Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow 0128164026, 9780128164020

Table of contents :
Cover
Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow
Copyright
Contents
Part I Introduction1
Part II Impact of PEF on bioaccessibility/bioavailability and development of nutraceuticals/food additives49
Part III Reduction of toxic/contaminants assisted by PEF101
Part IV Improvement of the efficiency of industrial processes153
Part V Patents, commercial applications and limitations of pulsed electric field treatment (or maybe safety aspects of PEF ...
List of Contributors
Part I: Introduction
1 How does pulsed electric field work?
1.1 Introduction
1.2 Cell membrane permeabilization
1.3 Critical value/dielectric breakdown
1.3.1 Models applied for dielectric breakdown
1.4 Electroporation on different systems
1.4.1 Spherical cells
1.4.2 Nonspherical geometrically regular cells
1.4.3 Irregularly shaped cells
1.4.4 Cells in dense suspensions and tissues
1.5 Main parameters affecting the cell membrane electroporation
1.5.1 Electric field strength
1.5.2 Pulse duration
1.5.3 Pulses number and pulse frequency (delay between pulses)
1.5.4 Pulse shape
1.5.5 Cell size
1.6 Conclusions
References
2 An overview of the potential applications to produce healthy food products based on pulsed electric field treatment
2.1 Introduction
2.2 Retention of valuable compounds
2.3 Reduction of food contaminants (toxins, pesticides)
2.4 Potential applications of pulsed electric field in food industry
2.5 Challenges of pulsed electric field technology
References
Part II: Impact of PEF on bioaccessibility/bioavailability and development of nutraceuticals/food additives
3 Health promoting benefits of PEF: bioprotective capacity against the oxidative stress and its impact on nutrient and bioa...
3.1 Introduction
3.2 Carrots (Daucus carota)
3.3 Grapes (Vitis vinifera)
3.4 Orange (Citrus sinensis)
3.5 Tomato (Solanum lycoperiscum)
3.6 Milk and milk products
3.7 Fruit and vegetable mixture combinations
3.8 Conclusion
References
Further reading
4 Pulsed electric field (PEF) as an efficient technology for food additives and nutraceuticals development
4.1 Introduction
4.2 Principles of pulsed electric field treatment
4.3 Factors affecting pulsed electric field treatment efficiency
4.3.1 Pulse parameters
4.3.2 Tissue parameters
4.3.3 Media parameters
4.4 Advantages of pulsed electric field–assisted extraction
4.5 Application of pulsed electric field treatment in food additives and nutraceuticals extraction
4.5.1 Dietary polyphenols
4.5.2 Colorants
4.5.3 Lipids
4.5.4 Stabilizers
4.5.5 Proteins
4.6 Application of pulsed electric field treatment in plant secondary metabolites production
4.7 Conclusion
References
Part III: Reduction of toxic/contaminants assisted by PEF
5 Pulsed electric field as a sustainable tool for the production of healthy snacks
5.1 Definition of “snacks”
5.2 Need for healthy snacks
5.3 Acrylamide formation in snacks
5.4 Impact of raw material on acrylamide formation
5.5 Industrial chips processing
5.6 Acrylamide reduction through chips processing
5.7 Acrylamide reduction with pulsed electric field
5.8 Fat in snack products
5.9 Reduction of the fat content in fried snacks
5.10 Dried snacks
5.11 Industrial implementation
References
6 Effect of pulsed electric field on Maillard reaction and hydroxymethylfurfural production
6.1 Introduction
6.2 Impact of pulsed electric field on Maillard reaction
6.3 Effects of pulsed electric field on furfural and hydroxymethylfurfural formation
6.4 Conclusion
References
7 The potential of pulsed electric fields to reduce pesticides and toxins
7.1 Introduction
7.2 Pesticides
7.3 Toxins
7.4 Conclusion
Acknowledgment
References
Part IV: Improvement of the efficiency of industrial processes
8 PEF as an alternative tool to prevent thermolabile compound degradation during dehydration processes
8.1 Introduction
8.1.1 Drying and osmotic dehydration as a heat and mass transfer–based process
8.2 Impact of pulsed electric field on dehydration processes
8.2.1 Impact of pulsed electric field on drying kinetics
8.2.2 Impact of pulsed electric field on physicochemical properties of dried food
8.3 Role of pulsed electric field in osmotic dehydration
8.3.1 Impact of pulsed electric field on osmotic dehydration kinetics
8.3.2 Impact of pulsed electric field on physicochemical properties of osmo-dehydrated food
8.4 Conclusion
Acknowledgments
References
Further reading
9 Modification of food structure and improvement of freezing processes by pulsed electric field treatment
9.1 Introduction
9.2 Progress of freezing of food products
9.3 The application of pulsed electric field treatment prior to freezing
9.4 Cryoprotectants utilization in freezing process
9.5 The use of cryoprotectants in combination with pulsed electric field treatment prior to freezing process
9.6 The comparison of the influence of pulsed electric field and other nonthermal treatments on freezing progress and the q...
9.7 Conclusion
Acknowledgment
References
10 Pulsed electric field applications for the extraction of compounds and fractions (fruit juices, winery, oils, by-product...
10.1 Introduction
10.2 Need for pulsed electric field application in for the extraction of compounds and fractions
10.3 Improvement in fruit juice yields
10.4 Improvement in wine preparation
10.5 Extraction of bioactive compounds from fruits
10.6 Impact of pulsed electric field on the oil yields
10.7 Extraction of bioactive compounds from by-products and wastes
10.8 Conclusion
References
11 Pulsed electric field–treated insects and algae as future food ingredients
11.1 Introduction
11.2 Application of pulsed electric field for treatment of microalgae biomass
11.2.1 Application of pulsed electric field for induction of stress response, stimulation, and mutation of microalgae biomass
11.2.2 Application of pulsed electric field for inactivation of microorganisms and extraction improvement
11.3 Application of pulsed electric field for treatment of insect biomass
11.3.1 Application of pulsed electric field for the inactivation of insects
11.3.2 Application of pulsed electric field for the insect cell permeabilization
11.3.3 Extraction of intracellular compounds from insect biomass
11.4 Outlook
References
Part V: Patents, commercial applications and limitations of pulsed electric field treatment (or maybe safety aspects of PEF utilization)
12 Industrial scale equipment, patents, and commercial applications
12.1 Introduction
12.2 Historical background of pulsed electric fields commercialization
12.3 Industrial equipment
12.4 Current industrial applications
12.4.1 Mass transport enhancement
12.4.2 Cutting and peeling improvement
12.4.3 Shelf life extension of juices
12.4.4 Process control options
12.5 Relevant early stage patents
12.6 Conclusions and opportunities for the future
References
13 Limitations of pulsed electric field utilization in food industry
13.1 Introduction
13.2 Electrochemical reactions during pulsed electric fields process
13.3 Effects of electrochemical reactions on the pulsed electric fields process
13.3.1 Electrode corrosion
13.3.1.1 Food safety and regulation
13.3.1.2 Food quality
13.3.1.3 Electrode lifetime and equipment reliability
13.3.2 Electrode fouling
13.3.3 (Partial) Electrolysis
13.3.4 Secondary reactions
13.4 Limitation of electrochemical reactions
13.5 Conclusion
References
14 Consumer attitudes regarding the use of PEF in European Union: the example of Poland
14.1 Introduction
14.2 Brief introduction of nonthermal technologies
14.2.1 Pulsed electric field
14.2.2 High hydrostatic pressure (HPP)
14.2.3 Ultrasound
14.2.4 Cold plasma
14.3 Assessment of consumers’ behavior on the food market
14.4 The understanding of the concept of nonthermal food processing technology and the knowledge of use
14.4.1 Labeling of food products processed by nonthermal technologies
14.4.2 Attitude of respondent group of consumers toward the nonthermal food processing technologies
14.4.3 The risks associated with the use of nonthermal food processing technologies
14.5 Conclusion
References
Further reading
Index
Back Cover

Citation preview

PULSED ELECTRIC F I E L D S T O O B TA I N H E A LT H I E R A N D S U S TA I N A B L E F O O D FOR TOMORROW

PULSED ELECTRIC F I E L D S T O O B TA I N H E A LT H I E R A N D S U S TA I N A B L E F O O D FOR TOMORROW Edited by FRANCISCO J. BARBA Nutrition and Food Science Area, Preventive Medicine and Public Health, Food Sciences, Toxicology and Forensic Medicine Department, Faculty of Pharmacy, Universitat de Vale`ncia, Vale`ncia, Spain

OLEKSII PARNIAKOV Elea Vertriebs- und Vermarktungsgesellschaft mbH, Quakenbru¨ck, Germany

ARTUR WIKTOR Department of Food Engineering and Process Management, Faculty of Food Sciences, Warsaw University of Life Sciences, Warsaw, Poland

Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1650, San Diego, CA 92101, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom Copyright © 2020 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www. elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 978-0-12-816402-0 For Information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Charlotte Cockle Acquisitions Editor: Megan R. Ball Editorial Project Manager: Liz Heijkoop Production Project Manager: Joy Christel Neumarin Honest Thangiah Cover Designer: Mark Rogers Typeset by MPS Limited, Chennai, India

Contents List of Contributors...................................................................................xiii

Part I

Introduction ........................................................................................ 1

Chapter 1 How does pulsed electric field work? ...........................................3 Urszula Tylewicz

1.1 Introduction ...........................................................................................3 1.2 1.3 1.4 1.5

Cell membrane permeabilization .........................................................4 Critical value/dielectric breakdown ......................................................8 Electroporation on different systems ................................................ 10 Main parameters affecting the cell membrane electroporation .................................................................................... 13

1.6 Conclusions ......................................................................................... 17 References.................................................................................................. 18

Chapter 2 An overview of the potential applications to produce healthy food products based on pulsed electric field treatment...............................................................................................23 Alica Lammerskitten, Artur Wiktor, Oleksii Parniakov and Nikolai Lebovka

2.1 Introduction ......................................................................................... 23 2.2 Retention of valuable compounds.....................................................25 2.3 Reduction of food contaminants (toxins, pesticides) ....................... 30 2.4 Potential applications of pulsed electric field in food industry ....... 34 2.5 Challenges of pulsed electric field technology ................................. 38 References.................................................................................................. 40

v

vi

Contents

Part II

Impact of PEF on bioaccessibility/bioavailability and development of nutraceuticals/food additives ...................... 49

Chapter 3 Health promoting benefits of PEF: bioprotective capacity against the oxidative stress and its impact on nutrient and bioactive compound bioaccessibility ...................................51 Zhenzhou Zhu, Fang Wang, Qiang Xia, Yunfei Li, Shahin Roohinejad, Krystian Marszałek, Elena Rosello´-Soto and Francisco J. Barba

3.1 3.2 3.3 3.4

Introduction ......................................................................................... 51 Carrots (Daucus carota) ......................................................................56 Grapes (Vitis vinifera) ......................................................................... 58 Orange (Citrus sinensis) ..................................................................... 59

3.5 Tomato (Solanum lycoperiscum) ......................................................59 3.6 Milk and milk products ....................................................................... 60 3.7 Fruit and vegetable mixture combinations ....................................... 60 3.8 Conclusion ........................................................................................... 61 References.................................................................................................. 62 Further reading .......................................................................................... 64

Chapter 4 Pulsed electric field (PEF) as an efficient technology for food additives and nutraceuticals development..................65 Mahesha M. Poojary, Marianne N. Lund and Francisco J. Barba

4.1 Introduction ......................................................................................... 65 4.2 Principles of pulsed electric field treatment......................................66 4.3 Factors affecting pulsed electric field treatment efficiency.............. 69 4.4 Advantages of pulsed electric field assisted extraction ................. 74 4.5 Application of pulsed electric field treatment in food additives and nutraceuticals extraction............................................. 75 4.6 Application of pulsed electric field treatment in plant secondary metabolites production .................................................... 88 4.7 Conclusion ........................................................................................... 90 References.................................................................................................. 91

Contents

Part III

vii

Reduction of toxic/contaminants assisted by PEF ............ 101

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks ........................................................103 Robin Ostermeier, Kevin Hill, Stefan To¨pfl and Henry Ja¨ger

5.1 Definition of “snacks”..................................................................... 103 5.2 Need for healthy snacks ................................................................. 104 5.3 Acrylamide formation in snacks .................................................... 105 5.4 Impact of raw material on acrylamide formation ......................... 107 5.5 Industrial chips processing............................................................. 108 5.6 Acrylamide reduction through chips processing.......................... 111 5.7 Acrylamide reduction with pulsed electric field ........................... 113 5.8 Fat in snack products ...................................................................... 115 5.9 Reduction of the fat content in fried snacks ................................. 117 5.10 Dried snacks .................................................................................... 119 5.11 Industrial implementation .............................................................. 120 References................................................................................................ 123

Chapter 6 Effect of pulsed electric field on Maillard reaction and hydroxymethylfurfural production ................................................129 Amin Mousavi Khaneghah, Mohsen Gavahian, Qiang Xia, Gabriela I. Denoya, Elena Rosello´-Soto and Francisco J. Barba

6.1 Introduction ....................................................................................... 129 6.2 Impact of pulsed electric field on Maillard reaction ....................... 132 6.3 Effects of pulsed electric field on furfural and hydroxymethylfurfural formation .................................................... 134 6.4 Conclusion ......................................................................................... 136 References................................................................................................ 137

viii

Contents

Chapter 7 The potential of pulsed electric fields to reduce pesticides and toxins ......................................................................141 Noelia Pallare´s, Josefa Tolosa, Mohsen Gavahian, Francisco J. Barba, Amin Mousavi-Khaneghah and Emilia Ferrer

7.1 Introduction ....................................................................................... 141 7.2 Pesticides ........................................................................................... 144 7.3 Toxins ................................................................................................ 145 7.4 Conclusion ......................................................................................... 148 Acknowledgment ..................................................................................... 149 References................................................................................................ 149

Part IV

Improvement of the efficiency of industrial processes ..................................................................................... 153

Chapter 8 PEF as an alternative tool to prevent thermolabile compound degradation during dehydration processes ..........155 Artur Wiktor, Anubhav Pratap Singh, Oleksii Parniakov, Viacheslav Mykhailyk, Ronit Mandal and Dorota Witrowa-Rajchert

8.1 Introduction ....................................................................................... 155 8.2 Impact of pulsed electric field on dehydration processes ............. 160 8.3 Role of pulsed electric field in osmotic dehydration...................... 182 8.4 Conclusion ......................................................................................... 190 Acknowledgments ................................................................................... 191 References................................................................................................ 191 Further reading ........................................................................................ 202

Chapter 9 Modification of food structure and improvement of freezing processes by pulsed electric field treatment...........203 Magdalena Dadan, Malgorzata Nowacka, Jakub Czyzewski and Dorota Witrowa-Rajchert

9.1 Introduction ....................................................................................... 203 9.2 Progress of freezing of food products ............................................. 204

Contents

ix

9.3 The application of pulsed electric field treatment prior to freezing .............................................................................................. 206 9.4 Cryoprotectants utilization in freezing process............................... 208 9.5 The use of cryoprotectants in combination with pulsed electric field treatment prior to freezing process............................ 211 9.6 The comparison of the influence of pulsed electric field and other nonthermal treatments on freezing progress and the quality of food ................................................................................... 214 9.7 Conclusion ......................................................................................... 222 Acknowledgment ..................................................................................... 222 References................................................................................................ 222

Chapter 10 Pulsed electric field applications for the extraction of compounds and fractions (fruit juices, winery, oils, by-products, etc.) ............................................................................227 Rohit Thirumdas, Chaitanya Sarangapani and Francisco J. Barba

10.1 Introduction ..................................................................................... 227 10.2 Need for pulsed electric field application in for the extraction of compounds and fractions ........................................ 229 10.3 Improvement in fruit juice yields ................................................... 230 10.4 Improvement in wine preparation ................................................. 233 10.5 Extraction of bioactive compounds from fruits ............................ 234 10.6 Impact of pulsed electric field on the oil yields ............................ 235 10.7 Extraction of bioactive compounds from by-products and wastes .............................................................................................. 236 10.8 Conclusion ....................................................................................... 238 References................................................................................................ 240

Chapter 11 Pulsed electric field treated insects and algae as future food ingredients..................................................................247 Sergiy Smetana, Houcine Mhemdi, Samir Mezdour and Volker Heinz

11.1 Introduction ..................................................................................... 247

x

Contents

11.2 Application of pulsed electric field for treatment of microalgae biomass............................................................................................ 248 11.3 Application of pulsed electric field for treatment of insect biomass............................................................................................ 254 11.4 Outlook............................................................................................. 261 References................................................................................................ 262

Part V

Patents, commercial applications and limitations of pulsed electric field treatment (or maybe safety aspects of PEF utilization) ........................................................ 267

Chapter 12 Industrial scale equipment, patents, and commercial applications ..............................................................269 Stefan Toepfl, Jimmy Kinsella and Oleksii Parniakov

12.1 Introduction ..................................................................................... 269 12.2 Historical background of pulsed electric fields commercialization ........................................................................... 270 12.3 Industrial equipment....................................................................... 274 12.4 Current industrial applications....................................................... 275 12.5 Relevant early stage patents .......................................................... 278 12.6 Conclusions and opportunities for the future............................... 280 References................................................................................................ 280

Chapter 13 Limitations of pulsed electric field utilization in food industry ....................................................................................283 Gianpiero Pataro and Giovanna Ferrari

13.1 Introduction ..................................................................................... 283 13.2 Electrochemical reactions during pulsed electric fields process................................................................................... 286 13.3 Effects of electrochemical reactions on the pulsed electric fields process...................................................................... 289 13.4 Limitation of electrochemical reactions ........................................ 301

Contents

xi

13.5 Conclusion ....................................................................................... 306 References................................................................................................ 306

Chapter 14 Consumer attitudes regarding the use of PEF in European Union: the example of Poland ..................................311 Maryna Mikhrovska, Anna Ka¨ferbo¨ck, Emilia Skarzynska and Dorota Witrowa-Rajchert

14.1 Introduction ..................................................................................... 311 14.2 Brief introduction of nonthermal technologies ............................ 312 14.3 Assessment of consumers’ behavior on the food market ........... 314 14.4 The understanding of the concept of nonthermal food processing technology and the knowledge of use....................... 315 14.5 Conclusion ....................................................................................... 320 References................................................................................................ 321 Further reading ........................................................................................ 323 Index ......................................................................................................... 327

List of Contributors Francisco J. Barba Nutrition and Food Science Area, Preventive Medicine and Public Health, Food Sciences, Toxicology and Forensic Medicine Department, Faculty of Pharmacy, Universitat de Vale`ncia, Vale`ncia, Spain; Preventive Medicine and Public Health Department, Faculty of Pharmacy, Universitat de Vale`ncia, Vale`ncia, Spain Jakub Czyzewski Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences, Warsaw, Poland Magdalena Dadan Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences, Warsaw, Poland Gabriela I. Denoya National Institute for Agricultural Technology (INTA), Food Technology Institute, Hurlingham, Buenos Aires, Argentina; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina Giovanna Ferrari Department of Industrial Engineering, University of Salerno, Fisciano, Italy; ProdAl Scarl University of Salerno, Fisciano, Italy Emilia Ferrer Preventive Medicine and Public Health Department, Faculty of Pharmacy, Universitat de Vale`ncia, Vale`ncia, Spain Mohsen Gavahian Product and Process Research Center, Food Industry Research and Development Institute, Hsinchu, Taiwan, ROC Volker Heinz The German Institute of Food Technologies (DIL e.V.), Quakenbru¨ck, Germany Kevin Hill Elea Vertriebs- und Vermarktungsgesellschaft mbH, Quakenbru¨ck, Germany Henry Ja¨ger Department of Food Science and Technology, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria ¨ ck Faculty of Engineering, Department Food technology and Nutrition, Anna Ka¨ferbo University of Applied Sciences Upper Austria, Wels, Austria Amin Mousavi Khaneghah Faculty of Food Engineering, Department of Food Science, University of Campinas (UNICAMP), Campinas, Brazil Jimmy Kinsella Elea Vertriebs- und Vermarktungsgesellschaft mbH, Quakenbru¨ck, Germany Alica Lammerskitten Elea GmbH, Quakenbru¨ck, Germany Nikolai Lebovka Institute of Biocolloidal Chemistry Named After F. D. Ovcharenko, NAS of Ukraine, Kyiv, Ukraine Yunfei Li Department of Food Science and Technology, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, P.R. China

xiv

List of Contributors

Marianne N. Lund Department of Food Science, University of Copenhagen, Frederiksberg C, Denmark; Department of Biomedical Sciences, University of Copenhagen, Copenhagen N, Denmark Ronit Mandal Food Process Engineering Laboratory, Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada Krystian Marszałek Department of Fruit and Vegetable Product Technology, Prof. Wacław Da˛browski Institute of Agricultural and Food Biotechnology, Warsaw, Poland; Department of Chemistry and Food Toxicology, Institute of Food Technology and Nutrition, College of Natural Sciences, University of Rzeszo´w, Rzeszo´w, Poland Samir Mezdour UMR Food Process Engineering, AgroParisTech, INRA, University of ParisSaclay, Massy, France Houcine Mhemdi Sorbonne University, University of Technology of Compiegne, Laboratory of Integrated Transformation of Renewable Matter (UTC/ESCOM, EA 4297 TIMR), Research Center of Royallieu, Compiegne Cedex, France Maryna Mikhrovska Law Faculty, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine Amin Mousavi-Khaneghah Department of Food Science, Faculty of Food Engineering, State University of Campinas (UNICAMP), Campinas, Brazil Viacheslav Mykhailyk Institute of Engineering Thermal Physics, National Academy of Sciences of Ukraine, Kiev, Ukraine Malgorzata Nowacka Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences, Warsaw, Poland Robin Ostermeier Elea Vertriebs- und Vermarktungsgesellschaft mbH, Quakenbru¨ck, Germany; Department of Food Science and Technology, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria Noelia Pallare´s Preventive Medicine and Public Health Department, Faculty of Pharmacy, Universitat de Vale`ncia, Vale`ncia, Spain Oleksii Parniakov Elea Vertriebs- und Vermarktungsgesellschaft GmbH, Quakenbru¨ck, Germany Gianpiero Pataro Department of Industrial Engineering, University of Salerno, Fisciano, Italy Mahesha M. Poojary Department of Food Science, University of Copenhagen, Frederiksberg C, Denmark Shahin Roohinejad Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN, United States

List of Contributors

xv

´ -Soto Nutrition and Food Science Area, Preventive Medicine and Public Elena Rosello Health, Food Sciences, Toxicology and Forensic Medicine Department, Faculty of Pharmacy, Universitat de Vale`ncia, Vale`ncia, Spain Chaitanya Sarangapani School of Food Science and Environmental Health, Technological University Dublin, Dublin 1, Ireland Anubhav Pratap Singh Food Process Engineering Laboratory, Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada Emilia Skarzynska Department of Food Engineering and Process Management, Faculty of Food Sciences, Warsaw University of Life Sciences, Warsaw, Poland ¨ ck, Sergiy Smetana The German Institute of Food Technologies (DIL e.V.), Quakenbru Germany Rohit Thirumdas Department of Food Process Technology, College of Food Science & Technology, PJTSAU, Hyderabad, India Stefan Toepfl Elea Vertriebs- und Vermarktungsgesellschaft mbH, Quakenbru¨ck, Germany Josefa Tolosa Preventive Medicine and Public Health Department, Faculty of Pharmacy, Universitat de Vale`ncia, Vale`ncia, Spain Stefan To¨pfl Elea Vertriebs- und Vermarktungsgesellschaft mbH, Quakenbru¨ck, Germany Urszula Tylewicz Department of Agricultural and Food Sciences, Alma Mater Studiorum, University of Bologna, Campus of Food Science, Cesena, Italy Fang Wang School of Food Science and Engineering, Wuhan Polytechnic University, Wuhan, P.R. China Artur Wiktor Department of Food Engineering and Process Management, Faculty of Food Sciences, Warsaw University of Life Sciences, Warsaw, Poland; Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences (WULS-SGGW), Warszawa, Poland Dorota Witrowa-Rajchert Food Process Engineering Laboratory, Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada; Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences, Warszawa, Poland; Department of Food Engineering and Process Management, Faculty of Food Sciences, Warsaw University of Life Sciences, Warsaw, Poland Qiang Xia Department of Food Science and Technology, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, P.R. China Zhenzhou Zhu School of Food Science and Engineering, Wuhan Polytechnic University, Wuhan, P.R. China

How does pulsed electric field work?

1

Urszula Tylewicz Department of Agricultural and Food Sciences, Alma Mater Studiorum, University of Bologna, Campus of Food Science, Cesena, Italy

1.1

Introduction

The electroporation phenomenon of cell membranes has been known for several decades and the intensive research on pulsed electric field (PEF) technology has been performed as a promising nonthermal technology for both microbial inactivation and mass transfer enhancement (Barba et al., 2015; Donsı`, Ferrari, & Pataro, 2010; Tylewicz et al., 2017). Moreover, recently PEF has received increasing attention, because of the possibility for the manipulation of biological cells and tissues (Faurie, Golzio, Phez, Teissie´, & Rols, 2005; Go´mez Galindo, 2017; Poojary et al., 2017). The electroporation occurs when the biological cells are exposed to the external electric field in the form of short and intense electric pulses, with the intensity higher than threshold value for the electroporation. Electroporation of the cell membranes could promote transient or permanent pore formation, depending on different PEF parameters applied (electric field strength, pulse duration, pulse number, total time of treatment, etc.) and on the characteristics of the raw materials such as cell size and shape. With low electric field strength a reversible electroporation could be achieved, which means that the created pores reseal after removing the electrical field. This kind of electroporation could be used to incorporate a different functional substance or drugs into the biological tissue, assuring the survival of the electrically stimulated cells. When high electric field strength is used, the irreversible tissue permeabilization (permanent membrane damage) and consequently the cell death occur (Donsı` et al., 2010; Weaver & Chizmadzhev, 1996). There are several theories explaining the mechanism of the reversible electroporation and/or the electrical membrane Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00001-X © 2020 Elsevier Inc. All rights reserved.

3

4

Chapter 1 How does pulsed electric field work?

breakdown; however, the exact mechanism of electroporation is not yet fully understood. In the first part of the chapter a basic mechanism of electroporation is explained along with the introduction of membrane permeability, transmembrane potential, and the relation between these parameters. In the second part, key parameters that can have an influence on the efficiency of the PEF treatment are described.

1.2

Cell membrane permeabilization

The real mechanism of action of PEF is still not well understood. According to the empirical descriptions of Gossling (1960) and Doevenspeck (1961), there is a disruptive effect of electric fields on biological cells. Subsequently, the theory of dielectric breakdown of cell membranes has been raised by Zimmermann, Pilwat, and Riemann (1974) and Neumann and Rosenheck (1972). Biological cells, when exposed to external electric fields, revealed specific changes related to membrane permeability. These changes could be associated with the formation of transient pores in the membrane and consequently compromising its semipermeability (Balasa, 2017). According to Teissie, Golzio, and Rols (2005), the permeabilization of a cell membrane is achieved by five different steps: induction (trigger) (μm), expansion (ms), stabilization (ms), resealing (s), and memory (h). First of all, the formation of pores occurs when the externally applied electric field is above the electroporation threshold value, which is related to the transmembrane voltage. When transmembrane voltage, the sum of induced potential difference across the cell membrane and resting membrane potential, exceeds certain critical value, the electroporation takes place (Kranjc & Miklavcˇ icˇ , 2017). During the application of PEF on the cell, an induced transmembrane voltage (ΔVi) is created, which is locally associated with the dielectric properties of the plasma membrane. Using a physical model based on a thin, weakly conductive shell (the membrane with the conductivity λm), filled with an internal conductive medium (the cytoplasm with the conductivity λi), and immersed in an external conductive medium (conductivity λe), the induced transmembrane voltage could be explained by the following Laplace differential equation:

Chapter 1 How does pulsed electric field work?



 t ΔViðM; E; t Þ 5 2 fg ðλÞrcell Ee cosθðM Þ 1 2 exp 2 τm

ð1:1Þ

where M is the point on the cell that is considered, t is the time after application of electric field, f is a factor depending on the cell geometry, rcell is the radius of the cell, Ee is the external electric field strength, and θ(M) is the angle between the direction of the field and the normal of the cell surface in M. g(λ) is related to the different conductivities as (Zimmermann et al., 1974) "

# d 3 d = g ðλÞ 5 2λe 2λm 1 λi 1 ðλm 2 λiÞ rcell 2 2 3λm rcell 2 rcell rcell " #
 d 3 ðλi 2 λmÞðλm 2 λeÞ ð2λe 1 λmÞð2λm 1 λiÞ 1 2 rcell 2 rcell ð1:2Þ

where d is the thickness of the membrane (nm). The characteristic time constant of the membrane charging (τm) can be calculated by (Kinosita & Tsong, 1977) τm 5

rCmð2λe 1 λiÞ ð2λeλiÞ

ð1:3Þ

where Cm (0.51.0 μF/cm2) is the specific membrane capacitance. For mammalian cells, τm is calculated in the submicrosecond time range and it strongly depends on the buffer composition as the internal composition is fixed by the cell metabolism. The electroporation occurs as long as the field is maintained at an overcritical value (expansion step). Several authors observed that even though the leaky state of cell membrane was induced during the onset of the pulse, the structural reorganization of the membrane was observed on a much longer time scale (Hibino, Itoh, & Kinosita, 1993; Hibino, Shigemori, Itoh, Nagayama, & Kinosita, 1991; Teissie et al., 2005). The stabilization step is an important issue of cell membrane electroporation; in fact, the pores need to be stable enough to allow interaction of the intra- and extracellular media (Toepfl, 2006). Gabriel and Teissie (1999) reported that as soon as a field strength was subcritical, a strong decrease in the flow of the polar molecules was observed, even though the cell membrane remained permeable to polar compounds. The stabilization step is followed by slow resealing of the cell membrane (for seconds to minutes) and recovery of its semipermeability. It has been shown that the decrease in the number of permeabilized

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cells with postpulse incubation time was a first-order process and depended strongly on temperature (Rols & Teissie, 1990). Moreover, during the resealing process the production of reactive oxygen species in the permeabilized part of the cell surface was observed (Teissie et al., 2005). Finally, the memory effect was observed, which means that some changes in the membrane properties remained present on a time scale of hours, but finally the cell behavior was back to normal. The resealing of the membrane is able to preserve the biological cell from lysis in most pulsing conditions. However, different cellular alterations may be induced making impossible the cell resealing, leading to cell death on the long term (Teissie et al., 2005). In general, the detection of the cellular tissue electroporation represents a difficult issue, mainly because the time range of pore formation is really short (submicrosecond) and also the pore area is extremely low, covering just 0.1% of the total membrane surface (Toepfl, 2006). In biological cells the cell membrane plays an important role in the transport of different components. The biological membrane is a complex assembly between proteins and a mixture of lipids, which are nonhomogenously distributed as it happened in fluid matrix but are accumulated locally. Moreover, the balance between active pumping and spontaneous leaks creates the ionic gradient across the membrane (Teissie, 2014). The cell membrane can act as a capacitor filled with dielectric material of low electrical conductance and a dielectric constant of about 2 (Zimmermann et al., 1974). The opposite polarity charges accumulate on both sides of the membrane, which induce perpendicular transmembrane potential of about 10 mV. When the external electrical field is applied to the biological material, an additional potential is created by movement of charges along the electric field lines (Toepfl, 2006). In Fig. 1.1 a scheme of impact of the cell membrane exposure to the external electric field is illustrated. As described in Fig. 1.1, the exposure of cells to external electric field (Ee) can lead to three different outcomes of electroporation process defined by three different threshold values. • Ee , Ec: The electric field applied is below the critical value (Ec) and no electroporation process occurs. • Ee . Ec: The electric field strength exceeds Ec values and temporary membrane permeabilization takes place. However, the electric field is still below irreversible electroporation threshold and cells can recover their integrity and remain viable after the end of electric field exposure.

Chapter 1 How does pulsed electric field work?

7

Figure 1.1 Scheme of mechanism of the cell membrane permeabilization induced by an external electrical field (Ee). Ec, Critical electric field strength. Source: Adapted from Donsı`, F., Ferrari, G., & Pataro, G. (2010). Applications of pulsed electric field treatments for the enhancement of mass transfer from vegetable tissue. Food Engineering Reviews, 2(2), 109130. https://doi.org/10.1007/s12393-010-9015-3.

Ee cEc : The electric field strength exceeds greatly Ec values and permanent membrane permeabilization takes place. This phenomenon leads to extensive leakage of intracellular content and cell death. In some cases, when the external electric field exceeds the threshold values of Ethermal, the electric field establishes high electric currents causing temperature increase and thermal damage to the cell (Kranjc & Miklavcˇ icˇ , 2017). Low-intensity PEF treatment with relatively low values of Ee (  20100 V/cm) can cause electroporation to some extent. In this case the process of resealing can be very quick in order to repair the membranes immediately after the turn of the electric field strength. This kind of electroporation is called reversible electroporation (Barba et al., 2015). The application of moderate PEF treatment can cause a loss of the permeability in some of the cells, while other are able to •

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Chapter 1 How does pulsed electric field work?

be resealed, and the insulating properties of the cell membrane can be recovered within several seconds after PEF treatment. In reversible electroporation, transient pores of small size are formed that reseal when the electric field is not supplied any more. Reversible permeabilization of cell membrane has been widely studied and used in biotechnology for the transfer of genetic materials (DNA) inside bacterial cells as well to improve fusion of cells (Chang, Chassy, Saunders, & Sowers, 1992). Electroporation is also used in biomedicine to allow the permeation of cytotoxin through the membranes of cancerous cells and to increase the concentration of the anticancer agent in solid tumors. Electrochemotherapy is now widely used, starting from the first clinical trials on head and neck tumors by Belehhradek et al. (1993). The reversible electroporation can also be applied in food processing. Pereira, Galindo, Vicente, and Dejmek (2009) studied the reversibility of the electroporation of potato cells, and they observed transient changes in the viscoelastic properties after PEF application with single 10251023 s rectangular pulses at electric field of 30500 V/cm. Tylewicz et al. (2017) observed the reversibility of the electroporation of strawberry tissue by preservation of the integrity of cellular structure by timedomain nuclear magnetic resonance and by maintenance of cell viability by fluorescence staining observed by fluorescence microscope. This reversibility was observed when 100 V/cm was applied and was compromised when higher electric field strength of 200 V/cm was used. On the other hand, high-intensity PEF treatment causes an irreversible damage of the cell membrane. Long-term changes in tissue electrical conductivity after PEF treatment application can also be related to osmotic flow and moisture redistribution inside the sample (Lebovka, Bazhal, & Vorobiev, 2001). This kind of electroporation has been widely investigated in food science, especially in extraction process (Barba et al., 2015; Parniakov, Barba, Grimi, Lebovka, et al., 2015; Parniakov, Barba, Grimi, Marchal, et al., 2015; Vorobiev & Lebovka, 2010) and ´ lvarez, microbial inactivation (Arroyo & Lyng, 2017; Saldan˜a, A Condo´n, & Raso, 2014).

1.3

Critical value/dielectric breakdown

In order to create a local dielectric rupture of the membrane and consequently inducing the formation of a pore, acting as a conductive channel, the overall potential should exceed a

Chapter 1 How does pulsed electric field work?

critical value of about 1 V. Also, the membrane properties should be considered as the compressibility, the permittivity, and the initial thickness (Schoenbach, Peterkin, Alden, & Beebe, 1997). This increase in permeability reestablishes the equilibrium of the electrochemical and electric potential differences of the cell plasma and the extracellular medium (Glaser, Leikin, Chernomordik, Pastushenko, & Sokirko, 1998). This equilibrium is known as a Donnan equilibrium, indicating dielectric breakdown (Zimmermann, Pilwat, Beckers, & Riemann, 1976).

1.3.1

Models applied for dielectric breakdown

An electromechanical model was developed, suggesting that the membrane, considered as a capacitor containing a perfectly elastic dielectric, subjected to an external electrical field is subjected to the mechanical compression. The mechanical instability occurs when there is an increase of the transmembrane potential, which causes an increase of the compression forces. In a model system of phosphatidylcholine bimolecular lipid layers, a good agreement between predicted breakdown voltage and assumed elastic parameters was observed by Crowley (1973). The electromechanical model is still one of the most accepted theories to explain the effect of external electrical fields on biological cells. The electric breakdown could be considered reversible if the pores induced are small in comparison to the membrane area, which is also related to the application of low electric field strength. Increasing the treatment intensity promotes formation of large pores and the reversible damage will turn into irreversible breakdown (Toepfl, 2006). Experimental studies have been performed in order to support this electromechanical compression model. A critical electric field strength, depending on the size and geometry of a cell, was found to be in the range of 12 kV/cm for plant cells and 1014 kV/cm for microbial cells (e.g., Escherichia coli). The gap of the electromechanical model is its too high simplification; in fact, the subsequent behavior such as resealing of pores, membrane conductance course, and transport phenomena are not considered. Therefore several other models have been proposed to predict the mechanisms at a molecular level, for example, the fluid mosaic model of a lipid bilayer with protein units embedded. These theories include the occurrence of membrane deteriorations and reorientations on the lipid bilayer and the protein channels as cause of increase in permeability (Toepfl, 2006).

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An extension of the electromechanical model was described by Dimitrov (1984). This model was used to describe the time course of field-induced breakdown of membranes, considering different parameters of cell membrane such as the viscoelastic properties, membrane surface tension, and molecular rearrangements, as well as pore expansion. Other models are based on molecular reorientation and localized defects within the cell membrane which are expanded and destabilized by exposure to an electric field. The presence of small pores of hydrophobic nature fluctuating in the lipid matrix was suggested to be the initial structural basis of electroporation (Chernomordik, 1992). The application of external electrical field could transform them into hydrophilic pores by reorientation. This could happen with increasing of pore radius above the value where the pore energies of both orientations coincide. If the pore radius is small, the formation of hydrophobic pores is more favorable, but at a range of 0.5 nm the pore energies of hydrophobic and hydrophilic pores become equal and pore inversion may occur (Glaser et al., 1998). These pores might also cause a loss of ability to regulate the intracellular pH (Simpson, Whittington, Earnshaw, & Russel, 1999) and short circuit of protein-pumps (Chernomordik, 1992). Both lipid domain and protein channels could be a site of the electroporation, since their functionality is influenced by the transmembrane potential. The gating potential for protein channels is in the range of 50 mV, which is smaller than the dielectric strength of a phospholipid bilayer. However, even though protein channels are opened by the application of electric field, it may not be sufficient to prevent the development of a transmembrane potential above the breakdown potential of the lipid bilayer (Toepfl, 2006).

1.4

Electroporation on different systems

The study on the electroporation has been conducted on different systems, such as (1) individual cells, (2) cell suspensions, and (3) tissue. The common important feature of each system is the fact that the cell membrane plays a great role in amplifying the applied electric field (Weaver & Chizmadzhev, 1996).

1.4.1

Spherical cells

In the case of spherical cell with a nonconducting membrane that is exposed to external electric field (Ee), the transmembrane

Chapter 1 How does pulsed electric field work?

potential distribution in the region surrounding the cell could be explained by the following Laplace equation with appropriate boundary conditions. ΔVi 5 1:5rcell Ee cosθ

ð1:4Þ

where ΔVi is the transmembrane voltage, rcell is the radius, and θ is the angle between the site on the cell membrane where ΔVi is measured and the direction of Ee. At the poles (θ 5 0,π) the potential drop of about 75% occurs across the membrane in the region near the cell, and the transmembrane electric field (Em) is higher than Ee. The amplification associated with this field concentration is Em/Ee 5 1.5rcell/ h 5 2 3 103 for rcell 5 10 μm, considering the membrane thickness (h) as 5 3 1027. Therefore as an example, when 10 μm radius cell is exposed to Ee, in order to achieve the transmembrane voltage of 0.5 V, the Ee of about 300 V/cm needs to be applied (Weaver & Chizmadzhev, 1996). According to Eq. (1.4), the critical transmembrane potential is attained with the external electric field decreasing with the cell radius. In order to promote the electroporation of cells in plant tissue, which are quite large (about 100 μm), the electric field required is of 0.55 kV/cm (Donsı` et al., 2010); however, even lower electric field strength (0.10.4 kV/cm) has been proved to provoke the electroporation of the plant tissue, in particular in apple (Dellarosa et al., 2016), strawberry (Tylewicz et al., 2017), and kiwifruits (Traffano-Schiffo, Laghi, Castro-Giraldez, Tylewicz, Ragni, et al., 2017; Traffano-Schiffo, Laghi, Castro-Giraldez, Tylewicz, Romani, et al., 2017; Traffano-Schiffo et al., 2016). For the small microbial or algal cells, with the dimensions of about 110 μm, a higher electric field is required (1080 kV/ cm) in order to promote the electroporation of their membrane (Barba et al., 2015).

1.4.2

Nonspherical geometrically regular cells

In more generalized models the sphere can be replaced by spheroid (e.g., an oblate spheroid as a model of an erythrocyte) or by ellipsoid (a geometrical body in which each of its three orthogonal projections is a different ellipse). A description of a cell is geometrically realistic if the thickness of its membrane is uniform, as it is in the case of spheres but not with spheroids or ellipsoids. In fact, the thickness of the membrane modeled in spheroidal or ellipsoidal coordinates is necessarily nonuniform, and by solving Laplace’s equation in these coordinates, the spatial distribution of the electric potential in a nonrealistic setting is obtained. However, in the case of

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cells surrounded by a physiological medium and with intact membranes that are nonporated the electric conductivity of the membrane can be neglected (i.e., the membrane is treated as an insulator). The ΔVi obtained in this way is still realistic, since the electric potential in each part of the cytoplasm is constant, and the geometry of the inner surface of the membrane does not affect the potential distribution outside the cell (Kotnik & Miklavcˇ icˇ , 2000).

1.4.3

Irregularly shaped cells

For an irregularly shaped cell the ΔVi cannot be solved as an elementary mathematical function but can be determined numerically by using modern computers and the finiteelements method implemented in software packages such as COMSOL Multiphysics (Pucihar, Kotnik, Valicˇ , & Miklavcˇ icˇ , 2006; Pucihar, Miklavcˇ icˇ , & Kotnik, 2009). With these methods it is possible to obtain ΔVi in quite accurate way, considering a sufficiently accurate determination of three-dimensional shape of the cell and using sufficiently fine spatial and temporal resolution (Kotnik, 2017).

1.4.4

Cells in dense suspensions and tissues

In real conditions the cells are rarely isolated. When they are sufficiently close to each other, there is a mutual distortion of the field caused by their proximity, which needs to be considered. Often, the cells are also in direct contact, forming twodimensional (monolayers attached to the bottom of a dish) or three-dimensional (tissues) structures, and they can even be electrically interconnected. In dilute cell suspensions the distance between the cells is much larger than the cells themselves, causing that the local field outside each cell is almost unaffected by the presence of other cells. Thus for cells representing less than about 1% of the suspension volume (e.g., for spherical cells with radius of about 10 μm, this corresponds to up to 2 million cells/mL), the deviation of the actual ΔVi from the one predicted is negligible. However, when there is an increase of the volume fraction occupied by the cells, the distortion of the local field around each cell by the presence of other cells in the neighborhood becomes more pronounced. In this case the ΔVi starts to differ noticeably from the predicted values, and an accurate estimation of the ΔVi must be assessed either numerically or by analytical approximations (Pavlin, Pavsˇelj, & Miklavcˇ icˇ , 2002;

Chapter 1 How does pulsed electric field work?

ˇ Susil, Semrov, & Miklavcˇ icˇ , 1998). The most appropriate model of dense cell suspensions is the one that resembles a facecentered cubic lattice, with uniform cell arrangement (Pavlin et al., 2002; Pucihar, Kotnik, Teissie, & Miklavcˇ icˇ , 2007). For larger volume fractions of the cells, the electrical properties of the suspension start to approach that of a tissue but only to a certain extent. The arrangement of cells in tissues does not necessarily resemble a face-centered lattice, and the uniform electroporation is difficult to obtain in tissues, because they generally consist of diversely shaped cells, various cell types (including vascularization), and cells connection through gap junctions, resulting in spatially varying and often anisotropic electrical properties. Therefore the exposure of the tissue to homogeneous external electric field does not mean that inside the tissue the field is distributed homogeneously; in fact, some cells are almost unavoidably electroporated more intensely than others (Dymek et al., 2015). In order to reduce field inhomogeneity, the electric field delivery to a tissue must be carefully designed by building a numerical model of the tissue, taking into account its particular structure; the number, size, shape, and positioning of the electrodes. These parameters need to iteratively optimize until sufficient field homogeneity is achieved inside the tissue or in a subtissue of interest. Once the tissue cells are electroporated, the electric conductivity and dielectric permittivity of the tissue change affecting the electric field distribution. In particular, when a train of pulses is delivered, these dynamic changes must also be considered for optimization of the results. In such applications the real-time measurements of tissue conductivity need to be performed to complement the numerical modeling, allowing subsequent pulses to be adapted to the detected increase of conductivity reflecting the extent of electroporation (Kotnik et al., 2015).

1.5

Main parameters affecting the cell membrane electroporation

The electroporation efficiency depends upon details of protocol used. The main parameters that can influence the electroporation are the intensity of treatment (electric field strength, pulse shape, pulse number, and the total treatment time) cell size, orientation in the electric field, extracellular media, and cytosol conductivity. These parameters and their combination are responsible for the temporary pores (reversible electroporation) or permanent pores (irreversible electroporation) creation.

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1.5.1

Electric field strength

The electric field strength of the pulses delivered on the cells is one of the critical parameters to trigger cell membrane permeabilization. In fact, as explained before, it directs the nature of the electroporation. At low PEF treatment the electroporated cells are able to recover quickly in order to repair their membranes immediately after PEF treatment. High-intensity PEF treatment instead causes the irreversible changes in cell membrane, leading to the damage and cell death (Barba et al., 2015). The cell membrane permeabilization is usually observed by the uptake of a fluorescent dye. The permeabilized cells (colored with dye) by the PEF application are detected only when the intensity of the electric field strength is higher than a critical threshold (Ec). It is important to highlight that in the untreated samples, a percentage of cells have a leaky membrane where the dye uptake spontaneously takes place; therefore this must be considered and corrected from the observed permeabilization (Teissie, 2017).

1.5.2

Pulse duration

The increase of pulse duration (pulse width) has been shown to be more efficient in cell membrane permeabilization. This increase when arrives to a plateau value close to 100% reflects that all cells are permeabilized when long pulses are delivered. Moreover, the critical parameter Ec decreases with an increase in the pulse duration (Teissie, 2017). Long duration pulses have been found to be more efficient for both microbial inactivation (Abram, Smelt, Bos, & Wouters, 2003; Martı´n-Belloso et al., 1997) and for the cell disintegration in the plant tissue (De Vito, Ferrari, Lebovka, Shynkaryk, & Vorobiev, 2008). Moreover, bipolar pulses instead of monopolar pulses can cause additional stress in the membrane structure, thus being more effective (Barba et al., 2015). Apart from pulse duration, also the total treatment time (Eq. 1.5), when the biological cells are exposed to the electric field (ttotal), plays an important role in the electroporation process: ttotal 5 tp UNp

ð1:5Þ

where tp is the duration of a single electric pulse and Np is the number of applied pulses.

Chapter 1 How does pulsed electric field work?

The different setting of the parameters for each specific PEF application is required for the electroporation process, among which the pulse amplitude, tp, and Np have the largest impact on the outcome of the treatment. Moreover, these parameters need to be chosen considering the targeted cell type, density of cells, and electrode geometry. However, the same effect of the treatment could be obtained by using equivalent pulse parameters, for example, instead of using a number of short, highvoltage pulses, it is possible to use longer pulses with lower voltage (Kranjc & Miklavcˇ icˇ , 2017). In fact, Knorr and Angersbach (1998) observed that keeping constant electrical energy per pulse, but changing electric field strength and pulse width, the cell disintegration index used for the quantification of cell permeabilization of potato tissue was at the same level. They suggested that the specific energy per pulse can be considered a suitable process parameter for the optimization of membrane permeabilization as well as for PEF-process development. The specific energy per pulse (W), expressed as kJ/(kg pulse) for exponential decay pulses, can be obtained from the following equation (Donsı` et al., 2010): W5

2 σEmax τp ρ

ð1:6Þ

where Emax is the peak electric field strength (kV/m), σ is the electrical conductivity (S/m), τ p is the pulse width (s), and ρ is the density of the product (kg/m3).

1.5.3

Pulses number and pulse frequency (delay between pulses)

Usually, not only a single pulse is delivered but also a train of pulses is applied to the biological cells. Therefore both the number of successive pulses and delay between each single pulse (frequency) need to be considered. Higher number of pulses showed to be more efficient on the electroporation phenomena in terms of microbial inactivation and cell disintegration index (Knorr & Angersbach, 1998; Tylewicz et al., 2016; Wiktor, Schulz, Voigt, Witrowa-Rajchert, & Knorr, 2015). In order to verify the effect of the repetitive pulses, the conductance measurements can be performed. Kinosita and Tsong (1979) observed that the membrane conductance was further increased by the repetitive pulses, but that a partial resealing occurs during the delay. In general, cumulative effects were observed by an enhanced transport when repeated pulses were

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Chapter 1 How does pulsed electric field work?

applied, showing more cells detected as permeabilized, until they arrive to a plateau level. Moreover, at a constant number of pulses/pulse duration, the electroporation was shown to be strongly affected by the delay (time) between pulses. Permeabilization of cell membrane was observed to be higher by application of low number of long pulses with a long delay rather than a repetition of short pulses (Teissie, 2017).

1.5.4

Pulse shape

The pulse shapes commonly used in PEF technology are either exponential decay or square (rectangular) wave pulses. The rectangular waveform (Fig. 1.2A) is defined as a periodic signal with period Tp, in which the amplitude alternates at steady frequency ( f ) between fixed minimum and maximum values. The duty cycle (D) of any rectangular wave is the ratio between high period T and total period Tp: D5

T U100% Tp

ð1:7Þ

The time taken for signal to rise from low to high level during PEF application is called rise time (trise), while the time taken to back from high to low level is called fall time (tfall). The duty cycle is measured at 50% intermediate levels also generally defined as full width at half maximum (Miklavcˇ icˇ & Kramar, 2014). The system to generate a square wave requires a switch with turn-off capability or a pulse-forming network. In general, this kind of switches is hardly available for high-power applications

ˇ c, ˇ D., & Kramar, P. (2014). Figure 1.2 Square-shaped (A) and exponential decay (B) pulse. Source: Adapted from Miklavci Basic electric concepts related to pulsed electric field. In J. Raso, & I. A´lvarez (Eds.), Proceedings of the school on application of pulsed electric fields for food processing (pp. 2529). Servicio de Publicaciones, Universidad de Zaragoza.

Chapter 1 How does pulsed electric field work?

systems; therefore a serial or parallel connection of switches or lumped or distributed pulse-forming networks with several sections of capacitors and inductive elements need to be used (Toepfl, 2006). The exponential decay pulses (Fig. 1.2B) occur when high voltage is applied by discharging of a high-voltage capacitor and the switching elements are simple. A comparison of energy performance of different pulse generation systems has been conducted by De Haan and Willcock (2002), concluding that an exponential decay system will not exceed an energy efficiency of 38%. They compared square wave pulses with a certain peak voltage Upeak and duration Tp to exponential ones by fitting blocks of Upeak and Tp under an exponential pulse, assuming that excess voltage of the exponential pulses results in excess losses.

1.5.5

Cell size

The cell size plays an important role in the induced potential during electroporation. The percentage of electropermeabilized cells in a population with heterogenous cell size increases with an increase of electric field strength. Large cells (e.g., plant cells) are much more sensible to low electric field strength in comparison to small cells (e.g., microbial cells). Moreover, large cells appear to be more fragile in a population (Teissie, 2014).

1.6

Conclusions

Electroporation of biological cells occurs when the externally applied electric field is above the electroporation threshold value. In reversible electroporation, transient pores of small dimensions are formed and reseal when the supply of electric field is terminated. The irreversible damage of cell membrane occurs when high-intensity PEF treatment is applied. The electroporation efficiency depends on different parameters such as electric field strength, pulse shape, pulse number, and the total treatment time and cell size. The detection of the cellular tissue electroporation represents a difficult issue; therefore many models have been developed in order to study the dielectric breakdown; however, in order to understand a real mechanism that governs the electroporation, further studies are necessary.

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References Abram, F., Smelt, J. P. P. M., Bos, R., & Wouters, P. C. (2003). Modelling and optimization of inactivation of Lactobacillus plantarum by pulsed electric field treatment. Journal of Applied Microbiology, 94, 571579. Arroyo, C., & Lyng, J. G. (2017). Pulsed electric fields in hurdle approaches for microbial inactivation. In Handbook of electroporation (Vol. 4, pp. 25912620). Balasa, A. (2017). Stress response of plants, metabolite production due to pulsed electric fields, Handbook of electroporation (4, pp. 25592571). Barba, F. J., Parniakov, O., Pereira, S. A., Wiktor, A., Grimi, N., Boussetta, N., . . . Vorobiev, E. (2015). Current applications and new opportunities for the use of pulsed electric fields in food science and industry. Food Research International, 77(Part 4), 773798. Belehhradek, M., Domenge, C., Luboinski, B., Orlowski, S., Belehradek, J., Jr., & Mir, L. M. (1993). Electrochemotherapy, a new antitumor treatment. Cancer, 72, 36943700. Chang, D. C., Chassy, B. M., Saunders, J. A., & Sowers, A. E. (1992). Guide to electroporation and electrofusion (pp. 429457). Harcourt Brace Jovanovich, Publishers, San Diego, CA: Academic Press Inc., 9167. Chernomordik, L. V. (1992). Electropores in lipid bilayers and cell membranes. In D. C. Chang, B. M. Chassy, J. A. Saunders, & A. E. Sowers (Eds.), Guide to electroporation and electrofusion. San Diego, CA: Academic Press. Crowley, J. M. (1973). Electrical breakdown of bimolecular lipid membranes as an electromechanical instability. Biophysical Journal, 13, 711724. De Haan, S. W. H., & Willcock, P. R. (2002). Comparison of the energy performance of pulse generation circuits for PEF. Innovative Food Science and Emerging Technologies, 3, 349356. Available from https://doi.org/10.1016/ S1466-8564(02)00069-3. Dellarosa, N., Ragni, L., Laghi, L., Tylewicz, U., Rocculi, P., & Dalla Rosa, M. (2016). Time domain nuclear magnetic resonance to monitor mass transfer mechanisms in apple tissue promoted by osmotic dehydration combined with pulsed electric fields. Innovative Food Science & Emerging Technologies, 37(Part C), 345351. Available from https://doi.org/10.1016/j. ifset.2016.01.009. De Vito, F., Ferrari, G., Lebovka, N. I., Shynkaryk, N. V., & Vorobiev, E. (2008). Pulse duration and efficiency of soft cellular tissue disintegration by pulsed electric fields. Food and Bioprocess Technology, 1, 307313. Available from https://doi.org/10.1007/s11947-007-0017-y. Dimitrov, D. S. (1984). Electric field-induced breakdown of lipid bilayers and cell membranes: A thin viscoelastic film model. The Journal of Membrane Biology, 78, 5360. Doevenspeck, H. (1961). Influencing cells and cell walls by electrostatic impulses. Fleischwirtschaft, 13(12), 968987. Donsı`, F., Ferrari, G., & Pataro, G. (2010). Applications of pulsed electric field treatments for the enhancement of mass transfer from vegetable tissue. Food Engineering Reviews, 2(2), 109130. Available from https://doi.org/10.1007/ s12393-010-9015-3. Dymek, K., Rems, L., Zorec, B., Dejmek, P., Go´mez Galindo, F., & Miklavˇciˇc, D. (2015). Modeling electroporation of the non-treated and vacuum impregnated heterogeneous tissue of spinach leaves. Innovative Food Science & Emerging Technologies, 29, 5564. Available from https://doi.org/10.1016/j. ifset.2014.08.006.

Chapter 1 How does pulsed electric field work?

Faurie, C., Golzio, M., Phez, E., Teissie´, J., & Rols, M. -P. (2005). Electric fieldinduced cell membrane permeabilization and gene transfer: Theory and experiments. Engineering in Life Sciences, 5(2). Available from https://doi.org/ 10.1002/elsc.200420068. Gabriel, B., & Teissie, J. (1999). Time courses of mammalian cell electropermeabilization observed by millisecond imaging of membrane property changes during the pulse. Biophysical Journal, 76, 21582165. Glaser, R. W., Leikin, S. L., Chernomordik, L. V., Pastushenko, V. F., & Sokirko, A. I. (1998). Reversible electrical breakdown of lipid bilayers: Formation and evolution of pores. Biochimica et Biophysica Acta, 940, 275287. Available from https://doi.org/10.1016/0005-2736(88)90202-7. Go´mez Galindo, F. (2017). Responses of plant cells and tissues to pulsed electric field treatment, Handbook of electroporation (4, pp. 26212635). Gossling, B.S. (1960). Artificial mutation of micro-organisms by electrical shock. United Kingdom, UK 845743. Hibino, M., Itoh, H., & Kinosita, K., Jr. (1993). Time courses of cell electroporation as revealed by submicrosecond imaging of transmembrane potential. Biophysical Journal, 64, 17891800. Available from https://doi.org/ 10.1016/S0006-3495(93)81550-9. Hibino, M., Shigemori, M., Itoh, H., Nagayama, K., & Kinosita, K., Jr. (1991). Membrane conductance of an electroporated cell analyzed by submicrosecond imaging of transmembrane potential. Biophysical Journal, 59, 209220. Kinosita, K., Jr., & Tsong, T. Y. (1977). Voltage-induced pore formation and hemolysis of human erythrocytes. Biochimica et Biophysica Acta, 471, 227242. Kinosita, K., Jr., & Tsong, T. Y. (1979). Voltage-induced conductance in human erythrocyte membranes. Biochimica et Biophysica Acta, 554, 479497. Knorr, D., & Angersbach, A. (1998). Impact of high-intensity electrical field pulses on plant membrane permeabilization. Trends in Food Science & Technology, 9, 185191. Kotnik, T. (2017). Transmembrane voltage induced by applied electric fields, Handbook of electroporation (2, pp. 11111127). Kotnik, T., & Miklavˇciˇc, D. (2000). Analytical description of transmembrane voltage induced by electric fields on spheroidal cells. Biophysical Journal, 79, 670679. Available from https://doi.org/10.1016/S0006-3495(00)76325-9. Kotnik, T., Frey, W., Sack, M., Haberl Megliˇc, S., Peterka, M., & Miklavˇciˇc, D. (2015). Electroporation-based applications in biotechnology. Trends in Biotechnology, 33(8). Available from https://doi.org/10.1016/j. tibtech.2015.06.002. Kranjc, M., & Miklavˇciˇc, D. (2017). Electric field distribution and electroporation threshold. In Handbook of electroporation (Vol. 2, pp. 10431058). Lebovka, N. I., Bazhal, M. I., & Vorobiev, E. (2001). Pulsed electric field breakage of cellular tissues: Visualization of percolative properties. Innovative Food Science & Emerging Technologies, 2, 113125. Available from https://doi.org/ 10.1016/S1466-8564(01)00024-8. Martı´n-Belloso, O., Vega-Mercado, H., Qin, B. L., Chang, F. J., Barbosa-Ca´novas, G. V., & Swanson, B. G. (1997). Inactivation of Escherichia coli suspended in liquid egg using pulsed electric fields. Journal of Food Processing and Preservation, 21, 193208. Available from https://doi.org/10.1111/j.17454549.1997.tb00776.x. Miklavˇciˇc, D., & Kramar, P. (2014). Basic electric concepts related to pulsed ´ lvarez (Eds.), Proceedings of the school on electric field. In J. Raso, & I. A

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application of pulsed electric fields for food processing (pp. 2529). Servicio de Publicaciones, Universidad de Zaragoza. Neumann, E., & Rosenheck, K. (1972). Permeability changes induced by electric impulses in vesicular membranes. The Journal of Membrane Biology, 10, 279290. Parniakov, O., Barba, F. J., Grimi, N., Lebovka, N., & Vorobiev, E. (2015). Extraction assisted by pulsed electric energy as a potential tool for green and sustainable recovery of nutritionally valuable compounds from mango peels. Food Chemistry, 192, 842848. Available from https://doi.org/10.1016/j. foodchem.2015.07.096. Parniakov, O., Barba, F. J., Grimi, N., Marchal, L., Jubeau, S., Lebovka, N., & Vorobiev, E. (2015). Pulsed electric field assisted extraction of nutritionally valuable compounds from microalgae Nannochloropsis spp. using the binary mixture of organic solvents and water. Innovative Food Science & Emerging Technologies, 27, 7985. Available from https://doi.org/10.1016/j. ifset.2014.11.002. Pavlin, M., Pavˇselj, N., & Miklavˇciˇc, D. (2002). Dependence of induced transmembrane potential on cell density, arrangement, and cell position inside a cell system. IEEE Transactions on Biomedical Engineering, 49, 605612. Available from https://doi.org/10.1109/TBME.2002.1001975. Pereira, R. N., Galindo, F. G., Vicente, A. A., & Dejmek, P. (2009). Effects of pulsed electric field on the viscoelastic properties of potato tissue. Food Biophysics, 4 (3), 229239. Available from https://doi.org/10.1007/s11483-009-9120-0. Poojary, M. M., Dellarosa, N., Roohinejad, S., Koubaa, M., Tylewicz, U., Go´mezGalindo, F., . . . Barba, F. J. (2017). Influence of innovative processing on γ-aminobutyric acid (GABA) contents in plant food materials. Comprehensive Reviews in Food Science and Food Safety, 16(5), 895905. Available from https://doi.org/10.1111/1541-4337.12285. Pucihar, G., Kotnik, T., Teissie, J., & Miklavˇciˇc, D. (2007). Electroporation of dense cell suspensions. European Biophysics Journal, 36, 173185. Available from https://doi.org/10.1016/j.bbagen.2006.06.014. Pucihar, G., Kotnik, T., Valiˇc, B., & Miklavˇciˇc, D. (2006). Numerical determination of the transmembrane voltage induced on irregularly shaped cells. Annals of Biomedical Engineering, 34, 642652. Available from https://doi.org/10.1007/ s10439-005-9076-2. Pucihar, G., Miklavˇciˇc, D., & Kotnik, T. (2009). A time-dependent numerical model of transmembrane voltage inducement and electroporation of irregularly shaped cells. IEEE Transactions on Biomedical Engineering, 56, 14911501. Available from https://doi.org/10.1109/TBME.2009.2014244. Rols, M. P., & Teissie, J. (1990). Electropermeabilization of mammalian cells. Quantitative analysis of the phenomenon. Biophysical Journal, 58, 10891098. Available from https://doi.org/10.1016/S0006-3495(90)82451-6. ´ lvarez, I., Condo´n, S., & Raso, J. (2014). Microbiological aspects ˜ a, G., A Saldan related to the feasibility of PEF technology for food pasteurization. Critical Reviews in Food Science and Nutrition, 54(11), 14151426. Available from https://doi.org/10.1080/10408398.2011.638995. Schoenbach, K. H., Peterkin, F. E., Alden, R. W. I., & Beebe, S. J. (1997). The effect of pulsed electric on biological cells: Experiments and applications. IEEE Transactions on Plasma Science, 25(2), 284292. Simpson, R. K., Whittington, R., Earnshaw, R. G., & Russel, N. J. (1999). Pulsed high electric field causes ‘all or nothing’ membrane damage in Listeria monocytogenes and Salmonella typhimurium, but membrane H 1 -ATPase is not a primary target. International Journal of Food Microbiology, 48, 110.

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ˇ Susil, R., Semrov, D., & Miklavˇciˇc, D. (1998). Electric field induced transmembrane potential depends on cell density and organization. Electroand Magnetobiology, 17, 391399. ´ lvarez Teissie, J. (2014). Cell membrane electropermeabilization. In J. Raso, & I. A (Eds.), Proceedings of the school on application of pulsed electric fields for food processing (pp. 2529). Servicio de Publicaciones, Universidad de Zaragoza. Teissie, J. (2017). Mechanistic description of membrane electropermeabilization, Handbook of electroporation (1, pp. 451472). Teissie, J., Golzio, M., & Rols, M. P. (2005). Mechanisms of cell membrane electropermeabilization: A minireview of our present (lack of?) knowledge. Biochimica et Biophysica Acta, 1724(3), 270280. Available from https://doi. org/10.1016/j.bbagen.2005.05.006. Toepfl, S. (2006). Pulsed electric fields (PEF) for permeabilization of cell membranes in food- and bioprocessing  applications, process and equipment design and cost analysis (Ph.D. dissertation). Berlin. Traffano-Schiffo, M. V., Laghi, L., Castro-Giraldez, M., Tylewicz, U., Rocculi, P., Ragni, L., . . . Fito, P. J. (2017). Osmotic dehydration of organic kiwifruit pretreated by pulsed electric fields and monitored by NMR. Food Chemistry, 236, 8793. Available from https://doi.org/10.1016/j.foodchem.2017.02.046. Traffano-Schiffo, M. V., Laghi, L., Castro-Giraldez, M., Tylewicz, U., Romani, S., Ragni, L., . . . Fito, P. J. (2017). Osmotic dehydration of organic kiwifruit pretreated by pulsed electric fields: Internal transport and transformations analyzed by NMR. Innovative Food Science & Emerging Technologies, 41, 259266. Available from https://doi.org/10.1016/j.ifset.2017.03.012. Traffano-Schiffo, M. V., Tylewicz, U., Castro-Giraldez, M., Fito, P. J., Ragni, L., & Dalla Rosa, M. (2016). Effect of pulsed electric fields pre-treatment on mass transport during the osmotic dehydration of organic kiwifruit. Innovative Food Science & Emerging Technologies, 38, 243251. Available from https:// doi.org/10.1016/j.ifset.2016.10.011. Tylewicz, U., Aganovic, K., Vannini, M., Toepfl, S., Bortolotti, V., Dalla Rosa, M., . . . Heinz, V. (2016). Effect of pulsed electric field treatment on water distribution of freeze-dried apple tissue evaluated with DSC and TD-NMR techniques. Innovative Food Science and Emerging Technologies, 37, 352358. Available from https://doi.org/10.1016/j.ifset.2016.06.012. Tylewicz, U., Tappi, S., Mannozzi, C., Romani, S., Dellarosa, N., Laghi, L., . . . Dalla Rosa, M. (2017). Effect of pulsed electric field (PEF) pre-treatment coupled with osmotic dehydration on physico-chemical characteristics of organic strawberries. Journal of Food Engineering, 213, 29. Available from https://doi.org/10.1016/j.jfoodeng.2017.04.028. Vorobiev, E., & Lebovka, N. I. (2010). Enhanced extraction from solid foods and biosuspensions by pulsed electrical energy. Food Engineering Reviews, 2(2), 95108. Weaver, J. C., & Chizmadzhev, Y. A. (1996). Theory of electroporation: A review. Bioelectrochemistry and Bioenergetics, 41, 135160. Wiktor, A., Schulz, M., Voigt, E., Witrowa-Rajchert, D., & Knorr, D. (2015). The effect of pulsed electric fields treatment on immersion freezing, thawing and selected properties of apple tissue. Journal of Food Engineering, 146, 816. Available from https://doi.org/10.1016/j.jfoodeng.2014.08.013. Zimmermann, U., Pilwat, G., Beckers, F., & Riemann, F. (1976). Effects of external electrical fields on cell membranes. Bioelectrochemistry and Bioenergetics, 3, 5883. Zimmermann, U., Pilwat, G., & Riemann, F. (1974). Dielectric breakdown in cell membranes. Biophysical Journal, 14, 881899.

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An overview of the potential applications to produce healthy food products based on pulsed electric field treatment

2

Alica Lammerskitten1, Artur Wiktor2, Oleksii Parniakov1 and Nikolai Lebovka3 1

Elea GmbH, Quakenbru¨ck, Germany 2Department of Food Engineering and Process Management, Faculty of Food Sciences, Warsaw University of Life Sciences, Warsaw, Poland 3Institute of Biocolloidal Chemistry Named After F. D. Ovcharenko, NAS of Ukraine, Kyiv, Ukraine

2.1

Introduction

In recent years, food availability in developed countries increased. For instance, from 2000 to 2018, global agricultural gross production value increased more than two times. What is interesting at the same time is that food consumer price index increased by 30% in average (Fig. 2.1) while average gross domestic product per capita almost doubled (Anonymous, 2019c). Increase of income followed by relatively smaller increase of food prices, together with the change of life style, has resulted in considerable changes in food consumption patterns (Kearney, 2010). It should be noted that world has made significant progress in raising food consumption per person with a rise of almost 400 kcal per person per day—going from 2411 to 2789 kcal per person per day between 1970 and 2001 (Alexandratos, 2006). Moreover, food consumption by changes in dietary behavior was strongly affected by urbanization. Thus the major consequences from a nutrition perspective of urbanization are a profound shift toward high-energy food, containing more fats and oils and more animal origin protein from meat and dairy foods. This results in a diet that is lower in fiber, vitamins, and minerals. A higher energy intake, combined with a lower energy expenditure in urban jobs (with reduced physical

Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00002-1 © 2020 Elsevier Inc. All rights reserved.

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Chapter 2 An overview of the potential applications to produce healthy food products

Agricultural gross production value (million USD)

24

4,500,000

Average food CPI with 2010 as a basis

3,000,000

190 180 170

1,500,000

0 2000

2016 Year

160 150 140 130

2000

120

2016

110 100 January

February

March

April

May

June

July

August September October November December

Figure 2.1 Average food CPI and agricultural gross production value in 2000 and 2018. CPI, Consumer price index. Source: Self-elaboration on the basis of FAO STAT.

activity by 10% 15%) might result in rapid advancement of obesity and diabetes. Actually, there are now more obese people than underweight or malnourished in the world (Caballero, 2007). Nevertheless, in the Western countries consumer health awareness continues to grow with the increasing availability of health-related information going hand in hand with the aging of populations and increased risk for lifestyle diseases. Interest in functional foods and drinks has been fueled by a desire for convenience, as well as health. Besides, busier lifestyles are making it harder to meet nutritional requirements using traditional food and drinks. Thereby, the market of healthy and tailored products is expanding, for example, in the sectors of child snack and cereal (Hegde, 2019). The quality and health beneficial effects of food consumed are an important key to tackle these challenges either by developing and offering new and healthier raw material or through development of healthy food ingredients to be included in meals on a daily basis. Therefore consumer’s growing interest to obtain products of greater nutritional quality with healthy properties has led the food industry and academics to develop new strategies in product development and food processing. However, there are some undesirable changes that could occur during its manufacturing. For example, in dried

Chapter 2 An overview of the potential applications to produce healthy food products

food production, mostly, the products look wrinkled with a dark color and loss of some bioactive compounds. Pulsed electric field (PEF) technology is the innovative valuable tool that can improve technological processes (e.g., drying and freezing), food design, and functionality; reduce food toxics/contaminants; improve extractability; and recover nutritionally valuable compounds in a diverse variety of foods (Barba et al., 2015). Over the last years, PEF has been intensively implemented to the food production lines. Several studies have been conducted to evaluate its impact on the processes of microbial inactivation, drying, cutting, etc. Applications of PEF systems are based on an electroporation of membranes without significant alteration of structure of cellular materials (Miklavcic, 2017). Processing with these systems significantly increases the yield, freshness, flavor, and nutritional values at moderate energy consumption. Thereby, in this chapter short description of the potential applications of PEF in food science and technology is overviewed. The development of healthy products, reduction of toxicity, and retention of key compounds in food products are discussed. Moreover, this chapter describes the most relevant aspects that rule the application of PEF technology to different foods. Finally, the benefits and challenges of this novel technology are introduced and discussed.

2.2

Retention of valuable compounds

It is now well accepted that a low consumption of fatty foods, a regular physical activity, and a high consumption of plant-derived foods help to maintain a good health status (Chan, See, Yusoff, Ngoh, & Kow, 2017). For instance, epidemiological studies have shown that the increased consumption of tomato and tomato-based products may reduce the risk of cardiovascular diseases, certain types of cancer, and atherosclerosis (Hedges & Lister, 2005). The reduction of these chronic diseases has been attributed to the presence of high amounts of some valuable bioactive compounds, such as carotenoids, especially to lycopene, which is the most abundant carotenoid in red-ripe tomatoes (Dannehl, Huyskens-keil, Eichholz, & Schmidt, 2011). The accumulation of carotenoids in tomato normally occurs during ripening. However, carotenoid production has been recently reported to be promoted by enzymatically mediated softening phenomena triggered by reactive oxygen species generated upon exposure to oxidative stress (Fanciullino, Bidel, & Urban, 2014).

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Chapter 2 An overview of the potential applications to produce healthy food products

PEF treatment has been proposed to be used as a preprocessing technique to produce tomato-based products with enhanced carotenoid contents (Gonza´lez-Casado, Martı´n-Belloso, ElezMartı´nez, & Soliva-Fortuny, 2018). After applying 30 pulses at 200 kV/m (2.31 kJ/kg), it was observed that the total carotenoid and lycopene concentrations in tomato tissue were enhanced by 50% and 53%, respectively. Concurrently, a significant improvement in lipophilic antioxidant capacity was stated. At such treatment conditions a deceleration in the respiration rate, RO2 and RCO2 , a drop in the ethylene production, and the induction of acetaldehyde synthesis were observed, as an evidence of the stress injury caused to tomato tissues. In addition, several quality attributes of tomato were significantly affected. Tomatoes subjected to 200 kV/m exhibited the greatest values of total soluble solids and pH, as well as a marked reddening and softening of the fruit. Potato starch and other starch cultivars with high amylose contents can induce higher resistant starch (RS) content in native starch granules during enzymatic reaction. RS is a benefit for people with metabolic disorders and has potential to be transformed into the slowly digestible starch (SDS) fractions (Ozturk, Koksel, Kahraman, & Ng, 2009; Pongjanta, Utaipattanaceep, Naivikul, & Piyachomkwan, 2009). The important feature of SDS is that it is digested slowly throughout the entire small intestine, which leads to a slow and prolonged release of glucose with a low glycemic index (Carlos-Amaya, Osorio-Diaz, Agama-Acevedo, Yee-Madeira, & Bello-Pe´rez, 2011). Foods containing high amounts of SDS tend to sustain plasma glucose levels, this may help to control and prevent diabetes and may also be beneficial to satiety, physical performance, improved glucose tolerance, and reduced blood lipid levels in both healthy individuals and those with hyperlipidemia (Jenkins et al., 2002). Therefore SDS is considered to be beneficial for the dietary management of metabolic disorders of common chronic diseases such as obesity, diabetes, and cardiovascular diseases. The effects of PEF treatment on the nanostructure of esterified potato starch and their potential glycemic digestibility has been investigated (Hong, Zeng, Han, & Brennan, 2018). PEF application induced deformations, protrusions, and pits on starch granules surface. The in vitro digestion suggested that the quantity of SDS fractions increased from 6.63% in the control sample to 17.53% for PEF treatment at 3.75 kV/cm. The effects of PEF treatment on polyphenols have been also studied. The higher concentrations of phenolic acids

Chapter 2 An overview of the potential applications to produce healthy food products

(chlorogenic acid) and flavonols (quercetin) were observed in PEFtreated tomato juice as compared to the conventional thermally treated (Odriozola-Serrano, Soliva-Fortuny, Herna´ndez-Jover, & Martı´n-Belloso, 2009). Other phenolic compounds such as ferulic, p-coumaric, and caffeic acids in tomato juices were also investigated during whole storage duration. It was observed that concentration of caffeic acid was increased over time, regardless the kind of processing, while p-coumaric acid was decreased during storage in PEF-treated sample. The increase of caffeic acid in tomato juices was directly related to hydroxylase activity, which converts p-coumaric acid into caffeic acid during the storage of the juice. Similarly, after treatment of orange juice with heat pasteurization and medium PEF, highest values of the total phenolic contents detected were 439.07 and 443.42 mg GAE/dm3, respectively. Comparison of phenolic compounds of orange juice processed by PEF and conventional thermal pasteurization has been performed (Agcam, Akyildiz, & Evrendilek, 2014). A significant difference in the total phenolic compounds was detected for different treatments. Total phenolic content of the samples processed with high energy was higher than those processed with low energy. It was attributed to the fact that PEF treatment enhanced the extraction of intracellular contents. Note that application of PEF even at relatively low electric fields can increase cell membrane permeability, accelerate mass transfer, and significantly enhance phenolic compounds extraction (Barba et al., 2015). The PEF processing is very attractive for treatment of berries that make up one of the largest proportions of fruits consumed in our diet due to their attractive flavor and color, as well as their great benefits to human health (Li, Chen, Zhang, & Fu, 2017). Generally, the increase of total phenolic content by PEF in grape wine ranged from 11% to 99%, depending on electric field strength, treatment time, storage time, and grape variety (Yang et al., 2016). For example, the effect of PEF treatment to improve phenolic compound extraction was compared among three grape varieties, Graciano, Tempranillo, and Grenache during two vintages (Lo´pez-Giral et al., 2015). For these varieties, PEF application increased color intensity, total polyphenol index, and total anthocyanins. The PEF effects were depended on the variety. For Tempranillo variety the most significant differences in the content of individual anthocyanins were observed, while for Grenache variety the major differences in the content of gallic acid, catechin, and epicatechin were detected. Graciano variety showed almost no differences in the amount of individual phenolic compounds released after PEF application. The effect of the PEF treatments

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Chapter 2 An overview of the potential applications to produce healthy food products

was depended on the initial concentration of compounds in the grape. The PEF treatment also improved antioxidant capacity (Lo´pez-Giral et al., 2015). The anthocyanin release and health-promoting properties of Pinot Noir grape juices after PEF processing have been evaluated (Leong, Burritt, & Oey, 2016). Compared to untreated control, PEF-treated samples of juice had more total phenolics and vitamin C, and higher scavenging activity (measured by DPPH assay), as well as stronger protective capacity on human intestinal Caco-2 cells against oxidative stress. Structural and biochemical changes induced by PEF on cabernet sauvignon grape berries have been studied (Cholet et al., 2014; Delsart et al., 2014). The PEF treatment performed at 4 kV/cm had limited effect on the polyphenol structure and pectic fraction, whereas the treatment with 0.7 kV/cm profoundly modified the organization of skin cell walls and resulted in reduction of mean degree of polymerization of tannins and less astringent in wine. The combination of densification and PEF treatment for selective polyphenols’ recovery from fermented grape pomace has been tested (Brianceau, Turk, Vitrac, & Vorobiev, 2015). Optimal PEF treatment (E 5 1.2 kV/cm; W 5 18 kJ/kg; ρ 5 1.0 g/ cm3) increased not only the content of total polyphenols from fermented grape pomace but also the ratio of total anthocyanins to total flavan-3-ols. It demonstrated the selective nature of PEF treatment in anthocyanin extraction. The changes in polyphenol profiles and color composition of freshly fermented wine due to PEF, enzymatic, and thermovinification pretreatments were analyzed (El Darra et al., 2016). The effects of PEF applied prior, during alcoholic fermentation or cold maceration were tested. The best results were obtained for the PEF applied during the cold maceration step. PEF treatments also improved the extraction of polyphenols from whole grapes during pressing (Grimi, Lebovka, Vorobiev, & Vaxelaire, 2009), vinification ´ lvarez, & Raso, 2010) and (Pue´rtolas, Herna´ndez-Orte, Sladan˜a, A from grape by-products (Boussetta, Vorobiev, Le, CordinFalcimaigne, & Lanoiselle´, 2012). The obtained data evidenced on the significant dependence of extraction efficiency and selectivity on the PEF protocol, state of the product, and time of PEF application. The PEF treatment was applied also in combination with different for processing orange, potato, apple, carrot, and other products (Barba et al., 2015; Grimi, Mamouni, Lebovka, Vorobiev, & Vaxelaire, 2011; Jaeger, Schulz, Lu, & Knorr, 2012; ´ lvarez, & Raso, 2013; Pue´rtolas, Cregenza´n, Luengo, Luengo, A

Chapter 2 An overview of the potential applications to produce healthy food products

´ lvarez, & Raso, 2013). For example, in the case of orange peels, A the samples were pressurized for 30 min at 5 bar, and PEF treatment applied at 1, 3, 5, and 7 kV/cm enhanced the extraction yield of total polyphenol up to 20%, 129%, 153%, and 159%, respectively (Luengo et al., 2013). The effects of PEF strength (E 5 0 35 kV/cm) and pulse rise time (PRT) (2 and 0.2 μs) on enzymatic activity, vitamin C, total phenols, antioxidant capacities, color, and rheological characteristics of fresh apple juice were also investigated (Bi et al., 2013). With increasing of E and PRT the residual activity of polyphenoloxidase and peroxidase decreased, and almost complete inactivation of both enzymes was achieved at 35 kV/cm and PRT of 2 μs. The content of polyphenols was significantly affected by the value of PRT. Thermal (at 90 C for 30 s) and PEF (at 35 kV/cm with a bipolar pulse of 4 μs wide) pasteurization of apple juice have been studied (Aguilar-Rosas, Ballinas-Casarrubias, NevarezMoorillon, Martin-Belloso, & Ortega-Rivas, 2007). The effects of variables on pH, total acidity, phenolic content, and volatile compounds were investigated. The measured variables were less affected by the PEF treatment than by the thermal pasteurization and PEF-treated juice retained most of the volatile compounds responsible for flavor of the apple juice better. It was concluded that PEF could be considered a feasible alternative for producing stable apple juice (Aguilar-Rosas, BallinasCasarrubias, Elias-Ogaz, Martin-Belloso, & Ortega-Rivas, 2013). The effects of PEF treatment variables (E 5 35 kV/cm, frequency 50 250 Hz, pulse width 1 7 μs, and pulse polarity) on the lycopene, vitamin C, and antioxidant capacities of tomato juice have been studied (Odriozola-Serrano, Aguilo´-Aguayo, Soliva-Fortuny, Gimeno-An˜o´, & Martı´n-Belloso, 2007). The PEF significantly affected the extracted amounts and the maximal relative lycopene content (131.8%), vitamin C content (90.2%), and antioxidant capacity retention (89.4%) when treatment was carried out using 1 μs pulse duration applied at 250 Hz in bipolar mode. The effects of PEF (35 kV/cm for 1500 μs of overall treatment time with bipolar pulses of 4 μs at 100 Hz) and heat pasteurization (90 C for 30 or 60 s) on carotenoids and phenolic compounds as well as on some quality attributes (pH, soluble solids, and color parameters) of tomato juice were compared (Odriozola-Serrano, Soliva-Fortuny, Gimeno-An˜o´, & Martı´nBelloso, 2008). The PEF has the ability to inactivate microorganisms and enzymes, while preserving the nutritional quality of the fresh-like food products. The PEF processing effects on quality and health-related constituents of plant-based foods and especially tomato juices have been extensively

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reviewed (Odriozola-Serrano, Aguilo´-Aguayo, Soliva-Fortuny, & Martı´n-Belloso, 2013; Odriozola-Serrano, Soliva-Fortuny, & Martı´n-Belloso, 2016).

2.3

Reduction of food contaminants (toxins, pesticides)

The PEF technology has the potential to improve the functionality, extractability, and the recovery of nutritionally valuable compounds in different food materials. In addition, several studies have shown that PEF technology can be used as a valuable tool to reduce food processing toxics and contaminants. The use of pesticides is well established in the agriculture for stabilizing the crop production. However, pesticide poisoning and its negative effects on environment and living organisms became a concern (Barba et al., 2015). There are dozens of evidences that the exposure to pesticides increases the risks of the development of chronic diseases (Cole et al., 2007). Among them, cancers, diabetes, neurodegenerative disorders such as Parkinson, Alzheimer, and amyotrophic lateral sclerosis, birth defects, and reproductive disorders. The development of chronic diseases in humans, caused by the intake of pesticide residues in food material, was reviewed in detail (Mostafalou & Abdollahi, 2013). Therefore in the midst of the increasing awareness about the risks of pesticides as well as the growing population and food demand, the need to reduce food pesticides and contaminants arises. Only a few studies have been performed yet for evaluating the impact of PEF technology on food pesticides (Chen et al., 2009; Zhang et al., 2012). An overall positive effect on the degradation of pesticides during PEF processing could be stated. For instance, a successful dissipation of methamidophos (O,Sdimethylphosphoramidothioate) and chlorpyrifos [O,O-diethylO-(3,5,6-trichloro-2-pyridinyl) phosphorothionate] spiked into apple juice was reported (Chen et al., 2009). The studied pesticides were chosen as representative examples, as they are active ingredients in most organophosphorus formulations. Thereby, it was observed that an increase in electric field strength and the number of pulses can have a significant impact on degradation of pesticides. The application of a higher voltage could increase the vibration and rotation of polar molecules, thereby facilitating the degradation of pesticides. In addition, chlorpyrifos was found much more labile to PEF treatment than methamidophos. Thus it was concluded that the chemical nature of

Chapter 2 An overview of the potential applications to produce healthy food products

pesticides determines their degradation pathway during PEF processing. However, as the chemical pathway was not revealed in the studies, no firm conclusion can be taken yet. It was demonstrated that successful degradation of diazinon [O,O-diethyl O-(4-methyl-6-(propan-2-yl)pyrimidin-2-yl) phosphorothioate] and dimethoate [O,O-dimethyl S-(2-(methylamino)-2-oxoethyl)dithiophosphate] in apple juice can be obtained by PEF treatment (Zhang et al., 2012). The extent of applied electric field strength and treatment time mainly governed the treatment efficacy; however, maximum degradation of diazinon (47.6%) and dimethoate (34.7%) was found for a treatment at 20 kV/cm for 260 μs. The authors associated the pesticide degradation to the presence of electrochemical reactions occurring during PEF treatment, which are linked to the release of FE21/ FE31 due to corrosion of stainless steel electrodes. Thereby, the formation of hydrogen peroxide and hydroxyl radicals was facilitated. These radicals were considered as responsible for the degradation of pesticides. The reduction in sample toxicity was also confirmed by toxicity studies based on photobacterium bioassay. In addition, different degradation behavior was noted between the two investigated pesticides as well. Another concern in food processing is related to the occurrence of Maillard reaction (Aljahdali & Carbonero, 2019). Even though this reaction is favorable for processes such as roasting, baking, and frying to achieve the desired level of color and flavor formation, it shows unwanted effects during drying, pasteurization, and sterilization processes. Among the negative effects are nutritional losses of essential amino acids and the formation of undesired heat derived, such as 5-hydroxymethylfurfural (HMF). HMF is formed by the reaction between reducing sugars and amino acids. Processing temperature and time are the key factors, influencing the extend of HMF-formation (Jaeger, Janositz, & Knorr, 2010; Koubaa et al., 2019). Several studies evidenced a low acute and chronic toxicity of HMF. However, HMF is characterized by a number of structural alerts (furan ring, α,β-unsaturated carbonyl group, and allylic hydroxylgroup), which pose a potential risk for genotoxic and carcinogenic diseases (Anese & Suman, 2013). PEF, as a nonthermal technology, does not lead to an increase in temperature during food processing and thus offers the potential to reduce the formation of undesired heat derivatives. The impact of PEF on the HMF concentration in strawberry, tomato, and watermelon juices was investigated (Jaeger et al., 2010). PEF-processed juice showed a slightly higher concentration of 5-hydroxymethylfurfura (HFM) than untreated one. However,

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the HMF formation of PEF-processed juice was significantly reduced compared to thermal processed one (Fig. 2.2). Nevertheless, the concentration of all treated juices remained below the maximum values (5 mg/L) allowed by the Association of the Industry of Juices and Nnectars from fruits and vegetables (Anonymous, 2019a). Additional studies showed similar results for orange, tomato, and apple juices. Moreover, slow browning rates were observed for PEF-treated juice, which seemed to be related to the high retention of ascorbic acid found in the juice (Corte´s, Esteve, & Frı´gola, 2008; Evrendilek, Celik, Agcam, & Akyildiz, 2017; Min & Zhang, 2003). Another intermediate product of Maillard reaction is acrylamide, which has neurotoxic and potential carcinogenic character. It is formed by the reaction between the amino acid asparagine and reducing sugars (Sansano, Heredia, Peinado, & Andre´s, 2017). Lowering the amount of aforementioned substrate in processed raw material can help to inhibit Maillard reaction and acrylamide production respectively. It was shown that a PEF pretreatment of potato tissue resulted in a reduction in content of sucrose by up to 28%, of fructose by up to 55%, and of glucose by up to 49%. This phenomenon could be referred to pore formation in cell membrane induced by PEF

Figure 2.2 HMF content of untreated, PEF-treated, and thermally treated juices. HMF, 5-Hydroxymethylfurfural; PEF, pulsed electric field. Source: Adapted from Jaeger, H., Janositz, A., & Knorr, D. (2010). The Maillard reaction and its control during food processing. The potential of emerging technologies. Pathologie Biologie, 58, 207 213.

Chapter 2 An overview of the potential applications to produce healthy food products

treatment. Thereby, cell permeabilization allowed an increased diffusion of intracellular compounds and thus an increased release of sugars (Jaeger et al., 2010). It should be noted that in 2017 the European Commission has issued Regulation (EU) 2017/2158 on reducing the presence of acrylamide in food. This regulation is based on the findings of European Food Safety Authority in 2015 that acrylamide potentially increases the risk of developing cancer. In addition, PEF treatment was shown as an alternative preservation technique in wine industry, replacing the usage of SO2 (Van Wyk, Silva, & Farid, 2019). This is of great interest, as a preservation of wine with SO2 can cause headaches, allergic reactions, asthma, abdominal pain, and bronchoconstriction and thus affect the consumer health negatively. It was stated that PEF treatment can ensure a production of wine that is safe for human consumption. Thereby, increasing the electric field intensity showed a greater effect than variations in specific energy input. Thus using electric field strength of 31, 40, and 50 kV/cm resulted in D-values of 181.8, 36.1, 13.0 μs. Oxalic acid and its salts can have deleterious effects on human nutrition and health, as oxalic acid can inhibit calcium absorption and facilitate the formation of kidney stones. Oca has been grown commercially in New Zealand since the 19th century with yields of between 20 and 40 t/ha and an estimated 2 million consumers, almost half of the total New Zealand population (Hermann & Heller, 1997). Despite the retention of starch, PEF treatment reduced tuber oxalate contents by almost 50% in some tissues and could potentially aid the development of low oxalate oca based foods (Liu, Burritt, Eyres, & Oey, 2018). With regards to allergen mitigation, PEF can induce changes in the structural characteristics of food allergens. For instance, the conformational changes in ovalbumin following PEF treatment, which lowered allergen antibody interaction, were observed (Toshiko, Takayuki, & Masayuki, 2004). PEF was also shown to induce glycosylation, alteration in secondary structure with a decrease in heat-induced aggregation in whey proteins (Sun, Yu, Zeng, Yang, & Jia, 2011). Conversely, for PEF treatment with various electric field strengths (0 35 kV/cm) at a frequency of 2 Hz to peanut and apple allergens, no significant structural modifications for the plant allergens was observed (Johnson et al., 2010). Therefore no conclusions can be made based on these limited studies until more investigations focusing on other allergenic proteins under similar PEF conditions or

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further studies relating to the effect of PEF on a variety of food allergens are available (Ekezie, Cheng, & Sun, 2018). Moreover, the presence of aflatoxin, a carcinogenic and toxigenic secondary metabolite produced by Aspergillus species, in food matrix has been a major worldwide problem for years now (Vijayalakshmi, Nadanasabhapathi, Kumar, & Sunny Kumar, 2018). Food processing methods such as roasting and extrusion have been employed for effective destruction of aflatoxins, which are known for their thermostable nature. The high-temperature treatment adversely affects the nutritive and other quality attributes of the food, leading to the necessity of application of nonthermal processing techniques such as ultrasonication, gamma irradiation, high pressure processing, and PEF Barba, Manuel, Saraiva, Cravotto, & Lorenzo, 2019). The study focused on analyzing the efficacy of the PEF process in the reduction of the toxin content, which was subsequently quantified using high performance liquid chromatography (HPLC) was performed (Vijayalakshmi et al., 2018). The process parameters of different pH model system (potato dextrose agar) artificially spiked with aflatoxin mix standard was optimized using the response surface methodology. The optimization of PEF process effects on the response of aflatoxin B1 and total aflatoxin reduction (%) by pH (4 10), pulse width (10 26 μs) fitted 2FI model and quadratic model, respectively. The response surface plots obtained for the processes were of saddle point type, with the absence of minimum or maximum response at the center point. The implemented numerical optimization showed that the predicted and actual values were similar, proving the adequacy of the fitted models, and also proved the possible application of PEF in toxin reduction. The rate of degradation of aflatoxin increased with an increase in moisture content of heated food (Rustom, Lo´pez-Leiva, & Nair, 1993). Hence, when the optimized parameters were adapted to the real food matrix the degradation percentage of toxin may vary with its moisture content (Vijayalakshmi et al., 2018).

2.4

Potential applications of pulsed electric field in food industry

The PEF processing has beneficial effects on the retention of valuable compounds (Gonza´lez-Casado et al., 2018), the reduction of food processing toxics and contaminants (Chen et al., 2009) and the extraction of intracellular contents (Agcam et al., 2014). A number of application fields for the food industry have been already proposed. Presently, the main applications of PEF

Chapter 2 An overview of the potential applications to produce healthy food products

technology with its health- and quality-related benefits are the gentle preservation of juice and the structure modification of potatoes. These applications are already successfully implemented in food industry. However, PEF provides great potential for further applications, for example, extraction, drying, and other processes (Siemer, To¨pfl, Witt, & Ostermeier, 2018). The rising health consciousness of customers also affects the snack market (Anonymous, 2019b). Especially in chips, the high fat content and the high amount of acrylamide levels remain a major concern. Thus consumer interest is shifting more and more toward “healthy” and “low-fat” chips and the industry is looking forward to meet the upcoming consumer demand (Baran Das & Srivastav, 2012; Stephens, 2018). The PEF technology was found to have positive impact on the frying process and the quality attributes of final product. The PEF treatment leads to electroporation of cell membrane, resulting in enhanced diffusion characteristics of the product. Due to faster water leakage and less moisture to be removed, the frying time can be shortened, which results in less heat load (Elea, 2018). Moreover, during washing of PEF-pretreated raw material, the amount of reducing sugars could be reduced by up to 55% (Jaeger et al., 2010). Studies evidenced that both a shorter frying time and a lower content of reducing sugars lead to a reduced acrylamide content of 52% for sweet potato chips, of 57% for beetroots chips and 19% for carrot chips (Elea, 2018). This optimization in frying process has beneficial effect on color and overall quality of snack product (Fig. 2.3). It was also stated that PEF pretreated products were characterized by less fathering and a smooth surface, which referred to the softer product structure. Thereby, less fathering and a shorter drying time can reduce the oil uptake of the product during frying. Accordingly, a reduction of oil uptake by up to 38% for snack products was stated (Janositz, Noack, & Knorr, 2011). Currently, more than 50 PEF systems are successfully installed worldwide in the potatoprocessing industry, mainly for the application in the production of chips and French fries and meanwhile it became a standard (Siemer et al., 2018). Heat processing is the most common method for shelf life extension of juices in which high temperatures are applied, which leads to the inactivation of both microorganisms and enzymes. However, high safety levels are accompanied by the degradation of sensorial, nutritional, and health-promoting attributes, that is, formation of undesirable flavors, oxidative degradation as well as pigment and vitamin losses (Agcam, Akyildiz, & Akdemir Evrendilek, 2016; Evrendilek et al., 2017).

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Chapter 2 An overview of the potential applications to produce healthy food products

Figure 2.3 Comparison between PEF treated (A) and untreated (B) vegetable chip (Elea, 2018). PEF, Pulsed electric field.

Against the background of the increasing consumer demand for safe and fresh-like products with enhanced nutritional and sensory properties, nonthermal techniques are gaining more and more attention in research and industry (Barba et al., 2015; Roobab, Aadil, Madni, & Bekhit, 2018). Several studies evidenced that PEF technology has the potential to inactivate yeast, mold, and bacterial cells—among them the well-known pathogens as Listeria, Bacillus, Escherichia coli, and Staphylococcus. Researchers found that an electric field strength of 20 kV/cm is sufficient to achieve a 3 6 log reduction of pathogenic microorganism (Ngadi, 2012; Roobab et al., 2018). The observed phenomenon is referred to PEF-induced permeabilization of cell membrane causing a loss of its barrier function and thus its activity. The combination of PEF and a mild thermal treatment (30 C 40 C) showed synergetic effects on the inactivation of microorganisms (Ngadi, 2012; Wouters, Alvarez, & Raso, 2001). Thereby, the thermal load as well as the dwell time are considerably lower/shorter compared to thermal processing. The PEF processing has therefore the ability to provide a shelf life of processed juice by several weeks to month without negatively affecting organoleptic and functional properties (Fig. 2.4) (Aadil et al., 2015; Siemer et al., 2018; Yang et al., 2016). Currently, PEF technology has already been successfully

Chapter 2 An overview of the potential applications to produce healthy food products

implemented by several manufacturers in European and Asian market (Siemer et al., 2018). Drying is one of the oldest methods of food preservation and widely used in food industry (Wiktor et al., 2016). Nowadays, different drying methods have been developed over the years. However, high operating and maintenance costs due to long drying times, as well as the need of high drying temperatures, remain a major concern of drying industry (Michailidis & Krokida, 2015). In recent years, growing interest was given to PEF technology as a predrying treatment for plant tissue and several studies were conducted to evaluate the impact of PEF pretreatment on the drying process and the quality of dried material. Thereby, it has been shown that PEF processing has the potential to shorten drying times, while keeping quality levels high. For instance, for convective drying, a drying time reduction for PEF-treated tissue of 8.2% for carrots (Wiktor et al., 2016), of 20% for raisins (Dev, Padmini, Adedeji, Gariepy, & Raghavan, 2008), and of 12% for apples (Wiktor et al., 2013) was stated as compared to untreated ones. Successful results have also been obtained for PEF-treated mango (Tedjo, Taiwo, Eshtiaghi, & Knorr, 2002) and bell peppers (Ade-Omowaye, Rastogi, Angersbach, & Knorr, 2002) prior to drying. For vacuum drying of plant material a reduction of drying time by up to

Figure 2.4 Color difference of untreated, thermally treated, and PEF-treated green smoothie (Elea, 2018). PEF, Pulsed electric field.

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27% was stated for potato slabs (Liu, Grimi, Lebovka, & Vorobiev, 2018) and by up to 42% for blueberries (Yu, Jin, & Xiao, 2017). Yu et al. (2017) observed as well that PEF pretreatment leads to a good preservation of anthocyanin, total phenolics, vitamin C, and antioxidant capacity of dried samples. Similar results were obtained for PEF-assisted freeze-drying. Several studies have shown that PEF treatment before freezedrying could reduce the freezing time of plant tissue, which leads to the formation of smaller ice crystals. Moreover, the PEF treatment decreased the drying time and resulted in a lower moisture content and a better visual quality of freeze-dried samples (Jalte´, Lanoiselle´, Lebovka, & Vorobiev, 2009; Parniakov, Bals, Lebovka, & Vorobiev, 2016; Wu & Zhang, 2014). Thereby, PEF treatment before freeze-drying resulted in a more uniform shape, clearer colors, and smaller shrinkage (Fig. 2.5).

2.5

Challenges of pulsed electric field technology

PEF technology does have some limitations. For example, any bacterial spores or mold ascospores in food products are usually resistant to PEF treatment, even at high intensity. This property could lead to a failure of the pasteurization process, resulting in a potential food safety hazard (Arroyo, Cebria´n, Paga´n, & Condo´n, 2012). In addition to the spores or ascospores, vegetative cells are resistant to PEF treatment under certain conditions. For instance, some studies have shown that

Figure 2.5 Untreated and PEF pretreated freeze-dried strawberries (Elea, 2018). PEF, Pulsed electric field.

Chapter 2 An overview of the potential applications to produce healthy food products

some microbial strains, such as Staphylococcus aureus, E. coli, and Salmonella typhimurium can tolerate the currently applied PEF treatment (Zhao, Yang, Shen, Zhang, & Chen, 2013). In order to ensure that PEF treatment adequately inactivates microorganisms in food products, it was concluded that it is important to identify and kill the most PEF-resistant microorganisms, such as Listeria monocytogenes, in food products ˜ a et al., 2009). Some microorganisms cannot be (Saldan completely killed by conventional PEF treatment. For instance, Zhao et al. (2011) quantified, in real time, PEF-induced damage on microbial cells in sterile phosphate buffer (10 mM, pH 7.0) using a flow cytometry method in combination with fluorescent staining techniques. The authors found that the proportion of sublethally injured cells reached a maximum after 50 pulses at 12.0 kV/cm for Saccharomyces cerevisiae and 16.5 kV/cm for Dekkera bruxellensis. These results show that electropermeabilization is not an all-or-nothing event (Wang et al., 2018). This statement also applies for the application of PEF for the inactivation of enzymes. Several studies have shown that PEF treatment could reduce enzymatic activity, but the resistance of enzymes to PEF varied between different types of enzymes. Therefore enzymatic inactivation is still discussed controversially in literature (Zhao, Yang, & Zhang, 2012). However, different studies showed that the combined approach of PEF technology and nonlethal processing temperatures (,50 C 53 C) leads to synergetic interactions (Riener, Noci, Cronin, Morgan, & Lyng, 2008, 2009; Shamsi, Versteeg, Sherkat, & Wan, 2008). The combination of both techniques showed higher inactivation levels than the single method on its own. For instance, Riener, Noci, Cronin, Morgan, and Lyng (2010) showed that the highest level of lipoxygenase inactivation in soya milk (84.5%) was achieved by using a combination of PEF treatment time of 100 μs at 40 kV/cm and a processing temperature of 50 C. Whether the PEF treatment or the thermal impact had the major impact on enzyme inactivation still has to be investigated. However, the intensity of electric field, treatment time, and temperature were identified as key factors in enzyme inactivation. Another hurdle to overcome is the release of metallic particles from the electrode material during PEF treatment, as it can affect the safety and the quality of PEF-processed food. A significant increase in the concentration of Fe, Cr, Zn, and Mn in PEFtreated beer compared to untreated one (P ,.05) was observed by Evrendilek, Li, Dantzer, and Zhang (2004). Moreover, the migration of metallic particles caused a significant loss in flavor

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and mouth feeling in PEF-processed samples. However, the foam condition, the color, and the overall acceptability of processed beer were not affected. The similar tendencies during PEF processing of milk were observed (Gad & Jayaram, 2014). It was stated that the release of metallic particle cannot be avoided, when using the typical conditions of PEF processing. Electrically driven electrochemical reactions were found to be the main reason for the migration of metallic particles. However, several studies showed that the characteristic of generated electric pulses have an impact on the corrosion of electrode material. By applying short electrical pulses and by avoiding a cumulative builtup of charges, the migration of electrode material can be limited (Evrendilek et al., 2004; Gad & Jayaram, 2014; Roodenburg, Morren, Iekje Berg, & de Haan, 2005). Another challenge of PEF technology is its difficulty to treat food products with high electrical conductivity. Several studies showed that at a constant energy input, an increase in conductivity leads to an decrease in the inactivation of several microorganisms (Go´ngora-Nieto, Pedrow, Swanson, & Barbosa-Ca´novas, 2003; Siemer, Toepfl, & Heinz, 2014; Wouters et al., 2001). The authors stated that this phenomenon is related to the fact that a high electrical conductivity of the treated product reduces the resistance of the chamber. Thus more energy is required to achieve a specific electrical field to guarantee cell permeabilization of plant or animal tissue or the desired level of microbial inactivation for liquid food preservation. Therefore when products high in salt content are processed, it is recommended to add the salt after PEF processing (Ngadi, 2012). However, in most of food materials the conductivity is fixed by their physical structure and chemical composition. In this case an adaption of electrode configuration and geometry with high-load geometry can help to achieve a better voltage distribution in the discharge (Siemer et al., 2014).

References Aadil, R., Zeng, X.-A., Ali, A., Zeng, F., Adil Farooq, M., Han, Z., et al. (2015). Influence of different pulsed electric field strengths on the quality of the grapefruit juice. International Journal of Food Science and Technology, 50, 2290 2296. Ade-Omowaye, B. I. O., Rastogi, N. K., Angersbach, A., & Knorr, D. (2002). Osmotic dehydration of bell peppers: Influence of high intensity electric field pulses and elevated temperature treatment. Journal of Food Engineering, 54 (1), 35 43. Agcam, E., Akyildiz, A., & Akdemir Evrendilek, G. (2016). A comparative assessment of long-term storage stability and quality attributes of orange

Chapter 2 An overview of the potential applications to produce healthy food products

juice in response to pulsed electric fields and heat treatments. Food and Bioproducts Processing, 99, 90 98. Agcam, E., Akyildiz, A., & Evrendilek, G. A. (2014). Comparison of phenolic compounds of orange juice processed by pulsed electric fields (PEF) and conventional thermal pasteurisation. Food Chemistry, 143, 354 361. Aguilar-Rosas, S., Ballinas-Casarrubias, M., Elias-Ogaz, L., Martin-Belloso, O., & Ortega-Rivas, E. (2013). Enzyme activity and colour changes in apple juice pasteurised thermally and by pulsed electric fields. Acta Alimentaria, 42(1), 45 54. Aguilar-Rosas, S. F., Ballinas-Casarrubias, M. L., Nevarez-Moorillon, G. V., Martin-Belloso, O., & Ortega-Rivas, E. (2007). Thermal and pulsed electric fields pasteurization of apple juice: Effects on physicochemical properties and flavour compounds. Journal of Food Engineering, 83(1), 41 46. Alexandratos, N. (2006). World agriculture: Towards 2030/50, interim report. An FAO perspective. London, UK: Earthscan, Rome, Italy: FAO. Aljahdali, N., & Carbonero, F. (2019). Impact of Maillard reaction products on nutrition and health: Current knowledge and need to understand their fate in the human digestive system. Critical Reviews in Food Science and Nutrition, 59(3), 474 487. Anese, M., & Suman, M. (2013). Mitigation strategies of furan and 5hydroxymethylfurfural in food. Food Research International, 51(1), 257 264. Anonymous. (2019a). AIJN, association of the industry of juices and nectars of the European Economic Community code of practice for evaluation of fruit and vegetable juice. Rue de la Loi 221 Box 5, B-1040 Brussels. Anonymous. Dried fruits and edible nuts market analysis, trends, and forecasts. (2019b). ,https://www.strategyr.com/market-report-dried-fruits-and-ediblenuts-forecasts-global-industry-analysts-inc.asp.. Anonymous. GDP per capita (current US). (2019c). ,https://data.worldbank.org/ indicator/ny.gdp.pcap.cd?start 5 2000.. Arroyo, C., Cebria´n, G., Paga´n, R., & Condo´n, S. (2012). Synergistic combination of heat and ultrasonic waves under pressure for Cronobacter sakazakii inactivation in apple juice. Food Control, 25(1), 342 348. Baran Das, A., & Srivastav, P. (2012). Acrylamide in snack foods. Toxicology Mechanisms and Methods, 22, 163 169. Barba, F., Manuel, J., Saraiva, A., Cravotto, G., & Lorenzo, J. (2019). Innovative thermal and non-thermal processing, bioaccessibility and bioavailability of nutrients and bioactive compounds. Woodhead Publishing. Barba, F. J., Parniakov, O., Pereira, S. A., Wiktor, A., Grimi, N., Boussetta, N., & Vorobiev, E. (2015). Current applications and new opportunities for the use of pulsed electric fields in food science and industry. Food Research International, 77, 773 798. Bi, X., Liu, F., Rao, L., Li, J., Liu, B., Liao, X., & Wu, J. (2013). Effects of electric field strength and pulse rise time on physicochemical and sensory properties of apple juice by pulsed electric field. Innovative Food Science & Emerging Technologies, 17, 85 92. Boussetta, N., Vorobiev, E., Le, L. H., Cordin-Falcimaigne, A., & Lanoiselle´, J.-L. (2012). Application of electrical treatments in alcoholic solvent for polyphenols extraction from grape seeds. LWT—Food Science and Technology, 46(1), 127 134. Brianceau, S., Turk, M., Vitrac, X., & Vorobiev, E. (2015). Combined densification and pulsed electric field treatment for selective polyphenols recovery from fermented grape pomace. Innovative Food Science & Emerging Technologies, 29, 2 8.

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Chapter 2 An overview of the potential applications to produce healthy food products

Gad, A., & Jayaram, S. (2014). Effect of electric pulse parameters on releasing metallic particles from stainless steel electrodes during PEF processing of milk. IEEE Transactions on Industry Applications, 50, 1402 1409. Go´ngora-Nieto, M. M., Pedrow, P. D., Swanson, B. G., & Barbosa-Ca´novas, G. V. (2003). Energy analysis of liquid whole egg pasteurized by pulsed electric fields. Journal of Food Engineering, 57, 209 216. Gonza´lez-Casado, S., Martı´n-Belloso, O., Elez-Martı´nez, P., & Soliva-Fortuny, R. (2018). Enhancing the carotenoid content of tomato fruit with pulsed electric field treatments: Effects on respiratory activity and quality attributes. Postharvest Biology and Technology, 137, 113 118. Grimi, N., Lebovka, N. I., Vorobiev, E., & Vaxelaire, J. (2009). Effect of a pulsed electric field treatment on expression behavior and juice quality of chardonnay grape. Food Biophysics, 4(3), 191 198. Grimi, N., Mamouni, F., Lebovka, N., Vorobiev, E., & Vaxelaire, J. (2011). Impact of apple processing modes on extracted juice quality: Pressing assisted by pulsed electric fields. Journal of Food Engineering, 103(1), 52 61. Hedges, L. J., & Lister, C. E. (2005). Nutritional attributes of tomatoes. In Crop & food research confidential report no, 1391. Hegde, A. Fruit snacks market value to hit $8 billion by 2025. (2019). Retrieved from ,https://www.globenewswire.com/news-release/2019/06/26/1874306/ 0/en/Fruit-Snacks-Market-value-to-hit-8-billion-by-2025-Global-MarketInsights-Inc.html. Hermann, M., & Heller, J. (1997). Andean roots and tubers: Ahipa, arracacha, maca and yacon. International Potato Center. Hong, J., Zeng, X. A., Han, Z., & Brennan, C. S. (2018). Effect of pulsed electric fields treatment on the nanostructure of esterified potato starch and their potential glycemic digestibility. Innovative Food Science and Emerging Technologies, 45, 438 446. Jaeger, H., Janositz, A., & Knorr, D. (2010). The Maillard reaction and its control during food processing. The potential of emerging technologies. Pathologie Biologie, 58, 207 213. Jaeger, H., Schulz, M., Lu, P., & Knorr, D. (2012). Adjustment of milling, mash electroporation and pressing for the development of a PEF assisted juice production in industrial scale. Innovative Food Science & Emerging Technologies, 14, 46 60. Jalte´, M., Lanoiselle´, J.-L., Lebovka, N., & Vorobiev, E. (2009). Freezing of potato tissue pre-treated by pulsed electric fields. Food Science and Technology, 42 (2), 576 580. Janositz, A., Noack, A.-K., & Knorr, D. (2011). Pulsed electric fields and their impact on the diffusion characteristics of potato slices. LWT—Food Science and Technology, 44(9), 1939 1945. Jenkins, D. J. A., Kendall, C. W. C., Augustin, L. S. A., Franceschi, S., Hamidi, M., Marchie, A., & Axelsen, M. (2002). Glycemic index: Overview of implications in health and disease. The American Journal of Clinical Nutrition, 76(1), 266S 273S. Johnson, P. E., der Plancken, I., Balasa, A., Husband, F. A., Grauwet, T., Hendrickx, M., & Mackie, A. R. (2010). High pressure, thermal and pulsed electric-field-induced structural changes in selected food allergens. Molecular Nutrition & Food Research, 54(12), 1701 1710. Kearney, J. (2010). Food consumption trends and drivers. Philosophical Transactions of the Royal Society of London B: Biological Sciences, 365(1554), 2793 2807.

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Koubaa, M., Roohinejad, S., Mungure, T. E., Alaa El-Din, B., Greiner, R., & Mallikarjunan, K. (2019). Effect of emerging processing technologies on Maillard reactions. Encyclopedia of Food Chemistry, 76 82. Leong, S. Y., Burritt, D. J., & Oey, I. (2016). Evaluation of the anthocyanin release and health-promoting properties of Pinot Noir grape juices after pulsed electric fields. Food Chemistry, 196, 833 841. Li, F., Chen, G., Zhang, B., & Fu, X. (2017). Current applications and new opportunities for the thermal and non-thermal processing technologies to generate berry product or extracts with high nutraceutical contents. Food Research International, 100, 19 30. Liu, C., Grimi, N., Lebovka, N., & Vorobiev, E. (2018). Effects of pulsed electric fields treatment on vacuum drying of potato tissue. Lebensmittel-Wissenschaft & Technologie, 95, 289 294. Liu, T., Burritt, D. J., Eyres, G. T., & Oey, I. (2018). Pulsed electric field processing reduces the oxalate content of oca (Oxalis tuberosa) tubers while retaining starch grains and the general structural integrity of tubers. Food Chemistry, 245, 890 898. Lo´pez-Giral, N., Gonza´lez-Arenzana, L., Gonza´lez-Ferrero, C., Lo´pez, R., Santamarı´a, P., Lo´pez-Alfaro, I., & Garde-Cerda´n, T. (2015). Pulsed electric field treatment to improve the phenolic compound extraction from Graciano, Tempranillo and Grenache grape varieties during two vintages. Innovative Food Science & Emerging Technologies, 28, 31 39. ´ lvarez, I., & Raso, J. (2013). Improving the pressing extraction of Luengo, E., A polyphenols of orange peel by pulsed electric fields. Innovative Food Science and Emerging Technologies, 17, 79 84. Michailidis, P. A., & Krokida, M. K. (2015). In S. Bhattacharya (Ed.), Conventional and advanced food processing technologies. Hoboken, NJ: John Wiley & Sons. Miklavcic, D. (Ed.), (2017). Handbook of electroporation (Vol. 10). Basel: Springer International Publishing AG. Min, S., & Zhang, Q. H. (2003). Effects of commercial-scale pulsed electric field processing on flavor and color of tomato juice. Journal of Food Science, 68(5), 1600 1606. Mostafalou, S., & Abdollahi, M. (2013). Pesticides and human chronic diseases: Evidences, mechanisms, and perspectives. Toxicology and Applied Pharmacology, 268(2), 157 177. Ngadi, M. O. (2012). Microbial decontamination of food by pulsed electric fields (PEFs). In A. Demirci, & M. O. Ngadi (Eds.), Microbial decontamination in the food industry: Novel methods and applications, Woodhead Publishing (pp. 407 449). ˜ o´, V., & Odriozola-Serrano, I., Aguilo´-Aguayo, I., Soliva-Fortuny, R., Gimeno-An Martı´n-Belloso, O. (2007). Lycopene, vitamin C, and antioxidant capacity of tomato juice as affected by high-intensity pulsed electric fields critical parameters. Journal of Agricultural and Food Chemistry, 55(22), 9036 9042. Odriozola-Serrano, I., Aguilo´-Aguayo, I., Soliva-Fortuny, R., & Martı´n-Belloso, O. (2013). Pulsed electric fields processing effects on quality and health-related constituents of plant-based foods. Trends in Food Science & Technology, 29(2), 98 107. ˜ o´, V., & Martı´n-Belloso, O. Odriozola-Serrano, I., Soliva-Fortuny, R., Gimeno-An (2008). Modeling changes in health-related compounds of tomato juice treated by high-intensity pulsed electric fields. Journal of Food Engineering, 89(2), 210 216. Odriozola-Serrano, I., Soliva-Fortuny, R., Herna´ndez-Jover, T., & Martı´n-Belloso, O. (2009). Carotenoid and phenolic profile of tomato juices processed by high

Chapter 2 An overview of the potential applications to produce healthy food products

intensity pulsed electric fields compared with conventional thermal treatments. Food Chemistry, 112(1), 258 266. Odriozola-Serrano, I., Soliva-Fortuny, R., & Martı´n-Belloso, O. (2016). Pulsed electric fields effects on health-related compounds and antioxidant capacity of tomato juice. In Handbook of electroporation, Springer Nature Switzerland AG, Cham (pp. 1 14). Ozturk, S., Koksel, H., Kahraman, K., & Ng, P. K. W. (2009). Effect of debranching and heat treatments on formation and functional properties of resistant starch from high-amylose corn starches. European Food Research and Technology, 229(1), 115 125. Parniakov, O., Bals, O., Lebovka, N., & Vorobiev, E. (2016). Pulsed electric field assisted vacuum freeze-drying of apple tissue. Innovative Food Science & Emerging Technologies, 35, 52 57. Pongjanta, J., Utaipattanaceep, A., Naivikul, O., & Piyachomkwan, K. (2009). Effects of preheated treatments on physicochemical properties of resistant starch type III from pullulanase hydrolysis of high amylose rice starch. American Journal of Food Technology, 4(2), 79 89. ´ lvarez, I., & Raso, J. (2013). PulsedPue´rtolas, E., Cregenza´n, O., Luengo, E., A electric-field-assisted extraction of anthocyanins from purple-fleshed potato. Food Chemistry, 136(3 4), 1330 1336. ´ lvarez, I., & Raso, J. (2010). ˜ a, G., A Pue´rtolas, E., Herna´ndez-Orte, P., Sladan Improvement of winemaking process using pulsed electric fields at pilotplant scale. Evolution of chromatic parameters and phenolic content of Cabernet Sauvignon red wines. Food Research International, 43(3), 761 766. Riener, J., Noci, F., Cronin, D. A., Morgan, D. J., & Lyng, J. G. (2008). Combined effect of temperature and pulsed electric fields on apple juice peroxidase and polyphenoloxidase inactivation. Food Chemistry, 109(2), 402 407. Riener, J., Noci, F., Cronin, D. A., Morgan, D. J., & Lyng, J. G. (2009). Combined effect of temperature and pulsed electric fields on pectin methyl esterase inactivation in red grapefruit juice (Citrus paradisi). European Food Research and Technology, 228, 373 379. Riener, J., Noci, F., Cronin, D. A., Morgan, D. J., & Lyng, J. G. (2010). A comparison of selected quality characteristics of yoghurts prepared from thermosonicated and conventionally heated milks. Food Chemistry, 119, 1108 1113. Roobab, U., Aadil, R., Madni, G., & Bekhit, A. (2018). The impact of nonthermal technologies on the microbiological quality of juices: A review. Comprehensive Reviews in Food Science and Food Safety, 17, 437 457. Roodenburg, B., Morren, J., (Iekje) Berg, H. E., & de Haan, S. W. H. (2005). Metal release in a stainless steel pulsed electric field (PEF) system: Part II. The treatment of orange juice; related to legislation and treatment chamber lifetime. Innovative Food Science & Emerging Technologies, 6(3), 337 345. Rustom, I. Y. S., Lo´pez-Leiva, M. H., & Nair, B. M. (1993). Effect of pH and heat treatment on the mutagenic activity of peanut beverage contaminated with aflatoxin B1. Food Chemistry, 46(1), 37 42. ´ lvarez, I., & Raso, J. (2009). ˜ a, G., Pue´rtolas, E., Lo´pez, N., Garcı´a, D., A Saldan Comparing the PEF resistance and occurrence of sublethal injury on different strains of Escherichia coli, Salmonella typhimurium, Listeria monocytogenes and Staphylococcus aureus in media of pH 4 and 7. Innovative Food Science & Emerging Technologies, 10(2), 160 165. Sansano, M., Heredia, A., Peinado, I., & Andre´s, A. (2017). Dietary acrylamide: What happens during digestion. Food Chemistry, 237, 58 64.

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Shamsi, K., Versteeg, C., Sherkat, F., & Wan, J. (2008). Alkaline phosphatase and microbial inactivation by pulsed electric field in bovine milk. Innovative Food Science & Emerging Technologies, 9(2), 217 223. Siemer, C., To¨pfl, S., Witt, J., & Ostermeier, R. (2018). Use of pulsed electric fields (PEF) in the food industry. In DLG expert report. Siemer, C., Toepfl, S., & Heinz, V. (2014). Inactivation of bacillus subtilis spores by pulsed electric fields (PEF) in combination with thermal energy—I. Influence of process and product parameters. Food Control, 39(1), 163 171. Stephens, K. (2018). Global snacking trends. The popularity of snacks and on-thego bars is increasing worldwide, allowing for an influx of innovative ingredients, flavors and concepts. Sun, W. W., Yu, S. J., Zeng, X. A., Yang, X. Q., & Jia, X. (2011). Properties of whey protein isolate dextran conjugate prepared using pulsed electric field. Food Research International, 44, 1052 1058. Tedjo, W., Taiwo, K. A., Eshtiaghi, M. N., & Knorr, D. (2002). Comparison of pretreatment methods on water and solid diffusion kinetics of osmotically dehydrated mangos. Journal of Food Engineering, 53(2), 133 142. Toshiko, K., Takayuki, O., & Masayuki, S. (2004). Effect of PEF on allergen molecule in aqueous solution. Seidenki Gakkai Koen Ronbunshu (in Japanese), 2004, 85 86. Van Wyk, S., Silva, F. V. M., & Farid, M. M. (2019). Pulsed electric field treatment of red wine: Inactivation of Brettanomyces and potential hazard caused by metal ion dissolution. Innovative Food Science & Emerging Technologies, 52, 57 65. Vijayalakshmi, S., Nadanasabhapathi, S., Kumar, R., & Sunny Kumar, S. (2018). Effect of pH and pulsed electric field process parameters on the aflatoxin reduction in model system using response surface methodology. Journal of Food Science and Technology, 55(3), 868 878. Wang, M.-S., Wang, L.-H., Bekhit, A. E.-D. A., Yang, J., Hou, Z.-P., Wang, Y.-Z., & Zeng, X.-A. (2018). A review of sublethal effects of pulsed electric field on cells in food processing. Journal of Food Engineering, 223, 32 41. ´ z, M., Nowacka, M., Chudoba, T., & WitrowaWiktor, A., Iwaniuk, M., Sled´ Rajchert, D. (2013). Drying kinetics of apple tissue treated by pulsed electric field. Drying Technology, 31(1), 112 119. Wiktor, A., Nowacka, M., Dadan, M., Rybak, K., Lojkowski, W., Chudoba, T., & Witrowa-Rajchert, D. (2016). The effect of pulsed electric field on drying kinetics, color, and microstructure of carrot. Drying Technology, 34(11), 1286 1296. Wouters, P. C., Alvarez, I., & Raso, J. (2001). Critical factors determining inactivation kinetics by pulsed electric field food processing. Trends in Food Science & Technology, 12(3), 112 121. Wu, Y., & Zhang, D. (2014). Effect of pulsed electric field on freeze-drying of potato tissue. International Journal of Food Engineering, 10(4), 857 862. Yang, N., Huang, K., Lyu, C., Wang, J., Huanga, K., Lyua, C., & Wanga, J. (2016). Pulsed electric field technology in the manufacturing processes of wine, beer, and rice wine: A review. Food Control, 61, 28 38. Yu, Y., Jin, T. Z., & Xiao, G. (2017). Effects of pulsed electric fields pretreatment and drying method on drying characteristics and nutritive quality of blueberries. Journal of Food Processing and Preservation, 41(6), 1 9. Zhang, J., Hou, J., Zhang, J., Chen, J., Chen, F., Liao, X., & Hu, X. (2012). Reduction of diazinon and dimethoate in apple juice by pulsed electric field treatment. Journal of the Science of Food and Agriculture, 92, 743 750.

Chapter 2 An overview of the potential applications to produce healthy food products

Zhao, W., Yang, R., Zhang, H. Q., Zhang, W., Hua, X., & Tang, Y. (2011). Quantitative and real time detection of pulsed electric field induced damage on Escherichia coli cells and sublethally injured microbial cells using flow cytometry in combination with fluorescent techniques. Food Control, 22 (3 4), 566 573. Zhao, W., Yang, R., Shen, X., Zhang, S., & Chen, X. (2013). Lethal and sublethal injury and kinetics of Escherichia coli, Listeria monocytogenes and Staphylococcus aureus in milk by pulsed electric fields. Food Control, 32(1), 6 12. Zhao, W., Yang, R., & Zhang, H. Q. (2012). Recent advances in the action of pulsed electric fields on enzymes and food component proteins. Trends in Food Science & Technology, 27(2), 83 96.

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Health promoting benefits of PEF: bioprotective capacity against the oxidative stress and its impact on nutrient and bioactive compound bioaccessibility

3

Zhenzhou Zhu1, Fang Wang1, Qiang Xia2, Yunfei Li2, Shahin Roohinejad3, Krystian Marszałek4,6, Elena Rosello´-Soto5 and Francisco J. Barba5 1

School of Food Science and Engineering, Wuhan Polytechnic University, Wuhan, P.R. China 2Department of Food Science and Technology, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, P.R. China 3 Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN, United States 4Department of Fruit and Vegetable Product Technology, Prof. Wacł aw Da˛browski Institute of Agricultural and Food Biotechnology, Warsaw, Poland 5Nutrition and Food Science Area, Preventive Medicine and Public Health, Food Sciences, Toxicology and Forensic Medicine Department, Faculty of Pharmacy, Universitat de Vale`ncia, Vale`ncia, Spain 6Department of Chemistry and Food Toxicology, Institute of Food Technology and Nutrition, College of Natural Sciences, University of Rzeszo´w, Rzeszo´w, Poland

3.1

Introduction

An increased interest has been shown over the last years regarding the application of pulsed electric field (PEF). PEF technology is applied for food preservation purposes as a nonthermal processing technique. Moreover, apart from this application, it can be useful for tailor-made processes with a wide range of applications. For instance, extraction assisted by PEF has been a hot topic, with hundreds of publications during the last two decades. In addition, the application of PEF in potato industry seems to be a fact due to its ability to reduce fat content and acrylamide (Barba et al., 2015).

Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00003-3 © 2020 Elsevier Inc. All rights reserved.

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Chapter 3 Health promoting benefits of PEF

In the beginning, the investigation on PEF was limited to equipment design and optimization, as well as microbial inactivation of foods (Barba, Koubaa, do Prado-Silva, Orlien, & Sant’Ana, 2017; Misra et al., 2017). However, at this stage of development, once the feasibility of PEF for some target applications has been confirmed, it is necessary to go further and explore the implications of PEF in the development of new healthy food products with enhanced beneficial properties on health (Pue´rtolas, Koubaa, & Barba, 2016). In this line, the determination of nutrient and bioactive compounds’ bioaccessibility and bioavailability after PEF has been established as a crucial step in the determination of the functional properties of the obtained products/extracts after applying this type of technology (Barba et al., 2015; Barba, Mariutti, et al., 2017; Barba & Orlien, 2017; Granato, Nunes, & Barba, 2017; Putnik et al., 2017); Fig. 3.1. PEF has been shown to have the ability to increase the release of some bioactive compounds (e.g., carotenoids), thus improving their bioaccessibility (Roohinejad, Everett, & Oey, 2014). This fact has been attributed

Figure 3.1 Impact of pulsed electric fields on bioaccessibility and bioavailability of nutrients and bioactive compounds from food matrices. Source: Adapted from Pue´rtolas, E., & Barba, F. J. (2016). Electrotechnologies applied to valorization of by-products from food industry: Main findings, energy and economic cost of their industrialization. Food and Bioproducts Processing, 100, 172 184 (Pue´rtolas & Barba, 2016) and Zhu, Z., He, J., Liu, G., Barba, F. J., Koubaa, M., Ding, L., et al. (2016). Recent insights for the green recovery of inulin from plant food materials using non-conventional extraction technologies: A review. Innovative Food Science and Emerging Technologies, 33, 1 9 (Zhu et al., 2016).

Chapter 3 Health promoting benefits of PEF

53

to the breakdown of cell membrane (Barba et al., 2015). Moreover, the investigation of the bioprotective capacity of the PEF-processed foods/extracts against the oxidative stress is also of great importance. The effects of PEF on nutrients and bioactive compounds’ extractability as well as bioaccessibility, from different food matrices, have been studied by several authors, although the literature on this is still scarce. Some of the most relevant findings are shown in Table 3.1. Table 3.1 Impact of pulsed electric field (PEF) processing on extractability, bioprotective effect, and bioaccessibility of nutrients and bioactive compounds. Food matrix

PEF processing parameters

Nutrient/bioactive compound

Main findings

References

Carrot

Pomace

Puree´ (White Belgian, Yellow Solar, Nantes, Nutri Red, and Purple Haze cultivars)

Carrot

Improved extraction of carotenoids from carrot pomace when electric field strength up to 1 kV/cm at 5 Hz. No significant increase observed when the frequency was increased .10 Hz Carotenoids, polyphenols, PEF-processed (303 kJ/ 0.3, 0.5, and kg) Purple Haze and 0.8 kV/cm. Energy anthocyanins, and Nutri Red carrots vitamin C input (303 vs increased the capacity 35 kJ/kg, at an to protect Caco-2 cells electric field resistance in strength of comparison to 0.5 kV/cm) untreated samples. Oxidative damage avoided by recovering the cell viability and inhibiting NO production 0.3, 1.9 kV/cm or β-Carotene Bioaccessibility of 0.9, 191 kJ/kg β-carotene for carrots after PEF treatment was comparable to conventional blanching

0.1 1 kV/cm; frequency of 5 75 Hz

Carotenoids

Roohinejad et al. (2014)

Leong, Oey, et al. (2016a)

Leong et al. (2018)

(Continued )

54

Chapter 3 Health promoting benefits of PEF

Table 3.1 (Continued) Food matrix

PEF processing parameters

Nutrient/bioactive compound

Main findings

References

35 kV/cm, bipolar 4 μs pulse width at 200 Hz for 1800 μs time 35 kV/cm, 4 μs bipolar pulses, 200 Hz, 1800 μs

Vitamin C and phenolic compounds

Increased bioaccessibility

RodriguezRoque et al. (2015)

cisIncreased Violaxanthin 1 neoxanthin bioaccessibility

Rodrı´guezRoque et al. (2016)

25 kV/cm, 50 400 pulses

Vitamin C, phenolic compounds, total carotenoid

Buniowska et al. (2016)

35 kV/cm, bipolar 4 μs pulse width at 800 Hz, for 750 μs

Vitamin C

Ascorbic acid not detected following intestinal digestion. Increase (phenolic compounds and anthocyanin). Increase total carotenoid Increased bioaccessibility

Pinot Noir variety

1.5 kV/cm, pulse frequency of 50 Hz, constant pulse width of 20 μs, 243 1033 pulses

Anthocyanins

Leong, Burritt, et al. (2016a)

Merlot grape variety

1.5 kV/cm, 15 or 70 kJ/kg and

Anthocyanins

PEF-pretreated juice showed a higher bioprotective capacity (125% for cell viability and 130% for LDH filtration). A strong relationship between the bioprotective capacity and malvidin3-O-glucoside Strong relationship between anthocyanins and the bioprotective

Fruit and vegetable mixture combinations

Fruit juice based beverages

Fruit juice mixture (orange, kiwi, pineapple, and mango) combined with water or milk or soymilk after applying PEF treatments Fruit juice mixture [50.75% (v/v) of papaya, 19.25% (v/v) of mango] combined with 30% (v/v) of Stevia rebaudiana infusion (2.5%, w/v) Vegetable soup “gaspacho”

Sa´nchezMoreno et al. (2004, 2005)

Grapes

Leong, Burritt, et al. (2016b) (Continued )

Chapter 3 Health promoting benefits of PEF

55

Table 3.1 (Continued) Food matrix

PEF processing parameters

Nutrient/bioactive compound

maceration time (0 14 days)

Main findings

References

capacity indicators. Enhanced bioprotective capacity against the oxidative stress induced by H2O2 in Caco-2 cells, measured using the 3(4,5-dimethythiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT) assay

Milk and milk products

1.4 1.8 kV/cm, 260 690 kJ/kg

Protein

PEF pretreatment at the Liu et al. highest energy used in (2017) the experiment (690 kJ/ kg) and pH 4 increased protein digestibility to a similar level noted after heating at 80 C

35 kV/cm, bipolar 4 μs pulse width at 800 Hz, for 750 μs

Vitamin C

Increased bioaccessibility

Orange juice

Sa´nchezMoreno et al. (2004, 2005)

Tomato

1 kV/cm/0, 1, 20, or 80 monopolar pulses, pulse width of 4 μs, 0.1 Hz frequency

Increased release of Jayathunge trans- and cis-lycopene et al. (2017) from tomato matrix during in vitro digestion when blanching followed by PEF at high intensity was used to preserve tomato juice, with  16% lycopene bioaccessibility (Continued )

56

Chapter 3 Health promoting benefits of PEF

Table 3.1 (Continued) Food matrix

PEF processing parameters 1. 90 Pulses at 1 Hz repetition rate. 210 Pulses delivered at 0.167 Hz within 30 min 2. 600 Pulses where delivered at 0.33 Hz

Nutrient/bioactive compound

Main findings

References

Insignificant changes in Bot et al. β-carotene and (2018) lycopene bioaccessibility under PEF or PEF heating assisted treatment in most of the selected tomato fractions. Significant decrease in lycopene bioaccessibility of tomato tissue and chromoplasts after the application of PEF and PEF assisted by heating was noted

LDH, Lactate dehydrogenase.

3.2

Carrots (Daucus carota)

Carrots contain c. 88% of water and are an important source of carbohydrates, micronutrients such as carotenoids that are responsible for their orange color, particularly β-carotene. β-Carotene is essential for vision, the good condition of the skin, the tissues, and for the good functioning of our immune system. Carrots are also an important source of vitamin E that has been involved in some beneficial properties such as blood cells’ stability, fertility, and antioxidant properties. Moreover, carrots also contain B group vitamins, such as folate and vitamin B3 or niacin and minerals (e.g., potassium, calcium, phosphorus, and iodine). Therefore at this stage of development, it is of great interest to evaluate how PEF affects the extractability of these compounds as well as their bioaccessibility. For instance, in a study conducted by Roohinejad et al. (2014), the impact of PEF processing (0.1 1 kV/cm; frequency of 5 75 Hz) and different oils on carotenoid extractability from carrots were evaluated. The authors observed significantly better extraction

Chapter 3 Health promoting benefits of PEF

of carotenoids from carrot pomace when they increased electric field strength up to 1 kV/cm at 5 Hz. However, no significant increase was observed when the frequency was increased .10 Hz. Moreover, carotenoid extraction yield differed according to the oil used, obtaining the highest amount when sunflower and soya bean oils were used, while the lowest amount was obtained for peanut oil. In another study the combination of PEF and thermodynamically stable microemulsions was evaluated to extract β-carotene from carrot pomace, obtaining promising results (Roohinejad, Oey, Everett, & Niven, 2014). For instance, PEF treatment with application of microemulsions for better extraction allowed for more β-carotene extraction in comparison to the extraction with 100% hexane or 100% glycerol monocaprylocaprate (Capmul MCM) oil. More recently, the effect of PEF on the bioprotective capacity of carrot pure´e of White Belgian, Yellow Solar, Nantes, Nutri Red, and Purple Haze cultivars against H2O2-induced oxidative damage was evaluated (Leong, Oey, & Burritt, 2016a). Several biomarkers were used to evaluate the health and cellular integrity: (1) cell viability, (2) membrane integrity, and (3) nitric oxide (NO) production in a human Caco-2 cell culture assay. They also evaluated the impact of PEF on antioxidant compounds (carotenoids, polyphenols, anthocyanins, and vitamin C). Purple Haze and Nutri Red carrots processed by PEF at the highest energy (303 kJ/kg) significantly increased the capacity of carrot puree to protect Caco-2 cells resistance in comparison to untreated samples. Oxidative damage has been avoided by recovering the cell viability and inhibiting NO production. Extraction of carotenoids forms Yellow Solar cultivar, with the lower concentration of pigments, treated by electric field strength 0.8 kV/cm was more effective in comparison to untreated samples and resulted in a higher concentration total carotenoids content in comparison to the untreated counterpart, leading to an improved bioprotective effect (Leong, Oey, et al., 2016a). This study indicates that PEF could add value to carrots by improving the bioavailability of carotenoids and bioprotective effects. PEF technology has also been used for improving calcium infusion to the blanched carrots. This study showed that application of PEF at 1.9 kV/cm was effective in improving the hardness of blanched carrots by 57% with reduction of infusion time up to 12.12 ms and calcium concentration up to 300 ppm in comparison to traditional overnight soaking in calcium chloride solution after blanching at 60 C for 30 min. This study indicates that bioaccessibility of β-carotene for carrots after PEF treatment was comparable to conventional blanching (Leong, Du, & Oey, 2018).

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3.3

Grapes (Vitis vinifera)

In a recent study the potential of PEF (1.5 kV/cm, pulse frequency of 50 Hz, constant pulse width of 20 μs, and 243 1033 pulses) to improve the beneficial properties of juices obtained from grapes of the Pinot Noir variety (Vitis vinifera L.) at different times of maceration was evaluated (Leong, Burritt, & Oey, 2016a). For this purpose the authors used Caco-2 human intestinal cell lines and evaluated the bioprotective capacity of the juices treated by PEF against the oxidative stress induced by H2O2 in Caco-2 cells. Authors used as biomarkers to evaluate the health and cellular integrity: (1) cell viability and (2) lactate dehydrogenase (LDH) filtration. PEF effect on the antioxidant compounds (total phenolic compounds, anthocyanins, and vitamin C) as well as the quality of the juice was also determined. The authors obtained a considerable improvement (1224%) in the content of malvidin-3-O-glucoside in the juice pretreated with PEF compared to the control sample (untreated). They also found an increase in total polyphenols (161%), vitamin C (119%) and noted higher total antioxidant capacity determined by DPPH (161%). In addition, the juice pretreated with PEF also showed a higher bioprotective capacity (125% for cell viability and 130% for LDH filtration). It should be noted that the authors found a strong relationship between the bioprotective capacity and malvidin-3-O-glucoside, while the nonsignificant relationship was established between total antioxidant capacity and malvidin-3-O-glucoside or total polyphenols. In another study the same research group evaluated the impact of PEF (1.5 kV/cm, 15 or 70 kJ/kg) and maceration time (0 14 days) on anthocyanin release on juice obtained from Merlot grape variety (Leong, Burritt, & Oey, 2016b). Moreover, they also studied the bioprotective capacity of PEF-pretreated juices against the oxidative stress induced by H2O2 in Caco-2 cells. Apart from cell viability and LDH filtration, nitric oxide production was used as a biomarker to evaluate the health and cellular integrity. Similar to the results found for Pinot Noir variety, in the same study, the authors also observed an increased release of anthocyanins from the grape skin in PEF-pretreated juices. Moreover, anthocyanin amount and profile differed according to the PEF processing conditions and maceration time. Interestingly, they also observed a strong relationship between anthocyanins and the bioprotective capacity indicators. In addition, Leong, Oey, and Burritt (2016b) also found an increased anthocyanin release of anthocyanins (malvidin, delphinidin, and petunidin glucosidic derivatives) in the Merlot grape juices pretreated by PEF (1.4 kV/cm, frequency of 50 Hz,

Chapter 3 Health promoting benefits of PEF

20 μs, 1033 pulses, total treatment time of 20.66 ms) immediately after the treatment and during subsequent 48 h storage. Moreover, they also found an enhanced bioprotective capacity against the oxidative stress induced by H2O2 in Caco-2 cells, measured using the 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, which is a useful indicator of the mitochondrial metabolic activity.

3.4

Orange (Citrus sinensis)

Although orange is a matrix widely studied, the literature evaluating the effects of PEF on its nutrient and bioactive compounds’ bioaccessibility/bioavailability is scarce. Some works showed an increase in vitamin C bioavailability of PEF-treated (35 kV/cm, bipolar 4 μs pulse width at 800 Hz, for 750 μs) orange juice after 14 days at 4 C compared to untreated samples (Sa´nchez-Moreno et al., 2004, 2005).

3.5

Tomato (Solanum lycoperiscum)

The potential of PEF pretreatment at moderate intensity to improve lycopene bioaccessibility in tomato was investigated (Jayathunge et al., 2017). Moreover, in the same study, the authors evaluated the impact of blanching, ultrasound, and PEF at high intensity on the lycopene bioaccessibility once prepared tomato juice. They found an increased lycopene bioaccessibility when PEF was applied at moderate intensity (1 kV/cm/0, 1, 20, or 80 monopolar pulses, pulse width of 4 μs, 0.1 Hz frequency), to obtain the tomato juice, independently of the PEF processing conditions. Moreover, an increased release of trans- and cislycopene from tomato matrix during in vitro digestion was observed when blanching followed by PEF at high intensity was used to preserve tomato juice, obtaining  16% lycopene bioaccessibility (Jayathunge et al., 2017). PEF and heat treatment assisted by PEF were applied to different tomato fractions. Application of PEF processing and traditional heating (applied alone or in combination with PEF) induced permeabilization of tomato cell membranes. However, insignificant changes in β-carotene and lycopene bioaccessibility were observed under PEF or PEF heating assisted treatment in most of the selected tomato fractions. The exceptions were tissues and chromoplasts. In both the cases a significant decrease in lycopene bioaccessibility after application of PEF and PEF assisted by heating was noted. Moreover, similar trends were observed for β-carotene bioaccessibility found in chromoplast fraction.

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Authors found that the reduction in carotenoids bioaccessibility was probably connected with modification in chromoplast membrane as well as changes in carotenoids protein complexes. Differences in the effects of PEF on bioaccessibility among different tomato fractions were also probably related to the tomato structure complexity (Bot et al., 2018).

3.6

Milk and milk products

The application of PEF (1.4 1.8 kV/cm, 260 690 kJ/kg) or heat treatment (60 C, 80 C for 10 min) at different pH levels (4, 5, 7, and 9) on the in vitro peptic digestion of ovomucindepleted egg white has been investigated by Liu, Oey, Bremer, Silcock, and Carne (2017). An insignificant protein digestibility at 60 C was observed, whereas increasing the temperature up to 80 C was much more effective for digestibility and could be connected with increasing of solution turbidity and proteins aggregation. This study also showed that ovotransferrin had higher affinity to pepsinolysis in comparison to ovalbumin or lysozyme. This phenomenon was clearly observed when the temperature of heating increased from 60 C to 80 C and was more markedly in comparison to PEF treatment at mild conditions. The advanced analysis identified proteolytic fragments from ovalbumin and lysozyme, exhibiting varied resistance to pepsinolysis. PEF pretreatment at the highest energy used in the experiment (690 kJ/kg) and pH 4 increased protein digestibility to a similar level noted after heating at 80 C. Moreover, the turbidity of the solution was insignificant in comparison to the untreated sample, showing potential for the production of digestible protein drinks with high consumer sensorial acceptability (Liu et al., 2017).

3.7

Fruit and vegetable mixture combinations

Over the last years, fruit and vegetable mixture combinations have gained attention as a useful strategy to improve the nutritional, bioactive, and sensorial quality of the final products. For instance, some authors have evaluated how PEF can affect the bioaccessibility of nutrients and bioactive components of these type of food matrices (Buniowska, Carbonell-Capella, Frigola, & Esteve, 2016; Rodrı´guez-Roque et al., 2016). For instance, an increased vitamin C and phenolic compound bioaccessibility were found for PEF-treated (35 kV/cm, 1800 μs) fruit juice based products compared to thermally

Chapter 3 Health promoting benefits of PEF

treated (90 C, 60 s) sample (Rodriguez-Roque et al., 2015). The same research group also evaluated the effect of PEF (35 kV/cm, 4 μs bipolar pulses, 200 Hz, and 1800 μs) on carotenoids (cis-violaxanthin and neoxanthin) bioaccessibility of fruit drinks prepared from orange, kiwi, pineapple, and mango combined with water, milk, or soymilk. They reported an increase of  80% in the bioaccessibility of carotenoids compared to control (untreated) (Rodrı´guez-Roque et al., 2016). This might be attributed to the ability of PEF treatment to increase the carotenoid extractability (Esteve, Barba, Palop, & Frı´gola, 2009; Zulueta, Barba, Esteve, & Frı´gola, 2010, 2013). In another study, Buniowska et al. (2016) also found an increase in total polyphenols (37%), anthocyanins (16%), and carotenoid (12%) bioaccessibility of PEF-treated exotic juice (25 kV/cm, 50 400 pulses) compared to untreated samples. The authors attributed the enhanced bioaccessibility to rheological modifications after PEF treatments, thus facilitating the enzymatic hydrolysis of carotenoid esters into their free forms (Carbonell-Capella et al., 2016). Another possible explanation could be an enhanced degree of micellarization of carotenoids after PEF treatments, which resulted in increasing the amounts of the soluble carotenoids from the matrix.

3.8

Conclusion

PEF is a useful tool to improve carotenoid extractability of carrots. However, it depends on the electric field strength and frequency used. From the results of the different studies, it can be concluded that PEF processing of fruit juices can increase the bioaccessibility of carotenoids, due to its ability to promote cell disruption and improvements in enzymatic activity. The evaluation of bioprotective capacities using the Caco-2 cell assay is an interesting tool to show the potential of PEF to produce plant foods/extracts with a better phytochemical composition and that exhibits the ability to protect cells from oxidative stress. PEF 1 maceration can be a useful strategy to tailor phytochemical profile and obtaining plant foods/extracts with improved bioprotective capacities. Blanching followed by PEF at high intensity is a useful tool to increase lycopene bioaccessibility of PEF pretreated tomato products. Further studies need to be carried out to optimize PEF conditions for increasing bioaccessibility and bioavailability of nutritional compounds in the different food matrix.

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References Barba, F. J., Koubaa, M., do Prado-Silva, L., Orlien, V., & Sant’Ana, A. D. S. (2017). Mild processing applied to the inactivation of the main foodborne bacterial pathogens: A review. Trends in Food Science and Technology, 66, 20 35. Barba, F. J., Mariutti, L. R. B., Bragagnolo, N., Mercadante, A. Z., BarbosaCa´novas, G. V., & Orlien, V. (2017). Bioaccessibility of bioactive compounds from fruits and vegetables after thermal and nonthermal processing. Trends in Food Science and Technology, 67, 195 206. Barba, F. J., & Orlien, V. (2017). Processing, bioaccessibility and bioavailability of bioactive sulfur compounds: Facts and gaps. Journal of Food Composition and Analysis, 61, 1 3. Barba, F. J., Parniakov, O., Pereira, S. A., Wiktor, A., Grimi, N., Boussetta, N., . . . Vorobiev, E. (2015). Current applications and new opportunities for the use of pulsed electric fields in food science and industry. Food Research International, 77(4), 773 798. Bot, F., Verkerk, R., Mastwijk, H., Anese, M., Fogliano, V., & Capuano, E. (2018). The effect of pulsed electric fields on carotenoids bioaccessibility: The role of tomato matrix. Food Chemistry, 240, 415 421. Buniowska, M., Carbonell-Capella, J. M., Frigola, A., & Esteve, M. J. (2016). Bioaccessibility of bioactive compounds after non-thermal processing of an exotic fruit juice blend sweetened with Stevia rebaudiana. Food Chemistry, 221, 1834 1842. Carbonell-Capella, J. M., Buniowska, M., Barba, F. J., Grimi, N., Vorobiev, E., Esteve, M. J., . . . Frı´gola, A. (2016). Changes of antioxidant compounds in a fruit juice-stevia rebaudiana blend processed by pulsed electric technologies and ultrasound. Food and Bioprocess Technology, 9(7), 1159 1168. Esteve, M. I., Barba, F. J., Palop, S., & Frı´gola, A. (2009). The effects of nonthermal processing on carotenoids in orange juice. Czech Journal of Food Sciences, 27(Spec. Iss.), S304 S306. Granato, D., Nunes, D. S., & Barba, F. J. (2017). An integrated strategy between food chemistry, biology, nutrition, pharmacology, and statistics in the development of functional foods: A proposal. Trends in Food Science & Technology, 62, 13 22. Jayathunge, K. G. L. R., Stratakos, A. C., Cregenza´n-Albertia, O., Grant, I. R., Lyng, J., & Koidis, A. (2017). Enhancing the lycopene in vitro bioaccessibility of tomato juice synergistically applying thermal and non-thermal processing technologies. Food Chemistry, 221, 698 705. Leong, S. Y., Burritt, D. J., & Oey, I. (2016a). Evaluation of the anthocyanin release and health-promoting properties of Pinot Noir grape juices after pulsed electric fields. Food Chemistry, 196, 833 841. Leong, S. Y., Burritt, D. J., & Oey, I. (2016b). Effect of combining pulsed electric fields with maceration time on Merlot grapes in protecting Caco-2 cells from oxidative stress. Food and Bioprocess Technology, 9(1), 147 160. Leong, S. Y., Du, D., & Oey, I. (2018). Pulsed electric fields enhances calcium infusion for improving the hardness of blanched carrots. Innovative Food Science and Emerging Technologies, 47, 46 55. Leong, S. Y., Oey, I., & Burritt, D. J. (2016a). Pulsed electric field improves the bioprotective capacity of purees for different coloured carrot cultivars against H2O2-induced oxidative damage. Food Chemistry, 196, 654 664. Leong, S. Y., Oey, I., & Burritt, D. J. (2016b). Pulsed electric field technology enhances release of anthocyanins from grapes and bioprotective potential against oxidative stress. IFMBE Proceedings, 53, 47 50.

Chapter 3 Health promoting benefits of PEF

Liu, Y.-F., Oey, I., Bremer, P., Silcock, P., & Carne, A. (2017). In vitro peptic digestion of ovomucin-depleted egg white affected by pH, temperature and pulsed electric fields. Food Chemistry, 231, 165 174. Misra, N. N., Koubaa, M., Roohinejad, S., Juliano, P., Alpas, H., Ina`cio, R. S., . . . Barba, F. J. (2017). Landmarks in the historical development of twenty first century food processing technologies. Food Research International, 97, 318 339. Pue´rtolas, E., & Barba, F. J. (2016). Electrotechnologies applied to valorization of by-products from food industry: Main findings, energy and economic cost of their industrialization. Food and Bioproducts Processing, 100, 172 184. Pue´rtolas, E., Koubaa, M., & Barba, F. J. (2016). An overview of the impact of electrotechnologies for the recovery of oil and high-value compounds from vegetable oil industry: Energy and economic cost implications. Food Research International, 80, 19 26. Putnik, P., Barba, F. J., Lorenzo, J. M., Gabri´c, D., Shpigelman, A., Cravotto, G., & Bursa´c Kovacevi´c, D. (2017). An integrated approach to mandarin processing: Food safety and nutritional quality, consumer preference, and nutrient bioaccessibility. Comprehensive Reviews in Food Science and Food Safety, 16 (6), 1345 1358. Rodriguez-Roque, M. J., de Ancos, B., Sanchez-Moreno, C., Cano, M. P., ElezMartinez, P., & Martin-Belloso, O. (2015). Impact of food matrix and processing on the in vitro bioaccessibility of vitamin C, phenolic compounds, and hydrophilic antioxidant activity from fruit juice-based beverages. Journal of Functional Foods, 14, 33 43. Rodrı´guez-Roque, M. J., De Ancos, B., Sa´nchez-Vega, R., Sa´nchez-Moreno, C., Cano, M. P., Elez-Martı´nez, P., & Martı´n-Belloso, O. (2016). Food matrix and processing influence on carotenoid bioaccessibility and lipophilic antioxidant activity of fruit juice-based beverages. Food and Function, 7(1), 380 389. Roohinejad, S., Everett, D. W., & Oey, I. (2014). Effect of pulsed electric field processing on carotenoid extractability of carrot pure´e. International Journal of Food Science and Technology, 49(9), 2120 2127. Roohinejad, S., Oey, I., Everett, D. W., & Niven, B. E. (2014). Evaluating the effectiveness of β-carotene extraction from pulsed electric field-treated carrot pomace using oil-in-water microemulsion. Food and Bioprocess Technology, 7 (11), 3336 3348. Sa´nchez-Moreno, C., Cano, M. P., de Ancos, B., Plaza, L., Olmedilla, B., Granado, F., . . . Martı´n, A. (2004). Pulsed electric fields-processed orange juice consumption increases plasma vitamin C and decreases F2-isoprostanes in healthy humans. The Journal of Nutritional Biochemistry, 15(10), 601 607. Sa´nchez-Moreno, C., Pilar Cano, M., De Ancos, B., Plaza, L., Olmedilla, B., Granado, F., . . . Martı´n, A. (2005). Intake of Mediterranean vegetable soup treated by pulsed electric fields affects plasma vitamin C and antioxidant biomarkers in humans. International Journal of Food Sciences and Nutrition, 56(2), 115 124. Zhu, Z., He, J., Liu, G., Barba, F. J., Koubaa, M., Ding, L., . . . Vorobiev, E. (2016). Recent insights for the green recovery of inulin from plant food materials using non-conventional extraction technologies: A review. Innovative Food Science and Emerging Technologies, 33, 1 9. Zulueta, A., Barba, F. J., Esteve, M. J., & Frı´gola, A. (2010). Effects on the carotenoid pattern and vitamin A of a pulsed electric field-treated orange juice-milk beverage and behavior during storage. European Food Research and Technology, 231(4), 525 534.

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Zulueta, A., Barba, F. J., Esteve, M. J., & Frı´gola, A. (2013). Changes in quality and nutritional parameters during refrigerated storage of an orange juice-milk beverage treated by equivalent thermal and non-thermal processes for mild pasteurization. Food and Bioprocess Technology, 6(8), 2018 2030.

Further reading Breithaupt, D. E., Alpmann, A., & Carrie`re, F. (2007). Xanthophyll esters are hydrolysed in the presence of recombinant human pancreatic lipase. Food Chemistry, 103(2), 651 656.

Pulsed electric field (PEF) as an efficient technology for food additives and nutraceuticals development

4

Mahesha M. Poojary1, Marianne N. Lund1,2 and Francisco J. Barba3 1

Department of Food Science, University of Copenhagen, Frederiksberg C, Denmark 2Department of Biomedical Sciences, University of Copenhagen, Copenhagen N, Denmark 3Nutrition and Food Science Area, Faculty of Pharmacy, Universitat de Vale`ncia, Vale`ncia, Spain

4.1

Introduction

In the past few decades the global food processing industry has seen staggered technological changes to meet the demands of increasing population and to adapt to the varying consumers’ preferences. A number of new and promising technologies have been developed aiming at increasing productivity, quality, and safety attributes of foods as well as reducing waste, cost, and environmental impact. Since consumers are demanding for minimally processed “natural-like” foods, the nonthermal food processing technologies such as high-pressure processing, ultrasound treatment, pulsed light treatment, high-voltage discharge, cold plasma treatments are gaining increasing attraction. Among these emerging technologies the pulsed electric field (PEF) technology has received considerable attention in food processing and preservation sectors owing to its superior efficacy in microbial inactivation and quality preservation. Historically, this technology has been used for pasteurization, gene transfection, drying, and juice extraction from fruits and vegetables. In the recent years, it has also been escalated to extract a wide range of food additives and nutraceuticals from plants, algae, and industrial by-products (Misra et al., 2017).

Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00004-5 © 2020 Elsevier Inc. All rights reserved.

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Chapter 4 Pulsed electric field (PEF) as an efficient technology

Nutraceuticals are foods or food additives with pharmaceutical properties. They are derived from natural sources, primarily plants, and microorganisms (Granato, Nunes, & Barba, 2017). The term “nutraceuticals” is often linked or interchanged with other terms such as “functional foods,” “bioactive compounds,” “natural food ingredients,” and “dietary supplements.” Certain proteins, fatty acids, fiber, plant extracts, and secondary metabolites have been used as nutraceuticals to provide various health benefits and to prevent diseases (Moldes, Vecino, & Cruz, 2017; Nasri, Baradaran, Shirzad, & Rafieian-Kopaei, 2014). The demand for nutraceutical and functional foods is growing, particularly in the developed countries, and so the global nutraceutical market is expanding constantly. Industries are focusing on gentle and efficient (in terms of productivity and purity) techniques to produce nutraceuticals due to the cost and quality concerns. Recently, there has been a sharp increase in the number of industries and institutions adopting PEF equipment for the production of food additives and nutraceuticals. In biomolecule extraction sectors, it has been considered as a green technology as it substantially minimizes the use of toxic solvents. In addition, PEF has reported to have negligible impact on the structure and stability of the bioactive compounds and thereby helps in retaining their content and quality. Moreover, the PEF treatment at mild intensity can be used for bioproduction of various secondary metabolites of added value. However, the overall cost associated with equipment and implementation, operational energy and the scalability is a matter for further consideration.

4.2

Principles of pulsed electric field treatment

The extraction of metabolites from vegetative cells requires diffusion of solvent into the cell and subsequent mass transfer of metabolites into the bulk of the extraction medium. The process of extraction can be accelerated by modifying the physical properties of the sample (e.g., milling, maceration, and peeling) or by application of external extraction aids (such as heat, pressure, sonication, and agitation). The PEF treatment can act as an external aid that improves the efficiency of solvent extraction by improving diffusion and mass transfer through the phenomenon called membrane “electroporation” or “electropermeabilization.” In practice, PEF-mediated membrane electroporation is achieved by applying pulses of moderate-to-high electric field

Chapter 4 Pulsed electric field (PEF) as an efficient technology

67

Figure 4.1 Schematic representation of PEF extraction system (A), PEF induced creation of potential across the cell membrane (B), cell membrane before electroporation (C), electroporation of membrane (D), and resealing of membrane after PEF treatment (E). PEF, Pulsed electric field.

to the samples placed between two electrodes in a conducting medium (Fig. 4.1A and B). In extraction applications the electric field strength may vary between 0.1 and 20 kV/cm, while the pulse duration falls in the range of nanosecond to millisecond. The instrument size may range from laboratory scale to pilot scale batch or continuous flow reactors. The molecular mechanism of electroporation induced by PEF is not yet well established. However, the most accepted theory is based on the “transmembrane potential (ΔΦ) breakdown model” proposed by Sale and Hamilton (1968). According to this model, the application of external PEF on a biological cell induces a transmembrane potential (ΔΦ) across its semipermeable cell membrane. If the applied field strength (E) increases the transmembrane potential beyond the physiological transmembrane potential (termed critical transmembrane voltage), the membrane loses its semipermeable property and encompasses cell lysis. The critical ΔΦ value for eukaryotic cells has been estimated to be 1 V (0.7
1.5 V), although it varies based

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Chapter 4 Pulsed electric field (PEF) as an efficient technology

on the treatment and sample type (Coster & Zimmermann, 1975; Sale & Hamilton, 1968). The transmembrane potential for a cell suspended in a medium can be calculated according to Eq. (4.1) based on Maxwell’s equation on spherical coordinates (Maxwell, 1873) with the following assumptions: (1) the cell is spherical, (2) the radius of the cell (r) is far greater than the membrane thickness, and (3) the resistivity of the membrane is higher than those of the intracellular and the extracellular media. ΔΦ 5

3 rE 2

ð4:1Þ

Neumann, Sowers, and Jordan (1989) later proposed a modified equation (Eq. 4.2) for the calculation of ΔΦ, based on the Schwan equation of basic electromagnetic theory (Pauly & Schwan, 1959). In this equation, θ is the angle between a locus of the cell membrane at which ΔΦ is measured and the direction of the applied electric field. The equation indicates that the maximum ΔΦ or the highest degree of electroporation occurs when θ 5 0 or 180 or |cosθ| 5 1, that is, at loci of the cell membrane facing the electrodes. ΔΦ 5

3 rE  cosθ 2

ð4:2Þ

Similarly, Zimmermann, Pilwat, and Riemann (1974) and Zimmermann (1986) proposed a “dielectric breakdown” theory while investigating the disintegration of blood cells and microorganisms under PEF. According to this theory, the cell membrane can be modeled as a capacitor filled with a fluid of low dielectric constant. When a cell is present in a medium of relatively higher dielectric constant (e.g., liquid foods), the free charges will accumulate at either side of the membrane due to the difference in the dielectric constants (Fig. 4.1B). The application of external electric field increases transmembrane potential, ΔΦ (Eq. 4.1), and causes compression of the membrane due to attraction between opposite charges. When ΔΦ reaches around 1 V (critical transmembrane potential) with increasing E, the membrane loses its structural integrity by forming micropores (electroporation). A further increase in E results in irreversible electroporation due to the formation of larger pores. Overall, the mass transfer using electroporation is a dynamic process consisting of several sequences of events (Fig. 4.1B
E). Firstly, the application of external potential induces the charging of membranes (Fig. 4.1B) followed by destabilization of its molecular conformation and formation of pores (Fig. 4.1D). This step could occur in the time scale of microseconds,

Chapter 4 Pulsed electric field (PEF) as an efficient technology

however, depends largely on the nature of the cell and the strength of the applied electric field. The charging time for potato tissues was reported to be 3.0 μs when E 5 E0 5 180 V/cm (Angersbach, Heinz, & Knorr, 2000). In the second step, if the external electric field is continuously applied, the pore radii expand and additional pores are formed throughout the duration of pulses. This step lasts for several microseconds to a few milliseconds. In the last step, after the treatment duration, the pores may or may not be resealed, which is governed by the treatment parameters and the tissue type. The resealing could last for a few seconds to hours (Pataro, Ferrari, & Donsi, 2012) (Fig. 4.1E). It should, however, be noted that the formation of pores itself does not contribute to the mass transfer. The mass transfer is mediated by diffusion phenomenon, which occurs more readily when the cells are electroporated. The PEF-induced electroporation of cell membrane can be temporary or permanent, depending largely on the process parameters and the nature of the sample. Typically, temporary or reversible electroporation occurs when the pluses are applied in several nanoseconds to microseconds range. In case the pores reseal within a time scale of seconds (Granot & Rubinsky, 2008). At this time interval the intracellular matrix can be transferred to the extracellular space and vice versa, where extracellular components can be introduced into intracellular space. A greater number of pulses, longer pulse duration or an intense electric field strength can irreversibly or permanently damage the membrane integrity and cause cell lysis, possibly due to loss of homeostasis. However, in most cases, the permanent electroporation depends on both PEF parameters and the cell type. For instance, microbial cell lysis can be achieved by PEF treatment at higher electric field strength (E 5 20
50 kV/cm) or moderate electric field strength (E , 5 kV/cm) with varying pulse duration (1025
1023 s) (Timmermans et al., 2019; Toepfl, Heinz, & Knorr, 2007; Vorobiev & Lebovka, 2016), while electroporation of plant cells can be achieved at much lower electric field strength compared to microbial cells but generally with a longer treatment time (E 5 200
1000 V/cm for 1024
1021 s) (Vorobiev & Lebovka, 2016).

4.3

Factors affecting pulsed electric field treatment efficiency

The PEF treatment efficiency is affected by pulse parameters, physicochemical properties of the biomaterial (cell or tissue), and the treatment medium. In the majority of the extraction

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Chapter 4 Pulsed electric field (PEF) as an efficient technology

studies the PEF treatment has been used as a pretreatment step prior to the solvent extraction; therefore it is difficult to assess the individual effects of these parameters. However, the studies on microbial inactivation, gene transfection, and secondary metabolite production have clearly shown that the treatment parameters greatly affect the degree of electroporation. Therefore by controlling the PEF treatment parameters, one can achieve reversible or irreversible electrophoresis that could eventually be used in selective extraction of metabolites.

4.3.1

Pulse parameters

The pulse parameters such as electric field strength, pulse duration, pulse polarity, and pulse frequency could affect the degree of electroporation. However, the electric field strength and the treatment duration are considered as the two major influential factors. For parallel electrodes the applied electric field strength (E ) is defined as the ratio between the applied voltage (V) and the distance between two electrodes (d), as given by the following equation: E5

V d

ð4:3Þ

The treatment duration is defined by the product of pulse width (τ, in s) and number of pulses (n). In general, higher electric field strength and longer treatment time lead to better tissue damage by causing irreversible electroporation. For instance, the disintegration of onion tissue was reported to be increased with the electric field strength up to 500 V/cm; nevertheless, the further increase in the field strength did not increase in any ion leakage, presumably due to complete rupture of the cell membrane (Ersus, Oztop, McCarthy, & Barrett, 2010). It should, however, be noted that increasing electric field strength and treatment time accompanies increased energy consumption. Although lower electric field strength (E 5 20
100 V/cm) may induce electroporation to a certain extent, such pretreatment may not be suitable in extraction process as pores may reseal quickly after PEF treatment (reversible electroporation). In the case of potato tissues, for instance, reversible electroporation can occur if moderate electric field strength of 30
500 V/cm is applied in submicrosecond range (1025
1023 s) (Pereira, Galindo, Vicente, & Dejmek, 2009), while irreversible electroporation occurs when the applied electric field strength is above 700 kV/cm (Angersbach et al., 2000). In general, the longer pulse durations (100
1000 μs) and moderate

Chapter 4 Pulsed electric field (PEF) as an efficient technology

electric field strength beyond the critical field are optimal for electroporation of plant cells. The critical electric field strength for apple tissue, potato tissue, and potato cell suspensions is reported to be in the range of 150
200 V/cm; however, a significant permeabilization was noticed only when the field strength was raised to 400
800 V/cm (Fig. 4.2). In the case of microbial inactivation in liquid foods, a treatment with higher pulse frequency ( f 5 the number of pulses per unit time, Hz) for shorter duration reported to provide better efficiency (Amiali, Ngadi, Muthukumaran, & Raghavan, 2010; Charles-Rodrı´guez, Neva´rez-Moorillo´n, Zhang, & Ortega-Rivas, 2007). Conversely, lower frequencies ( f , 1 Hz) appear to cause greater degree of disintegration compared to higher frequencies ( f 5 1
5000 Hz) in plant tissues (Asavasanti, Ristenpart, Stroeve, & Barrett, 2011; Ersus et al., 2010). Moreover, it is essential to apply uniform electric fields to control degree of electroporation, which is in turn dependent on the pulse generator, the geometry of the electrodes, and the design of the PEF treatment cavity. The pulse shape (square, exponential, and oscillatory) and the pulse polarity (monopolar and bipolar) can also affect the efficiency of electroporation. In the majority of the laboratoryscale experiments, researchers have applied square wave pulse as it is energy efficient and delivers uniform electric fields. The exponential decay pulse systems are used in large-scale treatment system due to cost concerns; however, it generates irreproducible field intensity and consumes relatively more energy.

Relative permeability

1.0

0.8

0.6

0.4

Potato tissue Apple tissue Fish tissue Potato cell culture

0.2

0.0 0.0

0.4

0.8

1.2

1.6

2.0

Electric field strength (kV/cm)

Figure 4.2 Effect of electric field strength on the electroporation of different tissue types. Relative permeability represents degree of electroporation and was calculated based on conductivity measurement. Source: Reproduced with permission from Angersbach, A., Heinz, V., & Knorr, D. (2000). Effects of pulsed electric fields on cell membranes in real food systems. Innovative Food Science & Emerging Technologies, 1(2), 135
149. https://doi.org/10.1016/S1466-8564(00)00010-2.

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Chapter 4 Pulsed electric field (PEF) as an efficient technology

Oscillatory pulses are not recommended as cells are minimally damaged at these conditions due to discontinuous exposure of cells for an extended time interval (Amiali et al., 2010). In the case of pulse polarity, bipolar pulses are generally more efficient than the monopolar ones. In bipolar pulse mode, the orientation of the applied electric field is reversed for a continuous interval (half negative and half positive pulse). The interval between positive and negative pulse, referred to as delay time, may be adjusted for the symmetric and asymmetric distribution of the PEF during the treatment time. Since the application of PEF induces rapid movement of charged species across the membrane, a sudden reversal in the alignment of the applied electric field results in corresponding reversal in the direction of the ions. This can induce additional stress on the cell membrane and enhance the susceptibility of the membrane toward electroporation (Barbosa-Ca´novas, GongoraNieto, & Swanson, 1999). In addition, bipolar pulse also reduces asymmetric electroporation, minimizes deposition of unwanted solids on the electrode surface, and consumes lower net energy (Barba et al., 2015). Overall, a square wave bipolar pulse could be the most suitable choice for extraction applications.

4.3.2

Tissue parameters

The efficiency of electroporation is also dependent on the physicochemical properties of the cell or tissue such as its size, membrane structure and thickness, intracellular electrolytes, ionic mobility, and water content. The critical ΔΦ value varies with tissue types, based on the structure and rigidity of the membrane. Moreover, there is an inverse relationship between the cell size and the ΔΦ value (see Eqs. 4.1 and 4.2); therefore cells with larger size are readily electroporated compared to smaller cells. The soft tissues such as pericarp and mesocarp of fruits and somatic cells of onion, potato, and apple generally require moderate electric field strength (E 5 0.1
2 kV/cm) while hard tissues with excessive lignification, including seeds, stalks, and stem, involve higher field strength (ranges up to 20 kV/cm) to attain the critical ΔΦ. The treatment duration to achieve effective cell disintegration could also vary depending on the tissue type (see Fig. 4.3A for some examples). As PEF induces cell disintegration based on the electromechanical instability of the membranes, the efficiency of electroporation can also change with the growth phase and maturity level of a given tissue. In a comparative study, Saunders et al. (1995) showed that tobacco protoplasts without any secondary thickening require the lowest electric field

Chapter 4 Pulsed electric field (PEF) as an efficient technology

73

Figure 4.3 (A) Effect of PEF treatment time on the cell disintegration of different tissues and (B) specific energy requirement for tissue disintegration. PEF, Pulsed electric field. Source: (A) Adapted from Ben Ammar, J., Lanoiselle´, J.-L., Lebovka, N. I., Van Hecke, E., & Vorobiev, E. (2011). Impact of a pulsed electric field on damage of plant tissues: Effects of cell size and tissue electrical conductivity. Journal of Food Science, 76(1), E90
E97. https://doi.org/10.1111/j.1750-3841.2010.01893.x (Ben Ammar, Lanoiselle´, Lebovka, Van Hecke, & Vorobiev, 2011) and (B) reproduced from Barba, F. J, Parniakov, O., Pereira, S. A., Wiktor, A., Grimi, N., Boussetta, N., . . . Vorobiev, E. (2015). Current applications and new opportunities for the use of pulsed electric fields in food science and industry. Food Research International, 77, 773
798. https://doi.org/10.1016/j.foodres.2015.09.015.

strength (E 5 0.4
1.1 kV/cm) compared to soybean cell suspension with intact cell wall (E 5 3
2.5 kV/cm) and the germinating pollen with thick wall (E 5 7.0
8.5 kV/cm). Secondary metabolites such as alkaloids, glucosinolates, phenolic compounds, and water-soluble pigments (anthocyanins), are usually accumulated in the vacuoles of plant cells (Fosket, 1994). Vacuoles have relatively smaller diameter compared to the size of the cell and occupy 30%
80% of the volume of the cell. It is surrounded by a single-layered membrane, called tonoplast, of thickness 8
12 nm (De, 2000). Extraction of secondary metabolites from vacuoles, therefore, requires lysis of both cell membrane and tonoplast. Owing to its small size, tonoplast requires relatively greater electric field strength for effective electroporation when compared to that of cell membrane. In the case of onion tissues a critical electric field strength of 67 V/cm was required for the disintegration of plasma membrane, while it was above 200 V/cm for tonoplast when 10 pulses of 100 μs were applied (Asavasanti, Ersus, Ristenpart, Stroeve, & Barrett, 2010).

4.3.3

Media parameters

The effect of media composition on the PEF treatment efficiency is less understood. A few reports suggested that ionic

74

Chapter 4 Pulsed electric field (PEF) as an efficient technology

strength and conductivity of the medium may affect the membrane electroporation, although it varied based on whether reversible electroporation or irreversible cell lysis was considered (Pucihar, Kotnik, Kandusˇer, & Miklavcˇ icˇ , 2001). In the case of microbial inactivation and gene transfection studies, some authors have reported that the conductivity of the medium is inversely proportional to the cell death (Brambach, Michels, Franzke, & Kettler, 2013; Pucihar et al., 2001), while a reverse phenomenon is reported in other literature (Rols & Teissie, 1989). Other studies have shown that a lower extracellular conductivity increased the efficiency of reversible electroporation (Silve, Leray, Poignard, & Mir, 2016). In the case of extraction studies the conductivity of the medium is not generally altered. However, the plant tissues or food by-products contain high extracellular ionic compounds (salts) that may affect the size of the cell (due to osmosis) and electrical conductivity when they are suspended in the aqueous medium during PEF treatment. The presence of sugars in the medium can cause cell shrinkage and reduce swelling that is observed when electric field is applied (Nesin, Pakhomova, Xiao, & Pakhomov, 2011). Moreover, the high-conductivity media may raise the temperature during the PEF treatment due to Ohmic or Joule heating, particularly when high frequency and long treatment duration are applied. The heat generated during the PEF treatment may have a positive or negative effect on the extraction efficiency. In low conducting medium, pulses of larger field amplitude can be used to get the desired level of electroporation (Ivorra, Villemejane, & Mir, 2010).

4.4

Advantages of pulsed electric field
assisted extraction

The conventional solvent extraction generally requires large volume of solvents to achieve intended yield. Moreover, the extraction takes relatively longer duration under the normal condition or otherwise requires heating or extensive milling to accelerate the process. On the other hand, PEF-extraction is relatively mild and often requires less solvent and in most cases does not employ external heating. The membrane electroporation induced by PEF improves the mass transfer, decreases the total extraction time, and increases the extraction yield. Moreover, the amount of toxic solvents can be substantially reduced, and green solvents such as water and binary mixture of ethanol and water can be used to recover a range of

Chapter 4 Pulsed electric field (PEF) as an efficient technology

added-value compounds such as polyphenols, vitamins, carbohydrates, and pigments. Another major attribution for PEF-assisted extraction is its lower energy consumption. If the treatment parameters for a given tissue are optimized, it practically consumes lower energy (see Fig. 4.3B) when compared to conventional tissue-damaging techniques such as thermal treatments ( . 100 kJ/kg), application of mechanical forces (20
40 kJ/kg), and enzymatic-assisted disintegration (60
100 kJ/kg) (Barba et al., 2015; To¨pfl, 2006). The ability of PEF treatment to control the degree of electroporation and pore dimensions can be exploited for selective extraction of bioactive molecules with superior purity (Grimi, Praporscic, & Lebovka, 2007; Parniakov et al., 2015). Unlike other thermal and nonthermal techniques, including Soxhlet extraction, high-voltage electrical discharges (HVEDs), ultrasound treatment, and pressurized liquid extraction, PEF treatment does not break the cell wall, thereby limits the mass transfer of unwanted larger organelles into the extraction solvent. Besides, the treatment is typically applied without increasing the temperature of the extraction medium significantly; therefore it causes minimal damage to the target compounds located within intracellular and extracellular space. Moreover, PEF itself does not affect the structure and stability of small molecules, including polyphenols, amino acids, lipids, and carbohydrates. However, a few studies have demonstrated that intense PEF treatment can modify protein structure, reduce vitamin C levels, and isomerize carotenoids although the effect is less severe compared to conventional thermal processing (Oms-Oliu, Odriozola-Serrano, Soliva-Fortuny, & Martı´n-Belloso, 2009; Zhao, Yang, Wang, & Lu, 2009).

4.5

Application of pulsed electric field treatment in food additives and nutraceuticals extraction

The PEF treatment in combination with solvent extraction has been used to extract a wide range of bioactive compounds and food additives from various biomaterials, including plants, algae, and food processing by-products. The typical extraction system consists of a pulse generator and a treatment chamber (Fig. 4.1A). The pulse generator is essentially made up of a high-voltage DC power source, a capacitor to store energy, and a controlling switch to discharge high-voltage pulses through

75

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Chapter 4 Pulsed electric field (PEF) as an efficient technology

the sample placed in the treatment chamber. The treatment chamber comprises two electrodes separated by an isolating material. The following sections provide a brief review of PEFassisted extraction of different food additives and nutraceutical compounds from various biomaterials.

4.5.1

Dietary polyphenols

Dietary polyphenols are considered as the most important class of nutraceutical compounds. They are secondary metabolites produced by plants where they play major role in defense mechanisms against oxidants, pathogens, and UV-radiation. In humans, polyphenols exhibit a wide array of biological activities, including antioxidant, antiinflammatory, anticancer, and antiaging activities [see Watson, Preedy, and Zibadi (2013) for detailed information on the effect of polyphenols on human health and disease]. The biological activity of polyphenols is mainly attributed to their interventions with reactive oxygen species (ROS). They are also widely used as food preservatives as they show antioxidant, antimicrobial, and antiglycation (i.e., inhibitors of Maillard reactions) activities (Gutie´rrez-del-Rı´o, Ferna´ndez, & Lombo´, 2018) and are considered natural ingredients as opposed to synthetically produced antioxidants such as butylated hydroxytoluene. The ability of polyphenols to inhibit Maillard reactions has been shown to be caused by effective trapping of α-dicarbonyls, which are reactive intermediates formed during Maillard reactions. Thus fortification of polyphenols into foods has shown to inhibit the formation of several undesired compounds such as acrylamide, off-flavors (both oxidation and Maillard derived), and Maillard reaction products, such as the aforementioned α-dicarbonyls as well as Nε-carboxymethyllysine (Kahkeshani, Saeidnia, & Abdollahi, 2015; Li et al., 2018; Lund & Ray, 2017). Dietary polyphenols are commonly found in fruits, vegetables, tea, seeds, seed oils, wine, and chocolate. To date, more than 8000 phenolic compounds have been identified in vascular plants. Based on their structure, they are classified into phenolic acids, flavonoids, stilbenes, and lignans (Fig. 4.4). Phenolic acids are hydroxybenzoic acid and hydroxycinnamic acid derivatives and found largely in dried fruits and grains. Caffeic, ferulic, coumaric, and sinapic acids are the most commonly found phenolic acids in plants. Flavonoids are the most studied class of polyphenols, accounting more than 60% of dietary polyphenol. They are further divided into flavonols, flavones, flavanones, isoflavones, and anthocyanins based on their structural properties.

Chapter 4 Pulsed electric field (PEF) as an efficient technology

77

Figure 4.4 Chemical structures of some selected dietary polyphenols.

Considering the wide range of applications, the PEF treatment has been investigated to extract polyphenols from various plant sources, including grapes, olives, and apple pomace. Based on the literature, it is evident that grape and its bioproducts (grape pomace, winery wastes) are the most extensively investigated matrices for the recovery of polyphenols. Grape tissue is a rich source of phenolic acids (gallic acid), flavonoids (catechin and epicatechin), anthocyanins, and stilbenoid (resveratrol). Dietary polyphenols from grapes are associated with reduced risk of cardiovascular disease and cancer (Xia, Deng, Guo, & Li, 2010). In an early study, Praporscic, Lebovka, Vorobiev, and Mietton-Peuchot (2007) showed that the application of PEF with an electric field strength of 750 V/cm for 100 μs increases the expression of juice by 78%. A subsequent investigation showed that PEF pretreatment also increases anthocyanins and total phenolic contents of fermented grape skin ´ lvarez, & Raso, 2008). extracts (Lo´pez, Pue´rtolas, Condo´n, A Although several recent investigations show that a lower electric field strength (200
800 V/cm) is sufficient to damage most type of plant tissues, a relatively higher electric field strength (E $ 3.0 kV/cm) is required for effective damage of grape tissues. In grapes, polyphenols are mainly accumulated in the skin, which is made up of outer layers of the cutinized epidermis and inner thick-walled layers of the hypodermis consisting of

78

Chapter 4 Pulsed electric field (PEF) as an efficient technology

polyphenols (Fereidoon, Ambigaipalan, & Chandrasekara, 2018). A lower electric field strength may not be sufficient to damage the hypodermis; in such case, an intense PEF treatment or a moderate PEF combined with heat could enhance the tissue damage. A PEF pretreatment of grape by-products at 3 kV/cm for 15 s (pulse number 5 10 and frequency 2 Hz) increased the recovery of total polyphenols up to 1.6-fold than the control extraction at 70 C [c. 350 μmol gallic acid equivalents (GAE)/g dry matter (DM) vs c. 220 μmol GAE/g DM] (Corrales, Toepfl, Butz, Knorr, & Tauscher, 2008). In addition, PEF resulted in the highest antioxidant contents compared to high-pressure treatment and ultrasonic treatment. Interestingly, PEF also enabled the selective extraction of anthocyanin monoglucosides (Corrales et al., 2008). A similar study showed the PEF pretreatment (E 5 1.3 kV/cm and treatment time 5 1 s) enhanced the extraction of total polyphenol contents from grape skins, although the yield was only slightly higher than the control samples (21 GAE/g DM vs 19 GAE/g DM) (Boussetta et al., 2009). The study, however, showed that the electric field strength and the number of pulses have a positive impact on the degree of electroporation (Fig. 4.5), and the maximal disintegration of grape cells was observed when the applied

Figure 4.5 Effect of electric field strength and number of pulses on the disintegration of grape skin cells. Source: Adapted from Boussetta, N., Lebovka, N., Vorobiev, E., Adenier, H., Bedel-Cloutour, C., & Lanoiselle, J. L. (2009). Electrically assisted extraction of soluble matter from chardonnay grape skins for polyphenol recovery. Journal of Agricultural and Food Chemistry, 57(4), 1491
1497. https://doi.org/ 10.1021/jf802579x.

Chapter 4 Pulsed electric field (PEF) as an efficient technology

79

electric field strength was 1.3 kV/cm and the treatment time was 1 s. The study also revealed that the extract contains a range of polyphenols, including catechin, epicatechin, kaempferol-3-O-glucoside, and quercetin-3-O-glucoside. Similar results were also reported later by Takaki, Hatayama, Koide, and Kawamura (2011). In the following study, Boussetta, Vorobiev, Le, Cordinfalcimaigne, and Lanoiselle´ (2012) showed that aqueous ethanol can be used as a treatment medium to recover polyphenols from grape seeds. Although they have used a relatively higher electric field strength (E 5 8
20 kV/cm), the total polyphenol yield increased with the applied electric field strength. Moreover, the combination of thermal and PEF-treatment enhanced the yield significantly (Fig. 4.6A). A subsequent mechanistic investigation revealed that pulsed arcs can be used to breakdown hard tissues such as grape seeds and provide superior extraction efficiency of polyphenols with lower specific energy requirements (Boussetta, Lesaint, & Vorobiev, 2013). It is known that PEF treatment for a shorter duration does not raise the temperature of the medium significantly. A treatment with single pulse of 2 kV/cm could cause a temperature

Figure 4.6 (A) Effect of PEF strength and the treatment temperature on the recovery of polyphenols from grape seeds and (B) increase in the medium temperature during PEF treatment due to Ohmic heating. PEF, Pulsed electric field. Source: Adapted from (A) Boussetta, N., Vorobiev, E., Le, L. H., Cordin-falcimaigne, A., & Lanoiselle´, J. (2012). Application of electrical treatments in alcoholic solvent for polyphenols extraction from grape seeds. LWT
Food Science and Technology, 46, 127
134. https://doi.org/10.1016/j.lwt.2011.10.016 and (B) El Darra, N., Grimi, N., Vorobiev, E., Louka, N., & Maroun, R. (2013). Extraction of polyphenols from red grape pomace assisted by pulsed ohmic heating. Food and Bioprocess Technology, 6, 1281
1289. https://doi.org/10.1007/s11947-012-0869-7.

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Chapter 4 Pulsed electric field (PEF) as an efficient technology

rise of about 0.55 C and with ten repeated pulses of 700 V/cm, it could be up to 0.68 C (Angersbach et al., 2000). However, a treatment with higher pulse duration can cause Ohmic heating and raise the temperature of the medium significantly (Fig. 4.6B) that may have positive effects on extraction yield. In this line, El Darra, Grimi, Vorobiev, Louka, and Maroun (2013) investigated the effect of PEF combined with Ohmic heating to extract polyphenols from red grape pomace. They have reported that a moderate PEF treatment of electric field strength 400 V/cm for 5 s raised the media temperature to 50 C and a subsequent solid
liquid extraction with 30% ethanol in water for 60 min yielded up to 620 mg GAE/100 g DM of polyphenols, which was significantly greater than the control samples (440 mg GAE/100 g DM). In a similar study, Brianceau, Turk, Vitrac, and Vorobiev (2015) reported that application of PEF on fermented grape pomace in the absence of conducting medium (E 5 1.2 kV/cm, density ρ 5 1.0 g/cm3) and a subsequent solvent extraction in 50% ethanol in water enhanced the yield of polyphenols and anthocyanins up to 13% and 15%, respectively. Although the cell permeability increased with increase in the applied electric field strength (the highest degree of permeabilization reached when E 5 3.0 kV/cm), it did not increase the yield of polyphenols. Furthermore, the rate of polyphenol extraction increased with temperature (20 C
50 C) in untreated samples; however, the PEF pretreatment combined with external temperature did not enhance the yield greatly (Brianceau et al., 2015). Oilseeds and their by-products are rich sources of dietary polyphenols. Polyphenols in seeds are primarily located on the seed coat, while cotyledons contain low amounts of polyphenols. The main polyphenols found in seed coats belong to the family of phenolic acids and flavonoids. Seeds with lignocellulosic materials and low moisture content generally require intense PEF treatment for the effective disintegration of tissues. Seeds with high DM must be rehydrated with water, as the presence of water in the sample material increases the conductivity and voltage, thereby offers a better PEF treatment efficiency. Moreover, ionization of water at high electric field strength could destabilize the cell membrane as a result of increased polarization. In a recent study the effect of PEF treatment on the extraction of polyphenols from flaxseed hulls was investigated with emphasis on understanding the effects of operating parameters, including electric field strength, treatment duration, solvent composition, and the rehydration duration of the hulls (Boussetta, Soichi, Lanoiselle, & Vorobiev, 2014).

Chapter 4 Pulsed electric field (PEF) as an efficient technology

The results revealed that a pretreatment, including rehydration of hulls for 40 min and an intense PEF treatment with an electric field strength of 20 kV/cm for 10 ms followed by solid
liquid extraction with alkaline ethanol (20% in water), enabled the recovery of 80% polyphenols from the hulls. The yield increased with the applied electric field strength (0
20 kV/cm). The PEF treatment can also be combined with other cell disintegration techniques to enhance the extraction yield. For instance, Teh, Niven, Bekhit, Carne, and Birch (2014) showed that a PEF pretreatment in 20% ethanol (30 V, frequency 30 Hz, and treatment time 10 s) followed by ultrasound-assisted extraction (200 W at 70 C for 20 min) maximized the recovery of total phenolic compounds and total flavonoids from defatted hemp seed cake (Teh et al., 2014). Under these conditions, 0.94 and 0.87 mg GAE/100 g FW of total polyphenols and total flavonoids, respectively, were recovered from the samples. The authors later showed that the similar treatment conditions can also be applied for defatted canola seed cakes (Teh, Niven, Bekhit, Carne, & Birch, 2015). In a similar study a PEF treatment of 13.3 kV/cm for 10 μs with a frequency of 0.5 Hz followed by a solid
liquid extraction with 10% ethanol at 60 C for 1 h allowed extraction of up to 400 mg GAE/100 g DM of total polyphenols from sesame seed cake, which was about twofold higher than the untreated samples (Sarkis, Boussetta, Blouet, et al., 2015). The diffusion kinetic experiments revealed that the PEF pretreatment increased the rate of mass transfer significantly, thereby enabled rapid extraction of polyphenols. The PEF treatment was also applied to papaya seeds to extract phenolic compounds (Parniakov, Rosello´-Soto, et al., 2015). A pretreatment with exponential decay pulses of electric field strength reaching B13.3 kV/cm (1
300 pulses of 2 s) and subsequent solid
liquid extraction at 50 C for 3 h yielded up to 30 mg GAE/L polyphenols. However, the yield was considerably lower than that obtained by samples treated with HVEDs (100 mg GAE/L). A lower yield of PEF treatment compared to HVED was attributed to lower degree of cell disintegration caused by PEF than that of HVED (65% vs 100%). The PEF pretreatment was also applied to extract phenolic compounds from various other tissues, including stem, leaves, bark, and peels. In a comparative study, PEF pretreatment resulted in superior recovery of polyphenols from vine shoots (B24 mg GAE/g DM) than the ultrasound treatments (B15 mg GAE/g DM); nevertheless, the yield was lower than that obtained with HVED treatments (34 mg GAE/g DM) (Rajha, Boussetta, Louka, Maroun, & Vorobiev, 2014). Moreover, the

81

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Chapter 4 Pulsed electric field (PEF) as an efficient technology

specific energy required to initiate the polyphenol extraction was greater for PEF treatment (  50 kJ/kg) than HVED treatments (  50 kJ/kg); however, it was considerably lower than that required for US treatments (  1010 kJ/kg). The effect of electric field strength on the extraction yield of polyphenols from borage leaves was investigated (Segovia, Luengo, CorralPe´reza, Raso, & Almajano, 2015). The results showed that increase in the electric field strength from 0 to 5 kV/cm increased the yield. The highest yield of 1.2 mg GAE/g FW was obtained after tissues were pretreated at 5 kV/cm for 60 μs, which was 6.6-fold higher than the untreated samples. Similar results were reported by Zderic and Zondervan (2016) and Zderic, Zondervan, and Meuldijk (2013) while investigating the effect of electric field strength (0.1
1.1 kV/cm) on the extraction of polyphenols from tea leaves. The study highlighted that a longer treatment duration was more effective with moderate electric field (E 5 0.4 kV/cm for 2.5 s), while equivalent yields can be obtained in shorter time if higher electric field strength (E 5 0.9 kV/cm for 1.5 s) is used. A study conducted by Yu, Bals, Grimi, and Vorobiev (2015) confirmed that rapeseed leaves require a higher electric field (20 kV/cm for 200 ms) strength compared to stems (5 kV/cm for 200 ms) for effective extraction of polyphenols. However, the increase of the electric field was also accompanied by coextraction of other metabolites. The highest purity of polyphenols was obtained when PEF treatment was carried out at 5 kV/cm (91.0%) as compared to that at 20 kV/cm (66.3%) and without PEF treatment (66%), indicating that selectivity is dependent on the applied electric field strength.

4.5.2

Colorants

Food colorants play a vital role in attracting consumers and increasing appetite. They are added to foods and food products to provide new color, enhance the original color, or to correct the intrinsic color variation. In some cases, food colorants also specify the quality of food products as the change in the color indicates exposure of the product to light, temperature, air, or moisture. Nowadays, industries are looking for natural food colorants owing to consumer demands for natural additives and increasing strict legislation toward synthetic colorants. Furthermore, certain natural colorants act as food preservatives and also provide additional health benefits. Pigments, including carotenoids, chlorophylls, anthocyanins, and betanin, are the most widely used natural colorants. They are extracted from

Chapter 4 Pulsed electric field (PEF) as an efficient technology

biomaterials by using organic solvents or water based on their solubility. Natural colorants, however, are considerably expensive compared to their synthetic counterparts due to cost associated with raw material and subsequent purification process. Since the majority of the natural colorants are susceptible to oxidation, a gentle processing condition is needed to improve the quality and quantity of the target colorants. In this line, PEF technology, being a nonthermal technique, is gaining increasing popularity for the extraction of natural colorants from various biomaterials. Carotenoids are lipophilic yellow
orange
red pigments produced by plants, algae, and some fungi. The most common carotenoids present in plants include lycopene (bright red pigment present in tomatoes), β-carotene (red-orange pigment abundant in carrot, gac fruit, and pumpkin), and lutein (yellow-red colored xanthophyll found in marigold petals). Astaxanthin, zeaxanthin, fucoxanthin, lutein, and β-carotenes are commonly found in microalgae and seaweeds (Poojary, Barba, et al., 2016; Poojary, Roohinejad, et al., 2016). Carotenoids are conventionally extracted using nonpolar solvent such as hexane or a binary mixture of hexane and acetone. However, nonconventional techniques such as supercritical fluid extraction are shown to provide superior selectivity and yield (Poojary, Barba, et al., 2016; Poojary, Roohinejad, et al., 2016). Several investigations have revealed that PEF can be used to extract carotenoids from plants and algae. A PEF pretreatment with electric field of 5 kV/cm for 90 μs has shown to improve lycopene recovery from tomato pomace. Interestingly, PEF did not have a significant impact on the recovery of lycopene from pulp; however, the recovery from the peel increased with the applied electric field strength. Furthermore, PEF treatment reduced the extraction duration from 200 to 85 min (Luengo, ´ lvarez, & Raso, 2014). A pretreatment with relatively lower elecA tric field of 0.6 kV/cm with a longer treatment time of 3 ms had positive impact on the extraction of β-carotene from carrot pomace in oil-in-water microemulsion medium (Roohinejad, Oey, Everett, & Niven, 2014). Furthermore, the PEF treatment was also used to extract a range of carotenoids from microalgae, particularly from Chlorella vulgaris and Nannochloropsis sp. In contrast to plant cells, considerably intense treatment is essential to disintegrate algal cells (E 5 4
25 kV). In the case of C. vulgaris an electric field strength of $ 10 kV/cm in microsecond range was required for irreversible electroporation; however, a lower electric field strength of $ 4 kV/cm was also efficient, but a longer treatment

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Chapter 4 Pulsed electric field (PEF) as an efficient technology

duration in the millisecond range was required (Luengo, Martı´nez, Coustets, et al., 2015). The presence of secondary thickening and a smaller cell diameter makes them less susceptible for PEF. For instance, a PEF pretreatment with an electric field strength of 20 kV/cm for 1
4 ms did not improve the carotenoid recovery from Nannochloropsis sp. (Grimi et al., 2014). Moreover, carotenoids are localized in internal organelles such as chloroplast, and disintegration of chloroplast requires an intense treatment due to their smaller size. In such cases, PEF in combination with moderate heat may enhance the cell disintegration by irreversible electroporation (Lebovka, Praporscic, Ghnimi, & Vorobiev, 2005; Postma et al., 2016). For instance, a PEF treatment with electric field strength of 25 kV/cm for 75 μs and a moderate thermal treatment at 40 C allowed 4.5-fold higher recovery of lutein from C. vulgaris (Luengo, Martı´nez, ´ lvarez, & Raso, 2015). Bordetas, A Betanin is a water-soluble red glycosidic food colorant abundant in beetroot and Opuntia fruits (prickly pear). It has been approved by the European Union as food additive with an E number E162 (Aguilar et al., 2015). It is commonly added to jam, jelly, ice cream, sauces, liquorice, and juice as a coloring agent and antioxidant. However, betanin is an unstable molecule and highly sensitive toward temperature, pH, light exposure, and other oxidizing environments. The PEF technology has been shown as a gentle tool to improve the recovery of betanin from beetroots. A PEF treatment at an electric field strength of 1 kV/cm (270 rectangular pulses of 10 μs duration) followed by an aqueous extraction for 1 h released 90% of total red color from beetroot compared to mechanical pressing (Fincan, Devito, & Dejmek, 2004). Application of higher electric field strength for shorter duration (E 5 7 kV/cm for 10 μs) was also reported to enhance the rate of extraction of betanin from beetroot tissues (Lo´pez, Pue´rtolas, Condo´n, Raso, & Alvarez, 2009). A treatment consisting of 1000 V/cm electric field strength applied for 0.1 s caused rapid disintegration of beetroot tissues and increased the rate of extraction of betanin during temperature assisted aqueous extraction (Loginova, Lebovka, & Vorobiev, 2011). A moderate electric field strength of 0.6 kV/cm in millisecond range (40 ms) or an intense treatment at 6 kV/cm in microsecond range (150 μs) allowed up to sevenfold increase in the betanin yield (800
1000 μg/g FW) from red beet tissues compared to control samples, nevertheless, a treatment with microsecond range shown to be more energy effi´ lvarez, & Raso, 2016). In the case of cient (Luengo, Martı´nez, A Opuntia a PEF pretreatment of 50 pulses (exponential decay

Chapter 4 Pulsed electric field (PEF) as an efficient technology

pluses of decay time  10.0 μs) was found to be optimal for aqueous extraction of colorants from its peel and pulp (Koubaa et al., 2016). Anthocyanins are water-soluble red
purple
blue flavonoid pigments that occur in plant tissues such as fruits, leaves, petals, and rhizomes. Anthocyanin-rich extracts are widely used a natural colorant (E number E163) as well as food supplements due to their various health-promoting effects (Khoo, Azlan, Tang, & Lim, 2017; Mateus & de Freitas, 2008). Consumption of anthocyaninrich foods has been linked with the lower risks of cancer, diabetes, and coronary heart disease (Pojer, Mattivi, Johnson, & Stockley, 2013). PEF has been used to improve the extraction of anthocyanins from red cabbage (Gachovska et al., 2010). A PEF treatment at 2.5 kV/cm for 0.75 ms caused disintegration of cabbage tissues and subsequently enhanced the total anthocyanin recovery 2.5fold higher than the untreated samples. The stability studies revealed that PEF did not accelerate the degradation of extracted anthocyanins, which is contrary to some previous studies that have shown that PEF could degrade anthocyanins significantly (Zhang et al., 2007, 2008). A similar study has shown that a PEF pretreatment at 3.4 kV/cm for 105 μs caused efficient disintegration of purple-fleshed potato and consequently resulted in a higher recovery of anthocyanins in aqueous medium (Pue´rtolas, ´ lvarez, & Raso, 2013). Similarly, PEF treatCregenza´n, Luengo, A ment enabled selective extraction of anthocyanins from fermented grape pomace with a 5.3-fold increase in the concentration (Barba, Brianceau, Turk, Boussetta, & Vorobiev, 2015).

4.5.3

Lipids

Vegetable oils are obtained from plants and algae. In plants, they occur mainly in seeds and nuts. They are important ingredients in many food products and added to improve taste, texture, and appearance. Oils rich in polyunsaturated fatty acids (flaxseed oil and walnut oil) are used as food supplements due to their health-promoting effects. They are usually extracted either by mechanical pressing (cold extraction, e.g., virgin olive oil production) or by chemical extraction using organic solvents such as hexane. The latter method is commonly practiced in commercial-scale processing of common vegetable oils as it is easier, faster, and produces better yield. In recent years, nonconventional techniques such as supercritical fluid extraction have also been used to extract vegetable oils as it does not require harmful solvents and has the lowest environmental impact (Bockisch, 1998).

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The application of PEF pretreatment before the conventional extraction of vegetable oils from oilseeds has shown to improve the extraction yield. For instance, a PEF pretreatment of 100 pulses at 1.3 kV/cm resulted in 7.4% increase in the virgin olive oil yield from fresh olives (Guderjan, To¨pfl, Angersbach, & Knorr, 2005), while the yield increased up to 54% when the olive paste was pretreated at 2 kV/cm for 150 μs (Pue´rtolas & Martı´nez De ˜ o´n, 2015). In addition, the PEF treatment presented Maran increased levels (up to 34%) of phytosterols in the extracted maize germ oil (Guderjan et al., 2005). Similarly, a PEF treatment with electric field strength of 7.0 kV/cm and 120 pulses resulted in irreversible permeabilization of rapeseed tissues and increased oil yield slightly higher compared to control extraction (Guderjan, Elez-Martı´nez, & Knorr, 2007). Moreover, PEF treatment enabled 20% increase in the α-tocopherol content in the extracted oil. Likewise, up to 5% increment in the oil yield was obtained after sesame seeds were treated by PEF (E 5 20 kV/cm, exponential decay pulse); however, the efficiency was lower than that obtained by HVED treatment (Sarkis, Boussetta, Tessaro, Marczak, & Vorobiev, 2015). A recent study showed that PEF can be used for commercial-level extraction of oils using pilot-scale ˜o´n, 2015). PEF treatment system (Pue´rtolas & Martı´nez De Maran A treatment with an electric field strength of 2 kV/cm improved the olive oil yield from olive paste by 13% and coextracted phenolic compounds, phytosterols, and tocopherols up to 11.5%, 9.9%, and 15.0%, respectively, higher than the control experiments (Pue´rtolas & Martı´nez De Maran˜o´n, 2015). Certain microalgae are also abundant and sustainable sources of microbial oil that can potentially substitute vegetable oils. They contain healthy fatty acids (omega-3 fatty acids) that can be used as food ingredients (Wells et al., 2017). However, the major investigations so far were directed toward using algal biomass for biofuel production (Zbinden et al., 2013).

4.5.4

Stabilizers

Stabilizers are compounds, usually polysaccharides, which are added to food products to provide and preserve structure, stability, and viscosity. Gelatin, starch, pectin, alginate, cellulose, and seed gums are well-known stabilizers used in food industries. The PEF technology has been used to extract stabilizers, particularly pectin, from various plant biomaterials. Pectin is a plant cell wall polysaccharide found abundantly in apple pomace, pears, plums, and citrus fruit peels. It is a source of dietary fibers and is extensively used as gelling agent in jams and jellies and as

Chapter 4 Pulsed electric field (PEF) as an efficient technology

stabilizers in various fruit- and milk-based beverages. It is traditionally extracted by boiling samples in acidic water followed by alcohol precipitation. Certain nonconventional techniques such as ultrasound-assisted extraction, microwave-assisted extraction, subcritical water extraction, and enzyme-assisted extraction have been shown to enhance the extraction efficiency greatly [reviewed in Adetunji, Adekunle, Orsat, and Raghavan (2017)]. Compared to other extraction techniques, the PEF-assisted extraction of pectin from plant tissues is much less investigated. Since pectin is a complex polysaccharide network present in the cell wall of plant tissues, PEF has the least effect on their extraction, although a study reported that PEF can improve pectin recovery from apple pomace (Yong-guang, Xiang-dong, Feng-xia, Qing-yu, & Gui-dan, 2009). However, the application of intense PEF of 18
30 kV/cm for a longer duration of 0.8
2.4 ms has been reported to reduce the degree of esterification and molecular weight of pectin in sugar beet pulp (Ma, Yu, Zhang, & Wang, 2012). The low molecular weight pectin is used as additives in beverages and in drug delivery applications.

4.5.5

Proteins

Protein is one of the essential nutrients. They provide energy and play a major role in growth and development. There is a growing interest among industries to produce protein-rich food products such as protein bars and protein-rich energy drinks, snacks, and breakfast meals. They are widely sold in the market with the aim of providing various benefits, including improving athletic performance, managing weight loss, and controlling appetite and satiety. Certain proteins and peptides also serve as functional ingredients by improving the physicochemical properties of foods and by providing additional health benefits and preventing disease. In addition, protein hydrolysates are also used to elicit flavors in food products. There is growing consumer demand for plant- and microalgae-based protein ingredients. In this view the use of PEF technology for recovering proteins from various plants, microalgae, and by-products has been investigated (Rajha et al., 2014); nevertheless, these studies do not state the potential application of extracted proteins. In general, an intense treatment is required to extract proteins from plant tissues. For instance, an electric field strength up to 5 kV/cm did not cause significant enhancement in the protein recovery from rapeseed leaves, while a treatment at 20 kV/cm resulted in up to 80% recovery (Yu et al., 2015). The PEF pretreatment, however,

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improves the rate of diffusion and avoids the need of high temperature and, thereby, improves the extraction efficiency (Parniakov, Rosello´-Soto, et al., 2015; Sarkis, Boussetta, Blouet, et al., 2015; Sarkis, Boussetta, Tessaro, et al., 2015). In the case of microalgae a pretreatment with electric field strength of 30.5 kV/cm for 1 μs improved the protein yield by 25% from Auxenochlorella protothecoides. Moreover, PEF pretreatment was found to be ideal for selective extraction of water-soluble proteins from marine algae Nannochloropsis sp. (Parniakov et al., 2015) and Ulva (Polikovsky et al., 2016). A comparison of PEF treatment efficiency to extract total cytoplasmic proteins from Nocardiopsis salina and C. vulgaris revealed that cells of C. vulgaris require relatively milder treatment conditions (E 5 3 kV/cm, pulse duration 5 2 ms) compared to N. salina (E 5 6 kV/cm, pulse duration 5 2 ms) due to their smaller size (Coustets, Al-Karablieh, Thomsen, & Teissie´, 2013). The rigid cell wall structures of these microalgae did not affect the recovery of proteins (Coustets et al., 2013).

4.6

Application of pulsed electric field treatment in plant secondary metabolites production

Plants accumulate secondary metabolites when they are subjected to external biotic (bacteria, fungi, viruses, or parasites) or abiotic stress (temperature, draught, light, mechanical wound). These secondary metabolites play an important role in defense mechanisms of plants against pathogens and herbivores and also for the regulation of the primary metabolites. On the other hand, these secondary metabolites have remarkable biological activities and increasingly used as medicine, nutraceutical, or food additives. As described in the earlier sections, the application of electrical pulses on plant tissues induces migration of intra- and extracellular ions and change in cell shape and membrane structure. Moreover, the application of PEF treatments at low to moderate intensities, a reversible electroporation can be induced, which is not lethal. These cumulative effects can be utilized to stress plant cells and, in turn, to induce the production of secondary metabolites. The exact molecular mechanism of stress induced by PEF to produce secondary metabolites is not yet available. It is, however, presumed that PEF can induce the accumulation of ROS within the cell, leading to oxidative stress that, in turn, activate the production of secondary

Chapter 4 Pulsed electric field (PEF) as an efficient technology

metabolites as a part of the defense mechanism. Besides, PEF at low-to-moderate intensities can boost the enzymatic activity in biological tissues (Poojary, Barba, et al., 2016; Poojary, Roohinejad, et al., 2016) that can further enhance the biosynthesis of certain secondary metabolites. In combination with plant biotechnology techniques, the PEF technology has been successfully utilized in the bioproduction of various classes of secondary metabolites, including phenolics, terpenoids, and, nitrogen and sulfur-containing bioactive compounds. When suspension cultures of Taxus chinensis were exposed to PEF at 0.1 V/cm for 30 min with a frequency of 50 Hz, about 30% increased intracellular accumulation of taxuyunnanine C, a bioactive taxoid, was noticed (Ye, Huang, Chen, & Zhong, 2004). In addition, the treatment also enhanced extracellular accumulation of phenolic compounds and taxuyunnanine C in the range of 6%
30%. A chemiluminescence assay for ROS revealed that PEF induced 35% higher ROS accumulation than that in the control. The PEF treatment also resulted in increased accumulation of O2•2 and H2O2, indicating the treatment induced oxidative burst, which in turn might have increased the accumulation of secondary metabolites. A similar study showed that the application of PEF at an electric field strength between 1.6 and 2.0 kV increased the biosynthesis of isoflavonoids (genistein, genistin, daidzein, and daidzin) in soy plant callus suspension culture by inducing physical stress on the tissue (Gueven & Knorr, 2011). The study showed that the treatment in the range of 1.5
1.8 kV/cm for 36 s causes reversible electroporation of cell membranes. However, a further increase in the electric field strength resulted in a decrease in isoflavonoid content, possibly due to irreversible electroporation. A subsequent study showed that the application of PEF (E 5 1.6 kV/cm, 10 pulses) stimulated the anthocyanin metabolism in the suspension culture of Vitis vinifera L. cv. Gamay Fre´aux by 30%
71% higher than the control, depending on the growth period (Cai et al., 2011). Moreover, the treatment also enhanced extracellular concentration of phenolic compounds by 11%. Similar results were reported in their subsequent study with the V. vinifera cell cultures, where PEF treatment resulted in 1.7-fold increase in the ¨ tu¨k, & total anthocyanin content (Saw, Riedel, Cai, Ku Smetanska, 2012). In the case of plant tissues the application of PEF in the range of 0.6 kV/cm (120 pulses) promoted the biosynthesis of phytosterols in maize germ cells by inducing stress response

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(Guderjan et al., 2005). Similarly, application of PEF in the range of 200
400 V/cm for 1 ms affected the metabolism of wounded potato tissues, characterized by changes in the hexose and amino acid pools after 24 h of treatment (Galindo et al., 2009). In the case of tomato fruits the application of PEF in the range of 0.4 2 2 kV/cm for 20 2 120 μs and a subsequent incubation for 24 h at 4 C improved the biosynthesis of polyphenols and lycopene up to 44% and 37%, respectively (Vallverdu´-Queralt, ´ -Queralt, Oms-Oliu, Odriozola-Serrano, et al., 2013; Vallverdu ´ -Queralt et al., 2013). The High et al., 2012; Vallverdu Performance Liquid Chromatography (HPLC) characterization of samples further revealed that the treatment particularly enhanced the levels of hydroxycinnamic acids, including caffeic acid-O-glucoside acid, chlorogenic acid, and caffeic acid by 170%, 152%, and 140%, respectively; and in the case of carotenoids the concentrations of 13-cis-lycopene, 9-cis-lycopene, and α-carotene were increased by 140%, 94%, and 93%, respectively (Vallverdu´-Queralt, Oms-Oliu, et al., 2013). The increase in the total polyphenol content was linked to the PEF-induced activation of phenylalanine ammonia-lyase, an enzyme involved in ¨ rsul, Gueven, biosynthesis of polyphenols in plants (Gu ´ -Queralt, Oms-Oliu, et al., Grohmann, & Knorr, 2016; Vallverdu 2012). In a successive study, the authors reported that the application of moderate-intensity PEFs (E 5 1 kV/cm for 64 μs, 0.1 Hz) on the whole fruit followed by incubation at 4 C for 24 h combined with a subsequent high-intensity PEF treatment on the extracted juice (E 5 35 kV/cm for 1500 μs, 100 Hz) is an effective protocol to increase the levels of phenolic compounds ´ -Queralt, Odriozola-Serrano, et al., in tomato juice (Vallverdu 2012).

4.7

Conclusion

Overall, the PEF technology is an efficient tool to produce a range of added-value compounds derived from plants and microorganisms. Owing to its nonthermal mode of operation, it is ideal for selective recovery of thermolabile compounds such as flavonoids, anthocyanins, carotenoids, betanin, and polyunsaturated fatty acids. Besides, as pretreatment step prior to conventional extraction, it reduces the extraction time and the need of organic solvents greatly. Moreover, PEF at low-tomoderate intensities induce abiotic stimulus or stress on plant tissues and is proposed as a promising tool for biosynthesis of

Chapter 4 Pulsed electric field (PEF) as an efficient technology

various secondary metabolites in cell cultures and food products. Although it is considered as energy efficient, the treatments parameters such as the electric field intensity and the treatment duration must be optimized in order to implement it as a cost-effective method in industrial levels. Further research should be directed toward understanding the effect of PEF on the stability of food components and also on developing pilot scale continuous treatment systems for high-throughput production of food additives and nutraceuticals.

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Chapter 4 Pulsed electric field (PEF) as an efficient technology

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chinensis. Biotechnology and Bioengineering, 88(6), 788
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5

Robin Ostermeier1,2, Kevin Hill1, Stefan To¨pfl1 and Henry Ja¨ger2 1

Elea Vertriebs- und Vermarktungsgesellschaft mbH, Quakenbru¨ck, Germany Department of Food Science and Technology, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria 2

5.1

Definition of “snacks”

Snacks are often considered as a small amount of food consumed between meals. Depending on the literature, the definition of snacks is based on the time of the day when they are consumed, the type or amount of ingested food, or even the location at consumption (Hess, Jonnalagadda, & Slavin, 2016). In general, every food consumed between regular meals is considered as a snack, including sandwiches, fresh fruits, confectionary, and crisps. What kind of snacks is consumed is highly dependent on the region. For instance, the sales for confectionary snacks in Europe are the highest, with a market share of $47 billion, while in North America salty snacks are leading the market with a share of $28 billion (The Nielsen Company, 2014). The lack of consensus in the definition of snacks in the literature makes it rather hard to determine whether snacking prevalence has increased or not in the last years. Overall, savory snacks include a broad variety of products such as chips, puffed and baked snacks, extruded snacks, popcorn, meat snacks, and snack nuts (Mathieu, 2014). While the global market for savory snacks continues to grow from $94 billion in 2015 to $138.2 billion estimated by 2020, the consumer demand has shifted from regular snacks, such as regular potato chips, toward healthier options such as baked or veggie chips (Riley, 2017). According to Levelle (2016), the veggie chips market has experienced an annual growth of 17% from 2016 to 2017. Veggie chips include raw material mainly from sweet Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00005-7 © 2020 Elsevier Inc. All rights reserved.

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potatoes, carrots, parsnip, or beetroot. Consumer choices on healthy snacks target not only higher nutrient, vitamin, and fiber availability but also low fat and acrylamide content. The growing trend of veggie chips, and therefore, unusual raw materials, production processes, and final product, poses new challenges for the primary producers, processors, and supply chain. Although different definitions for snacks are available in the literature, “snacks” will refer in this chapter to savory snacks, mainly whole tuber or root products that are cut, sliced, or shredded and afterward cooked, fried, dried, or partially processed. Nuts, dough- and starch-based snacks, or extruded products are not considered, since pulsed electric field (PEF) applications on such products have not been developed yet.

5.2

Need for healthy snacks

With consumers adopting fast-paced lifestyles, healthy snacks are becoming more important as often a snack may even replace a whole meal. Therefore the nutritional value of a snack is a growing concern for the consumers, whose purchase choices target products with health claims such as “low sugar” or “low fat” (Stephens, 2018). Innova Market Insights (2018) has listed “From snacks to mini meals” as its number 8 global food trend for 2018. This opens up the market for new, innovative snack products. Savory snacks are leading the global market, with the launch activity representing about 35% of the total activity. In addition, 4% of the snack launches have been labeled as “low fat” and 6% held the “no trans fat” claim. Moreover, the amount of “low sugar” claims increased from 2% in 2012 to almost 4% in 2018, further illustrating the importance of healthy products in today’s society. As the majority of snacks, especially chips, are still being fried, it is hard to produce a snack considered as healthy. Frying refers to food cooking in oil. When the product is placed in the fryer, a variety of reactions take place. First, the temperature of the product surface rises until it reaches the boiling point of water. The surface water starts turning into steam, thus evaporating from the product, which leads to the formation of air bubbles. Due to the evaporation of the water, pores are formed on the product surface, through which the hot oil can be absorbed. Because of the high temperature of the oil, the starch in the product starts to gelatinize, forming a crust around the product (Brennan, 2006). This process, however, poses a series of challenges for the

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks

industry. First, due to the immersion of the product into the hot oil, the fat content of such snacks is rather high, with around 30% 40% fat, resulting in a high-caloric product. Another serious problem is the formation of acrylamide. It is especially formed in a low moisture food matrix processed at high temperatures. Therefore chips are products with high acrylamide levels (600 2000 µg/kg) as at the end of the frying process low moisture levels are present (Das & Srivastav, 2012).

5.3

Acrylamide formation in snacks

Acrylamide is a chemical compound that belongs to the amides group. It is a white, crystalline solid with the chemical formula C3 H5 NO: The International Agency for Research on Cancer has classified acrylamide as a probable human carcinogen and it is suspected to have neurotoxic effects that can cause distal axonopathy, a condition characterized by ataxia and skeletal muscle weakness (Das & Srivastav, 2012). Acrylamide first came to attention in 2002 when the Swedish National Food Administration and the University of Stockholm discovered high amounts of acrylamide in carbohydrate-rich foods processed at temperatures of 120 C and above. There are several ways in which acrylamide can be formed, although the Maillard reaction is the most relevant for the food industry. During the Maillard reaction asparagine undergoes thermally induced decarboxylation and deamination. This process is greatly enhanced in the presence of reducing sugars such as glucose and fructose. The main mechanism of acrylamide formation is therefore the reaction of carbonyl compounds with asparagine, resulting in the formation of a decarboxylated Schiff base. As the Maillard reaction (Fig. 5.1) is also responsible for the formation of aroma and color compounds in the final product, such important processing step cannot just be neglected (Mottram, Wedzicha, & Dodson, 2002). Beside the before mentioned mechanism, minor amounts of acrylamide can also be formed from acrolein. When oil is heated to temperatures above the smoke point, glycerol is degraded to acrolein. Unsaturated fatty acids are known to further increase the formation of acrolein. In addition, polyunsaturated fatty acids can also derive in acrolein as a result of oxidization (Mestdagh, De Wilde, Delporte, Van Peteghem, & De Meulenaer, 2008). There are different factors influencing the formation of acrylamide, such as the concentration of the precursors, sugar and

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Figure 5.1 Formation of acrylamide during the Maillard reaction.

asparagine, the processing temperature and time, the pH, and the water content. It has been reported that snack foods from potato varieties with higher levels of reducing sugars lead to an increased formation of acrylamide (Serpen & Go¨kmen, 2009). The effect of the temperature and time has already been studied. As expected, the acrylamide content increases with increasing frying time. However, Rydberg et al. (2005) observed that after a prolonged processing time, the acrylamide content decreased again because the degradation of acrylamide becomes predominant. Barutcu, Sahin, and Sumnu (2009) found that the acrylamide content was 140 times higher in microwave-cooked mashed potato samples when the heating time was increased from 100 to 150 s. Regarding the concentration of precursors, it has been reported that an increase in monosaccharides (mainly glucose and fructose) and asparagine increased the acrylamide content in the product. Consequently, lowering the content in reducing sugars or asparagine leads to a reduction of acrylamide in the product. The addition of other free amino acids or protein-rich food components has been reported to greatly decrease the acrylamide formation. This is most likely due to competing reactions or the covalently binding of formed acrylamide (Rydberg et al., 2005). With respect to the pH value the formation of acrylamide seemed to be optimal at a pH value of 8. Addition of HCl, ascorbic acid, or citric acid into the food preparation led to a decrease in pH and the reduction of acrylamide levels. This can be explained by a decrease in the acrylamide formation rate at

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks

low pH, which is also responsible for the rapid degradation of this compound (Mulla, Bharadwaj, Annapure, & Singhal, 2011). Because of the scientific evidence supporting the negative impact of acrylamide on the human health, the European Union (EU) has adopted the commission regulation 2017/2158, which came into force on April 11, 2018. This is the first legally binding regulation with regards to acrylamide reduction in food. The long holding period (from 2002 till 2018) for such a regulation to come into force evidences the complexity of this issue and the workload involved. The main problem concerning acrylamide relies on the inability for its complete removal from foodstuff, as it is mainly formed via the Maillard reaction. Moreover, the levels of its two precursors in the raw material depend on the seasonality, local climate, and storage condition, which results in varying acrylamide content in different finished products. As a result, the regulation is using the as low as reasonably achievable principle. In addition, certain benchmarks have been set up on the extent of acrylamide reduction in certain products. For potato chips the current benchmark is at 750 µg acrylamide/kg product, a value already proposed by Nordic countries in 2016. These benchmarks might be realistic when interventions for acrylamide reduction are not in place yet. However, when mitigation measures are implemented, reaching such concentrations might be a challenge (Knott & Hill, 2018). While for the industry acrylamide is already a big concern, for customers the problem starts to come into the picture through press or media. According to a study conducted by DSM’s Global Insight Series, only 22% of the surveyed consumers from France, the United Kingdom, and the United States are aware of the health issues linked to acrylamide, while in Germany this value reaches 54%. Those who are aware, however, expect the producer to take actions in order to reduce the acrylamide content in food products (Green, 2018).

5.4

Impact of raw material on acrylamide formation

As already mentioned, one factor that influences the acrylamide content in the final product is the composition of the raw material. A high amount of reducing sugars will increase the acrylamide formation during processing. Therefore the snack industry is seeking raw materials with reduced amounts of sugars falling back on certain breeds. For potato chips, industrial suppliers aim for a reducing sugar content of about 0.15%. Varieties that meet those standards, for example, include

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“Marlen,” “Pirol,” or “Lady Rosetta” (Krause, Bo¨hm, & Loges, 2005), are just grown to supply the chips industry. However, there are more factors that influence the properties of the potato, such as the time of harvest, storage, and reconditioning. Potatoes that are harvested later in the season tend to present increased levels of reducing sugars, as starch is turned into sugar naturally to prepare the tuber for sprouting. This change is further facilitated by low storage temperatures. Storage conditions below 10 C increase the reducing sugar content leading to a browner product after processing. The ideal storage temperature for potatoes is about 10 C 13 C (Knott & Hill, 2018). For other snack products such as sweet potato chips, the issue becomes even more serious. As sweet potatoes present about the same amount of reducing sugars and asparagine as regular potatoes in a freshly harvested state, the same amount of acrylamide would be expected to be formed during processing (Lim, Jinap, Sanny, Tan, & Khatib, 2014). However, sweet potato tends to be more susceptible to acrylamide formation most likely due to the high content of sucrose, which is about 10 times higher than that in regular white potatoes. Although sucrose itself is not a reducing sugar, Pritchard and Adam (1994) stated that an increased sucrose content during maturation translates into an increased glucose content after storage for an extended amount of time. Similar issues arise for other raw materials used for veggie chips production too, such as carrots, parsnip, or beetroot. As already mentioned, potato breeders have developed low-sugar varieties over the years to meet the specifications from chips manufacturers on easily processable raw materials resulting in reduced browning and acrylamide formation. As veggie chips are relatively new on the market, low-sugar varieties are not available for the chips industry yet. Furthermore, the market for such special breeds is quite narrow as the majority of sweet potatoes, carrots, parsnip, or beetroots are not intended for use as fried chips and the veggie chips market is still limited as compared to the potato chips market. This makes it more difficult to produce vegetable chips with low acrylamide content. Although veggie chips are often considered as a healthy, colorful product with a new and different taste in comparison to potato chips, the high amount of sugars and tendency for browning during frying highlight the need for process and product improvement.

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks

5.5

Industrial chips processing

Commercial chips made from fresh vegetables contain frying vegetable oil and added seasonings. For the production of 1 t of chips, it takes about 4 t of raw material, which is delivered either directly to the processing line or to a storehouse for later processing. As there is only one harvesting season per year for most of the vegetables in the northern hemisphere, the raw material must be stored from September October until

Figure 5.2 PEF processing step implemented in the industrial potato chips production. PEF, Pulsed electric field.

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June July next year, when new harvest is available. Storage temperature and humidity are important to prevent molding and to control the development of reducing sugars (European Snacks Association, 2014). Fig. 5.2 shows the general processing steps of potato chips production with PEF implementation. The potatoes are sorted with regards to their size and to remove defective or spoiled tubers. Then, they are washed to remove dirt and debris. PEF treatment can be applied either before or after peeling without impact on the product quality. However, potato peeling can have great influence on the quality and yield of the final product. Nowadays, either abrasive or steam peeling is commonly used in the potato industry (Potatobusiness, 2018). However, steam peeling is not suitable for the production of potato chips, as the severe impact of heat leads to the formation of a “cooking ring” (a layer of gelatinized starch cells). Therefore the alternative abrasive peeling is preferred in the potato chips industry (Dornow Food Technology, 2016), where the abrasive surface of the peeler removes the peel, which is subsequently washed away with water. Abrasive peeling holds significant advantages, for example, low energy and capital costs, no quality damage as the process runs at room temperature, and a good appearance of the product surface. The disadvantages include a relatively high production loss of up to 25%, the high volume of diluted waste, and a relatively low throughput (Fellows, 2000). On the other hand, vegetables such as sweet potatoes, beet roots, or carrots are normally not peeled before/after industrial processing. After peeling the potatoes are cut into thin slices of 1.5 2.0 mm thickness. In order to produce accurately cut potato slices, the cutting knives have to be changed regularly, at least every second hour. For cuts such as crinkle, wave, or v-cut, special cutting knives have to be used. For continuously fried chips the slices are then washed in order to remove debris, fines, and reducing sugars from the surface (Moreira, CastellPerez, & Barrufet, 1999). In addition, starch is removed to avoid slices to stick together. Instead of cold washing, a blanching step is sometimes applied due to a positive impact on the final texture and color of the chips. Prior to frying, the slices are dried with an air knife to reduce the initial sample moisture and to remove the surface water (De Meulenaer, Medeiros, & Mestdagh, 2016). The frying step can be conducted either as a continuous or batch process. In batch frying the potato slices are directly placed inside the fryer at temperatures of 145 C 165 C. Due to the addition of the colder slices and the moisture evaporation,

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks

the temperature of the frying oil drops by about 20 C. Then, the temperature rises again, close to the initial oil temperature, upon which frying is finished. As compared to the continuous frying process, batch-fried chips, so-called kettle chips, are characterized by higher fat levels, more blistering, and a harder surface structure due to the presence of starch on the product surface (Riaz, 2016). In continuous frying the potato slices are fed to the fryer after a washing or blanching step at an initial frying temperature of about 175 C. Over the course of the frying, the oil temperature drops almost linearly, down to approximately 155 C, before exiting the fryer. Optionally, the frying process can be followed by a deoiling unit where oil is blown off with hot air or removed by centrifugal force. Prior to packaging, the chips are seasoned.

5.6

Acrylamide reduction through chips processing

With the new EU acrylamide regulation, producers are seeking ways to reduce the acrylamide level in the product without negatively affecting the taste or product quality. As acrylamide is formed during processing, as a result of the Maillard reaction, it is not possible to remove it directly from the raw material. However, it is possible to remove the precursors, especially reducing sugars, from the product before processing, for example, through washing and blanching the slices prior to frying. Washing removes starch and fines from the product surface, which reduces acrylamide formation (Meulenaer et al., 2016). An additional blanching step results in a uniform color distribution as acrylamide precursors are leached out (Pedreschi, Travisany, Reyes, Troncoso, & Pedreschi, 2009; Vinci, Mestdagh, De Muer, Van Peteghem, & De Meulenaer, 2010). Viklund, Olsson, Sjo¨holm, and Skog (2010) observed that blanching at 80 C for 3 min led to a reduction of 17% 66% in the content of reducing sugars. Consequently, acrylamide formation during frying could be reduced by 51% 73%, which was attributed to the washing out of reducing sugars during blanching. On the other hand, the significant difference between the reduction in the reducing sugars content and the acrylamide formation was related to the limited diffusivity of reducing sugars toward the surface where the formation of acrylamide occurs. Moreover, a disadvantage of very intense blanching is the loss in texture and nutrients.

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Besides blanching, acrylamide can also be reduced by finetuning the production process, for example, through the reduction in the frying time. Romani, Bacchiocca, Rocculi, and Dalla Rosa (2008) reported that an increase in frying time led to an exponential increase in acrylamide content. When the water was evaporated from the surface, the product started to heat up and upon reaching 120 C on the surface, the Maillard reaction and thus, acrylamide formation, were triggered. However, a reduction in the frying time might not always be feasible, as the Maillard reaction is also responsible for the formation of color and aroma components and a certain target moisture must be reached in the final product. Another step in the process optimization is the change in the frying temperature. Fiselier, Bazzocco, Gama-Baumgartner, and Grob (2006) found that isothermal frying at 167 C 170 C led to double the acrylamide content in potato sticks as compared to isothermal frying at 160 C or batch frying at an initial temperature of 170 C 175 C dropping to 140 C 145 C. As acrylamide formation takes place in the absence of moisture, the frying temperature toward the end of the process is more important than the initial temperature. However, the frying temperature cannot be lowered below 140 C without reducing crispiness and flavor, thus negatively impacting the product quality. Another possibility to reduce acrylamide formation during frying is the use of vacuum frying. Hidalgo, Delgado, and Zamora (2010) observed that oxygen removal during the frying process leads to less acrylamide being formed, which is attributed to mercaptans reacting with acrylamide and thus, forming addition products. This reaction has a very low activation energy and therefore runs at a high extent at low temperatures. However, if oxygen is involved in the process, the mercaptans are converted and acrylamide formation is not affected. Furthermore, vacuum frying is a quite expensive process with smaller capacities as compared to the standard continuous frying. In addition, vacuum fried chips exhibit a puffed texture not comparable to chips fried in batch or continuous. Additional mitigation tools are used on an industrial scale to reduce the acrylamide content during processing, for example, near infrared (NIR) technology, additives, and enzymes. As the acrylamide formation depends on the product moisture, improved process monitoring through NIR can contribute to reduce the level of acrylamide (Knott & Hill, 2018). Besides, there are some additives in the market that act as an “oxidation management solution” and naturally decrease the acrylamide content in the snack. Such products are based on natural

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks

rosemary extract, which due to the presence of citric acid reduces the formation of acrylamide (Halliday, 2008). Another additive in the market is Acrylow, a yeast that metabolizes the reducing sugars and reduces the acrylamide formation by 50% 95%, with promising results on large-scale industrial trials for baked goods and snack foods (Orkla, 2018). The most promising reduction of acrylamide does not take place during processing but rather involves the enzymatic treatment of the raw material with asparaginase prior to processing (Das & Srivastav, 2012). Commercially used asparaginase is produced by cloning of Aspergillus oryzae, with an optimal pH of 6 7 and good activity over pH 5 8. Although it is not suitable for application in all food products, it has provided good results in potato products such as French fries (Pedreschi, Kaack, & Granby, 2008), bakery products, or coffee. Ciesarova and Kiss (2006) reported that asparaginase could reduce the acrylamide formation in potato products as well as products prepared from dried potato powder by 90% 97%, without affecting taste or color. Pedreschi, Mariotti, Granby, and Risum (2011) observed about 17% acrylamide reduction when potato slices were pretreated with asparaginase. However, this value could be improved to about 75% by blanching prior to enzymatic treatment due to improved diffusion of the enzyme as well as of asparagine toward the product surface. Moreover, blanching also leads to leaching of reducing sugars and asparagine, which are precursors of acrylamide formation. However, enzymes are relatively expensive, require a residence time during the treatment and afterward, their separation from the reaction mixture, in order to be reused, can prove to be challenging. Moreover, they are prone to product or substrate inhibition and their products can cause allergies (Singh, Kumar, Mittal, & Mehta, 2016). In summary, the currently available solutions to reduce the acrylamide content in fried chips products are relatively expensive, difficult to implement on an industrial scale, often requiring a drastic change in the overall process, and they often impact the characteristics of the final product.

5.7

Acrylamide reduction with pulsed electric field

PEF is a technology that does not directly affect the formation of acrylamide but rather improves subsequent processing steps. The PEF treatment leads to the electroporation of the cell

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membrane and improves the diffusion characteristics of the product. Therefore during washing and blanching operations, up to 50% more glucose, which is a precursor of acrylamide, can be removed from the product (Janositz, Noack, & Knorr, 2011), thus reducing the formation of such a contaminant. Furthermore, water leaches out of the product as a result of the PEF treatment, and thus less moisture has to be removed from the product during frying, which results in shorter frying time. Liu et al. (2017) observed a browner color in PEF-treated sweet potato chips after frying, which implies that the frying temperature of the product can be reduced after PEF pretreatment. Guan et al. (2010) also reported that asparagine could be reduced in about 16% from the raw potatoes, and therefore the acrylamide content, following PEF treatment. According to a patent from Kalum and Vang Hendriksen (2007), PEF treatment can also increase the efficacy of the asparaginase treatment on the raw product. Due to the potato cell membrane being perforated by PEF, the diffusion of the enzyme into the cell is increased, which also contributes to a better contact with the substrate. Overall, there are two main effects directly or indirectly impacted by the PEF pretreatment that influence the final acrylamide content in chips. First, improved mass transfer due to PEF electroporation allows more acrylamide precursors (reducing sugars and asparagine) to be removed prior to the frying process, which can be enhanced by washing or blanching the slices after PEF treatment prior to frying. Second, a faster water removal from the electroporated cells after PEF pretreatment allows frying at lower temperature and shorter time, resulting in less heat load. In particular, the end of the frying process, where most of the acrylamide is formed due to the drier product environment, can be shortened. The second mechanism is particularly important for batch (kettle)-fried chips, as washing or blanching steps are not included in the production process. Fig. 5.3 shows how a typical frying curve can be improved due to PEF treatment. For the industrial batch production of vegetable chips, a reduction in the acrylamide content of 52% for sweet potatoes, 57% for beetroots, and 19% for carrots has been reported using PEF as a pretreatment (Elea GmbH, 2018). The abovementioned benefits associated to the PEF treatment mainly refer to the inhibition of acrylamide precursors and the improvement of frying conditions influencing acrylamide formation. However, the PEF pretreatment of whole tubers prior to chip processing can have further positive effects on the

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks

Figure 5.3 Kettle frying curve for untreated and PEF-treated sweet potatoes (Elea GmbH, 2018). PEF, Pulsed electric field.

acrylamide content. Foot, Haase, Grob, and Gonde´ (2007) found that removing the fines from the surface of tuber products prior to frying can contribute to acrylamide reduction, as fine cuts tend to overheat during frying resulting in higher acrylamide content. PEF pretreatment can improve cutting toward less fines production, so higher quality would be achieved while avoiding the removal step. Typically, the yield of potato chips production can be increased by more than 1.5% with PEF, as less fines, starch, and debris are present after slicing (Elea GmbH, 2018). With harder raw material and difficult cuts (wave cut, crinkle cut), the yield increases with PEF will be even more pronounced. In summary, PEF treatment results in softening of the raw material and therefore improved cutting behavior with less fines. Fig. 5.4 shows the difference on the cutting surface of an untreated and PEF-treated potato, as visualized by microscopy (Keyence VHX6000).

5.8

Fat in snack products

As deep frying is used to prepare the “classical chips,” the final product contains fat at about 20% 35%. The steady increase of snacking together with the consumption of fatty fast and convenience food has led to an increase in fat-related diseases, for example, cardiovascular diseases, obesity, and type II diabetes. The fat from deep-fried products contributes to such noncommunicable diseases in different ways. Important influence refers to the total fat uptake. In many Western countries

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Figure 5.4 Topographic surface of raw sliced potatoes (A) untreated and (B) PEF-treated (Elea GmbH, 2018). PEF, Pulsed electric field.

the energy uptake by fat is about 33% 40%, which is a major contributor to obesity and, in turn, can promote diabetes type II. Studies have also shown that an increased fat intake is linked to increased rates of breast, prostate, and colon cancer (Mehta & Swinburn, 2001). However, not only the amount of fat that is consumed is important but also the type of fat plays a major role. A high intake of saturated fats and trans-fatty acids is a risk factor for coronary heart diseases. During frying the frying medium is partly absorbed into the product and an exchange

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks

between the fat in the product and the deep-frying medium also takes place, resulting in a change of composition in free fatty acids. Therefore the choice of frying fat has a big influence on the fatty acid composition of the final product. From a nutritional standpoint, vegetables oils such as olive oil or rapeseed oil are preferred for frying as they have a high content of the monounsaturated oleic acid [Deutsche Gesellschaft fu¨r Fettwissenschaft e.V. (DGF), 2012]. However, fats with a high content of unsaturated fatty acids are not suitable for frying as they often present a low smoke point, low temperature, and low oxidation stability. Hydrogenized fats are often used for frying as they show less amount of the three main products formed during frying which are triacylglycerols (TG) dimers, oxidized TG monomers, and volatile compounds (McClements, Decker, & Elias, 2010). Less presents of these products in the oil increase the stability and therefore oil shelf life. During hydrogenation, unsaturated fatty acids are converted to saturated fatty acids (Ophardt & Rodriguez, 2013). However, the process of hydrogenation also leads to the formation of trans fats. Intake of trans-fatty acids represents a high risk for cardiovascular diseases by increasing the ratio of LDL to HDL cholesterol (Iqbal, 2014). Therefore the snack industry is seeking healthier while processing efficient fat sources. Nowadays, different blends of oils are often used in addition to stabilizing agents to prevent oxidization during frying. Oil uptake by the product is negligible while it is immersed into the hot fat and steam is evaporating from the product. The escaping vapor forms a protective layer around the product preventing the oil absorption. Therefore oil uptake mainly takes place at the very end of the frying process and after the product is removed from the fryer. Besides, the operating procedure to remove the product from the fryer, which, in turn, influences the adhesion of the oil to the product, seems to play an important role. Thus a proper shaking and draining of the product after frying is important (Iqbal, 2014). Finally, the frying time and temperature also affect the fat uptake by the product. If a moist product is fried at too high temperatures, a crust will be formed quickly on the product surface, trapping the steam inside the product and leading to a squishy product. On the other hand, if a relatively dry product is fried at high temperatures, the water will be steamed off and replaced by fat, thus making it greasy.

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5.9

Reduction of the fat content in fried snacks

As already mentioned, consumers’ fat intake is growing due to an increased consumption of snacks, fast and convenient food. Snack producers are looking for new low-fat snacks or try to reduce the fat content in their current products. In order to reduce the fat uptake during processing, several interventions can be implemented during the chips production. A very common and efficient pretreatment for some products relies on the partial drying of the product prior to frying, via, for example, hot air drying, microwave drying, hot air impingement, or osmotic dehydration (Moreno & Bouchon, 2008). Debnath, Bhat, and Rastogi (2003) found that an increased predrying time of snack products based on chickpea flour could reduce the oil uptake of the product by about 54%. Another way to reduce the fat content of snack products is by coating that allows a change in the oil absorption properties of the food surface. Special attention has been paid to the use of hydrocolloids with thickening or thermal gelling properties such as methylcellulose, hydroxypropyl methylcellulose, or alginates to reduce the oil uptake (Albert & Mittal, 2002; Mellema, 2003). Unfortunately, coating is not an option for classical continuous or batch-fried chips. Moreover, the frying conditions themselves have great influence on the fat uptake. Debnath et al. (2003) observed that an increase in the frying temperature also resulted in higher mass transfer, and thus in an increased oil uptake by the product. Dueik, Robert, and Bouchon (2010) observed a reduction in the fat uptake by vacuum fried carrot chips of up to 50%, as compared to atmospheric fried samples, which was attributed to the lower frying temperatures as well as lower vapor pressure of water. For vacuum fried potato chips an oil content reduction of 29% in the final product was observed most likely due to faster air diffusion into the pores as a result of the low pressure, thus obstructing the oil passage (Garayo & Moreira, 2002). The most important factor influencing the oil uptake by the product is the surface and microstructure of the food matrix itself (Pedreschi, Corte´s, & Mariotti, 2016). The surface area can simply be reduced by cutting the product thicker, resulting in less oil uptake. However, changing the product cut will result in different product characteristics, texture, and mouthfeel. Cracks and a rough surface will increase the surface area as well as the oil uptake by the product (Mehta & Swinburn, 2001). PEF

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks

technology can contribute to reduced oil uptake by the product since, due to the cell electroporation, intracellular water is released out of the product leading to a softer structure, which results in easier cutting, less feathering, and a smoother product surface (see Fig. 5.4) (Janositz et al., 2011). PEF also allows to create new cuts and shapes, such as a crinkle or wave cuts, for hard products such as sweet potatoes without cracking, thus reducing the oil uptake. Due to the PEF-induced cell electroporation, diffusion of liquids from the core to the surface of the product is facilitated and thus, the vapor pressure during frying increases, leading to a thicker vapor layer, reduced weight loss, and oil uptake by the product (Ignat, Manzocco, Brunton, Nicoli, & Lyng, 2015). In addition, the frying time can be reduced due to the moisture loss of the product prior to frying, which results in less oil uptake. Overall, the application of PEF prior to frying has been found to reduce the oil uptake up to 38% for snack products (Janositz et al., 2011).

5.10

Dried snacks

With rising consumers’ health concerns and the subsequent shift to healthier food habits, the demand for healthy snacks such as dried fruits, vegetables, and nuts has rapidly increased. With a global production scenario of 2826 MT and an annual growth of about 1.6%, the dried fruit market has undergone a significant growth. Overall, the dried snacks market is expected to reach a production of about 67 MT by 2022 (Global Industry Analysts, Inc., USA, 2018). In addition, dried vegetable snacks are also becoming more important within the snacks market, as no additional fat is used for their production. This leads to reduced energy density while preserving at the same time the nutritional value of the product (Chang, Alasalvar, & Shahidi, 2016). Overall, drying is one of the oldest food preservation methods. It reduces the water content of the product, leading to extended shelf life and reduced microbiological activity. Due to the reduced product weight, packaging and transport costs are reduced as well (Siemer, Toepfl, Witt, & Ostermeier, 2018). A variety of water removal methods are available to produce dried snacks, including hot air drying, vacuum drying, or freeze drying. Air drying is the oldest and most established method due to its low cost and ease of operation. However, air drying utilizes high drying temperatures and relatively long drying times, which often results in a reduction of the product quality with regards to color,

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flavor, and nutritional value. Numerous pretreatment steps have been investigated to improve the product quality of air-dried products, including blanching, sulfating, and osmotic treatment (Huang & Zhang, 2012). Leeratanarak, Devahastin, and Chiewchan (2006) found that blanching in combination with lower drying temperatures resulted in an overall improved color with no effect otherwise on the product quality. Osmotic pretreatment lowered the initial water content of the product, resulting in reduced drying times, and therefore less shrinkage and improved color properties (Aktas, Fujii, Kawano, & Yamamoto, 2007). Finally, sulfating contributed to the color retention of airdried pumpkin slices (Falade & Shogaolu, 2010). Vacuum drying in most cases is not suitable as a stand-alone method and it is often used in combination with other treatments, such as vacuum frying or freeze drying. Products made by vacuum freeze drying are characterized by a superior taste and texture, improved rehydration properties, and an increased porosity, in comparison to other drying methods (Huang & Zhang, 2012). The downside of this technology is that due to the low mass and heat transfer rates achieved under vacuum, the long drying time leads to high energy consumption and capital costs. Therefore vacuum freeze drying is only used for high-quality products (Duan, Zhang, & Mujumdar, 2007). Drying time and energy consumption can be reduced by the application of pretreatments such as the use of microwaves or PEF. Huang et al. (2009) applied microwave vacuum drying before or after freeze drying and observed a reduced drying time leading to energy savings of up to 50%. The use of PEF for freeze drying, and drying in general, can significantly reduce the drying times. Wiktor et al. (2013) observed a reduction in drying time of up to 12% at a field strength of 10 kV/cm, since the PEF-induced cell electroporation increased mass transfer (Angersbach & Knorr, 1997; Knorr & Angersbach, 1998; Toepfl, Siemer, & Heinz, 2014; Zimmermann, Pilwat, & Riemann, 1974). An increased water diffusion coefficient of up to 17% after PEF treatment was observed for carrots (Wiktor et al., 2016). Accelerated water diffusion to the product surface provides more water for the evaporation. Due to high surface water availability, the third drying phase in hot air drying, where the product surface heats up, is reached at a later point. This avoids the formation of a surface crust, leading to an improved product quality and texture (Parniakov, Bals, Lebovka, & Vorobiev, 2016). Moreover, the initial drying temperature can be increased to shorten the drying process, while the final drying temperature can be decreased (Ostermeier, Giersemehl, Siemer, To¨pfl, & Ja¨ger, 2018). Because of the reduced drying times and temperatures,

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks

Figure 5.5 Compact PEF system with combined generator and treatment area for up to 6 t/h (Elea GmbH, 2018). PEF, Pulsed electric field.

different benefits in the final product can be achieved, such as higher color retention or increased nutritional value (Siemer et al., 2018).

5.11

Industrial implementation

Considering the abovementioned benefits from using PEF as a pretreatment for snacks, its implementation on an industrial scale has been straightforward. Nowadays, industrial systems with capacities from 1 up to 70 t/h raw material are available. The implementation of a PEF system into a chips production line is relatively simple, as compared to other processing steps. The treatment itself only takes microseconds and the residence time of the tubers in the PEF system is about 5 10 s, depending on the throughput. This allows a fast implementation and an adequate integration within the production line. Most of the current industrial-scale PEF systems for tuber products consist of two parts, the pulse modulator and a treatment belt or rotating wheel with the treatment area included (Diversified Technologies Inc., 2018; Elea GmbH, 2018; Heat and Control, 2018). To facilitate the implementation into existing processing lines, compact all-in-one designs are also available (see Fig. 5.5). The average electrical consumption of a PEF system is comparatively low. It can be assumed that ,1 kW h/t raw material is required for a sufficient treatment. The treatment unit must

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Table 5.1 Average benefits, the cause of the benefits, and the resulting savings of applying pulsed electric field pretreatment on an industrial vegetable chip line (Elea GmbH, 2018; Fauster et al., 2018; Heat and Control, 2018). Benefit

Cause

Reduced frying time

Improved mass transfer

Greater throughput/batch size Improved color

Longer knife durability Less oil uptake Less fines, breakage, and starch losses during slicing and further processing Less doubles (slices sticking together) Improved texture New cuts from new raw material

Savings

5% 10% more capacity; lower energy consumption Improved mass transfer 5% more capacity Reduction of frying time and temperature; Up to 50% reduction in acrylamide; possible to leaking out of reducing sugars and eliminate blanching asparagine Tissue softening Up to 50% extended usage of knives Smoother cut; reduced surface area; 10% 15% oil reduction optimized frying process Smoother cut; flexible raw material; less 1.5% higher yield; better frying mechanical cell damage during slicing oil quality Creation of vapor barrier between the slices Homogeneous starch gelatinization Tissue softening

Less rejected product Increased crispiness More interesting products, new exotic raw material

be implemented within the production line. To avoid energy losses in pulse transmission cables, the generator must be placed within a certain radius. The PEF treatment is normally conducted before or after peeling, but always before slicing, as this is the first processing step benefiting from the PEF treatment and the subsequent softer raw material (see also Fig. 5.2). Table 5.1 shows the benefits reported by research and industry experts using PEF technology in snack processing. Furthermore, it indicates the source of the benefits and the associated savings. As the overall benefits and savings highly depend on the raw material, final product, processing steps, and line layout, the table only provides a general overview. For snacks that are conventional or freeze dried after PEF pretreatment, the following benefits have been reported (Alam, Lyng, Frontuto, Marra, & Cinquanta, 2018; Knorr, 2006; Ostermeier et al., 2018; Parniakov et al., 2016; Wiktor et al., 2013, 2016):

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks

• • • • • •

reduction of processing time lower energy consumption better color retention less shrinkage improved rehydration behavior higher amount of valuable compounds However, implementing an additional processing step within an existing production line involves additional expenses. The costs for a 6 t/h PEF system, considering an annual production of 24,000 t raw material, would amount to 6h/t raw material (depreciation of 3 years). Including additional expenses such as electricity consumption, the overall costs would be 7h/t raw material (Elea GmbH, 2018). Implementing a PEF system into a snack production line results not only in processing benefits but also in improved quality of the final product. Both have a positive impact on the return of investment (ROI) for a PEF system installation. The monetary savings significantly depend on the product/process benefits from PEF implementation and on the original production process and line layout. For instance, if the processing line includes state-of-the-art technology (except for PEF treatment), the savings will be less pronounced as compared to an old production line. However, industrial-scale implementation of more than 100 PEF systems in the past years has shown typical ROI of 3 months up to 2 years (Elea GmbH, 2018). Fauster et al. (2018) reported 78% less feathering and 43% reduced breakage for potato sticks produced on an industrial scale. Moreover, a reduction of 17% in starch losses was also observed. All these benefits, and corresponding savings, will result in greater production yield ( . 1.5%) and a fast ROI.

References Aktas, T., Fujii, S., Kawano, Y., & Yamamoto, S. (2007). Effects of pretreatments of sliced vegetables with trehalose on drying characteristics and quality of dried products. Food and Bioproducts Processing, 85(3), 178 183. Alam, M. R., Lyng, J. G., Frontuto, D., Marra, F., & Cinquanta, L. (2018). Effect of pulsed electric field pretreatment on drying kinetics, color, and texture of parsnip and carrot. Journal of Food Science, 83(8), 2159 2166. Albert, S., & Mittal, G. S. (2002). Comparative evaluation of edible coatings to reduce fat uptake in a deep-fried cereal product. Food Research International, 35(5), 445 458. Angersbach, A., & Knorr, D. (1997). Anwendung elektrischer Hochspannungsimpulse als Vorbehandlungsverfahren zur Beeinflussung der Trocknungscharakteristika und Rehydratationseigenschaften von ¨ rfeln. Food/Nahrung, 41(4), 194 200. Kartoffelwu

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Barutcu, I., Sahin, S., & Sumnu, G. (2009). Acrylamide formation in different batter formulations during microwave frying. LWT—Food Science and Technology, 42(1), 17 22. Brennan, J. G. (2006). Food processing handbook. Weinheim: Wiley-VCH, 25.09.18. Chang, S. K., Alasalvar, C., & Shahidi, F. (2016). Review of dried fruits: Phytochemicals, antioxidant efficacies, and health benefits. Journal of Functional Foods, 21, 113 132. Ciesarova, Z., & Kiss, E. (2006). Impact of L-asparaginase on acrylamide content in potato product. Journal of Food and Nutrition Research, 45, 141 146, 18.09.18. Das, A. B., & Srivastav, P. P. (2012). Acrylamide in snack foods. Toxicology Mechanisms and Methods, 22(3), 163 169, 25.09.18. Debnath, S., Bhat, K. K., & Rastogi, N. K. (2003). Effect of pre-drying on kinetics of moisture loss and oil uptake during deep fat frying of chickpea flour-based snack food. LWT—Food Science and Technology, 36(1), 91 98. Deutsche Gesellschaft fu¨r Fettwissenschaften e.V. (DGF). (2012). Optimum deep frying. Available from ,http://www.dgfett.de/material/optimum_frying.pdf. 28.01.20 Diversified Technologies Inc. Food and wastewater processing. (2018). Available from ,http://www.divtecs.com/food-and-wastewater-processing/. 29.10.18. Dornow Food Technology. (2016) Steam peeling—Mechanical peelings in small, medium and large-scale industrial enterprises. What peeling method is used where?. Available from ,http://www.dornow.de/de/englisch/Q-Prospekte/ Q104e5.pdf. 02.10.18. Duan, X., Zhang, M., & Mujumdar, A. S. (2007). Studies on the microwave freeze drying technique and sterilization characteristics of cabbage. Drying Technology, 25(10), 1725 1731. Dueik, V., Robert, P., & Bouchon, P. (2010). Vacuum frying reduces oil uptake and improves the quality parameters of carrot crisps. Food Chemistry, 119(3), 1143 1149. Elea GmbH. Elea technology. (2018). Available from ,http://elea-technology.de/. 29.10.18. Green, E. (2018). Acrylamide: Majority of consumers aware of the carcinogen are concerned, finds DSM survey. Available from ,https://www. foodingredientsfirst.com/news/dsm-70-percent-of-consumers-who-areaware-of-acrylamide-are-concerned-about-potential-health-effects.html. 17.09.18. European Snacks Association. (2014). Chip/crisp manufacturing—Preparation. European Snacks Association. Available from http://www.esasnacks.eu/crispmanufacturing-preparation.php 02.10.18. Falade, K. O., & Shogaolu, O. T. (2010). Effect of pretreatments on air-drying pattern and color of dried pumpkin (Cucurbita maxima) slices. Journal of Food Process Engineering, 33(6), 1129 1147. Fauster, T., Schlossnikl, D., Rath, F., Ostermeier, R., Teufel, F., Toepfl, S., & Jaeger, H. (2018). Impact of pulsed electric field (PEF) pretreatment on process performance of industrial French fries production. Journal of Food Engineering, 235, 16 22. Fellows, P. J. (2000). Food processing technology. Principles and practice, second edition, Teile 1 4. CRC Press. Fiselier, K., Bazzocco, D., Gama-Baumgartner, F., & Grob, K. (2006). Influence of the frying temperature on acrylamide formation in French fries. European Food Research and Technology, 222(3 4), 414 419.

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks

Foot, R. J., Haase, N. U., Grob, K., & Gonde´, P. (2007). Acrylamide in fried and roasted potato products: A review on progress in mitigation. Food Additives and Contaminants, 24(Suppl. 1), 37 46. Garayo, J., & Moreira, R. (2002). Vacuum frying of potato chips. Journal of Food Engineering, 55(2), 181 191. Global Industry Analysts, Inc., USA. Dried fruits and edible nuts market trends. (2018). Available from ,https://www.strategyr.com/MarketResearch/ infographTemplate.asp?code 5 MCP-6241. 12.10.18. Guan, Y.-G., Wang, J., Yu, S.-J., Zeng, X.-A., Han, Z., & Liu, Y.-Y. (2010). A pulsed electric field procedure for promoting Maillard reaction in an asparagineglucose model system. International Journal of Food Science & Technology, 45 (6), 1303 1309, 19.09.18. Halliday, J. (2008). Vitiva improves Inolens 4 for oil stability, colour. Slovenian natural extracts supplier Vitiva is introducing a new version of its Inolens rosemary extract, targeted at increasing the shelf-life and stability of food grade oils and fats. Available from ,https://www.foodnavigator.com/Article/ 2008/05/14/Vitiva-improves-Inolens-4-for-oil-stability-colour. 26.09.18. Heat and Control. Want your potato chips to be healthier? Better tasting? We have the solution. (2018). Available from ,http://www.heatandcontrol.com/ news-product.asp?npid 5 274. 29.10.18. Hess, J. M., Jonnalagadda, S. S., & Slavin, J. L. (2016). What is a snack, why do we snack, and how can we choose better snacks? A review of the definitions of snacking, motivations to snack, contributions to dietary intake, and recommendations for improvement. Advances in Nutrition (Bethesda, Md.), 7(3), 466 475, 21.09.18. Hidalgo, F. J., Delgado, R. M., & Zamora, R. (2010). Role of mercaptans on acrylamide elimination. Food Chemistry, 122(3), 596 601. Huang, L.-l, & Zhang, M. (2012). Trends in development of dried vegetable products as snacks. Drying Technology, 30(5), 448 461, 12.10.18. Huang, L.-l, Zhang, M., Mujumdar, A. S., Sun, D.-F., Tan, G.-W., & Tang, S. (2009). Studies on decreasing energy consumption for a freeze-drying process of apple slices. Drying Technology, 27(9), 938 946. Ignat, A., Manzocco, L., Brunton, N. P., Nicoli, M. C., & Lyng, J. G. (2015). The effect of pulsed electric field pre-treatments prior to deep-fat frying on quality aspects of potato fries. Innovative Food Science & Emerging Technologies, 29, 65 69, 01.10.18. Innova Market Insights. Healthy snack trends: Mini meals, protein, fruit, popcorn, nuts, and more. Nutritional outlook. (2018). Available from ,http:// www.nutritionaloutlook.com/food-beverage/healthy-snack-trends-minimeals-protein-fruit-popcorn-nuts-and-more. 24.09.18. Iqbal, M. P. (2014). ‘Trans fatty acids—A risk factor for cardiovascular disease’. Pakistan Journal of Medical Sciences, 30(1), 194 197. Janositz, A., Noack, A.-K., & Knorr, D. (2011). Pulsed electric fields and their impact on the diffusion characteristics of potato slices. LWT—Food Science and Technology, 44(9), 1939 1945, 19.09.18. Kalum, L., & Vang Hendriksen, H. (2007). Process for treating vegetable material with an enzyme, US12057608. Knorr, D., & Angersbach, A. (1998). Impact of high-intensity electric field pulses on plant membrane permeabilization. Trends in Food Science & Technology, 9 (5), 185 191. Knorr, S. T. A. D. (2006). Pulsed electric fields as a pretreatment technique in drying processes. Stewart Postharvest Review, 2(4), 1 6.

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Knott M. and Hill J. (2018). Spotlight on acrylamide. Snacks Magazine Autumn, 38 41, 28.01.20. Krause, T., Bo¨hm, H., & Loges, R. (2005). Kartoffeln fu¨r pommes und chips. Available from ,http://orgprints.org/8714/1/kartoffeln_f%C3%BCr_pommes. pdf. 26.09.18. Leeratanarak, N., Devahastin, S., & Chiewchan, N. (2006). Drying kinetics and quality of potato chips undergoing different drying techniques. Journal of Food Engineering, 77(3), 635 643. Levelle C. (2016). 8 Snack trends to watch for in 2017. Available from ,http:// www.cspdailynews.com/snacks-candy/8-snack-trends-watch-2017. 28.01.20. Lim, P. K., Jinap, S., Sanny, M., Tan, C. P., & Khatib, A. (2014). The influence of deep frying using various vegetable oils on acrylamide formation in sweet potato (Ipomoea batatas L. Lam) chips. Journal of Food Science, 79(1), T115 T121. Liu, T., Dodds, E., Leong, S. Y., Eyres, G. T., Burritt, D. J., & Oey, I. (2017). Effect of pulsed electric fields on the structure and frying quality of “kumara” sweet potato tubers. Innovative Food Science & Emerging Technologies, 39, 197 208. Mathieu, P. (2014). Savoury snacks myths & truths. Available from ,http://www. esasnacks.eu/myths_fact_sheet_Jun2014.pdf. 21.09.18. McClements, D. J., Decker, E., & Elias, R. J. (2010). Oxidation in foods and beverages and antioxidant applications. Oxford; Philadelphia, PA: Woodhead Publishing, 28.09.18. Mehta, U., & Swinburn, B. (2001). A review of factors affecting fat absorption in hot chips. Critical Reviews in Food Science and Nutrition, 41(2), 133 154, 28.09.18. Mellema, M. (2003). Mechanism and reduction of fat uptake in deep-fat fried foods. Trends in Food Science & Technology, 14(9), 364 373. Mestdagh, F., De Wilde, T., Delporte, K., Van Peteghem, C., & De Meulenaer, B. (2008). Impact of chemical pre-treatments on the acrylamide formation and sensorial quality of potato crisps. Food Chemistry, 106(3), 914 922, 25.09.18. De Meulenaer, B., Medeiros, R., & Mestdagh, F. (2016). Acrylamide in potato products. In J. Singh, & L. Kaur (Eds.), Advances in potato chemistry and technology (pp. 527 562). Amsterdam: Elsevier AP, 10.10.18. Moreira, R. G., Castell-Perez, M. E., & Barrufet, M. A. (1999). Deep fat frying. Fundamentals and applications. Gaithersburg, MD: Aspen. Available from ,http://www.loc.gov/catdir/enhancements/fy0820/99020349-d.html.. Moreno, M. C., & Bouchon, P. (2008). A different perspective to study the effect of freeze, air, and osmotic drying on oil absorption during potato frying. Journal of Food Science, 73(3), E122 E128. Mottram, D. S., Wedzicha, B. L., & Dodson, A. T. (2002). Acrylamide is formed in the Maillard reaction. Nature, 419(6906), 448 449, 25.09.18. Mulla, M. Z., Bharadwaj, V. R., Annapure, U. S., & Singhal, R. S. (2011). Effect of formulation and processing parameters on acrylamide formation: A case study on extrusion of blends of potato flour and semolina. LWT—Food Science and Technology, 44(7), 1643 1648. Ophardt, C., & Rodriguez, A. (2013). Hydrogenation of unsaturated fats and trans fat. Available from ,https://chem.libretexts.org/Textbook_Maps/ Biological_Chemistry/Lipids/Fatty_Acids/ Hydrogenation_of_Unsaturated_Fats_and_Trans_Fat. 28.09.18. Orkla. Orkla Food Ingredients expands its acrylamide-reducing yeast technology licence agreement with renaissance BioScience Corp. (2018). Available from ,https://www.orkla.com/downloads/orkla-food-ingredients-expands-its-

Chapter 5 Pulsed electric field as a sustainable tool for the production of healthy snacks

acrylamide-reducing-yeast-technology-licence-agreement-with-renaissancebioscience-corp/. 26.09.18. Ostermeier, R., Giersemehl, P., Siemer, C., To¨pfl, S., & Ja¨ger, H. (2018). Influence of pulsed electric field (PEF) pre-treatment on the convective drying kinetics of onions. Journal of Food Engineering, 237, 110 117. Parniakov, O., Bals, O., Lebovka, N., & Vorobiev, E. (2016). Pulsed electric field assisted vacuum freeze-drying of apple tissue. Innovative Food Science & Emerging Technologies, 35, 52 57. Pedreschi, F., Corte´s, P., & Mariotti, M. S. (2016). Potato crisps and snack foods. In G. W. Smithers (Ed.), Reference module in food science. Amsterdam: Elsevier. Pedreschi, F., Kaack, K., & Granby, K. (2008). The effect of asparaginase on acrylamide formation in French fries. Food Chemistry, 109(2), 386 392. Pedreschi, F., Mariotti, S., Granby, K., & Risum, J. (2011). Acrylamide reduction in potato chips by using commercial asparaginase in combination with conventional blanching. LWT—Food Science and Technology, 44(6), 1473 1476, 18.09.18. Pedreschi, F., Travisany, X., Reyes, C., Troncoso, E., & Pedreschi, R. (2009). Kinetics of extraction of reducing sugar during blanching of potato slices. Journal of Food Engineering, 91(3), 443 447. Potatobusiness. Advanced peeling. (2018). Available from ,https://www. potatobusiness.com/processing/cutting/217-advanced-peeling. 02.10.18. Pritchard, M. K., & Adam, L. R. (1994). Relationships between fry color and sugar concentration in stored Russet Burbank and Shepody potatoes. American Potato Journal, 71(1), 59 68. Riaz, M. N. (2016). Snack foods, processing. In G. W. Smithers (Ed.), Reference module in food science. Amsterdam: Elsevier, 02.10.18. Romani, S., Bacchiocca, M., Rocculi, P., & Dalla Rosa, M. (2008). Effect of frying time on acrylamide content and quality aspects of French fries. European Food Research and Technology, 226(3), 555 560. Rydberg, P., Eriksson, S., Tareke, E., Karlsson, P., Ehrenberg, L., & To¨rnqvist, M. (2005). Factors that influence the acrylamide content of heated foods. Chemistry and Safety of Acrylamide in Food, 561, 317 328, 25.09.18. Riley, S. (2017). Consumer demand increases for healthy snacks. Available from ,https://www.foodengineeringmag.com/articles/96842-consumer-demandincreases-for-healthy-snacks. 17.09.18. Serpen, A., & Go¨kmen, V. (2009). Evaluation of the Maillard reaction in potato crisps by acrylamide, antioxidant capacity and color. Journal of Food Composition and Analysis, 22(6), 589 595. Siemer, C., Toepfl, S., Witt, J., & Ostermeier, R. (2018). Use of pulsed electric fields (PEF) in the food industry. In DLG expert report 2018. Singh, R., Kumar, M., Mittal, A., & Mehta, P. K. (2016). Microbial enzymes: Industrial progress in 21st century. 3 Biotech, 6(2), 174. Stephens, K. Global snacking trends. The popularity of snacks and on-the-go bars is increasing worldwide, allowing for an influx of innovative ingredients, flavors and concepts, INSIDER’s Snacks and Bars Digital Magazine, 11.01.18 Available from ,https://www.naturalproductsinsider.com/foods/globalsnacking-trends. 24.09.18. The Nielsen Company. Snack attack. (2014). Available from ,https://www. nielsen.com/content/dam/nielsenglobal/kr/docs/global-report/2014/Nielsen %20Global%20Snacking%20Report%20September%202014.pdf. 21.09.18.

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Toepfl, S., Siemer, C., & Heinz, V. (2014). Effect of high-intensity electric field pulses on solid foods. In D.-W. Sun (Ed.), Emerging technologies for food processing (pp. 147 154). Amsterdam: Academic Press. ˚ . I., Olsson, K. M., Sjo¨holm, I. M., & Skog, K. I. (2010). Acrylamide Viklund, G. A in crisps: Effect of blanching studied on long-term stored potato clones. Journal of Food Composition and Analysis, 23(2), 194 198. Vinci, R. M., Mestdagh, F., De Muer, N., Van Peteghem, C., & De Meulenaer, B. (2010). Effective quality control of incoming potatoes as an acrylamide mitigation strategy for the French fries industry. Food Additives & Contaminants. Part A, Chemistry, Analysis, Control, Exposure & Risk Assessment, 27(4), 417 425. ´ z, M., Nowacka, M., Chudoba, T., & WitrowaWiktor, A., Iwaniuk, M., Sled´ Rajchert, D. (2013). Drying kinetics of apple tissue treated by pulsed electric field. Drying Technology, 31(1), 112 119. Wiktor, A., Nowacka, M., Dadan, M., Rybak, K., Lojkowski, W., Chudoba, T., & Witrowa-Rajchert, D. (2016). The effect of pulsed electric field on drying kinetics, color, and microstructure of carrot. Drying Technology, 34(11), 1286 1296. Zimmermann, U., Pilwat, G., & Riemann, F. (1974). Dielectric breakdown of cell membranes. In U. Zimmermann, & J. Dainty (Eds.), Membrane transport in plants (pp. 146 153). Berlin, Heidelberg: Springer. Available from ,https:// www.cell.com/biophysj/pdf/S0006-3495(74)85956-4.pdf. 29.10.18.

Effect of pulsed electric field on Maillard reaction and hydroxymethylfurfural production

6

Amin Mousavi Khaneghah1, Mohsen Gavahian2, Qiang Xia3, Gabriela I. Denoya4,5, Elena Rosello´-Soto6 and Francisco J. Barba6 1

Faculty of Food Engineering, Department of Food Science, University of Campinas (UNICAMP), Campinas, Brazil 2Product and Process Research Center, Food Industry Research and Development Institute, Hsinchu, Taiwan, ROC 3Department of Food Science and Technology, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, P.R. China 4National Institute for Agricultural Technology (INTA), Food Technology Institute, Hurlingham, Buenos Aires, Argentina 5National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina 6Nutrition and Food Science Area, Preventive Medicine and Public Health, Food Sciences, Toxicology and Forensic Medicine Department, Faculty of Pharmacy, Universitat de Vale`ncia, Vale`ncia, Spain

6.1

Introduction

Maillard reaction (MR) can occur during processing, such as cooking and thermal sterilization, at high temperatures of foods containing reducing sugars, amino acids, and free peptides. These chemical reactions are responsible for the deterioration of proteins during food processing and storage (Barba, Carbonell-Capella, Esteve, & Frı´gola, 2013; Tamanna & Mahmood, 2015; Tessier & Birlouez-Aragon, 2012). MR consists of sequences of chemical reactions that are well described in the literature (Hemmler et al., 2017). During MR, some neoformed contaminants such as acrylamide and 5-(hydroxymethyl)furfural (HMF) are produced. HMF is an aldehyde generated from the decomposition of glucose and fructose and is formed as an intermediate product (de Oliveira, Coimbra,

Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00006-9 © 2020 Elsevier Inc. All rights reserved.

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de Oliveira, Zun˜iga, & Rojas, 2016) (Fig. 6.1). Acrylamide and HMF are considered as probably or potentially carcinogenic to humans or might be metabolized by humans to potentially carcinogenic compounds (Capuano & Fogliano, 2011). A

Figure 6.1 Schematic representation of Maillard reaction. (A) Amadori product formation and degradation (C7 core unit). (B) Diketosamine degradation (C12 core unit). (C) Degradation after C2-cleavage of the diketosamine (C10 core unit). (D) Degradation after C3-cleavage of the diketosamine (C9 core unit). Source: Adopted from Hemmler, D., RoullierGall, C., Marshall, J. W., Rychlik, M., Taylor, A. J., & Schmitt-Kopplin, P. (2017). Evolution of complex Maillard chemical reactions, resolved in time. Scientific Reports 7(1). https://doi.org/10.1038/s41598-017-03691-z, under a Creative Commons Attribution 4.0 International License.

Chapter 6 Effect of pulsed electric field on Maillard reaction and hydroxymethylfurfural production

comprehensive study on the health concerns that are associated with uncontrolled MR was conducted by Somoza (2005). This study revealed that several organs (e.g., kidney and vascular system) can be affected by MR products (MRPs) that may cause several disorders such as aging and diabetes (Fig. 6.2). Therefore there is a demand for appropriate processes, such as nonthermal techniques, which can avoid the formation of HMF during food processing. Gerrard (2006) discussed the progress that has been made and the challenges ahead in this area of science. Among the proposed techniques to minimize the undesirable MR, pulsed electric field (PEF) technology is probably one of the most attractive methods for the researchers due to its ability to process the food while minimizing the HMF formation. PEF process consists of applying an electrical current between two electrodes (Pue´rtolas & Barba, 2016) at the high frequencies and has been emerged to address the drawbacks of ohmic heating such as electrode corrosion and undesirable electrochemical reactions (Gavahian, Chu, & Sastry, 2018; Gavahian, Farahnaky, & Sastry, 2016; Gavahian, Lee, & Chu, 2018). This innovative technology has been previously used mainly due to its potential to inactivate microorganism, preservative effects regarding the nutritional and quality attributes of food products (Barba et al., 2015; Gabri´c et al., 2018; Misra, Martynenko, et al., 2017). For instance, this promising technology (together with the high hydrostatic pressures) can be

Figure 6.2 Some of the major health risks are associated with consumption of MRPs. MRPs, Maillard reaction products; NE, negative effects.

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considered as future nonthermal technologies in the food industry (Misra, Koubaa, et al., 2017). Due to the immense potential of electric pulses, only a limited number of applications have been developed, of which some of them turned into commercially scale. Recently, some of the potential applications of PEF have been reviewed, such as for inactivating microorganisms (Barba, Koubaa, do Prado-Silva, Orlien, & Sant’Ana, 2017; Gabri´c et al., 2018); retaining nutritional, physicochemical, and sensorial properties of food products (Corte´s, Barba, Esteve, Gonza´lez, & Frı´gola, 2008; Esteve, Barba, Palop, & Frı´gola, 2009; Gabri´c et al., 2018; Koubaa et al., 2017; Rosello´-Soto et al., 2018; Silva et al., 2017; Zulueta, Barba, Esteve, & Frı´gola, 2010); and/or improving extractability and bioaccessibility of bioactive compounds (Barba et al., 2017; Carbonell-Capella et al., 2016), extraction of compounds with added value from different food products, waste, and by-products, in order to develop new functional extracts as well as food additives and nutraceuticals (Granato, Nunes, & Barba, 2017; Pue´rtolas, Koubaa, & Barba, 2016). Moreover, this novel technology has also been used as an effective tool to reduce the formation of acrylamide in potato chips, improving fermentation, dehydration, and freeze thaw processes, as well as to reduce the formation of food processing contaminants (Barba et al., 2015), and among other applications. One of the common conclusions among the abovementioned reviews is that there is a need to study the target process, matrix, and compound in order to optimize processing conditions. In this context, PEF processing conditions can affect not only to prevent the growth of microorganisms and the retention of nutritional, physicochemical and quality properties but also to reduce the appearance of contaminants from processing, such as HMF, coming from the MR. In this chapter, some of the main implications of PEF technology on MR and the formation of HMF will be discussed.

6.2

Impact of pulsed electric field on Maillard reaction

MR depends strongly on many factors, including temperature, time, pH, reactant concentrations, and nature of reactants (i.e., type of sugar, type of amino acid, or protein). Due to its universality in foods, its critical role for food quality, its complexity in a reaction mechanism, and its high diversity of reaction by-products, MR, especially its reaction kinetics, has still gained increasing interest. A number of kinetic models, such as

Chapter 6 Effect of pulsed electric field on Maillard reaction and hydroxymethylfurfural production

multiresponse model, logistic, and Gompertz models, were proposed to understand reaction mechanisms (Brands & Van Boekel, 2002; Martins & Van Boekel, 2005; Quintas, Guimara˜es, Baylina, Branda˜o, & Silva, 2007). To control the extent of MR and minimize the detrimental effect of traditional thermal processing, some emerging technologies, such as microwave technology, vacuum frying, high hydrostatic pressure, PEF, and supercritical carbon dioxide treatment, have been employed to provide minimally processed food with good quality and safety (Casal, Ramı´rez, Iban˜ez, Corzo, & Olano, 2006; De Vleeschouwer, der Plancken, Van Loey, & Hendrickx, 2010; Granda & Moreira, 2005; Laguerre et al., 2011; Van Der Plancken et al., 2012). Mechanisms of the MR, which occurs in multiple steps and has different rate constants for every step, are still not well elucidated. Modeling this process is essential for food chemists to predict and control the browning reaction, which not only affects sensorial attributes but also the nutritional value of food. For instance, the impact of PEF on MR as well the MRPs was previously investigated (Wang et al., 2011). These authors showed that about 13% of glycine and 51% of glucose in a food model system were consumed during the PEF-induced MR. This study showed that PEF, especially at higher intensities (e.g., .30 kV/cm), can enhance the MR at low temperatures (,40 C). In a further study the same research group investigated the effects of electric field intensity and treatment time on MR kinetic parameters (Wang, Wang, Guo, Ma, & Yu, 2013). For this purpose the authors used glucose glycine aqueous model solutions (pH 9.0) that were subjected to PEF treatment at different electric intensities (10 50 kV/cm) and treatment times (0.8 4.0 ms). The authors observed a significant relationship between browning rate, treatment time, and PEF intensity, observing an enhanced browning when PEF parameters were increased. Moreover, they observed an increase in DPPH scavenging ability after increasing electric intensity and treatment time. The authors attributed this fact to the formation of MRPs. They also evaluated pH changes, as it is an important factor in MR. Previous studies found that the inhibition effect of pH on MR was not significant at the early stage, observing a linear decrease in pH value during MR. In the study conducted by Wang et al. (2013), the authors observed an increased decrease in pH when PEF intensity was higher, being this fact attributed to the enhanced reaction rate. Moreover, they attributed the initial decline of pH value of the reaction system to the formation of organic acids (formic acid, acetic acid) and the consumption of the amino group.

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Table 6.1 Impact of pulsed electric field (PEF) on the formation of hydroxymethylfurfural (HMF) and Maillard reaction in some food matrices. Food matrix

PEF conditions

Glucose glycine 10 50 kV/cm/0.8 4.0 μs aqueous solutions; pH 9.0 Apple juice

Strawberry juice

0 26.7 kV/cm/0 873.1 μs, 10 C 40 C, 0 500 pps frequency, and 0 147 J/s energy 35 kV/cm electric field strength for 1700 μs at 100 Hz

Emblica officinalis juice

26 kV/cm/1 μs monopolar pulses/500 μs

Orange carrot beverage

25 kV/cm/280 330 μs

Date juice

35 kV/cm for 1000 μs using pulses of 4 μs pulses at 100 Hz in bipolar mode

Main findings

References

First-Order kinetics was found to be a much more appropriate model to describe the effects of pulsed electric field on the Maillard reaction. HMF formation after 10 kV/cm

Wang et al. (2013)

Akdemir Evrendilek, Celik, Agcam, and Akyildiz (2017)

Decreased HMD formation compared to Aguilo´-Aguayo, Omsthermal treatment (90 C/30 s) Oliu, Soliva-Fortuny, and Martı´n-Belloso (2009) Replacing the thermal treatment with Bansal, Sharma, PEF decreased the concentration of HMF Ghanshyam, Singla, and the browning index of the juice. and Kim (2015) No significant levels of HMF Rivas, Rodrigo, Martı´nez, BarbosaCa´novas, and Rodrigo (2006) High-intensity pulsed electric fieldMtaoua, Sa´ncheztreated date juice had a lower HMF Vega, Ferchichi, and concentration compared to that of Martı´n-Belloso (2017) thermally pasteurized sample.

Sugar consumption was also evaluated as a useful indicator of MR. The authors observed an increased decrease of glucose with increased PEF treatment time, although the degree of browning of glucose glycine after using PEF was lower than classical heating, which confirms the ability of PEF treatment to reduce side reactions. Recent investigations have evaluated the impact of PEF on the HMF formation in various food matrices. Some of the most relevant studies are described in Table 6.1.

6.3

Effects of pulsed electric field on furfural and hydroxymethylfurfural formation

The impact of PEF (0 26.7 kV/cm/0 873.1 μs, 10 C 40 C, frequency of 0 500 pps, and 0 147 J/s energy) on the

Chapter 6 Effect of pulsed electric field on Maillard reaction and hydroxymethylfurfural production

formation of furfural and HMF in apple juice was evaluated (Akdemir Evrendilek et al., 2017). The authors observed that PEF induced the formation of furfural and HMF after the application of PEF at electric field strengths higher than 10 kV/cm and high levels of energy (80 140 J/s), corresponding to the highest levels at electric field strengths .25 kV/cm. However, under the applied conditions, they did not find a significant formation of furfural and HMF in the PEF-treated apple juices (Akdemir Evrendilek et al., 2017), while a significant formation was found after thermal treatment. HMF formation at lower concentrations was also reported to be formed with the PEF treatments of strawberry juice (Aguilo´Aguayo et al., 2009). The application of 35 kV/cm electric field strength for 1700 μs at 100 Hz in bipolar modeled to lower 5(hydroxymethyl)-2-furfural concentration in strawberry juice than did the heat processing (90 C for 60 or 30 s) (Aguilo´Aguayo et al., 2009). In another study, Bansal et al. (2015) also observed that the formation of HMF was not important (  1.5 mg/L) after the application of PEF processed juice (26 kV/cm/1 μs monopolar pulses/500 μs) to Emblica officinalis juice while compared with thermal-treated (90 C/60 s) juice (  8.0 mg/L). Moreover, these authors also found slower browning rates after PEF compared to the thermal treatment. They attributed these reduced browning rates to the high retention of ascorbic acid found in the juice. In fact, when not oxidized, ascorbic acid does not provide reactive carbonyl groups, which can be precursors of nonenzymatic browning reactions. Similar results were reported after PEF processing (25 kV/cm/280 330 μs) of an orange carrot beverage where the authors did not find any significant changes in the HMF content of the product in comparison with the nontreated sample (Rivas et al., 2006). In another study the impact of PEF (35 and 40 kV/cm/ 40 180 μs) on furfural formation in an orange juice milk beverage fortified with ω-3 fatty acids and oleic acid was also evaluated (Zulueta, Esteve, Frasquet, & Frı´gola, 2007). In this work the authors did not detect the intolerable levels of furfurals after PEF treatments. In a more recent study, Zulueta, Barba, Esteve, and Frı´gola (2013) studied the influence of PEF (25 kV/cm/57 C/280 μs) on HMF formation in an orange juice milk based beverage, immediately after processing and during subsequent storage 7 weeks at 4 C. They also compared the results obtained with other nonthermal technology such as high pressure (HP) processing (400 MPa at 42 C for 5 min), an equivalent energy input

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conditions, and a conventional thermal treatment (90 C/15 s). Based on their findings, no significant modifications in HMF content of the HP- and PEF-treated samples immediately after the treatments or during subsequent storage were noted. However, as can be expected, thermal treatment led to a significant increase in HMF content. Kumar et al. (2015) evaluated the formation of HMF in mango nectar after applying a thermal treatment (TT: 96 C for 300 and 600 s), PEF (38 kV/cm/24 μs/120 Hz), and a combined treatment consisting of PEF 1 thermal (96 C for 90 s). The authors observed an increased formation of HMF with storage and with TT. However, PEF treatment prevented the formation of HMF compared to the TT, being its concentration much lower after PEF treatment compared to the thermally treated one. In a more recent study the impact of PEF (20 40 kV/cm/ 100 360 μs/0% 2.5% (w/v) stevia) on HMF content of a fruit juice mixture sweetened with was evaluated. The authors observed the highest HMF content after the application of PEF at 40 kV/cm (Carbonell-Capella et al., 2017). Similarly, Mtaoua et al. (2017) observed that HIPEF-treated (35 kV/cm for 1000 μs using pulses of 4 μs pulses at 100 Hz in bipolar mode) date juice had lower HMF concentration than TT samples (90 C for 60 s).

6.4

Conclusion

PEF technique can be considered as an alternative technique to heat treatment for controlling the MR and the formation of HMF. Previously conducted research highlighted the possibility of replacing the traditional techniques with this nonthermal technique to minimize the undesirable MR in the food product, which is a key consideration for the production of healthy products in some cases. It should be noted that PEF might enhance the MR in some food products under special process conditions. Therefore, further investigations are necessary to elucidate the mechanisms of PEF promoting MR. For example, it should be noted that increased PEF intensities and treatment times enhanced the formation of MRPs; however, they promoted a decrease in pH value and glucose content in glucose glycine aqueous model solutions.

Chapter 6 Effect of pulsed electric field on Maillard reaction and hydroxymethylfurfural production

References Aguilo´-Aguayo, I., Oms-Oliu, G., Soliva-Fortuny, R., & Martı´n-Belloso, O. (2009). Changes in quality attributes throughout storage of strawberry juice processed by high-intensity pulsed electric fields or heat treatments. LWT Food Science and Technology, 42(4), 813 818. Akdemir Evrendilek, G., Celik, P., Agcam, E., & Akyildiz, A. (2017). Assessing impacts of pulsed electric fields on quality attributes and furfural and hydroxymethylfurfural formations in apple juice. Journal of Food Process Engineering, 40(5). Available from https://doi.org/10.1111/jfpe.12524. Bansal, V., Sharma, A., Ghanshyam, C., Singla, M. L., & Kim, K.-H. (2015). Influence of pulsed electric field and heat treatment on Emblica officinalis juice inoculated with Zygosaccharomyces bailii. Food and Bioproducts Processing, 95, 146 154. Barba, F. J., Carbonell-Capella, J. M., Esteve, M. J., & Frı´gola, A. (2013). Automating a 96-well microtiter plate assay for quick analysis of chemically available lysine in foods. Food Analytical Methods, 6(5), 1258 1264. Barba, F. J., Koubaa, M., do Prado-Silva, L., Orlien, V., & Sant’Ana, A. D. S. (2017). Mild processing applied to the inactivation of the main foodborne bacterial pathogens: A review. Trends in Food Science and Technology, 66. Available from https://doi.org/10.1016/j.tifs.2017.05.011. Barba, F. J., Mariutti, L. R. B., Bragagnolo, N., Mercadante, A. Z., BarbosaCa´novas, G. V., & Orlien, V. (2017). Bioaccessibility of bioactive compounds from fruits and vegetables after thermal and nonthermal processing. Trends in Food Science and Technology, 67. Available from https://doi.org/10.1016/j. tifs.2017.07.006. Barba, F. J., Parniakov, O., Pereira, S. A., Wiktor, A., Grimi, N., Boussetta, N., & Vorobiev, E. (2015). Current applications and new opportunities for the use of pulsed electric fields in food science and industry. Food Research International, 77. Available from https://doi.org/10.1016/j. foodres.2015.09.015. Brands, C. M. J., & Van Boekel, M. A. J. S. (2002). Kinetic modeling of reactions in heated monosaccharide-casein systems. Journal of Agricultural and Food Chemistry, 50(23), 6725 6739. Available from https://doi.org/10.1021/ jf011164h. Capuano, E., & Fogliano, V. (2011). Acrylamide and 5-hydroxymethylfurfural (HMF): A review on metabolism, toxicity, occurrence in food and mitigation strategies. LWT Food Science and Technology, 44(4), 793 810. Available from https://doi.org/10.1016/j.lwt.2010.11.002. Carbonell-Capella, J. M., Buniowska, M., Barba, F. J., Grimi, N., Vorobiev, E., Esteve, M. J., & Frı´gola, A. (2016). Changes of antioxidant compounds in a fruit juice-Stevia rebaudiana blend processed by pulsed electric technologies and ultrasound. Food and Bioprocess Technology, 9(7). Available from https:// doi.org/10.1007/s11947-016-1706-1. Carbonell-Capella, J. M., Buniowska, M., Cortes, C., Zulueta, A., Frigola, A., & Esteve, M. J. (2017). Influence of pulsed electric field processing on the quality of fruit juice beverages sweetened with Stevia rebaudiana. Food and Bioproducts Processing, 101, 214 222. ˜ ez, E., Corzo, N., & Olano, A. (2006). Effect of Casal, E., Ramı´rez, P., Iban supercritical carbon dioxide treatment on the Maillard reaction in model food systems. Food Chemistry, 97(2), 272 276. Available from https://doi.org/ 10.1016/j.foodchem.2005.03.047.

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Corte´s, C., Barba, F., Esteve, M. J., Gonza´lez, R., & Frı´gola, A. (2008). Total antioxidant capacity of refrigerated orange juice treated with pulsed electric fields. Proceedings of the Nutrition Society, 67(OCE), E34. Retrieved fromhttp://www.scopus.com/inward/record.url?eid 5 2-s2.0-47249101092 &partnerID 5 40&md5 5 76e44af8738bd54d3fb8406a65993014. ˜ iga, A. D. G., & Rojas, de Oliveira, F. C., Coimbra, J. S. D. R., de Oliveira, E. B., Zun E. E. G. (2016). Food protein-polysaccharide conjugates obtained via the Maillard reaction: A review. Critical Reviews in Food Science and Nutrition, 56(7), 1108 1125. De Vleeschouwer, K., der Plancken, I., Van Loey, A., & Hendrickx, M. E. (2010). The effect of high pressure-high temperature processing conditions on acrylamide formation and other Maillard reaction compounds. Journal of Agricultural and Food Chemistry, 58(22), 11740 11748. Esteve, M. I., Barba, F. J., Palop, S., & Frı´gola, A. (2009). The effects of nonthermal processing on carotenoids in orange juice. Czech Journal of Food Sciences, 27, S304 S306. (SPEC. ISS.). Gabri´c, D., Barba, F., Roohinejad, S., Gharibzahedi, S. M. T., Radoj´cin, M., Putnik, P., & Bursa´c Kova´cevi´c, D. (2018). Pulsed electric fields as an alternative to thermal processing for preservation of nutritive and physicochemical properties of beverages: A review. Journal of Food Process Engineering, 41(1). Available from https://doi.org/10.1111/jfpe.12638. Gavahian, M., Chu, Y.-H., & Sastry, S. (2018). Extraction from food and natural products by moderate electric field: Mechanisms, benefits, and potential industrial applications. Comprehensive Reviews in Food Science and Food Safety, 17(4), 1040 1052. Gavahian, M., Farahnaky, A., & Sastry, S. (2016). Ohmic-assisted hydrodistillation: A novel method for ethanol distillation. Food and Bioproducts Processing, 98, 44 49. Gavahian, M., Lee, Y.-T., & Chu, Y.-H. (2018). Ohmic-assisted hydrodistillation of citronella oil from Taiwanese citronella grass: Impacts on the essential oil and extraction medium. Innovative Food Science and Emerging Technologies, 48, 33 41. Gerrard, J. A. (2006). The Maillard reaction in food: Progress made, challenges ahead-Conference Report from the Eighth International Symposium on the Maillard reaction. Trends in Food Science and Technology, 17(6), 324 330. Available from https://doi.org/10.1016/j.tifs.2005.11.011. Granato, D., Nunes, D. S., & Barba, F. J. (2017). An integrated strategy between food chemistry, biology, nutrition, pharmacology, and statistics in the development of functional foods: A proposal. Trends in Food Science & Technology. Available from https://doi.org/10.1016/j.tifs.2016.12.010. Granda, C., & Moreira, R. G. (2005). Kinetics of acrylamide formation during traditional and vacuum frying of potato chips. Journal of Food Process Engineering, 28(5), 478 493. Available from https://doi.org/10.1111/j.17454530.2005.034.x. Hemmler, D., Roullier-Gall, C., Marshall, J. W., Rychlik, M., Taylor, A. J., & Schmitt-Kopplin, P. (2017). Evolution of complex Maillard chemical reactions, resolved in time. Scientific Reports, 7(1). Available from https://doi.org/ 10.1038/s41598-017-03691-z. Koubaa, M., Barba, F. J., Bursa´c Kovaˇcevi´c, D., Putnik, P., Santos, M. D., Queiro´s, R. P., & Saraiva, J. A. (2017). Pulsed electric field processing of fruit juices. Fruit Juices: Extraction, Composition, Quality and Analysis. Available from https://doi.org/10.1016/B978-0-12-802230-6.00022-9.

Chapter 6 Effect of pulsed electric field on Maillard reaction and hydroxymethylfurfural production

Kumar, R., Bawa, A. S., Rajeswara Reddy, K., Kathiravan, T., Subramanian, V., & Nadanasabapathi, S. (2015). Pulsed electric field and combination processing of mango nectar: effect on volatile compounds and HMF formation. Croatian Journal of Food Science and Technology, 7(2), 58 67. Laguerre, J.-C., Pascale, G.-W., David, M., Evelyne, O., Lamia, A.-A., & Ins, B.-A. (2011). The impact of microwave heating of infant formula model on neoformed contaminant formation, nutrient degradation and spore destruction. Journal of Food Engineering, 107(2), 208 213. Available from https://doi.org/ 10.1016/j.jfoodeng.2011.06.021. Martins, S. I. F. S., & Van Boekel, M. A. J. S. (2005). A kinetic model for the glucose/glycine Maillard reaction pathways. Food Chemistry, 90(1 2), 257 269. Available from https://doi.org/10.1016/j.foodchem.2004.04.006. Misra, N. N., Koubaa, M., Roohinejad, S., Juliano, P., Alpas, H., Ina`cio, R. S., & Barba, F. J. (2017). Landmarks in the historical development of twenty first century food processing technologies. Food Research International, 97, 318 339. Misra, N. N., Martynenko, A., Chemat, F., Paniwnyk, L., Barba, F. J., & Jambrak, A. R. (2017). Thermodynamics, transport phenomena and electrochemistry of external field assisted non-thermal food technologies. Critical Reviews in Food Science and Nutrition. Available from https://doi.org/10.1080/ 10408398.2017.1287660, 0(ja), 0. Mtaoua, H., Sa´nchez-Vega, R., Ferchichi, A., & Martı´n-Belloso, O. (2017). Impact of high-Intensity pulsed electric fields or thermal treatment on the quality attributes of date juice through storage. Journal of Food Processing and Preservation, 41(4), e13052. Pue´rtolas, E., & Barba, F. J. (2016). Electrotechnologies applied to valorization of by-products from food industry: Main findings, energy and economic cost of their industrialization. Food and Bioproducts Processing, 100. Available from https://doi.org/10.1016/j.fbp.2016.06.020. Pue´rtolas, E., Koubaa, M., & Barba, F. J. (2016). An overview of the impact of electrotechnologies for the recovery of oil and high-value compounds from vegetable oil industry: Energy and economic cost implications. Food Research International, 80, 19 26. Quintas, M., Guimara˜es, C., Baylina, J., Branda˜o, T. R. S., & Silva, C. L. M. (2007). Multiresponse modelling of the caramelisation reaction. Innovative Food Science and Emerging Technologies, 8(2), 306 315. Available from https://doi. org/10.1016/j.ifset.2007.02.002. Rivas, A., Rodrigo, D., Martı´nez, A., Barbosa-Ca´novas, G. V., & Rodrigo, M. (2006). Effect of PEF and heat pasteurization on the physical chemical characteristics of blended orange and carrot juice. LWT Food Science and Technology, 39(10), 1163 1170. ˜ es, Rosello´-Soto, E., Poojary, M. M., Barba, F. J., Koubaa, M., Lorenzo, J. M., Man J., & Molto´, J. C. (2018). Thermal and non-thermal preservation techniques of tiger nuts’ beverage “horchata de chufa”. Implications for food safety, nutritional and quality properties. Food Research International, 105, 945 951. Available from https://doi.org/10.1016/j.foodres.2017.12.014. Silva, E. S., Roohinejad, S., Koubaa, M., Barba, F. J., Jambrak, A. R., Vukuˇsic, T., et al. (2017). Effect of pulsed electric fields on food constituents. In Handbook of electroporation (Vol. 3). ,https://doi.org/10.1007/978-3-319-32886-7_31.. Somoza, V. (2005). Five years of research on health risks and benefits of Maillard reaction products: An update. Molecular Nutrition and Food Research, 49(7), 663 672. Available from https://doi.org/10.1002/mnfr.200500034.

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Tamanna, N., & Mahmood, N. (2015). Food processing and Maillard reaction products: Effect on human health and nutrition. International Journal of Food Science, 2015. Tessier, F. J., & Birlouez-Aragon, I. (2012). Health effects of dietary Maillard reaction products: The results of ICARE and other studies. Amino Acids, 42(4), 1119 1131. Van Der Plancken, I., Verbeyst, L., De Vleeschouwer, K., Grauwet, T., Heinio¨, R.-L., Husband, F. A., & Hendrickx, M. (2012). (Bio)chemical reactions during high pressure/high temperature processing affect safety and quality of plantbased foods. Trends in Food Science and Technology, 23(1), 28 38. Available from https://doi.org/10.1016/j.tifs.2011.08.004. Wang, J., Guan, Y.-G., Yu, S.-J., Zeng, X.-A., Liu, Y.-Y., Yuan, S., & Xu, R. (2011). Study on the Maillard reaction enhanced by pulsed electric field in a glycinglucose model system. Food and Bioprocess Technology, 4(3), 469 474. Available from https://doi.org/10.1007/s11947-010-0340-6. Wang, Z., Wang, J., Guo, S., Ma, S., & Yu, S.-J. (2013). Kinetic modeling of Maillard reaction system subjected to pulsed electric field. Innovative Food Science and Emerging Technologies, 20, 121 125. Zulueta, A., Barba, F. J., Esteve, M. J., & Frı´gola, A. (2010). Effects on the carotenoid pattern and vitamin A of a pulsed electric field-treated orange juice-milk beverage and behavior during storage. European Food Research and Technology, 231(4), 525 534. Zulueta, A., Barba, F. J., Esteve, M. J., & Frı´gola, A. (2013). Changes in quality and nutritional parameters during refrigerated storage of an orange juice-milk beverage treated by equivalent thermal and non-thermal processes for mild pasteurization. Food and Bioprocess Technology, 6(8), 2018 2030. Zulueta, A., Esteve, M. J., Frasquet, I., & Frı´gola, A. (2007). Fatty acid profile changes during orange juice-milk beverage processing by high-pulsed electric field. European Journal of Lipid Science and Technology, 109(1), 25 31. Available from https://doi.org/10.1002/ejlt.200600202.

The potential of pulsed electric fields to reduce pesticides and toxins

7

Noelia Pallare´s1, Josefa Tolosa1, Mohsen Gavahian2, Francisco J. Barba1, Amin Mousavi-Khaneghah3 and Emilia Ferrer1 1

Preventive Medicine and Public Health Department, Faculty of Pharmacy, Universitat de Vale`ncia, Vale`ncia, Spain 2Product and Process Research Center, Food Industry Research and Development Institute, Hsinchu, Taiwan, ROC 3Department of Food Science, Faculty of Food Engineering, State University of Campinas (UNICAMP), Campinas, Brazil

7.1

Introduction

Among the contaminants that could threaten human health, the proposed risks by pesticides, as common chemical compounds in the agricultural industry, are a matter of serious concern (Amirahmadi et al., 2017; Razzaghi et al., 2018; Yadolahi, Babri, Sharif, & Khaneghah, 2012). For instance, huge concentration of pesticides are widely used to protect crops against the pest infestation, resulting in residues on harvested crops, which can lead to health concerns among consumers (Banias, Achillas, Vlachokostas, Moussiopoulos, & Stefanou, 2017). In this context, in addition to serious environmental issues correlated with the use of pesticides, other types of chemical compounds such as herbicides, and fungicides have been also identified as a public concern (Nicolopoulou-Stamati, Maipas, Kotampasi, Stamatis, & Hens, 2016) (Fig. 7.1). According to available data, around 5.6 billion pounds of pesticide are consumed worldwide (Alavanja, 2009), which are associated with negative effects on human health (e.g., growth retardation) (Nicolopoulou-Stamati et al., 2016). On the other hand, the mycotoxins, as a serious concern for both food and feed, can be defined as secondary metabolites secreted by some fungal species belonging mainly to the

Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00007-0 © 2020 Elsevier Inc. All rights reserved.

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Pulsed electric field (PEF)

Pesticides: Chlorpyrifos Methamidophos

Fungicides: Pyrimethanil, vinclozolin, cyprodinil, procymidone

Figure 7.1 Chemical structures of the most commonly evaluated pesticides and fungicides in apple juice and wine after PEF treatments.

Aspergillus, Fusarium, Penicillium, and Alternaria genera (Khaneghah, Martins, von Hertwig, Bertoldo, & Sant’Ana, 2018; Majeed, Khaneghah, Kadmi, Khan, & Shariati, 2018; Marin, Ramos, Cano-Sancho, & Sanchis, 2013; Mousavi Khaneghah, Fakhri, Raeisi, Armoon, & Sant’Ana, 2018; Mousavi Khaneghah, Fakhri, & Sant’Ana, 2018). During different stages of processing as well as during storage, the growing of mycotoxigenic mold in contaminated foods can result in the formation of mycotoxins (Khaneghah, Chaves, & Akbarirad, 2017; Mousavi Khaneghah, Ismail, Raeisi, & Fakhri, 2018; Rastegar et al., 2017). Among 300 identified secondary metabolites, ochratoxin A, aflatoxins, fumonisins, zearalenone, patulin, and deoxynivalenol can be considered highly significant mycotoxins with adverse effects on food safety, the economy as well as human health (Marin et al., 2013). Besides the huge economic losses, mycotoxins could pose some adverse effects on human and animal’s health such as immunosuppression, neurotoxicity, estrogenicity, dermatotoxicity, teratogenicity, hepatotoxicity, carcinogenicity, and mutagenicity (Amirahmadi, Shoeibi, Rastegar, Elmi, & Mousavi Khaneghah, 2018; Heshmati, Zohrevand, Khaneghah, Mozaffari Nejad, & Sant’Ana, 2017). However, although mycotoxin contamination can be detected in a wide variety of food products, the prevalence of mycotoxins is mostly reported in agricultural crops such as barley, wheat corn, and rice (Amirahmadi et al., 2017; Majeed et al., 2018). The most commonly contaminated crops or substrates consist of cereals, nuts, oilseeds, dried fruits, coffee, spices, and

Chapter 7 The potential of pulsed electric fields to reduce pesticides and toxins

their byproducts. The contamination by mycotoxins occurs throughout the food chain, during field and/or in the postharvest stage. Significant economic losses are associated with the impact of mycotoxins on human health, animal productivity, and domestic and international trade. AFs, OTA, ZEA, trichothecens, FBs, and PAT are some of the mycotoxins with higher ¨ nu¨san, 2019). agroeconomic impact (FAO, 2018; U Food processing can have an impact on pesticide and mycotoxin levels, but the details remain unclear. Most publications are focused on the effect of processing techniques such as cleaning and milling of grains, microbiological fermentation or thermal processes such as cooking, boiling, and extrusion, among others (Cano-Sancho, Sanchis, Ramos, & Marı´n, 2013). Less information is available about the effect of emerging technologies in food processing such as high hydrostatic pressure, pulsed electric fields (PEFs), or ultrasound on pesticides and mycotoxin levels. Some authors have evaluated the impact of nonthermal processing such as gamma irradiation (Di Stefano, Pitonzo, & Avellone, 2014; Jalili, Jinap, & Noranizan, 2010), ozone gas (El-Desouky, Sharoba, El-Desouky, El-Mansy, & Naguib, 2012), among others. The impact of PEF could constitute an effective tool to reduce pesticides and mycotoxin levels of food matrices. PEF is an emerging nonthermal technology in the food industry that has been shown to maintain the sensory and nutritional properties of the food materials better than those of conventional thermal treatments (Barba, Koubaa, do PradoSilva, Orlien, & Sant’Ana, 2017; Barba et al., 2015; Gabri´c et al., 2018; Misra et al., 2017; Zulueta, Barba, Esteve, & Frı´gola, 2010). This innovative processing technique was also proved to be superior to traditional processing techniques in terms of processing time required (Yang, Huang, Lyu, & Wang, 2016) and, therefore, can reduce the process time and production cost while improving the process efficiency. In a PEF process an electric field is applied across the samples through PEF electrodes for some microseconds (Pue´rtolas & Barba, 2016; Pue´rtolas, Koubaa, & Barba, 2016; Zhu et al., 2016). This technique is different from that of ohmic heating (Gavahian, Farahnaky, Javidnia, & Majzoobi, 2012) and moderate electric field (Gavahian, Chu, & Sastry, 2018) mainly due to the applied frequencies and the treatment time. This technique has been successfully used for microbial decontamination (Puligundla, Pyun, & Mok, 2018) and the extraction process (Barba, Zhu, Koubaa, Sant’Ana, & Orlien, 2016; Koubaa et al., 2016; Lang & Jun, 2017; Pue´rtolas et al., 2016). Researchers have also explored the

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feasibility of PEF for pesticides and toxins removal from food materials. Some of the main findings are reported in the following sections.

7.2

Pesticides

The potential of PEF to reduce the concentration of pesticides in food products has been a matter of interest for several authors (Table 7.1). For instance, Chen et al. (2009) studied the impact of PEFs on the reduction of methamidophos and chlorpyrifos from apple juice. They found that PEF treatments at electric field strengths of 8 20 kV/cm and pulse number from 6 to 26 pulses led to significant degradations of both pesticides, being chlorpyrifos much more labile to PEF than methamidophos. They also observed that the degradation of both pesticides was increased when the electric field was augmented. They attributed this fact to the ability of high voltage increase to induce the vibration and rotation of polar molecules, thus facilitating the degradation of pesticides. In another study, the effects of PEF treatments on the degradation of pesticides diazinon and dimethoate from apple juice were studied (Zhang et al., 2012). These authors found a significant degradation of both pesticides after PEF treatments, with a significant decrease when electric field strength and treatment time were increased, observing the maximum degradation of Table 7.1 Effect of pulsed electric fields (PEF) on pesticides from food products. Matrix Compound

PEF treatment

Main findings

References

Apple juice

8, 12, 16, and 20 kV/ cm/40 C/6, 9, 12, 19, and 26 pulses/ 60 260 µs 8, 12, 16, and 20 kV/ cm/15 C 23.5 C/60, 90, 120, 190, and 260 µs 5 20 kV/cm/0.5 2 ms/10 160 kJ/L

Significant degradation of both pesticides being chlorpyrifos more labile than methamidophos. Increased degradation with enhanced electric field and time Significant degradation of both pesticides. Electric field strength and time had a significant effect

Chen et al. (2009)

Chlorpyrifos, methamidophos

Diazinon, dimethoate

Wine

Pyrimethanil, vinclozolin, cyprodinil, procymidone

Zhang et al. (2012)

Significant degradation fungicides. Delsart et al. Increased with enhanced PEF strength and (2015) energies

Chapter 7 The potential of pulsed electric fields to reduce pesticides and toxins

both diazinon (47.6%) and dimethoate (34.7%) after 260 µs PEF at electrical field strength of 20 kV/cm. More recently, the impact of PEF on four residual fungicides (pyrimethanil, vinclozolin, cyprodinil, and procymidone) in white wines was evaluated (Delsart et al., 2015). It was found that PEF significantly induced the degradation of these fungicides. Moreover, they observed that the effect of the strength and energy of PEF treatment on the degradation of these fungicides was higher than that of the treatment time.

7.3

Toxins

Mycotoxins are a type of toxins produced by fungi. Mycotoxins can be a problem at the level of human health. The composition regarding mycotoxins differs according to the food matrix studied. For example, the mycotoxins that are most frequently found in cereals are aflatoxins, ochratoxin A, fumonisins, deoxynivalenol, and zearalenone. These mycotoxins are not completely destroyed during the processing of cereals and can contaminate other final products. This is why over the last decades there have been numerous efforts to find different processes that can reduce the content of mycotoxins. In fact there are several processes that can have an effect on mycotoxins such as sorting, trimming, cleaning, milling, brewing, cooking, baking, frying, roasting, canning, flaking, alkaline cooking, nixtamalization, and extrusion. Generally, the greatest reduction is when higher temperatures are used, although normally they are not completely eliminated. In fact, different inactivation mechanisms are observed according to the type of mycotoxin evaluated and the type of treatment used (Bullerman & Bianchini, 2007). On the other hand, extrusion and roasting processes have been proved to be effective in reducing the concentrations of mycotoxin concentrations. It should be noted that this reduction is correlated with the elevated temperatures involved in these processes. For example, a previously conducted study showed that the extrusion process at the temperatures  150 C effectively reduced the concentrations of zearalenone, aflatoxins, deoxynivalenol, and fumonisins. On the other hand, running the process at an elevated temperature, that is, 160 C resulted in better elimination of fumonisins. The same enhanced detoxification effect was observed when the extrusion process was conducted in the presence of glucose. When the corn grits contaminated with fumonisin B1, mixed with 10% glucose, and subjected to

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the extrusion process, only 15% 25% of the fumonisin remained in the processed product. According to the authors, extrusion process also resulted in the formation of several degrades products of fumonisin such as N-(1-deoxy-D-fructos-1-yl) fumonisin B1, hydrolyzed fumonisin B1, and N-(carboxymethyl)—fumonisin B1. Moreover, rats were used to evaluate the toxicity of the extruded corn grits, and the results confirmed that extrusion process can reduce the toxicity of the fumonisin contaminated products (Bullerman & Bianchini, 2007). It is now accepted that PEF treatment can decrease the aflatoxins B1 and G1 produced by Aspergillus flavus (Eisa, Ali, ElHabbaa, Abdel-Reheem, & Abou-El-Ella, 2003) (Table 7.2). Researchers observed 75.6% and 82.8% when 4-day-old A. flavus cultures were subjected to PEF treatments up to 24 h at the frequencies of 0.50 and 50 Hz, respectively. The rising frequency of the PEF treatment from 0.1 to 0.4 kHz decreases the population of A. flavus slightly. On the other hand, an elevated frequency, that is, 0.8 kHz significantly enhanced the decontamination effects of PEF treatment. Moreover, multiple-exposure mode at different frequencies of PEF ranging from 0.5 to 0.8 kHz reduced the aflatoxin production rate by up to 99%. It should be noted that aflatoxin B1 was not detectable at different combined PEF

Table 7.2 Effect of pulsed electric fields (PEF) on toxins from food products. Matrix Compound PEF treatment Artificially Potato dextrose spiked aflatoxin agar

Aflatoxins

Model solution

Ricin

PEF: Pulse frequency (50 Hz), burst (10), energy (1 kJ), and for a time of 10 s Thermal treatment: 110 C 119 C/ 10 23.4 min/pH: 1.95 10 Output voltage (20% 65%), pulse width (10 26 µs), pH (4 10) 30 kV/cm, 10 300 ns per pulse

Main findings

References

Decrease after combined application of PEF 1 thermal treatment

Subramanian et al. (2017)

Increased pulse width and voltage decreased aflatoxin content

Vijayalakshmi et al. (2018)

Decrease in ricin toxicity or modification in the secondary structure (beta-sheet and beta-turn underwent transition) after PEF treatment. Reduced toxicity in mice of the PEF-treated ricin compared to the untreated one

Wei et al. (2016)

Chapter 7 The potential of pulsed electric fields to reduce pesticides and toxins

strengths. Multiple-exposure of yellow corn grains for 3 weeks to a combined treatment decreased the aflatoxin concentration, in both A. flavus inoculated and noninoculated grains as compared to that of the control sample. In addition, the study revealed that only slight changes occurred in the changes were observed in carbohydrates and protein contents of the PEFtreated samples (Eisa et al., 2003). In another study the effect of previously optimized heat treatment alone or in combination with PEF on artificially spiked aflatoxin in potato dextrose agar was evaluated and compared (Subramanian, Shanmugam, Ranganathan, Kumar, & Reddy, 2017). First, the authors optimized heat processing using a response surface methodology with temperatures of 110 C 119.8 C and times ranging from 10 to 20 min. They also optimized pH (from 4 to 10). After that, they evaluated the effect of PEF treatment (1 kJ/Pulse frequency of 50 Hz)/burst (10), for a time of 10 s) on aflatoxins combined with the optimal conditions for heat treatment and compared the results to those obtained for control samples (without PEF treatment). The authors observed a decrease in aflatoxins content in potato dextrose agar after using the combined treatment (thermal 1 PEF) compared to the treatments performed individually. More recently, Vijayalakshmi, Nadanasabhapathi, Kumar, and Sunny Kumar (2018) assessed the effectiveness of a PEF process in decreasing the concentrations of toxic compounds in model systems of potato dextrose agar that were artificially contaminated with aflatoxin. In this regard, the authors examined the concentrations of aflatoxins in the PEF-treated and -untreated samples by means of high-performance liquid chromatography technique. The authors also tried to optimize the decontamination effects of PEF treatment [output voltage (20% 65%), pulse width (10 26 µs), and pH (4 10)] through the response surface methodology by adjusting effective process parameters in aflatoxin reduction. The authors observed that pH was the main responsible of the changes in aflatoxin contents. Moreover, they also found the factors involved in aflatoxin B1 and total aflatoxin reduction fitted the 2FI polynomial model and quadratic model respectively, being of great importance to control moisture content when the experiments will be carried out in real food matrices. This study highlighted the importance of PEF process optimization for a successful aflatoxin removal from food materials. According to the authors, pulse width, food sample pH, and the applied voltage (voltage intensity) were among the crucial parameters that should be considered for maximizing the decontamination effects of PEF processes (Vijayalakshmi et al., 2018).

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Figure 7.2 The killing efficiency of 0.5 mL of PEF-treated and -untreated ricins at the initial concentration of 20 µg/mL on mice. Source: Wei, K., Li, W., Gao, S., Ji, B., Zang, Y., Su, B., . . .Wang, J. (2016). Inactivation of ricin toxin by nanosecond pulsed electric fields including evidences from cell and animal toxicity. Scientific Reports, 6,18781. Available from https://doi.org/10.1038/srep18781, with permission. This work is licensed under a Creative Commons Attribution 4.0 International License.

On the other hand, in a study conducted by Wei et al. (2016), these authors evaluated the effect of PEF (30 kV/cm, 10 300 ns per pulse) to inactivate ricin up to 4.2 µg/mL. In order to evaluate the effectiveness of PEF treatments, cells and mice were used. Then, ricin (without treatment or PEF-treated) was injected intraperitoneally directly and the mice were also exposed to inhalation to ricin. While 40% of the mice exposed to ricin previously treated by PEF survived, 100% of the mice exposed to ricin without previous treatment had to be sacrificed, thus demonstrating the efficacy of the PEF (Fig. 7.2). The authors attributed this positive effect of the PEF in the decrease in the toxicity of ricin to a modification in the secondary structure (beta-sheet and beta-turn underwent transition) of ricin after treatment, which was confirmed after carrying out an electrophoresis analysis in polyacrylamide gel with dodecyl sulfate of sodium (SDS PAGE) and circular dichroism.

7.4

Conclusion

PEF has shown good potential for application in the food industry, especially for liquid food pasteurization. Toxin and

Chapter 7 The potential of pulsed electric fields to reduce pesticides and toxins

pesticide removal is an emerging application of this nonthermal process. It was shown that PEF can successfully reduce the concentrations of some toxins (e.g., aflatoxin) and pesticides, (e.g. methamidophos and chlorpyrifos) from food materials. Furthermore, it was proved that this decontamination can be performed with limited negative effects on the product quality parameters as compared to those of traditional thermal technologies. Besides, researchers have highlighted the importance of PEF optimization in terms of process duration, pulse width, food sample pH, and the applied voltage (voltage intensity) for a successful decontamination process. However, further fundamental studies are required to understand the details of the mechanisms involved in pesticide and toxin removal from food samples by PEF.

Acknowledgment Noelia Pallare´s, Josefa Tolosa, Francisco J. Barba, and Emilia Ferrer would like to acknowledge Generalitat Valenciana for the financial support (IDIFEDER/ 2018/046—Procesos innovadores de extraccio´n y conservacio´n: pulsos ele´ctricos y fluidos supercrı´ticos) through European Union ERDF funds (European Regional Development Fund).

References Alavanja, M. C. R. (2009). Introduction: Pesticides use and exposure extensive worldwide. Reviews on Environmental Health, 24(4), 303 309. Amirahmadi, M., Kobarfard, F., Pirali-Hamedani, M., Yazdanpanah, H., Rastegar, H., Shoeibi, S., & Mousavi Khaneghah, A. (2017). Effect of Iranian traditional cooking on fate of pesticides in white rice. Toxin Reviews, 36(3), 177 186. Amirahmadi, M., Shoeibi, S., Rastegar, H., Elmi, M., & Mousavi Khaneghah, A. (2018). Simultaneous analysis of mycotoxins in corn flour using LC/MS-MS combined with a modified QuEChERS procedure. Toxin Reviews, 37(3), 187 195. Banias, G., Achillas, C., Vlachokostas, C., Moussiopoulos, N., & Stefanou, M. (2017). Environmental impacts in the life cycle of olive oil: A literature review. Journal of the Science of Food and Agriculture, 97(6), 1686 1697. Barba, F. J., Koubaa, M., do Prado-Silva, L., Orlien, V., & Sant’Ana, A. D. S. (2017). Mild processing applied to the inactivation of the main foodborne bacterial pathogens: A review. Trends in Food Science and Technology, 66, 20 35. Barba, F. J., Parniakov, O., Pereira, S. A., Wiktor, A., Grimi, N., Boussetta, N., & Vorobiev, E. (2015). Current applications and new opportunities for the use of pulsed electric fields in food science and industry. Food Research International, 77(4), 773 798. Barba, F. J., Zhu, Z., Koubaa, M., Sant’Ana, A. S., & Orlien, V. (2016). Green alternative methods for the extraction of antioxidant bioactive compounds from winery wastes and by-products: A review. Trends in Food Science and Technology, 49, 96 109.

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Bullerman, L. B., & Bianchini, A. (2007). Stability of mycotoxins during food processing. International Journal of Food Microbiology, 119(1 2), 140 146. Cano-Sancho, G., Sanchis, V., Ramos, A. J., & Marı´n, S. (2013). Effect of food processing on exposure assessment studies with mycotoxins. Food Additives and Contaminants Part A Chemistry, Analysis, Control, Exposure and Risk Assessment, 30(5), 867 875. Chen, F., Zeng, L., Zhang, Y., Liao, X., Ge, Y., Hu, X., & Jiang, L. (2009). Degradation behaviour of methamidophos and chlorpyrifos in apple juice treated with pulsed electric fields. Food Chemistry, 112(4), 956 961. Delsart, C., Franc, C., Grimi, N., de Revel, G., Vorobiev, E., & Mietton Peuchot, M. (2015). Effects of pulsed electric fields on four residual fungicides in white wines. In 1st world congress on electroporation and pulsed electric fields in biology, medicine and food & environmental technologies. Portoroˇz, Slovenia: Springer. Available from https://doi.org/10.1007/978-981-287-817-5_27 Di Stefano, V., Pitonzo, R., & Avellone, G. (2014). Effect of gamma irradiation on aflatoxins and ochratoxin A reduction in almond samples. Journal of Food Research, 3(4), 113 118. Eisa, N. A., Ali, F. M., El-Habbaa, G. M., Abdel-Reheem, S. K., & Abou-El-Ella, M. F. (2003). Pulsed electric field technology for checking aflatoxin production in cultures and corn grains. Egypt Journal of Phytopathology, 31, 75 86. El-Desouky, T. A., Sharoba, A. M. A., El-Desouky, A. I., El-Mansy, H. A., & Naguib, K. (2012). Effect of ozone gas on degradation of aflatoxin B1 and Aspergillus flavus fungal. Journal of Environmental and Analytical Toxicology, 2, 128. FAO. Food safety and quality. (2018). ,http://www.fao.org/food/food-safetyquality/a-z-index/mycotoxins/en/. Accessed 10.02.19. Gabri´c, D., Barba, F., Roohinejad, S., Gharibzahedi, S. M. T., Radoj´cin, M., Putnik, P., & Bursa´c Kova´cevi´c, D. (2018). Pulsed electric fields as an alternative to thermal processing for preservation of nutritive and physicochemical properties of beverages: A review. Journal of Food Process Engineering, 41(1), e12638. Available from https://doi.org/10.1111/jfpe.12638. Gavahian, M., Chu, Y.-H., & Sastry, S. (2018). Extraction from food and natural products by moderate electric field: Mechanisms, benefits, and potential industrial applications. Comprehensive Reviews in Food Science and Food Safety, 17(4), 1040 1052. Gavahian, M., Farahnaky, A., Javidnia, K., & Majzoobi, M. (2012). Comparison of ohmic-assisted hydrodistillation with traditional hydrodistillation for the extraction of essential oils from Thymus vulgaris L. Innovative Food Science and Emerging Technologies, 14, 85 91. Heshmati, A., Zohrevand, T., Khaneghah, A. M., Mozaffari Nejad, A. S., & Sant’Ana, A. S. (2017). Co-occurrence of aflatoxins and ochratoxin A in dried fruits in Iran: Dietary exposure risk assessment. Food and Chemical Toxicology, 106, 202 208. Jalili, M., Jinap, S., & Noranizan, A. (2010). Effect of gamma radiation on reduction of mycotoxins in black pepper. Food Control, 21(10), 1388 1393. Khaneghah, A. M., Chaves, R. D., & Akbarirad, H. (2017). Detoxification of aflatoxin M1 (AFM1) in dairy base beverages (Acidophilus milk) by using different types of lactic acid bacteria-mini review. Current Nutrition and Food Science, 13(2), 78 81. Khaneghah, A. M., Martins, L. M., von Hertwig, A. M., Bertoldo, R., & Sant’Ana, A. S. (2018). Deoxynivalenol and its masked forms: Characteristics, incidence, control and fate during wheat and wheat based products processing A review. Trends in Food Science and Technology, 71, 13 24.

Chapter 7 The potential of pulsed electric fields to reduce pesticides and toxins

Koubaa, M., Barba, F. J., Grimi, N., Mhemdi, H., Koubaa, W., Boussetta, N., & Vorobiev, E. (2016). Recovery of colorants from red prickly pear peels and pulps enhanced by pulsed electric field and ultrasound. Innovative Food Science & Emerging Technologies, 37(Part C), 336 344. Lang, Y., & Jun, H. (2017). High intensity pulsed electric field as an innovative technique for extraction of bioactive compounds—A review. Critical Reviews in Food Science and Nutrition, 57(13), 2877 2888. Majeed, M., Khaneghah, A. M., Kadmi, Y., Khan, M. U., & Shariati, M. A. (2018). Assessment of ochratoxin a in commercial corn and wheat products. Current Nutrition and Food Science, 14(2), 116 120. Marin, S., Ramos, A. J., Cano-Sancho, G., & Sanchis, V. (2013). Mycotoxins: Occurrence, toxicology, and exposure assessment. Food and Chemical Toxicology, 60, 218 237. Misra, N. N., Koubaa, M., Roohinejad, S., Juliano, P., Alpas, H., Ina`cio, R. S., & Barba, F. J. (2017). Landmarks in the historical development of twenty first century food processing technologies. Food Research International, 97, 318 339. Mousavi Khaneghah, A., Fakhri, Y., Raeisi, S., Armoon, B., & Sant’Ana, A. S. (2018). Prevalence and concentration of ochratoxin A, zearalenone, deoxynivalenol and total aflatoxin in cereal-based products: A systematic review and meta-analysis. Food and Chemical Toxicology, 118, 830 848. Mousavi Khaneghah, A., Fakhri, Y., & Sant’Ana, A. S. (2018). Impact of unit operations during processing of cereal-based products on the levels of deoxynivalenol, total aflatoxin, ochratoxin A, and zearalenone: A systematic review and meta-analysis. Food Chemistry, 268, 611 624. Mousavi Khaneghah, A., Ismail, E. S¸ ., Raeisi, S., & Fakhri, Y. (2018). Aflatoxins in cereals: State of the art. Journal of Food Safety, 38(6), e12532. Available from https://doi.org/10.1111/jfs.12532. Nicolopoulou-Stamati, P., Maipas, S., Kotampasi, C., Stamatis, P., & Hens, L. (2016). Chemical pesticides and human health: The urgent need for a new concept in agriculture. Frontiers in Public Health, 4, 148. Available from https://doi.org/10.3389/fpubh.2016.00148. Pue´rtolas, E., & Barba, F. J. (2016). Electrotechnologies applied to valorization of by-products from food industry: Main findings, energy and economic cost of their industrialization. Food and Bioproducts Processing, 100, 172 184. Pue´rtolas, E., Koubaa, M., & Barba, F. J. (2016). An overview of the impact of electrotechnologies for the recovery of oil and high-value compounds from vegetable oil industry: Energy and economic cost implications. Food Research International, 80, 19 26. Puligundla, P., Pyun, Y. R., & Mok, C. (2018). Pulsed electric field (PEF) technology for microbial inactivation in low-alcohol red wine. Food Science and Biotechnology, 27(6), 1691 1696. Rastegar, H., Shoeibi, S., Yazdanpanah, H., Amirahmadi, M., Khaneghah, A. M., Campagnollo, F. B., & Sant’Ana, A. S. (2017). Removal of aflatoxin B1 by roasting with lemon juice and/or citric acid in contaminated pistachio nuts. Food Control, 71, 279 284. Razzaghi, N., Ziarati, P., Rastegar, H., Shoeibi, S., Amirahmadi, M., Conti, G. O., . . . Mousavi Khaneghah, A. (2018). The concentration and probabilistic health risk assessment of pesticide residues in commercially available olive oils in Iran. Food and Chemical Toxicology, 120, 32 40.

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Subramanian, V., Shanmugam, N., Ranganathan, K., Kumar, S., & Reddy, R. (2017). Effect of combination processing on aflatoxin reduction: Process optimization by response surface methodology. Journal of Food Processing and Preservation, 41(6), e13230. Available from https://doi.org/10.1111/ jfpp.13230. ¨ nu¨san, N. (2019). Systematic review of mycotoxins in food and feeds in Turkey. U Food Control, 97, 1 14. Vijayalakshmi, S., Nadanasabhapathi, S., Kumar, R., & Sunny Kumar, S. (2018). Effect of pH and pulsed electric field process parameters on the aflatoxin reduction in model system using response surface methodology: Effect of pH and PEF on aflatoxin reduction. Journal of Food Science and Technology, 55 (3), 868 878. Wei, K., Li, W., Gao, S., Ji, B., Zang, Y., Su, B., . . . Wang, J. (2016). Inactivation of ricin toxin by nanosecond pulsed electric fields including evidences from cell and animal toxicity. Scientific Reports, 6, 18781. Available from https://doi. org/10.1038/srep18781. Yadolahi, M., Babri, M., Sharif, A. A. M., & Khaneghah, A. M. (2012). Pesticide residue determination in Shahr-E-Rey tomatoes using QuEChERS method. Advances in Environmental Biology, 6(8), 2434 2438. Yang, N., Huang, K., Lyu, C., & Wang, J. (2016). Pulsed electric field technology in the manufacturing processes of wine, beer, and rice wine: A review. Food Control, 61, 28 38. Zhang, Y., Hou, Y., Chen, J., Chen, F., Liao, X., & Hu, X. (2012). Reduction of diazinon and dimethoate in apple juice by pulsed electric field treatment. Journal of the Science of Food and Agriculture, 92(4), 743 750. Zhu, Z., He, J., Liu, G., Barba, F. J., Koubaa, M., Ding, L., . . . Vorobiev, E. (2016). Recent insights for the green recovery of inulin from plant food materials using non-conventional extraction technologies: A review. Innovative Food Science and Emerging Technologies, 33, 1 9. Zulueta, A., Barba, F. J., Esteve, M. J., & Frı´gola, A. (2010). Effects on the carotenoid pattern and vitamin A of a pulsed electric field-treated orange juice-milk beverage and behavior during storage. European Food Research and Technology, 231(4), 525 534.

PEF as an alternative tool to prevent thermolabile compound degradation during dehydration processes

8

Artur Wiktor1, Anubhav Pratap Singh2, Oleksii Parniakov3, Viacheslav Mykhailyk4, Ronit Mandal2 and Dorota Witrowa-Rajchert1 1

Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences (WULS-SGGW), Warszawa, Poland 2Food Process Engineering Laboratory, Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada 3 Elea Vertriebs- und Vermarktungsgesellschaft GmbH, Quakenbru¨ck, Germany 4Institute of Engineering Thermal Physics, National Academy of Sciences of Ukraine, Kiev, Ukraine

8.1

Introduction

Dehydration is a way of processing materials aiming toward extraction of moisture in order to inhibit deteriorative reactions or to prepare it before further processing. Dehydration can be performed using thermal drying, osmotic dehydration (OD), or mechanical removal of water (Zhang, Chen, Mujumdar, Zhong, & Sun, 2015). However, in the vast majority of cases, water is removed from the wet stocks by the means of drying. This process is applied in most of major industries, including coal, paper, wood, or pharmaceutical sector (Karthikeyan, Zhonghua, & Mujumdar, 2009; Kemp, 2017; Lu & Shen, 2007; Xu, Lu, Gao, Wu, & Li, 2017). Despite such huge popularity and versatility, drying is considered as one of the most energy intensive unit operations, which is related to the high value of the latent heat of vaporization of water (2257 kJ/kg at atmospheric pressure at sea level), which needs to be supplied to remove water (Kudra, 2004).

Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00008-2 © 2020 Elsevier Inc. All rights reserved.

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Dehydration is also a basic unit operation in food production. It is estimated that drying is responsible for c. 12% of total energy consumption in food and agricultural sector. What is interesting is that the share of drying in overall energy usage by industry is also estimated to 12% (Pirasteh, Saidur, Rahman, & Rahim, 2014). Taking into account the fact that industry is responsible for around 21% of greenhouse gases emission, drying can be considered as an important factor as well (Fischedick et al., 2014). Hence, it is obvious that a lot of effort has been put in dehydration, and especially drying technology development in the past 20 years (Fig. 8.1). As aforementioned, dehydration is one of the most popular food processing techniques. Reduced water content of food inhibits enzymatic and chemical reaction rate and slows down microbial activity, which can cause food spoilage. Such approach allows the surplus of crops to be stored even for a long time after harvesting. Additional benefits of food dehydration are not only associated with preservation but also with smaller mass and volume, which contributes to lower storage and transportation costs (Zhang et al., 2015). In food industry, as in the case of other industrial sectors, the most important way of food dehydration is drying. In turn, OD plays an important role as a pretreatment step applied prior to drying. Application of OD is crucial when it comes to processing of materials, the sensory properties of which have to be modified like in the case of dried cranberry production (Nowacka et al., 2018). Despite of many benefits, food dehydration exhibits also some drawbacks. Amid these disadvantages, besides abovementioned high energy consumption (which is specific for drying), thermal characteristic of the process should be mentioned. 1000

35 Sum of times cited

900 800

25

700 600

20

500 15

400 300

10

200

5 0 1995

100 2000

2005

Year

2010

2015

0 2020

Sum of times cited

Figure 8.1 The sum of times cited (’) and the number of articles (K) that contain “pulsed electric field” or “electroporation” or “highintensity electric field” and “drying” or “osmotic dehydration” published between 1999 and 2019.

Number of publications

30

Number of publications

Chapter 8 PEF as an alternative tool

Utilization of elevated temperature, crucial from the kinetic point of view, can lead to undesirable quality degradation of food. In turn, high temperatures combined with the presence of air can prompt oxidation of thermolabile compounds such as pigments or vitamins decreasing nutritional value of the final product (Zhang et al., 2015). Therefore currently all over the world scientists are working on different solutions, which aim to enhance drying and maintaining the quality of dried products. Pulsed electric field (PEF) pretreatment belongs to the most promising techniques that can be applied in order to facilitate drying and improve quality of dried food goods. Although the beginning of PEF research goes back to the 1960s, it is still considered as an emerging technology that is justified since its potential is not fully recognized.

8.1.1

Drying and osmotic dehydration as a heat and mass transfer based process

Drying and OD belong to mass and heat transfer based unit operations. It means that kinetics of these operations depend strongly both on processing parameters and material properties. Both drying and OD are diffusive processes. Driving force of the dehydration is related to the difference between partial vapor pressure of the material and surroundings, like it is in the case of drying, or to the gradient of osmotic pressure between material and surroundings (Honarvar & Mowla, 2012; Md Salim, Garie`py, & Raghavan, 2016). In the course of drying, two different periods can be distinguished (Fig. 8.2). During the first

Figure 8.2 Schematic representation of drying process. Re, External (convective) resistance of mass transfer; Ri, internal (diffusive) resistance of mass transfer; uk, critical moisture content; uo, initial moisture content; 1st, the first period of drying; 2nd, the second period of drying.

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period of drying material is heated up and free, capillary water presented on the surface of the material is evaporated. During this stage of the process, the external (convective) mass transfer resistance (Re) is higher than the internal (diffusive) mass transfer resistance (Ri), which is associated with high water content of the material. The drying rate and product temperature during this phase are constant and the kinetics of the process depend mainly on air temperature, flow rate and humidity, and water content of the material. The surface of food remains wet and temperature remains around wet bulb temperature of drying air. The first period lasts to the moment when internal and external mass transfer resistances are equal (Re 5 Ri), which occurs when the surface of the material starts to dry out and water start to percolate. From that point, related to the critical water content (uk), the second period of drying begins which is characterized by the falling drying rate. During this stage of the process, internal mass transfer resistance is higher in comparison to the convective one. Because of that, some of the energy delivered during drying is not consumed on water evaporation and material is heated up. The temperature of the food approaches the dry bulb temperature of drying air. The course of falling rate period of drying depends, as all of diffusive unit operations, on material properties and especially on its structure (Table 8.1). In contrast to drying, OD is a two-way mass transfer process during which the water (and some water-soluble solids) flows from dehydrated material into the surrounding (osmotic solution) and the solids from the osmotic solution go inside the material. The OD can be intensified by increase in temperature, agitation, utilization of osmotic agents with smaller molecular weight, or changing the geometry (thickness) of the processed samples. Table 8.1 The parameters influencing different drying periods. Drying period

Influencing parameters

First period of drying (constant rate period)

Drying temperature Air flow Air humidity Water content Material properties Pretreatment Dryer load and its characteristic

Second period of drying (falling rate period)

Chapter 8 PEF as an alternative tool

However, since OD is a heat and mass transfer based diffusion process, the cellular structure is of paramount importance. On the cellular level the organelles that essentially impact upon the course of OD are cell wall, vacuoles, and especially cell membrane, which is semipermeable (Chiralt & Fito, 2003). As mentioned earlier, the presence of these cellular structures affects the progress of the drying as well. Thus it can be stated that the cellular structure is the main limiting factor of both drying and OD. Increasing the drying temperature can of course intensify the progress of OD or drying, but it would negatively impact the nutritional quality of processed food and especially the bioactive compounds content. Adding to that, the second period of drying lasts usually much longer than the first period, during which temperature of food reaches the drying air temperature. Increasing the drying temperature can worsen the final product quality during second period. Thus, keeping all of abovementioned factors in mind, the most crucial thing, when it comes to intensification of drying or OD of plant origin foods, is related to the breaking down the cellular structure of the material. Operations that can be applied in order to break down the cellular structure of the material have a lot of drawbacks. Some of them, such as blanching, exhibits a thermal process, and thus they not only consume a lot of energy but also can cause degradation of thermolabile compounds (Witrowa-Rajchert, 2017). On the other hand, cutting launches the metabolic response of plant tissue, which increases respiration, ethylene production or, in some cases, browning, due to the oxidation of phenolic compounds (Lewicki, 1998). Very often to prevent these metabolic changes, a chemical treatment is applied which, in turn, worries some of the consumers. Cutting or grinding change the visual appearance of the product, which also influences its position on the market and its further utilization. It should be also emphasized that the operations that lead to the destruction of cellular structure and aim toward enhancement of OD or drying are applied on the very first stage of the technological process as a pretreatment step. Thus the impact of the pretreatment on both the process kinetics and the quality of dehydrated material is very crucial. The global market of dried fruits and vegetables is growing continuously. According to Market Research Future by 2023, its size would reach USD 38 billion with estimated compound annual growth rate (CAGR) of almost 8%, as reported by Ameco Research. Such situation is related mainly to the change of lifestyle and shifting of consumers’ preferences toward “healthier” alternatives of traditional snacks or ready-to-eat meals. A need

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Chapter 8 PEF as an alternative tool

for convenient, functional, natural food with potential to benefit people’s health in the sustainable manner will propel the production of dried foods. A good example, presented by Mintel in Global Food and Drinks Trends 2019 report, which illustrates these trends, is consumers seeking for food with antiinflammatory properties. Since these bioactive compounds are very often sensitive to high temperature, long processing, or exposure to oxygen, the processing technologies will need to be reshaped to deliver high-quality product. These outlooks justify that application of nonthermal technologies is more needful than ever before. Based on the literature data and successful commercialization in different food industry domains, PEF seems to be the most promising nonthermal pretreatment method for improvement of both drying kinetics and dried food quality (WitrowaRajchert, Wiktor, Sledz, & Nowacka, 2014).

8.2

Impact of pulsed electric field on dehydration processes

PEF treatment of food allows the cellular structure to be modified by the phenomenon of electroporation. This increases the permeability of the cell membrane with very limited or even without any thermal effect (Golberg, Fischer, & Rubinsky, 2010). This effect of PEF treatment is utilized to enhance the course of many different mechanical and/or heat and mass transfer based processes such as juice pressing (Bobinait˙e et al., 2015; Jaeger, Schulz, Lu, & Knorr, 2012), extraction (Fincan, 2015; Segovia, Luengo, Corral-Pe´rez, Raso, & Almajano, 2015), or freezing (Shayanfar, Chauhan, Toepfl, & Heinz, 2013; Wiktor, Schulz, Voigt, Knorr, & Witrowa-Rajchert, 2015; Wiktor, Schulz, Voigt, Witrowa-Rajchert, & Knorr, 2015; Wiktor, Sledz, et al., 2015). The degradation of microbial cell membranes is also beneficial when it comes to microbial inactivation and food preservation (Geveke et al., 2015; Moussa-Ayoub et al., 2017). PEF utilization does not change the shape or dimensions of the processed products. Since it depends on application of very short pulses characterized by very high electric field intensity, its energy consumption is far less the energy requirements of traditionally applied pretreatment methods (e.g., blanching) (Barba et al., 2015). Because of its nonthermal character and a prospect for cellular structure disintegration, PEF pretreatment shows a huge potential for improvement of drying and OD process in terms of process kinetics and product quality modification.

Chapter 8 PEF as an alternative tool

8.2.1

Impact of pulsed electric field on drying kinetics

Shorter drying time means in most cases shorter exposure to elevated temperature or, in the case of convective drying, shorter exposure to oxygen. Alteration of these unfavorable conditions contributes not only to reduction of energy consumption, environmental load, but also to better preservation of thermolabile compounds. Successful utilization of PEF pretreatment applied to enhance kinetics of different drying methods has been reported by many authors and exemplified by apples, carrots, onion, beetroot, and other plant origin material. Some of these applications are listed in Table 8.2. In general, it can be stated that PEF pretreatment can reduce drying from 1.6% to 57% depending on the drying technique and raw material. Most of the papers present the impact of PEF pretreatment on air drying and only few of them focus on other drying techniques such as vacuum or freeze-drying. For instance, Alam, Lyng, Frontuto, Marra, and Cinquanta (2018) reported that air drying of carrot subjected to PEF pretreatment was 27.3% shorter in comparison to air drying of untreated material. Lebovka, Shynkaryk, and Vorobiev (2007) stated that potatoes treated by PEF prior to air drying required c. 45% less time to be dried compared to untreated ones. In turn, freeze-drying times were reduced by 22.5% and 31.5% in comparison to untreated material in the case of apple and potato samples, respectively (Wu, Guo & Zhang, 2011; Wu & Zhang, 2014). Reduction of vacuum drying time by PEF application varies from 22% to 43% as reported for potato and blueberry, respectively (Liu, Grimi, Lebovka & Vorobiev, 2018; Yu, Jin, Fan, & Wu, 2018). Drying time reduction by PEF pretreatment is strongly associated with the electroporation phenomenon. Increased cell membrane permeabilization and leakage of intracellular fluids to extracellular surroundings facilitate the movement (diffusion) of water from inside the material toward its surface. Hence, the removal of water from PEF-treated material characterized by disintegrated cellular structure is enhanced. The analysis of relationship between the effectiveness of electroporation, expressed by the means of the cellular disintegration index, shows that there is a certain relationship between the level of cellular structure degradation and drying enhancement. Cellular disintegration index is a measure that provides information about the extent of degradation, irreversible electroporation of the material. It can take values from 0 for intact material to 1 for totally disintegrated one (Angersbach, Heinz, & Knorr, 1999;

161

Table 8.2 The impact of pulsed electric field (PEF) pretreatment on drying kinetics of different food matrices. Food matrix

Drying method

PEF parameters

Cell disintegration index ( )

Dehydration Reference time reduction (%)

Carrot

Air (convective) drying (T 5 40 C 60 C; perpendicular air flow of 6 m3/h) combined with OD (sucrose solution, 1 4 h) Air (convective) drying (T 5 40 C 60 C) Air (convective) drying (T 5 70 C; parallel air flow of 2 m/s) Oven drying (T 5 70 C)

E 5 0.6 kV/cm Ws 5 19 kJ/kg

N/A

6.1 22.6

E 5 0.6 kV/cm Ws 5 19 kJ/kg E 5 1.85 5 kV/cm Ws 5 5.63 80 kJ/kg

N/A

21.6

N/A

6.9 8.2

Wiktor, Nowacka, et al. (2016)

E 5 0.5 1.5 kV/cm Ws 5 0.6 56.5 kJ/kg

N/A

c. 11 30%a

Air (convective) drying (T 5 50 C 70 C; parallel air flow of 1 m/s)

E 5 0.9 kV/cm Ws 5 65.2 kJ/kg

0.8

Air (convective) drying (T 5 70 C; parallel air flow of 2 m/s) Convective (oven) drying (T 5 70 C)

E 5 5 10 kV/cm Ws 5 5 80 kJ/kg

0.38 0.88

13 27 (in the case of drying at 70 C the increase of drying time by 13) 2 13

Gachovska, Adedeji, Ngadi, and Raghavan (2008) Alam et al. (2018)

E 5 0.75 1.5 kV/cm 5 60 pulses; ti 5 100 300 μs E 5 1 kV/cm n 5 30 pulses; ti 5 100 μs E 5 0.8 kV/cm n 5 10 pulses; ti 5 1000 μs

N/A

0

Arevalo et al. (2004)

N/A

22.5

Wu et al. (2011)

0.18 0.96

E 5 1.25 kV/cm Ws 5 1.08 kJ/kg

0.9

20.8 37.9 Parniakov et al. (in the case of (2016b) sample with CDI 5 0.19 an increase of drying time by c. 7) Chauhan, Sayanfar, c. 30a and Toepfl (2018)

Apple

Freeze-drying (T 5 70 C, p 5 40 45 Pa) Vacuum cooling/ freeze-drying (T 5 40 C, p 5 1000 Pa)

Convective (oven) drying (T 5 60 C)

Amami, Khezami, Vorobiev, and Kechaou (2008)

Wiktor et al. (2013)

(Continued )

Table 8.2 (Continued) Food matrix

Drying method

PEF parameters

Cell disintegration index ( )

Dehydration Reference time reduction (%)

Potato

Air (convective) drying (T 5 30 C 70 C; perpendicular air flow of 6 m3 h) Convective (oven) drying (T 5 70 C)

E 5 0.3 0.4 kV/cm n 5 1 30,000, ti 5 1025 1023 s

0.4 1.0

c. 15 45a

Lebovka et al. (2007)

E 5 0.75 1.5 kV/cm n 5 5 120 pulses; ti 5 100 300 μs E 5 0.6 kV/cm tPEF 5 0.1 s

N/A

c. 27a

Arevalo et al. (2004)

N/A

22 27

Liu et al. (2018)

N/A

31.5

Wu and Zhang (2014)

0.98

c. 9a

E 5 0.4 kV/cm tPEF 5 0.1 s

 1.0

c. 32a

Ammar, Lanoiselle´, Lebovka, Van Hecke, and Vorobiev (2010) Shynkaryk et al. (2008)

E 5 1.07 kV/cm Ws 5 1 16 kJ/kg

c. 0.2 1.0

c. 3 30

Ostermeier et al. (2018)

E 5 1 kV/cm n 5 100

N/A

20

E 5 5 kV/cm ti 5 20 μs tPEF 5 90 150 s

N/A

c. 47 (to 18% reduction of initial mass)

Dev, Padmini, Adedeji, Garie´py, and Raghavan (2008) Lamanauskas, ˇ Satkauskas, Bobinait˙e, and Viˇskelis (2015)

E 5 2.5 4 kV/cm n 5 10

N/A

33 50a

E 5 2.5 kV/cm Ws 5 25.4 kJ/kg

0.75

22

Vacuum drying (T 5 40 C 70 C; p 5 30 kPa Freeze-drying (T 5 75 C; p 5 40 45 Pa) Freeze-drying (T 5 0 C; p 5 4 Pa) Red beetroot Onion

Raisins

Air (convective) drying (T 5 70 C; parallel airflow of 2 m/s) Air (oven) drying (T 5 45 C 75 C; airflow of 0.2 m/s) Air (convective) drying (T 5 65 C)

Actinidia Fluid bed drying kolomikta (T 5 50 C; perpendicular air flow of 50 m3/h) Okra Air (oven) drying (T 5 70 C) Coconut

Air (convective) drying (T 5 60 C; parallel air flow of 1 m/s) preceded by centrifugation (10,000 g for 10 min)

E 5 1.5 kV/cm n 5 45 pulses ti 5 120 μs E 5 0.4 kV/cm Ws , 5 kJ/kg

Adedeji, Gachovska, Ngadi, and Raghavan (2008) Ade-Omowaye, Angersbach, Taiwo, and Knorr (2001a,b)

(Continued )

Table 8.2 (Continued) Food matrix

Drying method

PEF parameters

Cell disintegration index ( )

Dehydration Reference time reduction (%)

Parsnip

Air (convective) drying (T 5 50 C 70 C; parallel air flow of 1 m/s) Air (convective) drying (T 5 40 C, parallel airflow of 2 m/s) Vacuum drying (room temperature, p 5 14 Pa) Freeze-drying (p 5 14 Pa) Air (convective) drying (T 5 50 C; parallel air flow of 2 m/s)

E 5 0.9 kV/cm Ws 5 65.8 kJ/kg

 1.0

4.6 28.8

Alam et al. (2018)

E 5 0.65 kV/cm n 5 65 ti 5 150 μs

RE

57

Telfser and Galindo (2019)

RE

33

RE

25

RE (without electroporated stomata) RE (with electroporated stomata) IE

18

47

0.38

33

Dermesonlouoglou, Chalkia, Dimopoulos, and Taoukis (2018)

N/A

30 43

Yu et al. (2016)

N/A

15

Liu et al. (2018)

N/A

20.4 34.7

Won et al. (2015)

Basil leaves

E 5 0.6 kV/cm n 5 65 pulses ti 5 120 μs E 5 0.6 kV/cm n 5 65 pulses ti 5 150 μs E 5 1.5 kV/cm n 5 65 pulses ti 5 150 μs Goji Air (convective) drying E 5 2.8 kV/cm berries (T 5 60 C for 300 min) n 5 750 preceded by OD (glycerol, 55 C, 60 min) E 5 2 kV/cm Blueberry Vacuum drying Ws 5 2.5 kJ/kg (T 5 45 C 75 C; 4 kPa) Radish Air (convective) drying E 5 1.446 kV/cm (T 5 80 C; airflow of n 5 87 tPEF 5 28 μs 1 m/s) Bell Air (oven) drying E 5 1 2.5 kV/cm pepper (T 5 45 C) ti 5 30 μs tPEF 5 1 4 s

Kwao et al. (2016)

37

IRE, irreversible electroporation; OD, Osmotic dehydration; RE, reversible electroporation. a Drying time estimated on the basis of drying curves provided in the article (as a time necessary to obtain MR 5 0.1).

Chapter 8 PEF as an alternative tool

Lebovka et al., 2007; Maskooki & Eshtiaghi, 2012). In other words, it can be used to assess the efficacy of PEF treatment. For instance, Ostermeier, Giersemehl, Siemer, To¨pfl, and Ja¨ger (2018) demonstrated that drying of onion samples characterized by a cell disintegration index equal to c. 0.22 (specific energy intake, Ws 5 1 kJ/kg) was only c. 3% shorter than the drying of untreated tissue. With an increasing electroporation efficient to c. 0.53 (Ws 5 4 kJ/kg), drying time decreased by 21% in comparison to control samples. Similar results were demonstrated by Lebovka et al. (2007) for air drying of potato or Parniakov, Bals, Lebovka, and Vorobiev (2016b) for vacuum freeze-drying of apple tissue. Also, Wiktor, Nowacka, et al. (2016) found significant correlation between drying kinetics and electrical conductivity, which is very often used to determine the cellular disintegration index. However, besides the fact that electroporation is a threshold phenomenon (Kandusˇer & Miklavcˇ icˇ , 2009), it can be also described as a saturated phenomenon. It means that there is a specific value of energy input above which the cell disintegration index reaches plateau (Lebovka, Bazhal, & Vorobiev, 2002). For instance, as demonstrated by Ostermeier et al. (2018) further increment of the cellular disintegration index (above 0.53) by application of higher specific energy input did not lead to greater drying time reduction. Cell disintegration index of onions treated by PEF at Ws 5 16 kJ/kg was equal to almost 1, but their drying time was only 16% lower than time stated for intact material. It should be also mentioned that delivery of the same specific energy input, but at different electric field strength does not always lead to the same cell disintegration index (Toepfl & Heinz, 2011) which is of course related to the “threshold” characteristic of electroporation phenomenon. From practical point of view, it means that the cell disintegration index (or other measures with potential to describe electroporation efficiency) should be used together with specific energy intake (Ws) to forecast drying course after PEF pretreatment. As mentioned earlier, the irreversible electroporation is recognized as a potential tool to improve many of heat and mass transfer based unit operations, including drying. However, it is possible to apply PEF using parameters capable of causing transient perforation of cell membrane. Such phenomenon is called reversible electroporation and can be achieved when external electric field induces a rise of transmembrane potential close to critical value (Kandusˇer & Miklavcˇ icˇ , 2009). The reversible electroporation is of interest when it comes to administration of particular substances inside the cell or in stress reaction

165

166

Chapter 8 PEF as an alternative tool

induction (Balasa, Janositz, & Knorr, 2010; Mercer & Armenta, 2011; Soliva-Fortuny, Balasa, Knorr, & Martı´n-Belloso, 2009). As the name suggests, after the reversible electroporation the cell can keep its viability and perform metabolic activities. It was however proved that PEF treatment can generate reactive oxygen species formation and thus cause the oxidative stress (Teissie, Eynard, Gabriel, & Rols, 1999). Moreover, even after sealing of transient pores, some of the changes in the cellular structure have not went back even after long time after the treatment—this phenomenon is called “memory effect” (Teissie, Golzio, & Rols, 2005). Hence, it could be stated that application of PEF using specific parameters can be considered as a sublethal factor with the potential of intracellular electroporation (Dymek, Dejmek, & Galindo, 2014; Esser, Smith, Gowrishankar, Vasilkoski, & Weaver, 2010). One of the first examples of utilization of reversible electroporation in food processing was related to improvement of freezing process by combining reversible electroporation with vacuum impregnation and cryoprotectant administration (Dymek, Dejmek, Galindo, & Wisniewski, 2015; Phoon, Galindo, Vicente, & Dejmek, 2008). Also, Kwao, AlHamimi, Damas, Rasmusson, and Galindo (2016) reported that application of PEF using parameters within the range of reversible electroporation can enhance drying kinetics. The researchers reported that PEF can affect the guard cells and stomatal apertures, which influence removal of moisture from the leaves. When using PEF at 0.6 kV/cm, they achieved reversible electroporation, but the guard cells were either electroporated or nonelectroporated, depending on the pulse width and pulse space. Drying time of samples with electroporated guard cells lasted 177 min, whereas basil leaves without electroporated stomata needed 228 min. It means that pretreatment that led to irreversible opening of stomatal apertures allowed drying process to be almost two times shorter than nonelectroporated guard cells variant. However, even though these treatments decreased drying time in comparison to intact material, they were not as sufficient as complete irreversible electroporation (E 5 1.5 kV/cm), which reduced drying time to 148 min. These results demonstrate that PEF can influence stomatal system activity inducing its opening, which can have sustained or permanent characteristic and thus enhance water removal from the leaves tissue. Transient changes of the epidermal tissue (reversible electroporation without guard cells permeabilization) also seemed to play important role in drying intensification both due to the time-limited leakage of intracellular content and possible injuries of guard cells subsidiary cells.

Chapter 8 PEF as an alternative tool

Reversible electroporation was also proved to be effective in enhancement of vacuum and freeze-drying processes (Telfser & Galindo, 2019). Such pretreatment allowed drying time to be reduced by 33% and 25% in the case of vacuum and freezedrying, respectively. In this experiment, authors evaluated the effect of PEF on air drying performed at 40 C and they have stated 57% reduction of drying time. For comparison purposes, drying time of basil leaves subjected to irreversible opening of guard cells and dried afterward at 50 C as reported by Kwao et al. (2016) was only 37% shorter in comparison to intact sample. It could be therefore expected that the effect of PEF pretreatment is more evident when drying is performed at lower temperatures. However, the literature of the subject is not very consistent and the effect of PEF on drying seems to be rather dependent on matrix than on temperature. For instance, Alam et al. (2018) demonstrated that drying of PEFtreated carrot lasted 95 and 84 min for process carried out at 50 C and 60 C, respectively. In turn, drying time at 70 C lasted 68 and 60 min for PEF and untreated material, respectively. It means that PEF pretreatment can even extend drying time. In contrary, results obtained by Wiktor, Nowacka, et al. (2016) indicate that it is possible to reduce drying time of carrot by 8%. at 70 C In the same publication, Alam et al. (2018) showed that the drying of parsnip subjected to PEF pretreatment followed opposite pattern than carrot. In other words, process aided by PEF and carried out at 50 C, 60 C, and 70 C was shorter by 0%, 5%, and 29% in comparison to the reference operation. Similar results were stated for PEF-treated onion tissue. Ostermeier et al. (2018) found out that the difference between drying times of PEF and intact samples rises with decreasing temperature of air during drying. The reduction of drying time carried out at 45 C was equal to 30%, whereas for the process performed at 60 C the decrease amounted to 21%. What is interesting was that the drying time of the PEF-treated samples dried at 75 C was not significantly lower in comparison to the untreated onions. The authors also emphasized that the effect of temperature increment on drying kinetics was more evident that the effect of a PEF pretreatment. However, no categorical statement can be given without any information about the quality of the material since elevated temperature of drying can negatively affect quality of dried food. The response of plant material subjected to PEF treatment followed by drying depends on many factors of both physical and chemical origin. Porosity is a parameter that impacts not only the effectiveness of the PEF treatment but also drying

167

168

Chapter 8 PEF as an alternative tool

course, especially in the second period of drying. As a general principle, the PEF pretreatment increases the effective water diffusion coefficient (Witrowa-Rajchert et al., 2014). However, the effect of PEF depends on pretreatment parameters, product properties, and drying conditions. For instance, okra ovendrying at 70 C was characterized by the effective diffusion coefficient of 0.46 3 1029 m2/s, whereas PEF pretreatment increased it to 0.69 0.81 3 1029 m2/s. The changes of diffusivity reported for apple exposed to PEF treatment followed by convective drying at 70 C ranged from 4% to 20% when compared to intact material (Wiktor et al., 2013). In turn, Arevalo, Ngadi, Bazhal, and Raghavan (2004) did not state any positive influence of PEF on diffusivity during drying of apples. The effective water diffusion coefficient tends to be strongly related to the effectiveness of electroporation, which was demonstrated by Wiktor, Nowacka, et al. (2016) as an example of carrot drying. The researchers found a significant positive (r 5 0.991) correlation between electrical conductivity of the treated samples and the effective water diffusion coefficient. Practical utilization of relationship between the effectiveness of electroporation and the water diffusion coefficient is of paramount importance. Since, the assessment of the electrical properties should be considered as a standard procedure after PEF treatment, it can allow drying kinetics to be forecasted as already mentioned. Literature data indicates also that the increment of the water diffusion coefficient follows the same both “threshold” and “saturation” characteristic as the electroporation phenomenon. For instance, Ostermeier et al. (2018) stated that diffusivity of dried onion tissue stayed within the same range even when specific energy intake was increased. Such data is worth paying attention due to the energy consumption related to overtreatment of the material. The potential of PEF for improvement of the effective water diffusion coefficient points out that drying temperature could be decreased when introducing PEF pretreatment without negative effect on kinetic. Some reports show that air temperature could be lowered by 20 C 25 C than usual in the case of PEFaided processing (Lebovka et al., 2007; Shynkaryk, Lebovka, & Vorobiev, 2008). Other results in turn, as those presented by Ostermeier et al. (2018), show that such clear and categorical conclusion cannot be made since the effect of PEF pretreatment depends strongly on the food matrix. In this connection, it can be stated that PEF-assisted drying parameters should rather be adjusted or adopted than taking directly the same as for drying without any pretreatment.

Chapter 8 PEF as an alternative tool

Some products, because of their composition or final utilization, have to be handled by more sophisticated drying techniques such as vacuum drying or freeze-drying. These methods, and especially freeze-drying, are considered as benchmarks regarding the quality of dried product (Zhang et al., 2015). Historically, these methods were applied mainly to dry heat and/or oxygen-sensitive products or to produce special purpose goods such as pharmaceutical products, space food, and extreme sport or military purpose food. Currently, vacuum or freeze-dried products serve also as a part of ready-to-eat meals, snacks, breakfast cereals, or even pet food. The market of freeze-dried products expands very rapidly—Technavio’s analysts estimate 2017 21 CAGR to be equal to 6.59% (Sarah, 2020). The biggest drawbacks of these processing methods are related to their operating and maintenance costs. Both processes are carried out for a very long time under vacuum, the generation of which is associated with high energy consumption. Moreover, freeze-drying course is related with water phase transition, which generates enormous energy expenditures—it is estimated that freeze-drying costs are from two to eight times more than air drying (Kesˇelj, Pavkov, Radojcˇ in, & Stamenkovi´c, 2017; Ratti, 2008). The heat transfer during operation under reduced pressure conditions occurs mainly by conduction and radiation, which generates some drawbacks as well. Vast majority of vacuum and freeze-drying units work in a batch mode in comparison to continuous-operating hot air dryers (Parikh, 2015). A need for overcoming these challenges and drawbacks and fulfilling market demands fuels development in the enhancement of drying methods operating at reduced pressure. There are some reports which indicate that PEF pretreatment can aid vacuum or freeze-drying of foodstuff. Liu et al. (2018) reported that potato samples initially treated by PEF and then vacuum-dried at 40 C 70 C exhibited higher drying rate in comparison to untreated samples. It is also interesting that temperatures of PEF-pretreated samples stayed lower for longer time during drying in comparison to the intact material. Such results clearly give evidence of better conditions of water removal by the means of volumetric evaporation during vacuum drying. As a consequence vacuum drying of PEF-treated samples was reduced by 22% 27% in comparison to the reference process. Positive effect of PEF treatment on drying kinetics was also demonstrated by Yu, Jin, Fan, and Xu (2016) on the example of blueberries. Blueberries are not an easy-to-dry material due to the presence of skin covered by a waxy outer layer that prevents removal of moisture (Zielinska & Markowski, 2016).

169

170

Chapter 8 PEF as an alternative tool

This skin hinders also the drying of some other fruits such as cranberries or grapes (Va´zquez, Chenlo, Moreira, & Cruz, 1997; Yongsawatdigul & Gunasekaran, 1996). In the case of PEFpretreated blueberries, the maximal drying time reduction (43%) was achieved when samples were dried at 45 C. Utilization of higher temperatures, 60 C and 75 C, preceded by PEF application resulted in reduction of drying time by 30% 33%. Electroporation of blueberry tissue facilitated volumetric removal of water. But the electrically induced injury of skin played an important role as well. The authors emphasized that more broken-skin blueberries were obtained following PEF pretreatment before vacuum drying. Since the main heat transfer mechanism during vacuum drying is conduction, another explanation of its improvement can be found in the data reported by Wiktor, Nowacka, et al. (2016). The authors demonstrated that the PEF treatment increases thermal conductivity of the plant tissue by up to 7.8%. From processing point of view, freeze-drying can be divided into four main operations: freezing, vacuum generation, sublimation, and condensation. Of course, within the dehydration step itself, two different stages can be distinguished such as main drying (sublimation) and final drying (desorption). Such abundance in different operations creates a lot of space for process improvement. For instance, there are reports demonstrating that PEF pretreatment can reduce freezing time of plant tissue (Parniakov et al., 2016a; Wiktor, Schulz, Voigt, Knorr, et al., 2015; Wiktor, Schulz, Voigt, Witrowa-Rajchert, et al., 2015; Wiktor, Sledz, et al., 2015). Thus the reduction of freezing time contributes to reduction of freeze-drying time. However, according to Ratti (2008), the biggest share of energy expenditures during freeze-drying is linked to the sublimation and vacuum, so the biggest savings can be achieved by facilitating sublimation phase and thus reduce drying time and energy. The literature of the subject demonstrates that these issues can be addressed by the implementation of PEF treatment. Wu et al. (2011) proved that PEF pretreatment can decrease freeze-drying time of apple by 22.5% in comparison to intact material. What more, owing to the improvement of drying kinetics, the authors stated that productivity per unit area can be also increased even by 28.5%. Similar observations were drawn for freeze-drying of potato subjected to PEF pretreatment, but the increment of productivity was 33% and drying time was reduced by 31.5% (Wu & Zhang, 2014). Such finding is important, especially, that freeze-drying productivity, in general, is limited by its batch mode operations. Interesting results were reported by

Chapter 8 PEF as an alternative tool

Parniakov et al. (2016b) for vacuum freeze-drying (pressure sets to 10 mbar) of apple tissue preceded by PEF pretreatment. In this experiment, after PEF treatment, samples were loaded into freeze-dryer and frozen due to the pressure drop (vacuum cooling). The pretreated apples achieved shelf temperature in a shorter time and drying time reduction depended strongly on the cellular disintegration index. Also a reduction of freezedrying time was found only for samples with a cellular disintegration index higher than 0.18. Analysis of sample temperature evolution indicated that material characterized by a cellular disintegration index of 0.96 achieved a temperature lower than 210 C, whereas the lowest temperature of the intact material did not exceed 25 C. Longer period of frozen state was beneficial for PEF samples in terms of drying, shrinkage prevention, better volume, and porosity retention. As in the case of air drying, there is limited information about impact of reversible electroporation on vacuum and freeze-drying. Existing reports demonstrate that PEF pretreatment leading to electroporation of guard cells can enhance drying kinetics of basil leaves (Telfser & Galindo, 2019). Based on the mechanism of drying kinetics improvement (opening of stomatal apertures), it can be assumed that the best results should be expected for leafy materials such as herbs. However, more research is needed in this domain to clear up all doubts and draw conclusion.

8.2.2

Impact of pulsed electric field on physicochemical properties of dried food

Quality changes of dried material depend on processing parameters of drying. As aforementioned, the vast majority of these alterations are related to the utilization of elevated temperature, long time, and, in some cases, presence of oxygen. The rate of many biochemical reactions depends on water activity which means that the intensity of quality changes during drying varies with time of processing and a part of the processed product. Should drying being considered only as a technique that aims toward preservation of the raw material, the character of these alterations is rather negative. However, drying very often is applied not only to preserve quality but also to create new properties or flavors as it is in the case of dried mushrooms or plums. Therefore the main factor that will impact upon assessment of nature of changes provoked by drying is the final utilization of dried products (Lewicki, 2006).

171

172

Chapter 8 PEF as an alternative tool

Admittedly, deterioration of bioactive compounds or natural pigments is negative effect of drying no matter the final application of dried food. Amid the physicochemical properties of dried food rehydration and hygroscopicity, texture, color, and concentration of bioactive compounds are considered as the most important ones. Table 8.3 presents the main findings regarding the impact of PEF pretreatment on selected quality parameters of dried plant origin food. Rehydration is one of the most important properties of dried food. In some cases, products are desired to have very good reconstitution properties and to absorb water (or any other liquid) very fast as it is in the case of instant soups. In turn, there are applications of dried food in which limited ability of water absorption is beneficial as it is in the case of crunchy and crispy ingredients of muesli (Barba et al., 2015). According to the literature, the effect of PEF treatment on reconstitution properties is ambiguous. Some of authors reported that rehydration capacity of dried material subjected to PEF pretreatment was higher in comparison to untreated material. However, Taiwo, Angersbach, and Knorr (2002b) demonstrated that apples treated by PEF before air drying exhibited worse ability to absorb water than intact samples. What is interesting is that the combination of PEF treatment with OD resulted in better rehydration capacity as compared to both untreated materials subjected to OD and not subjected to OD prior to drying. In other publication, Taiwo, Angersbach, and Knorr (2002a) demonstrated that dried apples subjected to OD and PEF pretreatment exhibited worse rehydration properties than untreated material. These differences probably were associated with different parameters of PEF applied prior to OD. It should be also emphasized that PEF-treated apple samples exhibited better or similar soluble solids retention during water soaking (Taiwo et al., 2002a,b). Similar results were also stated by Amami, Fersi, Khezami, Vorobiev, and Kechaou (2007) who investigated the impact of PEF pretreatment on rehydration properties of dried carrots. As it was found for apple tissue, carrot samples subjected before drying only to PEF treatment were characterized by lower rehydration capacity, whereas material treated before drying by PEF and OD exhibited higher rehydration capacity in comparison to untreated material. In turn, Gachovska, Simpson, Ngadi, and Raghavan (2009) working with the same food matrix did not find any differences in rehydration kinetics of untreated and PEF-treated samples. This data indicates that the impact of PEF pretreatment on reconstitution properties depends on both

Chapter 8 PEF as an alternative tool

173

Table 8.3 The impact of pulsed electric field (PEF) treatment on selected physicochemical properties of dried fruits and vegetables. Property

Matrix

Drying method

Rehydration

Apple

Air drying combined with OD

Carrot

Red beetroot Potato

Okra Basil leaves Texture

Apple

Carrot

Effect of PEF

Reference

Higher rehydration capacity Better soluble solids retention Air drying Lower rehydration capacity Better soluble solids retention Vacuum/freeze-drying Higher rehydration capacity Oven drying No changes Oven drying Lower rehydration capacity Better soluble solids retention Oven drying Higher rehydration capacity combined with OD Better soluble solids retention Air drying Lower rehydration capacity

Taiwo et al. (2002b)

Vacuum drying

Liu et al. (2018)

Oven drying Air drying Freeze-drying Vacuum drying Air drying combined with OD

Air drying Air drying combined with OD Oven drying Air drying

Lower rehydration capacity for samples dried at 70 C No changes for samples dried at 40 C Higher rehydration capacity Higher rehydration capacity Higher rehydration capacity No changes Higher compressive force after rehydration at temperature of 25 C 60 C No changes in compressive force after rehydration at 90 C Firmer texture after rehydration Firmer texture after rehydration Firmer texture after rehydration No changes for samples dried at 50 C and 60 C Firmer texture of samples dried at 70 C

Parniakov et al. (2016b) Gachovska et al. (2009) Amami, Fersi, Khezami, et al. (2007)

Shynkaryk et al. (2008)

Adedeji et al. (2008) Telfser and Galindo (2019)

Taiwo et al. (2002b)

Amami, Fersi, Khezami, et al. (2007)

Gachovska et al. (2009) Alam et al. (2018)

(Continued )

174

Chapter 8 PEF as an alternative tool

Table 8.3 (Continued) Property

Color

Matrix

Drying method

Effect of PEF

Reference

Red beetroot Potato

Air drying

Shynkaryk et al. (2008)

Vacuum drying

Parsnip

Air drying

Apple

Air drying

Similar texture after rehydration Lower cutting force of samples dried at 40 C Higher cutting force of samples dried at 70 C No changes for samples dried at 50 C and 60 C Firmer texture of samples dried at 70 C Lower values of L* at the beginning of rehydration at room temperature Higher values of L* at the end of rehydration at room temperature Higher values of L* at the beginning and end of rehydration at 90 C Lower values of L* at the beginning and end of rehydration at room temperature Higher values of L* at the beginning and end of rehydration at 90 C No changes of L* after rehydration No changes of L*, higher values of a*, lower values of b* Lower values of L*, no changes of a* and b* Higher L* and b* values, lower a* values, higher ASTA units No changes of L*, higher a* and b* values No visual differences

Air drying combined with OD

Carrot

Oven drying Air drying

Air drying Red bell pepper

Oven drying

Parsnip

Air drying

Blueberries Vacuum drying Air drying

Liu et al. (2018)

Alam et al. (2018)

Taiwo et al. (2002b)

Gachovska et al. (2009) Wiktor, Nowacka, et al. (2016) Alam et al. (2018) Won, Min & Lee (2015)

Alam et al. (2018) Yu et al. (2017) (Continued )

Chapter 8 PEF as an alternative tool

175

Table 8.3 (Continued) Property

Matrix

Drying method

Effect of PEF

Reference

Basil leaves

Air drying

No changes of L*, lower values of a* and higher or same values of b* Lower values of L*, no changes of a* and b* values Lower values of L*, no changes of a* and b* values Higher values of L*, no changes of a*, lower values of b* Lower values of L* and b*, higher values of a* Residue percentage: PEF treated: 28.4% 71.8% Untreated: 26.8% 41.3% Residue percentage: PEF treated: 10.2% 86.1% Untreated: 24.3% 82.3% Residue percentage: PEF treated: 17.8% 21.2% Untreated: 16.1% 18.5% Residue percentage: PEF treated: 18.5% 43.3% Untreated: 18.5% 45.5% PEF treated: 1190 mg/100 g Untreated: 1030 mg/100 g PEF treated: 97.11 mg/kg Untreated: 87.80 mg/kg Residue percentage: PEF treated: 13.1% 61.5% Untreated: 46.1% 65.4% Residue percentage: PEF treated: 33.3% 77.3% Untreated: 48.4% 70.3% Decrease of initial activity: PEF treated: 31% 39% Untreated: 43% Residue percentage: PEF treated: 28.4% 71.8% Untreated: 52.0% 76.3%

Kwao et al. (2016)

Air drying Vacuum drying Freeze-drying

Anthocyanin content

Kiwi fruit

Fluid bed drying

Blueberry

Air drying

Vacuum drying

Vitamin C content

Air drying

Vacuum drying

Antioxidant activity

Kiwi fruit

Fluid bed drying

Radish

Air drying

Blueberry

Air drying

Vacuum drying

Total phenolic content

Goji berry

Air drying combined with OD

Blueberry

Air drying

Telfser and Galindo (2019)

Lamanauskas et al. (2015) Yu et al. (2017)

Lamanauskas et al. (2015) Liu et al. (2018) Yu et al. (2017)

Dermesonlouoglou, Chalkia, et al. (2018) Yu et al. (2017)

(Continued )

176

Chapter 8 PEF as an alternative tool

Table 8.3 (Continued) Property

Matrix

Goji berry

Drying method

Effect of PEF

Vacuum drying

Residue percentage: PEF treated: 38.9% 99.4% Untreated: 54.6% 97.6% No changes

Air drying combined with OD

Reference

Dermesonlouoglou, Chalkia, et al. (2018)

OD, Osmotic dehydration.

pretreatment and drying parameters, which can lead to different structural changes. Such explanation was previously suggested by Ade-Omowaye et al. (2001a,b). Lower rehydration capacity of PEF-pretreated red beetroot was stated also by Shynkaryk et al. (2008). The researchers linked such results with higher shrinkage of PEF-treated samples. Such explanation stays in accordance with aforementioned data regarding the reconstitution properties of samples pretreated before drying only with PEF or by OD preceded by PEF. OD performed prior to drying can contribute to slight decrease of the shrinkage of the material after drying (Garcia, Mauro, & Kimura, 2007; Kim & Toledo, 1987; Raghavan & Silveira, 2001; Torringa, Esveld, Scheewe, van den Berg, & Bartels, 2001). Worse ability to absorb water was also reported by Liu et al. (2008) for vacuum-dried potato but only when samples were dried at 70 C. In the case of drying performed at 40 C, the differences between intact and PEF-treated material were negligible. Such situation can be related to the fact that drying in elevated temperatures leads to more severe microstructural changes than using low-temperature drying (Vega-Ga´lvez et al., 2015). Thus the effect of PEF treatment on microstructure of plant material can be even intensified by high-temperature drying. This can result in higher shrinkage of the material and it can explain aforementioned results regarding lower rehydration capacity of PEF-treated samples. However, the effect of PEF on rehydration properties of dried material seems to be not only parameters but also matrix-dependent issue. For instance, Adedeji et al. (2008) demonstrated that application of PEF prior to oven drying at 70 C can enhance rehydration kinetics during first 3 h of soaking of okra, but the differences between PEF and intact samples after 4 5 h of rehydration were irrelevant. Better

Chapter 8 PEF as an alternative tool

reconstitution properties of PEF-treated material were also stated by Telfser and Galindo (2019) in the case of basil leaves dried by convective and sublimation method. What is interesting is that vacuum-dried basil leaves exhibited similar water absorption behavior no matter if PEF was applied or not. In contrary, apples treated by PEF followed by vacuum freezedrying exhibited better rehydration properties in comparison to untreated material. In this case, however, the researchers reported smaller shrinkage and better porosity, which explains obtained results. The potential of PEF technology to modify textural properties of plant origin raw material was demonstrated by a number of researchers. For instance, Lebovka, Praporscic, and Vorobiev (2004) demonstrated that PEF reduces mechanical strength of carrot, apples, and potatoes. Wiktor, Gondek, et al. (2016) proved that PEF can change acoustic properties, which are an essential part of texture, of carrot tissue. Textural properties are also crucial for dried food goods regardless the product is consumed without or after rehydration. Nevertheless, most of the reports concern textural properties of rehydrated samples. Shynkaryk et al. (2008) showed that PEF treatment prior to drying has small impact on texture of red beetroot. Similar results were obtained by Taiwo et al. (2002b) for dried osmodehydrated apples but only when rehydration was carried out at 90 C. Apples rehydrated at 25 C 60 C exhibited firmer structure manifested by higher values of compressive force. Such situation was most probably associated with higher content of solids of PEF samples rehydrated at lower temperatures. The researchers paid attention to the fact that deformation strain of PEF-treated samples was significantly higher in comparison to untreated material when rehydration was carried out at 60 C and 90 C. These results may indicate that PEF provokes some changes in pectic substances or pectin-related enzymes, which at certain temperature may affect textural properties of plant material (Deng et al., 2018; Femenia, Bestard, Sanjuan, Rossello, & Mulet, 2000). Gachovska et al. (2009) demonstrated that carrots subjected to PEF treatment were characterized by firmer texture after rehydration in comparison to untreated samples. Similar results were obtained also for rehydrated carrot tissue by Amami et al. (2008). The increase of dried material resistance for cutting was, in turn, reported by Liu et al. (2018) for vacuumdried PEF-treated potato samples but only when drying was carried out at 70 C. In the case of drying performed at 40 C, the effect of PEF pretreatment was reverse. Such differences can be related with different shrinkage of the untreated and PEF-treated

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material. Similar observations were done for carrot and parsnip subjected to PEF treatment before air drying (Alam et al., 2018). The maximum load values of both dried carrot and parsnip obtained at 50 C and 60 C did not change significantly when drying was preceded by PEF application. In turn, PEF application increased the firmness of the material that was dried at 70 C. This effect was even more intense in the case of parsnip that is more abundant in starch. Color is one of the most important food properties since it forms the first impression affecting consumer behavior and perception of food quality. Color depends on many factors: chemical composition of food, processing method, and parameters or quality of raw material. Drying, and especially convective method, promotes some chemical reactions that are responsible for color changes in food, for instance Maillard reaction, caramelization, and oxidation or enzymatic browning (Rahman, 2008). PEF treatment due to the electroporation phenomenon can affect the color of fruit and vegetable tissue (Fig. 8.3). The rupture of cellular structure and degradation of organelles such as plastids or vacuoles (Lightbourn et al., 2008) can lead to liberation of metabolites, which will trigger decolorization or formation of other pigments. For instance, released phenolics can react with polyphenol oxidase (PPO), which will trigger the formation of dark pigments (Holderbaum, Kon, Kudo, & Guerra, 2010). Fig. 8.2 presents the intensity of browning of fresh apple tissue (var. Ligol) after PEF treatment in comparison to untreated samples. It is clear that electroporation intensified the formation of dark pigments due to the enhanced enzymatic browning. Such effect of PEF on color of raw apple tissue was also reported by Grimi, Mamouni, Lebovka, Vorobiev, and Vaxelaire (2010). Moreover, Wiktor, Sledz et al. (2015) showed that total color difference (ΔE) of apple tissue subjected to PEF treatment varied

Figure 8.3 Pictures representing the surface of untreated (0_0) and PEF (5_50; E 5 5 kV/cm; n 5 50 pulses) treated apple tissue during time (0 60 min). PEF, Pulsed electric field.

Chapter 8 PEF as an alternative tool

from 1.67 to 16.35. As demonstrated by Taiwo et al. (2002a), browning of apple induced by PEF treatment can be inhibited by soaking in ascorbic acid solution. The lightness of dried apples osmo-dehydrated for 6 h and treated by PEF was equal to 62.81, whereas intact material exhibited lightness of 54.15. After rehydration the lightness was equal to 55.02 and 55.23, for untreated and PEF-treated apples, respectively. However, some other results showed that color of reconstituted dried apples sliced subjected to PEF treatment, combined or not with OD, will depend also on temperature of rehydration (Taiwo et al., 2002b), which could be related to residual activity of enzymes responsible for browning reactions. Such results indicate that dipping in acidic solutions does not have to be a sufficient solution when it comes to color preservation of PEF-treated dried apple tissue. The effect of PEF on color of dried material depends strongly on matrix. According to the literature, PEF pretreatment does not change the lightness of dried carrot alike after reconstitution (Gachovska et al., 2009). Reports concerning the lightness of dried PEF-treated carrot are not consistent. For example, Wiktor, Gondek, et al. (2016) and Wiktor, Nowacka, et al. (2016) found no relevant changes of L* of carrots treated before drying by PEF but stated higher redness and lower yellowness of treated samples. In turn, Alam et al. (2018) demonstrated that dried carrots treated prior to drying by PEF were darker than reference samples but a* and b* parameters were not affected. These differences might be related to different parameters of PEF pretreatment or different varieties of raw material. Most probably, depending on PEF parameters, electroporation can lead to the release of intracellular content (i.e., carotenoids) into extracellular space or to leakage of more polar fraction of intracellular content to treatment medium, such as zeaxanthin and lutein (Augustynska, ´ Jemioła-Rzeminska, Burda, & Strzałka, 2015; Wiktor, Schulz, Voigt, Knorr, et al., 2015; Wiktor, Schulz, Voigt, Witrowa-Rajchert, et al., 2015; Wiktor, Sledz, et al., 2015). Beneficial role of PEF pretreatment for color preservation of dried plant tissue was also demonstrated for red bell pepper by Won et al. (2015). Plant origin material contains a lot of different bioactive compounds that can be a subject of degradation during drying. The rate and the extent of degradation depend also on the type of bioactive compound. For instance, vitamin C degradation after 30 min of heating at 60 C was equal to 50% and 65% in the case of carrot and pepper samples, respectively (Igwemmar, Kolawole, & Imran, 2013). In turn, vitamin B2 is one of the most heat-stable vitamins with heating-related losses varying from 10% to 20% (Fernandes, Rodrigues, Garcı´a-Pe´rez,

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& Ca´rcel, 2016; Riaz, Asif, & Ali, 2009). However, the extent of degradation of bioactive compounds depends also on factors related to processing. The conditions of conventional drying are generally favorable for degradation of bioactive compounds of food. High temperature and presence of oxygen coupled with very long processing time negatively affect the nutritional quality of food (Ottaway, 1993). Therefore it could be expected that PEF pretreatment, due to the drying time reduction, will increase the retention of thermolabile compounds. The electroporation will also facilitate the extractability of many molecules that are stored inside the cell organelles (Wiktor, Schulz, Voigt, Knorr, et al., 2015; Wiktor, Schulz, Voigt, Witrowa-Rajchert, et al., 2015; Wiktor, Sledz, et al., 2015). However, because of leakage of the intracellular content to the PEF treatment medium, liberation of both enzymes and substrates for enzymatically driven reactions, and the formation of free radicals and reactive oxygen species (Nuccitelli, Lui, Kreis, Athos, & Nuccitelli, 2013; Sato, Ohgiyama, & Clements, 1996), the retention of bioactive substances in the PEF-treated fruits and vegetables will be rather a superposition of all effects that PEF and drying alike can cause. The research data in this filed is rather meager and limited to both few matrices and few bioactive compounds only (Table 8.3). According to data reported by Yu, Jin, and Xiao (2017), anthocyanin content of PEF-treated blueberries was higher when drying was conducted by convective method and at 60 C and 75 C. In this case the residues percentage of anthocyanin was equal to 51.6% 71.8% and 26.8% 41.3% in the case of PEF-treated and -untreated dried fruits, respectively. What is interesting is that when the temperature of air during drying was equal to 45 C, control samples exhibited higher retention (35%) of anthocyanin in comparison to PEF pretreated material (28.4%). Similar results were obtained for total phenolics. Such behavior can be explained by electroporation phenomenon and the activity of the PPO—responsible for phenolic compounds degradation—which is reported to be optimal between 20 C and 50 C (Ansari, Khan, Mular, & Khan, 2017; Bello & Sule, 2012; Mizobutsi et al., 2010). Enzymes liberated after electroporation remained active in the blueberries during drying, which resulted in higher degradation of phenolics. The data on anthocyanin and total phenolic content of vacuum-dried blueberries supports this explanation. The effect of a PEF pretreatment on vitamin C content depended on matrix and drying technology alike. In the case of blueberries subjected to vacuum drying at relatively low temperatures 45 C and 60 C, the retention of vitamin C

Chapter 8 PEF as an alternative tool

content varied from 15.8% to 19.7% for the untreated material and from 18.5% to 18.8% for the PEF-treated samples. Statistical analysis did not reveal any significant differences between the intact and PEF samples. When vacuum drying was performed at higher temperature (75 C), the retention of vitamin C increased to 43.3% 45.5%, but the difference between the PEF and untreated fruits remained irrelevant (Yu et al., 2017). In the case of air drying, the PEF-treated samples exhibited slightly higher vitamin C content regardless of the utilized temperature. However, the significant positive effect of PEF was found only for samples processed at the lowest temperature (45 C). The higher retention of vitamin C stated for samples subjected to vacuum drying at 75 C is associated to high temperature, which can inhibit oxidative degradation of vitamin C, the lack of oxygen because of low pressure in the drying and the shortest drying time (Yu et al., 2017). High degradation of vitamin C found in the case of hot air-dried blueberries is a consequence of specific conditions of convective method—long drying time at the presence of air—and the activity of ascorbic acid oxidase. Liu et al. (2018) found that the optimal PEF treatment can decrease the activity of ascorbic acid oxidase as exemplified by the radish tissue. However, the researchers found out that the increment of electric field intensity above threshold value can increase the activity of that enzyme and thus lead to the degradation of vitamin C. In the case of radish tissue, critical from vitamin C stability point of view, electric field intensity was equal to 1400 V/cm. It means that the PEF-assisted drying requires optimization in order to achieve desired effect. In the case of radish drying, optimal PEF pretreatment (E 5 1446 V/cm; ti 5 28 μs, n 5 87) resulted in around 11% better retention in comparison to the samples dried using unsupported process (Liu , Song, Guo, Wang, & Liu, 2016). The data reported in the literature also for other plant matrices indicates that the PEF pretreatment does not negatively influence the vitamin C content in dried material. Lamanauskas et al. (2015) showed that vitamin C concentration in dried kiwi subjected to the PEF treatment was higher in comparison to the untreated material by 15%. The antioxidant activity is a superposition of many different factors among which the concentration of bioactive compounds plays predominant role. Thus it could be expected that the free radical scavenging activity of the PEF-processed dried plant material will be improved. Unfortunately, the data about antioxidant activity of the PEF-pretreated samples is limited. Yu et al. (2017) reported that blueberries subjected to

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electroporation prior to air drying at 45 C 75 C exhibited smaller (13.1% 61.5%) antioxidant activity than the untreated dried fruits (46.1% 65.4%). The results of antioxidant activity found in the case of vacuum-dried materials were the same from statistical point of view, regardless of the presence of pretreatment and they depended only on drying temperature. As aforementioned the concentration of bioactive compounds is one of many factors that affect the antioxidant activity. Amid other factors the interaction between particular compounds or their chemical structure should be listed (Jakobek, 2015; Mira et al., 2002). Therefore since the PEF treatment leads to the disintegration of the cellular structure, some of the liberated from compounds may react with molecules that possess antioxidant potential. Another explanation may be related to the fact that in some conditions antioxidants as polyphenols or carotenoids may exhibit prooxidant character. Prooxidant activity of these bioactive compounds is very often triggered at the presence of metals such as iron or cooper, which are present in biological systems (Eghbaliferiz & Iranshahi, 2016). Moreover, the metal ions can be released from the electrodes during the PEF application as demonstrated by Pataro, Falcone, Donsı`, and Ferrari (2014). Nevertheless, the scarcity of data about the effect of the PEF on the antioxidant activity should stimulate future research in this field.

8.3

Role of pulsed electric field in osmotic dehydration

OD is a potential technology by which partial removal of water from food is possible by placing them in a hypertonic ´ z, Nowacka, Chudoba, & sugar or salt solutions (Wiktor, Sled´ Witrowa-Rajchert, 2014). This results in an equilibrium condition in both food product and the solution. OD has got wide application in the preservation of fruits and vegetables since it lowers their water activity. OD is also preferred over other methods due to the retention of color, aroma, nutritional components, and flavor compounds (Yadav & Singh, 2014).

8.3.1

Impact of pulsed electric field on osmotic dehydration kinetics

The OD is a multicomponent mass transfer process (Fig. 8.4). Two countercurrent mass transfer flows govern the OD

Chapter 8 PEF as an alternative tool

Hypertonic solution

Food material

Water (WL) Solid gain (SG)

Figure 8.4 Typical representation of osmotic dehydration food materials. Water goes out from food matrix and solids come into it.

phenomenon, comprising (1) diffusion of water from the food into the hypertonic solution resulting in water loss (WL) and (2) diffusion of solids (solute) from the hypertonic solution into the product resulting in solid gain (SG) (Sunjka & Raghavan, 2004). These two mass transfer phenomenon continue to affect WL and SG until a dynamic equilibrium is reached, after which the mass exchange phenomenon might still continue, but WL and SG for the food product remain unaffected. The kinetics of OD enhanced by PEF has been discussed in detail by Ade-Omowaye, Talens, Angersbach, and Knorr (2003). Other researchers have employed Fick’s approximation to evaluate mass transfer using a transport process study using an effective mass transfer (diffusion) coefficient (Moreira & Sereno, 2003). Mavroudis, Gekas, and Sjo¨holm (1998) indicate free convection as a possible mechanism concerning solute transport during the first stage in OD of apple tissue, while diffusion dominates at later stages. Nevertheless, due to the mechanisms of the PEF process, any transport process (mass/heat/fluid transfer) is enhanced. This implies that SG and WL, both mass transfer processes, are also enhanced during or after PEF treatment. During PEF treatment, electroporation (electro-permeabilization) results in the cell membrane of the food products becoming perforated, which presents itself in formation of (or growth of existing) small plasmolemma pores. The process could be considered reversible until a particular PEF voltage application, beyond which irreversible disruption in the continuity of the cell is created. Here, it must be mentioned that a moderate pretreatment of E 5 0.3 1.5 kV/cm for less than 0.1 s generally does not affect the cell wall structure of majority of food plants and is a suitable pretreatment technique. Whether reversible or irreversible, some amount of moisture in food always migrates to the surface (Angersbach, Heinz, & Knorr, 2000), due to which a humidification of the tissue surface is noticed after completion of the PEF process (El Belghiti &

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Vorobiev, 2004). When conducted simultaneously, or on later exposure to a hypertonic solution, an increased mass transfer (both SG and WL) is noticed in such PEF-pretreated tissues, as compared to untreated tissues exposed to the same hypertonic solution. This coupled with the changes in the internal turgor pressure and electroosmotic pressure results in more solute flowing from inside the cells during PEF-assisted OD process (Amami, Vorobiev, & Kechaou, 2005). In a nutshell, this phenomenal explanation of the PEF-assisted OD process describes the current understanding of this process. A number of studies (Ade-Omowaye, Rastogi, Angersbach, & Knorr, 2002; Ade-Omowaye, Rastogi, Angersbach, & Knorr, 2003; Ade-Omowaye, Angersbach, Taiwo, & Knorr, 2001b; Amami, Fersi, Khezami, et al., 2007; Amami, Fersi, Vorobiev, et al., 2007; Amami, Vorobiev, & Kechaou, 2006; Dellarosa, Ragni, et al., 2016; Dellarosa, Tappi, et al., 2016; Dermesonlouoglou, Zachariou, Andreou, & Taoukis, 2016; Fincan & Dejmek, 2003; Taiwo et al., 2002b; Traffano-Schiffo et al., 2016) have investigated the effect of PEF-assisted OD in different food matrices. PEF pretreatment is effective to enhance water and solute transfer operations (Jemai & Vorobiev, 2003; Khezami, Jemai, Capart, & Vorobiev, 2010) and to osmotically remove water from fruits (Ade-Omowaye et al., 2001a,b; Amami et al., 2005; Rastogi, Eshtiaghi, & Knorr, 1999). It has generally been observed that both WL and SG increase with application of PEF during OD; however, some authors have found conflicting results too. For example, Taiwo et al. (2002b) found that PEF-assisted (2.67 kV/cm) OD of mangoes in a 50-degree Brix sucrose solution at 40 C for 5 h results in B30% increase of SG (from  0.63 to  0.82 g/g), but they witnessed a nonsignificant effect on WL. Similar increase in SG was also observed by Amami et al. (2005, 2006), and Dellarosa, Ragni, et al. (2016) for apples, but they witnessed a significant increase in WL as well, although the effect of PEF on SG was more pronounced than WL. On the other hand, Traffano-Schiffo et al. (2016) found the SG to decrease and WL to increase for PEFpretreated kiwifruit samples. They observed the effect of PEF to be more pronounced on WL as compared to SG. This suggests that although there is a general consensus that WL and SG increase on application of PEF, this might not necessarily be true in all cases, and depend inherently on the food matrix and processing conditions. Apart from the application of PEF, other process conditions such as temperature, static or agitating/moving osmotic solution, and addition of salts have also been studied. Mavroudis et al. (1998) found the mass transfer process during PEF-assisted OD

Chapter 8 PEF as an alternative tool

process to be a function of many variables such as the nature of the pretreatment process, process temperature, osmotic solution concentration and composition, immersion time, osmotic solution to-food ratio, and nature and geometry of food (Forni, Sormani, Scalise, & Torreggiani, 1997; Lerica, Mastrocola, Pinnavaia, & Bartolucci, 1985; McMinn & Magee, 1996). Amami et al. (2005, 2006) studied the effect of PEF on the concentration of the osmotic solution too (in addition to WL and SG) and noticed that at the optimum conditions of E 5 900 V/cm (energy consumption of 13.5 kJ/kg), solids concentration in their 44.5% w/w sucrose solution decreased. They proposed a twoexponential kinetic model that permitted the evaluation of convective and diffusion stages of the OD in presence of PEF. Ade-Omowaye et al. (2002) studied the effect of temperature during PEF-assisted OD of bell peppers using sucrose and sodium chloride as osmotic agents. They observed that an increase in temperature from 25 C to 55 C resulted in 32% 48% in WL and increase in E from 0.5 to 2.5 kV/cm resulted in 36% 50% increase in WL. This effect of temperature could be explained by the Arrhenius equation which dictates that temperature generally enhances the rate constants (diffusion/mass transfer coefficients). OD is usually conducted with agitation of the liquid solution to enhance the mass transfer coefficients and increase the overall mass transfer rate (Moreira & Sereno, 2003) by enhancing agitation. Agitated osmotic solution during OD exhibited greater weight loss than nonagitated ones (Bongirwar & Sreenivasan, 1977; Ponting, Walters, Forrey, Jackson, & Stanley, 1966). More recently, Amami, Fersi, Khezami, et al. (2007) observed that the combined application of PEF, centrifugal field, and OD in aqueous salt solution enhanced WL from the carrot tissue. The combination of PEF with salt enhanced both WL and SG. The application of centrifugal field during OD enhanced WL but reduced SG. The WL/SG ratio however remained approximately the same during the static OD; however, centrifugal field (agitation) increased the WL/SG ratio. Addition of salt during the static and centrifugal OD increased WL and SG but decreased the WL/SG ratios. Amami, Khezami, Jemai, and Vorobiev (2014) pretreated tissues of apple, carrot, and banana by PEF and subsequently osmotically dehydrated in an agitated flask at ambient temperature using a 65% sucrose solution as osmotic medium. Amami et al. (2014) studied the effect of stirring intensity through WL and SG under an impeller in a laminar flow (Re , 300) of the osmotic solution. They also employed a twoexponential kinetic model and evaluated the mass transfer

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coefficients and related them to the agitation intensity of the osmotic fluid. They found that at higher Reynolds number, WL and SG were higher too. Thus PEF-assisted OD could further be enhanced by inducing agitation or by incorporating salt into the osmotic solution (i.e., increase its concentration).

8.3.2

Impact of pulsed electric field on physicochemical properties of osmodehydrated food

PEF has been found to preserve the physicochemical properties of osmo-dehydrated food. Taiwo, Eshtiaghi, Ade-Omowaye, and Knorr (2003) found that the application of PEF before OD minimized changes in color and product compactness of strawberry halves. They also noticed that the samples treated with PEF had higher WL and leaching of the nutrients. Tylewicz et al. (2017) found that low PEF strengths of 100 V/cm were able to preserve cell viability of organic strawberries and simultaneously result in greater mass transfer and fresh-like characteristics of strawberries. The fresh-like characteristics have often been linked to the preservation of cell viability, as observed by Mauro et al. (2016) after 120 min in 40% of sucrose solution. In the study by Mauro et al. (2016), when 30% sucrose 1 3% of calcium lactate was used the cell viability was also preserved, while increasing quantity of calcium lactate up to 4% in 40% of sucrose compromised the cell viability. During PEF OD treatments, water migrates from the inner compartments toward the external ones, changing the physicochemical properties of products. Dellarosa, Tappi, et al. (2016) found that the medium (250 V/cm) and the high applied voltages (400 V/cm) resulted in loss of cell viability due to the irreversible damages of the membranes. On the other hand, the tissue treated with 100 V/cm showed metabolic indexes comparable to the fresh tissue indicating that the electroporation was only reversible and did not cause loss of cell viability. For strawberries, Cheng, Zhang, Adhikari, and Islam (2014) explained this phenomenon through microscopic images, wherein the relative space occupied by the vacuole decreased, while the one occupied by the cytoplasm and intercellular space increased. This phenomenon of cell membrane becoming more porous on electroporation has been established to be a function of temperature, intensity of the applied electric field, number of pulses, pulse shape, type of tissue, etc. (Buckow, Ng, & Toepfl, 2013) and has been found to be the leading cause of irreversible damages causing loss of cell

Chapter 8 PEF as an alternative tool

viability. Similar observations of water distributions have been observed for kiwifruit (Panarese et al., 2012; Tylewicz, Fito, Castro-Gira´ldez, Fito, & Dalla Rosa, 2011) and apples (Mauro et al., 2016). These observations suggest the existence of a threshold electric field beyond which cell viability deteriorates to impart undesirable changes in the tissues, and thus it is important to establish this threshold from the quality characteristics point of view as well. Color, as already mentioned as a major factor affecting food product acceptance, remains a factor that is still unclear on how PEF impacts it. In some case, PEF can inactivate enzymes responsible for color change; however, in other cases, PEF can also result in the leakage of intracellular content and enhance the activity of some other enzymes responsible for color changes. For example, color changes were reported for apple (Grimi et al., 2010; Wiktor, Schulz, Voigt, Knorr, et al., 2015; Wiktor, Schulz, Voigt, Witrowa-Rajchert, et al., 2015; Wiktor, Sledz, et al., 2015), white asparagus (Janositz, Semrau, & Knorr, 2011), blueberries (Yu et al., 2018), and strawberries (Tylewicz et al., 2017), while no color change was reported for green tea extract (Zhao, Yang, Wang, & Lu, 2009), red cherries (Sotelo et al., 2018), and carrot and tomato juices (Odriozola-Serrano, Soliva-Fortuny, Herna´ndez-Jover, & Martı´n-Belloso, 2009) that were subjected to PEF treatment. Wiktor, Schulz, Voigt, Knorr, et al. (2015), Wiktor, Schulz, Voigt, Witrowa-Rajchert, et al. (2015), and Wiktor, Sledz, et al. (2015) established that the change in the color parameters during PEF application is dependent on the material properties and the treatment conditions. In fact, the authors noticed the different behavior of carrot and apple tissues subjected to electric field strength at different intensities—with lower L* value of PEF-treated samples at high E, respectively, whereas higher L* values at low E. Generally, the darkening effect of PEF in carrots was more pronounced when the low-voltage treatment was applied, while in apple it was only observed with high voltage. Tylewicz et al. (2017) found similar trends with the luminosity of their organic strawberries, which increased significantly after the application of PEF at the intensity of 100 V/cm, while decreased due to the application of PEF at highest field intensity of 400 V/cm. They suggested that the darkening of the PEF-treated samples at high intensities could be related to the higher release of enzymes such as peroxidase and PPO and their substrates after the electroporation of the strawberry cell membrane. Chisari, Barbagallo, and Spagna (2007) confirmed the findings suggesting that the browning of the strawberry fruit during the storage

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was related to both oxidase activities. However, one of the interesting observations was that for OD treatment times .120 min, the PEF-treated samples had L* values significantly higher than untreated ones. Taiwo et al. (2003) also found that the prolonged pulse application induced reactions leading to decrease of lightness. Dermesonlouoglou, Chalkia, et al. (2018) found that PEF pretreatment modified the color of fresh and ODtreated goji berry leading to statistically significant lowering of the values of all color parameters (L: lightness/whiteness; a: redness; b: decreased yellowness) and a light brown color. They, however, did observe that the increase of PEF pulse number from 750 to 7500 did not significantly affect the color parameters L, a, b. While combining OD with high pressure processing, Nun˜ez-Mancilla, Pe´rez-Won, Uribe, Vega-Ga´lvez, and Di Scala (2013) obtained similar results, wherein L* was not significantly affected in strawberry during stand-alone OD process, while this parameter was influenced significantly by the application of high hydrostatic pressure. The hue angle (h degree) has also been used to track color change. Osorio et al. (2007) found the hue angle to decrease on PEF and OD treatments due to solubilization of pigments in the osmotic solution and degradation of anthocyanin induced by PEF treatment (Fathi, Mohebbi, & Razavi, 2011; Odriozola-Serrano, Soliva-Fortuny, Gimeno-An˜o´, & Martı´n-Belloso, 2008). Texture changes in osmo-dehydrated food products are generally associated with decrease of the firmness and hardness. OD results in plasmolysis, which causes shrinkage of the vacuole compartment, changes in size and structure of the cell walls of outer pericarp, and dissolution of the middle lamella, which in turn deteriorates the texture of the product (Chiralt & Talens, 2005; Panarese et al., 2012). On pretreatment with PEF the effect of firmness reduction is further enhanced due to enhancement of membrane permeability and rupture of internal structure on account of electroporation (Fincan & Dejmek, 2002; Wiktor, Gondek, et al., 2016). Taiwo et al. (2003) and Tylewicz et al. (2017) confirmed these hypotheses by observing a drastic decrease of the firmness and hardness of PEF-pretreated strawberry as compared to nondehydrated ones. While the effect was proportional to the electric field strength applied, Tylewicz et al. (2017) observed an enhancement in texture after elongated times of osmo-dehydration. This improvement in texture has been linked to greater penetration of Ca21 in the product matrix and could be utilized for optimization of certain category of products. Van Buggenhout, Grauwet, Van Loey, and Hendrickx (2008) and Mauro et al. (2016) have explained the role of

Chapter 8 PEF as an alternative tool

calcium ions as providing structural strength to the cell wall due to their interaction with pectic acid polymers that form cross-bridges to reinforce the cell adhesion, thereby reducing cell separation, which is one of the major causes of plant tissue softening. However, this better texture has not been observed in the samples treated at high PEF treatment (400 V/cm), probably because the tissue was already completely disintegrated after the PEF treatment, and did not permit the incorporation of calcium ions in the cell walls. Apart from Ca21, trehalose has also been utilized by Phoon et al. (2008) to improve the texture of PEF-assisted osmo-dehydrated products. PEF-assisted osmodehydrated apples have also been noticed to have accelerated freezing/thawing characteristics as compared to untreated apple disks (Parniakov et al., 2016a). This suggests that if a lowPEF strength and high-OD time in a strengthening solution (like those with Ca21) could result in an optimized PEF OD process from the perspective of texture, which are also better for subsequent freezing. Apart from color and texture, various other nutritional and physicochemical quality characteristics also play an important role in the overall quality of a food product. Generally, PEF pretreatments during OD process reduce the dehydration time (faster rate of moisture content loss) and enhance the shelf life (increased microbial stability), it but does not affect the nutritional quality. When fresh blueberries were osmo-dehydrated in cane sugar syrup, no significant differences were observed in total phenolics, antioxidants, anthocyanins, predominant phenolic acids, and flavanols on pretreatment with or without PEF (Yu et al., 2017), although they had longer shelf life and required lower dehydration times (120 to 28 h) for 3.0 g/g-initial-drymatter target moisture content. On comparison with a thermal pretreatment at 90 C and control (no pretreatment) before OD process, Yu et al. (2018) observed PEF pretreatment to enhance the dehydration efficacy of blueberries with less chemical degradation and more migration than thermal pretreatment. During the PEF pretreatments and OD, the PPO enzyme is induced and causes the degradation of anthocyanins and conversion of other phenolic compounds into brown pigments through a coupled oxidation mechanism (Kader, Rovel, Girardin, & Metche, 1997; Terefe, Delon, Buckow, & Versteeg, 2015). This reduction in nutrient compounds could be caused by their biochemical degradation and physical migration from fruits to liquid media during PEF pretreatments and OD (Yu et al., 2016). However, this quality degradation seems to be balanced by the decrease in dehydration time

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(which improves quality deterioration), and thereby nutritional parameters do not change significantly. Based on sensory tests, Dermesonlouogou, Zachariaou, et al. (2018) found PEFosmo-dehydrated frozen kiwifruits to have up to three times the shelf life as that of control. They also developed kinetic models for color change, vitamin loss, and sensory quality deterioration and found PEF-pretreated OD had significantly shorter time (30 min compared to 60 min for OD alone) and kiwifruits retained optimum quality and sensory characteristics. For bell peppers the vitamin C reduction was observed to be up to 50% lower for PEF OD process, as compared to OD standalone, while carotenoids remained largely unaffected (Ade-Omowaye et al., 2002). For goji berry fruits, PEF OD pretreatment enhanced the quality and sensory characteristics of the final air-dried goji berry product with minimum level of color change, high antioxidant capacity and total phenolic content, and desired sensory characteristics (Dermesonlouoglou et al., 2018). Thus it is seen that PEF pretreatments could provide great benefits to fruit processors and consumers; however, their effects on a number of food products still seem to be largely unexplored.

8.4

Conclusion

In general, drying is a highly energy-intensive food preservation process. This unit operation requires up to 12% of total industrial energy use in most developed countries (Roohinejad , Parniakov, Nikmaram, Greiner, & Koubaa, 2018). The second critical point in drying is the mass transfer through the cells and tissue of solid food. Due to their barrier function of intact cell membranes in the raw material, the diffusion is limited. The application of external electric field has a positive effect on any subsequent drying processes. Therefore utilization of PEF as a pretreatment is a new and unique approach, which allows the process kinetics to be enhanced and the quality to be improved without significant negative impact on bioactive compounds or nutritional quality. This makes it very competitive and valuable solution for heat and mass transfer based processes enhancement. PEF technology, regardless of the industrial branch, can be applied at the very beginning of the already existing processing lines, which makes them very easily to adjust. Moreover, this emerging technology allows reducing energy consumption and processing time and maintaining or improving the quality of processed plant food. However, current

Chapter 8 PEF as an alternative tool

limitations (e.g., high investment costs) have been delaying a wider implementation of these methods at the industrial scale, which required more attention to be solved. Regardless of their challenges, it is obvious that these methods offer clear environmental benefits by enhancing the overall energy efficiency of the process or by lowering nonrenewable resources utilization. Overall, PEF technology stays in accordance with sustainable development concept and makes it easier to introduce food that fits current trends.

Acknowledgments Part of the results presented in this work was supported by the Narodowe ´ i Rozwoju (Poland) within a framework of LIDER program, Centrum Badan NO. LIDER/017/497/L-4/12/NCBR/2013.

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Keˇselj, K., Pavkov, I., Radojˇcin, M., & Stamenkovi´c, Z. (2017). Comparison of energy consumption in the convective and freeze drying of raspberries. Journal on Processing and Energy in Agriculture, 21(4), 192 196. Khezami, L., Jemai, A. B., Capart, R., & Vorobiev, E. (2010). Drying kinetics study of food pulps by continuous relative humidity measurements: Air flowrate and electric field effects. Chemical Technology: An Indian Journal, 5(1), 45 50. ,http://www.tsijournals.com/abstract/drying-kinetics-study-of-food-pulpsby-continuous-relative-humidity-measurements-air-flowrate-and-electricfield-effects-1111.html.. Kim, M. H., & Toledo, R. T. (1987). Effect of osmotic dehydration and high temperature fluidized bed drying on properties of dehydrated rabbiteye blueberries. Journal of Food Science, 52(4), 980 984. Kudra, T. (2004). Energy aspects in drying. Drying Technology, 22(5), 917 932. Kwao, S., Al-Hamimi, S., Damas, M. E. V., Rasmusson, A. G., & Galindo, F. G. (2016). Effect of guard cells electroporation on drying kinetics and aroma compounds of Genovese basil (Ocimum basilicum L.) leaves. Innovative Food Science & Emerging Technologies, 38, 15 23. ˇ Lamanauskas, N., Satkauskas, S., Bobinait˙e, R., & Viˇskelis, P. (2015). Pulsed electric field (PEF) impact on Actinidia kolomikta drying efficiency. Journal of Food Process Engineering, 38(3), 243 249. Lebovka, N. I., Bazhal, M. I., & Vorobiev, E. (2002). Estimation of characteristic damage time of food materials in pulsed-electric fields. Journal of Food Engineering, 54(4), 337 346. Lebovka, N. I., Praporscic, I., & Vorobiev, E. (2004). Effect of moderate thermal and pulsed electric field treatments on textural properties of carrots, potatoes and apples. Innovative Food Science & Emerging Technologies, 5(1), 9 16. Lebovka, N. I., Shynkaryk, N. V., & Vorobiev, E. (2007). Pulsed electric field enhanced drying of potato tissue. Journal of Food Engineering, 78(2), 606 613. Lerica, C. R., Mastrocola, D., Pinnavaia, G., & Bartolucci, I. (1985). Osmotic dehydration of fruits: Influence of osmotic agents on drying behaviour and product quality. Journal of Food Science, 50, 1217 1226. Available from https://doi.org/10.1111/j.1365-2621.1985.tb10445.x. Lewicki, P. P. (1998). Effect of pre-drying treatment, drying and rehydration on plant tissue properties: A review. International Journal of Food Properties, 1(1), 1 22. Lewicki, P. P. (2006). Design of hot air drying for better foods. Trends in Food Science & Technology, 17(4), 153 163. Lightbourn, G. J., Griesbach, R. J., Novotny, J. A., Clevidence, B. A., Rao, D. D., & Stommel, J. R. (2008). Effects of anthocyanin and carotenoid combinations on foliage and immature fruit color of Capsicum annuum L. Journal of Heredity, 99(2), 105 111. Liu, C., Grimi, N., Lebovka, N., & Vorobiev, E. (2018). Effects of pulsed electric fields treatment on vacuum drying of potato tissue. LWT, 95, 289 294. Liu, Z., Song, Y., Guo, Y., Wang, H., & Liu, J. (2016). Optimization of pulsed electric field pretreatment parameters for preserving the quality of Raphanus sativus. Drying Technology, 34(6), 692 702. Lu, T., & Shen, S. Q. (2007). Numerical and experimental investigation of paper drying: Heat and mass transfer with phase change in porous media. Applied Thermal Engineering, 27(8 9), 1248 1258. Maskooki, A., & Eshtiaghi, M. N. (2012). Impact of pulsed electric field on cell disintegration and mass transfer in sugar beet. Food and Bioproducts Processing, 90(3), 377 384.

Chapter 8 PEF as an alternative tool

Mauro, M. A., Dellarosa, N., Tylewicz, U., Tappi, S., Laghi, L., Rocculi, P., & Dalla Rosa, M. (2016). Calcium and ascorbic acid affect cellular structure and water mobility in apple tissue during osmotic dehydration in sucrose solutions. Food Chemistry, 195, 19 28. Available from https://doi.org/10.1016/j. foodchem.2015.04.096. Mavroudis, N. E., Gekas, V., & Sjo¨holm, I. (1998). Osmotic dehydration of apples. Shrinkage phenomena and the significance of initial structure on mass transfer rates. Journal of Food Engineering, 38(1), 101 123. Available from https://doi.org/10.1016/s0260-8774(98)00090-9. McMinn, W. A. M., & Magee, T. R. A. (1996). Quality and physical structure of dehydrated starch-based system. Drying Technology, 15(6 8), 1961 1971. Available from https://doi.org/10.1080/07373939708917341. Md Salim, N. S., Garie`py, Y., & Raghavan, V. (2016). Effects of operating factors on osmotic dehydration of broccoli stalk slices. Cogent Food & Agriculture, 2(1), 1134025. Mercer, P., & Armenta, R. E. (2011). Developments in oil extraction from microalgae. European Journal of Lipid Science and Technology, 113(5), 539 547. Mira, L., Tereza Fernandez, M., Santos, M., Rocha, R., Helena Floreˆncio, M., & Jennings, K. R. (2002). Interactions of flavonoids with iron and copper ions: A mechanism for their antioxidant activity. Free Radical Research, 36(11), 1199 1208. Mizobutsi, G. P., Finger, F. L., Ribeiro, R. A., Puschmann, R., Neves, L. L. D. M., & Mota, W. F. D. (2010). Effect of pH and temperature on peroxidase and polyphenoloxidase activities of litchi pericarp. Scientia Agricola, 67(2), 213 217. Moreira, R., & Sereno, A. M. (2003). Evaluation of mass transfer coefficients and volumetric shrinkage during osmotic dehydration of apple using sucrose solutions in static and non-static conditions. Journal of Food Engineering, 57(1), 25 31. Available from https://doi.org/10.1016/s02608774(02)00217-0. Moussa-Ayoub, T. E., Ja¨ger, H., Knorr, D., El-Samahy, S. K., Kroh, L. W., & Rohn, S. (2017). Impact of pulsed electric fields, high hydrostatic pressure, and thermal pasteurization on selected characteristics of Opuntia dillenii cactus juice. LWT Food Science and Technology, 79, 534 542. Nowacka, M., Fijalkowska, A., Dadan, M., Rybak, K., Wiktor, A., & WitrowaRajchert, D. (2018). Effect of ultrasound treatment during osmotic dehydration on bioactive compounds of cranberries. Ultrasonics, 83, 18 25. Nuccitelli, R., Lui, K., Kreis, M., Athos, B., & Nuccitelli, P. (2013). Nanosecond pulsed electric field stimulation of reactive oxygen species in human pancreatic cancer cells is Ca21-dependent. Biochemical and Biophysical Research Communications, 435(4), 580 585. Nun˜ez-Mancilla, Y., Pe´rez-Won, M., Uribe, E., Vega-Ga´lvez, A., & Di Scala, K. (2013). Osmotic dehydration under high hydrostatic pressure: Effects on antioxidant activity, total phenolics compounds, vitamin C and color of strawberry (Fragaria vesca). LWT Food Science and Technology, 52(2), 151 156. Available from https://doi.org/10.1016/j.lwt.2012.02.027. ˜ o´, V., & Martı´n-Belloso, O. Odriozola-Serrano, I., Soliva-Fortuny, R., Gimeno-An (2008). Kinetic study of anthocyanins, vitamin C, and antioxidant capacity in strawberry juices treated by high-intensity pulsed electric fields. Journal of Agricultural and Food Chemistry, 56(18), 8387- 88393. Available from https:// doi.org/10.1021/jf801537f.

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Chapter 8 PEF as an alternative tool

Riaz, M. N., Asif, M., & Ali, R. (2009). Stability of vitamins during extrusion. Critical Reviews in Food Science and Nutrition, 49(4), 361 368. Roohinejad, S., Parniakov, O., Nikmaram, N., Greiner, R., & Koubaa, M. (2018). Energy Saving Food Processing. In Sustainable Food Systems from Agriculture to Industry (pp. 191 243). London: Academic Press. Sarah, S. Global Freeze Dried Foods Market 2017-2021, https://www.prnewswire. com/news-releases/global-freeze-dried-foods-market-2017-2021-300490286. html Accessed 14.01.20 Sato, M., Ohgiyama, T., & Clements, J. S. (1996). Formation of chemical species and their effects on microorganisms using a pulsed high-voltage discharge in water. IEEE Transactions on Industry Applications, 32(1), 106 112. Segovia, F. J., Luengo, E., Corral-Pe´rez, J. J., Raso, J., & Almajano, M. P. (2015). Improvements in the aqueous extraction of polyphenols from borage (Borago officinalis L.) leaves by pulsed electric fields: Pulsed electric fields (PEF) applications. Industrial Crops and Products, 65, 390 396. Shayanfar, S., Chauhan, O. P., Toepfl, S., & Heinz, V. (2013). The interaction of pulsed electric fields and texturizing, antifreezing agents in quality retention of defrosted potato strips. International Journal of Food Science & Technology, 48(6), 1289 1295. Shynkaryk, M. V., Lebovka, N. I., & Vorobiev, E. (2008). Pulsed electric fields and temperature effects on drying and rehydration of red beetroots. Drying Technology, 26(6), 695 704. Soliva-Fortuny, R., Balasa, A., Knorr, D., & Martı´n-Belloso, O. (2009). Effects of pulsed electric fields on bioactive compounds in foods: A review. Trends in Food Science & Technology, 20(11), 544 556. Sotelo, K. A., Hamid, N., Oey, I., Pook, C., Gutierrez-Maddox, N., Ma, Q., . . . Lu, J. (2018). Red cherries (Prunus avium var. Stella) processed by pulsed electric field—Physical, chemical and microbiological analyses. Food Chemistry, 240, 926 934. Available from https://doi.org/10.1016/j.foodchem.2017.08.017. Sunjka, P.S., & Raghavan, G.S.V. (2004). Assessment of pretreatment methods and osmotic dehydration for cranberries. Canadian Biosystems Engineering, 46, 3.35-3.40. ,http://www.csbe-scgab.ca/docs/journal/46/c0339.pdf.. Taiwo, K. A., Angersbach, A., & Knorr, D. (2002a). Rehydration studies on pretreated and osmotically dehydrated apple slices. Journal of Food Science, 67(2), 842 847. Taiwo, K. A., Angersbach, A., & Knorr, D. (2002b). Influence of high intensity electric field pulses and osmotic dehydration on the rehydration characteristics of apple slices at different temperatures. Journal of Food Engineering, 52(2), 185 192. Available from https://doi.org/10.1016/S0260-8774(01)00102-9. Taiwo, K. A., Eshtiaghi, M. N., Ade-Omowaye, B. I., & Knorr, D. (2003). Osmotic dehydration of strawberry halves: Influence of osmotic agents and pretreatment methods on mass transfer and product characteristics. International Journal of Food Science & Technology, 38(6), 693 707. Available from https://doi.org/10.1046/j.1365-2621.2003.00720.x. Teissie, J., Eynard, N., Gabriel, B., & Rols, M. P. (1999). Electropermeabilization of cell membranes. Advanced Drug Delivery Reviews, 35(1), 3 19. Teissie, J., Golzio, M., & Rols, M. P. (2005). Mechanisms of cell membrane electropermeabilization: A minireview of our present (lack of?) knowledge. Biochimica et Biophysica Acta (BBA)-General Subjects, 1724(3), 270 280. Telfser, A., & Galindo, F. G. (2019). Effect of reversible permeabilization in combination with different drying methods on the structure and sensorial quality of dried basil (Ocimum basilicum L.) leaves. LWT Food Science and Technology, 99, 148 155.

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Terefe, N. S., Delon, A., Buckow, R., & Versteeg, C. (2015). Blueberry polyphenol oxidase: Characterization and the kinetics of thermal and high pressure activation and inactivation. Food Chemistry, 188, 193 200. Available from https://doi.org/10.1016/j.foodchem.2015.04.040. Toepfl, S., & Heinz, V. (2011). Pulsed electric field assisted extraction A case study. Nonthermal processing technologies for food (pp. 190 198). Oxford: Blackwell Publishing. Torringa, E., Esveld, E., Scheewe, I., van den Berg, R., & Bartels, P. (2001). Osmotic dehydration as a pre-treatment before combined microwave-hot-air drying of mushrooms. Journal of Food Engineering, 49(2 3), 185 191. Traffano-Schiffo, M. V., Tylewicz, U., Castro-Giraldez, M., Fito, P. J., Ragni, L., & Dalla Rosa, M. (2016). Effect of pulsed electric fields pre-treatment on mass transport during the osmotic dehydration of organic kiwifruit. Innovative Food Science & Emerging Technologies, 38, 243 251. Available from https:// doi.org/10.1016/j.ifset.2016.10.01. Tylewicz, U., Fito, P. J., Castro-Gira´ldez, M., Fito, P., & Dalla Rosa, M. A. R. C. O. (2011). Analysis of kiwifruit osmodehydration process by systematic approach systems. Journal of Food Engineering, 104(3), 438 444. Available from https://doi.org/10.4315/0022-2747-38.7.388. Tylewicz, U., Tappi, S., Mannozzi, C., Romani, S., Dellarosa, N., Laghi, L., . . . Rosa, M. D. (2017). Effect of pulsed electric field (PEF) pre-treatment coupled with osmotic dehydration on physico-chemical characteristics of organic strawberries. Journal of Food Engineering, 213, 2 9. Available from https:// doi.org/10.1016/j.jfoodeng.2017.04.028. Van Buggenhout, S., Grauwet, T., Van Loey, A., & Hendrickx, M. (2008). Use of pectinmethylesterase and calcium in osmotic dehydration and osmodehydrofreezing of strawberries. European Food Research and Technology, 226(5), 1145 1154. Available from https://doi.org/10.1007/s00217-007-0643-7. Va´zquez, G., Chenlo, F., Moreira, R., & Cruz, E. (1997). Grape drying in a pilot plant with a heat pump. Drying Technology, 15(3 4), 899 920. Vega-Ga´lvez, A., Zura-Bravo, L., Lemus-Mondaca, R., Martinez-Monzo´, J., Quispe-Fuentes, I., Puente, L., & Di Scala, K. (2015). Influence of drying temperature on dietary fibre, rehydration properties, texture and microstructure of Cape gooseberry (Physalis peruviana L.). Journal of Food Science and Technology, 52(4), 2304 2311. Witrowa-Rajchert, D. (2017). Pulsed electric fields as pretreatment for subsequent food process operations. In D. Miklavˇciˇc (Eds.), Handbook of Electroporation (pp. 2439 2454). Berlin, Heidelberg: Springer, Cham. Wiktor, A., Gondek, E., Jakubczyk, E., Nowacka, M., Dadan, M., Fijalkowska, A., & Witrowa-Rajchert, D. (2016). Acoustic emission as a tool to assess the changes induced by pulsed electric field in apple tissue. Innovative Food Science & Emerging Technologies, 37, 375 383. Available from https://doi.org/10.1016/j. ifset.2016.04.008. ´ z, M., Nowacka, M., Chudoba, T., & WitrowaWiktor, A., Iwaniuk, M., Sled´ Rajchert, D. (2013). Drying kinetics of apple tissue treated by pulsed electric field. Drying Technology, 31(1), 112 119. Wiktor, A., Nowacka, M., Dadan, M., Rybak, K., Lojkowski, W., Chudoba, T., & Witrowa-Rajchert, D. (2016). The effect of pulsed electric field on drying kinetics, color, and microstructure of carrot. Drying Technology, 34(11), 1286 1296. Wiktor, A., Schulz, M., Voigt, E., Knorr, D., & Witrowa-Rajchert, D. (2015). Impact of pulsed electric field on kinetics of immersion freezing, thawing, and on mechanical properties of carrot. Food Science Technology Quality, 99, 124 137.

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Wiktor, A., Schulz, M., Voigt, E., Witrowa-Rajchert, D., & Knorr, D. (2015). The effect of pulsed electric field treatment on immersion freezing, thawing and selected properties of apple tissue. Journal of Food Engineering, 146, 8 16. Available from https://doi.org/10.1016/j.jfoodeng.2014.08.013. ´ z, M., Nowacka, M., Chudoba, T., & Witrowa-Rajchert, D. (2014). Wiktor, A., Sled´ Pulsed electric field pretreatment for osmotic dehydration of apple tissue: Experimental and mathematical modeling studies. Drying Technology, 32(4), 408 417. Available from https://doi.org/10.1080/07373937.2013.834926. Wiktor, A., Sledz, M., Nowacka, M., Rybak, K., Chudoba, T., Lojkowski, W., & Witrowa-Rajchert, D. (2015). The impact of pulsed electric field treatment on selected bioactive compound content and color of plant tissue. Innovative Food Science & Emerging Technologies, 30, 69 78. Witrowa-Rajchert, D., Wiktor, A., Sledz, M., & Nowacka, M. (2014). Selected emerging technologies to enhance the drying process: A review. Drying Technology, 32(11), 1386 1396. Won, Y. C., Min, S. C., & Lee, D. U. (2015). Accelerated drying and improved color properties of red pepper by pretreatment of pulsed electric fields. Drying Technology, 33(8), 926 932. Wu, Y., & Zhang, D. (2014). Effect of pulsed electric field on freeze-drying of potato tissue. International Journal of Food Engineering, 10(4), 857 862. Wu, Y., Guo, Y., & Zhang, D. (2011). Study of the effect of high-pulsed electric field treatment on vacuum freeze-drying of apples. Drying technology, 29(14), 1714 1720. Xu, K., Lu, J., Gao, Y., Wu, Y., & Li, X. (2017). Determination of moisture content and moisture content profiles in wood during drying by low-field nuclear magnetic resonance. Drying Technology, 35(15), 1909 1918. Yadav, A. K., & Singh, S. V. (2014). Osmotic dehydration of fruits and vegetables: A review. Journal of Food Science and Technology, 51(9), 1654 1673. Yongsawatdigul, J., & Gunasekaran, S. (1996). Microwave-vacuum drying of cranberries: Part I. Energy use and efficiency. Journal of Food Processing and Preservation, 20(2), 121 143. Yu, Y., Jin, T. Z., Fan, X., & Wu, J. (2018). Biochemical degradation and physical migration of polyphenolic compounds in osmotic dehydrated blueberries with pulsed electric field and thermal pretreatments. Food Chemistry, 239, 1219 1225. Available from https://doi.org/10.1016/j.foodchem.2017.07.071. Yu, Y., Jin, T. Z., Fan, X., & Xu, Y. (2016). Osmotic dehydration of blueberries pretreated with pulsed electric fields: Effects on dehydration kinetics, and microbiological and nutritional qualities. Drying Technology, 35(13), 1543 1551. Available from https://doi.org/10.1080/07373937.2016.1260583. Yu, Y., Jin, T. Z., & Xiao, G. (2017). Effects of pulsed electric fields pretreatment and drying method on drying characteristics and nutritive quality of blueberries. Journal of Food Processing and Preservation, 41(6), e13303. Zhang, M., Chen, H., Mujumdar, A. S., Zhong, Q., & Sun, J. (2015). Recent developments in high-quality drying with energy-saving characteristic for fresh foods. Drying Technology, 33(13), 1590 1600. Zhao, W., Yang, R., Wang, M., & Lu, R. (2009). Effects of pulsed electric fields on bioactive components, color and flavour of green tea infusions. International Journal of Food Science & Technology, 44(2), 312 321. Available from https:// doi.org/10.1111/j.1365-2621.2008.01714.x. Zielinska, M., & Markowski, M. (2016). The influence of microwave Assisted drying techniques on the rehydration behavior of blueberries (Vaccinium corymbosum L.). Food Chemistry, 196, 1188 1196.

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Further reading Tedjo, W., Taiwo, K. A., Eshtiaghi, M. N., & Knorr, D. (2002). Comparison of pretreatment methods on water and solid diffusion kinetics of osmotically dehydrated mangos. Journal of Food Engineering, 53(2), 133 142. Available from https://doi.org/10.1016/S0260-8774(01)00149-2.

Modification of food structure and improvement of freezing processes by pulsed electric field treatment

9

Magdalena Dadan, Malgorzata Nowacka, Jakub Czyzewski and Dorota Witrowa-Rajchert Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences, Warsaw, Poland

9.1

Introduction

Freezing process depends on the reduction of the food temperature of below its freezing point (i.e., cryoscopic temperature). The change of the state of matter—from liquid water to solid ice—is an accompanying effect of the temperature reduction. These two simultaneous phenomena impact and shape the technological opportunities of freezing utilization. Thus the aim of this process can be related to food preservation and long-term storage (Kozłowicz & Kluza, 2010; Leygonie, Britz, & Hoffman, 2012; Rickman, Barrett, & Bruhn, 2007) or to separation of water in cryoconcentration (Aider & De Halleux, 2009; Normohamadpor Omran, Pirouzifard, Aryaey, & Hasan Nejad, 2013; Sa´nchez, Ruiz, Ravento´s, Auleda, & Herna´ndez, 2010) and ´ freeze
drying (Ciurzynska & Lenart, 2011; Ratti, 2001) or finally to ice-cream production (Homayouni, Azizi, Ehsani, Yarmand, ´ & Razavi, 2008; Kaminska & Gaukel, 2009). Despite all the abovementioned technological aims of freezing, it should be emphasized that freezing is considered as one of the oldest and the most popular food preservation techniques. However, even if freezing is considered by consumers as one of the safest preservation techniques (Cardello, 2003) and in many cases, it allows to preserve the native quality of the food product to a very large extent in comparison to other processing methods (Rickman et al., 2007), there are some products that due to regular freezing processing show severe structural damages that Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00009-4 © 2020 Elsevier Inc. All rights reserved.

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make their quality unacceptable by consumers (James, Purnell, & James, 2015). Such products require additional care and special handling to maintain their quality after freezing
thawing cycle. In many cases, this aim can be achieved either by an application of faster freezing method, an introduction of a pretreatment step, and/or an addition of cryoprotectants. Therefore well-established position of freezing as preservation technique does not mean that everything was achieved on that topic. More likely, it should be rather said that because of the great popularity of freezing, a lot of research activity on this technique is required. Therefore in this chapter, the use of pulsed electric field (PEF) pretreatment and the addition of cryoprotectants that can be impregnated to the food by the means of PEF treatment have been discussed. Furthermore, the impact of PEF on the freezing kinetics and the quality of the product will be compared with other nonthermal technologies used with the freezing process, such as ultrasound (US), high hydrostatic pressure (HHP), or radio-frequency (RF) techniques.

9.2

Progress of freezing of food products

Freezing of food products can be presented by the means of freezing curves that express the dependency between time of the process and temperature of the product (Fig. 9.1). Generally, freezing process can be divided into the following stages ´ (Fennema, 1973; Kaminska & Lewicki, 2006; Mok, Choi, Park, Lee, & Jun, 2015): 1. Cooling of liquid-state product to its freezing point (In Fig. 9.1: section 1
30 in the case of food and 1
2 in the case of water). When considering the water, the cooling is

Figure 9.1 Freezing curve of water (the solid line) and food product (the dashed line).

Chapter 9 Modification of food structure

terminated by supercooling state, in which the temperature of liquid is below its freezing point but the water still does not solidify. The degree of supercooling is defined as the negative difference between the temperature in the nucleation point (2) and in the freezing point (3). Because of the substances diluted in food matrix and progressive reduction of the temperature, it is hard to observe supercooling phenomenon in food, which is evident in the case of water. The presence of any substance in water medium can impact on both freezing point and supercooling. The metastable character of supercooling effect is important regarding storage of fruits and vegetables below freezing point temperature since the nucleation of ice can affect the quality of fresh fruits and vegetables. 2. Phase transition (In Fig. 9.1: section 30
40 in the case of food; 3
4 in the case of water). During this stage crystallization of ice begins, heat of crystallization is released and needs to be taken away in order to freeze the product. It is worth emphasizing that freezing point temperature of food is changing during freezing process because of progressive change of concentration of soluble solids. The time of this step is called an effective freezing time. The length of this step is often related to the quality of the product—the longer the time of this step the bigger ice crystals are formed and cellular structure is more damaged. 3. Subcooling (In Fig. 9.1: section 40
5 in the case of food products; 4
5 in the case of water). During this stage, temperature of the product is being reduced up to the temperature assumed for the process. Point 6 shows the moment when both water and food achieve the temperature of freezing medium and freezing process ends. Freezing progress depends on the type of the processed food. As described earlier (regardless the type of the food), food freezing kinetics is little or sharply different in comparison to onecomponent physical solutions (Fig. 9.1). The biggest differences can be stated for solid-like plant or animal origin products. The cellular structure of these materials can be considered as discontinuous matrix—it consists of liquid phase entrapped in solidstate cell walls, which causes a number of implications for freezing kinetics. Water state of matter transition is a reversible phenomenon. However, in the case of freezing of food matrix, other irreversible phenomena and processes take place. For instance, freezing degrades the natural cellular structure of food, which affects the quality of food after thawing. As Dalvi-Isfahan et al. (2019) reported, the sensorial properties and texture changes induced by mechanical and biochemical stresses during freezing are

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related to crystal morphological characteristics. Generally, a smaller and more uniform size of crystals is desirable, as they resulted in a lesser tissue damage. Thus it can be stated that maintenance of the cellular structure would be beneficial for frozen food quality. It is generally known that this can be achieved by utilization of fast freezing techniques. On the other hand, freezing belongs to heat transfer
based operations and cellular structure limits their progress and kinetics. Thus it can be stated that ideal freezing technology delivers balance between these two opposite issues. There are two main approaches that allow to enhance kinetics of freezing and to maintain the quality of final product. The first one depends on the implementation of new, faster freezing technologies—that is, technological shift, replacement of old technology by the new, more efficient one. The second approach links to the introduction of additional step (pretreatment) to existing technology. It can be achieved by the using of nonthermal technologies, such as PEF or US. Furthermore, also the use of cryoprotectants that may be introduced to the food with osmotic dehydration (OD), vacuum impregnation (VI), or PEF treatments enhances the quality of frozen
thawed material and influences the pattern in which ice is propagated, as it will be explained next.

9.3

The application of pulsed electric field treatment prior to freezing

PEF treatment depends on an application of short-lasting high-intensity electric field pulses to food materials. Treated materials can be either liquid or solid like (Mahnicˇ -Kalamiza, Vorobiev, & Miklavcˇ icˇ , 2014). The phenomenon which is a consequence of PEF application is called electroporation, and it can be described (in a simplified manner) as an electrically induced perforation of the cell membrane. Depending on both processing parameters and properties of treated material, the electroporation can be reversible or irreversible (Raso et al., 2016). According to scientific literature, both reversible and irreversible electroporation can be adopted to be utilized as a pretreatment step prior to freezing (Barba et al., 2015; Dymek, Dejmek, & Galindo, 2014; Dymek, Dejmek, Galindo, & Wisniewski, 2015). However, the literature about impact of PEF on freezing is limited. Especially, there is a lack of reports concerning kinetics of freezing. Nevertheless, existing publications prove that PEF exhibits high potential regarding the improvement of freezing progress and the quality of final products.

Chapter 9 Modification of food structure

In the case of irreversible electroporation, the main reason why PEF can be beneficial for freezing and thawing kinetics can be attributed to the mechanism of pore formation and crystallization per se. Small fragments of ruptured cell membrane or cell wall can act as additional centers of crystallization. Cellular matrix destruction improves the conditions of heat transfer as well, leading to increment of thermal conductivity (Wiktor et al., 2016). All of that makes the freezing process faster. Ben Ammar, Lanoiselle´, Lebovka, Van Hecke, and Vorobiev (2010) studied the effect of PEF pretreatment (at 400 V/cm, bipolar pulses of near rectangular shape) on a course of potato freezing process. The authors stated that phase transition time during freezing of PEF treated samples was reduced by about 15% in comparison to intact material. Jalte´, Lanoiselle´, Lebovka, and Vorobiev (2009), who conducted similar experiment (400 V/cm, time 1024
0.3 s) using potato, as well, obtained similar results. Their research indicated that phase transition time during freezing can be reduced up to 40% by introduction of PEF pretreatment. Moreover, they have shown that there is a significant correlation between cellular disintegration index (that describes the effectiveness of PEF treatment) and freezing time. What is interesting, Ben Ammar et al. (2010) stated that PEF pretreatment applied prior to freeze
drying allowed to obtain material characterized by a regular form, a lesser shrinkage, and better visual properties in comparison to untreated samples. As aforementioned, according to the authors’ opinion, these effects were the consequence of a greater amount of smaller ice crystals formed during phase transition. Results obtained by Ben Ammar et al. (2010) demonstrated that the intracellular structure of material was highly disorganized, which influenced mechanical properties of pretreated material and could have impact on texture of thawed material. It needs to be emphasized that mechanical properties or drip loss of frozen
thawed material determine the technological usefulness of the product. The enhancement of freezing and thawing kinetics by introduction of pretreatment step (1.85
5 kV/cm; n 5 0
100 impulses, 0
80 kJ/kg) prior to freezing has been reported also for apple (Wiktor, Schulz, Voigt, Witrowa-Rajchert, & Knorr, 2015). In this case, total freezing time was reduced up to 17%, whereas total thawing time was reduced up to c. 23%. It is worth emphasizing that phase transition time during thawing of PEF pretreated samples was 52%
72% shorter in comparison to reference material. Similar results were reported for carrot—total freezing time of samples subjected to PEF treatment (1.85
5 kV/cm; n 5 0
100 impulses, 0
80 kJ/kg) was up to 32% shorter in

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comparison to untreated carrot, wherein total thawing time was reduced by PEF application maximally by 31% when compared to intact material (Wiktor, Schulz, Voigt, Knorr, & WitrowaRajchert, 2015). Both studies indicated that PEF treatment altered mechanical properties of plant tissue after thawing, causing softening of the material. Drip loss after thawing depended on both processing parameters and the type of processed material. For instance, in the case of apple, for all of the investigated PEF parameters, the drip loss after thawing increased significantly (or did not change) (Wiktor, Schulz, Voigt, Witrowa-Rajchert et al., 2015). In turn in the case of carrot, there were variants of PEF pretreatment that reduced drip loss by 14%
28% in comparison to untreated frozen
thawed samples (Wiktor, Schulz, Voigt, Knorr, et al., 2015). Also, Shayanfar, Chauchan, Toepfel, and Volker (2014) studied impact of PEF pretreatment (1 kV/cm, 100 pulses, and 4 Hz) on carrot samples. Results that they have obtained indicated that electroporated carrot samples were firmer than untreated frozen
thawed material. However, the same authors did not obtain satisfied results concerning texture preservation by PEF pretreatment (0.5 kV/cm, 100 pulses, and 4 Hz) when working with potato samples (Shayanfar, Chauhan, Toepfl, & Heinz, 2013). Of course, the ambiguous results are linked to different properties of these two raw materials and biological diversity, which alter the response of tissue to the PEF treatment.

9.4

Cryoprotectants utilization in freezing process

As mentioned earlier, the quality of frozen foods depends on the parameters of freezing process. When a cell undergoes freezing, the water is transformed into ice. During the formation of ice crystals, there is less water in cells and all substances soluble in cytosol are concentrated. Due to the desire to equilibrate the osmotic pressure, substances dissolved in the cytosol are increasing in concentration, leading to organelle dehydration. The permeability of protein
lipid membranes is also changing, which is crucial for cell integrity. Damage caused by osmotic stress, membrane permeability and cytoskeleton deformation destabilize the cell, and the physical damage caused by the formation of ice crys´ tals ultimately leads to cell death (Kozłowicz, 2012; Niwinska, 2016; Reid, 1997; Shafiur Rahman, 2007). Adverse effects, which link to the freezing phenomenon, as previously stated, can be partially sought by utilization of high freezing rates, which causes the

Chapter 9 Modification of food structure

formation of small ice crystal and less breakage of cell walls. Such approach improves the quality of thawed food—for instance, it affects the better texture of the product (Velickova et al., 2013). However, some changes can be reduced by the use of protective substances as cryoprotectants (James et al., 2015; MacDonald & Lanier, 1997; Velickova et al., 2013). Cryoprotectants are compounds that have the ability to protect foods from deleterious changes caused by freezing and thawing processes or storage at frozen conditions, resulting in a better quality of a product and extending the shelf life of frozen foods (Fig. 9.2) (James et al., 2015; MacDonald & Lanier, 1997). Cryopreservation method can be used not only to protect the quality of food products but also to stabilize biological materials and preserve microbial activity (Elliott, Wang, & Fuller, 2017; ´ Niwinska, 2016). Group of cryoprotectants includes sugars and sugar alcohols (glucose, galactose, lactose, sucrose, trehalose, raffinose, mannitol, and sorbitol), alcohols and derivatives (ethanol, glycerol, propylene glycol, and ethylene glycol), natural and synthetic polymers (milk proteins, whey proteins, dextrans, and polyethylene glycol), polyols, methylamines, inorganic salts (potassium phosphate and ammonium sulfate), and others. Moreover, some specific antifreeze proteins (AFP) can be obtained from microorganisms, plants, or fishes. Their role is to

Figure 9.2 The effect of cryoprotectants on cell during freezing (figure made by www.ct.waw.pl).

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Chapter 9 Modification of food structure

control the size, shape, and aggregation of ice crystals due to decreasing the freezing temperature and suppressing the growth of ice nuclei (Elliott et al., 2017; James et al., 2015; MacDonald & Lanier, 1997). Furthermore, also the use of ice-nucleating proteins (INPs) leads to beneficial changes in the structure of frozen foods. INPs are produced by bacteria and cause an increase of the ice nucleation temperature, and they decrease the degree of supercooling, which reduce the freezing time and support the nucleation of ice throughout the product (James et al., 2015). For the first time, cryoprotectants were used to examine the effect of glycerol on the survival of frozen poultry sperm. The research showed that the rapidly frozen sperm at 279 C or 2192 C kept in 15% glycerol, after thawing obtained full mobil´ ity and ability to fertilize the egg (Niwinska, 2016; Polge, Smith, & Parkers, 1949). Currently, cryoprotectants are used in many different industry domains: clinical medicine, biotechnology, food technology, and plant and animal biology of species conservation (Elliott et al., 2017). The cryoprotective effect of all compounds depends on the specific structure of their molecules and their molar mass. The effect of cryoprotective substances can be explained according to two patterns. The first is for low molecular weight substances, as they can affect the rate of ice formation, determining the size, shape, and distribution of ice crystals in the product. Low molecular weight substances increase the hydration of polypeptide chains, and they prevent their interaction during water freezing. The second theory is related to high molecular mass substances that have the ability to raise the glass transition temperature of ice crystals. Adding a high molecular weight compound to a freezing material results in a faster transfer of this product into the “glassy” state. In the supercooled state, due to the high viscosity increment of the solution, crystallization of the ice does not occur, because the water is immobilized in this structure (Kozłowicz, 2012; MacDonald & Lanier, 1997). Because of that cryoprotective mechanisms, some plants accumulate AFP in the apoplast and osmotically active substances in cytoplasm (Velickova et al., 2013). Cryoprotectants as polydextrose, sucrose, sorbitol, and their mixtures are often used to protect food after freezing. These substances are low in cost, safe, wide available and have good water solubility (James et al., 2015; Liu, Kong, Han, Chen, & He, 2014; Shafiur Rahman, 2007). For instance, glucose, trehalose, glycerol, or mannitol added to spinach leaves allowed leaves to exhibit lower drip loss after thawing, and they preserved color and texture (Temkov, Velickova, & Winkelhausen, 2014). In turn, cryoprotectants may be added to the surimi during their processing in order

Chapter 9 Modification of food structure

to prevent protein oxidation and reduce protein structural changes and mechanical damages of ice crystals during freezing and frozen storage as such situation impacts quality of final product (Liu, Chen, Kong, Han, & He, 2014; Liu, Kong et al., 2014; Oujifard, Benjakul, Prodpran, & Seyfabadi, 2013). Ben Ammar et al. (2010) examined the combination of PEF and OD (carried out in 4 wt.% sodium chloride water solution) and they reported that this combined treatment might help design the quality of final product by modification of its mechanical properties. Moreover, the addition of trehalose can effectively replace sorbitol or sucrose in surimi, providing cryoprotection against protein denaturation (Campo˜o, Tovar, Borderı´as, & Ferna´ndez-Martı´n, 2011), whereas treDean halose in combination with AFP during freezing of strawberry fruits improved the texture and decreased the drip loss after thawing (Velickova et al., 2013). What is more, cryoprotectants can be added to edible films, used to produce food packaging (Oujifard et al., 2013). Cryoprotectants are also added in ice cream (Kami´ nska-Dwo´rznicka, Gondek, Łaba, Jakubczyk, & Samborska, ´ 2019; Sliwi´ nska & Lesio´w, 2013) or frozen yogurts production (James et al., 2015). Cryoprotectants and antifreeze agents play a protective role during freezing and frozen storage of plant- and animaloriginated food. Their utilization contributes to maintaining higher nutritional value and sensorial quality of frozen
thawed food. New cryoprotectants are discovered, and hence, the scope and effectiveness of their practical applications are growing. Cryoprotectants agents may be introduced to fruit and vegetables with OD (Chiralt et al., 2001), VI process (Velickova et al., 2013), PEF treatment (James et al., 2015; Shayanfar et al., 2014), or the combination of PEF with OD (Ben Ammar et al., 2010; Parniakov, Bals, Lebovka, & Vorobiev, 2016; Parniakov, Lebovka, Bals, & Vorobiev, 2015) or PEF with VI (Demir, Dymek, & Go´mez Galindo, 2018; Dymek et al., 2015; Phoon, Go´mez Galindo, Vicente, & Dejmek, 2008). The PEF facilitates the transport of cryoprotectants into the cells and thus improves the effectiveness of cryoprotectant activity (James et al., 2015; Phoon et al., 2008).

9.5

The use of cryoprotectants in combination with pulsed electric field treatment prior to freezing process

In recent years, researchers are focused on the utilization of PEF in order to improve the uptake of cryoprotectants before

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freezing. The individual treatment (VI, OD in cryoprotectants, or PEF) may result in insufficient quality (especially texture) of thawed foodstuff. It can be due to the fact that the introduction of cryoprotectant agents into the extracellular space of the tissue may be carried out with VI, while the PEF treatment may help in their distribution in the intracellular space (Demir et al., 2018; Phoon et al., 2008). Analogously, the cryoprotectant molecules may be transported more efficiently into the cells of electroporated tissue during dehydrofreezing (partial dehydration by the means of OD before freezing) (Parniakov et al., 2015, 2016). Thus the combined treatments, such as PEF with VI (Demir et al., 2018; Dymek et al., 2015) or PEF with OD with cryoprotectants (Parniakov et al., 2015, 2016), may be beneficial for texture improvement of frozen
thawed material. Shayanfar et al. (2013, 2014) studied the possibility of combining PEF (100 pulses, 4 Hz, and 0.5 or 1 kV/cm, respectively) with cryoprotectants utilization (trehalose, glycerol, and calcium chloride solutions) in order to preserve quality (especially texture) after thawing. PEF treatment carried out in cryoprotectant solutions resulted in a firmer texture and higher drip loss of carrot in comparison to untreated material. In the case of potato, the presence of cryoprotectants during PEF treatment did not preserve the texture after thawing; however, the weight loss after thawing of these samples was smaller. From consumers’ point of view, it is also important that the procedure of pretreatment involving PEF and cryoprotectants utilization described in mentioned articles (Shayanfar et al., 2013, 2014) allowed better preservation of color of investigated tissue in comparison to untreated samples. In both studies the concentration of cryoprotectants was rather small, and it equaled to 1% w/w for each type of cryoprotectant. Moreover, time of sample immersion in the cryoprotectant solution was limited since the PEF treatment is a rapid technique. These issues are quite interesting considering scale-up of the process into industrial conditions. Czy˙zewski, Wiktor, Zubernik, Cichowska, & Witrowa-Rajchert (2018) applied VI in 20 % solutions of cryoprotectants, such as glycerol, trehalose, or calcium chloride, preceded by US and PEF treatments (10 impulses, 5 kV/cm, 0.5 Hz). The results were compared with VI and immersion in the same solutions. The results are rather ambiguous and indicate that combined treatments may reduce the total freezing time by 1%, 5%, and 16% for glycerol, CaCl2, and trehalose, respectively, in comparison to untreated carrot. However, when analyzing the phase transition time, it was strongly reduced by 58% for glycerol and by 46% for trehalose, and it increased by

Chapter 9 Modification of food structure

30% for CaCl2. Moreover, comparing the total freezing time with VI and immersion, it was proven that the US 1 PEF 1 VI treatment additionally reduced the process only when trehalose was used, which requires further investigations. However, the authors reported that the combined treatment contributed to obtain a high-quality carrot, due to the lowest drip loss and a strong texture of thawed carrot, especially when calcium chloride was used during processing. However, it needs to be emphasized that the results in the field of utilization of PEF with cryoprotectants are ambiguous probably because of different concentrations of cryoprotectant solutions and long treatment time. For instance, Parniakov et al. (2015) investigated properties of apple tissue after freezing and thawing with PEF pretreatment (800 V/cm, 10 pulses, varied series of pulses) combined with OD performed in 20% solution of glycerol acting as cryoprotectant. Obtained results showed that PEF with OD in 20% of glycerol caused decrease freezing temperature, as well as freezing time reduction. Moreover, it was possible to preserve textural properties in a greater extent after thawing in comparison to untreated material. Similar findings were reported (Parniakov et al., 2016) when the apple was treated with the same protocol but in a varied glycerol solution (0%
60%) at fixed time (180 min) of OD or at varied time of OD (0
180 min) in a constant concentration of glycerol (60%). The conformed presence of glycerol in the center of the sample resulted in a noticeably lower freezing temperature and a strong texture. Reports considering utilization of reversible electroporation combined with VI of cryoprotectants are extremely interesting and very promising in prevention against loss of the turgor and tissue collapse, especially in the case of leafy vegetables (Demir et al., 2018; Dymek et al., 2015; Go´mez Galindo & Dymek, 2017; Phoon et al., 2008). VI performed in trehalose preceded by PEF treatment (causing reversible electroporation) improved freezing tolerance of baby spinach leaves allowing them to maintain their turgor after thawing (Demir et al., 2018; Go´mez Galindo & Dymek, 2017; Phoon et al., 2008). Dymek et al. (2015) reported that PEF-assisted (25 exponential decay pulses of 100 µs time constant and amplitude of 350 V) VI in a presence of trehalose, glucose, mannitol, or sucrose decreases ice propagation rate, increases freezing point temperature of this material, which is rather unexpected, comparing with previously mentioned results, and requires further research. In turn, Demir et al. (2018) proved that when the cultivation temperature changed from 20 C to 5 C during growth, the survival of frozen
thawed

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Chapter 9 Modification of food structure

spinach was improved only when the combined treatment (VI 1 PEF) was applied before freezing. It has to be emphasized that this combined technique has been commercialized by OptiFreeze (http://optifreeze.se).

9.6

The comparison of the influence of pulsed electric field and other nonthermal treatments on freezing progress and the quality of food

In recent years, nonthermal techniques are considered in order to enhance different heat and diffusion processes in food industry. As it was described earlier, PEF, especially with cryoprotectants implementation, is a promising treatment before freezing of foodstuff. However, for the enhancement of freezing, also other nonthermal technologies have been investigated, such as RF, US, or HHP. The first two were used during the freezing process, and the last one was utilized as a treatment before, during, or after the freezing. The comparison of the influence of different nonthermal technologies on the freezing kinetics and the quality of thawed food is summarized in Table 9.1. As it can be seen, different techniques may decrease the freezing time, when proper parameters were selected, but the impact on the quality attributes was rather different. Mainly during freezing of PEF-treated, and during US-, HHP-, and RFassisted freezing, smaller and more uniform ice crystals were formed, but the mechanism of the crystals formation and their growth was different. For instance, as Otero, Solas, Sanz, de Elvira, and Carasco (1998) reported, when HHP was applied during the freezing process, it was noted that the pasteurization caused a high level of supercooling and a massive nucleation in the entire sample, as a result of isostatic pressure. In the next stage the growth of ice crystals at atmospheric pressure occurred. In turn, US enhances the crystallization due to the fact that cavitation bubbles, which are formed during the USassisted freezing, act as a nuclei center (Saclier, Peczalski, & Andrieu, 2010). Furthermore, a high amount of smaller crystals is created on account of power US application, and the heat transfer during crystals growth is also enhanced (Chow, Blindt, Chivers, & Povey, 2005; Delgado & Sun, 2001). RF pulses also may affect the size of crystals causing a formation of a large number of ice crystals of a lower size that are localized mainly

Table 9.1 The comparison of the impact of different nonthermal technologies on the freezing kinetics and the quality of thaweda food. Material

Freezing method

Impact on freezing kinetics or ice crystals’ size

Impact on the quality

References

After the treatment: Microstructure: no difference in microstructure of untreated and PEF-treated potato; PEF 1 treatment in 4% NaCl caused damage of the cells and structural disorder Texture: PEF caused a noticeable softening of the tissue, whereas PEF 1 treatment in 4% NaCl resulted in more rigid texture than untreated material Microstructure: PEF increased the structural damage and disorder, as well as the formation of intercellular voids. The crystals were formed outside the disrupted cells Texture: PEF in water or in different solutions caused the texture softening and the turgor loss, compared with untreated sample. The texture was more preserved after PEF in different solutions Weight loss: PEF treatment caused a lower weight loss than in untreated potato, especially when PEF in different solutions was performed Color/visual appearance: PEF in different solutions prevented the fresh-like color after thawing

Ben Ammar et al. (2010)

PEF treatment prior to freezing Potato

PEF treatment PEF 1 treatment in 4% NaCl Untreated

PEF and PEF 1 treatment in 4% NaCl reduced noticeably the effective freezing time by approximately 15%

Potato

PEF treatment Untreated

Increased freezing rate and decreased effective freezing time after PEF treatment, compared with untreated material

Potato

PEF treatment PEF treatment in 1% CaCl2 PEF treatment in 1% trehalose




PEF treatment in 1% glycerol

PEF treatment in 0.5% NaCl and 0.5% sucrose Untreated

Jalte´ et al. (2009)

Shayanfar et al. (2013)

(Continued )

Table 9.1 (Continued) Material

Freezing method

Impact on freezing kinetics or ice crystals’ size

Carrot

PEF treatment PEF treatment in 1% CaCl2 PEF treatment in 1% trehalose




PEF treatment in 1% glycerol PEF treatment in 0.5% NaCl and 0.5% sucrose Untreated

Carrot

PEF treatment Untreated

Apple

PEF treatment Untreated

Impact on the quality

Texture: the PEF in water or in different solutions pretreatment created a firmer tissue, compared with untreated sample. The texture was more preserved after PEF in CaCl2 Weight loss: PEF treatment caused a lower weight loss than in untreated potato. PEF in different solutions resulted in a higher weight loss, especially when PEF in CaCl2 was performed Color: no color change Decreased freezing time (especially time of Weight loss: at some parameters a lower phase transition) after PEF treatment, (by 14%
28%) and at some a higher compared with untreated material. The total weight loss was observed after PEF freezing time of PEF-treated carrot was up to treatment, in comparison to untreated carrot Texture: PEF decreased both compressive 32% shorter. The higher was the disintegration index, the lower was the total force (by 16%
87%) and compressive work (by 22%
84%), causing softening of the freezing time material PEF reduced the total freezing time up to Weight loss: PEF increased or did not 17%, in comparison to untreated material. change the weight loss, compared with The phase transition time was up to 33% untreated material Texture: PEF treatment significantly softened shorter A slightly lower freezing temperature after the material PEF treatment Color: PEF significantly changed the color of apple (especially lightness and aa parameter)

References Shayanfar et al. (2014)

Wiktor, Schulz, Voigt, Knorr, et al. (2015)

Wiktor, Schulz, Voigt, WitrowaRajchert et al. (2015)

PEF with VI treatment prior to freezing Spinach leaves

PEF 1 VI in 40% trehalose VI in 40% trehalose Untreated




Spinach leaves

PEF 1 VI in trehalose, glucose, sucrose, mannitol, or water VI in trehalose, glucose, sucrose, mannitol, or water

PEF, VI, and PEF 1 VI increased the freezing temperature. The freezing temperature of PEF 1 VI was higher than for PEF alone. The treatment in trehalose increased the freezing temperature most effectively PEF 1 VI in trehalose increased the ice propagation rate, compared to VI in trehalose. PEF 1 VI in water decreased the ice propagation rate compared to VI in water due to a significant leakage of water into extracellular space Demir et al.
Turgor/freezing tolerance: PEF 1 VI (2018) increased the percentage of surviving leaves after thawing due to accumulation of sugars

PEF treatment Untreated

Spinach leaves

PEF 1 VI in trehalose or in the mixture of trehalose, sucrose, glucose, and fructose Untreated

Turgor/freezing tolerance: PEF 1 VI in Phoon et al. trehalose drastically increased the freezing (2008) tolerance of spinach after thawing, showing maintained turgor, similar as for fresh leaves. VI and untreated sample after freezing
thawing showed the loss of turgor Dymek et al.
(2015)

PEF, US, and VI treatment prior to freezing Carrot

The following treatments in CaCl2, glycerol, or trehalose: US 1 PEF 1 VI Immersion VI Untreated

US 1 PEF 1 VI decreased the total freezing time compared to untreated carrot. In comparison to the immersion and VI, the combined treatments decrease the total freezing time when trehalose was used and increased when glycerol or CaCl2 was used

Weight loss: US 1 PEF 1 VI did not change statistically the weight loss in comparison to immersion and VI. The lowest drip loss was obtained when US 1 PEF 1 VI in CaCl2 was applied Texture: statistically the same texture after US 1 PEF 1 VI as for immersion and VI, slightly stronger texture when CaCl2 was used

Czyzewski et al. (2018)

(Continued )

Table 9.1 (Continued) Material

Freezing method

Impact on freezing kinetics or ice crystals’ size

Impact on the quality

References

PEF 1 OD in glycerol decreased freezing temperature and reduced freezing time to the greatest extent, OH 1 OD was less effective PEF 1 OD in glycerol decreased freezing temperature and reduced freezing time. Glycerol of a concentration of 60% was the most effective in reduction of effective freezing time

Texture: PEF 1 OD in glycerol preserved the textural properties after thawing in comparison to untreated material and OH 1 OD Texture: the texture at optimum PEF 1 OD parameters (60% glycerol, 90 min or 20% glycerol, 180 min) was comparable with the texture of fresh apple (0.90
0.95 vs 1.0)

Parniakov et al. (2015)

PEF with OD treatment prior to freezing Apple

Apple

OD in 20% glycerol PEF 1 OD OH 1 OD Untreated PEF 1 OD in glycerol (0%
60%) Untreated

Parniakov et al. (2016)

US-assisted freezing Common carp UIF IF (Cyprinus carpio) AF

Pork (longissimus muscle)

UIF IF AF

Smaller size and more uniform shape of ice crystals than in air frozen and immersive frozen fish after freezing and during storage

In comparison to AF and IF: Thawing and cooking loss: a significantly lower both thawing and cooking losses after freezing and during storage US freezing decreases the mobility and loss Texture: after freezing—statistically the of immobilized and free water lowest loss of shear force (reflecting muscle tenderness) after 180 days storage No change in the freezing temperature. In In comparison to AF and IF: Thawing and cooking loss: a significantly comparison to AF—the freezing time drastically decreased; in comparison to IF— lower both thawing and cooking loss the influence was associated with the power compared to AF, at some US parameters a significantly lower thawing loss and the of US. For most of the power levels (120, same cooking loss as for IF 180, and 240 W) the freezing kinetics was enhanced. The freezing time decreased more Color: no significant aa and ba change pH: no pH change effectively when 180 W was applied; for 300 W—a longer time than for IF was achieved

Sun et al. (2019)

Zhang et al. (2018)

Pork (longissimus muscle)

UIF IF AF

At certain UIF parameters a smaller size and more uniform shape of ice crystals were achieved than after AF and IF and during the storage. The UIF decreased the water migration during frozen storage Smaller size and more uniform shape of ice crystals than in air frozen and immersive frozen pork after freezing and during storage. The UIF decreased the water migration during frozen storage

Zhang et al. In comparison to AF and IF: (2019) Thawing and cooking loss: much lower thawing loss (1.2% vs 2.5% for IF and 4.6% for AF) and cooking loss (31.4% vs 32.4% for IF and 42.5% for AF) Texture: a lower cutting force (the lower is cutting force, the better is muscles tenderness) than after AF, the same as for IF. UIF muscles maintained the original muscle tissue state during storage Lipid oxidation: a higher lipid oxidation after freezing than after AF, IF, but after 180 days’ storage—the lowest oxidative degree Color: a higher aa value (preferred) and a lower La value (due to a lower water loss) than for AF and IF

HHP and freezing Eggplant

High pressure
assisted freezing Still AF Air blast freezing

Cured pork carpaccio

HHP (400, 600 MPa) of frozen product (immersion freezing) Untreated

A higher freezing rate during high pressure
assisted freezing than during still air and air blast freezing




In comparison to conventional air-freezing methods: Structure—material structure was better preserved. The material has the appearance of a fresh sample; no damage of the cell walls was observed. Microstructure damage was less dependent on the volume of the sample Texture—higher firmness Color: protective effect of the HHP on the color by a lower freezing temperature Organoleptic properties: better appearance scores, long-lasting and high-quality product

Otero et al. (1998)

Realini et al. (2011)

(Continued )

Table 9.1 (Continued) Material

Freezing method

Fresh minced HHP (400, 600 MPa) of frozen material beef and pork

Impact on freezing kinetics or ice crystals’ size

Impact on the quality

References




Antioxidant enzyme activity: the activity of enzymes was slightly reduced or not changed HHP was not recommended as a treatment due to a lack of significant differences in the physicochemical characteristics among treatments Protective effects on pressure inactivation: addition of 20% sucrose to liquid whole egg (protein) protected Escherichia coli Inactivation effect: liquid whole egg with addition of 50% sucrose mixture inactivated E. coli

Serra et al. (2007)

Untreated

Liquid whole egg
sucrose mixture

HHP (400 MPa) pretreatment and then frozen (AF)




Ueno, Hayashi, Kimizuka, & Shigematsu (2016)

RF-assisted freezing Pork (loin)

RF-assisted freezing in liquid nitrogen CF AF

RF-assisted freezing caused a large number of ice crystals with low size, located mainly in intracellular space; caused less cell disruption and decreased the freezing point

In comparison to CF and AF: Anese et al. Color—no observed color change (2012) Weight loss—much lower drip loss (1.5% vs approximately 4%) Texture—similar firmness as for fresh meat, significantly lower compared with AF and CF, due to a lower cell damage

AF, Air freezing; CF, cryofreezing; HHP, high hydrostatic pressure; IF, immersion freezing; OD, osmotic dehydration; OH, ohmic heating; PEF, pulsed electric field; RF, radio frequency; UIF, US-assisted immersion freezing; US, ultrasound; VI, vacuum impregnation. a Only in the case of work prepared by Ben Ammar et al. (2010), the properties were measured after the treatment, not in thawed samples.

Chapter 9 Modification of food structure

in intracellular space. As Anese et al. (2012) suggested, it can be caused by favoring water molecule torque. Considering the quality aspects of food, it can be stated that when PEF was applied alone, the texture was more soften and less accepted (Ben Ammar et al., 2010; Shayanfar et al., 2013, 2014; Wiktor, Schulz, Voigt, Knorr, et al., 2015, Wiktor, Schulz, Voigt, Witrowa-Rajchert et al., 2015). These negative aspects can be reduced when PEF is applied with different cryoprotectants (see Table 9.1), as it was described earlier (Section 9.5). US-assisted freezing is also a promising technique that resulted in obtaining a high-quality product after the freezing and during the storage (Sun, Sun, Xia, Xu, & Kong, 2019; Zhang, Haili, Chen, Xia, & Kong, 2018; Zhang, Xia, Liu, Chen, & Kong, 2019). US did not change the pH (Zhang et al., 2018), they reduce thawing and cooking loss (Sun et al., 2019; Zhang et al., 2018, 2019) and the products were characterized by better (Zhang et al., 2019) or unchanged (Zhang et al., 2018) color and the lowest oxidative degree after storage (Zhang et al., 2019). After comparison to HHP, it seems that the HHP may prevent deterioration of the microstructure, organoleptic properties, and color, as well as may result in a firmer structure (Otero et al., 1998; Realini, Guardia, Garriga, Perez-Juan, & Arnau, 2011). However, other studies indicated that the HHP after freezing is not recommended due to a limited influence on final product (Serra et al., 2007). Also promising results were obtained for RF treatment that resulted in unchanged color, reduced drip loss, a fresh-like texture, and lowered changes in the structure (Anese et al., 2012). However, this technique has not been fully investigated yet and requires studies concerning, for instance, the mechanism of ice formation and the effects on different food matrixes. Concluding, the aforementioned nonthermal technologies (US, HHP, RF, and PEF) may enhance the freezing kinetics in a satisfactory level. When considering also the quality, it seems that PEF in combination with VI, PEF 1 OD, and US 1 PEF 1 VI gave a high-quality product, similarly as after US-assisted freezing or RF freezing. RF in particular requires further investigations on different foodstuff, but current stage of knowledge allows to state that US-assisted freezing is an alternative to PEF with cryoprotectants treatments. Based on the presented data, it can be stated that PEF exhibits the highest technological readiness level (TRL9). However, further investigations should also comprise the financial aspects of each processing.

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9.7

Conclusion

Freezing by consumers is perceived as one of the most “natural” food preservation techniques. At the same time, it is one of the most energy intensive unit operations both because of processing and storage costs. Moreover, the quality of final product depends on freezing time, as well. A proper selection of the pretreatment step is very important since even if it will enhance the kinetics, it can affect the quality of final product. Considering available literature about effect of PEF on freezing, it seems that further research in this filed is reasonable. Results that have been published up to now indicate that PEF can enhance the kinetics of freezing and thus reduce the processing costs. The PEF causes the electroporation of the membranes, and thus it can facilitate the introduction of the cryoprotectant molecules into the intracellular space of the cells. As the studies indicate that the tissue after PEF-freezing process is often soft, thus it is reasonable to use combined treatments of PEF 1 cryoprotectants. It has been proved that such treatments as VI of cryoprotectants combined with PEF (VI 1 PEF) or PEF-assisted dehydrofreezing (PEF 1 OD) allow to obtain products with enhanced texture and maintained turgor, similarly as in the case of other nonthermal technologies, such as US or RF. However, it seems that PEF has the biggest potential of commercialization.

Acknowledgment The authors want to thank Dr. Artur Wiktor for his help in the preparation of the chapter.

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137. (in Polish, English abstract). Wiktor, A., Schulz, M., Voigt, E., Witrowa-Rajchert, D., & Knorr, D. (2015). The effect of pulsed electric field treatment on immersion freezing, thawing and selected properties of apple tissue. Journal of Food Engineering, 146, 8
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32.

Pulsed electric field applications for the extraction of compounds and fractions (fruit juices, winery, oils, by-products, etc.)

10

Rohit Thirumdas1, Chaitanya Sarangapani2 and Francisco J. Barba3 1

Department of Food Process Technology, College of Food Science & Technology, PJTSAU, Hyderabad, India 2School of Food Science and Environmental Health, Technological University Dublin, Dublin 1, Ireland 3 Nutrition and Food Science Area, Preventive Medicine and Public Health, Food Sciences, Toxicology and Forensic Medicine Department, Faculty of Pharmacy, Universitat de Vale`ncia, Vale`ncia, Spain

10.1

Introduction

Highly valuable extracts from plant products and their by-products are recovered by conventional or novel techniques by separation, precipitation, extraction, pretreatments, purification and product formation (Barba et al., 2017; Galanakis, Barba, & Prasad, 2015; Rosello´-Soto et al., 2016). The present demands can be met using novel techniques such as pulsed electric field (PEF) (Barba, Parniakov, et al., 2015; Pue´rtolas & Barba, 2016; Pue´rtolas, Koubaa, & Barba, 2016), high pressure (Barba, Terefe, Buckow, Knorr, & Orlien, 2015), high-voltage electrical discharges (Barba, Boussetta, & Vorobiev, 2015; Barba, Galanakis, Esteve, Frigola, & Vorobiev, 2015), and ultrasound (Rosello´-Soto, Galanakis, et al., 2015; Zhu et al., 2016), reducing the process time, increasing yield, improving quality, and also enhancing the functionality of extracts (Guarracino et al., 2018; Rosello´-Soto et al., 2014). One of the widely used novel technologies as the pretreatment for the enhanced extraction is PEF technology. It serves as an alternative

Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00010-0 © 2020 Elsevier Inc. All rights reserved.

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to the traditional heat treatments used for sterilization, enzyme inactivation, and enhanced bioactive compounds extraction from foods and other by-products (Gabri´c et al., 2018; Zulueta, Barba, Esteve, & Frı´gola, 2010; Zulueta, Barba, Esteve, & Frı´gola, 2013). PEF technology induces electrical pulses (microseconds) briefly which disrupts or modifies the cell membranes. The altered microstructure thus enhances extraction of bioactive compounds, pigments and other extracts or fractions from fruit juices, winery, oils, by-products, etc. (Lazaridesa, 2011; Pue´rtolas & Barba, 2016; Pue´rtolas et al., 2016). Extraction by pressing (mechanical expression) is commonly used in the production of sugar, wine, and fruit juices, for dehydration of biological wastes and in vegetable oil industries (Carbonell-Capella et al., 2016). The rigid wall components prevent easy damage of cell membranes and thus confine efficiency of the pressing extraction. Electrical treatments cause the damage of biological membranes through electroporation mechanism. Recently, PEF treatment has shown to be very effective for high disintegration of different fruit tissues. PEF processing uses brief electrical bursts into food product which causes minimal or no detrimental effect on food quality attributes used for processing liquid and semiliquid food products (Barbosa-Pereira, 2018). Recent developments have shown that PEF is efficient in sterilization, microbial inactivation and improving extraction efficiency. The increase in extraction efficiency is the occurrence of electro-permeabilization by the pore formation (due to dielectric breakdown) in the cell membrane (Salengke, Sastry, & Zhang, 2012) and the membrane damage. Electric power of 1 V causes dielectric cell membrane breakdown corresponding to 10 kV/cm field strength. The treatment is given by placing foods between two electrodes while applying high voltage pulses of 20
80 kV for different durations of microseconds. This result in an electric field applied in exponentially decaying, square wave, bipolar, or oscillatory pulses form causing pore formation and cell membrane rupture. The high-voltage pulses break the cell membranes of in liquid media by expanding existing pores (electroporation) or creating new ones. Electroporation depends on different processing parameters like the electric field intensity, the pulse duration, number of pulses and total treatment time (Pue´rtolas & Barba, 2016; Pue´rtolas et al., 2016). The other theories governing along with the electroporation are electro-hydrodynamics, electromechanical, electro-thermal

Chapter 10 Pulsed electric field applications for the extraction of compounds

and electro-osmotic instabilities (Vorobiev & Lebovka, 2009). The membranes of PEF-treated cells become permeable to small molecules; permeation causes swelling and eventual rupture of the cell membrane. This chapter briefs the synergistic effect of PEF as the pretreatment or in combination during the extraction process of juice, fragments and bioactive compounds and fragments from fruits and vegetables, winery, oils, and byproducts.

10.2

Need for pulsed electric field application in for the extraction of compounds and fractions

In industrialized countries, there is a rapidly increasing demand from the consumer for fresh-like, minimally processed food products and in developing countries, food storable without refrigeration are of special interest, because refrigeration is costly and not continuously available (Barba, Esteve, & Frı´gola, 2012a, 2012b; Gabri´c et al., 2018; Putnik, Barba, et al., 2017). The relevance of food composition for human health has increased consumers’ interest in the consumption of fruits and vegetables, as well as foods enriched in bioactive compounds and nutraceuticals (Granato, Nunes, & Barba, 2017; Teixeira et al., 2014). PEF is a novel technology works synergistically and provides safe, healthy products of high quality, optimal shelf life, improved microbial stability, sensory quality, nutritional & economic properties, convenient to use, incurs in less transportation and storage costs. PEF can also be used for the improvement of osmotic dehydration, extraction by solvent diffusion, or by pressing, as well as drying and freezing processes (Barba, Parniakov, et al., 2015; Carbonell-Capella et al., 2016). The biological membrane of the food is electrically pierced and losses its semipermeability temporarily or permanently (Villamiel et al., 2015), which can allow the selective recovery of high-added value compounds from different matrices. The mathematical modeling of the electric field and temperature distributions in a PEF treatment chamber depended on the fluid velocity profile, electric field distribution, and temperature distribution within the PEF treatment chamber (Salengke et al., 2012). Fruit and vegetables are a rich natural source of many antioxidants, including carotenoids, flavonoids, phenolic compounds, and vitamins, that provide protection against harmful

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free radicals (Barba, Esteve, & Frı´gola, 2014; Poojary et al., 2017; Putnik, Bursa´c Kovacevi´c, et al., 2017). Antioxidants block the oxidation processes by neutralizing free radicals and reducing the risk of certain types of cancer and other diseases (Bobinaite et al., 2015; Dohrmann et al., 2018). At present, consumers demand the best preservation of the sensory, nutritional, and health-related characteristics of plant-derived food products. The PEF-assisted extraction by diffusion has the widest potential in the modern industrial technology for fresh food plants (e.g., sucrose extraction from sugar beetroot, betalain extraction from red beet, inulin extraction from chicory, betacarotene extraction from carrot, and phenolic extraction from grapes) (Barba, Brianceau, Turk, Boussetta, & Vorobiev, 2015; Barba et al., 2017; Bermu´dez-aguirre, Mobbs, & Barbosa-ca´novas, 2011; Koubaa, Barba, et al., 2016). The main drawbacks of solvent extraction were the utilization of a power-consuming diffusion at high temperature and different types of solvents can be addressed by a PEF. This is also a modern green extraction using eco-friendly solvents such as water, which is the major reason why this technology is mostly used for industrial applications (Barba, Grimi, & Vorobiev, 2014; Koubaa, Rosello´Soto, et al., 2015; Misra et al., 2017).

10.3

Improvement in fruit juice yields

The mechanical compression during expression of fruits is the common method to extract the intracellular components. The main step in juice extraction is the cell disintegration that is crucial for liquid
solid separation of fruit juices. During the expression the intracellular components present in the coarse particles are difficult to extract. This often requires hot/thermal treatment to disintegrate the coarse particles that lead to thermal degradation of fruit tissues and other bioactive compounds. The pretreatment of fruits with PEF before pressing or during the pressing could significantly increase the juice yield (Carbonell-Capella et al., 2016). In traditional methods the enzymatic pretreatments have been used from past years but the incubation time required is too long (Mari´c et al., 2018; Renard, 2018; Zhu et al., 2018). The proteolytic enzymatic maceration in holding tanks is done for 30
60 min to enhance the apple juice yield (Schilling et al., 2007). This time can be reduced by using PEF treatment to induce cell disintegration. The effect of PEF was carried out by Schilling et al. (2007) on the yield and quality of apple juice at

Chapter 10 Pulsed electric field applications for the extraction of compounds

varying field strengths of 1, 3, and 5 kV/cm and compared the results with the enzymatic treatment. The yield of juice was significantly higher by 4.2% and 7.7% during the enzymatic maceration and PEF treatment, respectively, compared with the control extraction method. The authors concluded that the proteolytic enzyme maceration for 1 h resulted in lower juice yields compared to the PEF technology. Furthermore, the authors succeeded in extracting the pectin from the PEF-treated apple ´ lvarez, and Raso (2008) mash. Lo´pez, Pue´rtolas, Condo´n, A reported that the maceration time red grape processing can be reduced by 40%
50% by PEF pretreatment at a field strength of 5
10 kV/cm. A first industrial prototype for industrial application was installed in a juice-producing company in the United States, 2006 (Buckow, Ng, & Toepfl, 2013). Few authors employed PEF for the recovery and production of commercially interesting and high-value metabolites (natural pigments) from food; the improvement of fruit and vegetable juices yield in solid
liquid extraction (Bobinaite et al., 2015; Cullen, Tiwari, & Valdramidis, 2012; Guarracino et al., 2018; Jemai & Vorobiev, 2006; Takeuchi et al., 2009). A commercial-scale PEF processing system was used by Min and Zhang (2003) to study the flavor and aroma of tomato juice processed at 40 kV/cm for 57 μs. The authors analyzed various flavoring compounds in tomato juice such as trans-2-hexenal, 2-isobutylthiazole, and cis-3-hexanol and observed significantly higher retention of these compounds compared to unprocessed and thermally processed juice. The same PEF-processing system and operating parameters were used to study the lycopene and ascorbic content of juice (Min, Jin, & Zhang, 2003). The authors reported higher retention of ascorbic acid content and no significant change in the lycopene content. From the previous studies a conclusion can be made that the commercial scale PEF processing of tomato juice had a better quality preserving the natural flavor and aroma. PEF application on juice extraction affected the yield and quality by electro-induced formation and growth of pores in cellular improving yield and functional properties of some fruit and vegetable juices (Min & Zhang, 2001). Pue´rtolas, Luengo, ´ lvarez, and Raso (2012) reported that the application of exterA nal electric fields overcomes the elastic restoring forces leads to the compression of biological membranes resulting in membrane rupture. In another study, Tylewicz et al. (2016) observed an increasing trend in cell disintegration index (CDI) (Zp) with an increase in the electric field strength. The extent of

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Chapter 10 Pulsed electric field applications for the extraction of compounds

electroporation can be studied by analyzing the CDI. The CDI values ranged between 0 and 1 indicating the complete intact to complete disintegration (Wiktor, Schulz, Voigt, WitrowaRajchert, & Knorr, 2015). The CDI is calculated by the following equation:
CDI 5 1 2 b K 0h 2 K 0i =ðKh 2 Ki Þ where K0 h 2 K0 i are the electric conductivities of treated and intact samples, respectively, at low frequency, Kh 2 Ki are the electric conductivities of treated and intact samples, respectively, at high frequency. The CDI of blueberry fruits tissue was studied at different electric fields (Bobinaite et al., 2015). The authors observed that at higher electric field strengths, the disintegration was increased from 0.61 to 0.87 at 1 and 5 kV/cm, respectively. A similar increase in cell disintegration with increasing electric ´ lvarez, and Raso field intensity was also reported by Luengo, A ´ (2013) and Pue´rtolas, Cregenza´n, Luengo, Alvarez, and Raso (2013). In the same line, Boussetta, Soichi, Lanoiselle, and Vorobiev (2014) observed a 60% higher extraction of polyphenols at 0.61 of CDI. The PEF treatment has increased the electrical conductivity of the membranes resulting in the better permeabilization (Guderjan, To¨pfl, Angersbach, & Knorr, 2005). The authors reported an increase of 55% in cell disintegration at a specific energy of E 5 85 kg/cm, and a field strength of 7 kV/cm leading to an increase in the oil yield up to 45% from the rapeseed hulls. Several investigations have shown a direct relationship between the CDI and juice yields of various plant tissues. Apart from the electric field strength, time, and pulses, the application of pressure can vary the juice yield. Varying the pressure up to 30 bar has increased the juice yield of treated apple to 61%. For instance, a study on cold juice extraction from sugar beet “cossettes” (i.e., long grated particles) was investigated in a pilot scale multiplate and frame-pressing equipment (pressure of 5
15 bar; particles filling of 4.5
15 kg) (Jemai & Vorobiev, 2006), concluding that PEF-assisted cold pressing of sugar beet cossettes increased yield up to 80% in juice. An investigation carried out by Lebovka, Praporscic, and Vorobiev (2003) on the tissue texture of apples and carrots using a texture analyzer equipped with a PEF-treatment compression chamber, operated at moderate electric field strength E 5 400 V/cm, pressure P 5 0
1 bar, and different time regimes of pressing. The authors stated that operating pressing parameters and PEF pretreatment influenced the kinetics of mechanical deformation and final

Chapter 10 Pulsed electric field applications for the extraction of compounds

characteristics of juice. There was an increase in the juices yield and total polyphenols content enhancing the solid
liquid extractions due to the softening of the tissues. In another study, pretreatment of blueberry fruits (Vaccinium myrtillus L.) with PEF was investigated on the extraction yields and antioxidant compounds of juice obtained by pressing (Bobinaite et al., 2015). The authors observed a significant increase in the juice yield, total polyphenols, and anthocyanin content compared with the untreated sample. The results obtained from this study demonstrated the potential of PEF as a mild pretreatment method to improve the efficiency of the industrial processing of berry fruits. In another study on high-intensity PEF technology with following parameters of electric field strength (30
35 kV/cm), treatment time (50
2050 μs), pulse width (1
7 μs) on the watermelon juice quality piloted showed a higher retention of lycopene and vitamin C (Oms-Oliu, Odriozola-Serrano, Soliva-Fortuny, & Martı´nBelloso, 2009). The results of Schilling et al. (2007) concluded that the application of PEF not only increased the apple juice quality but also resulted in peroxidase and polyphenol oxidase enzymes inactivation which are key enzymes responsible for browning reactions.

10.4

Improvement in wine preparation

The wine has a long history of being served as a staple food in the western countries in an individual social’s life. Wine polyphenols play an important role as antioxidants and radical scavenging activity promoting sound health (Barba, Parniakov, et al., 2015). Apart from the antioxidant activity, polyphenols contribute to the color, bitter taste, and astringent (Pue´rtolas, Saldan˜a, ´ lvarez, & Raso, 2010). PEF-assisted biorefinery appliCondo´n, A cation and wine preparation have been studied by different authors (Barba, Zhu, Koubaa, Sant’Ana, & Orlien, 2016; Goettel, Eing, Gusbeth, Straessner, & Frey, 2013). For instance, a study was conducted to expose red wine to several intensities of PEF with variable exposure time during vinification resulting in increased extraction of major polyphenolic compounds when compared to classic wine-making (Teixeira et al., 2014). The authors observed values of sugar, alcohol, total acidity, volatile acidity, pH, and temperature after the treatment according to the legislation. However, there was a slight effect on the bioactive compounds of wines, which showed an enhanced extraction of flavan-3-ols due to the

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treatment. The PEF treatment showed a positive effect on the quality of wine by reducing the volatile acidity with a good sensory score (Gonza´lez-Arenzana et al., 2018). In another study, Lo´pez et al. (2008) reported that the PEF treatment did not affect the volatile acidity of CabernetSauvignon grape wine. However, there was a slight increase in the volatile acidity in the wine extracted from white grapes (cv. Garganega) (Comuzzo, Marconi, Zanella, & Querze`, 2018). The authors also observed an increase in the polyphenols which enhanced oxidative stability and improvement in the aroma of the grape wine. The improvement in the aroma was attributed to the increased extraction of additional aroma compounds. The obtained results evidenced that PEF-enhanced expression is a promising tool for the production of higher quality juices in the wine industry.

10.5

Extraction of bioactive compounds from fruits

Several novel extraction technologies have been also used to extract anthocyanins and compared to other extraction technologies, PEF has been used widely for extraction of pigments, sugar, and other value-added metabolites (Barba, Galanakis, ˇ ´ et al., 2015; Djilas, Canadanovi´ c-Brunet, & Cetkovi´ c, 2009). The brewery industry generates waste that could be used to yield a natural extract containing bioactive phenolic compounds (Barbosa-Pereira, Pocheville, Angulo, Paseiro-Losada, & Cruz, 2013). Fruits have bioactive compounds and for industrial processing, PEF application has been promising to increase the juice yield, quality, and quantity, as well as resulted in better extractability of bioactive compounds such as phenolic, anthocyanin, and antioxidant content. The common traditional methods used for the extraction of juice and bioactive compounds include pressing, grinding, heating reflux, solvent extractions, Soxhlet, maceration, etc. (Ben Rahal, Barba, Barth, & Chevalot, 2015; Koubaa, Barba, et al., 2015; Koubaa, Lepreux, Barba, Mhemdi, & Vorobiev, 2017; Koubaa, Mhemdi, et al., 2016; Rosello´-Soto et al., 2018; Zhu et al., 2017). The addition of any physical methods as an assistance to the extraction methods will enhance the yield of bioactive compounds extracted. The PEF-induced effects in pressing behavior were dependent upon pressing regimes and value of applied pressure. The operating pressing parameters and PEF pretreatment influenced the kinetics of mechanical deformation and final

Chapter 10 Pulsed electric field applications for the extraction of compounds

characteristics of juice (turbidity and total polyphenol contents). The combined application of PEF pretreatment and regime of progressively increasing pressure demonstrated the further synergetic effect and allowed producing a juice with low turbidity and higher polyphenolic content (Grimi, Lebovka, Vorobiev, & Vaxelaire, 2009). An increase in the apple juice yield by 12% was reported by Toepfl, Mathys, Heinz, and Knorr (2006) in 3 MPa applied pressure PEF-treated apple slices. Even at lower pressure values (0.2
0.3 MPa), an increase of 40% in the juice yield was observed by Bazhal and Vorobiev (2000). PEF-pretreated blueberry fruits (V. myrtillus L.), with 1, 3, and 5 kV/cm at 10 kJ/kg showed a significant increase in 43% higher of total phenols, 60% higher in total anthocyanin content compared to untreated sample (Bobinaite et al., 2015). PEF was used to increase the extraction of juice from alfalfa mash. The mash was subjected to a PEF treatment of 200 pulses at 1 Hz in two successions. The juice yield increased 38% and also the protein, mineral content, and the dry matter increased significantly compared to PEF-untreated samples (Gachovska, Kumar, Thippareddi, Subbiah, & Williams, 2008). An investigation was carried out by Guderjan et al. (2005) on the isoflavonoids content in the PEF-treated soybeans. The authors observed an increase in 20% and 21% of daidzein and genistein, respectively, when treated at field strength of 1.3 kV/cm compared to untreated samples. At similar field strengths, the authors reported an increase of 41.1% in the phytosterols yield values of maize germ oil. Toepfl et al. (2006) reported an increase in the extraction of phytosterols fractions in the oil after the PEF treatment due to the formation of secondary metabolite fractions. The PEF treatment has increased the tocopherols, polyphenols, phytosterols, and total antioxidants content in the different oils (Guderjan, Elez-Martı´nez, & Knorr, 2007). The authors stated that the increase in the bioactive compounds is due to the stressinduced reactions.

10.6

Impact of pulsed electric field on the oil yields

Pressing is the common method of oil extraction from the fruits or seeds along with the pretreatments such as cooking, maceration, and through solvent extraction (Koubaa, Mhemdi, et al., 2016). The preprocessing operations such as crushing, cooking, and heat result in oxidation rancidity and low quality

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of oils. The important step in an oil refinery is the maximum oil yield, the highest recovery of the solvent, and traceable amounts of oil in the residues. Guderjan et al. (2007) reported that at higher electric field strengths, the formation of irreversible pores enhanced the mass transfer resulted in higher oil yields. Similarly, the complex and coarse structure of the intact tissues resists the maximum extraction yields. Several investigations were carried out on the extraction of oil yields after the PEF treatments (Pue´rtolas et al., 2016). The application of PEF prior to oil extraction has increased the oil yield of maize germ by 7% (Guderjan et al., 2005). A similar increase in the oil percentage (13.3%) was observed by Pue´rtolas et al. (2016) for PEF-treated olive fruits. High-intensity PEF was used to study the extraction of volatile essential oils of Damask rose flowers (Yajun et al., 2017). The increase in electric field strength from 10 to 20 kV/cm resulted in the increase essential oil from 0.78% to 1.03%. PEF treatment led to a disintegration of cell structure and membranes enhancing the release of essential oil and bioactive compounds. Among the bioactive components released, the citronellol, linalool, and eugenol were found to be in higher percentages. In other study conducted by Guderjan et al. (2007) on the extraction of oil from the PEF pretreated rapeseeds, the oil yield was increased by 39% in hulled seeds at 7 kV/cm field strength and 120 pulses. From the various studies, it was observed that the oil yield differs according to electric field strengths applied, treatment time, the presence of hull, and extraction processes.

10.7

Extraction of bioactive compounds from by-products and wastes

During the postharvest operations in the fields and in foodprocessing industries, small, damaged fruits and by-products are thrown away or sorted out generating large amounts of food wastes causing a huge economic loss. Food losses may occur at every stage in supply chain management from the farm to fork. Due to improper handling and lack of processing equipment particularly in the tropical and subtropical countries resulted in higher percentages of food wastes. Over a decade the byproducts processing industries have gained importance in reusing the agrofood wastes resulting in high value-added products (Barba et al., 2016; Mari´c et al., 2018; Parniakov, Barba, Grimi, Lebovka, & Vorobiev, 2014, 2016; Parniakov et al., 2015;

Chapter 10 Pulsed electric field applications for the extraction of compounds

Rosello´-Soto, Koubaa, et al., 2015). The fruit by-products are a good source of bioactive compounds such as pectins, phenols, antioxidants, essential oils, organic acids, and dietary products (Sagar, Pareek, Sharma, Yahia, & Lobo, 2018). Barba et al. (2016) reported the extraction of bioactive compounds from the byproducts mainly varies with the complexity of food matrixes and the extraction method employed. In the recent decade the extraction of compounds and fractions from by-products using the PEF has attracted the technologists and industrialist. The valorization of wastes using PEF not only increased its economic value but also can be a useful alternative to solve the environmental problem (Pue´rtolas & Barba, 2016). Pue´rtolas et al. (2013) observed an increase in the anthocyanin content (from 28.9 to 61.5 mg) after the PEF treatment, mainly attributed to the higher diffusion coefficient and the solubility in the extraction medium. The major utilization of food waste is necessary for food security, increase in economic, and environmental benefits, as one-third of food which is produced is wasted globally and especially fruit and vegetable by-products are to be used to create into value-added products (Salim, Singh, & Raghavan, 2017). The bioactive compounds are extracted using traditional liquid
liquid or solid
solvent extraction technique having a lower yield, using organic solvents, and time-consuming. Other techniques for novel extraction are supercritical fluid extraction, PEF-assisted extraction, cavitation (hydrodynamic), etc. These shortened the time of extraction, increased efficiency, and yield and reduced the overall consumption of organic solvents. Olive kernels (Olea europaea) were pretreated with PEF to improve the extraction of polyphenols and proteins from the intracellular matrices (Rosello´-Soto, Barba, et al., 2015). The tomato by-products, namely, peel and seeds are a rich source of many bioactive, particularly carotenoids, with high antioxidant power. They are traditionally recovered by extraction with solvents, which is a time-consuming process and requires large quantities of solvents. By-products of cocoa bean shell and coffee silverskin were studied for polyphenol extraction using PEFassisted extraction which showed a 20% higher recovery of polyphenols and methylxanthines than the conventional extraction which have a potential application in food and health sectors. Although many of the studies showed a positive impact of PEF treatment on bioactive compounds and fraction extraction yields, in the investigation carried out by Redondo, Venturini, Luengo, Raso, & Arias (2018) they observed a decrease in the

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polyphenols content in the PEF-treated extracts of thinned peach by-product. The authors reported a decrease in the polyphenolic content in the presence of methanol as solvent, whereas in the presence of water there was an increase in the bioactive compounds. In another study carried out on the extraction of polyphenols from grape by-product using ethanol as solvent, a decrease in the extraction yields was observed compared to the aqueous extraction (Corrales, Toepfl, Butz, Knorr, & Tauscher, 2008). A slight increase in the anthocyanin content was observed after the treatment from the potato peels in the presence of ethanol as a solvent medium compared to water (Pue´rtolas et al., 2013). This clearly showed a synergistic relationship between the PEF treatment and the solvent used for extraction. The grape-pressed cake extracts resulted in better extractability and had higher amounts of total phenolic (63%), anthocyanins (78%), and antioxidant activity (65%) compared to untreated samples (Corrales et al., 2008). Sobrino Lo´pez (2010) studied the effect of PEF on the extraction of phenolic compounds during the fermentation of Tempranillo grapes. A treatment of 5 and 10 kV/cm increased the anthocyanin content by 21.5% and 28.6%, respectively, compared to control. In another investigation, Koubaa, Barba, et al. (2016) extracted the colorants betanin and isobutane from the red prickly pear peels after PEF treatment. The disruption of cells caused by the PEF treatment facilitated in the enhanced extraction of the colorants from the peels. Table 10.1 shows the major findings of the PEF treatment on juice yields, oils, winery, and by-products utilization.

10.8

Conclusion

The main advantages of using PEFs for the extraction of juice mainly consist of its ability to increase the yield as well as purity compared to the mechanical pressing of juice. Normal juice extraction procedures do not extract all of the juice from the intracellular matrices of plant materials. PEF has been reported to efficiently extract juice from a variety of plant materials. The high-intensity electric fields resulted in the formation of irreversible pores causing the electroporation of cell walls enhancing the extraction yields. PEF-assisted extractions resulted in higher quality of fruit juices with enhanced bioactive compounds as an eco-friendly method alternative to conventional extraction methods.

Chapter 10 Pulsed electric field applications for the extraction of compounds

Table 10.1 Effect of pulsed electric fields (PEFs) on the compounds and fractions extraction from the fruit juices, oils, winery, and by-products. Sample

Treatment parameters

Key findings

Apple juice

0
35 kV/cm, 75 μs

The concentration of vitamin C decreased by 36.6%. The antioxidant properties increased The decrease in the total carotenoids in the PEFtreated juice is very less compared to untreated juice after pasteurization The anthocyanin content was increased by 10-fold The alpha-tocopherols content was increase by 20% The total polyphenols extracted were 158% higher than the untreated. Naringin and hesperidin were found to be the highest amount in the extract The polyphenol content in the extract increased by 6.6 times than the untreated The polyphenols extraction reached by 9 times after 60 min of diffusion The betanines concentration increased by 9.5 times than the untreated

Orange juice 30 kV/cm, 100 μs

Grape skin 3 kV/cm, 3 s Rapeseed oil 7 kV/cm, 30 μs Orange peels

1
7 kV/cm, 5
50 pulses of 3 μs

Borage 1
7 kV/cm, leaves 5
150 μs Grape seeds 8
20 kV/cm, 4 ms Red beet

2
6 kV/cm, 10
80 μs

Grape skin

0.5
1.5 kV/cm, 10 μs Watermelon 35 kV/cm, 50 μs juice Blueberry 0
25 kV/cm, pulse fruit juice width (1
23 μs) Citrus juices 28 kV/cm, 100 μs

Flaxseed hulls Blueberry press cake

20 kV/cm, 10 ms 0
25 kV/cm, pulse width (1
23 μs)

Grape wine

4.6 kV/cm, 20 μs

The polyphenol and anthocyanin content was increased by 20% and 75%, respectively A slight increase in the lycopene content and 100% retention of antioxidant capacity The polyphenol, anthocyanin content, and antioxidant capacity were increased by 43%, 60%, and 31%, respectively No significant change in the hydroxymethylfurfura content of the juices Improvement in the extraction of polyphenols is reported The polyphenol, anthocyanin content, and antioxidant capacity were increased by 63%, 78%, and 65%, respectively The total polyphenols and anthocyanin content were increased by 69% and 87%, respectively. An improvement in the catechin and gallic acid concentration

Reference

Corte´s, Torregrosa, Esteve, and Frı´gola (2006) Corrales et al. (2008) Guderjan et al. (2007) Luengo et al. (2013)

Boussetta et al. (2014) Luengo, Martı´nez, A´lvarez, and Raso (2016) Donsi, Ferrari, Fruilo, & Pataro (2010) Oms-Oliu et al. (2009) Bobinaite et al. (2015)

Cserhalmi, Sass-Kiss, To´th-Markus, and Lechner (2006) Boussetta et al. (2014) Bobinaite et al. (2015)

Lo´pez-Giral et al. (2015)

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66. ˇ Zlabur, ˇ Koubaa, M., Rosello´-Soto, E., Sic J., Reˇzek Jambrak, A., Brnˇci´c, M., Grimi, N., . . . Barba, F. J. (2015). Current and new insights in the sustainable and green recovery of nutritionally valuable compounds from Stevia rebaudiana Bertoni. Journal of Agricultural and Food Chemistry, 63(31), 6835
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16. ´ lvarez, I., & Raso, J. (2008). Effects of Lo´pez, N., Pue´rtolas, E., Condo´n, S., A pulsed electric fields on the extraction of phenolic compounds during the fermentation of must of Tempranillo grapes. Innovative Food Science & Emerging Technologies, 9(4), 477
482. Lo´pez-Giral, N., Gonza´lez-Arenzana, L., Gonza´lez-Ferrero, C., Lo´pez, R., Santamarı´a, P., Lo´pez-Alfaro, I., & Garde-Cerda´n, T. (2015). Pulsed electric field treatment to improve the phenolic compound extraction from Graciano, Tempranillo and Grenache grape varieties during two vintages. Innovative Food Science & Emerging Technologies, 28, 31
39. ´ lvarez, I., & Raso, J. (2013). Improving the pressing extraction of Luengo, E., A polyphenols of orange peel by pulsed electric fields. Innovative Food Science & Emerging Technologies, 17, 79
84. ´ lvarez, I., & Raso, J. (2016). Effects of millisecond Luengo, E., Martı´nez, J. M., A and microsecond pulsed electric fields on red beet cell disintegration and extraction of betanines. Industrial Crops and Products, 84, 28
33. Mari´c, M., Grassino, A. N., Zhu, Z., Barba, F. J., Brn´ci´c, M., & Rimac Brn´ci´c, S. (2018). An overview of the traditional and innovative approaches for pectin extraction from plant food wastes and by-products: Ultrasound-, microwaves-, and enzyme-assisted extraction. Trends in Food Science and Technology, 76, 28
37. Min, S., Jin, Z. T., & Zhang, Q. H. (2003). Commercial scale pulsed electric field processing of tomato juice. Journal of Agricultural and Food Chemistry, 51 (11), 3338
3344. Min, S., & Zhang, Q. H. (2003). Effects of commercial-scale pulsed electric field processing on flavor and color of tomato juice. Journal of Food Science and Technology, 68(5), 600
1606. Misra, N. N., Koubaa, M., Roohinejad, S., Juliano, P., Alpas, H., Ina`cio, R. S., . . . Barba, F. J. (2017). Landmarks in the historical development of twenty first century food processing technologies. Food Research International, 97, 318
339. Oms-Oliu, G., Odriozola-Serrano, I., Soliva-Fortuny, R., & Martı´n-Belloso, O. (2009). Effects of high-intensity pulsed electric field processing conditions on lycopene, vitamin C and antioxidant capacity of watermelon juice. Food Chemistry, 115(4), 1312
1319. Parniakov, O., Barba, F. J., Grimi, N., Lebovka, N., & Vorobiev, E. (2014). Impact of pulsed electric fields and high voltage electrical discharges on extraction of high-added value compounds from papaya peels. Food Research International, 65(PC), 337
343. Parniakov, O., Barba, F. J., Grimi, N., Lebovka, N., & Vorobiev, E. (2016). Extraction assisted by pulsed electric energy as a potential tool for green and

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sustainable recovery of nutritionally valuable compounds from mango peels. Food Chemistry, 192, 842
848. Parniakov, O., Rosello-Soto, E., Barba, F. J., Grimi, N., Lebovka, N., & Vorobiev, E. (2015). New approaches for the effective valorization of papaya seeds: Extraction of proteins, phenolic compounds, carbohydrates, and isothiocyanates assisted by pulsed electric energy. Food Research International, 77(4), 711
717. Poojary, M. M., Putnik, P., Bursa´c Kovaˇcevi´c, D., Barba, F. J., Lorenzo, J. M., Dias, D. A., & Shpigelman, A. (2017). Stability and extraction of bioactive sulfur compounds from Allium genus processed by traditional and innovative technologies. Journal of Food Composition and Analysis, 61, 28
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4), 1330
1336. Pue´rtolas, E., Koubaa, M., & Barba, F. J. (2016). An overview of the impact of electrotechnologies for the recovery of oil and high-value compounds from vegetable oil industry: Energy and economic cost implications. Food Research International, 80, 19
26. ´ lvarez, I., & Raso, J. (2012). Improving mass transfer Pue´rtolas, E., Luengo, E., A to soften tissues by pulsed electric fields: Fundamentals and applications. Annual Review of Food Science and Technology, 3, 263
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395. Rosello´-Soto, E., Barba, F. J., Parniakov, O., Galanakis, C. M., Lebovka, N., Grimi, N., & Vorobiev, E. (2015). High voltage electrical discharges, pulsed electric field, and ultrasound assisted extraction of protein and phenolic compounds from olive kernel. Food and Bioprocess Technology, 8(4), 885
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310. Rosello´-Soto, E., Parniakov, O., Deng, Q., Patras, A., Koubaa, M., Grimi, N., . . . Barba, F. J. (2016). Application of non-conventional extraction methods: Toward a sustainable and green production of valuable compounds from mushrooms. Food Engineering Reviews, 8(2), 214
234. ˜ es, J., & Molto´, Rosello´-Soto, E., Poojary, M. M., Barba, F. J., Lorenzo, J. M., Man J. C. (2018). Tiger nut and its by-products valorization: From extraction of oil and valuable compounds to development of new healthy products. Innovative Food Science and Emerging Technologies, 45, 306
312. Sagar, N. A., Pareek, S., Sharma, S., Yahia, E. M., & Lobo, M. G. (2018). Fruit and vegetable waste: Bioactive compounds, their extraction, and possible utilization. Comprehensive Reviews in Food Science and Food Safety, 17(3), 512
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423. Tylewicz, U., Aganovic, K., Vannini, M., Toepfl, S., Bortolotti, V., Dalla Rosa, M., & Heinz, V. (2016). Effect of pulsed electric field treatment on water distribution of freeze-dried apple tissue evaluated with DSC and TD-NMR techniques. Innovative Food Science & Emerging Technologies, 37, 352
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Wiktor, A., Schulz, M., Voigt, E., Witrowa-Rajchert, D., & Knorr, D. (2015). The effect of pulsed electric field treatment on immersion freezing, thawing and selected properties of apple tissue. Journal of Food Engineering, 146, 8
16. Yajun, Z., Changmei, X., Susu, Z., Guangming, Y., Ling, Z., & Shujie, W. (2017). Effects of high intensity pulsed electric fields on yield and chemical composition of rose essential oil. International Journal of Agricultural and Biological Engineering, 10(3), 295
301. Zhu, Z., Jiang, T., He, J., Barba, F. J., Cravotto, G., & Koubaa, M. (2016). Ultrasound-assisted extraction, centrifugation and ultrafiltration: Multistage process for polyphenol recovery from purple sweet potatoes. Molecules, 21 (11), E1584. Available from https://doi.org/10.3390/molecules21111584. Zhu, Z., Li, S., He, J., Thirumdas, R., Montesano, D., & Barba, F. J. (2018). Enzyme-assisted extraction of polyphenol from edible lotus (Nelumbo nucifera) rhizome knot: Ultra-filtration performance and HPLC-MS2profile. Food Research International, 111, 291
298. Zhu, Z., Zhang, R., Zhan, S., He, J., Barba, F. J., Cravotto, G., . . . Li, S. (2017). Recovery of oil with unsaturated fatty acids and polyphenols from Chaenomeles sinensis (Thouin) Koehne: Process optimization of pilot-scale subcritical fluid assisted extraction. Molecules, 22(10). Available from https:// doi.org/10.3390/molecules22101788. Zulueta, A., Barba, F. J., Esteve, M. J., & Frı´gola, A. (2010). Effects on the carotenoid pattern and vitamin A of a pulsed electric field-treated orange juice-milk beverage and behavior during storage. European Food Research and Technology, 231(4), 525
534. Zulueta, A., Barba, F. J., Esteve, M. J., & Frı´gola, A. (2013). Changes in quality and nutritional parameters during refrigerated storage of an orange juice-milk beverage treated by equivalent thermal and non-thermal processes for mild pasteurization. Food and Bioprocess Technology, 6(8), 2018
2030.

Pulsed electric field treated insects and algae as future food ingredients

11

Sergiy Smetana1, Houcine Mhemdi2, Samir Mezdour3 and Volker Heinz1 1

The German Institute of Food Technologies (DIL e.V.), Quakenbru¨ck, Germany 2Sorbonne University, University of Technology of Compiegne, Laboratory of Integrated Transformation of Renewable Matter (UTC/ESCOM, EA 4297 TIMR), Research Center of Royallieu, Compiegne Cedex, France 3 UMR Food Process Engineering, AgroParisTech, INRA, University of Paris-Saclay, Massy, France

11.1

Introduction

Pulsed electric field (PEF) technology is foreseen as a rather flexible tool applicable for a range of cases from tender stimulation or stressing of living organisms to cell components disintegration. Effects of PEF application vary also dramatically depending not only on the properties of the application environment but also on the individual characteristics of organisms and their physiological and development state (Mohamed & Eissa, 2012). Application of PEF for novel food and feed sources (e.g., microalgae and insects) in general is following similar approaches. Effects observable in microalgae and insects depend on PEF intensity, number of pulses, treatment time, conditions of treatment environment (pH, water content, temperature, conductivity, ionic strength, etc.), and composition of target organisms. The physical and chemical characteristics of both microalgae and insects strongly influence the effects of PEF application. This chapter reviews the application of PEF to microalgae and insects as potential biomass treatment technology for the four main cases: stimulation, inactivation of microorganisms, extraction and drying improvement, and cell disintegration.

Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00011-2 © 2020 Elsevier Inc. All rights reserved.

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Satisfying the growing demand for proteins, notably for feeding of animals, and toning down the impact of animal husbandry on the environment, while at the same responding to public demand for product quality, are major challenges for international organizations, private operators, and agri-food researchers. Among several possible additional sources of proteins, the insect solution seems to be relevant and credible as a complementary option alongside other conventional ones (fish and soya). The development of an insect industry requires the development of technically reliable and economically viable transformation processes. The application of emerging technologies such as PEF for the valorization of insects seems an interesting way to explore. Unfortunately, the literature review marks the scarcity of works on this topic. The University of Technology of Compie`gne (France) and AgroParisTech (France) are the first laboratories to work on this subject. This chapter includes the first results of the research teams on PEF application for Tenebrio molitor treatment. These larvae are rich in water, proteins, and lipids. The objective of the study was to fractionate the raw material to obtain a liquid fraction rich in oil and a solid fraction rich in proteins according to the biorefinery concept. For this purpose, mechanical expression was used for insect dewatering and defatting. In order to enhance the pressing kinetics and to increase the extraction yield, PEF was applied as pretreatment. Results showed that the application of a pretreatment before pressing improves the extraction yield and reduces the extraction time. PEF seems to be a very promising technology for the treatment of insect biomass, specifically for the higher extraction yields. In fact, the application of the electrical treatment induces cell membranes permeabilization facilitating thus the extraction step at cold temperature and preserving the product quality. The results described in this chapter will be very useful to pave the way for insects’ valorization in the biorefinery concept.

11.2 11.2.1

Application of pulsed electric field for treatment of microalgae biomass Application of pulsed electric field for induction of stress response, stimulation, and mutation of microalgae biomass

PEF relies on external electric field to induce a critical electrical potential across the cell membrane, thus causing cell

Chapter 11 Pulsed electric field treated insects and algae as future food ingredients

disruption via electromechanical compression and electric field induced tension inducing pore formation in the membrane (electroporation). Such cell disruption effect can be reversible (ratio of total area of induced pores to the total surface area of the membrane is small) and irreversible (increased ratio of pores area to total membrane area) (Gu¨nerken et al., 2015). Induction of stress response, stimulation, induction of mutations, reversible release of intracellular material are relying on reversible effects applied at the upstream processes, often as an integrated part of microalgae cultivation. As indicated by some authors, similar levels of maximum reversible and irreversible permeabilization could be obtained for similar PEF conditions; however, pores with a maximum radius ranging from 0.8 to 0.9 nm do not affect cell division capability and reseal in few seconds (Bode´ne`s et al., 2019). It is assumed that periodic or constant stressing of microalgae with reversible PEF stimulation or electroporation can result in induction of protective features of cells. Protective mechanisms of cells stimulated by PEF should trigger accumulation of resources: increase in biomass yield and microalgae concentration (Gusbeth, Eing, Gottel, & Frey, 2013), increase in oil or protein content, and release of intracellular materials. For example, nanosecond PEF (nsPEF) is indicated to be applicable for microalgae processing through sublethal stress induction, targeted release of intracellular components, and induced cell apoptosis (Buchmann et al., 2018). PEF is a well-known method used to introduce DNA and proteins into microalgae cells, and to transform microalgal protoplasts, cell wall deficient mutants, and other thin-walled algal cells (Doron, Segal, & Shapira, 2016; Mun˜oz et al., 2018). Transformation of nuclear material has been an aim of PEF application in a few studies, which concentrated on Chlorella sp. (Chow & Tung, 1999; Wang, Wang, Su, & Gao, 2007), Scenedesmus obliquus (Guo et al., 2013), Chlamydomonas reinhardtii (Brown, Sprecher, & Keller, 1991; Shimogawara, Fujiwara, Grossman, & Usuda, 1998; Yamano, Iguchi, & Fukuzawa, 2013), Dunaliella sp. (Feng, Xue, Liu, & Lu, 2009; Sun, Gao, Li, Zhang, & Xu, 2006; Sun, Zhang, Sui, & Mao, 2008; Walker, Becker, Dale, & Collet, 2005), and Nannochloropsis sp. (Jeon et al., 2019; Kilian, Benemann, Niyogi, & Vick, 2011). It is indicated that efficiency of PEF for such applications depends not only on “classical” conditions described in this and other chapters but also on concentration of genetic material (Geada et al., 2018; Wang et al., 2007). Even though mechanisms of physiological and especially nuclear changes are not well investigated, application of PEF is proven to be effective for the

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transient expression of genes (Wang et al., 2007), expression of foreign genes in microalgae (Sun et al., 2008), high-level protein expression (Potvin & Zhang, 2010), or improvement of genetic transformation (Feng et al., 2009).

11.2.2

Application of pulsed electric field for inactivation of microorganisms and extraction improvement

Further effects discussed in this chapter rely more on irreversible cell disruption—an effect required to stop the development of microorganisms, enhance the release of intercellular material and increased rates of extraction or drying. PEF can be efficiently applied in upstream and downstream treatment processes for inactivation of microorganisms, competing or harmful for microalgae and potentially harmful for human health. Upstream PEF for inactivation of microorganisms is often applied for the water treatment as a part microalgae cultivation chain and acts as a treatment system to the complete culture media with selective effects (Rego et al., 2015). Such a system has proven to be efficient in dealing with free-living amoebae and other protozoan contamination (Rego et al., 2015; Vernhes, Benichou, Pernin, Cabanes, & Teissie´, 2002). From the one side, direct treatment of cultivation media with PEF can halt the development of microalgae (Spirulina) if treated with 50 impulses with a magnitude of 66.7 kV/cm (Qin et al., 2014). From the other side, PEF can protect Chlorella sp. cultures in tubular bioreactor from protozoans with an average of 900 V/cm, 65 μs pulses of 50 Hz in constant regime (Rego et al., 2015). A case study of applying nsPEF for culture media with Chlorella vulgaris allowed microbial contamination control while retaining the viability of microalgae cells (Buchmann et al., 2018). Increase in energy input with treatment at 15 kV/cm and a specific energy input of 100 kJ/kg results considerable reduction of microbial contamination as confirmed by the treatment of previously inoculated extracts of 7.1, 6.0, and 4.1 log cycles of Escherichia coli, Bacillus subtilis, and Candida utilis, respectively (Toepfl, Heinz, & Knorr, 2006). One of the main and well-known applications of PEF is the enhancement of recovery of high-added value components from microalgae such as proteins, carotenoids, chlorophylls, microelements, lipids, polyunsaturated fatty acids, and sterols, as well as volatile and phenolic compounds (Barba et al., 2015). Such components have a diverse application range from food,

Chapter 11 Pulsed electric field treated insects and algae as future food ingredients

cosmetics, pharmaceutical, and biofuel industries, but mild level of processing and avoidance of extensive chemical used for the extraction (’t Lam et al., 2017) make PEF especially applicable for the extraction of food ingredients. Multiple studies demonstrate the applicability of PEF for the enhancement of release and extraction of carbohydrates (Goettel, Eing, Gusbeth, Straessner, & Frey, 2013), lipids (Bensalem et al., 2018; Hosseini, Guionet, Akiyama, & Hosano, 2018; Sheng, Vannela, & Rittmann, 2012; Silve et al., 2018; Zbinden et al., 2013), proteins (Coustets, Al-Karablieh, Thomsen, & Teissie´, 2013; Jaeschke et al., 2019; Parniakov et al., 2015a), pigments, and carotenoids (Luengo, Martı´nez, Coustets, et al., 2015; Parniakov et al., 2015b; Toepfl et al., 2006). One of the approaches applied in research of PEF effects on microalgae concentrated on the identification of conductivity changes of concentrated nondried biomass after treatment (Carullo et al., 2018; ’t Lam et al., 2017; Pataro et al., 2017; Postma et al., 2016). Such indirect measurement allowed for expressed identification of the PEF efficiency, which was also confirmed with follow-up analysis of dry matter, carbohydrates, protein and phenolics content, and scanning electron microscopy (SEM) (Carullo et al., 2018; Pataro et al., 2017; Postma et al., 2016). Some studies although indicated that certain range of PEF treatment is not sufficient for substantial release of intracellular proteins (’t Lam et al., 2017). A few studies also concentrate on the possibility to use PEF for the improvement of phycocyanin and proteins extraction from Arthrospira platensis (which is formally a cyanobacteria but traditionally perceived as microalgae). It is defined that the minimum electric field intensity for detecting C-phycocyanin in the extraction medium should be 15 kV/cm with the application of 50 pulses of 3 μs (total treatment time 150 μs) (Martı´nez, ´ lvarez, & Raso, 2017). However, the same Luengo, Saldan˜a, A study indicates that higher electric field strength is required for shorter treatment periods. Another recent study indicates successful extraction of phycocyanin and proteins (up to 85.2 6 5.7 mg/g and 48.4 6 4.4 g
100 g21, respectively) from A. platensis after PEF treatment at 122 and 56 J/mL (Jaeschke et al., 2019). Moreover, the yield of these food ingredients can be increased with following incubation. A great diversity of microalgae, PEF application parameters, and treated media resulted in the range of studies indicating different efficiencies of PEF application for the release of intracellular components. Concentrated algae suspension (Auxenochlorella protothecoides) treated with square pulses with

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a duration of 1 μs, specific treatment energy of 52 211 kJ/kg suspension, electric field strength of 23 43 kV/cm, and biomass concentration of 36 167 g dry weight per kg suspension resulted in the spontaneous release of soluble components but not lipids (Goettel et al., 2013). The release of soluble materials by A. protothecoides was also highlighted at the PEF treatment of at 35 kV/cm and the pulse duration of 1 μs (Eing, Goettel, Straessner, Gusbeth, & Frey, 2013). These authors also indicated that lipid fraction remained intracellular but available for further extraction. Similar conclusions of ions and carbohydrates release with following oil extraction were indicated for suspension A. protothecoides PEF treated with energy of 0.25 MJ/kgDW and following incubation for 20 h at 25 C (Silve et al., 2018). The extractability of proteins, chlorophyll, and carotenoids, as well as protease activity of extracts from Spirulina and Chlorella after a PEF treatment demonstrates an increase of 27%, 80%, and 52.5% has been found for protein, chlorophyll, and carotenoids content in C. vulgaris extract after a treatment at 15 kV/cm and a specific energy input of 100 kJ/kg, respectively. Antioxidative activity of the extract can be increased by almost 100% (Toepfl et al., 2006). Application of PEF with synergistic effect of temperature (25 C 55 C) and total specific energy input (0.55 1.11 kWh/kgDW ) for C. vulgaris resulted in release of 25% 39% carbohydrates and 3% 5% proteins (Postma et al., 2016). Similarly, testing of a wide range of PEF parameters (1 40 pulses, 0.05 5 ms pulses, 7.5 30 kV/cm, 0.05 150 kWh/kgDW ) for C. vulgaris and Neochloris oleoabundans resulted in release of ions and only with high energy inputs in 13% of proteins release (’t Lam et al., 2017). Treated suspensions (106 cells/mL) of C. vulgaris, Nannochloropsis salina, and Haematococcus pluvialis with 4.5 6 kV/cm by 15 bipolar 2-ms trains with posttreatment incubation in salty buffer increased the release of proteins in two to eight times comparing to the control sample (Coustets et al., 2013). The investigation on the lowest energy costs for the extraction of lutein results in the conclusion on the treatment of fresh C. vulgaris biomass with 25 kV/cm to 100 μs at 25 C 30 C. Such conditions were able to increase the lutein extraction yield in 3.5- to 4.2-fold in comparison with the control sample (Luengo, ´ lvarez, & Raso, 2015). Microsecond range of Martı´nez, Bordetas, A PEF application (15 20 kV/cm, 25 pulses) is highlighted to be more energy saving and more efficient mode of carotenoid extraction from C. vulgaris than millisecond range. Energy required in microsecond range was five times lower (30 kJ/L) than in millisecond range (Luengo, Martı´nez, Coustets, et al., 2015). PEF can be an efficient tool to reach 50% of oil extraction

Chapter 11 Pulsed electric field treated insects and algae as future food ingredients

from C. vulgaris with simple skimming of oil extracted in the microalgae broth, comparing the control experiments with biomass concentration, drying, cell rupture using pressure, and organic solvent (Flisar, Meglic, Morelj, Golob, & Miklavcic, 2014). It is confirmed that PEF is applicable for the selective extraction of specific intracellular components. Application of PEF for Ankistrodesmus falcatus treatment results in 90% of the cells being lysed with a significant lipid recovery rate using ethyl acetate (Zbinden et al., 2013). Another study indicates that the extraction of β-phycoerythrin from the fresh biomass of Porphyridium cruentum into aqueous media triggered by PEF is effective at 8 or 10 kV/cm for 150 μs with following incubation time of 6 h. Untreated incubated cells do not release the pig´ lvarez, & Raso, 2019). PEF treatment at ment (Martı´nez, Delso, A 10 unipolar pulses of 5.5 kV/cm, a pulse duration of 5 μs, and a repetition frequency of 10 Hz in combination with mechanical stress (cyclic pressures) improves lipid extraction from C. reinhardtii (Bensalem et al., 2018). Application of short pulses (5 μs) of high electric field (4 6 kV/cm) is demonstrated to be efficient for the lipid extraction from C. reinhardtii. Moreover, lipid droplet redistribution within the cytoplasm during the PEF treatment shows effects also on intracellular structure (Bodenes, 2017; Bode´ne`s, Lopes, Pareau, Franc¸ais, & Le Pioufle, 2016). PEF is also efficient for oil extraction from Botryococcus braunii with 50 pulses, 16.7-J/mL energy consumption, 200-ns pulse duration, and 1-Hz pulse repetition frequency (Hosseini et al., 2018). PEF treatment was also compared with other permeabilization technologies and has been confirmed to be a milder technology than bed milling (’t Lam et al., 2017; Postma et al., 2016), sonification at basic conditions of pH 5 11 (Parniakov et al., 2015a), ultrasonification (Grimi et al., 2014), and high pressure homogenization (HPH) at 150 MPa (Carullo et al., 2018; Grimi et al., 2014). Some studies although indicate that not only cell disruption technology but also treated media conditions define the efficiency of extraction. For example, microwave, PEF, and ultrasound with temperature control can have similar significant enhancement of lipid extraction from microalgae (9% 13% increase) (Sheng et al., 2012). However, PEF is identified as more selective technology allowing for targeted components extraction. Thus it is more beneficial than sonification for Nannochloropsis pretreatment at normal pH conditions (pH 5 8.5) for selective extraction of proteins (Parniakov et al., 2015a). Similarly, PEF leads to more targeted selective extraction for carbohydrates (36%, w/w, of total

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carbohydrates), and low molecular weight proteins (5.2%, w/w, of total proteins) comparing to unselected description of cells into small pieces by HPH (Carullo et al., 2018). Other authors also highlight nonuniversal application of PEF treatment for the extraction of intracellular components: treatment of Nannochloropsis sp. (20 kV/cm, 1 4 ms, 13.3 53.1 kJ/kg) was ineffective for extraction of pigments (e.g., chlorophylls or carotenoids) without subsequent application of more potent disruption techniques (Grimi et al., 2014). It is noteworthy that disintegration of microalgae cells by PEF requires higher energy intensity than plant or animal cells. Efficiency of PEF application in the case of microalgae suspension treatment depends on the size of microalgae cells. For example, Chlorella sp. cells have diameter in a range of few μm. However, higher range of energy intensity required can be effectively used for the inplace treatment of microbial contamination of E. coli, B. subtilis, and C. utilis, respectively (Toepfl et al., 2006). The specific energy demand, required for microalgae cells proliferation and release of intracellular components, strongly depends on the concentration of the suspension and ranges from 0.42 kWh/kg for 10% dry cell weight to 239 kWh/kg for 0.03% dry cell weight (Eing et al., 2013; Gu¨nerken et al., 2015; Sheng et al., 2012).

11.3

Application of pulsed electric field for treatment of insect biomass

Insect-based food is being actively developed in Europe. It is still as niche industry, but it has a potential for a wider use as an ingredient, supplying the lack of food sources in the future. Edible insects demonstrate advantages as a sustainable food resource applicable as a substitute for food products (Smetana et al., 2018; Smetana, Mathys, Knoch, & Heinz, 2015; Smetana, Palanisamy, Mathys, & Heinz, 2016; Smetana, Schmitt, & Mathys, 2019). In certain conditions, production of insects is efficient and has a potential to be a climate-smart agricultural practice. Insect production so far is not relying on steroids, hormones, antibiotics, or direct-applied chemical-treatment products, which consumers try to avoid. While the nutritional profiles of insects are promising for their application as food ingredients (Dobermann, Swift, & Field, 2017; Kouˇrimska´ & Ada´mkova´, 2016; Rumpold & Schlu¨ter, 2013), insect biomass is yet not well researched in terms of food-processing functionality, human digestion, treatment

Chapter 11 Pulsed electric field treated insects and algae as future food ingredients

methods, etc. Therefore it is required to thoroughly investigate the applicability of existing and emerging food-processing technologies for the treatment of insect biomass in order to define a potential of insects to be applied as food ingredients. Further, this chapter reveals the potential of PEF.

11.3.1

Application of pulsed electric field for the inactivation of insects

Application of PEF for insects is not an obvious type of processing as insects do not represent either homogeneous or liquid material. However, scientific literature holds a few cases of PEF application to deal with insect biomass. The most known and prominent type of PEF application for insect is for food preservation and killing of pest insects. Despite quite a few studies, the intensity range of PEF application varies from nsPEF at 17.76 J/m3 (Pinpathomrat, Kaweeferngfu, Laphodom, Islam, & Kirawanich, 2011) to microsecond pulses (Hallman & Zhang, 1997) and to pulsed high-strength electric fields and radio-frequency radiation at 0.94 3 104 J/m2 (Ponomaryova, de Rivera y Oyarzabal, & Ruı´z Sa´nchez, 2008). Application of various intensities and frequencies of PEF and other pulsed electromagnetic fields to the living insects causes from moderate to high levels of mortality. The main aim of such experiments relates to finding the most efficient ways of quarantine treatments (increase in mortality). Thus application of nsPEF for the inhibition of mosquitos (Culex quinquefasciatus) results in 20% decrease of survival rate (Pinpathomrat et al., 2011). Microsecond applications of PEF (9.2 kV/cm2 in ten 50 μs pulses) to different stages of Mexican fruit fly (Anastrepha ludens) development result in inhibition rate of 97.1% for eggs and complete reduction of survival at other stages of development (Hallman & Zhang, 1997). At the same time, application of high-strength electric fields for granary weevil (Sitophilus granarius L.) treatment results in 40% 90% mortality (at voltages 5.5 10.5 kV, frequency 47.5 MHz, electric field intensity 180 350 kV/m, and exposures 5 60 s). A 100% of insect mortality is reached at field intensity of 2000 kV/m with treatment time of 1 30 s (Ponomaryova et al., 2008).

11.3.2

Application of pulsed electric field for the insect cell permeabilization

First, the impact of PEF on the cells permeabilization was studied. All the experiments were performed using a laboratory

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compression chamber and PEF-treatment system. The experimental setup consisted of a treatment cell and PEF generator (1500 V and 40 A). The compression chamber consisted of a support, a piston, and a cylindrical cavity compartment. The cavity compartment between two electrodes was filled with 5 g of uncompressed larvae forming a porous bed. In order to increase the conductivity of the porous bed before the application of PEF treatment, the larvae were compacted to increase the apparent density of the formed bed from 0.4 to 1 g/cm3. The electric field was then applied at different intensities from 200 to 1000 V/cm and the electrical conductivity was measured during the treatment. The tissue damage degree was characterized by calculating the permeabilization index Z that varies between 0 for untreated tissue and 1 when tissue is completely damaged. Results showed that increasing the initial apparent density of the larvae before the application of PEF treatment enhances the permeabilization kinetic (Fig. 11.1). At E 5 800 V/cm and the apparent density d $ 0.8 insect tissue was completely damaged (Z  1). At low density (d , 0.8) the tissue was partially damaged and the permeabilization index Z did not exceed 0.3 when d , 0.7. This result may be related to the high conductivity of the compacted tissue (expelling of air) implying better current flow through the sample and improving the treatment efficiency. An optimal apparent density of 0.8 g/cm3 was fixed for the next steps in the study. 1

0.75

d=0.5 d=0.6 d=0.7 d=0.8 d=1

Z 0.5

0.25

0

0

0.05

0.1

0.15

0.2

t, s

Figure 11.1 Permeabilization index Z versus time t for larvae tissue at different apparent density. With E 5 800 V/cm, N 5 100 trains, n 5 20 pulses, pulse duration ti 5 100 μs. Apparent density varies from 0.5 to 1 g/cm3.

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1

0.8

200 V/cm 400 V/cm 600 V/cm 800 V/cm 1000 V/cm

0.6

Z 0.4

0.2

0

0

0.05

0.1

t, s

0.15

0.2

The impact of PEF treatment intensity on the permeabilization kinetics was then studied by varying it from 200 to 1000 V/cm at d 5 0.8 g/cm3. Results showed that the effectiveness of the electric treatment depends on its intensity and duration. Curves in Fig. 11.2 show that the increase of the electrical intensity E enhances the permeabilization kinetic. For instance, permeabilization index reached at the end of the treatment (Zmax) increases from 0.3 for E 5 200 V/cm to 0.94 for E $ 800 V/cm. At 1000 V/cm, treatment duration of 50 ms was sufficient to provoke total damage of larvae. This duration increased to 100 ms at 800 V/cm. At lower intensities, E , 800 V/cm, the damage was partial even for long treatment time. The SEM images of larvae cell obtained for untreated and PEF-treated samples at different electric field strengths (E 5 400, 800, and 1000 V/cm) are presented in Fig. 11.3. The data show clearly the effect of PEF on the larvae cell structure. At 400 V/ cm a partial damage was detected for insect cells; however, some cells remained intact. At high intensity, E $ 800 V/cm, the cell membranes disintegrate, and the tissue forms a homogeneous continuous medium conforming the destruction of the cellular network. Fig. 11.4 represents the characteristic treatment time τ (time to reach Z 5 0.5) and the corresponding specific energy input at different PEF intensities. It can be shown that the treatment time required to damage 50% of cells decreased from 152 ms at E 5 400 V/cm to 22 ms at 1000 V/cm. This time is significantly higher than that required for other plant tissues. For example, for beetroot, a time of 10 ms is required at E 5 800 V/cm

Figure 11.2 Permeabilization index Z versus time t for larvae tissue at different electric field intensities (E 5 200, 400, 600, 800, and 1000 V/cm); treated larvae with N 5 100 trains, n 5 20 pulses, and pulse duration ti 5 100 μs.

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Control

400V/cm

800V/cm

1000V/cm

Figure 11.3 SEM of Tenebrio molitor cells before (control) and after PEF at different electric field (400, 800, and 1000 V/cm). PEF, Pulsed electric field; SEM, scanning electron microscopy.

(Mhemdi, Bals, Grimi, & Vorobiev, 2014). This difference may be attributed to the presence of chitin conferring high rigidity and resistance to the tissue. Higher PEF intensities also lead to lower energy consumption needed to semipermeabilize larval tissue. In fact, the energy input required to reach Z 5 0.5 decreases from 25 kJ/kg at low intensities to about 15 kJ/kg at high field intensity. This energy input is quite low and may be very attractive for the industrial implementation of the process as compared to very energy costly thermal (drying) and mechanical (grinding) treatments.

Chapter 11 Pulsed electric field treated insects and algae as future food ingredients

259

Zmax

0.9 0.6 0.3 0

τZ=0.5, s

0.3 0.2 0.1

QZ=0.5, KJ/Kg

0 30 20 10

E, V/cm

0

400

600

800

1000

Figure 11.4 Characteristic treatment time (τ) and specific energy (Q) to reach Z 5 0.5 of larvae tissue at different PEF intensities. PEF, Pulsed electric field.

200 ms 100 ms

Extraction yield,%

50 40 30 20 10 0

11.3.3

Treatment Control

400+P

600+P

800+P

Extraction of intracellular compounds from insect biomass

The effect of PEF treatment in the improvement of the extractability of intracellular compounds by mechanical pressing (60 bar and 15 min) was studied by monitoring dry matter analyses and by measuring the extraction yields of pressed liquid, water-soluble proteins, and lipids. Grinding was applied as treatment reference for comparison. Fig. 11.5 represents the juice expression yield from untreated, grinded, and PEF-treated larvae at different intensities (400, 600, and 800 V/cm) from 100 to 200 ms. The results

Figure 11.5 Liquidized components extraction from untreated (control: pressing) and treated larvae at different intensities (PEF and pressing, electric field varies from 400 to 800 V/cm). PEF, Pulsed electric field.

Chapter 11 Pulsed electric field treated insects and algae as future food ingredients

show that the application of PEF increased the extraction yield especially for E 5 800 V/cm and tPEF 5 200 ms. Indeed, under these conditions, the juice yield was increased from 41% to 55%. It can be concluded that the stronger cell disintegration led to a higher efficient extraction of intracellular compounds. Results highlight the PEF intensity and duration on the intensification of liquid content and intracellular compounds confirming the results previously obtained for the permeabilization kinetics. The optimal conditions are E 5 800 V/cm and tPEF 5 200 ms. Fig. 11.6 shows the lipids extraction yield and the concentration of proteins on the obtained liquidized components from untreated, PEF-treated, and grinded larvae. Results show that PEF (E 5 800 V/cm and tPEF 5 200 ms)-assisted pressing (P 5 60 bar and tpressing 5 15 min) allowed the extraction of 50% of lipids. As for the proteins, they have mainly been preserved in the pressing cake (40% of dry mass), since their concentration in the juice is very low (about 1 g/L). On the other hand, the reference treatment (grinding) permitted the extraction of 74% of lipids but it provoked the liberation of more proteins in the juice (1.80 g/L). Thus it can be concluded that PEF treatment allowed selective extraction of lipids and water from the larvae while preserving most of the protein in the press cake. Grinding induces a complete fragmentation of the material, while PEF treatment is less destructive explaining the selectivity of the extraction of lipids.

Lipids yield, %

80 60 40 20

Water soluble proteins, g/L

260

2 1.5 1 0.5

Treatment Control

Grinding

800V/cm+P

Figure 11.6 Oil yields extraction (A), concentration of proteins (B) in the juice of untreated (control: pressing), treated larvae (PEF and pressing), and grinded tissue. PEF, Pulsed electric field.

Chapter 11 Pulsed electric field treated insects and algae as future food ingredients

11.4

Outlook

Application of PEF technology is very promising for niche inplace microalgae treatment, downstream processing able to replace or complement other techniques. The most cases of applicability are for the enhancement of selective extraction of intracellular components such as carotenoids, carbohydrates, lipids, and, in certain cases, proteins. Successful industrial application of PEF for microalgae treatment will depend on cost efficiency such treatment in comparison with benchmark technologies. There are a few approaches that could potentially solve the issue. The first envisioned approach is dealing with the overcoming of efficiency bottleneck via integration of PEF in multistage cascade microalgae biorefinery. It is envisioned that future biorefinery concepts will target the valuable bioactive components extraction first, and then application of leftover biomass for lower application values purposes. Such approaches along with improvement in processing efficiency can “justify” costs of higher energy application in some cases. Another option relies on the further development and adaptation of PEF technologies for the specific application cases of microalgae processing. For example, a recent study, relying on the PEF technology further suggested a novel, energy-efficient, and chemical-free technique for both microalgal products extraction and cell inactivation. It relies on method using the copper oxide nanowire (CuONW) modified three-dimensional copper foam electrodes with a low applied voltage, which allowed for low energy consumption of 0.014 kWh/kg via the treatment of 2 V and 10 s (Bai, Huo, Wu, & Hu, 2019). Such examples demonstrate that further successful application of PEF for microalgae processing could be associated with the technological adaptations and progress. Studies on application of PEF for insects as a potential food ingredient are very scarce. More entomological and engineering research are needed to identify solid cases of PEF application for practical cases of insect biomass treatment for food purposes. Current case study presented in this chapter demonstrates the impact of pulsed electrical field for T. molitor larvae cell disintegration. PEF treatment enhances cells permeabilization and can induce total damage (Z  1) of larvae at the following optimal operating conditions: d 5 0.8, E 5 800 V/cm, and tPEF 5 200 ms. More importantly, this research for the first time evidences the benefits of PEF treatment for the selective extraction of lipids and the dehydration of the press cake while

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preserving the proteins in the press cake. It was shown that PEF-assisted pressing is a promising process to obtain a dry and defatted press cake with higher concentration of proteins. The results obtained during this study are very encouraging, promising and offer new possibilities for the valuable food components extraction from insects.

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Jaeschke, D. P., Mercali, G. D., Marczak, L. D. F., Mu¨ller, G., Frey, W., & Gusbeth, C. (2019). Extraction of valuable compounds from Arthrospira platensis using pulsed electric field treatment. Bioresource Technology, 283, 207 212. Available from https://doi.org/10.1016/j.biortech.2019.03.035. Jeon, S., Kang, N. K., Suh, W. I., Koh, H. G., Lee, B., & Chang, Y. K. (2019). Optimization of electroporation-based multiple pulses and further improvement of transformation efficiency using bacterial conditioned medium for Nannochloropsis salina. Journal of Applied Phycology, 31(2), 1153 1161. Available from https://doi.org/10.1007/s10811-018-1599-7. Kilian, O., Benemann, C. S. E., Niyogi, K. K., & Vick, B. (2011). High-efficiency homologous recombination in the oil-producing alga Nannochloropsis sp. Proceedings of the National Academy of Sciences of the United States of America, 108(52), 21265 21269. Available from https://doi.org/10.1073/ pnas.1105861108. Kouˇrimska´, L., & Ada´mkova´, A. (2016). Nutritional and sensory quality of edible insects. NFS Journal, 4, 22 26. Available from https://doi.org/10.1016/j. nfs.2016.07.001. ’t Lam, G. P., Postma, P. R., Fernandes, D. A., Timmermans, R. A. H., Vermue¨, M. H., Barbosa, M. J., . . . Olivieri, G. (2017). Pulsed electric field for protein release of the microalgae Chlorella vulgaris and Neochloris oleoabundans. Algal Research, 24, 181 187. Available from https://doi.org/10.1016/j. algal.2017.03.024. ´ lvarez, I., & Raso, J. (2015). Influence Luengo, E., Martı´nez, J. M., Bordetas, A., A of the treatment medium temperature on lutein extraction assisted by pulsed electric fields from Chlorella vulgaris. Innovative Food Science & Emerging Technologies, 29, 15 22. Available from https://doi.org/10.1016/j. ifset.2015.02.012. ´ lvarez, I., Teissie´, J., Rols, M.-P., & Luengo, E., Martı´nez, J. M., Coustets, M., A Raso, J. (2015). A comparative study on the effects of millisecond- and microsecond-pulsed electric field treatments on the permeabilization and extraction of pigments from Chlorella vulgaris. The Journal of Membrane Biology, 248(5), 883 891. Available from https://doi.org/10.1007/s00232-0159796-7. ´ lvarez, I., & Raso, J. (2019). Pulsed electric field Martı´nez, J. M., Delso, C., A permeabilization and extraction of phycoerythrin from Porphyridium cruentum. Algal Research, 37, 51 56. Available from https://doi.org/10.1016/j. algal.2018.11.005. ´ lvarez, I., & Raso, J. (2017). C˜ a, G., A Martı´nez, J. M., Luengo, E., Saldan phycocyanin extraction assisted by pulsed electric field from Arthrosphira platensis. Food Research International, 99, 1042 1047. Available from https:// doi.org/10.1016/j.foodres.2016.09.029. Mhemdi, H., Bals, O., Grimi, N., & Vorobiev, E. (2014). Alternative pressing/ ultrafiltration process for sugar beet valorization: Impact of pulsed electric field and cossettes preheating on the qualitative characteristics of juices. Food and Bioprocess Technology, 7(3), 795 805. Available from https://doi. org/10.1007/s11947-013-1103-y. Mohamed, M. E., & Eissa, A. H. A. (2012). Pulsed electric fields for food processing technology. Structure and function of food engineering. InTech. ,https://doi. org/10.5772/48678.. Mun˜oz, C. F., de Jaeger, L., Sturme, M. H. J., Lip, K. Y. F., Olijslager, J. W. J., Springer, J., . . . Wijffels, R. H. (2018). Improved DNA/protein delivery in microalgae—A simple and reliable method for the prediction of optimal electroporation settings. Algal Research, 33, 448 455. Available from https:// doi.org/10.1016/j.algal.2018.06.021.

Chapter 11 Pulsed electric field treated insects and algae as future food ingredients

Parniakov, O., Barba, F. J., Grimi, N., Marchal, L., Jubeau, S., Lebovka, N., & Vorobiev, E. (2015a). Pulsed electric field and pH assisted selective extraction of intracellular components from microalgae Nannochloropsis. Algal Research, 8, 128 134. Available from https://doi.org/10.1016/j. algal.2015.01.014. Parniakov, O., Barba, F. J., Grimi, N., Marchal, L., Jubeau, S., Lebovka, N., & Vorobiev, E. (2015b). Pulsed electric field assisted extraction of nutritionally valuable compounds from microalgae Nannochloropsis spp. using the binary mixture of organic solvents and water. Innovative Food Science & Emerging Technologies, 27, 79 85. Available from https://doi.org/10.1016/j. ifset.2014.11.002. Pataro, G., Goettel, M., Straessner, R., Gusbeth, C., Ferrari, G., & Frey, W. (2017). Effect of PEF treatment on extraction of valuable compounds from microalgae C. vulgaris. Chemical Engineering Transactions, 57, 67 72. Pinpathomrat, N., Kaweeferngfu, T., Laphodom, A., Islam, N. E., & Kirawanich, P. (2011). Inhibition of Culex quinquefasciatus (Diptera: Culicidae) viability by nanosecond pulsed electric field radiation. Journal of Electrostatics, 69(4), 339 344. Available from https://doi.org/10.1016/j.elstat.2011.04.012. Ponomaryova, I. A., de Rivera y Oyarzabal, L. N., & Ruı´z Sa´nchez, E. (2008). Interaction of radio-frequency, high-strength electric fields with harmful insects. Journal of Microwave Power and Electromagnetic Energy, 43(4), 17 27. Postma, P. R., Pataro, G., Capitoli, M., Barbosa, M. J., Wijffels, R. H., Eppink, M. H. M., . . . Ferrari, G. (2016). Selective extraction of intracellular components from the microalga Chlorella vulgaris by combined pulsed electric field temperature treatment. Bioresource Technology, 203, 80 88. Available from https://doi.org/10.1016/j.biortech.2015.12.012. Potvin, G., & Zhang, Z. (2010). Strategies for high-level recombinant protein expression in transgenic microalgae: A review. Biotechnology Advances, 28(6), 910 918. Available from https://doi.org/10.1016/j.biotechadv.2010.08.006. Qin, S., Timoshkin, I. V., Maclean, M., Wilson, M. P., MacGregor, S. J., Given, M. J., . . . Wang, T. (2014). Pulsed electric field treatment of microalgae: Inactivation tendencies and energy consumption. IEEE Transactions on Plasma Science, 42(10), 3191 3196. Available from https://doi.org/10.1109/ TPS.2014.2317522. Rego, D., Redondo, L. M., Geraldes, V., Costa, L., Navalho, J., & Pereira, M. T. (2015). Control of predators in industrial scale microalgae cultures with pulsed electric fields. Bioelectrochemistry, 103, 60 64. Available from https:// doi.org/10.1016/j.bioelechem.2014.08.004. ¨ ter, O. K. (2013). Potential and challenges of insects as Rumpold, B. A., & Schlu an innovative source for food and feed production. Innovative Food Science & Emerging Technologies, 17, 1 11. Available from https://doi.org/10.1016/j. ifset.2012.11.005. Sheng, J., Vannela, R., & Rittmann, B. E. (2012). Disruption of synechocystis PCC 6803 for lipid extraction. Water Science and Technology, 65(3), 567 573. Available from https://doi.org/10.2166/wst.2012.879. Shimogawara, K., Fujiwara, S., Grossman, A., & Usuda, H. (1998). High-efficiency transformation of Chlamydomonas reinhardtii by electroporation. Genetics, 148(4), 1821 1828. Silve, A., Kian, C. B., Papachristou, I., Kubisch, C., Nazarova, N., Wu¨stner, R., . . . Frey, W. (2018). Incubation time after pulsed electric field treatment of microalgae enhances the efficiency of extraction processes and enables the reduction of specific treatment energy. Bioresource Technology, 269, 179 187. Available from https://doi.org/10.1016/j.biortech.2018.08.060.

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Smetana, S., Ashtari Larki, N., Pernutz, C., Franke, K., Bindrich, U., Toepfl, S., & Heinz, V. (2018). Structure design of insect-based meat analogs with highmoisture extrusion. Journal of Food Engineering, 229, 83 85. Available from https://doi.org/10.1016/j.jfoodeng.2017.06.035. Smetana, S., Mathys, A., Knoch, A., & Heinz, V. (2015). Meat alternatives: Life cycle assessment of most known meat substitutes. The International Journal of Life Cycle Assessment, 20(9), 1254 1267. Available from https://doi.org/ 10.1007/s11367-015-0931-6. Smetana, S., Palanisamy, M., Mathys, A., & Heinz, V. (2016). Sustainability of insect use for feed and food: Life cycle assessment perspective. Journal of Cleaner Production, 137, 741 751. Available from https://doi.org/10.1016/j. jclepro.2016.07.148. Smetana, S., Schmitt, E., & Mathys, A. (2019). Sustainable use of Hermetia illucens insect biomass for feed and food: Attributional and consequential life cycle assessment. Resources, Conservation and Recycling, 144, 285 296. Available from https://doi.org/10.1016/j.resconrec.2019.01.042. Sun, G., Zhang, X., Sui, Z., & Mao, Y. (2008). Inhibition of pds gene expression via the RNA interference approach in Dunaliella salina (Chlorophyta). Marine Biotechnology, 10(3), 219 226. Available from https://doi.org/10.1007/s10126007-9056-7. Sun, Y., Gao, X., Li, Q., Zhang, Q., & Xu, Z. (2006). Functional complementation of a nitrate reductase defective mutant of a green alga Dunaliella viridis by introducing the nitrate reductase gene. Gene, 377, 140 149. Available from https://doi.org/10.1016/j.gene.2006.03.018. Toepfl, S., Heinz, V., & Knorr, D. (2006). Applications of pulsed electric fields technology for the food industry. In Pulsed electric fields technology for the food industry (pp. 197 221). https://doi.org/10.1007/978-0-387-31122-7_7. Vernhes, M., Benichou, A., Pernin, P., Cabanes, P., & Teissie´, J. (2002). Elimination of free-living amoebae in fresh water with pulsed electric fields. Water Research, 36(14), 3429 3438. Available from https://doi.org/10.1016/ S0043-1354(02)00065-9. Walker, T. L., Becker, D. K., Dale, J. L., & Collet, C. (2005). Towards the development of a nuclear transformation system for Dunaliella tertiolecta. Journal of Applied Phycology, 17(4), 363 368. Available from https://doi.org/ 10.1007/s10811-005-4783-5. Wang, C., Wang, Y., Su, Q., & Gao, X. (2007). Transient expression of the GUS gene in a unicellular marine green alga, Chlorella sp. MACC/C95, via electroporation. Biotechnology and Bioprocess Engineering, 12(2), 180 183. Available from https://doi.org/10.1007/BF03028646. Yamano, T., Iguchi, H., & Fukuzawa, H. (2013). Rapid transformation of Chlamydomonas reinhardtii without cell-wall removal. Journal of Bioscience and Bioengineering, 115(6), 691 694. Available from https://doi.org/10.1016/ j.jbiosc.2012.12.020. Zbinden, M. D. A., Sturm, B. S. M., Nord, R. D., Carey, W. J., Moore, D., Shinogle, H., & Stagg-Williams, S. M. (2013). Pulsed electric field (PEF) as an intensification pretreatment for greener solvent lipid extraction from microalgae. Biotechnology and Bioengineering, 110(6), 1605 1615. Available from https://doi.org/10.1002/bit.24829.

Industrial scale equipment, patents, and commercial applications

12

Stefan Toepfl, Jimmy Kinsella and Oleksii Parniakov Elea Vertriebs- und Vermarktungsgesellschaft mbH, Quakenbru¨ck, Germany

12.1

Introduction

The application of pulsed electric fields (PEF) as an innovative technology can be used in various areas of the food industry. The main objective of such treatment is to influence the product cell structure. The cells of different origin: plant, animal, or microbial can be affected by PEF. All cells are surrounded by a phospholipid bilayer, so called cell membrane. PEF processing allows the targeted permeabilization of biological cell membranes. This effect, termed electroporation, results in release of intracellular substances and/or cell death. Pore formation occurs when, by an external electrical field, a transmembrane potential of approx. 1 V is induced. Dependent on treatment intensity, pores can be reversible or irreversible (see Chapter 1: How does pulsed electric field work?). Field strength, energy input and treatment temperature are critical processing parameters, as are product properties such as pH, conductivity, and presence of lipids or particles. For the microorganisms contained in the liquid product, the loss of the border to the environment means the loss of viability. Plant cells lose their turgor pressure when subjected to the PEF treatment and the increase in the membrane permeability results in an easier mass transport. Note that valuable and nutritious food components such as proteins, vitamins, minerals, and flavors are not affected by PEF. The first attempts to implement PEF for treatment of different food tissues were started in the 1940s-50s in Germany, Ukraine and Moldova. Due to limited availability of pulsed

Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00012-4 © 2020 Elsevier Inc. All rights reserved.

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power switiching technologies and the need to identify commercially viable applications it has taken decades berfore PEF has been brought into industrial use. The first commercial application of PEF technique has been reported in 2006 (Toepfl, Heinz, & Knorr, 2006); currently PEF is well industrialized in several branches of the food industry, for example, French fries industry. Therefore this chapter is introducing the history of industrial application of PEF technology. Moreover, it is giving an overview of current applications. Finally, the current status of patents and a discussion of advantages and challenges of this emerging technique will be presented.

12.2

Historical background of pulsed electric fields commercialization

In Europe the first application of pulsed high voltage currents with the aim to induce artificial mutation has been reported in 1960 (Gossling, 1960). He reported a partial microbial kill, dependent on treatment intensity for Streptococcus lactis and recultivated the survivors to find mutations. At the same time, German engineer Doevenspeck (1960) had filed a patent where he described the setup of a pulse modulator as well as a continuously operated treatment chamber. In that time a typical PEF system for food treatment consisted of a high voltage pulse generator and a treatment chamber where the media is exposed to the electrical field. At large, in the Dovenspeck’ Patent, the pulsed power is generated by repetitive discharge of energy stored in a capacitor bank across a high voltage switch; mercury switch tubes have been suggested (To¨pfl, 2006). However, the electrical treatment of food by PEF has been studied even earlier in Ukraine since end of the 1940s. One of the Ukrainian scientists Zagorul’ko (1958) performed his investigations of effects of electrical current on sugar beet tissue in the 1948 50. He had discovered that the action of AC or DC current directly applied to the sugar beet can cause of plasmolysis of biological cell. The proposed method allowed obtaining a colorless saturation diffusion juice at room temperatures. The estimated energy consumptions were extremely low in the range of 4 5 kJ/kg. Already, in the 1953, he has proposed to use the PEF for the purpose of electroplasmolysis. The electrical drawing of his pulse generator in presented in Fig. 12.1. This generator produced exponential pulses with the duration of 20 µs and allowed PEF treatment at electric field strength of E 5 20 kV/cm. Simultaneously, another Ukrainian scientist

Chapter 12 Industrial scale equipment, patents, and commercial applications

Figure 12.1 Scheme of pulsed generator for electroplasmolis investigation (Sitzmann et al., 2016). Source: Reused with permission.

Figure 12.2 Industrial scale setup for AC electro plasmolysis of apples (Sitzmann et al., 2016). Source: Reused with permission.

Flaumenbaum (1949) gave the first fundamental analysis of the electrical treatment of fruits and vegetables before the extraction of juice. For the first time, he had also constructed the industrial scale setup for AC electro plasmolysis (Flaumenbaum, 1953) (Fig. 12.2). A raw material was delivered with a help of an elevator through a receiving hopper on the rotating electrodes and was forced through a gap between electrodes into a bottom hopper. From the bottom hopper the treated raw material was forwarded directly into a press basket or into an intermediate tank. This system was manufactured, installed and operated in the years 1949 50 at Tiraspol fruit factory, Chisinau winery and other Moldavian wineries.

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From that time the different type schemes of rotating electrodes, blade and linear types systems were proposed. However, just a few of the proposed constructions had been fabricated and tested due to a very limited financial support. Concurrently, in cooperation with the German company Baumgarten Fischindustrie in Bremerhaven, in the early 1960s, Doevenspeck produced fishmeal and fish oil from poor stinking herring offal by cracking the cells with PEF before separating solids and liquids by using a screw press. The original correspondence between Doevenspeck and his partners shows that the experts on site especially noticed that contrary to expectations, the whole process was very low-odor. Also, together with another fishmeal producing factory, Lohmann & Co. in Cuxhaven, he experimented on fish processing. The results showed that PEF treated fishmeal was high quality and had a longer shelf life. The vitamin A content did not change essentially during 6 months storage. In addition, there was almost no oxidation of the residual oil in the final fish meal. Besides, Doevenspeck worked in cooperation with the sewage plant operators in the Nienburg. They have achieved a 20% increase of methane yield by using PEF. Another industrial trial of PEF at canning factor in Ukraine was conducted in 1966 with production capacities of 3 t/h (Kogan, 1968). A noticeable increase in juice yield was observed. For example, the electrical treatment of apples allowed the increasing of juice yield up to  11% 20%. However, the number of technical difficulties (electrical arcing between electrodes, nonhomogeneous treatment, and limitations of electrical generators power) had not permitted the following industrial application of such PEF system. Later on, in 1980, the collaboration of Heinz Dovenspeck and the R&D center of Krupp Industrietechnik GmbH has resulted in the development of trademarks ELCRACK and ELSTERIL. That pilot plant was consisting of a high voltage pulse generator with a peak voltage of 15 kV and a repetition rate of 22 Hz. The storage capacity was varied between 0.5 and 5 µF, an ignitron was used to discharge the electrical energy stored (Grahl, 1994). In Krupp’s continuously operating pilot plant the material through put was up to 250 kg/h. After a successful validation at pilot scale, two industrial scale plants of 10 t/h plant for producing rendered fats from slaughterhouse by-products in Germany and 22 t/h plant for production of high-grade fishmeal and fish oil from herring in Egersund, Norway. The total process in Norway consisted of the ELCRACK system, a subsequent separation of free liquid and a screw press for slurry separation. The fluid was separated in water

Chapter 12 Industrial scale equipment, patents, and commercial applications

and oil phase by a decanter centrifuge and separators. Protein was removed from the aqueous phase using an ultrafiltration. After the installation of the first equipment, many problems arouse concerning the electrode stability, subsequent liquid solid separation, as well as protein recovery after the treatment, the installation was dismantled after a few months of operation. From today’s point of view the failure of this first installation was not only related to the ELCRACK PEF technique, which was a small part of the total installation only, but to introduction of several novel techniques at one time. Due to design and implementation of too sophisticated separation technology and realization of a whole fish processing unit without prior experience, the equipment had to be taken back by Krupp (To¨pfl, 2006). During this time the interest in PEF application increased at a research level; a numerous number of working groups in Universities as well as commercial activities followed (Sitzmann, Vorobiev, & Lebovka, 2016). Therefore from 1988 Krupp initiated together with the Technical University of Hamburg, an EU-project on sterilization of juices and milk in a pilot scale. Within this project the influence of PEF on food components such as vitamins, enzymes, and flavor carriers was investigated for the first time (Grahl, 1994; Grahl, Sitzmann, & Ma¨rkl, 1992). In cooperation with TU Berlin where Sitzmann’s generator was placed, he investigated until 1996 several possible applications. For example, cell cracking of fruits (Sitzmann & Heinz, 1996) in order to increase the yield of juices. Later on, in another part of Europe, the industrial scale experiments were also done at Odessa (Ukraine) juice plant using different plant tissues (carrots, plums, apricots, grapes, and apples) (Sitzmann et al., 2016). Furthermore, the trials on aqueous extraction assisted by DC treatment (10 V/cm) of sugar beet cossets have been initiated in Ukraine (Bazhal, Kupchik, & Vorona, 1984). The data evidenced the positive effect of application of electric field on an enhancement of sugar extraction and improvement a quality of raw juice. These results triggered the industrial scale trials on Yagotin sugar factory (Ukraine) during the 1986 87 seasons. However, the technical difficulties did not permit the following use of this pilot. Later on, different research groups were continuing the investigation of PEF effects on various plant material (Botoshan & Berzoj, 1994; Kolpakov, Botoshan, Berzoj, & Zakharchuk, 1991). These studies resulted in the development of different pilot scale experimental setups on application of electroplasmolysis. However, all these constructions were also not widely

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industrialized due to the technical difficulties and the absence of necessary financial support. In 1995 Pure Pulse Technologies a subsidiary of Maxwell Laboratories developed a continuous processing system called CoolPure for the treatment of up to 2000 L/h. For research use a pilot system called CoolPure Jr. was available, to be operated at a flow rate of 6 10 L/h at a maximum field strength of 50 kV/cm. In the same year a letter of no objection has been released by the Food and Drug Administration for the use of PEF technology for food preservation; in 1996 the treatment of liquid egg has been approved with certain conditions to be accepted (To¨pfl, 2006). Meanwhile the first commercial PEF application for fruit juice preservation in the United States has been reported in 2005 (Clark, 2006). In a scale of 200 L/h, premium quality juices are treated at Genesis, Eugene, United States, a fruit juice cooperative using an Ohio State University system. They were used to distribute unpasteurized, premium fruit juices. However, due to the United States financial crisis in 2007, the Genesis company was bankrupted. Nowadays, most of the PEF systems installed in the food industry are produced and distributed by the German company, Elea GmbH. They have installed over 100 PEF systems that are in full-scale operation around the world in many different food and beverage sectors. PEF has become a standard operation technique in the potato-processing snack industry since 2010. Till now more than 80 PEF systems are used in this industry world-wide. Typical throughputs for systems in the chips industry lie between 1 and 10 t/h, and French fry processing the line capacities are considerably higher with 10 60 t/h (Siemer, To¨pfl, Witt, & Ostermeier, 2018)

12.3

Industrial equipment

The use of PEF requires a pulse modulator to supply high voltage pulses and a treatment chamber where the product is exposed to the electric field. Up until the 1990s, spark gaps and vacuum tubes with poor durability were applied for power switching. During the last decade the development of highpower semiconductors has allowed design of industry ready PEF systems with high treatment capacities. Today’s industrial scale systems are based on transformers or Marx generators. In the first case a low voltage switch is applied in combination with a pulse transformer. Marx generators use a stack of

Chapter 12 Industrial scale equipment, patents, and commercial applications

capacitors, charged in parallel and discharged in series to allow for a very high-power conversion rate. The typical average power of a PEF unit is in a range of 20 400 kW. PEF is applied continuously, while the food is pumped or conveyed through a treatment chamber containing at least two electrodes. The electrode configuration impacts the flow pattern, treatment homogeneity, and electrical properties, whereas overprocessed volume elements may cause unnecessary quality deterioration, underprocessed product can lead to product safety concerns. Colinear chambers have shown good treatment homogeneity and cleanability for pumpable products. Chamber diameters range from 2 mm in lab systems up to 100 mm in industrial units. For solid products (roots and tubers) forced transport is required and belts or rotating systems are used. Products are submerged in water to improve energy efficiency.

12.4

Current industrial applications

12.4.1

Mass transport enhancement

PEF treatment of fruit and vegetable mashes, such as those obtained from apples, grapes, or carrots, increases juice yield and enhances release of valuable compounds such as colors or antioxidants. Making use of continuous liquid solid-separation techniques such as belt presses or decanters, a high quality, premium juice can be produced at high yield without the need for maceration enzymes. Treatment of sugar beets with PEF increases extraction yields and reduces heat and energy requirements during sugar production. For grapes an enhanced release of anthocyanins and bioactive substances has been reported through the use of PEF. Similar results have been found for other plant tissues such as red beet, broccoli, or kale. Low energy use and short processing times make PEF a viable alternative to the traditional processes of mechanical grinding, hotbreak, and enzyme maceration. PEF induced release of intracellular moisture also allows acceleration of drying processes. For potato, onion, or bell pepper a drying time reduction of up to 25% was reported for convective air-drying following PEF treatment.

12.4.2

Cutting and peeling improvement

PEF-induced membrane permeabilization results in the loss of turgor pressure and significant tissue softening. As a result, subsequent handling, pumping, and/or cutting processes are

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Figure 12.3 Two parallel (2 3 25 t/h) Elea PEF systems installed in a commercial processing facility for French fries. PEF, Pulsed electric fields.

facilitated. After PEF treatment of potatoes using an energy input of 1 2 kJ/kg improved cutting is observed, causing less fracture and smoother cut surfaces. PEF is currently used to replace conventional preheating of potatoes (60 C, 30 min) and improve the cut quality for industrial production of French fries. Fig. 12.3 shows a PEF industrial potato processing system with a capacity of up to 60 t/h. In addition to reduced energy, time and water requirements, increased release of sugars and reduced fat uptake are major benefits. Besides potatoes, other products such as fresh or frozen vegetables benefit from PEF pretreatments and R&D work is currently focusing on that area. PEF can enhance peeling of fruits and vegetables. Following PEF treatment, tomato and prune peels are loosened and easily removed. In comparison to steam peeling the energy requirements for peeling are significantly lower. In contrast to lye peeling, no neutralization is required and pollution of effluents is reduced.

12.4.3

Shelf life extension of juices

Recently, the category of healthy, freshly squeezed fruit and vegetable juices has shown significant growth in the United States and Europe. PEF allows shelf life extension of fresh fruit and vegetable juices without compromising product freshness or quality. A treatment with an energy input of 100 120 kJ/kg results in a 5 log inactivation of microbes in orange juice. As

Chapter 12 Industrial scale equipment, patents, and commercial applications

temperature has a synergetic effect on PEF efficacy, combined approaches can be used to reduce the amount of electrical energy required and make use of (often existing) preheaters and cooling devices. In Fig. 12.4 an industrial installation for extension of shelf life in fruit juices is shown. Dependent on treatment intensity, the shelf life is increased from 7 to 10 days for untreated juice to up to 21, 40, or even 60 days for PEF treated juice. PEF-treated products are on market shelves in Germany, The Netherlands, and the United Kingdom. In the United States industrial scale tests are ongoing. Current PEF processing equipment has a maximum capacity of up to 5000 L/h. Larger volumes are processed through the use of parallel units. In comparison to a standard thermal processing of juices, the product heat load is significantly lower. The total processing costs including investment and operation are in a range of 0.02 $/L of product, making PEF a commercially viable alternative to other nonthermal processing techniques. Application of PEF to protein-based products such as dressings and dairy products is of high interest. The low extent of protein denaturation and fouling, as well as increased equipment uptime have been identified as major benefits of PEF in comparison to a traditional thermal pasteurization.

Figure 12.4 Elea PEF system installed in fruit juice factory, 2 units with a capacity of 1600 L/h each. PEF, Pulsed electric fields.

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12.4.4

Process control options

Whenever a new processing technology is applied in the food industry, it requires suitable process control and the establishment of a Hazard Analysis and Critical Control Points program. PEF processing for cell disintegration typically occurs at a noncritical control point, whereas PEF use for preservation occurs at a critical control point. The consistent delivery of sufficient PEF treatment intensity has to be maintained and recorded at all times. In preliminary research the required PEF treatment intensity and energy delivery is elaborated at the lab scale in challenge tests for each product type. Later, during industrial-scale processing, the energy delivery for each product type is continuously monitored by detection of pulse voltage and current. Power delivery to the product is validated by comparing the calculated expected product temperature rise to the measured product temperature rises both pre- and posttreatment. Making use of an internal algorithm any underprocessed product can be diverted or disposed of according to the manufacturer’s operation protocols.

12.5

Relevant early stage patents

Even considering the use of (pulsed) electric fields in a comparably new technology, there are more than 15,000 patents applied for or granted. Important early patents in application of pulsed fields for food treatment were filed by Heinz Doevenspeck in 1960, describing process and device for gaining different phases from dispersed systems (DE 1237541). In detail he identified that PEF shows the following advantages compared to existing technologies: (1) extensive suppression of electrolysis; (2) wide prevention of temperature increase; (3) high profitability by lowenergy consumption; (4) mild treatment of raw materials and preservation of biological activity; and (5) killing of pathogenic germs. In 1967 he filled another patent together with a German brewery. The patent has focused on a low temperature (25 C) conservation method for beer with the positive side effect of almost no changes of color and taste during the subsequent storage phase. Subsequently he has worked for Krupp, Germany, developing “ELCRACK” and “ELSTERIL” processes, for the inactivation of vegetative microorganisms in milk and fruit juices with an electric field strength up to 30 kV/cm, but

Chapter 12 Industrial scale equipment, patents, and commercial applications

heating due to high energy dissipation and consequently high costs of operation inhibited a successful industrial application. However, as early as 1950 the Ukrainian scientists Mil’kov and Zagorul’ko have filed a patent on a method of preparation and purification of sugar beet raw juice and an electroplasmolizator for implementing this method (SU 89009) (Zagorul’ko, 1958). Fig. 12.5 presents the developed system for the continuous electrical treatment. In this setup, electricity was applied between two rotating metallic belts (electrodes) 1 and 2. It was stated that the proposed methods are nonthermal, and an increase in temperature during the treatment for a time of 0.001 s was about 0.5 C. Later patents have focused on certain applications of PEF or specific pulse generator or treatment chamber design. PurePulse Technologies, San Diego, United States filed a patent on electric fields use in a range of 10 25 kV/cm for microbial inactivation. The effect on fruit juice quality was investigated by Dunn and Perlman (1987) showing an increase of shelf life of about 1 week. A continuous system for microbial decontamination and a colinear treatment chamber has been filed by Bushnell in the 1990s. For PEF use in vegetable, wine and sugar industry research groups from TU Berlin as well as Karlsruhe Research Centre have filed patents in the 1990s and early 2000s. Subsequently the focus in patent applications has been put on combination processes, for example, PEF use and subsequent drying or frying processes or the use of PEF to enhance uptake of active agents or enzymes into cell or tissue structure.

Figure 12.5 Scheme of belt type PEF treatment chamber (Sitzmann et al., 2016). PEF, Pulsed electric fields. Source: Reused with permission.

279

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Chapter 12 Industrial scale equipment, patents, and commercial applications

An example is the use of PEF for the conservation of plant material as in US8563060, EP2201084B1 of 2007. This invention relates to the plant material comprising with cryoprotectants in tissue by means of Vacuum Impregnation and PEF. That helps to maintain fresh-like structure, texture, aroma, and nutritional value of the products even after freezing/thawing. As a number of intellectual property rights have expired or not been continued for many PEF applications freedom to operate can be assumed. For specific pulse generator or treatment chamber designs, application on new products or combination processes or process control options a case by case examination will be required.

12.6

Conclusions and opportunities for the future

PEF application enables cell disintegration and microbial decontamination of food products. Recent developments of pulsed power systems have supported successful technology transfer, from lab scale to industrial application, of PEF processing for fruit juice and vegetable processing. Ongoing equipment design research will result in increased treatment capacities and development of additional applications of PEF to foods. Future PEF processing applications for shelf life extension of protein-based drinks, dressings, soups, dairy products and beer are likely, as are applications for extraction improvements in wine, micro- and macro-algae production. Bacterial endospores can be inactivated through the combined use of thermal and PEF processes. Research on continuous, low thermal load sterilization of pumpable foods is currently under development.

References Bazhal, I. G., Kupchik, M. P., Vorona, L. G., et al. (1984). Extraction of sugar from sugar beet in electrical field. Electronics Treatment of Materials, 1, 79 82. Botoshan, N. I., & Berzoj, S. E. (1994). The electroplasmolysis phenomenon in the biological media and the perspective of its application in food processing industry. Elektronnaya Obrabotka Materialov, 2, 73 76. Clark, P. (2006). Pulsed electric field processing. Food Technology, 60, 66 67. Doevenspeck, H. (1960) Verfahren und Vorrichtung zur Gewinnung der einzelnen Phasen aus dispersen Systemen. pp. 237 541. Dunn, J. E., & Pearlman, J. S. (1987). Methods and apparatus for extending the shelf life of fluid food products, US Patent, US4695472A, published 1997-09-22.

Chapter 12 Industrial scale equipment, patents, and commercial applications

Flaumenbaum, B. (1949) Electrical treatment of fruits and vegetables before extraction of juice. In: Proc Odessa Technol Inst Cann Ind, Vol. 3. pp. 15 20. Flaumenbaum, B. 1953. Commercial application of the method of electrical preprocessing fruits before pressing. In: Proc Odessa Technol Inst Food Refrig Ind, Vol. 5. pp. 37 50. Gossling, B. S. (1960). Artificial Mutation of micro-organisms by electrical shock. Grahl, T. (1994). Abto¨ten von Mikroorganismen mit Hilfe elektrischer Hochspannungsimpulse. TU Hamburg-Harburg. Grahl, T., Sitzmann, W., Ma¨rkl, H. (1992). Killing of microorganisms in fluid media by high-voltage pulses. In: G. Kreysa, A. J. Diesel (Eds.), DECHEMA biotechnology conferences. pp. 675 8. Kogan, F. (1968). Electrophysical methods in canning technologies of foodstuff. Kolpakov, E. K., Botoshan, N. I., Berzoj, S. E., & Zakharchuk, A. V. (1991). Intensification of a technological process for obtaining fish meal through application of electroplasmolysis. Elektronnaya Obrabotka Materialov, 1, 64 65. Siemer, C., To¨pfl, S., Witt, J., & Ostermeier, R. (2018). Use of pulsed electric fields (PEF) in the food industry. Sitzmann, W., & Heinz, V. (1996). Die schonende Herstellung naturbelassener Sa¨fte mit Hilfe eines physikalischen Niedertemperaturverfahrens. Food Technology Magazine, 7, 28 32. Sitzmann, W., Vorobiev, E., & Lebovka, N. (2016). Applications of electricity and specifically pulsed electric fields in food processing: Historical backgrounds. Innovative Food Science and Emerging Technologies, 37, 302 311. Available from https://doi.org/10.1016/J.IFSET.2016.09.021. Toepfl, S., Heinz, V., & Knorr, D. (2006). Application of pulsed electric fields technology for the food industry. In J. Raso, & V. Heinz (Eds.), Pulsed electric fields technology for the food industry fundamentals and applications (pp. 197 221). New York: Springer Science 1 Business Media, LLC. To¨pfl, S. (2006). Pulsed electric fields (PEF) for permeabilization of cell membranes in food- and bioprocessing Applications, process and equipment design and cost analysis. Technischen Universita¨t Berlin. Zagorul’ko, A. (1958). Obtaining of diffusion juice with the help of electroplasmolysis. Central Research Institute of Sugar Industry.

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Limitations of pulsed electric field utilization in food industry

13

Gianpiero Pataro1 and Giovanna Ferrari1,2 1 2

Department of Industrial Engineering, University of Salerno, Fisciano, Italy ProdAl Scarl
University of Salerno, Fisciano, Italy

13.1

Introduction

Pulsed electric field (PEF) is one of the most advanced nonthermal processing methods, which has received considerable attention during the last decades due to its potential to create valuable and sustainable alternatives to conventional methods in food processing, in which partial or total disintegration of biological (microbial, plant, and animal) cells is a crucial step. In PEF processing the food matrix is typically placed in direct contact with charged metal electrodes of either batch or continuous treatment chamber and exposed to repetitive (up to kHz) short duration (µs
ms) electric field pulses of low (0.1
1 kV/cm), moderate (1
5 kV/cm), or high intensity (15
40 kV/cm), supplied by a high-voltage pulse generator (Raso et al., 2016). The pulses commonly used in PEF treatments are unipolar or bipolar, with either exponential or square-wave shape. Depending on the treatment intensity, size, and morphological characteristics of biological cells, the application of electric pulses may cause reversible or irreversible pore formation on the cell membranes, referred to as electroporation or electropermeabilization (Kotnik, Miklavcˇ icˇ , & Mir, 2001), as well as the induction of local structural or functional changes in the food matrix with reduced energy costs (SolivaFortuny, Balasa, Knorr, & Martı´n-Belloso, 2009). As a result, various applications have been identified in different sectors of food industry, where PEF system might easily be implemented into existing processing lines due to its continuous flow operability with very short processing times while providing the food processor with the opportunity to produce new and value-added food products with enhanced quality attributes preferred by consumers. Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00013-6 © 2020 Elsevier Inc. All rights reserved.

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Chapter 13 Limitations of pulsed electric field utilization in food industry

At high treatment intensity ( . 15 kV/cm), PEF induces irreversible pores formation of cell membranes of microbial cells, which make the technology a suitable gentle alternative to traditional thermal processing methods for liquid food pasteuriza´ lvarez, Condo´n, & Raso, 2014). When applied to tion (Saldan˜a, A plant tissues at moderate electric field strengths (1
5 kV/cm), PEF causes irreversible permeabilization of cell membrane, which makes the technique suitable to replace energy- and time-consuming conventional (e.g., thermal, mechanical, or enzymatic) cell disintegration methods, as a pretreatment step for mass transfer improvement prior to dehydration, extraction, or pressing operation (Barba et al., 2015; Bobinait˙e et al., 2015; Donsı`, Ferrari, & Pataro, 2010; Mahnicˇ -Kalamiza, Vorobiev, & Miklavcˇ ic, 2014; Parniakov, Bals, Lebovka, & Vorobiev, 2016; Pataro et al., 2018). In addition, the application of low or moderate electric field strengths (,2 kV/cm) can also be used to induce local structural modification of plant tissues, which has been shown to facilitate unit operations of food industry, such as cutting and peeling, as well as to induce stress responses and secondary metabolite biosynthesis in fresh produce (Arnal et al., 2018; Soliva-Fortuny et al., 2009). In recent years, improvement in treatment chamber design that imparts more uniform treatment to food with minimum increase in temperature (Buckow, Baumann, Schroeder, & Knoerzer, 2011; Gerlach et al., 2008; Toepfl, Heinz, & Knorr, 2007), and the development of high pulsed power system that enables up-scaling of the volumes to be treated, led to the first industrial applications of the technique in the sector of fruit juice expression and preservation (Barba et al., 2015; Golberg et al., 2016), and, especially, in the potato processing industry where a number of PEF units with a capacity of up to 60 t/h are already in operation all over the world (Toepfl, 2018). However, although the technology is heading for wider industrial application, several limitations still hinder the commercialization of PEF technology and its integration in processes of food industry. One of the challenges is the development of more reliable and affordable pulse generation systems with sufficient electrical field strength, power, and repetition rate, as well as the optimization of the overall PEF system design, in order to fulfill current industrial requirements in terms of throughput and treatment uniformity. Moreover, several technological issues, economical pitfall, consumer acceptance, and regulatory aspects, as well as toxicity risks still

Chapter 13 Limitations of pulsed electric field utilization in food industry

remain and have to be addressed prior to the full exploitation of PEF technology in different sectors of food industry, especially in those requiring high treatment intensity. Most of these limitations are related to the unavoidable electrochemical reactions that occur at the electrode
food interface as a result of the current that is flowing through PEF treatment chamber, especially those leading to corrosion and fouling of the electrodes, electrolysis of water, migration of electrode material components, and chemical changes that may occur into the product stream under treatment. As will be discussed in more detail in the following sections of this chapter, these reactions are undesired and must be minimized, since they may affect PEF commercialization through safety, quality, process efficiency, equipment reliability, and cost aspects. Nevertheless, although electrochemical reactions and corrosion are well known in other fields, the occurrence of these side effects of PEF treatment has been recognized and discussed only since 1990s, when a method to avoid or limit electrochemical reactions and fouling of electrodes in a PEF treatment system was suggested (Bushnell, Clark, Dunn, & Lloyd, 1995a,b). Since then, several research groups have addressed the problem of electrochemical reactions in PEF treatment systems, mainly caused by increased industrial interest. Most of the attention has been focused on the phenomenon of metal release and electrode corrosion and on how these topics can be predicted and quantified (Gad & Jayaram, 2011, 2012a; Go´ngora-Nieto, Sepu´lveda, Pedrow, Barbosa-Ca´novas, & Swanson, 2002; Kotnik et al., 2001; Master, Schuten, & Mastwijk, 2007; Moonesan, George, Aucoin, & Jayaram, 2012; Morren, Roodenburg, & de Haan, 2003; Pataro, Falcone, Donsı`, & Ferrari, 2014; Pataro, Barca, Donsı`, & Ferrari, 2015a,b, 2017; Roodenburg, Morren, Berg, & de Haan, 2005a,b; Saulis, Rodait˙e-Risˇevicˇ ien˙e, & Snitka, 2007). However, no or very limited attention has been paid on the effect on chemical and sensorial properties of food-treated products and possible toxicity problems (Evrendilek, Dantzer, Li, & Zhang, 2004; Sun, Bai, Zhang, Liao, & Hu, 2011; Zhao et al., 2012). From all those studies, it has been highlighted that electrode reactions occurring in a PEF chamber are a very complex phenomena, whose extent depends on many factors, which can be classified as processing parameters, design parameters, and treatment medium characteristics (Table 13.1). Moreover, it has been also stated that although electrode corrosion and other electrochemical reactions are largely unavoidable in the long-term trials, especially when PEF is carried out under severe treatment conditions.

285

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Chapter 13 Limitations of pulsed electric field utilization in food industry

Table 13.1 Main parameters affecting electrochemical reactions during pulsed electric fields treatments. Process parameters

Design parameters

Treatment medium properties

Electric field strength Total specific energy Pulse length Polarity Frequency Pulse shape Flow rate Temperature

Treatment chamber • Configuration • Electrode material • Electrode area • Electrode surface roughness Pulse generator • Circuit topologies • Type of switch

Composition Electrical conductivity (σ) pH Halides (e.g., chlorides) Presence of gas bubble


Figure 13.1 Simplified scheme of a continuous flow PEF system with a parallel plate chamber configuration. PEF, Pulsed electric fields.

13.2

Electrochemical reactions during pulsed electric fields process

A PEF system mainly consists of a pulse generator electrically connected to a treatment chamber where two metal electrodes are placed in direct contact with a liquid food (or any electrolyte solution) (Fig. 13.1). Electrochemistry defines this system as an electrochemical cell, which is a device capable of either generating electrical energy from chemical reactions

Chapter 13 Limitations of pulsed electric field utilization in food industry

(galvanic cell) or facilitating chemical reactions by an external source of electrical energy responsible for driving an electrical current through the cell (electrolytic cell). When the PEF chamber is filled with an electrolyte solution, immediately at each electrode
electrolyte interface, in order to maintain the condition of electroneutrality, an ionic double layer is developed. This layer, which consists of charged particles and/or of orientated dipoles, is analogous, from an electrical point of view to a parallel combination of a resistor (Faradaic impedance) and a capacitor (Morren et al., 2003). When no external voltage is applied to the electrodes, only low-level reactions occur at each electrode
electrolyte interface, but the two competing reactions reach an equilibrium, whereby the currents are equal. This equilibrium exchange current flows across the interface in both directions resulting in a net current of zero (Morren et al., 2003). During pulse treatment, due to the application of a potential difference across the electrodes, an electrical current pass through the cell occurs, and charges build up across the double layer take place (Bockris, Reddy, & Gamboa-Aldeco, 2002). When the applied voltage is such that the potential drop across the double layer is below a certain threshold voltage, no electrochemical reactions occur, except some low-level reactions due to the exchange current. The current to charge the double-layer capacitor up to its threshold voltage (Uth), which is typical of the reaction potential of electrode material (B1
2 V), is called the charging current. How fast the double layer is charged is called the threshold time tth (in µs) which can be determined by Eq. (13.1) (Morren et al., 2003): tth 5

C 0dl U 0th j

ð13:1Þ

where j is the current density (in A/cm2) through the chamber, while the quoted parameters represent the equivalent values of the specific capacitance (capacitance per unit of area, Cdl, in µF/cm2) and reaction potential (Uth, in V) of the two
electrode
electrolyte interfaces in series (i.e., C 0dl 5 1=2 Cdl and U 0th 5 2Uth ). Specific double-layer capacitance for common electrode material are stainless steel 30 µF/cm2, platinum 48 µF/ cm2, titanium 50 µF/cm2, glassy carbon 250 µF/cm2, and DSA (dimensionally stable anode material) 2000 µF/cm2 (Amatore, Berthou, & Hebert, 1998; Scromeda & Katsube, 2008). When the external voltage that is applied to the cell is such that the potential drop across the double layer (Udl) overcomes the threshold voltage (Uth), in order to preserve the charge

287

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Chapter 13 Limitations of pulsed electric field utilization in food industry

conservation principle, electrochemical (Faradaic) reactions will occur: oxidation reaction (i.e., loss of electrons) will take place at the electrode surface which behaves as anode (Eq. 13.2) and reduction reaction (i.e., gain of electrons) at the electrode surface which behaves as cathode (Eq. 13.3) (Morren et al., 2003). A-An1 1 n  e2

ð13:2Þ

An1 1 ne2 -A

ð13:3Þ

where A is the generic species at the electrode
electrolyte interface and n is the number of electrons (e2). The current resulting from this change in oxidation state is termed the Faradaic current because it obeys Faraday’s law and is a direct measure for the rate of the redox reactions. If during PEF treatment unipolar pulses are applied, the electrode connected to high voltage will behave as anode, while the grounded electrode will behave as cathode. If, instead, bipolar pulses are applied, the cathode and anode interchange places according to the pulse repetition frequency. Therefore in this latter case, the electrochemical reactions of oxidation and reduction will occur alternatively at the same electrode site (Pataro et al., 2017; Roodenburg et al., 2005a). The electrode reactions can consist of a quite complicated chain of chemical reactions, involving mass transport of electro-active species to the electrode, electron transfer across the electrode interface, and the transport of the reaction products back to the solution (Morren et al, 2003). An overview of possible electrochemical reactions relevant to chemical changes of foods, gas evolution, formation of toxic compounds, and electrode corrosion is given in Table 13.2. Which of the half-reactions occurs depends on the relative ease of each of the competing reactions. As general rule, the reactions with the more negative half-cell reduction potential occur at the anode as oxidation and the reactions with the more positive half-cell reduction potential occur at the cathode as reduction (Pataro et al., 2017). After pulsing (i.e., when PEF system is switched off), due to either concentration differences around the electrodes or to surface material changes, the behavior of cell may shift from electrolytic to galvanic. Thus if the treatment chamber is not dried up, chemical reactions, which may involve food components, are likely to spontaneously proceed even with no external voltage applied (Pataro et al., 2017).

Chapter 13 Limitations of pulsed electric field utilization in food industry

289

Table 13.2 Possible electrochemical reactions at the electrode/medium interface. Electrochemical reaction

Threshold potential (V)a

Reaction nos.

11.36 11.23 10.70 0.00 20.83

(13.i) (13.ii) (13.iii) (13.iv) (13.v)

11.19 10.77 20.04 20.28 20.26 20.45 20.74 20.91 21.63 21.66 22.37 22.71

(13.vi) (13.vii) (13.viii) (13.ix) (13.x) (13.xi) (13.xii) (13.xiii) (13.xiv) (13.xv) (13.xvi) (13.xvii)

Electrochemical-induced changes in foodstuff

Cl2(g) 1 2e222Cl2(aq) O2(g) 1 4H1(aq) 1 4e222H2O(l) O2(g) 1 2H1(aq) 1 2e22H2O2(aq) 2H1(aq) 1 2e22H2(g) 2H2O(l) 1 2e22H2(g) 1 2OH2(aq) Metal release from electrodes

Pt21(aq) 1 2e22Pt(s) Fe31(aq) 1 e22Fe21(aq) Fe31(aq) 1 3e22Fe(s) Co21(aq) 1 2e22Co(s) Ni21(aq) 1 2e22Ni(s) Fe21(aq) 1 2e22Fe(s) Cr31(aq) 1 3e22Cr(s) Cr21(aq) 1 2e22Cr(s) Ti21(aq) 1 2e22Ti(s) Al31(aq) 1 3e22Al(s) Mn21(aq) 1 2e22Mn(s) Na1(aq) 1 e22Na(s)

a Standard reduction potentials with respect to normal hydrogen electrode (NHE), to which is arbitrarily assigned a half-cell potential equal to zero. Source: Data from Arning, M. D., & Minteer S. D. (2007) Electrode potentials. In C. G. Zoski (Ed.), Handbook of electrochemistry. Amsterdam, The Netherlands: Elsevier. pp. 813
827 (Arning & Minteer, 2007).

13.3

Effects of electrochemical reactions on the pulsed electric fields process

During PEF treatment, various electrochemical reactions can potentially occur, which may result in chemical changes in food products, electrode corrosion, electrode fouling, and electrolysis of water. In addition, some of the products of those electrochemical reactions may initiate a number of secondary chemical reactions involving food components, even after pulse treatment has been completed. Fig. 13.2 depicts the main side effects of all those electrochemical and chemical processes, which will be discussed in more detail in the following sections.

290

Chapter 13 Limitations of pulsed electric field utilization in food industry

Figure 13.2 Side effects of electrochemical reactions during PEF treatment. PEF, Pulsed electric fields.

13.3.1

Electrode corrosion

Electrode corrosion is one of the main consequences of the electrochemical reactions occurring at the electrode
electrolyte interface of a PEF treatment chamber. The dissolution of the anode material due to oxidation of the metal of the electrode, as described by Reactions (13.vi)
(13.xvi) in Table 13.2, is responsible for this phenomenon. Although the concentration of dissolved metals in the treated medium does not represent the actual rate of electrode reactions due to the deposition of part of the dissolved metals on the electrode surface, it has been used as an index to show how electrode’s corrosion varies with various parameters. For instance, voltage, pulse shape, pulse duration and frequency, current magnitude and chamber geometry, which play a role in the charging process of the double-layer capacitors (Eq. 13.1), are from great impact on the type and amount of corrosion products (Gad & Jayaram, 2011, 2012a; Kotnik et al., 2001; Master et al., 2007; Moonesan et al., 2012; Morren et al., 2003; Pataro et al., 2014; Pataro, Barca, Donsı`, & Ferrari, 2015b; Roodenburg et al., 2005a,b). Similarly, also the electrode material through its chemical inertness and Cdl value (Eq. 13.1) can be an important factor affecting the corrosion rate (Amatore et al., 1998; Go´ngora-Nieto et al., 2002). The composition as well as the chemical
physical properties of the treatment medium can also play an important role (Gad & Jayaram, 2012b; Pataro et al., 2014, 2015b; Roodenburg et al., 2005b). Many food products contain chlorides and have pH between 3 and 5, which is a very corrosive combination. Halides such as chlorides, in fact, are active species that may contribute to the

Chapter 13 Limitations of pulsed electric field utilization in food industry

enhancement of the oxidation half-cell reactions at the anode, including those causing the release of metals from the electrodes (Pataro et al., 2014, 2015b). Low-pH-treated medium often results in higher concentration of migrated metals (Gad & Jayaram, 2011, 2012a; Pataro, Donsı`, & Ferrari, 2012; Roodenburg et al., 2005b). Thus acidic food products, such as most fruit juices, may face higher problems with electrode material migration than nonacidic products, especially when PEF is carried out under severe processing conditions using electrochemically active electrode material. Moreover, highly conductive foods such as tomato juice, milk, and orange juice may experience a higher rate of electrode material migration, due to the high current flow that pass through the medium with high conductivity (Gad & Jayaram, 2012b; Pataro et al., 2012). Although the electrode corrosion might represent an opportunity to introduce essential minerals into the processed foods, the metal ions migrated into the PEF-processed foods are basically contaminants and may cause toxicity problems, as well as affect food quality, equipment reliability, treatment efficiency, and electrode lifetime (Evrendilek et al., 2004; Morren et al., 2003; Pataro et al., 2014; Roodenburg et al., 2005a, 2005b; Saulis et al., 2007).

13.3.1.1

Food safety and regulation

For the safety aspect of PEF processing, the type and amount of electrode material released in the processed products must be within the health safety regulations before introducing it as processed food to the market (Gad & Jayaram, 2012a; Roodenburg et al., 2005a). From a toxicological point of view, in fact, the major risk to public health is associated with the migrated metals in the processed products. Different regulations dealing with contaminants and toxins in food dictated by the European Union are mainly concerned with the presence of heavy/toxic metals, rather than with the main metallic elements constituting the materials used as electrodes in a PEF chamber. In the Commission Regulation (EC) No 1881/ 2006 (2006) and Codex Alimentarius Commission (CODEX STAN 193-1995) (1995), there are standards stated only for the maximum levels of heavy metals (arsenic, cadmium, lead, and mercury) in certain foods. Similarly, the Codex General Standard for Fruit Juices and Nectars (CODEX STAN 247-2005) (2005) states, “the products covered by the provisions of this Standard should comply with those maximum levels for contaminants established by the Codex Alimentarius Commission for these

291

292

Chapter 13 Limitations of pulsed electric field utilization in food industry

products.” The European legislation, on the quality of water intended for human consumption (Directive No 98/83/EG), is the only one which mentions the main metallic elements of stainless steel, which is one of the most popular electrode materials of PEF chamber. The maximum allowable values (MAV) stated by this standard for iron, chromium, nickel, and manganese are 200, 50, 20, and 50 µg/L, respectively. There are no maximum values mentioned for the elements of other materials used as electrode in a PEF chamber, such as titanium and platinum. The migrated concentration of metallic elements from the stainless steel electrodes of a PEF chamber in liquid medium are summarized in Table 13.3 and compared with the MAV of iron, chromium, nickel, and manganese mentioned in the European legislation for drinking water (Directive No 98/83/EG). Although any comparison among data found in current literature is very difficult, it can be concluded that the migration of electrode material to the liquid food during PEF processing is unavoidable. However, depending on process conditions, composition (e.g., the presence of halides) and properties (e.g., pH and conductivity) of food products, and chamber geometry, the concentration of the main metallic elements may remain within the legislation limits (Directive No 98/83/EG). These data, therefore, prove that in a well-designed PEF system, the metal release may be effectively reduced, as will be discussed in more detail later in this chapter.

13.3.1.2

Food quality

Apart from safety aspects, the quality of PEF-processed foods should be capable of competing with other conventional preservation methods. Although several studies have concluded that PEF treatment can preserve quality and sensory attributes of food products (Buckow, Ng, & Toepfl, 2013; Odriozola-Serrano, Aguilo´-Aguayo, Soliva-Fortuny, & a Martı´n-Belloso, 2013), the released electrode material may cause alteration in color, flavor, and taste of PEF-processed foods, which may stand against consumers’ acceptance to this technology (Evrendilek et al., 2004; Gad & Jayaram, 2012b; Sun et al., 2011). In particular, with respect to sensory “taste” aspect, if it is assumed that the consumer can sense the increase in the metal content in terms of its percentage increase from the initial value, then food products may face a problem of metallic mouth feeling (Gad & Jayaram, 2012b). However, because the food composition itself may enhance or inhibit any metallic mouth feeling, accurate

Table 13.3 Migrated concentration of metallic elements from stainless steel electrodes in pulsed electric fields processed liquid food products. Treatment medium

Treatment conditions

Metal concentration (µg/L) Fe

Trizma-HCl buffer (pH 7, σ 5 2 mS/cm) Trizma-HCl buffer (pH 7, σ 5 3.5 mS/cm) Citrate-phosphate buffer (pH 7, σ 5 2 mS/cm) Citrate-phosphate buffer (pH 3.5, σ 5 2 mS/cm) 20 mM NaCl solution (pH 7, σ 5 2.2 mS/cm) Orange juice (pH 3.8, σ 5 3 mS/cm) Apple cider (pH 3.8, σ 5 2.8 mS/cm) Orange juice (pH 4.1, σ 5 4.5 mS/cm) Beer (pH 4.3, σ 5 0.99 mS/cm) Milk (2% fat) (pH 6.9, σ 5 5.5 mS/cm)

Parallel plate Uniplar pulses 31 kV/cm, 100 J/mL, 2 L/h Parallel plate Unipolar pulses 31 kV/cm, 100 J/mL, 2 L/h Parallel plate Unipolar pulses 31 kV/cm, 100 J/mL, 2 L/h Parallel plate Unipolar pulses 31 kV/cm, 100 J/mL, 2 L/h Cofield Unipolar pulses 30 kV/cm; 50 J/mL, 360 L/h Cofield Unipolar pulses 30 kV/cm; 50 J/mL, 360 L/h Opposing convex electrode surface 40 kV/cm; 300 J/mL, 30 L/h Opposing convex electrode surface 40 kV/cm; 300 J/mL, 30 L/h Opposing convex electrode surface 40 kV/cm; 300 J/mL, 30 L/h Opposing convex electrode surface 40 kV/cm, 300 J/mL, 30 L/h

Cr

Ni

References

Mn

4278

389

472

46

Pataro et al. (2014)

4928

769

916

108

Pataro et al. (2012)

17.3

, LOD

, LOD

, LOD

Pataro et al. (2012)

48.3

7

7

, LOD

Pataro et al. (2012)

0.23

, 0.94

, 1.04

, LOD

Roodenburg et al. (2005a)

13

, LOD

, LOD

, LOD

Roodenburg et al. (2005b)

808

22

NA

NA

Gad and Jayaram (2012b)

1029

26

NA

NA

Gad and Jayaram (2012b)

245

17

NA

NA

Gad and Jayaram (2012b)

317

13

NA

NA

Gad and Jayaram (2012b) (Continued )

Table 13.3 (Continued) Treatment medium

Treatment conditions

Metal concentration (µg/L) Fe

Beer (σ 5 1.6 mS/cm)

Anthocyanins solution

Citrate-phosphate buffer (pH 3.5, σ 5 2.2 mS/cm) MAVa

Cofield Bipolar pulses 41 kV/cm, 175 µs, 3.6 L/h Parallel-plate Unipolar pulses 10 kV/cm, 8000 µs Cofield Bipolar pulses 28 kV/cm, 75 J/mL, 125 L/h

Cr

Ni

References

Mn

2859

526

NA

134

Evrendilek et al. (2004)

32,730

20,630

10,870

670

Sun et al. (2011)

3

NA

NA

NA

Kim and Zhang (2010)

200

50

20

50

Directive No 98/83/EG

LOD, Limit of detection; NA, not available. a MAV means maximum allowable values for iron, chromium, nickel, and manganese in water intended for human consumption as stated by the European legislation for drinking water (Directive No 98/83/EG).

Chapter 13 Limitations of pulsed electric field utilization in food industry

conclusions require carrying out sensory tests by trained and/or untrained panelists. As an example, by comparing the concentration of metallic elements released from the stainless steel 316 electrodes of a cofield chamber in the beer samples before and after the PEF processing, a significant increase has been observed in the concentration of iron, chromium, manganese, and zinc ions (Table 13.2). Sensory analysis revealed that the migration of these metal elements into the PEF-treated beer samples impacted on the flavor of this carbonated beverage. Some of the panelists indicated a metallic mouth feeling in some of the samples. However, except for flavor and mouth feeling, there was no significant difference in foam condition, color, and overall acceptability of the control and PEF-treated samples (Evrendilek et al., 2004). In conclusion, sensory analyses should be performed to evaluate the acceptance of PEF-processed products against either conventionally or unconventionally processed foods or fresh products.

13.3.1.3

Electrode lifetime and equipment reliability

Corrosion can cause serious damages to the electrodes, whose surface roughness can increase as a direct consequence of either metal release from the anode or partial deposition of metal oxides on the cathode. The erosion of the electrode surface is generally more severe on the high voltage electrode (anode) surface than ground electrode (cathode) (Kim & Zhang, 2011; Pataro et al., 2014; Saulis et al., 2007). Long-term trials or large amount of electric charge transferred through the unit area of the electrode made of noninert material can markedly increase the electrode erosion to such an extent, which might create distortion or local enhancements of the electric field within the treatment zone. This may represent one more source of the possible inhomogeneity of the PEF treatment, in addition to those typically linked to electrode geometry, temperature profile throughout the treated product, and flow dynamics during the treatment, which may markedly impair PEF treatment uniformity, as well as reduce treatment efficiency during the operation (Donsı`, Ferrari, & Pataro, 2007; Jaeger, Meneneses, & Knorr, 2009; Pataro, Senatore, Donsi, & Ferrari, 2011; Saulis et al., 2007). The increase in surface roughness may also facilitate the occurrence of the dielectrical breakdown of food, which is observed as a spark, thus limiting the intensity of the electric pulses that could be applied to the treatment chamber (Saulis et al., 2007). Because the ultimate goal of

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some applications, such as liquid food pasteurization by PEF, is to reach the desired level of microbial inactivation without over processing, each cell has to be exposed to an electric treatment of sufficient intensity and any inhomogeneity of the electric field is undesirable (Pataro et al., 2011; Saulis et al., 2007). Thus it could be stated that condition of electrode surface could be considered as critical control point in food pasteurization process, since any damage to the electrode surfaces could arise some food safety risk. Moreover, the occurrence of dielectric breakdown of the food is generally characterized as causing damage on the electrode surfaces in the form of pits as well as promoting undesired electrochemical reactions, which may lead to the formation of high reactive species (e.g., free radicals), evolution of gas bubbles, and increased pressure, leading to treatment chamber explosions. Furthermore, corrosion and arcing may contribute to reduce the reliability and lifetime of pulse generator (e.g., switching devices) (Toepfl et al., 2007) as well as drastically reduce the lifetime of the electrodes to few hours of operation (Kim & Zhang, 2011; Pataro et al., 2014; Roodenburg et al., 2005b; Saulis et al., 2007), thus reducing the technical feasibility of PEF technology. In particular, predictions of lifetime expectancy of the electrodes based on the measured values of the amount of dissolved metals after PEF processing and microscopy observation of morphology of electrode surface highlighted the key role placed by the chemical properties of the electrode material, the processing conditions, the chamber configuration, and the treatment medium characteristics. As an example, by comparing the corrosion resistance of four different electrode materials, titanium, platinized titanium, stainless steel 316, and boron carbide during PEF process (28 kV/cm, 76 J/mL) of a citrate-phosphate buffer solution (pH 3.5, σ 5 2.2 mS/cm), it has been found that titanium was the most corrosion-resistant material as electrode in PEF system. After 35 h of PEF process, titanium electrodes showed no noticeable changes in the surface morphology, while platinized-titanium showed the first signs of corrosion and erosion already after 14 h. Stainless steel 316 electrodes showed clear evidence of corrosion in both ground and high electric field electrodes after 12-h PEF processing exhibiting severe pitting corrosion. Boron carbide was the least corrosion-resistant material in PEF processing, being corrosion noticeable by the eyes already after 12 h, while other materials were not, after the same processing time. Moreover, it has been also shown that the durability of stainless steel electrodes can be further shortened to less than 3 h of PEF (21 kV/cm, 100 J/mL) operation

Chapter 13 Limitations of pulsed electric field utilization in food industry

when contacted with a treatment medium containing chlorides, which is known to trigger intense localized dissolution of the metal surface (pitting corrosion) (Pataro et al., 2014).

13.3.2

Electrode fouling

During PEF processing of food products, such as milk or protein-rich solutions, a film of food particles, which can consists of protein and or other materials (referred herein as a fouling agent), can collect, or agglomerate, on the electrode(s) surface of the treatment chamber (Fig. 13.3). The formation of this film, or fouling of the electrode(s), is an undesirable side effect that is believed to be due to electrochemical mechanism, such as electrophoresis. Specifically, under the influence of the external electric field, charged particles (e.g., relatively large protein molecules), suspended in a fluid food product, are moved toward the oppositely charged electrode and concentrated within a boundary layer that is adjacent to the electrode (Bushnell et al., 1995a,b). During electrophoretic process the electrodes themselves, that is, the materials from which the electrodes are made, do not participate in electrophoresis other than to generate the electric field (Bushnell et al., 1995a,b).

Figure 13.3 Electrochemical mechanism of electrophoresis occurring in the operation of the PEF treatment chamber. PEF, Pulsed electric fields.

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For some products, significant fouling of the electrode can occur after only a few minutes of system-operating time. For other products the time that the fouling of the electrodes becomes significant can be a few hours or longer. It has been noted that, for example, when the food product consists of raw milk, the fouling occurs only on the anode (i.e., the electrode to which the electrons flow); the cathode (i.e., the electrode from which the electrons flow) remains relatively free of any film buildup or agglomeration (Bushnell et al., 1995a,b). Unfortunately, the agglomeration of the fouling agent on the electrode(s) during extended processing periods can cause several problems such as local electric field distortion and arcing within the treatment zone, thus lowering the PEF performance, and possibly arising safety problems. In addition, it can cause fouling or contamination of the system, and in some cases, can even cause the flow of fluid food product to stop (Bushnell et al., 1995a,b).

13.3.3

(Partial) Electrolysis

Liquid, solid, or mashed food products subjected to PEF treatment contain variable amount of water. Electrolysis of water is, therefore, one of the most likely reactions that can result from PEF processing of food products (Bushnell et al., 1995a,b). The primary products of the electrolysis of water are oxygen (O2 gas) at the anode and hydrogen (H2 gas) at the cathode. The reaction equations are given in Table 13.2 (Reactions 13.ii, 13.iv, and 13.v). The liberation of these gaseous molecules after electrolysis might trigger other undesired electrochemical reaction involving food components and electrode materials as well as the formation of electrical arch inside the treatment chamber, thus causing technological and food-safety problems and reducing the treatment efficiency. Molecular oxygen generated by electrolysis, for example, can promote the oxidative degradation of several food components, particularly phenolic compounds, lipids, and vitamins such as ascorbic acid (Vitamin C), as well as lead to the formation of toxic compounds, such as H2O2 (Reactions 13.ii and 13.iii in Table 13.2). Moreover, oxygen may also involve electrode corrosion, or formation of insulating species on the electrode surfaces partially passivating the electrodes (Tzedakis, Basseguy, & Comtat, 1999). Because of the high flammability and explosive nature, uncontrolled liberation of hydrogen might pose safety concerns

Chapter 13 Limitations of pulsed electric field utilization in food industry

in large-scale continuous PEF systems. Sometimes, anodic half-reactions for electrode corrosion (Reactions 13.vi
13.xvi in Table 13.2) may be accompanied with one of the cathodic halfreactions for electrolysis (Reactions 13.iv and 13.v in Table 13.2) resulting in electrode corrosion with H2(g) generation. In addition, especially when there is a significant amount of chloride ions in the treated medium, cathodic half-reactions for electrolysis (Reactions 13.iv and 13.v in Table 13.2) may also be coupled with the anodic half-reaction (Reaction 13.i in Table 13.2), resulting in H2(g) and Cl2(g) generation. Moreover, gas bubbles formed by electrolysis, or present in the case of sparking products or released due to local increase in temperature, have a lower dielectric breakdown strength than the liquid media. The different dielectric properties of gas bubbles can cause a significant drop in electric field strength, in particular, in boundary regions of bubbles (Go´ngora-Nieto, Pedrow, Swanson, & Barbosa-Ca´novas, 2003), possibly leading to underprocessing of treated food product, thus causing food-safety problems. In addition, the lower dielectric permittivity of air and gas bubbles causes a concentration of potential within the bubbles increasing the chance for a dielectric breakdown and arcing, thus reducing the treatment efficiency and the lifetime of the PEF equipment (Toepfl et al., 2007).

13.3.4

Secondary reactions

Products generate from electrochemical reactions during PEF treatments may initiate a number of secondary chemical reactions also involving food constituents, which may lead to changes in pH, electrical conductivity, color, flavor, and chemical composition of treated food products, as well as the formation of toxic compounds, even after pulse treatment has been completed (Morren et al., 2003). Metal ions that are migrating from the electrodes into the medium can participate in several secondary chemical reactions (Rodait˙e-Risˇevicˇ ien˙e, Saule, Snitka, & Saulis, 2014). For example, iron ions (Fe12 and Fe13) released from the stainless steel anode behave as a Lewis acid and may hydrolyze the water molecules in the medium, according to the following reaction (Eq. 13.xviii): ð32nÞ1 Fe31 1 nH1 ðaqueousÞ 1 nH2 O3FeðOHÞn

ð13:xviiiÞ

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Due to this reaction, the pH is reduced at the anode. Similarly, secondary reaction that generates OH2(aqueous) ions (Eq. 13.xix) may have considerable effects in increasing the pH of the treated medium in the vicinity of the cathode: 2 31 Fe21 ðaqueousÞ 1 H2 O2 3FeðaqueousÞ 1 OH 1 OH

ð13:xixÞ

where H2O2 can be generated by Reaction (13.iii) (Table 13.2). Numerical and experimental results showed pH-shifts of up to 4.04 units already after PEF treatment of 34 µs at electric field strength of 10 kV/cm of a salt solution with an initial pH of 7.1 (Meneses, Jaeger, & Knorr, 2011). These local changes of pH occurring during a PEF treatment are important to be considered since activity and stability of enzymes and microbial resistance to PEF treatments differ considerably at different pH values (Meneses et al., 2011). Moreover, pH changes can affect degradation of natural antioxidant compounds such as ascorbic acid (Assiry, Sastry, & Samaranayake, 2006), as well as the stability of pigments such as anthocyanins (Sun et al., 2011), thus potentially altering color, nutritional and functional properties of food products. Since food systems are generally rich in ligands, the migrated transition metal ions can form various coordination complexes. Those metal complexes typically have characteristic colors, and therefore, they may involve alteration of color of the processed foods. As an example, change in visual color of cyanidin-3glucoside and cyanidin-3-sophoroside solutions in PEF processing has been related to the copigmentation with metallic ions (Sun et al., 2011). It is also known that some transition metal ions have catalytic effects for certain food reactions, such as lipid oxidation. Therefore the electrode corrosion may have an impact on flavor quality of the processed food products. In addition, electrogenerated metal ions, such as Fe21(aq) and Fe31(aq) can undergo further spontaneous reactions with OH2 in the aqueous stream to form iron hydroxide Fe(OH)2(s) and/or Fe(OH)3(s). These compounds, in turn, can react with various compounds present in the medium by complexation or electrostatic attraction, which is usually followed by coagulation. Therefore if organic compounds are present in the solution, iron ions can make complexes with them (Rodait˙eRisˇevicˇ ien˙e et al., 2014). Products derived from electrolysis and corrosion reactions occurring in the microenvironments of the electrodes may also generate oxygen-containing free radicals, such as hydroxyl (•OH) (Eq. 13.xix), hydroperoxyl (•OOH), and superoxide anion (O2•2) radicals, as well as the molecules such as H2O2 (Reaction 13.iii in

Chapter 13 Limitations of pulsed electric field utilization in food industry

Table 13.2) and singlet oxygen (1O2). These reactive oxygen species (ROS) can aggressively attack food components, in particular, lipids, vitamins, and amino acids/proteins, causing oxidative degradation of those nutrients, as well as consume antioxidants present in food formulations (Zhao et al., 2012). To this purpose, it has been shown that lecithin, a phospholipid extracted from yolk, was oxidized under PEF treatment, likely due to the oxidative agents (ROS) induced by PEF. Therefore in addition to the nutritional losses, the oxidation of food components leads to production of undesirable flavor, toxic, and color compounds, which make foods less acceptable or unacceptable to consumers. In products containing chloride compounds, as many food products do, it cannot be excluded that PEF can result in the production of active chlorine species with high redox potentials, including dissolved chlorine gas (Cl2) produced by electrolysis at the anode (Reaction 13.i, in Table 13.2), hypochlorous acid (HOCl) formed by the hydrolysis of Cl2 (Eq. 13.xx), and hypochlorite anions (OCl) (Eq. 13.xxi) (Zhao et al., 2012): Cl2 1 H2 O-HOCl 1 H1 1 Cl2 ðpH , 5Þ

ð13:xxÞ

HOCl-OCl2 1 H1 ðpH . 5Þ

ð13:xxiÞ

From one side the production of these compounds can cause the treated product to be toxic even after pulse treatment has been completed. On the other hand, however, it has been also suggested that the effect of PEF on microorganisms is at least partly the result of a secondary process, in particular, the production of chlorine compounds and ROS, which can act as bactericides, thus improving the pasteurization efficiency of PEF treatment. Reyns, Diels, and Michiels (2004) reported the generation of bactericidal and mutagenic compounds by a PEF treatment, even if they operated with 300 pulses at a pulse length of 2 µs and 26.7 kV/cm, a treatment intensity much higher than required for liquid food preservation. Therefore particular attention has to be paid, from one side, to minimize the electrochemical changes in PEF process, as will be described in the next paragraph; on the other hand, role played by the electrochemical reaction products with respect to chemical food safety and microbial safety needs to better elucidated.

13.4

Limitation of electrochemical reactions

Electrochemical reactions and therefore electrode corrosion, electrode fouling, electrolysis, and, eventually, chemical changes

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in the processed product are due to nature of PEF process and are unavoidable when typical conditions for PEF processing are applied. This is especially true for applications requiring high treatment intensity (e.g., microbial inactivation). Several causes for electrochemical reactions have been identified. A major cause is the presence of direct (DC) leak currents through the treatment chamber occurring when the switch in a pulsed power system is open. This especially occurs when the switching devices are configured by semiconductor components, which are known to be poor electrical insulators under high-voltage conditions. Solid-state devices as thyristor and insulated-gate bipolar transistor are based on semiconductor technology. The extent of electrochemical reaction and corrosion that originate from DC leak currents can be severe but can be avoided by using pulse transformers (at the expense of deviations from an ideal pulse shape) and by applying a DC offset compensation during pulsed operation (Mastwijk, 2007). A second cause is related to the current that is flowing through PEF treatment chamber during the pulse treatment and the consequent charging process of the double-layer capacitor. In order to prevent the double-layer capacitor from charging to a potential greater than the reaction potential, as well as to avoid the cumulative buildup of charges that occur, all the residual charges from one electrode during the discharge period must be removed so that a “zero net charge” is delivered (Bushnell et al., 1995b). Fortunately, electric pulse parameters, treatment chamber design, and electrode material are important parameters that can help to avoid full charging of the double-layer capacitors, thus allowing to control or reduce the extent of electrochemical reactions. However, during repetitive pulsing, it is necessary to provide some mechanism to reset the electrodes to zero potential between pulses. Automatic discharge can be obtained by applying symmetric or asymmetric bipolar pulses, which may help to significantly reduce the amount of electrochemical reactions. Experiments, in fact, have shown that some of these reactions are partially reversed if the pulse is immediately followed by a pulse with opposite polarity (Kotnik et al., 2001; Roodenburg et al., 2005a). When unipolar pulses are applied, instead, a key role is played by the pulse repetition frequency as it determines the time available for the double layer to lose the charge accumulated in the time elapsing between the deliveries of two consecutive electric pulses to the PEF chamber. Therefore in order to

Chapter 13 Limitations of pulsed electric field utilization in food industry

minimize the extent of electrode reactions utilizing unipolar pulses, the PEF treatment system should provide the energy required for the specific application utilizing sufficiently low pulse repetition frequency (Pataro et al., 2014, 2015b). The use of multiple treatment chamber in line and electrically connected in parallel might be a strategy to achieve the high flow rates required for industrial applications while keeping as low as possible the pulse frequency. In addition, to minimize the extent of the electrode reactions to a tolerated maximum level, the pulse length of the applied pulses should be shorter than the maximum pulse length defined in Eq. (13.1), so that only a small portion of the applied potential builds up across the two double-layer capacitors (Morren et al., 2003). The maximum allowable pulse length depends on the current density and the electrochemical properties of the electrode material (Eq. 13.1). The current density, in turn, is related to the applied voltage, medium conductivity, and chamber geometry. A higher field strength in the same treatment chamber (i.e., a higher applied voltage) results in a higher current density. Thus for higher field strength, the pulse duration should be decreased (Morren et al., 2003). The geometry of the treatment chamber along with medium conductivity has a decisive impact on the intrinsic electrical resistance of the chamber and, therefore, on current density. PEF treatment of food products with different conductivity (in the same chamber) will require adjustment of pulse length. As an example, orange juice, which has a typical conductivity of 0.3 S/m, can be treated with longer pulses than tomato juice, which has a typical conductivity of 2 S/m. On the other hand, for the same treated product, usage of a treatment chamber configuration featuring relatively high value of the electrode area (i.e., low intrinsic electrical resistance, such as in the case of parallel plate configuration) will lead to higher current density, thus requiring the application of shorter pulse. In contrast, usage of a treatment chamber with low electrode area (i.e., high intrinsic electrical resistance, like for a colinear electrode configuration) will result in lower value of the current density, thus allowing the use of higher pulse length. Hence, it can be concluded that for PEF treatment of a given food product, strategies such as reduction of the build-up area (as in the case of cofield chambers), as well as keeping the applied voltage and pulse length as the minimum value required for generating sufficient electric field and electrical energy for the specific application, can help to significantly reduce the amount of electrochemical reactions.

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On the other hand, for PEF treatment of a food product using a certain field strength, the only way to increase the maximum allowable pulse length is to increase the value of Cdl (Morren et al., 2003). As previously reported in this chapter, the value of the double-layer capacitance depends on the type of material used and on the treatment chamber geometry. Some materials are developed with a very high value of Cdl (stainless steel , platinum , titanium , carbon) (Amatore et al., 1998; Go´ngora-Nieto, et al., 2002). These materials can be used to increase the maximum allowable pulse length. However, although the selection of pulse conditions for PEF processing and electrode material with high Cdl value allows the potential for electrochemical change to be minimized, it should be noted that these conditions do not eliminate the potential for all electrochemical reactions, as some reactions will have formal potentials less than this minimum value. However, they do limit the electrochemical reaction potential to those having formal potentials less than about that of the selected cutoff. Maybe coating of the electrodes with conductive polymers might help to further reduce corrosion (Morren et al., 2003). In addition, selecting more stable electrode material can help to prevent corrosion and food contamination. Titanium can be recommended as electrode material in PEF system due to its high corrosion resistance, which comes from the formation of protective titanium oxide film on the surface, leading to long lifetime and toxicological safety (Kim & Zhang, 2011). PEF treatment of packaged food without direct contact to the electrodes has been also suggested as a way to avoid both electrode corrosion and postprocess contamination (Roodenburg et al., 2010). This will require the development of food grade plastic conductive (film) electrodes to be integrated within the package for prepacked PEF treatment. However, before this new class of electrode material can be utilized in PEF treatment systems, several issues need to be considered in more detail. For instance, the material electrodes used for PEFinpack treatment will need to be integrated in a (multilayered) package that should have certain gas permeability. Also how a sufficient (and homogeneous) electric field strength can be induced or if the required pulse energy can be transferred into the product will have also to be addressed (Roodenburg et al., 2010). Finally, the interactions between electric field applied and food grade packaging material need to be elucidate, since PEF could trigger changes in the chemical compounds that are incorporated within polymeric packaging materials leading to the formation of (hazardous) chemicals, as well as promote

Chapter 13 Limitations of pulsed electric field utilization in food industry

their migration to the food product. All these aspects need to be clarified before commercial application of PEF to prepacked foods in order to avoid that any potential transfer to the food does not raise safety concerns changes the composition of the food in an unacceptable way or deteriorates its taste and odor. A further cause of electrochemical reactions is represented by the occurrence of dielectric breakdown of food and associated arcing, which cause current flow in a narrow channel and promote undesired electrochemical reactions, bubbles formation, and electrode damages due to pitting corrosion. Intrinsic electrical resistance, homogeneity of the electric field strength within the treatment zone, and reduction and generation of enhanced field areas are some other important design criteria for avoiding the occurrence of dielectric breakdown. In addition, the presence of gas bubbles should be avoided by degassing the treatment media before treatment, processing under pressure, particularly, in the case of sparkling products and avoiding electrochemical effects at the electrode/ media interface. Finally, as previously described in this chapter, the presence of electrochemical reaction products in the processed food, such as metal ions released from the electrodes of the PEF chamber or ROS generation, may arise safety problems. However, it should be noted that several compounds naturally present in food formulations or added during their preparation could contribute to mitigate the issues associated with the presence of these high reactive species. As an example, citric acid is widely used in the food and beverage industries as an acidulant, pH control agent, and flavoring. However, it is also one of the well-known sequestrants frequently used in food formulations to chelate metal ions that catalyze certain food reactions, such as lipid oxidation, thus, giving protection from the development of off-flavors and off-odors in certain foodstuffs. Moreover, since food systems are inherently complex and consist of natural antioxidants, such as tocopherols, and other phenolics, polyphenolic compounds, and vitamins, some amount of electrochemically generated ROS could be tolerated without undergoing significant changes during long storage periods. For instance, it has been shown that vitamin C, as a natural antioxidant widely contained in foods, could effectively quench free radicals under PEF treatment and inhibit the oxidation of lipid, representing a way to minimize the impact of PEF treatment on food quality (Zhao et al., 2012). However, this is an area that has not been fully elucidated, and further research is required.

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13.5

Conclusion

Commercial exploitation of PEF technology in food industry appears to be, at present, more realistic and focused to applications that require low or moderate treatment intensity, such as those based on the induction structural modifications or permeabilization of plant tissues. In the food sector of fruit-juice preservation, instead, where high-treatment intensity is required, in spite of the first industrial application, several disadvantages and pitfall still remain, which hinder the commercialization of PEF technology. In this food sector a task, still challenging, is the development of PEF systems capable of fulfilling current industrial requirements in terms of high-volume capacity, food safety regulation, long-term reliability, and cost aspects. Moreover, the electrochemical reactions that unavoidably occur under the typical PEF processing conditions required for food preservation, especially those leading to corrosion and fouling of the electrodes, electrolysis of water, migration of electrode material components, and chemical changes, is considered one of the challenges facing the commercialization of the PEF technology. However, due to the complexity of the electrochemical phenomena occurring at the electrode
food interface of a PEF chamber, whose extent depends on a large number of process, design, and product factors, the reduction of electrode reactions, rather than a complete prevention, might be preferred as long as the metal concentration and undesired chemical changes in the processed product remain within the limits dictated by food regulations. Thus the present challenge is to reduce the amount of electrochemical reactions by modifying the pulse generator systems, improving treatment design and selecting more stable electrode materials while taking into account chemical
physical properties of food under treatment, in order to improve the technical feasibility of PEF technology as well as to maintain chemical food safety.

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388. Jaeger, H., Meneneses, N., & Knorr, D. (2009). Impact of PEF treatment inhomogeneity such as electric field distribution flow characteristics and temperature effects on the inactivation of E. coli and milk alkaline phosphatase. Innovative Food Science and Emerging Technologies, 10, 470
480. Kim, M., & Zhang, H.Q. (2011). Improving electrode durability of pef chamber by selecting suitable material. In H. Q. Zhang, G. V. Barbosa-Ca´novas, V. M. Balasubramaniam, C. P. Dunne, D. F. Farkas, & J. T. C. Yuan (Eds.), Nonthermal processing technologies for food (pp. 201
212). Hoboken, NJ: IFT Press-Blackwell Publishing Ltd. Kotnik, T., Miklavˇciˇc, D., & Mir, L. M. (2001). Cell membrane electropermeabilization by symmetrical bipolar rectangular pulses. Part II. Reduced electrolytic contamination. Bioelectrochemistry, 54, 91
95. Mahniˇc-Kalamiza, S., Vorobiev, E., & Miklavˇcic, D. (2014). Electroporation in food processing and biorefinery. The Journal of Membrane Biology, 247, 1279
1304. Available from https://doi.org/10.1007/s00232-014-9737-x. Master, A. M., Schuten, H. J., & Mastwijk, H. C. (2007). In H. L. M. Lelieveld, S. Notermans, & S. W. H. de Haan (Eds.), Food preservation by pulsed electric fields (pp. 201
211). New York: CRC Press. Mastwijk, H. C. (2007). Pulsed power systems for PEF in food industry. In J. Raso, & V. Heinz (Eds.), Pulsed electric fields technology for the food industry (pp. 223
237). New York: Springer. Meneses, N., Jaeger, H., & Knorr, D. (2011). pH-changes during pulsed electric field treatments—Numerical simulation and in situ impact on polyphenoloxidase inactivation. Innovative Food Science and Emerging Technologies, 12, 499
504.

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Moonesan, M. S., George, S., Aucoin, M., & Jayaram, S. H. (2012). Effect of process parameters on the inactivation of microorganisms and electrode reactions during pulsed Electric field treatment of liquid food. In Conference BFE 2012, international conference bio & food electrotechnologies, Salerno, Italy. pp. 54
58. Morren, J., Roodenburg, B., & de Haan, S. W. H. (2003). Electrochemical reactions and electrode corrosion in pulsed electric field (PEF) treatment chambers. Innovative Food Science and Emerging Technologies, 4, 285
295. Odriozola-Serrano, I., Aguilo´-Aguayo, I., Soliva-Fortuny, R., & a Martı´n-Belloso, O. (2013). Pulsed electric fields processing effects on quality and healthrelated constituents of plant-based foods. Trends in Food Science & Technology, 29, 98
107. Parniakov, O., Bals, O., Lebovka, N., & Vorobiev, E. (2016). Pulsed electric field assisted vacuum freeze-drying of apple tissue. Innovative Food Science and Emerging Technologies, 35, 52
57. Pataro, G., Barca, G. M. J., Donsı`, G., & Ferrari, G. (2015a). On the modeling of electrochemical phenomena at the electrode solution interface in a PEF treatment chamber: Methodological approach to describe the phenomenon of metal release. Journal of Food Engineering, 165, 34
44. Pataro, G., Barca, G. M. J., Donsı`, G., & Ferrari, G. (2015b). On the modelling of the electrochemical phenomena at the electrode solution interface of a PEF treatment chamber: Effect of electrical parameters and chemical composition of model liquid food. Journal of Food Engineering, 165, 34
44. Pataro, G., Carullo, D., Bakar Siddique, Md. A., Falcone, M., Donsı`, F., & Ferrari, G. (2018). Improved extractability of carotenoids from tomato peels as side benefits of PEF treatment of tomato fruit for more energy-efficient steamassisted peeling. Journal of Food Engineering, 233, 65
73. Pataro, G., Donsı` G., & Ferrari G. (2012). Metal release from stainless steel electrodes of a PEF treatment chamber. In International conference bio & food electrotechnologies (BFE2012), Salerno, Italy. pp. 29
33. ISBN 978-88-903261-8-9. Pataro, G., Donsı`, G., & Ferrari, G. (2017). Modeling of electrochemical reactions during pulsed electric field treatment. In D. Miklavcic (Ed.), Handbook of electroporation (pp. 1
30). Springer International Publishing AG. Available from http://dx.doi.org/10.1007/978-3-319-26779-1-5-1. Pataro, G., Falcone, M., Donsı`, G., & Ferrari, G. (2014). Metal release from stainless steel electrodes of a PEF treatment chamber: Effects of electrical parameters and food composition. Innovative Food Science and Emerging Technologies, 21, 58
65. Pataro, G., Senatore, B., Donsi, G., & Ferrari, G. (2011). Effect of electric and flow parameters on PEF treatment efficiency. Journal of Food Engineering, 105, 79
88. Raso, J., Frey, W., Ferrari, G., Pataro, G., Knorr, D., Teissie, J., & Miklavˇciˇc, D. (2016). Recommendations guidelines on the key information to be reported in studies of application of PEF technology in food and biotechnological processes. Innovative Food Science and Emerging Technology, 37, 312
321. Reyns, K. M., Diels, A. M., & Michiels, C. W. (2004). Generation of bactericidal and mutagenic components by pulsed electric field treatment. International Journal of Food Microbiology, 93, 165
173. Rodait˙e-Riˇseviˇcien˙e, R., Saule, R., Snitka, V., & Saulis, G. (2014). Release of iron ions from the stainless steel anode occurring during high-voltage pulses and its consequences for cell electroporation technology. IEEE Transactions on Plasma Science, 42(1), 249.

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Roodenburg, B., de Haan, S. W. H., van Boxtel, L. B. J., Hatt, V., Wouters, P. C., Coronel, P., & Ferreira, J. A. (2010). Conductive plastic film electrodes for pulsed electric field (PEF) treatment—A proof of principle. Innovative Food Science and Emerging Technologies, 11, 274
282. Roodenburg, B., Morren, J., Berg, H. E., & de Haan, S. W. H. (2005a). Metal release in a stainless steel pulsed electric field (PEF) system. Part I. Effect of different pulse shapes; theory and experimental method. Innovative Food Science and Emerging Technologies, 6, 327
336. Roodenburg, B., Morren, J., Berg, H. E., & de Haan, S. W. H. (2005b). Metal release in a stainless steel pulsed electric field (PEF) system. Part II. The treatment of orange juice; related to legislation and treatment chamber lifetime. Innovative Food Science and Emerging Technologies, 6, 337
345. ´ lvarez, I., Condo´n, S., & Raso, J. (2014). Microbiological aspects ˜ a, G., A Saldan related to the feasibility of PEF technology for food pasteurization. Critical Reviews in Food Science and Nutrition, 54(11), 1415
1426. Saulis, G., Rodait˙e-Riˇseviˇcien˙e, R., & Snitka, V. (2007). Increase of the roughness of the stainless-steel anode surface due to the exposure to high-voltage electric pulses as revealed by atomic force microscopy. Bioelectrochemistry, 70, 519
523. Scromeda, N., & Katsube, T. J. (2008). Electrochemical double-layer capacitance of metals, including some precious metals: preliminary results. In N. Scromeda, & T. J. Katsube (Eds.), Geological Survey of Canada, Current Research. 2008
5, 8, Available from https://doi.org/10.4095/225015. Soliva-Fortuny, R., Balasa, A., Knorr, D., & Martı´n-Belloso, O. (2009). Effects of pulsed electric fields on bioactive compounds in foods: A review. Trends in Food Science and Technology, 20, 544
556. Sun, J., Bai, W., Zhang, Y., Liao, X., & Hu, X. (2011). Effects of electrode materials on the degradation, spectral characteristics, visual colour, and antioxidant capacity of cyanidin-3-glucoside and cyanidin-3-sophoroside during pulsed electric field (PEF) treatment. Food Chem., 128(3), 742
747. Toepfl, S. (2018). A brief history of Pulsed Electric Fields (PEF) use in potato industry ,https://elea-technology.de/a-brief-history-of-pulsed-electric-fieldspef-use-in-potato-industry/.. Toepfl, S., Heinz, V., & Knorr, D. (2007). High intensity pulsed electric fields applied for food preservation. Chemical Engineering and Processing, 46(6), 537
546. Tzedakis, T., Basseguy, R., & Comtat, M. (1999). Voltammetric and coulometric techniques to estimate the electrochemical reaction rate during ohmic sterilization. Journal of Applied Electrochemistry, 29(7), 821
828. Zhao, W., Yang, R., Liang, Q., Zhang, W., Hua, X., & Tang, Y. (2012). Electrochemical reaction and oxidation of lecithin under pulsed electric fields (PEF) processing. Journal of Agricultural and Food Chemistry, 2012(60), 12204
12209.

Consumer attitudes regarding the use of PEF in European Union: the example of Poland

14

Maryna Mikhrovska1, Anna Ka¨ferbo¨ck2, Emilia Skarzynska3 and Dorota Witrowa-Rajchert3 1

Law Faculty, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine Faculty of Engineering, Department Food technology and Nutrition, University of Applied Sciences Upper Austria, Wels, Austria 3Department of Food Engineering and Process Management, Faculty of Food Sciences, Warsaw University of Life Sciences, Warsaw, Poland 2

14.1

Introduction

Developing and implementation of new technologies in food industry are needed to meet the challenges of increased competition, globalization, and the growing dynamic and varying consumer demands. The changes observed in recent on consumer behavior on the food market are primarily due to the increase in affluence of society, the dynamic development of foreign trade, an increase of knowledge of consumers about health and nutrition, changes in lifestyle and consumption patterns of soci´ eties modeled on western countries (Babicz-Zielinska, 2010; Fleszar & Stasiak, 2006; Ku´smierczyk & Szczepieniec-Puchalska, 2008). Increased awareness and consumers’ demand in relation to food are mainly manifested by desire of buying safe, good flavor, easy in use, high-quality food products, which have a positive impact on the health and condition of the human body. These consumer needs caused the beginning of searching for new, unconventional technologies body (Bruhn, 2007; Ku´smierczyk & Szczepieniec-Puchalska, 2008). Emerging food processing technologies are offering solution to some of these challenges by meeting the consumers’ preferences, though consumers are often skeptical against new foods since uncertain, unknown, or unfamiliar wording goes along with risk perception. While conventional food processing uses wording such as cooking, heating, and freezing that is familiar Pulsed Electric Fields to Obtain Healthier and Sustainable Food for Tomorrow. DOI: https://doi.org/10.1016/B978-0-12-816402-0.00014-8 © 2020 Elsevier Inc. All rights reserved.

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to the consumers and therefore accepted, emerging, and fewer known technologies are facing this hurdle. Consumers’ opinion has a huge impact on success and failure of products on the market. Concerns about the new food are frequently caused by a lack of knowledge of European consumers. For example, rejection of genetically modified food is a commonly occurring phenomenon while organic foods on the other hand are warmly ´ welcome (Wilczynska & Wittbrodt, 2012). Until now the research about the consumers’ attitude to the emerging technologies has been performed in few countries. However, the data about the consumers’ behavior regarding these techniques in the Central and Eastern Europe, which should be considered as a big and emerging market for food industry, is limited. In order to assess the consumers’ attitude to nonthermal food processing technologies lately 200 Polish citizens (113 women and 87 men) were surveyed about the concept of nonthermal food processing. They were asked to fill in a questionnaire on the general behavior of consumers in the food market, on knowledge of the consumers on nonthermal food processing technologies, and on attitudes of consumers toward nonthermal food processing technologies. Data generated from this survey shows the attitude of consumers to new technologies and their knowledge of these, which will help to introduce new products processed with nonthermal technologies with a suited marketing strategy. Moreover, consumers’ attitude to the names of nonthermal technologies and their risks perception was part of the evaluation.

14.2

Brief introduction of nonthermal technologies

In this chapter, four nonthermal food processing technologies will be presented and discussed, which are pulsed electric fields (PEFs), high hydrostatic pressure (HHP), ultrasound (USN), and cold plasma (CP).

14.2.1

Pulsed electric field

PEF technology can be used for preservation of liquid or semiliquid food products and structure modification purposes. Therefore the product is placed between two electrodes and subjected to short high-voltage pulses. Technology of PEFs can cause limited changes in sensory properties and nutritional value of the food product and effective inactivation of microorganisms and enzymes at low temperature, which are the main advantages of

Chapter 14 Consumer attitudes regarding the use of PEF

this technology. Moreover, PEF can be used to support a variety of processes, including making of fruit juices and wine production, which makes the phenolic compounds are extracted more effectively what has the influence on the color, astringency, and acidity of the wine (Barba et al., 2015; Pereira & Vincente, 2010; Wiktor & Witrowa-Rajchert, 2012; Gachovska, Kumar, Thippareddi, Subbiah, & Williams, 2008; Morales-de La Pen˜a, Elez-Martı´nez, & Martı´nBelloso, 2011; Toepfl, Siemer, Saldana-Navarro, & Heinz, 2014; Lebovka, Shynkaryk, & Vorobiev, 2007).

14.2.2

High hydrostatic pressure (HPP)

During HPP processing, food is treated by high pressure— above 350 MPa for a period of time from several seconds to several minutes. This technology results in the inactivation of microorganisms and enzymes at low temperature while preserving the low molecular weight compounds such as vitamins, natural colors, and flavors. HPP is now commonly used all over the world in the food industries, for processing different groups of food—deserts, fruit juices and concentrate, dairy, rice products, guacamole, ´ dezoysters and other seafood, meat, ham, and salads (Bermu Aguirre & Barbosa-Ca´novas, 2011; Heinz & Buckow, 2010).

14.2.3

Ultrasound

USN can inactivate microorganisms and enzymes due to protein denaturation. This technology is also used for meat crushing, emulsion formation and acceleration of unit operations such as extraction, filtration, drying, and freezing. Other applications are degassing of liquid food products, accelerating the oxidation and reduction reactions, extraction of enzymes and proteins, inactivation of enzymes, washing, and cleaning. The advantages of USN are noninvasiveness of the process—safety and lack of microbiological hazards; possibility of the exact characteristics of the internal structure of the material; the ability to know the processes precisely—their kinetics and changes that occur in food treated by USN; shortening the processing time; helps to retain the taste, aroma, and color; reduction of pathogens at lower temperatures; competitive energy costs and low maintenance costs (Chemat & Khan, 2011; Patist & Bates, 2008; McClements, 1995).

14.2.4

Cold plasma

CP is still relatively poorly known decontamination technology. CP consists of constant reactive species where the most

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chemically reactive species are molecules containing oxygen and nitrogen—O, O2, O3, OH•, NO•, NO2. They react on the food surface and can therefore be used for preservation of fresh food, unprocessed, and partially processed meat, fish, and other perishable products, convenient food, food for special purpose, designed foods—an innovative healthy food and dietary supplements. Advantages of CP are low temperature of the process (20 C 30 C); low energy consumption of the process compared to thermal sterilization; low equipment costs, compared with conventional technologies; inactivation of a large variety of microorganisms: Gram-positive and Gram-negative bacteria, spores, fungi, and viruses on various surfaces; inactivation of enzymes (Niemira, 2012; Pankaj et al., 2014; Rød, Hansen, ´ z, Nowacka, & WitrowaLeipold, & Knøchel, 2012; Wiktor, Sled´ Rajchert, 2013; Basaran, Basaran-Akgul, & Oksuz, 2008).

14.3

Assessment of consumers’ behavior on the food market

Assessment of consumers’ overall behavior on the food market has shown that consumers are interested in the issue of nutrition. They declared that they read the labels of food products (63.1% of women and 59.8% of men), thus suitably worded information on food packages can both respond to current questions of consumers, as well as be a reliable source of information on, for example, nonthermal food processing technologies. Fig. 14.1 shows the consumers’ answers on the question: “What factors have influenced on shopping decisions you make? (You can select more than one answer).”

Figure 14.1 Consumers’ answers on the question “What factors have influence on shopping decisions you make? (You can select more than one answer)”.

Chapter 14 Consumer attitudes regarding the use of PEF

Figure 14.2 Consumers’ answers on the question: “What on your opinion determines the quality of the food? (You can select more than one answer)”.

For most consumers the most important factors influencing their purchasing decisions are the price of the food and its quality, which, in the opinion of consumers meant the nutritional value of the product, its safety (health aspect), and palatability—what shows Fig. 14.2—consumers’ answer on the question: “What on your opinion determines the quality of the food? (You can select more than one answer).” Therefore appealing to high-quality food products processed by nonthermal technologies can increase the degree of acceptance of these technologies by the average consumer. Consumers in recent days are more interested in the healthy lifestyle, and proper nutrition is increasingly turning to healthrelated food products—pay attention to the nutritional value and expect natural taste and appearance of the food product, from whom expect the highest possible quality. Information campaigns highlighting the advantages of food products processed by nonthermal technologies (including high nutritional value, unchanged taste characteristics, and security) could help to increase the acceptance of these technologies by consumers.

14.4

The understanding of the concept of nonthermal food processing technology and the knowledge of use

The study in Poland showed the concept of nonthermal food processing technologies is predominantly not known. In the

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group of 200 surveyed consumers, only 38 people declared knowledge of the concept of which 71% were students or graduates from food science or food science related topics. In the world, high hydrostatic pressure, PEF, and USN are used in food production on an industrial scale. However, according to our best knowledge, CP is still in the study phase and is not used on an industrial scale. When asked about the use of nonthermal-technologies, consumers indicated properly high pressure (81% consumers), PEF (39% consumers), and USN (48% consumers) as technologies used in the world on an industrial scale in food processing. CP was erroneously indicated by 43% consumers, as the technology used in the world on an industrial scale in food processing. Even though in Poland USN is used in food technology on an industrial scale, only 35% surveyed consumers were able to identify it while most consumers erroneously indicated the use of high pressure (70% consumers). In this case, knowledge of consumers who were students or graduates of courses related to food science did not differ significantly from other consumers.

14.4.1

Labeling of food products processed by nonthermal technologies

Consumers show willingness to be informed about new technologies and their use in the food industry even if this causes short-term negative feelings such as distrust or uncertainty. The majority of consumers wanted to know more about these technologies, than only short description. It has been shown that nutrition claims about the benefits associated with the use of specific food processing technologies, reduced the fear of consumers against this type of food, and improved acceptance and increased likelihood of consumption of such food products (Cardello, 2003; Jaeger, Knorr, Szabo´, Ha´mori, & Ba´na´ti, 2015). However, health claims cannot be placed arbitrary on the products as these are strictly defined in Regulation (EU) No 1047/2012. Especially when not knowing the brand consumers declared frequent reading food labels for information about them. Giving more information about the used technology and highlighting that this has positive impact on the product rises the acceptance and even causes that consumers find it as characterized by high quality. Consumers seek food products that offer special benefits as healthy properties, good flavor, convenience, and which are environmental-friendly. Therefore emphasizing the benefits related to using new technologies in food production

Chapter 14 Consumer attitudes regarding the use of PEF

can increase its consumers’ acceptance (Bruhn, 2007; Deliza, Rosenthal, Abadio, Silva, & Castillo, 2005; Deliza, Rosenthal, & Silva, 2003).

14.4.2

Attitude of respondent group of consumers toward the nonthermal food processing technologies

The scientific literature indicates that consumers’ feeding behavior affects stimulating factors—curiosity and the search for novelty and inhibitory factors—fear of novelty and resistance to change. The dominance of the inhibitor factors over the stimulating can lead to nutritional neophobia, nutritional disorders (monotony), and deficiencies of nutrients leading to disease conditions. Consumers’ behavior in relation to the “novel food” is connected by sociodemographic condition of consumers. Young and educated consumers are more receptive to the new products when less wealthy consumers show aversion to novelty and nutritional neophobia (Da˛browska & ´ Babicz-Zielinska, 2011). In the mind of consumers, many names of new food processing technologies cause negative associations. Fig. 14.3 shows consumers’ answers to the question “Do any of these names of food processing technologies evokes in your opinion any negative associations?”. In general, men showed higher concern toward the names of new food processing technologies than women. Irradiation, pulsed X-rays, CP, addition of bacteriocins, genetic engineering, and ultraviolet light caused mostly negative associations both among women and men. The least negative associations among nonthermal food processing technologies were for high hydrostatic pressure, PEF, USN, and CP. It is interesting that the consumer perception toward the name of a modified atmosphere (packaging) technology caused negative feelings among 22% women and 39% men, while a protective atmosphere (packaging) technology, which is interchangeably used the name of this technology in Poland, where the survey took place, caused negative feelings among only 2% women and 7% men. Such results may be due to the negative perception of the word “modified” by many consumers that may be associated with serious interference in the product. Equally interesting is the attitude of consumers toward the microwave, which, although used for a long time in Europe, both on an industrial scale in food production and in average

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Figure 14.3 Consumers’ answers on the question “Do any of these names of food processing technologies evokes in your opinion any negative associations?”.

households and the information on them are constantly being expanded and accessible for the average consumer, microwaves still cause a lot of controversies and consumers are still not convinced to microwaves (31% women and 38% men assessed negatively the name of this technology). In the past, it was shown that in general women showed a higher concern against all the names of the new food processing technologies than men. The names of many new food processing technologies cause great concern and negative connotations among consumers such as, genetic engineering, irradiation, and pulsed X-rays (Cardello, 2003). Food processed by high pressure was more acceptable to the consumers when compared with products processed by PEF. An important issue is assembly of the name of the technology— PEF—which seems to raise negative connotations and invokes the fear of electricity. Changing the name from “PEFs” to “micro-pulse” or other name may solve this issue. Consumers, when choosing between products processed by high pressure and PEF, tended to products processed by high pressure, which

Chapter 14 Consumer attitudes regarding the use of PEF

in addition to PEF offer the same benefits associated with much less risk (Jaeger et al., 2015; Nielsen et al., 2009; Olsen, Grunert, & Sonne, 2010).

14.4.3

The risks associated with the use of nonthermal food processing technologies

When introducing nonthermal processes and other new technologies that are unknown to the consumers, they react with reservation and negative preconceptions. The most frequently indicated by consumers’ negative impacts of the use of nonthermal technologies were higher product price (high hydrostatic pressure—31%, PEF—35%, USN—33%, CP—36% consumers), abnormality of the product (38%), worse quality of the product (35%), the risks associated with long-term effect on the human body (31%), reduced vitamin content (30%), and a higher degree of processing (33%). As an example, according to the consumers, CP causes fear of danger to humans, the formation of new toxic compounds and a negative impact on the environment. It has been reported that technologies that cause the least negative effects are the high hydrostatic pressure and USN. For these techniques, the most common negative effects were the higher price of the product, worse product quality, and abnormality of the product. Following most common negative effects were, as for other technologies are higher price of the product (35%), risk associated with long-term effect on the human body (34%), reduced vitamin content and a higher degree level of processing of the product (30%), abnormality of the product (29%), and worse product quality (28%). Obtained results in Poland were in accordance with the results stated in studies conducted in other countries. Research conducted on 3000 consumers in the United Kingdom, Germany, and France showed that high-pressure technology was accepted by the majority of consumers in Germany and France. Two important factors were, first, the fact that the price of food product processed by high pressure did not exceed the price of a conventional product and second health beneficial effects associated with the use of high pressure. It has been shown that consumers who saw more individual benefits of using new technologies were more likely to buy these types of products (Butz et al., 2003). In the United States a study conducted on 225 consumers showed that the risk perceived by consumers was the most

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important factor affecting the interest and acceptance of new technologies. That led to the conclusion that despite the real risk, the risk perceived by consumers is a critical factor in the successful introduction of new products, processed by new technologies, on the food market (Cardello, Schutz, & Lesher, 2007). Consumers in The Netherlands, Belgium, Spain, and Finland showed a neutral attitude toward new technologies such as high hydrostatic pressure freezing, even though the technology was not known to them. After sharing them with information about the technology, consumers consider it to be acceptable, especially considering beneficial effects on food products arising from the use of high pressure (Lampila & La¨hteenma¨ki, 2007). Studies conducted on consumers in Denmark, Norway, Slovenia, Hungary, Serbia, Slovakia, and Czech Republic have shown that consumers from the countries of Northern Europe were more skeptical in relation to high pressure and PEF technologies compared to consumers in Eastern Europe. For consumers in Northern Europe, in contrast to consumers from Eastern Europe, a major drawback of juices processed by nonthermal technologies was their long shelf life, which meant that consumers were convinced that there have been additives added to this food. Other disadvantages of high pressure and PEF, in the opinion of consumers from Northern Europe, were their suspected impact on the environment and a small amount of information about them. The disadvantage of baby food products processed by nonthermal technologies according to consumers from Eastern Europe was their higher price, which for consumers from Northern Europe was a significant advantage, as consumers thought that if the food is more expensive, it means that it has a higher quality, and this will be better for the children (Nielsen et al., 2009). Studies have shown that in general consumers are more likely to by high pressure pasteurized and USN products while having aversions against PEFs and CP.

14.5

Conclusion

Nonthermal technologies are quite new on the market and their working concepts seem to be complex to grasp for the consumers who demand transparency. Despite its many advantages, unfortunately, they arouse negative feelings among many consumers who do not have any knowledge about nonthermal technologies. Therefore consumers approach them with great caution. The perceived risks are likely to be the main critical

Chapter 14 Consumer attitudes regarding the use of PEF

factors of market success since it influences consumers’ behavior regardless of actual risks and benefits. As for technologies in general, consumers are inclined to be more positive toward technologies they understand. Since this is the key to achieve customer acceptance, communication effort in the form of tailored marketing is needed to prevent and reduce negative response, as well as increasing the possibility of market success. Marketing and advertisement for novel technologies are unexplored and rarely to find. Therefore skepticism among consumers could also come from lacking information provided from the industry using one of these technologies. Advertising the processing method by highlighting the naturalness of foods as well as factual information about safety can as a result increase the acceptance of new food technologies and improve the likelihood of consumption. According to different studies, scientists and media are the most trusted sources when it comes to inform the public about the new nonthermal technologies. This should act as a starting point when it comes to prepare information campaigns about nonthermal technologies—about the possible uses in food production, benefits, and influence of these technologies on human nutrition, which would be reliable source of information for consumers (Rollin, Kennedy, & Wills, 2011). Furthermore, it is important to investigate and assess consumers’ attitudes to these new technologies and their expectations in relation to new food products to develop suitable communication strategies (i.e., educational campaign and trustworthy source of information) in order to improve the knowledge of the consumers and convince them that it is worth to use the emerging technologies.

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Bruhn, C. M. (2007). Enhancing consumer acceptance of new processing technologies. Innovative Food Science & Emerging Technologies, 8(4), 555 558. Butz, P., Needs, E. C., Baron, A., Bayer, O., Geisel, B., Gupta, B., . . . Tauscher, B. (2003). Consumer attitudes to high pressure food processing. Journal of Food Agriculture and Environment, 1, 30 34. Cardello, A. V. (2003). Consumer concerns and expectations about novel food processing technologies: Effects on product liking. Appetite, 40(3), 217 233. Cardello, A. V., Schutz, H. G., & Lesher, L. L. (2007). Consumer perceptions of foods processed by innovative and emerging technologies: A conjoint analytic study. Innovative Food Science & Emerging Technologies, 8(1), 73 83. Chemat, F., & Khan, M. K. (2011). Applications of ultrasound in food technology: Processing, preservation and extraction. Ultrasonics Sonochemistry, 18(4), 813 835. ´ Da˛browska, A., & Babicz-Zielinska, E. (2011). Zachowania konsumento´w w stosunku do z˙ywno´sci nowej generacji. Hygeia Public Health, 46(1), 39 46. Deliza, R., Rosenthal, A., Abadio, F. B. D., Silva, C. H., & Castillo, C. (2005). Application of high pressure technology in the fruit juice processing: Benefits perceived by consumers. Journal of Food Engineering, 67(1), 241 246. Deliza, R., Rosenthal, A., & Silva, A. L. S. (2003). Consumer attitude towards information on non conventional technology. Trends in Food Science & Technology, 14(1), 43 49. Fleszar, J., & Stasiak, J. (2006). Czynniki i motywacje zakupu z˙ ywno´sci ´ ekologicznej konsumento´w rynku koszalinskiego. Journal of Research and Applications in Agricultural Engineering, 51(2), 36 41. Gachovska, T. K., Kumar, S., Thippareddi, H., Subbiah, J., & Williams, F. (2008). Ultraviolet and pulsed electric field treatments have additive effect on inactivation of E. coli in apple juice. Journal of Food Science, 73(9), 412 417. ¨r Heinz, V., & Buckow, R. (2010). Food preservation by high pressure. Journal fu Verbraucherschutz und Lebensmittelsicherheit, 5(1), 73 81. Jaeger, H., Knorr, D., Szabo´, E., Ha´mori, J., & Ba´na´ti, D. (2015). Impact of terminology on consumer acceptance of emerging technologies through the example of PEF technology. Innovative Food Science & Emerging Technologies, 29, 87 93. Ku´smierczyk, K., & Szczepieniec-Puchalska, D. (2008). Zmiany w konsumpcji z˙ ywno´sci w Polsce. Przemysł Spo˙zywczy, 12, 6 13. Lampila, P., & La¨hteenma¨ki, L. (2007). Consumers’ attitudes towards high pressure freezing of food. British Food Journal, 109(10), 838 851. Lebovka, N. I., Shynkaryk, N. V., & Vorobiev, E. (2007). Pulsed electric field enhanced drying of potato tissue. Journal of Food Engineering, 78(2), 606 613. McClements, D. J. (1995). Advances in the application of ultrasound in food analysis and processing. Trends in Food Science & Technology, 6(9), 293 299. Morales-de La Pen˜a, M., Elez-Martı´nez, P., & Martı´n-Belloso, O. (2011). Food preservation by pulsed electric fields: An engineering perspective. Food Engineering Reviews, 3(2), 94 107. Nielsen, H. B., Sonne, A. M., Grunert, K. G., Banati, D., Polla´k-To´th, A., Lakner, Z., . . . Peterman, M. (2009). Consumer perception of the use of high-pressure processing and pulsed electric field technologies in food production. Appetite, 52(1), 115 126. Niemira, B. A. (2012). Cold plasma decontamination of foods. Annual Review of Food Science and Technology, 3, 125 142.

Chapter 14 Consumer attitudes regarding the use of PEF

Olsen, N. V., Grunert, K. G., & Sonne, A. M. (2010). Consumer acceptance of high-pressure processing and pulsed-electric field: A review. Trends in Food Science & Technology, 21(9), 464 472. Pankaj, S. K., Bueno-Ferrer, C., Misra, N. N., Milosavljevi´c, V., O’Donnell, C. P., Bourke, P., . . . Cullen, P. J. (2014). Applications of cold plasma technology in food packaging. Trends in Food Science & Technology, 35(1), 5 17. Patist, A., & Bates, D. (2008). Ultrasonic innovations in the food industry: From the laboratory to commercial production. Innovative Food Science & Emerging Technologies, 9(2), 147 154. Pereira, R. N., & Vicente, A. A. (2010). Environmental impact of novel thermal and non-thermal technologies in food processing. Food Research International, 43(7), 1936 1943. Rød, S. K., Hansen, F., Leipold, F., & Knøchel, S. (2012). Cold atmospheric pressure plasma treatment of ready-to-eat meat: Inactivation of Listeria innocua and changes in product quality. Food Microbiology, 30(1), 233 238. Rollin, F., Kennedy, J., & Wills, J. (2011). Consumers and new food technologies. Trends in Food Science & Technology, 22(2), 99 111. Toepfl, S., Siemer, C., Saldana-Navarro, G., & Heinz, V. (2014). Overview of pulsed electric fields processing for food. In D.-W. Sun (Ed.), Emerging technologies for food processing. San Diego, CA: Academic Press. ´ z, M., Nowacka, M., & Witrowa-Rajchert, D. (2013). Mo˙zliwo´sci Wiktor, A., Sled´ zastosowania niskotemperaturowej plazmy w technologii z˙ ywno´sci. ZywnoscNauka, Technologia, Jakosc, 90, 5 14. Wiktor, A., & Witrowa-Rajchert, D. (2012). Zastosowanie pulsacyjnego pola elektrycznego do wspomagania proceso´w usuwania wody z tkanek ro´slinnych. Zywnosc-Nauka, Technologia, Jakosc, 81, 22 32. ´ Wilczynska, A., & Wittbrodt, M. (2012). Wiedza młodzie˙zy akademickiej o z˙ ywno´sci genetycznie modyfikowanej i jej postawy wobec tego zagadnienia. Zeszyty Naukowe Akademii Morskiej W Gdyni, 73, 16 22.

Further reading Angersbach, A., Heinz, V., & Knorr, D. (1999). Electrophysiological model of intact and processed plant tissues: Cell disintegration criteria. Biotechnology Progress, 15, 753 762. Buckow, R., Ng, S., & Toepfl, S. (2013). Pulsed electric field processing of orange juice: A review on microbial, enzymatic, nutritional, and sensory quality and stability. Comprehensive Reviews in Food Science and Food Safety, 12(5), 455 467. Eurobarometer. (2006). Risk issues. Special Eurobarometer 238/Wave 64.1. Brussels: TNS Opinion & Social. Ferna´ndez, A., & Thompson, A. (2012). The inactivation of Salmonella by cold atmospheric plasma treatment. Food Research International, 45(2), 678 684. Gallego-Jua´rez, J. A., Riera, E., de la Fuente Blanco, S., Rodrı´guez-Corral, G., Acosta-Aparicio, V. M., & Blanco, A. (2007). Application of high-power ultrasound for dehydration of vegetables: Processes and devices. Drying Technology, 25, 1893 1901. Grabowski, M., & Da˛browski, W. (2014). Technologie plazmowe do sterylizacji z˙ ywno´sci. Przemysł Spo˙zywczy, 4, 4 6.

323

324

Chapter 14 Consumer attitudes regarding the use of PEF

Hugas, M., Garriga, M., & Monfort, J. M. (2002). New mild technologies in meat processing: High pressure as a model technology. Meat Science, 62(3), 359 371. Kaczmarski, Ł., & Lewicki, P. P. (2005). Zastosowanie technik ultrad´zwie˛kowych w przetwarzaniu z˙ ywno´sci. Przemysł Spo˙zywczy, 9, 34 36. ´ Kozirok, W., Baumgart, A., & Babicz-Zielinska, E. (2012). Postawy i zachowania konsumento´w wobec z˙ ywno´sci prozdrowotnej. Bromatologia i Chemia Toksykologiczna XLV, 3, 1030 1034. Kry˙za, K., & Szczepanik, G. (2010). Zastosowanie zimnej plazmy jako nowoczesna technologia zabezpieczania surowco´w z˙ ywno´sciowych. Available from ,http://food.rsi.org.pl/dane/Artyku__._Plasma._Kry__a__Szczepanik. pdf. Accessed 19.05.14. Lewicki, P. P. (1998). Tendencje w rozwoju technologii z˙ ywno´sci. Przemysł Spo˙zywczy, 9, 31 35. Matser, A. M., Krebbers, B., Van den Berg, R. W., & Bartels, P. V. (2004). Advantages of high pressure sterilization on quality of food products. Trends if Food Science & Technology, 15, 79 85. Misra, N. N., Tiwari, B. K., Raghavarao, K. S. M. S., & Cullen, P. J. (2011). Nonthermal plasma inactivation of food-borne pathogens. Food Engineering Reviews, 3(3 4), 159 170. Moreau, M., Orange, N., & Feuilloley, M. G. J. (2008). Non-thermal plasma technologies: New tools for bio-decontamination. Biotechnology Advances, 26 (6), 610 617. ´ z, M., Jurek, N., & Witrowa-Rajchert, D. (2012). Nowacka, M., Wiktor, A., Sled´ Drying of ultrasound pretreated apple and its selected physical properties. Journal of Food Engineering, 113(3), 427 433. Nowacka, M., & Witrowa-Rajchert, D. (2011). Innowacyjne procesy wste˛pne stosowane przed suszeniem owoco´w i warzyw. Przemysł Spo˙zywczy, 9, 34 38. Pietrzak, D. (2010). Perspektywy stosowania wysokich cisnien w produkcji ˙ zywnosci wygodnej z miesa drobiowego. Zywno´ sc´ Nauka Technologia Jako´sc´, 17(2), 16 28. ´ w przemy´sle Pietrzak, D., & Mroczek, J. (2002). Zastosowanie wysokich ci´snien mie˛snym. Przemysł Spo˙zywczy, 10, 38 41. Rastogi, N. K. (2010). Opportunities and challenges in nonthermal processing of foods. In M. L. Passos, & C. P. Ribeiro) (Eds.), Innovation in food engineering. New techniques and products (pp. 3 58). Boca Raton, FL: CRC Press. Regulation. Regulation (EC) No 1924/2006 of the European Parliament and of the Council of 20 December 2006 on nutrition and health claims made on foods. (2006). Regulation. Commission Regulation (EU) No 1047/2012 of 8 November 2012 amending Regulation (EC) No 1924/2006 with regard to the list of nutrition claims. (2011). Regulation. Regulation (EU) No 1169/2011 of the European Parliament and of the Council of 25 October 2011 on the provision of food information to consumers, amending Regulations (EC) No 1924/2006 and (EC) No 1925/2006 of the European Parliament and of the Council, and repealing Commission Directive 87/250/EEC, Council Directive 90/496/EEC, Commission Directive 1999/10/EC, Directive 2000/13/EC of the European Parliament and of the Council, Commission Directives 2002/67/EC and 2008/5/EC and Commission Regulation (EC) No 608/2004. (2012). ¨ ter, O., Boguslawski, S., & Knorr, D. (2003). Impact Schubring, R., Meyer, C., Schlu of high pressure assisted thawing on the quality of fillets from various fish species. Innovative Food Science & Emerging Technologies, 4(3), 257 267.

Chapter 14 Consumer attitudes regarding the use of PEF

Stryczewska, H. D. (2011). Technologie zimnej plazmy. Wytwarzanie, modelowanie, zastosowania. Elektryka, 217, 41 61. Thirumdas, R., Sarangapani, C., & Annapure, U. S. (2015). Cold plasma: A novel non-thermal technology for food processing. Food Biophysics, 10(1), 1 11. Wan, J., Coventry, J., Swiergon, P., Sanguansri, P., & Versteeg, C. (2009). Advances in innovative processing technologies for microbial inactivation and enhancement of food safety pulsed electric field and low-temperature plasma. Trends in Food Science & Technology, 20(9), 414 424. Witrowa-Rajchert, D. (2012a). Ultrad´zwie˛ki w produkcji z˙ ywno´sci projektowanej. Przemysł Spo˙zywczy, 11, 41 43. Witrowa-Rajchert, D. (2012b). Pulsacyjne pole elektryczne (PEF) zastosowanie w produkcji z˙ ywno´sci projektowanej. Przemysł Spo˙zywczy, 7, 32 34.

325

Index Note: Page numbers followed by “f” and “t” refer to figures and tables, respectively

A Abrasive peeling, 110 AC electro plasmolysis of apples, 270 271, 271f Acrylamide formation, 32 33, 129 131 during frying, 111 112 impact of raw material on, 107 108 Maillard reaction, 111 112 in potato chips, 132 in potato products, 113 in snacks, 105 107, 106f Acrylamide reduction with chips processing, 111 113 with pulsed electric field, 113 115 Added-value compounds, 74 75, 90 91 Adverse effects, 208 209 Aflatoxin, 34, 146 147 AFP. See Antifreeze proteins (AFP) Agglomeration, 298 Agricultural gross production value, 23 24, 24f Air drying, 119 120 α 2 dicarbonyls, 76 Anastrepha ludens, 255 Ankistrodesmus falcatus, 253 Anthocyanins, 28, 58 59, 85, 179 180, 237 238 Antifreeze agents, 210 211 Antifreeze proteins (AFP), 209 210 Antioxidants, 58, 229 230 Arthrospira platensis, 251 Ascorbic acid oxidase, 179 180 Aspergillus flavus, 146 147

Aspergillus oryzae, 113 Aspergillus species, 34 Automatic discharge, 302 303 Auxenochlorella protothecoides, 87 88, 251 252

B Baby food products, 320 Batch (kettle)-fried chips, 114, 115f β 2 Carotene, 56 57, 59 60 β 2 phycoerythrin, 253 Betanin, 84 85 Bioaccessibility/bioavailability nutrients and bioactive compounds, 53t, 59 carrots (Daucus carota), 56 57 fruit and vegetable mixture combinations, 60 61 grapes (Vitis vinifera), 58 59 milk and milk products, 60 orange (Citrus sinensis), 59 tomato (Solanum lycoperiscum), 59 60 Bioactive compounds, 25 26, 52f, 159, 171 172, 180 182 bioaccessibility/ bioavailability, 59 extractability, 52 53 extraction, 227 228, 234 235 by-products and wastes, 236 238 and nutraceuticals, 229 nutrients and. See Nutrients and bioactive compounds oil and, 236

Biological cell membranes, 4, 6, 229, 269 Biological tissue, 3 Biomolecule extraction sectors, 66 Bipolar pulse mode, 14, 72 Blanched carrots, 57 Blueberry fruits, 169 170, 179 180 cell disintegration index of, 232 PEF-pretreated, 235 pretreatment, 233 Boron carbide, 296 297 Botryococcus braunii, 253 Brewery industry, 234 By-products, extraction of bioactive compounds from, 236 238

C Caco-2 human intestinal cell, 57 59, 61 Caffeic acid, 26 27 Capillary water, 157 158 Carbohydrate-rich foods, 105 Carotenoids, 25 26, 56 57, 83, 180 182 bioaccessibility, 59 60 Carrots (Daucus carota), 56 57 CDI. See Cell disintegration index (CDI) Cell disintegration index (CDI), 231 232 of blueberry fruits, 232 Cell disintegration methods, 259 262, 278, 284 Cell electroporation, 119 Cell membranes, 269 electroporation of, 3, 5 6

327

328

Index

Cell membranes (Continued) parameters affecting, 13 17 irreversible damage of, 17 permeabilization, 4 8, 7f, 14 16, 161 165, 248 irreversible, 284 reversible, 8 Cell size, 17 Cells permeabilization, insects, 255 258, 256f, 257f Cellular disintegration index, 161 165, 170 171, 207 208 Cellular structure, and osmotic dehydration, 159 Cellular tissue electroporation, 6 Cell wall deficient mutants, 249 250 Characteristic treatment time, 257 258, 259f Charging current, 287 Chemical-free technique, 261 Chemiluminescence assay, 89 Chips processing, acrylamide reduction through, 111 113 Chlamydomonas reinhardtii, 253 Chlorella sp., 249 250 Chlorella vulgaris, 83 84, 87 88, 250, 252 253 Chloride compounds, 301 Chlorpyrifos, 30 31, 144 Chronic diseases, 30 Cold juice extraction, 232 233 Cold plasma (CP), 313 314 Colinear chambers, 275 Color, 178 179, 187 188 Colorants, 82 85 Commercial application of PEF technique, 269 270 Commercial chips, 108 109 Commercialization, of PEF technology, 270 274, 284 285 Commercial-scale PEF processing system, 231

Compression chamber, 255 256 COMSOL Multiphysics, 12 Conductive polymers, 302 303 Continuous frying process, 110 111 Continuous processing system, 274 Control extraction method, 230 231 Convective and sublimation method, 176 177 Conventional drying, 179 180 Conventional food processing, 311 312 Conventional preservation methods, 292 295 Cooling, 204 205 CoolPure, 274 CoolPure Jr., 274 Copper oxide nanowire (CuONW), 261 Corrosion, 285 electrode. See Electrode corrosion Cossettes, 232 233 CP. See Cold plasma (CP) Cracks, 118 Critical control point, 295 296 Critical value/dielectric breakdown, 8 10 models applied for, 9 10 Cryopreservation method, 209 210 Cryoprotectants utilization in combination with pulsed electric field treatment, 211 214 in freezing process, 208 211 implementation, 214 221 Crystallization, 210 Culex quinquefasciatus, 255 CuONW. See Copper oxide nanowire (CuONW) Cutting and peeling, 284 improvement, 275 276 Cytosol, 208 209

D Dark pigments formation, 178 179 Decontamination technology, 313 314 Deep-fried products, 115 117 Dehydration processes, 155 of biological wastes, 228 pulsed electric field impact on, 160 182 Dehydrofreezing, 211 212 Dekkera bruxellensis, 38 39 Delay time, 72 Detoxification effect, 145 146 Diabetes type II, 115 117 Dielectric breakdown theory, 68. See also Critical value/dielectric breakdown Dietary behavior, urbanization and, 23 24 Dietary polyphenols, 76 82, 77f Dilute cell suspensions, 12 13 Disintegrated cellular structure, 161 165 Donnan equilibrium, 8 9 Double-layer capacitors, 302 303 Dried fruits, 159 160 impact of PEF treatment on vegetables, 173t Dried potato, 113 Dried snacks, 119 120 Drip loss after thawing, 207 208, 210 211 Drying kinetics improvement, 171 pulsed electric field on, 161 171 Drying methods, 37 38 Drying process, 155, 157f, 190 191, 250, 257 258 and osmotic dehydration, 157 160 parameters influencing, 158t rate and product temperature, 157 158 Duty cycle, 16

Index

E Eco-friendly solvents, 230 Effective freezing time, 205 Effective water diffusion coefficient, 165 168 ELCRACK system, 272 273, 278 279 Electrical treatment of food, 270 Electric field strength, 14, 70 71, 77 78, 81 82 on electroporation, 71f Electricity consumption, 122 123 Electrochemical reactions cause of, 305 of electrophoresis, 297f limitation, 301 305 in pulsed electric fields system, 285 288, 286t, 289t effects, 289 301, 290f electrode corrosion. See Electrode corrosion electrode fouling, 297 298 (partial) electrolysis, 298 299 secondary reactions, 299 301 Electrochemotherapy, 8 Electrode configuration, 275 Electrode corrosion, 290 297 anodic half-reactions for, 298 299 electrode lifetime and equipment reliability, 295 297 food quality, 292 295 food safety and regulation, 291 292 Electrode electrolyte interface, 287, 290 Electrode fouling, 297 298 Electrode lifetime, 295 297 Electrode reactions, 288 Electrode surface, 295 Electrogenerated metal ions, 300 Electrolysis (partial), 298 299 Electromagnetic theory, 68 Electromechanical model, 9

extension of, 10 gap of, 9 Electroneutrality, 287 Electropermeabilization, 66, 228, 283 Electrophoresis, 297, 297f Electroplasmolysis, 270, 271f, 273 274 Electroporation process, 8, 156f, 179 180, 206, 228 229, 269, 283 of blueberry, 169 170 of cell membranes, 3, 13 17, 35, 69, 113 114 cell size, 17 electric field strength, 14 pulse duration, 14 15 pulse shape, 16 17 pulses number and pulse frequency, 15 16 on different systems, 10 13 cells in dense suspensions and tissues, 12 13 irregularly shaped cells, 12 nonspherical geometrically regular cells, 11 12 spherical cell, 10 11 efficiency, 17, 72 73 electric field strength on, 71f mass transfer using, 68 69 mechanism, 4 molecular mechanism of, 67 68 phenomenon, 161 165, 178 179 and pore dimensions, 75 reversible, 3 4, 7 8 by values, 6 7 ELSTERIL system, 272 273, 278 279 Emblica officinalis, 135 Emerging food processing technologies, 311 312 Emerging nonthermal technology, 143 144 Emerging technologies, 133, 190 191 application, 248 in food processing, 143 Enzymatic inactivation, 38 39

329

Equipment reliability, 295 297 Ethylene production, 159 European Commission Regulation (EU) 2017/ 2158, 32 33 European Food Safety Authority in 2015, 32 33 Exponential decay pulse systems, 16f, 17, 71 72, 81 External electrical field, 6 7, 7f, 68 69 homogeneous, 13 External voltage, 287 288 Extraction of bioactive compounds from by-products and wastes, 236 238 from fruits, 234 235 efficiency, 228 food additives and nutraceuticals. See Food additives and nutraceuticals extraction improvement, 250 254 of intracellular compounds, 253 254, 259 260 lipids, 260 by pressing, 228 Extraction of compounds and fractions pulsed electric field application for, 229 230 Extrusion process, 145 146

F Falling drying rate, 157 158 Fall time, 16 Faraday’s law, 288 Fast freezing techniques, 205 206 Fat intake, 117 118 in snack products, 115 117 Fat reduction, 117 119 Finite-elements method, 12 Fishmeal producing factory, 272 Flavonoids, 76, 81 Flow cytometry method, 38 39 Fluid mosaic model, 9

330

Index

Fluorescence microscope, 8 Food additives and nutraceuticals extraction PEF treatment application, 75 88 colorants, 82 85 dietary polyphenols, 76 82 lipids, 85 86 proteins, 87 88 stabilizers, 86 87 Food colorants, 82 83 Food composition, for human health, 229 Food consumption, 23 24 Food contaminants, reduction of, 30 34 Food dehydration, 156 157 Food industry diffusion processes in, 214 221 emerging market for, 312 emerging nonthermal technology in, 143 144 integration in processes, 284 285 new technologies in, 311 pulsed electric field in, 34 38 potential applications, 34 38 sectors of, 283 Food market assessment of consumers’ behavior, 314 315 Food model system, 133 Food pesticides. See Pesticides Food preservation techniques, 203 204 Food processing methods, 34, 143, 156 157 Food products, 228 freezing process of, 204 206 liquid and semiliquid, 228 processed by nonthermal technologies, 316 317 Food quality, 214 221, 292 295 Food safety hazard, 38 39 and regulation, 291 292 Food waste, 237

Fouling of electrode, 297 298 Freeze-drying, 37 38, 120, 161 165, 169 171 Freezing process, 203 204, 204f application of pulsed electric field treatment, 206 208 cryoprotectants utilization in, 208 211 of food products, 204 206 nonthermal technologies on, 215t nonthermal treatments and food quality, 214 221 as preservation technique, 203 204 Freezing thawing cycle, 203 204 French fries, 113 industry, 269 270 Fresh-like characteristics, 186 187 Fried chips, 108, 110 Fruit juice based products, 60 61 Fruit juice quality, 279 Fruit juice yields, improvement in, 230 233 Fruits and vegetables, 229 230 by-products, 237 consumption, 229 electrical treatment, 270 271 juices, 231 232 mashes, 275 mixture combinations, 60 61 with osmotic dehydration, 211 PEF-treated, 179 180 shelf life extension of juices, 276 277 Frying process, 104 105, 110 111 acrylamide formation during, 111 112 Functional foods, 66 Fungal species, 141 142 Furfural formation, 134 136

G Gas bubbles by electrolysis, 299

Glycerol solution, 213 Glycosylation, 33 34 Grape-pressed cake extracts, 238 Grapes (Vitis vinifera), 58 59 Green solvents, 74 75 Green technology, 66 Grinding, 259

H Half-cell reaction, 288 Hazard Analysis and Critical Control Points program, 278 Health and cellular integrity, 57 58 Healthy food products on pulsed electric field (PEF) treatment, 25, 28 29 applications, 25 26 challenges of, 38 40 densification and, 28 food contaminants, reduction of, 30 34 in food industry, potential applications, 34 38 and nonlethal processing temperatures, 38 39 structural and biochemical changes, 28 valuable compounds, retention of, 25 30 Healthy snacks, 103 104. See also Snack(s) consumer choices on, 103 104 demand for, 119 need for, 104 105 Heat and mass transfer based process, 157 160 Heat processing, 35 37 Heat treatment, optimized, 147 Hexane, 85 High hydrostatic pressure (HHP), 214 221, 313 High-intensity PEF treatment, 14, 236 High molecular mass substances, 210

Index

High pressure homogenization (HPH), 253 High-voltage pulse generator, 228 229, 283 Historical background, of PEF commercialization, 270 274 HMF formation, 134 H2O2-induced oxidative damage, 57 Homogeneous external electric field, 13 HPH. See High pressure homogenization (HPH) HHP. See High hydrostatic pressure (HHP) Hydrogenized fats, 115 117 Hydrophilic pores, 10 Hydrophobic pores, 10 Hydroxycinnamic acids, 89 90 5-hydroxymethylfurfural (HMF), 31, 32f, 129 131, 134t furfural and, 134 136 Hypodermis, 77 78

I Ice crystals formation, 208 210 Ice-nucleating proteins (INPs), 209 210 Inactivating microorganisms, 132 Industrial application, 231, 269 270 for AC electro plasmolysis, 270 271, 271f current, 275 278 cutting and peeling improvement, 275 276 mass transport enhancement, 275 process control options, 278 shelf life extension of juices, 276 277 equipment, 274 275 Industrial chips processing, 108 111

Industrial implementation, snack(s), 120 123 Industrial scale systems, 274 275, 278 Industry acrylamide, 107 Industry domains, 210 Inhibitory factors, 317 Innovative processing technique, 131 132, 143 144 INPs. See Ice-nucleating proteins (INPs) Insects, 247 biomass, PEF for treatment, 254 260 cells permeabilization, 255 258, 256f, 257f extraction of intracellular compounds, 259 260 inactivation of, 255 industry development, 248 insect-based food, 254 as potential food ingredient, 261 262 valorization, 248 Intellectual property rights, 280 Internal mass transfer resistance, 157 158 International Agency for Research on Cancer, 105 Intra- and extracellular media, 5 6 Intracellular compounds, 251 252, 254 extraction of, 253 254, 259 260 Intracellular electroporation, 165 168 Intracellular water, 118 Intrinsic electrical resistance, 305 In vitro peptic digestion, 26, 60 Ionic double layer, 287 Irregularly shaped cells, 12 Irreversible electroporation, 70 71, 161 168, 206 208 Irreversible permeabilization, of cell membrane, 284

331

Isoflavonoids, 89, 235 Isothermal frying, 112

J Juice extraction, 230 Juice yield, 272

K Kettle-fried chips, 110 111, 114, 115f Kinetic models, 132 133

L Laplace differential equation, 4 5, 10 11 Lipids, 85 86 bilayer, 9 extraction, 260 oxidation, 300 Lipophilic antioxidant capacity, 25 26 Liquid and semiliquid food products, 228 Liquid food pasteurization, 295 296 Liquid product, 269 Liquid solid-separation techniques, 272 273, 275 Listeria monocytogenes, 38 39 Living insects, 255 Long duration pulses, 14 Low-intensity PEF treatment, 7 Low molecular weight compounds, 210, 313 Lutein, 83 84, 179, 252 253 Lycopene, 83 bioaccessibility, 59 61

M Maillard reaction (MR), 31 33, 76, 129 131, 130f acrylamide formation during, 105, 106f pulsed electric field on, 132 134, 134t Maillard reaction products (MRPs), 129 131, 131f Malvidin-3-O-glucoside, 58 Mammalian cells, 5

332

Index

Marx generators, 274 275 Mass transfer process, 182 185 Mass transport enhancement, 275 MAV. See Maximum allowable values (MAV) Maximum allowable values (MAV), 291 292 Mechanical expression, 228 Media parameters, 73 74 Membrane electroporation, 66 67, 73 75 Membrane permeabilization, 15 “Memory effect”, 165 168 Merlot grape variety, 58 59 Metabolic disorders, of chronic diseases, 26 Methamidophos, 30 31, 144 Microalgae, 86, 247, 261 biomass, PEF for treatment inactivation of microorganisms and extraction improvement, 250 254 stress response, stimulation, and mutation of, 248 250 cells, disintegration of, 254 cultivation chain, 250 high-added value components, 250 251 physical and chemical characteristics, 247 Microbial cell lysis, 69 Microbial cell membranes, 160 Microorganisms, 38 39, 301 inactivation of, 250 254, 313 314 Microwave vacuum drying, 120 Mild pretreatment method, 233 Milk and milk products, 60 Moist product, 117 Molecular oxygen, by electrolysis, 298 Monounsaturated oleic acid, 115 117 MR. See Maillard reaction (MR) Mutation, of microalgae biomass, 248 250

Mycotoxins, 141 142, 145 contamination by, 142 143 prevalence, 142

N Nannochloropsis, 253 254 Nannochloropsis sp., 83 84, 87 88 Nanosecond PEF (nsPEF), 248 249 application, 255 for culture media with Chlorella vulgaris, 250 Natural and synthetic polymers, 209 210 Natural antioxidants, 305 Natural colorants, 82 83 “Natural-like” foods, 65 Natural pigments, 171 172 Near infrared (NIR) technology, 112 Neochloris oleoabundans, 252 253 Neo-formed contaminants, 129 131 NIR technology. See Near infrared (NIR) technology Nocardiopsis salina, 87 88 Noncommunicable diseases, 115 117 Nonelectroporated guard cells, 165 168 Nonlethal processing temperatures, 38 39 Nonpolar solvent, 83 Nonspherical geometrically regular cells, 11 12 Nonthermal food processing technologies, 31, 34, 51, 65, 131, 159 160, 206, 221 222, 312 cold plasma, 313 314 concept of, 315 320 on freezing process, 215t high hydrostatic pressure, 313 pulsed electric field, 312 313 respondent group of consumers, 317 319

risks associated with, 319 320 ultrasound, 313 Nonthermal processing methods, 143, 283 Normal juice extraction procedures, 238 Novel extraction technologies, 132, 227 228, 234 “Novel food”, 317 nsPEF. See Nanosecond PEF (nsPEF) Numerical model, 13 Nutraceuticals, 66, 229 Nutrients and bioactive compounds bioaccessibility/ bioavailability, 53t, 59 carrots (Daucus carota), 56 57 fruit and vegetable mixture combinations, 60 61 grapes (Vitis vinifera), 58 59 milk and milk products, 60 orange (Citrus sinensis), 59 tomato (Solanum lycoperiscum), 59 60 impact of PEF on, 52f, 53t Nutritional value of snack, 104

O Ohmic heating, 131 Oil absorption properties, 118 Oil extraction, 235 236 Oilseeds, 80 81 Oil yields extraction, 260f impact of pulsed electric field on, 235 236 Olea europaea, 237 Olive kernels (Olea europaea), 237 Onions, cell disintegration index of, 161 165 Orange (Citrus sinensis), 59 Organic solvents, 85 Oscillatory pulses, 71 72, 228 229

Index

Osmo-dehydrated food, 186 190 Osmotic dehydration (OD), 155 160, 156f food materials, 183f fruit and vegetables with, 211 pulsed electric field role in, 182 190 kinetics, 182 186 of osmo-dehydrated food, 186 190 Ovomucin-depleted egg white, 60 Oxalic acid, 33 Oxidation management solution, 112 Oxidative damage, 57 Oxidative stress, 58 59, 61, 88 89

P Patents, relevant early stage, 278 280 Pathogens, 35 37 p-coumaric acid, 26 27 Pectic acid polymers, 188 189 Pectin, 86 87 Pectin-related enzymes, 177 178 PEF-assisted dehydrofreezing, 222 PEF-assisted extraction, 230 advantages, 74 75 OD process, 183 184 of pectin, 87 polyphenol extraction using, 237 PEFs. See Pulsed electric fields (PEFs) Pepsinolysis, 60 Peptides, 87 Permeabilization cell membrane, 4 8, 7f, 14 16, 161 165 technologies, 253 Pesticides, 30 34, 141, 144 145 and fungicides, 142f and mycotoxin, 143 pulsed electric fields on, 144t

Phase transition, 205 Phenolic acids, 76 78 Phenolic compounds, 26 27 bioaccessibility, 60 61 Phenylalanine ammonia-lyase, 89 90 pH model system, 34 Phospholipid bilayer, 10, 269 Phycocyanin, 251 Physical model, 4 5 Physicochemical properties, pulsed electric field on, 173t of dried food, 171 182 Pilot-scale PEF treatment system, 86 Pilot system, 274 Pinot Noir variety (Vitis vinifera L.), 58 Plant- and animal-originated food, 211 Plant- and microalgae-based protein ingredients, 87 88 Plant biotechnology techniques, 89 Plant secondary metabolites production, PEF in, 88 90 Plasmolysis, 188 189 Plastids or vacuoles, 178 179 Poland, nonthermal food processing technology attitude of respondent group of consumers, 317 319 food products processed by, 316 317 risks associated with, 319 320 Polypeptide chains, 210 Polyphenols, 180 182 dietary, 76 82 in seeds, 80 81 Polyunsaturated fatty acids, 85, 105 Pore formation, 269 Porosity, 165 168 Porphyridium cruentum, 253

333

Postharvest operations, 236 237 Potato chips production, 107 109, 109f freezing process, 207 208 peeling, 110 starch, 26 Potato-processing industry, 35, 51, 274 276, 284 Power-consuming diffusion, 230 PPO enzyme, 189 190 Predrying treatment for plant, 37 38 Preprocessing operations, 235 236 Pressing, 228, 235 236 Process control options, 278 Process optimization, 112 Product cell structure, 269 Prooxidant activity, 180 182 Protective mechanisms of cells, 248 249 Protein-based products, 277 Protein-rich food products, 87, 106 Proteins, 87 88, 272 273 denaturation, 210 211 growing demand for, 248 phycocyanin and, 251 Proteolytic enzymatic, 230 231 Pulse and delay, 15 16 duration, 14 15 number and frequency, 15 16 positive and negative, 72 shape, 16 17 Pulsed electric fields (PEFs), 3, 25, 28 29, 156 157, 156f, 247 acrylamide reduction with, 113 115 altered mechanical properties, 207 208 application, 4 5, 51 in compounds and fractions extraction.

334

Index

See Extraction of compounds and fractions average electrical consumption of, 121 benefits, 122t cell membrane permeabilization, 4 8, 7f challenges of, 38 40 on color of dried material, 179 commercialization, 270 274 critical value/dielectric breakdown, 8 10 models applied for, 9 10 densification and, 28 on drying kinetics, 161 171, 162t effective water diffusion coefficient, 165 168 effect on reconstitution properties, 172 176 effect on rehydration properties, 172 176 effects on furfural and hydroxymethylfurfural formation, 134 136 effects on toxins from food products, 146t efficiency, factors affecting, 69 74 media parameters, 73 74 pulse parameters, 70 72 tissue parameters, 72 73 of electric field strength, 79 80 electrochemical reactions in. See Electrochemical reactions electroporation on different systems, 10 13 cells in dense suspensions and tissues, 12 13 irregularly shaped cells, 12 nonspherical geometrically regular cells, 11 12 spherical cell, 10 11 extraction system, 67f in food additives and nutraceuticals extraction.

See Food additives and nutraceuticals extraction for freeze drying, 120 freezing process by. See Freezing process for fruit juice preservation, 274 of grape by-products, 78 79 healthy snacks production. See Snack(s) and heat treatment, 59 60 on HMF concentration, 31 32 impact on dehydration processes, 160 182 influence of, 214 221 insects on. See Insects on Maillard reaction. See Maillard reaction (MR) microalgae. See Microalgae microsecond applications of, 255 and nonlethal processing temperatures, 38 39 nonthermal food processing technologies, 312 313 on nutrients and bioactive compounds. See Nutrients and bioactive compounds optimization, 34 on pesticides, 141, 144 145, 144t on physicochemical properties, 173t of dried food, 171 182 in plant secondary metabolites production, 88 90 on polyphenols, 26 28 principles, 66 69 real mechanism of, 4 role in osmotic dehydration. See Osmotic dehydration (OD) stainless steel electrodes in, 292, 293t treatment chamber, 279f

Pulsed power systems, 280, 302 Pulse-forming networks, 16 17 Pulse generator, 75 76, 270 for electroplasmolis, 271f Pulse parameters, 70 72 Pulse polarity, 71 72 Pulse rise time (PRT), 28 29 Pulse shape, 71 72 Pulse transformers, 302 Pulse transmission cables, 121 Pulse treatment, 287 Purple Haze and Nutri Red carrots, 57

Q Quadratic model, 147

R Raw material, 177 178, 270 271 Reactive oxygen species (ROS), 76, 300 301 Rectangular waveform, 16 Red beetroot, 176 177 Reduction acrylamide formation with chips processing, 111 113 fat content in fried snacks, 117 119 with pulsed electric field, 113 115 of food contaminants (toxins, pesticides), 30 34 Refrigeration, 229 Regular snacks, 103 104 Regulation (EU) No 1047/2012, 316 Rehydration, 172 176 Resealing process, 5 6 Residual fungicides, 145 Resistant starch (RS), 26 Retention of valuable compounds, 25 30 Return of investment (ROI), 122 123 Reversible electroporation, 3 4, 7 8, 17, 69 71, 73 74,

Index

88 89, 165 168, 206, 213 214 on vacuum and freeze-drying, 171 RF freezing, 221 Ricin, 148 Rise time, 16 ROS. See Reactive oxygen species (ROS) Rotating electrodes, 272 RS. See Resistant starch (RS)

S Saccharomyces cerevisiae, 38 39 Safest preservation techniques, 203 204 Saturated fats, 115 117 Savory snacks, 103 104 SDS fractions. See Slowly digestible starch (SDS) fractions Secondary chemical reactions, 299 301 Secondary metabolites, 141 142 Shelf life extension of juices, 276 277 Short-term negative feelings, 316 Single-layered membrane, 73 Sitophilus granarius L., 255 Slow browning rates, 32 Slowly digestible starch (SDS) fractions, 26 Snack(s), 103 104 acrylamide formation in. See Acrylamide formation dried, 119 120 industrial chips processing, 108 111 industrial implementation, 120 123 industry, 107 108, 115 117 nutritional value of, 104 potato-processing industry, 274 276 products, 108 fat in, 115 118 Solid gain (SG), 182 186

335

Solid liquid extractions, 81, 231 233 Solid-state devices, 302 Sophisticated drying techniques, 169 170 Spinach, frozen thawed, 213 214 Square wave bipolar pulse, 72 Stabilization step, 5 6 Stabilizers, 86 87 Stainless steel electrodes, 292, 293t Stand-alone method, 120 State-of-the-art technology, 122 123 Steam peeling, 110 Stimulation, of microalgae biomass, 248 250 Strawberry fruits AFP during freezing of, 210 211 cell membrane, 187 188 Streptococcus lactis, 270 Stress response exact molecular mechanism of, 88 89 of microalgae biomass, 248 250 Subcooling, 205 Sugar beet raw juice, 279 Sugar consumption, 134 Supercooling, 204 205 Supercritical fluid extraction, 83, 85 Sweet potato chips, 108

degradation, 159 preservation, 161 165 3-(4,5-dimethythiazol-2-yl)-2,5diphenyl tetrazolium bromide (MTT), 58 59 Tissue damage degree, 255 256 Tissue parameters, 72 73 Tomato (Solanum lycoperiscum), 59 60 Tomato-based products, 25 26 Tomato by-products, 237 Tonoplast, 73 Toxic compounds, 298 Toxicity, 31 Toxic solvents, 74 75 Toxins, 30 34, 145 148, 291 292 Traditional thermal processing methods, 133, 284 Trans-fatty acids, 115 117 Transmembrane potential (ΔΦ) breakdown model, 67 68 Transmembrane voltage, 4 5, 10 11 Treated materials, 206 Treatment duration, 70 71 Trehalose, 210 211 TRL9. See Technological readiness level (TRL9) Two-exponential kinetic model, 185 186 2FI polynomial model, 147 Two-way mass transfer process, 158

T

Ultrasound (US), 204, 206, 212 221, 313 Unsaturated fatty acids, 105, 115 117 Untreated, 36f frozen thawed material, 207 208 and PEF pretreated, 36f, 37f, 38f US-assisted freezing, 214 221

Taxus chinensis, 89 Taxuyunnanine C, 89 Technological readiness level (TRL9), 221 Temporary electroporation, 69 Tenebrio molitor treatment, 248 Textural properties of plant material, 177 178 Thermal and nonthermal techniques, 75 Thermolabile compounds, 156 157

U

V Vaccinium myrtillus L., 233

336

Index

Vacuoles of plant cells, 73 Vacuum freeze drying, 37 38, 120, 161 165, 169 171 Vacuum fried chips, 112, 118 Vacuum impregnation (VI), 206, 211 214, 222 Valorization of insects, 248 of wastes, 236 237 Valuable compounds, 25, 30, 34 35 retention of, 25 30 Value-added products, 237 Vegetable oils, 85

Vegetables, 159 160, 229 230 impact of PEF treatment on, 173t Vegetative microorganisms, 278 279 Veggie chips, 103 104, 108 Vitamin C degradation, 179 180 Vitis vinifera L., 89

W Wastes, extraction of bioactive compounds from, 236 238

Water absorption, 172 176 Water loss (WL), 182 186 Water removal methods, 119 120 Wine preparation, improvement in, 233 234 WL. See Water loss (WL)

Y Yellow Solar cultivar, 57

Z Zeaxanthin, 179 “Zero net charge”, 302