Biopolymer Nanostructures for Food Encapsulation Purposes 9780128156636, 0128156635

Table of contents :
Content: Section 1: Milk protein nanostructures Section 2: Other protein nanostructures Section 3: Polysaccharide nanostructures Section 4: Synthetic biopolymer nanostructures

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In the Name of GOD, The Compassionate, The Merciful

Dedication To Dr. Mustafa Chamran and all beloved martyrs who served as brave commanders and sacrificed their life during sacred defense—Iraq’s Saddam imposed war upon Iran (1980–88).

Human Beings (A poem by Saadi) Human beings are members of a whole In creation of one essence and soul If one member is afflicted with pain Other members uneasy will remain If you have no sympathy for human pain The name of human you cannot retain

Tomb of Saadi, Shiraz, Iran Saadi (born as Ab u-Muḥammad Muṣliḥ al-Dīn bin Abdall ah Shīr azī, also known as Saadi Shirazi), was a famous Poet from Iran, who lived between 1210 AD and 1292 AD. Saʿdī is considered one of the greatest Persian poets ever. Rose Garden (Persian: ‫ )ﮔﻠﺴﺘﺎﻥ‬and orchard (Persian: ‫ )ﺑﻮﺳﺘﺎﻥ‬is a major work both in the Persian literature and world literature. The works have been school books throughout the Persian culture through more than 500 years, from India to the east to the Balkans in the west. And they have great importance for the understanding of the Muslim mindset. Fruit Garden of Saʿdī is part of the Universal Library.

Biopolymer Nanostructures for Food Encapsulation Purposes

Nanoencapsulation in the Food Industry

Biopolymer Nanostructures for Food Encapsulation Purposes Volume 1

Edited by

Seid Mahdi Jafari

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 © 2019 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. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN 978-0-12-815663-6 For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Charlotte Cockle Acquisition Editor: Nina Rosa de Araujo Bandeira Editorial Project Manager: Karen Miller Production Project Manager: Omer Mukthar Cover Designer: Miles Hitchen Typeset by SPi Global, India

Contributors

Nadia Ahmadi Department of Food Science and Technology, College of Agriculture, Isfahan University of Technology, Isfahan, Iran Safoura Akbari-Alavijeh Department of Food Science and Technology, College of Agriculture, Isfahan University of Technology, Isfahan, Iran Omnia M. Ali Cancer Nanotechnology Research Laboratory (CNRL); Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt Elham Assadpour Department of Food Science and Technology, Baharan Institute of Higher Education, Gorgan, Iran Adnan A Bekhit Cancer Nanotechnology Research Laboratory (CNRL); Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt; Pharmacy Program, Department of Allied Health, College of Health Sciences, University of Bahrain, Manama, Bahrain Giulia Bonacucina School of Pharmacy, University of Camerino, Camerino, Italy Ana I. Bourbon Department of Life Sciences, International Iberian Nanotechnology Laboratory, Braga, Portugal Marco Cespi School of Pharmacy, University of Camerino, Camerino, Italy Huaiqiong Chen Department of Animal and Food Sciences, Texas Tech University, Lubbock, TX, United States Yeming Chen State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, People’s Republic of China € Ozgenur Coşkun Department of Food Engineering, ˙Istanbul Sabahattin Zaim € I˙stanbul, Turkey University (I˙ZU), Kadria A. Elkhodairy Cancer Nanotechnology Research Laboratory (CNRL); Department of Industrial Pharmacy, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt

xviii

Contributors

Ahmed O. Elzoghby Cancer Nanotechnology Research Laboratory (CNRL); Department of Industrial Pharmacy, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt; Division of Engineering in Medicine, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States Maria Jose Fabra Food Quality and Preservation Department, IATA-CSIC, Valencia, Spain Seid Reza Falsafi Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Milad Fathi Department of Food Science and Technology, College of Agriculture, Isfahan University of Technology, Isfahan, Iran May S. Freag Cancer Nanotechnology Research Laboratory (CNRL); Department of Pharmaceutics, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt; Division of Engineering in Medicine, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States I˙brahim G€ ulseren Department of Food Engineering, I˙stanbul Sabahattin Zaim € I˙stanbul, Turkey University (I˙ZU), Yosra Hashem Cancer Nanotechnology Research Laboratory (CNRL); Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt Yufei Hua State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, People’s Republic of China Seid Mahdi Jafari Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Mehri Karim Department of Food Science and Technology, College of Agriculture, Isfahan University of Technology, Isfahan, Iran Iman Katouzian Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan; Nano-encapsulation in the Food, Nutraceutical, and Pharmaceutical Industries Group (NFNPIG), Universal Scientific Education and Research Network (USERN), Tehran, Iran Najeh Maissar Khalil Department of Pharmacy, Pharmaceutical Nanotechnology Laboratory, Midwestern Parana State University, Guarapuava, Brazil

Contributors

xix

Sherine N Khattab Cancer Nanotechnology Research Laboratory (CNRL), Faculty of Pharmacy; Department of Chemistry, Faculty of Science, Alexandria University, Alexandria, Egypt Xiangzhen Kong State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, People’s Republic of China Amparo Lo´pez-Rubio Food Quality and Preservation Department, IATA-CSIC, Valencia, Spain Daniel A. Madalena Centre of Biological Engineering, University of Minho, Braga, Portugal Rubiana Mara Mainardes Department of Pharmacy, Pharmaceutical Nanotechnology Laboratory, Midwestern Parana State University, Guarapuava, Brazil Arlete Marques Department of Life Sciences, International Iberian Nanotechnology Laboratory; Centre of Biological Engineering, University of Minho, Braga, Portugal Joana T. Martins Centre of Biological Engineering, University of Minho, Braga, Portugal Rafaela Nunes Centre of Biological Engineering, University of Minho, Braga, Portugal Parvin Orojzadeh Student Research Committee, Department of Food Technology, National Nutrition and Food Technology Research Institute, Shahid Beheshti University of Medical Sciences, Tehran, Iran  Ilja Gasan Osojnik Crnivec University of Ljubljana, Biotechnical Faculty, Department of Food Science and Technology, Chair of Biochemistry and Food Chemistry, Ljubljana, Slovenia Kang Pan W. K. Kellogg Institute for Food and Nutrition Research, Kellogg Company, Battle Creek, MI, United States Ricardo N. Pereira Centre of Biological Engineering, University of Minho, Braga, Portugal Diego Romano Perinelli School of Pharmacy, University of Camerino, Camerino, Italy

xx

Contributors

Ana C. Pinheiro Centre of Biological Engineering, University of Minho, Braga; Instituto de Biologia Experimental e Tecnolo´gica, Avenida da Repu´blica, Quinta-do-Marqu^es, Estac¸a˜o Agrono´mica Nacional, Oeiras, Portugal Natasˇa Poklar Ulrih University of Ljubljana, Biotechnical Faculty, Department of Food Science and Technology, Chair of Biochemistry and Food Chemistry, Ljubljana, Slovenia Somayeh Rahaiee Department of Biotechnology, Amol University of Special Modern Technologies, Amol, Iran Oscar L. Ramos Centre of Biological Engineering, University of Minho, Braga; Universidade Cato´lica Portuguesa, CBQF - Centro de Biotecnologia e Quı´mica Fina – Laborato´rio Associado, Escola Superior de Biotecnologia, Porto, Portugal Rui M. Rodrigues Centre of Biological Engineering, University of Minho, Braga, Portugal Hadis Rostamabadi Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Rezvan Shaddel Department of Food Science and Technology, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, Ardabil, Iran Niloufar Sharif Department of Food Science and Technology, School of Agriculture, Shiraz University, Shiraz, Iran Lı´via S. Simo˜es Centre of Biological Engineering, University of Minho, Braga, Portugal Afsaneh Taheri Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Chuanhe Tang Department of Food Science and Technology, South China University of Technology, Guangzhou, China Jose A. Teixeira Centre of Biological Engineering, University of Minho, Braga, Portugal Mohamed Teleb Cancer Nanotechnology Research Laboratory (CNRL); Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt Leslie Thompson Department of Animal and Food Sciences, Texas Tech University, Lubbock, TX, United States

Contributors

xxi

Anto´nio A. Vicente Centre of Biological Engineering, University of Minho, Braga, Portugal Hailey Wooten Department of Animal and Food Sciences, Texas Tech University, Lubbock, TX, United States Weihao Wu State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, People’s Republic of China Mohammad Yousefi Student Research Committee, Department of Food Science and Technology, Tabriz University of Medical Sciences, Tabriz, Iran Mahboobeh Zare Faculty of Medicinal Plants, Amol University of Special Modern Technologies, Amol, Iran Caimeng Zhang State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, People’s Republic of China

Preface to the series

Enthusiasm for the consumption of healthy and functional food products has been dramatically expanded with the growth of industrial life and obesity among people. Therefore, many researches have focused on novel topics, such as nanoencapsulation in preparing healthy cuisine. Nanoencapsulation is a new field of science combining different fields of technology in general and encapsulation in particular. Encapsulation can be defined as the technology of encasing bioactive compounds in solid, liquid, or gaseous states in matrices, which can be released under particular circumstances with a controlled rate. Recently, according to perception of material properties and their reaction at the nanoscale research, the encapsulation area has moved to the nanoencapsulation field. The fabricated nanocarriers provide better opportunity for interaction, high bioavailability, solubility, and permeation due to their larger surface area. Also, nanoencapsulated ingredients enable targeted release plus high stability against harsh digestive steps, process conditions, and environment stresses. Selecting the best method for nanoencapsulation of distinct food bioactive ingredients is the main step for designing an efficient delivery system in healthy food and functional products. Considering different techniques applied for fabricating nanoscale carriers, we have classified nanoencapsulation technologies into five groups based on the main mechanism/ingredient in our previous books (Elsevier, 2017). Due to substantial and overwhelming research activities on nanoencapsulation of food bioactive ingredients and nutraceuticals in recent years, it is necessary to work on specialized and in-depth book titles devoted to different groups of nanocarriers. On the other hand, release, bioavailability, characterization, safety, and application of nanoencapsulated ingredients in different food products are some other important topics which deserve to have some relevant book titles to provide more detailed information and discussions. Therefore, the Book Series “Nanoencapsulation in the food industry” has been defined to address these emerging topics and cover the recent cutting-edge researchers in this field. Seven Volumes defined in this Series have the Titles as following: l

l

l

l

l

l

l

Vol. 1: Vol. 2: Vol. 3: Vol. 4: Vol. 5: Vol. 6: Vol. 7:

Biopolymer Nanostructures for Food Encapsulation Purposes Lipid-Based Nanostructures for Food Encapsulation Purposes Nanoencapsulation of Food Ingredients by Specialized Equipment Characterization of Nanoencapsulated Food Ingredients Release and Bioavailability of Nanoencapsulated Food Ingredients Application of Nano/Micro-encapsulated Ingredients in Food Products Safety and Regulatory Issues of Nanoencapsulated Food Ingredients

xxiv

Preface to the series

This Book Series would be useful for a diverse group of readers including food technologists, food engineers, nanotechnologists, nutritionists, food colloid experts, pharmacists, cosmetic experts, physicists, chemists, microbiologists, biotechnologists, engineers, and those who are interested in novel technologies in the area of food formulations, functional foods, and nutraceutical delivery systems. We hope this Book Series will stimulate further research in this rapidly growing area and will enable scientists to gain more practical knowledge about different nanocarriers and their properties to solve their particular problems. Seid Mahdi Jafari Gorgan, Iran

Preface to Vol. 1

Nanoencapsulation as a main research field of Food Nanotechnology is an enabling fast-growing technology which has the potential to revolutionize the food systems. The unusual properties of materials that are on the nanometer length scale (10 9 m), over common food molecules may lead to the modification of many macroscale characteristics, such as texture, microstructure, taste, and other sensory attributes, processability, and stability during shelf life. In other words, in the past, a wide range of food products were technically not feasible to manufacture but are possible today through development and design of nano-structured food formulations. On the other hand, nutraceutical delivery systems through nanocarriers are promising and emerging approaches for improving the health-promoting features of food bioactive ingredients and nutraceuticals. One of the main technologies for preparing nanoencapsulated bioactive ingredients and nutraceuticals is application of biopolymer nanostructures from different protein, carbohydrate, and chemical sources. This first Volume in the Series “Nanoencapsulation in the food industry” will guide the readers how to fabricate biopolymer nanostructures and apply them for food encapsulation purposes. Recent results obtained by international experts in this field will be provided to make a framework for expansion of relevant studies in similar fields such as nanoencapsulation of various food ingredients and nutraceuticals by biopolymer nanostructures. Obtained nanoencapsulated ingredients can be applied in formulation of food products beneficial for health-improving purposes and also, for optimization of the final food products in terms of techno-functional and economic issues. The overall aim of the Biopolymer Nanostructures for Food Encapsulation Purposes is to bring science and applications together on nano-scale biopolymers with emphasis on encapsulation of food bioactive ingredients and pharmaceuticals that enable novel/enhanced properties or functions. This book is covering recent and applied researches in all disciplines of bioactive and nutrient delivery. All chapters emphasize original results relating to experimental, theoretical, formulation, and/or applications of nano-structured biopolymers for food encapsulation purposes. After presenting a brief overview of biopolymer nanostructures in Chapter 1, nanocarriers made from milk proteins have been covered in Section A including nanoparticles of casein micelles (Chapter 2), nanostructures of whey proteins (Chapter 3), nanotubes of alpha-lactalbumin (Chapter 4), nanofibrils of beta-lactoglobulin (Chapter 5), nanoparticles of lactoferrin (Chapter 6), and nanoparticles of bovine serum albumin (Chapter 7). Section B has been devoted to protein nanostructures from other animal and plant resources, namely, nanostructures of gelatin (Chapter 8), zein (Chapter 9), soy proteins (Chapter 10), gluten (Chapter 11), and silk fibroins (Chapter 12). Another

xxvi

Preface to Vol. 1

important group of biopolymer nanostructures, that is, polysaccharide-based nanocarriers have been explained in Section C including nano-hydrogels of alginate (Chapter 13), nanostructures of chitosan (Chapter 14), nanostructures of starch (Chapter 15), nano-helices of amylose (Chapter 16), nanostructures of cellulose (Chapter 17), and nanostructures of gums (Chapter 18). Finally, Section D deals with nanocarriers made from chemical biodegradable polymers such as PLA, PGA, PLGA, PCA, and PEG (Chapter 19), and dendrimers (Chapter 20). All who are engaged in micro/nano-encapsulation of food, nutraceutical, and pharmaceutical ingredients worldwide can use this book as either a textbook or a reference which will give the readers a good and recent knowledge and potentials of biopolymer nanostructures, as well as their novel applications in developing bioactive delivery systems. We hope this book will stimulate further research in this rapidly growing area and will enable scientists to get familiar with biopolymer nanostructures as an important group of nanocarriers. 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 is to my family for their understanding and encouragement during the editing of this great project. Seid Mahdi Jafari Gorgan, Iran December, 2018

An overview of biopolymer nanostructures for encapsulation of food ingredients

1

Elham Assadpour*, Seid Mahdi Jafari† *Department of Food Science and Technology, Baharan Institute of Higher Education, Gorgan, Iran, †Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

1

Introduction

Nanoencapsulation is an emerging field of research which has been the focus of many recent studies in both drug and nutraceutical delivery. It has been claimed that when the size of particles is reduced to the nanoscale, there is a dramatic increase in the surface-to-volume ratio which provides many attractive and unique properties to the nanoparticles (Faridi Esfanjani, Assadpour, & Jafari, 2018; Rafiee & Jafari, 2018). For instance, by producing biopolymeric nanocarriers, more available active sites are exposed on the surface of these delivery systems, which would be very beneficial for their absorption through the mucus-adhering mechanism within the digestive system of the body (Faridi Esfanjani & Jafari, 2016; Jafari & McClements, 2017; Katouzian, Faridi Esfanjani, Jafari, & Akhavan, 2017). On the other hand, penetration of nanocapsules into the cells and through the membranes would be much easier compared to microcapsules (Rafiee, Nejatian, Daeihamed, & Jafari, 2018). Moreover, this higher surface-to-volume ratio enhances the interaction of nanocarriers with enzymes, microorganisms, and other target agents such as receptors in tissue cells, which again results in higher efficiency of nanocapsules ( Jafari & McClements, 2017; Rezaei, Fathi, & Jafari, 2019). In this chapter, after a brief overview of different nanocarriers for the encapsulation of food bioactive ingredients and their morphologies, most common approaches for the production of biopolymeric nanocarriers will be explained. Then, individual biopolymers which can have potentials as nanostructures/ nanocarriers for the delivery of food bioactives will be shortly covered. More comprehensive details have been provided in the following chapters for each biopolymer.

2

Different nanocarriers based on composition and preparation method

Food bioactive-loaded nanocarriers have been classified by Jafari (2017a, 2017b) into five different groups based on the main mechanism/ingredient used to make nanocarriers for the food industry. They include lipid-based nanocarriers, Biopolymer Nanostructures for Food Encapsulation Purposes. https://doi.org/10.1016/B978-0-12-815663-6.00001-X © 2019 Elsevier Inc. All rights reserved.

2

Biopolymer Nanostructures for Food Encapsulation Purposes

nature-inspired nanocarriers, specialized equipment produced nanocarriers, biopolymerbased nanocarriers, and other miscellaneous nanocarriers as presented in Table 1. There could be some overlaps in this classification; for example, some biopolymers are applied in specialized equipment techniques, but this classification is based on the Table 1 An overview of different nanocarriers for the food industry No.

Main groups

1

Lipid-based nanocarriers

Techniques/ nanocarriers Nanoemulsions

No. 1 2 3

Nanostructured phospholipid carriers Nano-lipid carriers 2

3

4

Nature-inspired nanocarriers

Special equipmentbased nanocarriers

Biopolymerbased nanocarriers

4 5 6

Caseins

7 8 9 10

Cyclodextrins Amylose Ferritin Electrospinning

11 12 13 14

Electrospraying Nano-spray dryer Micro/ nanofluidics Single biopolymeric nanoparticles

15 16

Complexed biopolymer nanocarriers Conjugated biopolymer nanocarriers Nano-gels

20 21 22 23

Nanotubes

Different strategies Single emulsions: Oil in water (O/W); Water in oil (W/O) Double emulsions: W/O/W; O/W/O Structural emulsions: Single interface layer; double interface layer Liposomes: Monolayer; multilayer Phytosomes: Monolayer; multilayer Structural liposomes/phytosomes: With coatings Solid lipid nanoparticles (SLNs) Nano-structured lipid carriers (NLCs) Smart lipid carriers Alpha, beta, gamma-caseins Alpha, beta, gamma-cyclodextrins Single helix; double helix Single injection nozzle; Double injection

17 18 19

24 25 26 27

Protein nanoparticles made by desolvation Polysaccharide nanoparticles made by precipitation Protein + protein Polysaccharide + polysaccharide Protein + polysaccharide Protein + polysaccharide

Hydrogels Organogels/oleogels Mixed gels Protein nanotubes made with α-lactalbumin

An overview of biopolymer nanostructures for encapsulation of food ingredients

3

Table 1 Continued No.

Main groups

5

Miscellaneous nanocarriers

Techniques/ nanocarriers

No.

Different strategies

Nanocrystals

28 29

Chemical polymer nanoparticles

30

Bioactives within crystals Bioactive crystals within other nanocarriers Nanocarriers made with chemical polymers such as poly-D,L-lactide (PLA), poly-γ-glutamic acid (PGA), poly-capro-lactone acid (PCA), and polyethylene glycol (PEG) Dendrimers Niosomes Cubosomes and hexosomes Magnetic nanoparticles Silica nanoparticles Carbon nanotubes Quantum dots Gold nanoparticles

Nanostructured surfactants Inorganic nanocarriers

31 32 33 34 35 36 37 38

main mechanism of nanocapsule formation. Selection of an appropriate technology for the production of food bioactive-loaded nanocarriers depends on many factors, such as desired release profile and delivery purposes, physicochemical properties of the final product, economic considerations, available equipment, technical knowledge, and so on (Arpagaus, Collenberg, R€ utti, Assadpour, & Jafari, 2018; Gharehbeglou, Jafari, Hamishekar, Homayouni, & Mirzaei, 2019; Mokhtari, Jafari, & Assadpour, 2017; Tavakoli, Hosseini, Jafari, & Katouzian, 2018). Another important issue is that nanocarriers are not necessarily spherical nanoparticles; different morphologies and structures of final nanocarriers can be achieved based on the applied materials/technologies, which are briefly outlined as follows:

2.1 Spherical nanocarriers They could be in the form of nanocapsules or nanospheres (Faridi Esfanjani & Jafari, 2016; Katouzian et al., 2017). Nanospheres (multiple core or matrix) can be defined as matrix systems utilized for the uniform dispersal of bioactive components such as those nanocarriers formed as nanogels, casein micelles, dendrimers, and biopolymer nanocomplexes, while nanocapsules (single core or shell-core) are vesicular systems where bioactive compounds are encapsulated within a cavity consisting of an inner liquid core which in turn is surrounded by a polymeric membrane including nanocarriers made with cyclodextrins, liposomes, nanoemulsions, solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), and niosomes. Also, from a physical point of view, these nanocarriers can be “liquid” such as those prepared with nanoemulsions, nanoliposomes, biopolymer nanoparticles, SLNs, and cyclodextrins, or “solid” such as nanoparticles made with nano-spray dryer, electrospraying, and nanocrystals.

4

Biopolymer Nanostructures for Food Encapsulation Purposes

2.2 Tubular nanocarriers They should have at least one dimension in the nanoscale (usually their cross section in nanosized) to be considered nanocarriers, although their length could be higher than 1000 nm (Assadpour & Jafari, 2018). Within this group, we can include nanofibers (produced by electrospinning), nanotubes (from certain proteins such as α-lactalbumin), nanofibrils (for instance from β-lactoglobulin), and nano-helix structures (such as those from amylose). Bioactive components can be embedded within their hollow cavity.

2.3 Laminated nanocarriers This morphology of nanocarriers could be observed as nano-layers or nanocomposites which are commonly formulated for active/smart packaging and coatings.

3

Different techniques for preparation of biopolymeric nanocarriers

Production of bioactive-loaded nanocarriers is more complex than generating microcapsules, and more advanced and sophisticated technologies are needed for the preparation of nanodelivery systems (Assadpour, Jafari, & Esfanjani, 2017; Mehrnia, Jafari, Makhmal-Zadeh, & Maghsoudlou, 2017; Raei, Rajabzadeh, Zibaei, Jafari, & Sani, 2015). In general, there are three main approaches for preparation of biopolymeric nanostructures including top-down strategies, bottom-up strategies, and a combination of them. In top-down strategies, nanosystems are formed by instrumental/high energy processes which involves size reduction to nano-scale by milling, microfluidization, high pressure homogenization, ultrasonication, electrospinning, electrospraying, nano spray drying, micro/nanofluidics, and vortex fluidic system. In bottom-up strategies, nanomaterials are provided by low energy/formulation-based methods from small ingredients like self-assembly of molecules and atoms to nanosize, formation of protein-polysaccharide coacervates, desolvation, precipitation, conjugation, layer-by-layer deposition, microemulsification, and templating. A brief overview of these methods has been summarized in Fig. 1.

4

Different biopolymer nanostructures for encapsulation of food ingredients

Biopolymeric nanocarriers are defined as submicron biopolymeric particles, which can be used for nanoencapsulation of bioactive compounds. Biopolymeric nanocarriers can be fabricated by individual biopolymers such as lactoferrin nanoparticles, starch nanoparticles, alginate nanohydrogels, and α-lactalbumin nanotubes, or by complexation/conjugation of two different biopolymers such as protein-polysaccharide nanocomplexes (e.g., pectin-whey protein nanocarriers).

An overview of biopolymer nanostructures for encapsulation of food ingredients

5

Fig. 1 Different top-down and bottom-up techniques for preparation of biopolymeric nanocarriers.

Fig. 2 Different biopolymers/polymers for preparation of food encapsulating nanostructures.

There are various biopolymers sources to prepare food bioactive-loaded nanocarriers as shown in Fig. 2 including milk proteins, other animal and plant proteins, polysaccharides, and biodegradable chemical polymers which will be briefly described in the following sections.

6

Biopolymer Nanostructures for Food Encapsulation Purposes

4.1 Milk protein nanostructures 4.1.1 Nanoparticles of casein micelles Caseins are one of the most studied food proteins as vehicles for bioactives (Haratifar & Guri, 2017). Casein, the primary protein fraction in milk, represents
80% of the total protein in the cow milk and other dairy products (Hambraeus & L€ onnerdal, 2003; Semo, Kesselman, Danino, & Livney, 2007). αS1-, αS2-, β-, and κ-casein, which are in weight ratio of 4:1:4:1, are four phosphoproteins that form casein micelles in cow’s milk (Huppertz, Fox, & Kelly, 2018; Tavares, Croguennec, Carvalho, & Bouhallab, 2014). It is inexpensive, readily available, biodegradable, highly stable, and is GRAS (Semo et al., 2007). Additionally, it has hydrophobic and hydrophilic regions which provide exceptional surface-active and stabilizing properties. To obtain commercial caseins, native caseins are separated from skimmed milk adjusting its pH to its isoelectric point (pI) via acid addition, followed by alkaline treatment to ionize the precipitated casein. Caseinates, frequently ¼ sodium caseinate (NaCas) are then obtained via drying procedure (Bylund, 2015). Compared to casein, caseinate powders are readily water soluble and are commonly used in the delivery system preparation. Casein can self-assemble into nano-sized casein nanoparticles, which was termed as “casein micelle” by Beau in 1921 (Fox & Brodkorb, 2008). Casein micelles are not toxic and have a unique structure that can contain calcium and phosphorus. Unlike casein micelles, the structure of submicelles of NaCas contains no colloidal calcium phosphate, indicating no calcium phosphate cross-linkage between the caseins in NaCas submicelles. Hydrophobic and electrostatic interactions are the main forces in maintaining the structural integrity (Chu, Ichikawa, Kanafusa, & Nakajima, 2007). Various models have been proposed according to the data on physicochemical properties of casein micelles and behavior of the four casein fractions mentioned before. Coat-core, subunit (submicelles), and internal structure models are the three most discussed models (Phadungath, 2005). All the models indicate the hydrophobic interior of casein micelles, which are more suitable to interact with hydrophobic bioactive compounds, but not hydrophilic ones. This explains why most of the reported capsules, as summarized in Chapter 2, focused on hydrophobic bioactives. Within the micelle structure, the inner core is made up mostly of αs- and β-caseins and is more hydrophobic while the exterior of the micelle has more scattered κ-caseins and is more hydrophilic (Bhat, Dar, & Singh, 2016; Faridi Esfanjani & Jafari, 2016; Haratifar & Guri, 2017). The native casein micelle itself has a particle size of about 500 nm but it can be reassembled to achieve a smaller particle size. It is hypothesized that the casein micelle structure is disrupted at certain conditions, exposing the hydrophobic domains, which can bind the hydrophobic compounds. Upon returning to the normal conditions, the casein micelles are thereof reassembled, creating new and bioactive-loaded nanoparticles. More details about preparing bioactive-loaded casein nanostructures and different mechanisms have been provided in Chapter 2.

An overview of biopolymer nanostructures for encapsulation of food ingredients

7

4.1.2 Nanostructures of whey proteins Whey proteins are the soluble protein fraction in milk mostly encompassed of globular proteins, such as β-lactoglobulin (β-lg) and α-lactalbumin (α-la) which comprise almost 50% and 20% of the total protein content, respectively. These proteins are now considered valuable by-products from the cheese industry, relatively inexpensive, classified as GRAS (generally recognized as safe) ingredients, being eventually the most studied globular proteins (Mohammadi, Jafari, Assadpour, & Faridi Esfanjani, 2016; Nicolai & Durand, 2013). Solutions of native whey proteins have the ability to form rigid irreversible aggregates when heated at temperatures above their denaturation temperature (
60°C). These protein aggregates are currently used in several food formulations due to their functional, nutritional, and biological properties (i.e., amino acid composition, digestibility behavior, and excellent sensory characteristics) (Bryant & McClements, 1998; Ramos et al., 2017). Aspects such as protein-protein interactions, aggregation pathways, aggregates’ morphologies, and processing techniques determine much about the functionality and ability to form protein gels and nanohydrogels (Abaee, Mohammadian, & Jafari, 2017) which will be discussed in Chapter 3. Digestibility of whey protein nanostructures is a widely studied topic due to their enzymatic digestion resistance in the native state (e.g., native β-lg nanoparticles are resistant to proteolysis in the stomach) (Bohn et al., 2017; Li, Cui, Ngadi, & Ma, 2015; Li, Liu, & Yu, 2015; Sarkar, Goh, Singh, & Singh, 2009), or when they are produced at certain production conditions (e.g., semiunfolded state) (Madalena et al., 2016). Nevertheless, whey protein-based nanoparticles have been shown to be appropriate nanosized delivery structures for the protection of bioactive ingredients that are susceptible to digestion conditions (e.g., riboflavin (Madalena et al., 2016), green tea catechins (Shpigelman, Cohen, & Livney, 2012), among others) or poorly absorbed in the small intestine due to poor water solubility (e.g., curcumin (Li, Cui, et al., 2015; Li, Liu, et al., 2015), lutein (Eriksen, Luu, Dragsted, & Arrigoni, 2017; Zhao, Shen, & Guo, 2018), among others). Studies regarding the assessment of whey protein digestibility and bioaccessibility (i.e., the amount of bioactive compound that has been released to the aqueous medium and is ready to be absorbed) and bioavailability (i.e., the amount of bioactive compound that has been absorbed and enters the bloodstream) of food ingredients (Lucas-Gonzalez, Viuda-Martos, Perez-Alvarez, & Fernandez-Lopez, 2018) can be found in the literature using in vitro and in vivo digestion models. Whey protein-based nanostructures, and their fractions, have been developed and applied as suitable carriers for a range of food ingredients including antioxidants, antimicrobials, flavors/odors, fatty acids, minerals, or bioactive peptides (Faridi Esfanjani & Jafari, 2016; Loveday, Rao, & Singh, 2012). Some examples of whey protein-based nanostructures, including the bio-based material entrapped bioactive ingredient, activity, nanostructured size, and encapsulation efficiency, are explained in Chapter 3. The general aspects comprising the characterization of whey proteinbased nanostructures are similar to the employed techniques for other organic nanostructures. Parameters like size, structure, morphology, surface properties, and biological interaction are essential to define structure-function relationships and

8

Biopolymer Nanostructures for Food Encapsulation Purposes

ensure the desired functionality ( Jafari & Esfanjani, 2017). Several techniques are available to perform the characterization of such parameters, but because each has its advantages and limitations, complementary techniques must be combined to attain an accurate characterization ( Jafari, Esfanjani, Katouzian, & Assadpour, 2017). In Chapter 3, the techniques commonly used to characterize whey protein-based nanostructures will be briefly presented.

4.1.3 Nanotubes of α-lactalbumin α-Lactalbumin is a globular protein contained in mammalian-milk whey. In addition to its therapeutic and nutritional properties, the ability of this protein to form nanotubes during hydrolysis and self-assembly is of interest which makes it a green candidate in the form of nanotubular structures to be employed as nanocarriers especially in the food and pharmaceutical industries as bioactive and drug molecules. α-Lactalbumin constitutes almost 3%–5% of proteins in bovine milk and 17% of total bovine whey proteins. This nutritional protein is present in lactose synthase enzyme, which in turn synthesizes lactose (Qin et al., 2017). It encompasses a 123-residue peptide chain with a total molecular weight of 14.2 kDa. It has large α and smaller β domains. Two short 310 plus 3 principal α-helices form the α domain and a series of loops, a 310 α-helix together with three-stranded antiparallel β-sheet build the β-domain of the protein. The α and β domains are connected together via two disulfide bridges. One of the interesting features of α-lactalbumin is its ability to bind to metal cations, especially its affinity to Ca2+ leads to the enhancement of its stability (Bomhoff, Sloan, McLain, Gogol, & Fisher, 2006). The conformation of α-lactalbumin is altered at the pH polycation, polycation -> polyanion), as well as variation of formulation (varied alginate and chitosan mass and charge ratio) and polysaccharide characteristics (fraction of guluronic acid units for alginate, degree of acetylation for chitosan, varied molecular weight for both) and produced particles of varied shapes and forms (aggregating flocks, spherical particles, linear segments) within several size ranges (102–104 nm) and wide range of surface charge (Table 3). Homogenization prevents the formation of bulk gel in the solution with low crosslinking agent concentration. Therefore at higher intensities and homogenizer configurations that provide more efficient dispersing the particle size is decreased, for example, reaching particle sizes 100 nm vs. 1000 nm for 24,000 vs. 11,000 RPM, and 100 nm vs. 6 μm when large or small dispersing elements were used, respectively (Sæther et al., 2008). The polymer ratio and the molecular weight and the mixing order of the copolymers significantly affect the diameter and to some degree also the surface charge of the polyelectrolyte complexes (Ghasemi, Jafari, Assadpour, & Khomeiri, 2017, 2018). Generally, the smallest particles are obtained with low molecular weight components, low G content alginate, and by mixing order via addition of one polymer into a surplus amount of the oppositely charged polymer (Sæther et al., 2008; Sarmento et al., 2007). Furthermore, Sæther et al. (2008) reported the formation of large alginate/chitosan aggregates (>104 to 105 nm) at neutral charge ratios, whereas alginate/chitosan net charge ratios below 0.5 and above 2 were sufficient to enable formation of particles smaller than 500 nm. In this respect, particle size (and by definition, zeta potential) was also pH dependent. Similarly, the mechanism requires pregelation with the cross-linker to form compact nano-sized alginate domains which are strengthened by the subsequent addition of polycation. When the addition order is reversed, the compact egg-box structure is not formed and the particle size increases (Rajaonarivony et al., 1993). Among the bioactive food ingredients, compounds within the vitamin B family have been extensively studied for encapsulation, as they are (i) especially unstable against various environmental conditions and are thus prone to degradation during processing or storage and (ii) as nanoencapsulation improves their adsorption. Azevedo et al. (2014) studied encapsulation and controlled release of riboflavin (vitamin B2) in alginate/chitosan nanoparticles, where the system was stable at 4°C for the duration of 5-month observation. The release behavior of vitamin at 25 and 37°C in acidic and neutral conditions indicates release occurs predominantly due to polymer matrix relaxation (Case II transport). Furthermore, delivery of antimicrobial agents is one of the current topics in food applications. Zohri et al. (2010) and Zimet et al. (2018) have studied encapsulation of

Table 3 Selected bioactive ingredients (ηe—encapsulation efficiency) encapsulated in alginate (alg)/chitosan (cs) or chitosan/alginate polyelectrolyte complexes (dp—particle diameter, Vζ—zeta potential, PDI—polydispersity index) at different feed compositions (calg—alginate concentration, ccs—chitosan concentration) Bioactive ingredient

Vitamin B2 Nisin Nisin BSA BSA BSA

BSA

Carrier matrix Na alginate (41–219 kDa)/chitosan (47–400 kDa) Ca alginate (15.9 kDa)/ chitosan Alginate/chitosan Ca alginate (300–400 cp) /chitosan (50–190 kDa) Na alginate/chitosan TPP quaternized chitosan/alginate Ca alginate (550 mL/g)/ quaternized chitosan (68 kDa) TPP quaternized chitosan (200 kDa)/alginate

calg; ccs (% w/w) 0.1; 0.1

alg:cs ratio

ηe (%)

dp (nm)

Vζ (mV)

0.01:1–17:1

–

100–6000

+60 to 60

CR

PDI

Source Sæther et al. (2008)

0.063; 0.04

1.6:1

55.9

104

30

0.3

17; 8.3

2:1

90–95

205

47

0.3

0.03–0.07; 0.015–0.009 8.3–16.7; 16.7–8.3 0.009–0.02; 0.11 0.07; 0.01

2:1–8:1

12–36

40–472

2:1–1:2

60–75

205–403

24 to 53 +15 to 47

0.4

1:6–1:12

14.5–100

113

+4

6:1–6:5

10–40

280–1152

+10

0.003–0.011; 0.14

1:13–1:47

96–99

138–232

+5 to +11

0.2

Azevedo et al. (2014) Zohri et al. (2010) Zimet et al. (2018) Zohri et al. (2011) Xu et al. (2003) Li et al. (2007) Chen et al. (2007) Continued

Table 3 Continued Bioactive ingredient Resveratrol

Resveratrol

Insulin

Insulin

Insulin

Carrier matrix

calg; ccs (% w/w)

Quaternized chitosan (50–10 kDa)/alginate (75–150 kDa) TPP quaternized chitosan (50–10 kDa)/alginate (75–150 kDa) Ca alginate (291, 369, 447 kDa)/chitosan (5, 50, 500 kDa) TPP chitosan (119 kDa)/ alginate(4–74 kDa)

0.015–0.075; 0.15

TPP chitosan (150 kDa) coated in alginate (3.5–7 cp)

alg:cs ratio

ηe (%)

dp (nm)

Vζ (mV)

PDI

Source

1:2–1:10

46–51

311–390

+36 to +19

0.3

Min et al. (2018)

48–57

340–380

+3 to 44

0.3–0.4

0.05; 0.012

4.3:1

79–83

781–4895

0.011; 0.15

1:14

41–52

250–525

+42 to +47

0.15–0.35 coating

1:3–1:5

55–80

240–320

15 to 5

0.2–0.4

BSA, bovine serum albumin; CR, charge ratio (where mass ratio of 1:1 corresponded to charge ratio of 1.2:1); MCT, medium chain triglycerides; TPP, tripolyphosphate.

Sarmento et al. (2007, 2008) Goycoolea, Lollo, Remun˜a´nLo´pez, Quaglia, and Alonso (2009) Zhang et al. (2018)

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355

cationic food preservative nisin in alginate/chitosan nanoparticles and its antimicrobial activity to S. aureus and L. monocytogenes. In both cases, domination of alginate within the overall structures was reflected in overall negative zeta potential values and good colloidal stability (at 20 to 50 mV). The studies suggest that entrapment is mostly due to nisin-alginate interactions, whereas chitosan provides structural stabilization. The monodisperse nisin-loaded alginate/chitosan nanoparticles provided relatively fast release of nisin (> 80% released within 5 h), high encapsulation efficiency, and reportedly exhibited higher antibacterial activity for raw and pasteurized milk products than Ca alginate microparticles, which was attributed to the native antimicrobial activity of chitosan itself. A vast array of particles was studied for antimicrobial activity in meat where the nanoparticles displayed sustained activity over time, both in in vitro (89% inhibition at 37°C during 24 h incubation, higher activity than free nisin within 27-day inhibition at 4°C) and in vivo assays (prolonged inhibition of growth in vacuum sealed, refrigerated beef samples as compared to free nisin), showing good potential for antibacterial application and extending of shelf life for various food products. The strength of the complexation method lies in the ability to control the particle charge. The net surface charge of the polyelectrolyte particles is crucial for facilitating the interaction with desired ingredients. If the surface charge is positive or uncharged, it will provide hydrophilic affinity, whereas negatively charged nanoparticles will show tendency for hydrophobic adsorption. In this way, alginate systems can be modified with polycationic networks for encapsulation of hydrophobic and poorly adsorbed components. BSA and resveratrol are the common model poorly adsorbed components for delivery via encapsulation in food applications, and some important potential in material development with important implication for the food applications has been demonstrated also in the field of encapsulation of insulin (Table 3). Zohri et al. (2011) evaluated the effect of polymeric ratios on the characteristics of alginate/LMW chitosan (2-:1–1:2) nanoparticles for the encapsulation of BSA. The highest entrapment efficiency of 70% was achieved at ratio of 1:1 (70%, dp ¼ 205 nm, Vζ ¼ + 15 mV) with the narrowest particle size distribution, confirming that the smallest and most homogeneous particles are produced when the interacting functional groups of both polymers are in equal proportion. The weight surplus of either of the polymers resulted in larger particles, negative average zeta potential, and up to 10% lower entrapment. The release profiles of BSA show higher levels of burst release (60% released within the first 15 min) from 2:1, delayed gradual release (70% release) within 2 h, and inhibited release for 1:2 alginate/chitosan particles. In order to provide a designated system for delivery of poorly adsorbed components, alginate/chitosan nanoparticles were prepared in conjunction with chitosan quaternization in several studies (Chen et al., 2007; Li et al., 2007; Min et al., 2018; Xu et al., 2003), as due to the introduction of aliphatic and aromatic acyl groups, these materials exhibit strong electrostatic attraction to hydrophobic species, as can be seen from good encapsulation efficiencies and surface charges in Table 3. Furthermore, the optimal alginate/chitosan weight ratio for low G content alginate and quaternized chitosan with high deacetylation degree was determined experimentally by Li et al. (2007) at 6: 1 (280 nm), as opposed to 1: 1 (1550 nm). It has been

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Biopolymer Nanostructures for Food Encapsulation Purposes

further reported that varying the acetylation degree of chitosan from 0.61 to 0.95 resulted in practically unchanged particle diameters, whereas the encapsulation efficiency of BSA was increased by >10% Similarly, by increasing the molecular weight of chitosan, the BSA encapsulation efficiency was increased fourfold. The results are indicating that depending on the desired ingredient for encapsulation, the possibilities for the smallest particle preparation may not always be in tune with the required structural properties of the polyelectrolyte complex and the desired level of encapsulantingredient interaction. The particles exhibited gradual and stable prolonged release of the encapsulated component in vitro, reaching up 22% of released BSA in simulated intestinal fluid and up to 100% release in simulated gastric fluid within 100 h of observation. Min et al. (2018) compared quaternized chitosan/high molecular weight alginate, tri-polyphosphate cross-linked quaternized chitosan/alginate, and tri-polyphosphate cross-linked quaternized chitosan particle for controlled release and improved cellular uptake of resveratrol. Alginate-containing nanoparticles were monodispersed, exhibited lower particle diameters and encapsulation efficiencies, and exhibited prolonged release within 6 h of observation at different pH values (3–9) in comparison to cross-linked chitosan particles. Chitosan/alginate particles that were not cross-linked exhibited highest cellular uptake in comparison to their cross-linked counterpart, but lower than cross-linked chitosan. Alginate particles inhibited around 80% of Caco-2 cancer cell growth, whereas >90% growth inhibition was recorded for resveratrol in cross-linked chitosan particles. Alginate/chitosan nanostructures exhibit transmucosal delivery features, which have been well documented in the field of insulin delivery. Goycoolea et al. (2009) studied insulin encapsulation in tri-polyphosphate cross-linked chitosan/alginate, wherein 41%–52% hormone encapsulation efficiencies were achieved. Following intranasal administration to rabbits, free insulin in solution was poorly adsorbed, whereas the insulin-loaded nanoparticles elicited significant adsorption enhancement, as reflected by maximum 14% and maximum 35% decrease of glucose levels at 30 and 45 min postadministration, respectively. The hypoglycemic effect corresponding to nanoparticle administration was significantly prolonged by up to 5 h with respect to the control. Similarly, Zhang et al. (2018) encapsulated insulin in alginate/chitosan nanoparticles for intestinal mucus penetration. Rat intestine studies showed that mucus penetration, permeation, and uptake were dependent on the surface charge and coating polymer, where negatively charged particles (Vζ   25 mV) with alginate outer coating exhibited two to threefold higher mucus penetration ability than positively charged (Vζ  +30 mV) chitosan particles. The low viscosity low G content alginate coating exhibited the best permeation (apparent permeability coefficient up to 3.5  106 cm/s vs. 1  106 cm/s for insulin in solution). These findings are important for designing delivery systems for nutraceuticals and other well-defined food ingredients.

4.2 Hydrogel templating methods Alginate nano-hydrogel templating methods are based on the spatial confinement and gelation of alginate containing phase within nanocavities in dispersions, and typically include (i) emulsification, where the template cavities are formed as single-phase

Nano-hydrogels of alginate for encapsulation of food ingredients

357

droplets, as well as (ii) micelle and liposome formation, where the single or multilayered spherical barriers are formed between aqueous and hydrophobic solvents by extended molecules with pronounced hydrophobic and hydrophilic regions.

4.2.1 Emulsion templating For the purpose of alginate nano-hydrogel templating, emulsions are formed by high energy (mechanical input) or low energy (via phase inversion temperature—PIT or phase inversion composition—PIC control) methods. In the latter approach, nanoemulsions are typically achieved with the use of small molecule surfactants and in absence of strong mechanical agitation (McClements & Jafari, 2018). Upon emulsification, the alginate containing water phase is gelled using various approaches, and consecutively the solvents are separated from the particles. Typically, templates are performed as (i) oil-in-water (O/W) emulsions for alginate nanocapsules formation to enable encapsulation of hydrophobic or poorly adsorbed compounds, and as (ii) water-in-oil (W/O) nanoemulsions for alginate nanocapsules formation at the water/oil interface or resulting in alginate nanospheres with a wide variety of applications.

4.2.1.1 Oil-in-water emulsions Emulsification offers several opportunities for delivery of oils, including their entrapment into alginate hydrogels (Table 4). Turmeric oil was studied as a model oily compound for the encapsulation within Ca2+ cross-linked alginate nanocapsules by Lertsutthiwong et al. (2008). Sonication was required to achieve uniform size distribution. Ethanol and acetone were investigated as possible solvents for the oil phase, where ethanol provided faster diffusion from the oil droplet into the water phase, resulting in smaller particles (dp ¼ 264 nm, Vζ ¼  17.4 mV). The capsules with 1:1 oil:alginate ratio gradually became larger during 45-day storage at 25°C, but maintained their size at 4°C. An increase in the oil concentration or oil/alginate mass ratio resulted in an increase in the average size of the nanocapsules (threefold size increase at 4:1 oil:alginate ratio). In another study (Lertsutthiwong et al., 2009), turmeric oil was encapsulated with emulsification in alginate/chitosan complexes. Chitosan content below 10 wt% in alginate was found to be optimal for the formation of stable nanocapsules, and the thickness of the capsule wall was determined at 10 nm. In accordance with general principles of the complexation technique, the smallest alginate/chitosan particles (dp ¼ 522 nm, Vζ ¼  22.2 mV) were found to be formed after Ca2+ pregelation and subsequent addition of low molecular weight chitosan. These materials also exhibited high recovery (67%) and unhindered physical stability during 4-month long storage at 4 and 25°C. As emulsification is performed at mild conditions, this encapsulation technique is also suitable for the encapsulation of structure dependent, heat sensitive components. Raei et al. (2015) examined encapsulation of camel lactoferrin in calcium alginate. Full encapsulation efficiency was achieved with an emulsification procedure performed at slightly elevated temperatures (61°C), where the smallest average particle

358

Table 4 Encapsulation (ηe—encapsulation efficiency) of food ingredients in alginate (calg—alginate concentration) nanoparticles prepared by emulsification (dp—particle diameter, Vζ—zeta potential, PDI—polydispersity index) Oil in water emulsions Bioactive ingredient Turmeric oil Turmeric oil

Ca alginate (80–120 kDa) Alginate (80–120 kDa)/ chitosan (41, 2 kDa) Ca alginate

Oleoyl alginate ester

Solvent/ surfactant

calg (% w/w)

ηe (%)

Vζ (mV)

dp (nm)

Ethanol/P80

PDI

23 to 14 23 to 19

78–234

Lertsutthiwong et al. (2008) Lertsutthiwong et al. (2009)

Ethanol/P80

0.05

52–68

162–777

Glycerol/P80

0.2, 0.5

39–100

336–807

6 to 3

0.5–0.7

727–53

32

0.4–0.1

Methylene chloride/P80

Source

Raei, Rajabzadeh, Zibaei, Jafari, and Sani (2015) Li et al. (2015)

Water in oil emulsions Bioactive ingredient Folic acid

Carrier matrix

Resveratrol

70:30 Ca alginate-pectin (26–30 DE) Ca alginate

Peppermint phenolic extract

Ca alginate (12–40 kDa)

calg (% w/w)

ηe (%)

dp (nm)

Vegetable oil/ PGPR

1

80

345

Unpublished data

Vegetable oil/ PGPR Canola oil/P80

2

24

250

0.5–1.0

4–10

90–4533

Isteni
c et al. (2015) Mokhtari, Jafari, and Assadpour (2017)

Oil/surfactant

DE, degree of esterification; PGPR, polyglycerol polyricinoleate; P80, polysorbate 80.

Vζ (mV)

PDI

Source

Biopolymer Nanostructures for Food Encapsulation Purposes

Camel milk lactoferrin Vitamin E

Carrier matrix

Nano-hydrogels of alginate for encapsulation of food ingredients

359

size was achieved (dp ¼ 336 nm, Vζ ¼  6.2 mV). The particles appear to have good characteristics for the protection during transport through the upper gastrointestinal tract, as no release of lactoferrin was detected during the first hour of the release test at both acidic and neutral pH values. Li et al. (2015) encapsulated vitamin E in oleate alginate ester (OAE) particles and separated various size fractions to study the effect of particle size. The average particle size of the initial batch was 451 nm, whereas by gradually increasing the centrifugation intensities, fractions with decreasing mean diameters (see Table 4), decreasing PDI (0.4 to 0.1), and decreasing loading capacities (12 to 5%) were obtained. In comparison with free vitamin E, the OAE nanocapsules increased the transport of vitamin E across Caco-2 cells, and the adsorption in the rat jejunum. Both of these uptake parameters were linearly increased as a function of particle size decrease, the smallest particles (50 nm) thus exhibiting three to ninefold increased values in comparison to the largest particles (730 nm) or free vitamin E, respectively.

4.2.1.2 Water-in-oil emulsions A procedure for the preparation of Ca alginate nanoparticles in W/O emulsions was described by Machado et al. (2012). The method was based on phase inversion temperature and consisted of mixing decane and Na alginate aqueous solutions in the presence of a surfactant with limited solubility in decane at 40°C. With 1–2 wt% alginate, thermodynamically stable nanoemulsions were formed (50–80 nm droplet size), whereas 0.5 wt%. alginate droplets in emulsion exhibited growth. Gelation was achieved with addition of aqueous solution of CaCl2. Particles were separated by dilution and equilibration (addition of CaCl2 solution to facilitate particle separation and addition of decane to improve surfactant extraction) and decanting overnight at the defined PIT. By employing a similar approach, Paques, van der Linden, van Rijn, and Sagis (2013) prepared alginate submicron beads (200–1000 nm), employing 1 wt% alginate and medium chain triglyceride oil containing low amounts of polyglycerol polyricinoleate (PGPR) as surfactant. In this variation of the emulsification procedure, CaCl2 nanoparticles are added to the emulsion in the form of an MCT dispersion, allowing the particles to migrate to the emulsion droplet interface, where they dissolve into alginate solution, enabling external gelation, where the beads are more extensively cross-linked on their surface. The method was further adapted to enable internal gelation for obtaining nanobeads (200–2000 nm) with a uniform degree of alginate cross-linking throughout the alginate structure. An example of the particles prepared with this approach for the encapsulation of folic acid in alginate/pectin nanocapsules (unpublished data) and the corresponding size-dependent release is presented in Fig. 4 and Table 4. For internal gelation, water-insoluble CaCO3 nanoparticles were dispersed within the alginate solution, together with a slow hydrolyzing acidifier. The alginate mixture was then emulsified in MCT oil with PGPR and gently mixed for several hours to allow for the acidification, subsequent dissociation of Ca2+, and consequential gelation of alginate nanospheres (Paques, Sagis, van Rijn, & van der Linden, 2014).

360

Biopolymer Nanostructures for Food Encapsulation Purposes

Fig. 4 Morphology and particle size distribution with SEM micrograph insets of Ca alginate/ pectin nanocapsules as prepared at the Biotechnical Faculty, University of Ljubljana (unpublished data) by W/O templated external gelation (left). Measurements were performed with Supra VP (Carl Zeiss AG, Germany) scanning electron microscope (acceleration voltage of 1 kV, 30 μm aperture size, 3 mm working distance) and FIJI software package (Schindelin et al., 2012) for biological image analysis. Release levels are shown and compared to reference (right). The alginate/pectin nanocapsules (denoted as: nano) provided thermal protection and delayed release of folic acid at temperatures relevant for food processing and/or pasteurization in comparison to corresponding alginate/pectin microbeads (denoted as: micro; dp  150 μm). Error bars are denoting the standard deviation. Release was determined in dH20 (ρ ¼ 18.2 MΩ cm) and followed by reverse phase chromatography (Agilent 1260 Infinity HPLC system equipped with DA-detector and the Zorbax Eclipse Plus C18 4.6  150 mm, 3.5 μm column).

As an alternative to water-soluble CaCl2, formation of a network between low molecular weight alginate and water-soluble low molecular weight chitosan (i.e., oligochiotsan) has been demonstrated by Wang and He (2010), resulting in W/O emulsion templated monodisperse alginate/chitosan nanospheres (dp ¼ 136 nm) with good biocompatibility, 88% encapsulation efficiency of the encapsulated BSA, 2 h release delay, and sustained release within the 24-h observed time window. Mokhtari et al. (2017) have thoroughly examined the use of low energy W/O templating for internal gelation of alginate, where nanoencapsulation of peppermint phenolic extract was performed in order to prevent its oxidation and volatilization. Efficient emulsification and gelation was achieved through special configuration of the stirring magnets and by spraying the CaCl2 solution on the surface of the prepared emulsions. Nanospheres with a wide range of size and extract encapsulation efficiencies were obtained by systematic investigation of individual contents of alginate, Ca2+, canola oil, and polysorbate 80. The authors report that by lowering the alginate concentration (down to 0.5% w/v alginate in the aqueous phase) and increasing the oil content within the 400–800 mL range, the size of the obtained Ca alginate nanoparticles could be drastically decreased. The same functionality was observed to a lower extent for decreasing the availability of Ca2+ (from 0.15 to 0.05 M, while

Nano-hydrogels of alginate for encapsulation of food ingredients

361

maintaining the 1:1 ratio of aqueous/oil phase) and surfactant (100–300 μL). The smallest nanospheres exhibited an average diameter of 90 nm, and the size was found to further decrease by dehydration to 60 nm. However, decreasing the particle size was accompanied by a roughly threefold decrease in encapsulation efficiency and the particles with the optimal encapsulation efficiency (6%) and size (785 nm) were achieved at the lowest content of all the studied components. Using the W/O emulsification external gelation approach and food approved ingredients, Isteni
c et al. (2015) encapsulated resveratrol in Ca alginate nanospheres. In order to obtain a working formulation, 1%–2% (w/w) alginate, and two different weight ratios of CaCl2-in-oil:alginate-in-oil of 2:1 and 3:1 were tested. The formulation comprising 2% alginate and 2:1 CaCl2 nanoparticles-in-oil: alginate-in-oil ratio was found to be successful, whereas other combinations were not observed to be sufficiently gelled. The spheres exhibited improved burst release, and complete release of the resveratrol was observed within the first 10 or 120 min, at low or neutral pH, respectively, indicating the approach is more suitable for preservation purposes.

4.2.2 Liposomal templating In micellar or liposomal templating, alginate is enclosed in liposomes. Next, the lipid bilayer of the liposome is temporarily partly destabilized (e.g., by heating), in order to enable penetration of the external gelling ions and consequential gelation within the liposome core. A detergent is added in order to remove the liposome structure, releasing the formed Ca alginate hydrogel nanoparticles. Hong et al. (2008) used the described principle to prepare template liposomes with high bilayer melting temperature based on zwitterionic lipid 1,2-dipalmitoyl-snglycero-3-phosphocholine (DPPC), anionic lipid dicetyl phosphate (DCP), and cholesterol as a permeation enhancer. Low molecular weight alginate (145 kDa) was encapsulated within liposomes, and the entry of Ca2+ ions into the liposome core was facilitated by repeated cycling from 0 to 60 °C. After removal of the bilipid layer, Ca alginate nanogels with a narrow size distribution and diameters from 65 to 85 nm were obtained (with liposome sizes from 50 to 100 nm) at the lower end, and by adjusting the DPCC/DCP ratio, liposomes of 400–500 nm were obtained. De Santis, Diociaiuti, Cametti, and Masci (2014) produced nanohydrogels of similar dimensions (80–100 nm) using low molecular weight polysaccharide mix consisting of alginate and hyaluronic acid, which were cross-linked with L-Lysine ethyl ester dihydrochloride within polyion complex micelles. An alternative approach to liposome templating by formation of alginate nanospheres within the liposome core is the production of hollow alginate/chitosan nanocapsules by adsorption onto the liposome surface and subsequent surfactantaided removal of the liposome forming molecules. Cuomo et al. (2012) prepared positively charged phosphatidylcholine/DDAB liposomes, which were coated with alternating layers of alginate and chitosan until the surface charge neutralization point was exceeded (reaching zeta potential of +40 or  40 mV) at each step and the lipid core was removed by Triton X-100. The obtained alginate/chitosan-loaded liposomes exhibited a homogeneous particle dimensions (PDI < 0.2) and increasing size with

362

Biopolymer Nanostructures for Food Encapsulation Purposes

the addition of each layer, from 135 nm for the first layer to 300 nm after the deposition of fifth layer onwards. The hollow alginate/chitosan particles exhibited slightly reduced size compared with their liposome filled counterparts and exhibit major variations in size depending on the bulk solution pH and in dependence on the outer polyelectrolyte layer, but generally exhibiting larger diameters at higher pH values, which may be an interesting function for targeted delivery systems.

4.3 Electrospinning and electrospraying Electrohydrodynamic processes generate electrically charged streams of polymer solutions that can be either spinned for the production of fibers (i.e., electrospinning) or sprayed to obtain particulate matter (i.e., electrospraying) (Faridi Esfanjani & Jafari, 2016). Apart from the mode of final dispersion, the two processes are distinguished by feed concentrations, where lower concentrations with low viscoelastic properties are necessary to obtain fine droplets, whereas at higher concentrations sufficient level of polymer entanglements allow for the formation of fibers with controlled structural properties and orientation (Bhushani & Anandharamakrishnan, 2014; Wen, Wen, Zong, Linhardt, & Wu, 2017). Due to tunable morphology and structural strength, and the inherent ability to form sheets and mats, nanoencapsulation of heat-sensible active components via electrospinning is of great interest for bioactive food packaging and topical food coating applications, where fibrous materials with antimicrobial or probiotic performance are sought and are primarily based on combinations with chitosan, which has well known and researched antimicrobial activity. Pharmaceutical and medical applications involve development of wound dressings and tissue engineering (Bhattarai & Zhang, 2007; Bonino et al., 2011). Via electrospraying, the same compounds can be sprayed directly on the food surface in the form of edible films and coatings; however due to nozzle and viscosity constrains, as well as required coating thicknesses, electrospraying is currently practically achievable at the microparticle domain ( Jafari, 2017). Relatively new advances in electrostatic droplet generation techniques (Nedovic et al., 2001; Watanabe, Matsuyama, & Yamamoto, 2001; Xie & Wang, 2007) enabled Ghayempour and Mortazavi (2013, 2014) to demonstrate a coaxial jet electrospraying method that was used to prepare Ca alginate nanocapsules (80–160 nm average diameter) for encapsulation of peppermint essential oil. The nanocapsules encapsulated 96% of initial essential oil, which was protected from degradation and maintained its antimicrobial activity with 100% reduction against S. aureus and E. coli. The main challenge in electrospinning of alginate nanofibers is its limited solubility (up to 2 wt% at neutral pH for HMW alginate) and high viscosity. Alginates therefore require addition of carrier materials (e.g., polyethylene glycol—PEG or poly(vinyl alcohol)—PVA), special cosolvents, and/or surfactants, in order to achieve sufficient polymer concentration and optimal jet whipping motion, which enable weaving the polymer into ultrafine, bead-free alginate nanofibers (Safi, Morshed, Hosseini Ravandi, & Ghiaci, 2007), as reflected in the selection of produced materials in Table 5. In the same concentration range, alginates with high viscosity favor the

Fibers produced

calg (% w/w)

V (kV)

WD (cm)

dtip (mm)

qfeed (mL/h)

df (nm)

Source

Ca alginate/PEG (100 kDa) Na alginate (700–900 cp)/PEG (300 kDa) Na alginate (700–900 cp)/PVA (50 kDa) Ca alginate (1.2 kDa)/ PVA (35–50 cp) Ca alginate (3500 cp)in glycol:water (2:1) Na alginate/PEG (9000 kDa) L Ca alginate/PEG (9000 kDa) L Ca alginate (37 kDa)/ PEG (600 kDa) F127 Ca alginate (196 kDa)/ PEG (600 kDa) F127 Ca alginate (196 kDa)/ PEG (600 kDa) T Na alginate (37 kDa)/ PEG (600 kDa) F127

0.5–2

15

20

3

0.5

46–266

0.6–1.4

11

10

0.7

99

Lu, Zhu, Guo, Hu, and Yu (2006) Safi et al. (2007)

0.6–1.4

12

10

0.7

118

2.8–3.6

16–18

1.6–2.4

28

12

2

0–40

1–2

98–192 6.3

120–300

10–25

0.2–1.5

174–246

0–40

15

0.2–10

80–400

11.2

10–15

15

0.7

0.5–0.75

150

2.8

10–15

15

0.7

0.5–0.75

140

2.8

10–15

15

0.7

0.5–0.75

150

12

0.7

0.5

221–249

10.6

0.3

Tarun and Gobi (2012) Nie et al. (2008) Kim and Park (2009) Park, Park, and Kim (2010) Bonino et al. (2011)

Nano-hydrogels of alginate for encapsulation of food ingredients

Table 5 Electrospinning of alginate/co-polymer nanofibers (df—fiber diameter) at different feed compositions (calg—alginate concentration in feed, PEG: poly ethylene glycol, PVA: poly vinyl alcohol) and operating parameters (V—voltage, WD—working distance, dtip—tip aperture size, qfeed—feed flow) for recent applications in nano spray drying of alginates

Bonino et al. (2012) 363 Continued

364

Table 5 Continued Bioactive ingredient

L. rhamnosus GG

calg (% w/w)

V (kV)

WD (cm)

dtip (mm)

qfeed (mL/h)

df (nm)

Source

Alginate (250 cp)-pectin (70:30)/PEG(900 kDa) Alginate/PVA

1.7 1.7 2.6

20–22 20–22 22

18 18 10

1.0 1.0

0.4 0.4 1.2

150 40 60–580

Alborzi, Lim, and Kakuda (2013) Ceylan et al. (2018)

Surfactant used—F127: pluronic F127; L: lecithin; P80: polysorbate 80; T—Triton X-100. Procedures are typically performed at near ambient temperature (e.g., 20–30°C) in a relatively dry atmosphere (e.g., 30%–55% RH).

Biopolymer Nanostructures for Food Encapsulation Purposes

Vitamin B9

Fibers produced

Nano-hydrogels of alginate for encapsulation of food ingredients

365

formation of beads or beaded nanofibers, whereas low viscosity alginates produce bead-free nanofibers. Similarly, maintaining the alginate type, at low alginate concentrations ultrafine nanofibers are produced, whereas at increased concentrations, bead formation is facilitated by electrospinning. The hydrosoluble copolymers such as PEG and PVA interact with alginates through hydrogen bonding to reduce the overall viscosity thus making the mixed feed to be spinnable (Bhattarai, Li, Edmondson, & Zhang, 2006; Bonino et al., 2011). Furthermore, as these copolymers are soluble in water, several authors have reported that they can be recovered after electrospinning to obtain pure alginate nanofibers (Bonino et al., 2011; Dı´az, Ferna´ndez-Nieves, Barrero, Ma´rquez, & Loscertales, 2008). Generally, the copolymers are required for electrospinning of alginate, whereas the addition of small amount of surfactants (e.g., lecithin, pluronic F127 and polysorbate for food use, or Triton X-100 for research purposes) is used in order to increase alginate concentrations in the blend for systems that have reached the onset of fiber formation (Bhattarai & Zhang, 2007; Bonino et al., 2011; Ghayempour & Mortazavi, 2013; Kim & Park, 2009). The produced nanofibers are subsequently cross-linked to maintain their structural integrity in water. This is typically achieved by CaCl2 solution, often in aqueous ethanol solution, or even by complete replacement of water by ethanol, in order to reduce the gyration radius of Ca2+ alginate hydrogel and consequentially achieve compaction of the polymer fibrils and decreased swelling degree of the prepared hydrogels in comparison to cross-linking performed in water (Gurikov & Smirnova, 2018; Robitzer, David, Rochas, Renzo, & Quignard, 2008). Furthermore, several cross-linking steps may be applied to gradual loss of the structural integrity of these fibers in water and ionic solutions. For example, Bhattarai and Zhang (2007) prepared completely water insoluble fibers by further cross-linking Ca alginate nanofibers with epichlorohydrin, glutaraldehyde, hexamethylene diisocyanate, or adipic acid hydrazide to obtain materials that were designated for use in different chemical or biological environments. The obtained fibers maintained their structure through 7-day incubation in simulated body fluid. Additional electrospinning apparatus configurations offer more advanced approaches for the modulation of nanofibers material properties. For example, side-by-side electrospinning technique allows the introduction of several compounds, which are not joined until immediately before jet formation, providing the opportunity for in situ copolymer complexation. Using this technique, Jeong et al. (2011) prepared alginate/chitosan complexation which was carried out during the fiber formation process, to obtain water stable and compact nanofibers (df ¼ 100 nm) low swelling ratios which required no further cross-linking, yet still allowed subsequent PEG extraction. Alborzi et al. (2010, 2013) encapsulated vitamin B9 (folic acid) into alginate–pectin–polyethylene glycol electrospun fibers, using either low- or medium-viscosity alginates. The encapsulated vitamin was completely retained over 40 days in dark and less for the fibers when stored in dark in acidic conditions, as compared to the unencapsulated folic acid, that exhibited 92% degradation during the first day at the same conditions. The nanofibers exhibited higher vitamin retention than alginate alone, and the alginate and pectin blend was more efficient in comparison to those prepared from alginate alone. Although the low viscosity alginate-based nanofibers

366

Biopolymer Nanostructures for Food Encapsulation Purposes

exhibited bead-free morphologies, which was not the case for the incorporation of medium viscosity alginate, the recovery and stability of folic acid within both types of nanofibers exhibited similar behavior. The protecting effect was attributed to physical entrapment of the vitamin within the modified alginate and pectin structure in acidic media. Ceylan et al. (2018) encapsulated L. rhamnosus GG probiotic into alginate/PVA nanofibers for probiotic coating of fish fillets. >80% (at  10 log CFU/mL) of the introduced probiotic bacteria survived the nanoencapsulation procedure. The microbiological tests have shown that both bare (df ¼ 60 nm, Vζ ¼  6.3 mV) and probiotic-loaded (df ¼ 580 nm, Vζ ¼  7.7 mV) nanofibers efficiently delayed the total mesophilic aerobic bacteria and total psychrophilic bacteria growth in fish fillets, whereas only the probiotic-loaded nanofibers delayed the growth of yeast and molds.

4.4 Nano spray drying Conventional spray drying equipment allows for the preparation of particles in the 5 mm–10 μm range where applied atomization techniques provide relatively large droplet diameters and wide size dispersity. A relatively recently developed piezoelectric-driven vibrating mesh atomizer (Arpagaus, 2012) enables preparation of nanoparticles within the 100 nm range in the laboratory. Here, droplets are dispersed by sonication through the mesh at size ranges below the micron mesh window diameter and dried at mild conditions in a medium-velocity cocurrent laminar flow (Arpagaus, Collenberg, R€ utti, Assadpour, & Jafari, 2018). Consecutively, the dry particles are harvested in the electrostatic particle collector, where high product detainment is achieved, reaching yields above 90% (Blasi, Schoubben, Giovagnoli, Rossi, & Ricci, 2010). Soluble spray dried alginate nanoparticles can be prepared (Fig. 5 and Table 6), in order to obtain stable powdered formulations to enhance emulsifying and in situ gelling properties of alginate, prolong stability, improve dispersibility, and simplify handling and dosing of various bioactive compounds (Blasi et al., 2010; De Cicco, Porta, Sansone, Aquino, & Del Gaudio, 2014; Oliveira et al., 2013). The use of nano spray drying for food applications has great potential due to ease of handling and material preparation; however, only a few of such studies have been currently reported in the literature (Table 6). Depending on the required particle size, reported alginate concentrations for nano spray drying range from 0.1 to 1% (w/w) and cause mesh clogging above 0.5 or 1% (w/w), depending on mesh aperture, alginate viscosity, and molecular weight. Such carriers enable immediate release upon ingestion (e.g., for tabletop use) or addition in water (e.g., for use in non-drink-related food processing). Furthermore, alginate nanoparticles have promising aspects for various mucosal delivery applications of nutraceuticals and pharmaceutical ingredients, enabling fast release in both gastric and enteric conditions, reaching complete release within a matter of minutes for hydrophilic components (Oliveira et al., 2013). Combination with other biopolymers results in nano spray dried powders for controlled prolonged release for hydrophobic compounds, such as for essential oils

Nano-hydrogels of alginate for encapsulation of food ingredients

367

Fig. 5 Morphology and particle size distribution with SEM micrograph insets of sodium alginate powders (C01: calginate ¼ 0.1 wt%; C05: calginate ¼ 0.5 wt%; M4: 4.0 μm mesh, M55: 5.5 μm mesh, M7: 7.0 μm mesh), as prepared at the Biotechnical Faculty, University of Ljubljana (unpublished data) by means of B€uchi Nano Spray Dryer B90 (Ti ¼ 80 °C, To  40°C, qair ¼ 133 L/min, Pair ¼ 45 mbar, qfeed ¼ 0.25 mL/min). For all materials, yields between 70 and 80% were achieved. Measurements were performed with FEI Quanta 250 scanning electron microscope (acceleration voltage of 10–15 kV, 1.5–2.0 spot size, 10 mm working distance) and FIJI software package (Schindelin et al., 2012) for biological image analysis.

encapsulated in alginate/cashew gum where the component was gradually released within one or 2 days (Oliveira et al., 2013). Long-term stability has also been reported, for example, De Cicco et al. (2014) reported 6-month preservation of the watersoluble compounds within alginate/pectin particles. Furthermore, alginate coating of nano spray dried solid lipid nanoparticles, as well as nanostructured lipid carriers, resulted in strong repulsion among particles, thus providing excellent colloidal stability (Wang et al., 2016). Recent spray-drying procedures allow formulation of cross-liked alginate gels during spray drying internal gelation, and the obtained particles provide a more gradual release in water required for targeted gut delivery in comparison to soluble Na alginate particles. Cross-linking is achieved upon atomization via temporally or temperature-

368

Table 6 Operating conditions (dm—mesh aperture size, Ti—inlet temperature, qgas—drying gas flow) and the resulting material properties (dp—particle diameter, Vζ—zeta potential) for recent applications in nano spray drying of alginates (calg—alginate concentration in solution) Bioactive component

calg (% w/w)

dm (μm)

Na alginate (4 cp)

0.1

Na alginate (50 cp)

0.13

Vitamin B12

Na alginate (54 kDa)

0.1

Essential oil

Alginate (54 kDa)/ cashew gum (110 kDa) (1:3–3:1) Alginate

Ti (°C)

qgas (L/min)

4.0, 5.5, 7,0

80

133

4.0, 7.0 4.0, 7.0

110

100

120

130

0.2, 0.5, 1.0

–

170

580

0.4

5.5

100

Na alginate (20 cp)

Glyceryl behenate Oleic acid

Alginate

120

dp (nm)

Vζ (mV)

370, 390, 1210 390, 480, 780 760 to 5500 >1000 E

Source Unpublished data

Blasi et al. (2010)

W

36 to 30

Oliveira, Guimara˜es, Cerize, Tunussi, and Poc¸o (2013) de Oliveira et al. (2013)

300

86

Wang et al. (2016)

250–280

85 to 80

223–399

E, DLS measurements of swollen alginate particles in ethanol, W, DLS measurements of partly solubilized particles in deionized water.

Biopolymer Nanostructures for Food Encapsulation Purposes

Carrier matrix

Nano-hydrogels of alginate for encapsulation of food ingredients

369

controlled release of gelling multivalent ions. The technique involves suspending insoluble CaCO3 within the Na alginate feed solution in combination with the addition of either a weak acid (Popeski-Dimovski, 2015) allowing for slow gelation during spray-drying, or an acid neutralized with a volatile base ( Jeoh-Zicari, Scher, Santa-Maria, & Strobel, 2011) allowing for gelation triggered by decrease of pH due to base volatilization at operating temperatures of the spray-dryer.

4.5 Combined techniques 4.5.1 Core-shell and layer-by-layer nanoparticle preparation Using various nanoencapsulation approaches, further variations of the procedures can be performed. For example, the coacervation process can be performed: (i) with simultaneous linking of alginate and chitosan networks in the presence of an ionic cross-linker (typically CaCl2 or tripolyphosphate) to obtain nanoaggregates, (ii) by pregeling the initial biopolymers (alginate with CaCl2, chitosan by tripolyphosphate) and subsequently adding the oppositely charged biopolymer to obtain core–shell particles, where the encapsulated components are located in the core, (iii) or following pregel, by repeatedly exposing the particle to polyelectrolytes with interchanging opposite charges, to provide multiply layered materials. (iv) Alternatively, for the synthesis of a core-shell particle, the core can be prepared by templating, liposome preparation, nano spray drying and such, and the opposed charged outer biopolymer coat can be then applied via electrostatic interactions.

4.5.1.1 Liposome-alginate-chitosan nanoparticles Haidar et al. (2008) demonstrated layer-by-layer self-assembly of monodisperse liposome–alginate–chitosan nanoparticles (dp ¼ 383 nm, Vζ ¼ 44.6 mV) for the delivery of BSA. The system exhibited high encapsulation efficiency (up to 80%), eliminated the protein burst release feature, and provided sustained linear release within 30-day observation time. Liu et al. (2017) performed a similar layer-by-layer electrostatic deposition of alginate and chitosan in vitamin C-loaded monodisperse anionic liposomes (dp ¼ 58 nm, Vζ ¼  6.3 mV). The obtained coated structures (dp ¼ 297 nm, Vζ ¼  15.0 mV) provided structural stabilization and long-term protection from oxidation and hydrolysis of the encapsulated compound, maintained the organoleptic properties, and assured high microbiological stability of the receiving food product (mandarin juice) during 90-day long storage at 4°C.

4.5.1.2 Solid core-alginate-chitosan In a similar approach to alginate polyelectrolyte complexation, alginate nanoparticles can be formed by electrostatic deposition of alginate on sufficiently negatively charged solid particles. For hydrophobic active ingredients, layer-by-layer synthesis can provide valuable properties in aqueous environments, as the application of a hydrophobic core can assure sufficient encapsulation efficiencies, and the subsequent polysaccharide coatings can overcome obstacles of lipid handling in water. Chitosan- and alginate-coated

370

Biopolymer Nanostructures for Food Encapsulation Purposes

lipid nanoparticles were prepared by Fathi and Varshosaz (2013) in order to enhance the antioxidant functionality of flavonoid hesperetin for the fortification of milk (Table 2). Various procedural aspects of the lipid core preparation are discussed in Fathi et al. (2013). For comparison, hesperetin was directly encapsulated in various polysaccharides in absence of the lipid core, where encapsulation efficiencies were negligible (up to 6%), whereas 40%–60% of hesperetin was retained within the lipid core. The alginate/chitosan-coated lipid core exhibited slower release profiles in gastric condition than uncoated formulations. Furthermore, sensory analysis showed that both the bitter taste associated with flavonoids, as well as the yellow color of hesperetin, were successfully masked by the described delivery system. As an example where the solid core can represent the encapsulated component itself, Hu and McClements (2015) describe the preparation of alginate-coated zein particles with 80 nm core, 40 nm shell, and a net electrical charge of 21 mV. The particles were across a wide pH range (3–8) and were stable at heating (at 90°C for 120 min), as well as during storage at 4 and 25°C for 45 days. Furthermore, the solid core can be selected as a size determining coating nucleus as well as due to its additional functionality. Magnetite particles were incorporated into alginate/chitosan particles for the immobilization of lipase in order to achieve facile separation of the immobilized enzyme (Liu et al., 2012). The layer-by-layer approach was performed by controlled cross-linking of sodium alginate with Ca2+ in dispersion of Fe3O4 particles, followed by product separation with a magnet. The particles were further coated with chitosan via a self-assembly technique, obtaining either negatively charged alginate coated (30 mV) or alginate-chitosan layered (+35 mV) superparamagnetic nanospheres with 50–60 nm diameters. The highest enzymatic activity and enzyme reusability was determined for covalently immobilized lipase on the surface of magnetite-alginate-chitosan spheres.

4.6 Liposome entrapment The entrapment technique of nanoparticles within larger, typically micro-sized alginate structures, does not necessarily classify as nanoencapsulation method. However, it does enable sequestration and handling of small nanoparticles with superior colloidal properties, which cannot be harvested by usual methods. In particularly, nanogels obtained with templating and liposomes are not easily recovered and often require ultracentrifugation, which is impractical for commercial food applications. The prepared liposomes are thus introduced into gelled alginate microparticles, which are postulated to enable delivery to the designated part of the gut, where the alginate is degraded by the residential microbiota and the liposomes become available for mucosal uptake. Apart from simplified recovery and handling, as well as enabled use of nanoparticles in traditional encapsulation applications, the entrapment within alginate and alginate-based hydrogels provides long-term protection of the encapsulated component. Liposome entrapment has been demonstrated as chemically unstable oily nutraceuticals, such as vitamin B5 and polyphenol antioxidant epigallocatechin gallate (Isteni
c et al., 2016; Ota et al., 2017), in order to enable their incorporation into long

Nano-hydrogels of alginate for encapsulation of food ingredients

371

shelf life food products. Both functional compounds were encapsulated into proliposomes using the method described by Perrett, Golding, and Williams (1991), allowing for the formation of liposomes with 200–400 nm outer dimensions, and consecutively microencapsulated with an electrostatic vibrating nozzle device within 240–300 μm alginate/pectin microbeads for pantothenic acid and 320–350 μm for phenol-containing alginate and chitosan microbeads. With liposomes, 75% encapsulation efficiency of pantothenic acid was achieved which was not increased by microencapsulation and the beads exhibited prolonged stability within 7-day observation period, where pantothenic acid release was mainly driven by diffusion-controlled mechanism. In the case of encapsulation of epigallocatechin gallate, negligible amounts of the polyphenol were encapsulated in both polysaccharide networks (below 1%), and the majority of the components was released within 20 min. On the other hand, 97 and 99% of the components were retained when liposomes were present and were linearly released in comparable amounts for alginate or chitosan microbeads, reaching roughly 3% release at ambient temperature, pH values above 4 at the end of two-week observation period. The system provided superior protection properties for the designated application, as 30% of free epigallocatechin gallate was degraded during in fruit nectar (pH ¼ 3.8) stored at ambient conditions, in 14 days, while three to fivefold less degradation was observed in liposomes or liposomes in chitosan (5%) or liposomes in alginate (10%). Similarly, trimyristin was studied as a model saturated fat for lipid delivery and storage aspects (Strasdat & Bunjes, 2013). The lipid nanoparticles were prepared by high pressure homogenization and the emulsified monodispersed droplets with diameters of 80–90 nm were subsequently deposited within Ca alginate microbeads obtained by electrostatic droplet generation (330–1350 μm), or spray-drying (20–100 μm). The authors developed the use of differential scanning calorimetry for detecting errors in the lipid processing during nanoencapsulation. The lyophilization procedure was found to be insufficient for preservation, as it dramatically altered the state of the incorporated lipid. The lipid-containing particles were, however, successfully frozen in the presence of monosaccharide cryoprotectants, demonstrating feasible and straightforward storage approaches are possible even for these advanced nanostructured materials.

5

Conclusion and further remarks

In this chapter we demonstrate that although alginate may not be the material of first choice in nanoencapsulation, its wide availability, wide range of chemical properties, and diverse functionality provide for a versatile carrier or carrier base for a variety of food applications. Importantly for nanoencapsulation, the vast array of available and customizable alginate networks in combination with various cross-linking approaches enable preparation of materials with controlled morphology, size, internal structure, and surface properties. Furthermore, its inherent properties, such as burs release and rejection of hydrophobic compound can be significantly improved by

372

Biopolymer Nanostructures for Food Encapsulation Purposes

combination of alginate with appropriate anionic or cationic polysaccharides or via alginate functionalization. Due to the continuous progress in the fields of material science and food technology, increasing food applications in nanoencapsulation with alginate are to be expected. Carriers with an increased content of alginate are foreseen, where the opportunities for nanoencapsulation lie in the nonexploited approaches for nonconventional cross-linking, achieving desired properties with ligands, alginate grafting, as well as biotechnological and enzymatic modification.

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Further reading Sabra, W., Zeng, A.-P., & Deckwer, W. D. (2001). Bacterial alginate: physiology, product quality and process aspects. Applied Microbiology and Biotechnology, 56(3–4), 315–325. Saquing, C. D., Tang, C., Monian, B., Bonino, C. A., Manasco, J. L., & Alsberg, E. (2013). Alginate-polyethylene oxide blend nanofibers and the role of the carrier polymer in electrospinning. Industrial and Engineering Chemistry Research, 52(26), 8692–8704.

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Safoura Akbari-Alavijeh*, Rezvan Shaddel†, Seid Mahdi Jafari‡ *Department of Food Science and Technology, College of Agriculture, Isfahan University of Technology, Isfahan, Iran, †Department of Food Science and Technology, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, Ardabil, Iran, ‡ Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

1

Introduction

Nanotechnology involves development, manipulation, and application of materials at nanometer scale. The manipulation at this scale leads to the creation of novel materials which may have the same composition but widely varying properties. This way, nanotechnology promotes the development of a new generation of current products and processes for a variety of industries like engineering, telecommunications, electronics, agriculture, medicine, cosmetics, and food (Augustin & Oliver, 2012; Augustin & Sanguansri, 2009). In the food industry, nanotechnology has been used for development of nanoscale processes and ingredients, for example, encapsulation of new functional materials, and also methods and instrumentation to improve food safety, nutritional value, and biosecurity. Today, nanoencapsulation as an emergent field of nanotechnology using nanostructure materials involves entrapping bioactive agents, enabling targeted delivery, enhancing the resistance to thermal and mechanical stresses, using lower quantity of chemical and synthetic preservatives to provide superior organoleptic characteristics (Abaee, Mohammadian, & Jafari, 2017; Akhavan, Assadpour, Katouzian, & Jafari, 2018; Jafari & McClements, 2017; Katouzian, Faridi Esfanjani, Jafari, & Akhavan, 2017). The important issue considering application of nanoencapsulation in the food industries is to utilize renewable source-based biopolymers of natural origin as carriers ( Jafari, Fathi, & Mandala, 2015). Moreover, the carrier materials must be food grade and resistant in food systems within processing, storage, and utilization (Mokhtari, Jafari, & Assadpour, 2017). The most compatible biopolymers for this purpose are largely combined with repeating units of monosaccharides, amino acids, or lipids. Some examples of the biopolymers are proteins (e.g., whey protein isolate and zein), polysaccharides (e.g., pectin, alginate, dextran, and chitosan), and lipids (e.g., intermediate-chain triglycerides, tristearin, and corn oil) (Chassenieux, Durand, Jyotishkumar, & Thomas, 2013; Faridi Esfanjani & Jafari, 2016; Fathi, Martı´n, & Biopolymer Nanostructures for Food Encapsulation Purposes. https://doi.org/10.1016/B978-0-12-815663-6.00014-8 © 2019 Elsevier Inc. All rights reserved.

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McClements, 2014). The exclusive properties of polysaccharides have made them one of the most suitable choices for delivery systems. Polysaccharides have a great ability to be modified in order to obtain the desired features. Besides, they show a good resistance to stress conditions like high temperatures. On the other hand, they are able to bind or entrap various bioactive food substances (both hydrophilic and hydrophobic compounds) via their functional groups. Depending on their ionic groups, several polysaccharides are anionic (e.g., alginate), cationic (e.g., chitosan), or neutral (e.g., starch). These variations let polysaccharides to reveal several functional features like solubility, gelation, thickening, surface activity, water holding capacity, digestibility, and emulsification (Akbari-alavijeh, Soleimanian-zad, Sheikh-zeinoddin, & Hashmi, 2017; Assadpour & Jafari, 2018; Azevedo, 2013; Fathi et al., 2014). This chapter critically reviews the properties, processing, and applications of chitosan nanostructures for nanoencapsulation of food materials and discloses several of the advantages and limitations of various processes. Nutritional and functional proficiencies of various chitosan-based nanocarrier systems are also provided.

2

Physical and chemical properties of chitosan

2.1 Native chitosan Chitosan as the second most numerous natural biopolymer next to cellulose is a linear polycationic, biodegradable, nontoxic, and biocompatible polysaccharide isolated from the N-deacetylation of chitin composed of copolymers of deacetylated units of D-glucosamine and acetylated units of N-cetyl-D-glucosamine joined by β (1,4) glycosidic linkages (Azevedo, 2013; Fathi et al., 2014; Luo & Wang, 2013; Shahidi, Arachchi, & Jeon, 1999). The chitin is isolated from cuticle of walls of fungi, insects, and exoskeletons of marine arthropods. When converting chitin to chitosan, the ratio of glucosamine/N-acetyl glucosamine goes up which is generally defined as the degree of deacetylation (Hosseinnejad & Jafari, 2016). Therefore at higher percentage of N-acetyl glucosamine, the biopolymer is denominated chitin and at higher degree of € glucosamine, the biopolymer is called chitosan (Hamed, Ozogul, & Regenstein, 2016; Ramı´rez et al., 2010). The considerable structural similarity among cellulose, chitin, and chitosan has been presented in Fig. 1. As shown, chitosan is combined with repeating units of 2-amino-2-deoxy-β-D-glucan, where the presence of amine groups leads to some particular features (e.g., ready for chemical reactions, antimicrobial effect, salt formation with acids, and a high charge density) (Azevedo, 2013; Ramı´rez et al., 2010; Sundar, Kundu, & Kundu, 2010). Furthermore, the unique property of chitosan, because of the positive charges on its amino groups, makes it the only commercially available water-soluble cationic biopolymer (Hamed et al., 2016). The existence of D-glucosamine in structure of chitosan causes its pH sensitivity as it is solvable in dilute acids (pH < 6.0–6.5), however it is unsolvable at neutral and alkaline pH limits (Fathi et al., 2014; Hamed et al., 2016). The protonation of amino groups using acids is the reason for enhancement of

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Fig. 1 Structural comparison among cellulose (A), fully acetylated chitin (B) and fully deacetylated chitosan (C) representing their similarity. ´ ., Rodrı´guez, A. T., Alfonso, L., Peniche, C., (Reproduced with permissions from Ramı´rez, M. A Experimental, E., & Nacional, I. et al. (2010). Chitin is a biodegradable polymer widely spread in nature. Biotecnologia Aplicada, 27, 270–276.)

solubility which increases the degree of electrostatic repulsion and the polarity along the chitosan chain (Azevedo, 2013). Two main characteristics of chitosan, dictating its usage for various applications, which can definitely influence on its features are percentage of deacetylation (40%– 98%) and molecular weight (3.8–2000 kDa) (Mourya & Inamdar, 2008; Sundar et al., 2010). Some other exclusive properties of chitosan are the great adsorption and mucoadhesive nature, film-forming ability, antifungal activity, promoting metabolic changes, and development of micro/nanoparticles (Azevedo, 2013; Fathi et al., 2014). Considering all mentioned before, chitosan is suitable for a vast range of applications in pharmaceuticals, medical, cosmetics, environmental, agriculture, and food sectors.

2.2 Modified chitosan The existence of reactive functional groups (hydroxyl and amino groups) as well as the cationicity makes chitosan a desired biopolymer and suggests many manipulation methods for developing a broad spectrum of derivatives as presented in Table 1 (Harish Prashanth & Tharanathan, 2007; Mourya & Inamdar, 2008).

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Table 1 Modification processes of chitosan Process type

Method

Depolymerization

Chemical - Acid hydrolysis - Deamination Physical - Heating (microwave/ oven/radiation) Enzymatic - Chitosanase - Protease/lipase/ pectinase

Substitution

Chain elongation

- Quaternization (methylation) - Acylation/ alkylation - Thiolation/ sulfation - Sugar modification - Metal chelation Cross-linking Graft copolymerization

Products Glucosamine + Acetic acid 2,5-Anhydromannitol + N2 + Oligomers Glucosamine+ N-acetyl glucosamine + Chitooligomers (n ¼ 2–8) and Low molecular weight chitosan (Mw ¼ 5–20 kDa) Glucosamine + N-acetyl glucosamine + Chitooligomers (n ¼ 2–3) Glucosamine + N-acetyl glucosamine + Chitooligomers (n ¼ 2–8) and Low molecular weight chitosan (Mw ¼ 5–20 kDa) Trimethylchitosan chloride, N- propyl- N, N-dimethyl chitosans Acylchitosans, Carboxyalkyl/(aryl) Chitosans Thiolated chitosan (chitosan-thioglycolic acid, chitosan-2-iminothiolane conjugate) 1-Deoxygalactic-1-yl-, 1-deoxymelibiit-1-ylchitosans Cross-linked chitosans acrylonitrile, methylmethacrylate, methylacrylate and vinylacetate g-chitosans

(Reproduced with permission from Harish Prashanth, K. V. & Tharanathan, R. N. (2007). Chitin/chitosan: modifications and their unlimited application potential – an overview. Trends in Food Science and Technology, 18(3), 117–131; Mourya, V. K. & Inamdar, N. N. (2008). Chitosan-modifications and applications: opportunities galore. Reactive and Functional Polymers, 68(6), 1013–1051.)

The high molecular weight of chitosan subjects it to depolymerization (chitonolysis) to produce lower molecular weight chitosans, called chitooligomers. Various techniques including physical, chemical, and enzymatic methods have been introduced for depolymerization of chitosan. Chitosan oligomers possess extra functional properties such as antifungal and antimicrobial activities, antitumor activity, and immunoenhancing effects. Furthermore, they have short chain lengths and low molecular weights and subsequently, they possess a lower viscosity, and are soluble in neutral media, and their bioavailability considerably enhances in vivo (Harish Prashanth & Tharanathan, 2007; Mao et al., 2004; Mourya & Inamdar, 2008). The chemical method for depolymerization is restricted to acidic hydrolysis by heating which have some drawbacks like low efficiency, residual acidity, and high cost. Acid degradation is not specific and the process goes randomly producing different monomers. Nitric acid, chloridric acid, and phosphoric acid have been widely used for this

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purpose. The depolymerization can also be carried out efficiently by physical methods like heating or radiation that produces chitosan with a low molecular weight in a short time. Moreover, by the enzymatic methods, chitosan is able to be simply degraded by a variety of enzymes containing chitosanases, chitinases, lysozyme, hemicellulases, cellulases, pectinase, lipases, proteases, and even amylases. The reaction and product formation in enzymatic depolymerization could be controlled by temperature, pH, as well as reaction duration which makes it the preferred technique among all depolymerization methods (Harish Prashanth & Tharanathan, 2007; Mao et al., 2004; Mourya & Inamdar, 2008). Substitution and chain elongation are two other strategies to modify the chitosan structure. Quaternization or methylation as a main substitution method has been widely investigated. The mucoadhesive properties of chitosan increase at higher degrees of methylation and in parallel, enhancement of the cationicity and interaction with negatively charged mucin leading to mucoadhesion. Antibacterial and antifungal activity of quaternized chitooligomers has also been confirmed previously (Guo et al., 2007; Mourya & Inamdar, 2008; Ru´narsson et al., 2007). The alkylation could be promoted by introduction of alkyl group on the atoms of N and O in chitosan structure synthesizing hydroxyalkyl or carboxyalkyl chitosans. In this category, carboxymethyl chitosan has been utilized as a super porous, pH sensitive, and cross-linked hydrogel or complex nanoparticle to develop food or drug delivery systems because of its unique physicochemical and biological characteristics as well as water solubility features (Chen et al., 2004; Hamed et al., 2016; Lin, Liang, Chung, Chen, & Sung, 2005; Muzzarelli, 1988; Teng, Luo, & Wang, 2013). Acylated chitosan derivatives are also obtained in aqueous acidic/alcoholic mediums with a better solubility range in organic solvents due to the introduction of hydrophobic branches. The hydrophobic moiety and the ester linkage facilitating the enzymatic hydrolyzation make the acylated chitosans as a desirable biodegradable coating material (Mourya & Inamdar, 2008). Thiolated chitosans are derived by coupling the primary amino groups with reagents containing thiol functions. The thiolated polymers so-called thiomers are biodegradable hydrophilic structures with considerable biological effects such as mucoadhesive properties, permeation enhancing of paracellular markers through intestinal mucosa, and cohesive and gelling properties to form an efficient controlled release delivery system (Mourya & Inamdar, 2008; Ngo et al., 2015). Other important bioactive derivatives of chitosan are chitosan sulfates. The sulfation of chitosan has been carried out using various methods combining sulfating agents and reaction media under microwave irradiation or heating at different temperature ranges. Sulfation of chitosan leads to conversion of some amino groups to anionic centers providing better polyelectrolyte properties which can be applied to develop a potential carrier for food or drug in the form of micelles, microcapsules, or nanocapsules (Hamed et al., 2016; Jayakumar, Nwe, Tokura, & Tamura, 2007; Ngo et al., 2015). Since the specific role of sugars for recognition of bacteria, viruses, and cells has been discovered, sugar modification of chitosan has been widely investigated. Initially, sugar-bound chitosan was synthesized using reductive N-alkylation of chitosan by sodium cyanoborohydride and sugar–aldehyde derivative or unmodified sugar.

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Biopolymer Nanostructures for Food Encapsulation Purposes

Also, the N-alkylation of chitosan can be done in aqueous alcoholic media containing various aldehydes, monosaccharides, and disaccharides. Both biological effects and unique rheological properties of sugar-modified chitosans have gain lots of interests (Mourya & Inamdar, 2008; Ngo et al., 2015). Chain elongation is another approach for modification of chitosan which can be performed by cross-linking and graft copolymerization. The fragmented chitosan chains over cooling at 4°C can lead to an extensive cross-linking. In fact, the higher degree of crystallinity and conformational changes in molecular structure of chitosan are due to the interactions (hydrogen or hydrophobic bonds) between acetylated and nonacetylated fragments (Harish Prashanth & Tharanathan, 2007). Graft copolymerization has also been carried out by various methods, typically with a redox system to develop the covalent binding of the graft molecule onto the chitosan backbone. The free amino groups of deacetylated units and the hydroxyl groups of the C3 and C6 of acetylated or deacetylated units are mostly targeted in chitosan grafting. It has recently been reported that upon initial deviation followed by grafting, the water solubility and bioactivities of chitosan-like antioxidant and antibacterial capacities would be improved. The grafting can be promoted by free radicals, enzymes, radiation, and cationic polymerization. Grafted chitosans have intensive applications in designing controlled delivery systems of bioactive molecules. Overall, the literature review indicates that the grafted chitosans are promising biopolymers for biomedical purposes ( Jayakumar, Prabaharan, Reis, & Mano, 2005; Ngo et al., 2015).

3

Chitosan nanostructures: Processes and properties

Today, nanostructured materials have been defined as the materials showing totally new chemical and physical features, so vary notably from the origin with the same chemical structure. Nanostructures are the substances with at least one dimension in nanoscale (15 days is vital for hydrolysis of starch with HCl ( Jenkins & Donald, 1997; Le Corre et al., 2010; Wang et al., 2003). Acid hydrolysis treatment has been commonly utilized for the decomposition of starch granules and the generation of SNDs. As aforementioned, during the selective acid hydrolysis of starch granules, the amylopectin crystalline nano-lamellae are resistant to acid treatment which are extracted through degradation of the amorphous phases (Dufresne, 2014; Le Corre et al., 2010; Le Corre & Angellier-Coussy, 2014). Gonc¸alves, Noren˜a, da Silveira, and Brandelli (2014) prepared nanoparticles from pinha˜o starch, by employing both acid treatment (HCl for 50 days at 22 °C) and sonication (power of 100 W and 30 cycles of sonication for 1 min). They suggested that the mean particle sizes of SNDs produced by ultrasound and acid hydrolysis were about 453 and 22 nm, respectively. Also, in comparison with ultrasound-processed starch, the starch modified by acid treatment was more soluble, more hygroscopic, as well as more translucent. Recently, Amini and Razavi (2016) developed a fast and effective method to generate SNDs using ultrasound and H2SO4 hydrolysis. After applying suggested methods, in less than an hour, the round-edge SNDs were

428

Biopolymer Nanostructures for Food Encapsulation Purposes

produced with diameters below 50 nm. Moreover, by applying the optimized process condition of SNDs preparation with H2SO4, Angellier, Choisnard, Molina-Boisseau, Ozil, and Dufresne (2004) suggested that this hydrolysis provided a shorter fabrication time and greater yield of SNDs (15 wt%) than that of HCl hydrolysis (0.5 wt%). Kim, Park, Kim, and Lim (2013) successfully obtained a high production yield (78%) of spherical waxy corn SNDs with sizes of 50–90 nm through application of cold acid hydrolysis (H2SO4 3.16 M for 6 days at 4 °C) followed by ultrasonication. Furthermore, platelet-like SNDs with dimensions of below 100 nm are efficaciously prepared through dry heating under acidic conditions (different levels of 1.0 M HCl: 1.2, 1.4, or 1.6 mL and various hydrolysis times: 2, 4, or 8 h) by Kim, Kim, Park, and Kim (2017). Additionally, Gong et al. (2016) successfully fabricated tubular-shaped SNDs from normal corn starch using H2SO4 hydrolysis at 4 °C over 5 days and subsequent treatment with 1 wt% ammonia. Recently, Mukurumbira, Mariano, Dufresne, Mellem, and Amonsou (2017) reported that Amadumbe SNDs as aggregated particles with squarelike platelet morphology and the size of 50–100 nm can be successfully produced through acid hydrolysis of Amadumbe starch granules.

4.1.2

Enzymatic hydrolysis

In comparison with acid hydrolysis, limited researches have been focused on the production of SNDs using enzymatic treatment. It is reported that a 3 h enzymatic treatment of waxy rice starch by α-amylase promoted the disintegration of starch granules through the elective hydrolysis of amorphous parts (Kim, Park, & Lim, 2008). In the last decades, simultaneous utilization of enzymatic and acid treatment has been utilized to produce SNDs. It is believed that acid hydrolysis of starch granules pretreated with hydrolysis enzymes could substantially decrease the fabrication time of SNDs (Hao, Chen, Li, & Gao, 2018; Le Corre et al., 2010). Platelet-like SNDs with a width around 15–30 nm, length of 20–40 nm, and thicknesses from 4 to 7 nm were successfully prepared using the abovementioned approaches (Dufresne, 2008, 2014). Morever, LeCorre, Vahanian, Dufresne, and Bras (2011) proposed a 2 h enzymatic hydrolysis of a native starch with glucoamylases to decrease the preparing duration of SNDs. At a same degree of hydrolysis 70%, the pretreated SNDs showed to have a higher production yield; however, their particle size was larger (around 145 nm) comparing to the ones attained from samples with no pretreatment (typically ranging from 50 to 100 nm). Hao et al. (2018) reported that the pores and indentations generated through the enzymatic hydrolysis created a pathway for the acids to penetrate into the starch granules, facilitated the hydrolysis of amorphous areas, and reduced the treatment time.

4.1.3

Reactive extrusion

Based on the reviewed literature, some researchers have focused on the preparation of SNDs by means of reactive extrusion. This process is known as a simultaneous reaction during the processing of polymers with an extrusion (Song et al., 2011). During

Nanostructures of starch for encapsulation of food ingredients

429

the reactive extrusion, SNDs could be fabricated using cross-linking reactions by appropriate cross-linkers, namely, glyoxal that is considered to be “regenerated” SNDs (Le Corre et al., 2010). It is believed that, owing to the limited water content of the starch granules, gelatinization would not take place completely during extrusion process. Nevertheless, it was noted that under the high shear, temperature, and pressure which are applied during the reactive extrusion process, the cleavage of covalent linkages and hydrogen bonds (within and between amylose amylopectin molecule) could be occurred, which might easily torn the starch granule apart into nanometric scale particles (Kim et al., 2015; Lai & Kokini, 1990). A high imputed energy of extrusion gives rise to mechanical damage of starch granules. During the preparation of SNDs with better functional properties for food applications and other areas, care should be taken to investigate the factors affecting the extrusion conditions. These factors consist of operating conditions such as pressure, heat, mechanical shear, melting temperature, screw speed, and moisture content (Kim et al., 2015; Lai & Kokini, 1990; Song et al., 2011). In a review by Song et al. (2011), the mechanism of SNDs production during extrusion has been systematically investigated. The authors revealed that after the extrusion process of starch matrix at 100 °C in the absence of any cross-linking agent, prepared extrudate contained nano-sized starch particles of 300 nm. Although, at the 75 °C extrusion process, the incorporation of 2% glyoxal (as appropriate cross-linker) facilitated the particle size reduction to around 160 nm.

4.1.4

Microfluidization

A microfluidizer is a high-pressure homogenizer, that by using a hydraulic shear, impact, attrition, impingement, forceful turbulence and cavitation, induces size reduction ( Jafari, He, & Bhandari, 2006; Singh et al., 2017). It forcibly passes the semicrystalline starch solutions through the micro-channels using a high pressure displacement pump, resulting in micro or nano-sized droplets based on the number of homogenizer passes. In this respect, Liu, Wu, Chen, and Chang (2009) employed a microfluidizer operating at a pressure of 207 MPa and produced high-amylose maize SNDs with particle size ranging from 10 to 20 nm without degradation of starch crystalline structure. They concluded that higher the number of homogenization passes, the smaller the particle size (Liu et al., 2009).

4.1.5

Ultrasonication

Ultrasonication approaches rely on high-frequency sound waves typically >20 kHz ( Jafari et al., 2006; Falsafi et al., 2019), which can be utilized to prepare SNDs. A bench-top sonicator has a piezoelectric probe which produces strong disruptive forces at its tip (Gogate & Kabadi, 2009). After immersion in a sample, ultrasonic waves move through the liquid media and generate cavitation micro-bubbles which keep to expand until they collapse. This implosion inaugurates shock waves, which in turn generate a jet stream inside the solution, pressurizing the dispersed droplets,

430

Biopolymer Nanostructures for Food Encapsulation Purposes

and causing their size decrement, and even preventing nanoparticle aggregation. Evaluating the effective parameters has indicated that droplet size reduction is mainly correlated with the raising of input power and sonication time (Leong, Wooster, Kentish, & Ashokkumar, 2009; Falsafi, Maghsoudlou, Aalami, Jafari, & Raeisi, 2018). Boufi et al. (2018) successfully prepared platelet-like SNDs with particle size of about 30–40 nm with a high-intensity ultrasonication technique working at 24 KHz for 75 min; however, the crystallinity of the starch diminished through the sonication conditions applied in their research. Sun, Fan, and Xiong (2014) fabricated three waxy corn SNDs with the particle size of 30–50 nm, 20–50 nm, and even 20–60 nm using ultrasonic-assisted oxidation method including: one oxidation-one sonication, two oxidation-two sonication, and one oxidation using 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-one sonication treatment, respectively. Moreover, Haaj et al. (2013) proposed a simple and environmentalfriendly method to fabricate nano-sized SNDs from standard and waxy maize starches, namely, high power ultrasonication (up to 90 min, at 24 kHz, and at low temperatures of 8–10 °C). They reported that, for both starches investigated, application of sonication up to 75 min diminished the starch granules size, reaching particle sizes of 30–250.

4.2

Bottom-up techniques for preparation of SNDs

The bottom-up strategies for preparation of SNDs can be categorized into eight fundamental techniques including (1) nanoprecipitation, (2) emulsification technique, (3) electrohydrodynamic processing, (4) nano-spray drying, (5) enzymolysis and recrystallization, (6) γ-ray irradiation, (7) self-assembly, and (8) polyelectrolyte complex formation.

4.2.1

Nanoprecipitation

As described by Campardelli, Della Porta, and Reverchon (2012), antisolvent nanoprecipitation, as an easy, cost-effective, and reproducible procedure, has been largely employed in the fabrication of synthetic or natural nano-sized polymeric particles (Mugheirbi, Paluch, & Tajber, 2014). This technique is including the addition of a nonsolvent phase to a starch suspension to prompt super-saturation of the solution, nucleation of the particles, and eventually, the creation of hydrosols comprising nano-scale particles (Dong, Ng, Shen, Kim, & Tan, 2011). By monitoring some critical process factors, for example, the type of solvent or antisolvent, starch concentration, reaction temperature, stirring rates, and volume ratios of starch suspension and antisolvent phases, a variety of food ingredient particles with controlled size and desired morphology can be successfully produced by this method (Qin, Liu, Jiang, Xiong, & Sun, 2016; Sinha, M€ uller, & M€ oschwitzer, 2013; Tan et al., 2009; Wu et al., 2016). The prominent researches about the utilization of nanoprecipitation technique for production of SNDs in line with a summary of the relevant results are listed in Table 2.

Goals

Observations

Type of starch

Reference

Systematic evaluation of the structure, morphology, and physicochemical characteristics of seven SNDs with different amylose contents (0.8%– 69.0%) Fabrication of the starch dimethylsulfoxide (DMSO) nanoparticles through the nanoprecipitation of starch dispersion into different nonsolvents under controlled circumstances Generation of worm-like amylopectin nanoparticles by drop-wise addition of various amounts of ethanol to the starch suspension

The prepared spherical or elliptical SNDs had average diameters of 30–75 nm. Furthermore, application of smaller starch granules led to the production of smaller SNDs Solvents of higher affinity resulted in the smaller sizes of precipitated SNDs

High amylose corn starch, waxy corn starch, tapioca starch, sweet potato starch, normal corn starch, potato starch, and pea starch

Qin et al. (2016)

Corn starch

Wu et al. (2016)

The amylopectin SNDs produced with a width of about 10–20 nm and a length of 200–500 nm. The spherical-shaped amylose nanostructures were also ranged between 20 and 50 nm. In comparison with the amylose SNDs, the amylopectin SNDs revealed more amorphous structures and a lower relative crystallinity The increase in concentration of ethanol was associated with the decrease in the concentration of amylose solution. Also, by simultaneous ultrasonication precipitation, amylose nanoparticles reduced to 160 nm

Potato starch

Qin et al. (2016)

Amylose

Dong, Chang, Wang, Tong, and Zhou (2015)

Investigating the influence of temperature and type of solvent on size and morphology of prepared nanoparticles

431

Continued

Nanostructures of starch for encapsulation of food ingredients

Table 2 Most recent researches on the application of nanoprecipitation to prepare SNDs

432

Table 2 Continued Observations

Type of starch

Reference

Preparation of SNDs by pouring tiny drops of dissolved sago starch suspension to the excess absolute ethanol

Increasing the ratio of starch solution to ethanol from 1:10 to 1:20, changed the morphology of SNDs from fibrous to a blend of spherical and lengthened fiberlike structure ranging from 300 to 400 nm in diameter. Additionally, the presence of various surfactants (e.g., hexadecyl (cetyl) trimethylammonium bromide (CTAB) and Tween 80) restricted the growth of SNDs and decreased the mean size (250–300 nm and 150–200 nm in the presence of CTAB and Tween 80, respectively) of the nanoparticles The fabricated vesicles from starch mixed esters were around 200–700 nm in diameter Increasing the starch concentration in the acetone from 1 to 20 mg/mL, increased the Z-average of starch-based nanospheres from 249 to 720 nm The spherical and oval-shaped SNDs ranging from 10 to 20 nm fabricated via starch–butanol by nanoprecipitation and enzymatic treatment.

Sago starch

Chin et al. (2011)

Waxy corn starch

Tan, Xu, Li, Sun, and Wang (2010) Tan et al. (2009)

To develop a simple and robust route for preparing starch nano-vesicles from starch mixed esters Preparation of size-controlled nanospheres using acetylated starch by adding drops of water to acetone solution containing acetate starch Fabrication of SNDs through complex formation with n-butanol

Waxy corn starch

Corn starch

Kim and Lim (2009)

Biopolymer Nanostructures for Food Encapsulation Purposes

Goals

Nanostructures of starch for encapsulation of food ingredients

4.2.2

433

Emulsification technique

Emulsion is a biphasic dispersion of two immiscible phases in which oil phase is dispersed in water (O/W) or vice versa (W/O). In an emulsion, colloidal droplets are stabilized via a suitable surfactant under mechanical stirring (Mason, Wilking, Meleson, Chang, & Graves, 2006) (Assadpour, Maghsoudlou, Jafari, Ghorbani, & Aalami, 2016). The small droplet diameters attained in nanoemulsions (typically PIT

w/o Emulsion

Cool

w/o

o/w/o

o/w T = PIT

Emulsion inversion point method

Bicontinuous microemulsion

Heat

T < PIT

o/w Emulsion Spontaneous emulsification method PIT method

Fig. 10 Schematic representation of low-energy approaches: emulsion inversion point method, spontaneous emulsification, and phase inversion temperature. Reprinted with permission from Piorkowski, D. T., & McClements, D. J. (2014). Beverage emulsions: Recent developments in formulation, production, and applications. Food Hydrocolloids, 42, 5–41.

Nanostructures of gums for encapsulation of food ingredients

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proper for fabrication or modification of nanoemulsions. The electrostatic charges on the high molecular weight gums can result in a better and long-term physical stability of nanoemulsions via the immobilization of the emulsion droplets by repulsive effects (Dickinson, 1992). Shamsara et al. (2015) fabricated double layer oil in water emulsions based on apricot gum and lactoglobulin, and the effect of sonication on stability of emulsions was evaluated. The results indicated that in mixing ratio of 1:8 (apricot gum:lactoglobulin), completely stable emulsion (10 days in room temperature) was created and sonication time and amplitude had a remarkable effect on decreasing diameter and zeta potential, and positive effect on emulsion stability. The increase of apricot gum in emulsion system enhanced the stability due to increase of viscosity in continuous phase. Further, at the high concentrations of apricot gum, polysaccharide–protein and protein–protein interactions in competition with fine particles would reduce the interfacial potential, which might decrease the zeta potential.

4

Application of gums for encapsulation of different food ingredients

The most important reasons for encapsulation of bioactive ingredients are improvement in stability, less evaporation and degradation of volatile actives (aroma), masking unpleasant feelings during eating (bitter taste and astringency of natural substances), preventing reactions with other components in food products (oxygen or water), and immobilizing cells or enzymes in food processing. Different gums have been applied for encapsulation of food bioactive components which will be discussed in the following sections.

4.1 Flavoring agents and essential oils Flavor is one of the most important components of a food system. Food flavor consists of various lipophilic and aromatic compounds with molecular weights between 100 and 250 g/mol which includes hydrocarbons, alcohols, aldehydes, ketones, esters, acids, sulfides, and so on (Zuidam & Heinrich, 2010). Flavors are often encapsulated to improve handling during processing, stability, extending shelf life at the proper time and rate, and this is gained by different technical encapsulation methods with different gum polymers as wall materials. The different techniques for encapsulation of flavors in micro and nanoscale include spray drying ( Jafari et al., 2008, 2013; Shiga et al., 2001), electrospraying, extrusion, emulsification ( Jafari et al., 2012), and coacervation (Lv et al., 2014) which have been long studied. Spray drying is a popular method for encapsulation of hydrophobic flavor compounds because of its ease and low cost process resulting in small particles but there are some disadvantage such as reconstitution capability and high surface oil (Fuchs et al., 2006; R
e, 1998; Turchiuli et al., 2005). Oliveira et al. (2014) studied the alginate/cashew gum nanoparticles formed by spray drying for encapsulation of L. sidoides (LS) essential oil; the encapsulated essential oil had a high loading and

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Biopolymer Nanostructures for Food Encapsulation Purposes

good encapsulation efficiencies. Particle sizes were in the range of 223–399 nm with spherical morphologies (little roughness). The addition of cashew gum to alginate demonstrated a quicker release at an appropriate oil loading due to maximizing the hydrophilic property of the matrices; the faster release was indicated for alginate:cashew gum of 1:3 ratio. Herculano, de Paula, de Figueiredo, Dias, and Pereira (2015) used the cashew gum as wall material for nanoencapsulation of Eucalyptus staigeriana essential oil, and the antimicrobial activity of nanoparticles on Gram-positive (Listeria monocytogenes) and Gram-negative bacteria (Salmonella enteritidis) was investigated. The size of nanoparticles and encapsulation efficiencies were in the range of 27.70–432.67 nm and 24.89%–26.80%, respectively. Nanoencapsulated oil is introduced as a natural food preservative due to great activity of nanoparticles against bacteria specially Gram-positive ones. Lippia sidoides essential oil has also been successfully encapsulated in chitosan/ cashew gum particles (Paula, Sombra, de Freitas Cavalcante, Abreu, & de Paula, 2011) and results demonstrated that thermal properties and sustained release improved with incorporation of essential oil and adding cashew gum. Paula, Oliveira, Carneiro, and de Paula (2017) used different ratios of chitosan with various gums (cashew gum, chicha gum, and angico gum) for encapsulation of L. sidoides essential oil by spray drying. The size of nanoparticles was in the range of 17–800 nm, and cashew gum and chicha gum indicated high oil loading values (15.6%; 14.7%). The ratio of chitosan:gum and polysaccharide properties considered as major parameters in nanoencapsulation. Coacervation as a simple and nondestructive technique, with good control release properties is an additional method that often is applied for gum nanoparticles and has received attention for flavor encapsulation. The most common gum participant in complex is gum Arabic. The process of coacervation begins with a solution of Arabic gum and another biopolymer like gelatin. The selected flavor is added to them, afterwards mixing in high speed and heating, and for creating equal and opposite charges on Arabic gum and gelatin, the pH is altered from neutral to acidic. Separation takes place into a polymer-rich layer based on strong attractive forces between two polymers, which consist of small droplets of flavor oil loaded within gelatin and Arabic gum, and an aqueous layer. These can be further completed by changing to a basic pH pursued by application of cross-linking agent (chemical or enzymatic) for stabilizing (Leclercq, Harlander, & Reineccius, 2009). Lv et al. (2014) investigated the formation of gelatin/gum Arabic complexes in nanoscale for encapsulation of jasmine essential oil. Results showed nanocapsules loaded with jasmine essential oil which were successfully fabricated and cross-linked by transglutaminase; nanocapsules cross-linked at alkaline conditions could tolerate the water bath of 80°C for 7 h. The heat-resistant characteristics are dependent on the electrostatic interactions between gelatin and gum Arabic. The effect of particle size on encapsulation efficiency and in optimization of flavor retention was clear (Reineccius, 2004; Soottitantawat et al., 2005). In the study of Jafari et al. (2007a, 2007b, 2007c), they specified that smaller particles compared to larger particles had lower surface oil amount and poorer flavor retention. The nanoencapsulation of L. sidoides essential oil in nanogel of cashew gum/chitosan by spray drying technique under different

Nanostructures of gums for encapsulation of food ingredients

553

conditions was evaluated by Abreu, Oliveira, Paula, and de Paula (2012). Nanogels were prepared to display sizes in the range 335–899 nm; with enhancing the chitosan content in the matrix, larger particles were fabricated which had a slower release. In encapsulation of D-limonene with electrosprayed A. homolocarpum seed gum nanoparticles, Khoshakhlagh et al. (2017) found that the morphology of nanocapsules altered to nanofibers by enhancing the flavor content to 30%. In other words, the aggregated irregular shaped nanoparticles were formed from electrospraying of seed gum solution. After addition of 10% and 20% D-limonene, spherical nanocapsules were obtained. In nanocapsules loaded with 10% and 20% D-limonene, encapsulation efficiency was 87%–93%. Rezaei et al. (2016) synthesized electrospun almond gum/PVA nanofibers successfully as a delivery system for vanillin. It was found that in the content of almond gum (56%), PVA (14%) and vanillin (30%), vanillin could be successfully electrospun to create nanofibers with an average diameter of 77 nm. The results of thermal analysis demonstrated that loading vanillin in almond gum/PVA nanofiber enhanced thermal stability of it which makes the composite a candidate for using in high temperatures (180°C and above) (Table 3).

4.2 Bioactive oils and essential fatty acids Polyunsaturated fatty acids such as omega-3 and omega-6 fatty acids have been introduced for providing potential health benefits when consumed regularly at adequate concentrations (McClements, 2010). The major omega-3 fatty acids, called EPA and DHA are very essential in human health which must be acquired from diet. Fish oil is a cheap and major source of essential fatty acids, both omega-3 and omega-6 fatty acids (Boran, Boran, & KaraCAm, 2008; Kaya & Turan, 2008), and has been used for fortification and supplementation of foods. The main limitation parameters in the use of fish oil into food products are low aqueous solubility which results in lower bioavailability, undesirable organoleptic property (odor and taste), highly susceptible to oxidation, and a reactive nature due to its high degree of unsaturated longchain omega-3 fatty acids (Gokoglu, Topuz, & Yerlikaya, 2009; Huang & Weng, 1998). Therefore there is a need to carriers for delivery and protection of sensitive essential fatty acids; micro/nanoencapsulation methods with various gum shell materials such as complex coacervation of gelatin-Arabic gum (Habibi, Keramat, Hojjatoleslamy, & Tamjidi, 2017; Piacentini, Giorno, Dragosavac, Vladisavljevi
c, & Holdich, 2013; Tamjidi, Nasirpour, & Shahedi, 2014), complex coacervation of whey protein isolate and gum Arabic (Eratte, Wang, Dowling, Barrow, & Adhikari, 2014), gum Arabic/casein/beta-cyclodextrin particles by spray drying (Li, Xiong, Wang, Regenstein, & Liu, 2015), gum Arabic and sage polyphenol-loaded particles (Binsi et al., 2017), cashew gum particles by spray drying (Botrel et al., 2017), nanoconjucate of methylcellulose, maltodextrin, and Arabic gum (Tirgar, Jinap, Zaidul, & Mirhosseini, 2015); caseinate/gum Arabic nanocomplexes (Ilyasoglu & El, 2014), and chia seed gum nanoparticles (de Campo et al., 2017), are applied in order to reduce the oxidation and increase the bioactive characteristic of essential fatty acids in aqueous food products.

554

Table 3 Application of different gum nanostructure for encapsulation of food ingredients

Technique

Particle diameter (nm)

Vitamin A

Electrospinning

90.25–169.95

Vanillin

Electrospinning

77

D-limonene

Electrospraying

65.68  8.80

Curcumin

Polyelectrolyte complexation

250–290

Almond gum

Curcumin

Electrospinning

98–169

Gum tragacanth (GT)/poly(vinyl alcohol) Xanthan gumchitosan

Curcumin

Electrospinning

104

Enhance biological properties

Nanofibers

Curcumin

Electrospinning

910

Nanofibers

Gelatin/gum Arabic

Jasmine essential oil

Complex coacervation

51.7–384.4

Cashew gum

Eucalyptus staigeriana essential oil Kaffir lime oil

Spray dryer

27.70–432.67

Coacervation

457.87

High encapsulation efficiency, physical stability Good heat-resistance capability against humid heat (80°C) Greater activity against Gram-positive bacteria Physical stability

Gum Cress seed mucilage/PVA Almond gum/ PVA Alyssum homolocarpum gum Chitosan and gum Arabic

Arabic gum and maltodextrin

Function Increased thermal stability Increased thermal stability Protection of from degradation Increased antioxidant activities, stability and delay the release of curcumin Enhance solubility

Delivery system Nanofibers Nanofibers

References Fahami and Fathi (2018) Rezaei et al. (2016)

Nanocapsules

Khoshakhlagh et al. (2017)

Nanoparticles

Tan et al. (2016)

Nanofibers

Rezaei and Nasirpour (2018) RanjbarMohammadi and Bahrami (2016) Shekarforoush et al. (2018)

Nanocapsules

Lv et al. (2014)

Nanoparticles

Herculano et al. (2015)

Nanoparticles

Biopolymer Nanostructures for Food Encapsulation Purposes

Bioactive compound

Fish oil

Coacervation

232.3

DHA

Spray drying

Bene hull polyphenols

Curcumin

Nanocomplexes Nanocapsules

Ilyasoglu and El (2014) Singh et al. (2018)

High-pressure homogenizer

736.9 and 1918

Increase solubility and oxidative stability

W/O/W emulsions

Delfanian et al. (2018)

250–290

Tan et al. (2016)

205  4.24

Nanoparticles

de Campo et al. (2017)

Guar gum, starch

Folic acid

Electrospraying

Sub-micron

Nanocapsules

P
erez-Masia´ et al. (2015)

Arabic gum, cashew gum

Vitamin B12

Nano spray drying

232 and 301

Nanoparticles

Oliveira et al. (2013)

Whey protein isolate and gum Arabic Whey protein concentrate, Angum gum, gum Arabic

Vitamin E

High-pressure homogenization

110

Emulsions

Ozturk et al. (2015)

Crocin

Spontaneous method

429 and 695

Increase antioxidant activities Thermally stable at temperatures up 300° C, higher stability against oxidation Greater encapsulation efficiency, improved folic acid stability Controlling the release rate kinetics even in acidic or alkaline pH conditions Grade vitaminenriched delivery systems High thermodynamic stability

Nanoparticles

Chia seed oil

Polyelectrolyte complexation Emulsification

Double emulsions (W1/ O/W2)

Mehrnia et al. (2016) 555

780

Enrichment of fruit juice Enhance bioavailability and oxidative stability

Nanostructures of gums for encapsulation of food ingredients

Caseinate, gum Arabic Arabic gum, starch, sodium caseinate, maltodextrin Soy protein isolate/whey protein isolate, and basil seed gum Chitosan and gum Arabic Chia mucilage

Continued

556

Table 3 Continued

Gum

Technique

Particle diameter (nm)

α-Amylase

Sol–gel polymerization

6.1

Thyme essential oil Quercetin

Sonication

385.2–756.1

Antisolvent precipitation

197

Function High stability, affinity and catalytic property of α-amylase Protection from physical damages Lower stability to thermal processing and pH ¼ 1.2

Delivery system

References

Nanohybrids

Singh and Kumar (2011)

Emulsions

Hassani and Hasani (2018) Doost, Muhammad, Stevens, Dewettinck, and Van der Meeren (2018) Samrot, Burman, Philip, Shobana, and Chandrasekaran (2018) Li et al. (2018)

Nanoparticles

Tamarind seed gum

Clindamycin

Eectrohydrodynamic atomization

163.86

Antibacterial activity

Nanofibers

Zein/Arabic gum

Thymol

Pickering emulsions

Submicron

Antibacterial delivery

Nanoparticles

Biopolymer Nanostructures for Food Encapsulation Purposes

Carboxymethyl tamarind gum– silica Chitosan-Arabic gum system Almond gum/ shellac

Bioactive compound

Nanostructures of gums for encapsulation of food ingredients

557

In the study of Ilyasoglu and El (2014), stable and soluble nanocomplex gums based on electrostatic attraction between sodium caseinate and gum Arabic were prepared and its utilization in the enrichment of fruit juices was investigated. Findings indicated that nanocomplexes had a high encapsulation efficiency (78.88) and could enrich formulated products with a proper bioaccessibility and might help in excluding the insufficient intakes of essential fatty acids. de Campo et al. (2017) evaluated the nanoencapsulation of chia seed oil (a source of polyunsaturated fatty acid, mainly linoleic and linolenic acids) by spray drying of chia seed mucilage emulsion as wall material. The acquired results indicated that the nanoparticles had a high encapsulation efficiency and loading capacity. Nanoencapsulation of chia seed oil enhanced the physical, thermal (stable at temperatures up 300°C), and oxidative stability. In some cases, the use of carbohydrates and proteins alone as wall materials caused a poor encapsulation and poor loading, due to high viscosity of solutions especially at high concentrations, so the combination of gum with other polymers can improve characteristics of wall materials in encapsulation. In the study of Singh et al. (2018), the combination of wall materials from various categories of gums (Arabic), carbohydrates (starch), proteins (sodium caseinate), polymers (maltodextrin), was applied for the nanoencapsulation of DHA oil by spray drying technique. Optimized formulations obtained in concentration of Arabic gum (8.56), starch (9.63), sodium caseinate (21.41), and maltodextrin (19.27) which had a low size (780 nm) with spherical shape, high encapsulation efficacy (98.46%), and good oxidative stability. Thus this study indicated that combination of wall materials was better for the effective encapsulation of DHA oil for improving its bioavailability, shelf life, and oxidative stability (Table 3).

4.3 Vitamins and minerals Minerals and vitamins or micronutrients are very essential ingredients for retaining physiological functions in body. Vitamins are available as water-soluble vitamins (thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B8), folic acid (B9), cobalamin (B12), ascorbic acid (C), and fat-soluble vitamins (retinol, carotene (A), cholecalciferol (D), tocopherol (E), and phylloquinones (K). Minerals are defined as essential chemical elements necessary for sustaining normal metabolic functions in our body (Gharibzahedi & Jafari, 2017). Minerals are classified into two categories: macro or major minerals (calcium, magnesium, phosphorous, sodium, potassium) and micro or trace (chromium, copper, fluoride, iodine, manganese, iron, molybdenum, selenium, zinc). Macrominerals are required by the body in larger amounts whereas microminerals are required in trace amounts. Although various foods (animal and plant) are the source of vitamins and minerals, some group of people such as vegetarians or vegans, the elderly, pregnant and lactating women does not get enough vitamin (Bonnet et al., 2010; Guzun-Cojocaru, Cayot, Loupiac, & Cases, 2010). The direct fortification of minerals and vitamins into food is not facile. Some micronutrients may create undesirable effects to the sensory properties and quality of the food such as color altering, unpleasant flavor, sandy texture, decreased nutritional value, and sometimes accelerate chemical reactions leading to toxic

558

Biopolymer Nanostructures for Food Encapsulation Purposes

compounds. Furthermore, the sensitivity of some micronutrients to environmental (temperatures, light, oxygen, moisture content) can lead to degradation during preparation, processing, and storage (Giroux et al., 2013; Guzun-Cojocaru et al., 2010; Jim
enez-Alvarado, Beristain, Medina-Torres, Roma´n-Guerrero, & Vernon-Carter, 2009; Stevanovi
c & Uskokovi
c, 2009). The effective platform to solve these challenges is encapsulation technology, which is a novel strategy for enhancing bioavailability, shelf life, and controlled release of entrapped vitamins and minerals. In order to improve the properties of particles containing vitamins in fortification and formulation of foods, a suitable method and a proper coating material should be considered; the coating materials applied for encapsulation of vitamins consist of chitosan, zein, and whey proteins (Fernandez, Torres-Giner, & Lagaron, 2009); maltodextrin, starches, and gums (Henry & Heppell, 1998). They can be used either lonely or in combination with other components such as surfactants, chelatants, and crosslinking agents. There has been a growing interest in application of electrospinning technique in encapsulation of sensitive ingredients because of being a simple technique, and neither high temperatures nor organic solvents are used in this method. Electrospun fibers have been considered in encapsulation of bioactive compounds such as vitamins (Alborzi et al., 2013) (Table 3). Fahami and Fathi (2018) used the fine electrospun fibers created by combination of cress seed gum/poly vinyl alcohol for encapsulation of vitamin A. Fiber capsules were in the range of 90.25–169.95 nm and the optimum encapsulated samples had a high encapsulation efficiency (97%) and loading capacity (29.51%). Thermal stability of vitamin A is enhanced by encapsulation therefore it could be formulated in food materials that their temperature processing is high. Characterization of particles indicated that the crystallinity structure and the size of nanofibers after encapsulation increased. The diameter of encapsulated particles was important in retention time of the nutrients and permitted a controlled release in the intestinal gut affected by the solution properties (mainly surface tension and viscosity) and the process parameters. P
erez-Masia´ et al. (2015) in encapsulation of folic acid within whey protein concentrate (WPC) matrix and a commercial resistant starch, through nano spray drying and electrospraying demonstrated that no structures created from resistant starch solutions because of their very low apparent viscosity, Therefore guar gum as a thickening agent was added to starch solution in order to increase the viscosity and improve the molecular interactions between the carbohydrate chains. Further, guar gum prevented the precipitation of folic acid during the encapsulation process. Emulsification method is another technique for encapsulation of micronutrients. The advantage of this method is that it is flexible because it can be applied to encapsulate both water- and oil-soluble substances (Abbas, Da Wei, Hayat, & Xiaoming, 2012; Akhavan, Assadpour, Katouzian, & Jafari, 2018; Fang & Bhandari, 2010; Zuidam & Heinrich, 2010). Ozturk et al. (2015) used the whey protein isolate (WPI) and gum Arabic for formation and stabilization of emulsion-based delivery systems for vitamin E acetate. Both emulsifiers created droplets that were stable without aggregation at temperatures ranging from 30°C to 90°C for 30 min (pH ¼ 7). At low emulsifier concentrations, WPI was much more effective than gum Arabic producing fine droplets. Whereas gum Arabic stabilized emulsions were more stable against

Nanostructures of gums for encapsulation of food ingredients

559

environmental stresses which can be due to differences in the stabilizing pattern of WPI (electrostatic repulsion) and gum Arabic (steric repulsion). The effect of NaCl and salt on nanoemulsions demonstrated that emulsions containing Arabic gum were stable over a wider range of concentrations (0–500 mM NaCl) and pH levels (2–8). However, WPI nanoemulsions became unstable in heating above 60°C in the 150 mM sodium chloride.

4.4 Phenolic compounds and phytochemicals Phenolic compounds are a major group of bioactive compounds from simple molecules to complex structures which are widely applied for biological targets in food and pharmaceutical industrials. Phenolic compounds depending on their chemical structure are available as water-soluble (phenolic acids, phenyl propanoids, flavonoids, and quinones) and water-insoluble (condensed tannins, lignins, and cell-wall bound hydroxycinnamic acids). These bioactive compounds have a diversity of biological properties and benefits such as antioxidant, anticancer, antimicrobial, and many other characteristics (Esfanjani & Jafari, 2016). In many food processes, they are employed as natural additives (antioxidants, coloring agents, nutritional supplementation, and preservative agents). Utilization of pure phenolics in biological formulations is limited because of their low permeability, bioavailability and solubility, fast release, and easily degradation against environmental parameters (physical, chemical, biological conditions). For instance, brown color, undesirable odors with a remarkable loss in activity happens due to quick oxidation in phenolic compounds; thus designing of micro or nanocapsule carriers as a practical strategy is needed to dominate explained limitations (Assadpour, Jafari, & Esfanjani, 2017). There are many researches which have used different methods with biodegradable polymers especially for micro-encapsulation of phenolic compounds. Recently, polymeric and lipid nanoparticles have also been introduced due to simple design and synthesis, and structure alteration and direct effect on the site of action in smart bioactive carriers (Faridi Esfanjani, Assadpour, & Jafari, 2018; Rafiee & Jafari, 2018) as shown in Fig. 11. On the other hand, gum nanocarriers are appealing choices for controlled delivery systems owing to their desirable physicochemical characteristics. Various gum-based nanoencapsulation systems have been developed via emulsions (Delfanian et al., 2018), nanofibers (Ranjbar-Mohammadi and Bahrami, 2016; Rezaei & Nasirpour, 2018; Shekarforoush et al., 2018), and protein– polysaccharide soluble nanocomplexes (Sheikhzadeh, Alizadeh, Rezazad, & Hamishehkar, 2016; Tan et al., 2016) for the encapsulation of lipophilic polyphenols (Table 3). Curcumin is a hydrophobic, antioxidant, and natural colorant polyphenolic compound which encompasses antimicrobial, antiinflammatory, and anticancer characteristics used as a therapeutic compound. However, its low water solubility and oral bioavailability, sensitivity to environmental stresses (light), thermal treatment, and neutral or alkaline pH circumstances restrict the utilization of curcumin in pharmaceutics or food industry (Rafiee et al., 2018). Therefore the development of curcumin in various carriers or delivery systems can overcome these challenges. Sheikhzadeh

560

Biopolymer Nanostructures for Food Encapsulation Purposes

Fig. 11 Schematic representation of nanoencapsulated phenolics by polymeric, natural, and equipment-based methods. Reprinted with permission from Esfanjani, A. F., & Jafari, S. M. (2016). Biopolymer nanoparticles and natural nano-carriers for nano-encapsulation of phenolic compounds. Colloids and Surfaces B: Biointerfaces, 146, 532–543.

et al. (2016) synthesized nanoparticles by interaction between Arabic gum and sodium caseinate. In the optimum encapsulation circumstances (0.21 wt % sodium caseinate, 0.5 wt % Arabic gum, pH ¼ 5), mean average diameter and encapsulation efficiency were 72 nm and 81%, respectively. In another study, Tan et al. (2016) produced chitosan and Arabic gum complexes as a carrier for curcumin. They optimized the encapsulation circumstances. Nanoparticle (250–290 nm) with a high degree of uniformity were created in pH ¼ 4.0 and gum Arabic to chitosan ratio of 1:1. The encapsulation efficiency and loading capacity of curcumin reported more than 90% and 3.8%, respectively. Furthermore, use of interactions led to enhancement of the antioxidant capacity, stability of curcumin, and delaying in curcumin release in simulated gastric fluid. Delfanian et al. (2018) fabricated soy protein isolate (SPI) or whey protein isolate/ basil seed gum (SPI-BSG) multiple emulsions as nanocarriers for Bene hull

Nanostructures of gums for encapsulation of food ingredients

561

polyphenols (Pistacia atlantica subsp. Mutica). Z-average size and encapsulation efficiency of WPI-BSG and SPI-BSG emulsions were 736.9 nm, 90.9% and 1918 nm, 92.88%, respectively. The nanoemulsions synthesized by SPI-BSG exhibited higher antioxidant effects (lowest oxidative changes) due to better controlled release. Ranjbar-Mohammadi and Bahrami (2016) developed poly (ε-caprolactone)/gum tragacanth/curcumin loaded nanofibers by electrospinning technique. The technical parameters to minimized diameter were optimized based on four variables (feed rate, voltage, distance between nozzle and collector, and polymer concentration) by using response surface methodology (RSM) and artificial neural networks (ANN). The results showed that both ANN and RSM models demonstrated agreement with the predicted fiber diameter. In RSM, minimized diameter was created in polymer concentration of 4.2% (w/v), distance between the capillary and collector 20 cm, exerted voltage of 20 kV, and flow rate of 0.5 mL/h. Curcumin 3% (w/v) was loaded successfully in gum tragacanth/PVA nanofibers which could be a great candidate for disease treatment. Rezaei and Nasirpour (2018) produced loaded composite nanofibers based on almond gum/PVA and almond gum/PVA/β-cyclodextrin with curcumin. The results demonstrated that the fiber diameters were in the range of 98–169 nm. The diameter of almond gum/PVA/β-cyclodextrin was lower compared with almond gum/PVA fiber. Thermal stability of nanofibers enhanced with adding curcumin in two solutions. The almond gum nanofiber enhanced the solubility of curcumin thus introduced as an appropriate carrier for hydrophobic compounds. Shekarforoush et al. (2018) produced stable nanofibers by the electrospinning of xanthan–chitosan viscoelastic gels for the encapsulation and release of curcumin. Owing to hydrophobic properties of curcumin, the adhesion characteristics of nanofibers were decreased. After 120 h, at pH ¼ 2.2 and neutral media, amount of curcumin were 20% and 50%, respectively. Electrospun xanthan–chitosan nanofibers due to high encapsulation efficiency, physical stability in aqueous media, and with long-term pH-stimulated release characteristics were introduced as a carrier for the encapsulation of hydrophobic bioactive compounds.

4.5 Enzymes Enzymes (green biocatalysts) from plant or animal sources have been used in food applications for centuries. Compared with regular catalysts, enzymes can easily be degraded and the processing and storage circumstances affect their stability; so there is need for the approaches to enhance the enzyme stability such as enzyme immobilization, enzyme modification, protein, and medium engineering. Enzyme immobilization indicates interaction of enzyme onto large structures such as macromolecules and polymers, via adsorption, covalent binding, and encapsulation (Elnashar et al., 2014; Islan et al., 2013; Martı´nez et al., 2013). Entrapment/encapsulation of enzyme molecule involves the attachment of enzyme within a polymeric network which can be dense (entrapment) or hollow (encapsulation), while authorizing for the flow of substrates and products. Adding of polymers on the surface of enzyme molecules may be applied to alter the surface characteristics, and leading to higher enzyme loading per

562

Biopolymer Nanostructures for Food Encapsulation Purposes

unit mass of particles and enhancement of enzyme stability (Jia et al., 2003; Mozhaev, 1993). Inclusion of encapsulated enzymes during cheese making excludes loss of enzyme in whey, increases the yield, improves enzyme distribution, and excludes extensive and quick proteolysis (Anjani et al., 2007). Different nanostructures, generally creating a large surface area for the immobilization of enzymes, have been introduced for enzyme stabilization. Reduction of the size of enzyme–carrier polymer can generally enhance the efficiency of immobilized enzymes (Jia et al., 2003) (Table 3). Nanoencapsulation of enzymes as biocatalysts allows to enhance their protection, stability and reusability, control selectivity and easily attainable to substrates; thus the nanoencapsulation of enzymes creates opportunities to enhance the activity of biocatalyst where previously it was not possible; for instance the incorporation of enzyme in nanostructure materials such as nano hydrogel matrix increased thermal stability of the unstable enzyme (Sawada & Akiyoshi, 2010). Gum polymers such as xanthan, Arabic (Lambert, Weinbreck, & Kleerebezem, 2008), carrageenan, and others would seem to be an appropriate choice to interact with and protect enzymes against harsh environments. Liu et al. (2011) fabricated freezedried bionanocomposites prepared from chitosan/xanthan hydrogel, and applied for encapsulating a model enzyme (firefly luciferase), and release behavior of the enzyme from the hydrogels was evaluated. It was concluded that enzyme successfully stabilized in the freeze-dried hydrogel, the release rate of the enzyme was faster in pH ¼ 6.0 than in pH ¼ 8.0. The addition of the montmorillonite nanoclay changed the enzyme release rates. The release rate of enzyme molecule from the samples produced via the montmorillonite nanoclay was manifestly lower than without that. This would be cooperated to vary the protein binding properties in the present hydrogel samples. This study suggested that hydrogel formulation is a proper candidate for encapsulating bioactive materials such as enzymes. In the study of Singh and Kumar (2011), α-amylase was immobilized by adsorption in carboxymethyl tamarind gum–silica nanohybrids, for starch hydrolysis. The results demonstrated that immobilization improved affinity, thermal, and catalytic characteristics of amylase. The pH ¼ 4 and temperature of 40°C reported as optimum conditions for the hydrolysis reaction. The enzyme was stable in the gum–silica nanohybrids matrix and its activity did not alter even after 90 days storage at 4°C. Singh and Ahmed (2012), fabricated gum Arabic–gelatin–silica nanohybrids with silver nanoparticles for diastase α -amylase immobilization. They concluded that incorporation of silver nanoparticles can remarkably increase the shelf life of the nanohybrids for enzyme immobilization. The enzyme stability, activity, and thermal stability (27–47°C) increased upon immobilization and its activity did not alter even after 30 days storage at 40°C.

5

Conclusion and further remarks

Although the application of traditional gums has extended, native and new gums have been introduced with special qualities. There is a massive domain for research on new gums and mucilage acquired from plants and could be further extracted and purified in

Nanostructures of gums for encapsulation of food ingredients

563

future as novel natural polymers for development of various delivery systems in the food industry. Some of native gums can be extracted for their functional properties. These have found application not only in formulation of foods but also being useful for development of nanostructures. Some future developments may need identification, selection, and design of the new sources of biopolymers to be applied as wall material to encapsulate, protect, and target the delivery of bioactive ingredients, novel types of fabrication methods that can be applied to produce biopolymer nanoparticles with novel or improved functional characteristics and eventually formulated foods with improved physicochemical or sensory characteristics. However, it is also essential that the compounds and preparation methods used be economically practical for large-scale production; the natives gums offer several advantages (nontoxicity, flexibility, bioavailability, biodegradability, readily availability, accessibility of reactive sites for molecular interactions, ability to control functional properties) for the entrapment and nanoencapsulation of sensitive ingredients, therefore the future prospective of native gums seems promising and pivotal for food industries. However, the application of structurally organized gum nanoparticles in the food industry especially native gums is still in its primary exploration phase and requires fundamental studies in several areas. Natural gums can be improved to have tailormade products for delivery systems and thus can emulate with the synthetic additives existent in the market. The main problem that should be considered in application of new source (native gums) or new technologies is to ensure that they are safe for widespread employment in commercial foods; thus toxicological studies should also be done.

References Abbas, S., Da Wei, C., Hayat, K., & Xiaoming, Z. (2012). Ascorbic acid: microencapsulation techniques and trends—A review. Food Reviews International, 28(4), 343–374. Abbastabar, B., Azizi, M. H., Adnani, A., & Abbasi, S. (2015). Determining and modeling rheological characteristics of quince seed gum. Food Hydrocolloids, 43, 259–264. Abreu, F. O., Oliveira, E. F., Paula, H. C., & de Paula, R. C. (2012). Chitosan/cashew gum nanogels for essential oil encapsulation. Carbohydrate Polymers, 89(4), 1277–1282. 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. Al-Assaf, S., Phillips, G. O., & Amar, V. (2009). Gum ghatti. In Handbook of Hydrocolloids (2nd ed., pp. 477–494). Alborzi, S., Lim, L. T., & Kakuda, Y. (2013). Encapsulation of folic acid and its stability in sodium alginate-pectin-poly (ethylene oxide) electrospun fibres. Journal of Microencapsulation, 30(1), 64–71. Amini, A. M., & Razavi, S. M. (2012). Dilute solution properties of Balangu (Lallemantia royleana) seed gum: Effect of temperature, salt, and sugar. International Journal of Biological Macromolecules, 51(3), 235–243. Anderson, D. M. W., & Stoddart, J. F. (1966). Studies on uronic acid materials: Part XV. The use of molecular-sieve chromatography in studies on acacia senegal gum (Gum Arabic). Carbohydrate Research, 2(2), 104–114.

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Tolstoguzov, V. B. (1997). Protein-polysaccharide interactions. In Food Science and Technology (pp. 171–198). New York: Marcel Dekker. Turchiuli, C., Fuchs, M., Bohin, M., Cuvelier, M. E., Ordonnaud, C., Peyrat-Maillard, M. N., et al. (2005). Oil encapsulation by spray drying and fluidised bed agglomeration. Innovative Food Science & Emerging Technologies, 6(1), 29–35. Wang, B., Adhikari, B., & Barrow, C. J. (2014). Optimisation of the microencapsulation of tuna oil in gelatin–sodium hexametaphosphate using complex coacervation. Food Chemistry, 158, 358–365. Wang, T., Hu, Q., Zhou, M., Xue, J., & Luo, Y. (2016). Preparation of ultra-fine powders from polysaccharide-coated solid lipid nanoparticles and nanostructured lipid carriers by innovative nano spray drying technology. International Journal of Pharmaceutics, 511(1), 219–222. Williams, P. A., & Phillips, G. O. (2000). Handbook of Hydrocolloids. Boca Raton: CRC Press. Williams, P. A., & Phillips, G. O. (2009). Gum Arabic. In Handbook of hydrocolloids (2nd ed., pp. 252–273). Yang, W., Sousa, A. M. M., Li, X., Tomasula, P. M., & Liu, L. (2017). Electrospinning of guar gum/corn starch blends. SOJ Materials Science and Engineering, 5(1), 1–7. Ye, A. (2008). Complexation between milk proteins and polysaccharides via electrostatic interaction: Principles and applications—A review. International Journal of Food Science & Technology, 43(3), 406–415. Ye, A., Flanagan, J., & Singh, H. (2006). Formation of stable nanoparticles via electrostatic complexation between sodium caseinate and gum arabic. Biopolymers: Original Research on Biomolecules, 82(2), 121–133. Yuan, Y., Gao, Y., Zhao, J., & Mao, L. (2008). Characterization and stability evaluation of β-carotene nanoemulsions prepared by high pressure homogenization under various emulsifying conditions. Food Research International, 41(1), 61–68. Zaeim, D., Sarabi-Jamab, M., Ghorani, B., Kadkhodaee, R., & Tromp, R. H. (2018). Electrospray-assisted drying of live probiotics in acacia gum microparticles matrix. Carbohydrate Polymers, 183, 183–191. Zahi, M. R., Liang, H., & Yuan, Q. (2015). Improving the antimicrobial activity of D-limonene using a novel organogel-based nanoemulsion. Food Control, 50, 554–559. Zahi, M. R., Wan, P., Liang, H., & Yuan, Q. (2014). Formation and stability of d-limonene organogel-based nanoemulsion prepared by a high-pressure homogenizer. Journal of Agricultural and Food Chemistry, 62(52), 12563–12569. Zhao, X., Qiao, L., & Wu, A. M. (2017). Effective extraction of Arabidopsis adherent seed mucilage by ultrasonic treatment. Scientific Reports, 7, 40672. Zuidam, N. J., & Heinrich, E. (2010). Encapsulation of aroma. In Encapsulation technologies for active food ingredients and food processing (pp. 127–160). New York, NY: Springer.

Further reading Chranioti, C., & Tzia, C. (2014). Arabic gum mixtures as encapsulating agents of freeze-dried fennel oleoresin products. Food and Bioprocess Technology, 7(4), 1057–1065. Gharsallaoui, A., Roudaut, G., Chambin, O., Voilley, A., & Saurel, R. (2007). Applications of spray-drying in microencapsulation of food ingredients: An overview. Food Research International, 40(9), 1107–1121.

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Diego Romano Perinelli, Marco Cespi, Giulia Bonacucina School of Pharmacy, University of Camerino, Camerino, Italy

1

Introduction

The word nutraceutical derived from “nutrition” and “pharmaceutical” and it was created by Stephen L. DeFelice, founder of the Foundation for Innovation in Medicine (FIM, Cranford in 1989) (Brower, 1998). He defined nutraceuticals as “any substance that is a food or a part of the food and provides medical or health benefits, including the prevention and treatment of diseases” (Brower, 1998; DeFelice, 1995). Nowadays, food ingredients are viewed not only a source of nutrients but they possess an important role for the health of consumers ( Jafari & McClements, 2017). Recently, different kinds of polymeric-, lipid-based and inorganic nanocarriers have been studied to improve the bioavailability and clinical efficacy of nutraceuticals (Akhavan, Assadpour, Katouzian, & Jafari, 2018; Faridi Esfanjani & Jafari, 2016). Also, they have been investigated to achieve a therapy based on nutraceuticals and chemotherapeutic agents for the prevention and treatment of cancer (Arora & Jaglan, 2016). Food nanotechnology is a field of developing interest and it could open up many new possibilities for the food industry. The use of nanocarriers for the encapsulation and delivery of nutraceuticals can help to avoid the limits associated with the oral administration (Siddiqui et al., 2009). Nanoencapsulation is one of the most promising technologies to entrap bioactive compounds (Ezhilarasi, Karthik, Chhanwal, & Anandharamakrishnan, 2013), being able to bring innovation and improvement to the characteristics of food, such as texture, taste, sensory attributes, coloring strength, processability, and stability during shelf life (Assadpour & Jafari, 2018; Rafiee & Jafari, 2018). Furthermore, nanotechnology can also increase solubility in water, thermal stability, and oral bioavailability of bioactive molecules (Huang, Yu, & Ru, 2010; McClements, Decker, Park, & Weiss, 2009) both in nutraceuticals and functional foods (McClements et al., 2009; Silva, Cerqueira, & Vicente, 2012). Nanoencapsulation assures the protection of the bioactive compounds (polyphenols, micronutrients, enzymes, antioxidants, and fatty acids) and also the achievement of a controlled release at targeted sites (Faridi Esfanjani & Jafari, 2016; Gouin, 2004; Katouzian & Jafari, 2016). Furthermore, nanosystems encapsulating food ingredients Biopolymer Nanostructures for Food Encapsulation Purposes. https://doi.org/10.1016/B978-0-12-815663-6.00019-7 © 2019 Elsevier Inc. All rights reserved.

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are being formulated with the claims that they offer improved taste, texture, and consistency (Katouzian, Faridi Esfanjani, Jafari, & Akhavan, 2017; Pathakoti, Manubolu, & Hwang, 2017). Thus nanotechnology could improve many aspects of food and agricultural products as, for example, the security of manufacturing, processing, and shipping and delivering of functional food ingredients, and the development of new functional materials. A key field in food nanotechnology is the encapsulation of food flavors (Idolo Imafidon & Spanier, 1994) and antioxidants (Esfanjani & Jafari, 2017; Rafiee, Nejatian, Daeihamed, & Jafari, 2018). Food components such as lycopene and carotenoids formulated as nanoparticulate systems are becoming commercially available with the advantages of an increased bioavailability compared to their traditional goods. Omega 3 and omega 6 fatty acids, probiotics, prebiotics, vitamins, and minerals represent other examples of bioactive compounds formulated as nanosystems (Gharibzahedi & Jafari, 2017; Watanabe, Iwamoto, & Ichikawa, 2005). Despite nanotechnology representing an expensive and often impractical strategy to be implemented on an industrial scale (Weiss, Takhistov, & McClements, 2006), different innovative systems such as micelles, nanoliposomes, nanoemulsions, biopolymeric nanoparticles and cubosomes, and nanosensors are formulated to ensure food safety (Esposito et al., 2005; Ligler et al., 2003; Nasongkla et al., 2006; Yih & Al-Fandi, 2006). Cooking oils represent an example of the application of nanotechnology in the food sector. In fact, cooking oils containing nutraceuticals and flavor enhancers in nanocapsules, and nanoparticles, which are able to bind and remove chemicals from food (Sozer & Kokini, 2009), have been formulated. The main issue related to the late application of nanotechnology in the food sector is associated with the lack of worldwide accepted rules or regulations for nanotechnology that involve the labeling of the food products and consumer health aspects. Thus, the existing general regulations make difficult and time consuming the introduction of innovative nano-ingredients in food products ( Jafari, Katouzian, & Akhavan, 2017). For this reason, most expected nanoapplications in the food market regard food packaging and only few actual food products (Sharma, Dhiman, Rokana, & Panwar, 2017). However, FDA has approved methodologies and techniques supporting the inclusion of nanotechnology-based ingredients for mass consumption (Chau, Wu, & Yen, 2007) as, for example, the production of vitamins in the form of micelles and of small (nano) detectors of viruses. Another important issue is represented by the use of biodegradable and edible polymers for nanoencapsulation and active packaging. Food industries are interested in edible polymers because they are compatible with a broad spectrum of foods and can improve the quality of their products, also increasing their shelf life. Moreover, micro- and nanoencapsulation of bioactive compounds with edible and biodegradable polymer coatings may help to control their release under specific conditions and to protect them from moisture, heat, or other extreme conditions, by enhancing, at the same time, their stability and viability. Edible biopolymers have been developed from different sources, including fungal exopolysaccharides (pullan) or fermentation by-products (polylactic acid) (Shit & Shah, 2014).

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Polymeric nanocarrier systems developed from biodegradable and biocompatible polymers are solid colloidal particles having a diameter preferably less than 80%), though those prepared with PCL were characterized by a greater size and narrower size distribution. From a morphological point of view, the microparticles prepared with the two polymers were always spherical but characterized by different surfaces. In the case of PCL, the surface was smooth and without visible pores, while for the PHBV the particles surface was rough and rich of pores. Interestingly, the resveratrol solid state changed from crystalline to amorphous after the encapsulation process using both PHBV and PCL. Microparticles showed a slower release profile than the pure resveratrol, even with different characteristics as a function of the considered polymer: PHBV microspheres had a faster release governed by erosion, while for PCL the release was slower and the mechanism was identified as anomalous behavior, that is a superposition of diffusion and erosion phenomena. In both cases, an initial burst release was observed. The antioxidant capacity of resveratrol was also investigated. PHBV and PCL microparticles were less effective compared to the pure compound, although the authors highlighted as the test has been performed only about 1 h after preparation of aqueous solutions to be tested. Thus, most of the resveratrol was yet encapsulated and consequently nonavailable to perform its activity. Finally, compatibility with erythrocytes was verified. Taking into account that pure resveratrol does not possess hemolytic effect, the encapsulated microspheres gave comparable results. According to the authors, the sustained release of microparticles, their antioxidant activity after 1 h, and the absence of any hemolytic effect render these systems very promising from a pharmaceutical point of view (Mendes et al., 2012). A summary of the most relevant studies on the PCL-based nanosystems for the encapsulation of food bioactive compounds are reported in Table 4.

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Table 4 Summary of PCL-based nanosystems for the encapsulation of food bioactive compounds Encapsulated active ingredient

Nanosystem

References

Rosmarinic acid Resveratrol Eugenol

PCL microsphere PCL microsphere PCL nanocapsule

Fish oil

PCL nanocapsule

Curcumin

PCL/chitosan nanoparticles PCL nanocapsule PCL microsphere

Kim et al. (2010) Mendes et al. (2012) Choi, Soottitantawat, Nuchuchua, Min, and Ruktanonchai (2009) Choi, Ruktanonchai, Soottitantawat, and Min (2009) Choi, Ruktanonchai, Min, Chun, and Soottitantawat (2010) Liu et al. (2012)

Quercetin

Bixin

4

PCL nanocapsule

Weiss-Angeli et al. (2012) Natarajan, Krithica, Madhan, and Sehgal (2011) Lobato et al. (2013)

Conclusion and further remarks

Food nanotechnology is an emerging area of application for colloidal systems as micelles, nanoparticles, nanocapsules, and microspheres. Particularly, the encapsulation of nutraceutical ingredients derived from food in biodegradable synthetic polymers offers some advantages in comparison to their unencapsulated dosage form of administration. These advantages include the protection from degradation and oxidation, thus prolonging the stability over time of natural ingredients and the increase of their apparent solubility, resulting in an enhanced bioavailability. Biodegradable synthetic polymers resulted to be effective in encapsulating these classes of compounds and are assumed to show a low potential in inducing toxicological effects both in vitro and in vivo. Despite the numerous satisfactory experimental studies being conducted, trials on the most promising nanoformulations intended for human administration should be undertaken to evaluate their actual safety and effectiveness in vivo.

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Nanoencapsulation of food ingredients by dendrimers

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Mohammad Yousefi*, Parvin Orojzadeh†, Seid Mahdi Jafari‡ *Student Research Committee, Department of Food Science and Technology, Tabriz University of Medical Sciences, Tabriz, Iran, †Student Research Committee, Department of Food Technology, National Nutrition and Food Technology Research Institute, Shahid Beheshti University of Medical Sciences, Tehran, Iran, ‡Department of Food Materials and Process Design Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

1

A brief overview of dendrimers

What is a dendrimer? Before answering this question, it is better to look at a tree?!! Tree branches serve to keep the leavers in the space. These leaves show several functions such as restraining the sun light intensity, modifying the atmosphere beneath them, maximum usage of sun energy, and so on. In a similar instance, neurons in brains possess a branching structure which helps the brain to analyze myriad data in a very short time. In the molecular level, natural polysaccharides like amylopectin, glycogen, and dextran own branching forms which aid them to store a lot of energy (Sunder, Heinemann, & Frey, 2000). Dendrimers are artificial macromolecules which have a tree-like structure, enabling them to efficiently encapsulate and deliver a wide variety of bioactive compounds. Dendrimers have been denoted as the “Polymers of the 21st century” (Trivedi et al., 2012). The term “dendrimer” has been invented from two Greek words, the word “dendron” and “meros,” meaning tree and part, respectively (Zhou, Shan, Hu, Yu, & Cong, 2018). Dendrimer chemistry science was first presented in 1978 by Buhleier, Wehner, and V€ogtle (1978). They first designed a synthetic cascade molecule. Seven years later, Tomalia et al. (1985) synthesized the first groups of dendrimers. Simultaneously, Newkome, Yao, Baker, and Gupta (1985) reported designing the analogous macromolecule structures. They named them “arborols,” which in Latin, “arbor” means a tree. The terms hyperbranched polymers, arborescent polymers, and cascade molecules are likewise used, but “dendrimer” is the reputable one. In a review paper, Moorefield and Newkome (2003) particularly investigated the host-guest (encapsulation) ability utilizing dendrimers. This feature of dendrimers was previously studied by Jansen, Janssen, de Brabander-van den Berg, and Meijer (1994) and Crooks, Zhao, Sun, Chechik, and Yeung (2001). Several instances of host-guest interactions of phenylazomethine dendrimers also have been reported by Yamamoto et al. (Cho, Takanashi, Higuchi, & Yamamoto, 2005; Higuchi, Shiki, Ariga, & Yamamoto, 2001; Satoh, Nakashima, Kamikura, & Yamamoto, 2008; Yamamoto, Higuchi, Shiki, Tsuruta, & Chiba, 2002). Biopolymer Nanostructures for Food Encapsulation Purposes. https://doi.org/10.1016/B978-0-12-815663-6.00020-3 © 2019 Elsevier Inc. All rights reserved.

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In general, dendrimers are three-dimensional, monodispersed, and hyperbranched molecules with defined host-guest and molecular weights traits (Cheng, Xu, Ma, & Xu, 2008; Kesharwani et al., 2015). The three-dimensional form of dendrimers is composed of a multifunctional inner core, branched constituents, and surface groups (Svenson & Tomalia, 2012) (Fig. 1). The core structure contains cavities which create channels and cages with the aim of branches’ folding structures. The presence of numerous chain ends gives a dendrimer abilities such as high miscibility and solubility and high reactivity. Also, the surface of a dendrimer is modifiable using several active groups, so that the dendrimer solubility is intensely affected by the nature of these groups (Tripathy & Das, 2013). Dendrimers are usually classified by their generations which refer to the quantity of branching cycles (layers) that are built during the synthesis. In detail, dendrimers are composed of an interior section and intermittent layers of two monomers, so that every

Fig. 1 A schematic representation of dendrimer structure. (Reproduced with permission from Kesharwani, P., Banerjee, S., Gupta, U., Mohd Amin, M.C.I., Padhye, S., Sarkar, F.H., et al. (2015). PAMAM dendrimers as promising nanocarriers for RNAi therapeutics. Materials Today, 18(10), 565–572.)

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pair of this monomer layer builds a shell (generation) (Fig. 2). Depending on the generation, dendrimers have 2 to 10 nm diameter (Garg, Singh, Arora, & Murthy, 2011). Core molecules have multiple reaction sites, even the simplest one, ammonia contains three amine reaction sites. The core molecule is combined with a monomer molecule which reacts with the reaction sites of core to create the first branch. This monomer molecule possesses two reactive groups. Then, a second monomer molecule reacts with the first layer, building the second layer and completing the first generation. Each unreacted end pertaining to the second monomer gives a reaction site which can mix with multiple molecules. This provides other branches and reactions sites for producing the next generation. Dendrimers, owing to their monodispersity and controllable size, are considered as brilliant carriers for a wide spectrum of molecules which can be entrapped in the dendrimer interior section or interact with the surface groups of dendrimer. Guest molecules, mostly lipophilic, are encapsulated in the core of dendrimers via Van der Waals or apolar forces. Dendrimers can be employed for carrying drugs and food bioactive compounds and modifying their properties such as protection, solubility enhancement, targeted delivery, controlled release, and many more (Singh, Rehni, Kalra, Joshi, & Kumar, 2008). The solubility enhancement and the release properties of dendrimers are mainly based on factors including dendrimer size and concentration, core, terminal functionality, pH, and temperature. Hydrogen bonding, hydrophobic interactions, and ionic interactions are the feasible ways by which dendrimers apply their solubilizing trait (Gupta, Agashe, Asthana, & Jain, 2006). In general, hydrophilic

Surface active groups Branching units G3 G2 G1 Functional interior core

Monomers

Fig. 2 A schematic representation of dendrimers generations, branching units, and end groups.

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end groups of dendrimers can make them soluble in water, but dendrimers containing hydrophobic cores with hydrophobic peripheries can make them soluble in oil (Abbasi et al., 2014). In the most of cases, dendrimers have the hydrophobic core and hydrophilic surface which makes them static unimolecular micelles (Cao & Zhu, 2011). These forms of micelles have the potential to solubilize many insoluble drugs and bioactive molecules (Gupta, Agashe, & Jain, 2007; Kesharwani, Jain, & Jain, 2014; Sˇebestı´k, Reinisˇ, & Jezˇek, 2012). Drug release from dendrimer-drug conjugates has a substantial role on the efficiency of dendrimers. When drug is attached to a dendrimer, the release should be achieved by chemical or physical modifications such as chemical erosion or dendrimer swelling. In this concern, covalent conjugate shows higher entrapment and controlled drug release behavior (Kurtoglu, Mishra, Kannan, & Kannan, 2010), for instance, PEGylated dendrimers can cause improved permeation and holding of drugs (Menjoge, Kannan, & Tomalia, 2010; Zhu et al., 2010). Several features have been attributed to dendrimers and some of them are as follows (Lee, MacKay, Frechet, & Szoka, 2005; Pasut, Scaramuzza, Schiavon, Mendichi, & Veronese, 2005; Singh et al., 2008; Tomalia, Reyna, & Svenson, 2007): l

l

l

l

l

l

l

l

l

Adjustable pharmacokinetic and biodistribution traits via controlling the size and conformation of dendrimers. Potential to be designed and functionalized by multiple number of drugs, ligands, chromophores at their interiors and/or peripheries. Dendrons (branching structures) likewise can be exploited to accurately increment the drug-loading capacity. High chemical and structural homogeneity. Under controlled synthesis and degradation conditions. Significantly lower viscosity compared to linear polymers. High miscibility and solubility. High penetration capabilities into the cell membrane which leads to the increased cellular uptake of drugs. High density of ligand. In opposite of linear polymers, increasing the dendrimer generations, the density of ligands increases at the surface, so that, this can strengthen the connection between ligand and receptor and enhance the targeting of joined substances. Non- or very low-immunogenicity related to the most dendrimer peripheries amended with polyethylene glycol (PEG) or small functional groups.

Despite these benefits, dendrimers encounter with some challenges pertained to transferring between the laboratory and clinic. High costs for the preparation of increased generation dendrimers are another obstacle. Furthermore, enhanced quality control examinations are needed to ensure that multicomponent dendrimers contain the appropriate components at correct ratios (Lee et al., 2005). Concerning types of dendrimers, they are classified into two major groups: chiral dendrimers and achiral dendrimers. Chiral dendrimers are different from achiral ones since (1) their shape usually is chiral and not spherical, (2) their end groups can be chiral, and (3) chiral scaffolds into the chiral dendrimer can be detectable using optical measurements. Some reputable achiral dendrimers include polypropylenamine (POPAM), polyamidoamine (PAMAM), the hybrid architecture of POPAM and PAMAM

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(POMAM), polylysine, stilbenoid, hyperbranched polybenzenes, and polyester dendrimers (Vogtle, Richardt, Werner, & Rackstraw, 2009). The idea of chirality in dendritic structures traces back to Denkewalter, Kolc, and Lukasavage (1985) patent, describing the architecting of peptide-like dendrimers from L-lysine units. Chiral dendrimers are divided according to the site in which chiral molecules are fixed. Accordingly, five groups of dendrimers have been synthesized in which dendrimers have (Vogtle et al., 2009): (1) Chiral core with achiral branching units such as Frechet-type poly(aryl ether) dendrimers (Walter & Malkoch, 2012) (2) Chiral surface groups such as peripherally tryptophan-substituted arborol (Newkome, Lin, & Weis, 1991) (3) Chiral branching units such as the dendrimer containing trimesic acid in core with 1,2-diol branching units (Salamonczyk, 2011) (4) Achiral core with at least 3 different dendrons such as the dendrimer with pentaerythritol as core and Frechet’s aromatic ether as branches (Hourani & Kakkar, 2010) (5) Chiral core with chiral surface groups and chiral branching units such as dendrimers based on dihydroxypyrrolidine (Hari, Kalaimagal, Porkodi, Gajula, & Ajay, 2012).

Many researches have mentioned the “glycodendrimer” and “peptide dendrimer” terms. Glycodendrimers are composed of dendrimers which have carbohydrates at their structures. Based on the position of carbohydrate at dendrimers, they are classified into the three groups: (1) dendrimers with saccharide residues on their peripheries (carbohydrate-coated dendrimers), (2) dendrimers with a sugar unit in the core (carbohydrate-centered dendrimers), and (3) dendrimers with carbohydrates branches (carbohydrate-based dendrimers) (Roy, Shiao, & Rittenhouse-Olson, 2013; Turnbull, Kalovidouris, & Stoddart, 2002). One of the most widely used glycodendrimers is cyclodextrin-based dendrimer (CD-dendrimer). Cyclodextrins can easily entrap a variety of liquid, gas, and solid hydrophobic compounds without using covalent bonds. Cyclodextrins do not trigger the immune system and show low toxicity body. A myriad number of applications for these compounds have been described: gene therapy, drug delivery systems, many applications in food industries, and so on. When cyclodextrins are incorporated into a dendritic structure, the dendrimer can heighten cyclodextrins features by its favorable properties (Namazi & Heydari, 2014; Toomari, Namazi, & Akbar, 2015). Dendrimers containing surface peptides attached to a dendrimer scaffold and dendrimers having amino acids in their structures as core or branching units are both named as “peptide dendrimers.” These kinds of dendrimers have the abilities to act as protein antiviral and anticancer agents, gene and drug delivery systems, and protein mimics (Gu, Luo, She, Wu, & He, 2010; Luo et al., 2012; Reymond & Darbre, 2012). Lysine is a prevalent amino acid used in constituting dendrimers. Dendrimers containing lysine in the core with octapeptide and tetrapeptide peripheries have been utilized as antimicrobial agents. These dendrimers were less toxic to body cells, more resistant to proteolysis, stronger antimicrobial agents, and also more soluble in the aqueous phase compared to their linear polymeric counterparts (Tam, Lu, & Yang, 2002).

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Dendrimer synthesizing methods

Nowadays, dendrimer synthesizing is accomplished with precise methods. The synthesis process utilized for the preparation of dendrimers has a full control over the critical designing parameters such as topology, shape, flexibility, size, and interior or surface chemistry. Many of these syntheses depend on traditional reactions such as the Williamson ether synthesis or Michael reaction, whereas others involve the usage of novel chemistry and techniques such as organo-phosphorus chemistry, solid-phase synthesis, organo-silicon chemistry, or other modern methodologies (Jeevanandam, San Chan, & Danquah, 2016). The majority of dendrimers are produced through covalent bonds (El Kazzouli, Mignani, Bousmina, & Majoral, 2012; Gonza´lez et al., 2011; Wang, Su, Ding, & Yang, 2013). There are likewise structures achieved by metal-ligand bonds (Bazzicalupi et al., 2013; Yancey et al., 2013). Dendrimers are usually synthesized using two methods of divergent or convergent (Walter & Malkoch, 2012). which will be explained in the following sections.

2.1 Divergent technique for the synthesis of dendrimers In the divergent method, the dendrimer rises from the core molecule toward the space. The multifunctional core molecule interacts with monomer molecules having two dormant and one active functional groups giving rise to the first generation. After that, another periphery is activated to interact with new monomers. This procedure is repeated to build higher generations of dendrimers (Menjoge et al., 2010). The divergent method is utilized to produce dendrimers at large quantity. The main problem of this approach is incomplete reactions of peripheries leading to defects in the structure of dendrimers. To prevent these unfavorable reactions, a large amount of reagents is needed in all stages. Besides, precisely purification steps are needed for obtaining a desired dendritic structure. The total yield is significantly low at this methodology. However, the feasibility to amend the surface of dendrimers is the most highlighted advantage of the divergent approach. By changing the peripheries, the overall physical and chemical traits of dendrimers can be adjusted to specific requirements (Martinho et al., 2014).

2.2 Convergent technique for the synthesis of dendrimers The convergent technique was established to cover the divergent synthesis weaknesses. In this approach, the construction of dendrimer is started from the surface groups and advances inwards. Basically, this method involves the connection of surface groups to a generation and the connection of the generations to the inner core. The structure formed before the final connection of dendrons to the core molecule is called “wedge.” Generally, three to four wedges with different peripheries join to the core (Ledin, Friscourt, Guo, & Boons, 2011). The convergent method in comparison to the divergent one has some advantages. It is moderately simple to purify the final dendrimer. The emerging of defects in the final

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product is diminished. It is possible to do subtle works on dendrimers by precise attachment of intended functional groups at the surface of the dendrimer. However, this approach does not permit the creation of high generations owing to steric obstructions happening at the reactions of the core molecule with dendrons (Walter & Malkoch, 2012).

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Safety of dendrimers

In most cases, dendrimers, as for having a numerous surface groups, exhibit less or more toxicity. For instance, cationic dendrimers containing amino groups at their surfaces such as polypropyleneimine (PPI) and PAMAM dendrimers demonstrate concentration/generation-dependent hemolysis and toxicity, while dendrimers with anionic or neutral constituents have been specified to be less hemolytic and less toxic. One of the methods describing the toxicity of dendrimers is the evaluation of their contribution in producing reactive oxygen species (ROS) as the triggering agents of cell death by several pathways, including DNA damage, caspase activation, or cytokine. In this concern, Mukherjee and Byrne (2013) showed an initial maximum at ROS levels when using 0.5 to 1.16 μM PAMAM (generation 6) after nearly 1 hour, while for 1.3 to 2.23 μM of PAMAM, the maximum value was seen at 0.5-hour exposure. Also, by increasing the generation levels from G4 to G6, the amount of produced ROS was incremented. Also, it has been reported that PAMAM G2 and G4 fluidized the membrane of mitochondria, causing mitochondrial depolarization which led to the disruption of phosphorylation system. Furthermore, the direct toxic impact was observed on the effective factors of mitochondrial respiratory (Labieniec & Watala, 2009). The dendrimer’s cytotoxicity, apart from the concentration and generation, pertains to the charge density. For example, it was shown that anionic PAMAM G3.5 was less toxic compared to cationic PAMAM. Similarly, unmodified PPI G4 dendrimers containing amino end groups were more harmful in comparison with sugarmodified PPI ones ( Janaszewska et al., 2012). The toxicity of cationic dendrimers is attributed to their interactions with cell’s membrane proteins initiating the changes of their conformations resulting in necrosis and/or apoptosis (Singh et al., 2008). Cytotoxicity of dendrimers containing amino-terminated groups can be reduced by fractional or complete revision of the peripheries with neutral or negatively charged elements. In addition, the structural shape of dendrimers likewise affects their toxicity. Dendrimers’ globular structures generally show less toxicity. This can be justified by the lower adhesion of the globular and less flexible dendritic structures to the surface of cells owing to the smaller hydrodynamic volume of globular structures in comparison with the corresponding linear polymers (Boas & Heegaard, 2004; Fischer, Li, Ahlemeyer, Krieglstein, & Kissel, 2003). In this regard, Frechet-type polyether dendrimers form a higher globular and rigid structure as for shifting from G3 to G4. PAMAM dendrimer moves to higher rigidity at G4.5. Also, a globular nature of PPI is observed at G4 (Mintzer & Grinstaff, 2011). Therefore a mass of dendrimers utilized at biomedical applications are G4 or higher generations.

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On the most important feature of dendrimers is their biodegradable nature. This property prevents the accumulation of dendrimers and lessens their toxicity. Dendrimers can degrade via several ways, including hydrolytic, enzymatic, photolytic, and geometrically disassembling degradations, or by degrading under reduced conditions. Dendrimers having polyester backbones are prominent examples from point of view of hydrolytic degradability (Twibanire & Grindley, 2014). Their rate of cleavage is faster than PAMAM dendrimers. For example, it was shown that polyester dendrimers containing 2,2-bis propionic acid as backbone and hydroxyl groups as surface agents demonstrate excellent biocompatibility and degradability nature, and are noncytotoxic to the primary cells of humans, whereas neutral PAMAM dendrimers exhibited dose-dependent cytotoxicity at these cells (Feliu et al., 2012). Various designs have been proposed to accelerate the cleavage of dendrimers. In this regard, the addition of disulfides or enzyme substrates within the dendritic structure is a promising approach. Disulfides are frequently added to the backbone of dendrimers to ensure the efficient and fast release of its payload along with decreasing its toxicity under reducing conditions existed inside the cells. For instance, it was reported that poly(amido amine) (PAA) dendrimers having 2-methyl cystamine disulfide groups were degraded under intracellular reducing conditions at approximately 1 h (Elzes, Akeroyd, Engbersen, & Paulusse, 2016). Concerning the enzymatic degradation, new groups of dendrimers named “self-immolative dendrimers” have been designed in which a particular enzymatic trigger in the focal section of the dendrimer initiates the cleavage of the dendritic structure and disassembly of all bonded components (da Silva Santos, Igne Ferreira, & Giarolla, 2016; Guo, Zhuang, Wang, Raghupathi, & Thayumanavan, 2014; Seidi, Jenjob, & Crespy, 2018). Amir and Shabat (2004) employed phenylacetamide as a triggering agent for penicillin-Gamidase (PGA), resulting in fragmentation of the dendrimer. Self-immolative dendrimers are useful in a wide spectrum of scientific areas. Nevertheless, there are difficulties associated with designing higher generation self-immolative dendrimers owing to the steric hindrance which limits the incorporation of substrate on a dendrimer (Roth, Green, Gnaim, & Shabat, 2015).

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Application of dendrimers for encapsulation of food bioactive ingredients

Most bioactive compounds such as carotenoids, essential fatty acids, essential oils, some vitamins and phenolic compounds, and so on, have the hydrophobic nature; hence they cannot be freely formulated at an intended dosage (Akhavan, Assadpour, Katouzian, & Jafari, 2018; Assadpour & Jafari, 2018; Faridi Esfanjani, Assadpour, & Jafari, 2018; Katouzian, Faridi Esfanjani, Jafari, & Akhavan, 2017). Furthermore, nearly 15% of launched bioactive ingredients display a suboptimal performance due to their poor solubility. Lack of permeability and solubility causes low bioavailability (Assadpour, Jafari, & Esfanjani, 2017; Jafari & McClements, 2017). The modification of the surface of bioactive components is a common approach for improving their solubility and bioavailability. The surface of these ingredients

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is incremented by decreasing the particle size, but it involves organic solvents and destructive methods. However, labile bioactive compounds are sensitive to these tough conditions. Besides, the reduction of particle size has difficulties such as the stability problems during large-scale producing. Recently, delivery systems have been utilized to heighten the bioavailability of bioactive compounds (Abaee, Mohammadian, & Jafari, 2017; Faridi Esfanjani & Jafari, 2016; Katouzian & Jafari, 2016). Dendrimers offer a new approach for solubilizing these ingredients, providing a distinctive polyvalency and nanocontainer trait for the bioactive compounds delivery (Kannan, Nance, Kannan, & Tomalia, 2014; Kulhari, Pooja, Prajapati, & Chauhan, 2011). Dendrimers can protect their contents from hostile situations inside the food and body such as enzymatic degradation, pH variations, and first pass effects. Dendrimers can be exploited to attain control release of the bioactive ingredients as needed. Resveratrol and curcumin are two important phenolic compounds which have recently been entrapped by dendritic structures (Chauhan, 2015; Wang et al., 2013) (Rafiee, Nejatian, Daeihamed, & Jafari, 2018). Resveratrol has been utilized for the prevention of aging, cardiovascular diseases, inflammation, and cancer. In spite of these benefits, resveratrol demonstrates a short half-life (