Postharvest disinfection of fruits and vegetables 9780128126981, 0128126981

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POSTHARVEST DISINFECTION OF FRUITS AND VEGETABLES

POSTHARVEST DISINFECTION OF FRUITS AND VEGETABLES

Edited by

MOHAMMED WASIM SIDDIQUI Department of Food Science and Post-Harvest Technology, Bihar Agricultural University, Sabour, India

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 © 2018 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN 978-0-12-812698-1 For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Andre Gerhard Wolff Acquisition Editor: Patricia Osborn Editorial Project Manager: Karen Miller Production Project Manager: Paul Prasad Chandramohan Cover Designer: Mark Rogers Typeset by SPi Global, India

DEDICATION

For My Loving Brothers Mohammed Faeem Siddiqui & Mohammed Javed Siddiqui Who Always Encourage Me for Academic Ventures

CONTRIBUTORS J. Abraham Domı´nguez-Avila Coordination of Food Technology of Plant Origin, Center for Research in Food and Development, Hermosillo, Mexico Ghan Shyam Abrol College of Horticulture & Forestry, Central Agriculture University, Jhansi, India A. Aguayo-Acosta Department of Biological Sciences, Autonomous University of Nuevo Leon, San Nicolas, Mexico Luis M. Anaya-Esparza Food Microbiology Laboratory, Department of Agricultural and Livestock Sciences, University of Guadalajara, University Center of Los Altos, Tepatitla´n de Morelos, Mexico J. Angulo-Parra Superior Technological Institute of Guasave, TecNM, Guasave, Mexico Bindvi Arora Division of Food Science and Postharvest Technology, ICAR-Indian Agricultural Research Institute, New Delhi, India Vasudha Bansal Department of Food Engineering and Nutrition, Center of Innovative and Applied Bioprocessing, Mohali, India David F. Bridges United States Department of Agriculture, Agricultural Research Service, Western Regional Research Service, Produce Safety and Microbiology Research Unit, Albany, CA, United States Andrea Cardoso de Aquino Department of Food Engineering, Federal University of Ceara, Fortaleza, Brazil L. Coronado-Partida Technological Institute of Tepic-TecNM, LIIA-Biotechnology Laboratory, Tepic, Mexico J.E. Da´vila-Avin˜a Department of Biological Sciences, Autonomous University of Nuevo Leon, San Nicolas, Mexico Luciana de Siqueira Oliveira Department of Food Engineering, Federal University of Ceara, Fortaleza, Brazil

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Contributors

Neeru Dubey Amity International Center for Post Harvest Technology & Cold Chain Management, Amity University, Noida, India Kaliana Sitonio Ec¸ a Department of Food Engineering, Federal University of Ceara, Fortaleza, Brazil Gustavo A. Gonza´lez-Aguilar Coordination of Food Technology of Plant Origin, Center for Research in Food and Development, Hermosillo, Mexico R. Gonza´lez-Estrada Technological Institute of Tepic-TecNM, LIIA-Biotechnology Laboratory, Tepic, Mexico Gajanan Gundewadi Division of Post Harvest Technology, ICAR-Indian Agricultural Research Institute, New Delhi, India P. Gutierrez-Martı´nez Technological Institute of Tepic-TecNM, LIIA-Biotechnology Laboratory, Tepic, Mexico Riadh Ilahy Laboratory of Horticulture, National Agricultural Research Institute of Tunisia, Ariana, Tunisia Alka Joshi Division of Food Science and Postharvest Technology, ICAR-Indian Agricultural Research Institute, New Delhi, India Venkata Satish Kuchi Department of Postharvest Technology, College of Horticulture, Dr. YSRHU, Anantharajupeta, India Deepak Mehta Department of Food Engineering and Nutrition, Center of Innovative and Applied Bioprocessing, Mohali, India Vigya Mishra Department of Post Harvest Technology, College of Horticulture, Banda University of Agriculture & Technology, Banda, India Efigenia Montalvo-Gonza´lez Integral Laboratory of Food Research, Technological Institute of Tepic, Tepic, Mexico Mahmoudreza Ovissipour Department of Food Science and Technology, Virginia Polytechnic Institute and State University, Blacksburg; Virginia Seafood AREC, Hampton, VA, United States Alemwati Pongener ICAR-National Research Centre on Litchi, Muzaffarpur, India

Contributors

Priyanka Prasad Department of Food Engineering and Nutrition, Center of Innovative and Applied Bioprocessing, Mohali, India S.K. Purbey ICAR-National Research Centre on Litchi, Muzaffarpur, India A. Ramos-Guerrero Technological Institute of Tepic-TecNM, LIIA-Biotechnology Laboratory, Tepic, Mexico S. Vijay Rakesh Reddy ICAR-Central Institute for Arid Horticulture, Bikaner, India C. Rodrı´guez-Pereida Technological Institute of Tepic-TecNM, LIIA-Biotechnology Laboratory, Tepic, Mexico Shruti Sethi Division of Food Science and Postharvest Technology, ICAR-Indian Agricultural Research Institute, New Delhi, India R.R. Sharma Division of Post Harvest Technology, ICAR-Indian Agricultural Research Institute, New Delhi, India Swati Sharma ICAR-National Research Centre on Litchi, Muzaffarpur, India Setareh G. Shiroodi Department of Food Science and Technology, University of California, Davis, CA, United States Mohammed Wasim Siddiqui Department of Food Science and Postharvest Technology, Bihar Agricultural University, Sabour, Bhagalpur, India Dinesh Singh Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi, India Deepsikha Thakur Amity Institute of Organic Agriculture, Amity University Uttar Pradesh, Noida, India Lucicleia Barros Vasconcelos Department of Food Engineering, Federal University of Ceara, Fortaleza, Brazil Vivian C.H. Wu United States Department of Agriculture, Agricultural Research Service, Western Regional Research Service, Produce Safety and Microbiology Research Unit, Albany, CA, United States C. Zoellner Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, NY, United States

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ABOUT THE EDITOR

Mohammed Wasim Siddiqui Dr. Mohammed Wasim Siddiqui is an Assistant Professor and Scientist in the Department of Food Science and Post-Harvest Technology, Bihar Agricultural University, Sabour, India and author or coauthor of more than 35 journal articles, more than 40 book chapters, and several conference papers. He has more than 20 books to his credit published by Elsevier, United States, CRC Press, United States, Springer, United States, and Apple Academic Press, United States. He is the Founder Editor-in-Chief of two book series titled “Postharvest Biology and Technology” and “Innovations in Horticultural Science” being published by Apple Academic Press, New Jersey, United States, where he is a senior acquisitions editor for Horticultural Science as well. He also established an international peer reviewed journal “Journal of Postharvest Technology.” Dr. Siddiqui has been serving as an editorial board member and active reviewer of several international journals including Horticulture Research (Nature Publishing Group), Postharvest Biology and Technology (Elsevier), PLoS One (PLOS), LWT—Food Science and Technology (Elsevier), Food Science and Nutrition (Wiley), Journal of Plant Growth Regulation (Springer), Acta Physiologiae Plantarum (Springer), Journal of Food Science and Technology (Springer), Indian Journal of Agricultural Science (ICAR), and so on. Dr. Siddiqui has received numerous awards and fellowships in recognition of research and teaching achievements. Recently, he was conferred with the Glory of India Award2017, Best Researcher Award-2016, Best Citizens of India Award-2016, Bharat Jyoti Award-2016, Outstanding Researcher Award-2016, Best Young Researcher Award2015, Young Scientist Award-2015, and the Young Achiever Award-2014 for the outstanding contribution in research and teaching from several organizations of national and international repute. He was also awarded Maulana Azad National Fellowship Award from the University Grants Commission, New Delhi, India. He is an Honorary Board Member and Life Time Author Society for Advancement of Human and Nature (SADHNA), Nauni, Himachal Pradesh, India. He has been an active member of organizing committee of several national and international seminars/conferences/summits. He is one of the key members in establishing the World Food Preservation Center (WFPC), LLC, United States. Currently, he is an active associate and supporter of

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About the Editor

WFPC, LLC, United States. Considering his outstanding contribution in science and technology, his biography has been published in “Asia Pacific Who’s Who,” Famous Nation: India’s Who’s Who, “The Honored Best Citizens of India,” and Emerald Who’s Who in Asia. Dr. Siddiqui acquired BSc (Agriculture) degree from Jawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur, India. He received MSc (Horticulture) and PhD (Horticulture) degrees from Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, India with specialization in the postharvest biotechnology. He has received several grants from various funding agencies to carry out his research projects. He is dynamically indulged in teaching (graduate and doctorate students) and research, and he has proved himself as an active scientist in the area of postharvest biotechnology.

PREFACE

Global fruit and vegetable production has increased many folds since last few decades. In spite of increased production, we are still lagging behind to properly utilize the produce. Most of the developing countries are losing up to 30%–40% of total fruit and vegetable production due to inadequate postharvest handling practices. There are several factors responsible for huge postharvest losses including poor postharvest infrastructure such as storage and transportation facilities. Postharvest biotic and abiotic stresses can aggravate the ripening/senescence resulting in the early decay. Biotic stresses including infection of bacteria and fungus render commodity unsalable. Several microorganisms have been identified causing a number of postharvest diseases in fruits and vegetables. Irrespective of the countries, the farmers belong to poor and middle class families. Using the most successful and established techniques such as cold/CA storage are beyond the capacity of common/small farmers. They need to have some cheap and easy to apply technologies with practical implications. Besides, consumers are increasingly concerned about the quality and safety of produce they buy. Therefore, appropriate approaches and technologies are needed to reduce postharvest microbial infections assuring safe produce for health and environment. Postharvest produce washing and cleaning have been well studied to avoid/reduce the incidence of microbes. Washing is the recommended postharvest practice but it has been reported that the washing of produce with simple water results in faster deterioration. Various new technologies including sanitizers have been developed for reducing the levels of microorganisms on surfaces of fruits and vegetables which are responsible for postharvest diseases and foodborne illnesses. In addition to chlorination, disinfection of fruits and vegetables using ozone, pulsed light, irradiation, plasma technology, organic acid, hydrogen peroxide, hot/cold water, electrolyzed water, natural antimicrobial agents, etc., have been developed and suggested recently, without affecting the natural quality. International markets generally reject shipments of fruit and vegetables containing unauthorized pesticides, with chemical residues exceeding permissible limits, and/or with inadequate labeling and packaging. Postharvest management technologies determine food quality and safety, competitiveness in the market, and the profits earned by producers. The book “Postharvest Disinfection of Fruits and Vegetables” will determine the scope of emerging eco-friendly technologies developed to reduce microbial infection for maintaining the postharvest quality and safety. The book covers an analysis of the several methodologies pointing out the significant advantage and limitations of each

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Preface

technique. This book will be a standard reference work for the fresh produce industry in postharvest handling and management for preserving the quality of fresh fruits and vegetables. The editor is confident that this book will prove to be a unique reference work in the field of postharvest produce quality maintenance. The information can be used in postharvest disinfection along with maintaining cosmetic appeals of fresh fruits and vegetables. The editor would appreciate receiving new information and comments to assist in the future development of the next edition.

CHAPTER 1

Postharvest Diseases of Fruits and Vegetables and Their Management Dinesh Singh*, R.R. Sharma† *

Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi, India Division of Post Harvest Technology, ICAR-Indian Agricultural Research Institute, New Delhi, India

†

1. INTRODUCTION Fruits and vegetables are considered as perishable crops compared to cereals, pulses, and oil seed crops. Most of them have very high moisture content (about 70%–95% water), usually have a large size (5–5 kg), exhibit a higher respiration rate, and usually have a soft texture, all of which favor the growth and development of several diseases caused by microorganisms between the periods of harvest and consumption. Postharvest losses to fruits and vegetables in developing countries have been estimated to be about 30%–50% or more (Salunkhe and Desai, 1984). Fruits and vegetables are living organisms and their marketable life is largely affected by the prevailing temperature, relative humidity, the composition of the atmosphere during and after harvest, and the type and degree of infection by the microorganisms or insects. They deteriorate during storage through loss of moisture, decay caused by pathogens, rodents, loss of stored energy, loss of nutrients and vitamins (Desai and Pathak, 1970; Majumdar and Pathak, 1989; Pathak, 1997), undergo physical losses because of pests and disease attack, along with a loss in quality arising from physiological disorders, fiber development, greening (potatoes), root growth, sprouting, rooting, shoot growth, and seed germination. In addition, contamination of foodstuff by mycotoxins, which are elaborated by plant tissues in response to fungal attack, is also responsible for postharvest losses.

2. PATHOGENS CAUSING POSTHARVEST DISEASES Several pathogens such as fungi and bacteria are responsible for causing diseases in fruits and vegetables. However, it is well known that the major postharvest losses are caused by fungi, such as Alternaria, Aspergillus, Botrytis, Colletotrichum, Diplodia, Monilinia, Penicillium, Phomopsis, Rhizopus, Mucor, and Sclerotinia, and bacteria, such as Erwinia and Pseudomonas (Table 1) (Barkai-Golan, 2005; Sharma et al., 2009). Most of these organisms are weak pathogens in that they can only invade damaged produce. Physical damage plays an important role in postharvest deterioration and is the primary cause of the losses. Various Postharvest Disinfection of Fruits and Vegetables https://doi.org/10.1016/B978-0-12-812698-1.00001-7

© 2018 Elsevier Inc. All rights reserved.

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Postharvest Disinfection of Fruits and Vegetables

Table 1 Major postharvest diseases of fruits and vegetables and causal agents Name of the Causal pathogen Affected fruits and Reference(s) disease vegetables

Anthracnose

Colletotrichum gloeosporioides

Avocado, mango, banana, papaya, guava, citrus fruits, etc.

Anthracnose crown rot

Colletotrichum musae

Banana

Bacterial soft rot

Erwinia carotovora ssp. carotovora Erwinia spp.

Bitter rot

Colletotrichum gloeosporioides

Tomato, pepper, melon, squash, pumpkin, cucumber, cabbage, cauliflower, lettuce, celery, broccoli, spinach, asparagus, pea, bean, potato, sweet potato, onion, garlic, etc. Pome and stone fruits

Black heart, brown rot Black lesion, black rot Black lesion, dark spots

Black pit Black rot

Prusky et al. (1983), Eckert (1977), Singh and Thakur (2003), Robert et al. (2012), Lima et al. (2013), and Sellamuthu et al. (2013) Eckert (1977, 1990), Slabaugh and Grove (1982), and Sakinah et al. (2013) McDonald et al. (1999), Fallik et al. (2002), Phokum et al. (2006), Bhat et al. (2012)

C. fructicola Fusarium moniliforme Stemphylium radicinum Stemphylium botryosum

Pear Banana, pineapple

Edney and Burchill (1967), Janisiewicz et al. (2003), and Masoud et al. (2013) Li et al. (2013) Barkai-Golan (2005)

Carrot

Maude (1966)

Pome fruits, papaya, grape, tomato, lettuce, etc.

Pseudomonas syringae Aspergillus niger

Citrus fruits

Dickens and Evans (1973), Sivan and Barkai-Golan (1976), BarkaiGolan (2005), Llorente et al. (2010), and Toselli et al. (2012) Mirik et al. (2005)

Dates, grape, tomato, melon, onion, garlic, etc.

Barkai-Golan (2005), Irkin and Korukluoglu (2007), Storari et al. (2012), and Ramı´rez et al. (2013)

Hybrid Membrane System Design and Operation

Table 1 Major postharvest diseases of fruits and vegetables and causal agents—cont’d Name of the Causal pathogen Affected fruits and Reference(s) disease vegetables

Black rot, stalk rot, crown rot, soft rot Blue mold

Ceratocystis paradoxa

Banana, pineapple

Penicillium expansum

Mainly pome and stone fruits

Blue mold Brown rot

Penicillium italicum Monilinia fructicola

Mainly citrus fruits Mainly stone fruits

Brown rot

Monilinia laxa

Stone as well as pome fruits

Brown rot

Phytophthora citrophthora Pantoea agglomerans, P. ananatis, and P. allii Neofabraea species

Citrus fruits

Crown rot

Fusarium pallidoroseum, Acremonium spp.

Banana

Crown rot, cigarend rot Crown rot, finger rot, stalk rot stem-end rot

Verticillium theobromae Botryodiplodia theobromae

Banana

Dry or soft rot

Fusarium spp.

Tomato, pepper, eggplant, squash, pumpkin, watermelon, cabbage, celery, artichoke, asparagus, corn, carrot, potato, sweet potato, onion, garlic, etc.

Bulb rot

Bull’s eye rot of

Onion

Apple

Banana, citrus fruits, avocado, mango, etc.

Jamaluddin (1979) and Yadahalli et al. (2007) Barkai-Golan (2005), Palou et al. (2013), and Masoud et al. (2013) Ramı´rez et al. (2013) Barkai-Golan (2005), Yin et al. (2013), and Sisquella et al. (2013) Barkai-Golan (2005), Zhu and Guo (2010), and Marietta et al. (2012) Pane et al. (2001) and Vicent et al. (2012) Vahling-Armstrong et al. (2016)

Michalecka et al. (2016) Barkai-Golan (2005), Uman˜a-Rojas and Garcı´a (2011), and Renganathan and Muthukumar (2012) Igeleke and Ayanru (2006) Barkai-Golan (2005) and Renganathan and Muthukumar (2012) Barkai-Golan (2005), Sriram et al. (2010), Hou et al. (2012), and Thuy et al. (2013)

Continued

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Postharvest Disinfection of Fruits and Vegetables

Table 1 Major postharvest diseases of fruits and vegetables and causal agents—cont’d Name of the Causal pathogen Affected fruits and Reference(s) disease vegetables

Dry rot Fruit rot, dark spot, sooty mold

Fusarium sambucinum Alternaria alternata

Gray mold

Botrytis cinerea

Green mold

Penicillium digitatum

Lenticel rot

Gloeosporium album Cladosporium herbarum

Olive-green mold, sooty mold

Potato Apple, pear, peach, plum, cherry, grapes, papaya, tomato, pepper, brinjal, cucurbitaceous vegetables, cabbage, cauliflower, broccoli, pea, beans, carrot, potato, sweet potato, and onion, etc. Strawberry, raspberry, cherry, grapes, apple, pear, cherry, peach, plum, persimmon, citrus, kiwifruit, tomato, pepper, brinjal, cucumber, squash, melon, pumpkin, cabbage, cauliflower, lettuce, broccoli, pea, beans, carrot, onion, potato, sweet potato, etc. Exclusively citrus fruits

Apple, pear, etc. Dates, grapes, apple, pear, cherry, plum, peach and stone fruits, papaya, fig, tomato, pepper, melon

Bojanowski et al. (2013) Spalding (1980), Eckert and Ogawa (1985), BarkaiGolan (2005), Yin et al. (2012), and Kadam (2012)

Eckert and Ogawa (1988), Chalutz et al. (1988), McLaughlin et al. (1990), Coertze and Holz (1999), Emmanuel and Bernard (2002), Thomas et al. (2012), and Fortunati et al. (2017)

Eckert and Ogawa (1985), Porat et al. (2000a,b), and Ncumisa et al. (2013) Edney et al. (1977) Latorre et al. (2011)

Hybrid Membrane System Design and Operation

Table 1 Major postharvest diseases of fruits and vegetables and causal agents—cont’d Name of the Causal pathogen Affected fruits and Reference(s) disease vegetables

Pink mold

Trichothecium roseum

Sour rot

Geotrichum candidum

Spots or bacterial soft rot

Pseudomonas syringae

Stem-end rot Stem-end rot Stem-end rot, dry black rot Stem-end rot, stalk rot, finger rot, crown rot

Alternaria citri Phomopsis citri Phoma caricaepapayae Diplodia natalensis

Stem-end rot; black spot Watery soft rot

Alternaria alternata

Watery soft rot, watery white rot

Sclerotinia sclerotiorum

Watery white rot

Rhizopus stolonifer

Mucor piriformis

Pome and stone fruits, banana, avocado, tomato, melon, etc. Citrus fruits, tomato

Tomato, cucumber, melon, squash, asparagus, cabbage, cauliflower, lettuce, celery, broccoli, spinach, pea, bean, onion, etc. Citrus fruits Citrus fruits Papaya Citrus fruits, avocado, mango, banana, etc.

Avocado, mango, papaya, persimmon Tomato, strawberry, raspberry Citrus fruits, cabbage, cauliflower, lettuce, celery, broccoli, artichoke, pea, bean, carrot, brinjal, melons, cucumber, pumpkin, squash, onion, garlic, etc. Apple, pear, peach, plum, cherry, grapes, avocado, papaya, strawberry, raspberry, cherry, tomato, pepper, eggplant, carrot, melon, pumpkin, squash, pea, bean, sweet potato, etc.

Wang et al. (2008) and Bello (2008) Talibi et al. (2012a,b) and Thornton et al. (2010) Smith et al. (1991), Leonard et al. (2010), and Marı´a et al. (2011)

Hiroshi et al. (2007) Wolken (1949) Martins et al. (2010) Brown and Burns (1998) and Sriram and Poornachanddra (2013) Prusky et al. (2006) Borve and Vangdal (2007) and Borve et al. (2008) Mei et al. (2012) and Margaret et al. (2013)

Franc
es et al. (2006) and Fabrı´cio et al. (2010)

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types of injuries can be sustained before and after the harvest of produce. Injury can be caused by weather, insects, birds, rodents, and farm implements. Injuries to fruits usually occur when the produce is dropped onto a hard surface, before, during, or after packing, but injury is not usually apparent immediately. Later, bruising may also take place, but it is seen only externally (e.g., apples) or it may be evident only on peeling (e.g., potatoes). Compression bruising may result from the overstocking of bulk produce in storehouses or from the overfilling of the packaging (e.g., grapes). Vibration damage can occur in under-filled packs, especially during long distance road transportation. The damaged produce is attacked by various microorganisms, resulting in a progressive decay, which may affect the entire produce (Snowdon, 1990).

3. THE INFECTION PROCESS Microorganisms infect the produce, while still immature on the plant (preharvest infection) or during harvesting and subsequent handling and marketing operations (postharvest infection). The postharvest infection process is greatly aided by mechanical injuries to the peel of the produce, such as, fingernail scratches and abrasions, rough handling, insect punctures, and cut stems. The infection may occur by direct penetration of the cuticle or entry through stomata, lenticels, wounds, or abscission of scar tissue. Furthermore, the physiological condition of the produce, the temperature, and the formation of the periderm also significantly affect resulting in two types of infection, that is, preharvest infection and postharvest infection.

3.1 Preharvest Infection Preharvest infection of fruits and vegetables may occur through several avenues, such as direct penetration of the peel, infection through natural openings on the produce, and infection through the damaged portion. Several types of pathogenic fungi are capable of initiating the infection process on the surface of floral parts, and on sound, developing fruits. The infection is then arrested, which remains quiescent until after harvest, when the resistance of the host decreases and conditions become favorable for the growth of the pathogen, that is, when the fruit begins to ripen or its tissues become senescent (Barkai-Golan, 2005). Such “latent infections” are important in the postharvest wastage of many tropical and subtropical fruits, such as anthracnose of mangoes and papayas, crown rot of bananas, and stem-end rot of citrus. For example, spores of Colletotrichum germinate in moisture on the surface of the fruit and the end of the germ tube swells within several hours of germination and forms a structure known as appressorium, which may or may not penetrate the fruit peel before the infection is arrested. Weak parasitic fungi and bacteria may also gain access to immature fruits and vegetables through natural openings such as stomata, lenticels, and growth cracks. Again, this infection may not develop until the host becomes less resistant to the invading organism,

Hybrid Membrane System Design and Operation

such as when the fruits ripen. It appears that sound fruits and vegetables can suppress the growth of these organisms for a considerable time (Barkai-Golan, 2005). For example, spores of Phlyctaena vagabunda penetrate apple lenticels before harvest, which cause fruit rotting around the lenticels in the storage.

3.2 Postharvest Infection Many fungi that cause considerable wastage of produce are unable to penetrate the intact peel of produce, but readily invade via any break point in the peel. The damage is microscopic but is sufficient for the pathogens present on the crop to grow on it. In addition, the cut stem is a frequent point of entry for microorganisms and stem-end rots are important forms of postharvest spoilage of many fruits and vegetables (Barkai-Golan, 2005). For example, postharvest infection by Sclerotina and Colletotrichum is very common in many fruits through direct penetration of the peel. The infection of postharvest produce is caused by the infection to the different parts of the plants, such as floral infection, stem-end infection, and quiescent infection, which are described below. 3.2.1 Floral Infection There are several examples that indicate that infection by microorganisms occurs through floral parts in many fruits. For example, Botrytis cinerea on black currant (McNicol and Williamson, 1988) and raspberry (Dashwood and Fox, 1988), Monilinia laxa on plums (Schagbauer and Holz, 1990), and Lasiodiplodia theobromae on citrus fruits (Nadel, 1944; Minz, 1946) infect the produce at floral parts. In anthracnose of mango, an additional fruit infection may arise from quiescent infections at the base of the ovary. 3.2.2 Stem-End Infection Endophytic colonization of the inflorescence is an important mode of infection for the mango fruit caused by Dothiorella dominicana ( Johnson et al., 1992). Colonization by stem-end rot fungi, L. theobromae and Phomopsis citri, in the peduncle and pedicel of citrus fruits is restricted by the wound periderm and the cuticle. These fungi do not enter fruit until abscission occurs. Postharvest treatment with the growth hormone 2,4-dichloro phenoxy acetic acid (2,4-D) was therefore introduced to prevent abscission of the buttons (Eckert and Eaks, 1989). 3.2.3 Quiescent Infection The time between initial infection and appearance of disease symptoms is known as the latent or quiescent period (Berger and Bartz, 1982; Swinburne, 1983). The term “quiescent” refers to a dormant parasitic relationship, which after some time changes to an active one (Barkai-Golan, 2005). A fungus may become quiescent at the initiation of germination, germ tube elongation, appressorium formation, penetration, or

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subsequent colonization. According to Swinburne (1973), the failure to germinate or to develop beyond any subsequent stage is due to adverse physiological conditions temporarily imposed by the host, either directly on the pathogen or indirectly by modification in its pathogenic capability.

4. FACTORS AFFECTING THE DEVELOPMENT OF INFECTION The surrounding environment of the produce always plays an important role in the development of infection by the pathogens and in the subsequent postharvest wastage of the produce. The high temperature and high humidity favor the development of postharvest decay, and chilling injury generally predisposes tropical and subtropical produce levels and the correct humidity can restrict the rate of postharvest decay by checking the rate of ripening or senescence, repressing the growth of the pathogen, or both (BarkaiGolan, 2005). In addition, several other factors also affect the rate of development of infection in fruits and vegetables. For example, the fruit peel, which acts as a selective medium, is generally attacked by several fungi. Many vegetables have a pH > 4.5 and consequently bacterial rots are much more common in vegetables. Ripening fruits are more susceptible to wastage than immature fruits. Hence, treatments that slow down the rate of ripening (e.g., low temperature) will also retard the growth of decay organisms. Vegetables with the underground storage organs, for example, potato, cassava, yam, sweet potato, etc., are capable of forming layers of specialized cells (wound periderm) at the site of the injury, thus restricting the development of postharvest decay. During commercial handling of potato, periderm formation is promoted by 10–14 days storage at 7–15°C and 95% RH, a process known as curing. A type of curing process (possible by desiccation) has been shown to reduce the wastage of oranges by Penicillium digitatum. When the fruits are held at higher temperature (30°C) and humidity (90%) for several days, the orange peel becomes turgid and lignin are synthesized in the injured flavedo tissue, which affects the entry of microorganisms and thereby the decay.

5. MANAGEMENT OF POSTHARVEST DISEASES OF FRUITS AND VEGETABLES The basic methods for the control of postharvest diseases in fruits and vegetables involve three different approaches: (i) prevention of infection, (ii) elimination of incipient or latent infections, and (iii) prevention of spread of the pathogen in the host tissue. The main objective of postharvest fruit disease management is to keep the fruit diseasefree or symptom-free until it is marketed or consumed. Hence, the management strategies should aim at prevention, eradication, and delaying the symptoms of diseases during transit and storage of fruits and vegetables (Sharma and Alam, 1998; Barkai-Golan, 2005).

Hybrid Membrane System Design and Operation

To manage postharvest diseases of fruits and vegetables, the treatments are broadly divided into three groups, that is, physical, chemical, and biological. The effectiveness of treatment depends on the ability of the treatment or agent to reach the pathogen, the level and sensitivity of the infection, and the sensitivity of the host produce. The various methods of postharvest disease control of fruits and vegetables have been described briefly in the following sections.

5.1 Physical Treatments The postharvest diseases of fruits and vegetables may be controlled by various physical treatments, such as heat removal and low temperature storage, high temperature treatments, magnetic fields, and radiation. The various radiations include sound, ultrasound, radio, microwave, infrared, visible light, ultraviolet (UV), X-rays, gamma rays, and cathode ray spectra. Some are highly fungicidal, while others are less effective (Eckert and Sommer, 1967). Among these, a few have been used potentially in postharvest treatments of fruits and vegetables, which are described briefly. 5.1.1 Use of Gamma Irradiation Gamma irradiation can penetrate the produce and inactivate the deep-seated pathogens. Mature fruits are relatively resistant to radiation damage because cell division rarely occurs in immature tissues ( Johnson et al., 1990). Doses required to eradicate infections range from 2000 to 3000 Gy, in some cases as low as 1000 and in others as high as 6000 Gy, which is far higher than the dose required for disinfection (75–300 Gy) (Barkai-Golan et al., 1969; Barkai-Golan et al., 1977). In most cases, the radiation dose required for disease control is harmful to fruit quality. Lasiodiplodia, which causes stem-end rot of mango fruits, can be controlled effectively by gamma irradiation. In general, gamma irradiations have been very successful in controlling postharvest diseases in several fruits and vegetables (Table 2). Recently, a number of more or less technologically advanced methodologies, for example, irradiation combined with other types of treatments and induced Table 2 Use of gamma rays for postharvest disease control in fruits and vegetables Crops Minimum dose required (Gy) Maximum dose tolerated (Gy)

Apple Apricot, peaches, nectarin Avocado Lemon Orange Strawberry Grapes Tomato

150 200 – 150–200 200 200 – 300

100–150 50–100 25 250 200 200 25–50 100–150

9

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Postharvest Disinfection of Fruits and Vegetables

disease-resistance, have been developed to control postharvest diseases as well as to increase the quality and storage life of fresh commodities ( Jeong and Jeong, 2017). Synergistic effects of gamma irradiation combined with heat treatment (38°C for 4 days) contributed to the 5–10-fold increase in the inactivation of spores of postharvest pathogens (Temur and Tiryaki, 2013). Heat treatment may also affect the susceptibility of the host to pathogens by triggering the synthesis of an inhibitory substance in the peel. The combination of hot water and gamma irradiation synergistically reduced fungal development in tomato fruits, resulting in 1.7% and 10.0% infection rates by B. cinerea and Rhizopus stolonifer, respectively. Moreover, a hot water dip (HWD) followed by irradiation at 0.5 kGy totally eliminated the decay caused by Alternaria alternata for 8 days at 23°C in mango fruits (Spalding and Reeder, 1986). However, the combination of hot water with irradiation is not commonly used on fruits due to the detrimental effect it has on the quality of treated clementines and the contradictory results presented in different studies (Brodrick et al., 1976; Palou et al., 2007; Mahmoud et al., 2011). Another study suggested that a combined treatment of 0.5 kGy of gamma irradiation with hot water (47°C for 7 min) inactivates Penicillium expansum but does not prevent the growth of B. cinerea and Alternaria tenuis. In addition, the fungal population on mangoes was reduced by treatment with hot water (55°C for 5 min) and 1 kGy of gamma irradiation (El-Samahy et al., 2000). A similar study on tomato found that decay caused by B. cinerea, R. stolonifer, and A. alternata is reduced with a combined treatment of 1 kGy of gamma irradiation and a HWD at 50°C for 2 min (Barkai-Golan et al., 1993). Palou et al. (2007) used sodium carbonate, which is an alternative to synthetic fungicides to control citrus postharvest disease because it is inexpensive and can be used with a minimal risk of damage to the fruits. A combination of sodium carbonate with an X-ray irradiation dose of 0.875 kGy is more effective in controlling P. digitatum and Penicillium italicum compared to a single treatment. Several investigations have shown the inhibitory nature of nanosilver particles (NA) associated with sterilization (Kim et al., 2011; Jung et al., 2014). Gamma irradiation showed no antifungal activity at a dose of 1 kGy, but in combined treatments with NA or nanosized silica silver (NSS) at concentrations above 1 μg L 1, the same dose of gamma rays showed the strongest antifungal activity. In addition, a study has suggested that combination of irradiation with cold storage is also promising for the control of postharvest diseases. The growth of Colletotrichum acutatum on apples was dramatically inhibited when gamma irradiation was combined with storage at 0°C for 4 months compared to those stored at 20°C (Kim et al., 2011). Recently, a study demonstrated that the germination of P. expansum spores was completely inhibited with a 0.6 kGy dose of gamma rays when combined with storage at 1°C, without causing any significant physical changes in apples (Mostafavi et al., 2012).

Hybrid Membrane System Design and Operation

5.1.2 Use of Low Temperature Use of low temperature is considered very important in controlling decay in several fruits and vegetables. Low temperature may slow down the growth of the pathogens, but it also slows down the fruit ripening process. Temperature management is important in reducing physiological deterioration and preventing moisture loss and shriveling as well as reducing disease incidence. For this reason, with many commodities refrigeration can be considered a supplement to fungicidal treatments in several fruits and vegetables (Barkai-Golan, 2005). Between 0 and 30°C, every 10°C increase in temperature increases metabolic activity two- or threefolds. In general, it is recommended to store fruits and vegetables at the lowest possible temperature that does not harm the host. With many fruits and vegetables, the lowest desirable temperature is just above the freezing temperature. Certain varieties of apples, pears, plums, peaches, and grapes can thus be stored between 0 and 2°C. It is commonly observed that apples and pears stored at slightly below 0°C are attacked by B. cinerea, P. expansum, and Cladosporium. The pathogenic growth of most fungi, however, is completely stopped at temperature near 0°C. Rhizopus spp. was found to be highly susceptible to chilling injury near 0°C (Barkai-Golan, 2005). Since chilling injury is very common among fruits and vegetables, storage or transport of these commodities must be at higher than 0°C. Certain varieties of apples, avocados, bananas, citrus, mangoes, papayas, and pineapples as well as many vegetables, particularly members of Solanaceae and Cucurbitaceae are injured below 5°C or 10°C. Bananas are chilled at temperature near 15°C. In chilling injuries, the tissues turn brown and sometimes disease resistance is decreased. For example, A. tenuis (McColloch and Worthington, 1952) and Geotrichum candidum (Butler, 1960) develop readily during ripening if mature-green tomato fruits are previously stored below a critical temperature between 5 and 10°C. Similarly, Segall (1967) reported postchilling susceptibility of tomatoes to Erwinia caratovora and Aerobacter cloaceae. However, it is apparent that the effectiveness of refrigeration is limited by (i) delay in heat removal, (ii) lack of adequate refrigeration facilities, (iii) a need to remove the commodities from refrigeration to complete the ripening process in some cases, (iv) the inability to use the lowest temperatures because the commodities are susceptible to chilling injury, and (v) the ability of some postharvest pathogens to grow at temperatures below the freezing point of fruits and vegetables. 5.1.3 Heat Treatment of the Produce The use of heat for killing pathogenic fungi is a very old concept. It was first reported for the control of decay in citrus fruits in 1922 (Fawcett, 1922). Prestorage heat treatments to

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Postharvest Disinfection of Fruits and Vegetables

control decay are often applied for a relatively short time, because the target pathogens are found on the surface or in the first few cell layers under the peel of the fruit or vegetable. Heat may be applied to fruits and vegetables in several ways such as HWDs, vapor heat, or hot dry air or by hot water rinsing and brushing (Barkai-Golan, 1973; Barkai-Golan and Phillips, 1991; Klein and Lurie, 1991; Lurie, 1998; Fallik et al., 1996, 2001; Itoh, 2003). However, the major factors to be considered while developing postharvest heat treatments are: (i) thermal sensitivity of target organism, (ii) location of the target organism in or on the fruit, and (iii) thermal sensitivity of the fruit. These factors largely determine temperature, duration, and type of the heat treatment required. Heat treatment in the form of either moist hot air or HWDs has been commercialized for the control of postharvest diseases in several fruits, such as papayas, mangoes, and stone fruits. This eco-friendly technique has been used to control postharvest diseases in many fruits and vegetables (Tables 3 and 4). Hot water treatment reduces the severity of various fruit rots (Pathak et al., 1976; Majumdar and Pathak, 1991). The advantages of HWDs are that it controls surface infections as well as infections that have penetrated deep into the peel, and it leaves no chemical residues in the produce. HWDs must be precisely administered as the range of temperature necessary to control disease (50–55°C) can also damage the produce. It is believed that moist heat has greater lethality for two reasons: (a) enzymes are more readily coagulated when hydrated and (b) heat is transferred more readily in wet air. However, aerated steam has been found to be effective against some diseases. An apparatus fabricated on the basis of design used by Baker (1969) has been employed with good results against postharvest diseases of papayas, mangoes, guavas, and citrus (Gupta and Pathak, 1990; Patel, 1991; Vyas, 1993). Aerated steam is found to be more effective than hot water treatment against spore germination and disease severity. It appears that in aerated steam treatment, latent heat of vaporization is transferred to the spore fruit when steam condenses and it coagulated enzymes of the pathogens more effectively.

5.2 Chemical Treatments Chemical control of postharvest diseases of fruits and vegetables has become an integral part of the handling and successful marketing of citrus, bananas, and grapes. The level of control of fruit decay depends upon the marketing strategies for the commodity and the type of infection. For citrus, which has a relatively long postharvest life, the aim of the treatment is to prevent primary infection and sporulation so that nearby fruits are not contaminated. Strawberry has a short postharvest life and its treatment is aimed at preventing the spread of gray mold that infects the strawberries in the field. In other words, the treatment has to match the subsequent marketing of the commodity. There is no

Hybrid Membrane System Design and Operation

Table 3 Hot water treatments for controlling decay in some fruits and vegetables Hot water dip Time (min)

Disease controlled

A. Hot water dip treatments Apple 45

10

Avocado

40–42

20–30

Bean

52

0.5

Ber

50

5

Cherry

52

2

Guava

46

Kinnow

Fruit crop

Temperature (°C)

Possible injuries

References

Botrytis rot and Penicillium rots Colletotrichum rot

Reduced storage rot

Edney et al. (1977)

– –

–

Bhat (2004)

Slight discoloration

Johnson (1968)

35

Pythium butleri and Sclerotinia sclerotiorum Anthracnose rot Codling moth and Botrytis rot Botrytis rot

Wells and Cooley (1973) Wells and Cooley (1973)

–

50

2

Penicillium rot

–

Lemon

52–53

5–10

–

Litchi

52

2

Alternaria and Penicillium rots Brown rot

Stella et al. (2008) Singh and Thakur (2002) Houck (1967)

Mango

52

5

Anthracnose rot

No stem rot control

Melon

57–63

0.5

Fungal diseases

–

Orange

53

5

Blue and gray molds

Poor degreening

Papaya

48–49

20

–

Peach

50

2.5–3

Fungal diseases Brown rot, Rhizopus rot

Some browning

Motile skin

Scott et al. (1982) Spalding and Reeder (1972) King et al. (1969) and Teitel et al. (1989) Smoot and Melvin (1965) Hunter et al. (1969) Smith and Anderson (1975) and Singh et al. (2006) Continued

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Postharvest Disinfection of Fruits and Vegetables

Table 3 Hot water treatments for controlling decay in some fruits and vegetables—cont’d Hot water dip Temperature (°C)

Time (min)

Disease controlled

Possible injuries

References

Pepper (bell) Potato

53

1.5

Soft rot

Slight spotting

57.5

20–30

Tomato

39, 45

60 min

Johnson (1968) Ranganna et al. (1998) McDonald et al. (1999)

Fruit crop

– Bacterial soft rot

B. Hot water rinsing and brushing treatments Apple 55 10 s Storage rots

–

–

Grape fruit Kumquat

59–62

20 s

Green mold

–

58

20

Green mold

Decay

Litchi

55

20 s

–

Peel browning

Mango

46–65

10–25

Anthracnose

–

Melon

59

15

E. coli

–

Orange

56

20 s

Green mold

Decay

Sweet pepper Tangerine

55

15

56

20 s

Tomato

52

15

Gray and Black mold Green mold rot –

Decay incidence Surface wounding –

Maxin et al. (2012) Porat et al. (2000b) BenYehoshua et al. (2000) Lichter et al. (2000) Ryo et al. (2012) Fallik et al. (2000) Fatemi and Borji (2011) Fallik et al. (1999) Porat et al. (2000a) Ilic et al. (2001) and Fallik et al. (2002)

point in treating a short-life commodity with a fungicide that has a long residual activity. The success of a chemical treatment for disease control depends on the initial spore load, the depth of the infection within the host tissues, the growth rate of the infection, the temperature and humidity, and the depth to which the chemical can penetrate the host

Hybrid Membrane System Design and Operation

Table 4 Control of postharvest diseases of fruits by hot air treatment Hot air treatment Fruit crop

Temperature (°C)

Time (min)

RH (%)

Apple

55

15 s

100

Melon

30–90

35

Low

Peach

54

15

80

Strawberry

43

30

90

Disease

Bitter rot, blue mold rot Fungal diseases Brown rot, Rhizopus rot Alternaria rot, Gray mold rot, Rhizopus rot

Possible injuries

References

Deterioration

Edney and Burchill (1967)

Marked breakdown –

Teitel et al. (1989) Smith et al. (1964)

–

Smith and Worthington (1965)

tissues. Moreover, the applied chemical must not be phytotoxic (i.e., it must not injure the host tissue) and must fall within the ambit of the local food additive laws. About 20 organic compounds have been extensively evaluated as postharvest treatments to control diseases of perishable crops. First-generation postharvest fungicides (e.g., sodium o-phenylphenate (SOPP), dichloran, sec-butylamine, etc.) are effective in preventing decay by wound invading pathogens (e.g., Penicillium, Rhizopus, etc.) but have little effect on the development of latent and other deep-seated infections. Fungicides developed since 1965 have shown a higher degree of efficacy against latent infections as well as protective and antisporulant action in controlling certain postharvest diseases. Few specific antibacterial compounds have been developed for postharvest use and, until recently few fungicides were effective against Pythiaceous fungi, mucors, Alternaria, and Geotrichum, and diseases incited by these pathogens were difficult to control. Even compounds that showed in vitro activity against these fungi did not necessarily prevent disease development in the host, apparently because the fungicides were unable to penetrate to sites of latent or established infections or fungicides were inactivated by the host tissue. For controlling postharvest diseases of fruits and vegetables, fungicides can be applied in different ways as described further. 5.2.1 Preharvest Chemical Treatments In most cases, control of postharvest diseases should start before harvest in the orchard itself. The possibility of controlling well-established pathogens by postharvest

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Postharvest Disinfection of Fruits and Vegetables

disinfection is very less as most fungicides are unable to penetrate deeply into the tissues, and effective concentrations of the fungicide would not reach deep-seated infections. Hence, the effective way to reduce infections initiated in the field, including quiescent infections, is the application of broad-spectrum protective fungicides to the fruits on the plant itself. Preharvest spraying of citrus fruits in the groove with fixed copper compounds to inhibit incipient infections of brown rot (Phytophthora citrophthora) in the fruit peel is quite common. In this case, the preventive sprays control the penetration of the fungal zoospores into the fruits, which are on the tree. Furthermore, success of the preventive sprays depends on the time of infection, as germination of the zoospores depends on water; the sprays should be applied prior to the rains (Timmer and Fucik, 1975). Protective sprays in the plantation have been widely used to prevent anthracnose (Colletotrichum gloeosporioides) in various tropical and subtropical fruits, as this fungus penetrates the young fruits on the tree and establishes a quiescent infection. The developing fruits are sprayed to prevent spore germination and subsequent formation of appressoria and infective hyphae, which are the quiescent stages of the fungus. Spraying of orchard every 7–14 days successfully prevents anthracnose on mangoes (Prusky et al., 1983), papayas (Alvarez et al., 1977), and bananas (Slabaugh and Grove, 1982), and postharvest diseases in some other fruits (Singh and Thakur, 2003). Field sprays of mancozeb on papaya have been reported to reduce postharvest Rhizopus soft rot, probably by reducing field-initiated fruit diseases caused by Colletotrichum and Phomopsis species; lesion caused by these fungi may serve as courts of infection for R. stolonifer, which requires wounds to penetrate the host (Nishijima et al., 1990). Fungicidal sprays using systemic benzimidazole compounds, during the flowering period, successfully controlled both preharvest and postharvest diseases in the early 1970s ( Jordan, 1973). However, as a preharvest spray, continuous use of systemic fungicide especially the benzimidazole group should be avoided for the development of resistance by Penicillium sp. 5.2.2 Sanitation Fruits and vegetables that are injured during harvesting, sorting, packaging, or transportation, and have succeeded in avoiding infection by wound pathogens, are still liable to come into contact with pathogens during packing or storage. As disease development requires the presence of a given pathogen along with an available wound for penetration, a reduction in either of these factors will lead to the suppression of disease development (Eckert, 1990; Barkai-Golan, 2005). Wounding to the produce can be minimized by careful harvesting, sorting, packaging, and transportation, including preventing the fruit from falling at all stages. Regarding the avoidance of wounds one should remember that physiological injuries are also caused by cold, heat, oxygen deficiency, and other environmental stresses, which predisposes the commodity to attack by wound pathogens.

Hybrid Membrane System Design and Operation

A general reduction in wounds also reduces the chances of infection of fruits and vegetables by pathogens during transit and storage; such factors should also be taken into consideration while packaging or storing the fruits or vegetables (Barkai-Golan, 2005). The source of pathogen should be immediately removed either by disposal of rotten fruits and vegetables or by immersing it in a disinfectant solution like formaldehyde, isopropyl, alcohol, quadronic ammonium compounds, and sodium or calcium hypochlorite, in a special container (Eckert, 1990). Steam may also be used to sanitize citrus boxes (Klotz and DeWolfe, 1952). 5.2.3 Postharvest Chemical Treatments Injuries to the produce created during harvesting, handling, and packaging are the major sites of invasion by postharvest wound pathogens; the protection of wounds by chemicals will considerably decrease decay in storage. Among the various types of wounds, injuries are created in severing the crop from the plant or cuts created deliberately during handling procedures, such as stem cuts in banana hands or petiole cuts in celery intended for export. Other potential sites of infection are the natural openings in the host surface, such as lenticels and stomata, the sensitivity to infection of which is increased by wounding or after washing the commodity in water. An efficient disinfection process should reach the pathogenic microorganisms accumulated in all those sites (Eckert, 1978; Eckert and Ogawa, 1985). Different chemicals, such as biphenyl (diphenyl), SOPP, thiabendazole, carbendazim, dicloran, iprodione, prochloraz, and ridomil, have been used to control postharvest decay in devel fruits and vegetable successfully (Table 5). Aluminum-containing salts provided strong inhibition of all the tested pathogens (Alternaria solani, B. cinerea, Fusarium sambucinum, Pythium sulcatum, and R. stolonifer) with minimal inhibitory concentration of 1–10 mM. Aluminum chloride and aluminum sulfate are generally the most effective, inhibiting the mycelial growth of pathogens by as much as 47% and 100%, respectively, at a salt concentration of 1 mM. When applied at 5 mM, aluminum sulfate also provided 28% and 100% inhibition of dry rot and cavity spot, respectively. Aluminum chloride (5 mM) reduced dry rot by 25%, whereas aluminum lactate (5 mM) decreased cavity spot lesions by 86%. These results indicate that various aluminum-containing salts may provide an alternative to the use of synthetic fungicides to control these pathogens (Kolaei et al., 2013). Youssef et al. (2014) demonstrated that both sodium carbonate and bicarbonate exert a direct antifungal effect on P. digitatum and induce citrus fruit defence mechanisms to postharvest decay. 5.2.4 Plant Growth Regulators Plant growth regulators are known to delay senescence and the onset of fruit rots. It is reported that indole acetic acid and maleic hydrazide were most effective against Aspergillus rot and Rhizopus rots of papaya fruits, while planofix (NAA, used at 0.01%) checked

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Table 5 Fungicides recommended for the control of postharvest diseases of fruits and vegetables Fungicide Fruit/Vegetable Effect against disease(s) Reference(s)

Biphenyl

Citrus

P. digitatum and P. italicum

Sodium orthophenylphenate (SOPP)

Citrus

P. digitatum and P. italicum

Dicloran

Stone fruits

Sulfur dioxide

Grapes

Soft-watery rot (Rhizopus stolonifer) Gray mold (Botrytis cinerea)

Thiabendazole and Carbendazim

Citrus

Citrus Sone fruits Apples

Mango, banana, and papaya Pineapple Iprodione

Cucumbers, tomatoes, eggplant Apple

Penicillium digitatum, P. italicum, and stem-end rot fungi Diplodia natalensis and Phomopsis citri Brown rot caused by Monilinia fructicola Blue mold (Penicillium expansum), gray mold (Botrytis cinerea), and lenticel rot (Gloeosporium spp.) Anthracnose (Colletotrichum gloeosporioides) Black rot (Ceratocystis paradoxa) Botrytis rot

Penicillium rot

Stone fruits

Monilinia and Rhizopus rots

Mango

Alternaria rot

Sweet potato

Black spot

Eckert and Eaks (1989) Dave et al. (1980) and Eckert and Wild (1983) Ravetto and Ogawa (1972) Eckert and Ogawa (1988) and Coertze and Holz (1999) Singh and Thakur (2005) Singh and Thakur (2005) Eckert (1977,1990) Eckert (1977,1990)

Eckert (1977,1990) Eckert and Ogawa (1985) Lorenz (1988)

Bompeix and Margat (1977) Bompeix and Margat (1977) Prusky et al. (1981) Droby et al. (1984)

Hybrid Membrane System Design and Operation

Table 5 Fungicides recommended for the control of postharvest diseases of fruits and vegetables— cont’d Fungicide Fruit/Vegetable Effect against disease(s) Reference(s)

Imazalil

Citrus Mango Apple, pears, persimmon

Prochloraz

Penicillium digitatum and P. italicum Alternaria rot Alternaria rot

Tomatoes

Gray mold (Botrytis cineraria)

Mango and papaya

Anthracnose and stem-end rot

Muskmelons

Guazatine

Citrus Melons

Fusarium and soft rots caused by Geotrichum and Rhizopus rot Geotrichum rot Geotrichum and Alternaria rots

Metalaxyl (ridomil) Fosetyl al (Fosetyl aluminum)

Citrus

Phytophthors rots

Citrus

Phytophthors rots

Citrus

Green mold (Penicillium digitatum)

Harding (1976) Spalding (1982) Spalding (1980) and Eckert and Ogawa (1985) Manji and Ogawa (1985) Muirhead (1981) and Knights (1986) Wade and Morris (1983) Brown (1983) Wade and Morris (1983) Cohen (1981,1982) Gaulliard and Pelossier (1983) Eckert and Ogawa (1985)

all rots except Fusarium rot in postinoculation treatment. Thakur et al. (1974) studied the effect of growth regulators (2,4-D, 2,4,5-T, NAA, ascorbic acid, and gibberellic acid) in the control of postharvest fungal diseases of apples, mangoes, pomegranates, bananas, potatoes, brinjals, and tomatoes caused by Rhizopus spp. and reported these to be effective in controlling rots. Similarly, Tak et al. (1985) reported that rovral (500 ppm), maleic hydrazide (100 ppm), and hydrogenated groundnut oil proved to be most effective both as pre- and postinoculation treatment to control fruit rot of apples caused by A. alternata. 5.2.5 Methods of Application There are several methods by which the fungicides can be applied to the fruits and vegetables for controlling postharvest diseases. These methods include dipping, electrostatic sprays, dusting, fumigation, and use of chemical pads as described in the following sections.

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Postharvest Disinfection of Fruits and Vegetables

5.2.5.1 Dipping

In this method, the produce or part of it is immersed in water containing an appropriate concentration of a chemical, which is toxic to the disease-causing fungi (Daines, 1970). The produce may be passed below a shower of the diluted chemical, which is called as “cascade application.” For improving the effectiveness of dips, additives may be included in the formulation. These include wetting agents (e.g., Teepol or TritonX-100), which reduce the surface tension and allow a better coating of the chemical on the produce, and acids such as citric acid, which lowers the pH of the fungicide and can make it more effective. The effectiveness of the fungicidal treatment may be enhanced by heating the water into which fruits are kept. For example, in the control of mango anthracnose, postharvest dips in fungicides in cold water rarely reduced the level of infection, but when fungicide is applied in hot water, complete control could be achieved. Benomyl (500 ppm) applied in water at 55°C for 5 min appeared to be greatly effective without damaging the fruit. In this case, the fruits are passed over rollers, which constantly revolve the fruits to ensure that all sides are evenly exposed to the spray. The cascade applicator is a modification of this method whereby the fungicide is applied as a liquid under the cut crowns, which are placed upwards, because this is the area where the fungi are likely to attack the fruit. 5.2.5.2 Electrostatic Sprays

The concept of breaking up the pesticide solution into fine droplets and then enabling them with an effective electric charge was first developed for field sprays. The main advantage of this system is the increased uniformity of application of spraying materials. Similarly, there is no loss of biological activity of the materials with such sprays. The principle on which they work is that all particles have the same electrical charge and thus they repel each other. They are attracted towards crop and then form a thin even layer/coat. This method was developed for the application of fungicides on potatoes. Now-a-days, this technique is being used in managing decay in several fruits in many advanced countries. 5.2.5.3 Dusting

Various dusts can be applied to crops after harvest for the control of postharvest diseases. Fungicidal chemicals diluted in an inert carrier, such as talc, are available for postharvest use and such formulations have been used on potatoes as they are being loaded into store. 5.2.5.4 Fumigation

Fumigation is also considered an effective method of chemical application in some fruits. It has several promising applications. Fumigation can be carried out immediately after harvest to prevent infection of injuries on the fruits to be transported to long distances, degreened before processing, or to be held for several days before processing. Sulfur dioxide (SO2) is mainly used as a fumigation agent for controlling postharvest diseases

Hybrid Membrane System Design and Operation

of Vitis venifera, that is, grapes. This is achieved by placing the boxes of fruits in a gas-tight room and the gas is introduced from a cylinder in appropriate concentrations. A fumigation treatment, which results in a residue of 5–18 ppm SO2 in the grapes is found to be sufficient to control decay of berries. Its toxicity to B. cinerea spores was found to be proportional to temperature over the range 0–30°C. Treatment of grape berries with 1.0% SO2 for 20 min has also been found to be equally effective (Ryall and Harvey, 1959). SO2 can be corrosive, especially to metals, because it combines with atmospheric moisture to form sulfurous acids. If applied in high concentration, it can even bleach the color of black grapes. Especially, sodium metabisulfite impregnated pads are available which can be packed into individual boxes of fruits for a slower release of sulfur dioxide. Acetaldehyde fumigation of Sultania grapes at 5000 ppm for 24 h has been shown to reduce decay of berries by 92% as compared to untreated fruits. It is noteworthy that with this concentration, neither residues of SO2 remain nor an off flavor is developed in the berries (Avissar et al., 1989). Paper pads or wraps impregnated with diphenyl fungicide are commonly applied to citrus fruits. The chemical vaporization protects the fruits from fungal infection. Similarly, ecnazene is reported to be applied as a fumigant in bulk stores, because of the technical difficulties in its application, it is normally applied only by the contractors (Burden and Wills, 1989). 2-aminobutane could also be used as a fumigant in stored potatoes. Fumigating oranges with 2-aminobutane has also been recommended for postharvest disease control (Eckert, 1969).

5.2.5.5 Chemical Pads

Paper pads impregnated with fungicidal chemicals were, for the first time, developed for the banana to prevent infections during transportation. These are also known as crown pads and are used to prevent the fungal infections on the cut crowns of fruits. The pads are made from several layers of soft paper previously soaked in a fungicide (often thiobendazole) and then dried. The pad also absorbs the latex, which exudes from the cut surface and prevents the staining of the banana fingers. Furthermore, potassium aluminum sulfate may be added to the pads, which helps to coagulate the latex in bananas. The crown pads proved to be very effective in controlling crown rot in bananas and its residue levels are very low.

5.3 Biological Control There are many potentially biological control strategies: (i) constitutive or induced resistance, (ii) natural plant products, and (iii) antagonistic microorganisms, to control postharvest diseases of fruits and vegetables. A brief description about these strategies is as follows.

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Postharvest Disinfection of Fruits and Vegetables

5.3.1 Development and Use of Resistant Varieties Development and use of resistant varieties against pathogens is considered the most reliable method of disease management. However, it appears that a little attention has been paid to develop resistant varieties/hybrids against postharvest pathogens in horticultural crops. For developing resistant-type crops, certain desirable characteristics have to be incorporated into the susceptible varieties from the selected fruit and vegetable varieties, which are resistant to postharvest pathogens naturally (Wilson and Wisniewski, 1989). In general, we prefer those varieties, which have thin peel, have low tannin content, and high sugar content, but unfortunately, all these factors favor susceptibility to postharvest pathogens. A plant breeder needs to recognize the resistance to postharvest diseases, which is different from the field resistance and hence, a breeding program should be developed to use only this type of resistance. Tubers of somatic hybrids produced by protoplast fusion between Solanum brevidens, a diploid, nontuber bearing wild species, and a tetraploid potato (Solanum tuberosum) have been screened for resistance to bacterial soft rot, caused by Erwinia sp. The resistance was incorporated into S. tuberosum, which is now sexually transferable. Bestfleisch et al. (2015) evaluated of 107 genotypes of strawberry (Fragaria L.) genetic resources for resistance to B. cinerea under controlled conditions by establishing an artificial inoculation assay. Among them five cultivars such as Diana, Joerica, and Kimberly, and Fragaria virginiana “Wildmare Creek,” and Fragaria vesca subsp. Bracteata showed partly resistant genotypes against pathogen with mean disease levels of 15.6 billion US dollars (CDC, 2016). Among 31 foodborne pathogens, five that contribute to acquired foodborne illnesses causing death are Salmonella (nontyphoidal), Toxoplasma gondii, Listeria monocytogenes, Norovirus, and Campylobacter spp. Nearly half of the foodborne illnesses are caused by fresh produce including fruits, vegetables, and nuts. Worldwide 1.5 billion cases of illness and 3 million deaths occur annually (Al-Haq et al., 2005). In addition, demand for fresh produce and ready to eat products is increasing which increases the risk of foodborne illnesses. Although hazard analysis critical control point (HACCP) has been implemented by food plants, still there is a high risk of foodborne illnesses outbreak. In the near future Food Safety Modernization Act and Produce Safety Alliance might support the industry to reduce the cross contamination and foodborne illnesses. However, still there is a strong demand for applying different methods of sanitation, and processing to inactivate and reduce the pathogens in foods. The food industry has applied and studied different sanitation technologies through the food chain. There are numerous sanitizing chemicals in food industry, including chlorine-based chemicals, peroxide mixtures, quaternary ammonium compounds (QUATS), acid anionic, hydrogen peroxide, peracetic acid, and iodine (Taylor et al., 1999; Marriott, 2006; Al-Qadiri et al., 2016). There are several criteria for use as an applicable sanitizer such as ability to significantly reduce the number of microorganisms, avoid cross contamination, being compatible with processing practices and available technical capabilities, affordable, safe to use, with no or minimum impact on quality, and approved by regulatory agencies. However, many of these technologies have disadvantages such as low efficacy, high cost, chemical residue, adverse impacts on nutritional value, quality, and consumer acceptance. Electrolyzed water gained more attraction in recent years as one of the safe sanitizers in food industry. Postharvest Disinfection of Fruits and Vegetables https://doi.org/10.1016/B978-0-12-812698-1.00003-0

© 2018 Elsevier Inc. All rights reserved.

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Postharvest Disinfection of Fruits and Vegetables

2. HISTORY AND TERMINOLOGY Electrolyzed water was first developed around 1900 in Russia for water regeneration, water decontamination, and for sanitizing medical devices. However, it was used for the first time for food processing in soda industry in Japan in 1980 (Al-Haq et al., 2005; Hricova et al., 2008; Rahman et al., 2016). Electrolyzed reduced water (ERW) with pH of 8–10 has been developed for health benefit and studied in 1931 in Japan, and its first application in agriculture was initiated in 1954. In 1960, it was applied for medical purposes as a health-beneficial water in 1960, and in 1966 the Ministry of Health, Labour, and Welfare of Japan confirmed that ERW was effective for chronic diarrhea, indigestion, abnormal gastrointestinal fermentation, antacid, and hyperacidity (Shirahata et al., 2012). With recent development in technology, industries have been attempted to improve the electrolyzed water technology, and it has become more popular and gained more attraction as a promising nonthermal technology, particularly for food industry. Zeng and Zhang (2010) classified the history of electrolyzed water development into five stages, of which the last two stages were modified in this chapter which is more relevant to food application as follows: - Discovery of water electrolysis phenomena (1800–1920s). - Industrialized for hydrogen production for industrial application such as ammonia production and petroleum refining (1920–1970s). - Systematic innovations and improvement in the system’s proton exchange membrane to answer the military and space demands (1970s–present). - Rapidly developing and improving the system for using electrolyzed waters in medical and food industry (present). - Rapidly increasing neutral electrolyzed water (NEW) production units and companies due to the huge demand in food industry (2010–present). Different names have been given to electrolyzed water by researchers and industry including, acidic oxidizing water (AOW), acidic electrolyzed water (AEW, AcEW, AcE water), electrochemically oxidizing water, aqua oxidation water, chlor aqueous solution, electrolyzed oxidizing (EO) water, electronically generated chlorine water, electronically prepared chorine water (EPCW), electrolyzed strong acid aqueous solution (ESAAS), electrolyzed strong acid water (ESAW), functional water, activated water, redox water, sterilox water, strong ionized water, superoxide water, NEW.

3. PRODUCTION OF ELECTROLYZED WATER Electrolyzed water is produced by electrolysis of dilute sodium chloride solutions in an electrolysis chamber, divided by a diaphragm, which separates the anode and the cathode. During electrolysis, sodium chloride is dissolved in deionized water, which dissociates

Electrolyzed Water Application in Fresh Produce Sanitation

into Cl
with negative charge, and Na+ with positive charge. Meanwhile, water molecules are electrolyzed and form hydroxide (OH
) and hydrogen ions (H+). Ions with negative charge (Cl
and OH
) move to the anode to give up the electrons and form oxygen gas (O2), chlorine gas (Cl2), hydrochloric acid (HCl), hypochlorite ion (OCl
), and hypochlorous acid (HOCl). Positively charges ions (H+, Na+) move to cathode to obtain electrons and become hydrogen gas (H2), and sodium hydroxide (NaOH). At the end of the electrolysis process, two solutions are formed including acidic solution in anode, with a pH of 2–3, an oxidation-reduction potential (ORP) of >1000 mV, and an active chlorine content (ACC) of 10–90 ppm (depending on the salt concentration), and alkaline solution in cathode, with a pH of 10–13, and ORP of
800 to
900 mV (Al-Haq et al., 2005; Hricova et al., 2008) (Fig. 1). Recently, industries and researchers have reported the generation of NEW with a pH of 7–8, and ORP of 750–1000 mV (Al-Haq et al., 2005; Hricova et al., 2008), and slightly acidic electrolyzed water (SAEW) with a pH of 5–6.5 and ORP of approximately 850 mV (Nan et al., 2010). The NEW is produced by mixing the anodic solution with OH
ions or by electrolysis of NaCl in a single-cell unit (Hricova et al., 2008; Rahman et al., 2016), while SAEW is generated by the electrolysis of HCl alone or in combination with NaCl in a single-cell unit (Forghani et al., 2015; Rahman et al., 2016).

Amperage

Oxygen

Hydrogen H+

H+

Oxygen bubbles

H+, O2

Cl2 + H2O HOCl + H+ + Cl–

HO–

HO–

H2O

Diaphragm

H2O

Hydrogen bubbles

HO–, H2

–

Cl

Cl–

Na+

Na+

Na+ + OH– NaOH

Fig. 1 Electrolyzed water production unit separated by diaphragm.

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4. THE ADVANTAGES AND DISADVANTAGES OF ELECTROLYZED WATER Electrolyzed water has many advantages compared to other sanitizing technologies, which are as follows: 1. It can be generated on-site and is relatively inexpensive. 2. It provides electrolyzed water with consistent quality, which can also be stored and has 1–2 years of shelf life. 3. It can be produced by electrolysis of water with dilute salt solution such as NaCl, KCl, or MgCl2, which makes it safe for the environment (Koseki et al., 2002; Al-Haq et al., 2005). 4. Its application reduces the safety and cost issues with handling, storage, and application of chlorine solution. 5. In the case of NEW it is safer for operators and employees since it does not generate chlorine gas. 6. It is easy to modify the chlorine concentration to achieve desired concentrations based on the application. 7. It can be converted to the regular water after application, without releasing harmful gases. 8. According to some researchers, electrolyzed water does not cause resistance in microorganisms (Al-Haq et al., 2005). 9. It is more effective than chlorine (Koseki et al., 2001; Issa-Zacharia et al., 2011). Consequently, the formation of chloramines and trihalomethanes is less (Al-Haq et al., 2005). 10. It can also prevent enzymatic browning during storage of foods in modified atmospheric packaging (Koseki et al., 2002; Go´mez-Lo´pez et al., 2007). 11. Electrolyzed water has less cytotoxicity and less impact on the quality attributes of food materials. In the case of AEW, it is less corrosive and has less impact on quality compared to other acidic solutions. 12. NEW has many advantages due to its neutral pH and the available form of chlorine (Deza et al., 2003). 13. NEW gained US Department of Agriculture (DA) certificate for the production of organic produce. Electrolyzed water, similar to other technologies, has its own disadvantages, which include the following: 1. AEW is corrosive for some metals and synthetic resin. 2. Its efficacy reduces significantly when comes in contact with organic materials particularly proteins due to its reaction with protein (Iwasawa and Nakamura, 1993). 3. In the case of AEW, the machine can generate chlorine gas which is not safe for the operator. 4. The instrument is expensive.

Electrolyzed Water Application in Fresh Produce Sanitation

5. AEW contains free chlorine which is phytotoxic to plants and damage plant tissues which make its application in farms impossible (Schubert et al., 1995). 6. Sublethal doses of AEW and NEW can trigger toxin production in mold such as deoxynivalenol (DON) in Fusarium (Audenaert et al., 2012). In general, NEW has more benefits and less disadvantages compared to AEW due to its pH and available form of chlorine which can make it more effective, and less corrosive.

5. THE MECHANISMS OF ANTIMICROBIAL ACTIVITY OF ELECTROLYZED WATER Extensive research on electrolyzed water has been conducted by many researchers on cell suspension, contact surfaces, fresh produce, plants, live animals, poultry, seafood, meat, and food plant (environmental sanitation). The results from these studies show that electrolyzed water is a promising technology for sanitation, disease control, and preventive control. Antimicrobial mechanism of electrolyzed water has not been fully understood (AlHaq et al., 2005; Hricova et al., 2008). The antimicrobial activity of electrolyzed water strongly depends on pH, oxidation reduction potential (ORP), and the form and concentration of available chlorine (Al-Haq et al., 2005; Hricova et al., 2008; Rahman et al., 2016). Electrolyzed water can be discussed as a hurdle technology since it has different parameters which are responsible for its antimicrobial properties. Fig. 2 shows the biosphere of a bacterium in response to pH and ORP. Microorganisms have their biosphere (red) in which they can survive and grow, while in the blue area, electrolyzed water ORP 1200

800

0

–400 mV 0

4

8 pH

Fig. 2 Biosphere of a bacterium in response to pH and ORP.

12

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Postharvest Disinfection of Fruits and Vegetables

prevent their growth because of acidic condition, and high ORP. Generally, bacteria can grow in a pH rang of 4–9. Aerobic bacteria can grow at the ORP rang of +200 to +800 mV, and anaerobic bacteria grow between
700 and + 200 mV (Hricova et al., 2008). In AEW, low pH reduces bacterial growth making the bacterial cell more sensitive to active chlorine by changing the cell membrane (Hricova et al., 2008). However, the presence of chlorine, the available form of chlorine, and ORP are the main contributors in bacterial inactivation (Al-Haq et al., 2005; Hricova et al., 2008). High ORP in electrolyzed water causes modification of metabolic fluxes and ATP production, because of the change in electron flow in cell. Active chlorine can destroy membranes of the microorganisms, decarboxylate the amino acids, inhibit oxygen uptake and oxidative phosphorylation coupled with leakage of some macromolecules, inhibit glucose oxidation by chlorine-oxidizing sulfhydryl groups, form toxic N-chlorine derivatives of cytosine, disrupt protein synthesis, react with nucleic acids, purines, and pyrimidines, and unbalance metabolism of key enzymes (Kiura et al., 2002; Koseki and Itoh, 2001; Mahmoud et al., 2004; Mahmoud, 2007; Hricova et al., 2008). Some researchers have reported that AEW had similar antibacterial activities at pH range between 2.6 and 7, against L. monocytogenes, and Escherichia coli 0157:H7, when adequate chlorine (>2 ppm) was provided (Park et al., 2004). Some other researchers reported that the high ORP is the main reason for bacterial reduction (Liao et al., 2007; Huang et al., 2008). While some other researchers reported bacterial inactivation in lower ORP. For example, Rahman et al. (2012) found 5-log reduction in bacteria using electrolyzed water with ORP between 500 and 700 mV. In addition, Koseki et al. (2001) reported that the ORP is not the main factor for inactivation of the bacteria, because ozone also has high ORP, while its antimicrobial properties is significantly less than electrolyzed water. It seems that the main reason for the inactivation of the bacteria in electrolyzed water is the synergistic effect of different parameters, and also the availability of free chlorine (Huang et al., 2008). The antimicrobial efficacy of electrolyzed water strongly depends on different parameters such as pH, available form of chlorine, ORP, current, water flow rate and salt concentration, storage condition, electrolyte and electrode materials, water temperature, and hardness of water. One of the advantages of using ORP for evaluating the properties of electrolyzed water is the real-time monitoring of antimicrobial properties of the electrolyzed water. The ORP could be measured by a probe in a real-time monitoring system, however, for chlorine determination, kits are required and it does not provide real-time information about the antimicrobial properties of the electrolyzed water. Antimicrobial activity of electrolyzed water depends highly on the pH and the on fact how pH can determine the available form of chlorine (Hricova et al., 2008; Rahman et al., 2016). Hypochlorous acid (HOCl) is the strongest form of chlorine, which shows sanitizing power 80 times greater than hypochlorite (ClO
) when the pH is around

Electrolyzed Water Application in Fresh Produce Sanitation

Available chlorine present as HOCl %

100 90 OCl–

Cl2

80

NEW

70 AEW

60

HOCl

50 40 30 20 10 0

1

2

3

4

5

6

7

8

9

10

11

12

pH value

Fig. 3 Relationship between pH and available form of chlorine.

5–6.5 (Rahman et al., 2016). At lower pH, HOCl is dissociated to Cl2 gas, and at higher pH it forms ClO
(Rahman et al., 2016) (Fig. 3). The proportion of the HOCl and ClO
in the water depends on the pH (Fig. 3). In alkaline conditions (pH 7) ClO
is the predominat chlorine type, while at pH below 7, HOCl is the predominant. At very low pH, formation of toxic Cl2 gas occurs: HOCl + HCl , H2 O + Cl2 Active chlorine species including Cl2, ClO
, and HOCl contribute to microbial inactivation. Fukuzaki (2006) explained the mode of action of chlorine. Technically, the main reason for inactivation of the bacteria is the penetration properties of HOCl and ClO
. Ionized ClO
is not able to penetrate the microbial cell membrane because of the existence of the hydrophobic lipid bilayer and some protective cell wall structures, and the fact that the cell of a pathogenic bacteria is negatively charged by nature. Negative charge of the hypochlorite ions (ClO
) will be repulsed by the negative charge of the pathogenic bacterial cell wall, resulting in weak oxidizing action only outside of the cell. The neutral HOCl can penetrate the cell wall of the pathogenic microorganism very easily, thus making it a very effective disinfectant which can act on both outside and inside of the microorganism. HOCl can also penetrate slime layers, cell walls, and protective layers of microorganisms (Rahman et al., 2016). In addition, HOCl can kill the bacteria by oxidizing sulfhydryl groups of certain enzymes, disrupting the protein synthesis, and oxidative decarboxylation of amino acids to nitrites and aldehydes.

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The current, water flow rate, and salt concentration also impacts the properties of electrolyzed water. Increase in water flow rate causes an increase in electric current due to electrolysis of more salt solution (Hsu, 2003). Increasing bacterial reduction by increasing the water flow rate was reported for E. coli and L. monocytogenes (Rahman et al., 2012). The salt concentration has linear relation with the chlorine concentration (Hsu, 2003; Ovissipour et al., 2015; Rahman et al., 2016). Application of all chlorine-based sanitizers has one dramatic drawback, which is the evaporation of chlorine over time and HOCl breakdown, particularly in open conditions (Al-Haq et al., 2005; Hricova et al., 2008; Rahman et al., 2016). It has also been shown that even under sealed condition, due to the self-decomposition, the chlorine concentration reduced, however, it is significantly less than that under open conditions (White, 1998). Rahman et al. (2012) showed that the antimicrobial activities of electrolyzed water were retained up to 6 days and 14 days, under open and closed storage conditions. Agitation can increase the chlorine loss during the storage by increasing the evaporation. For example, Len et al. (2002) reported that the electrolyzed water lost all chlorine after 30 h of agitation. It was shown that electrolyzed water stored at refrigerated temperature was more stable than the one stored at 25°C (Fabrizio and Cutter, 2003). The form of electrolyzed water has significant impact on the shelf life. Generally, the shelf life of the NEW is significantly more than AEW (Nagamatsu et al., 2002; Cui et al., 2009).

6. THE EFFECT OF ELECTROLYZED WATER ON PRE- AND POSTHARVEST MICROORGANISMS INACTIVATION Controlling the plant disease in pre- and postharvest, and in greenhouses, can reduce waste, increase the profit, and provide secure food for human. Moreover, there is a big concern about using pesticides due to their impact on environment, workers’ safety, fungicide resistances, and public health (Al-Haq et al., 2005). Hence, there is a big demand for developing green and environmentally friendly solutions as fungicide. Electrolyzed water has been applied by many researchers for plant disease control in pre- and postharvest stages. For example, Grech and Rijkenberg (1992) injected AEW into a citrus micro-irrigation system to control waterborne pathogens, for example, Phytophthora spp., Fusarium spp. algae, and skin-forming bacteria. Their results showed that AEW was able to kill all the mentioned organisms. However, their results showed that nematodes were resistant to chlorine in water. The effects of electrolyzed water on some organisms on plants are listed in Table 1. Bonde et al. (1999) studied the effect of AEW on germination of Tilletia indica spores in wheat, and observed that applying AEW for 20 min eliminated fungi such as Aspergillus, Cladosporium, and Penicillium spp.

Electrolyzed Water Application in Fresh Produce Sanitation

Table 1 List of Organisms, Plants, and Treatments Applied for Sanitation Organism Plant Solution Outcome

Reference

Tilletia indica Teliospore

Wheat

AEW 16 ppm ACC

Bonde et al. (1999)

E. coli

Alfalfa, and Broccoli seeds germination Tomato

AEW, ACC: 66 ppm; pH: 2.7; ORP: 1161 mV AEW, ACC: 35 ppm; pH: 2.6; ORP: 1025 mV

Significantly increased the germination No significant reduction

Significant reduction, fruits performance either enhanced or not affected

Abbasi and Lazarovits (2006)

Gerbera Daisy

AEW, ACC: 49–54 ppm; pH: 2.6; ORP: 1053 mV

Mueller et al. (2003)

- Relatively thinwalled species (e.g., Botrytis, Monilinia) - Thicker-walled, pigmented fungi (e.g., Curvularia, Helminthosporium) Powdery mildew, downy mildew, gray mold

Greenhouse water

AEW, ACC: 55 ppm; pH: 2.6; ORP: 1079 mV

Sprayed twice a week and when sprayed every other week, alternating with fungicides - Totally killed - After 2 min, significantly reduced

commercial rose varieties (Rosa sp) (Orlando and Versilia varieties)

NEW, ACC: 50 and 75 ppm; pH: 5; ORP: 850 mV

Fernandez et al. (2011)

Powdery mildew

Peach trees once a week

AEW, ACC: 10–20 ppm; pH: 2.5; ORP: 1050 mV

Significant control, however, some curled leaflets appeared with this application Significantly reduction

Xanthomonas campestris pv. Vesicatoria (bacterial spot pathogen, Streptomyces scabies (potato scab pathogen), Fusarium oxysporum f. sp. lycopersici (root rot pathogen) Powdery Mildew

Kim et al. (2006)

Buck et al. (2002)

Schoerner and Yamaki (1999) Continued

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Postharvest Disinfection of Fruits and Vegetables

Table 1 List of Organisms, Plants, and Treatments Applied for Sanitation—cont’d Organism Plant Solution Outcome

Reference

AEW, ACC: 30, 40, 50 ppm; pH: 2.3; ORP: 1170 mV

Significantly reduction

Fujiwara et al. (1998a)

Downy mildew (Pseudoperonospora cubensis Rostowzew)

Leaves of cucumber (Cucumis sativus L. cv. Shapu 7) Cucumber (Cucumis sativus L, cv. Naoyoshi)

AEW, ACC: 32 ppm; pH: 2.8; ORP: 1120 mV

Fujiwara et al. (1998b)

Pepino mosaic virus

Tomato

EW, ACC: 0.2 and 0.5 ppm, for 60 and 30 min exposing

Defense gene expression

Plants of Nicotiana tabacum cv. Petite Havana SR-1 and Malus domestica cv. Fuji parcel of Malus domestica cv. Dallago

NEW, ACC: 250 ppm; pH: 6.5 and 9;

After 17 days, downy mildew was controlled perfectly Significantly reduction, no side effect on color, and nutritional value Increasing plant resistance, no side effect on plant performance

Powdery mildew (Sphaerotheca fuliginea Pollacci)

Bandte et al. (2016)

Zarattini et al. (2015)

Buck et al. (2002) was able to inactivate 22 different fungal species with AEW, and reported that all thin-walled species were killed by AEW in 30 s, and thick-walled species were reduced or killed in longer time (2 min). Abbasi and Lazarovits (2006) reported that when the tomato seeds were immersed in AEW for 1 and 3 min, it significantly reduced the populations of Xanthomonas campestris pv. Vesicatoria from the surface of the seeds without affecting seed germination. Bandte et al. (2016) studied the effect of electrolyzed water on tomato virus (Pepino mosaic) in irrigation water. They reported that exposing the fruits to electrolyzed water can significantly reduce the virus and improve the quality and growth of the fruits. Zarattini et al. (2015) studied the effect of NEW with pH of 6.5 (HClO) and electrolyzed water with pH of 9 (ClO
) on plants Petit Havana SR-1 (Nicotiana tabacum), Fuji

Electrolyzed Water Application in Fresh Produce Sanitation

(Malus domestica) and on parcel of M. domestica Dallago gene expression and defense mechanisms. It has been reported that electrolyzed water can kill the plant pathogens, however, it is not clear that if this property is only due to the biocide activity or there is also a positive effect on the plant. They found that electrolyzed water is able to induce resistance in plants, mechanism of which will be discussed in next the section. Electrolyzed water has also been used by many researchers as a postharvest control system for increasing the shelf life, improving the quality, sanitation, controlling mold and foodborne pathogens, etc. Acidic electrolyzed water was used in frozen state with different chlorine concentrations against L. monocytogenes and E. coli O157:H7 (Koseki et al., 2004a). The results showed that iced electrolyzed water with 250 ppm chlorine had the highest bacterial reduction. However, this concentration of chlorine caused physiological disorders in lettuce. Koseki et al. (2004b) reported that cucumbers and strawberries washed with alkaline electrolyzed water (pH 11.3) for 5 min and then immersed in AEW (pH 2.6) for 5 min showed a strong bacterial and fungal reduction, and it is more effective compared to ozone and sodium hypochlorite treatments. Guentzel et al. (2010) studied the effect of electrolyzed water on grapes and peaches artificially inoculated with Botrytis cinerea and Monilinia fructicola, respectively. The electrolyzed water with 25, 50, 75, and 100 ppm free chlorine and exposure time of 10 min were able to induce 6 log spores per ml reduction. Application of electrolyzed water for apples did not prevent lesion formation on fruit previously inoculated with Penicillium expansum, but cross contamination of wounded apples from decayed fruit or by direct addition of spores to a simulated dump tank was significantly reduced (Okull and Laborde, 2004). Whangchai et al. (2010) studied the effect of electrolyzed water on the reduction of Penicillium digitatum growth on tangerine. They have reported that electrolyzed water can totally deactivate spores within 1 min. In commercial trials conducted in Sicily (Italy) a 93% reduction in Penicillium spp. population in citrus wash water was observed 1 h after treating with electrolyzed water when water was supplemented with 1.25% of sodium bicarbonate (SBC), whereas, in the electrolyzed tap water without any salt, similar results were observed after 7 h. In addition, no rot development was observed in fruit exposed to electrolyzed SBC solution, whereas in the absence of salt, the rotten rate was 70% (Fallanaj et al., 2013). Jemni et al. (2014) studied the effect of UV-C, ozone, and electrolyzed water on the quality of palm. Their results showed that all treatments were able to decrease the microbial load significantly. Lee et al. (2014) used NEW for removing indigenous flora on cabbage and carrot both in laboratory and processing line. In laboratory scale, they studied the effect of different hypochlorous acid concentrations (100, 150, and 200 ppm), different ratio of sample

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Postharvest Disinfection of Fruits and Vegetables

weight to NEW volume (1:5, 1:10, and 1:20), and different exposing times (5, 10, 20, and 30 min) using 2 kg of shredded cabbages and carrots. In processing line study, the feasibility of the NEW treatment was studied on an actual processing line (20 kg), including cutting, three washing steps (two air bubble washes for 5 min each and 150 ppm NEW for 5 min at ratio of 1:10), rinsing (5 min), and dehydration (5 min). Overall, more bacterial reduction was observed when HOCl concentration and treatment time were increased. The results showed 3.3–3.5 log CFU/g reductions at maximum conditions (NEW 200 ppm, 1:20, 30 min) in the coliform counts, however, some changes in color of both carrot and cabbage were reported. Ding et al. (2015) studied the effect of SAEW and ultrasound on microbial loads of fresh cherry tomatoes and strawberries. They found that ultrasound can improve the antibacterial properties of SAEW significantly. Va´squez-Lo´pez et al. (2016) investigated the NEW impacts on tomato rot (Fusarium oxysporum, Galactomyces geotrichum, and Alternaria sp.). The NEW chlorine concentrations were 10, 30, and 60 ppm, and fruits were exposed to the solutions for 3, 5, and 10 min. NEW with 60 ppm chlorine is effective enough to control the fungal rot in tomatoes.

7. THE EFFECT OF ELECTROLYZED WATER ON BACTERIAL INACTIVATION ON FRESH PRODUCE The market for fresh produce is growing in the food industry due to the healthy diet development in restaurants, changing life style, and increased awareness of the importance of healthy diet. Particularly for the fresh-cut produce, fruits, ready salads, etc., there is a big demand in the market, however, fresh-cut produce market is limited because of their short shelf life and decline in quality post-processing due to biochemical changes associated with wounding compared to intact vegetables. On top of the postharvest spoilage, frequency of foodborne illness outbreaks associated with fresh produce has increased due to increased demand for fresh produce (Rahman et al., 2011). This might be due to the processing steps such as peeling and cutting, which can increase the risk of cross contamination. In addition, initial microbial load, harvest methods, harvest region, water source can influence the final product microbial load. Water is used in postharvest processing of fresh produce to remove dirt and soil, cool, hydrate, and to transport the product, and if the water becomes contaminated with microbial pathogens, cross contamination occurs among the products and equipment surfaces. Sanitization during washing steps can help to control microbial hazards. Chlorine is one of the most widely used antimicrobial in minimally processed fresh produce processing. However, reaction of chlorine with some compounds in food can lead to the formation of carcinogenic chlorinated compounds, and therefore there is a need for finding an alternative. Different sanitation methods have been applied for fresh produce, including rinsing the produce in a mixture of lemon juice and vinegar (Sengun and Karapinar, 2004, 2005), anolyte water, and chlorinated water

Electrolyzed Water Application in Fresh Produce Sanitation

(Workneh et al., 2003). Chlorine dioxide, ozone, and thyme essential oil have also been used to sanitize the produce (Singh et al., 2002). A 3-log reduction in microbial load was observed in response to heat treatment (Alegria et al., 2009, 2010), acidified sodium chlorite (Ruiz-Cruz et al., 2007), peroxyacetic acid (Vandekinderen et al., 2009), and irradiation (Chaudry et al., 2004) treatment. Warm water (Klaiber et al., 2004) and electrolyzed water (Izumi, 1999) have also been found to decrease the bacterial populations. Electrolyzed water has been used for killing foodborne pathogens, although it has some limitations like other disinfectants for the inactivation of microorganisms in whole and minimally processed produce (Go´mez-Lo´pez et al., 2007). Venczel et al. (1997) reported the inactivation of Clostridium perfringens spores by NEW. Venkitanarayanan et al. (1999) reported the inactivation of cultures of E. coli O157:H7, Salmonella enteritis, and L. monocytogenes by approximately 7 log CFU/mL using AEW. Subsequent studies have also proved the efficacy of EO water to inactivate human pathogens both in vitro (Nakajima et al., 2004; Ovissipour et al., 2015) and inoculated onto vegetable surfaces (Deza et al., 2003; Sharma and Demirci, 2003; Abadias et al., 2008), AEW and NEW for contact surfaces (Al-Qadiri et al., 2016), and food processing (Shiroodi et al., 2016; Ovissipour et al., 2018). The effect of AEW with 30 ppm chlorine and water with 200 ppm chlorine was studied on E. coli O157:H7, S. enteritis, and L. monocytogenes on the surfaces of tomatoes. The results showed that water with 200 ppm chlorine and AEW reduced the number of pathogens by 4.69–4.87 log CFU and 7.46–7.85 log CFU per tomato, respectively (Bari et al., 2003). Guentzel et al. (2008) reported 4.0–5.0 log reductions of E. coli, Salmonella typhimurium, S. aureus, L. monocytogenes, and Enterococcus faecalis on spinach after dipping for 10 min in NEW at 100 and 120 ppm total residual chlorine. However, they reported limit of efficacy for lettuce surface with 0.25-log reduction for E. coli and 2.43–3.81 logs for the rest. For minimally processed produce, AEW and NEW were able to decrease the number of E. coli O157:H7, Listeria innocua and Salmonella choleraesuis inoculated individually and in a mixture on apples by 1.2–2.4 logs, a limited decontamination level but equal or more effective than that achieved with sodium hypochlorite (Graca et al., 2011). On strawberries, EO water was as effective as chlorinated water for inactivation of E. coli O157:H7 cells (Hung et al., 2010). Deza et al. (2003) reported the effectiveness of NEW treatment on tomatoes against E. coli, S. typhimurium, L. monocytogenes, and Salmonella enteritidis with >5 log CFU/cm2 reduction. In strawberries, 0.96 and 0.93 log reductions were achieved for yeasts and molds and total aerobic bacteria, respectively, upon treating with SAEW containing 34 ppm active chlorine at pH 6.49 (Ding et al., 2015). These results are similar to those reported by Hao et al. (2011), in which the treatment of fresh-cut cilantro in SAEW for 5 min resulted in 1.56 and 1.64 log CFU/g reductions in total aerobic bacteria and yeasts and molds, respectively. They reported that SAEW is a promising food sanitizer which may be considered as an alternative to NaOCl solution and would reduce the amount of active chlorine used in fresh produce.

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Apples and their products which are contaminated with the common storage rot fungus P. expansum, contain patulin which is a mycotoxin. Using 100% or 50% EO water containing 60 ppm free chlorine could reduce P. expansum viable spore populations by >4 and 2 log in aqueous suspension and wounded apples, respectively (Okull and Laborde, 2004). EO water was able to control brown rot in wound-inoculated fruits, but reduced disease incidence. Koseki et al. (2004b) reported that EO water did not reduce the bacteria in strawberry which might be due to the surface structure of the strawberry fruit. There are many achenes (seeds) that render its surface structure uneven and complex. These studies showed that the surface properties of fruits can strongly impact the efficacy of EO water. Exposure time, chlorine concentration, pH, available form of chlorine, other technologies combined with electrolyzed water, agitation speed during the sanitation, chemical composition of produce can impact the efficacy of the electrolyzed water against bacteria (Rahman et al., 2016). Electrolyzed water can be used in combination with other technologies, and it has been shown that its efficacy can be improved in many cases. Koseki et al. (2004c) used mild thermal processing (50°C) in combination with alkaline electrolyzed water for treating vegetables for 5 min and subsequent washing with chilled acidic electrolyzed water (4°C) for 1 or 5 min. They have reported 3–4 log CFU/g reduction in E. coli O157:H7 and Salmonella on lettuce. Koide et al. (2011) used mild heated (45°C) and SAEW for sanitizing sliced carrots and their results showed total aerobic bacteria, mold, and yeast populations were significantly low after mildly heated SAEW treatment. Park et al. (2009) used 1% citric acid and alkaline electrolyzed water heated at 40°C, against Bacillus cereus both vegetative and spore form in brown rice and reported 4.21 and 3.57 log reduction, respectively. Low concentration electrolyzed water heated at 40°C and ultrasound were used against E. coli O157:H7 on lettuce and 3.18 log reduction was reported, and the shelf life has improved. Mansur and Oh (2015) studied the impact of temperature on the sanitizing efficacy of SAEW (ACC 5 ppm, pH 6.28, exposure time 3 min) on fresh-cut kale. The treatment resulted in >1.5 and 2 log CFU/g reduction in L. monocytogenes at 4 and 7°C, respectively. Afari et al. (2015) studied NEW (155 ppm chlorine; pH: 7.52; ORP: 760) effect on E. coli O157:H7, and S. typhimurium CT 104 on fresh produce (Romaine and Iceberg lettuce, and tomato) using an automated washer at simulated food service conditions at different times (1–30 min) and different agitation speeds (40 and 65 rounds per min; rpm). They have reported that time and agitation speed significantly increased the bacterial log reduction.

Electrolyzed Water Application in Fresh Produce Sanitation

Ding et al. (2015) used SAEW (33 ppm chlorine; pH: 6.48; ORP: 853), and ultrasound (40 kHz, 10 min) on cherry tomatoes and strawberries to analyze the total aerobic bacterial count and different quality attributes. They have reported that ultrasound can increase the efficacy of the SAWE. Some researchers also found that the traditional sanitizers such as lactic acid (2%) showed higher antibacterial properties compared to AEW (Tirawat et al., 2016).

8. THE EFFECT OF ELECTROLYZED WATER ON PLANT PHYSIOLOGY AND QUALITY 8.1 Induce Resistance Navarro-Rico et al. (2014) studied the effect of NEW and AEW on broccoli microbial load and total phenolic contents and reported that electrolyzed water could decrease the microbial load significantly, and increase the total phenolic contents up to 30%. Generally, electrolyzed water can be an abiotic stress that may induce a total phenolic content increase in the plant which can improve the resistance. Zarattini et al. (2015) studied the effect of NEW at the pH of 6.5 (HClO) and electrolyzed water at the pH of 9 (ClO
) on tobacco and apple gene expression and defense mechanisms. It has been reported that electrolyzed water can kill plant pathogens, however, it is not clear if this property is only due to the biocide activity or there is also a positive effect on the plant. They found that electrolyzed water is able to induce resistance in plants, the mechanism of which will be discussed in the next section. They determined the genes which are responsible for the defense against fungi, and reported that member of the PR genes have the key role. They exposed the plants to electrolyzed waters at different time intervals and measured the level of gene expression. They have reported that gene expression was elevated only for 6 h after first treatment, 48 h after second treatment (PR changed 40 times) (14 days after first treatment), and 96 h after third treatment (PR changed 100 times) (35 days after first treatment). It has been reported that for tobacco plant, the gene expression depended on the concentration of chlorine in electrolyzed water. For example, the highest gene expression was observed in plants treated by 250 ppm, and weak gene expression was observed in plants treated by 125 and 500 ppm, suggesting that 250 ppm is the optimal concentration for tobacco plants. In addition, they found that the available form of chlorine, which depends on the pH of the solution, has significant impact on the gene expression. At neutral pH, chlorine is available as hypochlorous acid (HOCl), while at alkaline pH it is mainly hypochlorite (OCl
). After treating the tobacco with electrolyzed waters with different pHs including 6.5 (HOCl) and 9 (OCl
), they have reported that alkaline electrolyzed water triggers an overexpression that is limited to some of the PR genes such as PR1a, and PR2, while other genes are not upregulated. After the second treatment (14 days after the first

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one), PR1a, and PR2 increased 100 times and 10 times, respectively, after treating with alkaline solution, while in the case of neutral pH (HOCl), an increase of 1000 times and 100 times were reported. These results indicate that hypochlorous acid is essential to achieve a strong and long-lasting activation of plant defense. The mechanism is not understood very well, however, researchers claimed that this might be due to the increase in salicylic acid production which is an important hormone and acts as the endogenous defenses activator. The salicylic acid concentration increased 10 times in samples treated with NEW compared to the control group, which might improve the defense system at least partially. In another study, same researchers used electrolyzed water in chamber on 1-year-old apple tree and in orchard on 20-year-old apple tree. They found the same results as tobacco and reported that electrolyzed water was able to trigger a defensive response in apple trees in first exposure. Interestingly, gene expression was higher in trees in orchard compared to that in chamber. Fallanaj et al. (2016) studied the effect of electrolyzed water, and electrolyzed water with NaHCO3 on green mold inactivation, and to induce resistance in citrus fruits against green mold. Activity and gene expression of phenylalanine ammonia-lyase, peroxidase, chitinase, and b-1,3-glucanase in fruit tissue were evaluated and results showed an increase in the activity of all tested enzymes in the treated tissue at 12–24 h posttreatment compared to the control fruit. Peroxidase and phenylalanine ammonia-lyase activity were strongly activated in electrolyzed water with NaHCO3 in treated tissue at 12 and 24 h posttreatment. Both enzymes are considered important in host resistance mechanisms, since peroxidase is involved in lignin formation and phenylalanine ammonia-lyase is the first enzyme involved in the phenylpropanoid pathway, which help fruit tissues to better respond to pathogen attack by establishing biochemical defensive barriers. In addition, chitinase and b-1,3-glucanase activity were increased by electrolyzed water with NaHCO3 compared to the other treatments. Chitinase and b-1,3glucanase are able to hydrolyze fungal cell components (chitin and glucans), and, in combination, they have been shown to inhibit the growth of several pathogenic fungi (Schlumbaum et al., 1986; Sela-Buurlage et al., 1993). Gene expression was used to confirm the biochemical results. The relative expression of peroxidase and phenylalanine ammonia-lyase genes was higher in electrolyzed salt-treated tissues compared to the other treatments. In particular, on the tissue treated with electrolyzed water with NaHCO3, the induction was maximum at 6 and 12 h posttreatment for peroxidase and phenylalanine ammonia-lyase, respectively. The results from this study showed that electrolyzed water with NaHCO3 upregulated the same pattern of genes involved in the general response to stresses, such as salt stress or oxidative stress, so the induction caused by treatment might sum up to host natural defense mechanism.

Electrolyzed Water Application in Fresh Produce Sanitation

8.2 Quality Changes One of the negative impacts of the electrolyzed water is their impact on quality, particularly during the postharvest in fresh produce and fresh-cut produce. Koseki and Itoh (2001) reported that cut vegetables subjected to immersion in AEW (42.3 mg/L available chlorine, pH at 2.5), NaOCl solution (150 mg/L available chlorine, pH at 9.3), or tap water (0.3 mg/L available chlorine, pH at 7.0) for 10 min showed 15–20% reductions in ascorbic acid content for cut cabbage, 10%–15% reductions for cut lettuce, and 30–35% reductions for cut cucumber. Koide et al. (2011) used SAEW (23 ppm chlorine, pH: 5.5) alone and in combination with mild heat (45°C), on fresh-cut carrot. They did not observe any change in hue and chroma of color, hardness, ascorbic acid, and β-carotene content. Rahman et al. (2011) applied AEW in combination with 1% citric acid at 50°C for fresh-cut carrot. They have reported that the combination of disinfects improve the antimicrobial properties and increase the shelf life of the fresh produce. Navarro-Rico et al. (2014) applied NEW, AEW, and NaClO (70 and 100 ppm chlorine) for fresh-cut broccoli and studied the shelf life and total phenolic compounds during 15 days of storage at 4°C. Total phenolic compounds in EW treated samples were 16–30% higher compared to NaClO-treated samples. However, in contrast with these results, other researchers did not observe total phenolics changes after applying EW (Martı´nez-Herna´ndez et al., 2013). They also studied the activity of different enzymes including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and glutathione reductase (GR). Among them, APX, and GPX activities after EW treatment did not show significant changes compared to NaClO. However, SOD and CAT activities significantly decreased after applying EW around 13–37%, and 40–46%, respectively, compared to NaClO. Technically, EW has shown strong and stable SOD- and CAT-like activities due to high level of dissolved molecular hydrogen produced in EW during electrolysis of water. Hence, the SOD- and CAT-like activities of EW could contribute to the scavenge ring of reactive oxygen species produced throughout the shelf life of the fresh-cut produce. Jemni et al. (2014) studied the effect of UV-C in combination with ozone, and NEW (100 ppm chlorine; pH: 6.99; ORP: 870) on shelf life and quality of date palm during 30 days storage at 20°C. NEW and UV-C combination had the lowest weight loss after 30 days compared to different doses of UV-C alone, and ozone and UV-C combination. UV-C combined with NEW and ozone showed highest total phenolic contents and total sugar content. Washing with AEW containing 16.8 ppm chlorine did not affect the color of cilantro leaves, however, the AEW-treated samples stored at 0°C for 14 days showed less aroma than water-washed samples, which might be correlated to their high tissue electrolyte leakage (Wang et al., 2004).

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The effect of different treatments including tap water, SAEW (20 ppm chlorine; pH: 5.85; ORP: 815), AEW (80 ppm chlorine; pH: 2.48; ORP: 1134), NaClO solution (103 ppm chlorine; pH: 10; ORP: 500), alone and in combination with heat (45°C) were applied for fresh-cut cilantro (Hao et al., 2015). They reported that SAEW showed the advantage in keeping the overall quality (electrolyte leakage, texture, and smell) compared to other treatments and it might be a better choice for fresh-cut cilantro compared to AEW. The SAEW had higher pH and lower chlorine which might have caused less cell damage in cilantro. Ding et al. (2015) studied the effect of SAEW in combination with ultrasound on cherry tomatoes and strawberries and found that, except for firmness of cherry tomatoes which decreased, the other quality attributes including total soluble solids, total titratable acidity, and vitamin C did not change.

8.3 Regulation Legislation for process water sanitizer in the United States may be regulated by FDA and/ or US Environmental Protection Agency (EPA) depending on the product which is washed and processing location. For fresh-cut produce, sanitizers are regulated by the FDA as a secondary direct food additive and for raw fresh produce that are washed in the fields sanitizers are considered as “pesticides” that are regulated by the EPA. Japanese Ministry of Health and Welfare approved AEW with 20–60 ppm chlorine, and SAEW with 10–30 ppm chlorine (Koide et al., 2009). The FDA approved HOCl application 21 CFR 173.315 for chemicals used in washing or to assist in the peeling of fruits and vegetables. Hence, since the main compound in NEW is HOCl, it might be regulated by the same CFR. The USDA authorized NEW application for organic products.

9. FUTURE OF ELECTROLYZED WATER Electrolyzed water applications in different sections have already been proved. It appears electrolyzed water has the potential for being used as one of the useful sanitizers in food, aquaculture, agriculture, medical, and energy industry. Recently, many start-up companies and industries started commercialization and marketing of different types of electrolyzed water all around the world. There are many companies worldwide that have been established for producing pure electrolyzed water solutions with different chlorine concentrations for different applications. For example, AquaOx LLC in the United States is producing two types of electrolyzed water with different hypochlorous acid concentrations which have been tested in food plants and for medical applications. Additionally, this company is using these solutions for treating plant diseases by spraying them on the trees. It seems in near future electrolyzed water could be sold in stores for using as home sanitizer. The small electrolyzed

Electrolyzed Water Application in Fresh Produce Sanitation

water machines are also available which could be installed in restaurant and medicals offices for the sanitation and disinfection of contact surfaces and instruments. The use of electrolyzed water for treating plant disease or in aquaculture for sanitizing and treating pathogenic microorganism can provide pesticide-free and drug-free fresh products for human consumption. Furthermore, electrolyzed water impacts on wound healing and its wound sanitation application have been approved, there are several companies that produce diluted hypochlorous acid for wound treatment. It has become clear that electrolyzed water is one of the promising sanitizers for future, which can provide pesticide- and drug-free food products.

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CHAPTER 4

Hydrogen Peroxide (H2O2) for Postharvest Fruit and Vegetable Disinfection
a Cardoso de Aquino, Luciana de Siqueira Oliveira, Kaliana Sitonio Ec¸ a, Andre
ia Barros Vasconcelos Lucicle Department of Food Engineering, Federal University of Ceara, Fortaleza, Brazil

1. INTRODUCTION Sanitization of fresh fruits and vegetables after harvest is a major important step at its postharvest handling. The occurrence of foodborne outbreaks related to contaminated fresh products could be decreased by disinfection procedures besides of they have promoted economic benefits by reducing spoilage losses by 50% or more and by increasing postharvest shelf life of fruits and vegetables (Alexandre et al., 2012; Felizini et al., 2016). Sanitizing agents are among the most frequently used process to reduce/eliminate spoilage and pathogenic microorganism from fresh products. The chlorine is the most common disinfectant agent applied to sanitize fresh products as well as processing equipment surfaces. However, its use at a level recommended by the US Food and Drug Administration (FDA) (50–200 mg L 1 total chlorine) does not show effectiveness to eliminate spoilage microorganisms, achieving only approximately 2–3 log reduction in native microflora. In addition, the chlorine decomposition releases toxic by-products and can form carcinogenic compounds when undergoes reaction with organic matter in water (Mani-Lo´pez et al., 2016; Ukuku et al., 2005), and so the use of alternative disinfectants has been studied. Hydrogen peroxide (H2O2), also termed hydrogen dioxide, is an alternative sanitizing agent widely used for fruits and vegetables. It is used in both liquid and gas form for preservative, disinfection, and sterilization applications (McDonnell, 2014). Although H2O2 has been discovered in 1818 by Louis Th
enard, its use as a disinfectant was first proposed by B. W. Richardson in 1891 (Linley et al., 2012). This chemical compound of low molecular weight (34.014 g/mol) present its structure with each oxygen connected to the other oxygen and to one of the hydrogen atoms and the bond angles between each oxygen and hydrogen is 102 degrees. Oxidizing agent H2O2 is widely used as potent biocide due its antimicrobial property, presenting advantage over other sanitizing agents by broad spectrum of antimicrobial Postharvest Disinfection of Fruits and Vegetables https://doi.org/10.1016/B978-0-12-812698-1.00004-2

© 2018 Elsevier Inc. All rights reserved.

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activity has been shown to be effective against several microorganisms such as bacterial endospores and protozoal cysts and depending on its specific use it can also act on infectious proteins such as prions (Linley et al., 2012; McDonnell, 2014). Hydrogen peroxide also highlights the lack of environmental toxicity since it completely decomposes to water and oxygen by catalase or peroxidase that use it as a substrate, and the fact that the residue left on fresh products after application can be also removed by rinsing with water immediately after treatment to avoid reactions with food constituents (Alexandre et al., 2012; Felizini et al., 2016). These advantages make hydrogen peroxide generally recognized as safe (GRAS) for food applications by the FDA (Felizini et al., 2016). However, the way in which hydrogen peroxide is used and in particular its concentrations are factors that influence its effectiveness and safety.

2. CONCENTRATIONS AND COMBINED TREATMENT Low-concentration hydrogen peroxide, between 1% and 5%, have been used to in food and packaging materials for sanitizing (Parish et al., 2003). Ukuku et al. (2005) studied the use of hydrogen peroxide (2.5%) and its combination (1% of H2O2) with sodium lactate (1%), nisin (25 μg/mL), and citric acid (0.5%) to evaluate their antimicrobial effect against bacteria (Escherichia coli O157:H7, and Listeria monocytogenes), yeasts, and molds on two types of fresh-cut melon (cantaloupe and honeydew). They showed that washing treatment with hydrogen peroxide solution (2.5%) could reduce the microorganism population added during the fruit cutting, substantially. However, the combined treatment was more effective than the isolated use of hydrogen peroxide solution. Besides hydrogen peroxide (H2O2) is known as oxidant agent with bacteriostatic and bactericidal effect, Ukuku et al. (2005) verified that the total inactivation of Salmonella populations on inoculated whole and minimally processed fresh-cut melon was not achieved with the use high concentrations of hydrogen peroxide (5.0%). Its concentra€ tion can be compared with nearly 200 ppm of chlorine treatment (Olmez and Kretzschmar, 2009). Alexandre et al. (2012) verified that the application of 5% of H2O2 provided high reductions of microbial loads (total mesophiles, Listeria innocua, and total coliforms) in red bell peppers, strawberries, and watercress. However, at 5%, negative impacts on quality factors, especially surface color, were observed by sensorial analysis. Comparing the sanitizing effect of H2O2 (1% and 5%) with sodium hypochorite, the first one was significantly more effective than sodium hypochorite for both concentrations, nevertheless, overall 1% was considered the best option, because it promoted sanitizer effect and retained the quality factors satisfactorily. A study about the effect of different sanitizer compounds [ethanol (70%); H2O2 (5%); nisin (125 mg L 1); surfactant (2%), and sodium hypochlorite (from 100 to 4000 mg L 1)]

Hybrid Membrane System Design and Operation

applied to pepper observed reductions in native biota [total mesophilic aerobic bacteria (TMAB), lactic acid bacteria (LAB), molds, and yeasts], however, the antimicrobial effect was proportional to the exposure time and solution concentration (Mani-Lo´pez et al., 2016). In relation to LAB a similar reduction for almost all tested sanitizers was obtained, including H2O2, giving a highlight to the combination of surfactant with sodium hypochlorite or ethanol. For TMAB counts, the treatment with ethanol alone, for 120 min, was the most effective one, while H2O2 and surfactant (2000 mL L 1) had similar results. Nisin, known as antimicrobial substance, could not promote microbial inactivation even for long contact time exposure. Van de Velde et al. (2016) studied the use of a commercial sanitizer based on peracetic acid (Oxilac Plus) with 5% peracetic acid, 20% hydrogen peroxide and water to optimize the conditions of disinfection process, yet minimizing the damage to total phenolic compounds of strawberry. The combination was proposed, in this case, considering quaternary equilibrium formed and its decomposition products (oxygen and acetic acid) avoiding the formation of toxic or carcinogenic compounds generated by chlorine solutions, for example. Although this combination is environmentally friendly diverse effects were still observed since the chemical structure of the phenolic compound (flavonoids, phenolic acids, hydrolysable tannins and condensed tannins) were different. Hydrogen peroxide is a friendly sanitizer as it can reduce of microbial load without production toxic compounds. Its association with other traditional sanitizers or disinfectors has been studied in different fruits and vegetables with satisfactory results. The increase of concentration and time of expose are directly proportional to the degree of microbial inhibition, however, high concentration can promote loss of quality.

3. MECHANISM OF DISINFECTION OF H2O2 Several studies have shown potential effectiveness of hydrogen peroxide as a sanitizing agent for produce (Sapers, 2001; Ukuku et al., 2005; Alexandre et al., 2012). However, little has been discussed on the exact mechanism of H2O2 as antimicrobial agent. It is well known that H2O2 is a potent oxidizing agent and becomes highly toxic undergoes reaction with biomolecules such as proteins, lipids, and nucleic acids leading to cellular damages. Thus, based on the oxidative reactivity, the mechanism of action of antimicrobial H2O2 was proposed which is related to both strong oxidizing power and capacity to generate through its indirect oxidizing effects other cytotoxic oxidative species—hydroxyl radicals, singlet oxygen species, and hydrogen peroxides which also has biocidal action of damaging the membrane lipids as well as the DNA (Felizini et al., 2016; Linley et al., 2012). Inactivation of membrane respiratory chain enzymes and damage to DNA are the mechanisms of antimicrobial action proposed for hydrogen peroxide. Thus oxidative

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capacity of H2O2 provides both bacteriostatic and bactericidal activities making it a potential disinfectant directly toxic to pathogens and spoilage microorganisms.

4. INFLUENCE OF HYDROGEN PEROXIDE ON NUTRITIONAL COMPOUNDS, QUALITY FACTORS, AND SENSORIAL ASPECTS The consumption of fresh fruits and vegetables is in most of the cases advantageous to consumers when compared with the processed ones, since phytochemical compounds (thermal and photosensitive) can be maintained. However, their perishability implies very short shelf life due mainly to the growth of microorganisms. The use of sanitizers is considered a crucial step and alternative to reduce the microbial load and to extend shelf life instead of traditional conservation processes (using high temperature and/or pressure). However, chemical compounds (alone or in combination) commonly used for decontamination processes (chlorine dioxide, sodium hypochlorite, citric acid, ethanol, hydrogen peroxide, nisin, sodium lactate, and chlorine solutions) can influence the fresh fruit and vegetable composition, quality, and sensorial attributes. For this propose, several researchers have studied the influence of the sanitizer on the fruits and vegetables aspects (Van de Velde et al., 2016; Mani-Lo´pez et al., 2016; Alexandre et al., 2012; Ukuku and Fett, 2005). Physical properties such as texture can be influenced by the use of H2O2, because of its ability to change lipid and protein structures, basic constituent of cellular membranes, promoting loss of quality related to firmness of vegetal tissue, which were verified by sensorial and mechanical tests (Mani-Lo´pez et al., 2016). On the other hand, for short duration (1 min of immersion), a treatment with 50 mg L 1 of H2O2 was not enough to promote loss of firmness (Silveira et al., 2008). The lipid and protein oxidation reactions caused by H2O2 contact can intensify the formation of the typical pungent smell reported by the judges (Mani-Lo´pez et al., 2016). It is common to see studies on microorganism reductions; however, results on the impact of treatments on the nutrient and phytochemical content of the fruits and vegetables are scarce. The color parameter was strongly affected by the immersion, probably due to the leaching. Loss of greenness was observed in peppers treated with hydrogen peroxide (5%, 30 or 120 min) or sodium hypochlorite (10,000 mg L 1, 120 min) (Mani-Lo´pez et al., 2016). Anthocyanins were also affected by hydrogen peroxide or its decomposition products forming colorless compounds, because of the action of cleaving carbon-carbon € bond (Ozkan et al., 2005). Van de Velde et al. (2016), in a study with strawberries, observed that, however, their results were also influenced by the presence of peracetic acid in the sanitizer solution. Considering the oxidant properties of the H2O2 and the fact that anthocyanins are bioactive compounds with high antioxidant capacity, the deleterious damages should be more intensively studied. In a previous study, Van de Velde et al. (2015), a significant change in these general quality attributes (pH, total acidity, Brix) of strawberries was observed. On the other

Hybrid Membrane System Design and Operation

hand, a slightly decrease was observed in the bioactive compound content (anthocyanins, phenolic compounds, vitamin C) of strawberry in a treatment under refrigeration (2°C) during 1 week of storage. It is important to analyze the influence of hydrogen peroxide treatment on the nutritional compounds, quality atributes, and sensorial aspects of horticulture products once their composition (macro and micronutrients and structure could react differently.

5. PERFORMANCE OF HYDROGEN PEROXIDE BASED ON THE APPLICATION METHODS The processes of sanitizing raw food materials, as well as areas, equipment, tools for food processing, among others, carried out by washing with potable water can succeed in eliminating only some of the microorganisms present on the surfaces, they do not act as disinfectant. The washing stage is crucial. According to Baviera et al. (2016) these processes require the use of large quantities of water, making it essential to recycle water to save resources and minimize the environmental impact of this practice. In washing systems with water recirculation, if the water is not disinfected properly, it acts as a means of transferring microorganisms, leading to cross contamination. In order to avoid washing water from becoming a channel through which infection is spread by cross contamination, it must be ensured that its microbiological quality is maintained. For this, disinfecting products can be used, for example, hydrogen peroxide, always making sure that degradation products and residues from the antimicrobial agent used do not pose a risk to the health of the consumer or the environment, they do not alter the organoleptic properties of products (Gil et al., 2009; Kyanko et al., 2010), and that they can be combined with plant protection products without degrading them. With regard to the efficacy of hydrogen peroxide in the food industry, some studies have shown that the form of application of this compound may influence the results obtained.

6. APPLICATION METHODS The use of hydrogen peroxide (2.5%–5.0%) washes for reducing native microflora and Salmonella populations on inoculated whole and minimally processed fresh-cut cantaloupe has also been investigated (Ukuku et al., 2001; Ukuku, 2004). Total inactivation of inoculated Salmonella populations was not achieved (Ukuku, 2004). The effectiveness of the use of hydrogen peroxide vapor (HPV) against spores of Clostridium botulinum was evaluated as a method for the decontamination of environments where this pathogen has been handled ( Johnston et al., 2005). Spores were dried on stainless steel slides and exposed to HPV in a sealed glovebox enclosure, then transferred to a quenching agent at regular intervals during the exposure period, before survivors were cultured and enumerated. The HPV was found to be effective at deactivating spores of toxigenic C. botulinum, nontoxigenic Clostridium spp. and Geobacillus stearothermophilus

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dried on stainless steel surfaces. The HPV could be used to decontaminate cabinets and rooms where C. botulinum has been handled. The cycle parameters should be based on studies carried out with relevant spores of this organism, rather than based on inactivation data for G. stearothermophilus spores, which have been used in the past as a standard biological challenge for disinfection and sterilization procedures. The HPV could provide an attractive alternative to other decontamination methods, as it was rapid, residue-free and did not give rise to the health and safety concerns associated with other gaseous decontamination systems. An in vitro comparison was performed of an HPV system (Bioquell) and an aerosolized hydrogen peroxide (aHP) system (Sterinis) (Holmdahl et al., 2011). The tests were conducted in a purpose-built 136 m3 test room. One HPV generator and two aHP machines were used, following manufacturers’ recommendations. Three repeated tests were performed for each system. The microbiological efficacy of the two systems was tested using 6-log Tyvek-pouched G. stearothermophilus biological indicators (BIs). The indicators were placed at 20 locations in the first test and 14 locations in the subsequent two tests for each system. All BIs were inactivated for three HPV tests, as compared with only 10% in the first aHP test and 79% in the other two aHP tests. The peak hydrogen peroxide concentration was 338 ppm for HPV and 160 ppm for aHP. The total cycle time (including aeration) was 3 and 3.5 h for the three HPV tests and the three aHP tests, respectively. Monitoring around the perimeter of the enclosure with a handheld sensor during tests of both systems did not identify leakage. One HPV generator was more effective than two aHP machines for the inactivation of G. stearothermophilus BIs, and cycle times were faster for the HPV system. Applying the technique of submersion hydrogen peroxide (2.5%) alone or hydrogen peroxide (1%) in combination with nisin (25 Ag/mL), sodium lactate (1%), and citric acid (0.5%) (HPLNC) were investigated as potential sanitizers for reducing E. coli O157:H7 or L. monocytogenes populations on whole cantaloupe and honeydew melons (Ukuku et al., 2005). The form of application for all the washing treatments, based on hydrogen peroxide, occurred by submerging the fruits under the 3 L surface of washing solution and manually rotating for 5 min to ensure a complete coverage of the surfaces with solution (Ukuku et al., 2005). It is also important to mention no-touch automated environment disinfection systems. No-touch automated room disinfection systems may prevent such a spread of contamination. Hydrogen peroxide is one of the most common no-touch automated room disinfection systems. The HPV systems are divided into two different systems: vaporized hydrogen peroxide, vapor and noncondensing, and HPV, vapor and condensing (Otter and Yezli, 2011). Zonta et al. (2016) tested the efficiency of two systems of hydrogen peroxide applications: an aerosolized hydrogen peroxide system and another application system by nebulization, against the spread of noroviruses (NoV).

Hybrid Membrane System Design and Operation

Human noroviruses are among the worldwide leading causes of acute gastroenteritis (Patel et al., 2008; Pringle et al., 2015). The primary transmission route is the fecal-oral route, via person-to-person contact, by consumption of contaminated food or water (Lopman et al., 2003; Scallan et al., 2011; Mathijs et al., 2012), or via contact with a contaminated surface (Otter and Yezli, 2011). Contaminated surfaces can be found in industrial and food processing facilities and in health-care settings (hospitals, care homes) and contribute to the transmission of viruses (Otter and Yezli, 2011). According to Zonta et al. (2016) the nebulization of hydrogen peroxide showed a clear virucidal effect, on two different carriers and the use of nebulization should be promoted complementarily with conventional disinfection methods in health-care settings and food processing facilities to reduce viral load and spread of contamination. Murdoch et al. (2016) conducted a comparative study made on the efficacy of 5%, 10%, and 35% weight by weight (w/w) hydrogen peroxide solutions when applied using an automated room disinfection system. Six-log biological indicators of methicillinresistant Staphylococcus aureus (MRSA) and G. stearothermophilus were produced on stainless steel coupons and placed within a large, sealed, environmentally controlled enclosure. In all 5% hydrogen peroxide was distributed throughout the enclosure using a Bioquell HPV generator (BQ-50) for 40 min and left to reside for a further 200 min. The 5% and 10% hydrogen peroxide solutions failed to achieve any reduction in MRSA, but achieved full kill of G. stearothermophilus spores at 70 and 40 min, respectively. Overall, 35% hydrogen peroxide achieved a 6 log reduction of MRSA after 30 min and full kill of G. stearothermophilus at 20 min. The concentration of 5% hydrogen peroxide within the enclosure after the 20 min dwell was measured at 9 ppm. This level exceeds the 15-min short term exposure limit (STEL) for hydrogen peroxide of 20 ppm. In summary, the users of automated hydrogen peroxide disinfection systems should review system efficacy and room reentry protocols in light of these results. Another example of technique for applying hydrogen peroxide is spraying. This method was performed on iceberg lettuce. Hadjok et al. (2008) studied the use of UV and hydrogen peroxide (H2O2) for decontaminating fresh produce (Hadjok et al., 2008). Samples of iceberg lettuce were inoculated with E. coli O157 and then sprayed with H2O2 and subjected to UV light. The same authors observed greater reductions with UV/H2O2 treatments than with 300 mg L 1 chlorine for a range of products including Romaine lettuce, spinach, cauliflower, broccoli, Spanish onion, and tomato (Hadjok et al., 2008). Becker et al. (2017) studied the virucidal efficacy of an automated ultrasound probe disinfector, using the three-step procedure according to European and German test methods. This system uses sonicated hydrogen peroxide mist (35%) at elevated temperature (50°C) in a closed chamber with control of all parameters within a 7-min cycle. In the first step of examination, the peroxide solution was tested in a quantitative suspension. In the second step, the virucidal efficacy of hydrogen peroxide solution was evaluated in a hard surface carrier test. Finally, the efficacy was evaluated by the automated system using stainless steel carriers inoculated with test virus and positioned at different levels inside the

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chamber. There was a reduction, demonstrated with all methods using the automated device, of A 4 log 10 of virus titre, including carrier tests with murine norovirus, adenovirus, and parvovirus.

7. CONCLUSION Hydrogen peroxide can be an effective alternative in the process of sterilization and disinfection of fruits and vegetables in general, besides preserving their quality attributes and extending their shelf life after harvest. Compared with the effectiveness of chlorate, the most applied disinfectant for fresh products, hydrogen peroxide presented a higher capacity to eliminate microorganisms. An important characteristic of H2O2 is that it does not react with water or organic material forming carcinogenic compounds. The main applications of hydrogen peroxide solutions (1%–5%) are direct immersion of the product in a liquid solution and vapor aspersion. It also can be used in isolation or in combination with other sanitizers. The last option can increase its effectiveness against pathogenic and spoilage microorganisms (bacteria, fungi, and yeasts). Some parameters have a high influence in its effectiveness as concentration, application time, and temperature. All the presented factors shows that H2O2 is versatile, safe, and environmentally friendly alternative as a sanitizer.

REFERENCES Alexandre, E.M.C., Branda˜o, T.R.S., Silva, C.L.M., 2012. Assessment of the impact of hydrogen peroxide solutions on microbial loads and quality factors of red bell peppers, strawberries and watercress. Food Control 27, 362–368. Baviera, J.M.B., P
erez, G.F., Martı´nez, G.P., Rodrı´guez, R.L., 2016. Report of the Scientific Committee of the Spanish Agency for Consumer Affairs, Food Safety and Nutrition (AECOSAN) in relation to the use of an antimicrobial aqueous solution containing hydrogen peroxide, acetic acid and peroxyacetic acid as a processing aid on citrus fruits and tomatoes, and their wash water. Revista del Comit
e Cientı´co 23, 21–43. Becker, B., Bischoff, B., Brill, F.H.H., Steinmann, E., Steinmann, J., 2017. Virucidal efficacy of a sonicated hydrogen peroxide system (trophon® EPR) following European and German test methods. GMS Hyg. Infect. Control 12 (2), 1–8. Felizini, E., Lichter, A., Smilanik, J.L., Ippolito, A., 2016. Disinfecting agents for controlling fruit and vegetable diseases after harvest. Postharvest Biol. Technol. 122, 53–69. Gil, M., Allende, A., Lo´pez Ga´lvez, F., Selma, V., 2009. Hay alternativas al cloro como higienizante para productos de IV Gama. Hortic. Inter. 69, 38–45. Hadjok, C., Mittal, G.S., Warriner, K., 2008. Inactivation of human pathogens and spoilage bacteria on the surface and internalized within fresh produce by using a combination of ultraviolet light and hydrogen peroxide. J. Appl. Microbiol. 104, 1014–1024. Holmdahl, T., Lanbeck, P., Wullt, M., Walder, M.H., 2011. A head-to-head comparison of hydrogen peroxide vapor and aerosol room decontamination systems. Infect. Control Hosp. Epidemiol. 32 (9), 831–836. Johnston, M.D., lawson, S., Otter, J.A., 2005. Evaluation of hydrogen peroxide vapour as a method for the decontamination of surfaces contaminated with Clostridium botulinum spores. J. Microbiol. Methods 60 (3), 403–411.

Hybrid Membrane System Design and Operation

Kyanko, M.V., Russo, M.L., Ferna´ndez, M., Pose, G., 2010. Efectividaddel a´cido perac
etico sobre lareduccio´n de la carga de esporas de mohos causantes de pudricio´nposcosecha de frutas y hortalizas. Inf. Technol. 21 (4), 125–130. Linley, E., Denyer, S.P., McDonnell, G., Simons, C., Maillard, J.Y., 2012. Use of hydrogen peroxide as a biocide: new consideration of its mechanisms of biocidal action. J. Antimicrob. Chemother. 67, 1589–1596. Lopman, B.A., Adak, G.K., Reacher, M.H., Brown, D.W.G., 2003. Two epidemiologic patterns of norovirus outbreaks: surveillance in England and Wales, 1992–2000. Emerg. Infect. Dis. 9 (1), 71–77. Mani-Lo´pez, E., Palou, E., Lo´pez-Malo, A., 2016. Effect of different sanitizers on the microbial load and selected quality parameters of “chile de a´rbol” pepper (Capsicum frutescens L.) fruit. Postharvest Biol. Technol. 119, 94–100. Mathijs, E., Stals, A., Baert, L., Botteldoorn, N., Denayer, S., Mauroy, A., et al., 2012. A review of known and hypothetical transmission routes for noroviruses. Food Environ. Virol. 4 (4), 131–152. McDonnell, G., 2014. The Use of Hydrogen Peroxide for Disinfection and Sterilization Applications. Patai’s Chemistry of Functional Groups. Murdoch, L.E., Bailey, L., Banham, E., Watson, F., Adams, N.M.T., Chewins, J., 2016. Evaluating different concentrations of hydrogen peroxide in an automated room disinfection system. Lett. Appl. Microbiol. 63 (3), 178–182. € Olmez, H., Kretzschmar, U., 2009. Potential alternative disinfection methods for organic fresh-cut industry for minimizing water consumption and environmental impact. LWT Food Sci. Technol. 42 (3), 686–693. Otter, J.A., Yezli, S., 2011. A call for clarity when discussing hydrogen peroxide vapour and aerosol systems. J. Hosp. Infect. 77 (1), 83–84. € Ozkan, M., Yemenicioglu, A., Cemeroglu, B., 2005. Degradation of various fruit juice anthocyanins by hydrogen peroxide. Food Res. Int. 38, 1015–1021. Parish, M.E., Beuchat, L.R., Suslow, T.V., Harris, L.J., Garret, E.H., Farber, J.M., et al., 2003. Methods to reduce/eliminate pathogens from produce and fresh-cut produce. Compr. Rev. Food Sci. Food Saf. 2, 161–173. Patel, M.M., Widdowson, M.A., Glass, R.I., Akazawa, K., Vinj
e, J., Parashar, U.D., 2008. Systematic literature review of role of noroviruses in sporadic gastroenteritis. Emerg. Infect. Dis. 14 (8), 1224–1231. Pringle, K., Lopman, B., Vega, E., Vinje, J., Parashar, U.D., Hall, A.J., 2015. Noroviruses: epidemiology, immunity and prospects for prevention. Future Microbiol 10 (1), 53–67. Sapers, G.M., 2001. Efficacy of washing and sanitizing methods for disinfection of fresh fruit and vegetable products. Food Technol. Biotechnol. 39 (4), 305–311. Scallan, E., Hoekstra, R.M., Angulo, F.J., Tauxe, R.V., Widdowson, M.A., Roy, S.L., et al., 2011. Foodborne illness acquired in the United States-major pathogens. Emerg. Infect. Dis. 17 (1), 7–15. Silveira, A.C., Conesa, A., Aguayo, E., Artes, E., 2008. Alternative sanitizers to chlorine for use on fresh-cut Galia (Cucumis melo var. catalupensis) melon. J. Food Sci. 73 (9), 405–411. Ukuku, D.O., 2004. Effect of hydrogen peroxide treatment on microbial quality and appearance of whole and fresh-cut melons contaminated with Salmonella spp. Int. J. Food Microbiol. 95, 137–146. Ukuku, D.O., Fett, W.F., 2005. Effect of nisin in combination with EDTA, sodium lactate, potassium sorbate for reducing Salmonella on whole and fresh-cut cantaloupe. J. Food Prot. 67, 2143–2150. Ukuku, D.O., Pilizota, V., Sapers, G.M., 2001. Influence of washing treatments on native microflora and Escherichia coli population of inoculated cantaloupes. J. Food Saf. 21, 31–47. Ukuku, D.O., Bari, M.L., Kawamoto, S., Isshiki, K., 2005. Use of hydrogen peroxide in combination with nisin, sodium lactate and citric acid for reducing transfer of bacterial pathogens from whole melon surfaces to fresh-cut pieces. Int. J. Food Microbiol. 104 (2), 225–233.
., Lila, M.A., 2015. Impact of a new postharvest disinfection Van de Velde, F., Grace, M.H., Pirovania, M.E method based on peracetic acid fogging on the phenolic profile of strawberries. Postharvest Biol. Technol. 117, 197–205. Van de Velde, F., Vaccari, M.C., Piagentini, A.M., Pirovani, M.E., 2016. Optimization of strawberry disinfection by fogging of a mixture of peracetic acid and hydrogen peroxide based on microbial reduction, color and phytochemicals retention. Food Sci. Technol. Int. 22 (6), 485–495. Zonta, W., Mauroy, A., Farnir, F., Thiry, E., 2016. Virucidal efficacy of a hydrogen peroxide nebulization against murine norovirus and feline calicivirus, two surrogates of human norovirus. Food Environ. Virol. 8, 275–282.

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CHAPTER 5

Ultrasonic Processing Technology for Postharvest Disinfection Efigenia Montalvo-González*, Luis M. Anaya-Esparza†, J. Abraham DomínguezAvila‡, Gustavo A. González-Aguilar‡ *

Integral Laboratory of Food Research, Technological Institute of Tepic, Tepic, Mexico Food Microbiology Laboratory, Department of Agricultural and Livestock Sciences, University of Guadalajara, University Center of Los Altos, Tepatitla´n de Morelos, Mexico ‡ Coordination of Food Technology of Plant Origin, Center for Research in Food and Development, Hermosillo, Mexico †

1. INTRODUCTION The consumption of fresh fruits and vegetables (FFVs) has increased in recent years, because they are an essential part of a healthy diet, and their intake is continually recommended by many health organizations around the globe (FAO/WHO, 2008). Increased attention has been paid to the quality and safety of FFVs and other fresh foods, in synergy between individual health-conscious consumers and government agencies (Alexandre et al., 2012). The disinfection methods used on fresh foods during the production chain (harvesting, postharvest handling, processing, and transportation) are mainly washing with water and/or chemical sanitizing solutions (Sapers, 2001). Chlorinated solutions are widely used due to their simple handling, low cost, water solubility, and stability over prolonged storage periods. Unfortunately, chlorine is linked to the formation of potentially mutagenic or carcinogenic reaction by-products (USDA, 2011), which imposes limitations on its indiscriminate use. It has been demonstrated that certain microorganisms are more tolerant to chlorinated compounds than others (Ramos et al., 2013), which has lead several European countries to ban its use on fresh products (FAO/WHO, 2008). But the complete removal or inactivation of microorganisms from FFVs continues to be a challenge, because an effective disinfection process that can be safely and efficiently used on these kinds of products has been difficult to perfect. Some bacteria are attached or entrapped on the surfaces of FFVs and are not readily accessible to the sanitizers (Seymour et al., 2002), which further complicates the problem. Hence, an effective and safe water-based disinfection method that can be used on FFVs is still required. Some emerging technologies are an alternative to the use of chlorine-based solutions (USDA, 2011), and in particular, ultrasound (US). It has been demonstrated that US is an excellent option to clean surfaces in the electronics industry, and its use has been recommended on FFVs (Chemat et al., 2011; Sa˜o Jose et al., 2014b). The first study that used Postharvest Disinfection of Fruits and Vegetables https://doi.org/10.1016/B978-0-12-812698-1.00005-4

© 2018 Elsevier Inc. All rights reserved.

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US as a disinfection agent on FFVs was conducted in 2002 by Seymour et al. Since then, many experiments have been conducted that focused on different methods to evaluate the influence of US in combination with chemical solutions on FFVs.

2. PHYSICAL PRINCIPLES OF ULTRASOUND IN AN AQUEOUS MEDIUM The US is a form of energy that is transmitted by sound waves at frequencies of up to 20 kHz. Ultrasonic power is easily transferred through the treated medium (Mason et al., 1996), and can be measured in terms of power (W), intensity (W/cm2), or acoustic energy density (W/mL) (O’Donnell et al., 2010). High-intensity US, with frequencies of 20–100 kHz, generates an intense pressure, shear force, and a temperature gradient into the material, which physically disrupts its structure, or promotes different chemical reactions (Earnshaw et al., 1995). When acoustic energy passes through a medium, particularly an aqueous one, a continuous undulation motion is produced by the mechanical vibrations and three types of waves are generated: (1) longitudinal waves that move in the direction of the displacement, (2) shear waves that are perpendicular to the movement to the original waves, and (3) Rayleigh waves, which travel very close to the surface of the medium (Mulet et al., 1999). At the time of wave propagation, alternating compression/expansion cycles are generated by different types of waves. During these cycles, millions of small bubbles are formed, which grow by absorbing energy from the medium, and when they cannot absorb more energy, they become unstable and violently implode. This releases high amounts of energy, in a process known as cavitation, which is the most significant way that transmits ultrasonic power with in a liquid medium (Mason et al., 1996). The collapse of a cavitation bubble can occur on the surface of a cell wall or in close proximity to it. When it happens on the surface of a cell, it can potentially punch holes through the cell wall, which further exposes new surfaces to an increasing mass and energy transfer, and culminates in the disruption of the structure and function of the cell wall, as demonstrated by Li et al. (2017). There are discontinuous and continuous US systems, and because of the conformation of discontinuous systems (Fig. 1A and B), they are the most widely used for disinfection of FFVs (Table 1). In contrast, continuous systems (Fig. 1C) are only used in liquid products. A major advantage of US over other techniques in the food industry is that sound waves are generally considered safe, nontoxic, and they do not generate unpleasant odors and are environmentally friendly (Chemat et al., 2011). The physical and chemical effects of an US treatment are closely related to the operational parameters such as amplitude, frequency, treatment time, temperature, volume processed among others (Ramos et al., 2013; Millan-Sango et al., 2017).

Ultrasonic Processing Technology for Postharvest Disinfection

Fig. 1 (A) and (B) Immersion batch and (C) continuous flow through ultrasonic systems. (Adapted from Anaya-Esparza, L.M., Velázquez-Estrada, R.M., Roig, A.X., García-Galindo, H.S., Sayago-Ayerdí, S.G., Montalvo-González, E., 2017. Thermosonication: an alternative processing for fruit and vegetable juices. Trends Food Sci. Technol. 61, 26–37.)

3. EFFECTS OF ULTRASOUND ON SPOILAGE AND PATHOGENIC MICROORGANISMS Under natural conditions, the outer layer of FFVs provides a natural barrier for microorganisms, but this natural barrier is lost during postharvest handling. The surfaces of FFVs can be smooth, rough, porous or irregularly shaped, thus, the adherence of microorganisms to them varies, as does the effectiveness of the sanitizing method. The removal of microorganisms from the surfaces of FFVs is a challenge that the industry has yet to perfect (Sa˜o Jose et al., 2014b). High-intensity US alone, or in combination with some sanitizers, has been used to facilitate the disinfection of many FFVs (Table 1), and the results vary according to the experimental conditions and the type of microorganism. Wang et al. (2009) demonstrated a positive correlation between roughness (R2 ¼ .96) and adhesion of Escherichia coli O157:H7 on the surfaces of FFVs with different surface roughness. Nonetheless, an increased elimination rate (3 log CFU/cm2) of Salmonella enterica and E. coli from the surfaces of green pepper and melon was obtained, when US and organic acids (such as 1% lactic and acetic acid) were simultaneously applied to them (Sa˜o Jose et al., 2014b). The authors mentioned that surface roughness of the FFVs had a direct influence on the effectiveness of the US treatment. These results are in agreement with those reported by other authors who used US (5–10 min) to disinfect the surfaces of lettuce, alfalfa, spinach, radish sprout, apples with normal surfaces and apples, pears, and truffles with cut surfaces, with or without organic/chemical

103

Table 1 Use of ultrasound, alone or in combination with chemicals to eliminate spoilage and pathogenic microorganisms from different fruits and vegetables Microbial a Form of the Ultrasonic Experimental reduction (log Fruit or vegetable Microorganism microorganism Treatment equipment conditions cycles) Reference

Strawberry

Salmonella enterica

Vegetative cells

US + peracetic acid (40 mg/L)

Cucumber

Cronobacter sakazakii

Vegetative cells

US + peroxyacetic acid (150 ppm)

Alfalfa

1)

Salmonella enterica 2) Escherichia coli 1) Total aerobic bacteria 2) Yeast and molds Salmonella enterica

Vegetative cells

US alone

Vegetative cells

US + EOO (0.01%)

Lettuce

Cronobacter sakazakii

Vegetative cells

US + NaOCl (200 ppm)

Tomato

1)

Vegetative cells

US alone

Strawberry

Lettuce

Lettuce

Total aerobic bacteria 2) Yeast and molds Escherichia coli

Vegetative cells

Vegetative cells

US alone

US + EOO (0.01%)

Ultrasonic water bath at 500 W Ultrasonic water bath at 380 W b Probe of 31 mm diameter Ultrasonic water bath at 60 W Ultrasonic water bath at 200 W Ultrasonic water bath at 200 W Ultrasonic water bath

Ultrasonic water bath at 200 W

40 kHz; 5 min

2.0

37 kHz; 60 min

3.1

26 kHz; 90 μm; 5 min

(1)

33 kHz; 60 min

(1)

(2)

(2)

Alves do Rosa´rio et al. (2017) Bang et al. (2017)

1.4 1.9

Millan-Sango et al. (2017)

1.6 1.5

Gani et al. (2016)

26 kHz; 90 μm; 5 min

3

Millan-Sango et al. (2016)

37 kHz; 100 min

4.44

Park et al. (2016)

45 kHz; 100%; 19 min

1)

Pinheiro et al. (2015)

26 kHz; 90 μm; 5 min

4.6

2)

2.95 90%) 376 W/cm2 and 10 min Phenoloxidase (20%) Manothermosonication Pectin esterase (70°C, 300 kPa, 2 min) (94%)

–

–

–

–

–

–

–

–

–

–

Tiwari et al. (2009a,b,c) Saeeduddin et al. (2015)

18

–

–

–

–

–

–

–

–

–

Knorr et al. (2004) Costa et al. (2013) Kuldiloke (2002)

Manothermosonication Pectin esterase (80°C, 200 kPa, 5 min) (96%)

–

–

–

–

–

Kuldiloke (2002)

– –

8 –

7.9  0.1 0.66  0.1 68 6.1 9.8

– –

–

35

–

–

Cao et al. (2010) Adekunte et al. (2010) Zenker et al. (2003)

0.3 min at 72°C, cavitation intensity 0.008 mg/L/min 1.05 W/mL, 10 min

40 kHz, 20°C, 10 min 20 kHz, 2–10 min, 24–61 μm 60°C, 220 s

Pectinmethyl esterase (89%)

–

240

Continued

Table 2 Effect of ultrasonication on enzyme inactivation and on extraction of bioactive compounds of fruits and vegetables—cont’d Shelflife Bioactive S. No Product Treatment conditions Enzyme inactivation (days) TSS (%) TA (%) Vc (mg/100 g) compounds

11

Tomato

Manothermosonication (62.5°C, 200 kPa) 24 kHz, 60–70°C

12

Tomato juice

13

Tomato juice

14

Tomato juice

15

Purple cactus pear juice

16

Purple cactus pear juice

Pectinmethyl esterase and Polygalacuronase Pectic enzymes Manothermosonication (undetectable) (20 kHz, 2 kg pressure, 117 lm amplitude and 70°C Polygalacturonase Manothermosonication (62%) (20 kHz, 2 kg pressure, 117 lm amplitude and 70°C Amplitude level 40% and – 60% for 10, 15, 25 min; 80% Amplitude level 80% for – 3,5,8,10, 15, 25 min

17

Blackberry juice

Amplitude level 40%– 100%, 20 kHz,10 min

18

Orange juice

19

Orange juice (Calcium added)

– Amplitude level 40%, 70%, 100%, 20 kHz, 2,6, 10 min Amplitude level 89.2 μm, – 20 kHz, 2,4, 6, 8, 10 min

–

Pectic enzymes (90%)

–

References

Lopez et al. (1998) Wu et al. (2008)

–

–

–

–

–

–

–

–

–

–

Vercet et al. (2002)

–

–

–

–

–

Vercet et al. (2002)

–

12.1–13

5.0–5.1

300–350 mg/L –

–

12.1–13

5.0–5.4

300–400 mg/L –

–

–

–

–

30

–

–

34–39

94% anthocyanin retention –

6

–

–

40–43

–

Zafra-Rojas et al. (2013) Zafra-Rojas et al. (2013) Tiwari et al. (2009a, 2009b, 2009c) Tiwari et al. (2009a, 2009b, 2009c) Go´mez-Lo´pez et al. (2010)

20

Red grape juice

Amplitude level 24–61 μm, 20 kHz, 0–10 10 min

–

–

–

–

21

Strawberry juice

– Amplitude level 60, 90,120 μm, 20 kHz, 3, 6, 9 min, 25, 40, 55°C

–

–

–

22

Pineapple juice

376 W/cm2 and 10 min

42

–

–

23

Cranberry juice

– Amplitude level 60, 90,120 μm, 20 kHz, 3, 6, 9 min, 20, 40, 60°C

–

–

–

24

Prebiotic cranberry juice

600 and 1200 W/L + high – pressure (450 mPa, 5 min)

–

–

–

25

Pear juice

750 W, 20 kHz, 10 min, 25, 45, 65°C

–

–

–

–

26

Blueberry juice

13, 43, 73 J/mL, 20 kHz

–

–

–

–

–

–

Retention of anthocyanin content, cyanidin (97.5%), malvanidin (48%), delphenidin (81%) – Less degradation of anthocyanins (0.7–44%) – 30% increase in phenolic compounds – More percentage of aromatic compounds Organic acids Increased anthocyanin retention content (>90%) (24%) Increased Increased retention of retention of phenolic ascorbic compounds acid – Retention of anthocyanin

Tiwari et al. (2010)

Dubrovic et al. (2011)

Costa et al., 2013

Jambrak et al. (2017)

Gomes et al. (2017)

Saeeduddin et al. (2015)

Mohideen et al. (2015) Continued

Table 2 Effect of ultrasonication on enzyme inactivation and on extraction of bioactive compounds of fruits and vegetables—cont’d Shelflife Bioactive S. No Product Treatment conditions Enzyme inactivation (days) TSS (%) TA (%) Vc (mg/100 g) compounds

27

Strawberry juice

25 kHz, 0, 15, 30 min

–

–

–

–

–

28

Red grape juice

0–135 Hz, 20–40 min, 25–50°C

–

–

–

–

–

29

Carrot juice

14

–

–

Ascorbic acid retention (100%)

30

Grapefruit juice

– 24 kHz, 120 μm amplitude at 50°C, 54° C, and 58°C for 10 min, 2204.40, 2155.72, 2181.68 mW/mL 30, 60, and 90 min, – 28 kHz, 20°C

–

–

31

Cantaloupe 376 W/cm2 10 min melon juice

–

–

–

Enhancement of bioactive compounds Retention of total anthocyanin content Retained carotenoids (>98%),

Improved total antioxidant activity 30% reduction in phenolic compounds

References

Bhat and Goh (2017) Nafar et al. (2013)

Martı´nez-Flores et al. (2015)

Aadil et al. (2013)

Fonteles et al. (2012)

Hybrid Membrane System Design and Operation

The compounds mainly reside in the cells of the tissues and the application of ultrasound maximizes the targeted surface area and leads to complete extraction (Balachandran et al., 2006). The mechanism of ultrasound induces cavitation bubbles in the liquid medium of the treated sample and increases the hydrophobic property of the extraction medium (Vilkhu et al., 2008). Thus, hydrophobic bubbles create the environment for extracting the polar compounds (Li et al., 2004). It was found that ultrasound-assisted extraction incremented the release of polyphenolic compounds from 17% to 35% (Vilkhu et al., 2008). Other benefits of using ultrasonic stimulated extraction include reduced processing time, minimized energy input, and less environmental footprints (Chemat and Khan, 2011). The loss of ascorbic acid has been reported to be reduced (below 15%) in thermosonication treatment as compared to the greater losses (up to 90%) with traditional thermal processes (Anaya-Esparza et al., 2017), furthermore ascorbic acid content in grapefruit juice was increased (up to 14%, 27%, 28%) by ultrasonic treatment (28 kHz, 20°C, 30, 60, and 90 min) followed by storage of grapefruit juice at 4°C (Aadil et al., 2013). The significant retention of bioactive compounds as well as their less degradation are presented in Table 2. The importance and effectiveness of independent variables of ultrasonic treatment for extraction of plant-based bioactive compounds can be put in the order of frequency, followed by temperature, and then exposure time (Nafar et al., 2013). Martı´nezFlores et al. (2015) reported the complete stability of ascorbic acid in carrot juice during 20 days of storage at 4°C when thermosonication at 24 kHz, 120 mm, 2 min, and 58°C was applied. Aadil et al. (2013) observed higher extraction of total flavonoids (30%) and significant increase in both DPPH-free radical scavenging activity and total antioxidant capacity in grapefruit juice samples by ultrasonic treatment at 28 kHz, 20°C, and 90 min. The increase in total polyphenolic content and total antioxidant activity was found to be 85% and 33%, respectively, followed by ultrasonic treatment (25 kHz, 20°C, 30 min) in strawberry juice (Bhat and Goh, 2017). Other studies also demonstrated the significant effect of power ultrasonication in the extraction of polyphenols and higher antioxidant activity in strawberry (Gani et al., 2016), anthocyanins in blueberry juice (Farhadi Chitgar et al., 2017) organic acids, fructo-oligosaccharides, and aromatic compounds in cranberry juice (Gomes et al., 2017; Jambrak et al., 2017). Moreover, higher retention of ascorbic acid, total phenols, and flavonoids in pear juice was observed by ultrasonic treatment at 25°C in comparison to the ultrasonic treatment at increased temperature from 45°C to 65°C with a constant time of 10 min in all treatments (Saeeduddin et al., 2015). The increase in total phenolic compounds and carotenoids by ultrasonication might have been caused by mechanical disruption of the cell wall (depending on structure and lignin content of cell wall) and ultimate release of these compounds (Costa et al., 2013). The propagation of ultrasound waves result into phenomenon of cavitations that causes mass transfer of extractable compounds. The formation of cavities leads to high-velocity collision that fastens the diffusion. Therefore, cavitations on surface of

169

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Postharvest Disinfection of Fruits and Vegetables

the tissue foster the breakdown of the compounds (Soria and Villamiel, 2010). Therefore, diffusion through the plant cell walls makes the washing out of the cellular contents, thereby enhancing the rate of extraction. In addition, the combination of pressure, heat, and turbulence lead to implosion of cavity bubbles (Soria and Villamiel, 2010). The application of ultrasound to fruits and vegetable covers both pre- and postharvest in order to improve the quality of the fresh produces (Awad et al., 2012).

3.2 Effect on Organoleptic Properties and Consumer Acceptance Ultrasonication is one of the food processing techniques that possess the advantage of food preservation, in contrast to thermal methods, which put deleterious postprocessing effect on the appearance (like color), flavor, and aroma of the fruits and vegetables. Therefore, another effective alternative in the form of ultrasonication can cover some of the limitations of the thermal methods. Other advantages of sonication (such as reduced processing time, lower energy input, and less tangible treatment process) have made it superior over laborious treatment and extraction methods (Tiwari et al., 2009a,b,c). Today, consumers’ inclination toward the minimally processed and natural flavor-rich products has drifted the interest of food technologists to explore nondestructive methods like sonication. It was found that ultrasonication has no such detrimental effect on sensory properties of fruit and vegetable products. Ultrasonication helps in developing aromatic compounds in fruit juices which is reported earlier in cranberry juice nectar and apple juice nectar ( Jambrak et al., 2017; Sˇimunek et al., 2013). Moreover, it was also found that ultrasonication does not significantly change color or sensory properties of some fruits and vegetable products (such as red pepper, celery, lettuce, peas, etc.) (Bantle and Eikevik, 2011; Kwak et al., 2011; Sagong et al., 2011; Sch€ ossler et al., 2012; Seymour et al., 2002) as presented in Table 3. Furthermore, pleasing flavor has also been reported in orange juice after ultrasonication and heat treatment at 500 kHz, 240 W for 15 min (Valero et al., 2007). In addition, minor color changes and turbidity were also found in apple cider sample which was ultrasonic-heated at 20 kHz for 17.7 min at 40°C (Ugarte-Romero et al., 2006). Overall, the changes in sensory properties are dependent on ultrasonication time and intensity applied to food product. Changes in viscosity or texture are mainly affected by ultrasound intensity applied to food. Cavitation causes shear which is the major factor that decreases the viscosity of thixotropic fluid (certain gels that are thick) (Seshadri et al., 2003). Ultrasound has no such effect on texture or viscosity of food. For example, apple slices were ultrasonically dried at 90 W for 3.5 min, in which minor textural properties were observed (Sabarez et al., 2012) (Table 4). Moreover, ultrasound decreases the drying time which allows for more water elimination in dried apple slices (Brncic et al., 2010). In addition to this, ultrasound treatment also resulted in lower moisture content, higher glass transition temperature, and rehydration ratio, which is ultimately a significant aspect of ultrasonication on texture of Fuji dried apples (Deng and Zhao, 2008).

Table 3 Effect of ultrasonication on sensory properties of fruits and vegetables S. No Food Processing conditions Techniques

1

Cranberry juice and nectar

20 kHz, 3–9 min, 60–120 μm, 20–60°C

Ultrasound

2

Apple juice and nectar

21 kHz, 3–9 min, 60–120 μm, 20–60°C

Ultrasound

3

Cubes of red pepper Fresh-cut celery

4.9 μm, 7 h, 10 s ultrasound and 90 s recovery phase 40 kHz, 60°C, 15 min and 40 kHz, 59°C, 17 min 40 kHz, 5 min

6

Organic fresh lettuce Peas

7

Orange juice

20 kHz, 15 min, 600 W, 95.2 μm, 45°C

8

Orange juice

500 kHz/240 W for 15 min

Freeze-drying and ultrasound Ultrasound, heat and 2% calcium propionate Ultrasound and 2% organic acids Freeze-drying and ultrasound Ultrasound, heat and natural antimicrobials Ultrasound

9

Apple cider

20 kH, 17.7 min, 40°C

Ultrasound and heat

10

Fresh iceberg lettuce Fresh pepper

32–40 kHz, 10 min

Ultrasound and chlorine Ultrasound

4

5

11

6°C, 24 h

32–40 kHz, 10 min

Effect on sensory properties

References

Developed more aromatic compounds in comparison with the untreated sample Developed more aromatic compounds in comparison with the untreated sample No effect on product quality No significant color change (Sensory)

Jambrak et al. (2017)

No significant change was observed in sensory No change in color

Sagong et al. (2011)

Pleasant flavor for consumers No effect on product quality Minor color changes and turbidity of the samples No significant color change (sensory) No significant color change (sensory)

Sˇimunek et al. (2013)

Sch€ ossler et al. (2012) Kwak et al. (2011)

Bantle and Eikevik (2011) Ferrante et al. (2007)

Valero et al. (2007) Ugarte-Romero et al. (2006) Seymour et al. (2002) Seymour et al. (2002)

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Postharvest Disinfection of Fruits and Vegetables

Table 4 Effect of ultrasonication on textural properties of fruits and vegetables Processing Combination of Effect on viscosity/ Food conditions methods textural properties

Apple slices

Ultrasonic-assisted convective drying Organic fresh 40 kHz, 5 min Ultrasound and lettuce 2% organic acids Dried apple 24 kHz, 200 W, Ultrasonication as pretreatment slices 50% and 100% before infrared amplitude drying Edamame

Dried apples (Fuji)

90 W, 3.5 min

Minor differences in texture

No significant change was observed in texture Ultrasound reduces the time of drying and allows elimination of more water from the apple slices 58-W, 0.7 min, Power ultrasound Water-holding power of edamame after 50%,–20C. prior to freeze thawing is 92% drying Ultrasound treatment 50/60 Hz, 117 V, Pulsed vacuum resulted in lower and 185 W and ultrasound moisture content, as pretreatments higher glass transition temperature and rehydration rate, and less penetration of calcium ions in dried apples

References

Sabarez et al. (2012) Sagong et al. (2011) Brncic et al. (2010)

Xu et al. (2009) Deng and Zhao (2008)

4. CONCLUSION The present reported study though showed the efficacy of ultrasonication treatment in disinfecting the fresh produce like fruits and vegetables, however, further studies are needed in order to explore the long effect of ultrasonication in sustenance of shelf life of fruits and vegetables. Though, the results are promising for inactivation of microbes and enzymes, optimization is needed to achieve the quality parameters by keeping processing at lower temperature. The status of nonthermal methods can be maintained thoroughly while processing the food products by keeping the temperature below 70°C. The positive outcome is that, with the use of ultrasonication, the usage of chemicals for disinfection can be put to minimum. Moreover, the property of extracting bioactive compounds adds another advantage, through which the functional properties of treated fresh produce can be enhanced. In light of this new development, more rigorous research is needed to evaluate the antimicrobial effects for advanced usage at industrial level.

Hybrid Membrane System Design and Operation

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c, T., 2013. Aroma profile and sensory properties of ultrasound-treated apple juice and nectar. Food Technol. Biotechnol. 51 (1), 101–111. Sivapalasingam, S., Friedman, C.R., Cohen, L., Tauxe, R.V., 2004. Fresh produce: a growing cause of outbreaks of foodborne illness in the United States, 1973 through 1997. J. Food Prot. 67 (10), 2342–2353. Soria, A.C., Villamiel, M., 2010. Effect of ultrasound on the technological properties and bioactivity of food: a review. Trends Food Sci. Technol. 21 (7), 323–331. Tiwari, B.K., Muthukumarappan, K., O’Donnell, C.P., Cullen, P.J., 2009a. Inactivation kinetics of pectin methylesterase and cloud retention in sonicated orange juice. Innovative Food Sci. Emerg. Technol. 10 (2), 166–171. Tiwari, B.K., O’Donnell, C.P., Cullen, P.J., 2009b. Effect of sonication on retention of anthocyanins in blackberry juice. J. Food Eng. 93 (2), 166–171. Tiwari, B.K., O’Donnell, C.P., Muthukumarappan, K., Cullen, P.J., 2009c. Effect of sonication on orange juice quality parameters during storage. Int. J. Food Sci. Technol. 44 (3), 586–595. Tiwari, B.K., Patras, A., Brunton, N., Cullen, P.J., O’Donnell, C.P., 2010. Effect of ultrasound processing on anthocyanins and color of red grape juice. Ultrason. Sonochem. 17 (3), 598–604. Ugarte-Romero, E., Feng, H., Martin, S.E., Cadwallader, K.R., Robinson, S.J., 2006. Inactivation of Escherichia coli with power ultrasound in apple cider. J. Food Sci. 71(2). Valero, M., Recrosio, N., Saura, D., Mun˜oz, N., Martı´, N., Lizama, V., 2007. Effects of ultrasonic treatments in orange juice processing. J. Food Eng. 80 (2), 509–516. Vercet, A., Sa´nchez, C., Burgos, J., Montan˜
es, L., Buesa, P.L., 2002. The effects of manothermosonication on tomato pectic enzymes and tomato paste rheological properties. J. Food Eng. 53 (3), 273–278. Vilkhu, K., Mawson, R., Simons, L., Bates, D., 2008. Applications and opportunities for ultrasound assisted extraction in the food industry—a review. Innovative Food Sci. Emerg. Technol. 9 (2), 161–169. Walkling-Ribeiro, M., Noci, F., Riener, J., Cronin, D.A., Lyng, J.G., Morgan, D.J., 2009. The impact of thermosonication and pulsed electric fields on Staphylococcus aureus inactivation and selected quality parameters in orange juice. Food Bioprocess Technol. 2 (4), 422. Wordon, B.A., Mortimer, B., McMaster, L.D., 2012. Comparative real-time analysis of Saccharomyces cerevisiae cell viability, injury and death induced by ultrasound (20kHz) and heat for the application of hurdle technology. Food Res. Int. 47 (2), 134–139. Wu, J., Gamage, T.V., Vilkhu, K.S., Simons, L.K., Mawson, R., 2008. Effect of thermosonication on quality improvement of tomato juice. Innovative Food Sci. Emerg. Technol. 9 (2), 186–195.

Hybrid Membrane System Design and Operation

Wu, T., Yu, X., Hu, A., Zhang, L., Jin, Y., Abid, M., 2015. Ultrasonic disruption of yeast cells: Underlying mechanism and effects of processing parameters. Innovative Food Sci. Emerg. Technol. 28, 59–65. Xu, H., Zhang, M., Duan, X., Mujumdar, A.S., Sun, J., 2009. Effect of power ultrasound pretreatment on edamame prior to freeze drying. Dry. Technol. 27 (2), 186–193. Zafra-Rojas, Q.Y., Cruz-Cansino, N., Ramı´rez-Moreno, E., Delgado-Olivares, L., Villanueva-Sa´nchez, J., Alanı´s-Garcı´a, E., 2013. Effects of ultrasound treatment in purple cactus pear (Opuntia ficus-indica) juice. Ultrason. Sonochem. 20 (5), 1283–1288. Zenker, M., Heinz, V., Knorr, D., 2003. Application of ultrasound-assisted thermal processing for preservation and quality retention of liquid foods. J. Food Prot. 66 (9), 1642–1649. Zheng, L., Sun, D.W., 2006. Innovative applications of power ultrasound during food freezing processes—a review. Trends Food Sci. Technol. 17 (1), 16–23. Zhou, B., Feng, H., Luo, Y., 2009. Ultrasound enhanced sanitizer efficacy in reduction of Escherichia coli O157: H7 population on spinach leaves. J. Food Sci. 74 (6), M308–M313.

FURTHER READING Bilek, S.E., Turantaş, F., 2013. Decontamination efficiency of high power ultrasound in the fruit and vegetable industry, a review. Int. J. Food Microbiol. 166 (1), 155–162. Elhariry, H.M., 2011. Attachment strength and biofilm forming ability of Bacillus cereus on green-leafy vegetables: cabbage and lettuce. Food Microbiol. 28 (7), 1266–1274. Ferrario, M., Guerrero, S., 2017. Impact of a combined processing technology involving ultrasound and pulsed light on structural and physiological changes of Saccharomyces cerevisiae KE 162 in apple juice. Food Microbiol. 65, 83–94. Leadley, C.E., Williams, A., 2006. Pulsed electric field processing, power ultrasound and other emerging technologies. In: Brennan, J.G. (Ed.), Food Processing Handbook, pp. 201-235. ISBN 3-527-30719-2. Negro, C., Tommasi, L., Miceli, A., 2003. Phenolic compounds and antioxidant activity from red grape marc extracts. Bioresour. Technol. 87 (1), 41–44. Ukuku, D.O., Fett, W.F., 2006. Effects of cell surface charge and hydrophobicity on attachment of 16 Salmonella serovars to cantaloupe rind and decontamination with sanitizers. J. Food Prot. 69 (8), 1835–1843. Ulusoy, B.H., Colak, H., Hampikyan, H., 2007. The use of ultrasonic waves in food technology. Res. J. Biol. Sci. 2 (4), 491–497.

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CHAPTER 9

Heat Treatment of Fruits and Vegetables Alemwati Pongener, Swati Sharma, S.K. Purbey ICAR-National Research Centre on Litchi, Muzaffarpur, India

1. INTRODUCTION Fruits and vegetables have, for long, been important items of human diet as sources of carbohydrates, proteins, organic acids, vitamins, and minerals. Of late they have attracted the attention of stakeholders, from scientists and researchers through producers to ultimate consumers, because of the interest that has been generated by the ever-increasing knowledge that fruits and vegetables are rich sources of health-beneficial nutraceuticals and polyphenol-rich bioactive compounds. In addition to being known as “Protective Foods,” fruits and vegetables also provide a variety to human diet, through differences in color, shape, taste, aroma, and texture. However, when plant and plant parts/products are used as human food, there is always a postharvest component that leads to loss. As astonishing as it may sound, postharvest losses account for a staggering 25%–40% of total agricultural produce in tropical countries like India, with reports that India wastes more food than what is consumed in the whole of the United Kingdom in a year (CSR Journal, 2015). While almost a billion people go hungry at one end, almost one-third of the 1.3 billion tonnes produced per year is wasted at the other end (Gustavsson et al., 2011). Fruits and vegetables, being biological entities, continue to respire and undergo metabolic processes even after being detached from the plant. Exposure to unfavorable storage regimes, insect pests, and disease pathogens not only cut short their postharvest life but also reduces quality and consumer acceptability. While the use of synthetic chemicals to control insect pests, diseases, and physiological disorders is still rampant, consumers are increasingly aware of the potential health hazards posed by these chemicals. There is a growing demand, the world over, for reducing the postharvest use of chemicals against pathogens and insects. Thus, over the recent years, researchers have felt the urgent need to develop safe, effective, and nondamaging physical treatments for disinfection and disinfestation of horticultural produce—a research area that still continues unabated. Heat/thermal treatment of fruits and vegetables is an efficient, easy, safe, and costeffective means for postharvest decay control as well as for the maintenance of proper postharvest quality. Over the years, heat treatments have been employed for achieving postharvest solutions such as insect disinfestations, control of decay and diseases, alleviation of chilling injury, and maintenance of fruit quality during storage. Temperature-

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time combination for different heat treatments ranges from 35°C to 39°C in hot air for days to up to 63°C in hot water for less than a minute. Normally, higher temperatures are employed for insect disinfestation and control of microorganisms. Thermotherapy has been used for more than a century to free plant materials from pathogens. Postharvest heat treatments are used for insect disinfestations, disease and decay control of fruits and vegetables, to modify commodity responses to other stresses and to maintain fruit quality during storage. Heat treatment has been successfully employed to maintain firmness of tomatoes, potatoes, carrots, and strawberries; preserve color in broccoli, kiwifruit, lettuce, celery, and asparagus; prevent overripening in melons and cantaloupe; and improve shelf life in grapes, peaches, plums, etc. This chapter summarizes the effect of postharvest heat treatment on disease and insect-pest control in fruits and vegetables, ripening and postharvest quality of fresh fruits and vegetables, taking into account various facets of postharvest metabolic processes including ethylene evolution, respiration, softening, color changes, aroma volatiles production, and induction of resistance to heat and chilling injury. Heat treatment in combination with other safe postharvest technologies is also discussed in the light of published studies.

2. METHODS OF HEAT TREATMENT Basically, three methods are employed to heat commodities viz. hot water, vapor heat, and hot air. Of late, heat treatment alone or in combination with other postharvest treatments are being tried and tested with promising results. A variety of fungi are responsible for postharvest decay of fruits and vegetables. Generally, these pathogens, including their spores and latent infections, are localized either on the surface or in the first few layers under the peel of the produce. The insect-pest infestation can affect any part of the fruit or vegetable. Thus, heat treatment for insect disinfestation requires exposure of fruits and vegetables to higher temperature for longer duration. On the other hand, heat treatment for fungal disinfection or decay control consists of comparatively shorter duration of treatment at relatively lower temperature. Therefore, based on the duration, heat treatment can be short (up to 1 h) or long term (up to 4 days). Hot water and hot air treatment (HAT) is being used for both fungal and insect control, while vapor heat treatment (VHT) is specifically intended for insect disinfestation. Heat treatment leads to a variety of metabolic, physiological, biochemical, and molecular changes within the treated commodity and studies to ascertain the response of a commodity are usually done after the produce is subjected to HAT.

2.1 Hot Water Treatment Water is an efficient medium of heat transfer owing to its high heat capacity. Hot water treatment (HWT) is accomplished either through dipping or spraying. As stated earlier, HWT is usually used for fungal disinfection. Postharvest dips are done at comparatively

Heat Treatment of Fruits and Vegetables

lower temperature and for shorter duration lasting few minutes. This milder treatment is done because only the surface of the commodity requires heating. Fruits and vegetables can generally tolerate water temperatures of 50–60°C for up to 10 min, while shorter exposure at these temperatures can effectively control many postharvest plant pathogens (Barkai-Golan and Phillips, 1991). Generally, for insect disinfestation, the time of dipping/immersion can last up to 1 h or more at temperatures 70%) at chitosan concentrations of 1.0% (Fig. 1). A decrease in spore production (sporulation) at concentrations higher than 1.0% of chitosan was observed (Lo´pez-Mora et al., 2013; Gutierrez-Martı´nez et al., 2017) (Table 1). These authors also report changes in spore morphology (area, length, and shape) according to treatment and/or incubation time compared to untreated spores. Conversely, low concentrations of chitosan (0.05% and 0.20%) markedly inhibited the mycelial growth of Botrytis cinerea isolated from peach (Prunus persica), Japanese pear (Pyrus pynfolia), and kiwi (Actinidia deliciosa) (Du et al., 1997). In addition, at chitosan concentration of 0.5% a 81% of inhibition on mycelial growth of Rhizopus stolonifer isolated from soursop (A. muricata) was obtained (Ramos-Guerrero et al., 2018).

Days 2

4

6

8

10

12

Alternaria alternata-Control A. alternata + Chitosan 0.05%

A. alternata + Chitosan 0.1%

A. alternata + Chitosan 0.5%

A. alternata + Chitosan 1%

Fig. 1 Alternaria alternata isolated from “Tommy Atkins” mango, during 12 days at 20°C in PDA medium, alone or with different concentrations of low molecular weight chitosan. Table 1 Inhibition (%) of chitosan treatments against postharvest pathogens isolated of banana and mango fruits Treatment Colletotrichum sp. Fusarium sp.

Control Chitosan 0.5% Chitosan 1.0% Chitosan 1.5% Chitosan 2.0%

0.00a 32.5b 94.3c 100d 100d

0.00a 12.0a 90.5b 93.2b 100b

Note: Different letters indicate significant differences by columns (P < .05).

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In contrast, A. alternata isolated from seeds (sorghum, soybean, rice, and wheat) and Sclerotinia sclerotiorum, pathogen of carrots (Daucus carota L.) showed inhibition of their radial growth only at high concentrations of chitosan (4%) (Cheah et al., 1997; Ziani et al., 2009). Other studies suggest that chitosan may have a fungicidal or fungistatic effect depending on the concentration used. For example, the mycelial growth of Colletotrichum gloeosporioides (Penz.) Penz. and Sacc. isolated from papaya, was totally inhibited at chitosan concentrations of 2.5% and 3.0% during 7 days, while at 0.5% and 1.5% concentration the fungus began to grow on the second and fourth day, respectively. In addition, reduction in sporulation and morphological changes in conidia (area and elliptic form factor) were observed at chitosan concentrations above 1.5% (Bautista-Ban˜os et al., 2003). However, at chitosan concentration of 1.5%, the fungicidal effect on the growth of B. cinerea, A. alternata, C. gloeosporioides, and R. stolonifer is associated with the degree of deacetylation of chitosan (El Ghaouth et al., 1992b). El Ghaouth et al. (1994), observed ultrastructural and cytochemical changes in the interaction of chitosan-B. cinerea in bell pepper (Capsicum annuum L. cv. Bellboy), finding that hyphae exposed to chitosan presented several degrees of cell disorganization with loss of integrity and degradation of protoplasm, whereas in the absence of this biopolymer the hyphae maintained a normal appearance. Romanazzi et al. (2017) reported that the mode of action of chitosan against fungi caused adverse effects on fungal membrane affecting its permeability, inducing morphological changes in hyphae as well as in reproductive structures.

4.2 In Vivo Assessments In the area of postharvest management, there are a few studies that report alterations directly on phytopathogenic fungus or alterations due to chitosan-fruit interaction. For example, the incidence of anthracnose in soursop was reduced by 80%, whereas in mango and banana fruit a total control of diseases (100%) with the coating of chitosan was obtained. All fruits treated with chitosan showed a lower percentage of weight loss compared to the untreated ones (Gutierrez-Martı´nez et al., 2017). Robles-Villanueva (2016) reported that applying chitosan at low concentrations (0.05%) in garlic bulbs inhibited the incidence of disease by Penicillium citrinum by 49%, on the other hand the combination of chitosan with organic salts and peroxide hydrogen was able to inhibit the disease development by 75%. The chitosan coating also provided effective postharvest control against gray and blue mold caused by B. cinerea and Penicillium expansum in tomato fruits stored at 25°C and 2°C (Liu et al., 2007). Similar results were obtained for table grapes (De Oliveira et al., 2014), papaya (Dotto et al., 2015), and apple (Li et al., 2015). Chitosan showed antifungal activity against Rhizoctonia solani, the rice pox pathogen; by applying two types of acid-soluble chitosan (with different degrees of deacetylation) a range of disease inhibition from 31% to 84%, and 66% to 91% lesion diameter was obtained (Liu et al., 2012). In pear fruit, chitosan treatments

Chitosan for Postharvest Disinfection of Fruits and Vegetables

reduced the disease incidence, as well as a reduction in lesion diameter caused by Alternaria kikuchiana and Physalospora piricola was obtained (Meng et al., 2010). Recently, chitosan nanoparticle coating and chitosan-loaded nanoemulsion were used for postharvest disease control of fruits such as “Gala” apple, banana, papaya, and strawberry inoculated by Colletotrichum musae or C. gloeosporioides (Zahid et al., 2012; Eshghi et al., 2014; Pilon et al., 2015). In addition, it has been proposed that the inhibitory effect of chitosan against pathogenic fungi on fruits could also be related to their ability to stimulate plant defense systems, such as the phenylalanine ammonia-lyase enzyme, the main precursor of phenolic compounds (Dang et al., 2010), and the antioxidant activity (polyphenol oxidase and peroxidase) (Li et al., 2015) in fruits coated with chitosan. The fungicidal activity of chitosan has been associated with its cationic character. The interaction of free amino groups, positively charged in acid medium with the negative residues of the macromolecules exposed to the wall of the fungi, change the permeability of the plasma membrane, with consequent alteration in its main functions (Benhamou, 1992). Other possible explanations for the fungicidal activity of chitosan are related to the inhibition of the synthesis of some enzymes present in fungi (El Ghaouth et al., 1992a) or the occurrence of cytological alterations, as reported in the case of B. cinerea (Barka et al., 2004), and occurrence of vesicles and/or empty cells lacking cytoplasm (Bautista-Ban˜os et al., 2017).

5. CHITOSAN CAPACITY AS A BACTERICIDE IN FRUITS AND VEGETABLES Research on the antimicrobial properties of chitosan has been a long journey of scientific exploration and technological development (Kong et al., 2010). Chitosan has been investigated as an antimicrobial material against a wide range of organisms such as algae, bacteria, yeasts, and fungi in experiments involving in vivo and in vitro interactions with chitosan in different forms: solutions, films, and composites (Goy et al., 2009). Several investigations have demonstrated the antibacterial ability of chitosan in a large variety of bacteria. In general, chitosan is considered to be a bactericidal or bacteriostatic (Li et al., 2013). These studies have evaluated their bactericidal and bacteriostatic effectiveness, reaching high inhibition rates and offering advantages over other disinfectants due to their null toxicity in mammalian cells. Table 2 presents minimal inhibitory concentration (MIC) of chitosan against various bacteria (Rabea et al., 2003). Chitosan is active against bacteria such as Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, Listeria monocytogenes, and some fungi, including B. cinerea, Fusarium oxysporum, and Pyricularia oryzae (Sa´nchez-Machado et al., 2015). Due to the antifungal and antibacterial activities, chitosan has been successfully used to maintain the microbial quality of fruits and vegetables postharvest. Concerning food protection of plant origin foods, there are a wide range of investigations with the application of chitosan coatings for fruits and vegetables as indicated by La´rez-Vela´squez (2008). Devlieghere et al. (2004) reported the

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Table 2 Bactericidal effect of chitosan (Rabea et al., 2003) Microorganism MIC (ppm)

Bacillus cereus Agrobacterium tumefaciens Escherichia coli Klebsiella pneumoniae Pseudomonas fluorescens Staphylococcus aureus Erwinia sp. Erwinia carotovora subsp. Corynebacterium michiganense Micrococcus luteus Xanthomonas campestris

1000 100 20 700 500 20 500 200 10 20 500

inhibition of psychotropic bacteria in strawberries and lettuces, increasing the shelf life as well as preserving the organoleptic properties. Ayala (2015) points out the application by spraying this biopolymer on vegetables and on some fresh fruits such as tomatoes and blackberries. Li et al. (2010) reported a significant reduction in disease incidence and lesion diameter of broccoli inoculated with Pseudomonas fluorescens, pretreated or posttreated with six different combinations of chitosan solutions. Higueras et al. (2015) prepared chitosan films incorporated with hydroxypropyl-β-cyclodextrin and carvacrol, showing antibacterial activity against S. aureus and E. coli after 20 days of storage at 25°C and relative humidity of 43%. Jovanovic et al. (2016) showed that population of L. monocytogenes ATCC-19115 inoculated in grated black radish in the presence of chitosan-gelatin (0.5%) films decreased from 5 log10 CFU/g to undetectable levels after 3 days at 4°C. The mechanisms of antibacterial action of chitosan have not been fully understood, however, different mechanisms have been proposed. The electrostatic interaction between positively charged chitosan (cationic polyelectrolyte) and negatively charged microbial cell membrane (Gram negative such as E. coli, Pseudomonas aeruginosa, Vibrio parahaemolyticus, and S. typhimurium) could alter the barrier properties of the outer membrane of the microorganism. Specifically, the NH3+ groups of chitosan interact with the phosphoryl groups present in the phospholipids of Gram negative bacteria (La´rezVela´squez, 2008) resulting in the release of the intracellular protein components of the microorganism (Rodrı´guez-Nu´n˜ez et al., 2014). Chung and Chen (2008) have determined that the output of bacterial intracellular material is favored by higher degrees of acetylation in both Gram negative and Gram positive bacteria. Conversely, in the case of some Gram positive bacteria (such as S. aureus, Bacillus cereus, L. monocytogenes, Lactobacillus plantarum, and Lactobacillus bulgaricus) due to the lack negative charges on the cell membrane, the mechanisms could be attribute to the

Chitosan for Postharvest Disinfection of Fruits and Vegetables

presence of pores on the membrane, so chitosan could enter into cells affecting vital functions, interacting with DNA, interfering with the synthesis of messenger RNA, and protein synthesis. Besides, it is pointed out that the selective interaction of chitosan with traces of metals could inhibit the production of toxins as well as the microbial growth (La´rez-Vela´squez, 2008). According to Sony and Seema (2015) the antibacterial effect depends on the molecular weight, degree of deacetylation, and degree of polymerization of chitosan; as well as environmental conditions, such as pH, type of microorganism, and neighboring components (Hosseinnejad and Jafari, 2016).

6. CHITOSAN CAPACITY AS AN ANTIVIRICIDE IN FRUITS AND VEGETABLES The nucleic acid of most plant viruses consists of RNA protected by the protein shell; they can enter into cells only through wounds or by vectors (Iriti and Varoni, 2015). The antiviral activity is one of the various biological activities reported to chitosan (Malerba and Cerana, 2016). It is documented that chitosan activity against plant viruses is due to the capability of the biopolymer to stimulate plant immune response, instead of a direct effect on virus (El Hadrami et al., 2010; Iriti and Varoni, 2015). Chitosan is recognized as a potent inducer, enhancing the plant responses locally and systematically around infection sites, leading to early signaling events accumulating defense-related metabolites. These events modulate plant responses that are effective in a diverse pathogens including virus (El Hadrami et al., 2010). It is important to mention that the antiviral defense induced by chitosan depends not only on species of plant but also on its structure (polymerization degree), molecular weight, and the type of the virus (Davydova et al., 2011; Chirkov, 2001; Iriti and Varoni, 2015). In a previous study, with plants beans a higher chitosan-induced resistance was obtained against the systemic pathogen bean mild mosaic virus (BMMV) by applying chitosanlow molecular weight chitosan (Kulikov et al., 2006). The better efficacy of low molecular weight chitosan can be attributed to the better penetrating ability across the epidermal tissues leading to the induction of resistance (Iriti and Varoni, 2015). However, in other studies good results have been reported on the use of chitosan at high molecular weight in potato (Solanum tuberosum) plants against systemic infection of potato virus X (PVX) avoiding virus expansion on plant tissues (Chirkov, 2001). On the other hand, the application of chitosan at 0.1% in tobacco was effective against tobacco necrosis necrovirus (TNV) reducing significantly the necrotic lesions induced by the virus (83%) (Iriti et al., 2006). Besides the antiviral response induced by the application of chitosan on plants, the coating formed by the biopolymer can protect them against mechanical damage avoiding wounds formation as well as virus penetration.

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7. CONCLUDING REMARKS The disinfection process is a very important stage to control the postharvest deterioration of fresh horticultural products. This stage may precede other postharvest technologies and in some cases, disinfection becomes the main technology of the plant system. A very important consideration is that most of the disinfectants used in postharvest leave no toxic waste and that the impact on the environment is minimal in relation to its potential benefits in the conservation of fruits and vegetables. The reports on the application of chitosan in vitro tests have shown a high antifungal capacity in the majority of fungi that attack tropical fruits, inhibited spore germination, mycelial growth, sporulation, and even reporting the presence of conidia and fungal hyphae deformations. Caused by different concentrations of chitosan, increasing concentrations results in greater inhibition of fungus growth. Depending on the molecular weight of chitosan and the pathogenic fungus strain will be the results on its inhibition. It is important to mention that there exist fungi strains resistant to chitosan, possibly due to the composition of their wall and cell membrane, for which it is necessary to develop systems combined between chitosan and another substance of organic origin, preferably. On the other hand, in vivo evaluations indicate the potential of curative or preventive effects, important for latent infections in fruits such as mango, jackfruit, banana, among others. Not less important is its bactericidal effect especially in those that cause gastrointestinal diseases and therefore treatments should be based on chitosan and other elements, such as ethanol, hydrogen peroxide, either individually or in combination. Chitosan is currently an excellent disinfectant of fruits and vegetables preventing the growth and development of pathogenic fungi and bacteria, giving as a result vegetable products free of pathogens with good post-harvest quality. The ability to induce defense mechanisms is an important feature to maintain horticultural products during storage and commercialization with minimal postharvest deterioration. It is recommended to carry out more evaluations at the level of packaging, thus to propose the chitosan as a disinfection system against pathogens, considering its organic origin, nontoxic and nonpolluting, could replace the use of fungicides and bactericides in the postharvest handling of horticultural products.

ACKNOWLEDGMENTS The authors are grateful to Mexico’s Science and Technology Council (CONACYT-SAGARPA) for funding research project (291472) and supporting Master’s and PhD students, as well as the Tecnolo´gico Nacional de Mexico (TecNM) for funding research project (5214-14-P).

REFERENCES Aulakh, J., Regmi, A., 2013. Postharvest Food Losses Estimation-Development of Consistent Methodology. Food and Agriculture Organization, .pp. 1–34. Available at: http://www.fao.org/fileadmin/templates/ ess/documents/meetings_and_workshops/GS_SAC_2013/Improving_methods_for_estimating_post_ harvest_losses/Final_PHLs_Estimation_6-13-13.pdf (Accessed 18 August 2017).

Chitosan for Postharvest Disinfection of Fruits and Vegetables

Ayala, V., 2015. Antimicrobial effect of chitosan: a review. Rev. Sci. Agroaliment. 2, 32–38. Barka, E., Eullaffroy, P., Climent, C., Vernet, G., 2004. Chitosan improves development, and protects Vitis vinifera L. against Botrytis cinerea. Plant Cell Rep. 22, 608–614. Barkai-Golan, R., 2001. Postharvest Diseases of Fruits and Vegetables. Elsevier Science, The Netherlands, p. 442. Bautista-Ban˜os, S., Lo´pez-Herna´ndez, M., Bosquez-Molina, E., Wilson, C.L., 2003. Effect of chitosan and plant extracts on growth of Colletotrichum gloeosporioides, anthracnose levels and quality of papaya fruit. Crop Prot. 22, 1087–1092. Bautista-Ban˜os, S., Herna´ndez-Lo´pez, M., Bosquez-Molina, E., 2004. Growth inhibition of selected fungi by chitosan and plant extracts. Rev. Mexicana Fitopatol. 22, 178–186. Bautista-Ban˜os, S., Ventura-Aguilar, R., Correa-Pacheco, Z., Corona-Rangel, M., 2017. Chitosan: a versatile antimicrobial polysaccharide for fruit and vegetables in postharvest—a review. Rev. Chapingo Ser. Hort. 23, 103–121. Benhamou, N., 1992. Ultrastructural and cytochemical aspects of chitosan on Fusarium oxysporum f. sp. radicis-lycopersici, agent of tomato crown and root rot. Phytopathology 82, 1185–1193. Beru´men-Varela, G., Coronado-Partida, L., Ochoa-Jimenez, V., Chaco´n-Lo´pez, M., GutierrezMartı´nez, P., 2015. Effect of chitosan on the induction of disease resistance against Colletotrichum sp. in mango (Mangifera indica L.) cv Tommy Atkins. Investigacio´n y Ciencia 66, 16–21. Chandra, S., Chakraborty, N., Dasgupta, A., Sarkar, J., Panda, K., Acharya, K., 2015. Chitosan nanoparticles: a positive modulator of innate immune responses in plants. Sci. Rep. 5. Cheah, L., Page, B., Shepherd, R., 1997. Chitosan coating for inhibition of sclerotinia rot of carrots. J. Crop Hortic. Sci. 25, 89–92. Chirkov, S., 2001. The antiviral activity of chitosan (review). Prikl. Biokhim. Mikrobiol. 38, 5–13. Chung, Y., Chen, C., 2008. Antibacterial characteristics and activity of acid-soluble chitosan. Bioresour. Technol. 99, 2806–2814. Dang, Q., Yan, J., Li, Y., Cheng, X., Liu, C., Chen, X., 2010. Chitosan acetate as an active coating material and its effects on the storing of Prunus avium L. J. Food Sci. 75 (2), 125–131. Davydova, V., Nagorskaya, V., Gorbach, V., Kalitnik, A., Reunov, A., Solov’eva, T., Ermak, I., 2011. Chitosan antiviral activity: dependence on structure and depolymerization method. Appl. Biochem. Microbiol. 47, 103–108. De Oliveira, C., Magnani, M., De Sales, C., Pontes, A., Campos-Takaki, G., Stamford, T., De Souza, E., 2014. Effects of chitosan from Cunninghamella elegans on virulence of postharvest pathogenic fungi in table grapes (Vitis labrusca L.). Int. J. Food Microbiol. 171, 54–61. Devlieghere, F., Vermeulen, A., Debevere, J., 2004. Chitosan: antimicrobial activity, interaction with food components and applicability as a coating on fruit and vegetables. Food Microbiol. 21, 703–714. Dotto, G., Vieira, M., Pinto, L., 2015. Use of chitosan solutions for the microbiological shelf life extension of papaya fruits during storage at room temperature. LWT Food Sci. Technol. 64 (1), 126–130. Du, J., Gemma, H., Iwqhori, S., 1997. Effects of chitosan coating on the storage of peach, Japanese pear, and kiwifruit. J. Jpn. Soc. Hortic. Sci. 66, 15–22. El Ghaouth, A., Arul, J., Grenier, J., Asselin, A., 1992a. Antifungal activity of chitosan on two postharvest pathogens of strawberry fruits. Phytopathology 82, 398–402. El Ghaouth, A., Arul, J., Asselin, A., Benhamou, N., 1992b. Antifungal activity of chitosan on post-harvest pathogens: induction of morphological and cytological alterations in Rhizopus stolonifer. Mycol. Res. 96, 769–779. El Ghaouth, A., Arul, J., Wilson, C., Benhamou, N., 1994. Ultrastructural and cytochemical aspects of the effect of chitosan on decay of bell pepper fruit. Physiol. Mol. Plant Pathol. 44, 417–432. El Hadrami, A., Adam, L., El Hadrami, I., Daayf, F., 2010. Chitosan in plant protection. Mar. Drugs 8, 968–987. Eshghi, S., Hashemi, M., Mohammadi, A., Badii, F., Mohammadhoseini, Z., Ahmadi, K., 2014. Effect of nanochitosan-based coating with and without copper loaded on physicochemical and bioactive components of fresh strawberry fruit (Fragaria x ananassa Duchesne) during storage. Food Bioprocess Technol. 7 (8), 2397–2409. FAO, 2011. Global food losses and food waste – extent, causes and prevention. Available at: http://www. fao.org/docrep/014/mb060e/mb060e00.pdf (Accessed 8 July 2017).

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Feliziani, E., Lichter, A., Smilanick, J., Ippolito, A., 2016. Disinfecting agents for controlling fruit and vegetable diseases after harvest. Postharvest Biol. Technol. 122, 53–69. Goy, R., Britto, D., Assis, O., 2009. Review of the antimicrobial activity of chitosan. Polı´meros 19 (3), 241–247. Gutierrez-Martı´nez, P., Bautista-Ban˜os, S., Beru´men-Varela, G., Ramos-Guerrero, A., Herna´ndezIban˜ez, A., 2017. In vitro response of Colletotrichum to chitosan. Effect on incidence and quality on tropical fruit. Enzymatic expression in mango. Acta Agron. 66 (2), 282–289. Higueras, L., Lo´pez-Carballo, G., Gavara, R., Herna´ndez-Mun˜oz, P., 2015. Incorporation of hydroxypropyl-β-cyclodextrins into chitosan films to tailor loading capacity for active aroma compound carvacrol. Food Hydrocoll. 43, 603–611. Hosseinnejad, M., Jafari, S., 2016. Evaluation of different factors affecting antimicrobial properties of chitosan. Int. J. Biol. Macromol. 85, 467–475. Iriti, M., Varoni, E., 2015. Chitosan-induced antiviral activity and innate immunity in plants. Environ. Sci. Pollut. Res. 22, 2935–2944. Iriti, M., Sironi, M., Gomarasca, S., Casazza, A., Soave, C., Faoro, F., 2006. Cell death-mediated antiviral effect of chitosan in tobacco. Plant Physiol. Biochem. 44, 893–900. Jovanovic, D., Klaus, S., Niksic, P., 2016. Antimicrobial activity of chitosan coatings and films against Listeria monocytogenes on blackradish. Rev. Argent. Microbiol. 48 (2), 128–136. Kong, M., Chen, X., Xing, K., Park, H., 2010. Antimicrobial properties of chitosan and mode of action: a state of the art review. Int. J. Food Microbiol. 144, 51–63. Kulikov, S., Chirkov, S., Il’ina, A., Lopatin, S., Varlamov, V., 2006. Effect of the molecular weight of chitosan on its antiviral activity in plants. Appl. Biochem. Microbiol. 42, 200–203. La´rez-Vela´squez, C., 2008. Some potentialities of chitin and chitosan for uses related to agriculture in Latin America. Rev. UDO Agrı´cola 8 (1), 1–22. Li, H., Yu, Y., 2001. Effect of chitosan on incidence of brown rot, quality and physiological attributes of postharvest peach fruit. J. Sci. Food Agric. 81, 269–274. Li, B., Liu, B., Su, T., Wang, F., Tang, Q., Fang, Y., Xie, G., Sun, G., 2010. Effect of chitosan solution on the inhibition of Pseudomonas fluorescens causing bacterial head rot of broccoli. J. Plant Pathol. 26, 189–193. Li, B., Shan, C., Ge, M., Wang, L., Fang, Y., Wang, Y., Xie, G., Sun, G., 2013. Antibacterial mechanism of chitosan and its applications in protection of plant from bacterial disease. Asian J. Chem. 25 (18), 10033–10036. Li, H., Wang, Y., Liu, F., Yang, Y., Wu, Z., Cai, H., Li, P., 2015. Effects of chitosan on control of postharvest blue mold decay of apple fruit and the possible mechanisms involved. Sci. Hortic. 186, 77–83. Liu, J., Tian, S., Meng, X., Xu, Y., 2007. Effects of chitosan on control of postharvest diseases and physiological responses of tomato fruit. Postharvest Biol. Technol. 44 (3), 300–306. Liu, H., Tian, W., Li, B., Wu, G., Ibrahim, M., Tao, Z., Wang, Y., Xie, G., Li, H., Sun, G., 2012. Antifungal effect and mechanism of chitosan against the rice sheath blight pathogen, Rhizoctonia solani. Biotechnol. Lett. 34, 2291–2298. Lo´pez-Mora, L., Gutierrez-Martı´nez, P., Bautista-Ban˜os, S., Jimenez-Garcı´a, L., Zavaleta-Mancera, H., 2013. Evaluacio´n de la actividad antifu´ngica del quitosano en Alternaria alternata y en la calidad del mango ‘tommy atkins’ durante el almacenamiento. Rev. Chapingo Ser. Hortic. 19 (3), 315–331. Malerba, M., Cerana, R., 2016. Chitosan effects on plant systems. Int. J. Mol. Sci. 17, 996. Mendez, S., Mondino, P., 1999. Control biolo´gico postcosecha en Uruguay. Horticultura Internacional 7, 29–36. Meng, X., Yang, L., Kennedy, J., Tian, S., 2010. Effects of chitosan and oligochitosan on growth of two fungal pathogens and physiological properties in pear fruit. Carbohydr. Polym. 81, 70–75. Monarul, I., Shah, M., Masum, M., Mahbubur, R., Molla, A., Shaikh, R., 2011. Preparation of chitosan from shrimp shell and investigation of its properties. Int. J. Basic Appl. Sci. 11 (1), 116–130. Pilon, L., Spricigo, P., Miranda, M., De Moura, M., Assis, O., Mattoso, L., Ferreira, M., 2015. Chitosan nanoparticle coatings reduce microbial growth on fresh-cut apples while not affecting quality attributes. Int. J. Food Sci. Technol. 50 (2), 440–448. Rabea, E., Badawy, E., Stevens, C., Smagghe, G., Steurbaut, W., 2003. Chitosan as antimicrobial agent: applications and mode of action. Biomacromolecules 4, 1457–1465.

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Ramos-Guerrero, A., Gonza´lez-Estrada, R., Hanako-Rosas, G., Bautista-Ban˜os, S., AcevedoHerna´ndez, G., Tiznado-Herna´ndez, M., Gutierrez-Martı´nez, P., 2018. Use of inductors in the control of Colletotrichum gloeosporioides and Rhizopus stolonifer isolated from soursop fruits: in vitro tests. Food Sci. Biotechnol. 1–9. Robles-Villanueva, B., 2016. Evaluacio´n de sistemas no convencionales en el control de enfermedades de postcosecha de bulbos de ajo. Tesis de Maestrı´a en Ciencias en Alimentos, Instituto Tecnolo´gico de Tepic, Nayarit, Mexico. Rodrı´guez-Nu´n˜ez, J., Madera-Santana, T., Sa´nchez-Machado, D., Lo´pez-Cervantes, J., Soto-Valdez, H., 2014. Chitosan/hydrophilic plasticizer-based films: preparation, physicochemical and antimicrobial properties. J. Polym. Environ. 22, 41–51. Romanazzi, G., Sanzani, S., Bi, Y., Tian, S., Gutierrez-Martı´nez, P., Alkan, N., 2016. Induced resistance to control postharvest decay of fruit and vegetables. Postharvest Biol. Technol. 122, 82–94. Romanazzi, G., Feliziani, E., Ban˜os, S., Sivakumar, D., 2017. Shelf life extension of fresh fruit and vegetables by chitosan treatment. Crit. Rev. Food Sci. Nutr. 57 (3), 579–601. Sa´nchez-Machado, D., Lo´pez-Cervantes, J., Rodrı´guez-Nu´n˜ez, J., 2015. Antimicrobial effect of different chitosan preparations against selected food borne pathogens. Int J Pharm. Bio. Sci 6 (1), 204–212. Sargent, S., Ritenour, M., Brecht, J., 2000. Abbott, University of Florida Cooperative Extension Service, (Ed.), Handling, Cooling and Sanitation Techniques for Maintaining Postharvest Quality. Institute of Food and Agriculture Sciences, pp. 2–17. Singh, V., Hedayetullah, M., Zaman, P., Meher, J., 2014. Postharvest technology of fruits and vegetables: an overview. J. Postharvest Technol. 2 (2), 124–135. Sony, P., Seema, N., 2015. Antibacterial effect of chitosan and its derivatives. Natl. J. Physiol. Pharm. Pharmacol. 5 (2), 119–124. USFDA, 2013. GRAS notice inventory. GRN No. 397. Available at: www.fda.gov (Accessed 9 January 2013). Xoca-Orozco, L., Cuellar-Torres, E., Gonza´lez-Morales, S., Gutierrez-Martı´nez, P., Lo´pez-Garcı´a, U., Herrera-Estrella, L., Vega Arreguı´n, J., Chaco´n-Lo´pez, A., 2017. Transcriptomic analysis of avocado Hass (Persea americana mill) in the interaction system fruit-chitosan-Colletotrichum. Front. Plant Sci. 8, 956. Yu, T., Li, H., Zheng, X., 2007. Synergistic effect of chitosan and Cryptococcus laurentii on inhibition of Penicillium expansum infections. Int. J. Food Microbiol. 114, 261–266. Zahid, N., Ali, A., Manickam, S., Siddiqui, Y., Maqbool, M., 2012. Potential of chitosan loaded nanoemulsions to control different Colletotrichum spp. and maintain quality of tropical fruits during cold storage. J. Appl. Microbiol. 113 (4), 925–939. Ziani, K., Ferna´ndez-Pan, I., Royo, M., Mate, J., 2009. Antifungal activity of films and solutions based on chitosan against typical seed fungi. Food Hydrocoll. 23 (8), 2309–2314.

FURTHER READING Landi, L., Feliziani, E., Romanazzi, G., 2014. Expression of defense genes in strawberry fruits treated with different resistance inducers. J. Agric. Food Chem. 62 (14), 3047–3056. Rappussi, M., Pascholati, S., Benato, E., Cia, P., 2009. Chitosan reduces infection by Guignardia citricarpa in postharvest ‘Valencia’ oranges. Braz. Arch. Biol. Technol. 52 (3), 513–521. Wang, S., Gao, H., 2013. Effect of chitosan-based edible coating on antioxidants, antioxidant enzyme system, and postharvest fruit quality of strawberries (Fragaria x aranassa Duch.). LWT Food Sci. Technol. 52 (2), 71–79.

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CHAPTER 13

Gaseous Chlorine Dioxide for Postharvest Treatment of Produce David F. Bridges, Vivian C.H. Wu

United States Department of Agriculture, Agricultural Research Service, Western Regional Research Service, Produce Safety and Microbiology Research Unit, Albany, CA, United States

1. INTRODUCTION Fresh produce commodities are commonly treated after harvest to reduce microorganisms and improve shelf life. However, there are numerous types of treatments that are currently practiced, or proposed, for use in fresh produce industries. Irrespective of the active ingredient or the method of application, every treatment must adhere to specific criteria in order to be acceptable for use. First, it must be able to decrease any existing microorganisms to improve the shelf life and reduce incidences of foodborne illness. The preservation of sensory and nutritional attributes is also a must to keep produce foods appealing to consumers and subsequently marketable. And finally, there cannot be any unacceptable levels of toxic by-products or residues. Chlorine, applied to wash solutions in the forms of sodium hypochlorite (NaOCl) or calcium hypochlorite (Ca(OCl2)), is the most commonly used postharvest treatment in the produce industry (Goodburn and Wallace, 2013). Nonetheless, chlorinated wash systems are unignorably flawed because they are only effective in a narrow pH range, have reduced antimicrobial capabilities when additional organic matter is present, are environmentally unfriendly, and can form carcinogenic trihalomethanes during treatment (Go´mez-Lo´pez et al., 2013; Goodburn and Wallace, 2013; Richardson et al., 1998). Although there are alternative types of active ingredients that can be added to produce rinses [e.g., hydrogen peroxide (H2O2)], antimicrobial washes, as a whole, suffer from a few key problems. The large volumes of water needed for treatment can cause pathogen cross contamination; especially when water is recycled for economic and environmental purposes (Alwi and Ali, 2014). Additionally, any residual moisture after treatment creates an environment that promotes mold growth (Go´mez-Lo´pez et al., 2009). Gaseous treatments have emerged as potential alternatives to aqueous antimicrobial washes and benefit from using little, if any, water and can treat areas and irregularities on produce surfaces that aqueous antimicrobials have difficulty in reaching (Go´mez-Lo´pez et al., 2008b). Chlorine dioxide, in a gaseous phase, has emerged as a treatment with great promise for use and implementation in current produce infrastructures due to simple generation Postharvest Disinfection of Fruits and Vegetables https://doi.org/10.1016/B978-0-12-812698-1.00013-3

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methods, powerful antimicrobial properties, and the ability to extend the shelf-life of the produce (Wu, 2016). Chlorine dioxide (ClO2) can be synthetically made in an aqueous or gaseous form, and is distinctly different from elemental chlorine in behavior. In a gaseous phase, ClO2 will exothermically breakdown into chloride (Cl ) and oxygen and light exposure will further this decomposition. ClO2 reaction with produce foods can cause the formation of chloride, chlorite (ClO ), chlorate (ClO3 ), and perchlorate (ClO4 ) ions. While chloride and chlorite by-products are not of concern, chlorate is toxic to humans and perchlorate has been associated with thyroid problems. However, studies looking at by-product residues following ClO2 treatment have indicated that parameters can be established to prevent accumulation of measurable levels of chlorate and perchlorate; chlorine dioxide residues have also been shown to decrease over time (Kaur et al., 2015; Smith et al., 2014, 2015; Wu and Rioux, 2010). Chlorine dioxide simultaneously has an oxidative capacity 2.5 greater than chlorine and also reacts more selectively; thus making it a more powerful treatment while producing fewer unwanted by-products (Beuchat et al., 2004). It was first used as a disinfectant at the beginning of the 20th century and currently the US Environmental Protection Agency (EPA) and Food and Drug Administration (FDA) have approved ClO2 for the treatment of poultry processing water and for produce washes if residual ClO2 levels do not exceed 3 ppm. Although numerous studies have shown that both aqueous and gaseous forms of ClO2 are effective antimicrobial treatments, gaseous ClO2 is more effective, at equal concentrations, than aqueous solutions as it can penetrate spaces and treat bacteria that ClO2 washes cannot (Beuchat et al., 2004; Mahmoud and Linton, 2008; Sy et al., 2005b; Wu and Kim, 2007; Wu and Rioux, 2010). Gaseous ClO2 treatment has become increasing popular for use by pharmaceutical and medical device industries both in the United States and in the Europe due to maintaining a gaseous phase a room temperature, temperature and pH insensitivity, and the ability to be easily monitored and accurately controlled (Wu, 2016).

2. GENERATION AND IMPLEMENTATION OF GASEOUS CHLORINE DIOXIDE Gaseous chlorine dioxide can be easily generated on-site through different methodologies. One commonly used method is to expose sodium chlorite (NaClO2) to a chlorine-nitrogen gas atmosphere (2:98%) in a generator to produce pure ClO2 (Czarneski and Lorcheim, 2005). Other methodologies include exposing sodium chlorite solution to molecular chlorine, Aseptrol tablets, and a dry precursor system developed by ICA Tri Nova, LLC (Wu, 2016; Wu and Kim, 2007). The main advantage gaseous chlorine dioxide treatment has compared to aqueous solutions is that the gaseous form has more penetrability and can reach microbes that would normally be protected from liquids by irregularities on the produce surface. However, treatment must occur in a sealed chamber in order to ensure human safety and the gas must be generated on-site (Lee et al., 2004; Wu, 2016).

Gaseous Chlorine Dioxide for Postharvest Treatment of Produce

Treatment efficacy depends on numerous variables which need to be assessed; gas concentration being the most logical to start with. The total mass load of plant tissue needs to be known to establish the amount of gas required to be generated for treatment, but, exposing equivalent masses of two different commodities to the same treatment parameters will not result in the same levels of microbial reduction. This observed change in efficacy is due to differences in the total surface area available for gas consumption and overall moisture content. For example, 1 kg of raspberries will have a much larger total surface area than 1 kg of tomatoes; thus increasing the amount of gas needed to ensure an even distribution of treatment (Park and Kang, 2017). Chlorine dioxide also reacts more efficiently in the presence of water, meaning that ClO2 will react quickly when treating produce commodities with high moisture content (e.g., baby-cut carrots; Park and Kang, 2015a). Conditions in the treatment area will also have a big influence on antimicrobial efficacy. For example, higher levels of environmental relative humidity (>70%) increases antimicrobial effectiveness of ClO2 exposure (Park and Kang, 2015a). Additionally, fresh produce is typically stored in a refrigerated setting and humid environments combined with low temperatures promote the formation of condensation and subsequent mold growth. At lower temperatures gases are also kinetically slower, meaning that longer exposure times would be needed to ensure gas treatments remain effective. Low-dose treatments coupled with long exposure times (>5 h) are most effective type of treatment. Long exposure times allows for more even distribution of gas reaction by produce surfaces and continuous release of gas in low quantities can help prevent plant bleaching; indicating that storage or transportation steps are logical places for treatment during postharvest processing. However, it is not as simple as just generating some gas within a warehouse or truck. Outside of the infrastructural changes needed for safe handling of chlorine dioxide, the setting must be airtight, well circulated, and have a highly controllable environmental to ensure both treatment efficacy and human safety. Pilot scale studies focusing on factors such as pathogen reduction, shelf life extension, and economic burden must be performed using industrial realistic produce masses and settings to make gaseous intervention more appealing to the agricultural industry.

3. ANTIMICROBIAL EFFECT OF GASEOUS ClO2 TREATMENT 3.1 Bacterial Reduction There have been numerous studies that have focused on the reduction of pathogenic bacteria (specifically Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes) on many types fresh produce commodities following gaseous ClO2 treatment. These include, but are certainly not limited to, berries, tree fruits, tomatoes and peppers, leafy greens, and root vegetables.

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Using berry models, Sy et al. (2005a) demonstrated that a gaseous ClO2 treatment of 8.0 mg/L for 120 min resulted in a reduction in viable Salmonella of up to 1.54 log CFU/g on raspberries, 3.67 log CFU/g on blueberries, and 4.41 log CFU/g on strawberries. Also using strawberries, Han et al. (2004) investigated continues chlorine dioxide exposure at reducing E. coli O157:H7 and L. monocytogenes. After exposure to 0.2 mg/L for 15 and 30 min, E. coli O157:H7 was reduced by 1.2 log CFU/strawberry and 2.4 log CFU/ strawberry, respectively. A treatment of 0.6 mg/L for 15 and 30 min further increased reduction of E. coli O157:H7 to 1.9 log CFU/strawberry and 3.0 log CFU/strawberry. L. monocytogenes was reduced by 1.8 log CFU/strawberry and 2.8 log CFU/strawberry after treatment with 0.2 mg/L ClO2 for 15 and 30 min. Increasing the dose to 0.6 mg/L further reduced L. monocytogenes by 2.6 log CFU/strawberry and 3.6 log CFU/strawberry, respectively. Given that fruits harvested from trees have been sources of both E. coli O157:H7 and Salmonella outbreaks, the antibacterial efficacy of postharvest gaseous chlorine dioxide treatment of tree fruits has been investigated. Using concentrations ranging from 4.1 to 8.0 mg/L, reductions in E. coli O157 (>8 log CFU), Salmonella (4.21 log CFU), and L. monocytogenes (>5.0 log CFU/g) have been observed (Du et al., 2002, 2003; Sy et al., 2005b); a similar reduction in Salmonella (> 5 log CFU) on oranges was also observed after 0.5 mg/L treatments for 10–14 min at 90%–95% humidity (Bhagat et al., 2011). Studies with stone fruit have reported a 3.23 log CFU reduction in Salmonella on peaches after a 20-min exposure to 4.1 mg/L gaseous ClO2 (Sy et al., 2005b) and 2.0 log CFU/g reductions in L. monocytogenes and E. coli O157:H7 on plums after 30-ppmv treatment for 20 min (Kim and Song, 2017). Gaseous chlorine dioxide treatment of green bell peppers and tomatoes have been very effective with (>6 log CFU/g) reductions in E. coli O157:H7, Salmonella, and L. monocytogenes reported (Han et al., 2001, 2002; Park and Kang, 2017). Effective treatment of Salmonella has also been reported with reductions of 4.33 log CFU after 4.1 mg/L for 25-min and 7.36 log CFU after 50-min exposure to 0.85 mg ClO2. However, changing the treatment temperature from 25°C to 4°C decreased the reduction to 3.95 log CFU indicating that at lower temperatures treatments, a longer exposure time is needed as gas diffusion is a function of temperature (Netramai et al., 2016; Sy et al., 2005b). A number of studies targeted at implementing a gaseous ClO2 treatment have revolved around using spinach or lettuce models. Gaseous chlorine dioxide generated through dry chemical sachets in a 20-L cabinet was used to treat E. coli O157:H7, S. Typhimurium, and. L. monocytogenes inoculated on lettuce leaves by Lee et al. (2004). Treatments of 4.3, 6.7, and 8.7 mg of gas for 30 min, 1 h, and 3 h resulted in pathogen reductions ranging from 3 to 6 log CFU/g (Lee et al., 2004). Also using lettuce, Mahmoud and Linton (2008) have reported 3.9 and 2.8 log CFU reductions in E. coli O157:H7 and S. enterica after 10 min exposure to 5 mg/L gaseous ClO2. Previously, reductions in E. coli O157:H7, S. Typhimurium, and L. monocytogenes were in the range

Gaseous Chlorine Dioxide for Postharvest Treatment of Produce

from 3.3 to 3.4 after 10 ppmv treatment of spinach for 10 min. Increasing the dosage and exposure time to 50ppmv and 15 min (at 90% RH) reduced the three bacterial pathogens down to undetectable levels (Park and Kang, 2015a,b). There have been relatively few studies on antibacterial effectiveness of gaseous ClO2 on root vegetables. Singh et al. (2002) investigated gaseous chlorine dioxide treatment of carrots and found a 3 log CFU/g reduction in E. coli O157:H7 with 1 mg/L gaseous ClO2 exposure for 15 min. Also using carrots, Sy et al. (2005b) reduced E. coli O157: H7, S. enterica, and L. monocytogenes by 5.62, 5.15, and 5.88 log CFU, respectively, after exposure to 4.1 mg/L ClO2 for 20–30 min. Wu and Rioux (2010) investigated the gaseous chlorine dioxide-induced reduction in total native microorganisms, yeasts and molds, and inoculated Pseudomonas aeruginosa on potatoes. A >5 log CFU/potato reduction in natural microbes was observed after treatment of 40 mg/L for 5 h. At the same treatment time and concentration, P. aeruginosa was reduced by 5.8 log CFU/potato. Residual ClO2 was also shown to decrease naturally over time (Wu and Rioux, 2010).

3.2 Fungal Reduction Compared to studies looking at bacterial reduction, comparatively fewer studies have focused on chlorine dioxide causing fungal reduction/inhibition. Wu and Rioux (2010) earlier showed that after exposure to 40 mg/L ClO2 for 5 h, total yeast and mold counts on potatoes were reduced by 5.3 log CFY/potato. In contrast, Sun et al. (2014) only reported a 1.7 log CFU/g reduction in yeasts and molds after exposure to ClO2 blueberries. However, they only used 2.5 mg of gas for their treatments. Sy et al. (2005b) found a maximum yeast and mold reduction of 2.65 log CFU/peach and 1.68 log CFU/apple after 4.1 mg/L exposure; with onions and tomatoes showing no significant reduction. Studies focused on the inhibition of specific pest molds have been investigated as well. For example, Colletotrichum actuatum on blueberries was previously reduced by 2.0 log CFU/g after exposure to 2.5 mg of ClO2 gas (Sun et al., 2014). Additionally, Alternaria alternata and Stemphylium vesicarium inoculated on roma tomatoes had significantly slower growth rates after exposure to 10 mg/L ClO2 for 5-min (Trinetta et al., 2013). Given the vast discrepancy observed in fungal reduction, and the large amount of taxonomic diversity found in the community of postharvest pest molds, it is likely that ClO2 exposure could have considerably different effect on different types of mold. For instance, Arango et al. (2016) concluded that chlorine dioxide has a minimal inhibition effect on stopping Botrytis cinerea growth on strawberries.

3.3 Antiviral Effect To the authors’ knowledge, there have been no published studies at this point that have used gaseous chlorine dioxide to reduce foodborne viruses (e.g., human norovirus and hepatitis A) on produce foods. However, Yeap et al. (2016) did look at reduction in

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Murine Norovirus (MNV-1), a commonly used surrogate for human norovirus, after exposure to gaseous chlorine dioxide on stainless steel coupons. Treatment of MNV-1 on coupons with 4 mg/L ClO2 reduced the number if viable particles down to undetectable levels (initial inoculum of 107 PFU/coupon) in as little as 1 min at 85% relative humidity. Furthermore, transmission electron microscope (TEM) imaging showed that gaseous ClO2 exposure disrupted the viral and capsid structure. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis coupled with western blot showed that 2 L/min ClO2 treatment degraded MNV-1 major capsid protein (VP1) after 5 min, further demonstrating an antiviral effect, and the VP1 gene was not detected from RNA extracted from MNV-1 after this treatment combination (Yeap et al., 2016).

3.4 Antimicrobial Mechanisms Damage to the cell membrane and subsequently increasing membrane permeability and disrupting protein synthesis is thought to be the primary antibacterial mechanism of ClO2 (Aieta and Berg, 1986; Park and Kang, 2015a). Alteration of membrane permeability following ClO2 treatment results in an influx of potassium ions, subsequently disrupting the transmembrane ion gradient. Increased membrane permeability also can allow for oxidation of structural proteins and lipids in the bacterial outer membrane (Praeger et al., 2018). ClO2 has been shown to react, in order of reactivity, to cysteine, tyrosine, tryptophan, histidine, and proline. Although cysteine has been demonstrated to have the highest reactivity with ClO2, perhaps due the sulfhydryl side group, it has been suggested that protein denaturation via tryptophan and tyrosine attack contributes to the major antimicrobial effect of ClO2 (Sharma and Sohn, 2012). Using a Saccharomyces cerevisiae model, Zhu et al. (2013) additionally showed that inhibition of proper enzymatic action, damage to cell walls and membranes, and ion leakage all contribute to cell death from ClO2 exposure. As mentioned earlier, ClO2 also can cause damage to viral proteins and RNA (Yeap et al., 2016).

4. INCREASES IN SHELF LIFE FOLLOWING GASEOUS ClO2 TREATMENT Compared to research on antimicrobial capabilities of gaseous ClO2, there are few successful studies at this point demonstrating ClO2 gas exposure extending shelf life. On the lower end of the spectrum, Go´mez-Lo´pez et al. (2007) increased the shelf life of grated carrots 1 day after reducing psychrotrophic counts by 1.7 logs after treatment with 1.33 mg/L gaseous ClO2. On more substantial levels, treatment of 5 mg/L for 10 min increased the shelf life of strawberries from 8 to 16 days (Mahmoud et al., 2007) and from 3 to 9 days for cantaloupe (Mahmoud et al., 2008). Most studies have focused on shelf-life extension through the reduction of native mesophiles, psychrotrophs, yeasts, and molds or artificially introduce spoilage organisms like Erwinia carotovora (Mahovic et al., 2007) or

Gaseous Chlorine Dioxide for Postharvest Treatment of Produce

P. aeruginosa (Wu and Rioux, 2010). However, it is also important to look at what is happening to the plant itself during gaseous ClO2 exposure. Using a strawberry plant model, Wang et al. (2014) demonstrated that ClO2 exposure reduced fruit weight loss, softening, and decay during storage and induced closing of stomata. Similar reduction in weight loss after ClO2 exposure was also observed with cherry tomatoes (Sun et al., 2017). Weight loss in fruit is largely attributed to water vapor transpiration through the produce surface by stomata, wounds, and blossom/stem scars and Wang et al. (2014) demonstrated that roughly 50% of strawberry stomata were closed during storage after ClO2 treatment, indicating that ClO2-induced stomatal closing could serve as a mechanism to extend shelf-life (Bai and Plotto, 2011; Valero et al., 2013). The opening and closing of stomata is controlled by turgor pressure of two associated guard cells. In normal conditions, CO2 induces an influx of potassium ions (K+) which increases the turgor pressure of the guard cells and opens the stomata. If by some mechanism ClO2 interferes with K+ influx and turgor pressure maintenance, the stomata would predictably stay closed and thus reduce water loss (Wang et al., 2014). Decrease in plant firmness during storage is associated with alterations in cellular structures (e.g., cell wall), fungal infection, loss of turgor pressure, and presence of polygalacturonase, pectin methylesterase, and other pectin enzymes (Paull et al., 1999). ClO2 exposure has been previously shown to inhibit enzymes, such as peroxidase and polyphenol oxidase, that have been associated with senescence softening (Sun et al., 2014). Furthermore, ClO2 can inhibit ethylene synthesis by reducing expression of LeACS2, LeACS4, and LeACO1 and subsequently delay ripening (Guo et al., 2014). Slowing down the ripening process subsequently prevents alternation of cell-wall polysaccharides and pectin structure; maintaining plant firmness for longer periods of time (Bonnin and Lahaye, 2013).

5. SENSORY ATTRIBUTES Gaseous chlorine dioxide treatment in relatively high concentration has previously been associated with sensory degradation of produce in a few studies; mainly through change in color. Browning of leafy greens and fruit following ClO2 treatment has been previously reported (Go´mez-Lo´pez et al., 2008a; Sy et al., 2005b). Browning of fruits and vegetables, in most cases, is caused by oxidation of phenols to quinones which further polymerize into melanins (Go´mez-Lo´pez, 2002). It is known that ClO2 can oxidize phenols (Napolitano et al., 2005), indicating that this reaction could be the possible cause of browning from treatment. Bleaching following treatment has also been reported by authors (Wu, 2016). Oxidation of oligosaccharides, such as cellulose and hemicellulose, is thought to be the primary mechanism behind bleaching. ClO2 reaction with, and subsequent degradation, of chlorophyll has also been proposed as cause of plant tissue

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bleaching (Go´mez-Lo´pez et al., 2009). Therefore, treatment condition should be optimized where it is sufficient enough to cause a significant reduction in microorganism populations and the quality of the produce remains.

6. CONCLUSIONS While there are numerous studies out there showing great promise and potential for use of gaseous chlorine dioxide in postharvest processing, almost all these studies fall short in the fact that they are all small-scale, laboratory experiments. It has been redundantly established at this point that gaseous ClO2 can reduce bacterial pathogens on produce; especially in a lab setting. However, there is a concerning lack of studies looking at reduction of viral and protozoan pathogens as well as the interaction of microbes and plant tissues before and after treatment. Before gaseous chlorine dioxide can be successfully implemented by the agricultural industry, a priority needs to be placed on studies addressing glaring gaps in the literature and those scaling up from industrial unrealistic smallscale studies.

REFERENCES Aieta, E.M., Berg, J.D., 1986. A review of chlorine dioxide in drinking water treatment. J. Am. Water Works Assoc. 78, 62–72. Alwi, N.A., Ali, A., 2014. Reduction of Escherichia coli O157, Listeria monocytogenes and Salmonella enterica sv. Typhimurium populations on fresh-cut bell pepper using gaseous ozone. Food Control 46, 304–311. Arango, J., Rubino, M., Auras, R., Gillett, J., Schilder, A., Grzesiak, A.L., 2016. Evaluation of chlorine dioxide as an antimicrobial against Botrytis cinerea in California strawberries. Food Packag. Shelf Life 9, 45–54. Bai, J., Plotto, A., 2011. Coatings for fresh fruits and vegetables. In: Edible Coatings and Films to Improve Food Quality. CRC Press, Taylor & Francis, Boca Raton, pp. 185–242. Beuchat, L.R., Pettigrew, C.A., Tremblay, M.E., Roselle, B.J., Scouten, A.J., 2004. Lethality of chlorine, chlorine dioxide, and a commercial fruit and vegetable sanitizer to vegetative cells and spores of Bacillus cereus and spores of Bacillus thuringiensis. J. Food Prot. 67, 1702–1708. Bhagat, A., Mahmoud, B.S., Linton, R.H., 2011. Effect of chlorine dioxide gas on Salmonella enterica inoculated on navel orange surfaces and its impact on the quality attributes of treated oranges. Foodborne Pathog. Dis. 8, 77–85. Bonnin, E., Lahaye, M., 2013. Contribution of cell wall modifying enzymes on the texture of fleshy fruits: the example of apple. J. Serbian Chem. Soc. 78, 417–427. Czarneski, M.A., Lorcheim, P., 2005. Isolator decontamination using chlorine dioxide gas. Pharm. Technol. 29, 124–133. Du, J., Han, Y., Linton, R., 2002. Inactivation by chlorine dioxide gas (ClO 2) of Listeria monocytogenes spotted onto different apple surfaces. Food Microbiol. 19, 481–490. Du, J., Han, Y., Linton, R., 2003. Efficacy of chlorine dioxide gas in reducing Escherichia coli O157: H7 on apple surfaces. Food Microbiol. 20, 583–591. Go´mez-Lo´pez, V.M., 2002. Some biochemical properties of polyphenol oxidase from two varieties of avocado. Food Chem. 77, 163–169. Go´mez-Lo´pez, V., Devlieghere, F., Ragaert, P., Debevere, J., 2007. Shelf-life extension of minimally processed carrots by gaseous chlorine dioxide. Int. J. Food Microbiol. 116, 221–227.

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Go´mez-Lo´pez, V.M., Devlieghere, F., Ragaert, P., Chen, L., Ryckeboer, J., Debevere, J., 2008a. Reduction of microbial load and sensory evaluation of minimally processed vegetables treated with chlorine dioxide and electrolysed water. Ital. J. Food Sci. 20, 321–331. Go´mez-Lo´pez, V.M., Ragaert, P., Debevere, J., Devlieghere, F., 2008b. Decontamination methods to prolong the shelf-life of minimally processed vegetables, state-of-the-art. Crit. Rev. Food Sci. Nutr. 48, 487–495. Go´mez-Lo´pez, V.M., Rajkovic, A., Ragaert, P., Smigic, N., Devlieghere, F., 2009. Chlorine dioxide for minimally processed produce preservation: a review. Trends Food Sci. Technol. 20, 17–26. Go´mez-Lo´pez, V.M., Marı´n, A., Medina-Martı´nez, M.S., Gil, M.I., Allende, A., 2013. Generation of trihalomethanes with chlorine-based sanitizers and impact on microbial, nutritional and sensory quality of baby spinach. Postharvest Biol. Technol. 85, 210–217. Goodburn, C., Wallace, C.A., 2013. The microbiological efficacy of decontamination methodologies for fresh produce: a review. Food Control 32, 418–427. Guo, Q., Wu, B., Peng, X., Wang, J., Li, Q., Jin, J., Ha, Y., 2014. Effects of chlorine dioxide treatment on respiration rate and ethylene synthesis of postharvest tomato fruit. Postharvest Biol. Technol. 93, 9–14. Han, Y., Linton, R., Nielsen, S., Nelson, P., 2001. Reduction of Listeria monocytogenes on green peppers (Capsicum annuum L.) by gaseous and aqueous chlorine dioxide and water washing and its growth at 7°C. J. Food Prot. 64, 1730–1738. Han, Y., Floros, J., Linton, R., Nielsen, S., Nelson, P., 2002. Response surface modeling for the inactivation of Escherichia coli O157: H7 on green peppers (Capsicum annuum) by ozone gas treatment. J. Food Sci. 67, 1188–1193. Han, Y., Selby, T., Schultze, K., Nelson, P., Linton, R., 2004. Decontamination of strawberries using batch and continuous chlorine dioxide gas treatments. J. Food Prot. 67, 2450–2455. Kaur, S., Smith, D.J., Morgan, M.T., 2015. Chloroxyanion residue quantification in cantaloupes treated with chlorine dioxide gas. J. Food Prot. 78, 1708–1718. Kim, H.-G., Song, K.B., 2017. Combined treatment with chlorine dioxide gas, fumaric acid, and ultraviolet-C light for inactivating Escherichia coli O157: H7 and Listeria monocytogenes inoculated on plums. Food Control 71, 371–375. Lee, S.-Y., Costello, M., Kang, D.-H., 2004. Efficacy of chlorine dioxide gas as a sanitizer of lettuce leaves. J. Food Prot. 67, 1371–1376. Mahmoud, B., Linton, R., 2008. Inactivation kinetics of inoculated Escherichia coli O157: H7 and Salmonella enterica on lettuce by chlorine dioxide gas. Food Microbiol. 25, 244–252. Mahmoud, B.S., Bhagat, A., Linton, R., 2007. Inactivation kinetics of inoculated Escherichia coli O157: H7, Listeria monocytogenes and Salmonella enterica on strawberries by chlorine dioxide gas. Food Microbiol. 24, 736–744. Mahmoud, B., Vaidya, N., Corvalan, C., Linton, R., 2008. Inactivation kinetics of inoculated Escherichia coli O157: H7, Listeria monocytogenes and Salmonella Poona on whole cantaloupe by chlorine dioxide gas. Food Microbiol. 25, 857–865. Mahovic, M.J., Tenney, J.D., Bartz, J.A., 2007. Applications of chlorine dioxide gas for control of bacterial soft rot in tomatoes. Plant Dis. 91, 1316–1320. Napolitano, M.J., Green, B.J., Nicoson, J.S., Margerum, D.W., 2005. Chlorine dioxide oxidations of tyrosine, N-acetyltyrosine, and dopa. Chem. Res. Toxicol. 18, 501–508. Netramai, S., Kijchavengkul, T., Sakulchuthathip, V., Rubino, M., 2016. Antimicrobial efficacy of gaseous chlorine dioxide against Salmonella enterica typhimurium on grape tomato (Lycopersicon esculentum). Int. J. Food Sci. Technol. 51, 2225–2232. Park, S.-H., Kang, D.-H., 2015a. Antimicrobial effect of chlorine dioxide gas against foodborne pathogens under differing conditions of relative humidity. LWT Food Sci. Technol. 60, 186–191. Park, S.-H., Kang, D.-H., 2015b. Combination treatment of chlorine dioxide gas and aerosolized sanitizer for inactivating foodborne pathogens on spinach leaves and tomatoes. Int. J. Food Microbiol. 207, 103–108. Park, S.-H., Kang, D.-H., 2017. Influence of surface properties of produce and food contact surfaces on the efficacy of chlorine dioxide gas for the inactivation of foodborne pathogens. Food Control 81, 88–95.

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Paull, R.E., Gross, K., Qiu, Y., 1999. Changes in papaya cell walls during fruit ripening. Postharvest Biol. Technol. 16, 79–89. Praeger, U., Herppich, W.B., Hassenberg, K., 2018. Aqueous chlorine dioxide treatment of horticultural produce: effects on microbial safety and produce quality—a review. Crit. Rev. Food Sci. Nutr. 52, 318–333. Richardson, S., Thruston, A., Caughran, T., Collette, T., Patterson, K., Lykins, B., 1998. Chemical by-products of chlorine and alternative disinfectants. Food Technol. 52, 58–61. Sharma, V.K., Sohn, M., 2012. Reactivity of chlorine dioxide with amino acids, peptides, and proteins. Environ. Chem. Lett. 10, 255–264. Singh, N., Singh, R., Bhunia, A., Stroshine, R., 2002. Efficacy of chlorine dioxide, ozone, and thyme essential oil or a sequential washing in killing Escherichia coli O157: H7 on lettuce and baby carrots. LWT Food Sci. Technol. 35, 720–729. Smith, D., Ernst, W., Giddings, J., 2014. Distribution and chemical fate of 36Cl-chlorine dioxide gas during the fumigation of tomatoes and cantaloupe. J. Agric. Food Chem. 62, 11756–11766. Smith, D., Ernst, W., Herges, G., 2015. Chloroxyanion residues in cantaloupe and tomatoes after chlorine dioxide gas sanitation. J. Agric. Food Chem. 63, 9640–9649. Sun, X., Bai, J., Ference, C., Wang, Z., Zhang, Y., Narciso, J., Zhou, K., 2014. Antimicrobial activity of controlled-release chlorine dioxide gas on fresh blueberries. J. Food Prot. 77, 1127–1132. Sun, X., Zhou, B., Luo, Y., Ference, C., Baldwin, E., Harrison, K., Bai, J., 2017. Effect of controlled-release chlorine dioxide on the quality and safety of cherry/grape tomatoes. Food Control 82, 26–30. Sy, K.V., McWatters, K.H., Beuchat, L.R., 2005a. Efficacy of gaseous chlorine dioxide as a sanitizer for killing Salmonella, yeasts, and molds on blueberries, strawberries, and raspberries. J. Food Prot. 68, 1165–1175. Sy, K.V., Murray, M.B., Harrison, M.D., Beuchat, L.R., 2005b. Evaluation of gaseous chlorine dioxide as a sanitizer for killing Salmonella, Escherichia coli O157: H7, Listeria monocytogenes, and yeasts and molds on fresh and fresh-cut produce. J. Food Prot. 68, 1176–1187. Trinetta, V., Linton, R.H., Morgan, M.T., 2013. Use of chlorine dioxide gas for the postharvest control of Alternaria alternata and Stemphylium vesicarium on Roma tomatoes. J. Sci. Food Agric. 93, 3330–3333. Valero, D., Dı´az-Mula, H.M., Zapata, P.J., Guillen, F., Martı´nez-Romero, D., Castillo, S., Serrano, M., 2013. Effects of alginate edible coating on preserving fruit quality in four plum cultivars during postharvest storage. Postharvest Biol. Technol. 77, 1–6. Wang, Z., Narciso, J., Biotteau, A., Plotto, A., Baldwin, E., Bai, J., 2014. Improving storability of fresh strawberries with controlled release chlorine dioxide in perforated clamshell packaging. Food Bioprocess Technol. 7, 3516–3524. Wu, V.C.-H., 2016. Chlorine Dioxide (ClO2), Postharvest Management Approaches for Maintaining Quality of Fresh Produce. Springer International Publishing, Switzerland, pp. 209–218. Wu, V.C., Kim, B., 2007. Effect of a simple chlorine dioxide method for controlling five foodborne pathogens, yeasts and molds on blueberries. Food Microbiol. 24, 794–800. Wu, V.C., Rioux, A., 2010. A simple instrument-free gaseous chlorine dioxide method for microbial decontamination of potatoes during storage. Food Microbiol. 27, 179–184. Yeap, J.W., Kaur, S., Lou, F., DiCaprio, E., Morgan, M., Linton, R., Li, J., 2016. Inactivation kinetics and mechanism of a human norovirus surrogate on stainless steel coupons via chlorine dioxide gas. Appl. Environ. Microbiol. 82, 116–123. Zhu, C., Chen, Z., Yu, G., 2013. Fungicidal mechanism of chlorine dioxide on Saccharomyces cerevisiae. Ann. Microbiol. 63, 495–502.

CHAPTER 14

Sodium and Calcium Hypochlorite as Postharvest Disinfectants for Fruits and Vegetables Vigya Mishra*, Ghan Shyam Abrol†, Neeru Dubey‡ *

Department of Post Harvest Technology, College of Horticulture, Banda University of Agriculture & Technology, Banda, India College of Horticulture & Forestry, Central Agriculture University, Jhansi, India ‡ Amity International Center for Post Harvest Technology & Cold Chain Management, Amity University, Noida, India †

1. INTRODUCTION Postharvest handling of fruits and vegetables usually involves the use of flumes, water dump tanks, spray washers, or hydrocoolers for washing and precooling of harvested commodities when dirt, organic matter and disease-causing pathogens accumulate in process water. This water may contain sanitizers for disinfection of fruits and vegetables. Disinfection of fresh fruit and vegetables after harvest is an essential primary step of postharvest handling which is done with an objective to maintain commodities and facilities free of fungal postharvest pathogens and bacterial human pathogens in order to improve food safety. Removal/destruction of postharvest pathogens that accumulate on the fruit surface before and during harvest is a direct benefit of disinfection which by itself can prevent decay after storage.

2. DISINFECTION: DEFINITION AND OBJECTIVES Disinfection is the treatment given to commodities or process water in order to inactivate or destroy pathogenic bacteria, fungi, viruses, cysts, and other microorganisms. It is a part of an overall sanitation and safety management program and can be achieved by using disinfectants or sanitizers like hydrogen peroxide, ClO2, sodium and calcium hypochlorite, etc., or may use physical processes such as microfiltration or ultraviolet illumination. The goal of disinfection is to prevent the transfer of these organisms from process water to produce and from one produce item to another during postharvest handling thus improving the microbial safety for human consumption.

3. DISINFECTION BY CHLORINATION Chlorination of process water is one of the primary elements of a properly managed postharvest sanitation program. In conjunction with an overall safety management program, Postharvest Disinfection of Fruits and Vegetables https://doi.org/10.1016/B978-0-12-812698-1.00014-5

© 2018 Elsevier Inc. All rights reserved.

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chlorination is generally effective, comparatively inexpensive and may be implemented in operations of any size. Disinfection by chlorination has had many applications in horticulture such as propagation, production, harvest, postharvest handling, and marketing of fresh fruits and vegetables for many decades. Chlorination has been routinely used in postharvest treatments as well like postharvest cooling water, in pretreatments (i.e., calcium for firmness enhancement), and during rehydration at shipping destinations. Primary uses of chlorine have been to inactivate or destroy pathogenic bacteria, fungi, viruses, cysts, and other microorganisms associated with seed, cuttings, irrigation water, farm or horticultural implements and equipment, contact surfaces, and human contact with fresh produce during harvesting and handling operations and also the prevent their transfer from one item to another (Table 1).

4. FORMS OF CHLORINE USED FOR FRESH FRUITS AND VEGETABLES Chlorine (Cl) is a very potent disinfectant with powerful oxidizing properties. It is soluble in water (Fig. 1). This solution, called chlorine (or chlorinated) water, consists of a mixture of chlorine gas (Cl2), hypochlorous acid (HOCl), and hypochlorite ions (OCl ) in amounts that vary with the pH of water. The terms free chlorine, reactive chlorine, and available chlorine are used to describe the amount of any form of chlorine available for oxidative reaction and disinfection. Chlorine being used in agriculture applications is commercially available in following forms as approved by the US Environmental Protection Agency (EPA). Important terms

• Free or available chlorine is the amount of chlorine in the form of chlorine gas, hypochlorous acid or hypochlorite ion. The rate at which bacteria are inactivated is proportional to the concentration of available chlorine. • Combined chlorine is the quantity of chlorine that has reacted with nitrogencontaining compounds in the water such as ammonia to form chloramines that do not work well in a sanitizing capacity. • Total chlorine is the sum of free (available) and combined chlorine.

4.1 Chlorine Gas (Cl2) It is the least expensive disinfectant but most demanding source of chlorine from a safety and monitoring point of view. It is generally restricted to use in very large operations and its use requires automated, controlled injection systems with in-line pH monitoring. Chlorine gas reduces the pH of water below 6.5. It is commonly used for situations

Sodium and Calcium Hypochlorite as Postharvest Disinfectants

Table 1 Postharvest application of chlorine-based disinfectants in fresh fruits and vegetables Application rate Application Commodities (μG/ML) Benefits

Harvest totes Butt

General sanitation Celery, lettuce

50–150 Spray 150–200

Head spray

Cauliflower

50–100 with plastic overwrap

Dump tanks and flotation tanks Flumes

Tomato, pepper, citrus, apples, pears

50–400

Tomatoes, sweet potatoes Wash water sanitation General sanitation for sorters and packers

150–200 with heat 75–150 25–75

Bacteria, surface microbial load reduction Microbial elimination

Source ice disinfection Cooling water sanitation Disinfection of CaCl2 treatment water

25–50

Coliform elimination, virus

50–300

Bacteria, surface microbial load reduction Bacteria, fungi

Wash spray bars Glove dips, Boot dips (walk-thru) Ice Injection Hydrocooler Calcium pressure infusion Minimally processed vegetables Abrasive peelers Packing line sanitation

Retail trim and wash

10–50

Bacteria, fungal spores Prevent bacterial rot and enzymatic browning Prevent floret browning (bacteria, fungi, and enzymatic browning from harvest damage) Bacteria, fungal spores surface microbial load reduction Bacteria, fungal spores

Wash and cooling water sanitation

50–200

Bacteria, surface microbial load reduction

Wash water sanitation Conveyor belts, pads, diverters, chutes, etc.

50–200

Bacteria, surface microbial load reduction Biofilm prevention, general microbial reduction on contact surfaces

Wash water sanitation

Chlorinated foams or chlorinated water sprays (variable) 25–50

NaOH + HOCl NaOCl + H2O HOCl H+ + OCl− HOCl + HCl H2O + Cl2

Fig. 1 Forms of chlorine in wash water.

Bacteria, surface microbial load reduction

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in which soil, plant debris, and decaying fruit or vegetables may enter early stages of washing and grading.

4.2 Calcium Hypochlorite (CaCl2O2) It is the most common source of chlorine used for disinfection of produce and produce process water. Registered formulations are 65% or 68% active ingredient (a.i.). It is available as a granulated powder, compressed tablets, or large slow-release tablets. It is more stable than liquid sodium hypochlorite for use in dry storage. Phytotoxicity (bleaching or burning) of produce can occur if calcium hypochlorite granules fail to dissolve in cool wash water or in a hydrocooler system. Therefore, granules are fully dissolved in warm water before adding them to cooling or wash water. Besides disinfection benefits, calcium hypochlorite has also been reported to improve the shelf life and disease resistance of fruits and vegetables by supplementing calcium to the cell wall.

4.3 Sodium Hypochlorite (NaOCl) This compound is commonly used in small-scale operations. It is generally used in concentrations of 5.25%–12.75% (a.i.) in liquid form, because the solid forms readily absorb water from air and release chlorine gas. Only registered formulations are approved for use on produce, for example, household bleach is not a registered material for produce. Sodium hypochlorite is generally more expensive than other forms of chlorine due to the added shipping cost of the water-based formulations. Excess sodium buildup from repeated applications of sodium hypochlorite to recirculating water may damage sensitive horticultural produce.

4.4 Chlorine Dioxide (ClO2) It is a yellow to red gas with 2.5 times the oxidizing potential of chlorine gas. Chlorine dioxide is explosive at concentrations above 10% (a.i.) or at temperatures above 130°C (266°F). On-site generation of chlorine dioxide is also available by combining chlorine gas and sodium chlorite or by combining sodium hypochlorite, hydrochloric acid, and sodium chlorite. As with chlorine gas, the safety hazards associated with the use of chlorine dioxide demand detailed attention to proper engineering controls to prevent or reduce exposure. Violent explosions can occur when chlorine dioxide comes into contact with ammonium compounds. The disinfecting power of chlorine dioxide is relatively constant within a pH of 6–10. It is effective against most microbes at concentrations of 3–5 ppm (parts per million) in clean water. It is more expensive than other chlorine compounds due to on-site generation, specialized worker safety programs, and closed injection systems for the containment of concentrate leakage and fumes from volatilization.

Sodium and Calcium Hypochlorite as Postharvest Disinfectants

Currently, chlorination is one of the few chemical options available to control postharvest diseases. When used in connection with other proper postharvest handling practices, chlorination is effective and relatively inexpensive. It poses little threat to health or the environment. Many types of postharvest disorders and infectious diseases affect fresh fruits and vegetables (Table 2) and efficient use of disinfectants is helpful in the prevention of many fungal and bacterial diseases. Generally disorders are the result of stresses related to excessive heat, cold, or improper mixtures of environmental gases such as oxygen, carbon dioxide, and ethylene and cannot be controlled by chlorination or most other postharvest chemicals. Total chlorine refers to the total available and combined chlorine that is present in water and still available for disinfection and oxidation of organic matter. Although combined chlorine compounds are more stable than available chlorine forms, they are slower in disinfectant action. In process water, the desired form of chlorine is hypochlorous acid, which is a much more effective bactericide than the hypochlorite ion. Although hypochlorous acid concentration is highest at pH 6.0, the best compromise of activity and

Table 2 Common postharvest diseases of major fruits and vegetables Commodity (fruit/vegetables) Diseases Causal organism

1. Mango

2. Banana 3. Grapes

4. Apple

5. Pomegranate

6. Peaches and plums

7. Tomatoes and peppers

Anthracnose Stem-end rot Rhizopus rot Crown rot Anthracnose Blue mold Gray mold Rhizopus rot Alternaria rot Blue mold Gray mold Aspergillus fruit rot Alternaria rot Gray mold Brown rot Rhizopus rot Gray mold Blue mold Alternaria rot Alternaria rot Soft rot Bacterial soft rot Bacterial soft rot

Colletotrichum gloeosporoides Botryosphaeria spp. Rhizopus stolonifer Fusarium spp. Colletotrichum musae Penicillium sp. Botrytis cinerea Rhizopus stolonifer Alternaria alternata Penicillium spp. Botrytis cinerea Asprgillus niger Alternaria alternata Botrytis cinerea Monilinia fructicola Rhizopus stolonifer Botrytis cinerea Penicillium sp. Alternaria sp. Alternaria alternata Rhizopus stolonifer Erwinia spp. or Pseudomonas spp. Erwinia sp. Pseudomonas spp.

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Table 3 A comparison of three commercially available forms of chlorine Commercially available Commercially concentrations Cost Safety Source available form

Chlorine gas

Compressed liquid

Calcium hypochlorite

Tablet or granulated powder Water-based formulation

Sodium hypochlorite

100% free active chlorine 65% or 68% free active chlorine 5%–15% free active chlorine

Low capital, low operation High capital, high operation High capital, high operation

Threat of gas leak or explosion Hazardous due to higher percent chlorine Relatively safer than chlorine gas and calcium hypochlorite due to low level of chlorine

stability is achieved by maintaining a water pH between 6.5 and 7.5. At low pH, chlorine gas is released from water. Commercially chlorinated water is produced by adding either chlorine gas, calcium hypochlorite [Ca(ClO)2], or sodium hypochlorite (NaOCl) to water. These forms of chlorine vary in nature and cost (Table 3).

5. SODIUM AND CALCIUM HYPOCHLORITES: AS DISINFECTANTS Sodium and calcium hypochlorites were first registered for use as pesticides in 1957. In February 1986, Environment Protection Agency (EPA) issued a Registration Standard for sodium and calcium hypochlorites and concluded that no additional scientific data would be necessary to register or reregister products that contain sodium hypochlorite from 5.25% to 12.5% or calcium hypochlorite from 65% to 70%, as long as the products contain no other active ingredients, no inert ingredients other than water and bear Toxicity Category I labeling.

5.1 Advantages and Disadvantages Among all chlorinated inorganic disinfectants, sodium or calcium hypochlorite has been an important part of a properly managed horticultural sanitation program for several decades due to following advantages: • Very effective postharvest disinfectants of fungus and bacteria in fruits and vegetables. • Minimize the redistribution and transfer of pathogens from adhering soil, infested fruit or vegetable surfaces, or debris to noninfested surfaces through harvest and trimming cuts or natural plant surface openings.

Sodium and Calcium Hypochlorite as Postharvest Disinfectants

• It can be used for water disinfection, primarily for harvest and postharvest handling and cooling. • Inexpensive in comparison to other disinfectants. • Easy availability. • It may be implemented in operations of any size or scale. Sodium and calcium hypochlorites are used in laundries, swimming pools, ponds, drinking water, and other water and wastewater systems; on food and nonfood contact surfaces; and as a postharvest, seed, or soil treatment on various fruit and vegetable crops. Hypochlorites control pathogenic bacteria, fungi, and algae that can cause diseases in human beings and animals. These are better known as bleach and are widely used compounds whose chemical and toxicological properties are extensively documented in the published literature. However, they also have few major disadvantages which have been discussed below: • lower effectiveness in turbid waters contaminated with organic and some inorganic compounds; • may not be effective against parasites; • taste and odor are unacceptable to some; • chlorine forms complex compounds with organic material which may be detrimental to health over time; • chlorine degrades over time; • contact time is required; • chemical dosage varies with water quality which is difficult to test every time and everywhere; • chlorine can be hazardous if used improperly. Requires quality control process to ensure product reliability—chlorine fumes and contact with skin are hazardous; • concern about the potential long-term carcinogenic effects of chlorination by-products; • relatively short shelf life; • uncertain concentration and shelf life, susceptibility to gaps in supply chain, high transportation costs and difficulty in dispensing precise quantities.

5.2 Sodium Hypochlorite (NaOCl) Liquid sodium hypochlorite (NaOCl) is the most commonly used form of chlorine in postharvest operations which include use in hydrocoolers, flume tanks, spray bars, and cooling water in fruit/vegetable packinghouses. NaOCl is often the erroneously chosen chemical based on a perceived low cost as compared to alternatives. The error lies in the actual versus perceived use cost. The effectiveness of NaOCl is greatly depends on the water pH and the cleanliness of the water source. At a pH of 6.5, chlorine in the form of hypochlorous acid (HOCl) is

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indeed an effective antimicrobial agent; however, many packinghouses do not monitor or manage the water pH due to the added cost of testing and acid injection to properly control the alkalinity. Chlorine demand is also typically misunderstood, since chlorine becomes bound to organic matter, soil and other debris, which eliminates the effectiveness. The actual residual of chlorine required to kill or control microbes continuously increases, as some microbes may potentially become resistant to chlorine with extended use. Sodium hypochlorite is a strong oxidizer with broad spectrum antimicrobial activity (Bloomfield, 1996). NaOCl in water ionizes to Na+ and the hypochlorite ion in equilibrium with hypochlorous acid (HOCl), the active moiety (Dychdala, 1983). HOCl damages microbe cell membranes, proteins, and nucleic acids by oxidative degradation upon contact (McDonnell and Russell, 1999). NaOCl is a relatively inexpensive and non-residual chemical that is widely used to reduce bacterial and fungal contamination on fruit and vegetable surfaces, processing equipment, and in flower vase solutions (Suslow, 1997). NaOCl is commonly used in the concentrations range of 50–200 mg/L depending on the commodity and mode of application. The products of the sodium hypochlorite-water reaction are hypochlorous acid (HOCl) and sodium hydroxide (NaOH) and the further dissociation of hypochlorous acid is the hypochlorite ion (OCl ). The term of free chlorine does not include combined chlorine compounds that are not available for the oxidative reactions such as chloramines (Blatchley III, 1994). Although hypochlorous acid (HOCl) is more effective than the hypochlorite ion (OCl ), under alkaline conditions which are promoted by the formation of NaOH the equilibrium shifts to the hypochlorite ion (OCl ) (Kim and Hensley, 1997). It is reported that at pH 7.0, which is the target pH for the fresh-cut industry, the percentages of HOCl and OCl are 78% and 22%, respectively (Combrink and Grobbelaar, 1984). Despite the fact that the concentration of HOCl increases as the pH decreases, the solution becomes corrosive to the food contact equipment at lower pH values (Boyette et al., 1993; Kim and Hensley, 1997). Chlorine in the form of a sodium hypochlorite solution or as a dry powdered calcium hypochlorite can be used in hydrocooling or wash water as a disinfectant. Some pathogens such as Cryptosporidium, however, are resistant to chlorine and even sensitive ones such as Salmonella and Escherichia coli may be located in inaccessible sites on the plant surface. For the majority of vegetables, chlorine in wash water should be maintained in the range of 75–150 ppm. The antimicrobial form, hypochlorous acid, is mostly available in water with a neutral pH (6.5–7.5). The effectiveness of chlorine concentrations are reduced by temperature, light, and interaction with soil and organic debris. The wash water should be tested periodically with a monitoring kit, indicator strips, or a swimming pool-type indicator kit. Concentrations above 200 ppm can injure some vegetables (such as leafy greens and celery) or leave undesirable off-flavors.

Sodium and Calcium Hypochlorite as Postharvest Disinfectants

NaOCl when dissolved in water, ionizes to Na+ and the hypochlorite ion in equilibrium with hypochlorous acid (HOCl). HOCl damages microbe cell membranes, proteins and nucleic acids by oxidative degradation upon contact.

5.3 Calcium Hypochlorite The most common source of chlorine used in postharvest chlorination is calcium hypochlorite. Calcium hypochlorite is also one of the allies in the ongoing fight against foodborne disease. It is mixed with water to various strengths to kill germs found on industrial food processing and preparation surfaces and play an important role in keeping our food supply safe. It is commercially available in the form of either a granulated powder or large tablets. Most commercial formulations are 65% calcium hypochlorite, with the balance consisting of stabilizers and inert materials. Calcium hypochlorite is relatively stable as long as it is kept dry and can be stored for extended periods. The property that makes it stable also makes it difficult to dissolve completely in water. Adding granulated calcium hypochlorite directly to the water often results in undissolved particles that adhere to the produce, causing undesirable bleaching and chlorine burns. This problem is particularly common in hydrocoolers because calcium hypochlorite dissloves very slow in cold water. Therefore, always dissolve granulated calcium hypochlorite in a small quantity of lukewarm water before adding it to the wash tank or hydrocooler. Calcium hypochlorite may be obtained in tablets that are added directly to the hydrocooler or wash tank to eliminate the problem of chlorine burns. Calcium hypochlorite tablets dissolve slowly to yield a continuous supply of chlorine to the water. Therefore, they must be positioned carefully to ensure proper mixing of the chemical with the water. A comparison of sodium and calcium hypochlorites is presented in Table 4.

5.4 Postharvest Applications of Sodium and Calcium Hypochlorites • NaOCl treatment of rose flowers was more effective in reducing B. cinerea infection than several registered fungicides when tested under laboratory conditions. Applying NaOCl prior to commercial shipment also provided the most consistent disease control for a broad range of rose cultivars (Andrew et al., 2010). • Household bleach solutions containing NaOCl were found effective for use as a postharvest dip treatment. From a commercial perspective also, these products were found relatively inexpensive, readily available, and can be easily incorporated into postharvest disease control practices. NaOCl is already approved for contact sterilization of fruits and vegetables (Food and Drug Administration, 2009). • Sanz et al. (2002) reported that the solutions of 50 mg/L free chlorine without pH control and 100 mg/L free chlorine at pH 7
0 prepared from sodium hypochlorite

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Table 4 A comparative study of sodium and calcium hypochlorite

Parameters Chemical name

Sodium hypochlorite Sodium oxychloride, hypochlorous acid, sodium salt

Formula Common names Molecular weight Form

NaOCl, NaClO, ClNaO Liquid bleach

Calcium hypochlorite Calcium hypochlorite Calcium oxychloride Chlorinated lime Ca(ClO)2 or CaCl2O2 Powder Chlorine

74.439 g/mol

142.976 g/mol

A colorless or slightly yellow watery liquid with an odor of household bleach Commercially available in strengths approximately 15% by weight It can be added to the receiving stream by gravity, by the use of a chemical metering pump, or by physically dumping it

White granular solid (or tablets compressed from the granules) with an odor of chlorine It contains 70% available chlorine

Strength Use

Oxidizing effect Method of preparation of chlorine water

Mode of application

Same Sodium hypochlorite causes a rise above 7.5 in therefore pH must be reduced prior to treatment of produce. For leafy green vegetables with a high surface area to volume due to crevices and uneven surfaces, liquid sanitizers may not have a direct contact with all surfaces contaminated by bacteria. Adding surfactants reduces the surface tension of the water to allow a uniform distribution of chlorinated water on leaf surface and deeper penetration into pores (Suslow, 1997).

It can be added to the receiving stream by use of pellets or by mixing a solution of water and calcium hypochlorite, decanting the solution into a tank and using a small chemical feed pump Same Powder or tablets are dissolved in water prior to treatment of fresh produce. An additional water tank containing warm water is often required to assure that Ca(ClO)2 is completely dissolved prior to mixing with the cooler water for sanitation. If calcium hypochlorite is not completely dissolved, bleaching of the produce can be observed. The pH needs to be checked and lowered to assure the chlorinated water pH is below 7.5 (Suslow, 1997). For example, 200 ppm chlorinated water can be made by mixing 1.16 g of calcium hypochlorite with 65% active ingredient with 3.8 L (about 1 gal) of water.

Chlorinated water is applied by either submerging or spraying the fresh produce. Submerging involves loading produce into a long channel filled with cool, chlorinated water, allowing for surface contact. Submersion for 1 min, in a concentration of 75–200 ppm total chlorine, commonly achieves a microbial reduction of approximately 1.3–1.7 log units (Beuchat et al., 1998). Spray application of chlorinated water can also be done during hydrocooling, in which the produce is placed on a conveyor belt that simultaneously cools and sanitizes it in a longer period of time.

Sodium and Calcium Hypochlorite as Postharvest Disinfectants

rendered the highest microbial reduction with minimum damages for artichoke and borage, respectively. • In a study by Tomas-Callejas et al. (2012) NaOCl was found to be effective in preventing cross contamination of E. coli O157:H7 in fresh-cut Red Chard baby leaves. Evaluation of efficacy of sodium and calcium hypochlorite salts on disinfection of some fresh commodities is presented in Table 5.

6. IMPORTANT CONSIDERATIONS FOR PROPER CHLORINE DISINFECTION While going for postharvest disinfection of fruits and vegetables using sodium and calcium hypochlorites following key points must be taken care.

6.1 Source of Water Potable water must be used for all postharvest operations including washing, grading, and cooling. Contaminated water or water taken and used directly from rivers or holding ponds must not be used for operations as it can transmit diseases that decay the produce or adversely affect human health. Another reason to avoid such water is that some pathogens are not easily killed by chlorination, even under optimal conditions, therefore, beginning with clean potable water is the best preventive step available. While using a nondomestic water source, water quality evaluations should be performed by a certified analytical lab.

6.2 Temperature Although chlorine activity slightly increases with temperature, some chlorine gas is lost to the atmosphere at warmer temperature due to increased rate of volatilization. Low temperature and improper pH values in hydrocooling, for example, can greatly reduce disinfection efficiency.

6.3 Organic Matter Chlorine is highly reactive with leaves, soil, and any plant or vegetable matter whenever oxygen is present. Each chemical reaction reduces the amount of active chlorine. Changing chlorinated water frequently or filtering out organic matter and debris is essential for effective sanitation. Also, prewashing very dirty produce can prolong the useful life of chlorinated cooling water.

6.4 Concentration of Disinfectant and Exposure Time Disinfection is best accomplished by deriving contact (exposure) times and concentrations through direct experience for each type of produce and local conditions (Table 6).

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E. coli O157:H7 and Salmonella spp. E. coli O157:H7 and Salmonella spp. E. coli O 157:H7

Product

References

Alfalfa seeds

Fett (2002a)

Mung bean seeds Chinese cabbage leaves

Fett (2002b) Inatsu et al. (2005)

Stopforth et al. (2008) Allende et al. (2009) Niemira (2008) Allende et al. (2008)

Calcium hypochlorite

1900–18,000 mg/L

Calcium hypochlorite

1900–18,000 mg/L

5, 10, 15, and 20 min 5, 10, and 15 min

Sodium hypochlorite with and without acidification (citric acid: 1000 mg/L) Acidified sodium chlorite

100 mg/L

15 min

1200 mg/L

60 and 90 s

E. coli O157:H7, Salmonella spp. and L. monocytogenes

Leafy greens

Sodium hypochlorite

200 mg/L

1 min

E. coli O157:H7, total plate count and yeasts and molds

Fresh-cut cilantro

Sodium hypochlorite

300 and 600 mg/L

3 min

E. coli O157:H7

Sodium hypochlorite

200 mg/L

Product stored for 14 days at 5°C

E. coli O157:H7 and natural microflora

Lettuce varieties Shredded carrot

Postharvest Disinfection of Fruits and Vegetables

Table 5 Evaluation of efficacy of sodium and calcium hypochlorite salts on produce and process water Sanitizer Concentration Exposure time Target microorganism

Sodium and Calcium Hypochlorite as Postharvest Disinfectants

Table 6 Chlorine concentration for some major fruits and vegetables Fruit/vegetable Chlorine concentration (ppm)

Globe Artichoke Asparagus Broccoli Carrot Cauliflower Celery Cucumbers Lettuce Melons Mushrooms Peas Potatoes Pumpkin Radishes Tomatoes Turnips Yams

100–150 100–150 100–150 100–150 100–150 100 100–150 100–150 100–150 100–150 50–100 200–600 100–200 100–150 200–350 100–200 100–200

Exposure times of 3–5 min at concentrations of 50–75 ppm or less (1–1.5 oz of calcium hypochlorite at 65% a.i. per 100 gal of water provides 50–75 ppm) maintained at pH 6.5 is generally adequate for controlling most postharvest pathogens present in washing/process water (Suslow, 1997). The length of time the produce is actually in contact with the chlorinated water affects the ability of the active chlorine, hypochlorous acid, to inactivate pathogens. Generally, a 1–2-min exposure is sufficient, but be sure to follow the EPA label for your specific sanitizer. The practical duration of contact exposure is generally 10–15 min.

6.5 Sensitivity of Microorganisms Microorganisms differ in their sensitivity to chlorine, for example, bacteria are most sensitive, many fungal spores are less sensitive, and some spore-forming animal parasites are highly insensitive. In practice, total chlorine concentrations may need to exceed 300 ppm to sustain sufficient available chlorine activity in process water throughout the daily use cycle.

6.6 Types of Produce Caution must be used as some produce are sensitive to surface bleaching or pitting at higher concentrations of chlorine. For example, bell peppers are not affected by

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250 ppm available chlorine but carrots may lose the intensity of their orange color and celery and asparagus may develop light brown surface pits when exposed to chlorine concentrations exceeding 250 ppm.

6.7 Improving Chlorination Efficacy (by Using Surfactants) Chlorine kills only what it directly contacts. Typically the extent of microbial population reduction on plant surfaces is limited to a 10–100-fold reduction, depending on many factors (Brackett, 1994). Water films that form on very small contours on plant surfaces may prevent the chlorinated water from directly contacting target microorganisms. The efficacy of chlorination on water disinfection and microbial load reduction on product surfaces may be enhanced by adding approved surfactants (Segall, 1968; Spotts and Cervantes, 1989; Spotts and Peters, 1982) like polysorbate 80, other sorbitan esters and chlorine potentiator to process water. These are also regarded as “Performance Enhancers” and may reduce water surface tension and increase the effectiveness of chlorination by increasing the penetration of hypochlorous acid into plant contours and natural openings. Recently, further enhancement in disinfection has been achieved by using ultrasound equipment attached to wash tanks.

6.8 pH of Chlorine Solution At low pH values, toxic chlorine gas is produced, so the pH of the solution should never drop below 5. pH values below 6.5 are corrosive to processing equipment and will reduce equipment life. Above pH 7.5, the formation of hypochlorite ion (OCl ) occurs and reduces the effectiveness of sanitation. The solution should be held between pH values 6.5 and 7.5 to produce hypochlorous acid (HOCl). Recirculated chlorinated water should be monitored for pH and changed as needed (McGlynn, 2004). If the pH is found to be outside of the necessary range, sodium carbonate is added to raise the pH and hydrochloric acid, vinegar or sodium bisulfate is added to lower the pH (Grubinger, 2008). A test kit will allow the user to determine how much acid or base must be added to be within the desired range.

6.9 Monitoring, Control, and Documentation Processes Accurate monitoring, control, and recording of disinfection procedures and performance are important considerations to achieve successful disinfection of fruits and vegetables. The chlorine concentration and pH of chlorinated process water should be checked frequently with the help of pH strips, colorimetric kits, or electronic sensors. The optimal frequency of testing is best determined through on-site experience. In general, monitoring is done more frequently if concentration of suspended materials in the water increases. Different tests measure different forms of chlorine; some are accurate only at very low

Sodium and Calcium Hypochlorite as Postharvest Disinfectants

concentrations. Dilution of most process water with distilled or deionized water is required to obtain useful results from these tests. Select a chlorine test kit based on DPD (N,N-diethyl-p-phenylenediamine) that specifically tests for available (reactive) chlorine. Become familiar with what is being measured and how water quality affects the results. Hydrochloric acid (HCl) or citric acid is commonly used to maintain wash or cooling water at a pH of 6.5–7.5. Some automated cooling systems monitor the oxidation reduction potential (ORP) of process water using probes that measure activity in millivolts (mV). The relationship between ORP, contact time, and microbial inactivation for chlorine-based oxidizers in laboratory tests and field confirmation tests are used to establish the setting for the system. For example, an ORP set point of 600–650 mV is commonly used in hydrocooling systems. Accurate chlorine estimation generally requires more detailed and time-consuming procedures than many operators will commit. Since chlorine tests do not distinguish HOCl and OCl2, it is also important to monitor and control the pH of the water system. The dynamic balance of the two forms of hypochlorite in water changes dramatically between pH 6.5 and 8.0. The faster acting antimicrobial form, HOCl, exists as 95%– 80% of the “free chlorine” is detected with paper test strips at pH 6.5–7.0. This level drops to less than 20% at pH higher than 8.0. Therefore, although a strong color reaction on the test paper or colorimetric kit is observed during monitoring, the effectiveness of the disinfectant is far less at high pH. This is particularly problematic for fruit and vegetable applications, which typically have short contact times. Continuous flow systems employed without monitoring may apply unnecessary, undesirable, potentially unhealthy, or unlawful levels of disinfectant to water systems. Even when monitoring is practical, too often no record of disinfection potential of the water is kept.

6.10 Oxidation-Reduction Potential Oxidation-Reduction Potential (ORP), measured in millivolts (mV), has recently been introduced to fresh produce packers and shippers as an easily standardized approach to water disinfection for harvest and postharvest handling. Operationally, much like a digital thermometer or pH probe, ORP sensors allow the easy monitoring, tracking, and automated maintenance of critical disinfectant levels in water systems that fit in well to a foundation of Good Agricultural Practices (GAPs) and the evolving agricultural equivalents of Hazard Analysis Critical Control Point (HACCP) programs (Rushing et al., 1996). Traditionally chlorine or hypochlorite has been monitored by qualitative assessments of ppm total and/or free available chlorine. Titration kits, or more commonly chemical impregnated paper strips, estimate the range of antimicrobial forms of chlorine (the most effective is hypochlorous acid or HOCl) in the water solution. There is no test kit that differentiates the more active HOCl from the far less active ionic form, hypochlorite (OCl ).

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The ORP offers many advantages to “real-time” monitoring and recording of water disinfection potential, a critical water quality parameter. Improvements in probe design and continuous analog recording (paper strip or revolving chart) or computer-linked data input are available. Probes have been integrated to audible, visual, and remote alarm systems to notify the operator of out-of-range operation. The ORP is ideal for automated injection systems and can be combined with pH control injections to optimize performance. Handheld devices are affordable and essential backup to cross-reference the operation of an in-line probe. A primary advantage is that using ORP for water system monitoring provides the operator with a rapid and single-value assessment of the disinfection potential of water in a postharvest system. Research has shown that at an ORP value of 650–700 mV, spoilage bacteria and bacteria such as E. coli and Salmonella are killed within a few seconds. Spoilage yeast and the more sensitive type of spore-forming fungi are also killed at this level after a contact time of a few minutes or less.

6.11 Other Important Considerations Under typical harvest operations of many fruits and especially leafy vegetables adhering soil and organic debris can be a problem and greatly reduce disinfection efficiency. Vegetables, in particular, are often harvested on heavy ground after rainfall and may arrive at a packing facility with problematic volumes of soil on totes, bins, cartons, pallets, and the product itself. Chlorine is highly reactive with leaves, soil, and any plant or vegetable matter whenever oxygen is present. Each chemical reaction reduces the amount of active chlorine in the water. The chlorine demand of agricultural water sources is often far higher and more prone to rapid fluctuations than sources for drinking water. Changing chlorinated water frequently or filtering out organic matter and debris is essential for effective sanitation. Prewashing harvest bins, palletized totes, pallet skids, and, if possible, very dirty produce can prolong the useful life of chlorinated cooling water. Removing field soil before sending bins or palletized loads of harvested crop into flotation tanks, chemical treatment showers, or hydrocoolers will greatly aide in pathogen inactivation, chlorine use efficiency, and minimize the production of chlorinated disinfection by-products. The issue of disinfection by-products may be of particular concern for vegetables grown in organic or muck soils with a high humic fraction.

7. CHLORINATION OF MINIMALLY PROCESSED FRUITS AND VEGETABLES The specific operations involved in preparation of fresh-cut and minimally processed fruits and vegetables can facilitate attachment and stimulate microbial growth, which includes diverse complexes of spoilage microorganisms harmful to human health (Sapers et al., 2006). Therefore, fresh-cut and minimally processed produce must be

Sodium and Calcium Hypochlorite as Postharvest Disinfectants

managed in primary production phases and elaborated for marketing following strict control procedures for reducing overall quality loss and assuring its safety to consumers (Artes et al., 2009). Fruits and vegetables used for salad and dessert are generally consumed raw thus increasing the chances of microbial spoilage which may lead to food poisoning. Hence, washing and disinfection is a key step that contributes to effectively reducing microbial load across the supply chain (Artes et al., 2009; Beuchat, 2000). Chlorine in various approved agricultural and food grade formulations are the most widely used disinfectant in the fresh-cut industry. However, there is a concern about the use of NaClO by the fresh-cut industry due to its low effectiveness in the presence of organic matter, and the formation of known or potentially carcinogenic or mutagenic by-products such as chloroform and haloacetic acids (Hrudey, 2009; Nieuwenhuijsen et al., 2000; Olmez and Kretzschmar, 2009; Richardson et al., 2007).

8. TOXICITY In the past, very high rates of chlorine were often used because it was felt that no residue was left on produce at consumption (Anon., 1997; Combrink and Visagie, 1982; Endemann, 1969; Rabin, 1986). At high pH, chlorine reacts with organic nitrogen-based materials to produce mildly toxic chloramines. Sodium and calcium hypochlorites are extremely corrosive and can cause severe damage to the eyes and skin, therefore they have been assigned to Toxicity Category I, indicating the highest degree of toxicity, for these acute effects. However, no subchronic or chronic studies on sodium and calcium hypochlorites are needed, due to their simple chemical nature and structure. In the presence of oxygen, these compounds react easily with organic matter and convert readily into sodium chloride (table salt) and calcium chloride (road salt). Widely used in disinfecting water supplies for nearly a century, the hypochlorites have been proven safe and practical to use. One concern with the use of sodium and calcium hypochlorites in treating water and wastewater systems is that they may result in the formation of trihalomethanes in drinking water which are considered potential carcinogens (Richardson et al., 2000). The use of protective clothing, including safety glasses or goggles and chemicalresistant gloves, is still required when handling and applying products that contain sodium or calcium hypochlorite as the active ingredient, due to the acute toxicity of these products. In addition, reentry levels must be met before entering swimming pools or hot tubs/spas treated with sodium or calcium hypochlorite, and reentry intervals must be observed before using sprayed or fogged food and nonfood contact surfaces. Concern for the potential hazards associated with chlorine reaction by-products and issues of wastewater disposal have heightened efforts to evaluate and register alternative water sanitation and surface disinfestation treatments for produce.

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9. DIETARY EXPOSURE Residues of sodium and calcium hypochlorites may remain on certain food crops as a result of their disinfectant uses. However, these residues pose no known hazard to human health. Preharvest and postharvest uses of calcium hypochlorite on all agricultural commodities are exempted from the requirement of a tolerance, or legal residue limit, because they pose no known hazard to the public health. Sodium hypochlorite is among the few substances which are “generally recognized as safe,” or generally recognized as safe (GRAS). Food additive regulations are established for several food processing uses of the hypochlorites. Sodium hypochlorite may be used in washing and lye peeling of fruits and vegetables. Sodium or calcium hypochlorite may be used as a final sanitizing rinse on food processing equipment.

10. ENVIRONMENTAL FATE The environmental fate data requirements for the hypochlorite salts are primarily satisfied by the document, Ambient Water Quality Criteria for Chlorine (EPA, 2000). In fresh water, the hypochlorites breakdown rapidly into nontoxic compounds when exposed to sunlight. In seawater, chlorine levels decline rapidly; however, hypobromite (which is acutely toxic to aquatic organisms) is formed. The EPA believes that the risk of acute exposure to aquatic organisms is sufficiently mitigated by precautionary labeling and making requirements for pollutant discharge elimination system mandatory.

11. LEGAL CONCERNS The use of chlorination for produce washing (chlorinated water in direct contact with produce) has been banned in a few countries other than the United States and may affect the export of chlorinated produce. Concern for the potential hazards associated with reaction by-products of chlorine and wastewater disposal have heightened the efforts to evaluate and register alternative water disinfection and surface sanitizer treatments for produce and postharvest handling. Organic growers must use chlorine with caution, as it is classified as a restricted material. The California Certified Organic Farmers regulations permit a maximum of 4 ppm residual chlorine, measured downstream of the product wash (Anon., 1997). Growers certified by other agencies should check with their certifying agent.

12. CONCLUSION Hypochlorite salts of chlorine are widely used for both washing produce and sanitizing equipment, tools, and surfaces in the packinghouse. Among different chlorine disinfectants sodium and calcium hypochlorites are widely used for postharvest disinfection of

Sodium and Calcium Hypochlorite as Postharvest Disinfectants

fruits and vegetables. These two agents are readily available in the market, inexpensive, and can be easily incorporated into washing solutions due to their soluble nature. These are widely used for disinfection of fruits and vegetables. However, concentration of these chemicals should be taken care while using with different types of commodities as higher concentration of these chemicals may damage some sensitive commodities like leafy vegetables. Besides, other key points like pH of the solution, temperature, exposure time, etc., must be taken into consideration while using these salts for postharvest disinfection of fruits and vegetables. These salts come under GRAS category and can be safely used as a surface disinfectant for food surfaces.

REFERENCES Allende, A., Gonzalez, R.J., McEvoy, J., Luo, Y., 2008. Assessment of sodium hypochlorite and acidified sodium chlorite as antimicrobial agents to inhibit growth of Escherichia coli O157:H7 and natural microflora on shredded carrots. Int. J. Veg. Sci. 13, 51–63. Allende, A., McEvoy, J., Tao, Y., Luo, Y., 2009. Antimicrobial effect of acidified sodium chlorite, sodium chlorite, sodium hypochlorite, and citric acid on Escherichia coli O157:H7 and natural microflora of freshcut cilantro. Food Control 20, 230–234. Andrew, J.M., Kristy, L.M., et al., 2010. Sodium hypochlorite: a promising agent for reducing Botrytis cinerea infection on rose flowers. Postharvest Biol. Technol. 58 (3), 262–267. Anon., 1997. Safety first. Potato Business World 5 (6), 13–14. Artes, F., Gomez, P., et al., 2009. Sustainable sanitation techniques for keeping quality and safety of fresh cut plant commodities. Postharvest Biol. Technol. 51, 287–296. Beuchat, L.R., 2000. Use of sanitizers in the raw fruits and vegetables processing. In: Alzamora, S.M., Tapia, M.S., Malo, L. (Eds.), Minimally Processed Fruits and Vegetables: Fundamental Aspects and Applications. Aspen Publications, Gaitherburg, ND, pp. 63–78. Beuchat, R.L., Nail, B.V., Adler, B.B., Clavero, M.R.S., 1998. Efficacy of spray application of chlorinated water in killing pathogenic bacteria on raw apples, tomatoes and lettuce. J. Food Prot. 61, 1305–1311. Blatchley III, E.R., 1994. Disinfection and antimicrobial processes. Water Environ. Res. 66 (4), 361–368. Bloomfield, S.F., 1996. Chlorine and Iodine Formulations. In: Ascenzi, J.M. (Ed.), Handbook of Disinfectants and Antiseptics. Marcel Dekker, Inc., New York, NY, pp. 133–158 Boyette, M.D., Ritchie, D.F., et al., 1993. Chlorination and postharvest disease control. AG NC Agric. Ext. Serv. 414–416. Brackett, R.E., 1994. Microbiological spoilage and pathogens in minimally processed refrigerated fruits and vegetables. In: Wiley, R.C. (Ed.), Minimally Processed Refrigerated Fruits and Vegetables. Chapman and Hall, New York, pp. 269–312. Combrink, J.C., Grobbelaar, C.J., 1984. Influence of temperature and chlorine treatments on post-harvest decay of apples caused by Mucor piriformis. Technical Communication, 0(192), South Africa Department of Agriculture and Water Supply, No. 192, pp. 19–20. Combrink, J.C., Visagie, T.R., 1982. Chlorination of dump tank water to reduce post-harvest rot in apples. DFGA 32 (pt. 2), 61–63 (66). Dychdala, G.R., 1983. Chlorine and Chlorine Compounds. In: Block, S.S. (Ed.), Disinfection, Sterilization, and Preservation. Lea and Febiger, Philadelphia, PA, pp. 157–182. Endemann, G.E.F., 1969. The chlorination of dump tanks. S. Afr. Citrus J. 422 (21), 23–24. Environmental Protection Agency (EPA), 2000. Toxicological Review of Chlorine Dioxide and Chlorite. EPA/635/R-00/007. Fett, W.F., 2002a. Factors affecting the efficacy of chlorine against Escherichia coli O157: H7 and salmonella on alfalfa seed. Food Microbiol. 19, 135–149. Fett, W.F., 2002b. Reduction of Escherichia coli O157:H7 and Salmonella spp. on laboratory-inoculated mung bean seed by chlorine treatment. J. Food Prot. 65, 848–852.

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Food and Drug Administration (FDA), 2009. Indirect Food Additives: Adjuvants, Production Aids, and Sanitizers. Code of Federal Regulations Title 21, vol. 3, part 178, Section 178.1010. Grubinger, V., 2008. Post-Harvest Washing of Fresh Produce to Reduce Food Safety Risks. University of Vermont Extension, Brattleboro. Hrudey, S.E., 2009. Chlorination disinfection by-products, public health risk tradeoffs and me. Water Res. 43, 2057–2092. Inatsu, Y., Bari, M.L., et al., 2005. Efficacy of acidified sodium chlorite treatments in reducing Escherichia coli O157:H7 on Chinese cabbage. J. Food Prot. 68, 251–255. Kim, Y.H., Hensley, R., 1997. Effective control of chlorination and dechlorination at wastewater treatment plants using redox potential. Water Environ. Res. 69 (5), 1008–1014. McDonnell, G., Russell, A.D., 1999. Antiseptics and desinfectants: activity, action, and resistance. Clin. Microbiol. Rev. 12, 147–179. McGlynn, W., 2004. Food Technology Fact Sheet: Guidelines for the Use of Chlorine Bleach as a Sanitizer in Food Processing Operations. Oklahoma State University. Niemira, B.A., 2008. Irradiation compared with chlorination for elimination of Escherichia coli O157:H7 internalized in lettuce leaves: influence of lettuce variety. J. Food Sci. 73, 208–213. Nieuwenhuijsen, M.J., Toledano, M.B., Elliot, P., 2000. Uptake of chlorination disinfection by-products; a review and a discussion of its implications for exposure assessment in epidemiological studies. J. Expo. Anal. Environ. Epidemiol. 10, 586–599. Olmez, H., Kretzschmar, U., 2009. Potential alternative disinfection methods for organic fresh-cut industry for minimizing water consumption and environmental impact. LWT Food Sci. Technol. 42, 686–693. Rabin, J., 1986. Pack tomatoes for higher profits—chlorinating packing shed wash water improves quality. Am. Veg. Grow. 34 (8), 12. Richardson, S.D., Thruston Jr., A.D., Caughran, T.V., Chen, P.H., Collette, T.W., Schenck, K.M., Lykins Jr., B.W., Rav-Acha, C., Glezer, V., 2000. Identification of new drinking water disinfection byproducts from ozone, chlorine dioxide, chloramine, and chlorine. Water Air Soil Pollut. 123, 95–102. Richardson, S.D., Plewab, M.J., et al., 2007. Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products in drinking water: a review and roadmap for research. Rev. Mutat. Res. 636, 178–242. Rushing, J.W., Angulo, J.J., et al., 1996. Implementation of a HACCP program in a commercial freshmarket tomato packinghouse: a model for the industry. Dairy Food Environ. Sanit. 16 (9), 549–553. Sanz, S., Gimenez, M., et al., 2002. Effectiveness of chlorine washing disinfection and effects on the appearance of artichoke and borage. J. Appl. Microbiol. 93, 986–993. https://doi.org/10.1046/j.13652672.2002.01773.x. Sapers, G.M., Gorny, J.R., Yousef, A.E. (Eds.), 2006. Microbiology of Fruits and Vegetables. CRC Press, Boca Raton, p. 634. Segall, A., 1968. Reducing postharvest decay of tomatoes by adding a chlorine source and the surfactant Santormerse F85 to water in field washers. Fla. State Hort. Soc. Proc. 81, 212–214. Spotts, R.A., Cervantes, L.A., 1989. Evaluation of disinfestant-flotation salt-surfactant combinations on decay fungi of pear in a model dump tank. Phytopathology 79 (1), 121–126. Spotts, R.A., Peters, B.B., 1982. Use of surfactants with chlorine to improve pear decay control. Plant Dis. 66 (8), 725–727. Stopforth, J.D., Mai, T., Kottapalli, B., Samadpour, M., 2008. Effect of acidified sodium chlorite, chlorine, and acidic electrolyzed water on Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes inoculated onto leafy greens. J. Food Prot. 71, 625–628. Suslow, T., 1997. Chlorination in the production and postharvest handling of fresh fruits and vegetables. In: Fruit and Vegetable Processing. vo. 6, University of California, Davis, pp. 1–15. Tomas-Callejas, A., Lopez-Galvez, F., Sbodio, A., Artes, F., Artes-Hernandez, F., Suslow, T.V., 2012. Chlorine dioxide and chlorine effectiveness to prevent Escherichia coli O157:H7 and Salmonella crosscontamination on fresh-cut Red Chard. Food Control 23, 325–332.

FURTHER READING Anon., 1970. Prolong produce freshness. Food Eng. 42 (1), 115–116.

CHAPTER 15

Commercial Disinfectants in Skirmishing Postharvest Diseases Venkata Satish Kuchi*, Riadh Ilahy†, Mohammed Wasim Siddiqui‡ *

Department of Postharvest Technology, College of Horticulture, Dr. YSRHU, Anantharajupeta, India Laboratory of Horticulture, National Agricultural Research Institute of Tunisia, Ariana, Tunisia ‡ Department of Food Science and Postharvest Technology, Bihar Agricultural University, Sabour, Bhagalpur, India †

1. INTRODUCTION The most important attribute of fruits and vegetables is “Quality” which is the “degree of goodness or defencelessness” which can be professed by consumer. It cannot be improved after harvest, but proper postharvest handling procedures can maintain quality. To improve the food safety, it is essential to free the horticultural produce from microorganisms like bacterial and fungal pathogens. Disinfection of postharvest pathogens that accumulate on the fruit surface before and during harvest is a direct benefit to prevent decay after storage. Use of sanitized water for washing and cleaning the harvested produce is an essential step for prolonging storage life (Sargent et al., 2000). Quality of horticultural produce can be improved by using disinfectants, fungicides, germicides, natural chemical compounds, and generally recognized as safe (GRAS). Disinfectants are the agents, such as heat, irradiation or chemical, that disinfects by destroying, neutralizing, or inhibiting the growth of disease-carrying microorganisms. Sanitizers are used to reduce, but not necessarily eliminate, microorganisms from the inanimate environment to levels considered safe as determined by public health codes or regulations (https:// extension.psu.edu/what-is-a-disinfectant-or-sanitizer) whereas fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores (https://en.wikipedia.org/wiki/Fungicide), germicide is any substance that kills germs or other microorganisms. Ozone is a powerful germicide—the gas kills the germs almost immediately (https://www.collinsdictionary.com/dictionary/english/germicide). The GRAS fungicides that leave low or non-detectable residues in the commodity are actively sought in research programs, natural chemical compounds are the naturally occurring plant products that have antifungal properties. The most common disinfecting agent that can be applied as spray or dip is chlorine. Sanitation may be followed by treatment with one or more fungicides, which deposit a residue in the product that inhibits decay pathogens that infect later or escaped the action of the sanitizers. Sanitizers are also widely used to minimize contamination of produce with pathogens of human health concern (Go´mez-Lo´pez, 2012). Fungal decay pathogens Postharvest Disinfection of Fruits and Vegetables https://doi.org/10.1016/B978-0-12-812698-1.00015-7

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differ in many ways from human pathogens. Unlike Salmonella spp., Listeria spp., Escherichia coli, and other human pathogens and viruses, plant pathogens can grow rapidly within and digest the host tissue because the plant is a primary food source. A fundamental need when fruit and vegetables are handled is sanitation of harvest bins, wash solutions, rotary brushes, belts, grading, and other processing equipment (Adaskaveg et al., 2002).

2. ROLE OF DISINFECTANTS IN POSTHARVEST DISEASE MANAGEMENT On arrival at the packinghouse, in order to remove soil particles and other contaminants, fruits and vegetables should be washed with water containing disinfectants as disinfectantfree water contains fungal spores and bacteria that may infect the produce. The principal disinfectants used are chlorine compounds, ozone, ethanol, hydrogen peroxide, organic acids, and electrolyzed water (EW).

3. CHLORINE COMPOUNDS 3.1 Hypochlorite It is the most commonly used sanitizer in water purification and food industries. When fruits and vegetables are disinfected with this solution, pathogen propagules die rapidly and there will be cessation of infection. Commercially, chlorine gas, sodium hypochlorite (NaOCl), and calcium hypochlorite (CaCl2O2) are used (Suslow, 1997). Protonated hypochlorite (hypochlorous acid), the most active component, inactivated 95% of the conidia of Penicillium digitatum, the causal agent of citrus green mold (Smilanick et al., 2002).

3.2 Chlorine Dioxide This compound (ClO2) has equal or greater antimicrobial potency than chlorine. It is similar to hypochlorite in potency for the control of microorganisms, but since it is a dissolved gas with less oxidation strength it retains its activity better than the more reactive hypochlorite when suspended organic matter is high (White, 1999).

3.3 Ozone Among chlorine, chlorine dioxide, hydrogen peroxide, and peracetic acid, ozone (O3) is most potent biocide (Weavers and Wickramanayake, 2001). Its effect on microorganisms is a function of concentration, temperature, length of exposure, and the substrate on which they reside. Fungi are more resistant to ozone than nonspore-forming bacteria (Restaino et al., 1995). Two approaches were used to evaluate the storage of fresh products in ozone atmospheres: (1) low concentration, more number of days, and (2) a very

Commercial Disinfectants in Skirmishing Postharvest Diseases

high concentration at intervals during storage. Ozone gas toxicity is greatly influenced by humidity; if