosensor for visual detection. This interesting application allows users with almost no experience to carry out a simple and fast analysis with high accuracy and reproducibility. Gao and coworkers developed a DNA-AuNPs-based lateral flow nucleic acid biosensor for visual detection of microRNA in biological samples. The operation principle is based on the sandwich-type hybridization reaction between an AuNPs-labeled DNA probe and the miRNA-215. Thus the accumulation of AuNPs on the test zone of the device enables the visual detection of miRNA-215 by a colored band in the lateral flow device. The biosensor designed in this way was able to detect concentration as low as 60 pM of miRNA-215 (Gao et al., 2014). More recently, Della Pelle et al. designed a colorimetric strategy for the determination of sugar content in food samples. Since sugar molecules form AgNPs reducing Ag1 and stabilizing the suspension, this feature is used to detect different types of sugar by the movement in plasmonic band (B430 nm) of AgNPs. In this way, a colorimetric detection is carried out. The AgNPs-based method was applied to the determination of sugars content in soft drinks and apple extracts with high reproducibility (RSD # 9.4%) and good recovery values (from 86.1% to 117.7%) (Della Pelle, Scroccarello, Scarano, & Compagnone, 2019).

11.6.2 Fluorescent biosensors Fluorescence is one of the most sensitive techniques in analysis (Chen, Song, Xiong, & Peng, 2013) and its combination with biosensors increases and improves significantly its applications in different fields, particularly in food analysis (Nishi, Isobe, Zhu, & Kiyama, 2015). For instance, the reduced form of NADH is

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fluorescent, while the oxidized form (NAD1), does not present any fluorescent behavior. This is an advantage because all the reactions based on NAD1/NADH could be incorporated with fluorescence-based biosensors (Sharma et al., 2018). On the other hand, most of the analytes used in moiety biorecognition are nonfluorescent. Fluorescein and rhodamine were the first organic dyes used for fluorescent labeling. Additionally, QDs (Anfossi et al., 2018; Lu, Chen, & Hu, 2017), upconverting NPs (Au and AgNPs) (Wu et al., 2012), and organic polymer NPs comprise good fluorophore nanomaterials that are highly used in the construction of fluorescent biosensors (Rhouati et al., 2016). Ramezani et al. detected kanamycin in real samples using a fluorescent biosensor based on catalytic recycling activity of exonuclease III (Exo III), AuNPs, and FAM-labeled complimentary strand of aptamer (CS) (Ramezani, Danesh, Lavaee, Abnous, & Taghdisi, 2016). In this work, the aptamer was bound to CS to form a dsDNA, leaving the surface of AuNPs in the presence of kanamycin. When adding Exo III, the aptamer was recycled from dsDNA, increasing the intensity of fluorescence in the solution. Upon addition of kanamycin, aptamer was bound to the target and CS remained on the surface of AuNPs, leading to a weak fluorescence emission. Using this method, kanamycin was successfully determined in milk and serum samples with a LOD calculated to be as low as 321 pM. Silica shell-protected Ag2S QDs (45 nm in thickness) provides a label emitting in the IR region (896 nm) (Srinivasan, Thiruppathiraja, Subramanian, & Dinakaran, 2014). This allowed a sensitive sandwich assay of Cryptosporidium parvum. The C. parvum Ab antioocysts-immobilized Ag2S@silica NPs were used as detector probes and these biosensors exhibited excellent analytical performance toward the detection of C. parvum with LOD of 10 oocysts/mL. Fluorescein-loaded porous silica NPs served as a label in a sandwich assay for the pathogenic strain of E. coli (Hu et al., 2016). Well-synthesized fluorescein-enriched hollow silica nanospheres were functionalized as immune labels of E. coli O157:H7 for a sandwich-type immune reaction between this bacterium and magnetic NPs (Fe3O4@SiO2). The E. coli O157:H7 cells were captured, magnetically separated, and quantified based on the fluorescence intensity of the fluorescein released from (bio)labels of the fluorescein-enriched hollow silica nanospheres. This analytic process can be achieved with a detection limit of 3 cfu/mL. Huang et al. carried out the ultrasensitive detection of OTA by using hydrogen peroxide-induced fluorescence quenching of mercaptopropionic acid-modified CdTe QDs. The fluorescence of CdTe modified with the capture Ab was quenched by the presence of hydrogen peroxide. The competitive assay format for OTA used the tracer based on an OTA 2 catalase conjugate. Thus in the absence of OTA, the bound catalase decomposed the hydrogen peroxide, and the fluorescence was recovered. The achieved LOD of 0.05 pg/mL was 300 3 lower compared with that of a conventional ELISA technique with HRP as the label (Huang et al., 2016). More recently, Jiang and coworkers used AgNPs-based fluorescence-quenching lateral flow immunoassay with competitive format (cLFIA) to determine OTA levels in commercial beverages. The reliability of the cLFIA method was evaluated through analysis of OTA-spiked red grape wine and juice samples. The cLFIA platform

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exhibited a LOD of 0.06 ng/mL OTA in wine (Jiang et al., 2017). OTA has also been determined using aptasensor constructions. In a recent work, Wang et al. reported the development of a new high-sensitivity fluorescent aptasensor for the detection of OTA based on tuning aggregation/disaggregation behavior of GQDs by structure-switching aptamers (Wang, Zhang, Pang, Zhang, & Guo, 2017). At the beginning the fluorescence is quenched by aggregation of GQDs. When the OTA is added, GQDs suffer a disaggregation due to the combination of OTA with the GQDs
aptamer complex, and thus the fluorescence reappears. In this way, the amount of OTA is proportional to the fluorescence intensity presented in the assay. This new fluorescent sensing system can be used to measure and monitor OTA levels with a very low LOD of 13 pg/mL. Guo et al. implemented an indirect competitive immunoassay through multiplex planar waveguide fluorescence immunosensor (MPWFI) for rapid, sensitive, and simultaneous quantification of AFM1 and melamine in milk samples. By applying the principle of immunoreaction and total internal reflect fluorescent, determination of AFM1 and melamine was achieved with a LOD of 0.045 and 13.37 ng/mL respectively, providing the determination of AFM1 with no significant interference of melamine in milk samples (Guo et al., 2016). A Fo¨rster resonance energy transfer (FRET)-based method has been developed using an aptasensor for detection of AFB1 in food samples. Aptamer-conjugated QDs are adsorbed onto AuNPs due to the interaction of aptamers with AuNPs yielding a quenching in the fluorescence of QDs. Upon the addition of target (AFB1), the aptamers bind to AFB1, delivering the AuNPs which result in fluorescence recovery. Using this method, AFB1 was determined with a LOD of 3.4 nM and within a linear range of 10
400 nM (Sabet, Hosseini, Khabbaz, Dadmehr, & Ganjali, 2017).

11.6.3 Localized surface plasmon resonance-based biosensors LSPR occurs when the conduction electrons in metallic surface/nanostructures move in a collective oscillation in the conduction band (Jones, Osberg, Macfarlane, Langille, & Mirkin, 2011). As a consequence, the surface of metal absorbs in the UV-Vis range, leading to a characteristic SPR spectrum. Both the intensity and position of SPR strongly depend on the size, shape, and composition of the surface/ nanostructures, as well as the dielectric properties of the surrounding environment (Ghosh & Pal, 2007; Ringe et al., 2012). As can be inferred, this property is useful for the colorimetric detection of an analyte in conjunction with a nanobiosensor platform. Depending on the metallic surface, plasmon resonance can be classified as a surface plasmon polariton (SPP), which will only exist at a metallic thin-layer surface, leading to the propagation of charge waves; and LSPR which relies on the electron oscillation that takes place in discrete nanostructures, in general smaller than the incident wavelength (Li, Cushing, & Wu, 2015). The former is the most commonly used in nanobiosensors platforms. When using the LSPR as colorimetric probes, two types of plasmonic sensors can be developed: (1) the LSPR peak wavelength shifts when an analyte binds to the surface of metal plasmonic NPs, changing the

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local refractive index (Homola, 2003); and (2) in the presence of a certain analyte, the plasmonic fields of multiple NPs are coupled, provoking a change in the color registered, as a consequence of a shift in the LSPR. In this sense, AuNPs are the most commonly used due to the chemical stability, biocompatibility, and the ease by which color changes can be visualized by naked-eye observation. If those features are combined with biological recognition moieties, such as, aptamers, ssDNA, Abs, and enzymes, the detection capability is highly enhanced due to the specificity that such biomolecules bring. According to these principles, Hosseini (2015) used a chemiluminescence (CL) method based on aptamers-conjugated AuNPs to detect AFB1. In this case, a color change is provoked by the aggregation of AuNPs induced by desorption of the AFB1 binding aptamer from the surface of AuNPs as a result of the aptamer target interaction, leading to the apparent color change of the solution. A LOD as low as 0.5 nM was obtained, as well as high detection sensitivity, which was increased by employing CL and using the catalytic activity of aggregated AuNPs, during a luminol-hydrogen peroxide reaction. Ben Haddada and coworkers designed a stable AuNPs bioconjugated for the detection of Staphylococcal Enterotoxin A (SEA) using LSPR as a transduction mechanism. The AuNPs bioconjugates were prepared by covalently attaching anti-SEA Ab by reacting Traut’s reagent with lysine residues to generate thiol groups that bound to gold atoms on the AuNPs surface. The measurement relies on the binding between the anti-SEA modified AuNPs and SEA antigen with the consequent changes in the color of colloidal solution. This color change is directly related to the SEA concentration, with a LOD of 5 ng/mL in milk samples (Ben Haddada et al., 2017). Guerreiro and coworkers developed conjugated molecular-imprinted polymer (MIP)-Au nanodisks to determine wine astringency in saliva samples. In an attempt to simulate the wine astringency inside the mouth by mimicking this sensorial system, they developed a sensing platform consisting of LSPR combined with surface MIP, which was then used to monitor polyphenol interactions with salivary proteins and further astringency estimation. The LSPR/MIP sensor provided a linear response for astringency expressed in pentagalloyl glucose units in concentrations ranging from 1 to 140 μmol/L (Guerreiro, Teixeira, De Freitas, Sales, & Sutherland, 2017). The sensor was also applied to wine samples, correlating well with sensorial analysis obtained by a trained panel. Oh et al. developed a plasmonic sensor using an aptamer-modified AuNPs monolayer device to detect and quantify S. typhimurium in pork meat. The AuNPs (average diameter of 20 nm) were deposited uniformly on a transparent glass substrate and the developed AuNPs-based plasmonicactive sensing chips were then conjugated successfully with aptamers by a simple dipping adsorption method. By specific interaction of the S. typhimurium with the aptamer-modified NPs, a color appearance was registered, which allowed the detection of the foodborne pathogen. The functionalized LSPR sensing device exhibited high sensitivity and excellent selectivity, even in the presence of different background microorganisms. The developed chip also produced a quantitative detection of Salmonella with an upper detection limit of 104 cfu/mL in pure culture, as well as in artificially contaminated pork meat samples (Oh et al., 2017). For more details, see Fig. 11.4A. Mishra and collaborators achieved the detection of

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melamine in liquid milk samples by using the LSPR of unmodified AuNPs. The biosensing system was designed by direct interaction of melamine with the AuNPs, provoking a color change, from wine-red to blue, by the NPs aggregation effect. The biosensing device constructed with optical fibers was found to be low cost, simple, and well-proven for the detection of melamine. Under the optimized conditions, the detection response of LSPR biosensing system was found to be linear in melamine detection in the concentration range from 0 to 0.9 μM with a LOD of 33 nM (Mishra et al., 2017). The fiber optic probe-based localized SPR biosensor (FOLSPR) has been found to be a very useful for developing nanobiosensing platforms. This method was first introduced by Jeong et al. with successful results (Jeong et al., 2013). Recently Xu et al. used a similar construction to design a Ω-shaped FOLSPR for the detection of S. typhimurium in chicken samples (Xu et al., 2018). The Ω-shaped fiber optic device exhibits a high sensitivity because of the unique geometry employed. The functioning principle of the biosensor relies on the immobilization of aptamers on the surface of the FOLSPR platform. The aptamer could specifically capture S. typhimurium resulting in an intense change in the absorption peak. The designed FOLSPR biosensor achieved a high detection sensitivity for S. typhimurium with a

Figure 11.4 (A) Detection of Salmonella typhimurium in pork using the aptamer-based LSPR sensing chip. (a) Pork extract. (b) Dipping the LSPR sensing chip in the pork extract. (c) Sensing of the binding of Salmonella typhimurium to the aptamer-based LSPR sensing chip. (d) Determination of the concentration of S Salmonella typhimurium in the pork extract. (B) Experimental setup of the Ω-shaped FOLSPR biosensor. Inset (a) the photo of the Ω-shaped fiber optic; (b) illustration of the combination of bacteria and aptamers. Source: (A) Reprinted with permission from Oh, S. Y., Heo, N. S., Shukla, S., Cho, H.-J., Vilian, A. T. E., Kim, J., . . . Huh, Y. S. (2017). Development of gold nanoparticle-aptamerbased LSPR sensing chips for the rapid detection of Salmonella typhimurium in pork meat. Science Reports, 7, 10130. Copyright 2017 Springer Nature Publishing AG. (B) Reprinted with permission from Xu, Y., Luo, Z., Chen, J., Huang, Z., Wang, X., An, H., & Duan, Y. (2018). Ω-shaped fiber-optic probe-based localized surface plasmon resonance biosensor for real-time detection of Salmonella typhimurium. Analytical Chemistry, 90, 13640
13646. Copyright 2018 American Chemical Society.

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LOD of 128 cfu/mL, as well as good selectivity for S. typhimurium detection compared to other bacteria (see Fig. 11.4B).

11.6.4 Surface-enhanced Raman scattering-based biosensors Raman spectroscopy is a very powerful technique because it provides a real spectral fingerprint of compounds. This technique has taken on a big importance for chemical analysis and characterization, mainly due to the precise information that it provides about the sample (Sharma, Frontiera, Henry, Ringe, & Van Duyne, 2012). However, the main drawback of this technique lies in the weak intensity of the Raman signal. To overcome such a disadvantage, some methods such as SERS have been proposed. SERS amplifies the Raman signal by several orders of magnitude (Sharma et al., 2012; Schlu¨cker, 2014), enabling its use in single-molecule detection. Combined with the high specificity provided by nanobiosensors, SERS-based sensors have become a really powerful sensing platform in food analysis. Taking into account the outstanding features of SERS-based biosensors, Yan et al. carried out the detection of CAP using the hot Au core
Ag shell nanostructures (Au@AgNSs) by the SERS-based aptasensing method (Yan, Yang, Zhuang, Wu, & Zhang, 2016). First, the SERS transduction signal was achieved by embedding the Cy5-labeled DNA aptamer between the Au and Ag layer. As the CAP binds the specific DNA strand containing some of its complementary nucleotides, the SERS signal is greatly decreased as a criterion of the chloramphenicol presence. By using this method, the detection of CAP was obtained with high selectivity and specificity, as well as a LOD of 0.19 pg/mL, which is among the lowest values obtained so far. Li et al. (2017) determined AFB1 using a SERS-based aptasensor. An aptamer for AFB1 partially hybridized with c-DNA was released after the recognition of AFB1. This aptamer immediately hybridized with hairpin-DNA on the surface of an Au-sputtered film. With the help of Exo III, the dsDNA was hydrolyzed leaving a short ssDNA on the Au surface and releasing c-DNA for a recycling process. After that, a SERS probe (consisting of 4-nitrothiophenol-modified captured DNAAuNPs conjugates) was captured on the Au film surface by DNA hybridization, and the SERS signal could be registered. The increase in SERS signal is a confirmation of the presence of AFB1. Using this method, the detection of AFB1 with a LOD as low as 0.4 fg/mL was obtained. Ma and coworkers reported a novel immunosensor combined with SERS-based detection to determine amantadine (AMD) in chicken (Ma et al., 2018). The SERS probe was prepared by modifying Au nanoflowers with 5,50 -dithiobis-(2-nitrobenzoicacid) (DTNB) and N-(1-adamantyl) ethylenediamine conjugated denatured BSA (AEDA-dBSA). The former was used as a SERS detection molecule while the latter was the binding site with the recognition element. Additionally, the capture probe was anti-AMD monoclonal Abfunctionalized MBs. The detection was achieved by a specific immunoreaction between the free AMD and SERS nanoprobe competing for the limited binding sites of monoclonal Ab-functionalized MBs. The results showed that the SERSbased immunosensor was sensitive, simple, and reliable to determine AMD in chicken samples with a LOD of 0.005 ng/mL.

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A SERS-based aptasensor has also been used for the ultrasensitive detection of microcystin-LR (MC-LR) (He, Wu, Cui, & Jin, 2019). For the preparation, MC-LR aptamer was adsorbed onto the surface of AuNPs, whilst the corresponding c-DNA was anchored to MNPs to carry out magnetic separation. In the presence of the target molecule, MC-LR and the aptamer-AuNPs bind together in a competitive reaction in such a way that the magnetic separation c-DNA-MNPs conjugates lead to a decrease in the SERS signal. By quantifying the SERS signal decrease, a detection of MC-LR is successfully achieved. E. coli O157:H7 in ground beef was also detected using a membrane filter-assisted SERS strategy. In this work, the target bacteria could be captured and separated by Ab-MNPs, after that, Ab-modified AuNPs with a Raman reporter was anchored to the bacteria previously separated. Finally, the bacteria
nanoparticle complexes were left on the filter membrane and the SERS identification/quantification was carried out over the filter. Using this method, E. coli O157: H7 was detected in extremely low concentrations (10 cfu/mL) from both pure culture and ground beef samples (Cho, Bhandari, Patel, & Irudayaraj, 2015).

11.7

Nanomechanical biosensors for food safety and control

Nanoscale mechanical transducers allow the precise monitoring of force, displacement, or mass changes (from pN to fg levels) induced by the binding of a biomolecule. This fact has formed the basis for building effective biomolecule detection devices, in which biotarget-induced mechanical stresses or mass changes at the surface of nanomechanical transducers are monitored (Tamayo, Kosaka, Ruz, San Paulo, & Calleja, 2013; Tang, Wang, Xu, Li, & Liu, 2012). Scanning probe microscopy-based biosensors rely on the above mentioned principle. Emerging applications in food science include qualitative macromolecule and polymer imaging, quantitative structure analysis, molecular interaction, molecular manipulation, surface topography, and nanofood characterization (Yang et al., 2007). Some examples will be briefly described in the following subsections. The recognition layers immobilized on the surface of micro- and nanomechanical transducers are critical components for tailoring the mechanical-based recognition event. For example, Abs or aptamers can be used as recognition elements in connection with microcantilevers for selective biotarget detection, using the mechanical events caused by such binding interactions as the signal (Shekhawat & Dravid, 2015).

11.7.1 Scanning probe microscopy-based biosensors Scanning probe microscopy (SPM) allows for the detection of nanoscale displacement (,0.2 nm accuracy) and atomic-level forces (BpN range). In particular, static and dynamic force
distance curves allow the detection of nanoscale interactions of biomolecules, viruses, DNA, and living biological entities after SPM tip modification. Such functionalization can be carried out with aptamers, Abs, and enzymes, which

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can enhance the biosensing capability and specificity of the biosensor. For example, force
distance curve-based atomic force microscopy (AFM) has been applied to image and detect filamentous bacteriophages extruding from living bacteria. The new approach offers considerable opportunities for bacterial monitoring and control in complex food samples with high resolution, selectivity, and sensitivity. A tip functionalized with a Ni21 complex was used in connection with AFM detection for individual bacteriophages identification. The characteristic pull-off forces of histidine residues in the bacteriophage with the complex allow monitoring of the binding events and form the basis for the biorecognition (Alsteens, Trabelsi, Soumillion, & Dufrene, 2013). Ricin toxin detection (bound to a gold surface) has been achieved by using an Ab-functionalized tip, achieving single-molecule resolution (subfemtomolar detection limit). Briefly, the tip was modified with a specific aptamer as a probe molecule to bind the target molecule of ricin on the surface of Au(III) (using the lipoic acid
N-hydroxysuccinimide ester molecule as a linker) (Wang, Guo, Chen, Park, & Xu, 2012). This strategy is illustrated in Fig. 11.5A. With a similar approach, two DNA aptamers were used for the label-free detection of S. typhimurium by AFM in the presence of other bacterial strains. The limit of detection was determined to be 3 3 104 cfu/mL (Wang, Park, Xu, & Kwon, 2017).

11.7.2 Microcantilever-based biosensors In microcantilevers, the biotarget-induced changes can be monitored either by static deflection (via the creation of surface tensions and subsequent microcantilever binding) or dynamic resonance frequency/amplitude (via mass changes/increase) changes. Since such detection mechanisms are based on nonselective generated mechanical stresses, target specificity can be achieved by immobilization of a specific probe (Zhang et al., 2017). An array of Au
Si microcantilevers functionalized with specific peptides and Abs has been applied to detect the presence of Salmonella serovar in phosphate buffer solution. By monitoring the adsorption-induced deflection of the microcantilevers in real time, the selection of proper binding compounds was conducted. The authors found that the peptide MSal 020417 has a better binding affinity and specificity than a commercially available anti-Salmonella Ab. The microcantilever sensors also allow distinguishing between different bacterial strains (see Fig. 11.5B) (Wang, Morton, et al., 2014). An aptamer-based microcantilever array sensor for the detection of FB1 was developed. A linearity range from 0.1 to 40 μg/mL was achieved, with a LOD of 33 ng/mL. The sensor exhibited good specificity over OTA and deoxynivalenol and was successfully applied in food and agricultural products (Chen, Bai, Li, & Zhang, 2015). A similar method relies on Ab-immobilized microcantilever resonators to effectively identify total aflatoxins and OTA, at low concentrations (3 ng/mL and less than 6 ng/mL, respectively) (Ricciardi et al., 2013). AFB1 has been detected by using a microcantilever array-based immunosensor functionalized with a sulfhydrylated anti-AFB1-Ab. Deflection of the microcantilever corresponding to different AFB1 concentrations was monitored in real time,

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Figure 11.5 (A) SPM-based biosensor for ricin detection and schematic of atomic force microscopy recognition experiments. The atomic force microscopy recognition signal is generated by the interaction between the probe molecule aptamer/antibody and the target molecule ricin. (B) Microcantilever-based biosensor for Salmonella detection. AntiSalmonella antibody (2 μg/mL) was immobilized on the cantilever surface and three bacterial solutions were detected, as shown in the right part of the Figure. Source: (A) Reprinted with permission from Wang, B., Guo, C., Chen, G., Park, B., & Xu, B. (2012). Following aptamer-ricin specific binding by single molecule recognition and force spectroscopy measurements. Chemical Communications, 48, 1644
1646. Copyright 2012 Royal Society of Chemistry. (B) Reprinted with permission from Wang, X., Shan, Y., Gong, M., Jin, X., Lv, L., Jiang, M., & Xu, J. (2019). A novel electrochemical sensor for ochratoxin A based on the hairpin aptamer and double report DNA via multiple signal amplification strategy. Sensors & Actuators, B: Chemical, 281, 595
601. Copyright 2014 American Chemical Society.

with a detection limit of 0.03 ng/mL for AFB1 in peanut samples (Zhou, Wu, Liu, Wu, & Zhang, 2016).

11.8

Micromotor-based (bio)sensing approaches

Humans have developed artificial micro/nanoscale machines analogous to the macroscopic ones in our lives. Man-made micromotors are microscale devices that can

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move autonomously in solution by converting an energy input into motion (Wang & Pumera, 2015). Micro/nanomotors hold considerable promise for many applications in the biomedical area, environmental remediation, or analytical sensing. Micromotors can be fabricated by several techniques, for example, photolithography, electron-beam deposition, or template electrodeposition (Wang, 2013). Such artificial nano-, micro-, and millimeter-scale motors utilize different propulsion mechanisms for their motion based on different energy sources, such as ultrasonic, or magnetic fields, through consumption of fuels, or via physicochemical processes. Bubble-propelled micromotors (mainly hydrogen peroxide-driven catalytic micromotors) have led to a fundamentally new approach in (bio)chemical assays, where the movement generated by the propulsion of motor around the sample greatly enhanced the target contacts and, hence, the sensitivity of the assay due to increased binding efficiency. This effect is important to consider when low sample and reagent volumes are accessible (Orozco et al., 2011; Maria-Hormigos, JuradoSa´nchez, & Escarpa, 2018). Moreover, Marangoni effect-powered micromotors (via physicochemical processes) can rapidly disperse enzyme in a contaminated sample, enhancing the enzyme 2 substrate interactions without external stirring and the need for chemical and physical action (Garcı´a-Carmona, Moreno-Guzma´n, Gonza´lez, & Escarpa, 2017; Moreno-Guzma´n, Jodra, Lo´pez, & Escarpa, 2015). The incorporation of carbon nanomaterials in micromotors can enhance the propulsion performance due to an increased catalytic activity and improved bubble generation (Maria-Hormigos, Jurado-Sanchez, Vazquez, & Escarpa, 2016; Maria-Hormigos, Jurado-Sa´nchez, & Escarpa, 2017). Specifically, the surface properties of graphene have allowed the addition of different receptors for toxin detection (Esteban´ vila et al., 2016) or the capture and removal of agents and heavy Ferna´ndez De A metals (Vilela, Parmar, Zeng, Zhao, & Sa´nchez, 2016) and excellent fluorescencequenching (Molinero-Ferna´ndez, Moreno-Guzma´n, Lo´pez, & Escarpa, 2017; Molinero-Ferna´ndez, Jodra, Moreno-Guzma´n, Lo´pez & Escarpa, 2018). Moreover, the combination of CNTs or graphene with metal oxide and metal alloys is a suitable strategy for improving the speed and surface chemistry of artificial micromotors (Wang, Sofer, Eng, & Pumera, 2014) and for enhanced colorimetric detection of pollutants (Maria-Hormigos et al., 2018). More details can be found in more-focused recent reviews (Jurado-Sa´nchez & Escarpa, 2016; Jurado-Sa´nchez & Escarpa, 2017). Magnesium-gold (Mg-Au) microparticles propelled by redox corrosion have been exploited for electrochemical-assisted bioanalyte detection in microvolume electrodes. The micromotors act as “autonomous stirrers” for enhanced mass transport and as “enzyme mimics,” by generating local pH gradients for the degradation of target analytes. Thus Mg-Au micromotors have been used for the alkaline hydrolysis of nonelectroactive paraoxon into readily detectable p-nitrophenol. Chloride ions present in the supporting electrolyte promote the dissolution of a Mg(OH)2 layer passivating the Mg particles. Thus the spontaneous redox oxidation reaction between Mg and water generates hydrogen bubbles for autonomous propulsion along with OH2 ions for the degradation of paraoxon. Improved amperometric detection is accomplished by fixing the micromotors onto the SPE surface via a Ni layer incorporated in the micromotor body (Cinti et al., 2015). The Mg micromotors

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can also be used for detection of nonelectroactive diphenyl phthalate (DPP) by DPV in complex food samples. The alkaline pH (B11) induced by micromotor movement promotes the degradation of DPP into phenol which can be then detected (Rojas, Jurado-Sa´nchez, & Escarpa, 2016). Molinero-Ferna´ndez and coworkers developed a simple and fast method to determine simultaneously two concerning mycotoxins, that is, fumonisin B1 (FB1) and OTA, by using a graphene-based micromotors strategy. In this work the assay principle was based on the fluorescence quenching of free aptamer adsorbed on the surface of micromotor. The methodology was successfully applied to the determination of OTA and FB1 with LOD of 7 and 0.4 ng/mL, respectively (Molinero-Ferna´ndez et al., 2017; Molinero-Ferna´ndez, Jodra, Moreno-Guzma´n, Lo´pez, & Escarpa, 2018). Graphene QD (GQDs) have been used as active sensing elements in Janus micromotors, offering rapid and specific “On
Off” fluorescence detection of bacterial endotoxins (Jurado-Sa´nchez, Pacheco, Rojo, & Escarpa, 2017; Pacheco, Jurado-Sanchez, & Escarpa, 2018).

11.9

Conclusions and future directions

This chapter presents a current overview of recent developments in nano- and microscale biosensors for food analysis. Electrochemical biosensors are still essential tools for food safety assurance and monitoring. Current advances aim to improve the sensitivity, selectivity, and specificity with minimal sample treatment by the incorporation of metallic NPs, mainly gold due to the excellent features for modification with specific receptors such as aptamers and Abs. The main targets are bacteria (either whole cells or associated toxins) and mycotoxins. A few applications rely on graphene and CNTs for the same purpose, with some interesting recent advances using MoS2, which will undoubtedly lead to future developments due to the unique surface properties of such nanomaterials. Another important core is devoted to optical nanobiosensors with either colorimetric and fluorescent detection based mainly on the exploitation of aggregation-disaggregation of gold NPs. In fluorescent detection, dye-labeled specific probes are the preferably choice. As in the case of electrochemical biosensors, bacteria and mycotoxins are the main targets. Future aims should be directed at the improvement of multiplexing capabilities and to reduce the cost by designing portable and cost-effective biochips or the use of nanoscale sensing elements. Recent developments in this direction (also covered in this chapter) could lead to the use of self-propelled sensors, such as micromotors or microcantilever and field-effect transistor-based biosensors.

Acknowledgements A.E. acknowledges the Spanish Ministry of Economy, Industry and Competitiveness (CTQ2017
86441-C2-1-R) and the TRANSNANOAVANSENS program (S2018/NMT-4349)

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from the Community of Madrid and LaCaixa Impulse program. B.J.S. acknowledges the Spanish Ministry of Economy, Industry and Competitiveness (RYC-2015
17558, cofinanced by the EU), the Community of Madrid (CM/JIN/2019-007) and the University of Alcala´ (CCG19/CC-029). J.V.P.R. acknowledges the Spanish Ministry of Science, Innovation and Universities (FJCI-2017
32458).

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29.

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12

Zahra Mohammadi and Seid Mahdi Jafari Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

12.1

Introduction

In the current world, new threats to food safety are constantly emerging. Food safety is globalized, and the need to strengthen food safety systems in countries is increasingly felt. The importance of food safety has been highlighted to the extent that the World Health Organization (WHO) put forward its slogan in 2015 promoting improved food safety “from farm to plate” (Ahumada & Villalobos, 2009). However, any contamination, adulteration, spoilage, or pathogens of food or agricultural products can reduce nutrition values. In addition, consuming contaminated food can lead to a variety of foodborne illnesses and thus reduce food safety. Therefore nutrient monitoring and screening of adulterants and pathogens are the main issues in the food industry for evaluation of food quality and safety. The main disadvantage of current methods for assessing food safety such as cell culture and instrumental analysis is the long analysis time from several hours to days and usually a need to various pretreatment stages. For this purpose, new accurate, rapid, and low-cost detection techniques are growing (Rotariu, Lagarde, Jaffrezic-Renault, & Bala, 2016). Nanotechnology is a new technology which is being embraced by the whole world; more precisely, “Nanotechnology is not part of the future but the whole future.” Innovative solutions can be found using nanotechnology to counter the challenges of various industries, including the food industry. Nanostructures are divided into four groups according to the number of free dimensions: (1) zero dimensions [nanoparticles (NPs), nanoclusters, and quantum dots]; (2) one dimension (nanorods, nanotubes, and nanofibers); (3) two dimensions (nano-thin films); and (4) three dimensions (nanocomposites and nanostructured bulk materials) in the 1 100 nm range (Pathakoti, Manubolu, & Hwang, 2017). Recently, nanosensors have been used to detect adulterant and pathogenic materials in food packaging or during the process. At the nanoscale, materials exhibit unique properties physically and chemically that they do not exhibit in their original bulk form. The high surface area of nanomaterials allows for very large molecular interactions, which may result in higher sensitivity, faster detection, and fewer samples required for analysis. Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00012-1 © 2020 Elsevier Inc. All rights reserved.

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Therefore this chapter reviews the applications of nanosensors for the efficient detection of adulteration and spoilage in food products (Mercante, Scagion, Migliorini, Mattoso, & Correa, 2017). It should be mentioned that the general overview of nanobiosensors for the food industry is given in Chapter 11, Nanobiosensors for Food Analysis. A nanosensor is a highly sophisticated yet precise and sensitive system capable of detecting and responding to physical and chemical stimuli. The range of performance for these sensors is in nanometers, so they are highly precise and responsive, and can even react to the presence of several atoms in a single gas; they offer considerable improvements in speed, selectivity, and sensitivity compared to common chemical and biological methods. Also, when the recognizing part of the nanosensor has a biological nature, they are known as nanobiosensors (Joyner & Kumar, 2015). In general, sensors consist of two essential elements: a receptor and a transducer. The receptor can consist of any organic or inorganic material that interacts with the target analyte or its derivatives. On the other hand, the transducer is an element that converts the recognition event occurring between the analyte and the receptor into a measurable signal (Yin, Kim, Choi, & Lee, 2013). This signal can come in many forms, including electrical (Adhikari, Govindhan, & Chen, 2015), electrochemical (Rotariu et al., 2016), and optical (Koedrith, Thasiphu, Tuitemwong, Boonprasert, & Tuitemwong, 2014). Hence, nanomaterials including metal and metal oxide NPs, carbon nanotubes (CNTs), graphene and its derivatives, carbon nanofibers (CNFs), magnetic NPs, and electrospun nanofibers play an important role in the design of sensors and biosensors to detect adulteration and spoilage in food. The current chapter is focused on the recent advances in this field from the last 5 years and will not cover earlier published papers, unless considered necessary. Older publications are covered by chapters and review articles published previously.

12.2

Metal and metal oxide nanoparticles-based nanosensors

In physics and in metals, plasmons are defined as the mass oscillations of electron charges relative to their nuclei (positive charge). Surface plasmons are plasmons that are confined to the surface and interact strongly with light beams coming to the surface of metals. Frequencies less than the surface plasmon frequency are reflected by the metal because the electrons at the metal surface block the electric field of light like a barrier. In most metals, the surface plasmon frequency is at the frequencies of UV light, so almost all visible light is reflected, thus the appearance of most metals is white and bright (perfectly reflecting visible light). In general, surface plasmons play an important role in the optical properties of metals and semiconductors. Surface plasmons in metals are significantly affected by the size and morphology of metal particles as well as by the dielectric properties of the environment around which the metal surface is adjacent. Metals such as silver and gold have a very strong visible plasmon resonance, while many other intermediate metals have

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only a weak and broad absorption band in the UV region. It is recalled that metals in the form of NPs have much higher surface area and thus have higher surface plasmon activity. On the other hand, the dielectric properties of an environment can be greatly altered by the presence of a chemical agent (analyte). These two points lead to a new concept: surface plasmons of metal NPs can be used to detect various types of molecules and proteins present in the environment. In other words, this concept has brought about widespread application of surface plasmon resonance phenomena, including enhanced surface spectroscopy and biological, chemical, and molecular sensors (Zeng, Baillargeat, Ho, & Yong, 2014). Generally, two types of surface plasmons are used to produce plasmon-based sensors: propagating surface plasmon resonance (PSPR); and localized surface plasmon resonance (LSPR). In the PSPR method, the fading electromagnetic waves are surrounded by the metal dielectric contact surface, while in the LSPR, the electromagnetic waves are confined to the metal nanostructures. Sensors made by both methods are sensitive to local refractive index variations, so that by binding the target particle to the surface, the refractive index variations can be detectable. In this method, the particle-to-surface bonding is directly converted to the signal and does not require labeling; whereas in conventional optical sensors, chromophores and fluorophores are required. Due to the high surface sensitivity, label-free and realtime measurement of events, the number of PSPR-based sensors is increasing and researchers are developing them for identifying molecular binding through binding sites. The LSPR-based sensors are easily adjustable and modifiable so that the shape, size, and chemical composition of NPs as the main sensing elements can be tuned; this advantage, along with other benefits of PSPR, will help researchers. LSPR-based nanosensors are used to identify chemicals and biomaterials. In most cases, the plasmonic band is displaced due to the specific binding of the target molecules to the surface, which is used as a signal for detection (Choi & Choi, 2011). Metal NPs, such as gold (Au) and silver (Ag) NPs, and metal oxide NPs, such as titanium dioxide (TiO2), zinc oxide (ZnO), and silica (SiO2) NPs, are used in many high-tech applications including sensors, absorbent materials, drug delivery systems, and antimicrobial materials (Dargahi et al., 2016; Dizaj, Lotfipour, BarzegarJalali, Zarrintan, & Adibkia, 2014; Falcaro et al., 2016; Gautier, Allard-Vannier, Munnier, Souce´, & Chourpa, 2013). Herein, Au and Ag NPs have emerged as strong tools in sensing applications due to their remarkable optical properties.

12.2.1 Gold nanoparticles Au NPs are particularly attractive for detection because of their high surface area. Researchers investigated Au NPs for biodetection because they are easily bioconjugated to various ligands, including antibodies, DNA, and aptamers. They also have unique optical and electromagnetic properties that make them widely used to enhance sensor sensitivity (Yang, Kostov, Bruck, & Rasooly, 2009). Melamine (1,3,5-triazine-2,4,6-triamine, C3H6N6) is a synthetic chemical compound which is illegally added to milk products because of its high level of nitrogen

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(66% by mass) in order to produce a high incorrect reading when measuring total protein based on total nitrogen (Ai, Liu, & Lu, 2009). Gas chromatography-mass spectrometry (GC-MS) is the official method of melamine detection specified by the US Food and Drug Administration (FDA). The quantification limit of this method is 0.05 10 mg/kg (Bittar et al., 2017). Given the importance of this issue, extensive studies have been conducted on the detection of this adulterant using AU NPs with simple, low-cost, and highly sensitive methods with a detection limit of 0.05 mg/L (Kumar, Seth, & Kumar, 2014), 6 ppb (Kuang et al., 2011), and even 1 ppb (Ai et al., 2009). These limits of detection are much lower than the strictest melamine safety requirement of 2.5 ppm in the United States and EU and 1 ppm for infant formula in China. As shown in Fig. 12.1, the general mechanism of most of these methods is that the colloidal solution of Au NPs is a red color (absorbance peak around 523 nm), indicating proper dispersion of Au NPs; on aggregation caused by melamine it changes to a blue color (absorbance peak around 640 nm) (Kumar et al., 2014). Au NP-based chemical resonance energy transfer was also proposed as a new strategy for the highly sensitive detection of melamine. This technique was based on the inner effect of Au NPs on a bis(2,4,6-trichlorophenyl) oxalate (TCPO) hydrogen peroxide fluorescein system, which led to a significant decrease in the chemiluminescence signal. Since melamine causes Au NPs to aggregate and change the color of solution, therefore the energy transfer between the TCPO hydrogen peroxide fluorescein chemiluminescence reaction and Au NPs in the presence of melamine could not occur. As a result, chemiluminescence severity

Figure 12.1 Schematic representation for the mechanism of melamine detection in milk products using gold nanoparticles and visual color changes from red to blue in the presence of 1 ppm melamine (Kumar et al., 2014).

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is restored. The detection limit was reported to be 3 3 10213 mol/L (Du, Wang, & Zhang, 2015). Another milk adulteration is “Synthetic milk” which is prepared by adding approximately 1.2 g/L of detergent in water. Organic dyes such as methylene blue and azure A are commonly used to detect detergent. Unmodified Au NPs were used to detect anionic detergents in milk due to their 1000 times higher extinction coefficient than that of organic dyes. The detection limit of this method was 23 and 92 ppb for sodium dodecylbenzenesulfonate and commercial anionic detergents, respectively (Kumar, Kumar, Manhas, & Navani, 2016). Moreover, Triton X-100 can modify citrate-capped Au NPs to stabilize Au NPs under conditions of high ionic strength and wide pH range. The detection limit of Triton X-100-Au NPs can be 5.1 nM by UV Vis spectroscopy and 1.0 μM by the naked eyes. It can be also extended to be served as a test paper (Gao, Huang, & Wu, 2018). Among food products, fraud of meat products has also become a major concern for Muslim consumers, often by substitution of expensive meat for a cheaper material, such as pork and horse meat for beef. There are several food authentication methods for species identification including chromatographic analysis, immunological assays, and DNA profiling (Rao, Richt, & Hsieh, 2016; von Bargen, Dojahn, Waidelich, Humpf, & Brockmeyer, 2013). Various studies on the application of Au NPs for Halal authentication in meat and meat products have been published; Subara & Jaswir (2018) covered an excellent review of past progress in this field. Au NP sensors can be changed depending on the measured analytes and other parameters such as size and shape. Au NPs aggregate upon interaction with specific proteins due to the different electrostatic properties of DNA, which results in different surface plasmon resonance. In these studies, Au NPs in sizes of 3 20 nm were used in different samples, such as pork and horsemeat adulteration in beef burger and chicken meatballs, and monitoring chicken tissue in meats and meat products, with the detection limits of 12.3 fg/μL to 230 μg/L (Subara & Jaswir, 2018). Table 12.1 provides an overview of the types of nanomaterials used in nanosensors for the detection of adulterants in the food industry. Au NPs are also used in the detection of pathogens in food (Garrido-Maestu et al., 2017; Kong et al., 2018; Uusitalo et al., 2017); herein we will only present selected examples from new ones. Since milk is a rich source of nutrients, it is attacked by numerous types of bacteria, such as E. coli, Salmonella, Bacillus, and Listeria. The detection of viable metric Bacillus cereus was conducted using a propidium monoazide-asymmetric polymerase chain reaction (asPCR) and unmodified Au NPs. The long genomic DNA fragments adsorbed on Au NPs, which were stabilized against salt-induced aggregation. The limit of detection for viable emetic B. cereus was 9.2 3 101 CFU/mL in 0.01 M phosphate-buffered saline and 3.4 3 102 CFU/mL in milk, which was lower than the maximum limit imposed by the Commission Regulation (EC) No 2073/2005 (500 CFU/mL) (Li et al., 2018). In other research, a wireless antibody-free biosensor was designed and developed for the rapid detection of pathogenic bacteria in milk using dextrin-capped Au NPs as markers. A case study was performed on E. coli and a threshold of 5 log CFU/mL bacteria was reported. This noncontact and wireless RFID compatible sensor tag

Table 12.1 Overview of nanomaterial-based sensors for the detection of different adulterants in food analysis. Target analyte

Nanomaterials

Method/technique

Linear range

Limit of detection

References

Melamine

Au NPs

Colorimetric

0.1 2 mg/L

0.05 mg/L

Crown ether-Au NPs Au NPs Au NPs

Colorimetric

10 500 ppb

6 ppb 1 ppb 3 3 10213 mol/L

Kumar et al. (2014) Kuang et al. (2011) Ai et al. (2009) Du et al. (2015)

SDBS/ADs

Triton X-100-Au NPs Ag NPs Ag- dopamine NPs p-NA-Ag NPs Ag NPs Ag NPs

Colorimetric Chemiluminescence resonance energy transfer Colorimetric

0 2.5 μM

5.1 nM 1.0 μM

Gao et al. (2018)

Colorimetric Colorimetric Colorimetric Colorimetric Colorimetric

4 170 μM 0.08 10 μM 1000 10,000 ppb 0.033 1.50 mg/L 0.2 1.6 mg/L

2.32 μM 10 ppb 100 ppb 0.009 mg/L 0.04 mg/L

Ag NPs

Colorimetric

0 5 ppm

0.1 ppm

Ag NPs

Colorimetric probe

500 10,000

252 ppb

Ag NPs

Colorimetric

0.1 5 ppm

0.5 ppm

Au NPs

Colorimetric

25 300/100 900 μg/mL

23/92 μg/mL

Ping et al. (2012) Ma et al. (2011) Han and Li (2010) Bittar et al. (2017) Kumar, Kumar, Mann, et al. (2016) Varun et al. (2017) Borase et al. (2015) Daniel et al. (2017) Kumar, Kumar, Manhas, et al. (2016)

3.2 3 10212 3.2 3 1027 mol/ L

Glucose

HCT/CTD/ IDP/RSP/ VST

Urea

CNT IONPs-Au NPs

Electrical conductance Colorimetric

300 nM

Li et al. (2017)

20 100 μM

20 μM

SPE-HPLC

0.2 100 μg/mL

MWCNT

SPE-HPCE

1 50 μg/mL

MWCNT

1 500 ng/mL 66 nM 20.6 mM

4.7 nM

GNPlt-CNT

SPE-UPLC ESI-MSMS NonEnzymatic electrochemical detection Amperometry

0.014 0.053 μg/ mL 0.058 0.157 μg/ mL 0.022 0.30 ng/mL

Bustami et al. (2017) Zeng, Li, et al. (2015) Zeng, Wu, et al. (2015) Hu et al. (2016)

MWCNT

0.1 0.8 mg/mL

33 μA/(mg/mL)

GNPlts/GND

SPCE

0.1 0.9 mg/mL

0.005 mg/mL

PA6-PPy NFs/ZnO

ESP/electrochemical detection SPCE

0.1 250 mg/dL

0.011 mg/dL

1 3 1024 1 3 1029 mol/l

1 3 1029 mol/L

Gtip SPE & UPLC MS/MS iEESI-MS

0.1 200 ng/mL

1.8 5.6 ng/mL

NF/Ag-NSWCNTs/GCE

Sucrose

CarboxilatedMWCNT

FFN/PHPH/ BMT/SBN Hemoglobin

Gr AP-GO

0.9 μL whole blood or 300 mg raw meat

Kumar and Sundramoorthy (2018) Kumar et al. (2015) Kumar et al. (2020) Migliorini et al. (2018) Bagal-Kestwal and Chiang (2019) Jin et al. (2017) Song et al. (2017)

(Continued)

Table 12.1 (Continued) Target analyte

Nanomaterials

Method/technique

Linear range

Limit of detection

References

Sudan I

Gr/β-CD/PtNPs/ GCE GO@PDA AuNPs

DPV

0.005 66.68 μM

1.6 nM

CV

0.3 67.55 μM

0.015 μM

MWCNT/GCE rGO/Au NPs/GCE

Amperometry DPV

1.01 3 1026 1.22 3 1024 M 0.1 58.5 μM

34.6 nM 0.011 μM

ErGO/GCE

LSV

0.04 8.0 μM

0.01 μM

Fe3O4/GCE

CV

0.01 20 μM

0.001 μM

CNF/SPCE

CV

0.5 500 pg/mL

0.5 pg/mL

MoS2 NPs-CNF

Amperometry

0.3 135 μM

0.15 μM

PAMAM-Fe3O4/ GCE Halochromic NFs

Amperometry

1 3 1028 3.07 3 1026 M

5 3 1029 M

Palanisamy et al. (2017) Palanisamy, Thangavelu, et al. (2016) Yang et al. (2010) Palanisamy, Sakthinathan, et al. (2016) L. Zhang et al. (2013) Yin, Zhou, et al. (2011) Lim and Ahmed (2016) Qianwen et al. (2019) Yin, Cui, et al. (2011) Tripathy et al. (2019)

Porcine serum albumin Vanillin Bisphenol A pH sensor/milk adulteration

ESP

AD, Anionic detergents; Ag NPs, silver nanoparticles; AP, amylopectin; Au NPs, gold nanoparticles; β-CD, β-cyclodextrin; BMT, bumetanide; CNF, carbon nanofiber; CNT, carbon nanotube; CTD, chlortalidone; CV, cyclic voltammetry; DPV, Differential pulse voltammetry; ESP, electrospinning; FFN, fenfluramine; GCE, glassy carbon electrode; GND, graphitized nanodiamond; GNPlt, graphene nanoplatelets; GO, graphene oxide; Gr, graphene; Gtip, graphene tip; HCT, hydrochlorothiazide; HPCE, high-performance capillary electrophoresis; HPLC, high-performance liquid chromatography; IDP, indapamide; iEESI-MS, internal extractive electrospray ionization mass spectrometry; IONPs, iron oxide nanoparticles; LSV, linear sweep voltammetry; MS, mass spectrometry; MWCNT, multiwalled carbon nanotube; N, nitrogen doped; NF, Nafion; NFs, nanofibers; PA6, polyamide 6; PAMAM, polyamidoamine; PDA, polydopamine; PHPH, phenolphthalein; p-NA, p-nitroaniline; PPy, polypyrrole; PtNPs, platinum nanoparticles; rGO, reduced graphene oxide; SDBS, sodium dodecylbenzenesulfonate; SPCE, screen-printed carbon electrode; SPE, solid-phase extraction; SWCNT, single wall carbon nanotube; RSP, reserpine; SBN, sibutramine; UPLC, ultraperformance liquid chromatography; VST, valsartan; ZnO NPs, zinc oxide nanoparticles.

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can be used for real-time monitoring of the quality of milk through the supply chain (Karuppuswami, Matta, Alocilja, & Chahal, 2018). In another interesting research, a combination of the isothermal recombinase polymerase amplification (RPA) with unmodified Au NPs was used to detect Salmonella in milk (detection limit of 50 CFU), which was a more accurate, faster, and less expensive method than the national standard detection method (GB4789.4) (Chen, Zhong, Luo, Zhang, & Huang, 2019). Another application of Au NPs is in the detection of biogenic amines as a spoilage marker in meat products. These biogenic amines, such as histamine, tyramine, phenylethylamine, and cadaverine, are caused by bacterial decarboxylation of amino acids and could not be detected by smelling the odor because they are created even in meat preserved at 5 C for more than 10 days. In one study, Au NPs were used to measure the amount of histamine and histidine in chicken meat with sensitivity and limit of detection of 6.59 3 1024 and 0.6 μM, respectively. The increase in the electric field is near the surface of the Au NPs, which decreases rapidly with the distance from the surface of the electric field, and the light passing through the Au NPs has an increase in the plasmon resonance frequency occuring for the intermediate metals at visible wavelength. By observing the changes in electron density on the surface, chemically bonded molecules can be detected that result in a shift in the maximum plasmon absorption. In fact, this is why Au NPs are used as sensitive sensors (El-Nour, Salam, Soliman, & Orabi, 2017).

12.2.2 Silver nanoparticles Ag NPs have better properties compared to Au NPs including higher extinction coefficients, sharper extinction bands, higher ratio of scattering to extinction, and extremely high field enhancements. Despite these advantages, Ag NPs have been used far less in sensor development, with the exception of sensors based on surfaceenhanced spectroscopies, due to their lower chemical stability. However, there have been recent developments to effectively protect Ag NPs and improve their chemical stability, so that researchers have explored alternative strategies for developing optical sensors and imaging labels based on the considerable optical properties of these metal NPs (Caro, Castillo, Klippstein, Pozo, & Zaderenko, 2010). Ag NPs similar to Au NPs aggregate in the presence of melamine and result in their yellow-to-red color change, due to the shift of surface plasmon band to longer wavelengths. Numerous studies have been done on the detection of melamine using Ag NPs. Label-free Ag NPs were used as a probe with a detection limit of 2.32 μM. In this study, the borohydride reduction method was used to synthesize Ag NPs, which resulted in homodispersal of Ag NPs. In fact, the negatively charged citrate ions cover Ag NPs and the electrostatic force counteracts the van der Waals force effects between the molecules (Ping et al., 2012). The limit of detection of the analyte may vary depending on the type of reducing and stabilizing agent used for Ag NPs synthesis. For example, the limit of detection for Ag NPs synthesized using dopamine (Ma, Niu, Zhang, & Cai, 2011) and p-nitroaniline (Han & Li, 2010) have been reported to be 10 and 100 ppb, respectively.

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One interesting solution suggested for the synthesis of stable colloidal Ag NPs is the use of factorial design to optimize the concentrations of AgNO3 and NaBH4. The stability of NPs synthesized with a mean diameter of 14 nm was reported for at least 5 days at 4 C. Strong interaction was established between the Ag NPs and the amine groups, which increased the sensitivity of detection for melamine in milk products because no stabilizing agents were used in this method; the detection limit can be reached at 0.009 mg/L (Bittar et al., 2017). In other studies, rapid sensing of melamine in milk by 35-nm diameter unmodified Ag NPs (Kumar, Kumar, Mann, & Seth, 2016) and green synthesized Ag NPs (Varun, Daniel, & Gorthi, 2017) was reported with a detection limit of 0.04 mg/L and 0.1 ppm, respectively. AgNO3 was used as a precursor and ascorbic acid as a reducing agent for green synthesis of Ag NPs in the aforementioned research. Dispersed Ag NPs give strong absorption in UV Vis spectra around 397 nm. On the other hand, the exocyclic amino groups of melamine (positive charge) attach to these citrate ions on the surface of Ag NPs (negative charge). Thereby hydrogen bonding between Ag NPs and melamine molecules cause aggregation of Ag NPs and produce visual color changes with the appearance of new absorption maxima around 540 nm, as shown in Fig. 12.2. More and more Ag NPs aggregate as the concentration of melamine increases and absorption spectra around 540 nm increase simultaneously (Kumar, Kumar, Manhas, et al., 2016). The green synthesis of Ag NPs with leaf extracts including Jatropha gossypifolia (Borase et al., 2015) and Parthenium (Daniel, Julius, & Gorthi, 2017)

Figure 12.2 Schematic representation for the mechanism of melamine detection in milk products using silver nanoparticles and visual color changes from yellow to red in the presence of 1 ppm melamine (Kumar, Kumar, Mann, et al., 2016).

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also yielded good results for single-stage melamine detection. In general, melamine detection with Ag NPs is performed in two steps. The first step requires the synthesis and functionalization of Ag NPs and the second step involves detection of melamine using functionalized Ag NPs. Green synthesis of Ag NPs is not only an ecofriendly process but also a rapid (less than 20 s) and one-step method for analyte detection. In this strategy, the analyte interferes with the biosynthesis of the NPs and then is detected by the NPs. In addition to all the applications of Ag NPs in detecting adulterants, they are also helpful in detecting food spoilage. Biofunctionalized Ag NPs using cysteine and histidine were applied for the detection of milk spoilage at the initial stages based on measuring the percentage of lactic acid which is formed in spoiled milk. In the mixture of Ag NPs with fresh milk, lactic acid, initial spoiled milk, and final spoiled milk no color change was observed. Thiol group in cysteine and imidazole group in histidine bonded Ag NPs to lactic acid which led to the aggregation of NPs and color change (Madhavan, Qotainy, & Nair, 2019). Ag NP-based nanosensors can also be used as a specific detection tool for postharvest onion spoilage. The organosulfur compounds released during the storage and spoilage of onion, is visually detectable using the colloidal solution of Ag NPs. Sachdev, Kumar, Maheshwari, Pasricha, and Baghel (2016) have reported a study in this area. In the 10-day monitoring of deterioration, the yellow Ag NPs solution first became orange and then pink and eventually turned colorless with increasing days of spoilage. This research was conducted without any interference from moisture, atmospheric O2 or CO2. UV Vis spectroscopy and colorimetric analysis confirmed that Ag NPs are a specific and sensitive sensor for the volatile sulfur compounds. The Ag NPs solution showed no color change in the presence of healthy onions and their absorbance (430 nm) was observed to be very close to the wavelength of Ag NPs (425 nm) (Sachdev et al., 2016). Given the global food shortage that is mainly caused by postharvest spoilage and agricultural waste, nanosensors based on Ag NPs can be used as rapid detection tools for the spoilage of agricultural and horticultural products such as fruits. A Nigerian research team conducted a case study on the banana (Musa acuminata). Green synthesis of NPs has several advantages mentioned in Chapter 7, Green Synthesis of Metal Nanoparticles by Plant Extracts and Biopolymers, and on the other hand, microorganisms such as bacteria, algae, and fungi have the ability to reduce and oxidize metal ions and turn them into metal or metal oxide NPs. Accordingly, Ag NPs were biosynthesized from Bacillus subtilis in this study. 1,2Benzenedicarboxylic acid, bis(2-methyl propyl) ester, is a volatile compound that is released from Musa acuminata during spoilage. As shown in Fig. 12.3A, the colloidal solution of Ag NPs obtained by this method was a reddish-brown color which, when exposed to this volatile compound, was first changed to light brown (day 4) and finally turned transparent (day 10). Fig. 12.3B is the plausible mechanism of spoilage detection for Ag NPs. The released volatile compounds approach the aggressive Ag NPs and undergo an electrometric effect. This method has also been suggested to investigate the spoilage of other fruits (Omole, Torimiro, Alayande, & Ajenifuja, 2018).

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Figure 12.3 (A) Color changes of biosynthesized silver nanoparticles exposed to volatile metabolites released during banana spoilage from day 0 to day 10; (B) a plausible mechanism of silver complexation with 1,2-benzenedicarboxylic acid, bis (2-methyl propyl) ester (Omole et al., 2018).

Another study has been done on the basis of the scientific fact that by changing the size and interparticle distance of noble metal NPs such as Ag, their LSPR changes. In this study, a plasmonic membrane was used as a hybrid material based on Ag NPs embedded in bacterial cellulose. When the nanopaper was exposed to ammonia gas released due to meat and fish spoilage, the population density of Ag NPs was reduced which was associated with a decrease in UV Vis spectroscopy

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absorption. In these conditions, the color of plasmonic nanopaper was turned from amber to gray. Limits of detection also changed from 30.3 to 0.574 ppmv of ammonia with increasing exposure time (2 8 h) (Heli, Morales-Narva´ez, Golmohammadi, Ajji, & Merkoc¸i, 2016). Table 12.2 presents an overview of the types of nanomaterials used in the nanosensors for detection of spoilage in the food industry.

12.3

Carbon nanomaterial-based nanosensors

In the last decade, much research has been done on the use and application of carbon NPs for developing sensors. Recently, graphene, as one of the new carbon allotropes, has surpassed CNTs in the production of sensors. But carbon NPs are not limited to graphene and nanotubes, so structures such as NPs, nanofibers, and nanoporous carbon materials can also be classified. One of the most major reasons for the development of carbon nanomaterial-based sensor is that these materials have considerable stability in addition to having a regular nanoscale structure; hence they are stable even when not functional (Llobet, 2013).

12.3.1 Carbon nanotubes After the discovery of CNTs in 1991, they quickly became a subject of interest to researchers, and CNT-based sensors were developed for various applications due to their inherent properties, including their ultrahigh specific surface area and their amazing mechanical, electrical, and thermal properties. Accordingly, these sensors make it possible to detect extremely small amounts of analyte very quickly. These nanostructures are named for their physical shape, and are made of hollow cylindrical carbon atoms. They are approximately 1 nm in diameter and 1 100 microns in length (Katouzian & Jafari, 2019). The tubing angle and tube radius determine the metallic or semiconductor properties of these nanostructures. The nanotubes are divided into two groups of single-wall CNTs (SWCNTs) and multiwalled CNTs (MWCNTs). SWCNTs consist of only one single layer of graphene cylinders (a sheet of regular hexagons); whereas in MWCNTs, many graphene sheets (approximately 50) are piped (Zhou, Bai, Wang, & Xie, 2009). CNTs adhere together naturally by van der Waals forces. These nanotubes are bonded together using the Sp2 bond, similar to the interaction between graphite layers. Sp2 bond is stronger than Sp3 and is a bond between alkanes and diamonds, resulting in the unique structural strength of the nanotubes. Such strong bonds decrease the activity of nanotubes with the surrounding molecules. Therefore functionalizing CNTs is an appropriate tool to improve their sensitivity and selectivity in the fabrication of sensors. Generally, CNTs are produced using these three techniques: (1) arc discharge; (2) laser ablation; and (3) chemical vapor deposition (CVD). Among the different methods of CNTs production, laser radiation is the most expensive and arc discharge is a less efficient method. The CVD method is the best option for the industrial production of CNTs. The reason for this is its

Table 12.2 Overview of nanomaterial-based sensors for the detection of spoilage in food analysis. Target analyte

Nanomaterials

Method/technique

Linear range

Limit of detection

References

Bacillus cereus

Au NPs

Colorimetric

9.2 3 3 101 9.2 3 3 106 CFU/ mL

Li et al. (2018)

Escherichia coli

d-Au NPs

RFID

3.4 3 3 102 CFU/ mL 5 log CFU/mL

Salmonella

Au NPs

RPA

50 CFU

Histamine

Au NPs

Colorimetric

Spoiled milk

Cys & His-Ag Nps Ag Nps

Colorimetric Colorimetric

Ag Nps

Colorimetric

NH3

Ag Nps

NO2/NH3

Cobalt porphyrin/ SWCNT SWCNT

plasmonic nanopaper Chemiresistive detection Electrical resistance

Organosulfur compound BDCA-bis ester

O2/CO/H2O/N2/ NO2/NH3/SO2 Ethylene

SWCNT CNT

Bucky-paper resistance Electrical conductance

0.6 12 μM

0.6 μM

10 1000 μL

30.3 ppm

0 10 ppm

,0.5 ppm 2 ppm/ 1% ,100 ppm 50 ppm

Karuppuswami et al. (2018) Chen et al. (2019) El-Nour et al. (2017) Madhavan et al. (2019) Sachdev et al. (2016) Omole et al. (2018) Heli et al. (2016) Liu et al. (2015) Kong et al. (2000) Goldoni et al. (2003) Li et al. (2017)

Xanthine

CarboxilatedMWCNT

Brettanomyces bruxellensis Lactic acid

Au NPs-rGO

pH sensor

Pt NPs/ graphitized CNF SPCE Halochromic NFs

Enzymatic electrochemical detection Amperometry

0.6 58 μM

0.6 μM

Devi et al. (2011)

102 106 CFU/mL

56 CFU/mL

Amperometry

10 2000 μM

6.9 μM

Borisova et al. (2017) Loaiza et al. (2015)

ESP

Devarayan and Kim (2015)

Au NPs, Gold nanoparticles; BDCA-bis ester, 1,2-benzenedicarboxylic acid, bis (2-methyl propyl) ester; CFU, colony forming unit; CNF, carbon nanofiber; CNT, carbon nanotube; Cys, cysteine; d-Au NPs, dextrin-capped Au NPs; ESP, electrospinning; His, histidine; MWCNT, multiwalled carbon nanotube; PtNPs, platinum nanoparticles; RFID, radio frequency identification; rGO, reduced graphene oxide; RPA, recombinase polymerase amplification; SPCE, screen-printed carbon electrode; SWCNT, single wall carbon nanotube.

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price/unit ratio as well as the potential of growing nanotubes on the desired substrate (Llobet, 2013). The electronic properties of CNTs are deeply sensitive to the chemical environment of nanotubes. This sensitivity is a good tool for applying nanotubes in the sensor field. CNTs were used as gas sensors for the first time in the year 2000. Kong et al. (2000) succeeded in fabricating a transistor by connecting two metal contacts to the single nanotubes and creating a metal/nanotube/metal structure that could change due to different voltages. The conductance of these nanotubes was investigated in the presence of nitrogen dioxide and ammonia vapors. The SWCNT is a hole-doped semiconductor and the results showed that by applying a positive gate voltage to this system, the conductance was reduced threefold (Kong et al., 2000). Goldoni, Larciprete, Petaccia, and Lizzit (2003) investigated the relationship between gaseous sensing properties and defects and contaminants at the surface of SWCNTs. They evaluated the effect of oxygen, nitrogen, carbon monoxide, moisture, nitrogen dioxide, sulfur oxide, and ammonia on the photoemission spectra changes of nanotubes before and after the thermal treatment in ultrahigh vacuum. Heat treatment on nanotubes reduces the number of structural defects, which are caused by purification or removal of pollutants such as catalyst particles. After heat treatment, the electronic spectra of SWCNTs has lost its sensitivity to oxygen, nitrogen, carbon monoxide, and moisture, while being sensitive to ammonia, nitrogen dioxide, and sulfur oxide. Therefore some of the intrinsic properties conceived for pure nanotubes or those that are slightly heated are affected by contaminants, defects, or catalytic particles (Goldoni et al., 2003). Some studies show that functionalizing the sidewall of nanotubes improves the binding of specific compounds to the nanotubes and improves their sensitivity and selectivity. In the nanotube-based sensor configurations, nanotubes are attached to the metal source and drain electrodes. The nanotube is functionalized with a molecular receptor, which selectively binds to the target molecule and thereby changes the conductivity properties of nanotube. In general, it is due to variations in surface charge density. Therefore the target molecule acts as a kind of electrostatic gate, effectively enabling its detection. As mentioned above, CNTs are highly sensitive to small changes in their immediate environment, making them ideal electrical elements for chemical sensors. These sensors have been used to detect important biological molecules such as glucose and ethylene (Li, Hodak, Lu, & Bernholc, 2017). Li et al. (2017) provided two paradigmatic sensor configurations to detect molecules through ab initio calculations: a noncovalently functionalized nanotube for glucose detection and a covalently functionalized nanotube for ethylene detection. They reported the sensitivity to ethylene is mainly due to diminished electron transfer between the CNTs and the copper(I) complex. On the other hand, the sensitivity to glucose is mainly due to the formation of a negatively charged boronate anion complex, which affects the local electrostatics around the nanotube (Li et al., 2017). Combining nanotubes with other techniques allows the detection of several adulterants simultaneously. For example, MWCNT-dispersive solid-phase extraction

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followed by high-performance liquid chromatography (Zeng, Li, Wu, Zhang, Xie, & Sun, 2015), high-performance capillary electrophoresis (Zeng, Wu, Li, Lu, & Sun, 2015), and UPLC ESI-MS-MS (Hu, Zeng, He, You, & Sun, 2016) were developed for simultaneous determination of six to ten illegal adulterants, such as hydrochlorothiazide, chlortalidone, indapamide, reserpine, and valsartan, in antihypertensive functional foods. In all methods, the target chemicals in the samples were ultrasonically extracted with acetonitrile, then cleaned-up with MWCNTs. Finally, the analytes were separated from MWCNTs by the three aforementioned techniques. The technique of UPLC ESI-MS-MS had shorter retention times and was the most sensitive of all the methods with a much lower limit of detection (0.022 0.30 ng/mL) and limit of quantification (0.075 0.99 ng/mL). Urea is another adulterant that is added to diluted milk to show more nitrogen content. Naturally, the concentration of urea in milk is 3.1 6.6 mM, whereas the allowable range of urea in milk is 0.2 0.4 mg/mL and any deviation from this concentration indicates the milk as being adulterated. Most current urea detection methods employ the enzyme-based sensor technology (Ibrahim et al., 2017; Kaushik et al., 2009; Solanki, Kaushik, Ansari, Sumana, & Malhotra, 2008; Tak, Gupta, & Tomar, 2013; Velychko et al., 2016). As the research progressed, these enzymatic biosensors were improved over the years 2008 17, so that their sensitivity was changed from 124.84 μA/mM/cm2 to 0.32 nA/mM, their detection limit from 499 to 2 μM, and the response time from 10 to 3 s. These enzymatic techniques have some disadvantages including high fabrication cost and poor stability. A nonenzymatic electrochemical method for the detection of urea was reported in which a glassy carbon electrode was modified using Ag NPs decorated nitrogen-doped SWCNTs (Ag-N-SWCNTs) and a layer of Nafion. SWCNTs were mixed with silver nitrate and melamine (as the nitrogen source) and through a one-step thermal-reduction method, the Ag-N-SWCNTs were synthesized. The synergetic effect between Agand N-SWCNTs led to an enhanced electrocatalytic activity for the oxidation of urea (Fig. 12.4). High sensitivity, lower limit of detection, and fast response time of this fabricated electrode were reported as being 141.44/μAmM/cm, 4.7 nM, and 3 s, respectively. This modified electrode is also capable of storage under ambient conditions without loss of activity and exhibited high selectivity toward urea with good repeatability and reproducibility (Kumar & Sundramoorthy, 2018). Xanthine (systematic name 3,7-dihydropurine-2,6-dione) is one of the products of purine metabolism. Since ATP is degraded into xanthine after the death of a fish which increases with storage, xanthine detection can be considered as a freshness indicator of fish. In a study, the optimum current was reported within 4 s at pH 5 7.0 and 35 C, when polarized at 0.4 V. The biosensor lost 50% of its initial activity after 200 uses over a period of 100 days (Devi, Yadav, & Pundir, 2011). Although nonfunctionalized SWCNTs are known to detect amines chemiresistively, a study improved the sensitivity and specificity of nanotubes to amines by functionalizing them. Chemiresistive detectors made of cobalt porphyrin/SWCNT composites were used to detect biogenic amines such as putrescine and cadaverine and to investigate the spoilage of raw meat. Changes in the oxidation state of metal, the electron-withdrawing character of the porphyrinato ligand, and the counteranion,

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Figure 12.4 (A) Schematic representation of silver nanoparticles-decorated nitrogen-doped single-wall carbon nanotube synthesis. (B) Nonenzymatic electrocatalytic oxidation of urea at Nafion/silver nanoparticles-decorated nitrogen-doped single-wall carbon nanotube/glassy carbon electrode (Kumar & Sundramoorthy, 2018).

can lead to improvements in sensitivity toward amines, which are detected rapidly at sub-ppm concentrations and with a high selectivity (Liu, Petty, Sazama, & Swager, 2015). One of the biggest frauds in the juice industry is the addition of cane and beet invert sugars to fruit juices to imitate the natural sucrose glucose fructose profile. Numerous investigations have been reported for the detection of sucrose by electrodes with the three types of enzymes including invertase, glucose oxidase, and peroxidase/mutarotase but with limitations such as cross-reactivity with feedback enzyme inhibition and less sensitivity (Fitriyana & Kurniawan, 2015). Interesting research was conducted to fabricate an electrochemical platform for saccharide or sucrose analysis using a biocomposite of nanomaterials. For this purpose, hydrogels were prepared from two natural polysaccharides, gum Arabic and corn flour, and

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reinforced by platinum NPs anchored with carboxyl-functionalized CNTs. Then, invertase and glucose oxidase were entrapped in a gum Arabic corn flour hybrid matrix. Screen-printed carbon electrodes were modified with the aim of developing a highly sensitive electrochemical biosensor system for the detection of sucrose using this enzyme nanocomposite matrix. The reported limit of detection was 1 3 1029 mol/L (Bagal-Kestwal & Chiang, 2019).

12.3.2 Graphene and its derivatives Graphene, the youngest member of the carbon nanomaterial family, was introduced to the world of science and technology in the year 2004 by Andre Geim and Konstantin Novoselov at the University of Manchester. Graphene is a twodimensional sheet of sp2-bonded carbon atoms in a hexagonal lattice structure. This family includes fullerene as zero-dimensional material, CNTs as one-dimensional nanomaterials, and graphite as three-dimensional materials. Apart from monolayer and two-layer graphene, graphene with three to 10 layers is called few-layer graphene and between 10 and 30 layers is called multilayer graphene, thick graphene, or thin graphite nanocrystals. In graphene, carbon atoms do not consume one of their capacities. This vacancy, which is actually an extra electron, can form offsheet with other atoms. This free or suspended capacity can bind to functional groups or other radical atoms in the environs. Various approaches for producing graphene have been reported. These methods include mechanical and chemical exfoliation of graphite and CVD (Georgakilas, Perman, Tucek, & Zboril, 2015). Graphene oxide (GO), reduced graphene oxide (rGO), and graphene quantum dots (GQDs) are the main representatives of this group. GO is typically produced by Hummer’s method through oxidative exfoliation of graphite using KMnO4 and H2SO4 (Bagheri, Jafari, & Eikani, 2019; Joz Majidi et al., 2019). rGO can be gained by treating GO with reducing agents, such as hydrazine and l-ascorbic acid, (Zhang et al., 2010). GQDs are usually made by thermal oxidation of GOs or other carbon precursors (Shen, Zhu, Yang, & Li, 2012). Many attractive features differentiate graphene from other carbon materials such as massive specific surface area (2630 m2/g), excellent electrical conductivity, high inherent conductivity (200,000 cm2/V/s), magnificent mechanical stiffness, and unique optical properties. It has an almost twofold higher effective surface area and is more cost-effective than CNTs. In addition, it has an extremely uniform surface that is responsible for the greater homogenous surface functionalization (Sundramoorthy & Gunasekaran, 2014). Due to the unique physical and electrochemical properties mentioned above, graphene has been extensively explored in the field of electroanalytical chemistry. In addition to the electrical conductance over the large surface of graphene, it also efficiently attaches to analyte molecules and fast electron transfer, leading to the greater sensitivity of graphene-modified electrodes (Chen, Feng, & Li, 2012). A wide range of chemical and biological binding strategies have been developed for precise functional groups (e.g., amine, sulfonate, carboxyl, acid chloride, hydroxyl) on graphene for surface modification, respectively (Georgakilas et al., 2012). Similarly, different methods have been developed to modify the surface by conjugating graphene to long-

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chain polymers and/or nanomaterials. Graphene has been widely used in biosensors and diagnostics to detect a wide range of analytes (e.g., urea, glucose, dopamine, ascorbic acid, uric acid, glutamate, hydrogen peroxide, xylene, protein biomarkers, cholesterol, hemoglobin, saccharides, and cancer cells) (Kuila et al., 2011; Liu, Dong, & Chen, 2012). In a study to detect urea, graphene nanoplatelets conjugated with urease were applied. Urea is hydrolyzed by urease, producing ammonium and carbonic ions. The principal purpose of this research was to efficiently sense these ions. The conjugated graphene nanoplatelets urease was immobilized on the working region of CNTs-coated screen-printed electrodes and utilized for amperometric sensing. The developed platform is reusable and can be used around 20 times without any significant changes in results when stored in 0.02 M potassium phosphate buffer with pH 5 7 at 4 C after proper washing (Kumar et al., 2015). In another recent study, nanocomposites made with urease-immobilized graphene nanoplatelets and graphitized nanodiamonds were used for direct and mediator-free electrochemical sensing of urea. The schematic for the sensing mechanism of proposed sensing platform is shown in Fig. 12.5. The sensor proposed in this research had advantages such as higher enzyme loading, higher charge transfer to the electrode surface, and higher effective surface area, resulting in higher sensitivity. The ammonium and carbonic ions produced during the hydrolysis of urea were adsorbed onto the composite surface to generate a current at 0 V, which presented a significant correlation with the concentrations of urea samples (prepared in the range between 0.1 and 0.9 mg/mL with a limit of detection of 5 μg/mL). This platform exhibited a response time of 20 s with a sensitivity of 806.3 μA (mg/ mL)/1/cm2. The best storage conditions for this sensor were 0.02 M potassium phosphate buffer at pH 5 7 and 4 C, which maintained the constant sensor performance even after 25 repetitive usages (Kumar et al., 2020).

Figure 12.5 Schematic for the sensing mechanism of graphene nanoplatelet/graphitized nanodiamond-based nanocomposite for mediator-free electrochemical sensing of urea: (A) graphitization of nanodiamonds (NDs) by heating at 1200 C in the presence of argon; (B) hydrolysis of urea into ions by the urease enzyme; and (C) incorporation of graphitized nanodiamonds (GNDs) into layers of exfoliated functionalized graphene nanoplatelets (fGNPlts) followed by the deposition of ions onto the composite surface upon the hydrolysis of urea (Kumar et al., 2020).

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With the increase in problems caused by overweight and the desire to have an ideal body, the consumption of slimming supplements has also increased. The problem is that some of these supplements are purchased online, which increases the possibility of fraud. In this regard, Jin, Li, Guo, Li, and Shen (2017) determined four synthetic adulterants—fenfluramine, phenolphthalein, bumetanide, and sibutramine—in slimming supplements using a graphene-based pipette tip solid-phase extraction and ultraperformance liquid chromatography tandem mass spectrometry. The sensitivity of this method was evaluated using the parameters of a limit of detection and limit of quantification, which were 1.8 and 5.6 ng/mL, respectively. They evaluated four kinds of commercial slimming supplements with this technique and reported the presence of sibutramine with a content of 3.6 to 20.3 mg/g. Phenolphthalein was also found in these samples at less than 5.2 mg/g content (Jin et al., 2017). GO can be activated by amylopectin, which is used to selectively adsorb hemoglobin from various blood and meat samples (such as chicken, duck, sheep, mouse, pigeon, turtledove, and meat juice), and ultimately to determine the type of meat. Direct internal extractive electrospray ionization mass spectrometry can also be used to increase sensitivity. Song et al. (2017) succeeded in detecting the adulteration of sheep blood with only 2% chicken blood using this technique. The analysis time required was 4 min, which included the analyte extraction and sample loading. The required sample amount was also reported to be 0.9 μL whole blood or 300 mg raw meat (Song et al., 2017). Sudan I (1-phenylazo-2-naphthol) is a synthetic azo dye, frequently found in adulterated chili powder, curry products, and sauces. This adulterant is detectable by a platinum NPs-decorated graphene-β-cyclodextrin-modified electrode with a limit of detection of 1.6 nM and sensitivity of 2.82 μA/μM/ cm2 (Palanisamy, Kokulnathan, Chen, Velusamy, & Ramaraj, 2017). According to previous studies, it has also been suggested to use the glassy carbon electrode modified with graphene (cyclic voltammetry) (Palanisamy, Thangavelu, Chen, Thirumalraj, & Liu, 2016), MWCNTs (amperometry) (Yang, Zhu, & Jiang, 2010), rGO/Au NPs (differential pulse voltammetry) (Palanisamy, Sakthinathan, Chen, Thirumalraj, Wu, Lou, & Liu, 2016), and electrochemically rGO (linear sweep voltammetry) (Zhang et al., 2013) to detect Sudan I. Yeast Brettanomyces bruxellensis (Brett) is a major source of red wine spoilage that is resistant to various conditions such as nutrient deficiencies, ethanol, and sulfur dioxide. To identify this yeast, Borisova et al. (2017) proposed an Au-rGO hybrid nanomaterial-based electrochemical immunosensor. The fabricated electrode allowed the amperometric detection of Brett in buffered solutions and red wine samples in the range of 10 106 and 102 106 CFU/mL, with low detection limits of 8 and 56 CFU/mL, respectively (Borisova et al., 2017). Since the hydrogen bonding between fluorine and ammonium is significant, another study theoretically investigated whether fluorofunctionalized graphene can be used to detect ammonium and simple amines and consequently fish spoilage. For this purpose, the amounts of energy for the highest occupied molecular orbital, the energy of the lowest unoccupied molecular orbital, the difference of them, global electron density transfer, and electronic density of states were calculated for

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pristine graphene and fluorofunctionalized graphene at M06-2X/6 311 G11(d,p) level of theory. The results of this study demonstrated that the fluorofunctionalized graphene can be applied as a bioelectronic nose in the detection of seafood spoilage (Rouhani, 2019).

12.3.3 Carbon nanofibers CNFs, like other single-dimensional nanostructures such as nanowires and nanotubes, have attracted the attention of many researchers due to their unique electrical, thermal, and mechanical properties. CNFs are cylindrical nanostructures with graphene layers in the form of stacked cones, cups, or plates (no hollow core), but with many edge sites arranged on the outer wall. Multimicron-diameter carbon fibers are usually produced by pyrolysis of commercial polyacrylonitrile (PAN) and CNFs several tens to hundreds of nanometers in diameter by the CVD method, which is a complex process that requires time and cost. On the other hand, CNFs can be obtained under different controlled conditions with low cost and high growth rate by the electrospinning method. A polymer such as PAN is used as a carbon source. This polymer is combined with suitable solvents and heated to below boiling point and then used as a polymer solution in the electrospinning process (Llobet, 2013). Electrospun nanofibers (see Section 12.5) are heat-treated for several hours at 300 C 400 C. Subsequently, the product is calcined and carbonized in the absence of oxygen (in argon or nitrogen atmosphere) at 700 C 1000 C. The end product will be CNFs of 40 400 nm in diameter and 70 microns in length (Inagaki, Yang, & Kang, 2012; Kim et al., 2007). Porcine serum albumin (PSA) is known as an important allergen found in pork meats. In a study, 4-carboxyphenyl layer was electrografted onto a surface of CNFmodified screen-printed carbon electrodes for covalent attachment of antibodies by carbodiimide chemistry for the detection of PSA, as a marker for pork adulteration in raw meat. The large surface area of CNFs increased the antibody immobilization capacity and electronic conductivity, thus improving the sensing capacity of the electrodes. A low detection limit of 0.5 pg/mL was achieved (Lim & Ahmed, 2016). Vanillin is a phenolic aldehyde with the molecular formula of C8H8O3, which is an important flavorant with full milk aroma. Synthetic vanillin is now used more often than natural vanilla extract as a flavoring agent in foods, beverages, and pharmaceuticals. However, excessive intake of vanillin can lead to some undesirable consequences to the consumers. Specifically, a high dose can cause potential damage to the human liver and kidney. Qianwen et al. (2019) prepared an electrochemical sensor based on electrospun molybdenum disulfide (MoS2) NPs composite CNFs modified glassy carbon electron for the detection of vanillin. They used XRD, SEM, and Raman spectrum characterization methods to investigate the morphology and microstructure of the material. Fig. 12.6 clearly confirms that MoS2 nanosheets vertically anchor around the surface of CNF. The optimum conditions for this sensor to detect vanillin were 7.0 μL MoS2-CNF, pH 5 10.0, and applied potential of 0.55 V, which showed a good linear response

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Figure 12.6 SEM images of (A) MoS2-CNF; (B) MoS2@CNF (Qianwen et al., 2019).

in the range of 0.3 135 μM and the detection limit was 0.15 μM (Qianwen et al., 2019). Lactic acid or lactate detection has a key role in various fields. An increase in Llactate concentration in eggs is an indicator of spoilage by contamination or incubation. Contamination of fruit juices with lactic acid-producing bacteria often remains unnoticed for a long time, allowing the bacteria to spread and infect huge volumes of juice. L-Lactate concentration in blood is essential for the diagnosis of patient conditions in intensive care and during surgery. CNFs can also be used in the lowcost fabrication of an amperometric biosensor for the detection of lactate in wines and ciders using covalent immobilization of lactate oxidase on Pt NPs/graphitized CNF screen-printed carbon electrodes. The ability of graphitized CNFs to promote electron-transfer reactions and the high catalytic activity of Pt NPs toward hydrogen peroxide, allow the development of a sensitivity-enhanced electrochemical lactate biosensor. The linear range and limit of detection were reported to be 10 2000 and 6.9 μM, respectively. Moreover, 90% of the signal was kept after 3 months storage at room temperature, while 95% was retained after 18 months at 220 C (Loaiza et al., 2015).

12.4

Magnetic nanoparticles-based nanosensors

Magnetic NPs are referred to as particles of an independent nature with a maximum size of 100 nm containing magnetic elements. These particles have unique physical and chemical properties that are dramatically different from the bulk state of the material (Osaka et al., 2006). Among NPs, magnetic particles have attracted the most attention due to their easy separation with an external magnetic field and their high capacity for use in a variety of fields such as advanced materials production, medicine, diagnostic techniques, energy, and food (Alam, Ahmad, Pranaw, Mishra, & Khare, 2018; Christopher, Anbalagan, Kumar, Pannerselvam, & Vaidyanathan, 2016; Dey et al., 2017; Tietze et al., 2015). Generally, magnetic NPs contain magnetic elements such as iron, cobalt, nickel, and their chemical constituents. In the

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food application of magnetic NPs, it is important to examine the safety or toxicity of these particles. Hence among the types of magnetic NPs, iron oxide NPs, especially superparamagnetic Fe3O4 (magnetite) NPs, have been the most commonly used in food due to their lack of toxicity, good compatibility, and lack of preservation of residual magnetism after removal of the external magnetic field. Also, by modifying the surface, iron oxide magnetic NPs can be functionalized with special groups such as NH2, COOH, and OH to be suitable for further binding to molecules with various applications (Cao et al., 2012). There are various methods for producing magnetic NPs such as coprecipitation, hydrothermal, sol gel, microemulsion, and polymer utilization methods, among which coprecipitation is one of the most common and controllable methods. In this process, alkali materials (sodium hydroxide or ammonia) are commonly used to produce iron oxide NPs. The size of iron oxide NPs in this method depends on various factors such as the molar ratio of iron salts, type of salt and alkali used, their composition ratio, mixing rate, pH, temperature, and nitrogen presence (Gregorio-Jauregui et al., 2012). One of the most effective techniques to prevent oxidation of magnetic NPs in the presence of air and water is to create a layer of particles on them and to form a core shell structure that stabilizes them. For example, iron NPs have higher magnetic strength than their oxide state and can be used as a superparamagnet. On the other hand, although NPs do not attract each other with their magnetic properties, they tend to aggregate due to their high energy. Therefore the application of a coating on these NPs not only prevents their aggregation but also provides specific and suitable properties such as biocompatibility and stability (Kinoshita et al., 2003). Among the various metals used to form a layer on iron oxide NPs, Au NPs have received more attention due to their stability and synthesis method. The Au-coated NPs are highly biocompatible and readily react with biomolecules such as polypeptides, nucleic acids, and polysaccharides. On the other hand, it has also been reported that amino groups and cysteine residues in proteins strongly bind to gold colloids (Gole, Vyas, Phadtare, Lachke, & Sastry, 2002). On this basis, research has been conducted to fabricate the heterogeneous NPs of iron oxide Au using an electrostatic self-assembly technique. Finally, glucose oxidase was immobilized on the carboxylate-modified iron oxide Au NPs and examined for glucose detection using an ABTS assay. The results showed that using these NPs to construct colorimetric glucose sensors could be a desirable option (Bustami, Moo-Young, & Anderson, 2017). Magnetic NP-based DNA extraction can also be used as part of visual and rapid detection of duck meat in adulterated beef with both the lateral flow strip platform and on PCR. Thus the magnetic NPs synthesized in this study (type of NPs not reported) were added to a DNA-containing tube and after 5 min were able to extract DNA samples under the applied magnetic field (Qin et al., 2019). Magnetic NPs, when used as electrode modifiers, can significantly increase the electron transfer between the analyte and the electrode due to their high charge transfer capacity. This, in turn, results in significant improvement of the sensitivity of electrode or (bio)electrochemical sensors (Yin, Cui, et al., 2011; Yin, Zhou, et al., 2011). Yin, Cui, et al. (2011) developed a simple and sensitive electrochemical method for

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measuring Sudan I dye based on a carbon electrode modified with cyclic voltammetric magnetite NPs. The modified sensor compared, when with the unmodified carbon electrode, clearly showed electrocatalytic activity toward Sudan I oxidation, which corresponded to an increase in the peak oxidation current and a decrease in the peak oxidation potential (Yin, Zhou, et al., 2011). In another study, Yin, Zhou, et al. (2011) prepared a very simple and sensitive electrode for measuring bisphenol A in milk samples, while optimizing the electrode with polyamidoamine-modified magnetite. Compared to the unmodified electrode, the improved electrode not only significantly increased the peak acidification current, but also reduced the additional oxidation potential which resulted in a significant increase in the sensitivity of the method (Yin, Cui, et al., 2011).

12.5

Nanofiber-based nanosensors

Electrospinning is a process for the production of thin and ultrathin fibers, which was first invented in 1930. This unique, fast, simple, and low-cost technique is used to produce a variety of fibers, including polymer and ceramic fibers with diameters from 1 nm to several microns (Rostami, Yousefi, Khezerlou, Aman Mohammadi, & Jafari, 2019). By definition, electrospun nanofibers refer to fibers smaller than 1000 nm in diameter. Typical electrospinning equipment consists of four main parts: (1) highvoltage power supply; (2) syringe pump; (3) metallic spinneret; and (4) conductive collector, as represented in Fig. 12.7A. The principle of this process is based on applying a very high voltage to a capillary needle and pulling the polymer solution out of it due to the electrostatic force generated by strong fields with a high potential difference (5 50 kV), which transforms, accelerates, and narrows the small volume of the polymeric solution (Rezaei, Fathi, & Jafari, 2019). It becomes very thin in the form of fibers. In this process, a drop of solution is held by the surface tensile force on the tip of nozzle and becomes heavily charged under the strong electric field between the nozzle and the collector. When the voltage reaches the threshold, the electrostatic force overcomes the surface tension of the solution and a cone is formed at the end of the drop, called the Taylor cone. Then a very thin jet exits the Taylor cone. A very sharp decrease in diameter occurs during the transition from the relatively large cone-shape to thin fibers as a result of the bending instability of the jet that plots a turbulent path during rotation. Fibers with diameter of 20 20,000 nm can be produced in this method by choosing the appropriate polymer and solvent (Mercante et al., 2017). Recently, a comprehensive review paper investigated the methods and applications of electrospinning and electrospun nanofibers (Xue, Wu, Dai, & Xia, 2019). The combination of high surface area and porosity offers the possibility to construct multifunctional nanostructures by functionalizing the nanofiber surface with a wide range of nanomaterials (such as graphene, CNTs, NPs), as shown in Fig. 12.7B, thus providing the electrospun nanofibers with novel and/or improved (bio)sensing performances. In a study to detect milk adulteration, a paper-based scalable pH sensor derived from electrospun halochromic nanofibers was synthesized. The sensor manifested into three unique color-signatures corresponding to pure (6.6 # pH # 6.9), acidic

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Figure 12.7 Illustration of (A) typical electrospinning equipment setup; (B) the electrospinning of multifunctional nanofibers containing different types of materials (Mercante et al., 2017).

(pH , 6.6), and basic (pH . 6.9) milk samples, enabling a colorimetric detection mechanism. The thicknesses of pure nylon nanofibers and the composite nanofibers were observed to be in the range 100 200 nm. The sensor strip was dipped in a milk sample and then imaged with a smartphone (Tripathy, Reddy, Vanjari, Jana, & Singh, 2019). Due to the deep concern over the addition of urea to milk and its damage to consumer health, another way to detect urea is to use electrospun nanofibers of polyamide 6 (PA6) and polypyrrole (PPy) modified with ZnO NPs and enzyme urease applying a simple electrostatic process. In fact, ZnO adsorbs onto the surface of the nanofibers due to hydrogen bonding or electrostatic interactions between the carboxylic groups ( COOH) from the Liosperse 511 (dispersing agent) and the amino groups from PPy and amide nitrogen from PA6, respectively. The limit of detection for this biosensor was reported to be 0.011 mg/dL, lower than in other similar studies (2 13.5 mg/dL) (Migliorini et al., 2018).

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Electrospinning-based nanosensors (nanofibers) can be embedded as a chemical barcode in food packaging that is sensitive to the metabolites produced by the spoilage of food. As a result of their reaction, the color of packaging is changed and warns customers about their avoidance. Agarwal, Raheja, Natarajan, and Chandra (2012) were able to exhibit color variations in the pH range of 1 10 using nylon 6 and a combination of five different dyes (Phenol Red, Methyl Red, Bromothymol blue, Phenolphthalein, and Bromocresol Green) (Fig. 12.8). They applied an electrospinning method to produce this indicator. The nanosensors produced by the researchers were also durable for a long period (6 months) over a wide range of temperature, humidity, and pH. SEM images of electrospun nanocomposite fibers with dyes showed the successful formation of nanofibers with diameters of 40 50 nm. It also took about 3 s for the color changes, which was very fast (Agarwal et al., 2012). In a study by Devarayan and Kim (2015), an eco-friendly, reversible, universal sensor based on electrospun cellulose nanofiber with natural pigments extracted from red cabbage (anthocyanin) was investigated. The results showed this sensor could detect pH values in the range of 1 14 and its sensitivity to pH was stable at different temperatures and for a long time (Devarayan & Kim, 2015).

12.6

Conclusion

Nanosensors and nanobiosensors constructed to detect adulterants and spoilage in the food products mentioned in this chapter have been a powerful alternative to conventional methods that require time and money. With the progress of nanosensor technology by researchers, more sensitive and selective sensors have been developed which enable an instant and online analysis of complex mixtures without the need to prepare and with small sample sizes. The accuracy and other features mentioned above have also been improved by functionalizing the nanomaterials employed in the production of nanosensors (NPs, nanotubes, and nanofibers) or by using several techniques simultaneously. Despite all these advantages, interference in real-sample analysis, reproducibility, and toxicity of nanomaterials are issues that

Figure 12.8 Color variations in the pH range of 1 10: (A) reference dye solution and (B) electrospun nylon 6 nanofibers with universal indicator (Agarwal et al., 2012).

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need to be considered. More research is required into the use of other nanomaterials, such as quantum dots and nanowires, to design novel nanosensors in the food industry.

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Liu, S. F., Petty, A. R., Sazama, G. T., & Swager, T. M. (2015). Single-walled carbon nanotube/metalloporphyrin composites for the chemiresistive detection of amines and meat spoilage. Angewandte Chemie International Edition, 54(22), 6554 6557. Liu, Y., Dong, X., & Chen, P. (2012). Biological and chemical sensors based on graphene materials. Chemical Society Reviews, 41(6), 2283 2307. Llobet, E. (2013). Gas sensors using carbon nanomaterials: A review. Sensors and Actuators B: Chemical, 179, 32 45. Loaiza, O. A., Lamas-Ardisana, P. J., An˜orga, L., Jubete, E., Ruiz, V., Borghei, M., . . . Grande, H. J. (2015). Graphitized carbon nanofiber Pt nanoparticle hybrids as sensitive tool for preparation of screen printing biosensors. Detection of lactate in wines and ciders. Bioelectrochemistry, 101, 58 65. Ma, Y., Niu, H., Zhang, X., & Cai, Y. (2011). One-step synthesis of silver/dopamine nanoparticles and visual detection of melamine in raw milk. Analyst, 136(20), 4192 4196. Madhavan, A. A., Qotainy, R., & Nair, R. (2019). Synthesis of functionalized silver nanoparticles and its application as chemical sensor. In Paper presented at the 2019 Advances in Science and Engineering Technology International Conferences (ASET). Mercante, L. A., Scagion, V. P., Migliorini, F. L., Mattoso, L. H., & Correa, D. S. (2017). Electrospinning-based (bio) sensors for food and agricultural applications: A review. TrAC Trends in Analytical Chemistry, 91, 91 103. Migliorini, F. L., Sanfelice, R. C., Mercante, L. A., Andre, R. S., Mattoso, L. H., & Correa, D. S. (2018). Urea impedimetric biosensing using electrospun nanofibers modified with zinc oxide nanoparticles. Applied Surface Science, 443, 18 23. Omole, R., Torimiro, N., Alayande, S., & Ajenifuja, E. (2018). Silver nanoparticles synthesized from Bacillus subtilis for detection of deterioration in the post-harvest spoilage of fruit. Sustainable Chemistry and Pharmacy, 10, 33 40. Osaka, T., Matsunaga, T., Nakanishi, T., Arakaki, A., Niwa, D., & Iida, H. (2006). Synthesis of magnetic nanoparticles and their application to bioassays. Analytical and Bioanalytical Chemistry, 384(3), 593 600. Palanisamy, S., Kokulnathan, T., Chen, S.-M., Velusamy, V., & Ramaraj, S. K. (2017). Voltammetric determination of Sudan I in food samples based on platinum nanoparticles decorated on graphene-β-cyclodextrin modified electrode. Journal of Electroanalytical Chemistry, 794, 64 70. Palanisamy, S., Sakthinathan, S., Chen, S.-M., Thirumalraj, B., Wu, T.-H., Lou, B.-S., & Liu, X. (2016). Preparation of β-cyclodextrin entrapped graphite composite for sensitive detection of dopamine. Carbohydrate Polymers, 135, 267 273. Palanisamy, S., Thangavelu, K., Chen, S.-M., Thirumalraj, B., & Liu, X.-H. (2016). Preparation and characterization of gold nanoparticles decorated on graphene oxide@ polydopamine composite: Application for sensitive and low potential detection of catechol. Sensors and Actuators B: Chemical, 233, 298 306. Pathakoti, K., Manubolu, M., & Hwang, H.-M. (2017). Nanostructures: Current uses and future applications in food science. Journal of Food and Drug Analysis, 25(2), 245 253. Ping, H., Zhang, M., Li, H., Li, S., Chen, Q., Sun, C., & Zhang, T. (2012). Visual detection of melamine in raw milk by label-free silver nanoparticles. Food Control, 23(1), 191 197. Qianwen, M., Yaping, D., Li, L., Anqing, W., Dingding, D., & Yijun, Z. (2019). Electrospun MoS2 composite carbon nanofibers for determination of vanillin. Journal of Electroanalytical Chemistry, 833, 297 303.

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Qin, P., Qiao, D., Xu, J., Song, Q., Yao, L., Lu, J., & Chen, W. (2019). Rapid visual sensing and quantitative identification of duck meat in adulterated beef with a lateral flow strip platform. Food Chemistry, 294, 224 230. Rao, Q., Richt, J. A., & Hsieh, Y.-H. P. (2016). Immunoassay for the detection of animal central nervous tissue in processed meat and feed products. Journal of Agricultural and Food Chemistry, 64(18), 3661 3668. Rezaei, A., Fathi, M., & Jafari, S. M. (2019). Nanoencapsulation of hydrophobic and lowsoluble food bioactive compounds within different nanocarriers. Food Hydrocolloids, 88, 146 162. Available from https://doi.org/10.1016/j.foodhyd.2018.10.003. Rostami, M., Yousefi, M., Khezerlou, A., Aman Mohammadi, M., & Jafari, S. M. (2019). Application of different biopolymers for nanoencapsulation of antioxidants via electrohydrodynamic processes. Food Hydrocolloids, 97, 105170. Available from https://doi. org/10.1016/j.foodhyd.2019.06.015. Rotariu, L., Lagarde, F., Jaffrezic-Renault, N., & Bala, C. (2016). Electrochemical biosensors for fast detection of food contaminants trends and perspective. TrAC Trends in Analytical Chemistry, 79, 80 87. Rouhani, M. (2019). Fluoro-functionalized graphene as a promising nanosensor in detection of fish spoilage: A theoretical study. Chemical Physics Letters, 719, 91 102. Sachdev, D., Kumar, V., Maheshwari, P. H., Pasricha, R., & Baghel, N. (2016). Silver based nanomaterial, as a selective colorimetric sensor for visual detection of post harvest spoilage in onion. Sensors and Actuators B: Chemical, 228, 471 479. Shen, J., Zhu, Y., Yang, X., & Li, C. (2012). Graphene quantum dots: Emergent nanolights for bioimaging, sensors, catalysis and photovoltaic devices. Chemical Communications, 48(31), 3686 3699. Solanki, P. R., Kaushik, A., Ansari, A. A., Sumana, G., & Malhotra, B. (2008). Zinc oxidechitosan nanobiocomposite for urea sensor. Applied Physics Letters, 93(16), 163903. Song, L., Xu, J., Chingin, K., Zhu, T., Zhang, Y., Tian, Y., . . . Chen, X. (2017). Rapid identification of meat species by the internal extractive electrospray ionization mass spectrometry of hemoglobin selectively captured on functionalized graphene oxide. Journal of Agricultural and Food Chemistry, 65(32), 7006 7011. Subara, D., & Jaswir, I. (2018). Gold nanoparticles: Synthesis and application for halal authentication in meat and meat products. International Journal on Advanced Science, Engineering and Information Technology, 8(4 2), 1633 1641. Sundramoorthy, A. K., & Gunasekaran, S. (2014). Applications of graphene in quality assurance and safety of food. TrAC Trends in Analytical Chemistry, 60, 36 53. Tak, M., Gupta, V., & Tomar, M. (2013). Zinc oxide multiwalled carbon nanotubes hybrid nanocomposite based urea biosensor. Journal of Materials Chemistry B, 1(46), 6392 6401. Tietze, R., Zaloga, J., Unterweger, H., Lyer, S., Friedrich, R. P., Janko, C., . . . Alexiou, C. (2015). Magnetic nanoparticle-based drug delivery for cancer therapy. Biochemical and Biophysical Research Communications, 468(3), 463 470. Tripathy, S., Reddy, M. S., Vanjari, S. R. K., Jana, S., & Singh, S. G. (2019). A step towards miniaturized milk adulteration detection system: Smartphone-based accurate pH sensing using electrospun halochromic nanofibers. Food Analytical Methods, 12 (2), 612 624. Uusitalo, S., Popov, A., Ryabchikov, Y. V., Bibikova, O., Alakomi, H.-L., Juvonen, R., . . . Meglinski, I. (2017). Surface-enhanced Raman spectroscopy for identification and discrimination of beverage spoilage yeasts using patterned substrates and gold nanoparticles. Journal of Food Engineering, 212, 47 54.

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Varun, S., Daniel, S. K., & Gorthi, S. S. (2017). Rapid sensing of melamine in milk by interference green synthesis of silver nanoparticles. Materials Science and Engineering: C, 74, 253 258. Velychko, T., Soldatkin, О, Melnyk, V., Marchenko, S., Kirdeciler, S., Akata, B., . . . Dzyadevych, S. (2016). A novel conductometric urea biosensor with improved analytical characteristic based on recombinant urease adsorbed on nanoparticle of silicalite. Nanoscale Research Letters, 11(1), 106. von Bargen, C., Dojahn, J. r, Waidelich, D., Humpf, H.-U., & Brockmeyer, J. (2013). New sensitive high-performance liquid chromatography tandem mass spectrometry method for the detection of horse and pork in halal beef. Journal of Agricultural and Food Chemistry, 61(49), 11986 11994. Xue, J., Wu, T., Dai, Y., & Xia, Y. (2019). Electrospinning and electrospun nanofibers: Methods, materials, and applications. Chemical Reviews, 119(8), 5298 5415. Yang, D., Zhu, L., & Jiang, X. (2010). Electrochemical reaction mechanism and determination of Sudan I at a multi wall carbon nanotubes modified glassy carbon electrode. Journal of Electroanalytical Chemistry, 640(1-2), 17 22. Yang, M., Kostov, Y., Bruck, H. A., & Rasooly, A. (2009). Gold nanoparticle-based enhanced chemiluminescence immunosensor for detection of Staphylococcal Enterotoxin B (SEB) in food. International Journal of Food Microbiology, 133(3), 265 271. Yin, H., Cui, L., Chen, Q., Shi, W., Ai, S., Zhu, L., & Lu, L. (2011). Amperometric determination of bisphenol A in milk using PAMAM Fe3O4 modified glassy carbon electrode. Food Chemistry, 125(3), 1097 1103. Yin, H., Zhou, Y., Meng, X., Tang, T., Ai, S., & Zhu, L. (2011). Electrochemical behaviour of Sudan I at Fe3O4 nanoparticles modified glassy carbon electrode and its determination in food samples. Food Chemistry, 127(3), 1348 1353. Yin, P. T., Kim, T.-H., Choi, J.-W., & Lee, K.-B. (2013). Prospects for graphene nanoparticle-based hybrid sensors. Physical Chemistry Chemical Physics, 15(31), 12785 12799. Zeng, L., Li, Y., Wu, X., Zhang, J., Xie, J., & Sun, C. (2015). Simultaneous determination of 10 adulterants in antihypertensive functional foods using multi-walled carbon nanotubes-dispersive solid-phase extraction coupled with high performance liquid chromatography. Journal of Chromatographic Science, 53(9), 1611 1621. Zeng, L., Wu, X., Li, Y., Lu, D., & Sun, C. (2015). Multiwalled carbon nanotube-dispersive solid-phase extraction followed by high performance capillary electrophoresis for simultaneous determination of six adulterants in antihypertensive functional foods. Analytical Methods, 7(2), 543 550. Zeng, S., Baillargeat, D., Ho, H.-P., & Yong, K.-T. (2014). Nanomaterials enhanced surface plasmon resonance for biological and chemical sensing applications. Chemical Society Reviews, 43(10), 3426 3452. Zhang, J., Yang, H., Shen, G., Cheng, P., Zhang, J., & Guo, S. (2010). Reduction of graphene oxide via L-ascorbic acid. Chemical Communications, 46(7), 1112 1114. Zhang, L., Zhang, X., Li, X., Peng, Y., Shen, H., & Zhang, Y. (2013). Determination of Sudan I using electrochemically reduced graphene oxide. Analytical Letters, 46(6), 923 935. Zhou, W., Bai, X., Wang, E., & Xie, S. (2009). Synthesis, structure, and properties of singlewalled carbon nanotubes. Advanced Materials, 21(45), 4565 4583.

Nanoencapsulated bioactive components for active food packaging

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Arezou Khezerlou1 and Seid Mahdi Jafari2 1 Department of Food Science and Technology, Faculty of Nutrition and Food Sciences, Tabriz University of Medical Sciences, Tabriz, Iran, 2Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

Abbreviations AMPs Antimicrobial peptides DPPH 2,2-Diphenyl-1-picrylhydrazyl EAB Elongation at break EGCG Epigallocatechin gallate EO Essential oil HP High pressure HPLC High-performance liquid chromatographic HPMC Hydroxy propyl methylcellulose PL Pulsed light SPI Soy protein isolate TS Tensile strength WPI Whey protein isolate WVP Water vapor permeability

13.1

Introduction

Changes in the current lifestyles of modern consumers have led to growing demands for nutritious, healthy, and safe fresh products (Cagri, Ustunol, & Ryser, 2004). One of the most important criteria for producing such products is packaging. Nowadays, packaging technologies have extensively developed, resulting in the fabrication of passive, active, smart, and intelligent packages (Salgado, Di Giorgio, Musso, & Mauri, 2019). A package is considered active when the purpose is the inactivation/ degradation of undesirable compounds that can decrease the commercial shelf life of food (Lee, 2010; Suppakul, Miltz, Sonneveld, & Bigger, 2003). In general terms, active packaging employs components such as antioxidants and antimicrobials to protect foods from contamination or degradation by creating a barrier to the outside Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00013-3 © 2020 Elsevier Inc. All rights reserved.

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environment, and promoting the product shelf life (Vahedikia et al., 2019; Vermeiren, Devlieghere, de Kruijf, & Debevere, 2000). Active packaging can be produced with the addition of substances like scavengers of oxygen, ethylene, moisture, and carbon dioxide, and the release of antimicrobial and antioxidant agents (Fang, Zhao, Warner, & Johnson, 2017). A proposed classification of various active packaging systems are antioxidant and antimicrobial films and coatings, nanofiber packaging scavengers and absorbers (Karam, Jama, Dhulster, & Chihib, 2013). Furthermore, consumers’ concerns about multiple disorders related to the use of chemical preservatives have led to an increasing tendency toward the application of natural compounds for food preservation (Huang et al., 2011; Kim, Cadwallader, Kido, & Watanabe, 2013). In this respect, bioactive compounds, such as phenolic compounds, carotenoids, essential oils, peptides, and antimicrobial agents, have been studied for their use in food protection against microbial and oxidation spoilage, which has been a trending subject in recent years (Hashemi Tabatabaei, Jafari, Mirzaei, Mohammadi Nafchi, & Dehnad, 2018; Hoseinnejad, Jafari, & Katouzian, 2018). Nanoencapsulation technology can be used to generate new food packaging; this method is a useful alternative to protect bioactive compounds while providing their controlled release (Sozer & Kokini, 2009). Encapsulated bioactive compounds are widely used in many industries, such as medical, pharmaceutical, and food. Nanoencapsulation as a promising technique that presents various benefits, including reduction in the volatility of aromatic compounds, improving the oxidative stability, limiting bioactive interactions with food components and preserving their stability from aggressive actions of oxygen, humidity, and, light, as well as enhancing their bioavailability and efficacy (Assadpour & Jafari, 2019b; Eltayeb, Stride, & Edirisinghe, 2015; Katouzian & Jafari, 2016; Quintanilla-Carvajal et al., 2014). The main aim of encapsulating bioactive compounds is to increase bioavailability and stability, which would be suitable for their use in food packaging and increase their beneficial effects (Huang, Li, & Zhou, 2015). The significant advantages of nanoencapsulation are the increase of control in additive release and the potentials for the dispersion of water-insoluble compounds, requiring small quantities of these often expensive compounds to achieve similar protective effects in food (Augustin & Hemar, 2009; Peng, Wei, Wang, & Gu, 2014). For example, it has been reported that nanoencapsulation of pomegranate polyphenols can enhance their activity against carcinogenic agents (Shirode et al., 2015). This chapter will detail the effects of nanoencapsulated bioactive compounds in active food packaging on their physicochemical and mechanical properties and also their application in various food products. The controlled release and migration of bioactive ingredients from active packaging to food is also investigated.

13.2

Bioactive compounds

Bioactive compounds are secondary metabolites found in small quantities in various plants (Kris-Etherton et al., 2002). These are mostly hydrophobic and poorly

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Figure 13.1 Chemical structures of some common bioactive compounds.

soluble compounds. The major class of bioactive compounds are (1) terpenes and terpenoids (approximately 25,000 types), (2) alkaloids (about 12,000 types), and (3) phenolic compounds (about 8000 types). Fig. 13.1 illustrates the chemical structures of major bioactive compounds incorporated into active packaging in recent years. 1. Terpenes are characterized by a carbon skeleton of an isoprene unit, and terpenoid compounds are modified terpenes that may also contain other functional groups, commonly oxygen; examples of these compounds are limonene, carvone, squalene, humulene, lycopene, (α-, β-, γ-) carotene, and vitamin A (LaLonde, 2005). 2. Alkaloids are characterized by a nitrogen atom in a heterocyclic ring; in addition to carbon, hydrogen, and nitrogen, they may also contain oxygen, sulfur, and other elements;

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examples of alkaloid compounds are quinine, caffeine, piperine, nicotine, and theobromine (Ziegler & Facchini, 2008). 3. The basic structural feature of phenolic compounds is one aromatic ring of hydroxyl groups; examples of phenolic compounds are phenolic acids, flavonoids, and tannins. These compounds have high antioxidant activity (Giada, 2013).

Bioactive compounds are essential for human health owing to their multiple biological effects, such as reduction in risk factors of cardiovascular diseases, and antioxidant, antimutagenic, anticarcinogenic antiallergenic, antiinflammatory, and antimicrobial activities (Ham et al., 2009; Parvathy, Negi, & Srinivas, 2009). The bioactive compounds used in different commercial industries, such as pharmaceutical, food, and chemical, have low bioavailability and improving the stability of these compounds has gained special attention (Azmir et al., 2013; Rezaei, Fathi, & Jafari, 2019). In low concentrations, they can act as antioxidants, and preserve food from oxidative damage, while a high concentration could result in oxidation products with proteins, carbohydrates, and minerals (Parr & Bolwell, 2000). Bioactive compounds are extracted from natural sources by solid liquid extraction using organic solvents and other techniques, such as supercritical fluid extraction, highpressure processes, microwave-assisted extraction, subcritical water extraction, and ultrasound-assisted extraction (Jafari, Mahdavee Khazaei, & Assadpour, 2019; Markom, Hasan, Daud, Singh, & Jahim, 2007; Martins, Aguilar, Garza-Rodriguez, Mussatto, & Teixeira, 2010; Sarfarazi, Jafari, Rajabzadeh, & Feizi, 2019).

13.3

Nanoencapsulation of bioactive ingredients

Many bioactive ingredients can be directly applied into food systems, but their direct use could be limited due to their low solubility in water or lipids, high volatility, partial inactivation owing to interactions with substances in the food matrix, neutralization, rapid diffusion, or strong flavor (Lambert, Skandamis, Coote, & Nychas, 2001); hence, additional methods to efficiently protect them against chemical degradation, and improve their solubility and bioactivity should be developed. To eliminate these drawbacks, many methods have been suggested like the application of emulsification, edible packaging, encapsulation, etc. But in recent years one of the best methods for the protection of functional properties of bioactive compounds is the nanoencapsulation strategy (Assadpour & Jafari, 2019a; Assadpour, Jafari, & Esfanjani, 2017; Hosseini, Tajiani, & Jafari, 2019). Nanoencapsulation is defined as a way to entrap bioactive compounds within carrier materials at the nanoscale range in order to protect them or deliver them to the targeted site (Jafari & McClements, 2017b; Rafiee, Nejatian, Daeihamed, & Jafari, 2019). The selection of the nanoencapsulation method depends on the physical and chemical properties of the core and type of coating material and the final application of the products (Jafari, 2017). Various nanoencapsulation methods are mostly used for bioactive ingredients, including coacervation, nanoprecipitation, inclusion complexation, emulsification, supercritical fluids, and electrospraying/

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electrospinning (Go´mez-Mascaraque, Lagaro´n, & Lo´pez-Rubio, 2015; Rostamabadi, Falsafi, & Jafari, 2019b; Taheri & Jafari, 2019). Some potential applications of nanoencapsulation have been observed in pharmaceutical as well as cosmetics and food industries (Akhavan, Assadpour, Katouzian, & Jafari, 2018; Rezaei et al., 2019). Besides the benefits mentioned, nanoencapsulation systems improve the controlled release of bioactive compounds and limit their contact to oxygen, water, or light (Jafari & McClements, 2017a; Mozafari et al., 2006). In the last few years, there has been an enormous increase in published studies on the nanoencapsulation of food bioactive ingredients because of these benefits. A brief overview on nanoencapsulation of bioactive compounds through different methods and their application in active packaging has been provided in Table 13.1, and will be discussed in the following sections.

13.4

Different bioactive-loaded nanocarriers applied in active food packaging

13.4.1 Phenolic compounds Phenolic compounds are phytochemicals that exist in all plant sources, and their concentration varies between 0.5 and 5.0 g per 100 g dry weight of plant (Khoddami, Wilkes, & Roberts, 2013). Phenolic compounds have a high antioxidant potential by scavenging radicals, making them appropriate for decreasing the risk of developing different illnesses, such as cardiovascular, neurodegenerative, diabetes, cancer, and the cognitive function diseases (Minatel et al., 2017). Phenolic compounds degrade quickly and are also sensitive to oxygen, heat, and light (Faridi Esfanjani & Jafari, 2016). Several strategies have been developed to improve the bioavailability of phenolic compounds, including lipid-based nanocarriers (Assadpour & Jafari, 2019b; Faridi Esfanjani, Assadpour, & Jafari, 2018). The astringent and bitter taste of many of these molecules restricts their application in the food industry and oral medications. There have been various studies into the nanoencapsulation of phenolic compounds and their use in active packaging. Makwana, Choudhary, Dogra, Kohli, and Haddock (2014) nanoencapsulated cinnamaldehyde by nanoliposomes, which showed great antibacterial effects against E. coli W1485 and B. cereus. In a study by Liu et al. (2015), chitosan nanoparticles were used as a nanoencapsulation system for tea polyphenols, which provided the best antioxidant activity with 80% encapsulation efficiency after 6 weeks of storage. Antioxidant films with the addition of EPCG nanocapsules as bioactive compounds were fabricated and characterized, showing a high DPPH scavenging efficiency (Liang et al., 2017). Bao, Xu, and Wang (2009) designed a nanoencapsulation system for tea polyphenols by loading them into chitosan nanoparticles and applied them in gelatin films. It was showed that the antioxidant activity of this system could be improved by adding nanoencapsulated tea-polyphenols. Pe´rez-Co´rdoba et al. (2018) encapsulated

Table 13.1 Recent studies on nanoencapsulation of bioactive compounds applied in active packaging. Type of nanocarrier

Method of preparation

Type of packaging

Bioactive compound

Brief results

References

Nanoliposome

Solvent sonication

Film

Cinnamaldehyde

Good antimicrobial properties

Nanoemulsion

High amplitude ultrasonic homogenization Microfluidization

Film

Lemongrass, carvacrol and cinnamaldehyde α-Tocopherol, cinnamaldehyde, garlic oil

Good antimicrobial properties

Makwana et al. (2014) Ibrahim and Soliman (2016) Pe´rezCo´rdoba et al. (2018) Ghadetaj et al. (2018)

Nanoemulsion

Film

High antioxidant activity and barrier properties against UV

Improved mechanical and barrier properties

Nanoemulsion

Surfactant of Tween 80 using sonication

Film

Nanoliposome

Thin-film dispersion

Film

Grammosciadium ptrocarpum Bioss essential oil Cinnamon

Nanoliposome

Thin-film hydration and sonication Thin-film hydration and sonication

Film

Urtica dioica L.

Film

Thyme

Interfacial deposition of preformed polymers Interfacial deposition of preformed polymers

Film

Lycopene

Reduce lipid oxidation

Film

β-Carotene

Preserving food safety and prolonging the shelf life

Nanoliposome

Nanocapsule Nanocapsule

Good antimicrobial properties Improved the thermal and WVP properties High stable TE-containing nanoliposomes

Wu et al. (2015) Haghju et al. (2016) Aziz and Almasi (2018) Assis et al. (2017) Assis et al. (2018)

Nanocapsule

Nanocapsules

Interfacial deposition of preformed poly-ecaprolactone High pressure homogenization Nanoprecipitation

Film

Bixin

Good antioxidant properties

Pagno et al. (2016)

Film

Nisin Z

Good antibacterial properties

Film

α-Tocopherol

High antioxidant activity and barrier properties against UV and visible light

Imran et al. (2012) Noronha et al. (2014)

Nanoliposome

Sonication

Film

Nanoparticle

Self-assembly

Nanofiber

Orange essential oil, limonene Nisin

Nanophytosome

Thin-film hydration

Nanofiber

Cinnamon

β-cyclodextrin ε-polylysine nanoparticle Nanocapsule Nanosphere

Ionic gelation

Nanofiber

Thyme essential oil

Emulsification diffusion

Coating

α-Tocopherol

Enhancing stability

β-cyclodextrin inclusion complex

Coprecipitation

Film

Cinnamon essential oil

Good antibacterial properties

Nanoliposome

Good antibacterial properties High antibacterial and low cell toxicity effects Decreased pH, TBA, TVB-N value

Jime´nez et al. (2014) Cui et al. (2017) Nazari et al. (2019) Lin et al. (2018) ZambranoZaragoza et al. (2014) Wen et al. (2016)

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cinnamaldehyde, α-tocopherol, and garlic oil in nanoemulsions using the microfluidization technique. The results showed that cinnamaldehyde (89.6%) and garlic oil (61.6%) had an encapsulation efficiency higher than α-tocopherol (45.2%). The average size and ζ-potential values for nanoemulsions loaded with active compounds varied between 111.0 130 nm and 212 to 216 mV, respectively. Li, Yin, Yang, Tang, and Wei (2012) encapsulated thymol in zein 2 sodium caseinate nanoparticles using an antisolvent technique. The particle size and zeta potential of the complexes were around 200 nm and 240 mV, respectively. The kinetic release profile of thymol nanoparticle-based films showed a burst effect followed by subsequent slower release.

13.4.2 Carotenoids Carotenoids are water-insoluble natural pigments that are found in plants and microorganisms (Paiva & Russell, 1999; Rostamabadi, Falsafi, & Jafari, 2019a). Hydrocarbon carotenoids are so-called carotenes and they can be acyclic (lycopene), monocyclic (γ-carotene), or bicyclic (β-carotene and α-carotene). Oxygenated carotenoids are named xanthophylls [e.g., zeaxanthin and lutein (hydroxy), echinenone (oxo), and violaxanthin (epoxy)] (Rodriguez-Amaya, 1997). Carotenoids have been of note to health experts because they have provitamin A activity, modulate the enzymatic actions of lipoxygenases, and activate the expression of genes for the production of proteins (Bendich, 1993; Pfander, 1992; Socaciu, 2007). Also, carotenoids have antioxidant properties by quenching singlet oxygen and trapping peroxyl radicals, which is related to the number of conjugated double bonds in their structure (Fiedor & Burda, 2014; Stahl & Sies, 2003). Increasing the intake of a diet enriched with carotenoids can lower the risk of chronic illnesses, implying they can improve health (Elliott, 2005; Johnson, 2002; Tanaka, Shnimizu, & Moriwaki, 2012). They are sensitive to oxygen and light and have a low solubility and stability (Burri, 2013; Ogilvy & Preziosi, 2012). Carotenoids are interesting ingredients for active food packaging. Assis, Lopes, Costa, Flˆores, and de Oliveira Rios (2017) successfully nanoencapsulated lycopene by interfacial deposition of preformed polymers via incorporation into cassava starch films, which showed an enhanced antioxidant activity compared to the free lycopene. Cassava starch-based films with bixin nanocapsules incorporated during casting showed a better antioxidant activity, which makes them appropriate for preserving food safety and extending their shelf life (Pagno, de Farias, Costa, de Oliveira Rios, & Flˆores, 2016). It was reported that cassava starch films containing β-carotene-loaded lipid-core nanocapsules show a stronger protection of lipid oxidation than free β-carotene incorporated into films (Assis, Pagno, Costa, Flˆores, & Rios, 2018).

13.4.3 Essential oils Essential oils (EOs) are formed by plants and spices as secondary metabolites and can be found in various plant parts (i.e., flowers, twigs, buds, wood, leaves, bark,

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roots, and seeds). They can be extracted by several procedures (Adorjan & Buchbauer, 2010; Bakkali, Averbeck, Averbeck, & Idaomar, 2008; Hill, Gomes, & Taylor, 2013). EOs are hydrocarbons (terpenes and sesquiterpenes) and oxygenated compounds (alcohols, aldehydes, ketones, esters, ethers, lactones, and phenol ethers) (Guenther & Althausen, 1948). The constituents of EOs are categorized into two groups: the main group is terpenes and terpenoids and the second group includes aromatic and aliphatic compounds, which are characterized by a low molecular weight (Bakkali et al., 2008). Carvacrol, thymol, linalool, 1,8-cineole, camphor, menthol, limonene, α, β-thuyone, α-phellandrene, geraniol, and eugenol are the main chemical compounds in EOs (Osorio-Tobo´n, Silva, & Meireles, 2016; Pichersky, Noel, & Dudareva, 2006). They are oxidized in the presence of heat, oxygen, and light, and have a high volatility. There are many reports on the application of EOs in food packaging due to their antifungal, antioxidant, and antibacterial properties. For example, Haghju, Beigzadeh, Almasi, and Hamishehkar (2016) applied thin-film hydration and sonication methods to prepare soy-lecithin nanoliposomes loaded with nettle extract. Nanoliposome were prepared with an average size of 107 136 nm and encapsulation efficiency of 70% for nettle extract components. In a recent work, Thymus vulgaris extract (TE) was loaded into nanoliposomes with a particle size of 355 nm and a zeta potential between 30 and 60 mV (Aziz & Almasi, 2018). In a study by Ibrahim and Soliman (2016), bioactive oil nanoemulsions prepared by highamplitude ultrasonic homogenization decreased microbial growth at low concentrations (0.1% w/w). Pabast, Shariatifar, Beikzadeh, and Jahed (2018) prepared Satureja plant EO-loaded nanoliposomes by a thin-film hydration sonication method. The encapsulation efficiency and average size of nanoliposomes reached 46% 69% and 93 96 nm, respectively. Wu et al. (2015) prepared nanoliposomes containing cinnamon EO (CEO) using thin-film ultrasonic dispersion with a particle size of 107 nm, encapsulation efficiency .84%, and zeta potential of 130 mV, which were suitable for use in active packaging. Gahruie, Ziaee, Eskandari, and Hosseini (2017) prepared Zataria multiflora EO (ZMEO) nanoemulsions using a high-intensity sonication method. The results suggested that at high sonication times, the average droplet size was decreased; it reached 90.9 nm after 10 min sonication. Ghadetaj, Almasi, and Mehryar (2018) fabricated nanoemulsions confining Grammosciadium ptrocarpum Bioss. EO (GPEO) with a diameter of 118 nm by employing water and Tween 80 as a nonionic surfactant, which provided high antioxidant activity (20.86%) for nanoemulsions of 1% GPEO. Alexandre, Lourenc¸o, Bittante, Moraes, and do Amaral Sobral (2016) added ginger EO (GEO)-loaded nanoemulsions into gelatin films. The size of the produced nanoemulsions were 150, 137, and 133 nm, for 1%, 3%, and 5% of GEO, and zeta potential varied between 29.3 and 31.0 mV. In a study by Nazari et al. (2019), cinnamon EOnanophytosomes were prepared by a thin-film hydration method that were around 65 nm and 92% in mean particle diameter and encapsulation efficiency, respectively; the particles were slightly homogeneous in size and shape. Some examples of applied nanoencapsulated essential oils in active packaging have been provided in Table 13.1.

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13.4.4 Peptides and antimicrobial agents Antimicrobial peptides (AMPs) are protein molecules which are produced by multicellular organisms (fungi, amphibians, and mammals). Different AMPs play important roles in the control of foodborne pathogenic and spoilage microorganisms, reducing the risk of chronic diseases, and improving the immune system, and in addition many have other beneficial functions (e.g., antioxidant, antithrombotic, antihypertensive, immunomodulatory, and antitumor activities) (Fjell, Hiss, Hancock, & Schneider, 2012; Nguyen, Haney, & Vogel, 2011). They are usually relatively short amino acid chains (i.e., 12 100 amino acids), positively charged (net charge of 12 to 19 mV), and amphipathic molecules; the activity of different peptides depends on a number of parameters, such as the amino acid sequence and composition (Jenssen, Hamill, & Hancock, 2006; Peters, Shirtliff, & Jabra-Rizk, 2010). The AMPs, such as bacteriocins (nisin, pediocin, lacticin, enterocin A, and lactoferrin) have been used in food preservation (Ahmad et al., 2017; Perez Espitia et al., 2012). These compounds can be applied into polymer matrices to develop antibacterial packaging owing to their significant inhibitory effects against microorganisms. Many studies have been carried out in the area of nanoencapsulating antimicrobial compounds in packaging materials during recent years. Lysozyme and nisin are maybe the most used AMPs in the food industry as food biopreservatives. For example, Imran et al. (2012) nanoencapsulated nisin by nanoliposomes formulated through soy-lecithin. The encapsulation efficiency was 50% and the size of the nanocarriers was around 151 nm. In another study, Cui, Wu, Li, and Lin (2017) produced poly-g-glutamic acid/chitosan (GC) nanoparticles by a self-assembly technique to encapsulate nisin; the results showed a mean size of 214.3 402.1 nm, encapsulation efficiency (27.1% 49.3%), and zeta potential (35.8 46.1 mV). Silva, Vilela, Almeida, Marrucho, and Freire (2018) investigated the incorporation of lysozyme nanofibers into pullulan-based packaging. The antioxidant activity was about 77% for 15% lysozyme within the fibers. Montero et al. (2019) analyzed the possibility of encapsulating shrimp peptide fractions in nanoliposomes. These liposomes provided the highest stability, with a z-average of  100 nm, a zeta potential of 253.87 mV, and a relatively high encapsulation efficiency (  52%).

13.4.5 Vitamins In addition to the bioactive ingredients mentioned above, various functional ingredients like flavors and aromas, vitamins, enzymes, minerals, and probiotics can also be added into the packaging matrix, in order to improve their functionalities. Noronha, de Carvalho, Lino, and Barreto (2014) prepared α-tocopherol nanocapsules by a nanoprecipitation method and then added them to methylcellulose (MC) films. The results showed that the addition of nanocapsules to MC films increased the antioxidant activity. Mirzaei-Mohkam, Garavand, Dehnad, Keramat, and Nasirpour (2019) encapsulated α-tocopherol in polycaprolactone using a sonication technique with a high encapsulation efficiency (88.43% 99.66%) and antioxidant

Nanoencapsulated bioactive components for active food packaging

503

activity (68.85%). Galindo-Pe´rez, Quintanar-Guerrero, Mercado-Silva, RealSandoval, and Zambrano-Zaragoza (2015) fabricated nanoparticles through emulsification diffusion method for the nanoencapsulation of tocopherol. They concluded that the film systems had a size of 190 260 nm (PDI 5 , 0.3) and a zeta potential .|35| mV.

13.5

Effects of bioactive-loaded nanocarriers on packaging properties

13.5.1 Effect on antimicrobial properties One of the greatest reasons for food degradation is spoilage by the growth of pathogenic microorganisms (Viuda-Martos et al., 2011). Lipid oxidation and changes in the organoleptic properties of foods can be accelerated by spoilage microorganisms (Saggiorato et al., 2012). Bioactive compounds are added to packaging materials with the aim of a controlled rate of release of the antimicrobials entities during storage and distribution, resultinng in minimization or even elimination of undesirable microorganisms and thus an increased storage period (Zhang, Hortal, Dobon, Bermudez, & Lara-Lledo, 2015). Meanwhile, the incorporation of bioactive compounds can improve the antibacterial properties of active packaging (Table 13.2). Makwana et al. (2014) investigated the antimicrobial properties of free and nanoencapsulated cinnamaldehyde into polylactic acid (PLA) films against G 2 (E. coli) and G 1 bacteria (B. cereus). They found that B. cereus was more susceptible (4.81 log10 CFU/mL reduction), while the sensitivity of E. coli was low (2.01 log10 CFU/mL reduction). In addition, cinnamaldehyde nanoemulsions incorporated in chitosan films have shown a greater inhibition effect on C. albicans than E. coli and S. aureus (Chen et al., 2016). Gelatin films incorporated with CEO nanoliposomes were tested against E. coli, S. aureus, and A. niger. The nanoactive films containing CEO nanoliposomes showed a better control of pathogens compared to the gelatin CEO films after storage for 3 days (Wu et al., 2015). Otoni et al. (2014a) studied the antibacterial activities of pectin/papaya puree with cinnamaldehyde nanoemulsions against two G (E. coli, Salmonella enterica) and two G 1 bacteria (L. monocytogenes, S. aureus). They found that cinnamaldehydeadded films markedly inhibited the growth of tested microorganisms; however, the inhibitory effects varied with regard to droplets size. Cinnamaldehyde nanoemulsions-loaded films showed greater effectiveness against G 1 bacteria than G , since the hydrophilic outer membrane of G bacteria acts as a barrier for the diffusion of hydrophobic compounds (Fisher & Phillips, 2006). Pe´rez-Co´rdoba et al. (2018) evaluated gelatin chitosan-based films loaded with α-tocopherol, cinnamaldehyde, and garlic oil on the growth of Pseudomonas aeruginosa and L. monocytogenes. It was reported that P. aeruginosa exhibited a greater sensitivity compared to L. monocytogenes, due to the synergistic effects of chitosan and active compounds.

Table 13.2 Recent studies on the effect of nanoencapsulated bioactive compounds in the antibacterial properties of active packaging. Polymer matrix

Bioactive components

Target microorganism

Main results

References

Polylactic acid

Cinnamaldehyde

E. coli W1485, B. cereus

Makwana et al. (2014)

Pectin/papaya puree

Cinnamaldehyde

Zein sodium caseinate

Thymol

E. coli (ATCC 11229), S. aureus L. monocytogenes (ATCC 15313), Salmonella enterica E. coli, Salmonella

Gelatin chitosan

α-Tocopherol, cinnamaldehyde, garlic oil Cinnamon essential oil

Pseudomonas aeruginosa (ATCC 15692), L. monocytogenes (ATCC 35152) E. coli, S. aureus, A. niger

Pullulan

lysozyme

S. aureus

HPMC

Thymus daenensis essential oil

E. coli (ATCC 25922), Salmonella typhi (PTCC 1609), Shigella dysenetriae (PTCC 1188), Shigella flexneri (PTCC 1234),

Reduced growth of B. cereus ,5 CFU/g and E. coli ,3 CFU/ g Improved antimicrobial properties with smaller droplets Inhibitory effect on E. coli, Salmonella Inhibitory effect on Pseudomonas aeruginosa Reduced growth of E. coli, S. aureus, A. niger until third day Increased antibacterial activity with increasing content of nanofibers. Inhibitory effects on the growth of bacteria and molds

Gelatin

Otoni et al. (2014a) Li et al. (2012) Pe´rez-Co´rdoba et al. (2018) Wu et al. (2015)

Silva et al. (2018)

Moghimi et al. (2017)

Acinetobacter baumannii (Clinical strain), Klebsiella peneumoniae (clinical strain), S. aureus (ATCC 25923), S. epidermidis (ATCC 1435), B. subtilis (ATCC 465), Enterococcus faecalis (ATCC 29212), Enterococcus faecium (clinical strain), methicillinresistant S. aureus, C. albicans L. monocytogenes

HPMC

Nisin

Chitosan

Urtica dioica L. (NE)

S. aureus (ATCC 25923)

Whey protein isolate

Thyme

Whey protein isolate

Grammosciadium ptrocarpum Bioss. essential oil

Basil seed gum

Zataria multiflora essential oil

S. aureus (ATCC-19111), E. coli O157:H7 (ATCC-11775) L. monocytogenes ATCC-13932, E. coli O157:H7, ATCC-11775, Salmonella typhimurium ATCC14028, Pseudomonas aeruginosa ATCC27853 B. cereus (ATCC 11778), E. coli (ATCC 35218)

Chitosan

Cinnamaldehyde

E. coli, S. aureus, C. albicans

Inhibiting the growth of L. monocytogenes Increased antibacterial activity with NEloaded nanoliposomes Decreasing the growth of E. coli, S. aureus High antimicrobial activity with GEO nanoemulsions

Imran et al. (2012) Haghju et al. (2016)

Reduced .3 log CFU/g of B. cereus and E. coli Inhibited the growth of E. coli, S. aureus, C. albicans

Gahruie et al. (2017)

Aziz and Almasi (2018) Ghadetaj et al. (2018)

Chen et al. (2016) (Continued)

Table 13.2 (Continued) Polymer matrix

Bioactive components

Target microorganism

Main results

References

Gelatin

Ginger essential oil

No antimicrobial activity due to low concentration

Alexandre et al. (2016)

Corn starch sodium caseinate Starch carboxymethyl cellulose Polylactic acid

Orange essential oil, limonene Rosemary essential oil Cinnamon essential oil

S. aureus (ATCC 29,213), Pseudomonas aeruginosa (ATCC 15442), E. coli (ATCC 25,922), Salmonella enteritidis (ATCC 13,076) L. monocytogenes (CIP 82110)

Not antilisterial activity

Jime´nez et al. (2014) Mohsenabadi et al. (2018) Wen et al. (2016)

S. aureus E. coli, S. aureus

High inhibitory effects on S. aureus MIC values: 1.0 mg/ mL (S. aureus) and (E. coli)

Nanoencapsulated bioactive components for active food packaging

507

The antimicrobial activity of hydroxypropyl methylcellulose (HPMC) edible films incorporated with nisin was investigated with regards to the control of L. monocytogenes (Imran et al., 2012). HPMC films with free and encapsulated nisin had better antimicrobial activity against L. monocytogenes, compared with 100% encapsulated and free nisin. In another study carried out by Silva et al. (2018), lysozyme nanofibers were incorporated into pullulan to obtain films with a high antimicrobial activity against S. aureus. Pullulan films containing the highest concentration of lysosome nanofibers reduced the growth of S. aureus by 2 3 log CFU/cm2 after 48 h. Li et al. (2012) studied the antimicrobial effects of active films containing thymol encapsulated within zein sodium caseinate nanoparticles; the inhibitory effect of films was dependent on the loading of thymol, being mainly effective against E. coli and Salmonella at thymol-to-zein ratios of 30% 2 40%. Moghimi, Aliahmadi, and Rafati (2017) investigated the antimicrobial effect of HPMC with nanoemulsions of Thymus daenensis EO (F1: wild, F2: cultivated) against seven G 1 (S, aureus, S. epidermidis, B. subtilis, Enterococcus faecalis, Enterococcus faecium, methicillin-resistant S. aureus), six G 2 (E. coli, Salmonella typhi, Shigella dysenetriae, Shigella flexneri, Acinetobacter baumannii, Klebsiella peneumoniae), and a fungus (Candida albicans). They found that G 1 bacteria, except S. typhi, were more susceptible to T. daenensis EO (F2) (high amount of thymol and carvacrol), while G bacteria were very sensitive to the applied T. daenensis EO (F1) (high amount of p-cymene). It was also observed that the antibacterial effects of F2 were greater than F1 against C. albicans. EO of G. ptrocarpum Bioss incorporated in whey protein isolate (WPI) edible films, showed that the films obtained with nanoemulsion encapsulated forms had higher levels of antibacterial characteristics, and it showed an increasing trend at higher EO concentrations (Ghadetaj et al., 2018). Edible films based on gelatin were incorporated with a nanoemulsion of ginger EO (GEO). The results presented antimicrobial activity of GEO against Pseudomonas aeruginosa and S. aureus, while film formulations did not show any antimicrobial activity against tested bacteria. In a work performed by Gahruie et al. (2017), EO of Zataria multiflora (1%, 2%, and 3%) were added to film-based basil seed gum and their effects on B. cereus and E. coli were studied. The films containing 3% Zataria multiflora EO decreased viable cell count of B. cereus and E. coli by about 3 log CFU/mL. The antimicrobial effects of chitosan films with Urtica dioica L. extract-loaded nanoliposomes against S. aureus also showed that these films had a less inhibitory zone compared with free extract, since encapsulation of the active compounds causes slow release and leads to lower antimicrobial effectiveness (Haghju et al., 2016). Similarly, Jime´nez, Sa´nchez-Gonza´lez, Desobry, Chiralt, and Tehrany (2014) did not observe any antimicrobial activity of the corn starch sodium caseinate composite films containing orange EO or limonene, which could be owing to their low antilisterial activity. Starch carboxymethyl cellulose (CMC) films with rosemary EO encapsulated in benzoic acid chitosan nanogels revealed a high antibacterial activity against S. aureus (Mohsenabadi, Rajaei, Tabatabaei, & Mohsenifar, 2018).

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13.5.2 Effect on antioxidant properties The use of antioxidant agents and oxygen scavengers in the packaging prevents or slows down the oxidation reactions in foods (Hosseini et al., 2019). The challenges with the use of bioactive compounds are losses in activity and content during storage (Wu et al., 2013). Many efforts have been made to combine bioactive compounds into food packaging for controlling release, which can retard the oxidation of food products and extend storage time (Colı´n-Cha´vez, Soto-Valdez, Peralta, Lizardi-Mendoza, & Balandra´n-Quintana, 2013; Sanches-Silva et al., 2014). Various phenolic compounds have been incorporated into films, which can improve antioxidant activity (Akhtar et al., 2012; Wu et al., 2013). One of the most promising novel systems to protect active compounds from premature reactions with oxygen and light is nanoencapsulation before incorporation into the film matrix. For example, Liang et al. (2017) studied the antioxidant activity of films prepared from chitosan hydrochloride (CHC) incorporated with EGCG-loaded nanocapsules; these films had higher antioxidant properties than the control film. Liu et al. (2015) produced gelatin films and used the DPPH method to show that tea polyphenol nanoparticles improved antioxidant properties of gelatin film. Wang et al. (2019) used gelatin to prepare biodegradable films supplemented by anthocyanins-loaded CHC and CMC nanocomplexes. The results showed that scavenging activity of control and gel-CHC/CMC-anthocyanin films were 29.5% and 87.3% at 25 C, respectively. Esmaeili and Ebrahimzadeh Fazel (2016) added Ferulago angulata EO-loaded nanocapsules in MC films and determined the DPPH radical scavenging activity; higher nanocapsule concentrations increased the scavenging activity of films, probably due to the amount and strength of added antioxidant compounds. Li et al. (2012) made antimicrobial films with thymol-loaded zein 2 sodium caseinate nanoparticles and measured radical scavenging activity. Increase of thymol-to-zein ratios, from 0% to 40%, resulted in an increased DPPH scavenging activity from 25% to 52%. Almasi, Zandi, Beigzadeh, Haghju, and Mehrnow (2016) reported that the antioxidant activity of chitosan films containing Urtica dioica L.-loaded nanoliposomes was less than the free extract and pure chitosan. In another study, Aziz and Almasi (2018) showed that WPI films containing TE-loaded nanoliposomes had an antioxidant activity lower than free TE. Mirzaei-Mohkam et al. (2019) fabricated CMC films containing α-tocopherol nanocapsules and used the DPPH method to show that the films containing 70% nanocapsules had higher antioxidant properties compared with other films.

13.5.3 Effect on mechanical properties The tensile properties of food packaging materials, such as the tensile strength (resistance to elongation, TS), the percent elongation at break (EAB) (capacity for stretching), and the elastic modulus are analyzed through tensile tests (ASTM D882, 2001; Vieira, da Silva, dos Santos, & Beppu, 2011). These are generally important for an active packaging as it needs to retain its cohesion integrity and be resistant to external stress during utilization, storage, and handling. These properties

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are primarily dependent on the nature of polymer, type of bioactive agent, procedure applied to formulating the final product, and processing and storage conditions (Auras, Singh, & Singh, 2005; Shojaee-Aliabadi et al., 2014). The interaction between bioactive ingredients with polymer matrix can influence the mechanical and structural properties of the resulting packaging, that can be positive or negative depending on the polymer and bioactive ingredient. The effect of nanoencapsulated bioactive compounds on the mechanical properties of active packaging is summarized in Table 13.3. Incorporation of tea polyphenol-loaded chitosan nanoparticles (TPCN) into a gelatin-based film caused a significant enhancement in TS and reduction in EAB compared by 100 bloom value to the control film (Chen et al., 2017). In a study by Chen et al. (2016), cinnamaldehyde nanoemulsions decreased the TS and increased the EAB, by crosslinking between cinnamaldehyde and chitosan. The effect of adding α-tocopherol nanocapsules on the mechanical properties of MC films has also been reported. Incorporation of α-tocopherol into the formulation resulted in a significant decrease in TS, while increasing the EAB (Noronha et al., 2014). When TPCN were added to gelatin films, TS greatly decreased and EAB slightly decreased (Bao et al., 2009). Also, cassava starch films with added lycopene nanocapsules significantly increased TS value; EAB value showed an increase at 2% concentration of lycopene nanocapsules (Assis et al., 2017). According to Silva et al. (2018), the tensile properties of chitosan films improved with the incorporation of lysozyme nanofibers. The maximum EAB occurred for pullulan film (6.63%), whereas those with 1.0% and 15.0% lysozyme nanofiber presented a 61% and 80% reduced EAB value, respectively, but there were no significant differences on the TS value compared to control films. Otoni, Pontes, Medeiros, and Soares (2014b) reported that EO acted as a plasticizer for MC films. They demonstrated that the addition of oregano and clove bud EOs brought about a threefold increase in EAB of MC films; however, the addition of EOs had no significant effect on TS values. Other studies have also shown this plasticizing effect, such as carvacrol and cinnamaldehyde in soy protein isolate (SPI) films (Otoni, Avena-Bustillos, Olsen, Bilbao-Sa´inz, & McHugh, 2016), epigallocatechin gallate in chitosan films (Liang et al., 2017), cinnamon in polyvinyl alcohol nanofibers (Nazari et al., 2019), Zataria multiflora EO in basil seed gum (Gahruie et al., 2017), ginger EO in gelatin films (Alexandre et al., 2016), and Thymus daenensis EO in HPMC films (Moghimi et al., 2017). In a study by Otoni et al. (2014a), a significant increase in TS was reported by 72% pectin papaya films after cinnamaldehyde addition at 15% by an antiplasticizing effect. In cassava starch films with added bixin nanocapsules, TS value increased significantly from 12.13 to 14.40 MPa when the bixin nanocapsules concentration increased from 0% to 2%; for concentrations .2%, the films exhibited a significant decrease in TS. Nevertheless, an inverse impact was observed in relation to EAB. This suggests that the interactions between hydrophobic compounds and film-forming polymers yield increased spacing between macromolecule chains, reducing the ionic and hydrogen bonding between the chains, and thus leading to the improved structural properties of the films (Pagno et al., 2016). According to

Table 13.3 Effect of nanoencapsulated bioactive compounds on the mechanical and barrier properties of active packaging. Polymer

Methylcellulose Cassava starch Cassava starch Cassava starch Gelatin Chitosan

Bioactive components (BC)

α-Tocopherol

Lycopene Bixin β-Carotene Tea polyphenols Epigallocatechin gallate Gelatin chitosan Cinnamaldehyde, α-tocopherol, garlic oil Chitosan Cinnamaldehyde Soy protein Cinnamaldehyde Carvacrol isolate Low methoxyl Cinnamaldehyde pectin/papaya puree High methoxyl pectin/papaya puree Gelatin Anthocyanins Methylcellulose Ferulago angulate essential oil

TS (MPa)

E (%)

WVP Without BC

O2

Without BC

With BC

Without BC

With BC

57.82

23.19

17.91

30.03

3.09 14.40 6 1.69 3.09 6 0.1 62.6 6 3.7 6.44 6 0.28

2.66 1.94 6 0.37 2.63 6 0.18 41.0 6 3.4 18.10 6 4.10

134.59 2.19 6 0.35 134.59 6 2.69 18.5 6 3.4 22.50 6 4.32

166.03 34.34 6 3.40 319.74 6 3.35 18.8 6 3.1 3.93 6 2.58

19.0 6 2.1

9.8 6 3.7

101.4 6 4.5

39.2 6 3.6

98.26 6 5.69 2.61 6 0.54 2.61 6 0.54 5.36 6 0.42

7.57 6 1.34 2.52 6 0.21 1.97 6 0.11 6.53 6 0.68

4.16 6 0.47 172.4 6 45.8 172.4 6 45.8 246.10 6 22.96

12.61 6 2.21 373.6 6 50.4 417.7 6 36.8 145.70 6 16.68

1.42 6 0.29 2.89 6 0.24 2.89 6 0.24 3.10 6 0.1

3.91 6 0.59 2.83 6 0.09 2.99 6 0.28 2.90 6 0.1

4.84 6 0.29

8.36 6 0.15

191.6039.38

180.27 6 13.75 3.26 6 0.02

2.95 6 0.02

0.99 6 0.15 50.281

1.91 6 0.07 21.31

192.07 6 4.79 10.208

219.34 6 2.53 28.00

0.36 0.202 6 0.008 0.36 6 0.05 0.179 6 0.004

With BC

Without BC

0.55 0.273 6 0.018 0.44 6 0.03 0.224 6 0.013 15.67 6 0.62

References With BC Noronha et al. (2014) Assis et al. (2017) Pagno et al. (2016) Assis (2017) 15.50 6 0.65 Bao et al. (2009) Liang et al. (2017) Pe´rez-Co´rdoba et al. (2018) Chen et al. (2016) Otoni et al. (2016) Otoni et al. (2014a)

Wang et al. (2019) Esmaeili and Ebrahimzadeh Fazel (2016)

Clove bud Oregano essential oil Thymol

5.40 6 1.13 5.40 6 1.13

6.11 6 1.26 7.61 6 1.32

20.46 6 2.71 20.46 6 2.71

56.61 6 5.59 54.77 6 1.66

4.4 6 0.7

2.9 6 0.5

115.7 6 21.8

97.7 6 11.1

0.35 6 0.05

0.40 6 0.04

Cinnamon Cinnamon Urtica dioica L. Thyme

4.80 6 0.32 8.97 6 1.57 58.39 6 0.43 7.07 6 0.31

45.32 6 5.06 6.50 6 1.07 48.45 6 0.70 8.67 6 0.57

47.89 6 3.12 65.41 6 6.49 13.43 6 0.55 14.54 6 1.21

11.07 6 5.1 85.71 6 8.61 16.37 6 0.38 19.65 6 2.87

4.84 6 0.27 2.33 6 0.1 12.54 3 10212 3.6 3 10210

1.07 6 0.04 1.96 6 0.05 10.79 3 10212 3.3 3 10210

0.565 6 0.16

0.325 6 0.09

95.21 6 19.692 85.57 6 45.51

2.75 6 0.07

3.04 6 0.13

19.74 6 1.86

34.64 6 2.12

21.55 6 2.24

39.54 6 2.01

2.649 6 0.23

3.051 6 0.18

11.405 6 1.19

14.411 6 1.54

2.937 3 1027

4.103 3 1027

Gelatin

Rosemary essential oil Zataria multiflora essential oil Grammosciadium ptrocarpum Bioss essential oil Thymus daenensis essential oil Ginger essential oil

F1 36.2 6 0.7 19.3 6 1.0 F2 36.2 6 0.7 22.6 6 0.7 30.2 6 3.3 29.7 6 1.4

14.1 6 0.4 14.1 6 0.4 48.2 6 4.9

9.02 6 0.3 14.2 6 0.04 56.0 6 5.9

HPMC Pullulan

Nisin Lysozyme

59.0 6 6.8 35.0 6 4.4

6.0 6 3.3 6.63 6 1.1

2.6 6 0.7 1.34 6 0.10

Methylcellulose

Quinoa protein/ chitosan Polyvinyl alcohol Gelatin Chitosan Whey protein isolate Starch CMC Basil seed gum Whey protein isolate

HPMC

37.0 6 2.5 31.3 6 2.3

Otoni et al. (2014b)

0.30 6 0.01

0.30 6 0.01

0.77 6 0.03

0.95 6 0.10

Robledo et al. (2018) Nazari et al. (2019) Wu et al. (2015) Haghju et al. (2016) Mohsenabadi et al. (2018) Gahruie et al. (2017) Ghadetaj et al. (2018)

7.4 6 1.6

10.8 6 0.8

Moghimi et al. (2017) Alexandre et al. (2016) Imran et al. (2012) Silva et al. (2018)

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Assis et al. (2018), EBA increased and TS decreased after the incorporation of β-carotene nanocapsules in cassava starch films. In another study, Esmaeili and Ebrahimzadeh Fazel (2016) reported a decrease in TS and an increase in EAB of MC films containing Ferulago angulata EO due to hydrophobic interactions between phenolic compounds and film-forming polymers. The TS and EAB were higher for nanoemulsified films than macroemulsion and control films. This behavior suggests that the plasticizing effect of EO droplets is decreased in the nanoscale and thus reduces film flexibility (Ghadetaj et al., 2018). Haghju et al. (2016) investigated the properties of chitosan-based films containing Urtica dioica L. nanoliposomes at different concentrations (0%, 0.5%, 1%, and 1.5% w/w). Based on their findings, TS was reduced after incorporation of Urtica dioica L. nanoliposomes in chitosan films, but did not significantly affect EAB except for 1.5% w/w, which was affected by the cross-linking with the chitosan matrix.

13.5.4 Effect on barrier properties The barrier properties (water vapor and oxygen) for the packaged foods are crucial factors because they may transfer from the internal or external environment through the polymer matrix; thus the determination of these properties is required in order to achieve the desirable quality, safety, and shelf life (Bedane, Ei´c, FarmahiniFarahani, & Xiao, 2015). The special barrier necessity of any package is associated with the product characteristics and the intended end-use application. The water vapor and oxygen barrier is determined by permeating the amount of water vapor/ oxygen per unit of area and time in a packaging material. Oxygen permeability and water vapor permeability (WVP) of a packaging container for food products have an important role on its preservation. For instance, polymer packaging with a low oxygen permeability coefficient leads to reduced oxygen pressure inside the container meaning that oxidation is retarded, and thus extending the shelf life of the product (Miller & Krochta, 1997; Siracusa, Rocculi, Romani, & Dalla Rosa, 2008). The effects of nanoencapsulated bioactive compounds on the barrier properties of active packaging are summarized in Table 13.3. Otoni et al. (2014a) found that the addition of cinnamaldehyde (15%) decreased the WVP of pectin/papaya puree films by the antiplasticizing impact of phenolic compounds consistent with the changes in tensile properties. Otoni et al. (2016) reported a significant decrease of WVP for carvacrol and cinnamaldehyde introduced in SPI films. The improvement of water barrier properties depends on the concentration, type of lipid, particle size, and emulsifier. Assis et al. (2017) reported that the addition of lycopene nanocapsules increased the WVP of cassava starch films. No effect was observed at 2% and 5% concentration of lycopene nanocapsules; however, the higher concentration (8%) led to a reduction of WVP due to its hydrophobic character. In another study, the presence of bixin nanocapsules in cassava starch films increased the WVP. It was reported that the addition of bixin nanocapsules in the cassava starch films causes an increase in the cohesive forces of the film network, increasing the transport of water vapor through the film matrix, which in turn can increase the WVP (Pagno et al., 2016).

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A similar effect was observed by Robledo et al. (2018) and Alexandre et al. (2016), so that the WVP of quinoa protein/chitosan and gelatin films after the addition of thymol and ginger, respectively, was similar to the control film. According to Imran et al. (2012), HPMC films containing nisin in nanoemulsion form (free and encapsulated) decreased the permeability to oxygen. This was explained by the presence of nisin in nanoactive films, which makes the matrix more compact. Bao et al. (2009) showed a decrease in WVP of gelatin films due to the addition of TPCN. Furthermore, the addition of TPCN improved the oxygen barrier property of gelatin films. Chen et al. (2016) reported that WVP of chitosan films increased when levels of cinnamaldehyde nanoemulsions increased at different humidities. It was reported that WVP of polyvinyl alcohol nanofibers decreases from 4.84 to 1.07 3 10210 g/m.s.Pa after the incorporation of cinnamon-loaded nanophytosomes. The decrease in WVP following the incorporation of EOs has been shown in several works, for example, rosemary EO encapsulated in chitosan nanogel in starchCMC films (Mohsenabadi et al., 2018), Urtica dioica L nanoliposomes in chitosan films (Haghju et al., 2016), and G. ptrocarpum Bioss EO nanoemulsions in WPI (Ghadetaj et al., 2018). However, the presence of ginger EO did not significantly affect the WVP with respect to the pure gelatin films (around 0.3 gmm/hm2 kPa) (Alexandre et al., 2016).

13.6

Controlled release and migration of bioactive compounds from active food packaging

There are many potential advantages for the use of bioactive ingredients in active packaging; nevertheless, there is a major concern about the possible risks related to migration from the packaging into the foods, where it can be harmful to human health (Pilevar, Bahrami, Beikzadeh, Hosseini, & Jafari, 2019). Basically, a material moves from the point where its concentration is high to where its concentration is low, and this phenomenon continues until the concentration of the migratory material reaches equilibrium in both environments (Huang et al., 2015). Food composition, type of polymer, high level of film hydration, and concentration of migrant substance can influence the migration mechanism of active ingredients into the food matrix; furthermore they can enhance the release rate of bioactive compounds from the film matrix into the food or simulant. In addition, high temperatures also are effective because they increase the mobility of the molecules of active agents. The migration because of chemical affinity/solubility between the migrant and the food simulant/food may be hastened owing to the film thickness (Kuorwel, Cran, Sonneveld, Miltz, & Bigger, 2013). For this purpose, the potential for migration or release of the active agents can be investigated through migration tests. Fig. 13.2 shows the packaging released substances into the food and scavenging systems. As previously represented, the addition of antioxidant or antimicrobial compounds into edible films and coatings could alter their functional properties, such as

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Figure 13.2 Parameters related to active release and scavenging food packaging systems.

mechanical and barrier properties, thus altering the release and bioactivity of the compounds. Edible films and coatings also could control the release of bioactive ingredients using simple factors like temperature, humidity, changes in pH, and mechanical properties of the matrix. Various factors are effective in determining the release from packaging like molecular form, size, polarity, and weight of bioactive compound. However, additional treatments like cross-linking could be used to modify the structure. The cross-linking could also provide a much better controlled release necessary for active packaging applications. The release of an active compound from a matrix may be controlled by melting, diffusion, degradation, or particle fracture or a combination of them (Quiro´s-Sauceda, Ayala-Zavala, Olivas, & Gonza´lez-Aguilar, 2014). Common approaches to achieve controlled release are blending two or more different polymers (by extrusion compounding process) and multilayer structures (active compound placed into surface layer for direct contact with food) (Chen, Chen, Xu, & Yam, 2019). One of the valid solutions for controlling the release of bioactive compounds in packaging can be nanoencapsulation. Examples of scientific studies on bioactive release form food packaging loaded with different nanocarriers are listed in Table 13.4. For example, the release of tea polyphenols was investigated by Liu et al. (2017). These authors incorporated the nanoparticles into gelatin and different food simulants (50% ethanol solution at 4 C and 95% ethanol, at 25 C, for 10-day contact period). It was reported that tea polyphenols were released faster and greater from films in 50% ethanol (4 C) than in 95% ethanol (25 C) fatty food stimulant, which increased with swelling in water. The release profiles of tea polyphenols from all films were similar; the diffusion coefficient in 50% ethanol was double that of 95% ethanol. Liang et al. (2017) determined the release of EGCG

Table 13.4 Overview of studies on the release of bioactive compounds from active packaging. Active agent

Matrix

Bioactive compounds

Release conditions

Main result

References

Phenolic compounds

Gelatin

Tea polyphenols

50% ethanol (4 C) 95% ethanol (25 C)

Liu et al. (2017)

Chitosan

Epigallocatechin gallate Cinnamaldehyde

Anthocyanins

Ethanol 95% and 50% (25 C) 10 and 50% (v/v) ethanol water 50 mL Milli-Q water (25 C) 95% ethanol (25 C)

Gelatin

Cinnamon essential oil (CEO)

0.25% v/v ethanol (4 C, 40 C)

Methylcellulose

Ferulago angulata

95% (v/v) ethanol (20 C)

Released faster in 50% ethanol (4 C) Swelling induced release Increased the release rate at higher EGCG Released faster in 50% ethanol Increased the release rate from 28% to 44% Gel-CHC/CMC-ACNs was effective to delay the release of anthocyanins Decreased the CEO release rate with addition of CEO nanoliposomes Increased the release rate with increasing of FEO

Whey protein isolate

Grammosciadium ptrocarpum

Water (4 C, 25 C, and 40 C)

Chitosan

Urtica dioica L.

Water; 95, 10% ethanol; 3% acetic acid (4 C, 25 C, 40 C)

Chitosan Zein-sodium caseinate Gelatin

Essential oils

Thymol

Increased the release rate at higher temperatures Swelling induced release Decreased release rate in 95% ethanol with nanoencapsulation of NE

Liang et al. (2017) Chen et al. (2016) Li et al. (2012) Wang et al. (2019) Wu et al. (2015)

Esmaeili and Ebrahimzadeh Fazel (2016) Ghadetaj et al. (2018) Almasi et al. (2016)

(Continued)

Table 13.4 (Continued) Active agent

Matrix

Bioactive compounds

Release conditions

Main result

References

Whey protein isolate

Thyme

95% ethanol (4 C, 25 C, 40 C)

Aziz and Almasi (2018)

Carotenoids

Xanthan gum

β-carotene

Cyclohexane (4 C)

Others

Methylcellulose

α-Tocopherol

CMC

α-Tocopherol

95% (v/v) ethanol (25 C) 95% (v/v) ethanol

Decreased release rate in 95% ethanol with nanoencapsulation of TE Maximum release for β-carotene/ xanthan gum was 39.7 μg/g Increased the release rate after 1h Increased the release rate at higher concentrations, temperatures and storage times

ZambranoZaragoza et al. (2017) Noronha et al. (2014) MirzaeiMohkam et al. (2019)

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517

incorporated into chitosan films in various simulants (95% and 50% ethanol) after 10 days at 25 C. Using chromatography, they detected the presence of EGCG in chitosan zein films with a mass ratio of 5:1. They also found that the release rate of EGCG increased at higher levels of nanocapsules in the films. Consequently, the release of EGCG was relatively rapid into food simulant while the concentration oscillates between times. Chen et al. (2016) measured the release of cinnamaldehyde incorporated into chitosan films in various simulants (at 10% and 50% (v/v) ethanol water solvents). The release rate of cinnamaldehyde was higher in the samples with higher alcohol content (50%), possibly due to the nonpolarity of cinnamaldehyde. Li et al. (2012) studied the release of thymol from zein sodium caseinate nanoparticle-based films and reported that the release rate of thymol increased from 28% to 44% after 6.5 h with increasing thymol-to-zein ratios. Moreover, thymol was preferably retained within the nanoparticles, which was capable of forming H-bonding with zein, a proline-rich protein. Wang et al. (2019) showed that the release rate of anthocyanin nanocomplexes (ACNs) was much faster from gelatin ACNs films (18.7%) than gelatin chitosan/CMC ACNs films (9.0%) into 95% ethanol after 120 h. Wu et al. (2015) produced a gelatin film with cinnamon EO (CEO) nanoliposomes and studied the release of cinnamon into food simulants (ethanol 0.25 v/v at 4 C and 40 C). The authors showed that more than 60% and 80% CEO was released at 11 and 99.5 h, respectively; thus it can improve time-controlled release to increase the shelf life of food products. In another study, Esmaeili and Ebrahimzadeh Fazel (2016) investigated the release of Ferulago angulata EO (FEO) nanocapsules from MC films into 95% (v/v) ethanol at 20 C for 10 days by high-performance liquid chromatography (HPLC). Higher concentration of FEO nanocapsules in the films increased the release rate of phenolic agents of EO from MC-based films to the substitute food simulant. Ghadetaj et al. (2018) investigated the release of G. ptrocarpum Bioss. EO incorporated into WPI films immersed in water for 168 h at 4 C, 25 C, and 40 C. It was reported that temperature increased the release rate of EO from WPI films to food simulant (water). The swelling ratio of films was reported to be 1184% and could be controlled by the release rate. Almasi et al. (2016) studied the release rate of nettle extract (NE)-loaded nanoliposomes from chitosan films into water, 3% acetic acid, 10% ethanol, and 95% ethanol after 7 days at 4 C, 25 C, and 40 C. A decrease of antioxidant release rate in 95% ethanol was observed with the addition of NE nanoliposomes, and the effect of temperature on release rates was low from nanoactive films when storage temperature increased from 4 C to 40 C. The diffusion coefficient for chitosan films containing 1.5% w/w encapsulated NE was 18.80 3 1027 cm2/s at 25 C. Noronha et al. (2014) studied the release of α-tocopherol nanocapsules from MC films into 95% (v/v) ethanol after 10 days at 25 C. They reported a burst effect at 1 h and extended release of α-tocopherol to the food simulant. They also found that a constant concentration of α-tocopherol nanocapsules was released from MC under the same conditions. A study by Mirzaei-Mohkam et al. (2019) determined the release of α-tocopherol in CMC films into 95% ethanol as food simulant. The amount of α-tocopherol that migrated into the simulant increased with

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concentration and also was affected by temperature and storage time. ZambranoZaragoza, Quintanar-Guerrero, Del Real, Pin˜on-Segundo, and Zambrano-Zaragoza (2017) reported that the maximum controlled release of β-carotene for nanocapsules/xanthan gum and nanocapsules (25.5 and 39.7 g/g of fruit, respectively) was in the 9th day. The release kinetics of β-carotene from nanocapsule-based films can be described as a two-step; an initial controlled release of β-carotene (days 0 9) by burst effect, and a second steady decline in the β-carotene content (day 9 22) by continuous exudation of the fruit.

13.7

Application of active packaging loaded with nanoencapsulated bioactives in various food products

Active packaging can provide a packaging with antioxidant and/or antimicrobial properties and increased shelf life and quality, when applied to food. The overall performance of active packaging as oxidation protectors depends on its antioxidant and impeding oxygen ability. Several factors should be considered in the selection of packaging material and active agents, like temperature and environmental external factors for preventing oxidation, damage, or evaporation of volatile compounds, the chemical nature of packaging, chemical interaction of additives with polymer matrix, mass transfer coefficients, and physical properties of packaging materials (Han, 2005; Salgado, Ortiz, Musso, Di Giorgio, & Mauri, 2015). Many studies of the application of nanocapsules in active food packaging on a wide range of foods with the aim of studying their antioxidant and antibacterial effects have been reported; some examples are summarized in Table 13.5. As an example, Pabast et al. (2018) applied chitosan-free or nanoencapsulated Satureja plant EO edible coatings on cold-stored lamb meat to extend its shelf life. It was noted that these coating treatments caused a reduction in microbial growth and chemical spoilage. Sodium caseinate-based coatings containing ginger EO at 3 and 6% w/w were applied to extend the storage time of chicken breast fillets. Incorporation of 6% ginger in coating extended the shelf life and maintained the quality of chicken breast fillets (Noori, Zeynali, & Almasi, 2018). In recent research, Sharifimehr, Soltanizadeh, and Hossein Goli (2019) incorporated eugenol in Aloe vera coatings, which were used to coat pink shrimp. They retarded the formation of secondary oxidation products (7 days) and decreased drip loss and color changes with 20 g/L of Aloe vera and 30 mL/L of eugenol. In another study, the effect of chitosan coating with carvacrol nanoemulsions was evaluated on the preservation of green beans (Severino et al., 2015). It was reported that there was an antimicrobial effect against E. coli O157:H7 and S. typhimurium during storage. Moreover, authors reported that the combined treatment of coating, gamma irradiation, and modified atmosphere packaging resulted in a reduced microbial population.

Table 13.5 Application of active packaging containing nanoencapsulated bioactive compounds in various food products. Biopolymers

Bioactive components

Nanocarrier system

Food

Main conclusion

References

Chitosan

Satureja khuzestanica plant essential oil Thymol

Nanoliposome

Lamb meat

Pabast et al. (2018)

Nanoemulsion

Cherry tomatoes

Eugenol

Nanoemulsion

Shrimp

Thyme essential oil Carvacrol, mandarin, bergamot and lemon essential oils Nettle essential oil

Nanoparticle

Poultry meat

Nanoemulsion

Green bean

Increased antioxidant capacity, inhibitory effect against microbial growth and chemical spoilage Reduced growth of B. cinerea after 7 days at 5 C. A 30% level resulted in TBARs formation; drip loss and cooking loss decreased Good antimicrobial effect against C. jejuni Inhibitory effect on growth of E. coli and S. Typhimurium

Nanoemulsion

Beluga sturgeon

Gharibzahedi and Mohammadnabi (2017)

Cinnamon

Nanophytosome

Shrimp

α-Tocopherol

Nanoparticles, nanocapsule

Fresh cut apple

A 3.5% level of Nettle EO resulted in lowest changes on lipid oxidation, microbial growth and weight loss High antibacterial activity, increased shelf life Less browning index, maintaining firmness, extended shelf life

Quinoa protein/ chitosan Aloe vera

Gelatin Chitosan

Jujube gum

Polyvinyl alcohol Xanthan gum

Robledo et al. (2018) Sharifimehr et al. (2019) Lin et al. (2018) Severino et al. (2015)

Nazari et al. (2019) Zambrano-Zaragoza et al. (2014) (Continued)

Table 13.5 (Continued) Biopolymers

Bioactive components

Nanocarrier system

Food

Main conclusion

References

Xanthan Gum

Tocopherol

Nanocapsule

Fresh cut apple

Reduced enzymatic activity

Xanthan gum

β-Carotene

Nanocapsule

Fresh cut melon

Chitosan

Lemon, mandarin, oregano or clove essential oils Clove bud, oregano essential oils Mandarin essential oil Clove essential oil Ginger essential oil

Nanoemulsion

Vegetable products

Reduced loss of firmness and whiteness index Increased antimicrobial capacity with lemon; Reduced loss of firmness and color changes

Galindo-Pe´rez et al. (2015) Zambrano-Zaragoza et al. (2017) Sessa et al. (2015)

Nanoemulsion

Sliced bread

Inhibitory effect on yeasts and molds

Otoni et al. (2014b)

Nanoemulsion

Green beans

Donsı` et al. (2015)

Nanogel

Beef cutlets

Nanoemulsion

Chicken breast fillets

Nanoemulsion

Fresh-cut Fuji apples Cheese

Improved antimicrobial activity Good antimicrobial activity, extended shelf life Good antimicrobial activity, increased overall acceptance Inhibitory effect on growth of E. coli, extended shelf life Improved antimicrobial activity without any effect on sensory quality

Methylcellulose

Chitosan Chitosan Sodium caseinate Sodium alginate Polyethylene oxide

Lemongrass essential oil Nisin

Nanoparticles

Rajaei et al. (2017) Noori et al. (2018)

Salvia-Trujillo et al. (2015) Cui et al. (2017)

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521

Nanophytosomes containing cinnamon incorporated into PVA nanofibers by electrospinning technique had a low cell toxicity and high antibacterial activity and extended the shelf life of shrimp, indicating its high potential in active food packaging application (Nazari et al., 2019). In another study, thymol nanoemulsions were produced by spontaneous emulsification and ultrasound and were used to prepare quinoa chitosan films (Robledo et al., 2018). These films were applied on packs of cherry tomatoes, and inoculated with B. cinerea. The films exhibited antifungal activity at 5 C after 7 days compared with control samples. The thyme EO/β-cyclodextrin ε-polylysine nanoparticles incorporated into gelatin nanofibers and coated directly onto chicken showed a good antimicrobial effect against C. jejuni, and lower TBA, TVB-N, and pH values without any effect on sensory properties (Lin, Zhu, & Cui, 2018). A new development for the minimal browning effect on fresh-cut fruits is the use of browning-inhibitor agents in food packaging. In this case, nanoemulsions, nanoparticles, and nanocapsules of α-tocopherol have been incorporated into xanthan gum (Zambrano-Zaragoza, Mercado-Silva, Gutie´rrez-Cortez, CornejoVillegas, & Quintanar-Guerrero, 2014), improving the antibrowning effect and loss of firmness. Nanocapsules containing α-tocopherol were the best system followed by nanoemulsions and nanospheres. The effect of coating by xanthan gum with tocopherol nanocapsules was studied on the preservation of fresh-cut apples (Galindo-Pe´rez et al., 2015). Tocopherol nanocapsules exhibited over 50% reduction in the initial respiration rates, and lowest catalytic activity after 21 days of storage, showing a high potential application in preserving fresh-cut apples. In another study, β-carotene nanocapsules incorporated into xanthan coating showed lowest in the whiteness index and firmness; thereby, these coatings helped to preserve the melon quality and improved storage time up to 21 days (Zambrano-Zaragoza et al., 2017). EO-loaded nanoemulsions were added to a modified chitosan coating and applied to vegetable products (rucola leaves) which significantly extended the shelf life by about 3 7 days, without any alteration of palatability, color, firmness, and organoleptic properties (Sessa, Ferrari, & Donsı`, 2015). In another study, Otoni et al. (2014b) incorporated two EOs (clove bud and oregano) into MC films. The inhibitory effect of each formulation on the growth of molds and yeasts was investigated on sliced bread stored at 25 C. Results exhibited a good inhibitory effect of MC films containing both EOs against the growth of molds and yeasts, showing antimicrobial films could improve the shelf life of sliced bread. The antimicrobial activity of chitosan edible coatings incorporated with nanoemulsion of mandarin EO and its combination with a treatment of highpressure (HP) or pulsed light (PL) processing was used to control Listeria innocua on green beans at 4 C (Donsı` et al., 2015). A combination of HP and PL with chitosan film containing EO resulted in a reduction of cell count of around 4 and 2 Log cycles, at 400 MPa and 5 min for HP and 1.2 3 105 J/m2 for PL, respectively, indicating a synergism of antimicrobial effects. (Rajaei, Hadian, Mohsenifar, RahmaniCherati, & Tabatabaei, 2017) applied a chitosan coating incorporated with clove EOs encapsulated by chitosan myristic acid nanogel on beef cutlets. This led to a reduction in the Salmonella population and extended its shelf life. Salvia-Trujillo

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et al. (Salvia-Trujillo, Rojas-Grau¨, Soliva-Fortuny, & Martı´n-Belloso, 2015) studied the influence of adding nanoemulsions of lemongrass EO to a sodium alginatebased edible coating on the physicochemical properties of fresh-cut Fuji apples. Results showed that the incorporation of 0.5% and 1% (v/v) lemongrass in the coating had the potential for an extension of shelf life and maintenance of the quality of fresh-cut Fuji apples. In summary, the application as active packaging of a wide range of bioactive compounds nanoencapsulated in desirable material with antioxidant, antibacterial, and antifungal properties reduce the chemical and microbial spoilage, and improve the quality of foods with an increased storage time.

13.8

Perspective and future trends

The incorporation of nanoencapsulated bioactive compounds into active packaging has an effect on the mechanical, barrier, and antimicrobial properties of the packaging and this type of packaging is a highly promising field to preserve the quality and increase the shelf life of foods. This chapter has highlighted that nanoscale compounds have shown a great potential for the control of unfavorable impacts, including on lipid oxidation and microbial control, in order to prolong the storage time of foods. Active packaging that contains bioactive ingredients can play an important role in increasing the health-promoting effects of food on consumers through the production of healthier packaged foods. Many studies have been carried out regarding the nanoencapsulation of bioactive compounds with different methods. To summarize, the encapsulation of bioactive compounds has a number of benefits over direct application. Some important advantages of these strategies include the protection of volatile compounds, increasing their functionality, stability, and bioavailability, and the control of their release from the packaging material into food products. Nonetheless, deeper insight is required to solve the challenges of these methods including the interactions of nanosized particles with the food matrix, minimizing the costs, and reducing the loss of some properties of the packaging materials. Therefore these aspects should be studied to demonstrate their realworld application in many areas of food industries.

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Akhavan, S., Assadpour, E., Katouzian, I., & Jafari, S. M. (2018). Lipid nano scale cargos for the protection and delivery of food bioactive ingredients and nutraceuticals. Trends in Food Science & Technology, 74, 132 146. Akhtar, M. J., et al. (2012). Antioxidant capacity and light-aging study of HPMC films functionalized with natural plant extract. Carbohydrate Polymers, 89, 1150 1158. Available from https://doi.org/10.1016/j.carbpol.2012.03.088. Alexandre, E. M. C., Lourenc¸o, R. V., Bittante, A. M. Q. B., Moraes, I. C. F., & do Amaral Sobral, P. J. (2016). Gelatin-based films reinforced with montmorillonite and activated with nanoemulsion of ginger essential oil for food packaging applications. Food Packaging and Shelf Life, 10, 87 96. Almasi, H., Zandi, M., Beigzadeh, S., Haghju, S., & Mehrnow, N. (2016). Chitosan films incorporated with nettle (Urtica Dioica L.) extract-loaded nanoliposomes: II. Antioxidant activity and release properties. Journal of Microencapsulation, 33, 449 459. Assadpour, E., & Jafari, S. M. (2019a). Chapter 3—Nanoencapsulation: Techniques and developments for food applications. In A. Lo´pez Rubio, M. J. Fabra Rovira, M. martı´nez Sanz, & L. G. Go´mez-Mascaraque (Eds.), Nanomaterials for food applications (pp. 35 61). Elsevier. Available from https://doi.org/10.1016/B978-0-12-8141304.00003-8. Assadpour, E., & Jafari, S. M. (2019b). A systematic review on nanoencapsulation of food bioactive ingredients and nutraceuticals by various nanocarriers. Critical Reviews in Food Science and Nutrition, 59(19), 3129 3151. Available from https://doi.org/ 10.1080/10408398.2018.1484687. Assadpour, E., Jafari, S. M., & Esfanjani, A. F. (2017). Protection of phenolic compounds within nanocarriers. CAB Reviews, 12, 1 8. Available from https://doi.org/10.1079/ PAVSNNR201712057. Assis, R. Q., Lopes, S. M., Costa, T. M. H., Flˆores, S. H., & de Oliveira Rios, A. (2017). Active biodegradable cassava starch films incorporated lycopene nanocapsules. Industrial Crops and Products, 109, 818 827. Assis, R. Q., Pagno, C. H., Costa, T. M. H., Flˆores, S. H., & Rios, Ad. O. (2018). Synthesis of biodegradable films based on cassava starch containing free and nanoencapsulated β-carotene. Packaging Technology and Science, 31, 157 166. Augustin, M. A., & Hemar, Y. (2009). Nano- and micro-structured assemblies for encapsulation of food ingredients. Chemical Society Reviews, 38, 902 912. Available from https://doi.org/10.1039/B801739P. Auras, R. A., Singh, S. P., & Singh, J. J. (2005). Evaluation of oriented poly (lactide) polymers vs. existing PET and oriented PS for fresh food service containers. Packaging Technology and Science: An International Journal, 18, 207 216. Aziz, S. G.-G., & Almasi, H. (2018). Physical characteristics, release properties, and antioxidant and antimicrobial activities of whey protein isolate films incorporated with thyme (Thymus vulgaris L.) extract-loaded nanoliposomes. Food and Bioprocess Technology, 11, 1552 1565. Available from https://doi.org/10.1007/s11947-018-2121-6. Azmir, J., et al. (2013). Techniques for extraction of bioactive compounds from plant materials: A review. Journal of Food Engineering, 117, 426 436. Bakkali, F., Averbeck, S., Averbeck, D., & Idaomar, M. (2008). Biological effects of essential oils a review. Food and Chemical Toxicology, 46, 446 475. Bao, S., Xu, S., & Wang, Z. (2009). Antioxidant activity and properties of gelatin films incorporated with tea polyphenol-loaded chitosan nanoparticles. Journal of the Science of Food and Agriculture, 89, 2692 2700.

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incorporated plant essential oils with improved antimicrobial activity. Carbohydrate Polymers, 101, 582 591. Silva, N. H., Vilela, C., Almeida, A., Marrucho, I. M., & Freire, C. S. (2018). Pullulan-based nanocomposite films for functional food packaging: Exploiting lysozyme nanofibers as antibacterial and antioxidant reinforcing additives. Food Hydrocolloids, 77, 921 930. Siracusa, V., Rocculi, P., Romani, S., & Dalla Rosa, M. (2008). Biodegradable polymers for food packaging: A review. Trends in Food Science & Technology, 19, 634 643. Socaciu, C. (2007). Food colorants: Chemical and functional properties. CRC Press. Sozer, N., & Kokini, J. L. (2009). Nanotechnology and its applications in the food sector. Trends in Biotechnology, 27, 82 89. Available from https://doi.org/10.1016/j. tibtech.2008.10.010. Stahl, W., & Sies, H. (2003). Antioxidant activity of carotenoids. Molecular Aspects of Medicine, 24, 345 351. Suppakul, P., Miltz, J., Sonneveld, K., & Bigger, S. W. (2003). Active packaging technologies with an emphasis on antimicrobial packaging and its applications. Journal of Food Science, 68, 408 420. Taheri, A., & Jafari, S. M. (2019). Gum-based nanocarriers for the protection and delivery of food bioactive compounds. Advances in Colloid and Interface Science, 269, 277 295. Available from https://doi.org/10.1016/j.cis.2019.04.009. Tanaka, T., Shnimizu, M., & Moriwaki, H. (2012). Cancer chemoprevention by carotenoids. Molecules, 17, 3202 3242. Vahedikia, N., Garavand, F., Tajeddin, B., Cacciotti, I., Jafari, S. M., Omidi, T., & Zahedi, Z. (2019). Biodegradable zein film composites reinforced with chitosan nanoparticles and cinnamon essential oil: Physical, mechanical, structural and antimicrobial attributes. Colloids and Surfaces B: Biointerfaces, 177, 25 32. Available from https://doi.org/ 10.1016/j.colsurfb.2019.01.045. Vermeiren, L., Devlieghere, F., de Kruijf, N., & Debevere, J. (2000). Development in the active packaging of foods. Journal of Food Technology in Africa, 5, 6 13. Vieira, M. G. A., da Silva, M. A., dos Santos, L. O., & Beppu, M. M. (2011). Natural-based plasticizers and biopolymer films: A review. European Polymer Journal, 47, 254 263. Viuda-Martos, M., Mohamady, M., Ferna´ndez-Lo´pez, J., ElRazik, K. A., Omer, E., Pe´rezAlvarez, J., & Sendra, E. (2011). In vitro antioxidant and antibacterial activities of essentials oils obtained from Egyptian aromatic plants. Food Control, 22, 1715 1722. Wang, S., Xia, P., Wang, S., Liang, J., Sun, Y., Yue, P., & Gao, X. (2019). Packaging films formulated with gelatin and anthocyanins nanocomplexes: Physical properties, antioxidant activity and its application for olive oil protection. Food Hydrocolloids, 96, 617 624. Available from https://doi.org/10.1016/j.foodhyd.2019.06.004. Wen, P., et al. (2016). Fabrication of electrospun polylactic acid nanofilm incorporating cinnamon essential oil/β-cyclodextrin inclusion complex for antimicrobial packaging. Food Chemistry, 196, 996 1004. Wu, J., et al. (2015). The preparation, characterization, antimicrobial stability and in vitro release evaluation of fish gelatin films incorporated with cinnamon essential oil nanoliposomes. Food Hydrocolloids, 43, 427 435. Wu, J., Chen, S., Ge, S., Miao, J., Li, J., & Zhang, Q. (2013). Preparation, properties and antioxidant activity of an active film from silver carp (Hypophthalmichthys molitrix) skin gelatin incorporated with green tea extract. Food Hydrocolloids, 32, 42 51. Zambrano-Zaragoza, M., Mercado-Silva, E., Gutie´rrez-Cortez, E., Cornejo-Villegas, M., & Quintanar-Guerrero, D. (2014). The effect of nano-coatings with α-tocopherol and

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xanthan gum on shelf-life and browning index of fresh-cut “Red Delicious” apples. Innovative Food Science & Emerging Technologies, 22, 188 196. Zambrano-Zaragoza, M. L., Quintanar-Guerrero, D., Del Real, A., Pin˜on-Segundo, E., & Zambrano-Zaragoza, J. F. (2017). The release kinetics of β-carotene nanocapsules/ xanthan gum coating and quality changes in fresh-cut melon (cantaloupe). Carbohydrate Polymers, 157, 1874 1882. Available from https://doi.org/10.1016/j.carbpol.2016. 11.075. Zhang, H., Hortal, M., Dobon, A., Bermudez, J. M., & Lara-Lledo, M. (2015). The effect of active packaging on minimizing food losses: Life cycle assessment (LCA) of essential oil component-enabled packaging for fresh beef. Packaging Technology and Science, 28, 761 774. Ziegler, J., & Facchini, P. J. (2008). Alkaloid biosynthesis: Metabolism and trafficking. Annual Review of Plant Biology, 59, 735 769. Available from https://doi.org/10.1146/ annurev.arplant.59.032607.092730.

Reinforced nanocomposites for food packaging

14

Milena Martelli-Tosi1, Bruno Stefani Esposto2, Natalia Cristina da Silva1, Delia Rita Tapia-Bla´cido2 and Seid Mahdi Jafari3 1 Departamento de Engenharia de Alimentos, Faculdade de Zootecnia e Engenharia de Alimentos, Universidade de Sa˜o Paulo, Sa˜o Paulo, Brazil, 2Chemical Department, Faculty of Philosophy, Sciences and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Sa˜o Paulo, Brazil, 3Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

14.1

Introduction

Due to a global shift from reusable to single-use containers, plastics have been increasingly used for packaging applications in the last few decades (Geyer, Jambeck, & Law, 2017; Lagaron & Sanchez-Garcia, 2008; Pilevar, Bahrami, Beikzadeh, Hosseini, & Jafari, 2019). In 2015 the global plastic market reached 322 million tons, and approximately 49 million tons of plastics were employed for packaging purposes (Gan & Chow, 2018). A high barrier to water molecules and gases is a highly desirable property to be retained by polymeric materials intended for use in packaging. In this sense, this property has probably never received as much industrial attention as it has over the past few decades, when modern food and beverage packaging technologies that employ plastic materials began to be a topic of intense discussion (Lagaron & Sanchez-Garcia, 2008). Biopackaging is obtained from biodegradable materials, such as polysaccharides like chitosan, starch, and cellulose; proteins including gluten, gelatin, and zein; chemical polymers, for example, polycaprolactones (PCLs), polyvinyl alcohol (PVOH), copolymers (ethylene vinyl alcohol, EVOH), and polylactic acid (PLA) (Arvanitoyannis et al., 1997; Haugaard et al., 2001, Petersen et al., 1999); and polymers such as polyhydrooxyalkanoates (PHAs) and polypeptides produced by natural or genetically modified microorganisms (Lagaron & Sanchez-Garcia, 2008; Reguera et al., 2003). Although this kind of packaging is advantageous, it has some drawbacks when compared to synthetic plastics. These disadvantages include low thermal resistance, excessive brittleness, and insufficient barrier to oxygen and water. Therefore there is a great industrial and academic interest in obtaining synthetic and biodegradable materials with enhanced barrier properties and mechanical resistance for current and future food packaging applications (Hashemi Tabatabaei, Jafari, Mirzaei, Mohammadi Nafchi, & Dehnad, 2018; Vahedikia et al., 2019).

Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00014-5 © 2020 Elsevier Inc. All rights reserved.

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In this scenario, nanocomposites are a new class of composites consisting of nanoparticle-filled polymers (Dehnad, Mirzaei, Emam-Djomeh, Jafari, & Dadashi, 2014b; Hoseinnejad, Jafari, & Katouzian, 2018). They comprise multiphase materials where at least one of the constituent phases, commonly the nanofiller, has at least one dimension in the nanoscale range (Bandyopadhyay & Ray, 2019). Several nanoparticles have been used to reinforce natural matrices with a view to obtaining nanocomposites, for example, zinc oxide (Brayner et al., 2006; Emamifar et al., 2010), titanium dioxide (Gao et al., 2013; Lian, Zhang, & Zhao, 2016), silica (Hou et al., 2019), nanoclay (Bae et al., 2009; Ghelejlu, Esmaiili, & Almasi, 2016), nanocellulose (NC) (Alemdar & Sain, 2008a; Chen et al., 2009a, 2009b; Kaushik, Singh, & Verma, 2010; Leitner et al., 2007; Martelli-Tosi et al., 2018; Samir et al., 2004; Dehnad, Emam-Djomeh, Mirzaei, Jafari, & Dadashi, 2014a), and chitosan nanoparticles (Aouada, 2009; Moura et al., 2009; Greiner & Wendorff, 2007; Huang et al., 2003; Fan, Hu, & Shen, 2009; Hosseinnejad & Jafari, 2016; Nasti et al., 2009), which elicit improved mechanical, gas and water vapor barrier, and bioactive (antimicrobial activity) properties. These improvements derive from strong interactions between the matrices and the nanoreinforcements: the reinforcing nanoparticles are small (,100 nm), which provide the nanocomposites with a greater surface area than their bulk counterparts, consequently boosting their reactivity (Motaung & Linganiso, 2018) and strengthening them (Zhou, Wang, & Gunasekaran, 2009). Furthermore, the high aspect ratio of nanoparticles and their homogeneous dispersion in the polymer matrix changes the polymer chain molecular mobility and relaxation, thus increasing the nanocomposite mechanical and thermal resistance (Bumbudsanpharoke, Choi, & Ko, 2015). In addition, bonds established between the polymer and nanoparticles decreases the number of sites in the polymer chain that could interact with water molecules, thereby improving the nanocomposite barrier to water (Duncan, 2011; Mihindukulasuriya & Lim, 2014). The current chapter offers an overview of different types of inorganic and organic nanoparticles that are employed to reinforce polymeric matrices and of their effects on the properties of nanocomposites intended for food packaging.

14.2

Inorganic nanomaterials used in nanocomposites for food packaging

14.2.1 Oxides used in nanocomposites In an attempt to achieve composites with improved mechanical and active properties, oxide nanoparticles can be incorporated into synthetic and biodegradable polymers. These nanoparticles exhibit unique characteristics that can confer antimicrobial activity and UV shielding property to new useful composite-based packaging materials. Food packaging displaying UV shielding ability and antimicrobial action is important because it can protect products from degradation and

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extend their shelf life. Compounds such as zinc oxide, titanium dioxide, and silicon oxide have been used to produce reinforced nanocomposites. It should be mentioned that the antimicrobial activity of metal nanoparticles in food packaging has been discussed in Chapter 10, Metal Nanoparticles as Antimicrobial Agents in Food Packaging, of the current book.

14.2.1.1 Zinc oxide Zinc oxide nanoparticles (nano-ZnO) constitute a white odorless crystalline powder with interesting electrical, optical, catalytic, and photochemical properties. The powder can be synthesized by different methods that employ distinct variables such as time and temperature to generate nanoparticles with diverse sizes, shapes, and surface chemistry (Sruthi, Ashtami, & Mohanan, 2018). Precipitation in aqueous medium, sol gel methodology, hydrothermal synthesis, and thermal evaporation are some of the methods that have been used to prepare nano-ZnO (Pen˜a-Garcia et al., 2018; Sepulveda-Guzman et al., 2009; Shubha et al., 2019; Tian et al., 2015). Recent studies have shown that biodegradable polymers like starch and proteins are an environment-friendly alternative to synthetic plastics (Khanzadi et al., 2015; Oliveira et al., 2019). However, these composites present poor water vapor barrier properties and unsatisfactory mechanical strength and elongation, so improved properties are necessary for them to be competitive (Maniglia et al., 2014). To overcome this issue, ZnO has been extensively studied as a reinforcing material. NanoZnO addition to chitosan films results in stronger, less permeable, and effective antimicrobial nanocomposites (Rahman et al., 2018). Moreover, ZnO nanorods increase the contact angle and decrease the water-related properties (moisture content, water solubility, and water vapor permeability) of cassava starch films, providing the films with better UV shielding and antimicrobial properties (Guz et al., 2017). Three mechanisms can explain ZnO nanocomposite efficiency against bacteria. First, reactive oxygen species (ROS) including OH, H2O2, and O2 2 may emerge to react with biological macromolecules and kill bacteria (Dizaj et al., 2014). Second, Pasquet et al. (2014) observed that Zn21 ion release from zinc oxide confers antimicrobial activity against various bacterial and fungal strains. Lastly, nanoZnO can damage cell walls, disorganizing them and increasing the microbial membrane permeability (Brayner et al., 2006). Studies regarding synthetic polymers such as thermoplastics also exist. Threepopnatkul et al. (2014) and Zhang et al. (2017a) observed that nano-ZnO in PET (polyethylene terephthalate) and PBS (polybutylene succinate)-blended thin films or in PLA-coated paper inhibits E.coli and S. aureus. Furthermore, Li et al. (2017) reported that nano-ZnO added to LDPE (low-density polyethylene) matrix acts as a permeation barrier to O2 during the cold storage of peaches. Other researchers have evaluated the use of ZnO nanocomposites as packaging for different matrices and foods. Mangoes coated with carrageenan/nano-ZnO had a lower total acidity, steady firmness, and delayed discoloration and decay, not to mention that they incorporate a new antimicrobial activity feature (Meindrawan et al., 2018). Similarly, nano-ZnO addition to carboxymethyl cellulose (CMC) G

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coatings maintains the overall pomegranate aril quality by reducing the microbial load and growth (Saba & Amini, 2017). Gelatin/ZnO nanorod/clove oil nanocomposite films completely inhibit microbes during shrimp storage for 20 days (Ejaz et al., 2018), and PLA/nano-ZnO/essential oil films display antimicrobial and antioxidant action, diminishing lipid peroxidation in fish meat (Heydari-Majd et al., 2019). Besides that, ZnO nanocomposites also extend the bread and orange juice shelf life by 32 and 28 days, respectively (Emamifar et al., 2010; Noshirvani et al., 2017).

14.2.1.2 Titanium dioxide Titanium dioxide (TiO2) is an attractive inert material: it is inexpensive, nontoxic, chemically stable, and superhydrophilic, and it has high photocatalytic ability against numerous microbes, staining, odors, deterioration, and allergens (Ma et al., 2016). TiO2 exists in three different forms (rutile, anatase, and brookite) and has been used to block light and to provide a white appearance to products in the food and cosmetic industries (Le et al., 2012; Oleyaei et al., 2016). Many nano-TiO2 synthesis methods have been reported, including sol gel methodology, sonochemical method, and microemulsion. During the sol gel process, water addition hydrolyzes an alkoxide metal, which is followed by condensation and polynucleation reactions that generate inorganic polymeric oxide networks (Gao et al., 2013; Vargas & Rodrı´guez-Pa´ez, 2017). The sonochemical method uses ultrasonication to reduce metal ions to metal or metal oxide nanoparticles (Guo et al., 2011). A microemulsion consists of thermodynamically stable oil, surfactant, and aqueous phases that form nanometer-sized particles (nanoreactors) where droplets of the desirable reactant collide with each other (Karbassi et al., 2018; Li & Wang, 1999). Some studies have described that nano-TiO2 incorporation into various polymeric matrices improves the matrix mechanical and active properties and imparts better barrier properties, opaqueness, antibacterial, and UV light protection effects to packaging materials (Baek et al., 2018; Oleyaei et al., 2016). However, highly hydrophilic nano-TiO2 added to hydrophobic polymers can produce large clusters and agglomerates. To overcome this issue, Baek et al. (2018) first modified nanoTiO2 surfaces with oleic acid, to improve their nonpolar activity. Then, they added the modified nano-TiO2 (as a filler and plasticizer) to a PVA chitosan matrix to enhance the resulting nanocomposite antibacterial activity. Other authors have also reported that nanocomposites containing nano-TiO2 exert antibacterial action. Xie and Hung (2018) fabricated cellulose acetate TiO2 films that display antimicrobial efficacy against E. coli thanks to the TiO2 photocatalytic activity. This property is an effective method to remove bacterial contamination and follows a photocatalytic mechanism that resembles the mechanism followed by ZnO, culminating in the production of ROS that kill bacteria (Wang et al., 2016). Novel nanocomposites based on chitosan/PVA and TiO2 have been employed as packaging materials for soft white cheese. The results indicate antibacterial activity against Gram-positive (G 1 ) (S. aureus) and Gram-negative (G 2 )

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(Pseudomonas aeruginosa, E. coli) bacteria and fungi (Candidia albicans) (Youssef et al., 2015). Red grapes have been protected from microbial infection with a nanocomposite film made of chitosan TiO2, thus increasing the product shelf life by 7 days compared to the control (Zhang et al., 2017b). Another test has also shown that HDPE (high-density polyethylene)/CaCO3/nano-TiO2 blown films inhibit lactic acid bacterium and coliform growth in packaged cheese (Gumiero et al., 2013). Nano-TiO2 can block UV light and oxygen when they are incorporated into different polymers, thereby protecting the packaged food and delaying the nanocomposite degradation. Biodegradable matrixes such as potato starch films with added nano-TiO2 block more than 90% UV light (Oleyaei et al., 2016). Wheat starch films with added nano-TiO2 confer protection against UV-A, UV-B, and UV-C light (Goudarzi, Shahabi-Ghahfarrokhi, & Babaei-Ghazvini, 2017). Nano-TiO2 as a reinforcement material can also improve the nanocomposite mechanical and barrier properties. Better mechanical properties like tensile strength (TS) and elongation at break (EAB) have been achieved for nanocomposites containing well-dispersed nano-TiO2 in the polymer matrix (Kadam et al., 2017). Addition of 0.5 g nano-TiO2/100 g to bilayer gelatin/agar films raises the TS from 10.80 to 13.91 MP (Vejdan et al., 2016). Gelatin nanocomposites containing nanoTiO2 also have a significantly higher TS and EAB (He et al., 2012). Because the hydrophilicity of TiO2 can modify the water-related properties, nano-TiO2 addition decreases the water solubility, moisture, and water vapor permeability parameters of soluble soybean polysaccharide (SSPS) biodegradable films (Salarbashi et al., 2018). The same behavior has been reported for potato starch, wheat starch, and chitosan films with added nano-TiO2 (Goudarzi et al., 2017; Oleyaei et al., 2016; Zhang et al., 2017b). On the other hand, increasing nano-TiO2 concentration culminates in considerably larger contact angles for wheat gluten/NC films (El-Wakil et al., 2015). Furthermore, a study on pectin-based aerogels and nano-TiO2 has shown that nano-TiO2 can improve the nanocomposite thermal stability, suggesting that it can be used as a short-life package, including a delivery packaging for temperature-sensitive foods (Neˇsi´c et al., 2018).

14.2.1.3 Silicon dioxide (silica) Silica (SiO2) is a metalloid oxide with potential use in nanoparticle production through relatively simple and cost-effective processes. Sol gel methodology, reverse microemulsion, or flame spray pyrolysis can be applied to synthesize this oxide, which displays attractive characteristics for food packaging such as improved mechanical properties, antimicrobial activity, and thermal stability (Hashemi Tabatabaei et al., 2018). The properties of nano-SiO2 depend on particle shape, size, and morphology (spheres, ribbons, tubes, rods, and cubes), which will define their applications in nanocomposites (Mallakpour & Naghdi, 2018). The presence of siloxane and silanol groups on the nano-SiO2 surface grants the particles a hydrophilic property that can hinder the nanoparticle dispersion in polymeric matrices, ultimately forming agglomerates. In this event, surface modification is necessary to overcome the low compatibility between nano-SiO2 and the polymer (Mallakpour

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& Naghdi, 2018). However, good miscibility has been obtained between starch/ PVA blends and 3% nano-SiO2, affording a network structure that prevents water dissolution and increases the film mechanical properties (Tang et al., 2008). Chitosan biodegradable films with added nano-SiO2 have been studied as a coating material that could provide longer storage life for fruit and seeds. Jujube preservation with 0.04% nano-SiO2 lowers the red index, decay incidence, weight loss, and respiration rate after 32 days compared to the control (Yu et al., 2012). The hybrid film enhances the antioxidant activity and contents of reducing sugars in loquat fruit stored at 5 C for 40 days, indicating that the coating material has an acceptable external and internal quality (Song et al., 2016). Moreover, the same chitosan/nanosilica combination for film-coating improves the nanocomposite film water vapor and gas permeability and preserves Ginkgo biloba seeds, satisfactorily inhibiting mildew occurrence (Tian et al., 2019). Nano-SiO2 addition to other polymers with the aim of their potential use as food packaging has also been reported (Zhang et al., 2019). Konjac glucomannan/carrageenan coatings incorporated with nano-SiO2 have been optimized as 0.03% nanoSiO2, 0.6% carrageenan, and 0.48% konjac glunamannan. The coatings delay white mushroom deterioration by protecting the product against UV light effects and reducing moisture and gas transfer, consequently decreasing product respiration and extending storage by 5 12 days.

14.2.1.4 Other oxides Research into nanocomposites incorporated with other oxides is scarce. Their effects on nanocomposite properties resemble the effects reported for nano-ZnO, nano-TiO2, and nano-SiO2, including improved antimicrobial activity and mechanical and barrier properties. Recently, aluminum oxides have been introduced into nanocomposite packaging to achieve other features, such as product visibility and microwave and bending ability (Struller et al., 2014). The polymeric matrices that have been with added aluminum oxides include kefiran (Moradi, Esmaiili, & Almasi, 2019), chitosan (Moussout et al., 2018), and polybutylene succinate (Lule, Ju, & Kim, 2018). Polymer/CuO nanocomposites have been fabricated to obtain a novel polypropylene (PP) plastic with antimicrobial activity (Delgado et al., 2011) derived from Cu21 released from the nanocomposite bulk. The same effect has been observed by Beigmohammadi et al. (2016) for a LDPE/nano-CuO film that can reduce coliforms by 4.21 log CFU/g in UF cheese packed for 4 weeks. Magnesium oxide nanoparticles have been incorporated into PLA biofilms; maximum improvement in the TS and oxygen barrier properties has been obtained with 2% nano-MgO. This nanocomposite has promising application as food packaging material: it is transparent, can screen UV radiations, and is effective against E. coli, damaging approximately 46% of the bacterial culture after 12 h (Swaroop & Shukla, 2018). Other tests have shown that chitosan composites containing spherical nano-MgO display remarkable thermal stability and flame retardant, UV shielding, and moisture barrier properties (de Silva et al., 2017).

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Table 14.1 depicts an updated summary of recent nanooxide applications in composites for food packaging based on a previous review (Garcia, Shin, & Kim, 2018).

14.2.2 Nanoclays as polymer reinforcement fillers Among nanometric particles, clay materials are often used as polymer fillers to improve the nanocomposite physical properties and gas permeability and to lower their thermal expansion thanks to the fact that nanoclays have an extraordinarily high surface area. Clay nanoparticles have been studied for application in edible packages. Research into clay nanoparticles has demonstrated that the resulting composites are biodegradable. These nanoparticles seem to be associated with different polymers, such as whey proteins (Hedenqvist et al., 2006), wheat gluten (Olabarrieta et al., 2006), fish gelatin (Bae et al., 2009), chitosan (Casariego et al., 2009), starch (Chung, Liu, & Hoover, 2010), and soybean oil (Liu, Chang, & Wiesenborn, 2005). All the research works have described packaging with improved characteristics as compared to the parent packaging without added nanoparticles. Montmorillonite (MMT), a layered clay consisting of octahedral alumina sheets accommodated between two tetrahedral silica sheets (Khezrian & Shahbazi, 2018; Majeed et al., 2012), has been the most commonly employed. In general, layered clays display strong covalent bonds within their sheets, which makes their dispersion into polymers in nanocomposites difficult. Therefore clay modification is necessary to improve the compatibility between the matrix and the filler (Kotal & Bhowmick, 2015). Biodegradable polymer matrices generally have poor physical properties for food packaging applications, so MMT and other clays have been widely used as fillers to enhance the matrix mechanical and barrier properties. For example, chitosan/MMT nanocomposite films have increased TS and decreased EAB, which indicates a strong affinity between the biopolymer and the nanoclay. In addition, nano-MMT acts as a heat barrier, enhancing the nanocomposite overall thermal stability. Moreover, the chitosan/MMT nanocomposite has improved barrier properties, which reduces the oxygen and water permeability. This happens because nano-MMT is well dispersed in the matrix, and tortuous paths are created in the films, hindering the penetration of diffusing molecules (Kasirga, Oral, & Caner, 2012). Fish gelatin/nano-MMT presents the same behavior: the gelatin TS increases from 30.31 to 40.71 MPa when 5% clay is added to the matrix. Furthermore, the oxygen and water permeability is improved (Bae et al., 2009). Another interesting feature of nano-MMT is that it can act as a UV shield in food packaging and reduce negative photooxidation reactions. Molinaro et al. (2013) detected this property when they incorporated nano-MMT into PLA matrices: they verified up to 55% lower transmittance at 280 nm, but a similar film transparency. However, other authors have employed nano-MMT combined with other antimicrobial agents to obtain active packaging that could prolong the food shelf life. These active agents include essential oils, extracts, or even other nanoparticles, such as silver.

Table 14.1 Nanooxides used as reinforcement materials in food packaging. Nano oxide

Particle size

Matrix

Results

References

ZnO

B30 nm

PLA

Nanosize

PET/PBS

Stronger antimicrobial effect and inactivation of E. coli and S. aureus Inhibitory effect on E. coli and S. aureus

30 nm

LDPE

Decreased B. subtilis and E. aerogenes growth

Nanosize

Chitosan

35 45 nm

Chitosan (coating)

Nanosize

Cassava starch

Zhang et al. (2017a) Threepopnatkul et al. (2014) Esmailzadeh et al. (2016) Li et al. (2017) Rahman et al. (2018) Al-Naamani, Dobretsov, and Dutta (2016) Guz et al. (2017)

B6 nm B21 nm

Chitosan/carboxy methyl cellulose Potato starch

B21 nm

Cellulose acetate

Nanosize

Soluble soybean polysaccharide (cast film) Wheat starch (cast film)

TiO2

B20 nm

Peaches of superior chilling tolerance during cold storage Improved dielectric constant, conductivity, and antimicrobial activity E. coli, S. enterica, and S. aureus viability reduced by 99.9%

More efficient shielding of UVA radiation Higher solubility and water vapor permeability Extended cheese shelf life during storage period Decreased water-related properties Improved tensile strength Blockage of over 90% UV light Higher UV-A absorption and photodegradation rate Antimicrobial efficacy against E. coli Decreased water-related properties Increased tensile strength Promising antimicrobial activity range Decreased water-related properties

Youssef et al. (2018) Oleyaei et al. (2016) Xie and Hung (2018) Salarbashi et al. (2018) Goudarzi et al. (2017)

50 80 nm

Chitosan

15 30 nm

PVA chitosan

3 5 nm

Pectin (aerogel)

TiO2 (modified with oleic acid) TiO2 1 nanocellulose

Nanosize

PLA (cast film)

B20 nm

Wheat gluten

SiO2

20 nm

Konjac glucomannan/ carrageenan (coating) Agar/sodium alginate (cast film)

25 35 nm

Nanosize

Chitosan (coating)

15 nm

Chitosan (coating)

Nanosize

Chitosan (coating)

UV-protective properties against UV-A, UV-B, and UV-C light. Improved thermal properties Enhanced hydrophilicity Better mechanical properties Efficient antimicrobial activity against E. coli, S. aureus, Candida albicans, and Aspergillus niger. Leakage of cellular substances Extended red grape shelf life Improved antibacterial activity Improved mechanical, thermal, and antimicrobial properties Potential application for temperature-sensitive food storage UV-protective properties Better O2 and water barrier properties Improved mechanical and water barrier properties Coated paper sheets with good antimicrobial activity against G 1 and G 2 bacteria and yeast Lower gas permeability Delayed UV light effect Extended white mushrooms storage time Enhanced mechanical properties, water resistance, and thermal stability Improved film properties against UV light Enhanced antioxidant activity and contents of reducing sugars in jujube Preserved total flavonoid Preserved postharvest quality (decay and shrinkage rate, and firmness) of G. biloba seeds due to inhibited growth of externally contaminant microbes Enhanced antioxidant activity Improved chilling resistance, quality of loquat fruit

Zhang et al. (2017b)

Lian et al. (2016) Neˇsi´c et al. (2018) Baek et al. (2018) El-Wakil et al. (2015) Zhang et al. (2019) Hou et al. (2019) Yu et al. (2012)

Tian et al. (2019) Song et al. (2016) (Continued)

Table 14.1 (Continued) Nano oxide

Particle size

Matrix

Results

References

Al2O3

20 nm

Kefiran

Moradi et al. (2019)

CuO

B10 nm

Polypropylene

Increased tensile strength Decreased water-related properties Improved thermal stability Strong antimicrobial behavior against E. coli

MgO

,60 nm

PLA

B42 nm

Chitosan

Improved tensile strength, oxygen barrier properties Superior antibacterial efficacy Remarkable thermal stability and flame retardant, UV shielding, and moisture barrier properties

Delgado et al. (2011) Swaroop and Shukla (2018) de Silva et al. (2017)

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Addition of nano-MMT and essential oils to chitosan films positively influences fresh poultry meat preservation: nano-MMT confers improved barrier properties against UV rays and oxygen, preventing lipid oxidation and exchanges between the food and the exterior (Pires, de Souza, & Fernando, 2018). Although nano-MMT alone does not have antimicrobial activity, its presence effectively prevents microbiological growth in the nanocomposites: nano-MMT has a high specific area, so it can absorb the bacteria and immobilize them on the nanocomposite surface. Similarly, gelatin films containing nano-MMT and silver nanoparticles exhibit strong antibacterial activity against foodborne pathogens while they provide the nanoparticles with improved TS, hydrophobicity, and UV/water vapor barrier properties (Kanmani & Rhim, 2014). Bentonite, another clay consisting mostly of MMT, has been immobilized into a hydroxyethyl cellulose matrix to obtain films with a better TS and antimicrobial action against E. coli, S. aureus, and associated fungi (Alekseeva et al., 2019). Bentonite incorporation into chitosan/PVA/anthocyanin nanocomposites improves the water vapor barrier property and antibacterial activity mainly as a result of nanoclay content and anthocyanins, which suggests that this nanocomposite can be potentially applied as active food packaging (Koosha & Hamedi, 2019). Other clay materials can also be used as fillers in composites. One example of such clay is halloysite, a naturally occurring aluminosilicate mineral consisting of a gibbsite octahedral sheet [Al(OH)3] that can be modified with siloxane groups at the outer surface (Guimara˜es et al., 2010). Haloysite addition improves the nanocomposite mechanical properties and allows active compounds to be incorporated, which is useful for food packaging applications. LDPE films with incorporated nanohalloysite/essential oils efficiently avoid active compound loss during storage and display strong antibacterial action against pathogenic bacteria (Tornuk et al., 2018). Halloysite addition to soft cheese packaging containing nisin enhances the nanocomposite functional properties (Meira et al., 2016). There are also reports that halloysite positively affects other biopolymer matrices like chitosan, potato starch, and SSPS (He et al., 2012; Lee, Kim, & Park, 2018; Meira et al., 2016). Interesting results regarding the use of different nanoclays have been achieved. PLA nanocomposites reinforced with modified hectorite accelerate the plastic degradation process, and chitosan/laponite/silver nanoparticles can keep litchis fresher than PE films (Fukushima et al., 2013; Wu et al., 2018). These findings support the application of nanotechnology to expand the use of biodegradable matrices for food packaging purposes. Table 14.2 summarizes some of the clays that have recently been employed in different packaging matrices.

14.3

Nanocellulose-based nanocomposites for food packaging

Cellulose is the most abundant natural biopolymer on Earth, and it can be readily obtained from sustainable sources, such as plants (Moon et al., 2011), algae

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Table 14.2 Nanoclays used as reinforcement materials in food packaging. Nanoclay type

Matrix

Results

References

Montmorillonite

Soy protein 1 clove essential oil

Better release of clove oil active compounds, decreasing microbial growth and lipid autooxidation of tuna fillets Reduced lipid oxidation by half and microbiological contamination by 6% 16%, significantly prolonging poultry meat shelf life Improves film water vapor permeability, water resistance, and mechanical properties Increases tensile strength, decreases elongation at break, and provides strong antibacterial activity Increases UV barrier properties Enhances water vapor barrier and water resistance properties Provides an antimicrobial effect against E. coli and S. aureus Reduces tensile strength and water vapor permeability Decreases water vapor and oxygen permeability and increases glass transition temperature, tensile strength, and heat seal strength

Echeverrı´a et al. (2018)

Chitosan 1 essential oils

Chitosan 1 thistle milk extract

Gelatin 1 silver nanoparticles

PLA PVOH

Bentonite

Hydroxyethyl cellulose

Chitosan/PVA 1 anthocyanins Halloysite

Soluble soybean polysaccharide

Pires et al. (2018)

Ghelejlu et al. (2016)

Kanmani and Rhim (2014)

Molinaro et al. (2013) Liu et al. (2013)

Alekseeva et al. (2019)

Koosha and Hamedi (2019) Alipoormazandarani, Ghazihoseini, and Mohammadi Nafchi (2015)

(Continued)

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Table 14.2 (Continued) Nanoclay type

Matrix

Results

References

Potato starch

Increases tensile strength and decreases elongation at break and solubility in water Improves mechanical properties and accelerates PLA degradation Significantly prevents Ag nanoparticles release, extending litchi storage life

Sadegh-Hassani and Mohammadi Nafchi (2014)

Hectorite

PLA

Laponite

Chitosan

Fukushima et al. (2013)

Wu et al. (2018)

(Klemm et al., 2005), tunicates (Sacui et al., 2014), and some bacteria (Pacheco et al., 2017). Cellulose is the major lignocellulosic biomass component (around 35% 50%) and is located mainly in the plant cell wall (Hemmati, Jafari, & Taheri, 2019). It is a linear macromolecule consisting of D-anhydroglucose (C6H11O5) repeat units joined by β-1,4-glycosidic linkages with a degree of polymerization (DP) of around 10,000. Each repeat unit contains three hydroxyl groups (Hemmati, Jafari, Kashaninejad, & Barani Motlagh, 2018). The ability of these hydroxyl groups to form hydrogen bonds plays a major role in directing crystalline packing and governing the physical properties of cellulose materials (Bismarck, Mishra, & Lampke, 2005, Tapia-Bla´cido, Maniglia, & Martelli-Tosi, 2017). Fig. 14.1 shows the cellobiose repeat unit that makes up the cellulose fibrils. Cellulose is a polymorph, that is, it may appear in more than one form. One cellulose binding unit contains six hydroxyl groups and three oxygen atoms. Hence, crystal packaging can occur in different ways and may involve distinct cellulose units as well as changes in chain polarity. In plants, cellulose exists in two types of crystalline structures, cellulose I and cellulose II. Cellulose I is a native cellulose that is abundant in the environment, but it is less stable than other polymorphs. In turn, cellulose II has a highly durable structure and can be found in marine algae, too. It is generally crystalline and can be produced by alkaline treatment of cellulose I (Kafle et al., 2015). Besides cellulose I and II, other forms like cellulose III and cellulose IV also exist. Cellulose is an abundantly available raw material in nature. It is biodegradable and biocompatible and possesses attractive features, including low density, active surface for functionalization, and low cost, not to mention that it is considered efficient reinforcement for packaging (Kalia et al., 2014). For better cellulose incorporation into polymeric matrices, researchers have reduced the cellulose size and/or isolated crystalline NC (CNC) parts (Tapia-Bla´cido et al., 2017).

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Figure 14.1 Schematic representation of cellobiose.

14.3.1 Nanocellulose production from agroindustrial biomass Problems involved in recycling plastics and reducing fossil resources depletion have raised interest in environment-friendly and sustainable materials (Jafari et al., 2015). In this context, applying cellulose nanofibers as reinforcement in polymer matrices has attracted considerable attention because this strategy provides a unique combination of the physical and environmental properties of both constituents. Agroindustrial biomass such as corn, wheat, rice, soybean straw, sugarcane bagasse, and orange waste are sources of lignocellulosic materials (Tapia-Bla´cido et al., 2017). Research into NC production can be found in the literature (Alemdar & Sain, 2008b; Flauzino Neto et al., 2013; Martelli-Tosi et al., 2018). High lignocellulosic fiber availability and the need for a renewable source for polymer production have opened space for technological advances that add value to agroindustrial products and waste. However, the rigid and complex structure resulting from the spatial interaction among cellulose, hemicelluloses, and lignin limits lignocellulosic biomass conversion into the desired product (Oh et al., 2015). For this reason, the biomass has to be submitted to a pretreatment that separates the lignin matrix from the initial material, reduces the cellulose crystallinity, and hydrolyzes hemicellulose, so that the hydrolysate can be separated from cellulose (Hemmati et al., 2018). Next, cellulose has to undergo specific treatment to obtain nanofibrils or nanocrystals (Ogeda & Petri, 2010). Therefore nanofiber production from lignocellulosic material encompasses four main stages: (1) pretreatment to reduce the lignocellulose structure recalcitrance, (2) cellulose or hemicellulose hydrolysis, (3) acid or enzymatic hydrolysis to act on the cellulose fibril amorphous structure and to produce crystals, and (4) fragmentation of crystalline segments by a mechanical process. Table 14.3 shows some treatments that help to obtain NC. The pretreatment stage involves physical, biological, chemical, and physicochemical methods (Tapia-Bla´cido et al., 2017). Physical processes like comminution, extrusion, and irradiation mechanically break down the biomass ultrastructure, to improve enzymatic or chemical cellulose hydrolysis. Mechanical processes such

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Table 14.3 Nanocellulose production from agroindustrial residues. Agroindustrial residue

Treatment for nanofiber processing

Nanofiber dimensions

Reference

Wheat straw (WS) and soybean straw (SB)

Alkaline, acid, and mechanical treatment

Alemdar and Sain (2008a), Alemdar and Sain (2008b)

Wheat straw

Alkaline and steam treatment, followed by acid treatment (HCl) Alkaline treatment, bleaching, and highpressure homogenization. Alkaline treatment, bleaching, and highpressure homogenization Acid hydrolysis, bleaching, and alkali extraction

WS: diameter: 30 40 nm SB: diameter: 20 120 nm Length . 100 nm Diameter: 10 50 nm Diameter: 30 100 nm Length . 1 μm

Leitner et al. (2007)

Diameter: 2 4 nm Length . 1 μm

Dufresne, Dupeyre, and Vignon (2000)

Diameter: 2 11 nm Length: 360 1700 nm Diameter: 7 12 nm Length: 240 400 nm Diameter: 2 11 nm Length: 360 1700 nm C: diameter: 55 109 nm Length: 1.3 4.1 μm SB: diameter: 20 40 nm Length: 0.25 0.82 μm Diameter: 30 80 nm Length: 100 nm 1.8 μm Diameter: 5 6 nm

Mora´n et al. (2008)

Beetroot

Potato fibers

Sisal fibers

Pea fibers

Acid hydrolysis and bleaching

Cassava bagasse

Acid hydrolysis and ultrasound

Curaua (C) and sugarcane bagasse (SB)

Alkaline treatment and bleaching followed by enzymatic treatment (hemicellulases/ pectinases/ endoglucanases) and ultrasound

Wood pulp

Enzymatic hydrolysis (endoglucanases) and ultrasound

Wood cellulose

Enzymatic hydrolysis (endoglucanases)

Kaushik et al. (2010)

Chen et al. (2009a, 2009b)

Teixeira et al. (2010)

de Campos et al. (2013)

Filson, DawsonAndoh, and SchweglerBerry (2009) Paakko et al. (2007) (Continued)

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Table 14.3 (Continued) Agroindustrial residue

Treatment for nanofiber processing

Nanofiber dimensions

Reference

Cotton fibers

Enzymatic hydrolysis (endo- and exoglucanases) and centrifugation Enzymatic hydrolysis (commercial enzymes based on endo and exoglucanases and xylanases) 1 Ultraturrax 1 sonication Acid hydrolysis (H2SO4) 1 Ultraturrax 1 sonication

Diameter: 40 nm Length: 120 nm

Satyamurthy et al. (2011)

Diameter:15 nm Length . 1 μm Diameter:15 nm Length: 600 nm

Martelli-Tosi et al. (2018)

Soybean straw

as chipping, grinding, and milling by ball, two-roll, hammer, colloid, or vibro-energy (Behera, Arora, Nandhagopal, & Kumar, 2014) reduce the final lignocellulosic biomass particle size to 0.2 2 mm (Oh et al., 2015; Silva et al., 2012). Because reducing the lignocellulosic biomass size is a prerequisite to prepare materials for further biological or chemical pretreatment, one strategy is to combine physical treatment with chemical treatments (Oh et al., 2015). Chemical treatments employ different active agents, including ozone, acids, alkalis, peroxides, and organic solvents, which act as catalysts to disrupt biomass recalcitrance and to increase cellulose accessibility (Hendriks & Zeeman, 2009; Sanchez & Cardona, 2008). The currently promising chemical pretreatment technologies can be broadly categorized into alkaline, acid, sulfite, organosolvent, and ionic liquid pretreatments (Oh et al., 2015). Acid pretreatment with dilute sulfuric acid (H2SO4) effectively reduces the biomass recalcitrance because it removes hemicellulose, changes the cellulose crystallinity, and enhances the biomass porosity via lignin redistribution (Foston & Ragauskas, 2010; Hsu, Guo, Chen, & Hwang, 2010; Pu, Hu, Huang, Davison, & Ragauskas, 2013). Alkaline pretreatments use alkaline compounds such as potassium hydroxide (KOH), sodium hydroxide (NaOH), calcium hydroxide [Ca(OH)2, also known as lime], and aqueous ammonia as catalysts to open up the biomass structure, especially by solubilizing a large lignin portion in the alkali solutions (Oh et al., 2015). During alkaline pretreatments, the cellulose structure changes into a denser and thermodynamically more stable conformation than the native cellulose conformation (Ray, Das, & Mitra, 2009). Lignocellulose delignification via sodium chlorite bleaching has been traditionally applied in the pulp industry, but this process has been replaced with more environment-friendly methods like thermochemical reactions that use oxygen (Kafle et al., 2015) and hydrogen peroxide (AndradeMahecha et al., 2015). Enzymatic treatments employ xylanases and cellulases to hydrolyze lignocellulosic structures. Nevertheless, several compositional factors

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including the presence of inhibitors, cellulose crystallinity, and lignin content can limit the enzymatic treatment efficiency (Zhu, O’Dwyer, Chang, Granda, & Holtzapple, 2008). For this reason, other common pretreatments have been applied to facilitate enzymatic or acid hydrolysis. The pretreatment effect clearly depends on biomass composition and operating conditions, and a combination of pretreatment methods could improve the effectiveness of the whole process (Tapia-Bla´cido et al., 2017). NC can be extracted from the pretreated biomass by enzymatic or chemical hydrolysis, resulting in two different products: (1) cellulose nanocrystals (CNCs) or cellulose whiskers, generated by acid hydrolysis; and (2) cellulose nanofibrils (CNFs) or micro/nanofibrillated cellulose, produced by enzymatic hydrolysis and/or mechanical processes (Nechyporchuk, Belgacem, & Bras, 2016). Concentrated sulfuric acid is commonly employed in an acid hydrolysis reaction, which hydrolyzes the cellulose structure’s amorphous regions. CNCs typically have a rigid structure associated with a high degree of crystallinity (64% 74%), bearing negatively charged sulfate groups on their surface. In general, CNCs have diameters of 4 15 nm and are between 500 nm and 2 μm long, which greatly depend on the applied extraction procedure (Hemmati et al., 2019). Enzymatic and mechanical methods (e.g., high-pressure homogenizer), on the other hand, afford strongly entangled fibril bundles with nanometric diameter (5 110 nm) and micrometric length (a few micrometers) (de Campos et al., 2013; Kaushik et al., 2010; Martelli-Tosi et al., 2016; Paakko et al., 2007).

14.3.1.1 Case study: production of nanocellulose from soybean straw by enzymatic method Brazil is the second largest world producer of soybean, accounting for 30% of the global production. Soybean harvesting generates stalks, stems, and leaves, which are collectively designated soybean straw. According to estimates, the 2015/2016 harvest provided 116.3 million ton of soybean straw, which consists of cellulose (34% 35%), hemicelluloses (16% 17%), lignin (22%), extractives (6% 11%), ash (5% 11%), and other nonidentified compounds (10% 12%; for example, protein, pectin, acetyl groups, and glucuronic acid substitutes) (Cabrera et al., 2015; Martelli-Tosi et al., 2017; Wan, Zhou, & Li, 2011). Traditionally, soybean straw has been used for low-value purposes like livestock feeding. Because soybean straw has a low nutritional value, applying the entire residue is difficult. Thus soybean straw is an example of lignocellulosic materials that can be used as a source of cellulose nanofibers (Martelli et al., 2013). In this sense, our research group aimed to optimize the enzymatic hydrolysis conditions (enzyme activity variation and biomass concentration) to obtain NC from pretreated soybean. Pretreatment consisted of mechanical and chemical processes. Soybean straw had previously been washed with distilled water and dried at 50 C for 72 h in an oven with forced circulation (Q314M, Quimis, Brazil). Then, the dried samples were ground in a knife mill SL31 (Solab, Brazil) and sieved through 100-mesh sieves (Tyler series, 150 μm). The soybean straw underwent two chemical

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pretreatments with different NaOH solution concentrations, 5% (PT1) or 17.5% (PT2) (w/v), at 30 C for 15 h, followed by a bleaching step. The resulting fibers were bleached in 4% (w/v) H2O2 and 2% (w/v) NaOH solution; 0.3% (w/v) MgSO4.7H2O solution was added as stabilizer. The solution was cooled to room temperature, and the fibers were filtered and washed with distilled water until neutral pH was achieved, which was followed by rinsing with ethanol and acetone. Both pretreatments produced a material with lower hemicellulose and lignin content (about 10.7% and 9.5% hemicellulose and 3.6% and 3.7% lignin for PT1 and PT2, respectively). On the other hand, higher cellulose content (64% and 66% for PT1 and PT2, respectively) was obtained as compared to untreated soybean straw (39.8%). Comparison between PT1 and PT2 showed that PT2 yielded samples with the highest cellulose content. The pretreatments differed in terms of the first stage (alkaline pretreatment), that is, the alkaline solution (sodium hydroxide) concentration. This stage resulted in swelling, which caused physical changes in the fiber wall and facilitated reactants penetration and diffusion in the fiber structure (Andrade-Mahecha et al., 2015). Sodium hydroxide effectively attacks the linkage between lignin and hemicellulose in lignin-carbohydrate complexes (LCC); in particular, it cleaves the ether and ester bonds in the LCC structure. To produce the nanofibers by enzymatic hydrolysis (stage 2), a suspension of macerated soybean straw (PT1 or PT2) was prepared in acetate buffer (pH 5 4.0). Two specific concentrations (C) of soybean straw and two different enzymatic activities (EA) were employed: 2 and 6 g of pretreated soybean straw/100 g and 400 CMCU and 800 CMCU. The suspensions were heated to 50 C, and the commercial enzyme cocktail Optimash VR (xylanase/cellulase) was added and allowed to react for 42 h. After the enzymatic treatment, protein was denaturated and centrifuged (7000 rpm, 50 C, 10 min). The solids were resuspended in water, and the suspension was mechanically treated (Flauzino Neto et al., 2013). All the eight assays were analyzed for the nanofiber concentration in solution, and the suspension stability was calculated by zeta potential. The cellulose nanofiber concentration (CNF%/100 g of straw) was determined as a function of the concentration of dry matter in suspension (g/100 g) per concentration of pretreated soybean straw in the suspension (g/100 g), multiplied by 100%. The surface charge of nanofiber suspension was estimated by analyzing the zeta potential of aqueous nanofiber suspension aliquots, according to the procedure described by Teixeira et al. (2010). Table 14.4 depicts the specific conditions and the nanofiber concentrations and zeta potential. Variation in the initial straw concentrations and enzymatic activity changes the amount of obtained nanofibers and the suspension stability considerably for both PT1 and PT2. Increasing the amount of the enzyme together with rising straw concentration improves the nanofiber yield. This happens because a maximum nanofiber yield is achieved with 6.00 g of pretreated soybean straw/100 g and 800 CMCU: 6.30 and 6.42 g of nanofibers are achieved per mL of suspension for PT1 and PT2, respectively. The initial soybean straw concentration and the enzymatic activity also affect the zeta potential directly. As for suspension stability, the more stable suspensions derive from the lower pretreated soybean straw concentration for

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Table 14.4 Nanofiber concentration and zeta potential for PT1 and PT2 samples.

PT1

Pretreated soybean straw (g/100 g)

Enzymatic activity (CMCU)

Nanofiber concentration (g/mL of suspension)

Zeta potential (mV)

2.0

400 800 400 800 400 800 400 800

2.75 3.41 4.36 6.30 1.92 3.44 5.08 6.42

2 23.8 2 23.9 2 16.4 2 17.7 2 19.7 2 19.8 2 14.9 2 15.8

6.0 PT2

2.0 6.0

both conditions (PT1 and PT2). In general, nanofiber suspensions are stable in the range between 215 and 225 mV, as observed for all the tests included in Table 14.4. For both pretreatments, PT1 and PT2, maximum stability values are obtained with 2.00 g of pretreated soybean straw/100 g and 800 CMCU: 223.9 mV for PT1 and 219.8 mV for PT2. The zeta potential measures the suspension physicochemical stability. High zeta potential values, as in the case of PT1 and PT2 with 2.00 g of pretreated soybean straw/100 g and 800 CMCU, leads to the conclusion that large repulsive forces exist in the system, making particle aggregation difficult. In other words, a lower initial amount of soybean straw raises the odds of particle aggregation and results in more stable suspensions. Overall, the two pretreated soybean straws experience different effects during the process. The distinct biomass types give different enzymatic hydrolysis results. Soybean straw treatment with 17.5% NaOH is more feasible: it yields more cellulose (66%). Hence, a smaller quantity of starting material (2 g of pretreated soybean straw/100 g) with maximum enzymatic activity (800 CMCU) is a good condition to produce the cellulose nanofibers because this amount provides a considerable yield (3.44 g/mL of solution) of stable particles in suspension (219.8 mV).

14.3.2 Nanocellulose as a reinforcement in biodegradable polymers NC is a natural fiber that is extracted from cellulose on a nanoscale. NC has a diameter ,100 nm and a length in the range of micrometers. This fiber is biodegradable, has low weight and density, and stands out for its resistance properties, including high elastic modulus and TS (Dufresne, 2013; Moon et al., 2011). On the basis of size and morphology, NCs are grouped into three types: CNFs, CNCs, and bacterial NC (BNC). CNFs and CNCs originate from plants. CNFs are characterized by interconnected fibrils with diameters of 1 100 nm and lengths of 500 2000 nm; 100% of the particle chemical composition consists of amorphous and crystalline cellulose.

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CNFs are usually produced through a sequence of chemical or enzymatic steps followed by mechanical treatments (Abitbol et al., 2016; Nechyporchuk et al., 2016). In turn, CNCs resemble needles with diameter of 2 20 nm and length of 100 500 nm. In addition, 100% of their chemical composition corresponds to cellulose. CNC particles are predominantly cellulosic and crystalline (between 54% and 88%) and can be extracted from cellulose fibrils through acid hydrolysis, which removes the amorphous regions and keeps the crystalline particles (Dufresne, 2013; Lavoine et al., 2012; Moon et al., 2011). Fig. 14.2 illustrates these two types of pulp chips at smaller scales. BNC is a highly pure cellulose with a degree of crystallinity (90%). Unlike CNCs and CNFs, BNC is produced by a bacterium belonging to the species Acetobacter xylinum, which uses a fermentation process to generate a biogenic nanofiber network (Chiulan et al., 2016; Martı´nez-Sanz, Lopez-Rubio, & Lagaron, 2013). Due to its excellent properties and biodegradability, NC is attractive for applications in many fields and is particularly interesting for the preparation of nanocomposites: NC confers a high mechanical strength and superior thermal, light, and transparency properties to these composites (Dufresne, 2013; Potulski et al., 2014). Therefore several researchers have incorporated NC into natural or synthetic polymers, as will be shown below.

Figure 14.2 Schematic representation of CNFs and CNCs that can be extracted from cellulose chains by different processes.

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14.3.2.1 Nanocellulose polylactic acid composites PLA is a polymer that can be obtained from renewable sources which can potentially replace petroleum-based plastics (Suryanegara, Nakagaito, & Yano, 2009). PLA is easy to obtain because it is a synthetic polymer derived from natural raw materials such as cornstarch, rice, sugarcane, beet, and potatoes. Additionally, it is biodegradable, biocompatible, highly transparent, and easy to process (Kargarzadeh et al., 2018). PLA production may occur via direct lactic acid polycondensation or laccase ring polymerization. The latter process has raised great industrial interest because it results in a compound of high molecular weight and is well distributed at the moment that the packaging is manufactured. NatureWorks LLC and Corbion, the leading PLA manufacturers in the world, use laccase ring polymerization (Basu et al., 2016; Saini, Arora, & Kumar, 2016). Despite its extremely interesting mechanical properties, PLA’s water vapor barrier property and brittleness limit its performance in numerous sectors. In this context, the addition of a reinforcing material, like NC, to this matrix (Basu et al., 2016; Saini et al., 2016) could be an attractive solution. The compatibility between NC and the highly hydrophobic PLA has been studied (Basu et al., 2016; Lin et al., 2014). Three strategies can be used to improve the compatibility of this system, all of which are based on NC surface modification: (1) physical adsorption of a surfactant, which enhances NC dispersion in the PLA matrix and increases the thermal stability of the resulting composite at higher temperature (Kvien, Tanem, & Oksman, 2005; Petersson, Kvien, & Oksman, 2007); (2) chemical derivation based on silylation or acetylation techniques (Lin et al., 2011; Pei, Zhou, & Berglund, 2010), which regulates surface properties by promoting dispersion of the loaded NC; and (3) chemical grafting, through which the PLA polymer chains are entangled with similar polyesters, to improve interaction with the modified NC (Duquesne et al., 2017; Lin et al., 2011). Table 14.5 shows articles that deal with NC, modified or native, as a reinforcement applied to PLA matrices and highlights the main results obtained for PLA nanocomposites reinforced with NC as compared to pure PLA nanocomposites.

14.3.2.2 Nanocellulose starch composites Starch is an odorless, nontoxic, semicrystalline, and biodegradable polymer (Abdullah et al., 2017) that is easy to extract due to its insolubility in water. It can be obtained from barley, rye, potatoes, wheat, rice, corn, peas, manioc, banana, and oat, among other products (Ave´rous & Halley, 2009; Fama´ et al., 2015; Robyt, 2008). Although physical features such as size and shape depend on the starch origin, all the starch types present similar melting temperatures and degradation, which makes their use as a polymeric matrix difficult. Therefore starch gelatinization is necessary when it comes to producing biodegradable plastics (Schmitt et al., 2012). During starch gelatinization, crystalline structures are destroyed under high heat and pressure conditions, to preserve the amorphous structures in the presence of water and plasticizers. The intramolecular hydrogen bonds of starch starch type

Table 14.5 PLA with added nanocellulose and respective properties. Type of nanocellulose

Load concentration (%)

Processing methods

Improved properties

References

CNF

3 20

Melt compounding

1 2

Melt extrusion

Okubo, Fujii, and Thostenson (2009) Nakagaito et al. (2009)

10 90

Hot-compression

10

Hot-compression

0.1 1

Casting/hotcompression Melt compounding

Strain energy; fracture morphology Force module; tensile strength; hardness Storage module; tensile strength; hardness Force module; hardness Crystallinity Young’s modulus; tensile strength

20 2 20 8 32

CNF (acetylation and oxidation) CNF (POSS)

15 30

Casting Microencapsulation/ melt compounding Casting

3 7

Melt extrusion

BNC (silylation) CNF (alkylation) CNF (acetylation)

2 5 1 5 2 17

Melt compounding Casting Casting

CNF (amine functionalization)

5 15

Casting

Suryanegara et al. (2009)

Suryanegara, Nakagaito, and Yano (2010) Ding et al. (2015)

Storage module; flow resistance Tensile strength

Tanpichai, Sampson, and Eichhorn (2012) Kowalczyk et al. (2011) Wang and Drzal (2012)

Load dispersions; tensile strength

Bulota et al. (2012)

Load dispersions; hardness Load dispersions Load dispersions Load dispersion; thermal stability; hygroscopicity

Fox et al. (2013)

Load dispersions; tensile strength

Frone et al. (2013) Bae and Kim (2015) Tingaut, Zimmermann, and Lopez-Suevos (2010) Lu et al. (2015)

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are cleaved, and new intermolecular bonds of starch plasticizer type are formed (Khan et al., 2017). Despite the presence of a plasticizer, starch materials still have disadvantages compared with synthetic materials (e.g., water sensitivity, brittleness, and inferior mechanical properties). Several studies have pointed out that NC addition can improve the mechanical properties, resulting in high elastic modulus and increasing Young modulus (Lu, Weng, & Cao, 2005). Table 14.6 depicts some of the studies in which composites containing starch of different origins are reinforced with NC. All the matrices were prepared by casting.

14.3.2.3 Nanocellulose chitosan composites Chitosan is a polysaccharide that can be obtained by partial chitin deacetylationn (Hosseinnejad & Jafari, 2016). Due to its antimicrobial properties and ability to form mixtures with natural polymers, it has been investigated in several studies about films (Joz Majidi et al., 2019). Chitosan is used to prepare hydrogels, films, fibers, or sponges, and it is easy to process. However, the stability of products based on this compound is low because chitosan displays a hydrophilic character and is pH-sensitive (Rinaudo, 2006). Many techniques can be used to control the chitosan mechanical and chemical properties, including NC addition; chitosan and NC can be directly mixed because they both belong to the polysaccharide family and share hydrophilic properties. NC incorporation into chitosan-based matrices increases the resistance modulus, thermal stability, and water vapor resistance, attesting to the good NC dispersion in the chitosan matrix and to the easy interaction between NC and chitosan (Dehnad et al., 2014a). The literature reports on three more common methods to disperse NC in the chitosan matrix, which can be accomplished by (1) introducing the charge directly into the matrix; (2) introducing the charge after its chemical or physical treatment, to improve its interaction; or (3) processing on the basis of matrix cationic properties (Kargarzadeh et al., 2018). Table 14.7 summarizes the articles on NC dispersion in chitosan-based matrices and their major contributions.

14.3.2.4 Nanocellulose polycaprolactone composites PCL is a polymer of the aliphatic polyester family; it can be manufactured from crude oil. PCL is hydrophobic and fully biodegradable and bears a flexible and stretchable polymer chain. In addition to being widely commercially available, it is seen as a possible substitute for nondegradable polymers (Kaushik et al., 2010). Nevertheless, its low melting temperature limits its applications. To overcome this issue, PCL must be blended with other polymers or be subjected to radiation crosslinking, which enhances its properties. In this scenario, NC appears as a potential reinforcing agent to produce packages based on PCL matrices (Nakagaito et al., 2009). Some studies have demonstrated that PCL matrices and NC interact well, and that filler interfacial adhesion to the matrix is considerable. NC fills the PCL matrix

Table 14.6 Starch composites with added nanocellulose and their respective properties. Type of nanocellulose

Starch source

Starch concentration (%)

Plasticizer

Improved properties

References

CNC

Industrial

2 30

Glycerol

Cao et al. (2008)

Industrial

5 40

Glycerol

Industrial

5 24

Sorbitol

Pea

10

Glycerol

Industrial

1 20

Glycerol

Cassava

2 10

Cassava

0 1

Glycerol/ Sorbitol Glycerol

Young modulus; water resistance; tensile strength Storage module; Young modulus; water resistance; tensile strength Storage module; Young modulus; tensile strength Elongation at break; storage module; water resistance; tensile strength Storage module; Young modulus; water resistance; tensile strength Young modulus; tensile strength Antibacterial and antioxidant activity; air permeability; Young modulus; tensile strength

Lu, Zhu, and Ren (2006)

Saleem et al. (2018)

Chen et al. (2009a, 2009b)

Liu et al. (2010)

Zainuddin et al. (2013) Costa et al. (2014)

Industrial

1 5

Glycerol

CNF

Industrial

5 15

Glycerol

BNC

Industrial

1 5

Glycerol

Storage module; Young modulus; air permeability; tensile strength Storage module; Young modulus; air permeability; tensile strength Storage module; Young modulus; air permeability; tensile strength

Gonza´lez et al. (2015)

Kaushik et al. (2010)

Carmen (2006)

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Table 14.7 Chitosan matrices with added NC and their respective properties. Type of nanocellulose

Load concentration (%)

Processing methods

Improved properties

References

CNC

5 30

Casting

Li, Zhou, and Zhang (2009)

1 10

Casting

1 12

Casting

5 15

Casting

2

Microfluidization

6.5 and 14

Casting

5

Casting

5 20

Casting

2 20

Casting

1 5

Casting

Thermal stability; water resistance; tensile strength Crystallinity; water resistance Opacity; water resistance Thermal stability Elongation; tensile strength Crystallinity; Young modulus; water resistance; tensile strength Elasticity; breaking strength Elongation; thermal stability; Young modulus Crystallinity; thermal stability; tensile strength Antibacterial activity

CNF

Khan et al. (2012) Pereda et al. (2014) Celebi and Kurt (2015) Khan et al. (2014) Souza, Niehues, and Quadri (2016)

Nordqvist et al. (2007) Fernandes et al. (2010)

Hassan, Hassan, and Oksman (2011) Vela´squezCock et al. (2014)

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spacings: CNFs lead to a certain agglomeration, whereas BNC provides a more homogeneous matrix (Chen et al., 2014; Liu et al., 2013). However, application of NC modified by chemical grafting instead of being applied in its pure form improves the results due to a greater dispersion and better distribution (Liu et al., 2013; Wang, Cao, & Zhang, 2006). NC also enhances PCL nanocomposite crystallinity because NC modifies the polymer crystallinity state, yielding about 60% more crystalline polymers in films (Azeredo et al., 2012; Liu et al., 2013). These morphological changes in PCL nanocomposites directly impact on their mechanical properties, giving a material with reduced TS and EAB and increased elasticity modulus (Azeredo et al., 2012; Chen et al., 2014; Liu et al., 2013).

14.3.2.5 Nanocellulose alginate composites Alginate is a naturally occurring anionic polymer derived from seaweed. It has been extensively investigated due to its interesting properties: biocompatibility, low toxicity, low cost, and moderate gelation. Because it belongs to the polysaccharide family and can dissolve in water and form stable hydrogels, alginate is emerging as a promising matrix for NC-reinforced composites (Kargarzadeh et al., 2018). In general, studies have demonstrated good NC dispersion in alginate solutions, affording a stable and highly viscous suspension that results in a homogeneous matrix after treatment by the melt/evaporation method. The results have shown that alginate films with added NC exhibit a higher TS (Huq et al., 2012), lower water vapor permeability (Azeredo et al., 2012; Huq et al., 2012), and even barrier property against material corrosion (Chen et al., 2014). The use of alginate and chitosan with added NC has been proposed in the food industry; blends based on these materials are resistant to traction and present fat and water barrier properties (Liu et al., 2013).

14.3.2.6 Nanocellulose composites with proteins Proteins are polymers that can consist of up to 20 different amino acids. Therefore they display various functional properties and can potentially establish intermolecular bonds. Protein-based films can form bonds at different positions (Ou et al., 2005). In general, protein-based matrices have a high gas barrier efficiency and low water vapor permeability, which enables their use in biodegradable compound production. In the literature, soy protein is cited as an example of a potential matrix, but its sensitivity to water and its poor mechanical properties make its use difficult and call for the addition of a reinforcing filler like NC. Literature studies have described that the addition of NC to soy protein matrices furnishes films with a high Young’s modulus, better TS, higher water resistance, and good thermal stability (Martelli-Tosi et al., 2017; Wang et al., 2006). Gelatin is a protein that can be obtained by partial (acidic or basic) collagen hydrolysis. During this process, collagen chains are dissociated, and the insoluble material is converted to soluble material (Montero & Go´mez-Guille´n, 2000). Gelatin is interesting in industrial terms because it is produced on a large scale, and

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it derives from mammals or can be industrially synthesized. Gelatin stands out for its stability and consistency, but it has limited applications because it is sensitive to high temperatures. Therefore many papers have associated gelatin matrix with cellulose fillers as a way of improving its applications (Kargarzadeh et al., 2018). Studies have shown that gelatin matrices with added NC have enhanced water resistance and moisture barrier (Mondragon et al., 2015), better resistance and elasticity (Santos et al., 2014), higher oxygen barrier (George & Siddaramaiah, 2012) and are more homogeneous (Ning et al., 2015).

14.4

Other bionanomaterials used as reinforcement fillers in food packaging

Nanometric materials associated with polymer compositions give rise to nanocomposites with several interesting and prominent features for the biomaterials area. Regardless of the source, materials composed of nanofibers offer advantages like a higher contact surface in relation to the total volume of material and greater flexibility compared with other types of material. In addition to cellulose, studies have dealt with other materials that can be a source of nanofibers. Chitosan can be used to produce nanoparticles. It is obtained from chitin deacetylation, which is the second most abundant biopolymer in nature (Ifuku, 2014; Nair & Dufresne, 2003). There are several methods for chitosan nanofiber production, including electrospinning (Greiner & Wendorff, 2007; Huang et al., 2003), polymerization in mold (Aouada, 2009), ionic gelation (Fan et al., 2009; Nasti et al., 2009), and micellar reversion (Kafshgari et al., 2012). These diverse production methods stem from the fact that chitosan nanoparticles are soluble in aqueous solution, which avoids the use of hazardous solvents (Wilson et al., 2010). Chitosan nanoparticles can be used for nanoencapsulation (Akbari-Alavijeh, Shaddel, & Jafari, 2019) and are also employed as a reinforcing agent in edible/biodegradable films. Comparing chitosan with NC, the latter still results in better mechanical and intrinsic properties, for example, in papaya puree films (Barros-Alexandrino, Martelli-Tosi, & Assis, 2019). However, chitosan nanoparticles are an important reinforcement for application in edible packages because they provide improved properties compared with the parent pure materials (Martelli et al., 2013). In general, chitosan nanoparticles have attracted attention in the area of biomaterials due to their unique biodegradation, biocompatibility, antimicrobial, scarring, and miscibility properties (Joz Majidi et al., 2019; Kim et al., 2005; Rogovina et al., 2001; Shahzad et al., 2015).

14.5

Conclusion and future trends

Nanotechnology has contributed to the production of nanometric particles (,100 nm) that can act as fillers in natural and synthetic polymer matrices.

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Nanoparticles can be inorganic, such as oxides, clay, and silica, or organic, like starch, chitosan, and cellulose. These nanoparticles effectively improve nanocomposite water vapor and oxygen barrier and mechanical properties. Some nanoparticles also display antimicrobial activity and therefore yield active packaging. The way nanoparticles affect polymeric matrices depends on their compatibility with the polymer, their diameter/length ratio, and their source, among other factors. Despite the advantages of nanocomposites, nanoparticle production is expensive, demands high-cost industrial facilities, and requires production optimization, which may limit their use in food packaging. Moreover, nanoparticles may interact with food components during processing, storage, or distribution and therefore migrate into food. Hence, commercialization of nanocomposite-based consumer goods and packaging requires evidence of safety regarding nanoparticle release from composite materials during normal use, disposal, and recycling.

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Characterization and analysis of nanomaterials in foods

15

Cristian Dima1, Elham Assadpour2, Stefan Dima3 and Seid Mahdi Jafari2 1 Faculty of Food Science and Engineering, “Dunarea de Jos” University of Galati, Galati, Romania, 2Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran, 3Faculty of Science and Environment, “Dunarea de Jos” University of Galati, Galati, Romania

15.1

Introduction

The special characteristics of food nanoparticles (particle size, particle distribution, surface area and topography, surface charge, dispersion or aggregation state, composition and purity; hydrophobicity and solubility; chemical reactivity and bioactivity, etc.) bring the following advantages: they provide inclusion of ingredients and nutraceuticals in the food matrices without modifying the physical attributes (color, appearance, texture), and sensorial attributes (taste, smell); they also provide the protection of bioactives against the influence of external factors (temperature, light, oxygen) and the physicochemical factors acting during the passage of food through the gastrointestinal tract (GIT) (pH, ionic strength, enzymes); they provide the controlled release of bioactives, increase the bioavailability of bioactives, etc. (AkbariAlavijeh, Shaddel, & Jafari, 2019; Assadpour & Jafari, 2019b; Dima & Dima, 2016; Faridi Esfanjani, Jafari, & Assadpour, 2017). Unfortunately, some of these aspects are causes of potential toxicity risks for both inorganic (silver, iron oxide, titanium dioxide, silicon dioxide, and zinc oxide) and organic (lipids, proteins, and carbohydrates) nanoparticles in foods (McClements & Xiaol, 2017; Peters, Herrera-Rivera, Bouwmeester, Weigel, & Marvin, 2014b). Although the results regarding the safety of food-grade nanoparticles are sometimes contradictory or inconclusive, researchers caution food manufacturers on the concentration and characteristics of nanoparticles in foods. This is because nanoparticle interactions have been found with certain components of the digestive system, suspected of being the potential causes of various diseases (Wani, Masoodi, Jafari, & McClements, 2018). It was shown that certain nanoparticles, such as inorganic ones, caused lymphocyte infiltration, alteration of the intestinal mucus composition, and accumulated in the stomach, small intestine, liver, kidneys, and spleen (Bahadar, Maqbool, Kamal Niaz, & Abdollahi, 2016; Huang, Cambre, & Lee, 2017). More details about the safety and regulatory issues regarding nanomaterials in food have been provided in Chapter 16, Safety and Regulatory Issues of Nanomaterials in Foods. Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00015-7 © 2020 Elsevier Inc. All rights reserved.

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In order to optimize the physicochemical and functional characteristics of food-grade nanomaterials and to decrease the potential risks of using nanoparticles in foods, it was imperative to control and analyze both free food-grade nanomaterials, and foods prepared with nanoparticle-based delivery systems. That is why the control and analysis of foods manufactured with food nanomaterials and nanoparticle-based delivery systems posed two great challenges that experts in various fields, like materials science, physics, chemistry, mathematics, biology, medicine, etc., tried to solve. The first challenge refers to the performance of analysis instruments that should measure the physicochemical characteristics of nanoscale objects, or evince atom and molecule-level interactions, while another challenge refers to the difficulty of analyzing food-grade nanomaterials present in real food matrices, and in the digestive system or other human tissues and organs. If the initial challenge proved solvable as a result of diversifying and improving analysis devices and techniques, the other challenge is harder to surmount because of the complexity of physical and biochemical processes that nanoparticles participate in during processing, storing and ingesting the foods containing nanoparticles (Jafari, Esfanjani, Katouzian, & Assadpour, 2017a). The characteristics of nanoparticles in a food are in constant change as a result of their interaction with the environment where they are placed, such as chemical interactions (oxidation, hydrolysis), physical interactions (flocculation, swelling, degradation), pH and ionic strength variation, biochemical interactions, and enzymatic processes. Almost all scientific papers in specialized literature studying the preparation and behavior of nanomaterials in foods describe at least one analysis technique evincing an importance property of nanoparticles. Upon reviewing several scientific papers, it was concluded that in general, analytical instruments and specialized analysis techniques were developed for a certain feature, although there are cases when the same feature is analyzed by means of two or more techniques, or the same technique measures several features. According to their functionality and analysis techniques, the features of food-grade nanoparticles are grouped into physical features (surface morphology and structure, size, electric charge, mechanical properties, etc.), chemical characteristics (composition, encapsulation efficiency, biocomponent release, sensorial attributes), and biological features (antibacterial activity). Table 15.1 shows the characteristics of food-grade nanomaterials along with the relevant analysis techniques used. This chapter deals with the physical properties of food-grade nanoparticles as food ingredients, such as metal nanoparticles, metal oxide nanoparticles, and of nanoparticle-based delivery systems, such as lipid-based nanoparticles, polymerbased nanoparticles, and surfactant-based nanoparticles. These are used as colloidal systems for the delivery of bioactive ingredients and nutraceuticals, including flavors (citrus oil, mint oil, spice oil), antimicrobials (essential oils), antioxidants (tocopherols, carotenoids, flavonoids, phenolics), vitamins (A, D, C), lipid bioactives (ω-3 fatty acids, conjugated linoleic acids), and minerals (iron, calcium) (Assadpour & Jafari, 2019a; Assadpour, Jafari, & Esfanjani, 2017; Esfahani, Jafari, Jafarpour, & Dehnad, 2019).

Table 15.1 Overview of analytical methods used for food nanoparticles characterization. Analytical method

Acronym

Advantages

Disadvantages

Nanomaterial properties analyzed

References

A. Physical characterization of nanomaterials in foods Optical microscopy (bright field microscopy; dark field microscopy, ultramicroscopy)

OM

G G G

G

G

Polarizing microscopy

PL

G

Provides direct vision of the object Storage of the image obtained Wet or totally hydrated samples may also be analyzed Does not require special conditions (vacuum, dry or frozen sample) altering the real state of the sample Easily handled and cost-effective

G

Can distinguish between isotropic and anisotropic materials

G

G

G

Limited depth of focus Spatial resolution limited Difficulty eliminating optical aberrations and fixed magnification lenses Uses only a tiny amount of material for analysis, which may lead to false results

G G G

G

G G G G

Fluorescence microscopy Laser scattering confocal microscopy

FM LSCM

G G G

High spatial and temporal resolution Low sample consumption Specificity for fluorescent probes

G

G

Applies only to fluorophore species fluorescence Indicators to detect nonfluorescent chemical compounds are required

G

G

G

G

Shape Size Appearance

Gunning (2013), McClements (2015)

Analyzes birefringent materials Phase transition Shape Size Appearance Imaging structural components of nanoparticles (lipids, proteins etc.) Imaging of cells viability Molecular diffusion study Shape, size

Aguilera and Stanley (1999), Castan˜o et al. (2017), Robson et al. (2018)

Guo, Ye, Lad, Dalgleish, and Singh (2016), Mun et al. (2017), Silva et al. (2018), Zou et al. (2017)

(Continued)

Table 15.1 (Continued) Analytical method

Acronym

Advantages

Scanning electron microscopy

SEM

G

G

Direct measurement of the size/size distribution and shape of nanomaterials High spatial resolution (,1 nm)

Disadvantages

G

G

G

Environmental scanning electron microscopy

ESEM

G

Analyzes nanoparticles under natural conditions (in food matrices)

G

The material must be dry The insulating materials must be covered with conductive materials Expensive equipment Spatial resolution lower than SEM

Nanomaterial properties analyzed G

G G

G

G G

G

Transmission electron microscopy

TEM

G

G

Direct measurement of the size/size distribution and shape of nanomaterials High spatial resolution (,50 pm)

G

G G

G

Sample need to be thinned to thickness of 100 nm or less Poor sampling The analysis is performed under nonnatural conditions Expensive equipment

G

G

G G

References

Surface morphology Shape Size and size distribution

Dudkiewicz et al. (2011, 2019), Stockes (2013)

Surface morphology Shape Size and size distribution Molecular interactions Size and size distribution Shape heterogeneity Aggregation Dispersion

Luo et al. (2013), Mattarozzi et al. (2019), Stockes (2013), Tiede, Tear, David, and Boxall (2009)

Baxa (2018), Feng et al. (2016), Klang et al. (2012), Kuntsche et al. (2011), Silva et al. (2018)

Atomic force microscopy

AFM

G G

G G

Dry, wet, or liquid samples are used The samples are analyzed under natural conditions 3D images are obtained High spatial resolution (B0.1 nm)

G

G G

Particle adhesion at the tip of the cantilever Poor sampling Analysis within nanoparticles is limited

G

G G

G

G G G

Dynamic light scattering

DLS

G

G

G

Is applied to nanoparticles in different solvents It is an indestructible, rapid, and reproducible method Easily handled and cost-effective

G

G

G

Small-angle X-ray scattering

Nanoparticle tracking analysis

SAXS

G G

NTA

G

G

Nondestructive method It may analyze opaque polymer solutions, crystalline and amorphous solid particles, spherical particles, platelet and rod-like particles and systems complex with supramolecular organization Diluted liquid suspensions are analyzed Allow the determination of the translational diffusion coefficient

G

The results are influenced by the particle size and concentration The particles are considered to be spherical in shape Particle aggregation or flocculation affects the results Relatively low resolution

G

G

G

G G

G

Nanoparticle concentration and solvent viscosity affect the results

G

Size and size distribution Shape Structure and surface morphology Colloidal forces measurement Sorption Dispersion Aggregation Hydrodynamic size and size distribution Surface electrical charge

Gunning and Morris (2018), Iturri and Toca-Herrera (2017), Moffat et al. (2016), Pleshakova et al. (2018)

Particle size distribution Shape Structure

Sakurai (2017), Sapsford, Tyner, Dair, Deschamps, and Medintz (2011)

Hydrodynamic size

de Morais Ribeiro et al. (2018), Gallego-Urrea, Tuoriniemi, and Hassello¨v (2011), Vasco, Hawe, and Jiskoot (2010)

Bhattacharjee (2016), Mokhtari, Jafari, and Assadpour (2017), Sarabandi et al. (2019)

(Continued)

Table 15.1 (Continued) Analytical method

Acronym

Advantages

Differential centrifugal sedimentation

DCS

G

G

Sample preparation is simple and analysis time is short (15
30 min) Applies to different colloidal systems

Disadvantages

G

G

Laser Doppler electrophoresis or electrophoretic light scattering

LDE ELS

G G G G G

Is a nonintrusive method Very small sensing volume required Direct measurement of velocity No need for calibration Higher accuracy and better resolution

G

G

G

G

G

X-ray diffraction

XRD

G G G

Simplicity of sample preparation Rapidity of measurement High spatial resolution at atomic scale

G

G

G

Cannot independently measure particle size Requires device calibration Need only transparent fluids Single-point measurements Measurements are nonreproducible Electro osmotic effect affects the results Expensive equipment Applies only to crystalline materials Need a standard reference file of inorganic compounds (dspacings, hkls) The detection limit is lower for mixed materials

Nanomaterial properties analyzed G

G G

G

G G

References

The size of particles ranging within 5 nm
40 μm, suspended in a liquid Zeta potential Particles size distribution

Contado et al. (2016), Gollwitzer et al. (2016)

Crystalline structure of materials Phase transitions Material composition and purity

Hosseini et al. (2013), Mourdikoudis et al. (2018), Whitfield and Mitchell (2004)

Verkempinck et al. (2018), SalviaTrujillo et al. (2017)

Differential scanning calorimetry

DSC

G

G G G

Measurements can be made in solution, solid state or colloidal systems Rapidity of the determination No need calibration Small quantities of sample are used

G

G

Relative low accuracy and precision Interpreting the results is sometimes difficult

G G

G G

G

Shear rheology measurements




G

The viscosity and elasticity of liquid and semisolid nanomaterials can be measured

G

G

G

The results are affected by the low viscosity of biological fluids Large volumes of biological fluids are required Interface phenomena can produce artifacts in rheology data

G

Measurements can only be made in solution For UV analysis only quartz cuvettes are used

G

Phase transitions Thermodynamic parameters (enthalpy, entropy, heat capacity) Crystallinity Self-assembly study of supramolecular nanostructures Study of endothermic and exothermic reactions Small deformation and large deformation of nanomaterials in foods

Gill et al. (2010), BryndaKopytowska et al. (2018), Masavang, Roudaut, and Champion (2019), Mochizuki, Sogabe, Hagura, and Kawai (2019)

Concentration Molecular interactions Molecular structure Color of food nanomaterials Encapsulation efficiency

Baldock and Hutchison (2016), Dima and Dima (2018), Souza et al. (2014)

Dima et al. (2016), Gupta, Wang, and Vanapalli (2016)

B. Chemical characterization of nanomaterials in foods Ultraviolet and visible spectroscopy

UV
Vis

G

Qualitative and quantitative measurements can be made

G

G

G

G

G

G

(Continued)

Table 15.1 (Continued) Analytical method

Acronym

Advantages

Infrared spectroscopy Fourier transform infrared Attenuated total reflection Fourier transform infrared

IR FTIR ATR
FTIR

G

G G

G

G

Liquid, solid and gaseous samples can be analyzed The analysis time is very short Qualitative and quantitative measurements can be made Minimal or no sample preparation requirement Independence of sample thickness (ATR
FTIR)

Disadvantages

G

G

G

G

Raman spectroscopy

RAMAN

G

G

G

Nuclear magnetic resonance

NMR

G G G G

Exhibit much less interference from water, Minimum requirement for sample handling and preparation, Raman spectrum covers the spectral range between 4000 and 100 cm21

G

Nondestructive/noninvasive method Small quantities of sample are used. The analysis time is very short Sample preparation is not expensive

G

G

G

G

The accuracy varies with the wavelength range used Interference and strong absorbance of H2O (IR) Sometimes it requires internal standard Relatively low sensitivity in nanoscale analysis Small scattering cross section of many materials Require a high concentration (0.1
0.01 M) of a sample Low sensitivity Sometimes it requires internal standard Not applicable for long length proteins

Nanomaterial properties analyzed G

G

G

G

G G G

G

References

Molecular structure Molecular interactions

Moghbeli, Jafari, Maghsoudlou, and Dehnad (2019), Rui et al. (2017)

Detection of nanomaterials in food and drugs Molecular structure Molecular Interactions Molecular structure Molecular interactions

Craig, Franca, and Irudayaraj (2013), Li and Church (2014)

Hatzakis (2019), Rui et al. (2017)

Mass spectroscopy

MS

G G G G

High-performance liquid chromatography Gas chromatography

HPLC GC

G G

G G

G

High sensitivity Very small amount of sample required High mass accuracy Can be coupled with NMR and IR techniques

G

High sensitivity detection The analyzes are performed in a short time (minutes) Small amounts of sample are used Can be coupled with NMR, IR and MS techniques Volatile compounds are identified by GC

G

G

G

Cannot distinguish isomers of a compound Requires data base Equipments and analysis are expensive Requires internal standards

G

G

G

G

G G

G

Molecular weight Molecular structure Protein sequence

Di Stefano et al. (2012)

Compounds identification, Concentration Encapsulation efficiency Releasing rate

Li et al. (2019), Pezeshky, Ghanbarzadeh, Hamishehkar, Moghadam, and Babazadeh (2016), Prieto and Calvo (2017)

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The following sections will discuss the most important physical characteristics of food nanoparticles together with the representative techniques used in their analysis. Examples from specialized literature will be used to prove the impact of food nanoparticle features on food quality and safety, and the need for the control and analysis of nanomaterials in foods.

15.2

Morphological and microstructural analysis of nanomaterials in foods

The morphology and structural organization of food nanomaterials plays a major role in determining the physicochemical and sensorial properties of foods (Chen & Rosenthal, 2015). The size and shape of nanoparticles (spherical or nonspherical), the structure and electrical charge of the nanoparticle surface, the physical state (liquid, solid) of nanoparticles and their organization in the food matrices are characteristics defining the microstructure and morphology of a food item. These influence the main attributes of food, such as texture and mouthfeel, aroma, release and bioavailability of nutrients. That is why, when designing a food, and most specifically a functional food, the features of food-grade nanomaterials included should be taken into account. Thus solid or sharp-angled crystalline nanoparticles in minerals or spices are the best means to evince the taste of a food item. The distribution and organization of nanoparticles in a liquid or semisolid food matrix influence the sensorial attributes of foods. For instance, an increase in the number of droplets and a decrease in the size of oil droplets, as well as their distribution in an O/W emulsion improve the creamy “smoothness” of dairy products (Booth, 2005). Nanoemulsions are the most commonly used colloidal systems to deliver biocomponents in food matrices (Jafari, Paximada, Mandala, Assadpour, & Mehrnia, 2017b). The microstructure of nanoemulsions is dictated by the physicochemical characteristics and sensorial attributes of the designed food, and it is controlled by the preparation techniques of nanoemulsions, the materials used, and the food processing. The microstructure of nanoemulsions is determined by droplet concentration, their charge and size, as well as the localization of biocomponents or biopolymers used in preparing nanoemulsions (McClements & Jafari, 2018). Nanoemulsion concentration influences its stability, and the food texture, appearance, mouthfeel, and nutritional quality (Chen & Rosenthal, 2015; Piorkowski & McClements, 2014). The visual properties of emulsions like color and opacity are determined by droplet concentration, droplet size, and the refractive index differential between water and oil phases. Thus nanoemulsions whose droplet diameter is under 100 nm do not scatter light and are transparent, compared with conventional emulsions, which, owing to the large droplet size (d . 1 μm), have a milky appearance (Abbasi, Samadi, Jafari, Ramezanpour, & Shams Shargh, 2019). Emulsion
concen tration is expressed either as the dispersed phase volume fraction φV with


 φV 5 VD =VE , or as the dispersed phase mass fraction φm with φm 5 mD =mE ,

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where VD and mD are the volume and mass of emulsion droplets, respectively, and VE and mE are the total volume and mass of the emulsion. It is necessary to know the oil droplet concentration in an O/W emulsion, for instance to assess the amount of vegetable oil they may introduce into a low-fat product, or in the case of beverage emulsions, to assess the amount of oil, and lipophilic component, respectively, that are introduced in the beverage without altering its opacity and functionality. The concentration of nanoparticles may be found differently, according to their state. Thus the concentration of nanoparticles that can be isolated in the food matrix may be determined directly by filtration, sedimentation, and centrifugation. If the nanoparticles cannot be isolated, indirect methods are used, based on microscopic techniques, light scattering, and others, to be described below (McClements, 2015). The electrical charges of nanoparticles determine interactions between them and the salts or polyelectrolytes in continuous phase, forming aggregates that influence the optical, rheological, and sensorial properties of foods and beverages. Thus aggregation of the droplets in an emulsion by depletion flocculation mechanism improves the perception of sensorial attributes, such as “thickness” and “fattiness,” due to the increase of the system viscosity, while aggregation through the “bridging” flocculation mechanism increases the sensation of “dry” and “astringent” due to the alteration of tribological properties (Van Aken, Vingerhoeds, & de Hoog, 2007). As excellent text books are available (Gunning, 2013; Stockes, 2013; Thomas, Thomas, Zachariah, & Mishra, 2017) on the various types of devices and techniques for nanoparticle analysis, the following sections will deal with the basic principles of the main characterization techniques of nanomaterials in foods, without detailing all the construction and operation of instruments.

15.2.1 Optical microscopy Microscopic analysis is one of the commonest techniques for characterizing nanoparticle morphology. This technique has the advantage that the analyst has a direct view of the shape, color, and structure of nanoparticles, and the result of analysis is an image, which is easy to interpret compared to other methods whose analytical results are expressed in numbers, which more difficult to interpret. Decreasing size and complexity of material structure required the improvement of microscope performance. Nowadays there is a wide range of microscopes whose operating principles and characteristics allow for multifunctional and complex image analysis. These microscopes can analyze nanoscale objects, investigating the size, surface, and inner structure of particles, and even their chemical composition. Optical microscopy is the oldest analysis method of an object with a size of 100 μm, which is the lower limit of the size for an object perceived by the human eye. More than 350 years old, the optical microscope contributed to the development of natural sciences and medicine. As physicists collaborated with specialists in other fields, the optical microscope could develop extensively. Now there are optical microscopes that may enhance the real image of an object by 2000 times. Certain optical microscopes are fitted with a video camera to record images or are connected to a personal computer, whose software allows a complex analysis of

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microparticle size and structure (Hosseini, Jafari, Mirzaei, Asghari, & Akhavan, 2015). As compared to other analysis techniques, optical microscopy has the following advantages: it makes use of devices (optical microscopes) that are easily handled and cost-effective; it provides direct vision of the object and the storage of image obtained; wet or totally hydrated samples may also be analyzed, it does not require special conditions (vacuum, dry or frozen sample) altering the real state of the sample. The disadvantages of optical microscopy compared with other microscopic techniques are limited depth of focus, diffraction limited spatial resolution, difficulty eliminating optical aberrations and fixed magnification lenses (Gunning, 2013). In general, it is not possible to see particles ,500 nm with optical microscopy.

15.2.1.1 Bright field microscopy An optical microscope is made up of the following components: light source, lenses, eyepieces (oculars), and/or digital camera, as shown in Fig. 15.1. The light source produces a fascicle of light rays that pass through a condenser, being then directed to the specimen. The light passing undeflected through the specimen (if it allows) is projected by the objective and is uniformly spread on the entire image plane, to the diaphragm of the field glass, and the light diffused by the specimen determines a destructive interference, leading to more or less obscure areas. These areas of light and darkness piece together the real image of the object. The microscope consisting of various components, like lenses in the binocular eyepieces and in the objective is called a compound light microscope. Because it

Figure 15.1 Imaging modes of the optical microscope.

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contains its own light source in its base, a compound light microscope is also considered a bright field microscope. In order to visualize 3D images of objects, a stereomicroscope is used. It does not have a high-performance magnification, but can visualize details of large objects. The main characteristics that have a decisive influence on the optical microscope and other types of microscopes are resolution, magnification, and contrast. Resolution (R) is the microscope’s ability to distinguish two objects that are in the same vicinity; it is calculated by: R5

0:6λ n 3 sinα

(15.1)

where λ is wavelength of the light used, n is the refractive index of the fluid (air, oil) separating the object lens from the blade containing the specimen, and α is the lens opening angle. The product ðn 3 sinαÞ is called the numerical aperture. Since the angle of aperture α may not exceed 70 degrees, for an oil refractive index equal to 1.51 (like emulsions), and a radiation of about 550 nm, a resolution of 280 nm is obtained. In any case, when talking about the resolution of a microscope, it is more accurate to talk about the resolving power or limit of resolution of the microscope. The limit of resolution is the minimum distance for which two neighboring objects can be seen as separate through the microscope. The limit of resolution is better (R is lower) at a higher angle of aperture α, a higher refractive index n, and a lower light wavelength. The limit of resolution of about 280 nm is a theoretical construct, as in practice, in optical microscopy, it is no less than 1000 nm, due to the Brownian movement of small particles and certain flaws in the device components (McClements, 2015). The decrease in the limit of resolution may be achieved by means of radiation sources with
 a very low wavelength, such as X-ray ð 10 nmÞ and neutrons  3 3 1023 nm . Magnification is the ability of microscope to increase the real image of a number of times. The total magnification of an image is obtained by multiplying the power of objective lens which is at 4 3 , 10 3 , or 40 3 and the power of eyepiece which is typically 10 3 . The magnification of optical microscopes varies from 200 to 2000. Contrast is a microscope feature that makes a particle visible. It is determined by the difference between the refractive index of the particle and the environment. When the difference between refractive indices is small, the contrast is small and a microscopic analysis of colloidal systems is difficult to perform. In order to improve the contrast, the following microscopic techniques are used, in addition to bright field microscopy: oil immersion microscopy, dark field microscopy, phase contrast microscopy, differential interference contrast microscopy, confocal microscopy, fluorescence microscopy (FM), polarization microscopy, and Kohler illumination microscopy.

15.2.1.2 Dark field microscopy Dark field microscopy is based on light diffusion by the analyzed nanoparticles. In this technique, the sample is lighted laterally and not from below as in bright field

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microscopy. The light diffused by the particle is aimed toward the field glass of microscope, and the image of particle appears in this glass. If the particle is not present on the slide, light is not deflected from the horizontal into the objective, and the field glass appears as completely dark. If the light source is under the microscope slide, then between the light source and condenser lens, a device may be installed in order to prevent the light fascicle from passing through the particle (Fig. 15.1). In this case the field glass collects the light diffused by the particle. In the image, particles are shown as shiny dots against a black background. By means of this microscopic technique, one may detect nanoparticles with an average size of 20 nm. Due to particle diffusion, the technique of dark field microscopy was used as a study method for metallic colloids and the coagulation process (Kawano et al., 2013; Hiemenz & Rajagopolan, 1997).

15.2.1.3 Ultramicroscopy Ultramicroscopy is a variant of dark field microscope, allowing for the observation of nanoparticles as shiny dots. The ultramicroscope may follow the Brownian motion of the droplets in an emulsion. If the sample is inserted into an electric field, one may determine the electrophoretic mobility necessary in calculating the zeta kinetic potential. Other methods improving the image quality and microscope performance are the phase contrast method, used by Zernike, and the differential interference contrast method, used by Nomarski. The basic principle of these methods is to transform the small differences between refractive indices in high differences of light intensity, thus improving image contrast. In the Nomarski method, contrast increase is achieved by differential interference via a system of birefringent prisms. By adjusting contrast, the images obtained give the impression of 3D images. This method is at the forefront of microscopic technique, being found in many types of microscopes.

15.2.1.4 Polarizing microscopy Polarizing microscopy (PL) employs, as a method of contrast improvement, the behavior of polarized light when it passes through anisotropic or birefringent environments. For nonpolarized light, used in bright field microscopy, two vectorial components (electric and magnetic) propagate in perpendicular planes, while for polarized light, the two components propagate in one plane. When polarized light passes through anisotropic substances, this plane rotates and a specific image is formed in the field glass of the microscope. Polarized light is obtained when nonpolarized light passes through a polarizing prism (Nicol prism). Polarizing microscopy makes use of a bright field light microscope fitted with two polarizing prisms: one before the condenser, called the polarizer, and the other after objective lenses, called the analyzer. The image is obtained by rotating the two polarizing prisms (Fig. 15.2). If the two prisms are in a parallel orientation to each other, the plane of polarized light will be transmitted to the field glass under the form of a shiny field, and if the prisms are in a perpendicular position, polarized

Characterization and analysis of nanomaterials in foods

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Figure 15.2 Polarized light microscope.

light is no longer conveyed, and the field glass displays a dark field (Aguilera & Stanley, 1999). Thus the image obtained by polarizing microscopy contains shiny fields corresponding to the birefringent substances or structures, and dark fields corresponding to the isotropic substances or structures. This method has been used to study the composition and structure of foods containing birefringent substances, like starch, crystalline fats, muscle fibers, some flavoring materials and liquid crystalline emulsifiers. For instance, Castan˜o et al. (2017) studied the morphological and structural changes of starch granules (native potato, maize, chestnut) during melt blending by means of various analysis techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), and PL. The images obtained by PL showed the presence of “Maltese crosses.” These crosses are characteristic of crystalline substances. Melting leads to the destruction of isotropic areas of the starch granules in potatoes, and the number of Maltese crosses drops sharply. These crosses are replaced by the dark background, which is specific to isotropic substances. Another means of improving optical contrast, especially in uncolored objects, is the use of dyes and stains, which give specific colorations to classes of compounds (lipids, proteins, etc.) and even to certain chemical compounds (e.g., starch); this method is used in identifying lipids, proteins, carbohydrates, or microorganisms in foods. Table 15.1 shows the main dyes and stains used in the microscopic analysis of foods. Some of these substances are also used as indicators in FM, such as Oil red O, Sudan Black B, Sudan Black IV, Nil red, for oils and lipids identification; Toluidin Blue (acidified), iodine, potassium iodine, for polysaccharides gums, proteins, and bacteria; Trypan Blue for fungi and yeasts (Hazekamp, 2018).

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15.2.1.5 Fluorescence microscopy Fluorescence is the property of substances to emit light radiations as a result of interaction with a fascicle of electromagnetic radiations. If a molecule collides with a photon of a certain energy, it absorbs the energy and goes into a higher energy state. The relaxation of this molecule may take place by either heat release, or the reemission of a lower energy photon than the original one, as depicted in Fig. 15.3. This mechanism is at the basis of FM. The wavelength of the excitation light influences the spatial resolution of fluorescence microscope. When working with one-photon confocal imaging, the lateral and axial resolution may be of B200 and B500 nm, respectively. Resolution may be improved by various techniques, such as stimulated emission depletion. This technique improves spatial resolution by a size order, and consists of reducing the size of the excitation spot by using a second excitation laser (Fig. 15.3). In order to obtain images in FM, this microscope separates emitted light from excitation light. This process is achieved by a dichroic mirror and optical filters, that should be carefully selected, according to fluorescence indicators (http://www.omegafilters.com/ Products/Curvomatic). The most versatile fluorescence microscope is the epifluorescence microscope which contains, between the light source and the objective lens, a chromatic beam splitter or dichroic mirror, reflecting the excitation light, with a shorter wavelength, to the specimen, and conveys the fluorescent light, with a shorter wavelength, from the specimen to the eyepiece. Not all substances are fluorescent. Some substances have molecules that may emit fluorescence (self-fluorescence). They may be analyzed directly by FM. Some of them are used as fluorescence indicators and help detect nonfluorescent chemical compounds. Foods may contain several types of fluorescent compounds, such as chlorophyll, carotenoids, lignin, ferulic acid, elastin, collagen, some fats, vitamins, and flavorings. Some of these substances are found in the cell walls and hinder the analysis by means of FM of microorganisms, or tissues and organs.

Figure 15.3 Fluorescence microscope.

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15.2.1.6 Laser scattering confocal microscopy Laser scattering confocal microscopy (LSCM) or confocal laser scanning microscopy (CLSM) is based on the principles explained for FM. The main differences between LSCM and FM are (Sanderson, Smith, Parker, & Bootman, 2014): G

G

G

G

G

the excitation source (a bright point source, i.e., laser); placement of a pinhole aperture at the focal plane of image for reject out-of-focus light; the specimen is point-to-point illuminated (“scanning”); the image is obtained by scanning the confocal excitation and detection point across the specimen; and detection of emitted light intensity is done with a photomultiplier tube.

By using dyes and stains in bright field microscopy, especially in FM, the following were studied: identifying chemical compounds in foods (Dubreil, Biswas, & Marion, 2002); localizing biocomponents in various nanoparticle delivery systems (Silva et al., 2018); monitoring structural alterations of nanoparticles in food during digestion (Mun, Kim, McClements, Kim, & Choi, 2017); and identifying microparticles in tissues and organs (McClements & Xiaol, 2017). An important stage in developing analysis techniques for nanomaterials in foods is coupling microscopy and spectroscopy. Thus new techniques, like FTIR microscopy and RAMAN spectroscopy, allow for the localization and structural analysis of chemical compounds in plants (Jaeger, Pilger, Hachmeister, & Oberl¨ander, 2016), nanomaterials (Zhang, Hu, Wang, Zhou, & Liu, 2018), and food matrices (Wellne, 2013).

15.2.2 Electron microscopy The invention of electron microscopy (EM) is one of the most important steps in developing imaging analysis techniques. The results of research in the field of electronic microscopy led to the awarding of several Nobel prizes, such as Stefan Hell, Eric Betzig, and William Moerner (2014) and Jacques Dubochet, Joachim Frank, and Richard Henderson (2017), whose work led to the emergence of various highperformance techniques of imaging analysis, such as SEM, environmental scanning electron microscopy (ESEM), transmission electron microscopy (TEM), environmental transmission electron microscopy (ETEM), and atomic force microscopy (AFM). These high-performance electron microscopes have many applications in nanomaterials science, medicine, biology, astronomy, etc. Nowadays there are numerous scientific books and articles detailing the theoretical principles, technical aspects, and practical applications of EM (Gunning, 2013; Hazekamp, 2018; Stockes, 2013; Thomas et al., 2017).

15.2.2.1 Scanning electron microscopy Unlike light microscopy, where the image is obtained by the object’s interaction with a light fascicle, in electronic microscopy the image is obtained by the interaction of the object with a fascicle of electrons. According to the fascicle nature of

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electrons detected and converted into images, there are two main types of EM: SEM, where the image is the result of collecting the scattered electrons on the specimen surface; and TEM, collecting the electrons that penetrated the specimen and render its image. SEM is the commonest method used for high-resolution imaging of surfaces that can be employed to characterize nanoscale materials (Arpagaus, Collenberg, Ru¨tti, Assadpour, & Jafari, 2018; Mourdikoudis, Pallares, & Thanh, 2018). The main components of SEM are as follows (Fig. 15.4): G

G

G

G

G

G

G

G

the electron source, generating a fascicle of primary electrons (PEs); the column of electromagnetic lenses, guiding the primary electron fascicle; electron apertures, controlling the electron flux; a system of focusing the electron fascicle on the specimen surface; a storage chamber for the previously prepared specimen; a vacuum pump maintaining the lens column and specimen chamber under high vacuum (1025
1027 Pa); detectors collecting the ions resulted from the interaction of PEs and the specimen; and personal computer, to process and display the image.

In SEM, the image is the result of detecting sample scattered electrons. There is a high vacuum in both the column with the primary electron fascicle, and the specimen chamber, in order to avoid the collision of electrons with gas molecules, which would affect the image quality. The sample analyzed by SEM should be solid and electrically conductive. Liquid materials are solidified by various techniques, such as critical point drying, freeze drying, cryostage for frozen-hydrated specimens, and

Figure 15.4 Scanning electron microscope (SEM) and transmission electron microscope (TEM).

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insulating materials are covered in a thin layer of conductive materials (metals, salts, etc.) (Stockes, 2013). As a result of the interaction of the fascicle of PEs with the specimen, the following types of particles and radiations are obtained (Fig. 15.5): G

G

G

G

G

secondary electrons (SE), which are low energy (1
20 eV), being produced by the interaction of electrons in the incident fascicle with the valence electrons orbiting in the specimen atoms to be found at a depth of a few nanometers; Auger electrons, which are SE ejected from an inner shell of an ionized atom. The Auger electron energies are in the range of a few hundred eV to a few keV and are strongly absorbed within the specimen; backscattered electrons (BSE) with a higher energy (50 eV), being the electrons that have passed by the nuclei of specimen atoms found at a depth of 10
100 nm, and subsequently reflected or “backscattered” outside the specimen; X-ray photons, which are electromagnetic radiation produced by the interaction of electrons in the input fascicle with the electrons in the inner strata of atoms, found at a depth of 1
3 μm from the specimen surface. This radiation is used in the chemical analysis of specimens by spectral techniques (EDS, EMPA); and UV-ray photons, which are electromagnetic radiations emitted as a light fascicle (cathodoluminiscence), produced by electrons filling the holes formed by electron rejection.

Image formation in SEM also benefits from the contribution of SE, which adds to the registration of surface topography of the sample, and BSE, which adds to the image contrast. The SEM technique yields three-dimensional images providing

Figure 15.5 Types of particles and radiations obtained in electron microscopy.

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detailed information on the microstructure of particle surface. Since the intensity control of primary electron flux allows them to penetrate layers of several millimeters, SEM may be used to analyze surfaces with a high degree of corrugation. In any case, it must be taken into consideration that by increasing the energy of PEs, the signal of SE decreases, resulting in image quality loss.

15.2.2.2 Transmission electron microscopy A TEM microscope has the same components as a SEM microscope. The electron fascicle with an acceleration voltage ranging between 60 and 300 kV focuses on an ultrafine sample ,100 nm thick. In order to investigate nanoparticles, an acceleration of 80
200 kV is used (Kuntsche, Horst, & Bunjes, 2011). Some of the electrons in the fascicle reaching the specimen are elastically or inelastically scattered, as in the case of SEM, while some of the other electrons go through the sample. The final image is built with the information obtained from the transmitted electrons and is directly displayed on a fluorescent screen, or taken over by a camera and displayed on a PC screen. The resolution of the material is in proportion with the acceleration voltage, and the image contrast is given by the interaction of SE with the material. In TEM analysis, 2D images are obtained, providing information on the size, shape, and morphology of nanoparticles. The magnitude and resolution in the TEM technique are better than in SEM. Table 15.2 shows a comparison between the features of TEM and SEM techniques. Even if, due to certain features, like magnitude, spatial resolution, type of information obtained, the TEM technique is preferred by analysts, it also has certain limitations, such as the long time required, the complex cutting operations of sample in order to obtain very thin layers, difficulty of measuring a high number of particles, and the occurrence of false images due to orientation effects (Mourdikoudis et al., 2018). In order to simultaneously benefit from the advantages of both techniques, TEM microscopes have been recently improved, giving rise to a new technique of electronic microscopy, called scanning transmission EM (STEM). In STEM mode, the electron fascicle scans the specimen surface (the same as in SEM), while the image is built by transmitted electrons (the same as in TEM). Most modern TEM devices may be commuted to the “STEM” mode. When operating in STEM mode, analysts benefit from the advantages of both techniques: they can see the inner structure of sample with very high resolving power, and they may use the signals of X-rays and electron energy loss in spectroscopic tests such as energy-dispersive Xray spectroscopy (EDX) and electron energy loss spectroscopy (EELS).

15.2.2.3 Analysis of isolated food nanoparticles by electron microscopy The analysis of food nanoparticles by electronic microscopy may be performed by either the conventional techniques, that is, SEM and TEM, or various variants of these two, like ESEM, ETEM, or cryo-SEM and cryo-TEM, according to the nature of nanoparticles and the environment conditions; thus traditional SEM and TEM

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Table 15.2 The main differences between SEM and TEM techniques. Characteristics

SEM

TEM

Image formation

Scattered electrons (backscattered or secondary) are captured by electron detectors and this signal is convert into a voltage signal, which is amplified and gives rise to the image on a PC screen Samples are positioned at the bottom of the electron column Up to 30 kV

Transmitted electrons through specimen thin layer pass through a series of lenses below the sample. The image is directly shown on a fluorescent screen or via a charge-coupled device camera, onto a PC screen The sample is located in the middle of the column. 60
300 kV

Information on the sample’s surface and its composition

Information on the inner structure of the sample, such as crystal structure, morphology and stress state information 2D projections of the sample

Specimen location Acceleration voltages Purpose

Image Sample preparation

3D image of the surface of the sample The sample preparation of SEM is much simpler; Electrically conductive materials could be directed loaded in SEM for analysis; insulating materials need inductive coatings

Maximum magnification

B 3 1 2 3 3 106

Optimal spatial resolution

B0:5 nm

TEM sample need to be thinned to thickness of 100 nm or less by electropolishing, mechanical polishing, and focused ion beam milling methods

B5 3 107 ,50 pm

SEM, Scanning electron microscopy; TEM, transmission electron microscopy.

techniques are applied to the analysis of isolated nanoparticles in environment conditions. Wet or hydrated particles in food matrices are analyzed by the ESEM or ETEM techniques. In the past few years, a high number of scientific papers have been published on the analysis of nanoparticles, either free or included in food matrices, by means of EM. These papers deal with the analysis of size, shape, morphology, and topography of various nanoparticle surfaces, such as polymer nanoparticles (Dima, Patrascu, Cantaragiu, Alexe, & Dima, 2016), solid lipid nanoparticles (SLNs) (Tian, Lu, Li, & Hu, 2018), nanofibers (Rezaei, Nasirpour, & Fathi, 2015), nanomemulsions (Jensen, 2013), and nanoliposomes (Baxa, 2018) to be found in a model system or in real food matrices (James, 2009). Most studies refer to the analysis of single nanoparticles. In order to be analyzed by the classical EM techniques,

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synthesized nanoparticles undergo preparatory stages during which the real properties of nanoparticles may change. As many food-grade materials used in preparing nanoparticles are electrical insulating materials, they should be covered inelectrically conductive materials. Thus certain solid nanoparticles were fixed with osmium tetroxide and covered with gold particles, while nanoemulsions were fixed on filter paper by a combination of glutaraldehyde
malachite green and osmium tetroxide (Klang, Matsko, Valenta, & Ferdinand Hofer, 2012). Malachite green is a lipophilic dye allowing for the visualization of oil droplets in SEM analysis. The samples were dehydrated by a freezedrying method and covered in gold vapor. Glutaraldehyde is a chemical fixing agent that makes up a network with proteins, facilitating the water removal process. Without chemical fixation, the samples might be damaged by aggregation or collapse during dehydration. A major issue arising in chemical fixation is the formation of artifacts that make it difficult to interpret images. The staining method of samples is used in microscopic analysis in general, including electronic microscopy. There are negative and positive staining methods (Jensen, 2013). Negative staining means to cover the sample in a thin layer of heavy metal salts (molybdenum, tungsten, or uranium). These penetrate into the hydrophilic surface cavities, creating a negative contrast as a result of more intense electron scattering by metals than other materials in the specimen. In this case, the hydrophobic sites of specimen are left without the corresponding coloration, creating the necessary contrast for a good image. The positive staining presupposes a direct coloration of the specimen microstructure. It is due to the selective interaction of heavy metal salts with various substances (lipids, proteins) forming stains of different colors on the specimen section. The most commonly used negative and positive staining agents are uracil acetate, sodium phosphotungstate, lead citrate, phosphotungstic acid, and potassium permanganate. The uranyl acetate cations UO21 2 may interact in a different manner with the phosphate and carboxyl groups, acting as both positive staining and negative staining for lipids, proteins, etc. Image contrast is influenced by the interaction of staining agents with the components of colloidal system, nanoparticle concentration, the nature of components stabilizing the colloidal system, and the crystallinity state of the material. The disadvantage of using drying and staining techniques in visualizing nanoparticles by SEM and TEM is the possibility of modifying the shape and size of nanoparticles through shrinkage, dehydration, aggregation, or alteration of the inner nanostructure as a result of chemical interactions. In an extended overview, Klang et al. (2012) have shown several examples of factors influencing image quality in TEM and SEM for pharmaceutical nanoemulsions. Cryomicroscopy is an advancement in electronic microscopy based on sample freezing. For instance, a suspension is plunge frozen on a grid, then it is transferred to the TEM and viewed directly by the means of a cryotransfer holder. In order to analyze the inner microstructure of samples or single nanoparticles, it is convenient to use the freeze
fracture and etching technique. The particle surface in the frozen sample is also analyzed by means of the cryo-SEM method. In this technique,

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samples are frozen to subzero temperatures (typically near liquid nitrogen temperature: 2195 C or 78K). Considerable attention should be given to the cooling method and speed of the sample, in order to avoid the growth of ice crystals in hydrated samples. In this respect, it is recommended to use a high-pressure freezer at a cooling rate of 1,000,000 K/s rather than plunge freezing; the liquid and specimen turn vitreous instantaneously, without having enough time to form ice crystals that may damage the sample (Stockes, 2013). In freeze
fracture microscopy, for the preparation of specimen, the following activities take place: G

G

G

G

Fast freezing of nanoparticle suspensions. It may be performed by plunging the sample into a cooling liquid, like liquid nitrogen, or by other ultrafast freezing techniques, like jet freezing, spray freezing, and high-pressure freezing. In order to avoid the formation of big ice crystals, samples are sometimes treated with glycerol. Fracturing the frozen sample, performed under vacuum, at the temperature of liquid nitrogen using a liquid nitrogen-cooled microtome blade. The ice crystals at the surface of the fracture may be removed by sublimation, raising the sample temperature to 2100 C. Preparing replicas. In order to be as close as possible to the specimen topography, the fracture surface is shadowed with gold or platinum by blowing the vaporized metal at an angle of 45 degrees. The ultrathin metal layer is stabilized by covering it with a layer of electron-lucent carbon. Topography of the specimen surface is converted into a replica of metal and carbon of variable thickness. Peeling off the metal replica from the specimen is performed by bringing the sample to room temperature and pressure. The metal replica peels off by the chemical digestion of specimen with acid solutions, followed by detergent washing and drying. The replica obtained is subsequently analyzed by SEM or TEM.

FF-SEM and FF-TEM were applied in the characterization of soft nanosystems, like nanoliposomes, nanoemulsions, SLNs, microemulsions, thermotropic and lyotropic liquid crystalline nanoparticles, polymer-based colloids, and delivery systems for nucleic acids. Numerous authors have presented interesting overviews of EMbased methods for the characterization of nanomaterials in food, summarizing both sample preparation for EM and imaging approaches (Dudkiewicz et al., 2019; Klang et al., 2012; Kuntsche et al., 2011; Mattarozzi et al., 2017, 2019; Meister & Blume, 2017). The cryo-TEM method was successfully used in the analysis of liposomal structure. For example, Fox et al. (2014) studied the preparation and characterization of anionic liposomes loaded with bioactive proteins. The liposomes were prepared by rehydration and ultrasonication using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG). The bioactive protein was ID93-protein that is used as a prophylactic and therapeutic tuberculosis vaccine antigen. The interactions between anionic liposomes and ID93, structure of liposomes and ID93-loaded liposomes were analyzed by Cryo-TEM. The authors showed that the structure of free-protein liposomes contains unilamellar spherical vesicles consisting of a lipid bilayer surrounding an aqueous core; while in preparing protein-loaded liposomes, the results obtained consisted of a mixture of unilamellar and multilamellar liposomes. In order to better grasp the structure of

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aggregates obtained when liposomes were mixed with protein ID93, the authors also carried out a tomographic study of the images obtained. The tomographic method consists of rebuilding the 3D image by a series of projection 2D images of the same sample area obtained at incremental tilt angles relative to the electron beam. The tilted set of images can then be mathematically combined to reconstruct a 3D volume of the sample. The emulsion analysis by cryomicroscopy is more difficult to perform due to the chemical and structural complexity. The O/W emulsions contain an oil phase under the shape of different size droplets, and a continuous aqueous phase. In the interphase layer, on the droplet surface there are various components: surfactants, proteins, and certain polysaccharides influencing the microscopic image (Suvorova, 2017). Classical emulsions, whose droplet size is of a few microns, may be analyzed by optical microscopy, particularly by CLSM, with the staining technique (Gunning, 2013). Nanoemulsions are analyzed by EM, mainly by cryomicroscopy, which is more expensive, first and foremost due to the preparation stage, as it is time-consuming and requires good technical skills. Jensen (2013) authored an excellent PhD thesis on determining emulsion microstructure by means of cryomicroscopy. The author studied the ultrastructure of O/W emulsions, according to the following factors: emulsion composition and concentration, emulsifier type, and method of preparation. Also, a comparative study was carried out on the influence of operations involved in the preparation stage upon the changes in emulsion ultrastructure and cryo-SEM and cryo-TEM image quality. Thus chemical fixation was performed with 3% glutaraldehyde and 2.5% paraformaldehyde, inside agar pockets and capillary dialysis tubes. Sample cooling was achieved by three different methods: high-pressure freezing, freeze substitution, and plunge freezing. Samples were analyzed with TEM, SEM, and STEM EDS analysis. The images obtained confirmed modifications of emulsion microstructure according to the factors under investigation, and at the same time, evidenced the importance of techniques used in the preparation stage to improve image quality. Other researchers (Zhou et al., 2010) used the FF-TEM technique for evaluating the morphology of certain lecithin nanoemulsions prepared without synthetic emulsifiers. In the preparation stage, these authors performed the following operations: samples were first immersed into liquid ethane cooled by liquid nitrogen and then transferred into liquid nitrogen. Fracturing took place into the chamber of freezeetching apparatus at 2120 C and 39 3 1027 mbar. After being etched for 1 min, Pt
C was sprayed onto the fracture face at 45 degrees, and then C was sprayed at 90 degrees. The replicas were taken out of the chamber and placed on a copper gridmesh after washing with hexane. The structural modifications of lecithin nanoemulsions were studied according to the glycerol amount used in preparation. The analysis of FF-TEM images showed that emulsions prepared without glycerol have big droplets and an uneven distribution of sizes. When the glycerol content increases, droplet size decreases, so that only when the glycerol was used as continuous phase did the prepared emulsions have spherical droplets and a very homogeneous distribution of droplet size.

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15.2.2.4 Analysis of nanoparticles by environmental scanning electron microscopy Food matrices are complex solid, semisolid, or liquid systems, where nanoparticles react with other components, like water. That is why it is necessary to analyze nanoparticles in real conditions, within foods, which posed great difficulty and led to the devising of new techniques, like ESEM and AFM. Compared with the standard high vacuum EM, ESEM is a low-vacuum EM, since tests are performed at pressures of 6000
7000 Pa and a relative humidity (RH) of 100%. Microscopes used in the ESEM techniques have the following specifications: G

G

G

presence of gas in the electron column and the specimen chamber; presence of apertures to limit pressure in the electron column; and use of special detectors working in the presence of gases and insensitive to the VIZ radiations, fluorescence, or cathodoluminescence.

Gas plays an important role in altering the signal of SE; their number increases as a result of the collisions of PEs with gas molecules or the gas molecules among themselves. The image quality obtained by low-vacuum EM is influence by the balance between negative electric charges (electrons) and positive electric charges (ionized gas molecules). This charge balance is provided by controlling the following parameters: nature and pressure of the gas, distance between sample and detector, and the energy of PEs (Gunning, 2013). The presence of gas allows the analysis of solid insulating materials; as at a higher pressure, the number of collisions between gas molecules increases, resulting in a sufficiently high number of positive ions neutralizing the excess of ions formed by the interaction of PEs and dielectric specimen. The gases used in analysis of solid insulating materials are nitrogen, nitrous oxide, and carbon dioxide, for minimal pressures of 100
300 Pa (Stockes, 2013). In order to maintain the hydration degree of aqueous liquid materials, corresponding to natural conditions, ESEM uses water vapor at a controlled pressure. Thermodynamic balance is provided by cooling the specimen by a Peltier system, control of water activity, control of vapor pressure, the water loss rate in specimen, and control of water loss during pumping. For a specimen with a RH 5 75%, a temperature of 3 C, the upper pressure limit is ph 5 975 Pa, and the lower pressure limit is pi 5 545 Pa (Gunning, 2013). Although ESEM resolution is similar to the standard SEM in vacuum, it nevertheless decreases with lower water layer thickness around nanoparticles. For example, Doucet, Lead, Maguire, Achterberg, and Millward (2005) showed that by SEM, one may obtain clearer images, whose resolution is ,10 nm, but artifacts are formed by nanoparticle aggregation, and ESEM avoids nanoparticle aggregation, while the images obtained have a lower resolution (30
50 nm). ESEM was also used in characterizing certain polymer nanomaterials in native state (Peckys & de Jonge, 2014), certain vegetables and vegetable tissues (Kalab, Allan-Wojtas, & Miller, 1995), as well as the in situ investigation of dynamics of some phenomena like condensation and coalescence (Barkay, 2014), hydration of

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wheat flour (Roman-Gutierrez, Guilbert, & Cuq, 2002), dehydration of bacterial systems (Staniewicz et al., 2012), and structural alterations in meat processing treatments (James & Yang, 2011). Mattarozzi et al. (2019) studied the detection, visualization, and elemental composition of inorganic nanoparticles in air, raw materials, and food products along the pasta production chain (wheat ear, wheat, semolina, and pasta) by using two independent techniques: ESEM-EDS and inductively coupled plasma mass spectrometry (ICP-MS). The food products analyzed contained nanoparticles with a size ,150 nm, mainly containing Fe and Ti. An innovative technique used in analyzing fully hydrated samples is Wet-SEM. Here, the samples are placed in a steel holder and separated from the vacuum chamber by a membrane transparent to the electron beam. The image obtained has a resolution of 10
100 nm, using a standard SEM combined with a backscattered electron detector (James, 2009).

15.2.3 Atomic force microscopy AFM is a high-performance image analysis technique for materials at molecular and submolecular level. It is a complex device that can “visualize” materials in various environments (vacuum, air, liquid), can correlate the nanostructure of materials to their physicochemical and mechanical properties, like gelling, emulsification, adhesion, friction, and elasticity, or can investigate the heterogeneity of biological systems, contributing to the discrimination between healthy and cancer cells, and the development of regenerative medicine and tissue engineering (Jorba, Uriarte, Campillo, Farre´, & Navajas, 2017; Lekka, 2016). In an excellent review, published in 2018, Gunning and Morris provided the following definition of an AFM: An atomic force microscope (AFM) scans a tiny and extremely sharp tip that is mounted on the end of a flexible cantilever over the surface of samples - it is similar to the action of a stylus on a record player, but in terms of microscopy effectively a nano-profilometer. Unlike all other forms of microscopy, it has no lenses and does not image the sample by ‘viewing’, rather it does so by ‘feeling’ the surface of the sample.

The details on building and operating an AFM and its applications in the study of food microstructures are exhaustively presented in a paper “Probe microscopy and photonic microscopy: Principles and applications to food microstructure” by Morris (2013). The development of this analysis technique triggered the comprehension of several physicochemical mechanisms involved in food microstructure. This technique allows the analysis of materials in natural conditions, eliminating the aggressive operations on samples that occur in the preparation stages of electronic microscopy. The advantages of this technique are the following: elimination of any surface modification or coating prior to imaging; identification and elimination of artifacts, elimination or decrease of sample deterioration by the imaging probe, multifunctional analysis, good contrast, and high resolution. In agreement with Gunning and Morris (2018), AFM analyzes food microstructure, acting either as a microscope,

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by scanning the nanomaterial surface with a sharp probe, or as a spectroscope, by measuring the force between the cantilever tip and sample surface (Fig. 15.6). Thus AFM made it possible to obtain 3D images, contributing to identifying the structure of some biopolymers, like the ramified structure of pectins (Gunning, Bongaerts, & Morris, 2009) and amylose (Gunning et al., 2003), the helix structure of gellan (Gunning, Kirby, Ridout, Brownsey, & Morris, 1996) or the double helix of xanthan (Moffat, Morris, Al-Assaf, & Gunning, 2016). The knowledge of nanostructure for these biopolymers allowed the investigation of their functional properties and the explanation of jellification and emulsification mechanisms (Gromer, Penfold, Gunning, Kirby, & Morris, 2010; Gunning et al., 1996). Other authors used AFM to study the behavior of proteins at the interface, evincing the conformation alterations that influence the stability of emulsions or foams (Wilde, Mackie, Husband, Gunning, & Morris, 2004; Woodward, Gunning, Maldonado-Valderrama, Wilde, & Morris, 2010). Also, the study looked at the interactions between polymer chains in the complex systems of proteins
polysaccharides on the basis of preparing polymer nanoparticles by various methods. Jones and McClements (2011) wrote an interesting review on biopolymer nanoparticles formation by heat-treating electrostatic protein
polysaccharide complexes. In this paper, the authors explained formation mechanisms for globular protein
ionic polysaccharide complexes by heat treatment, and showed the influence of biopolymer type, protein
polysaccharide ratio, pH, ionic strength, and temperature on the characteristics of biopolymeric nanoparticles. AFM is one of the techniques used in determining the morphology and size of nanoparticles formed by heating a mixture of β-lactoglobulin and pectin (Jones & McClements, 2011). AFM force measurement is a method of investigating the complex interactions occurring on nanometric or micrometric scale. Thus by measuring the force that

Figure 15.6 Atomic force microscope (AFM) diagram.

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occurs when scanning the sample surface with a specific scanning tip and graphically representing the force-distance, a “spectrum” is obtained, expressing the interactions between the polymer chains or the colloidal particles, in certain conditions of concentration, pH, ionic strength, etc. (McClements, 2018). So, by means of this technique, elastic properties of synthetic polymers were studied (Giannotti & Vancso, 2007), as well as for biopolymers (Ng, Randles, & Clarke, 2007; Pleshakova, Bukharina, Archakov, & Ivanov, 2018). Similarly, the mechanism of anticancer action of modified pectins was studied by measuring the force occurring in the interaction of polymer chain with the tumor molecules (Gunning et al., 2009, 2013; Iturri & Toca-Herrera, 2017), and the dynamics of structure of carbohydrate molecules in mucin, which is in charge of the “glycocode” effect (Gunning et al., 2013; Iskratsch, Braun, Paschinger, & Wilson, 2009). The use of modified cantilevers allowed researchers to study the deformability of soft materials. Thus they studied the interaction between droplets of an emulsion in the presence of surfactants, proteins, and salts, using a cantilever whose tip captured an oil droplet able to interact with another oil droplet found in the aqueous phase on a glass slide (Gunning, Mackie, Wilde, Penfold, & Morris, 2005; Gunning et al., 2013). Some researchers studied the correlation between the structure of biopolymers and adsorption mechanism of the molecules on the oil droplet surface by means of AFM force spectroscopy (Gromer et al., 2010; Jamieson, Fewkes, Berry, & Dagastine, 2019), while others studied the involvement of biopolymer molecules in depletion effects and the structural alteration of liquid film between the oil droplets or air bubbles (Browne, Tabor, Grieser, & Dagastine, 2015; Ji & Walz, 2013; Shafi et al., 2019).

15.3

Analysis of particle size and size distribution of nanomaterials in foods

15.3.1 Impacts of nanoparticle shape and size on food quality and safety The shape and size of nanoparticles together with the particle size distribution (PSD) are important characteristics with a major impact on food quality and safety. Particle size influences the most important characteristics of food colloids, such as physical stability, appearance, nutrient release, and bioavailability.

15.3.1.1 Size versus stability In a colloidal system, colloidal particles make up the dispersed or discontinuous phase, and the dispersion environment is the continuous phase of the system. Colloidal systems which have no or weak interactions between the colloidal particles and the molecules of continuous phase (e.g., emulsions, suspensions) are called lyophobic colloids, and colloidal systems that have permanent interaction between the colloidal particles and the molecules of continuous phase (e.g., association colloids, polymer solutions) are called lyophilic colloids (McClements, 1999). The

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main difference between these two classes of colloids is thermodynamic stability. Lyophilic colloids, surfactant, and polymer solutions are forming different mesophasic structures (micelles, random coil, etc.). Since constant interactions occur between these structures and the dispersion environment, an interphase structure is hard to define. These structures are formed spontaneously, with the increase of total system entropy, which makes the Gibbs energy negative: ΔGmicellization 5 ΔHmicellization 2 TΔSmicellization

(15.2)

when ΔGmicellization , 0, lyophilic colloids are thermodynamically stable. Lyophobic colloids are obtained by energy consumption and are thermodynamically unstable. The positive value of Gibbs energy for lyophobic colloid formation is due to the increase of the interphase surface: ΔGLC 5 γΔA . 0, at constant interphase temperature and tension. ΔA 5 ALC 2 Ainitial c0

(15.3)

where ALC is the area of interphase surface for the lyophobic colloidal system, and Ainitial is the area of interphase surface for the system in the original state (e.g., the area of interphase O/W surface prior to emulsification). The interphase surface area is measured by means of a physical feature, called specific surface area (Asp). It is defined as the ratio between particle area and the particle mass and is calculated according to particle geometry, as follows: 1. For a system consisting of spherical particles of the same size (radius rs ): Asp 5

Atot n4πr 2 3 5 n4πr3 ρs 5 s ρrs mtot

(15.4)

3

2. For a system consisting of cylinder particles of the same size, radius rc and length L:


   n 2πrc2 1 2πrc L 2 1 1 5 Asp 5 1 ρ rc L nρπrc2 L

(15.5)

According to the value of L/rs ratio, there are the following specific geometries of the particles: G

thin rod: L .. rs Asp 5

G

2 ρrc

(15.6)

flat disk: L ,, rs

Asp 5

2 ρL

(15.7)

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ρ is the density of particle material. Specific surface area is expressed in m2/kg or m2/g. The experimental value of the specific surface area is determined by the adsorption of a gas on a colloidal system with uneven particles (different in shape and size). By applying Eq. (15.4), one may calculate the radius of an equivalent sphere used to further calculate the average diameters. According to the equations above, specific surface area increases with higher particle size. It means that when the particle size decreases, the system energy increases, and the thermodynamic stability decreases. However, a lyophobic dispersed system has a longer “lifetime” due to its physical stability. The physical stability of colloidal systems refers to their property to maintain unchanged in time the size, form, and even distribution of particles. This is kinetic stability, expressing the ability of a colloidal system to oppose the particles’ tendency to separate under the action of external forces (gravitation, centrifuge) or to aggregate under the action of internal forces (van der Waals, electrostatic, steric, hydrophobic, etc.). In all destruction mechanisms of colloidal systems, particle size is an important factor that may ensure system stability. Thus under the pull of gravity, particles travel through the dispersion environment at different speeds, according to particle size and environment viscosity, based on the equation:
 2 ρ2 2 ρ1 v5 grs2 9 η

(15.8)

Eq. (15.8) is applied to monodisperse systems, with spherical particles. According to Eq. (15.8), in a dispersion environment with viscosity (η) and density (ρ1), the slower the movement velocity of spherical particles (the better the kinetic stability), the smaller the particle size. The creaming or sedimentation velocity is proportional to the droplet size squared. If particle density is higher than the environment density (ρ2 . ρ1), then particles go downward and get separated by sedimentation, while if ρ2 , ρ1, particles travel upward and get separated by cremation. The guided particle movement under the action of gravity is opposed by the disorderly particle movement, called “Brownian motion.” The intensity of these types of motions is different, according to particle size. Thus in colloidal systems (e.g., emulsions), where particle size is r . 100 nm, the motion guided by gravity is more intense and determines their separation by sedimentation or cremation; while in colloidal systems where particles are smaller, r , 100 nm, Brownian motion is dominant, contributing to the increase of system stability (Piorkowski & McClements, 2014). According to Eq. (15.8), creaming or sedimentation velocity (v) may be manipulated, not only by controlling particle size, but also by modifying the viscosity of continuous phase (η)
or the difference between densities of the discontinuous and continuous phases ρ2 2 ρ1 . The viscosity control of the continuous phase is performed in the continuous phase through adding thickening agents, like proteins and polysaccharides. In O/W emulsions, oil droplets have a lower density than the aqueous

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phase, and concentrate in the upper part, forming a cream. In real food emulsions, oil droplets are covered in a variable thickness layer made up by the adsorption of biopolymer chains. Thus the particle density increases and may trigger their sedimentation. In order to control the density difference of two phases, to the purpose of increasing kinetic stability of beverage emulsions, weighting agents (brominated vegetable oils, ester gums, sucrose acetate isobutyrate) are added in the oil phase. Under the action of internal forces, particle aggregation occurs by various mechanisms: flocculation, coalescence, and Ostwald ripening. The total interaction potential between two colloidal particles in a dispersion environment is the sum of attractive or repulsive potentials: Utotal 5 UVDW 1 Uelectrostatic 1 Usteric 1 Uhydrophobic 1 Udepletion 1 ?

(15.9)

The types of potentials in Eq. (15.9) are detailed in numerous papers (Hiemenz & Rajagopolan, 1997; McClements, 1999). Some of these potentials, like the van der Waals potential (UVDW), depletion potential (Udepletion), and hydrophobic potential (Uhydrophobic) are attractive potentials, favoring particle aggregation; while the electrostatic potential (Uelectrostatic) and steric potential (Usteric) are repulsive potentials and contribute to the physical stability of colloidal systems. The mathematical equations of these potentials contain the particle size as an important factor influencing the interactions manifested in a colloidal system. For instance, the van der Waals potential (UVDW) is an attractive potential, increasing with a bigger particle size, according to Eq. (15.10): UVDW 5 2

Ars 12h

(15.10)

where A is the Hammaker constant, whose value depends on the properties of two phases, rs is the radius of spherical particles of the same size, and h is the distance between particles. The electrostatic potential (Uelectrostatic) is a repulsive potential, whose intensity increases with particle size (McClements, 1999): Uelectrostatic 5 6 2πε0 εR rs Ψ2 ln½1 6 expð 2κhÞ

(15.11)

where ε0 is dielectric constant of a vacuum (8.85 3 10212 C2/J/m), εR is the relative dielectyric constant of the medium, Ψ is surface potential, rs is radius of spherical particle, and κ is Debye length. Physical
 significance of Debye parameter κ, is given by the reciprocal of parameter κ21 whose measurement unit is length (m) and stands for the thickness of double layer: κ21 5



ε0 εR k B T P e2 n0i Zi2

12 (15.12)

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where n0i is the concentration of ionic species (i) in continuous phase (molecules per cubic meter), Zi is valence of ionic species (i); e is the elementary charge (1.602 3 10219 C), kB is Boltzmann constant (1.38 3 10223 J/K), and T is temperature. In Eq. (15.11) the signs “ 1 ” and “
” are used in calculating the electrostatic potential at constant surface potential and constant surface charge, respectively. Therefore the physical stability of colloidal systems is the result of contribution of two types of forces: repulsive forces, that oppose the destruction of colloidal system, and attractive forces, that contribute to the destruction of colloidal system. As both types of forces are influenced by the size of colloidal particles, it is imperative to have a careful check of these forces in order to provide maximum stability for the food system, and to remove or decrease the potential toxicity risk of nanoparticles.

15.3.1.2 Size versus appearance Particle size has an important influence on both the optical properties of food matrices (color, clarity, turbidity, lightness), and the sensorial attributes of foods, like creaminess, crispiness, roughness, etc. The main causes of optical properties in food colloids are the difference of refractive indices of the discontinuous and continuous phases, particle size, and concentration. Thus the increase in refractive index contrast, particle size, and concentration up to a threshold value determines the increase of lightness in an emulsion. Research showed that the lightness of an emulsion sharply increases in the concentration range 0%
5%, and then the lightness increases very slowly (Komaiko & McClements, 2015; Piorkowski & McClements, 2014). Small-particle colloidal systems, whose size is the same order as the light wavelength (about 500 nm) are transparent, as the dominant optical phenomena are reflection, refraction, diffraction, and to a lesser extent, the scattering of light. It is the case of nanoemulsions where d , 100 nm and whose appearance is transparent, which allows them to be used in manufacturing transparent beverages. When particle size increases, according to the Rayleigh theory, the intensity of the scattered light increases as well, according to the following equation: RðθÞ 5 8πN

 2  r 6 n2 21
1 1 cos2 θ 4 n2 12 λ

(15.13)

where RðθÞ is Rayleigh ratio which is directly proportional to the intensity of light scattered and the turbidity of colloidal system, respectively; N is the number of particles found in the volume unit; r is the particle radius; λ is the wavelength of incident radiation; n is the ratio of refractive indices of the particle and the continuous phase; and θ is the angle between incident and the scattered radiation. According to Eq. (15.13), the efficiency of light scattering is in direct proportion with r 6, λ24, and (n 2 1) 2. The larger the particles, the weaker the

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dependence of light scattering on r and λ. Therefore light scattering is maximal for r  Δn/λ  0.5. The appearance of O/W emulsions differ according to particle size, as follows: nanoemulsions with d  30 nm are grayish, almost transparent; emulsions with d  300 nm are bluish; emulsions with d  3 μm are white; and emulsions with d  30 μm are less white, sometimes colored (Walstra, 2003). The optical phenomena of colloidal systems have applications mainly in using nanoparticles to deliver nutrients in beverages. For example, by knowing the oil droplet size in an O/W emulsion, the oil amount that can be introduced in the beverage may be controlled to provide both the nutrient dosage required, and the beverage appearance. Thus it was shown that the limit between cloudy and the appearance of a product corresponds to a turbidity of 0.05 cm21 (at 600 nm). Emulsions with a droplet size between 200
400 nm are cloudy and may be used in various amounts according to the turbidity required by the final product (Piorkowski & McClements, 2014).

15.3.1.3 Size versus bioavailability The decrease in size of food-grade nanoparticles leads to the increase in total surface area favoring the processes of hydration, solubilization, dispersion, digestibility, nutrient release, and bioavailability, but it also increases the sensitivity of particles to processes of chemical degradation (oxidation) or enzymatic degradation. When passing through the GIT, the size of nano- and microparticles in foods alters as a result of digestion conditions (pH, ionic strength, presence of proteins, polysaccharides, enzymes, bile salts, etc.). Thus the size of nanoparticles increases due to the processes of flocculation, coalescence, and Ostwald ripening, while the size of microparticles or other larger particles decreases due to solubilization and enzymatic degradation (McClements, 2013). Also, it was reported that according to size, nanoparticles may pass through the intestinal wall and accumulate in various tissues and organs (Hillyer & Albrecht, 2001). Lately many researchers have been studying the alterations of micro- and nanoparticles when passing through the GIT (Augustin et al., 2011; Lin, Chen, Lin, & Fang, 2017; Liu, Hou, Lei, Chang, & Gao, 2012; Salvia-Trujillo & McClements, 2016; Salvia-Trujillo, Qian, Martı´n-Belloso, & McClements, 2013). For instance, Salvia-Trujillo and his colleagues (2013) researched the influence of particle size on lipid digestion and β-carotene bioaccessibility, using corn O/W emulsions with different initial droplet diameters: large (d43  23 μm); medium (d43  0.4 μm); and small (d43  0.2 μm). The emulsions prepared this way were subjected to digestion conditions corresponding to GIT (mouth, stomach, intestine). They noticed that in all GIT stages, the droplet size of all emulsions increased due to flocculation and coalescence. By determining the amounts of free fatty acids (FFAs) and β-carotene released during digestion, the authors showed that both the digestion of lipids, and bioavailability of β-carotene increased with the decrease of oil droplet size in emulsions, owing to the increase of contact surface between lipids and the pancreatic lipase.

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15.3.1.4 Size and shape versus toxicity Various researches have shown that shape and size have a crucial influence on the toxicity of nanomaterials (Gatoo et al., 2014; Huang et al., 2017; Khezerlou, AlizadehSani, Azizi-Lalabadi, & Ehsanic, 2018). Small size particles have a larger specific surface area, and interact with cellular components such as nucleic acids, proteins, fatty acids, and carbohydrates. Many authors reported that the shape and size of some nanoparticles, such as carbon nanotubes, silica, gold, nickel, titanium, and cerium oxide nanomaterials affect the biological membrane during endocytosis and phagocytosis and thus cause different types of cancer (Forest et al., 2017; Gatoo et al., 2014). The results found by most researchers showed that spherical nanoparticles are less toxic than rod-shaped nanoparticles and nanofibers. Thus it was discovered that rod-shaped Fe2O3 nanoparticles are more toxic than spherical Fe2O3 nanoparticles (Lee et al., 2014); TiO2 nanofibers with a length of 15 mm are more toxic than those with a length of 5 mm (Hamilton et al., 2009; Lin et al., 2014), and asbestos fibers 10 μm long cause lung carcinoma (Fubini, Fenoglio, Tomatis, & Turci, 2011).

15.3.2 Measurement of nanoparticle size by light scattering techniques Understanding the relation between particle size and food properties allows the improvement of production techniques for nanoscale food materials, as well as the investigation methods for shape, size, and PSD. Nanoparticles have different shapes and sizes, which makes it difficult to identify and characterize them in foods. Under the conditions of food (e.g., beverages) or in biological environment, particles change their size, shape, surface composition, and surface hydrophobicity either by aggregation, or by adsorbing various polymers on their surface, forming a so-called biomolecular corona (Xiao & Gao, 2018). The real shape and size of individual particles can be directly measured by microscopic methods, as shown in the previous sections. These methods are based on the image, counting, and statistical analysis of particle size (Contado, 2015). In reality, colloidal systems are polydisperse systems, with particles whose sizes range within various domains, forming size classes. The size of particles in a size class may be expressed by the midpoint particle radius or diameter. The concentration of particles in a size class is expressed by volume or number percent. The polydispersity of a system may be analyzed by means of PSD or the calculation of SPAN parameter. PSD is the particle fraction that is found in various size classes. The PSD analysis of colloidal systems is performed on the basis of histograms obtained by the graphical representation of variation in the volume percent with particle size, or variation of the number percent with particle size. To express the size of particles considered to be spherical, the rule is to use the mean diameter calculated according to the following three relations: P   ni di P The number-weighted mean diameter d10 5 ni

(15.14)

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P 3  ni d The surface-weighted mean diameter d32 5 P i2 ni di P 4  ni d The volume-weighted mean diameter d43 5 P i3 ni di In the analysis of particle size, it is vital to clarify the type of fraction used in expressing average values, as there are differences among these. For example, McClements (2013) showed that the volume-weighted and number-weighted mean radii calculated from PSD of the O/W emulsions are different: rV 5 149 nm and rN 5 86 nm, which means that the same colloidal system may be seen as a nanoemulsion (rN 5 86 nm), or a conventional emulsion (rV 5 149 nm), respectively, thus creating confusions in their use in food manufacturing. The general tendency is to use the volume-weighted mean diameter (d43) as it is more sensitive to larger particles, and provides complete information on the physical stability of colloidal systems. It is also recommended to fully represent PSD in a graphical form, evincing the central tendency and spread of mean values (distribution width) and the number of peaks, expressing a monomodal distribution (one peak), bimodal distribution (two peaks), or multimodal distribution (multiple peaks), as shown in Fig. 15.7. For a colloidal system to have a better physical stability, the system has to exhibit a narrow monomodal distribution (Piorkowski & McClements, 2014). PSD changes during the storage of a colloidal system or during the processing or consumption of food product provide information on the destabilizing mechanisms of colloidal system (flocculation, coalescence, Ostwald ripening) or the

Figure 15.7 Size and particle size distribution: (A) particle size distribution; (B) span parameter; (C) equivalent spherical diameter.

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adsorption degree of surfactants or biopolymers on the particle surface. A factor used in characterizing polydispersity of a colloidal system is SPAN factor, which is calculated as: SPAN 5

dvð90Þ 2 dvð10Þ dvð50Þ

(15.15)

where dvð90Þ , dvð10Þ , and dvð50Þ are volume size diameters at 90%, 10%, and 50% of the cumulative volume, respectively (Fig. 15.7). A small SPAN factor indicates a narrow size distribution while a high value of SPAN factor indicates a wide distribution in size and a high polydispersity. It is well known that in a disperse colloidal system, particles are not spherical in shape. In general, colloidal particles are anisometric and inhomogeneous, due to their inner structure and aggregation. The concepts equivalent sphere diameter and shape factor are used in characterizing particle shape. Equivalent sphere diameter is the diameter of a virtual sphere with the same properties as the particle, like the same volume (dv), the same surface area (ds), the same sedimentation velocity (df), the smallest diameter of a sieve orifice (de), and the diameter of the circle obtained by perpendicular projection of the particle (dp). The sphericity deviation (anisometry) is assessed by means of the shape factor (F) which is the square of the ratio between equivalent sphere diameters dv and ds, respectively:  2 dv ðVolumeÞ2=3 F5 5 4:836 ds Surface area

(15.16)

Particle anisometry increases with the decrease of shape factor. For example, a sphere has F 5 1, while a cylinder whose length/diameter 5 1, has F 5 0.87 (Walstra, 2003).
On  certain occasions, in order to describe the particle size, the radius of gyration Rg may be used. It is an average dimension used to characterize the spatial extension of a particle. The gyration radius is the distance from the rotation axis of a particle to a point where it is considered that the entire particle mass is concentrated. It is calculated by the average value of r2 and mass fraction as the weighting factor (Hiemenz & Rajagopolan, 1997): P mi r 2 R2g 5 P i mi

(15.17)

The same relation may be applied in calculating the radius of gyration of polymer coil. There are several measuring methods for the particle size and size distribution. Some of these methods, such as optical and electronic microscopy, count and measure directly the size of individual particles.

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The Coulter counter is a method of analyzing the individual particles in highly diluted dispersions, on the basis of altered electrical conductivity when electrically charged particles go through a narrow hole. Particles that are large, undeformable, smooth, and sufficiently isometric may be analyzed by fractioning in size classes by various techniques, such as sieving, gravitational, centrifugal, chromatographic, and electrophoretic separation. Other methods, like scattering of light or other radiation, analyze particle size and PSD in real colloidal systems (Table 15.2). When light radiation interacts with a colloidal system, several optical phenomena may occur, like refraction, reflection, and diffraction, due to the difference between the refractive index of the continuous phase and the dispersed phase. These phenomena cause scattering of light in all directions. The theoretical studies on light scattering were carried out according to the ratio between particle size (d) and wavelength of the incident radiation (λ). The following study models were put together (Brar & Verma, 2011): G

G

G

Rayleigh scattering (d/λ ,, 1), applicable to systems with particles much smaller than the wavelength of incident radiation (d  1/20λ). Mie scattering (d/λ  1) applicable to systems with a particle size most equal to the wavelength of incident radiation. Geometric scattering (d/λ .. 1) applicable to large particle systems.

Irrespective of the nature of colloidal system, a typical light scattering instrument consists of the following components, as shown in Fig. 15.8: G

G

light source, which is usually a laser; spectrometer, containing the optical components necessary to set the observation angle of scattered light;

Figure 15.8 Measurement of nanoparticles size by light scattering techniques: (A) dynamic light scattering technique; (B) and (C) intensity measurement and the corresponding autocorrelation function in dynamic light scattering.

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detector, which usually is a photomultiplier; and signal analyzer, which may be a spectrum analyzer or a correlator for dynamic measurements.

15.3.2.1 Static light scattering It is a classical application method of light scattering in stationary conditions, for direct measurement of the molar masses of polymers and the particle size in their native or aggregate state. The measurements are performed on diluted samples to avoid particle aggregation or multiple diffusion. This method relies on measuring the intensity of scattered light and calculating the particle radius by means of the Rayleigh rapport, written as:
 RðθÞ 5 KVp 1 1 cos2 θ

φ 1 1 2Bφ

(15.18)

where K5

  2π2 n20 dn 2 dφ λ4

(15.19)

dn is the variation of refractive index n0 is the refractive index of continuous phase; dφ in dispersion according to the volume fraction of dispersion—it is constant for a dispersed phase/continuous phase couple; φ is the
volume fraction of dispersion; Vp is the volume of particles considered as spherical 4πr 3 =3 ; and B is a virial coefficient characterizing the interaction types between two particles. Eq. (15.18) may also be written as:


 K 1 1 cos2 θ φ 1 5 1 2Bφ R ðθ Þ Vp

(15.20)

Since in the left-hand term of Eq. (15.20), K and angle θ are experimentally controlled, the graphical representation of Kφ=RðθÞ versus φ leads to a straight line for which the intercept and slope have the following significance: intercept 5 1/Vp and slope 5 2B. The value of the intercept yields the average value of the Vp, and the average particle radius, respectively. The slope of this straight line is equal to the second virial coefficient B, whose value is proportional to the energy potential of interaction between two particles. The negative value of the B coefficient means attraction, while a positive value means repulsion between particles.

15.3.2.2 Dynamic light scattering Dynamic light scattering (DLS) is also known as photon correlation spectroscopy or quasielastic light scattering. This method is used to determine the hydrodynamic diameter and PSD by measuring the time variation of intensity for the scattered

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radiation. In practice, a detector measures the intensity of scattered radiation at various time intervals (Δt). The detector can cover different scattering angles (45, 90 degrees). The intensity of scattered light, measured by the photomultiplier, oscillates around an average value due to the disorderly movement of particles. The signal measured is analyzed by a numerical correlator to the purpose of obtaining the self-correlating function of the signal. This function is the probability that at the time t 1 Δt, the particle is placed at the same point in space as at time t0, that is, the probability that the particle is in the same place. In the case of a small particle that moves fast, the probability is low, while for a large particle, the probability that it should stay in the same place is high, as it is hard for it to stray from its initial position. It means that for small particles, the signal varies slightly and the correlation persists for a long time, while for large particles the correlation disappears rapidly (Terray, 2007). According to Rayleigh’s theory, the intensity of scattered light varies in direct proportion to the radius to the power of six (Eq. 15.13). It means that a 10 nm particle scatters light a million times more than a 1 nm particle. That is why the Mie theory is applied in DLS, as it covers both the Rayleigh field (d , 1/10λ), and the particles whose diameter is comparable to the wavelength of incident light (500 nm). The smaller the particles, the more accurate the value measured. DLS measurements are influenced by the particle density, viscosity of the continuous phase, temperature, and refractive index of the continuous phase. During measurements, particles have to remain suspended in the continuous phase. That is why the low particle density and the controlled viscosity of continuous phase may prevent a possible sedimentation of the particles.

15.3.3 Nanoparticle tracking analysis Just like DLS, nanoparticle tracking analysis (NTA) relies on the analysis of disorderly movement of particles in a liquid suspension. This method analyzes individual particles, so the sample should be highly diluted (1500 3 ). The sample is illuminated by a laser, and by means of a microscope fitted with a video camera, the Brownian movement of individual particles is reconstructed. The image analysis yields the average distance traveled by each particle in the x and y directions. These values allow determination of the translational diffusion coefficient (Dt) used to calculate the hydrodynamic diameter by the Stokes
Einstein equation: dH 5

kB T 3πηDt

(15.21)

where kB is the Boltzmann constant, T is temperature, η is viscosity of the liquid, and Dt is the translational diffusion coefficient. The detection limit of this technique is 10
20 nm. de Morais Ribeiro, Couto, Leonardo Fernandes Fraceto, and de Paula (2018) carried out a comparative study on the application of DLS and NTA for assessing the

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size and polydispersity of liposomes and SLNs. The focus was on the advantages and limitations of the two techniques in the analysis of size, concentration, structure, and instability of colloidal systems. The results showed a lack of correlation for the nanoparticle size when measurements were performed by DLS and a lack of correlation for particle concentration when the NTA method was used. Other authors used NTA technique in tracking number concentration and size of DNA as a model of a fibrillar macromolecule (Yang et al., 2017), or identifying the Agnanoparticles in a chicken digest (Peters et al., 2014a, 2014b) and silicon oxide in tomatoes (Luo, Morrison, Dudkiewicz, Tiede, & O’Toole, 2013).

15.3.4 Small-angle X-ray scattering Small-angle X-ray scattering (SAXS) is a nondestructive method used in determining particle size, size distribution, shape, orientation, and structure of variety of polymers and polymer-conjugate nanoparticles. In SAXS, the crystalline or amorphous sample is subjected to an incident fascicle of monochromatic X-ray, whose wavelength is 0.1
1 nm. Due to the differences between electron density inside and on the surface of nanoparticles, the incident fascicle is scattered. The intensity of scattered radiation is measured by a detector covering small angles (0.05
5 degrees) (Contado, 2015). This method is better than DLS as it may analyze opaque polymer solutions, crystalline and amorphous solid particles, spherical particles, platelet (lamellar) and rod-like (cylindrical) particles with a size range between 1
100 nm, as well as systems forming complex aggregates with supramolecular organization (Sakurai, 2017). Also, unlike DLS, which only analyzes the size and distribution of aggregates in a colloidal system, SAXS may also analyze the distribution of particles in the aggregate.

15.3.5 Differential centrifugal sedimentation Another important class of analysis methods for tackling particle size relies on their separation in the colloidal system, into fractions with particles having close geometric features. Particle separation is due to the differences in density, size, shape, structure, and takes place under the action of a field-flow (gravitational, centrifugal, electric, etc.). The main techniques of particle separation are centrifugal particle sedimentation, differential centrifugal sedimentation (DCS), centrifugal liquid sedimentation (CLS), high-performance liquid chromatography (HPLC), hydrodynamic chromatography, size-exclusion chromatography, field-flow fractionation, capillary electrophoresis, diafiltration, and gel electrophoresis. The disadvantage of these methods is the fact that they cannot independently measure particle size. That is why these methods should be coupled with various detectors, like DLS, multiangle light scattering, UV
Vis, and ICP-MS (Mattarozzi et al., 2017). The DCS or CLS method measures the size of particles ranging within 5 nm
40 μm, suspended in a liquid.

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Experimentally, the nanoparticle suspension is injected in a transparent rotating disk partially filled with a series of solutions of different densities (e.g., sucrose solutions of various densities 40
120 g/kg). In rotation of a disk at a speed of about 20,000 rpm, heavier particles form a sediment at the disk edge, and lower density particles form a sediment toward the center of the disk. The sedimentation time is measured according to the intensity of a light fascicle (laser) scanning the disk surface. The sedimentation time is used in calculating the Stokes diameter, using the equation: 2


 312 ρ0 2ρl t02 5 Dp 5 Do 4 ρp 2ρl tp2

(15.22)

where D, ρ, and t are the diameter, density, and sedimentation time for the calibration system (D0, ρ0, t0), particle (Dp, ρp, tp), and the liquid in the disk (ρl). PVC particles 239 nm in diameter, and a density of 1385 g/cm3 may be used as a calibration system. The advantages of this method consist of the simple preparation stage, the possibility to analyze multimodel colloidal systems, and the analysis time of 15
30 min. In order to put together a complete characterization of nanoparticle size and size distribution, in various conditions, it is recommended to use several analysis techniques, whose results may be correlated, drawing conclusions as to colloidal stability. Gollwitzer et al. (2016) analyzed two types of nanoparticles: plain silica nanoparticles and aminofunctionalized silica nanoparticles. These nanoparticles were suspended in three different environments: in purified water, Tris
HCl buffer at a physiological pH, and in a cell culture medium containing 10% fetal bovine serum. Size and PSD were measured using DLS, CLS, SAXS, and particle tracking analysis (PTA). The results showed that average size of plain nanoparticles of silica in simple media (purified water and Tris
HCl buffer) are comparable in all the three methods used, giving rise to a monomodal PSD; while the functionalized nanoparticles exhibited in all environments a bimodal PSD in DLS, CLS, and SAXS analysis and a monomodal PDS in PTA. In the cell culture medium, nanoparticle size increased either by protein adsorption (the corona effect), or by flocculation of nanoparticles into larger aggregates, which compromised DLS measurements. The size of these particles was found by PTA.

15.4

Surface charge and zeta potential analysis of nanomaterials in foods

15.4.1 Surface charge of nanomaterials in foods Electric properties of nanoparticles are determined by the electric characteristics of materials used in preparation and the environment conditions where they are prepared

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or processed (pH, ionic strength, dielectric constant, etc.). Several types of food nanoparticles are manufactured by means of natural polymers with a polyelectrolyte structure, such as proteins and polysaccharides (Esfahani et al., 2019; Ghasemi, Jafari, Assadpour, & Khomeiri, 2017). Proteins are polyelectrolytes whose electric charge is strongly influenced by the pH value as compared to the isoelectric pH (pHi). For pH , pHi proteins are positively charged, due to the predominance of protonated amino groups, and for pH . pHi, proteins are negatively charged due to the ionized carboxyl groups. Most polysaccharides are negatively charged, due to the carboxyl groups (2COOH) or other groups, like sulfate (2SO4H, in carrageenan) forming negative ions at certain pH values, such as 2CO2 H2 2 CO2 2 ðpK a  3:5Þ and
SO4 H2 2 SO22 ð pK  2 Þ. Chitosan is an aminopolysaccharide that, in an acid a 4 environment, forms positive ions of ammonium by protonating the amino group: 2NH1 3 2 2 NH2 ðpK a  6:5Þ (Hosseinnejad & Jafari, 2016). Biopolymers are not only used as encapsulating material, many times they are intentionally added to the continuous phase and act as emulsifiers, stabilizers, thickening agents, etc. By their adsorption on the particle surface, these acquire electrical charges according to the nature of the polyelectrolyte and the composition of continuous phase. A case in point is gum Arabic. It is used as an emulsifier since its structure contains hydrophobic remains made up of amino acids that are adsorbed on the oil droplet surface, and hydrophilic remains made up of glucosidic units, which attribute negative charges to the oil droplet surface. The modification of nanoparticle charge can occur either by modifying the pH of continuous phase (proteins, chitosan), or by covering the nanoparticle surface via successive layers of biopolymers with opposing electrical charges, such as preparing particles by layer-by-layer (LbL) method. Together with the biopolymers, the nanoparticle surface may adsorb other chemical species, like ionic surfactants, metallic ions, nonmetallic anions, phospholipids, and bile salts, contributing to the electric charge of nanoparticles. The electrical charge has a crucial influence on the physicochemical and functional characteristics of nanoparticles. First and foremost, the electrical charge is an important factor contributing to the stability of colloidal systems. The electrical charge influences the repulsive electrostatic forces between particles. A high superficial charge determines the increase of stability in a colloidal dispersion. The intensity of superficial electrical charge is assessed by means of zeta electrokinetic potential, to be described next. The presence of the superficial electrical charge makes nanoparticles in food interact with other chemical species, forming complex aggregates that may form precipitates or sediments (Matalanis, Jones, & McClements, 2011). The electrical charge also influences the behavior of nanoparticles in food when they pass through the various segments of GIT. In oral phase, the cationic biopolymer nanoparticles may attach to the negative centers on the tongue surface, triggering the astringent taste. In gastric phase, the swelling degree of chitosan nanoparticles outweighs that of alginate nanoparticles due to the positive electrical charges that favor the interaction with water molecules (Dima et al., 2016). Also, it was shown that cationic biopolymers, like chitosan, have bioadhesive properties and determine the joining of particles in the mucus layer, triggering the release of biocomponents in different GIT sectors. Studies have shown that cationic

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biopolymer nanoparticles penetrate the epithelial layer of small intestine better than anionic or neutral biopolymer nanoparticles. It may cause on the one hand an increase in the bioavailability of encapsulated bioactives, and on the other hand an increase in the toxicity risk by nanoparticle accumulation in various organs and tissues (McClements & Xiaol, 2017).

15.4.2 Measurement of zeta potential (ζ) The electrical properties of nanoparticles are usually characterized by the electrokinetic potential, also called the zeta potential (ζ). The zeta potential occurs as a result of interaction between electrically charged particles and the chemical species in solution. A colloidal particle in the solution is surrounded by a fixed layer, called the Stern layer, made up of counterions directly adsorbed on the particle surface. Next to this layer, there is another one interacting with it, which is more diffuse and consists of ions distributed at random because of the electrical forces and thermal agitation. The border of this layer defines the hydrodynamic diameter of the particle at whose level the surface of shear or slipping plan is formed. The zeta potential occurs at the level of this plane, as depicted in Fig. 15.9. Therefore the zeta potential is the measure of the difference between bulk solution and the liquid layer associated with the particle. The zeta potential is dependent on pH and ionic strength of the solution containing colloidal particles. Its size is influenced by a parameter called the Debye length (κ21), defining the thickness of diffuse layer.

Figure 15.9 Measurement of zeta potential: (A) schematic model of electrical double layer; (B) schematic illustration of laser Doppler electrophoresis device; (C) production of fringes interferences in Doppler effect.

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The commonest measurement technique for the zeta potential is laser Doppler electrophoresis based on the determination of the electrophoretic mobility of particles. The electrophoretic mobility of particles is measured by means of a light fascicle coming from a laser. Generally speaking, the measurement of the zeta potential is performed together with the measurement of size and distribution of particles. According to the Doppler effect, a light fascicle interacting with a moving particle is scattered, resulting in radiation of a higher frequency than the frequency of incident radiation. The incident light fascicle is separated into two fascicles that are focused on the electrophoresis cell containing the colloidal system. Due to the interference, a network of parallel bright and shady fringes is formed in the sample (Fig. 15.9). While moving, a lit particle scatters light. It is taken over by the photomultiplier and, by means of a correlator, the PSD is calculated. The crossing of fringes by a particle occurs at a frequency depending on velocity, and on the translational diffusion coefficient (Dt), respectively. Under the action of an electric field E, a particle with the net electrical charge q moves through the continuous phase together with the fixed liquid layer (the hydrodynamic diameter), at an electrophoretic velocity ve. When the surface of shear identifies with the Stern surface and the particle is in a diluted solution where κ21 is large (i.e., κ is small), the electric potential Ψ identifies with the zeta potential (ζ), expressed by the following equation (Hiemenz & Rajagopolan, 1997, p. 542): ζ5

q expð 2κRÞ 4πεR

(15.23)

where R is the radius of spherical particle. Since κ is small, Eq. (15.23) may be written as: ζ5

q 1 q 1  4πεR expð 2κRÞ 4πεR ð1 1 κRÞ

(15.24)

ζ5

q κ21 4πεR ðR 1 κ21 Þ

(15.25)

or:

respectively: ζ5

q q q 2 5 4πεR 4πεðR 1 κ21 Þ 4πεRð1 1 κRÞ

(15.26)

Since κR ,, 1, Eq. (15.26) becomes: ζ5

q κ21 q 5 21 4πεR ðR 1 κ Þ 4πεR

(15.27)

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During electrophoresis, a spherical particle which is electrically charged is acted upon by two forces: an electric force (qE) and a friction force (6πηRve). For the equilibrium state: qE 5 6πεηR

(15.28)

By definition, electrophoretic mobility (u) is the ratio between electrophoretic velocity and electric potential: u5

ve q 5 6πηR E

(15.29)

Using Eq. (15.27), Eq. (15.29) becomes: u5

2ε ζ 3η

(15.30)

Eq. (15.30) allows the calculation of the zeta potential based on the electrophoretic mobility measured by the laser Doppler electrophoresis. The values of the zeta potential are the measure of physical stability of colloidal systems. For low values of zeta potential ( 210 mV , ζ , 1 10 mV), colloidal systems are unstable, while for values higher than 6 30 mV, colloidal systems have a high kinetic stability.

15.5

Analysis of crystallinity and phase transition in food nanomaterials

15.5.1 Crystallinity and phase transition in lipid-based nanoparticles Both bioactive compounds and encapsulating materials may be amorphous and crystalline substances. These states influence the characteristics of nanoparticles and the functionalized foods. For example, amorphous compounds have a higher solubility than crystalline ones, and consequently increased bioavailability. The encapsulation of crystalline hydrophobic bioactive compounds is a challenge, as in crystalline state hydrophobic compounds may influence particle size, rheology, stability of colloidal systems, GIT solubility, and absorption. To be encapsulated, crystalline hydrophobic compounds are first solubilized in carrier lipids (e.g., triacylglycerol oil) or in an organic solvent (alcohol or hydrocarbon). For example, when preparing O/W emulsions, the crystalline hydrophobic bioactive compound is heated at a higher temperature than its melting temperature (Tm) and then mixed with the liquid lipid forming the oil phase of emulsion. By cooling the emulsion under Tm there occurs a phase transition liquid
solid, forming nano- and microcrystals of various shapes and sizes, suspended in the aqueous phase (McClements, 2012).

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The size and shape of crystals is influenced by a series of factors, like chemical composition, molecular structure, cooling temperature and velocity, mechanical agitation, and presence of impurities. When an emulsion is slowly cooled, the crystal growth rate is higher than the nucleation rate, and that is why hydrophobic bioactive compounds as well as carrier lipids may turn into big crystals; while during fast cooling, the nucleation rate is higher and thus small crystals are formed, as they do not have enough time to grow. The presence of big crystals influences the stability, rheology, sensorial perception, and biological potential of emulsion-based delivery systems. Thus big crystals create a sensation of “grainy” or “sandy” in the mouth and decrease the bioavailability of bioactive compounds as a result of decreasing solubility (Da Silva, Renato Grimaldi, Calligaris, Cardoso, & Goncalves, 2017; McClements, 2012). When preparing lipid-based delivery systems, saponificable lipids are used, containing FFAs, phospholipids, and acylglycerols. According to the number of fatty acids attached to the glycerol molecule, acylglycerols are mono-, di-, and triacylglycerols (MAG, DAG, TAG). Out of these, TAGs make up the highest percentage in the composition of vegetable and animal lipids (Tavakoli, Naderi, Jafari, & Naeli, 2019). The fatty acids in TAGs may be saturated, for example, palmitic (C16:0) and stearic (C18:0) acids; or unsaturated, for example, oleic (C18:1) and linoleic (C18:2) acids. According to the length of saturated or unsaturated chain of fatty acids, TAGs may be medium-chain triglycerides or long-chain triglycerides. The nature of fatty acids influences certain special properties of TAGs, like oxidation, digestion rate, and lipid polymorphism. Lipid polymorphism is due to the organization of TAG molecules into certain structural units of different geometries (hexagonal, orthorhombic, and triclinic) known as α, β0 , and β polymorphic forms, respectively. Thermodynamic stability and the melting temperature of polymorphic forms of lipids decrease in the order: β . β0 . α (Fig. 15.10).

Figure 15.10 Crystallization forms of triacylglycerides.

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By cooling, TAGs initially crystallize in the α and β0 forms, but not in the β form, which, even if it is a more stable from a thermodynamic point of view, has a higher activation energy of nuclei formation. Under certain conditions of temperature, pressure, or the presence of impurities, less stable forms undergo the irreversible transformation to the more stable forms through a monotropic phase transformation. The dominant polymorphic form in a fat depends on its composition. Thus certain fats such as soybean, sunflower, peanut, corn, and olive oils tend to crystallize in the polymorphic β0 form, whereas cotton seed, palm, tallow oils, and milk fat mainly crystallize in the polymorphic β form (Da Silva, Ribeiro, & Santana, 2019; Ribeiro et al., 2015). Since the polymorphic transformation influences the physical and sensorial characteristics of the lipid-based delivery systems, it is imperative to provide the preparation and storage conditions so that the desired polymorphs should be preserved. The control of crystallization process and the polymorphic transformations is achieved by controlling the physical parameters, like the cooling rate, stirring process, or parameters referring to the composition of lipid system, like adding minor lipids to basic fats, using nucleating agents, and adding certain emulsifiers (Ribeiro et al., 2015). For instance, two innovative types of nanosystems for the delivery of bioactive compounds have been recently developed: SLNs and nanostructured lipid carriers (NLCs) (Katouzian, Faridi Esfanjani, Jafari, & Akhavan, 2017; Lin et al., 2017). Lipid crystallization plays a major role in stabilizing W/O emulsions and O/W/O double emulsions (Garti, Aserim, Tiunova, & Binyamin, 1999; Ghosh & Rousseau, 2011). Certain studies showed that α- and β0 -form fat crystals are more hydrophilic than β-crystals and have the tendency to get adsorbed at the oil
water interface, contributing to the stabilization of W/O emulsions by Pickering and network stabilization mechanisms (Ghosh, Pradhan, Patel, Haj-Shafiei, & Rousseau, 2015; Johansson, Bergensta˚hl, & Lundgren, 1995). Pickering stabilization was defined more than 100 years ago by its namesake (S. U. Pickering) as a steric stabilization of emulsions triggered by solid micro- and nanoparticles adsorbed on the oil
water interface. In the Pickering stabilization of emulsions, inorganic nanoparticles (hydroxyapatite, silica, metal nanoparticles, metal oxide nanoparticles) and organic nanoparticles (chitosan, cyclodextrin, polysaccharides, proteins, crystallized fats) are used (Chevalier & Bolzinger, 2013; Yang et al., 2017). Many researchers have studied the Pickering stabilization of W/ O emulsions by crystallizing fats (Pawlik, Kurukji, Norton, & Spyropoulos, 2016; Rousseau, 2013). The ability for Pickering stabilization of fat crystals depends on several factors, out of which the most important are size of crystals, concentration and morphology of crystals, interfacial film rheology, and wettability (Ghosh & Rousseau, 2011; Ghosh et al., 2015). Network stabilization of W/O emulsions is due to the complexity of the process of fat crystallization in the continuous phase. Food emulsions are complex systems that contain several chemical species, among which some may constitute nucleation germs. The disorderly growth of crystallites determines the formation of a solid 3D network enclosing the water droplets, avoiding the breaking down of emulsion. In

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order to increase the stability of W/O emulsions, certain researchers added precrystallized fat in the continuous phase (Hodge & Rousseau, 2005). Butter and margarine are two food systems in which W/O emulsions are stabilized by the Pickering mechanism and network crystals. Polarized light microscopy analysis shows that in butter emulsion stabilization is mainly provided by the network-type fat crystals, while in margarine the focus lies on the fat microcrystals covering water droplets and thus providing a Pickering stabilization (Rousseau, Ghosh, & Park, 2009). Recently, Di Bari, Macnaughtan, Norton, Sullo, and Norton (2017) studied crystallization in water-in-cocoa butter emulsions and the role of water droplets on fat crystallization and polymorphic transition. The analysis techniques used in determining polymorphism and crystallization kinetics were pulsed nuclear magnetic resonance and differential scanning calorimetry (DSC), respectively. By calculating the kinetic parameters according to the Avrami equation, the authors showed that in W/O emulsions, both the crystallization rate and phase transformation rate of cocoa butter increase in comparison to bulk cocoa butter.

15.5.2 Glass transition temperature (Tg) in polymer-based nanoparticles An important class of nanoparticles used in food functionalization consists of polymer-based nanoparticles. In order to prepare food-grade polymer nanoparticles, mainly natural biopolymers are used, like polysaccharides and proteins (Katouzian & Jafari, 2019; Rostamabadi, Falsafi, & Jafari, 2019b). In choosing polysaccharides and proteins as encapsulating materials, a series of factors were taken into consideration, like chemical structure, solubility, pH conditions, ionic strength, environment temperature and the vitreous transition temperature, electrical properties (pKa, electrokinetic potential), superficial properties, behavior toward the mono- and multivalent ions, susceptibility to enzymes, and chemical reactivity to other components. Polymer behavior when there is temperature variation is different. Thus crystalline polymers, mainly synthetic polymers, by heating pass from the solid crystalline state, where polymer chains are organized into certain structures, into the liquid state, where macromolecules are distributed disorderly. The temperature where the solid
liquid transition occurs is called melting temperature (Tm). Amorphous polymers have ramified chains, which cannot be packed regularly to form crystals. At low temperatures, randomly distributed polymer chains are immobile; they cannot rotate around chains nor move in space. The only possible moves are the atom vibrations. This state is called glassy state and it is considered a superchilled liquid where molecule movement was “frozen.” The glassy state is an unbalanced state which, within an infinite time frame, goes into the crystalline state (Zanotto & Mauro, 2017). In glassy state, the amorphous polymer is hard, rigid, and fragile. When the amorphous polymer is heated, segments of the entangled chains become mobile. This state is called the rubbery state and corresponds to a soft flexible material. The temperature at which the amorphous polymer makes a transition from the glassy to the rubbery state is called glass transition temperature (Tg) (Zanotto & Mauro, 2017).

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In general, natural biopolymers have an amorphous structure, but there are many semicrystalline natural polymers whose structure contains crystalline and amorphous domains (starch, cellulose, alginates, etc.). These polymers have better elastic properties as they combine the strength of crystalline polymers to the flexibility of amorphous polymers. In semicrystalline polymers, glass transition is a property pertaining solely to the amorphous region of the solid. According to the structure, a polymer may have one or several Tg values, or it may have Tg values within a certain range (Ebnesajjad, 2016). The value of Tg depends on the molecular weight of polymer, the content of water in other plasticizers, cooling or heating rate, and the strain rate (Ebnesajjad, 2016). Thus Tg increases with the increase of molecular weight of the substance, and decreases at higher water content in the material. It should be pointed out that melting and glass transition are two thermal processes that differ widely. Thus melting only refers to crystalline polymers or the crystalline domains within the semicrystalline polymers, while glass transition only refers to amorphous polymers or the amorphous domains within the semicrystalline polymers. An important difference between melting and glass transition is seen in the graphical representations of heat (enthalpy) variation with temperature (Fig. 15.11). So, when heating crystalline polymers to the melting temperature, the heat (enthalpy) increases at a steady rate, and at the melting temperature the heat received by the polymer rises, in isothermal conditions, until the entire amount of polymer is melted. This heat is called latent melting heat. After the polymer melts, the heat increases with growing temperature at a steady rate, corresponding to

Figure 15.11 Phase transitions to polymers: (A) crystalline polymers; (B) amorphous polymers; (C) semicrystalline polymers.

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heating the liquid. Under these circumstances, melting, just like freezing and boiling, are isothermal phase transformations, known as phase transformations of order I, as entropy (S), enthalpy (H), volume (V), and caloric capacity (Cp) of these transformations are discontinuous in the transition points, corresponding to the first derivatives of the Gibbs free energy: 

@G @T



 5 2 S;

p

   @G @H 5 V; 5 Cp @p p @T p

When heating amorphous polymers, caloric capacity increases at a steady rate up to Tg, whereupon the growth rate of caloric capacity with temperature is higher (the slope of graph is steeper). In this case, the polymer has no latent heat, as at the Tg, the movement of polymer chains is altered, resulting in the polymer fast transition from one phase into another. From a thermodynamic point of view, glass transition is considered an Ehrenfest second-order transition as the discontinuity is only seen in the second derivative of the Gibbs free energy: 

@2 G @T 2



 5 p

@S @T

  2    @G @V ; 5 2 @p T @p T p

(15.31)

Glass transition is accompanied by altered enthalpy, entropy, dielectric properties, or certain mechanical properties, like dynamic viscosity. That is why the methods of determining Tg are based on measuring the values of caloric capacity, Gʹ storage modulus, and Gʹ loss modulus. Tg is a vital parameter influencing the physicochemical characteristics of nanoparticles, sensorial attributes of foods, and chemical stability of bioactive compounds (Le Meste, Champion, Roudaut, Blond, & Simatos, 2002). Thus the control of dehydration processes of materials, like freeze drying, spray drying, extrusion, collapse, and crystallization is performed on the basis of glass transition diagrams. Similarly, glass transition influences the retention of biocomponents, or their release from nanoparticles. Dry nanoparticles in glassy state preserve their degree of volatile compound retention during storage in low-humidity conditions. The presence of water triggers a decrease in Tg as water acts as a plasticizer. The water molecules penetrate the “frozen” chains of polymer in glassy state and favor the transition to rubbery state, where, due to the increased mobility of polymer chains, nanoparticles swell and encapsulated compounds are released through swelling-controlled kinetics (Arifin, Lee, & Wang, 2006). Several authors have studied the effect of plasticizers on glass transition and the mechanical properties of some biopolymers. For example, the plasticization of starch from various sources was studied by means of polyols, such as glycerol, glycol, xylitol, and sorbitol (Ave´rous & Fringant, 2001; Da Ro´z, Carvalho, Gandini, & da Silva Curvelo, 2006; Zhang & Han, 2010). Da Ro´z et al. (2006) showed that the presence of amylosis in starch improves the plasticizing action of glycerol. By

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treating potato starch with glycerol, for a RH 5 53%, the tensile modulus was about 160 MPa, for high amylosis content, and about 120 MPa, for native starch. Upon studying the plasticizing effect of glycerol, sorbitol, and monosaccharides in starch films, Zhang and Han (2006) reported that glycerol-plasticized films had a Tg  270 C that was lower than starch films plasticized with other plasticizers. Also, Mohammadi, Cheng, and Karim (2011) found out that sorbitol-plasticized starch films exhibited a superior heat sealability to glycerol-plasticized films. Tg depends on the concentration of plasticizers in combination with polymers. Some authors proposed mathematical equations able to express the dependence of Tg on the mixture composition (Couchman, 1987; Gordon & Taylor, 1952). One of these equations is the Gordon Taylor formula, used to calculate Tg of the mixture (Tg(mixture)) by using the caloric capacities of pure components (Monnier, Maigret, Lourdin, & Saiter, 2017): TgðmixtureÞ 5

w1 Tg1 1 kw2 Tg2 w1 1 kw2

(15.32)

ΔC

where k 5 ΔCp2 ; wi is the weight fraction of component i, Tgi is the glass transition p1 temperature of component i, and ΔCpi is the heat capacity change of component i.

15.5.3 Measurement of crystallinity and phase transition in food nanomaterials This section describes the commonest techniques used in determining crystallinity and phase transitions in food nanomaterials.

15.5.3.1 X-ray diffraction There are numerous techniques using X-rays in the structural analysis of materials, be it qualitative or quantitative, such as X-ray fluorescence spectrometry, protoninduced X-ray emission spectrometry, SAXS, and XRD (Igwebike-Ossi, 2017). XRD is one of the first methods used to determine the crystalline structure of materials. It was developed on the basis of observations made by Max von Laue in 1912, according to whom in crystalline substances the atoms or molecules are distributed in an orderly fashion, in planes situated at fixed distances, similar to a grill, and may create a constructive interference with a monochromatic X-ray fascicle whose wavelength is comparable to the distance between atoms. Crystalline substances determine the coherent scattering of X-rays, while amorphous or semicrystalline substances trigger incoherent scattering, also called diffuse scattering. X-rays were discovered by Roentgen in 1895 and originate in the interaction of an electron fascicle (beta radiations) and a metal (anode), as a result of dislodging electrons in the inner layers of the metal. X-rays are electromagnetic radiations (photons) with very short wavelengths (1029
10211 m) and very high energy (1016
1020 Hz) (Fig. 15.12A).

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Figure 15.12 X-ray diffraction technique; X-ray formation mechanism; X-ray diffraction on crystalline materials; X-ray diffractometer diagram. (A) X-ray formation mechanism; (B) X-ray diffraction on crystalline materials; (C) X-ray diffractometer diagram.

Each metal used as an anode emits a fascicle of monochromatic X-rays, with a wavelength characteristic to the inner energy level of the atom where from the electron was dislodged (levels K, L, M. . .). That is why the analysis of X-rays emitted by a material allows determination of the metal types in the material composition (Fig. 15.12A). The main components of an X-ray diffractometer are X-ray tube, sample holder, and an X-ray detector (Fig. 15.12C). The X-ray tube consists of a metallic filament which by heating produces an electron fascicle, directed at high speed onto the surface of a metal producing the monochromatic X radiation. For instance, copper pro˚ . The monochromatic Xduces the radiation Kα with the wavelength of 1.5418 A ray fascicle of the wavelength λ interacts with the crystalline substance where the atoms are distributed in an orderly manner in different planes, situated at a certain interplanar distance (d) (Fig. 15.12B). When the difference between the distance covered by the incident rays reflected by atoms found in different layers [path length (interplanar) difference, d] is an integral multiple of wavelengths, a constructive interference occurs, according to the Bragg law: nλ 5 2dsinθ

(15.33)

where n (an integer) is the “order” of reflection, λ is the wavelength of incident Xrays, d is the interplanar spacing of crystal, and θ is the angle of incidence. A regular pattern of crystalline atoms produces a regular diffraction pattern which provides information about the crystal structure.

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The XRD technique has multiple applications in material science. It is used to determine the crystalline structure of materials, the study of phase transformations, determination of material composition and purity, etc. (Kvick, 2017). The crystallinity of a substance may be found by calculating the interplanar space d by means of a fascicle of monochromatic X-rays, whose wavelength and incidence angle θ are known. The results of an X-ray analysis are expressed under the form of diffractograms. Each crystalline substance has its own diffractogram, corresponding to a certain phase. To identify the crystalline structure of a phase, a diffractogram of an unknown compound is compared to the reference diffractograms within the international databases. The characteristics of a diffractogram provide more information on the physical state of the material. Thus the peak position shows the presence of phases, the peak height is proportional to the phase concentration, the peak width shows the size of crystallites, and the background hump is specific to the amorphous structure (Igwebike-Ossi, 2017). Hosseini, Zandi, Rezaei, and Farahmandghavi (2013) used XRD technique to determine the structure of chitosan powder and the oregano essential oil-loaded chitosan nanoparticles obtained by ionic cross-linking with sodium tripolyphosphate (TPP). They showed that chitosan powder has a high degree of crystallinity, proved by the peak found at 2θ, at 25 C, while the diffractogram for chitosan nanoparticles found no peak, which means that by TPP reticulation, chitosan loses its crystallinity. The XRD technique was used to determine the structure of classes of compounds with major roles in the daily operation of living organisms, like membranar phospholipids, proteins, and nucleic acids respectively. The XRD structural analysis of phospholipid powders showed that in solid state their molecules are organized as a bilayer. The two aliphatic chains attached to the glycerin molecule form different angles with the normal of the bilayer plane, and the “polar head” consisting of the remaining phosphoric acid is oriented almost parallel with the plane (Hauser, Pascher, Pearson, & Sundell, 1981), as shown in Fig. 15.13. In aqueous solutions, at higher concentrations than critical micelle concentration, phospholipids tend to self-assemble, forming aggregates of various structure and geometry, called mesomorphic phases or liquid crystalline phases. The identification of mesomorphic phases and phase transformations were achieved by various analysis techniques, like XRD, NMR, SEM, TEM, DSC, and nanoplasmonic sensing (Chen, Duˇsa, Witos, Ruokonen, & Wiedme, 2018; Hauser et al., 1981; Jackman, Ferhan, & Nam-Joon Cho, 2017; Luzzati, 1968; Tyler, Law, & Seddon, 2015). Upon examining the T-C phase diagrams of lipids, it can be seen that single-chain lipids (e.g., lysophosphatidylcholines, also called lysolecithins) are lyotrope, as phase transformations are due to the modification of water content, and double-chain lipids (e.g., lecithins) are thermotrope, as the phase transformation is mainly due to temperature change. The types of phases that occur with concentration or temperature variation are designated by various letters, like the following (Faucon & Meleard, 1993): G

the lamellar (anisotrope) phase, (Lα) is the result of organizing molecules into bilayer structures separated by water films (Fig. 15.14). Hydrocarbonated chains mostly have a “gauche” conformation, which makes the bistratum thickness to range between 0:8lc and

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Figure 15.13 Conformational structure of triacylglyceride molecules in (A) solid state; (B) aqueous solution; (A-1) dilauroil phosphatidyl ethanol amine; (A-2) dimyristoyl phosphatidyl choline; (A-3) phosphatidic dimyristoyl acid; (B) bilayer structure of dilauroil phosphatidyl choline.

Figure 15.14 The hypothetical phase diagram of monoacylglycerides.

G

1:6lc (where lc is the length of hydrocarbonate chain in a trans configuration). The aqueous film is B0.2
20 nm thick, according to the water content. the lamellar phase (Lβ) has a gel consistency. The amphyphylic molecules are also organized in bilayer structures whose chains have a trans configuration, more rigid than in the case of the (Lα). In this case, for double-chain lipids, thickness of the bilayer is almost double the nonpolar part. The orientation of hydrophobic chains may be perpendicular to

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G

631

the bilayer plane or at a certain angle in regard to the normal. Gelliform phases (Lβ) are formed at lower temperatures than the other mesophases; when the temperature increases they change into anisotrope lamellar phases (Lα). the hexagonal phases (H) are made up of cylindrical micelles, with a diameter of 1:5 2 2lc , organized as tubes in a hexagonal network. They can be under the form of direct hexagonal phases (HI) where the polar part of amphyphilic molecule is distributed on the cylinder surface, in contact with the aqueous environment, and the hydrophobic part is inside the cylinder; and inverse hexagonal phases (HII) where the hydrocarbon chain is distributed on the cylinder surface and the polar part is inside the cylinder where aqueous phase is also included. The hexagonal phases are optically anisotrope as they have just one symmetry axis. cubic phases consist of spherical micelles with a low number of aggregates, distributed in geometric structures with cubic symmetry. They are isotropic crystalline liquid phases and occur on low concentration domains between the lamellar and hexagonal phases, designated by I1 or I2 (Fig. 15.14).

The presence of these phases occurs when producing liposomes, hexosomes, and cubosomes and influences the stability, loading degree, and release rate of encapsulated biocomponents (Caddeo et al., 2019; Chen, Cheng, Swing, Xia, & Zhang, 2019; Rostamabadi, Falsafi, & Jafari, 2019a; Rostamabadi et al., 2019b).

15.5.3.2 Differential scanning calorimetry DSC is one of the commonest analysis techniques in the thermal analysis of materials. This method is based on measuring the dependency of caloric capacity on temperature. DSC is used in the study of phase transitions of substances in solution, in solid state or disperse systems. Generally, a scanning calorimeter is composed of two identical aluminum pans covered with a lid: one pan contains the sample to be analyzed sealed hermetically and the other pan contains an equal amount of reference substance (solvent, pure substance). Usually, the reference pan is empty and covered. There are two types of DSC systems differing by the operating manner, as shown in Fig. 15.15: G

heat flux DSC, where the sample and reference, connected by a thermoelectric metallic disk, are closed in one furnace (Fig. 15.15A). The temperature gap between sample and the reference, due to the enthalpy or caloric capacity changes, is proportional to the heat flow between them, measured by means of a thermocouple, according to Ohm’s law: q5

G

ΔT R

(15.34)

here q is sample heat flux, ΔT is temperature difference between sample and reference, and R is resistance of thermoelectric disk. power-compensation DSC, where the sample and reference are in two identical separate furnaces, and temperature is controlled independently by a system of temperature sensors (Fig. 15.15B). The two cells are heated (or cooled) simultaneously, quasiadiabatically at a constant rate (0.5
1.5 K/min). The differences between caloric capacity of the sample and reference occurring during heating or cooling are compensated by varying the power input to the two furnaces. Thus it is certain that all through the experiment, the difference

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Figure 15.15 Differential scanning calorimeters (DSC): (A) heat flux DSC; (B) power compensated DSC. between sample cell temperature and reference cell temperature is zero. The power required to compensate the temperature variation is the measure of difference between the caloric capacities of sample and the reference, also called excess caloric capacity:

ΔCp 5 Cpsample 2 Cpref

(15.35)

In DSC analysis, small amounts of substance are used, that is, (0.5 2 1.5 mg) as the difference ΔCp is small in phase transformations. The analysis results are expressed by thermograms obtained via the graphical representation of ΔCp with temperature. The variation of caloric capacities is due to the inner structural modifications of compounds, as a result of physical interaction disturbances, such as electrostatic and hydrophobic interactions, hydrogen bonds, and van der Waals forces, or the molecule configuration changes with temperature variation. All these changes result in phase transformations and are evinced in thermograms by peaks occurring at certain temperature intervals (Jelesarov & Bosshard, 1999). Phase transformations in biopolymers (proteins, polysaccharides, or lipids) are accompanied by the variation of thermodynamic parameters, such as partial specific heat capacity, Cp(T), enthalpy ðΔH Þ, entropy ðΔSÞ, and Gibbs free energy ðΔGÞ. A negative value of Gibbs free energy expresses stability of the phase under study (Gill, Moghadam, & Ranjbar, 2010). The partial specific heat capacity, Cp, provides information on the conformation of biopolymers within the temperature interval studied. For example, for globular proteins, Cp, at 25 C varies in the domain 1.2
2.3 J/K/g and linearly increases with the temperature on a slope of (6
8) 3 1023 J/K2 g. Deviations from these values show the loss of globular structure of the protein (Privalov & Dragan, 2007). Numerous research teams used DSC to analyze the stability of proteins (Wen et al., 2012), carbohydrates (Brynda-Kopytowska et al., 2018), and lipids (Miao &

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Mao, 2015). Ciurzy´nska, Jasiorowska, Ostrowska-Lige˛za, and Lenart (2019) studied the influence of aeration time on the structure and transition temperatures of some freeze-dried hydrocolloid gels prepared with low-methoxyl pectin and a mixture of xanthan gum and locust bean gum. DSC analysis showed that in most freeze-dried gels with low-methoxyl pectin aired for ,9 min, there were no amorphous forms, and they displayed endothermic peaks corresponding to the melting temperatures at 143.8 and 142.8 C, respectively. For the gel aired for 9 min, there occurred several amorphous domains that dropped the Tg to 44 C. Similarly, the DSC curve of this gel showed an endothermic peak at 141.6 C, corresponding to the melting point, and an exothermic peak at 229.9 C indicating the degradation of gel to pectin. Using the thermodynamic parameters determined by various DSC techniques, the crystallinity degree of materials may be assessed. Thus comparing the fusion enthalpy of a sample ðΔH Þ to that of a standard substance of 100% crystallinity ðΔHo Þ, the crystallinity degree of sample is calculated by the relation (Gill et al., 2010): %Crystallinity 5

ΔH 100 ΔHo

(15.36)

To calculate the crystallinity degree (Xc), without using the total crystallinity standard, the following equation is used:


ΔHf 2 ΔHc Xc 5 ΔHfo

 (15.37)

where Xc is the weight crystallized fraction of sample, ΔHf is enthalpy of fusion, ΔHc is the enthalpy of crystallization, and ΔHfo is the heat of fusion for the completely crystalline sample at the melting temperature (Kong & Hay, 2002). Recently the classical DSC technique has developed under the form of other techniques, with better performance and more diverse applicability. Among these techniques, the most widely used are modulated DSC, microelectromechanical systems-DSC, pressure perturbation calorimetry, and high-performance DSC (Knopp, Lo¨bmann, Elder, Rades, & Holm, 2016; Poel & Mathot, 2007; Yu, Wang, Lu, & Zuo, 2017; Zhai, Okoro, Cooper, & Winter, 2011).

15.6

Mechanical characteristics and analysis techniques of nanomaterials in food

15.6.1 Impacts of mechanical properties of food nanoparticles on food quality The mechanical properties of food nanoparticles play an important role in highlighting the sensorial attributes of foods, such as texture and mouthfeel. These two attributes differ by the manner of their perception. Thus texture of a food product is a

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complex concept resulting from the visual, auditory, tactile, and kinesthetic detection of foods, while the mouthfeel is the sensation perceived by the consumer while chewing food (Chung & McClements, 2014). Mastication is the totality of mechanical, chemical, and biochemical processes ensuring food fragmenting, their mixing with saliva, and the formation of food bolus. Swallowing the food bolus occurs under the control of oral receptors and is influenced by many factors, such as particle size, cohesiveness, elasticity, plasticity, moistening, and action of enzymes (Peyron & Woda, 2016). Texture and mouthfeel are evinced by different attributes, according to the physical state of foods. Solid food and soft solid food are mainly evaluated by the following attributes: crispness, crunchiness, cohesiveness, graininess, etc., while liquid foods (emulsions) are assessed by attributes like creaminess, richness, smoothness, sliminess, thickness, thinness, watery, firmness, hardness, and astringency (Chung & McClements, 2014; Kilcast, 2004). Out of the numerous factors impacting these sensorial attributes, an important role is played by the mechanical properties of food nanomaterials, such as viscosity, elasticity, flowability, and mechanical strength. For example, concentrated emulsions have a high viscosity, increasing the perception of “creaminess,” “smoothness,” “thickness,” and “fattiness.” These sensations may decrease by diluting emulsions or by reducing the fat content and its replacement with biopolymers (Chung & McClements, 2014). The interactions between colloidal particles may lead to the formation of aggregates increasing the viscosity of food dispersions. The particle size and shape, and continuous phase rheology are parameters influencing the oral perception of particles. Solid particles are perceived as smaller in the mouth than liquid and semisolid foods (emulsions, gels), and individual particles are perceived as smaller than those within food matrices. In general, it was shown that the critical size for the oral perception of particles within food matrices is between 2
200 μm (Engelen, Van Der Bilt, Schipper, & Bosman, 2005). Likewise, the mechanical properties of food nanomaterials affect the release of biocomponents, food processing, conduct transportation, food packing, and storage.

15.6.2 Instrumental mechanical assessment of liquid and soft nanoparticles in food There are various techniques for measuring the mechanical properties of food nanomaterials, applied in various conditions. Thus some techniques measure the mechanical properties of nanoparticles dispersed in continuous phase or in the food matrix, such as the viscosity and viscoelasticity of emulsions and suspensions measured with viscometers and rheometers; others measure the deformation and mechanic resistance of isolated nanoparticles. Also, some techniques may measure small deformations of particles, like oscillatory tests, AFM, micropipette technique, osmotic pressure method, optical tweezers, while others measure large deformation that bring about their destruction, like the compression of particles between plates (Guo, Xie, & Luo, 2014).

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15.6.2.1 Oscillatory tests; viscoelasticity of food materials The advantages of techniques that measure small deformations of nanoparticles are that nanoparticles are not broken, and the volume variation is low, so that it does not essentially influence the release of encapsulated components (Fery & Weinkamer, 2007). Studies showed that in the chewing process, the mechanical properties with small deformations of food materials, like the linear viscoelastic regime between stress and strain do not influence mastication. If the shear strain is above 70%, then the material deformation is large, and food materials undergo deformations and fragmentations similar to those in the mastication process (Ogata, Umeno, & Kohyama, 2008). Liquid colloidal systems (emulsions) or semisolid colloidal systems (gels) are considered to be non-Newtonian fluids as there is no linear relation between the shear stress and the shear rate. Their mechanical properties are in-between liquid viscosity and solid elasticity. That is why emulsions and gels are said to be viscoelastic. If a force acts upon them, they do not instantaneously undergo deformation, neither do they instantaneously go back to the initial shape when the force stops acting (Chung & McClements, 2018). The rheological properties of viscoelastic materials are time-dependent and characterized by the complex elastic modulus G which is the sum between elastic component, called storage modulus (Gʹ) and viscous component, called loss modulus (Gʺ): G  5 G0 1 iG00 These are determined by small amplitude oscillatory measurements, consisting of applying a sinusoidal stress on the material, after which the resulting sinusoidal strain is measured or vice versa (Bricen˜o, 2000). If a sinusoidal strain ðγ Þ is applied on a material, its mathematical equation is: γ 5 γ 0 1 sinðωtÞ where γ 0 is the amplitude of the strain wave and ω is the frequency of oscillation; then the corresponding stress response (τ) is: τ 5 τ 0 sinðωt 1 δÞ where τ 0 is the maximum amplitude of sinusoidal stress and δ is the phase angle or phase shift of the strain. Storage modulus (Gʹ) measures the stored energy per cycle while the loss modulus (Gʺ) measures dissipated energy per cycle, and they are calculated with the following equations: G0 5

τ0 τ0 cosδ and G00 5 sinδ γ0 γ0

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with: G00 5 tanδ G0 For perfect elastic solids, the entire energy is stored within the material, which means that Gʺ 5 0, and the stress and strain will be in phase; while for perfect viscous materials, the entire energy is dissipated (Gʹ 5 0) and the strain will be out of phase. Similarly, the viscoelastic properties of the material are also assessed according to the values of the phase angle ðδÞ of a material: δ 5 0 degrees for a perfect elastic solid (Hookean solid); δ 5 90 degrees for a perfectly viscous fluid (Newtonian fluid); and 0 , δ , 90 degrees for a viscoelastic material. At a given frequency, and a certain temperature, low values of the phase angle δ show a high level of material elasticity, that is, a low amount of dissipated energy per cycle. Also, the variation with frequency of the rheological parameters defined above provides information on the structural alterations occurring in the material. Thus together with DSC, small amplitude oscillatory measurement is an important method used in the study of glass transition of biopolymers (Dogan & Kokini, 2006). The rheological properties of viscoelastic materials are measured by means of various tools, whose performance allows for carrying out complex rheological tests according to time, temperature, shear rate, or oscillation frequency (McClements, 1999). There are two types of rheometers: some measure the stress occurring in the material under a given strain, and others measure the strain and rate of strain of material under a given stress. In the small amplitude oscillatory measurements, the magnitude of strain/stress used in the dynamic test is very small (0.1%
2%), where the material is in the linear viscoelastic range (Dogan & Kokini, 2006). A rheometer assesses the relation between shear stress (τ) and strain ðγ Þ or shear stress (τ) and shear rate ðγ_ Þ. Sometimes the variation of these rheological parameters is assessed according to time, frequency, and temperature. The most commonly used rheometers in small amplitude oscillatory measurements are rotational rheometers, in which, the material is sheared by rotating bodies with different geometries compared to other fixed surfaces, such as concentric cylinder, cone and plate, and parallel plates (Fig. 15.16B
D). For example, Pang, Deeth, Sopade, Sharma, and Bansal (2014) used a rotational rheometer with a cone (4 cm diameter; 2-degrees angle) and plate geometry to study the physical and microstructural properties of B-type gelatin for the variation of concentration, pH, and added milk protein. Dynamic oscillatory tests were performed in the linear viscoelastic region (0.5% strain at 1 Hz frequency). The authors studied the structural changes of gelatin in three processes: cooling from 40 C to 10 C at a cooling rate of 1 C/min; annealing by maturation of the gelling samples 2.5 h at 10 C; and heating from 10 C to 40 C at a heating rate of 1 C/min. The results showed that during the processes of cooling and annealing, two mechanical moduli (Gʹ and Gʺ) increased, with a faster increase of storage modulus (Gʹ) owing to gelatin jellification and gel maturation. During the heating process, a fast drop in the value of Gʹ was observed, which becomes lower than Gʺ due to gel melting.

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Figure 15.16 Small deformations measurements by oscillatory tests: (A) strain signal and the shifted stress response in oscillatory test; (B) concentric cylinders’ system; (C) cone and plate system; (D) parallel plates system.

15.6.2.2 Colloidal probe atomic force microscopy The AFM technique described before as a method of investigating nanomaterial morphology is also used to measure the small deformations of nanoparticles. In order to do so, the tool used is a cantilever having in its tip a colloidal particle (spherical microparticle) pressing on the surface of nanoparticle placed on a glass support, producing a nanodeformation (Fig. 15.17A). The AFM technique may measure forces between 10212 and 1026 N and detects deformations of membrane or nanoparticle shell that are under 1 nm (Fery & Weinkamer, 2007). The result of AFM manipulation is expressed by force
displacement curves analyzed according to various mathematical models (Neubauer, Poehlmann, & Fery, 2014). By AFM technique, one may study the mechanical characteristics of nano- and microparticles obtained by the LbL method (Neubauer et al., 2014), liposomes made from egg yolk
phosphatidylcholine with radius between 30 and 40 nm (Liang, Mao, & Simon Ng, 2004), and biological cells, like virus (Kuznetsov & McPherson, 2011). Dubreuil, Elsner, and Fery (2003) studied the mechanical properties by means of polyelectrolyte multilayer capsules using a method based on combining AFM and reflection interference contrast microscopy. In this technique, the nanoparticle pressed by a cantilever is fixed on a transparent solid mounted on the stage of an inverted optical microscope. The modification of contact area between compressed nanoparticle and the surface of transparent solid support is analyzed in images obtained by reflection interference contrast microscopy. Using the AFM technique, Lulevich, Radtchenko, Sukhorukov, and Vinogradova (2003) studied the deformation of nanoparticles loaded with water and polyanions. The

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Figure 15.17 Techniques for measuring of mechanical deformations of nanoparticles: (A) colloidal probe AFM; (B) micropipette technique; (C) osmotic pressure method; (D) counterrotating shear cell.

results showed that nanoparticles filled with polyanions are stiffer than the empty ones. After loading, polyanion nanoparticles were irreversibly deformed, while the empty nanoparticles were reversibly deformed. The authors explained the mechanical properties of nanoparticles studied based on both the excess osmotic pressure and the polymeric network formed.

15.6.2.3 Micropipette technique Micropipette technique is a simple and accessible method to evaluate the mechanical properties of nanoparticles, cells, and other biological materials. This technique has been successfully used in the study of mechanical deformation of liposomes and simple cells such as red blood cells. A micropipette has an inside diameter of about 1
10 μm (Fig. 15.17B). The nanoparticles are aspirated under controlled hydrostatic pressure and the deformation is monitored with the optical microscope (Hochmuth, 2000; Lee & Liu, 2014).

15.6.2.4 Osmotic pressure method The use of osmotic pressure as a method of studying the deformation of nanoparticles is due to the phenomenon of the passage of solvent inside the nanoparticle into the external environment or vice versa, depending on the chemical potential. For example, when the nanoparticles loaded with hydrophilic substances are suspended

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in an aqueous solution of biopolymers, there is a difference in the chemical potential of water from the internal and external phases (Fig. 15.17C). Because the chemical potential of water inside the nanocapsule is greater than that of continuous phase, the water inside passes into the continuous phase producing deformation of nanoparticle wall until it crumbles. The nanoparticle deformation study is performed by monitoring the osmotic pressure and microscopic visualization of the nanoparticle wall. The advantage of this method is that at the same time and under the same conditions, several nanoparticles are deformed. This technique was used in the study of double emulsions and polyelectrolytes nanoparticles prepared by the LbL method (Dima & Dima, 2018; Gao, Donath, Moya, Dudnik, & Mo¨hwald, 2001; Sagis, 2015). When the nanoparticles are subjected to large mechanical forces, then a large deformation of the nanoparticle wall occurs, until it breaks.

15.6.2.5 Large deformation measurements These deformations are studied with different devices, depending on the physical state of food nanomaterial or the food matrix type. For example, to mimic food chewing, the liquid or semisolid food systems are sheared or broken by means of rheometers or viscometers. These instruments measure the large deformations of nanomaterials. For evaluating the “thickness” of a fluid, apparent viscosity is determined as the ratio between shear stress and rate strain (Chung & McClements, 2014). The mechanical properties of nanoparticles, such as hardness, interfacial adhesion, friction, and lubrication, were determined using counterrotating shear cells or microfluidics-based contraction flow devices (Guo et al., 2014). A contraction flow device consists of transparent concentric cylinders or two parallel glass plates which can move vertically or rotate in opposite directions (Fig. 15.17D). Nanoparticles inserted between cylinders or between parallel glass plates are subjected to steady shear field and the nanoparticles deformation are expressed as a function of applied shear. Physical changes of the nanoparticle wall are captured with high-speed cameras.

15.7

Future trends

The development of nanotechnology has crucially influenced the food and agricultural sectors. Thus novel nanomaterials have been studied that have contributed to the development of smart packaging, the manufacture of pesticides and fertilizers that do not affect food safety and environmental conditions, and the creation of nanosensors for detecting contaminants in food. Also, nanotechnology has allowed the development of functional foods, with high nutritional qualities and with very different health benefits for consumers. In this context, in recent decades, the interest of scientists in the research of nanomaterial properties in food and the interaction mechanisms of nanomaterials with the human body has increased. Food nanoparticles are systems with special physicochemical and biological characteristics. Their size on a nanometric scale provides them with a high contact surface,

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facilitates absorption through biological membranes, influences the appearance of foods and contributes to the increased resistance to the action of bacteria. Knowing the characteristics of nanomaterials in foods is an important requirement for food producers because they influence the food quality and safety. That is why, lately, more and more research has been focusing on the development of new techniques for analyzing and controlling nanomaterials. Most analysis techniques apply to isolated nanoparticles or samples whose processing may alter the characteristics of nanoparticles. Due to the complexity of food matrices, it is necessary to improve the techniques of sampling and sample preparation, extraction, and separation of nanoparticles for their analysis. Therefore an important objective of today’s researchers is the invention of high-performance techniques that ensure a minimal processing of samples or analysis of nanomaterials under the real conditions of food matrix, organs, and tissues of the human body in which they accumulate or of the surrounding environment.

Acknowledgment This work was financial supported by an internal research grant of “Dunarea de Jos” University of Galati, contract number GI-02/01.03.2018.

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O¨zgu¨r Tarhan Department of Food Engineering, Engineering Faculty, U¸sak University, U¸sak, Turkey

16.1

Introduction

Nanotechnology has the great potential to be used for food applications in order to enhance textural and sensorial properties, improve consistency and shelf life, enrich the nutritional content of foods, increase bioavailability of nutraceuticals, and provide safety at contact surface through novel packaging materials (Jafari & McClements, 2017). The unique designable physicochemical characteristics of nanomaterials, due to their relatively large surface area to mass ratio, provide various functionalities in these applications. Food-based organic nanostructures derived from carbohydrates, lipids, and proteins such as nanoparticles, nanotubules, nanoemulsions, nanocapsules, and inorganic nanoparticles such as titanium oxide, zinc oxide, silicon dioxide, silver, clay, and carbon nanotubes are the various nanoscale components produced through different paths and used for different purposes in the food industry. The most widespread applications of nanotechnology in foods are the development of nanovehicles for food fortification and functional packaging purposes, and healthpromoting products for the controlled delivery of nutraceuticals (Acosta et al., 2009). An increasing number of food products containing nanoscale ingredients and additives have already been placed in the market (Bouwmeester, Brandhoff, Marvin, Weigel, & Peters, 2014; Chaudhry et al., 2008). Many foods, food supplements, packaging materials, contact devices, and baby and infant foods containing engineered nanoparticles have been recorded in databases (Sohal, O’Fallon, Gaines, Demokritou, & Bello, 2018). European inventories claiming nanoparticlecontaining foods have been declared as well. The continuously increasing market size of nanotechnology products of the food industry is estimated to reach approximately US$15 billion by 2020 (Naseer et al., 2018). Innovative food products manufactured using nanotechnology tools promise many benefits for consumers and industry. However, diverse nanomaterials ranging from organic to inorganic components might introduce some uncertainties and unforeseen impacts when used inadequately in agri-food materials. The potential risks to human health and environment through high exposure levels and widespread usage lead to serious public and environmental doubts (Amenta et al., 2015). Those issues should be taken into consideration to establish rules and policies for Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00016-9 © 2020 Elsevier Inc. All rights reserved.

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safe handling and consumption of nanotechnology-based agriculture and food products. The wide use of nanotechnology-based products leads to a high potential of exposure to nanoparticles via different routes. There are three main pathways for human exposure to nanomaterials (Jafari, Esfanjani, Katouzian, & Assadpour, 2017a). Those are dermal exposure occurring through skin in the case of direct contact with the cosmetics and drugs containing nanoparticles; inhalation occurring through volatile materials harboring nanoparticles; and ingestion occurring through uptake of food materials supplemented with nanoparticles. In all three cases, these ultrafine particles can enter into body, pass the cell barriers, and penetrate through tissues and organs, and thus could be deposited in various parts of the body. The reaction of the body and possible consequences arising from exposure might be highly dependent on the type and physicochemical characteristics of the nanoparticles (Wani, Masoodi, Jafari, & McClements, 2018). Organic nanoparticles based on carbohydrates, proteins, lipids, and vitamins are considered to be digestible, however, inorganic ones based on metallic chemicals such as silver, titanium, and silica are considered as indigestible. Current literature contains many in vitro and in vivo research studies tracking possible health consequences due to the exposure of nanoingredients in agri-food related products. Around the world, countries pay great attention to regulating the safe production and handling of nanomaterials to be used in the food industry (Jafari, Katouzian, & Akhavan, 2017b). Legislations, recommendations, and guidance introduced by legal authorities are significant tools to be considered in the assessment of potential risks and safety rules of nanotechnology used in foods (Amenta et al., 2015). The European Commission (EC), European Food Safety Agency (EFSA), Environmental Protection Agency (EPA), Organisation for Economic Cooperation and Development (OECD), International Standard Organization (ISO), Food and Drug Administration (FDA), World Health Organization (WHO), and Scientific Committees and Agencies are the major authorization bodies in Europe and the United States, and direct regulatory issues and guidelines related to nanomaterials in foods. Common regulatory procedures indicate the identification of nanomaterials through their size, surface characteristics, chemical composition, and stability, which are very crucial in order to determine their possible interactions and persistence in the body, thus providing data for risk assessment. Various analytical methods accompanied with imaginary techniques are widely used to detect and identify nanoparticles in foods in order to assess their potential risks or hazards. Additionally, in vitro and in vivo studies provide quite significant data to determine possible responses in the body against nanoparticles. Uncertainties and limited knowledge about the effects of nanoparticles incorporated into foods leading to health and safety concerns might be eliminated by welldefined regulations and legislations globally. That will provide transparency in the manufacture and supply of nanofood products, and thus public acceptance will be supported. In this chapter risk and hazard assessment, possible exposure routes, toxicological outcomes, and regulations and guidelines for risk evaluation and safety assessment will be discussed.

Safety and regulatory issues of nanomaterials in foods

16.2

657

Nanofood market

Nanofood can be defined as food that is cultivated, manufactured, processed, or packaged using nanotechnology, or harboring nanomaterials to improve its properties (Joseph & Morrison, 2006). Nanotechnology facilitates the desirable manipulation of food materials to improve technological properties, prolong shelf life, assess the sustainable quality and safety, and promote health. Consumer demands and preferences have directed manufacturers to produce novel foods with attractive features. Due to these promising impacts, many food companies have great interest in producing foods using this emerging technology. Globally, many big companies, including Heinz, Nestle, Unilever, and Kraft, have been investigating nanotechnology applications for food processing and packaging (Nano, 2030, 2014). A number of food products containing organic and inorganic nanoparticles have also been found in the market currently. Some European inventories have declared lists of products with the claim of containing nanoparticles that are already present in market (ANEC/BEUC, 2010; BUND database; Nanoproducts, 2013; Nanotech-data, 2013; Consumer Products Inventory, 2019; Nanodatabase, 2019). These databases reveal commercial food products containing nanoparticles are available in food itself and incorporated into packaging material. Bouwmeester et al. (2014) reported that 140 foodrelated products had been identified with the claim of harboring diverse nanoparticles based on the inventory of internet databases. Product category (agriculture, food additives, supplement, packaging nanomaterials), type, and producers are also mentioned in the list of products separately. Currently, over 500 foodrelated products have been claimed to be placed in the market (Nanodatabase, 2019; Nanotechnology Project, 2019). Nanofoods consist of organic nanoparticles like nanoliposomes, micelles, and nanocapsules for the targeted delivery of nutraceuticals and also inorganics, such as silica, silver, zinc, titanium, and clay (Bazana, Codevilla, & de Menezes, 2019; Park, Li, & Kricka, 2006). Those nanoparticles are used for different purposes due to their physicochemical properties. For example, clay nanoparticles are one of the most commercially used nanostructures in packaging materials with their excellent barrier properties (de Paiva, Morales, & Valenzuela Dıaz, 2008). Silver and titanium dioxide nanparticles added to packaging material provide preservation of food due to their antimicrobial activity (Bouwmeester et al., 2014). According to Bumbudsanpharoke and Ko (2015), the food and beverage industry show a continuously increasing trend in the use of nanomaterials for processing and packaging purposes. In particular, packaging materials functionalized with nanoparticles have been preferred by the food and beverage industry. According to market research reports, the global market size of nanomaterials in the food industry was about $6.5 billion in 2013, has been increasing by 12.7% annually, and is estimated to reach about $20.00 billion in 2020 (Naseer et al., 2018; Persistence Market Research, 2014). The European Institute for Health and Consumer Protection also declared the expected size of the food packaging market using nanomaterial will be about $20 billion in 2020 (Bumbudsanpharoke & Ko, 2015). Several representatives

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of commercial nanofood products currently containing nanoparticles have been given in Table 16.1. Manufacturers, suppliers, and consumers are all involved beneficiaries in the agri-food nanomarket. Besides their advantageous service in food processing, packaging, and nutrient delivery, those new products or additives may also lead to considerable risks for human health and the environment. Characteristic physicochemical properties, high surface area relative to small size, and widespread use make them available for overdose exposures with unpredictable hazardous consequences. All those issues can cause public concerns related to the safety of nanofoods and affect public preferences. In addition, limited regulatory procedures for the assessment of safety might discourage potential investors from dealing with the nanotechnology industry. The safety assurance of nanoenabled foods to be conducted via global legislations by considering well-defined nanomaterials, exposure dose limits, potential hazards, and thus informing the public would be helpful in reducing public doubts and promoting the market. Evaluation of risks and hazards by considering various critical aspects will be discussed in the following sections.

16.3

Risk assessment of nanostructures used in foods

Nanotechnological applications are developing enormously in the agri-food industry. A great interest in the facilities provided by this technology in pesticide detection, pathogen screening, maintenance and monitoring of food quality, improvement of shelf life, and enhancement of nutritive value has led to many nanofood products being introduced into the market (Dasgupta et al., 2015). Both food-based organic particles or other inorganic chemical particles can be used for the desired features. This may result in uncontrolled exposure of humans, animals, and the environment to those nanoparticles. Some of them can cross biological barriers in the human body and may enter vessels, organs, and cells (Bajpai et al., 2018; Su & Li, 2004). Inorganic nanoparticles such as carbon nanotubes, silver, silica, titanium, and zinc nanoparticles may exhibit unpredictable and hazardous safety problems for health and the environment with excess exposure or release. Some evidence indicating nanoparticles are taken up into organs such as liver, lungs, spleen, heart, and brain have been reported (Kreyling et al., 2002; Oberdo¨rster et al., 2002; Oberdorster et al., 2005). Exposure to titanium oxide nanoparticles increased pulmonary inflammation via inhalation and intracellular damage via penetration through skin (Oberdo¨rster, Ferin, & Lehnert, 1994; Oberdoo¨rster, 2001). Carbon nanoparticles also caused pulmonary inflammation and vascular disease (Brown, Stone, Findlay, MacNee, & Donaldson, 2000; Nemmar et al., 2002). Exposure to high doses of metallic nanoparticles may result in toxicity (HSE, 2006; Nel, Xia, Madler, & Li, 2006; Chau et al., 2017). The application of nanotechnology in the food industry may lead to potential risks due to the specific features of individual nanomaterials used. They are quite small in size and can be designed at the molecular level, thus potentially exhibiting

Table 16.1 Nanofood products present in the market currently. Product (commercial name)

Producer/country

Nanoparticle

Purpose/function

References

Nanoceuticals Slim Shake Chocolate

RBC Life Sciences/United States

Nanosized cacao (cacao nanoclusters)

Enhanced flavor

Nanotea

Shenzhen Become Industry & Trace Co., Ltd./ China Shemen Industries/Israel

Selenium

Increased bioavailability

Nanomicelles

Transport of nanoingredients

,http://www. nanotechproject.org/cpi/ products/nanoceuticalstmslim-shake-chocolate/. Accessed 05.09.19 ,http://www. nanotechproject.org/cpi/ products/nanotea/. Accessed 05.09.19 ,http://www. nanotechproject.org/cpi/ products/canola-active-oil/ . Accessed 05.09.19 ,http://nanodb.dk/en/ product/?pid 5 4171. Accessed 05.09.19 ,http://nanodb.dk/en/ product/?pid 5 4175. Accessed 05.09.19 ,http://nanodb.dk/en/ product/?pid 5 4172. Accessed 05.09.19 ,http://nanodb.dk/en/ product/?pid 5 3408. Accessed 05.09.19

Food processing/additives

Canola Active Oil

Eclipse Spearmint Chewy Mints

Mars Wrigley/ United States

TiO2

Coloring E171

Old el Paso Taco Seasoning Mix

Old el Paso, General Milles/ United States Mars Incorporated/ United States Alta Care Laboratories/ France

SiO2

Anticaking agent E551

TiO2

Coloring

Nanosized calcium

Remineralization, development and strengthening of the bones

m&m’s

Silvia Osteo Plus Tablets

(Continued)

Table 16.1 (Continued) Product (commercial name)

Producer/country

Nanoparticle

Purpose/function

References

,www.nanotechproject.org/ cpi/products/aquanova-rnovasol-r/. Accessed 29.08.19 ,http://nanodb.dk/en/ product/?pid 5 5079. Accessed 05.09.19 ,http://nanodb.dk/en/ product/?pid 5 5075. Accessed 05.09.19 ,http://nanodb.dk/en/ product/?pid 5 4405. Accessed 05.09.19 ,http://nanodb.dk/en/ product/?pid 5 4166. Accessed 5.09.19

Nurtaceutical supplements Aquanova Novasol

AQUANOVA AG/Germany

Nanomicelles

Delivery of nutrients/ bioavailability

Liposomal vitamin C

NanoNutra/ Denmark

Nanoliposomes

Dietary supplement to enhance bioavailability

Liquid ionic magnesium

Nanoscale ionic magnesium

Dietary supplement to enhance bioavailability

Nanosized minerals

24Hr Microactive CoQ10

Innotech Nutrition/ Canada Good State Health Solution/United States Genceutic Naturals

High levels of natural minerals for better daily absorption Increased stability against heat and light, sustained release and bioavailability

Nanoceuticals spirulina nanoclusters

RBC Life Sciences/United States

Natural ionic trace minerals

Nanosized coenzyme Q10 and ßcyclodextrin matrix Nanoscale ingredients

Increased absorption of nutrients

,http://www. nanotechproject.org/cpi/ products/nanoceuticalstmspirulina-nanoclusters/ . Accessed 5.09.19

NanoResveratrol

Life enhancement/ United States

Nanocellulose

Increased absorption of resveratrol

,http://www. nanotechproject.org/cpi/ products/nanoresveratroltm/ . Accessed 5.09.19

,www.nanotechproject.org/ cpi/products/ fresherlongertm-plasticstorage-bags/. Accessed 29.08.19 ,www.nanotechproject.org/ cpi/products/nurser/. Accessed 29.08.19 ,www.nanotechproject.org/ cpi/products/quan-zhou-huzheng-nanotechnology-coltd-r-nanosilver-storagebox-baoxianhe/. Accessed 29.08.19 ,www.nanotechproject.org/ cpi/products/ bluemoongoodstm-freshbox-silver-nanoparticlefood-storage-containers/. Accessed 29.08.19 Sekhon (2010), Cushen, Kerry, Morris, CruzRomero, and Cummins (2012), Duran and Marcato (2013)

Food packaging and containers FreshLonger plastic storage bags

Sharper Image/ United States

Ag nanoparticles

Antimicrobial protection

Nanosilver baby mug cup

Baby Dream Co., Ltd./Korea

Ag nanoparticles

Antimicrobial protection

Nanosilver storage box

Quan Zhou Hu Zheng Nano Technology Co., Ltd./China

Ag nanoparticles

Antimicrobial protection

Fresh box food storage containers

BlueMoonGoods, LLC/United States

Ag nanoparticles

Antimicrobial protection

Durethan KU2_2601

Lanxess Deutschland GmbH/ Germany

Nylon-nanoclay composite

Provide excellent barrier properties and strength

(Continued)

Table 16.1 (Continued) Product (commercial name)

Producer/country

Nanoparticle

Purpose/function

References

AegisTM OXCE

Honeywell Polymer (Honeywell International Inc Plantic Technologies Ltd Mitsubishi Gas Chemical Company, Inc

Nylon-nanoclay composite

Provide high-oxygen barrier packaging for beer and flavored alcoholic beverage Provide barrier properties

Cooper (2013), Peters and others (2011), Pico and Blasco (2012)

Maintain barrier layer for thermoformed containers

Bumbudsanpharoke and Ko (2015)

Plantic R1 Tray

Imperm Nylon nanocomposite

Starch-based nanoclay composite Nanoclay

Khemani et al. (2008)

Safety and regulatory issues of nanomaterials in foods

663

various novel physicochemical and biological properties. As this issue is directly related to human nutrition, health concerns and discussions on how to assess the safety of nanoparticle-containing foods are currently highlighted. Legal authorities in Europe and the United States have introduced a route map for the assessment of risks and recommended guidelines for the evaluation of safety in the use of nanoparticles in foods (EFSA, 2011a, b, 2018; FDA, 2011, 2012). Potential risks and toxicity issues due to inhalation and ingestion of those fine nanoparticles may lead to concerns and these should be clarified and eliminated. These nanomaterials, especially inorganic chemicals, can be accumulated in tissues and organs due to unlimited exposure and this may be associated with different health issues. Therefore risk assessment analysis described by international agencies (FDA, ESFA) should be followed properly by the manufacturers and suppliers (Bajpai et al., 2018; Shi et al., 2013; Yu et al., 2012). Healthy and sustainable food production should be protected strictly while educating the public about nanotechnology and nanofoods, health issues, and environmental safety. There is some guidance for the risk assessment of nanomaterials (OECD, 2013; ESFA, 2011, 2018). Test methods to follow for hazard assessment exist, however, characterization, standardization, and validation of methods need further improvement to better analyze potential risks (SCENIHR, 2007; OECD, 2013; Amenta et al., 2015). According to EFSA’s report (2011a, b) presenting “guidances on the risk assessment of the application of nanoscience and nanotechnology in food and feed chain,” physicochemical characterization and identification of hazards of nanomaterials have been achieved and potential risks due to application of nanotechnology in foods have been determined. The lack of knowledge about the characteristics and toxic potential of nanoparticles reported up to date make it harder to evaluate the hazards of engineered nanostructures and eliminate all the concerns. Several criteria are suggested for nanotoxicity assessment as follows: exposure assessment, toxicity evaluation, determining transportation, persistence and transformation abilities, recyclability, and sustainability of nanomaterials (Dreher, 2004; Chau et al., 2017). Potential exposure pathways and corresponding testing approaches are emphasized to identify and characterize the risks of nanomaterials. As stated above, transformation of nanoparticles after ingestion or inhalation might alter their surface properties and stability (Amenta et al., 2015). Therefore nanoparticles transporting through gastrointestinal tract or circulatory system may elicit different properties. In vitro studies conducted by simulated body conditions need to be verified by in vivo studies to track the response of nanomaterials via changing conditions. The potential risk level of nanoparticles blended in foods may vary due to their organic and inorganic structure. Organic nanoparticles based on carbohydrates, proteins, and lipids are mostly associated with the increased uptake of those nanoparticles, possibly leading to allergenic reactions. However, inorganic nanoparticles can cause more serious consequences, such as deposition in the organs and chronic cardiovascular diseases. Some reported current research related to potential risks associated with nanoparticles are given in Table 16.2.

Table 16.2 Potential risks associated with organic and inorganic nanoparticles used in foods. Nanoparticles

Purpose

Exposure route

Potential risks

References

No published work revealing their potential toxicity, GIT fate depends on digestibility, possible alteration of gut microbiota, bioavailability and bioactivity of supplemented material GIT fate depends on environmental conditions (pH, ionic strength), determining aggregation state of NPs, possibly promoted allergenicity due to digestion products, unpredictable effects of overdose uptake via enhanced nutraceutical bioavailability No published work revealing their potential toxicity and GIT fate after absorption, however unpredictable undesirable effects due to increased bioavailability of hydrophobic supplements

Joye et al. (2014), Le Corre et al. (2010), McClements and Xiao (2017), Myrick, Vendra, and Krishnan (2014)

Organic nanoparticles Carbohydrate NPs

Carrier matrices for food nutraceuticals and active agents

Oral uptake via incorporation in foods

Protein NPs

Transport and delivery system for nutrients, colorants, preservatives, and enhances bioavailability and functionality of the encased bioactives

Oral uptake via incorporation in foods

Lipid NPs

Colloidal delivery system for nutrients, colorants, antimicrobials, antioxidants, and increases bioavailability and functionality of the encased bioactives

Oral uptake via incorporation in foods

Jones and McClements (2010), Livney (2015), McClements and Xiao (2017), Rajendran, Udenigwe, and Yada (2016)

McClements and Rao (2011), McClements and Xiao (2012, 2017), Shin, Kim, and Park (2015), Yao, McClements, and Xiao (2015)

Inorganic nanoparticles Titanium NPs (TiO2)

Lightening agents used in foods including candies, gums, desserts, milk powders

Silica NPs (SiO2)

Anticaking agents improving flow properties of powdered foods including salt, spices, dried milk, and icing sugar

Silver NPs (AgNPs)

Antimicrobial agents used in foods (meats) and packaging materials and coatings

Oral uptake via incorporated in foods Estimated human exposure: 1.1 mg/kg (United Kingdom) (bw/ day) 2.2 mg/kg (United States) Oral uptake via incorporated in foods Estimated human exposure: 20 50 mg/day

Varying GIT fate and toxicity depending on size, shape, crystal form and aggregation state, accumulation in liver, kidney, spleen, lungs and leading damages in immune response, cardiovascular and blood system

Duan et al. (2010), McClements and Xiao (2017), Wang et al. (2007), Weir, Westerhoff, Fabricius, Hristovski, and von Goetz (2012)

Cytotoxicity via generation of ROS, increased level of ALT and accumulation in the liver due to high level of exposures

Oral uptake due to direct inclusion in foods and/or migration from packaging materials Estimated human exposure: 20 80 µg/day

Cytotoxicity based on size exhibited generation of ROS damaging cell membranes, organelles and nucleus. Also, altered gut microbiota, abnormal mucus content in intestines, lymphocyte infiltration, penetration through membranes and accumulation in the organs including intestines, liver, kidney, spleen, stomach, and brain

Dekkers et al. (2011), Frohlich and Roblegg (2012), Fulgoni, Keast, Bailey, and Dwyer (2011), McClements and Xiao (2017), Peters et al. (2012), So et al. (2008), van Kesteren et al. (2015), Yang et al. (2016) Cha et al. (2008), Frohlich and Roblegg (2012), Gaillet and Rouanet (2015), Hendrickson et al. (2016), Jeong et al. (2010), Kim et al. (2008, 2010, and 2012), McClements and Xiao (2017), Sharma, Siskova, Zboril, and GardeaTorresdey (2014), Williams et al. (2015)

(Continued)

Table 16.2 (Continued) Nanoparticles

Purpose

Exposure route

Potential risks

References

Zinc NPs (ZnO)

Antimicrobial agents used in foods and packaging materials, UV absorbers to protect foods, nutritional supplement for health

Oral uptake directly or via incorporation in foods, migration from packaging materials

Size and environment based GIT fate and toxicity, liver, kidney and lung injuries, and cell damage via generation of ROS

Iron NPs (Fe2O3)

Colorant used in foods (sausage casing) and dietary supplement

Oral uptake directly or incorporation in foods Estimated human exposure: 10 23 mg/day (in foods) 10 32 mg/day (in supplements)

Potential toxicity based on size, shape and crystallinity by generating ROS, no accumulation in tissues

EFSA (2016), Esmaeillou, Moharamnejad, Hsankhani, Tehrani, and Maadi (2013), Kang et al. (2015), McClements and Xiao (2017), Sirelkhatim et al. (2015), Wang et al. (2013, 2014) Hilty et al. (2010), McClements and Xiao (2017), Patil et al. (2015), Wu, Yin, Wamer, Zeng, and Lo (2014), Zimmermann and Hilty (2011)

bw, Body weight; GI, gastrointestinal; GIT, gastrointestinal tract; NP, nanoparticle; ROS, reactive oxygen species.

Safety and regulatory issues of nanomaterials in foods

667

The characteristics of nanoparticles should be defined to assess the risk and toxicity of nanoparticles (Chau et al., 2017). Particle size and mass, chemical composition, and surface properties of nanoparticles are critical in evaluating their structural features related to nanotoxicity (Nel et al., 2006; Oberdorster et al., 2005). Exposure rates, penetration routes through the body, and bioaccumulation may also determine the potential risks of nanoparticles (Oberdorster et al., 2005). Nanoparticles to be used in foods need to follow testing procedures to create data for safety assessment. Recent developments in the analytical methodologies and devices enable detection and determination of exposure and toxicity of nanoparticles in foods and food-related products (Bouwmeester et al., 2014). The most important point in risk assessment is characterization of the nanomaterials to be used in food matrices. Determination of physicochemical and biological properties, exposure limits and routes, and toxicity of nanoingredients directly provide data for safe use of them. Insufficient and inadequate characterization of nanostructures result in missing data of nanoingredients in safety assessment and their applicability as well. There are various sets of experimental approaches available for the hazard assessment of nanomaterials fabricated through different paths including detection, spectroscopic and chromatography-based methods, and immunoassays. Those will be discussed in the following section.

16.3.1 Detection and characterization of nanoparticles in foods Physicochemical properties including particle size, shape, aggregation and agglomeration state, chemical composition, surface charge, stability, porosity, and structural features are considered as critical for evaluating the toxic potential and hazardous nature of nanomaterials (Oberdorster et al., 2005). The EU’s definition for nanoparticles and the requirements for the analysis of food nanomaterials are well emphasized. A range of methods is essential to carry out the regulatory requirements. Investigation of size and morphology, chemical composition, surface characteristics, structural features and availability provide information for the assessment of eligibility for the safe consumption of nanomaterial-containing foods. Regulatory definitions especially related to size enforce the use of a very low detection limit of nanoparticles. As the particle size gets smaller, the sensitivity also gets smaller (Bouwmeester et al., 2014). Requirements for safety assessment of nanoparticles have been introduced by international authorities including the EC, FDA, ESFA, EPA, and WHO. Validated analytical methods are referenced for the investigation of the compatibility of nanomaterials with the regulations. Robustness and repeatability of the analytical methods used is important for the adequate evaluation of nanoparticle safety. It is not so easy to identify nanostructures in foods as they are complex matrices and the interferences are very possible. Therefore prior to analysis, sample treatment is required. The sample should be separated first from the food matrix with the least treatment. Nanoscale structures are quite reactive, thus their composition, size, and surface properties can be changed due to environmental conditions (Szakal et al., 2014). Nanostructures become a part of the complex food matrix

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Figure 16.1 Exposure routes of nanoparticles.

when integrated. Prior to detection, the target nanostructure should be separated from other matrix components. Analytical methods, mainly chromatography and spectroscopy, are widely used for separation and detailed analysis purposes. High-resolution microscopy is also another powerful tool in the analysis of nanomaterials. Organic nanoparticles, including carbohydrates, proteins, and lipids, and inorganics, including metal complexes, used in foods can be identified both qualitatively and quantitatively through those methods (Jafari & Esfanjani, 2017). Nanoparticles are detected and characterized through microscopy, spectroscopy, and chromatography techniques. Imaging is widely achieved by electron microscopy (EM). Morphological features such as size, shape, appearance, and surface roughness of the nanostructures in foods are commonly analyzed by EM. Also, energy dispersive X-ray spectroscopy (EDX) coupled with EM facilitates determination of the elemental composition of nanoparticles (Peters et al., 2012). Dynamic light scattering (DLS) is the most used spectroscopic tool for determination of size and size distribution in terms of hydrodynamic diameter (Filipe et al., 2010; Graveland-Bikker, Ipsen, Otte, & de Kruif, 2004). Mass spectroscopy (MS) coupled with liquid chromatography (LC) or gas chromatography (GC) are other important instrumental methods for tracking of nanoparticles in foods. Hydrodynamic chromatography (HDC) and field flow fractionation (FFF) chromatography combined with spectroscopic detectors are effective in separating nanoparticles as they provide size-based screening analysis (von der Kammer, Legros, Larsen, Loeschner, & Hofmann, 2011; Peters et al., 2011). Those methods enable a considerably high sensitivity and reliability with low detection limits. Limited treatment of a sample prior to analysis results in highly trusted data. Induced coupled plasma (ICP)-MS is also suggested for use in nanoparticle identification with a ng/L range detection limit (EC, 2011).

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669

16.3.2 Exposure routes to food nanoingredients Due to their smaller size, food nanoingredients can enter through tissues and organs in the body. Three basic ways for exposure to these nanoparticles include dermal contact, inhalation, and ingestion. Naturally many food ingredients can exist in the nanoscale, but they are not particularly designed nanomaterials. Also, their intake amounts can be considered as reasonable when the related foods are consumed. However, the intake of a specific nanoingredient-enriched food material may lead to overexposure, allergy, and toxicity. As a limited knowledge of possible risks of exposure to nanomaterials is available, handling of those should be kept under control. Legal authorities such as the EC and FDA publish guidelines for safe handling and use of nanomaterials. The three main exposure pathways mentioned above will be discussed in the following sections. All three are shown in Fig. 16.1.

16.3.2.1 Dermal exposure In dermal exposure, nanomaterials have the ability to penetrate through skin. This route is not common for food-incorporated nanoparticles. Nanomaterials existing in medical and cosmetic products are more widespread through dermal exposure. In the case of healthy and intact skin, the epidermis could protect it against nanoparticles (Hoet, Bru¨ske-Hohlfeld, & Salata, 2004). However some evidence has indicated that the skin and epidermis do not prevent all fine nanoparticles from entering the body. They can penetrate and translocate into some parts of body (Oberdorster et al., 2005; Tinkle et al., 2003). The translocation and deposition of nanomaterials in some parts of body, e.g., lymph nodes have been reported (Oberdorster et al., 2005). Inorganic nanoparticles may penetrate the skin and interact with the immune system (Kreilgaard, 2002). Also oxidative damage in the skin can be formed due to free radicals formed by inorganic nanomaterials (Wakefield, Green, Lipscomb, & Flutter, 2004). Limited evidence exists to suggest significant considerations for dermal exposure of nanoparticles, because detailed interaction mechanisms and possible health consequences are underway (Maynard, 2006; Chau, Wu, & Yen, 2007).

16.3.2.2 Inhalation Inhalation is the other main exposure route of nanomaterials in agri-food products and nonfood products as well. Volatile nanoparticles like nanoencapsulated aroma compounds, and essential oils can enter the body via inhalation. As stated above, the characteristics of nanoparticles are significant in the assessment of potential hazards. The particle size/size distribution and morphology, mass, chemical composition, structural features, and rate of accumulation for nanomaterials designate their toxicity and other hazards in the body (Maynard, 2006; Chau et al., 2007). Nanoparticles with a smaller size can travel deeper through lungs (Hoet et al., 2004). The ones with diameter ,10 nm are able to pass through the nasal cavity into lungs and penetrate into the alveolar region (Chau et al., 2007). Therefore lower-mass nanoparticles are more toxic when compared to the larger ones. Inhalation of inorganic nanoparticles such as titanium dioxide used as an

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antimicrobial agent in food packaging materials can result in accumulation in the lung, thus triggering chronic illnesses including pneumonia and pulmonary infections (Kim et al., 2003; Nel et al., 2006; Chau, 2007). Those ultrafine particles may also be able to pass the barrier of blood vessels, escape the defense system, and translocate out of the respiratory system through different mechanisms (Oberdorster et al., 2005). The reported evidence still lacks conclusive information about the consequences of the inhalation of nanoparticles in food-related environments. The potential hazards and toxicity based on inhalation of ultrafine particles needs to be evaluated by considering different cases individually (HSE, 2006; Chau et al., 2007).

16.3.2.3 Ingestion Exposure to nanoparticles in foods mostly occur by the direct ingestion of food products. Risk assessment of nanoparticles entering the body via ingestion of foods has special importance for the processed foods incorporated with nanomaterials. A large intestinal surface covered with microvilli is available for the nutrients and nanomaterials with proper size and surface characteristics. Due to interaction between nanoparticles and microvilli, the nanoparticles can penetrate into tissues and be absorbed at the target sites in the body (Chau et al., 2007; Chen, Remondetto, & Subirade, 2006). In vivo studies reported in the literature showed that nanoscale particles blended in foods are able to penetrate across the mucus barrier (Chau et al., 2007; Yang et al., 2016). Nanomaterials with a smaller particle size could penetrate faster through the mucus barrier and then could be distributed through tissues and organs via the bloodstream. Intestinal uptake occurs via absorption of nanomaterials through microvilli in the intestinal walls. In order to evaluate the bioavailability of nutraceutical nanomaterials, it is necessary to understand the biological mechanisms regulating uptake. The food partially digested in the oral cavity by mastication goes into the stomach to be dissolved in an acidic medium. The food macromolecules are broken down into fractions by the enzymes released by the stomach. If the dissolution of nanoparticle is undesirable, it needs to be encapsulated with enderic coatings and protected from the acidic environment and enzymes of the stomach (Acosta, 2009; Lee, Cho, Lee, Jeong, & Yuk, 2003). It depends on the stability of nanomaterials in acidic conditions. Then the ingested food enters the duodenum and mixes with bile salts released by the gall bladder for further breakdown. Two main mechanisms are considered for the absorption of nutrients through the small intestine, active and passive transport. In the case of active transport, bioactive ingredients pass through microchannels on the surface of epithelial cells under the control of related hormones. In the case of passive transport, a simple diffusion occurs across the epithelial tissue. Hydrophobic particles are highly permeable through intestines and absorbed via both active and passive transport, however hydrophilic ones have a low permeability and are absorbed via active transport only (Acosta, 2009; Ball, 2006; van de Waterbeemd, Lennern¨as, & Artursson, 2003).

Table 16.3 Current in vitro and in vivo studies presenting toxicity of nanoparticles used in foods. Nanoparticle

Bioactivity tests

Particle size and dose

Results

References

TiO2

The human colorectal adenocarcinoma cell line, HT-29

Penetration through intestinal cells and increased cell proliferation

Ammendolia et al. (2017)

TiO2

Human GI digestion model

,25 nm and 1, 2.5, 5, and 20 mg/cm2 (NP/cell culture media) 5 15 nm and R 5 0.12 (NP/ protein)

Cao et al. (2019)

TiO2

Model intestinal bacterial community

Simple protein coronas formed around nanoparticles, thus affect interactions among ingested NPs, food matrix and GI components Besides minor shifts, no major effect on human gut microbiota

TiO2

Human colon carcinoma Caco 2 cell line

SiO2

Human GI digestion model

SiO2

Human cell line, Caco-2 BBe1

SiO2

Human lung epithelial cells (A549)

In vitro studies

25 nm and 100 250 ppm NP in digestion media 30 nm and 106 1010 NP/cm2 (intestinal surface area)

7, 10 25 nm and 10, 50, 75 mg/ml (NP/ digestive juice) 9 26 nm and 1 mg/L (NP/cell culture media) 30 nm and 30 ppm (NP in cell culture media)

Dudefoi et al. (2017)

Adverse effects on the functions of intestinal epithelial cells such as disrupted membrane transport, increased generation of ROS and proinflammatory signaling High bioaccessibility achieved in the intestines due to low gelation with the low-dose silica Damaged cell membranes (disrupted brush borders of microvilli)

Guo, Martucci, MorenoOlivas, Tako, and Mahler (2017) Van Kesteren et al. (2015)

Efficient entrance of NPs through cell membrane, higher oxidative stress in the presence of some cations including cobalt and manganese

Limnach et al. (2007)

Yang et al. (2016)

(Continued)

Table 16.3 (Continued) Nanoparticle

Bioactivity tests

Particle size and dose

Results

References

ZnO

Human liver HepG2 cells

Simulated gastrointestinal digestion, cell culture with intestinal epithelial cell line (C2BBe1) and Caco2 cells

Increased cytotoxicity, lysosomal damage, intracellular accumulation, and release of inflammatory cytokines Cell membrane damage and mild toxicity

Zhou et al. (2017)

TiO2, SiO2, ZnO

AgNPs

Human GI digestion model

Adenocarcinoma human alveolar basal epithelial cells (A549)

Agglomeration of nanoparticles during gastric passage and breakdown into original size at reaching intestines Deposition of nanoparticles on the cellular layer dependent on NP size and density

Walczak et al. (2013)

Au NPs

20 nm and 0 32 µg/ ml (NP/cell culture media) TiO2 with 21 nm SiO2 with 12 nm ZnO with # 100 nm and 10 µg/cm2 (NP/cell culture surface) 60 nm and 10 µg/ml (NP/digestive juice) 20, 40, 80 nm and 40 and 60 mM final concentration of cell culture media

Gender-specific interaction, deposition through intestinal tissue, increased serum testosterone level Deposition in spleen and ovaries

Ammendolia et al. (2017)

McCracken, Zane, Knight, Dutta, and Waldman (2013)

Rischitor et al. (2016)

In vivo studies TiO2

Adult male and female rats

,25 nm and 1 2 mg/ kg (bw/kg)

TiO2

Oral exposure of rats

TiO2

Oral exposure of rats

,25 nm and 1 mg/kg (bw/kg) ,100 nm and 10 mg/ kg (bw/kg)

Promoted colon microinflammation and initiated preneoplastic lesions Potential contribution to autoimmune complications and cancer development

Tassinari et al. (2014) Bettini et al. (2017)

SiO2

Oral exposure of rats

7, 10 25 nm and 100, 500, 1000, 2500 mg/kg (bw/ day) 20 100 nm and 500 100 mg/kg (bw/day) 20 100 nm and 750 mg/kg (bw/ day) 22, 42, 71, 323 nm and 1 mg/kg (bw/ day)

SiO2

Oral exposure of rats

SiO2

Oral exposure of mice

AgNPs

Oral exposure of mice

AgNPs

Oral exposure of rats

14 6 4 nm and 9 mg/ kg (bw/day)

TiO2, SiO2, AgNP

Oral exposure of mice

12 16 nm and 2.5 mg/kg (bw/day)

Accumulation in spleen, increased fibrosis in liver

Van Kesteren et al. (2015)

Significantly elevated level of NP sın liver, kidney, lung and spleen. Also lower-sized NP excreted faster Reduced proliferation of B cells and T cells from spleen

Lee et al. (2014)

Distribution of small-sized (22, 42, 71 nm) particles to the organs (brain, lung, liver, kidney, testis), liver and kidney toxicity, inflammatory responses Distribution to the organs with the largest concentrations in liver, kidney, and intestines, and also found in brain and lungs Less toxicity with TiO2 and SiO2, whereas colitis-like symptoms and histological alterations in case of acute oral application of AgNPs

Kim, Lee, and Lee (2014) Park et al. (2010)

Loeschner et al. (2011)

Chen et al. (2017)

AgNPs, Silver nanoparticles; bw, body weight; GI, gastrointestinal; NP, nanoparticle; SAS, synthetic amorphous silica; SiO2, silica dioxide; ROS, reactive oxygen species; TiO2, titanium dioxide; ZnO, zinc oxide.

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Particle size, solubility, and chemical composition determine the residence time in the intestines. A longer residence time in the intestine indicates a higher dose of exposure. Use of bioadhesives (e.g., chitosan) or reducing the particle size of nanomaterials may increase persistence in the intestinal mucosa (Lai et al., 2007). Increased retention time may affect the bioavailability of nanoparticles harbored in foods. Additionally, the direct uptake of water-soluble nanoparticles can also be considerable for enhancement of the bioavailability of food ingredients (Acosta, 2009). Nanoparticle uptake determining the bioavailability of nanoingredients has been under investigation in the last two decades. Many research studies have been conducted and reported in the literature. However, comprehensive and conclusive data have not been published on this topic, yet.

16.3.3 Toxicological end points and outcomes Organic and inorganic nanomaterials are extensively used in food processing, mainly for nutritional fortification, enhanced bioavailability, and preservation purposes. Assessment of toxicity of these mostly relies on in vitro and in vivo studies reported in the literature. Based on characterization, especially with immunological assays, the identification of uptake dose and toxic potential of naoparticles is enabled. Table 16.3 represents a summary of some current research studies indicating the toxicological outcomes of nanoparticle exposure. Besides the benefits of nanotechnology, the potential toxicity and ecotoxicity due to nanoparticles have been under investigation. Due to their smaller size, nanoparticles can penetrate and translocate in circulatory and lymphatic systems, pass the biological barriers, and reach the tissues and organs (Bazana et al., 2019; Buzea, Blandino, & Robbie, 2007). Exposure of body tissues to the nanoparticles may elicit serious outcomes for human health. Based on their size, relatively large surface area, and chemical composition providing increased reactivity, nanomaterials entering the body can cause irreversible cell and tissue damage by oxidative stresses (Buzea et al., 2007; Walters, Pool, & Somerset, 2016). It is suggested that nanoparticles released in air, soil, and water cause long-term persistency in the environment and can be absorbed by organisms, leading to toxicological risks for ecology and also being deposited in agricultural and food products (Sia, 2017). Partial digestion of food nanoingredients after consumption or incomplete release of encapsulated nanoparticle may result in them passing through intestinal epithelials and entering the blood system, possibly to cause immunological reactions (Rezaei, Fathi, & Jafari, 2019). Nanoparticles absorbed through inhalation or skin may also cause oxidative stress, inflammation in organs, immunological, cardiovascular and pulmonary complications, deposition in body tissues, and toxicity (Buzea et al., 2007; Sia, 2017). There are ongoing in vitro research studies to clarify nanoparticle biological system interactions and process mechanisms. The exact quantification of nanoparticle exposure and the mechanism of action in terms of toxicity need to be described. Recently published in vivo studies on the investigation of the toxic potential of nanoparticles in agri-food products are promising. Introducing various novel and

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advanced techniques such as proteomics, genomics, and metabolomics will support the current tests for toxicological evaluation (Naseer et al., 2018). Acceleration and validation of the risk assessment can be better achieved in this manner. OECD guidelines define the list of parameters to characterize nanomaterials and requirements for nanospecific biological outcomes. Also those guidelines indicate the requirements for in vivo studies for the assessment of nanoparticle safety. In vivo studies might be conducted by human oral exposure of nanoparticle-containing diets. Animal studies might also include mixing the nanoparticles with feed or gavage preparations. Silver and silica nanoparticles used in vitro studies have shown that the physicochemical properties of nanoparticles are changing during passage through the digestive tract (Peters et al., 2012; Mwilu et al., 2013; Bouwmeester et al., 2014; Walczak et al., 2013).

16.3.3.1 Toxicity of organic nanoparticles Organic food nanoparticles are basically derived from carbohydrates, proteins, and lipids. Due to their chemical composition and structure, these nanoparticles exhibit different behaviors at various sites of gastrointestinal system, such as dissolvation and aggregation. McClements and Xiao (2017) have reported a detailed review about toxicity of organic and inorganic nanoparticles used in foods. In comparison to inorganic ones, organic nanoparticles have a lower toxicity. Lipid nanoparticles such as miscelles, vesicles, and liposomes are mostly used for encapsulation purposes (Katouzian & Jafari, 2016; Akhavan, Assadpour, Katouzian, & Jafari, 2018; Faridi Esfanjani, Assadpour, & Jafari, 2018). They increase stability, bioavailability, and functionality of encased active agents. Thus they may cause overdose exposure of the body against delivered bioactive agents due to enhanced bioavailability. Overdose exposure may promote allergenin response, toxicity, and unforseen health effects (McClements & Xiao, 2017). Casein miscelles present in milk are naturally occurring protein nanoparticles. This protein is highly affected by environmental conditions. Thus nanostructures are developed due to aggregation of protein units. In particular, protein nanoparticles such as spheres, fibers, and tubules are designed and fabricated for transport and delivery purposes (Katouzian & Jafari, 2019). The most common toxicological outcome associated with protein nanoparticles is enhanced allergenicity due to allergenic peptide units of protein nanomaterials. Altered bioavailability of encapsulated active agents may also promote overdose exposure and possible toxicity. Carbohydrate nanoparticles are derived from digestible (e.g., starch) and indigestible (e.g., cellulose) polysaccharides (Joye, Davidov-Pardo, & McClements, 2014; Le Corre, Bras, & Dufresne, 2010). As digestible carbohydrate nanoparticles are digested through the gastrointestinal system, their toxicity potential is relatively low (Rostamabadi, Falsafi, & Jafari, 2019), however indigestible ones absorbed by the body may lead to adverse effects due to the modified bioavailability of encapsulated materials (McClements & Xiao, 2017). Organic materials can also be used in combination to fabricate nanoparticles (Jones & McClements, 2010). There are a limited number of studies related to the nanotoxicity of organic structures. The

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most common outcomes as stated above are overdose exposure due to improved bioavailability and allergy problems. Further research is expected to provide more comprehensive data clarifying the potential toxicity of the organic nanoparticles used in food-related products.

16.3.3.2 Toxicity of inorganic nanoparticles Nanoparticles commonly used in food matrices are composed of inorganic materials. They may vary in size, structure, dissolvation, and aggregation states which are all critical parameters in determining gastrointestinal fate and their toxicity. The most important application of nanotechnology in foods is achieved through introducing nanoparticles in food packaging materials to prolong shelf life (Hoseinnejad, Jafari, & Katouzian, 2018). Currently, a variety of nanoparticles including silver, zinc oxide, titanium dioxide, and silica are incorporated in packaging materials to improve their functionality (Mohanty, Misra, & Nalwa, 2009; Tager, 2014; Bumbudsanpharoke & Ko, 2015). Each nanoparticle brings unique properties, such as improved barrier features, antimicrobial effect, and texturizing ability, to the carrier matrix. Nanoscale titanium nitrate (TiN) is an approved material for food contact surfaces (EFSA, 2012). Zinc oxide (ZnO) has less toxicity when compared to silver (Duncan, 2011; Silvestre, Duraccio, & Cimmino, 2011; Bumbudsanpharoke & Ko, 2015). The main concern related to nanoparticles in packaging material is migration of those nanoparticles through the food matrix. Especially, metallic nanoparticles used in food-related products for antimicrobial and texturizing purposes may have serious hazard potential to humans and the environment. Table 16.3 summarizes the toxicological outcomes of inorganic nanoparticles based on in vitro and in vivo studies. According to McClements and Xiao (2017), inorganic nanoparticles used in food matrices have potential risks due to spreading and accumulation through the gastrointestinal tract and circulatory system after ingestion. Silver nanoparticles used for antimicrobial effect can migrate from packaging film through food material (Echegoyen & Nerin, 2013; Mackevica, Olsson, & Hansen, 2016). In vivo studies revealed that ingested silver nanoparticles can deposit in various organs including liver, spleen, kidney, and small intestine, although the toxicological fate of those are still inconclusive (Gaillet & Rouanet, 2015; Kim et al., 2008). Zinc oxide nanoparticles are used to provide antimicrobial effect and UV-protection in food packaging materials and as dietary supplements (Wang et al., 2014; Sirelkhatim et al., 2014; EFSA, 2016). The generation of reactive oxygen species (ROS) and thus oxidative damage to cells are the possible hazards of ZnO nanoparticles (Bacchetta et al., 2014). Bioaccumulation of ZnO nanoparticles has not been reported yet. Another most common food grade inorganic nanoparticle is TiO2, which is used for lightening food material. Recent studies have shown the deposition of TiO2 nanoparticles in various organs which can lead to some tissue injuries after ingestion (Duan et al., 2010; Wang et al., 2007). Common findings from in vitro and in vivo studies revealed that based on size and structure, inorganic nanoparticles can penetrate through the cell walls in various

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parts of the gastrointestinal system and be deposited in organs, leading to oxidative damage and tissue injuries. Besides their benefits, all those adverse effects mean that legal authorities have prepared definite regulatory procedures.

16.3.4 Approaches for risk assessment of nanoparticles As stated previously, the identification of the specific features and potential toxicity of nanoparticles used in foods is the fundamental requirement of hazard assessment. Health effects via exposure to nanoparticles used for various purposes in foodrelated products have not been well-defined yet. Potential risks due to exposure routes, absorption mechanism in the body, distribution paths through tissues and organs after uptake, and interaction of those ultrafine particles with the biological system are currently under consideration; however, comprehensive data for the hazard evaluation are required (Bouwmeester et al., 2014). A number of approaches have been available to predict the potential risks of nanoparticles. Some of them determine risk level for lab-scale pure nanomaterials and do not evaluate risks for humans or the environment (Paik, Zalk, & Swuste, 2008; Van Duuren-Stuurman et al., 2012; Zalk, Paik, & Swuste, 2009; Ho¨ck et al., 2018). An alternative approach is based on separating nanoparticles into risk clusters using multiple criteria analysis including physicochemical properties, bioavailability, bioaccumulation, and toxic potential (Bouwmeester et al., 2014; Heock et al., 2013). A systematic approach, called NanoRiskCat, has been introduced by EPA to assess the exposure and hazard potentials of nanoparticle-containing products (Hansen, Baun, & Alstrup-Jensen, 2011). The evaluation process includes five color-coded ranks of which three indicate exposures for professional end-users, consumers, and the environment, and two indicate hazards for humans and the environment. The four potential exposure categories are high, medium, low, and unknown, based on the application of nanomaterial. The potential health risks of nanomaterials are documented through a series of analyses including their aspect ratio, adverse effect in the bulk form, and acute toxicity with the indicators assessing genotoxicity, mutagenicity, carcinogenicity, neurotoxicity, respiratory, and cardiovascular threats. For each of those, scientific data obtained should be interpreted with the help of literature review. Final categorization is performed by NanoRiskCat after processing all of the combined information and the exposure and hazard potential are determined. The presented approach has strong and weak sides. These analyses strongly need expert participation for interpretation and judgment (Bouwmeester et al., 2007). Another limitation or challenge is the inclusion of the newest data to be used in the evaluation of risks. Some constraints are due to the use of supportive systems as well (Marvin et al., 2013). Testing nanoparticles via animal experiments only is not sufficient for the assessment of safety when the variety of nanoparticles are considered. A set of testing approaches for safety assessment is applicable (Bouwmeester et al., 2014; Cockburn et al., 2012; Szakal et al., 2014). Assessment of physicochemical properties and stability in suspension, solubility and agglomeration ability using in vitro digestion models, persistence of nanoparticle in gut, uptake or bioavailability of

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nanoparticles, and dedicated in vivo studies, respectively, are the sequential tests for the assessment of nanomaterial safety (Bouwmeester et al., 2014). In vitro digestion models, including gastric and intestinal systems for food matrices containing silver and silica nanoparticles, have been studied (Peters et al., 2012; Walczak et al., 2013). Silica nanoparticles disappeared when successive digestion was achieved, however, in gastric digestion at low pH and high electrolyte concentration agglomerates are formed. More complex models better simulating the gut epithelium representatively have been used recently (Lefebvre et al., 2015). The human digestive tract with its high acidity and active enzymes may lead to changes in the physicochemical properties of nanoparticles. Interactions between nanoparticles and cells are mainly determined by the physicochemical properties of nanoparticles. Smaller nanoparticles are able to pass cell membranes more efficiently than the larger ones (Mahler et al., 2012). In another significant features, the surface charge of nanoparticles facilitates mucus entrapment and penetration through intestinal epithelium (Hussain, Jaitley, & Florence, 2001; des Rieux et al., 2007; Bouwmeester et al., 2014). The combination of in vitro approaches available currently provide applicable and robust data, however, more information is needed for the validation of these methods. In vivo tests evaluating oral uptake, distribution in the body, and potential health effects of nanoparticles are increasing in number. Assessment of toxicokinetic and toxicodynamic effects of nanomaterials are reported in a few studies. The retention of silver nanoparticles in some tissues of the body was reported after long-term oral exposure (Loeschner et al., 2011; van der Zande et al., 2012). The solubility and changes in agglomeration state of nanoparticles are significant parameters to determine the possible hazardous potential to the human body. In vitro studies with well-designed gastric system simulations are needed to support in vivo experiments. Inorganic chemical nanoparticles, such as titanium oxide, zinc oxide, and silica, used in food-related products are shown to have a high absorption and extensive distribution through body tissues and organs (Cho et al., 2013; van der Zande et al., 2012). The toxicological assessment of nanomaterials is mostly based on in vitro and in vivo studies of inorganic nanoparticles. Those studies should be accomplished with the analytical methods for determining features (size, composition, structure) and behaviors (dissolution, agglomeration) of nanomaterials in food, intestines, and tissues. This produces high-quality comprehensive findings for the assessment of toxicological outcomes of the use of nanoparticles (Bouwmeester et al., 2014).

16.4

Public perception and concerns

Commercial success of food products including nanostructures is directly related to public perception. The lack of information or misinformation about the safety of

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nanofoods or the purpose of using nanomaterials in foods have an effect on consumer preferences. An increase in the number of studies related to food nanotechnology has resulted in the processing and fabrication of novel and functional food products being placed in the market. Public concerns related to the safety of food products containing nanoparticles rise when consuming them. A comprehensive assessment of potential hazards and toxicity risks for health is required before the commercialization of the developed nanofood products. Regulatory guidelines published by some legal authorities in different parts of the world for the production, use, and analysis of nanotechnology products are currently available. Their potential impacts on humans and the environment are often emphasized. There are a vast amount of studies investigating the health risks of nanoparticles used in food products in vitro and in vivo. More research should be carried out to establish specific legal regulations to ensure food safety (Bazana et al., 2019; Pathakoti, Manubolu, & Hwang, 2017). With the increasing trend of using nanoparticles in foods for providing additional functionalities and benefits to manufacturers and consumers, industrial applications are gaining importance (Bazana et al., 2019). The European Commission introduced the regulation enforcing labeling of foods containing any nanoscale ingredients (EU, 2011, no 1169/2011). However difficulties have been experienced in the application of this regulation. Some products detected as containing nanoparticles did not have labels with those ingredients listed as “nano” (Ropers, 2019). In general, consumers have a limited knowledge about the ingredients in their foods. They are unaware of the potential hazards of nanoingredients, or the assessment of safety due to toxicological tests applied regularly (Bazana et al., 2019). Therefore there is a limited consumer acceptance in the presence of uncertainties in relation to safety aspects and legislation. An approach is suggested to determine public perception of the nanomaterialincorporated foods. This can be investigated using qualitative and quantitative objective methodologies consisting of sensory analyses and surveys. Consumer attitudes, beliefs, motivations, feelings, and reasons affect their decisions and perceptions of nanomaterial-containing foods (groups asked for their responses) (Gambaro, 2018; Giles, Kuznesof, Clark, Hubbard, & Frewer, 2015). According to Giles et al. (2015), the use of nanoparticles integrated in food packaging materials is likely to be acceptable while the use of them in the direct preparation of foods is not acceptable to consumers. Confidential and transparent regulations and guidances to be established for the production, use, and risk assessment related to food nanomaterials will influence and encourage consumer acceptance. In addition, educating consumers in order to make them aware of the benefits of nanotechnology and the related guidelines could help reduce consumer concerns and negative reaction against the nanoproducts (Bazana et al., 2019; Giles et al., 2015). Surveys are also significant tools to evaluate the consumer attitudes for the perception of nanotechnology-derived food products. Sustainable approaches to emphasize consumer perception and behavior enable comprehensive analysis based on differently formed consumer groups, along with their assessments of preferences and concerns (Bazana et al., 2019). McCarron (2016) conducted research investigating consumer

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acceptance of nanotechnology foods. The main findings are as follows: a large number of consumers have a lack of knowledge about nanotechnology; perception based on gender differs slightly and female acceptance of health-related nanofoods is greater; younger consumers have a greater knowledge and acceptance of food nanotechnology benefits. The application of nanotechnology in food packaging materials delivers important features to create active and smart packaging. The major risk associated with the nanoparticle-integrated packaging materials is the possible migration of the nanoparticles into food material (Mihindukulasuriya & Lim, 2014). This may potentially result in hazardous health effects (Echegoyen & Nerin, 2013). Research studies highlighting possible health risks caused by nanoparticle exposure, such as cellular damage, cardiovascular and pulmonary diseases, and toxicity, reveal the requirements for safety assessments in order to lower public concerns (Brown et al., 2000; Das, Saxena, & Dwivedi, 2008; Nemmar et al., 2002). For instance, Cushen and others (2013) detected silver nanoparticles migrating from PVC-based nanocomposite packaging material into the encased chicken meat. Although the migration level was lower than the defined limits, the impacts of migrating silver nanoparticles on health remain unclear. Consumer acceptance should be taken into consideration when proposing novel functional foods incorporated with nanomaterials. Consumers may have “nanophobia” toward nanotechnology products, which may adversely affect their commercial potential. Consumer perception and perspective toward nanoproducts differ highly and are influenced by the sociodemographic structure and marketplace (Zhuang et al., 2011; Mihindukulasuriya & Lim, 2014). More details about the consumer attitudes toward nanofoods and a case study are presented in Chapter 17, Consumer Expectations and Attitudes Toward Nanomaterials in Foods, of the current book.

16.5

Regulations in using nanomaterials for foods

There are worldwide efforts to regulate the fabrication and safe use of nanoparticles in agriculture and the food industry by legislation, recommendations, and guidelines. Processing of food materials using nanoparticles should follow procedures provided by regulations or guidances. Potential health risks associated with the integrated nanoparticles in foods require the control of manufacturing to ensure compliance with food safety standards. Regulatory systems with the capability of governing risks are necessary for the use of nanotechnology techniques in food industry. Based on EU regulations for food-related applications of nanotechnology, special considerations for the series of tests and requirements have been declared (ESFA, 2011). Regulations for nanomaterials used for food production and food packaging have been carried out by the FDA and EPA in the United States.

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Health risks and hazards of nanomaterials have been under investigation. As they are not fully clarified yet, consumers need to be protected from undesirable exposure risks via legal regulations. According to EFSA, materials to be used in the packaging systems should not have adverse effects on human health and the consumer should not be deceived (De Jong et al., 2005). The EU and FDA regulations stipulate the permitted maximum nanoparticle levels in food (Chaudhry et al., 2008). Another issue related to the regulation of nanomaterials is the economical parameters in using nanotechnology for commercial products. For example, producing smart composite packaging material using nanoparticles brings additional costs. As it has a relatively low profit margin, it is hard to meet regulatory requirements (Mihindukulasuriya & Lim, 2014). Labeling obligations derived by the EU for nanomaterials present in food content should be indicated (European Parliament and Council, 2011, 2012). By considering potential toxicity, inorganic nanoparticles need to have more attention when used in food applications. According to EU regulations, carbon black, titanium nitrate (TiN), and silicon dioxide nanomaterials are approved for use in food packaging. However, silver, aluminum, zinc oxide, and clay nanoparticles have not been authorized (Bumbudsanpharoke & Ko, 2017). Regulatory agencies in the United states and Europe have introduced policies and guidance for the handling of nanomaterials in foods (EFSA, 2011a, b, 2016; FDA, 2014a, b). Limited scientific evidence and uncertainties are the challenges in managing regulatory approval for nanoparticles food ingredients (McClements et al., 2016). The FDA have described the required assessment of new nanotechnology products and appropriate testing. Measuring physicochemical properties before, during, and after exposure with dose response toxicological tests might help to assess the transformation and characteristics of nanomaterial. According to EFSA, physicochemical characteristics of nanoparticles and their persistance in the food matrix and in the body after ingestion should be evaluated in order to determine retention of those nanoparticles in gastrointestinal tract. The main concerns related to nanoparticles are the impacts of these fine particles on the dynamics and reactions in the gastrointestinal system, varying absorption profiles through the intestines, uncontrolled antimicrobial effects, and translocation into organs and tissues (McClements et al., 2016). Regulatory guidance has focused on common issues and basic aspects. These are discussed in the following section.

16.5.1 Regulatory aspects of nanoparticles Regulatory guidance provides safe paths to follow for manufacturers, importers, and users to ensure the safety of nanofood products present in the market (Amenta et al., 2015). Health concerns and safety issues should be considered during the stages of fabrication, processing, packaging, and consumption of nanoparticleintegrated food materials, individually. Unfortunately, there is no specific legislation valid globally for the regulatory aspects of nanomaterials in food-related fields

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(Bajpai et al., 2018). Besides, many countries have no regulations at all for the safety assessment of nanoproducts. Insufficient knowledge of risk evaluation for human health and environment and lack of regulations for proper handling are the main issues limiting the market potential of nanoproducts produced via the rapidly emerging technology (Bazana et al., 2019). Food ingredients and additives fabricated through nanotechnology must be subjected to safety assessment prior to approval for use (Rasmussen et al., 2019). Guidelines for safety assessment have been introduced by the FDA (Pathakoti et al., 2017). Amenta et al. (2015) comprehensively discussed the EU and US legislation regulating the safe handling of food nanomaterials. Nanomaterials require a definition to describe and distinguish them from the others and recommendations for a nanomaterial definition have been given in legislation and policies by the EU (European Commission, 2011). The EC definition uses the range from 1 to 100 nm and serves as a reference vastly applicable through regulatory units for only defining the size of the particle. It refers to the external dimension of individual nanoparticles standing unbound or existing in the form of agglomerate or aggregate (Amenta et al., 2015; Rauscher et al., 2014; Roebben et al., 2014). Combined appropriate validated methods are recommended to determine the size/size distribution of nanomaterials (Linsinger et al., 2012). As stated before, nanoparticles may exhibit differences in terms of size and aggregation morphology with changing conditions in complex food matrices, therefore they should be defined carefully according to EFSA criteria (EFSA, 2011a, b). EC regulations cover the use of nanotechnology in food manufacturing as novel foods or novel food ingredients, including newly developed innovative foods (Amenta et al., 2015). A revised form of the previous regulations, “Novel Food Regulations” covers the production and processing of vitamins, minerals, and other substances containing engineered nanomaterials (EC, 2013). Synthetic inorganic materials such as silica (E551) and titanium dioxide (TiO2; E171), added to food for the improvement of some technological features of foods, are also implemented by EC regulations (European Parliament and Council, 2002a, 2008b, c, d, e; Amenta et al., 2015). Nanoscale forms of vitamins or minerals need safety assessments due to possible variations in nutritional value and bioavailability in comparison with their macroscaled forms (EC, 2013). Approval is required prior to marketing for the novel foods and food ingredients based on a risk assessment to ensure the inclusion of safe ingredients in foods. Also due to the changing features during the production or processing of nanomaterials, the assessment must follow new safety evaluation tiers. Regarding the inorganic nanoparticles widely used as food additives, calcium carbonate (CaCO3; E170) and silicon dioxide (SiO2; E551), titanium dioxide (TiO2; E171), silver (E174), and gold (E175) have been under investigation for the assessment of their potential health risks and toxicity (Amenta et al., 2015). Regulations related to food contact surfaces, such as active smart packaging materials, plastics, ceramics, and adhesives, point to specific definitions and measurements for safety assessment and authorization (EC, 2009; European Parliament and Council, 2011).

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16.5.2 Current legislations Worldwide, regulatory policies and guidelines for the safe handling and use of nanomaterials in the agri-food industry have been implemented. Several countries apply different approaches to assess the safety of food materials containing nanoparticles for various purposes. They have the opportunity to verify their regulatory cycles in relation to nanotechnology applications in the food industry. The regulations used mainly focus on the common issues, as described in Table 16.4.

16.5.2.1 The United States The FDA is the major authority in charge of the regulations for emerging technologies in food applications in the United States. Also, the EPA has declared a strategy for nanomaterial research and identified typical nanomaterials used in industry, selecting six of them to be tested (Amenta et al., 2015). Another effort for the investigation of possible effects of nanomaterials including nanosilver and nanotitania as food packaging ingredients for human and ecosystem was performed by the OECD (USEPA, 2013). The FDA published a report containing guidance for manufacturers to consider potential implications, safety concerns, and health impacts arising from the use of nanomaterials in FDA-approved products (USFDA, 2011). Another document, “Guidance for Industry: Assessing the Effects of Significant Manufacturing Process Changes, Including Emerging Technologies, on the Safety and Regulatory Status of Food Ingredients and Food Contact Substances, Including Food Ingredients that are Color Additives” was produced by the FDA in 2014 (USFDA, 2014b). The FDA recommends investigating toxicological profiles of food ingredients comprehensively by referring to the Code of Federal Regulations (CFR). The potential carcinogenicity, estimated dietary exposure, lack of interference in case of migration, and lack of hazardous environmental effect have been critical parameters for any substance to be used in food contact surfaces (USFDA, 2014a).

16.5.2.2 Europe Strategic action plans and organizations for nanoscience and nanotechnology applications have been introduced by the European Commission (EC, 2010a, b). “Guidance on the risk assessment of the application of nanoscience and nanotechnologies in the food and feed chain” released by EFSA declared the potential risks of nanoparticles used in industrial products. Also, the risk evaluation of those materials is required by determining physicochemical properties, surface morphology, chemical composition, and potential exposure levels (EFSA, 2011a, b). The need for adequate and validated testing approaches and methods providing reliable identification and characterization of nanomaterials contributed to stakeholders conducting additional research and evaluation in order to eliminate uncertainties (FAO/ WHO). EU legislation describes the amount of nanoparticles to be used in food directly or integrated to packaging materials. Regarding packaging applications, migration

Table 16.4 Legislative regulations related to nanoparticles used in foods. Country

Regulatory body/ initiative

Legal guide

Details

Reports

Details

Food and Drug Administration (FDA)

Federal Food, Drug and Cosmetic (FD&C) Act

Nanotechnology Task Force, FDA (2007), Guidance for Industry, FDA (2014a, b)

The regulations of food ingredients and food contact substances via emerging technologies (nanotechnology)

Environmental Protection Agency (EPA)

Safe and Drinking Water Act, EPA 2007 Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA)

Guidance for definitions and regulatory issues related with foods by the Secretary of Health and Human Services Risk assessment and regulation of drinking water Regulation of pesticides and risk assessment in food chain

FAO/WHO Technical Paper (2013)

Risk assessment and management of nanotechnologies in the food and agriculture sectors

America United States

Canada

Brazil

Food and Agriculture Organization of the United Nations (FAO) World Health Organization (WHO) Canadian Food Inspection Agency (CFIA) National Agency of Sanitary Surveillance (ANVISA) Ministry of Agriculture, Livestock and Food Supply (MAPA)

Food and Drug Acts

Authorization and Regulation of Food and Drug Approval and supervision of food, tobacco, medicine

Europe EU Countries

European Commission (EC) European Food Safety Authority (EFSA)

(EU) No 1169/ 2011

(EC) No 450/2009

Regulations on the provision of food information to consumers Regulations on active and intelligent materials used in processing and come into contact with food

ESFA (2011, 2018)

ESFA (2013, 2014)

EU COM(2008)

Regulatory aspects of nanomaterials

EFSA (2012, 2014, 2016a, b)

(EC) 258/97

Novel foods and food ingredients

EFSA (2014)

JRC Reference Report (2010)

Organisation for European Economic Co-operation (OECD) International Life Science Institute, Europe (ILSI, Europe) Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR)

OECD (2010)

. . ..

SCENIHR (2009)

Uncertainties and risk assessment of using nanoparticles in foods Annual reports on risk assessment of nanotechnology in foods

Safety assessment of food contact materials Safety and risk assessment of food additives Guidance for definition of nanomaterials for regulatory purposes Opportunities and risks of nanotechnologies Practical guidance for the safety assessment of ENMs in foods Risk assessment of products of nanotechnologies

(Continued)

Table 16.4 (Continued) Country

Regulatory body/ initiative

UK

Institute of Nanotechnology Institute of Food Science and Technology (IFST)

Legal guide

Details

Eurasia Russia

The Federal Service for the Protection of Consumer Rights and Human Well-Being of the Ministry of Health and Social Development (Rospotrebnadzor)

Sanitary Norms and Regulations (SanPIN)

Japan

Ministry of Health, Labour and Welfare

Food Sanitation Act

China

Ministry of Agriculture, Ministry of Health

Food Safety Law

Asia Regulations on residue limits for pesticides in foods, basic food and drug regulations, standards for foods and food additives

Reports

Details

Hong Kong

Center for Food Safety

Korea

Ministry of Food and Drug Safety (MFDS), Korean Food and Drug Administration (KFDA) Food Safety Standard Authority of India (FSSAI)

Food Sanitation Act

Foods Standards Australia New Zealand (FSANZ)

Australia New Zealand Food Standards Code

India

CFS Report (41) (2010)

Food Safety and Standards Act

Oceania Australia and New Zealand

ENM, Engineered nanomaterials.

Establishment of the regulations of the Food Standards

Risk assessment of nanotechnology in the food sector

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study results and possible health risks should be provided (EC, 2004, 2007). According to EC (2013), all food ingredients in the form of engineered nanomaterials must be indicated in the label of food products. The names of those ingredients must be followed by the word “nano” in brackets (FAO/WHO).

16.5.2.3 Canada The relevant authorities for food regulation in Canada are the Canadian Food Inspection Agency (CFIA) and Public Health Agency (PHAC). Food nanomaterials are covered by existing legislation and regulatory frameworks with the subtitle of nanospecific regulations. There is no specific regulation for the handling of nanomaterials in foods. Existing legislative units aim to minimize the health risks of nanomaterials in foods (Takeuchi, Kojima, & Luetzow, 2014).

16.5.2.4 Australia and New Zealand Food Standards Australia New Zealand (FSANZ) is the agency responsible for regulating the safe handling and use of food products produced through emerging technologies. This agency describes regulatory approaches for the safety of nanomaterials (FAO/WHO, 2013). Based on survey findings pointing out inadequate requirements for coding nanoparticle-integrated food packaging, FSANZ decided to manage the assessment of possible migration risks (Targer, 2014; FSANZ, 2014).

16.5.2.5 NonEU countries (Switzerland, Turkey, and Russia) Existing regulations are used to assess the safety of nanomaterials. Prior to application, nanomaterials must be reported with specific features related to composition, shape, particle size, surface area, aggregation state, and functionalization. Those are required to be submitted for registration by the request of Swiss Ordinance of 2010 (Schweizerischer Bundesrat, 2010). “The Federal Service for Surveillance of Consumer Rights Protection and Human Well-Being Office” in the Russian Federation is the office in charge following the use of nanotechnology in industry. A number of standards and methods for the evaluation of risks and assessment of safety of nanomaterials were developed and recognized by the Chief State Health Officer of the Russian Federation. Existing recommendations and guidelines released by the EFSA, OECD, FDA, and the FAO/WHO have been considered in the generation of risk assessment methods (Bumbudsanpharoke, 2017).

16.5.2.6 Asia Several Asian countries, including Iran, have founded references and certification systems for nanoscale products. Japan and Korea participate in the OECD Working Party on Manufactured Nanomaterials (WPMN) (Amenta et al., 2015). There is no specific legislation available for nanomaterials in Japan and regulation is achieved by existing legal laws. Nanotechnology research has been highlighted and

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prioritized in Japan in the last decade. Research projects focusing on the carcinogenicity of nanomaterials has been supported by the government (Bumbudsanpharoke & Ko, 2015). According to a survey conducted in 2010, the establishment of specific protocols and methods for safety assessment of nanomaterials was required in case of the presence of health risks arising (FAO/WHO, 2013). In 2011 guidance on the safety management of nanotechnology products was introduced by South Korea. The released document aimed to warrant the safety and advantages of nanoproducts for producers and users, improve public perception of nanotechnology-based products, and induce sustainable industrial development (Bumbudsanpharoke & Ko, 2015). Another initiative by the Korean government covered the establishment of a database for the safety assessment of nanomaterials with a systematic approach to creating a basis for qualified management including all stakeholders. In addition to a variety of ongoing research into the safety assurance of nanotechnology in foods, new guidelines and safety regulations related to the use of nanomaterials for food packaging purposes have been proposed by the Ministry of Food and Drug Safety (MFDS) of South Korea (Hwang et al., 2012). Another Asian country, Malaysia, currently has no specific regulations for the risk assessment and/or safety of nanotechnology-based products (FAO/WHO, 2013; Takeuchi et al., 2014). However, a number of research projects focusing on health, safety, and environmental impacts of nanotechnology in the agri-food sector have been presented (Bumbudsanpharoke & Ko, 2015).

16.5.2.7 South Africa The South African Nanotechnology Initiative, founded in 2002, determined the strategy of nanotechnology development in country (Cele, Ray, & Coville, 2009). Nanotechnology-derived food products have been regulated with specific articles of existing legislation. National Nanotechnology Strategy and Nanotechnology Innovation Centers established in South Africa for long-term nanotechnology research are expected to provide important data for the improvement of nanotechnology applications and related regulations (Bumbudsanpharoke & Ko, 2015).

16.5.2.8 South America Brazil is the most active country in nanotechnological research in South America (Foladori & Invernizzi, 2013; Foladori & Lau, 2014; Kay & Shapira, 2009). The establishment of effective regulations for nanotechnology for industry with developing standards, laws, and guidelines have been discussed comprehensively in Brazil in the last decade (FAO/WHO, 2013; NIA Nanotechnology Industries Association, 2011). Some attempts have been made to develop regulatory legislation. A significant proposal of labeling food and other items (drug and cosmetics) containing nanoparticles has not been approved as it was argued that labeling would harm industrial companies investing in nanotechnology. New proposals for the regulation of nanotechnology-derived manufacturing appropriate for investor companies are being undertaken currently (Bumbudsanpharoke, 2017).

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The regulation of nanomaterials related to food products has been achieved by different legislation (Amenta et al., 2015). Some can be emphasized here. EU legislation covering nanomaterials includes the Regulation on the Provision of Food Information to consumers (1169/2011), the Regulation on Plastic Food Contact Materials and Articles (10/2011), and the Regulation on Active and Intelligent Materials and Articles (450/2009). In order to support the commercial potential of nanotechnology-derived agrifood products, safe and harmonized approaches should be considered. The OECD, ISO, FAO, and WHO have created the Codex Alimentarius Commission, which is proposing to create international food standards and guidelines (Amenta et al., 2015).

16.6

Conclusion

Food products enriched with organic and inorganic nanoparticles have the capability of delivering special functionalities beneficial for manufacturers, suppliers, and consumers. Besides desirable technological impacts of nanoingredient-integrated materials in the food industry, there are also concerns related to the unpredictable adverse effects and risks on health and environment. Uncertainties due to exposure, absorption, and deposition risks toward those novel substances require comprehensive inspection of nanotechnology-based food materials. Legislative regulation for safe handling and use of nanotechnology, and potential risk assessments have been under consideration worldwide. Up-to-date respected authorities from the United States and European Union have introduced a number of documents regarding regulations and guidelines that are helpful for directing nanotechnology in industry. Today the nanofood market is about to reach $20 billion annually. Various nanotechnology-based novel agri-food products have been available on the market and currently show an increasing trend. Therefore more and more attention is being focused on regulatory frameworks to manage nanomaterial manufacturing and the potential risks. Precautions should be taken to ensure a high level of protection for humans and the environment, while providing the development of novel food products with beneficial functionalities and their global marketing (Amenta et al., 2015). Potential health risks, exposure routes, and regulatory guidelines and legislation for nanotechnology-based food materials have been reviewed in this chapter. The most common applications of nanotechnology are encountered in food packaging with inorganics and incorporated food supplements with organics (Bouwmeester et al., 2014). Engineered inorganic nanoparticles in foods such as silica, titanium, silver, and clay have been restricted to use in foods (Bouwmeester et al., 2014). Nanotechnology applications offer health benefits through controlled delivery and improved bioavailability of bioactive compounds. However, the assessment of safety and toxicity risks of these novel materials requires

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comprehensive research including in vitro and in vivo studies, and global legislation promising and promoting safe marketing and use (Bazana et al., 2019). A well-defined global regulatory approach should be developed for the safety assessment of nanofoods and transparently supported marketing. Each national government is required to generate rules for the regulation of nanoenabled food products, particularly with international cooperation, in order to establish global security systems to detect nanoparticles present in imported food materials (Bumbudsanpharoke, 2017). Also, each nation should implement legislative guidelines to protect health and environment against the uncontrolled use of nanomaterials in food-related products. The lack of knowledge on health and environmental effects and potential risks with uncertain toxicity levels has an effect on public perception and acceptance for the consumption of nanoparticle-containing food products.

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contraction. American Journal of Respiratory Cell and Molecular Biology, 28, 111 121. Kim, T. H., et al. (2012). Size-dependent cellular toxicity of silver nanoparticles. Journal of Biomedical Materials Research Part A, 100A, 1033 1043. Kim, Y. S., et al. (2010). Subchronic oral toxicity of silver nanoparticles. Particle and Fibre Toxicology, 7, 20. Kim, Y. S., et al. (2008). Twenty-eight-day oral toxicity, genotoxicity, and gender-related tissue distribution of silver nanoparticles in Sprague-Dawley rats. Inhalation Toxicology., 20, 575 583. Kreyling, W. G., Semmler, M., Erbe, F., Mayer, P., Takenaka, S., Schulz, H., et al. (2002). Translocation of ultrafine insoluble iridium particles from lung epithelium to extrapulmonary organs is size dependent but very low. Journal of Toxicology and Environmental Health, 65, 1513 1530. Kreilgaard, M. (2002). Influence of microemulsions on cutaneous drug delivery. Advanced Drug Delivery Reviews, 54, S77 S98. Lai, S. K., O’Hanlon, D. E., Harrold, S., Man, S. T., Wang, Y. Y., & Cone, R. (2007). Rapid transport of large polymeric nanoparticles in fresh undiluted human mucus. Proceedings of the National Academy of Sciences of the United States of America, 104, 1482 1487. Le Corre, D., Bras, J., & Dufresne, A. (2010). Starch nanoparticles: A review. Biomacromolecules, 11, 1139 1153. Lee, K. E., Cho, S. H., Lee, H. B., Jeong, S. Y., & Yuk, S. H. (2003). Microencapsulation of lipid nanoparticles containing lipophilic drug. Journal of Microencapsulation, 20, 489 496. Lee, J. A., Kim, M. K., Paek, H. J., Kim, Y. R., Kim, M. K., Lee, J. K., et al. (2014). Tissue distribution and excretion kinetics of orally administered silica nanoparticles in rats. International Journal Of Nanomedicine, 9(Suppl 2), 251 260. Lefebvre, D. E., Venema, K., Gombau, L., et al. (2015). Utility of models of the gastrointestinal tract for assessment of the digestion and absorption of engineered nanomaterials released from food matrices. Nanotoxicology, 9(4), 523 542. Available from https://doi. org/10.3109/17435390.2014.948091. Limnach, L. K., Wick, P., Manser, P., Gras, R. N., Bruinink, A., & Stark, W. J. (2007). Exposure of engineered nanoparticles to human lung epithelial cells: ınfluence of chemical composition and catalytic activity on oxidative stress. Environmental Science & Technology, 41, 4158 4163. Linsinger, T. P. J., Roebben, G., Gilliland, D., Calzolai, L., Rossi, F., Gibson, N., & Klein, C. (2012). Requirements on measurements for the implementation of the European Commission Definition of the Term “nanomaterial”. European Commission Joint Research Centre, Luxembourg. ,http://publications.jrc.ec.europa.eu/repository/bitstream/111111111/26399/2/irmm_nanomaterials%20%28online%29.pdf.. Livney, Y. D. (2015). Nanostructured delivery systems in food: Latest developments and potential future directions. Current Opinion In Food Science, 3, 125 135. Loeschner, K., Hadrup, N., Qvortrup, K., Larsen, A., Gao, X., Vogel, U., et al. (2011). Distribution of silver in rats following 28 days of repeated oral exposure to silver nanoparticles or silver acetate. Particle and Fibre Toxicology, 8, 18. Mackevica, A., Olsson, M. E., & Hansen, S. F. (2016). Silver nanoparticle release from commercially available plastic food containers into food simulants. Journal of Nanoparticle Research., 18, 1 11.

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Rezaei, A., Fathi, M., & Jafari, S. M. (2019). Nanoencapsulation of hydrophobic and lowsoluble food bioactive compounds within different nanocarriers. Food Hydrocolloids, 88, 146 162. Rasmussen, K., Rauscher, H., Kearns, P., Gonzalez, M., & Sintes, J. R. (2019). Developing OECD test guidelines for regulatory testing of nanomaterials to ensure mutual acceptance of test data. Regulatory Toxicology and Pharmacology, 104, 74 83. Rischitor, G., Parracino, M., La Spina, R., Urba´n, P., Ojea-Jime´nez, I., Bellido, E., . . . Colpo, P. (2016). Quantification of the cellular dose and characterization of nanoparticle transport during in vitro testing. Particle and Fibre Toxicology, 13, 47. Roebben, G., Rauscher, H., Amenta, V., Aschberger, K., Boix Sanfeliu, A., Calzolai, L., . . ., Stamm, H. (2014). Towards a review of the EC recommendation for a definition of the term “nanomaterial”: Part 2: Assessment of collected information concerning the experience with the definition. European Commission Joint Research Centre. ,https://ec. europa.eu/jrc/en/publication/eur-scientific-and-technical-research-reports/towardsreview-ecrecommendation-definition-term-nanomaterial-part-2-assessment-collected.. Ropers, M. H. (2019). Nanomaterials and food security: The next challenge for consumers, food industries and policies. Encyclopedia of Food Security and Sustainability, 2, 575 581. Rostamabadi, H., Falsafi, S. R., & Jafari, S. M. (2019). Starch-based nanocarriers as cuttingedge natural cargos for nutraceutical delivery. Trends in Food Science & Technology, 88, 397 415. SCENIHR, 2007. Opinion in the appropriateness of the risk assessment methodology in accordance with the technical guidance documents for new and existing substances for assessing the risks of nanomaterials. scientific committee on emerging and newly ıdentified health risks, Brussels from http://ec.europa.eu/health/archive/ph_risk/committees/04_scenihr/docs/scenihr_o_010.pdf SCENIHR (2009). Scientific committee on emerging and newly ıdentified health risks. risk assessment of products of nanotechnologies. Available at: http://ec.europa.eu/health/ archive/ph_risk/committees/04_scenihr/docs/scenihr_o_023.pdf. Schweizerischer Bundesrat. (2010). Verordnung u¨ber das Inverkehrbringen von Pflanzenschutzmitteln (Pflanzenschutzmittelverordnung, PSMV), 916.161. F. O. o. P. Health. Sekhon, B. S. (2010). Food nanotechnology—an overview. Nanotechnology, Science and Applications, 3(1), 1. Sharma, V. K., Siskova, K. M., Zboril, R., & Gardea-Torresdey, J. L. (2014). Organic-coated silver nanoparticles in biological and environmental conditions: Fate, stability and toxicity. Advances in Colloid and Interface Science, 204, 15 34. Shi, S., Wang, W., Liu, L., Wu, S., Wei, Y., & Li, W. (2013). Effect of chitosan/nano-silica coating on the physicochemical characteristics of longan fruit under ambient temperature. Journal of Food Engineering, 118, 125 131. Shin, G. H., Kim, J. T., & Park, H. J. (2015). Recent developments in nanoformulations of lipophilic functional foods. Trends in Food Science and Technology, 46, 144 157. Sia, P. (2017). Nanotechnology among innovation, health and risks. Trends in Food Science and Technology, 237, 1076 1080. Silvestre, C., Duraccio, D., & Cimmino, S. (2011). Food packaging based on polymer nanomaterials. Progress in Polymer Science, 36(12), 1766 1782. Sirelkhatim, A., et al. (2015). Review on zinc oxide nanoparticles: Antibacterial activity and toxicity mechanism. Nano-Micro Letters, 7, 219 242.

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Sohal, I. S., O’Fallon, K. S., Gaines, P., Demokritou, P., & Bello, D. (2018). Ingested engineered nanomaterials: State of science in nanotoxicity testing and future research needs. Particle and Fibre Toxicology, 15, 29. Su, S. L., & Li, Y. (2004). Quantum dot biolabeling coupled with immunomagnetic separation for detection of Escherichia coli O157:H7. Analytical Chemistry, 76(16), 4806 4810. Tager, J. (2014). Nanomaterials in food packaging: FSANZ fails consumers again. Chain Reaction, 122, 16 17. Tinkle, S. S., Antonini, J. M., Rich, B. A., Roberts, J. R., Salmen, R., DePree, K., & Adkins, E. J. (2003). Skin as a route of exposure and sensitization in chronic beryllium disease. Environmental Health Perspectives, 111, 1202 1208. von der Kammer, F., Legros, S., Larsen, E. H., Loeschner, K., & Hofmann, T. (2011). Separation and characterization of nanoparticles in complex food and environmental samples by field-flow fractionation. Trends in Analytical Chemistry, 30(3), 425 436. Wakefield, G., Green, M., Lipscomb, S., & Flutter, B. (2004). Modified titania nanomaterials for sunscreen applications e reducing free radical generation and DNA damage. Materials Science and Technology, 20, 985 988. Szakal, C., Roberts, S. M., Westerhoff, P., Bartholomaeus, A., Buck, N., Illuminato, I., et al. (2014). Measurement of nanomaterials in foods: Integrative consideration of challenges and future prospects. ACS Nano, 8, 3128 3135. Takeuchi, M. T., Kojima, M., & Luetzow, M. (2014). State of the art on the initiatives and activities relevant to risk assessment and risk management of nanotechnologies in the food and agriculture sectors. Food Research International, 64, 976 981. Tassinari, R., Cubadda, F., Moracci, G., Aureli, F., D’Amato, M., Valeri, M., . . . Maranghi, F. (2014). Oral, short-term exposure to titanium dioxide nanoparticles in SpragueDawley rat: Focus on reproductive and endocrine systems and spleen. Nanotoxicology, 8 (6), 654 662. United States Environmental Protection Agency (USEPA). (2013). Nanomaterials EPA is assessing. The United States Environmental Protection Agency Website. Available from: ,http://www.epa.gov/nanoscience/quickfinder/nanomaterials.htm.. Accessed 13.01.15. United States Food and Drug Administration (USFDA). (2011). Draft guidance for industry: Dietary supplements: New dietary ingredient notifications and related issues. 2011 July ed., Maryland. Available from: ,http://www.fda.gov/Food/GuidanceRegulation/ GuidanceDocumentsRegulatoryInformation/DietarySupplements/ucm257563.htm.. Accessed 6.11.14. United States Food and Drug Administration (USFDA). (2014a). CFR-Code of federal regulations title 21. Maryland. Available from: ,http://www.fda.gov/MedicalDevices/ Device-RegulationandGuidance/Databases/ucm135680.htm.. Accessed 05.11.14. United States Food and Drug AdministrationUSFDA). (2014b). Guidance for industry: Assessing the effects of significant manufacturing process changes, including emerging technologies, on the safety and regulatory status of food ingredients and food contact substances, including food ingredients that are color additives. Available from: ,http:// www.fda.gov/Food/GuidanceRegulation/GuidanceDocumentsRegulatoryInformation/ IngredientsAdditivesGRASPackaging/ucm300661.htm.. Accessed 5.11.14. van de Waterbeemd, H., Lennern¨as, H., & Artursson, P. (2003). Drug bioavailability: Estimation of solubility, permeability, absorption and bioavailability. Wiley-VCH. van der Zande, M., Vandebriel, R. J., Van Doren, E., Kramer, E., Herrera Rivera, Z., Serrano-Rojero, C. S., et al. (2012). Distribution, elimination, and toxicity of silver

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nanoparticles and silver ions in rats after 28-day oral exposure. ACS Nano, 6, 7427 7442. Van Duuren-Stuurman, B., Vink, S. R., Verbist, K. J., Heussen, H. G., Brouwer, D. H., Kroese, D. E., et al. (2012). Stoffenmanager Nano version 1.0: A web-based tool for risk prioritization of airborne manufactured nano objects. The Annals of Occupational Hygiene, 56, 525 541. van Kesteren, P. C. E., et al. (2015). Novel insights into the risk assessment of the nanomaterial synthetic morphous silica, additive E551, in food. Nanotoxicology, 9, 442 452. Walczak, A. P., Fokkink, R., Peters, R., Tromp, P., Herrera Rivera, Z. E., Rietjens, I. M., et al. (2013). Behaviour of silver nanoparticles and silver ions in an in vitro human gastrointestinal digestion model. Nanotoxicology, 7(7), 1198 1210. Walters, C., Pool, E., & Somerset, V. (2016). Nanotoxicity in aquatic invertebrates. In M. L. Larramendy (Eds.), Invertebrates experimental models in toxicity screening (pp. 13 34). IntechOpen. Wang, J., et al. (2007). Acute toxicity and biodistribution of different sized titanium dioxide particles in mice after oral administration. Toxicology Letters., 168, 176 185. Wang, Y., et al. (2013). Susceptibility of young and adult rats to the oral toxicity of titanium dioxide nanoparticles. Small, 9, 1742 1752. Wang, Y. L., et al. (2014). A combined toxicity study of zinc oxide nanoparticles and vitamin C in food additives. Nanoscale, 6, 15333 15342. Wani, T. A., Masoodi, F. A., Jafari, S. M., & McClements, D. J. (2018). Chapter 19—Safety of nanoemulsions and their regulatory status. Nanoemulsions (pp. 613 628). Academic Press. Weir, A., Westerhoff, P., Fabricius, L., Hristovski, K., & von Goetz, N. (2012). Titanium dioxide nanoparticles in food and personal care products. Environmental Science & Technology., 46, 2242 2250. Williams, K., et al. (2015). Effects of subchronic exposure of silver nanoparticles on intestinal microbiota and gut-associated immune responses in the ileum of Sprague-Dawley rats. Nanotoxicology, 9, 279 289. Wu, H. H., Yin, J. J., Wamer, W. G., Zeng, M. Y., & Lo, Y. M. (2014). Reactive oxygen speciesrelated activities of nano-iron metal and nano-iron oxides. Journal of Food and Drug Analysis., 22, 86 94. Yang, Y., et al. (2016). Survey of food-grade silica dioxide nanomaterial occurrence, characterization, human gut impacts and fate across its lifecycle. Science of the Total Environment., 565, 902 912. Yao, M., McClements, D. J., & Xiao, H. (2015). Improving oral bioavailability of nutraceuticals by engineered nanoparticle-based delivery systems. Current Opinion In Food Science, 2, 14 19. Yu, Y. W., Zhang, S. Y., Ren, Y. Z., Li, H., Zhang, X. N., & Di, J. H. (2012). Jujube preservation using chitosan film with nano-silicon dioxide. Journal of Food Engineering, 113, 408 414. Zalk, D. M., Paik, S. Y., & Swuste, P. (2009). Evaluating the control banding nanotool: A qualitative risk assessment method for controlling nanoparticle exposures. Journal of Nanoparticle Research, 11, 1685 1704. Zhou, Y., Fang, X., Gong, Y., Xiao, A., Xie, Y., Liu, L., & Cao, Y. (2017). The Interactions between ZnO nanoparticles (NPs) and -linolenic acid (LNA) complexed to BSA did not influence the toxicity of ZnO NPs on HepG2 cells. Nanomaterials, 7, 91. Zimmermann, M. B., & Hilty, F. M. (2011). Nanocompounds of iron and zinc: Their potential in nutrition. Nanoscale, 3, 2390 2398.

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Further reading Hamad, A. F., Han, J. H., Kim, B. C., & Rather, I. A. (2018). The intertwine of nanotechnology with the food industry. Saudi Journal of Biological Sciences, 25, 27 30. Hansen, S. F. (2017). React now regarding nanomaterial regulation. Nature Nanotechnology, 12, 714 716. Lee, J., Jeong, J.-S., Kim, S. Y., Park, M.-K., Choi, S.-D., Kim, U.-J., . . . Yu, W.-J. (2019). Titanium dioxide nanoparticles oral exposure to pregnant rats and its distribution. Particle and Fibre Toxicology, 16, 31. Limbach, L. K., Wick, P., Manser, P., Grass, R. N., Bruinink, A., & Stark, W. J. (2007). Exposure of engineered nanoparticles to human lung epithelial cells: influence of chemical composition and catalytic activity on oxidative stress. Environmental Science & Technology, 41, 4158 4163. McClements, D. J., & Xiao, H. (2012). Potential biological fate of ingested nanoemulsions: Influence of particle characteristics. Food & Function, 3, 202 220. McClements, D. J. (2013). Edible lipid nanoparticles: Digestion, absorption, and potential toxicity. Progress Journal of Lipid Research., 52, 409 423. Nanodatabase. (2014). ,http://nanodb.dk/en/. Accessed September 2018. Nanotech-data. (2018). ,http://www.nanodaten.de/site/page_de_garde.html. Accessed August 2018. Rauscher, H., Rasmussen, K., & Sokull-Kluttgen, B. (2017). Regulatory aspects of nanomaterials in the EU. Chemie Ingenieur Technik, 89, 224 231. United States Food and Drog Administration (USFDA). (2007). Nanotechnology a report of the USFDA. Food and Drug Administration, Nanotechnology Task Force. Available from ,https://www.fda.gov/science-research/nanotechnology-programs-fda/nanotechnology-task-force. Accessed 29.08.19.

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Shuoli Zhao1, Chengyan Yue2 and Jennifer Kuzma3 1 Department of Agricultural Economics, University of Kentucky, Lexington, KY, United States, 2Department of Applied Economics, Department of Horticultural Science, University of Minnesota, Saint Paul, MN, United States, 3School of Public and International Affairs, North Carolina State University, Raleigh, NC, United States

17.1

Nanotechnology application in food industry

Nanotechnology has been frequently described as the next scientific breakthrough that will revolutionize society (Balbus, Karen, Richard, & Scott, 2006). It involves the characterization, fabrication, and/or manipulation of structures, devices, or materials that have at least one dimension (or contain components with at least one dimension) that is approximately 1
100 nm in length (Dowling et al., 2004; Jafari & McClements, 2017). After the term nanotechnology was first introduced by Rochard Feynman in 1959 at a meeting of the American Physical Society (Khademhosseini & Langer, 2006), it has developed into a multidisciplinary field. The market potential of nanotechnology applications is projected to impact US$3 trillion across the global economy by 2020, and nanotechnology industries worldwide may employ at least 6 million workers by the end of the decade (Roco, Mirkin, & Hersam, 2011). The applications of nanotechnology are becoming increasingly competent in the food sector with evolutional contributions to the food safety from the farm field to the end market, leading to radical changes in the way food is stored, processed, monitored, and consumed (Alehosseini & Jafari, 2019; Cushen, Kerry, Morris, Cruz-Romero, & Cummins, 2012; Katouzian & Jafari, 2016). During agricultural production, nanomaterials can be used as smart coatings for agricultural inputs, such as fertilizer and pesticide, facilitating the targeted release of ingredients to achieve precise and efficient soil management (Scrinis & Lyons, 2007; Wani et al., 2019). For food manufactures, nanomaterials could benefit the market intermediaries and reduce the production costs by creating nonfouling surfaces to prevent clogging in process machines (Tepper et al., 2005). For food functionality, certain nanoparticles could create increased bioavailability with enriched nutrients or different flavors in novel food products (Garavand, Rahaee, Vahedikia, & Jafari, 2019; Koshani & Jafari, 2019). Handbook of Food Nanotechnology. DOI: https://doi.org/10.1016/B978-0-12-815866-1.00017-0 © 2020 Elsevier Inc. All rights reserved.

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17.1.1 Benefits of nanotechnology in food packaging Food safety is a major concern of many consumers (Jafari, Ghanbari, Dehnad, & Ganje, 2018). The fast-changing pace of people’s daily diet and food habits has brought increasing threats from foodborne pathogens to human health. With the application of nanotechnology, promising results have been developed in the area of food packaging (Dehnad, Emam-Djomeh, Mirzaei, Jafari, & Dadashi, 2014a; Hashemi Tabatabaei, Jafari, Mirzaei, Mohammadi Nafchi, & Dehnad, 2018). Given the natural benefits of nanosized dimensions, nanocomposites could dramatically improve the mechanical and barrier properties of packaging materials (Dehnad, Mirzaei, Emam-Djomeh, Jafari, & Dadashi, 2014b; Hoseinnejad, Jafari, & Katouzian, 2018). The incorporation of nanomaterials in food packaging is expected to improve the barrier properties of packaging materials and should thereby help reduce the use of raw materials and prolong the shelf life of packaged food products (Sozer & Kokini, 2009). Moreover, nanotechnology improves food shelf life by blocking harmful chemical reactions between food components and the external environment, and the antimicrobial properties of nanoparticle could help to remove extra oxygen or water vapor through direct interaction with the food (Bajpai et al., 2018; Joz Majidi et al., 2019). For food safety, nanopackaging not only serves as a passive foodborne disease barrier, it could also serve as an intelligent toxin detector to notify signs of quality instability (Vahedikia et al., 2019). For example, a recent development incorporates nanosensors into packaging material to detect the oxidation process in food through the change of color or other observable information in the packed food. This has been successfully applied in the packaging of dairy and meat products (Bumbudsanpharoke & Ko, 2015). With the increasing number of current and potential applications of nanotechnology in food packaging, the total nanopackaged food and beverage market has grown from US$4.13 billion in 2008 to US$6.5 billion in 2013 and is estimated to be growing at a compound annual growth rate of 12.7% to reach around US$15.0 billion in 2020 (Consumer News and Business Channel, 2014).

17.1.2 Potential risks of nanotechnology applications Despite the increasing opportunities surrounding nanotechnology applications, there are also concerns due to the potential negative effects (Jafari, Katouzian, & Akhavan, 2017; Rafiee, Nejatian, Daeihamed, & Jafari, 2019). One concern about human health is that certain nanomaterials in food could access tissues in the human body, resulting in the accumulation of toxic contaminants and causing unintended effects on human health (Cushen et al., 2012; Oberdo¨rster, Oberdo¨rster, & Oberdo¨rster, 2005). Some studies have expressed specific health risks including intracellular damage, pulmonary inflammation, and vascular disease (Brown, Stone, Findlay, MacNee, & Donaldson, 2000; Das, Saxena, & Dwivedi, 2008; Mihindukulasuriya & Lim, 2014). In the meantime, the production of nanopackaging will inevitably use nanoparticles on a large scale, which leads to possible particles’ migration into water, air,

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and soil to cause undesired consequences to the environment (Silvestre, Duraccio, & Cimmino, 2011). While existing studies indicate that the expected nanoparticle concentrations in the environment are substantially limited and present a low-level risk for biological system (Boxall, Tiede, & Chaudhry, 2007), more research is still needed on for how long and in which form the undesired nanoparticles will survive.

17.2

Consumer attitudes toward nanotechnology in food

The development and success of food technologies are shown to be contingent upon societal responses to their applications (Fischer, van Dijk, de Jonge, Rowe, & Frewer, 2012). However, in the case of nanopackaging and nanofood, the public awareness and knowledge are limited, and individuals do not have extensive experience with nanotechnology (Fischer et al., 2012; Lee, Scheufele, & Lewenstein, 2005; Siegrist, Stampfli, Kastenholz, & Keller, 2008). As a consequence, a lack of clear information decreases consumer confidence and compromises the acceptance of new nanoproducts despite their social benefits (Roosen, Bieberstein, Marette, Blanchemanche, & Vandermoere, 2011). Under such situation, it is important to explore consumers’ attitude toward the information on nanopackaging used for food products; and how information from different sources may influence public opinion toward and acceptance of nanotechnology, especially nanopackaging.

17.2.1 Consumer acceptance of food nanotechnology There are studies that have focused on consumer attitudes toward nanotechnology. Cobb and Macoubrie (2004) carried out phone surveys with 1536 US consumers to elicit their perceptions about nanotechnology; they found that the initial reaction was generally positive, and the perceived benefits were more prevalent than the perceived risks. Gaskell, Ten Eyck, Jackson, and Veltri (2005) compared preferences between the United States and European consumers and concluded that European consumers seemed to be less optimistic about nanotechnology. Furthermore, Siegrist et al. (2008) examined how consumers perceived nanofood and nanopackaging and showed that even though consumers were hesitant to buy either of them, nanopackaging was perceived as being more beneficial than nanofood. Yue, Zhao, Cummings, and Kuzma (2015a) and Yue, Zhao, and Kuzma (2015b) conducted choice experiments with 1117 US consumers; their results showed that nanofood evoked fewer negative reactions compared to genetically modified (GM) food. Most recently, Zhou and Hu (2018) examined consumer valuations for nanoattributes via a nationwide online survey; the results suggest that consumers discount canola oil if it is produced from nanoscale-modified seeds or is nanopackaged. In addition to the general attitude, studies have also shown that the initial attitude toward nanopackaged food products may change considerably as more detailed information becomes available. Fischer et al. (2012) investigated public reactions when different risk
benefit information about nanotechnology’s application in food

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was provided; their results showed that consumer perceptions changed significantly after the provision of the information. Roosen et al. (2011) evaluated the effect of information on consumers’ willingness to pay (WTP) for nanofoods and concluded that information had a significant influence on consumer WTP. Specifically, health information significantly decreased WTP, while societal and environmental information was not as important.

17.2.2 Factors affecting consumer acceptance of food nanotechnology 17.2.2.1 General attitudes toward new technology The success of new food technology application is largely determined by consumers’ initial attitudes; for nanotechnology application in food, consumer awareness is still low (Chaudhry et al., 2008; Siegrist et al., 2008), which is similar to genetic modification technology in its early stage. The majority of consumers are undecided or feel that they do not know enough to form a view. Under such circumstances, the level of comfort or ease of adopting new technology applications plays a significant role in the acceptance of nanotechnology (Silvestre et al., 2011). When it comes to the food industry, consumers’ attitudes are even more sensitive (Cushen et al., 2012). For example, several new food technologies in the past faced reluctant acceptance when they first appeared, such as canned food, pasteurized milk, microwave cooking and GM food (Miller, Lowrey, & Senjen, 2008). Recent studies show that a similar pattern occurs in nanotechnology and consumers are hesitant to buy nanofood or nanopackaged food (Siegrist, Cousin, Kastenholz, & Wiek, 2007). However, the use of nanotechnology in packaging seems to be more acceptable than the use of nanotechnology in food (Siegrist et al., 2008).

17.2.2.2 Environmental and health concern While governmental organizations such as the FDA have acknowledged the beneficial aspects of nanotechnology, they also admitted the lack of knowledge about the effects of nanotechnology on human and environmental health (FDA, 2007). Both concerns are expected to have a significant influence on consumers’ purchasing decision. The effect of nanostructures on human health, such as nanoparticle migration into the human body and binding nutrients, could also be caused by the interactions between nanoparticles and existing chemicals, which is especially true for nanoparticles used in food packaging (Chau, Wu, & Yen, 2007). More research has been focusing on the toxicity of materials at the nanolevel (particularly inorganic nanomaterials) to human health, and show possible oxidative damage, inflammatory reactions, and even signs of early tumor formation primarily due to the nanoparticles’ ability to cross cellular barriers (Bouwmeester et al., 2009; Carlson et al., 2008; Hoet, Bru¨ske-Hohlfeld, & Salata, 2004; Nel, Xia, Madler, & Li, 2006). For the environment, the potential fate of nanomaterials after disposal of the packaging

Consumer expectations and attitudes toward nanomaterials in foods

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may concern consumers who are environmentally aware (Boxall et al., 2007). To increase the consumer confidence in nanopackaging, further advancement calls for the transparent evaluation of nanomaterial migration in terms of its environmental responsibility (Mihindukulasuriya & Lim, 2014).

17.2.2.3 Preference for prolonging food shelf life A product shelf life is the period before the product becomes unacceptable for consumption from sensorial, nutritional, or safety perspectives (Ganje et al., 2016; Labuza & Fu, 1993). Shelf life is a critical attribute affecting consumer acceptance of a food product, and it serves as an anchor point (Lyndhurst, 2008) when consumers evaluate food product quality. If a food product reaches its expiration date, consumers’ purchase intention can greatly decrease even if its appearance, aroma, and flavor are still acceptable (Lyndhurst, 2008). In response to consumers’ needs, various technologies have emerged in the past decades to prolong the shelf life of foods, such as pasteurization, high-pressure processing, genetic modification, and novel food packaging, and most of those technologies reached widespread acceptance by consumers with only very few exceptions, for example, food irradiation (Ronteltap, van Trijp, Renes, & Frewer, 2007). The proven effectiveness of prolonging product life has, in turn, increased consumer confidence in novel food technologies (Hosseini, Tajiani, & Jafari, 2019). By far, nanopackaging is regarded as the most effective food packaging to prolong shelf life (De Azeredo, 2009). It can be used as an oxygen barrier layer in the extrusion manufacturing of bottles for fruit juices, dairy foods, beer, and carbonated drinks, or as nanocomposite layers in multilayer films to enhance the shelf life of a variety of foods, such as processed meats, cheese, confectionery, cereals, and boil-in-bag foods (Moraru et al., 2003). Other shelf life enhancements can be achieved by incorporating nanoclay into plastic matrices to improve thermal resistance or by employing silver nanocomposites to improve antimicrobial effectivity (Damm, Mu¨nstedt, & Ro¨sch, 2007).

17.2.2.4 Trust in institution Social trust, especially the trust in institutions such as third-party technology management, is known to be a key element to predict consumer’s WTP for food products produced using new technologies (Ronteltap et al., 2007). This trust is especially crucial for consumers when dealing with a new food technology that they have less knowledge of (Siegrist & Cvetkovich, 2000). As previous research has shown that most people were not familiar with the term nanotechnology (Gaskell et al., 2005), it is important to investigate the effect of trust in institutions on consumer attitudes toward nanopackaging. Trust in institutions has been proven to be a reliable indicator in consumer research of new technology applications. Frewer, Scholderer, and Bredahl (2003) and Chen and Li (2007) stated that trust in institutions is particularly important if consumers perceive they have no control over society’s adoption of a new

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technology. Rodrı´guez-Entrena, Salazar-Ordo´n˜ez, and Sayadi (2013) also concluded that consumer trust in institutions is positively related to their attitude toward GM foods. Specifically, for nanotechnology, Viscecchia, De Devitiis, Carlucci, Nardone, and Santeramo (2018) concluded a positive role of trust in institutions on willingness to buy with nanotech applications.

17.2.2.5 Reliance on governmental regulation With the rapid development of nanotechnology applications in the food industry, it is a great challenge to develop the corresponding regulations. Successful governmental regulation could ensure the development and deployment of nanotechnology (Chau et al., 2007). In the past decade, many nanotechnology initiatives, commissions, or centers have been launched by governments of the United States, Europe, Japan, China, and other countries around the globe (Chen, Weiss, & Shahidi, 2006). However, there is no current legislation entirely dedicated to the regulation of nanotechnology application in food (Arts et al., 2014), and the EU and some other countries regard the current legislation sufficient for the regulation of nanotechnology (Amenta et al., 2015). In the United States, the FDA was among the first governmental agencies that provided guidance documents for nanotechnology. The Nanotechnology Task Force Report released in 2007 provided legislative recommendations on what information the industry needs to clarify in their nanoproducts, and how regulatory policy could assist the development of technology to ensure safety. On June 24, 2014, the FDA further issued one draft and three final guidance documents pertaining to the use of nanotechnology in regulated products.

17.3

Case study—consumer preference and information provision in nanopackaged food

Prior studies investigating public attitudes and information effects on nanotechnology mostly used hypothetical instead of actual nanoproducts (Cobb & Macoubrie, 2004; Siegrist et al., 2007), and the estimated WTP values were hypothetical and might be biased (Bieberstein, Roosen, Marette, Blanchemanche, & Vandermoere, 2013). In this case study, we employ experimental auctions to investigate consumers’ WTP for actual nanopackaged food products. Furthermore, a structural equation model (SEM) is used to capture the complex relationship between attitudinal factors and consumer WTP, and how these relationships are influenced by the information about nanotechnology from various sources.

17.3.1 Theoretical framework and proposed hypothesis To examine how consumer’s attitudes and perceived information affect their WTP for nanopackaging, SEM is employed (Fig. 17.1). The core of this model is the

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Figure 17.1 Conceptual framework.

relationship between WTP from experimental auction and three attitudinal constructs, TECHACCEPT, CONCERN, and GOVERNROLE. Each of these three constructs corresponds to one piece of specific information (sourced from private industry, environmental agency, and governmental agency, see Table 17.1) that is provided to participants during the experiment. TECHACCEPT reflects consumer acceptance level for new technology in general, which corresponds to the positive statement from private industry. CONCERN is linked with the negative information from environmental agency, representing environmental and health concern caused by the application of nanotechnology in food packaging. GOVERNROLE indicates the importance of the government’s role in restricting the use of nanotechnology in food products, which is parallel to a neutral statement referenced from a governmental agency. In order to test and compare these relations under different information, we set up a three-round auction experiment with incremental information provided in each round. In light of previous consumer research on nanotechnology, we also measure the consumer attitudes toward prolonging the shelf life of food products (SHELFLIFE), and their trust in governmental regulation and certification of new technology (TRUST). Relevant to the factors affecting consumer acceptance discussed in Section 17.2.2, we propose the following hypothesizes to test the intercorrelations of the attitudinal constructs. Combining the controlling feature of shelf life amongst all food attributes, and the effectiveness of nanopackage in prolonging food shelf life, we hypothesize that: H17.1: Consumers’ preference for prolonging food shelf life positively relates to their acceptance of novel technologies employed in food products. Furthermore, given the effect of affect heuristic, consumers’ demand for longer shelf life may suppress their risk perceptions toward health and environment. Thus we hypothesize that:

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Table 17.1 Information from various sources displayed to the participants. Source

Information presented

Round 2 General information

Nanotechnology refers to materials, systems, and processes which exist or operate at the scale of atoms and molecules. This is a scale between 1 and 100 nanometers (nm). One nanometer is one millionth of a millimeter (mm). Materials at the nanoscale show novel properties that lead to novel applications in diverse fields like medicine, cosmetics, biotechnology, energy production and environmental science. There is uncertainty regarding how nanomaterials may interact with human health and the environment. Nanotechnology offers new opportunities for food industry application. Manufactured nanomaterials are already used in some food products, nutritional supplements and food packaging applications (Bieberstein et al., 2013; Roosen et al., 2011)

Round 3 Private Industry (Positive)

Environmental Agency (Negative)

Nanopackaging has created a modified atmosphere in packaging in order to control the flow of gases resulting in improving the shelf life of products like vegetables and fruits. One of the most promising innovations in smart packaging is the use of nanotechnology to develop antimicrobial packaging. Scientists at big name companies including Kraft, Bayer and Kodak, as well as numerous smaller companies, are developing a range of smart packaging materials that will absorb oxygen, detect food pathogens, and alert consumers to spoiled food. These smart packages, which will be able to detect public health pathogens such as Salmonella and E. coli. (NanoBio-RAISE Project, 2011) Antibacterial nanofood packaging and nanosensor technologies have been promoted as delivering greater food safety by detecting or eliminating bacterial and toxin contamination of food. However it is possible that nanomaterials (such as silver, zinc oxide and titanium dioxide) will migrate from antibacterial food packaging into foods, presenting new health risks. This appears inevitable where nanofilms or packaging are designed to release antibacterial onto the food surface in response to detected growth of bacteria, fungi or mold. Silver nanoparticles are found in an increasing number of consumer products such as food packaging, odor resistant textiles, household appliances and medical devices. The potential for nanosilver to adversely affect beneficial bacteria in the environment, especially in soil and water, is (Continued)

Consumer expectations and attitudes toward nanomaterials in foods

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Table 17.1 (Continued) Source

Information presented of particular concern. Conversely, there is also a risk that use of silver nanoparticles (“nanosilver”) will lead to the development of antibiotic resistance among harmful bacteria (Miller et al., 2008)

Governmental Agency (Neutral)

Nanopackaging has the potential to help improve the safety, shelf life, and convenience of food. At present there is insufficient data publicly available to reach meaningful conclusions on the potential toxicity of food or color additives incorporating nanomaterials, although the available information does not give us cause for concern (FDA, 2007)

H17.2: Consumers with a stronger preference for improved shelf life are less concerned with the influence of nanopackaging on health and environment. As it has been shown that higher trust in institutional regulation increases consumer confidence in restrictive governmental policies and reduces perceived uncertainty and risk (Ronteltap et al., 2007), we hypothesize the following two relationships: H17.3: More trust in institutional regulation on food technology reduces consumers’ concern about the application of nanotechnology in food products. H17.4: Trust in institutional regulation on food technology positively affects consumer attitude toward the governmental role in technology restriction. Given the fact that consumers are sensitive to new technology application in food, we hypothesize: H17.5: Consumers with higher acceptance of new technologies are willing to pay more for nanopackaged food products. Furthermore, combining both environmental and health concerns, we hypothesize that: H17.6: The more environmental and health concerns consumers have about nanopackaging, the less they are willing to pay for nanopackaged food products. It is of great interest to investigate how the importance of governmental regulations to US consumers affects their WTP for nanopackaged food products. Given this relationship is scarcely investigated by relevant literatures, we hypothesize based on the increasing policy initiatives around the globe that: H17.7: The more important governmental regulations on nanoproducts are to consumers, the less they are willing to pay for nanopackaged food products.

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17.3.2 Research material and methodology Our research protocol was submitted to and approved by the Institutional Review Board of the University of Minnesota. The detailed experimental and analytical methods are explained in this section.

17.3.2.1 Auction experiment Incentive compatible experimental auction is a powerful tool to elicit accurate consumer WTP for goods, and it has been used by researchers to investigate consumer WTP for various products (Harrison & Rutstro¨m, 2008; Umberger & Feuz, 2004). The auction mechanism used in the experiment was the Becker
DeGroot
Marschak (BDM) mechanism (Becker, Morris, & Marschak, 1964). Each participant submits the price he or she is willing to pay to purchase the product. If the bid for the auctioned good is equal to or higher than the randomly drawn market price, then the participant is required to buy the product. In this way, the auction mechanism is incentive compatible because bidders have no strategic incentive to bid above or below their true values. During the experiment, participants were explicitly made aware of the fact that bidding their true values was their best strategy.

17.3.2.2 Products The products used in the auction are conventional and organic applesauce (12 oz.), spinach salads (5 oz.), and roasted peanuts (12 oz.) in both regular packaging and nanopackaging. These three food products were chosen because they differed in their shelf lives: salad has a short shelf life, applesauce has a medium-level shelf life, and peanuts have a long shelf life. The label “Nano-Silver Technology” with the logo “Stays Fresh Longer” was used for nanopackages, which is the typical labeling information found on nanocontainers currently on the market.

17.3.2.3 Participants The experiment was conducted in St. Paul, Minnesota;109 participants were recruited through an advertisement in 13 local newspapers that have a wide readership in all the socioeconomic classes in the Minneapolis and St. Paul metropolitan area. The advertisement specified that only the grocery shopper in a household could participate in the experiment. To avoid bias, nanotechnology was not mentioned in the advertisement. Out of the 106 participants, 7 were dropped because of uncompleted information and invariant survey question answers.

17.3.2.4 Auction design The experimental auction consisted of three rounds of bidding, each with six products (conventional and organic salad, applesauce, and peanut). We followed the research protocol by Huffman, Rousu, Shogren, and Tegene (2007) and Liaukonyte, Streletskaya, Kaiser, and Rickard (2013) to present products sequentially. In the

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715

first round, participants submitted their bids for products that were not labeled as nanopackaged (plain-labeled), and no information was provided. In the second round and third round, all bidding items were labeled with “Nano-Silver Technology” and “Stays Fresh Longer.” In the second round, general information about nanotechnology from Roosen et al. (2011) was provided, and participants submitted their bids after viewing the information. In the third round, three sets of detailed information on nanotechnology from private industry, an environmental group, and the FDA were presented, and participants were asked to submit bids for the third time. The information from private industry is primarily positive, it states the potential applications of nanotechnology in food packaging and its advantages of prolonging shelf life. The environmental group’s information is quoted from Friends of the Earth, a well-known environmental protection group, and their statement is mainly negative, focusing on the harmful aspects of nanomaterials. Lastly, the FDA’s information is neutral, illustrating both the usefulness of nanotechnology for food industry and the uncertainty about the potential risks. The three sets of information in the third round are correspondingly related to the latent constructs of TECHACCEPT, CONCERN, and GOVERNMENT in the SEM model. As such, we can estimate the relative dominant effect of each set of information on WTP. The details of each information are shown in Table 17.1.

17.3.2.5 Auction procedure The diagrammatic representation of the experimental flow is shown in Fig. 17.2. The experiment was set up on a computer, which allowed for little interaction between the participants and the moderator, thus reducing potential errors caused by communications. Upon arrival at the experiment lab, participants were asked to sign a consent form. They were then instructed on how to use the computer and mouse to traverse from one screen to another, and entering the bids on the bidding sheet. Participants were informed that the exact same real products shown in the image were being auctioned and if a participant won the auction, he/she would receive the item and pay the market price. Before the formal auction started, there was a practice round with a candy bar to help the participants familiarize themselves with the auction procedure. Then in the third round of bidding, as three sets of information (positive, negative, and neutral) need to be provided sequentially on computer screens, we randomized the display sequence to control any possible order effects. Table 17.2 shows the randomized sequences and the number of participants in each sequence during the experiment. After three rounds of bidding, we randomly drew the binding round and binding product. If a participant’s bid for the binding product in the binding round is higher than its randomly drawn market price, she/he was required to purchase the product by paying the market price. Finally, after the auction procedure, participants were required to complete a postexperiment survey about their opinions and general preferences corresponding to our proposed latent constructs, along with typical sociodemographic questions.

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Figure 17.2 Experimental flow for the experimental auctions. Notes: The terms in ellipses represent latent constructs, and those in rectangles represent observed variables. The solid arrows represent structural equations (i.e., cause-and-effect relationships), and the dashed arrows represent measurement equations (relationships between observed variables and the latent constructs). To assign a fixed unit of measurement to the latent constructs, one of the λs representing the relationships between the observed variables and a latent construct is normalized to one.

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Table 17.2 Six different sequences of the information presented to the participants. Sequence

First information

Second information

Third information

No. of participants

1

Private industry

Government

17

2.

Private industry

Environmental group Government

21

3.

Government

Private industry

4.

Government

17

5.

Environmental group Environmental group

Environmental group Government

Environmental group Environmental group Private industry Private industry

17

Government

17

6.

Private industry

16

17.3.2.6 Structural equation model Our conceptual framework and hypotheses were tested by SEM (Hair, Black, Babin, Anderson, & Tatham, 2006), which is a multivariate technique that allows for the simultaneous estimation of a series of separate, but interdependent relationships between latent constructs (Bagozzi, 1994). Those latent constructs cannot be observed directly, and SEM is used to relate consumers’ WTP to their general attitudes, concerns, and social beliefs. The standard SEM consists of two parts, namely, the measurement model specifying the relationships between the latent variables and their constituent observed variables, and the structural model estimating the causal relationships between the latent variables (Toma, McVittie, Hubbard, & Stott, 2011). Given ξ is a vector of exogenous latent construct and η is a vector of endogenous latent construct, the relationship between a latent construct and its observed variables can be represented by a measurement model: x 5 Λx ξ 1 δ

(17.1)

y 5 Λy η 1 ε

(17.2)

where x and y are vectors of observed variables for the exogenous and endogenous latent constructs (ξ and η), respectively; Λx and Λy are matrices of coefficients relating the constructs ξ and η to observed variables x and y; and δ ε are the measurement error. Further into the relationships between the latent constructs, it can be represented as η 5 Γξ 1 Bη 1 E

(17.3)

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where Γ is a matrix of coefficients relating the exogenous to the endogenous latent constructs; B is a matrix of coefficients of the endogenous latent constructs in the structural model; and E is a vector of error. In order to estimate the model parameters (represented by θ), we minimize the ^ 5 Σðθ^ Þ and the observed discrepancy between the estimated covariance matrix Σ sample covariance matrix S. Using the AMOS 21.0 (Arbuckle, 2013) software package and maximum likelihood (ML) method, the discrepancy minimization function is defined as
FML ðS; ΣÞ 5 tr SΣ21 2 log SΣ21 2 k

(17.4)

where |  | represents the determinant of matrixes, tr indicates the trace and k is the total number of stochastic variables. Then the ML estimator of θ^ , is defined by θ^ 5 arg min FML ðS; ΣÞ θ

(17.5)

Next, we conducted several statistical tests for the goodness-of-fit of the measurement and structural model; the normed chi-square fit test (χ2 ) measures whether the predicted and the actual covariance matrix are identical, it is calculated by dividing the chi-square value (which is sensitive to the sample size) by the number of degrees of freedom. According to Arbuckle (2013), the goodness-of-fit is acceptable when normed chi-square is ,5, and the more conservative acceptable thresholds are between 1 and 3. The root mean square error of approximation (RMSEA) measures the discrepancy between the observed and estimated covariance matrix, and is recommended to be less than 0.10 (Hu & Bentler, 1999). Goodness-of-fit index (GFI) and comparative fit index (CFI) are derived from a comparison of the hypothesized model and the independent model. GFI indicates the overall percentage of observed covariance explained by the estimated covariance and CFI is based on the relative comparison of the fit of the proposed model to the fit of the null model. Both are acceptable when they are between 0.90 and 1 (Van Ittersum, Meulenberg, Van Trijp, & Candel, 2007). Finally, Tucker
Lewis nonnormed fit index (TLI) is an index that is similar to CFI and it is suggested to be .0.90 (Bentler, 1990).

17.3.3 Analysis results 17.3.3.1 Demographics and bidding average Table 17.3 summarizes the sociodemographic information of the participants. The average age of participants was 54, the average household income was US$61,432 dollars, and the average household size was 2.47 people per household. Seventythree percent of our participants were women, 57% of them had at least a college degree, and 56% of them were married. It was also reported that 67% of the sample had a job and 24% of the sample were retired. Compared to the US census data,

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Table 17.3 Summary statistics of respondents’ sociodemographic backgrounds. Characteristics

Description

Mean

Standard deviation

Gender Age

1 if female, 0 if male Age of participants at the time of auction Participants’ annual income in USD 1 if college graduate or higher, 0 otherwise 1 if married, 0 if single Number of people in the household

0.73 54.09

0.44 15.47

61,432 0.57

27,978 0.49

0.56 2.47

0.49 1.53

Annual income Education Marital status Household size

our sample has a higher percentage of females. This is because female household members are more likely to be responsible for shopping than men. The average WTP results and the percentage changes between different rounds are reported in Table 17.4. According to the mean WTP, both conventional and organic peanuts received the highest average WTP, followed by salad, and the average WTP for applesauce was the lowest. Comparing between conventional and organic products, all organic products had significantly higher average WTP. Comparing the change of WTP across different rounds, participants’ WTP increased from round 1 to round 2, when the general information about nanotechnology and nanolabeled products were presented. After given the detailed information from three sources in round 3, participants’ average WTP decreased by approximately 10%. The average WTP for plain-labeled products in round 1 and the average WTP of nanopackaged products in round 3 were similar for all products except for conventional applesauce (increased by 15%).

17.3.3.2 Measurement statistics The questions used to generate the latent constructs are reported in Table 17.5. Preference for prolonging food shelf life (SHELFLIFE) and trust in institutions (TRUST) were measured by three Likert-scale questions. General acceptance of new food technology (TECHACCEPT), environmental and health concerns toward nanotechnology food packaging (CONCERN), and reliance toward government regulation (GOVERNMENT) were measured by four questions. To test the reliability of each latent construct, Cronbach’s alpha values were calculated and reported in Table 17.5. Because of the diversity of questions used for generating SHELFLIFE and GOVERNMENT, their Cronbach’s alpha values were relatively low compared to other three constructs. In addition, the WTP constructs yielded satisfactory Cronbach’s alpha of 0.85, 0.92, and 0.94 for round 1, 2, and 3, respectively, representing reasonable reliability of the constructs (Nunnally & Bernstein, 1978). Furthermore, in order to examine the convergent and discriminant validities of the measurement model, the model fit statistics (Normed χ^2, P value, RMSEA, GFI, CFI, and TLI) were estimated and reported in Table 17.6. Most statistics suggest

Table 17.4 Summary statistics for bids by round. Applesauce Mean WTPs Round 1 Round 2 Round 3 WTP change Round 1
2 (%) Round 2
3 (%) Round 1
3 (%)

Organic applesauce

Peanut

Organic peanut

Salad

Organic salad

1.43 1.78 1.65

1.89 2.17 1.96

2.00 2.18 2.00

2.51 2.59 2.32

1.65 1.92 1.71

2.15 2.31 2.06

24.48 2 7.30 15.38

14.81 2 9.68 3.70

9.00 2 8.26 0.00

3.19 2 10.42 2 7.57

16.36 2 10.94 3.64

7.44 2 10.82 2 4.19

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Table 17.5 The observed indicators for latent constructs and the Cronbach’s alpha. Latent construct

Observed indicators

Scale

Alpha

Preference for prolonging food shelf life (SHELFLIFE)

x1 : Nanotechnology would help me buy in bulk and save money because the food would last longer. x2 : Products have expiration dates, extending the longevity is necessary to me. x3 : I would be very interested in nanotechnology packaging if it greatly extended the shelf life of a highly perishable product (e.g., salad mix). x4 : Governmental (e.g., FDA) regulation and certification of new technology is important to me if it is a component of the food (x1 ). x5 : Governmental (e.g., FDA) regulation and certification of new technology is important to me if the technology is in contact with the food (such as packaging). x6 : Governmental (e.g., FDA) regulation and certification of new technology is important to me if it is used in the preparation/processing of the food products. y1 : I am skeptical about adopting new technologies, because in the past some of them have proven risky for the health. y2 : New technologies in food scare me, so I avoid them.

1 5 Strongly disagree 5 5 Strongly agree

0.64

1 5 Strongly disagree 5 5 Strongly agree

0.91

1 5 Strongly agree 5 5 Strongly disagree

0.74

Trust in Institutions (TRUST)

General acceptance of new food technology (TECHACCEPT)

(Continued)

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Table 17.5 (Continued) Latent construct

Environmental and health concerns toward nanotechnology food packaging (CONCERN)

Reliance toward government regulation (GOVERNMENT)

Observed indicators y3 : I do not want to be the first to try a new technology. y4 : I would wait until a technology is proven to be safe before I adopt it. y5 : Nanoparticles leaching into the food. y6 : Impact on health. y7 : Impact on environment. y8 : Lack of research on the long-term effects. y9 : Governmental policies restricting the use of nanotechnology in food production are good for the human health. y10 : The government should carefully monitor the correct use of Nanotechnology in the medical, agricultural and food sectors. y11 : FDA approval is important to me. y12 : The government should establish a regulatory system to regulate nanotechnology, like what is now done for biotechnology.

Scale

Alpha

1 5 Not concerned 5 5 Extremely concerned

0.88

1 5 Strongly disagree 5 5 Strongly agree

0.67

that the model fit the data reasonably well (e.g., TLI: 0.92
0.95, RMSEA: 0.05
0.06), except GFI estimates (0.80) were lower than the normal threshold, which might occur when having relatively few (,250) participants. Next, the complete SEM, shown in Fig. 17.3, was estimated for each auction round. During the estimation, the errors of indicators for WTP construct (average WTP for each product) were allowed to correlate to ensure the model fit (additional analysis revealed that conclusions were not affected without correlating the WTPs). According to Table 17.6, the fit of complete model was reasonable (e.g., for round 2, RMSEA 5 0.06, GFI 5 0.80, CFI 5 0.95, TLI 5 0.94). While the measurement statistics for each round were acceptable in all three rounds, the statistics improved from round 1 to round 3.

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Table 17.6 Goodness-of-fit indices.

Measurement model Round 1 Round 2 Round 3 Structural model Round 1 Round 2 Round 3

Normed χ2

P

RMSEA

GFI

CFI

TLI

1.37 1.28 1.26

.00 .00 .00

0.06 0.05 0.05

0.81 0.81 0.82

0.93 0.95 0.96

0.92 0.95 0.95

1.41 1.33 1.32

.00 .00 .00

0.07 0.06 0.06

0.80 0.80 0.80

0.92 0.95 0.95

0.91 0.94 0.94

17.3.3.3 Model estimates The estimated coefficient, standard error, along with the standardized coefficient of the causal relationships between latent construct are reported in Table 17.7. Due to the fact that only WTP constructs vary across the three rounds of auction, the results for hypothesis H17.1 to H17.4 were consistent across the three rounds. Those hypotheses were statistically supported as follows: while participants’ preference for prolonging food shelf life (SHELFLIFE) increased their general acceptance of new food technology (TECHACCEPT), it reduced their environment and health concerns toward nanotechnology food packaging (CONCERN); the level of trust in institutions (TRUST) had a significantly positive impact on both environmental and health concern about nanotechnology food packaging (CONCERN) and reliance toward government regulation (GOVERNMENT). The correlations tested in H17.5 to H17.7, as the major hypotheses we are testing, varied by auction rounds. For H17.5, the acceptance level of new food technology had an insignificant effect on WTP in round 1 (when bidding for products with that are not labeled as nanopackaged, and no information was provided) and round 3 (when bidding for nanopackaged products after both general and detailed information were provided). However, in round 2 when only general information about nanotechnology was presented, the general food technology acceptance had a significant positive effect on the WTP for nanopackaged products. Also, in round 2, TECHACCEPT served as a mediator between SHELFLIFE and WTP, indicating people’s preference for longer shelf life indirectly increased their WTP for nanopackaged products. For H17.6, the causal relationship between concern about nanotechnology and WTP was not statistically significant in the first round. However, starting the second round, results showed that the level of environmental and health concerns significantly decreased participants’ WTP, and this negative relationship was even more evident in round 3 when participants received both the general and detailed information about nanotechnology. Again, considering rounds 2 and 3, CONCERN acted as the mediator between WTP and SHELFLIFE/TRUST, which established two indirect relationships: stronger preference for prolonging shelf life decreased the environmental and health concerns about nanopackages and led to an increase in WTP for nanopackaged food,

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Figure 17.3 Complete SEM model.

and stronger trust in institutions increased participants’ environmental and health concerns about nanopackages and thus decreased their WTP. For H17.7, in round 1, the supportiveness of government regulation restricting the use of nanotechnology directly led to a decrease in the WTP for the food products without nanopackage labels. Interestingly, this negative effect diminished for nanopackaged food products in rounds 2 and 3. A possible explanation is that the relationship tested in H17.7 is diluted by the dominance effect of other constructs (CONCERN and TECHACCEPT) after participants received the information. Nevertheless, in round 1, trust in institutions (e.g., FDA) indirectly decreased the WTP for food products with plain labels.

17.3.4 Discussion Several implications can be drawn from the SEM model results. First, in round 1, the only supported hypothesis was H17.7. Consumers with a higher reliance on

Table 17.7 SEM estimation results for each bidding round.

H17.7: GOVERNROLE ! WTP H17.6: CONCERN ! WTP H17.5: TECHACCEPT ! WTP H17.4: TRUST ! GOVERNROLE H17.3: TRUST ! CONCERN H17.2: SHELFLIFE ! CONCERN H17.1: SHELFLIFE ! TECHACCEPT

Round 1

Coefficient (S. E.) Round 2

Standardized coefficient Round 2

Round 3

Round 1

2 0.14 a (0.08) 2 0.01 (0.04) 2 0.05 (0.04) 0.48 (0.10)

0.12 (0.09) 2 0.25 (0.12) 0.15 (0.08) 0.46 (0.10)

0.03 (0.09) 2 0.31 (0.15) 0.09 (0.07) 0.47 (0.10)

2 0.10 0.01 2 0.05 0.58

0.06 2 0.12 0.10 0.54

0.02 2 0.15 0.06 0.56

0.25 (0.09) 2 0.29 (0.14)

0.25 (0.09) 2 0.29 (0.14)

0.25 (0.09) 2 0.29 (0.14)

0.32 2 0.25

0.33 2 0.25

0.32 2 0.26

0.90 (0.28)

0.89 (0.28)

0.92 (0.28)

0.53

0.54

0.54

Round 3

Notes: aa single asterisk ( ), double asterisks (  ), and triple asterisks (   ) denote significance at 5%, 1%, and 0.1% levels, respectively. The significance of the bold value here in the estimate of round 1, H17.7 is one star, ‘ ’.

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government regulations were willing to pay less for plain-labeled food products. It is possibly because cautious consumers pay more attention to labeling information when making purchases, and especially government issued labels (e.g., USDA organic). Since the experimental products in round 1 were plain-labeled, the more reliance participants had on governmental regulations, the lower participants’ WTP for the plain-labeled products. This implication is consistent with the previous findings that cautious consumers who seek government issued labels are more aware of and concerned about their wellbeing by engaging in behaviors that maintain a good state of health (Michaelidou & Hassan, 2010). In this case, they might relate the missing label information with potentially negative outcomes. The study also suggests that for nanopackaged food products, general information about nanotechnology triggers technology accepters’ higher WTP (H17.5). This is a straightforward relationship, according to survey response, technology accepters (1) were less skeptical about new technologies, (2) did not intend to avoid new technologies, (3) preferred to be the first to try new technologies, and (4) would not wait until a technology is proven to be safe before adopting. However, general information about nanotechnology dampened participants’ purchase intention if they had more environmental and health concerns (H17.6), possibly because of the negative statement made in the general information that “there is uncertainty regarding how nanomaterials may interact with human health and the environment.” It has been proved by previous studies that information on potential health and environmental risks significantly decreases consumer WTP for technologically modified products (Ronteltap et al., 2007; Roosen et al., 2011). This is especially true for food products, and consumers’ concern about food hazards are important determinants of their acceptance (Frewer et al., 2011; Miles & Frewer, 2001). Furthermore, nanopackaged food products along with general information decreased the participants’ reliance on governmental regulation (H17.7), partially led by the dominant effects of technology acceptance and environmental and health concerns. After giving the specific and detailed information of nanotechnology from private industry (positive), environmental agency (negative), and government (neutral), the average WTP decreased compared to that when only general information was provided. This reduction was majorly contributed by the negative statement from the environmental group. According to the estimation, the effect of environmental and health concerns became the only significant construct that impacted WTP (H17.6) in round 3. Aligned with the 10% decrease in WTP in round 2, we can conclude that once consumers have comprehensive understandings about nanotechnology application in food, the inevitable concerns about environment and health will lead to a significant reduction in their WTP for nanopackaged food products. Similar results have also been proven by previous studies. Roosen et al. (2011) studied consumer WTP for food produced with nanotechnology using information on health, society, and environment, and their study revealed that when all information is given, health information dominates and significantly decreases WTP. Macoubrie (2006) investigated various public concerns about nanotechnology and found that “long-term health effects” and “environmental footprint” were the two dominant concerns. Yue, Zhao, Cummings, and Kuzma (2015a) and Yue,

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Zhao, and Kuzma (2015b) also stated that the consumer might not reject nanofood outright as long as safety is ensured. Finally, shelf life, as the major benefit of nanopackaging, had a significant indirect effect on consumers’ WTP. In round 2, after general information was provided, participants were willing to pay a significant price premium on nanopackaged food products compared to plain-labeled food products in round 1. Given that the general information about nanotechnology was neutral, we can conclude that this price premium was largely contributed by the benefits that nanopackaging can provide in prolonging the shelf life of food products. In addition, based on the SEM estimation results, the more participants cared about prolonging product shelf life, the more acceptance they had toward general food technologies (H17.1) and the less they were concerned about environmental and health risks caused by nanopackaging (H17.2). Thus both the higher level of acceptance for new technology and the lower level of concern about environment and health passed on to an increase in consumer WTP (H17.5 and H17.6).

17.4

Conclusion and implications

Many food companies are developing nanotechnology-modified food packaging and it is critical to understand the informational and attitudinal factors that influence public acceptance of nanopackaging. This chapter first reviews the market situation for nanotechnology in the food packaging industry, including the benefits and potential risks of nanotechnology application in the food industry, the market trend for nanotechnology in food, consumer acceptance of nanotechnology in food, and the possible factors affecting consumer acceptance. Then we employed SEM to estimate experimental auction data to examine the major factors that influence public acceptance of nanopackaged food products and investigate the effect of information on consumer WTP. Three rounds of auctions were conducted with more information given in each round, and seven hypotheses were tested. Three implications can be drawn from our estimation results of the case study. First, from the standpoint of policy makers, and learning from the past genetic modification debates, the ignorance of health and environmental concerns may hinder public acceptance of new food technology. Thus it is extremely important to implement adequate regulations to ensure the safety standard of nanotechnology’s application in food products. Second, learning from the experience with GM food, it is also important to take public preferences of nanotechnology into account at the early stage of commercialization. Our results show that consumers’ WTP for nanopackaged food products are not influenced by the level of reliance on government regulation, but are affected by their attitude toward new technology and associated environmental/health concerns. Therefore during the process of designing regulatory standards for nanotechnology’s application in the food industry, it is crucial to ensure the transparency of any decision-making process by increasing communication with consumers in the

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early stages. Our result proved, again, that the formation of public response to emerging technologies is an integral part of developing a successful research and governance strategy with regard to such technologies (Ward & Barnes, 2001). Lastly, in order to achieve the market success for nanopackaged food products, an appropriate labeling and pricing strategy should be adopted. In our study, after gaining general information about nanotechnology, participants were willing to pay more for nanopackaged food products with the label indicating longer shelf life compared to the plain-labeled food products. However, once participants read detailed information about nanotechnology’s application in food, the price they were willing to pay for nanopackaged products decreased. Therefore although it is preferable for food products to have prolonged shelf life with nanopackaging, the right labeling information and acceptable price ranges are also determinant factors in consumer acceptance. As a result of these implications, public acceptance of nanopackaged food products will be largely dependent upon how transparent the industry is and how the government can protect them from uncertain hazards. Aligned with Duncan (2011), industry and government’s openness regarding what they are doing and why they are doing it regarding nanotechnology will go a long way toward assuaging public fears about nanopackaging.

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Index

Note: Page numbers followed by “f” and “t” refer to figures and tables, respectively. A Acetobacter xylinum, 552 Achyranthes bidentata polysaccharides (ABPs), 311 Acinetobacter baumannii, 264 Acrylamide, 428 Activated carbon, 116
120 adsorption isotherm equations for, 118
119 applications in food industry, 119
120 crystalline structure of, 116
117 porous structure of, 117
118 Active food packaging nanoencapsulated bioactive components for. See Nanoencapsulated bioactive components for active food packaging Active ingredients delivery of, 213 encapsulation of, 213 Active packaging, 384, 493
496, 501, 503, 518 Adsorbent clays, 109
112 Adsorption, 6, 107
108, 108f Adsorption isotherm equations for active carbon, 118
119 Adulteration/spoilage of food products carbon nanomaterial-based nanosensors, 471
481 carbon nanofibers (CNFs), 480
481 carbon nanotubes, 471
477 graphene and its derivatives, 477
480 magnetic nanoparticles-based nanosensors, 481
483 metal and metal oxide nanoparticles-based nanosensors, 460
471 gold nanoparticles, 461
467 silver nanoparticles, 467
471

nanofiber-based nanosensors, 483
485 nanoparticles/nanofibers for checking, 16
17 A-fetoprotein (AFP), 142 Aflatoxin B1 (AFB1), 429, 438, 441 Agglomeration, 56, 398
399 Agrofood processing, 73
74, 96, 97t Agroindustrial biomass, nanocellulose production from, 546
551 production of nanocellulose from soybean straw by enzymatic method, case study, 549
551 Alginates, 221
222, 559 Alkaline pretreatments, 548
549 Alkaloids, 495
496 Allium cepa, 272 α, β-thuyone, 500
501 α-lactalbumin (α-LA) nanoparticles, 347
349 α-linolenic acid (ALA), 175
176 α-phellandrene, 500
501 α-tocopherol, 502
503, 509 nanocapsules, 517
518 nanoemulsion, 214 4-Aminophenol, 273
274 Aminopropyltrietoxysilane, 390
391 Amomum villosum, 264
265 Amorphous polymers, 624
626, 625f Amylose nanohelices, inclusion complexation within, 316
317 Anodic stripping voltammetry (ASV), 423
426 Anthocyanin nanocomplexes (ACNs), 514
517 Anthocyanins, 366 Antimicrobial influence of metal nanoparticles in food packaging materials, 400
403

736

Antimicrobial influence of metal nanoparticles in food packaging materials (Continued) fungi (molds/yeasts), 402
403 impact of metal NPs on G 1 / 2 bacteria, 401
402 parasites/viruses, 403 Antimicrobial packaging, 381 nanoscale metal oxides in, 383
390 copper oxide-based nanomaterials, 384
385 gold and silver nanoparticles, 389
390 magnesium oxide-based nanoparticles, 388
389 titanium oxide-based nanomaterials, 385
387 zinc oxide-based nanomaterials, 387
388 Antimicrobial peptides (AMPs), 502 Antimicrobial properties, effect of bioactiveloaded nanocarriers on, 503
507 Antioxidant properties, effect of bioactiveloaded nanocarriers on, 508 Application of nanofluids in thermal processing of food products, 56
58 Application of nanotechnology in food industry, 705
707 benefits, 706 potential risks, 706
707 in food ingredients, 8
13 green synthesis of metal nanoparticles, 10
11 nanodelivery systems, enhancing the bioavailability of nutrients by, 12
13 nanoemulsions and nanosized ingredients, 8
10 nanoencapsulation, 11
12 in food processing, 2
8 nanoadsorbents and nanoporous materials, 6
7 nanofiltration (NF), 5
6 nanofluid thermal processing, 2
4 production of food nanomaterials by specialized equipment, 7
8 for improving food quality and packaging, 13
19 metal nanoparticles as antimicrobial agents, 13
14

Index

nanobased aptasensors for detection of food contaminants, 14
16 nanoencapsulated bioactive components, 17
18 nanoparticles/nanofibers for checking adulteration/spoilage of food products, 16
17 reinforced nanocomposites, 18
19 Asia, food regulation in, 688
689 Aspergillus flavus, 429 Atomic force microscopy (AFM), 135t, 224, 398, 442
443, 593, 602
604, 603f Atomization, 179 Auger electrons, 595 Australia and New Zealand, food regulation in, 688 Average diameters, 606 2,20 -Azino-bis(3-ethylbenzothiazoline-6sulfonic acid) (ABTS), 346
347 B Bacillus cereus, 463
467, 503 Bacillus subtilis, 361
362, 469 Backscattered electrons (BSE), 595 Bacterial NC (BNC), 552 Ball milling, 186
190, 187f Banana (Musa acuminata), 469 Barrier properties, effect of bioactive-loaded nanocarriers on, 512
513 Becker
DeGroot
Marschak (BDM) mechanism, 714 1,2-Benzenedicarboxylic acid, bis(2-methyl propyl) ester, 469 β-carotene, 164 β-lactoglobulin (BLG), 142, 353 Beverages, 229 Bicontinuous cubic phases. See Cubosomes Bilosomes, 309 Binary (double) emulsions, 209
210 Bioactive compounds, 39
40, 58, 61, 494
496, 495f Bioactive delivery systems, 306 Bioactive ingredients, 280
294 carotenoids, 287
288 classification and the structure, 287 in food, 287 health benefits and stabilities, 288 essential oils, 292
294

Index

classification and the structure, 292
293 in food, 294 health benefits and stabilities, 294 minerals, 290
292 classification and the structure, 290 in food, 290
291 health benefits and stabilities, 291
292 polyphenols, 280
286 classification and the structure, 280
281, 282t in food, 281
284 health benefits and stabilities, 284
286 vitamins, 288
290 classification and the structure, 289 in food, 289 health benefits and stabilities, 289
290 Bioactive-loaded nanocarriers applied in active food packaging, 497
503 carotenoids, 500 essential oils (EOs), 500
501 peptides and antimicrobial agents, 502 phenolic compounds, 497
500 vitamins, 502
503 Biobased nanodelivery systems, 345 Biofunctionalized FETs, 432 Biogenic amines, 428 Biopackaging, 18
19, 533 Biopolymer-based particles, 168 Biopolymeric particles, 183 Biopolymers, 13
14, 320, 519t, 618 in food packaging, 379
383 green synthesis of metal nanoparticles by, 10
11, 271
274 Bioreceptors, 419
422 surface functionalization of nanomaterials with, 420
422 Bis(2,4,6-trichlorophenyl) oxalate (TCPO)
hydrogen peroxide
fluorescein system, 461
463 Blend electrospinning, 174 Bombyx mori silk, 268 Botrytis cinerea, 402
403 Bovine serum albumin (BSA) nanoparticles, 347, 354
356, 362
363 Bragg law, 628 Brazil, food regulation in, 689 Brettanomyces bruxellensis, 479 Bright field microscopy, 588
589

737

Brijs 30, 215 Brownian motion, 606 Bubble-propelled micromotors, 445 Bu¨chi Nano Spray Dryer B-90, 180 Butea monosperma, 264
265 Butter, 624 C Calcium, 291 Camellia sinensis, 264, 281
282 Camphor, 500
501 Canada, food regulation in, 688 Candida albicans, 268 Capillary-based systems, 182 Carbohydrate nanoparticles, 674
675 Carbonaceous materials, instrumental methods for analysis of, 135t Carbon and semiconductor nanomaterials, 429
430 Carbon materials, 14, 381
382 Carbon nanofibers (CNFs), 480
481 Carbon nanohorns (CNHs), 418 Carbon nanomaterial-based nanosensors, 471
481 carbon nanofibers (CNFs), 480
481 carbon nanotubes, 471
477 graphene and its derivatives, 477
480 Carbon nanomaterials, 418
419 Carbon nanotubes (CNTs), 14
16, 130, 416
417, 432, 471
477 Carboxymethyl cellulose (CMC) coatings, 535
536 4-Carboxyphenyl layer, 480
481 Carcinoembryonic antigen (CEA), 142 Cardamom fruits, 264
265 Carotenoids, 287
288, 500 classification and the structure, 287 in food, 287 health benefits and stabilities, 288 Carrier materials used for nanoencapsulation of bioactive compounds, 318
325 combinations of different nanocarrier materials, 325 cyclodextrins, 323 lipids, 322
323 polysaccharides, 321
322 proteins, 319
321 surfactants, 323
325 Carvacrol, 500
501

738

Cascading, 186
188, 188f Cassava starch-based films, 500 Cataracting, 186
188, 188f Cation exchange capacity (CEC), 109
112 Cationic polysaccharides, 322 Cavitation phenomena, 169 Cellobiose, 543
545, 546f Cellulose, 543
545 Cellulose nanocrystals (CNCs), 549 Cellulose nanofibers (CNFs), 551
552 Cellulose nanofibrils (CNFs), 549 Chemical exfoliation (CHE), 131t Chemical vapor deposition (CVD), 130, 131t Chitosan, 221
222, 236
237, 269
270, 560, 617
618 Chitosan hydrochloride (CHC), 508 Chitosan nanoparticles, 560 Chloroamphenicol (CAP), 433 1,8-Cineole, 500
501 Cinnamaldehyde, 503 Cinnamaldehyde nanoemulsions-loaded films, 503 Cinnamon EO (CEO) nanoliposomes, 517 Citrus limetta, 272
273 Citrus limon, 272
273 Clay activation by acid attack, 116f montmorillonite (MMT) nanoclay, 391
393 various structures of, 392t Clay minerals, 109
116, 391 adsorbent clays, 109
112 classification of, 111t montmorillonite, modification of, 113
116 inorganic modification, 114
116 organic modification, 113
114 properties of clay mineral groups, 112t structure of, 109 Clean-in-place (CIP) procedure, 73 Clofazimine, 350
351 Coacervation, 220, 305
306, 351
358 Coarse-grained Monte Carlo simulation, 353 Coaxial electrospinning, 174 Coaxial electrospraying, 175
176 Cochlospermum gossypium, 272 Colloidal probe atomic force microscopy, 637
638 Colocasia esculenta L., 189
190

Index

Color and sensorial aspects, effect of nanocrystals on, 237
238 Colorimetric biosensors, 433
436 Comparative fit index (CFI), 718 Complexation/conjugation with proteins, 315
316 Compound light microscope, 588
589 CONCERN, 710
711, 715 Confocal laser scanning microscopy (CLSM). See Laser scattering confocal microscopy (LSCM) Consumer acceptance of food nanotechnology, 707
708 factors affecting, 708
710 environmental and health concern, 708
709 general attitudes toward new technology, 708 governmental regulation, reliance on, 710 preference for prolonging food shelf life, 709 trust in institution, 709
710 Consumer expectations and attitudes towards nanomaterials in foods, 23
25 Consumer preference and information provision in nanopackaged food, case study, 710
727 demographics and bidding average, 718
719 measurement statistics, 719
722 model estimates, 723
724 research material and methodology, 714
718 auction design, 714
715 auction experiment, 714 auction procedure, 715
716 participants, 714 products, 714 structural equation model, 717
718 theoretical framework and proposed hypothesis, 710
713 Copolymers, 18
19 Copper nanoparticles, 384
385 Copper oxide-based nanomaterials, 384
385 Coulter counter, 613 Covalent functionalization, 137 Critical speed, 186
188 Cronbach’s alpha values, 719
722, 721t

Index

Cryo-TEM method, 599
600 Cryomicroscopy, 598
600 Cryptosporidium parvum, 437 Crystalline NC (CNC), 545, 549, 551
552 Crystalline polymers, 625
626, 625f Crystallinity and phase transition in food nanomaterials, 621
633 glass transition temperature in polymerbased nanoparticles, 624
627 in lipid-based nanoparticles, 621
624 measurement, 627
633 differential scanning calorimetry (DSC), 631
633 X-ray diffraction (XRD), 627
631 Cubic phases, 631 Cubosomes, 309
312 Curcuma longa, 270 Curcumin, 270, 347 Cyclic oligosaccharides. See Cyclodextrins Cyclodextrins, 323 inclusion complexation within, 316
317 Cystoseira baccata, 266 D Dairy processing, nanofiltration (NF) in, 91
94 concentration and demineralization of whey, 91
92 demineralization of ultrafiltration
whey permeate, NF for, 92
93 lactic acid recovery by nanofiltration, 93
94 Dalbergia coromandeliana, 268 D-aminoacids (DAAs) biomarkers, 416
417 D-anhydroglucose, 543
545 Daphnia, 125 Dark field microscopy, 589
590 Debye length, 619 Debye parameter, 607
608 Decontamination, 125 Degree of polymerization (DP), 543
545 Dehumidified air spray drying, 181 Derivative thermogravimetry (DTG), 397 Dermal exposure, 667
668 Desolvation/nanoprecipitation/solvent displacement, 346
351 Desolvation. See Nanoprecipitation Differential centrifugal sedimentation, 616
617

739

Differential interference contrast method, 590 Differential pulse voltammetry (DPV), 140
141, 423
426 Differential scanning calorimetry (DSC), 135t, 397, 631
633, 632f Differential thermal analysis (DTA), 397 Dioscorea alata L., 189
190 2,2-Diphenyl-1-picrylhydrazyl (DPPH), 497
500, 508 Diphenyl phthalate (DPP), 445
446 1,2-Dipalmitoyl-sn-glycero-3phosphocholine (DPPC), 599
600 1,2-Dipalmitoyl-sn-glycero-3phosphoglycerol (DPPG), 599
600 2,2-Diphenyl-1-picrylhydrazyl (DPPH), 346
347 Direct hexagonal phases, 631 Dispersed phase, 191
192 5,50 -Dithiobis-(2-nitrobenzoicacid) (DTNB), 441 Dithiothreitol (DTT), 349
350 DNAzyme, 433 Dodecyl trimethyl ammonium bromide (DTAB), 172
173 Donnan effect, 5 Doppler effect, 620 dsDNA, 433
437 Dual-channel microfluidization, 163
164 Dynamic light scattering (DLS), 613f, 614
615, 667 E Edible coating materials, use of nanolaminates in, 232
234 Electrical characterization, 135t Electrochemical biosensors, 15
16, 422
423 Electrochemical nanobiosensors for food safety and control, 423
432 field-effect transistor-based biosensors, 432 with integrated nanomaterials and hybrid nanostructures, 423
430 carbon and semiconductor nanomaterials, 429
430 metallic nanoparticles, 423
429 nanopore membranes, electrochemical biosensing with, 430
431

740

Electrodialysis (ED), 190 Electrohydrodynamic devices, 171
177 solution blowing, 176
177 Electron energy loss spectroscopy (EELS), 596 Electron microscopy (EM), 593
602, 667 analysis of isolated food nanoparticles by, 596
600 environmental scanning electron microscopy, 601
602 scanning electron microscopy, 593
596 transmission electron microscopy, 596 types of particles and radiations obtained in, 595f Electrophoretic deposition (EPD), 130 Electrophoretic mobility, 621 Electrospinning, 171, 172f, 230, 483 Electrospinning-based nanosensors, 485 Electrospraying, 175 Electrospun nanofibers, 174 Emulsification
diffusion method, 211 Emulsifiers, 211
212 Emulsion, defined, 209
210 Emulsion electrospinning, 174
175 Encapsulation methods for nanodelivery of bioactive compounds, 294
318 coacervation, 305
306 complexation/conjugation with proteins, 315
316 cubosomes and hexosomes, 309
312 inclusion complexation within cyclodextrins and amylose nanohelices, 316
317 nano spray drying, 304
305 nanoemulsification, 295
304 nanoliposomes and niosomes, 306
309 nanoprecipitation, 317
318 nanostructured lipid carriers (NLCs), 313
314 solid lipid nanoparticles/nanocarriers (SLNs), 312
313 Encapsulation process, 174
175, 179
180, 186 Energy-dispersive X-ray spectroscopy (EDX), 596 Entrapment/encapsulation efficiency (EE), 220
221, 224 Entropy generation, 55
56

Index

Environmental scanning electron microscopy (ESEM), 593, 601
602 analysis of nanoparticles by, 601
602 Enzyme-linked immunosorbent assay (ELISA), 420, 437
438 Epigallocatechin gallate (EGCG), 175
176, 227
228, 508, 514
517 Epitaxial growth (EPG), 131t Equilibrium swelling analysis, 135t Equivalent sphere diameter, 612 Escherichia coli, 58, 264
265, 268
269, 361
362 Essential oils (EOs), 292
294, 500
501 classification and the structure, 292
293 in food, 294 health benefits and stabilities, 294 ETEM, 593 Ethyl cellulose and a dipolymeric carrier (ECMC), 317 Ethylene vinyl alcohol (EVOH), 18
19 Eudragit, 317 Eugenol, 500
501 Europe, food regulation in, 682
688 European Community, 405 Exergy efficiency, 55
56 Exonuclease I (Exo I), 426
428 F Fabricated nanoemulsions, 170
171 Face-centered cubic (fcc) crystalline structure, 262 Fat-soluble vitamins, 289 Ferulago angulata, 508
512 Ferulago angulata EO (FEO) nanocapsules, 517 Fiber optic probe-based localized SPR biosensor (FOLSPR), 440
441 Fickian diffusion, 226 Field-effect transistor-based biosensors, 423, 432 Field emission scanning electron microscopy, 135t Field flow fractionation (FFF) chromatography, 667 Flavonoids, 281, 283t Flourensia cernua, 234 Fluorescein-loaded porous silica NPs, 437 Fluorescence microscopy, 592, 592f

Index

Fluorescent biosensors, 436
438 Food and Drug Administration (FDA), 292 Food bioactives, 291
292, 306 Food ingredients, 8
13 green synthesis of metal nanoparticles, 10
11 nanodelivery systems, enhancing the bioavailability of nutrients by, 12
13 nanoemulsions and nanosized ingredients, 8
10 nanoencapsulation of, 11
12 Food packaging, 13
19 metal nanoparticles as antimicrobial agents in, 13
14 metal nanoparticles in, 381
383 nanobased aptasensors for detection of food contaminants, 14
16 nanoencapsulated bioactive components for, 17
18 nanoparticles/nanofibers for checking adulteration/spoilage of food products, 16
17 reinforced nanocomposites for, 18
19 solid-state additives in, 381 Food packaging materials antimicrobial influence of metal nanoparticles in, 400
403 fungi (molds/yeasts), 402
403 impact of metal NPs on G 1 / 2 bacteria, 401
402 parasites/viruses, 403 metal nanoparticles’ influence on different properties of, 393
400, 394f barrier properties, 394
396 mechanical properties, 396
397 morphology, 398
399 reactions/interactions, 399
400 thermal properties, 397 Food products application in thermal processing of, 56
58 nanoadsorbents and nanoporous materials for the food industry, 6
7 nanofluid thermal processing of food products, 2
4 Food Standards Australia New Zealand (FSANZ), 688 Fo¨rster resonance energy transfer (FRET)based method, 438

741

Fouling, 56 Fourier-transform infrared spectroscopy (FTIR), 135t, 399 Fruit juice and plant extract processing, application of nanofiltration in, 77
87 Fumonisin B1 (FB1), 446 Functional barrier (FB), 405 Functional foods, 305
306, 325 nanodelivery of bioactive compounds in, 325
326 Functionalization, 133
136 Fungi (molds/yeasts), 402
403 Fungi and yeasts, 267 Fusarium solani, 264 G Gambogenic acid (GNA), 311 Garlic oil, 503 Gas chromatography (GC), 667 Gas chromatography-mass spectrometry (GC-MS), 461
463 Gastrointestinal tract (GIT), 286, 315, 346
347, 359, 368 Gelatin, 559
560 Gelatin/ZnO nanorod/clove oil nanocomposite films, 535
536 Gelliform phases, 630
631 Generally Recognized as Safe (GRAS), 2, 208, 292, 318
320, 387 Genetic modification (GM) technology, 24
25 Geraniol, 294, 500
501 Gibbs energy, 604
605 Gibbs free energy, 231
232, 625
626 Ginger EO (GEO), 507 Ginkgo biloba, 538 Glass transition temperature, 624 in polymer-based nanoparticles, 624
627 Glassy carbon electrodes (GCE), 416
417 Glassy state, 624 Gliadin nanoparticles, 349
350 Glucose, 141
142, 474 Glucose oxidase (GOx), 419
420 Glutaraldehyde, 598 Glutaraldehyde cross-linking, 347 Glyceryl monooleate (GMO), 312 “Glycocode” effect, 603
604 Gold and silver nanoparticles, 389
390

742

Gold
chitosan nanocomposites, 269 Gold gate electrode, 432 Gold nanoparticles, 15, 262
263, 416
417, 461
467 Goodness-of-fit index (GFI), 718, 723t Gordon Taylor formula, 627 GOVERNROLE, 710
711, 715 Grammosciadium ptrocarpum Bioss. EO (GPEO), 501, 517 Gram-negative bacteria, 268 Graphene, 126
128 application in the food industries, 139
142 applications in the food nanosensors, 140
141 evaluation of food composition, 141
142 and its derivatives, 477
480 pros and cons of techniques used for production of, 133t structural model of, 127f synthesis methods, 131t, 132f toxicity of, 142
144 Graphene/graphene oxide-based nanocomposites, 138
139 in situ polymerization, 138 layer-by-layer (LbL) assembly, 139 melt mixing, 139 solution blending, 138
139 Graphene oxide (GO), 128, 418
419, 429, 477, 479 procedures of synthesis of, 134t reduction of, 127f, 129f, 131t structural model of, 127f toxicity of, 142
144 Graphene quantum dots (GQDs), 437
438, 446 Graphite family, 126
144 application of graphene in food industries, 139
142 applications in the food nanosensors, 140
141 evaluation of food composition, 141
142 functionalization, 133
137 future trends, 144 graphene, 126
128 graphene/graphene oxide-based nanocomposites, 138
139

Index

in situ polymerization, 138 layer-by-layer (LbL) assembly, 139 melt mixing, 139 solution blending, 138
139 graphene oxide, 128 properties and characterization, 130
133 reduced graphene oxide, 128
129 synthesis methods, 130 toxicity of graphene and graphene oxide, 142
144 Green chemistry, 257
259, 258f Green synthesis of metal nanoparticles by plant extracts and biopolymers, 10
11 gold nanoparticles, 262
263 green metal nanoparticles, applications of, 271
274 living organisms and biomolecules, synthesis of metal nanoparticles using, 263
271 fungi and yeasts, 267 natural compounds, 267
271 plants and algae, 263
266 silver nanoparticles, 261
262 Green tea (Camellia sinensis), 264 Guar gum (GG)
gold nanocomposite, 272
273 Gum kondagogu (Cochlospermum gossypium), 272 H Hairpin aptamer (HA), 426 Hancornia speciosa latex (HSB), 272 Heat exchangers, application of nanofluids in, 45
56 agglomeration and fouling, 56 entropy generation and exergy efficiency, 55
56 heat transfer enhancement by nanofluids, 46
51 pressure drop and pumping power, 51
53 thermal performance factor and effectiveness of heat exchangers, 53
55 Heat flux DSC, 631 Heat transfer coefficient (HTC), 2
4, 39, 50
51 Hevea brasiliensis, 264 Hexagonal phases, 631 Hexosomes, 309
312

Index

High-performance liquid chromatography (HPLC), 517 High-pressure (HP) techniques, 162
168 HP homogenization (HPH), 165
168 HP homogenizer, 165
168 microfluidizert homogenization process, 162
165 High-resolution Transmission electron microscopy (HRTEM), 135t Higuchi equation, 226 Histamine, 428
429 Homogenization valve, 167f Horseradish peroxidase (HRP), 142, 437
438 HRPanti-AFP (HRP-anti-AFP) conjugates, 142 Hydrocolloids, 212 Hydrodynamic chromatography (HDC), 667 Hydroxypropyl methylcellulose (HPMC), 507, 513 Hydroxytyrosol, 429
430 Hypromellose acetate succinate (HPMCAS), 350
351 I Image contrast, 598 Indigofera tinctoria, 265
266 Induced coupled plasma (ICP)-MS, 667 Inductively coupled plasma mass spectrometry (ICP-MS), 601
602 Ingestion, 669
670 Inhalation, 668
669 Inorganic nanomaterials used in nanocomposites for food packaging, 534
543 nanoclays as polymer reinforcement fillers, 539
543 oxides used in nanocomposites, 534
539 silicon dioxide (silica), 537
538 titanium dioxide, 536
537 zinc oxide, 535
536 Inorganic nanoparticles, toxicity of, 675
676 International Union of Pure and Applied Chemistry (IUPAC), 117
118 Inverse hexagonal phases, 631 Ipomea batatas L., 189
190 3-Isocyanatopropyltriethoxysilane, 390
391

743

Isolated food nanoparticles, analysis of by electron microscopy, 596
600 Isomorphous substitution, 112 Isothermal titration calorimetry (ITC), 353
354 J Jatropha gossypifolia, 468
469 Joint Committee on Powder Diffraction Standards (JCPDS), 399 K Kanamycin, 437 Korsmeyer
Peppas semiempirical model, 225
226 L Lactic acid, 481 recovery by nanofiltration, 93
94 Lamellar (anisotrope) phase, 629
630 Lamellar phase, 630
631 Langmuir and Freundlich isotherms, 7, 108 Langmuir model, 120 Laplace pressure, 210 Large deformation measurements, 639 Large unilamellar vesicles (LUVs), 308 Laser Doppler electrophoresis, 620
621 Laser scattering confocal microscopy (LSCM), 593 Latent melting heat, 625
626 Layer-by-layer (LbL) assembly, 139, 230
231, 358
365, 359f nanotubular formation through, 362
365 spherical nanoparticle formation through, 359
362 Layered nonmetal nanomaterials, 390
393 montmorillonite (MMT) nanoclay, 391
393 silicon dioxide nanoparticles, 390
391 Lecithin-stabilized nanoparticles, 350
351 Light scattering techniques, measurement of nanoparticle size by, 610
615 dynamic light scattering (DLS), 614
615 static light scattering, 614 Lignocellulose delignification, 548
549 Limit of resolution of the microscope, 589 Limonene, 500
501 Linalool, 294, 500
501

744

Liosperse 511, 484
485 Lipid-based delivery systems, 322
323 Lipid-based nanoparticles crystallinity and phase transition in, 621
624 Lipid crystallization, 623 Lipid polymorphism, 622 Lipids, 322
323 Lipophilic antioxidant encapsulation, 227 Liposomal delivery systems, 306
307 Liquid and soft nanoparticles, instrumental mechanical assessment of, 634
639 colloidal probe atomic force microscopy, 637
638 large deformation measurements, 639 micropipette technique, 638 oscillatory tests, 635
636 osmotic pressure method, 638
639 Liquid chemical methods, 4 Liquid chromatography (LC), 667 Liquid colloidal systems, 635 Liquid phase exfoliation (LPE), 131t Listeria monocytogenes, 268
269, 503 Loading capacity (LC), 224 Localized surface plasmon resonance (LSPR), 432
436, 438
441, 461 Locust bean gum (LBG) polysaccharide, 272
273 Loss modulus, 635 Low-density polyethylene (LDPE), 535, 543 Low-fat nanoemulsions, 215 Lyophilic colloids, 604
605 Lyophobic colloids, 605 M Macroemulsions, 209 Macropores, 118 Magnesium-gold (Mg-Au) microparticles, 445
446 Magnesium oxide-based nanoparticles, 388
389, 538 Magnetic beads (MBs), 419 Magnetic dispersive solid-phase extraction (MDSPE), 141 Magnetic nanoparticles, 419 Magnetic nanoparticles-based DNA extraction, 482
483 Magnetic nanoparticles-based nanosensors, 481
483

Index

Magnification, 589 Malachite green, 598 Maltese crosses, 591 Man-made micromotors, 444
445 Manothermosonication (MTS), 169 Marangoni effect-powered micromotors, 445 Margarine, 624 Mass spectroscopy (MS), 667 Mastication, 634 Maximum likelihood (ML) method, 718 Mean diameter (MD), 223 Mechanical exfoliation (MCE), 131t Mechanochemical processing (MCP), 387 Melamine, 461
463 Melting temperature, 624 Melt mixing, 139 Membrane-based separation, 93
94 Membrane emulsification, 191
192, 192f Membrane molecular weight cutoff (MWCO), 74, 74f Membrane processes, 87
88, 90f Membrane technology, 190
192 Menthol, 294, 500
501 2-Mercaptoethanol, 349
350 Mesopores, 118 Metal and metal oxide nanoparticles-based nanosensors, 460
471 gold nanoparticles, 461
467 silver nanoparticles, 467
471 Metal nanoparticles (MNPs), 14
15, 381
382, 423
429 green synthesis of by plant extracts and biopolymers, 10
11 fungi and yeasts, 267 gold nanoparticles, 262
263 green metal nanoparticles, applications of, 271
274 natural compounds, 267
271 plants and algae, 263
266 silver nanoparticles, 261
262 and semiconductor nanomaterials, 416
418 Metal nanoparticles as antimicrobial agents in food packaging, 13
14 on different properties of food packaging materials, 393
400, 394f barrier properties, 394
396 mechanical properties, 396
397

Index

morphology, 398
399 reactions/interactions, 399
400 thermal properties, 397 fungi (molds/yeasts), 402
403 impact of metal NPs on G 1 / 2 bacteria, 401
402 layered nonmetal nanomaterials, 390
393 montmorillonite (MMT) nanoclay, 391
393 silicon dioxide nanoparticles, 390
391 nanoscale metal oxides in antimicrobial packaging, 383
390 copper oxide-based nanomaterials, 384
385 gold and silver nanoparticles, 389
390 magnesium oxide-based nanoparticles, 388
389 titanium oxide-based nanomaterials, 385
387 zinc oxide-based nanomaterials, 387
388 parasites/viruses, 403 polymers/biopolymers in food packaging, 379
383 metal nanoparticles, 381
383 solid-state additives, 381 regulation for nanomaterials associated with food contact materials, 405 European Community, 405 US Food and Drug Administration, 405 safety issues of human contact to nanoparticles, 404
405 Metal oxide nanoparticles (MONPs), 14, 381
382, 384 Methylcellulose (MC) films, 502
503 Microcantilever-based biosensors, 443
444 Microchannel-based devices, 182 Microcystin-LR (MC-LR), 442 Microfluidic devices, types of, 182f Microfluidic process, 182
183 Microfluidizert homogenization process, 162
165 Microfluidized nanoemulsions, 164 Microfluidizer, 162
163, 163f Micromotor-based (bio)sensing approaches, 444
446 Micro/nanofibrillated cellulose, 549 Micro/nanofluidic systems, 181
184 Micropipette technique, 638

745

“Milling” techniques, 219 Minerals, 290
292 classification and the structure, 290 in food, 290
291 health benefits and stabilities, 291
292 Minimum bactericidal concentration (MBC), 272 Minimum inhibitory concentration (MIC), 272, 366
368 Ministry of Food and Drug Safety (MFDS), 689 miRNA-215, 436 Mixed metal oxide nanoparticles (MMONPs), 14, 381
382 Mixed metal oxides (MMOs), 383 Molecular-imprinted polymer (MIP)-Au nanodisks, 439
440 Monoacylglycerides, hypothetical phase diagram of, 630f Montmorillonite (MMT), 109
116, 391
393, 539 inorganic modification, 114
116 organic modification, 113
114 Multilamellar vesicles (MLVs), 308 Multiple light scattering (MLS), 224
225 Multiplex planar waveguide fluorescence immunosensor (MPWFI), 438 Multiwall CNTs (MWCNTs), 15
16, 46
48, 51, 418, 471 Musa acuminata, 469 N N-(1-adamantyl) ethylenediamine, 441 Nanoadsorbents, 6
7, 109
144 activated carbon, 116
120 adsorption isotherm equations for, 118
119 applications in the food industry, 119
120 crystalline structure of, 116
117 porous structure of, 117
118 clay minerals, 109
116 adsorbent clays, 109
112 montmorillonite, modification of, 113
116 structure of, 109 graphite family, 126
144 application of graphene in the food industries, 139
142

746

Nanoadsorbents (Continued) functionalization, 133
137 future trends, 144 graphene, 126
128 graphene/graphene oxide-based nanocomposites, 138
139 graphene oxide, 128 properties and characterization, 130
133 reduced GO (rGO), 128
129 synthesis methods, 130 toxicity of graphene and graphene oxide, 142
144 and nanoporous materials for food industry, 6
7 zero-valent iron nanoparticles (nZVI), 120
126 applications in food industry, 121
125 companies active in the production of, 124t reported procedures for the synthesis of, 122t safety and toxicity of, 125
126 Nanobased aptasensors for detection of food contaminants, 14
16 Nanobiocomposites, 13
14 Nanobiosensors for food analysis, 16
17 bioreceptors, 419
422 surface functionalization of nanomaterials with, 420
422 carbon nanomaterials, 418
419 electrochemical nanobiosensors for food safety and control, 423
432 carbon and semiconductor nanomaterials, 429
430 field-effect transistor (FET)-based biosensors, 432 metallic nanoparticles, 423
429 with nanopore membranes, 430
431 future directions, 446 magnetic nanoparticles, 419 metallic nanoparticles and semiconductor nanomaterials, 416
418 micromotor-based (bio)sensing approaches, 444
446 nanomechanical biosensors for food safety and control, 442
444 microcantilever-based biosensors, 443
444

Index

scanning probe microscopy (SPM)based biosensors, 442
443 optical nanobiosensors for food safety and control, 432
442 colorimetric biosensors, 433
436 fluorescent biosensors, 436
438 localized surface plasmon resonance (LSPR)-based biosensors, 438
441 surface-enhanced Raman scatteringbased biosensors, 441
442 transduction mechanisms, 422
423 Nanocellulose (NC), 534, 546, 549, 551 Nanocellulose
alginate composites, 559 Nanocellulose
chitosan composites, 555 Nanocellulose composites with proteins, 559
560 Nanocellulose
polycaprolactone (PCL) composites, 555
559 Nanocellulose
polylactic acid (PLA) composites, 553 Nanocellulose production from agroindustrial biomass, 546
551 production of nanocellulose from soybean straw by enzymatic method, case study, 549
551 Nanocellulose
starch composites, 553
555 Nanoclay families (NCs), 14, 381
382 Nanoclays as polymer reinforcement fillers, 539
543 Nanocoatings, 10 effect of on color changes associated with shelf life, 237 on textural changes, 236
237 on the physicochemical properties of food, 235
236 Nanocomposites, 384, 389 Nanocrystals effect on color and sensorial aspects, 237
238 preparation methods, 231
232 Nanodelivery of bioactive compounds challenges toward, 325
326 encapsulation methods for, 294
318 coacervation, 305
306 complexation/conjugation with proteins, 315
316 cubosomes and hexosomes, 309
312

Index

inclusion complexation within cyclodextrins and amylose nanohelices, 316
317 nano spray drying, 304
305 nanoemulsification, 295
304 nanoliposomes and niosomes, 306
309 nanoprecipitation, 317
318 nanostructured lipid carriers (NLCs), 313
314 solid lipid nanoparticles/nanocarriers (SLNs), 312
313 Nanodelivery systems, enhancing the bioavailability of nutrients by, 12
13 complex coacervation, 351
358 desolvation/nanoprecipitation/solvent displacement, 346
351 layer-by-layer (LbL) assembly, 358
365, 359f nanotubular formation through, 362
365 spherical nanoparticle formation through, 359
362 nano/microemulsions, 365
372 Nanodispersions, 168 Nanoemulsification, 295
304 Nanoemulsions, 208
217, 322
323, 597
598, 600 applications and their effect on food, 212
216 active ingredients, delivery of, 213 active ingredients, encapsulation of, 213 modifying structural/textural properties, 215
216 nutritional properties, improvement of, 214
215 preservation, 213
214 classification for food industries, 209
210 fabricated, 170
171 illustration of ultrasonication to produce, 170f microfluidized, 164 minimum inhibitory concentrations (MIC) of, 366
368 and nanosized ingredients for food formulations, 8
10 oil-in-water, 191
192 pickering, 164

747

pickering nanoemulsions and stabilization of emulsified foods, 217 preparation methods of, 210
212 high-energy methods, 210 low-energy methods, 211 selection of emulsifier/coemulsifier and compatibility, 211
212 sodium dodecyl sulfate (SDS), 165, 172
173 water-in-oil, 191
192 Nanoencapsulated bioactive components for active food packaging, 17
18 application, 518
522 bioactive-loaded nanocarriers, effects of, 503
513 on antimicrobial properties, 503
507 on antioxidant properties, 508 on barrier properties, 512
513 on mechanical properties, 508
512 bioactive-loaded nanocarriers applied in active food packaging, 497
503 carotenoids, 500 essential oils (EOs), 500
501 peptides and antimicrobial agents, 502 phenolic compounds, 497
500 vitamins, 502
503 controlled release and migration of bioactive compounds from active food packaging, 513
518 future trends, 522 nanoencapsulation of bioactive ingredients, 496
497 Nanoencapsulation of bioactive food ingredients carotenoids, 287
288 classification and the structure, 287 in food, 287 health benefits and stabilities, 288 carrier materials used for, 318
325 combinations of different nanocarrier materials, 325 cyclodextrins, 323 lipids, 322
323 polysaccharides, 321
322 proteins, 319
321 surfactants, 323
325 challenges toward nanodelivery of bioactive compounds, 325
326 essential oils, 292
294

748

Nanoencapsulation of bioactive food ingredients (Continued) classification and the structure, 292
293 in food, 294 health benefits and stabilities, 294 future direction, 326 minerals, 290
292 classification and the structure, 290 in food, 290
291 health benefits and stabilities, 291
292 nanodelivery of bioactive compounds, encapsulation methods for, 294
318 coacervation, 305
306 complexation/conjugation with proteins, 315
316 cubosomes and hexosomes, 309
312 inclusion complexation within cyclodextrins and amylose nanohelices, 316
317 nano spray drying, 304
305 nanoemulsification, 295
304 nanoliposomes and niosomes, 306
309 nanoprecipitation, 317
318 nanostructured lipid carriers (NLCs), 313
314 solid lipid nanoparticles/nanocarriers (SLNs), 312
313 polyphenols, 280
286 classification and the structure, 280
281, 282t in food, 281
284 health benefits and stabilities, 284
286 vitamins, 288
290 classification and the structure, 289 in food, 289 health benefits and stabilities, 289
290 Nanoencapsulation of food ingredients, 11
12 Nanofiber-based nanosensors, 483
485 Nanofibers, 597
598 preparation methods, 230 Nanofillers, 13
14, 380, 534 Nanofiltration (NF), 5
6 application in fruit juice and plant extract processing, 77
87 in dairy processing, 91
94 concentration and demineralization of whey, 91
92

Index

lactic acid recovery, 93
94 ultrafiltration
whey permeate, demineralization of, 92
93 generalities of nanofiltration membranes, 74
77 nanofiltration in sugar industry, 94
96 in valorization of high-added value compounds from food industry wastewaters, 96
99 winemaking applications of, 87
91 Nanofluid application in different heat exchangers, 45
56 agglomeration and fouling, 56 entropy generation and exergy efficiency, 55
56 heat transfer enhancement by nanofluids, 46
51 pressure drop and pumping power, 51
53 thermal performance factor and the effectiveness of heat exchangers, 53
55 application in thermal processing of food products, 56
58 influential factors on viscosity of, 43f preparation of, 44
45, 45f thermophysical properties of, 40
44, 41t density, 43
44 specific heat capacity, 44 thermal conductivity, 40
42 viscosity, 42
43 Nanofluid thermal processing of food products, 2
4 Nanofood, 1 Nanofood market, 657
658 Nanolaminates in edible coating materials, 232
234 preparation methods, 230
231 Nanolamination, 234 Nanoliposomes, 165, 306
309, 322
323, 501, 597
598 Nanomaterials in foods analysis of particle size and size distribution of, 604
617 differential centrifugal sedimentation, 616
617 dynamic light scattering (DLS), 614
615

Index

nanoparticle tracking analysis (NTA), 615
616 size and shape versus toxicity, 610 size versus appearance, 608
609 size versus bioavailability, 609 size versus stability, 604
608 small-angle X-ray scattering (SAXS), 616 static light scattering, 614 characterization and analysis of, 20
21 classification of, 1
2, 3t consumer expectations and attitudes towards, 23
25 crystallinity and phase transition in lipidbased nanoparticles, 621
624 future trends, 639
640 glass transition temperature in polymerbased nanoparticles, 624
627 liquid and soft nanoparticles, 634
639 colloidal probe atomic force microscopy, 637
638 large deformation measurements, 639 micropipette technique, 638 oscillatory tests, 635
636 osmotic pressure method, 638
639 measurement of crystallinity and phase transition, 627
633 differential scanning calorimetry (DSC), 631
633 X-ray diffraction (XRD), 627
631 mechanical properties of food nanoparticles on food quality, 633
634 morphological and microstructural analysis of, 586
604 atomic force microscopy, 602
604 electron microscopy, 593
602 optical microscopy, 587
593 surface charge of, 617
619 zeta potential analysis of, 619
621, 619f Nanomechanical biosensors for food safety and control, 442
444 microcantilever-based biosensors, 443
444 scanning probe microscopy (SPM)-based biosensors, 442
443 Nanomedicine, 1 Nanoparticle shape and size on food quality and safety, 604
610

749

size and shape versus toxicity, 610 size versus appearance, 608
609 size versus bioavailability, 609 size versus stability, 604
608 Nanoparticle size measurement by light scattering techniques, 610
615 dynamic light scattering (DLS), 614
615 static light scattering, 614 Nanoparticles/nanofibers for checking adulteration/spoilage of food products, 16
17 Nanoparticle tracking analysis (NTA), 615
616 Nanophytosomes, 521 Nanopore membranes, electrochemical biosensing with, 430
431 Nanoporous materials for food industry, 6
7 Nanoprecipitation, 317
318 NanoRiskCat, 676 Nanoscale metal oxides in antimicrobial packaging, 383
390 copper oxide-based nanomaterials, 384
385 gold and silver nanoparticles, 389
390 magnesium oxide-based nanoparticles, 388
389 titanium oxide-based nanomaterials, 385
387 zinc oxide-based nanomaterials, 387
388 Nanosciences, 1 Nanosensors, 459
460 Nanosized ingredients for food formulations, 8
10 Nanospheres, 218 Nano spray dryer, 177
181, 178f Nano spray drying, 220, 304
305 Nanostructured lipid carriers (NLCs), 313
314, 322
323, 623 Nanostructures, 279 Nano-TiO2, 537 Nanotubular formation through layer-bylayer assembly, 362
365 Natural biopolymers, 625 Natural compounds, 267
271 Nernst
Planck equation, 75 Nettle extract (NE)-loaded nanoliposomes, 517 New Zealand, food regulation in, 688

750

NF270 polypiperazineamide membrane, 78
85 Niosomal encapsulation, 306
307 Niosomes, 306
309 4-Nitrophenol, 273
274 Nomarski method, 590 NonEU countries (Switzerland, Turkey, and Russia), food regulation in, 688 Numerical aperture, 589 Nusselt number, 47
50, 53 Nutraceuticals, 180 Nutritional properties, improvement of, 214
215 O Ochratoxin A (OTA), 426, 437
438, 446 Oil-in-water nanoemulsions, 191
192, 209
210 Oleuropein, 369
370, 429
430 Olyeyl glycerate (OG), 312 Optical microscopy, 587
593 bright field microscopy, 588
589 dark field microscopy, 589
590 fluorescence microscopy, 592, 592f imaging modes, 588f laser scattering confocal microscopy (LSCM), 593 polarizing microscopy, 590
591, 591f ultramicroscopy, 590 Optical nanobiosensors for food safety and control, 432
442 colorimetric biosensors, 433
436 fluorescent biosensors, 436
438 localized surface plasmon resonance (LSPR)-based biosensors, 438
441 surface-enhanced Raman scattering-based biosensors, 441
442 Organic nanoparticles, toxicity of, 674
675 Oscillatory tests, 635
636 small deformations measurements by, 637f Osmotic pressure method, 638
639 Ostwald ripening rate, 370
372 Ouzo effect, 211 Ovalbumin (OVA) nanoparticles, 347
349 Overall heat transfer coefficient (OHTC), 45
46, 49, 59
61

Index

Oxides used in nanocomposites, 534
539 silicon dioxide (silica), 537
538 titanium dioxide, 536
537 zinc oxide, 535
536 Oxygenated functional groups (OFGs), 128 Oxygen permeability, 512 P Packaging material, 379
380 Packaging properties, effects of bioactiveloaded nanocarriers on, 503
513 antimicrobial properties, effect on, 503
507 antioxidant properties, effect on, 508 barrier properties, effect on, 512
513 mechanical properties, effect on, 508
512 Parasites/viruses, 403 Parthenium, 468
469 Particle size and size distribution of nanomaterials in foods, 604
617 differential centrifugal sedimentation, 616
617 impacts of nanoparticle shape and size on food quality and safety, 604
610 size and shape versus toxicity, 610 size versus appearance, 608
609 size versus bioavailability, 609 size versus stability, 604
608 measurement of nanoparticle size by light scattering techniques, 610
615 dynamic light scattering (DLS), 614
615 static light scattering, 614 nanoparticle tracking analysis (NTA), 615
616 small-angle X-ray scattering (SAXS), 616 Particle size distribution (PSD), 604, 610
612 PEGylated nano-GO (nGO-PEG), 142
144 Penicillium expansum, 402
403 Peptides and antimicrobial agents, 502 Peroxidase biosensors, 416
417 Pesticide control in foodstuffs, 426
428 Phase contrast method, 590 Phase inversion, 211 Phase inversion composition (PIC), 211

Index

Phase inversion temperature (PIT) method, 211, 366
368 Phase transformations, 625
626 Phase transition, 633
634 in lipid-based nanoparticles, 621
624 to polymers, 625f Phenolic compounds, 497
500. See also Polyphenols Phenylboronic acid (PBA), 423
426 Phoma glomerata, 267 2:1 Phyllosilicat minerals, 112 Physical vapor deposition (PVD), 4, 44 Physical vapor synthesis (PVS), 387 Physicochemical properties of food, effect of nanocoatings on, 235
236 Physisorption analysis, 135t Phytantriol (PHY), 312 Phytanyl glycerate (PG), 312 Pickering emulsions, 215, 237
238 Pickering nanoemulsions, 164, 208 Pickering stabilization, 623
624 Planetary ball mill, 189, 189f Plant extract processing, application of nanofiltration in, 77
87 Plant extracts and biopolymers green synthesis of metal nanoparticles by, 10
11 Plants and algae, 263
266 Plum pox virus (PPV), 432 Polarized light (PL) microscopy, 591, 591f, 624 Polarizing microscopy, 590
591 Polar lipids, 322
323 Poly(alpha-hydroxy acids), 221
222 Poly(amino acids), 221
222 Poly(anhydrides), 221
222 Polybutylene succinate (PBS), 535 Poly(D,L-aspartic acid) (PAsp), 353
354 Poly(D,L-glutamic acid) (PGlu), 353
354 Poly-D-lysine (PDL), 354
356, 362
363 Poly(ethyleneimine) (PEI), 353
354 Polyethylene terephthalate (PET), 535 Poly(ortho esters), 221
222 Polyalkylcyanoacrylate (PACA), 317 Polyamide 6 (PA6), 484
485 Polycaprolactones (PCLs), 18
19, 317 Polydispersity index (PDI), 168, 223, 346
347, 370
372 Polydopamine-AuNPs, 426
428

751

Polyethylene (PE), 380 Polyglycerol polyricinoleate (PGPR), 366 Polyhydrooxyalkanoates (PHAs), 18
19 Polyhydroxybutyrate (PHB), 397 Polyhydroxyphenols. See Polyphenols Polylactic acid (PLA), 18
19, 503 Polylactide (PLA), 317 Polylactide-co-glycolide (PLGA), 317 Polymer-based nanoparticles, glass transition temperature in, 624
627 Polymer chain entanglement, 175 Polymer/CuO nanocomposites, 538 Polymeric nanoparticles, 9
10, 217
229, 236 application food processing, 226
228 characterization of, 222
225 definitions and classification of, 217
218 effect of on physicochemical properties of food during storage, 228
229 mechanism of active delivery by, 225
226 preparation methods of, 219
222 stability of, 224
225 Polymer MW, 175
176 Polymers/biopolymers in food packaging, 379
383 metal nanoparticles, 381
383 solid-state additives, 381 Polymer solution flow rate, 173 Polyoxyethylenetype nonionic surfactants, 211 Polypeptides, 18
19 Polyphenolic compounds. See Polyphenols Polyphenols, 280
286 classification and the structure, 280
281, 282t in food, 281
284 health benefits and stabilities, 284
286 total polyphenols, 85 Polypropylene (PP), 380 Polypyrrole (PPy), 484
485 Polysaccharides, 229, 321
322 Polyvinyl alcohol (PVOH), 18
19 Polyvinylidene chloride (PVDC) charcoal, 116
117 Porcine serum albumin (PSA), 480
481 Potassium, 291 Potential risks of nanotechnology applications, 706
707

752

Power-compensation DSC, 631
632 Power ultrasound, 168
169 Pressure-driven membrane processes, 96 Propagating surface plasmon resonance (PSPR), 461 Protective colloids, 212 Proteins, 319
321 Pseudomonas aeruginosa, 264, 268, 423
426, 503, 507 1-Pyrenecarboxylic acid, 140
141 Q Quantum dots (QDs), 417
418 Quillaja saponin, 366 Quorum sensing (QS), 387 R Radius of an equivalent sphere, 606 Raman spectroscopy, 135t, 441 Rayleigh rapport, 614 Rayleigh theory, 608 Reactive oxygen species (ROS), 4, 58, 242, 271, 535, 675 Recovery factor, 77 Reduced graphene oxide (rGO), 128
129, 477 REDUX, 89
90 Regulations in using nanomaterials for foods, 679
690 in Asia, 688
689 in Australia and New Zealand, 688 in Canada, 688 in Europe, 682
688 in NonEU countries, 688 regulatory aspects of nanoparticles, 680
681 regulatory issues, 21
23 in South Africa, 689 in South America, 689
690 in United States, 682 Reinforced nanocomposites for food packaging, 18
19 chitosan nanoparticles, 560 future trends, 560
561 inorganic nanomaterials, 534
543 nanoclays as polymer reinforcement fillers, 539
543 silicon dioxide (silica), 537
538 titanium dioxide, 536
537

Index

zinc oxide, 535
536 nanocellulose-based nanocomposites, 543
560 agroindustrial biomass, nanocellulose production from, 546
551 nanocellulose
alginate composites, 559 nanocellulose
chitosan composites, 555 nanocellulose composites with proteins, 559
560 nanocellulose
polycaprolactone (PCL) composites, 555
559 nanocellulose
polylactic acid (PLA) composites, 553 nanocellulose
starch composites, 553
555 Release profile (RP), 224 Resolving power, 589 Response surface methodology (RSM), 170
171, 369
370 Reverse osmosis (RO), 5 Reynolds number, 47
50, 53 Ricin toxin detection, 443 Risk assessment of nanostructures used in foods, 658
677 approaches for risk assessment of nanoparticles, 676
677 detection and characterization of nanoparticles in foods, 665
667 exposure routes to food nanoingredients, 667
670 dermal exposure, 667
668 ingestion, 669
670 inhalation, 668
669 toxicity of inorganic nanoparticles, 675
676 of organic nanoparticles, 674
675 Root mean square error of approximation (RMSEA), 718 Rubbery state, 624 Russia, food regulation in, 688 S Safety and regulatory issues of nanomaterials in foods, 21
23 nanofood market, 657
658 public perception and concerns, 677
679 regulations in using nanomaterials for foods, 679
690

Index

in Asia, 688
689 in Australia and New Zealand, 688 in Canada, 688 in Europe, 682
688 in NonEU countries, 688 regulatory aspects of nanoparticles, 680
681 in South Africa, 689 in South America, 689
690 in United States, 682 risk assessment of nanostructures used in foods, 658
677 approaches, 676
677 detection and characterization of nanoparticles, 665
667 exposure routes to food nanoingredients, 667
670 toxicity of inorganic nanoparticles, 675
676 toxicity of organic nanoparticles, 674
675 Salmonella, 443
444, 463
467, 521
522 Salmonella enterica, 429 Salmonella typhimurium, 433, 439
441, 440f, 443 Scanning calorimeter, 631 Scanning electron microscopy (SEM), 135t, 224, 398, 591, 593
596, 594f, 597t Scanning probe microscopy (SPM)-based biosensors, 442
443 Scanning transmission electron microscopy (STEM), 135t, 596 Scanning tunneling microscopy, 135t Screen-printed electrode (SPE), 423
426 Secondary electrons (SE), 595 Self-assembled monolayers (SAM), 416
417, 421
422 Semicrystalline polymers, 625
626, 625f Semisolid colloidal systems, 635 Shelf life, effect of nanocoatings on color changes associated with, 237 Silica nanoparticles, 537
538, 676
677 Silica shell-protected Ag2S QDs, 437 Silicon dioxide nanoparticles, 390
391, 537
538 Silver nanoparticles, 261
263, 271
273, 389
390, 467
471, 675 Single-stranded DNA probe (ssDNA), 423
426

753

Single-wall CNTs (SWCNTs), 15
16, 418, 471, 474
476 Size distribution (SD), 223 Small-angle X-ray scattering (SAXS), 616 Small-particle colloidal systems, 608 Small unilamellar vesicles (SUVs), 308 Sodium dodecyl sulfate (SDS), 53, 165, 172
173 Solid lipid nanoparticles (SLNs), 165, 183, 192, 235
236, 312
313, 322
323, 597
598, 623 Solid-state nuclear magnetic resonance, 135t Soluble soybean polysaccharide (SSPS) biodegradable films, 537 Solution blowing, 175
177 Solution blow spinning, 176f Solution
diffusion model, 75 Solvent displacement. See Nanoprecipitation Sonication, 168
171 South Africa, food regulation in, 689 South America, food regulation in, 689
690 Soy protein isolate (SPI) films, 509 Specialized equipment, production of food nanomaterials by, 7
8 ball milling, 186
190, 187f electrohydrodynamic devices, 171
177 solution blowing, 176
177 future perspectives, 193 high-pressure (HP) techniques, 162
168 HP homogenizer, 165
168 microfluidizert homogenization process, 162
165 membrane technology, 190
192 micro/nanofluidic systems, 181
184 nano spray dryer, 177
181 sonication, 168
171 vortex fluidic device (VFD), 184
186, 185f Spherical nanoparticle formation through layer-by-layer assembly, 359
362 Spirulina microalga, 174 Spontaneous emulsification, 211 Spray drying, 177, 179
180, 220 Staphylococcus aureus, 264
265, 268, 361
362, 423
426, 507 Starch, 217, 553
555 Starch
carboxymethyl cellulose (CMC) films, 507 Starch nanoparticles, 168

754

Static light scattering, 614 Stokes diameter, 617 Stokes
Einstein equation, 615 Storage modulus, 635 Structural equation model (SEM), 710, 724f Sugar industry, nanofiltration in, 94
96 Supermicropores, 117
118 Surface charge analysis, 135t Surface charge of nanomaterials in foods, 617
619 Surface-enhanced Raman scattering (SERS), 432
433, 441
442 Surface functionalization of nanomaterials with bioreceptors, 420
422 Surface plasmon polariton (SPP), 438
439 Surface plasmon resonance (SPR), 262, 272
273, 423 Surfactants, 212, 323
325 Sweet potato (Ipomea batatas L.), 189
190 Switzerland, food regulation in, 688 Synthetic milk, 463 T Taro (Colocasia esculenta L.), 189
190 Taylor cone, 171
173, 230, 483 Tea polyphenol-loaded chitosan nanoparticles (TPCN), 509, 513 TECHACCEPT, 710
711, 715 Tensile strength (TS), 389 Terpenes, 495 Tetraethoxysilane, 390
391 Tetraterpenoids. See Carotenoids Textural changes, effect of nanocoatings on, 236
237 Texture, 214
215 Thermogravimetric analysis (TGA), 135t, 397 Thymol, 500
501 Thymus daenensis, 507 Thymus vulgaris extract (TE), 501 Titanium dioxide, 536
537 Titanium nitrate (TiN), 675 Titanium oxide-based nanomaterials, 385
387 Tocopherol nanocapsules, 521 Total antioxidant activity (TAA), 85 Toxicity of inorganic nanoparticles, 675
676 of organic nanoparticles, 674
675

Index

Toxicological and normative regulatory issues of nanoparticles, 238
242 Transducer, 17, 460 Transmission electron microscopy (TEM), 135t, 224, 398, 593, 594f, 596, 597t Triacylglycerides conformational structure of, 630f crystallization forms of, 622f Triacylglycerol (TAG), 622
623 1,3,5-Triazine-2,4,6-triamine, 461
463 Triton X-100 (TX-100), 172
173 Tucker
Lewis nonnormed fit index (TLI), 718 Tumbling mills, 186 Turkey, food regulation in, 688 Tweens 80, 215 Tyramine, 428
429 U Ultrafiltration (UF), 5 Ultramicroscopy, 590 Ultrasonication process, 169
170 Ultrasound, 168
169 Unilamellar vesicles (ULVs), 308 United States, food regulation in, 682 Urea, 475, 478 Urtica dioica L. nanoliposomes, 507
513 US Food and Drug Administration, 405 UV-ray photons, 589 UV-Visible spectroscopy, 135t V Vacuum spray drying, 181 Valorization of high-added value compounds, role of nanofiltration in from food industry wastewaters, 96
99 Van der Waals forces, 6
7, 107
108 Vanillin, 480
481 Viscoelastic materials, rheological properties of, 636 Viscosity of nanofluids, 42
43 Vitamin B9, 315 Vitamins, 288
290, 502
503 classification and the structure, 289 in food, 289 health benefits and stabilities, 289
290 Vitex negundo L., 272 Volume reduction factor (VRF), 77

Index

Vortex fluidic device (VFD), 7, 161
162, 184
186, 185f W Wastewater treatment, 108 Water-in-oil (W/O) emulsions, network stabilization of, 623
624 Water-in-oil (W/O) nanoemulsions, 191
192, 209
210 Water in oil in water (W/O/W) emulsions, 358 Water vapor permeability (WVP), 512
513 Wet-SEM, 602 Whey, concentration and demineralization of, 91
92 Willingness to pay (WTP), 24, 707
708, 719, 726
727 Winemaking applications of nanofiltration, 87
91 X Xanthine, 475
476 X-ray absorption near-edge spectroscopy, 135t X-ray diffraction (XRD), 135t, 399, 591, 627
631 X-ray photoelectron spectroscopy (XPS), 135t, 399 X-ray photons, 589

755

Xylooligosaccharides (XOs), 95 Y Yam (Dioscorea alata L.), 189
190 Z Zataria multiflora, 507, 509 Zataria multiflora EO (ZMEO) nanoemulsions, 501 Zein nanoparticles, 346
347, 350
351 Zein
sodium caseinate
pectin complex nanoparticles, 180 Zero-valent iron nanoparticles (nZVI), 120
126 applications in food industry, 121
125 companies active in the production of, 124t reported procedures for the synthesis of, 122t safety and toxicity of, 125
126 Zeta potential, 223, 346
347, 349
350, 357f, 358
361 measurement of, 619
621, 619f Zinc, 291 Zinc oxide, 535
536, 675 Zinc oxide-based nanomaterials, 387
388 Zingiber officinale, 272 Ziploc packaging, 233