Food Irradiation Research and Technology [1 ed.] 9780813808826, 0813808820

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Food Irradiation Research and Technology

The IFT Press series reflects the mission of the Institute of Food Technologists— advancing the science and technology of food through the exchange of knowledge. Developed in partnership with Blackwell Publishing, IFT Press books serve as essential textbooks for academic programs and as leading edge handbooks for industrial application and reference. Crafted through rigorous peer review and meticulous research, IFT Press publications represent the latest, most significant resources available to food scientists and related agriculture professionals worldwide.

IFT Book Communications Committee Ruth M. Patrick Dennis R. Heldman Theron W. Downes Joseph H. Hotchkiss Marianne H. Gillette Alina S. Szczesniak Mark Barrett Neil H. Mermelstein Karen Banasiak

IFT Press Editorial Advisory Board Malcolm C. Bourne Fergus M. Clydesdale Dietrich Knorr Theodore P. Labuza Thomas J. Montville S. Suzanne Nielsen Martin R. Okos Michael W. Pariza Barbara J. Petersen David S. Reid Sam Saguy Herbert Stone Kenneth R. Swartzel

Food Irradiation Research and Technology

EDITORS

Christopher H. Sommers • Xuetong Fan

Titles in the IFT Press series • Accelerating New Food Product Design and Development (Jacqueline H.P. Beckley, J.C. Huang, Elizabeth J. Topp, M. Michele Foley, and Witoon Prinyawiwatkul) • Biofilms in the Food Environment (Hans P. Blaschek, Hua Wang, and Meredith E.Agle) • Food Carbohydrate Chemistry (Ronald E.Wrolstad) • Food Irradiation Research and Technology (Christopher H. Sommers and Xuetong Fan) • Foodborne Pathogens in the Food Processing Environment: Sources, Detection and Control (Sadhana Ravishankar and Vijay K. Juneja) • High Pressure Processing of Foods (Christopher J. Doona, C. Patrick Dunne, and Florence E. Feeherry) • Hydrocolloids in Food Processing (Thomas R. Laaman) • Microbiology and Technology of Fermented Foods (Robert W. Hutkins) • Multivariate and Probabilistic Analyses of Sensory Science Problems (JeanFrancois Meullenet, Rui Xiong, and Chris Findlay) • Nondestructive Testing of Food Quality (Joseph Irudayaraj and Christoph Reh) • Nonthermal Processing Technologies for Food (Howard Q. Zhang, Gustavo V. Barbosa-Canovas, V.M. Balasubramaniam, Editors; C. Patrick Dunne, Daniel F. Farkas, James T.C.Yuan,Associate Editors) • Packaging for Nonthermal Processing of Food (J. H. Han) • Preharvest and Postharvest Food Safety: Contemporary Issues and Future Directions (Ross C. Beier, Suresh D. Pillai, and Timothy D. Phillips, Editors; Richard L. Ziprin,Associate Editor) • Regulation of Functional Foods and Nutraceuticals: A Global Perspective (Clare M. Hasler) • Sensory and Consumer Research in Food Product Design and Development (Howard R. Moskowitz, Jacqueline H. Beckley, and Anna V.A. Resurreccion) • Thermal Processing of Foods: Control and Automation (K.P. Sandeep) • Water Activity in Foods: Fundamentals and Applications (Gustavo V. BarbosaCanovas,Anthony J. Fontana Jr., Shelly J. Schmidt, and Theodore P. Labuza)

Christopher Sommers is a research microbiologist, and Xuetong Fan is a research food technologist. Both work for the Food Safety Intervention Technologies Research Unit, USDA-ARS-Eastern Regional Research Center, Wyndmoor, Pennsylvania. Sommers and Fan were co-moderators of the IFT symposium from which this book arose. Copyright © Blackwell Publishing and the Institute of Food Technologists 2006 All rights reserved Blackwell Publishing Professional 2121 State Avenue,Ames, Iowa 50014, USA Orders: Office: Fax: Web site:

1-800-862-6657 1-515-292-0140 1-515-292-3348 www.blackwellprofessional.com

Blackwell Publishing Ltd 9600 Garsington Road, Oxford OX4 2DQ, UK Tel.: +44 (0)1865 776868 Blackwell Publishing Asia 550 Swanston Street, Carlton,Victoria 3053,Australia Tel.: +61 (0)3 8359 1011 Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by Blackwell Publishing, provided that the base fee of $.10 per copy is paid directly to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923. For those organizations that have been granted a photocopy license by CCC, a separate system of payments has been arranged.The fee codes for users of the Transactional Reporting Service are ISBN13: 978-0-8138-0882-6; ISBN-10: 0-8138-0882-0/2006 $.10. First edition, 2006 Library of Congress Cataloging-in-Publication Data Food irradiation research and technology/edited by Christopher H. Sommers and Xuetong Fan.—1st ed. p. cm.—(IFT Press series) Includes bibliographical references and index. ISBN-13: 978-0-8138-0882-6 (alk. paper) ISBN-10: 0-8138-0882-0 (alk. paper) 1. Radiation preservation of food—Research. 2. Irradiated beef. I. Sommers, Christopher H. II. Fan, Xuetong. III. Series. TP371.8.F676 2006 664⬘.0288—dc22 2005028697 The last digit is the print number: 9 8 7 6 5 4 3 2 1

CONTENTS List of Contributors Preface

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Chapter 1. Introduction: Food Irradiation Moving On Joseph Borsa

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Chapter 2. Advances in Gamma Ray, Electron Beam, and X-ray Technologies for Food Irradiation Marshall R. Cleland

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Chapter 3. Regulation of Irradiated Foods and Packaging George H. Pauli

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Chapter 4. Toxicological Safety of Irradiated Foods Christopher H. Sommers, Henry Delincée, J. Scott Smith, and Eric Marchioni

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Chapter 5. Consumer Acceptance and Marketing of Irradiated Foods Ronald F. Eustice and Christine M. Bruhn

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Chapter 6. Detection of Irradiated Foods Eric Marchioni

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Chapter 7. Dosimetry for Food Processing and Research Applications Kishor Mehta and Kevin O’Hara

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Chapter 8. Mechanisms and Prevention of Quality Changes in Meat by Irradiation Doug U. Ahn and E.J. Lee

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Chapter 9. Irradiation as a Phytosanitary Treatment for Fresh 143 Horticultural Commodities: Research and Regulations Peter A. Follett and Robert L. Griffin

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Contents

Chapter 10. Low-Dose Irradiation of Fresh and Fresh-Cut Produce: Safety, Sensory, and Shelf Life Brendan A. Niemira and Xuetong Fan

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Chapter 11. Irradiation of Seafood with a Particular Emphasis 185 on Listeria monocytogenes in Ready-to-Eat Products Denise M. Foley Chapter 12. Ionizing Radiation of Eggs I. Álvarez, B.A. Niemira, X. Fan, and C.H. Sommers

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Chapter 13. Irradiation Treatment of Nuts Akua Kwakwa and Anuradha Prakash

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Chapter 14. Irradiated Ground Beef for the National School Lunch Program Xuetong Fan

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Chapter 15. Potential Applications of Ionizing Radiation Myung-Woo Byun, Cheorun Jo, and Ju-Woon Lee

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Chapter 16. A Future Uncertain: Food Irradiation from a Legal Perspective Denis W. Stearns

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Chapter 17. Technical Challenges and Research Directions in Electronic Food Pasteurization Suresh D. Pillai, Les Braby, and Joe Maxim

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Index

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LIST OF CONTRIBUTORS Doug U. Ahn Animal Science Department, Iowa State University,Ames, IA 50011, U.S.A. Phone: (515) 294-6595. E-mail: [email protected] Chapter 8 Ígnacio Álvarez Tecnología de los Alimentos, Facultad de Veterinaria, University of Zaragoza, 50013, Zaragoza, Spain. Phone: +34976761581. E-mail: [email protected] Chapter 12 Joseph Borsa MDS Nordion, Ottawa, Canada K2K 1X8, Canada. Phone: (613) 592-2790. E-mail: [email protected] Chapter 1 Les Braby National Center for Electron Beam Food Research, Institute of Food Science & Engineering,Texas A&M University, College Station,TX 77845, U.S.A. Phone: (979) 862-1798. E-mail: [email protected] Chapter 17 Christine M. Bruhn Center for Consumer Research, Department of Food Science & Technology, University of California, Davis, CA 95616, U.S.A. Phone: (530) 752-2774. E-mail: [email protected] Chapter 5 Myung-Woo Byun Radiation Food Science & Biotechnology Team,Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, 1266, Sinjeong-dong, Jeongeup, 580-185, Republic of Korea. Phone: (82) 63 570 3200. E-mail: [email protected] Chapter 15

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List of Contributors

Marshall R. Cleland IBA Techninogy Group, IBA-RDI E-Beam X-Ray Solutions, Edgewood, NY 11717, U.S.A. Phone: (631) 979-8718. E-mail: [email protected] Chapter 2 Henry Delincée Federal Research Centre for Nutrition and Food, Institute of Nutritional Physiology, Haid-und-Neu-Str. 9, 76131 Karlsruhe, Germany. Phone: +49 721-6625-401. E-mail: [email protected] Chapter 4 Ronald F. Eustice Executive Director, Minnesota Beef Council, 2950 Metro Drive # 102, Minneapolis, MN 55425, U.S.A. Phone: (952) 854-6980. E-mail: [email protected] Chapter 5 Xuetong Fan Eastern Regional Research Center,Agricultural Research Service, U.S. Department of Agriculture,Wyndmoor, PA 19038, U.S.A. Phone: (215) 836-3785. E-mail: [email protected] Chapter 10, Chapter 12, Chapter 14 Denise M. Foley Department of Biological Sciences, Chapman University, One University Drive, Orange, CA 92866, U.S.A. Phone: (714) 628-7209. E-mail: [email protected] Chapter 11 Peter A. Follett USDA,ARS, Pacific Basin Agriculture Research Center, Hilo, HI 96720, U.S.A. Phone: (808) 959-5470. E-mail: [email protected] Chapter 9 Robert L. Griffin USDA,APHIS, Plant Epidemiology and Risk Analysis Laboratory, Raleigh, NC 27606, U.S.A. Phone: (770) 228-7303. E-mail: [email protected] Chapter 9

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Cheorun Jo Radiation Food Science & Biotechnology Team,Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, 1266, Sinjeong-dong, Jeongeup, 580-185, Republic of Korea. Phone: (82) 63 570 3200. E-mail: [email protected]. Chapter 15 Akua Kwakwa Department of Physical Sciences, Chapman University One University Drive, Orange, CA 92866, U.S.A. Phone: (714) 744-7826. Chapter 13 E.J. Lee Animal Science Department, Iowa State University,Ames, IA 50011, U.S.A. Chapter 8 Ju-Woon Lee Radiation Food Science & Biotechnology Team,Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, 1266, Sinjeong-dong, Jeongeup, 580-185, Republic of Korea. Phone: (82) 63 570 3200 Chapter 15 Eric Marchioni Laboratoire de Chimie Analytique et Sciences de l’Aliment (UMR 7512), Faculté de Pharmacie, 74 Route du Rhin, F-67400 Illkirch Graffenstaden. Phone: 03.88.67.69.44. E-mail: [email protected] Chapter 4, Chapter 6 Joe Maxim National Center for Electron Beam Food Research, Institute of Food Science & Engineering,Texas A&M University, College Station,TX 77845, U.S.A. Phone: (979) 862-2036. E-mail: [email protected] Chapter 17 Kishor Mehta Senior Scientist Emeritus, IAEA, Bruenner Strasse 133-3-29,A-1210, Vienna,Austria. Phone: (43) 1-22 46 099. E-mail: [email protected] Chapter 7

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List of Contributors

Brendan A. Niemira Eastern Regional Research Center,Agricultural Research Service, U.S. Department of Agriculture,Wyndmoor, PA 19038, U.S.A. Phone: (215) 836-3784. E-mail: [email protected] Chapter 10, Chapter 12 Kevin O’Hara MDS Nordion, 447 March Road, Ottawa Ontario, K2K 1X8, Canada. Phone: (613) 592-3400 Ext. 2524. E-mail: [email protected] Chapter 7 George H. Pauli Associate Director for Science and Policy, HFS-205, Office of Food Additive Safety, Center for Food Safety and Applied Nutrition, Food and Drug Administration, 5100 Paint Branch Parkway, College Park, MD 20740-3835, U.S.A. Phone: (202) 418-3090. E-mail: [email protected] Chapter 3 Suresh D. Pillai National Center for Electron Beam Food Research, Institute of Food Science & Engineering,Texas A&M University, College Station,TX 77845, U.S.A. Phone: (979) 845-1921. E-mail: [email protected] Chapter 17 Anuradha Prakash Department of Physical Sciences, Chapman University, One University Drive, Orange, CA 92866, U.S.A. Phone: (714) 744-7895. E-mail: [email protected] Chapter 13 J. Scott Smith The Food Science Institute,Animal Science and Industry, 2008 Call Hall, Kansas State University, Manattan, KS 66506, U.S.A. Phone: (785) 532-5681. E-mail: [email protected] Chapter 4

List of Contributors Christopher H. Sommers U.S. Department of Agriculture,Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane,Wyndmoor, PA 19038, U.S.A. Phone: (215) 836-3754. E-mail: [email protected] Chapter 4, Chapter 12 Denis W. Stearns Marler Clark,Attoneys at Law, Seattle,WA 98104, U.S.A. Phone: (206) 346-1892. E-mail: [email protected] Chapter 16

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PREFACE Christopher H. Sommers, Ph.D.

Food Irradiation Is Already Here* At present there are approximately 60 commercial irradiation facilities operating in the United States. Many food scientists and technologists are unaware that the “food irradiation industry” is only a small part of a much larger industrial group dedicated to radiation processing. Every two years the International Meeting on Radiation Processing (IMRP) convenes, and presentations are made on the radiation processing of materials, medical and pharmaceutical products, cosmetics, vaccines, advances in irradiation technology and facilities, radiation dosimetry, and more. Published in Radiation Physics and Chemistry (Vol. 71[1-2], 2004), the collection of papers presented at IMRP-2003 in Chicago is 606 pages long and weighs in at 1 kilogram. It contains publications on the irradiation of spices, nutraceuticals, seafood, meat and poultry, and fruits and vegetables for inactivation of bacterial pathogens and parasites and phytosanitary purposes. Irradiation of food and agricultural products, as part of the larger radiation processing industry, is currently allowed by about 60 countries around the globe. In 1997, the U.S. Food and Drug Administration approved the use of ionizing radiation to inactivate pathogenic bacteria in red meat.Although some scientists and public health officials are frustrated by the slow pace with which irradiated ground beef is penetrating the U.S. market, I question whether that frustration is warranted. Many food scientists forget that it took almost 50 years for pasteurized milk to be accepted by the public in the United States. At the 2005 IFT Annual Meeting and Food Expo in Las Vegas, Ron Eustice of the Minnesota Beef Council reminded us that processors such as Sadex, Inc. (Sioux City, IA), Food Technology *Edited and reprinted from Sommers, C.H. Food Irradiation Is Already Here. Food Technology 58 (4):22. 2004.

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Services (Mulberry, FL), and the Institute for Food Science and Engineering (Texas A&M University) are still supplying irradiated meat and poultry to thousands of stores across the United States, even after the demise of Surebeam Corporation. In September 2004, Rochester, NY–based Wegman’s Food Markets, Inc. announced that Huisken BeSure™ irradiated beef patties are available at supermarkets in New York, New Jersey, and Pennsylvania. Thus, irradiated meat and poultry have not gone away. Although introduced too late in the 2004 school year to allow orders to be placed, irradiated ground beef was made available, on a voluntary basis, as part of the National School Lunch Program administered by the USDA’s Agricultural Marketing Service (AMS) and Food and Nutrition Service (FNS).Within the last year, the Child Nutrition Improvement and Integrity Act was amended to codify the procurement, labeling, and educational programs already developed by FNS and AMS for irradiated ground beef. Most important, Congress mandated that “States and school food service authorities are provided model procedures for providing factual information on the science and evidence regarding irradiation technology. . . .” The word “factual” is critical to the education process concerning irradiated foods. At USDA ARS’s Eastern Regional Research Center in Wyndmoor, PA, we investigate an array of thermal and nonthermal intervention technologies to improve the microbiological safety and quality of foods; such technologies include high-pressure processing, radio frequency electric fields, competitive microbial exclusion, UHT pasteurization, and vacuum-steam-vacuum surface treatment. In contrast to the private sector, we do not promote the use of specific technologies, such as irradiation, over that of others that would achieve the same objective. In other words, we are interested in objectively and comparatively evaluating the efficacy of a whole range of intervention technologies. That being said, what are the facts surrounding irradiation of ground beef? (1) Irradiation can inactivate pathogenic bacteria occasionally found in ground beef such as E. coli O157:H7, Salmonella, Staphylococcus aureus, and Listeria monocytogenes; (2) irradiation of food, including ground beef, does not make food radioactive; (3) irradiation, when used appropriately, does not change the aroma, taste, aftertaste, texture, or overall liking of ground beef, including frozen ground beef supplied as part of the National School Lunch Program; (4) there is no detectable increase in the risk of cancer associated with long-term consumption of radiation-pasteurized meat as determined by multispecies, multigeneration feeding studies conducted in animals; (5) irradiated ground beef is nutritious and wholesome; and (6) irradiation is effective

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only as part of a comprehensive program designed to improve the microbiological safety of ground beef, not to “clean up” unacceptable product. As scientists and technologists, we have a responsibility to ensure that educational materials provided to the public regarding food safety and processing technologies are based on sound science and fact, as opposed to misconceptions. Food Irradiation Research and Technology meets that goal.

Acknowledgements We would like to thank the Institute of Food Technologists and the IFT Non-Thermal Processing Division for their support, and Mark Barrett and Dede Pedersen for the guidance and patience during the completion of this work. We would also thank the contributors and authors to this book, who are experts in the field of food irradiation, chemistry, physics, consumer acceptance and education, and the law as applies to foodborne illness.

Food Irradiation: Research and Technology Edited by Christopher H. Sommers, Xuetong Fan Copyright © Blackwell Publishing and the Institute of Food Technologists 2006

Food Irradiation Research and Technology

Food Irradiation: Research and Technology Edited by Christopher H. Sommers, Xuetong Fan Copyright © Blackwell Publishing and the Institute of Food Technologists 2006

Chapter 1 INTRODUCTION: FOOD IRRADIATION MOVING ON Joseph Borsa, Ph.D.

Introduction There’s an old Chinese proverb that says, “May you live in interesting times.”With respect to food irradiation (Borsa 2000), today’s proponents and other observers of this technology have good reason to feel that indeed these are interesting times in this unfolding story. Studied intensively for more than half a century, and approved in some 50 countries around the globe for a wide variety of food products (ICGFI 2005), irradiation has been widely used for spices and other food ingredients for many years, but for perishables (meat and produce) it is just now emerging into a significant commercial reality.This essay focuses primarily on these emerging applications, in which just in the past half dozen years or so the changes in what we might call the food irradiation landscape have been dramatic and at times go well beyond that. These changes have been most pronounced in the United States but the effects are beginning to be felt in other countries around the globe as well. In the United States from basically a standing start at the beginning of this recent period, but powered by a high level of entrepreneurial energy and zeal, commercialization of irradiation technology in the food industry accelerated rapidly to reach heights far beyond anything previously achieved. Almost overnight, irradiated products appeared in literally thousands of retail and foodservice outlets (SureBeam 2001). Investors took notice (Titan Corp 2001) and millions of dollars were raised for ventures targeting the opportunity presented by the very real needs recognized in food safety (Osterholm and Norgan 2004) and quarantine security (IAEA 2004). The fact that those needs are evident all over the world added to the investment appeal. In these positive circumstances, 3

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interest in food irradiation rapidly escalated, giving rise to an exciting play in the investment world. Unfortunately, in 2004 a major business miscalculation intervened and this nascent industry suffered a significant setback just as it appeared to be getting over the hurdles associated with its launch. Not surprisingly, and to the great satisfaction of the skeptics and antitechnology activists, unreasonable expectations had exceeded the actual pace of adoption, especially by the major food processors, and the simple but inexorable math of the business world led SureBeam™, the most prominent player in the field, to declare bankruptcy (Egerstrom 2004).This failure caused considerable consternation and uncertainty in the fledgling industry, raising concerns as to whether it would survive the setback. Now, more than a year later and with the dust largely settled, it appears that emerging from this uncertainty is a restructured food irradiation industry that is gradually regaining momentum.The fundamental benefits offered by the technology remain the same (Olson 2004) and the new path forward, although lacking the brash boldness and dash of the SureBeam™ approach, offers prospects for a more sustainable long-term future.

Two Tracks Going Forward Two major separate driving forces are moving adoption of food irradiation forward. One is the need to effect microbial reduction, primarily for purposes of food safety enhancement. This need is associated especially with those foods that are derived from animals, although similar food safety needs are increasingly being recognized for fresh fruits and vegetables (Sewall and Farber 2001). Shelf-life extension constitutes a significant additional incentive for adoption of this technology, and in some specific applications it may serve as the primary benefit being sought. The second major driver is the need for an effective and environmentally friendly technology to disinfest fruits and vegetables for quarantine security purposes associated with interregional trade (NAPPO 2003). These two main driving forces translate into two distinct business opportunities on which the current implementation activities are centered. The Food Safety Track Irradiation with ionizing energy is very effective in killing many of the common microbial pathogens such as E. coli O157:H7, Listeria monocytogenes, Salmonella spp. and Vibrio spp., among others, that are significant contributors to foodborne illness. A major advantage of irradiation

Introduction: Food Irradiation Moving On

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for this purpose is that the food can be processed after it has been sealed in its final packaging, thereby reducing or eliminating entirely the possibility of recontamination following this treatment. This unique operational capability makes irradiation particularly suitable for (cold) pasteurization of ready-to-eat foods, such as hot dogs and other deli items, that are at risk of contamination with Listeria monocytogenes during postprocess slicing and packaging operations. How does irradiation fit into the overall food safety strategy, based on Hazard Analysis Critical Control Point (HACCP), which is now the dominant food safety paradigm in the food industry? Although the incidence of positive samples for both E. coli O157:H7 (USDA 2005) and Listeria monocytogenes (USDA 2003) has declined significantly since HACCP was made mandatory in the late 1990s, the need for further improvement remains.A simple calculation puts this into useful perspective.The latest sampling statistics from USDA-FSIS indicate that the incidence of ground beef samples testing positive for contamination with E. coli O157:H7 stands at 0.17% (USDA 2004). This translates into roughly 17 million pounds of such contaminated ground meat presumably randomly interspersed through the approximately 10 billion pounds of this product consumed annually in the United States. Expressed in terms of commonly consumed units of ground beef, this amount represents some 68 million average-size hamburger patties that are contaminated by this pathogen and which therefore have the potential to cause illness in consumers. Of course, this scenario is for only one pathogen; there are others, including some newly emerging ones, which multiply the risk. In the present situation eating such product with the documented levels of contamination becomes a statistical game of chance as to whether one gets exposed to this pathogen or not. Although the probability of falling ill due to consumption of a randomly selected hamburger borders on the infinitesimally small, this is one of those situations in which a very small probability multiplied by the very large number of people at risk amounts to a significant number of seriously sick people, as attested to by CDC statistics (Mead and others 1999). Of course, for those unlucky enough to actually become sick, or whose child gets hemolytic uremic syndrome (HUS), the talk of probabilities becomes irrelevant (STOP 2003).Thus the need for further improvement is still very real.The “zero tolerance” regulatory policy in effect for this pathogen (USDA 1999) reflects the seriousness of the hazard. In the context of HACCP irradiation is an excellent CCP (Molins and others 2001) for E. coli O157:H7 and other bacterial pathogens in ground beef and similar products. Its use would reduce the probability of contamination in the finished product by several orders of magnitude, de-

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pending on the specifics of any particular application. No other technology exists that can offer the convenience of processing in the final shipping cases, and even on pallets, while still treating every last gram of product to a standard that essentially guarantees absence of the target pathogen. Irradiation can offer to solid and semi-solid foods such as meat, poultry, and fish the same benefits that thermal pasteurization has brought to milk and other liquid products. In the past two years, since SureBeam™’s failure, two new irradiation plants for processing food for the purpose of microbial reduction have been commissioned in the United States. Of course, the ultimate success of these ventures will be decided in the market place, subject to all the realities, scrutiny, and judgments of the business world. On this basis it seems safe to predict that the days ahead will continue to provide “interesting times.” The Disinfestation Track Growth in international trade of agricultural products, especially tropical fruits and vegetables, is seen as a foundation component of the economic development strategy of many underdeveloped countries (World Trade Organization 2001). Disinfestation technology for quarantine security purposes is a critical enabler for such trade in agricultural products (Henson and Loader 2001). Currently, fumigation with methyl bromide is the predominant technology used for this purpose. However, the continuing availability of methyl bromide for this purpose is an open question, due to its ozone depleting potential. An international agreement (Montreal Protocol) is in effect to phase out the use of this chemical because of this negative effect on the environment (UNDP 2002). In addition, methyl bromide is phytotoxic to some commonly traded fruits and vegetables (Hallman 1998), bringing further pressure to bear to find a suitable alternative. Irradiation is increasingly being recognized as an excellent agent for disinfestation purposes, and there is considerable interest around the world in bringing this potential into reality. USDA-APHIS is playing a leading role in the effort to put in place the regulatory infrastructure needed to allow its use for products imported into the United States, as well as for export of American horticultural products. Success has already been achieved for irradiated products routinely being shipped from Hawaii to mainland United States (Hawaii Pride 2005). Efforts currently under way should lead, in the relatively short term, to expansion of the list of U.S. trading partner countries for which irradiation will be accepted as a suitable disinfestation measure for products shipped between them. It can be anticipated that successful establishment of irradiation as a quarantine se-

Introduction: Food Irradiation Moving On

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curity technology for trade involving the United States will rapidly lead to its use for this purpose in trade involving other trading partners.The recent commencement of shipment of irradiated Australian fruit to New Zealand (TVNZ 2004) represents a first step along this path. Currently, besides the Hawaiian and Australian/New Zealand examples, there is interest in and movement toward implementation of irradiation disinfestation as part of a trade-enabling infrastructure in several countries in different regions around the world, including the Asia-Pacific group and Latin America. The future for irradiation in this application looks bright indeed.

Bumps Still Remain on the Road Ahead Although implementation of food irradiation has taken great strides forward and is building momentum, it has not yet reached a condition of clear sailing. Several troublesome hindrances remain, which need to be addressed. On the regulatory front, much remains to be done, even in the United States, where most of the implementation progress to date has taken place. Specifically, petitions for clearance of irradiation for several categories of food that could benefit from this treatment continue to languish somewhere in the evaluation process.These include petitions for readyto-eat foods and for seafood. Elsewhere, an encouraging sign is that in some parts of the world, as in Brazil (ICGFI 2005), the authorities have granted blanket approval for irradiation of all foods, consistent with Codex Alimentarius recommendations (Codex 2003). Perhaps this will encourage other member states of Codex Alimentarius to base their national regulations for food irradiation on the international standard to which they are party. It seems likely that as food irradiation registers more and more successes, countries currently on the sidelines will join the growing movement toward greater acceptance and utilization of this powerful technology. Regulatory requirements for the labeling of foods that have been irradiated remain a deterrent to some processors who would otherwise use it on their products. This issue has been under review for several years now, but to date no suitable alternative has been put forth that would satisfy both the needs of industry to inform but not alarm consumers, and the consumers’ right to know.Also very important is the need to extend the list of clearances for irradiation of food packaging materials, to include more of the common modern polymers and films (ICGFI 2005). At present there is a major logistical impediment, stemming from the

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scarcity of processing capacity within reach of many food manufacturers that are interested in using irradiation.This difficulty can be alleviated only by building new capacity in strategic locations to provide easy access for those wishing to use it. Installation of contract service irradiators in distribution centers and cold storage warehouses that serve many clients would be a logical and cost-effective approach to meeting this logistical need. Such locations have the advantage of easy and convenient access for their clients without incurring any additional transportation costs. New irradiation systems currently available (Stichelbaut and Herer 2004) that can process fully loaded pallets of food allow seamless interfacing between the irradiation facility and the existing warehouse, distribution, and transportation networks that use pallets as the basic unit of product handling. Another challenge is that with some products the maximum dose that can be tolerated without sensory degradation is low enough that it can be difficult to effect the wanted benefit to the extent desired. Excellent research progress in improving the effectiveness of irradiation in such difficult cases is being made. Different approaches involve one or more of increasing the product tolerance to radiation (Kalsec 2005), increasing the sensitivity of pathogens to radiation so that lower doses can effect the needed kill (Chiasson and others 2004), and improvements to irradiator design permitting the delivery of more uniform dose distributions in product stacks (Stichelbaut and Herer 2004), thereby reducing the regions of overdose wherein the sensory degradation is most likely to occur.These and other technical issues will undoubtedly serve as the focus of research at universities and other institutions for some time to come. Summary Implementation of food irradiation continues to move forward. The biggest gains are happening in the United States, but progress is being made in other parts of the world as well. Both the food safety and the disinfestation applications are growing, with the disinfestation application being especially active. It seems likely that this expansion will continue for an extended period of time, perhaps decades. References Borsa J. 2000. Irradiation of Foods. In: Francis JF, editor.Wiley Encyclopedia of Food Science and Technology. 2nd ed.Vol. 3. New York: John Wiley & Sons. p.1428–1436. Chiasson F, Borsa J, Ouattara B, and Lacroix M. 2004. Radiosensitization of Escherichia coli and Salmonella Typhi in Ground Beef. J Food Protection 67 (6):1157–1162.

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Codex. 2003. Revised Codex General Standard For Irradiated Foods. Codex Stan 106-1983, Rev.1-2003. ftp://ftp.fao.org/codex/standard/en/CXS_106e_1.pdf Egerstrom L. 2004. Midwestern Meat Processors Scramble as Irradiation Firm Liquidates. Knight Ridder Business News, January 15. Hallman GJ. 1998. Efficacy of Methyl Bromide and Cold Storage as Disinfestation Treatments for Guavas Infested with Caribbean Fruit Fly.Tropical Science 38(4):229–232. Hawaii Pride. 2005. www.hawaiipride.com Henson S,Loader R.2001.Barriers to Agricultural Exports from Developing Countries:The Role of Sanitary and Phytosanitary Requirements.World Development (Oxford) 29(1):85–102. IAEA. 2004. Irradiation as a Phytosanitary Treatment of Food and Agricultural Commodities. IAEA-TECDOC-1427. IAEA,Vienna. 181 p. ICGFI. 2005. Clearance Database. www.iaea.org/icgfi/data.htm Kalsec. 2005. Managing Oxidation in Irradiated Meats. http://www.kalsec.com/products/ oxid_irrad_over.cfm Mead PS, Slutsker L, Dietz L, McCaig LS, Bresee JS, Shapiro C, Griffin PM, Tauxe RV. 1999. Emerg Infect Dis 5(5):607–625. Molins RA, Motarjemi Y, Kaferstein FK. 2001. Irradiation: A Critical Control Point In Ensuring The Microbiological Safety Of Raw Foods. Food Control 12(6):347–356. NAPPO. 2003. NAPPO Regional Standards Phytosanitary Measures (RSPM). RSPM No.19. Guidelines for Bilateral Workplans. www.nappo.org/Standards/NEW/RSPM19-e.pdf Olson D. 2004. Food Irradiation Future Still Bright. Food Technology 58(7):112. Osterholm MT, Norgan AP. 2004.The Role of Irradiation in Food Safety. New England J Med 350(18):1898–1901. Sewall AM, Farber JM. 2001. Foodborne Outbreaks in Canada Linked to Produce. J Food Protection 64(11):1863–1877. Stichelbaut F, Herer A. 2004.The Palletron: An X-ray Pallet Irradiator Designed for Food Products. Paper 49H-32. 2004 IFT Annual Meeting, July 12–16, Las Vegas, NV. http:// ift.confex.com/ift/2004/techprogram/paper_24302.htm STOP. 2003. Why Are People Still Dying From Contaminated Food? www.safetables.org/ pdf/STOP_Report.pdf SureBeam. 2001. Fact vs. Fiction: SureBeam Turns The Tide on Irradiated Foods. (Brief Article) Progressive Grocer 80(8):30. Titan Corp. 2001. Press release. March 16. SureBeam IPO priced at $10.00 per share. www.titan.com/investor/archives/pressreleases/2001/010316_surebeam.html TVNZ. 2004. Nuked Mangoes To Hit NZ Shops. TVNZ One News. 20 December. http:// tvnz.co.nz/view/news_national_story_skin/465318%3fformat=html UNDP. 2002. The Vienna Convention and the Montreal Protocol. http://www.undp.org/ seed/eap/montreal/montreal.htm USDA. 1999. Policy on Beef Products Contaminated with E. coli O157:H7. Federal Register: January 19. 64(11):2803–2805. http://www.fsis.usda.gov/OPPDE/rdad/FRPubs/ 97-068N.htm USDA. 2003. Listeria In FSIS Ready-To-Eat Products Shows Significant Decline. http:// www.fsis.usda.gov/OA/news/2003/rtedata.htm USDA. 2004. Microbiological Results of Raw Ground Beef Products Analyzed for Escherichia coli O157:H7. http://www.fsis.usda.gov/Science/2004_EColi_Positive_Results/ index.asp USDA. 2005. FSIS Ground Beef Sampling Shows Substantial E. coli O157:H7 Decline In 2004. http://www.fsis.usda.gov/News_&_Events/NR_022805_01/index.asp World Trade Organization. 2001. Trade and Development. http://www.wto.org/english/ tratop_e/devel_e/devel_e.htm

Food Irradiation: Research and Technology Edited by Christopher H. Sommers, Xuetong Fan Copyright © Blackwell Publishing and the Institute of Food Technologists 2006

Chapter 2 ADVANCES IN GAMMA RAY, ELECTRON BEAM,AND X-RAY TECHNOLOGIES FOR FOOD IRRADIATION Marshall R. Cleland, Ph.D.

Introduction Irradiation with ionizing energy is widely used to improve the physical, chemical, and biological properties of materials and commercial products.These diverse applications include curing solvent-free inks, coatings, and adhesives, crosslinking plastic and rubber materials, curing fiberreinforced plastic products, extracting nitrogen and sulfur oxides from combustion gases to reduce acid rain, decomposing toxic compounds in waste water, sterilizing medical devices and pharmaceuticals, and controlling insects and pathogenic organisms in fresh foods. Gamma rays from radioactive nuclides, energetic electrons from particle accelerators, and X-rays emitted by high-energy electron beams are suitable sources of ionizing energy for these applications because they can penetrate substantial thicknesses of solid materials. In comparison, ultraviolet (UV) radiation is used mainly for the treatment of surfaces, thin films, clear water, and air because of its shallow penetration in opaque materials. Typical UV radiation sources cannot provide enough photon energy to produce ionization in most materials. Gamma rays, energetic electrons, and X-rays transfer their energies to materials by ejecting atomic electrons, which can then ionize other atoms in a cascade of collisions.Therefore all of these energy sources can produce similar effects in any irradiated material. The choice of a radiation source for a particular application depends on such practical aspects as thickness and density of the material, dose uniformity ratio, minimum dose, processing rate, and economics. 11

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This chapter describes the characteristics of these ionizing energy sources, their relevant physical properties, methods for generating enough radiation power to meet industrial requirements, and some examples of processing facilities.

Basic Irradiation Concepts Definition and Units of Absorbed Dose The absorbed dose is proportional to the ionizing energy absorbed per unit mass of irradiated material.The effects of the treatment are related to this quantity, which is the most important specification for any irradiation process. The international unit of absorbed dose is the gray (Gy) (McLaughlin and others. 1989). 1 Gy = 1 joule/kilogram (J/kg) 1 Gy = 1 watt-second/kilogram (W-s/kg) 1 kGy = 1 kilojoule/kilogram (kJ/kg) 1 kGy = 1 kilowatt-second/kilogram (kW-s/kg) The obsolete unit of absorbed dose is the rad.This unit is often seen in older papers and is still used in some industries. 1 Gy = 100 rad 10 Gy = 1 krad 100 Gy = 10 krad 1 kGy = 100 krad 10 kGy = 1 Mrad 100 kGy = 10 Mrad Absorbed Dose vs. Emitted Radiation Power The definition of absorbed dose given above can be expressed by the following equation: Da = Fp P T / M

(1)

where Da is the average dose in kilograys (kGy), P is the emitted power of the radiation source in kilowatts (kW),T is the treatment time in seconds (s), and M is the mass of the material in kilograms (kg). Fp is a dimensionless factor that accounts for the fraction of emitted power absorbed by the material. In a typical industrial irradiation process, Fp may be in the range

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13

from 0.25 to 0.50.This power fraction depends on the size and shape of the object and the way it is oriented in the radiation field. Rearranging Equation (1) gives the mass processing rate (ASTM 2002a). M / T = Fp P / Da

(2)

This relationship can be called a unity rule because the processing rate is 1 kg/s with an emitted power of 1 kW, an average dose of 1 kGy, and a power absorption fraction of 1.0. Although these values do not correspond to most industrial processes, the unity rule is easy to remember and it provides a basis for quickly estimating actual processing rates by scaling with the appropriate values of Fp, P, and Da. The dose distribution within an irradiated object is seldom uniform, but it can be determined by Monte Carlo calculations (ASTM 2002b) or by dose mapping (ASTM 2003). For applications where the minimum dose (Dmin) is more important than the average dose Da, Equations (1) and (2) can be modified by replacing Da with Dmin and replacing Fp with fp, a reduced value of the power absorption fraction.The factor fp is based on the simplifying assumption that all parts of the object have received only the minimum dose (Cleland and others. 2002). Temperature Rise vs. Dose The absorption of thermal energy in any material causes a temperature rise according to the following equation: ⌬T = H / c

(3)

where ⌬T is the temperature rise in degrees Celsius (°C), H is the thermal energy absorbed in joules per gram (J/g), and c is the thermal capacity of the material in joules per gram per degree Celsius (J/g/°C). By analogy, the absorption of ionizing energy in any material causes a temperature rise according to the following equation: ⌬T = Da / c

(4)

where ⌬T is the temperature rise in degrees Celsius (°C), Da is the average absorbed dose in kilograys (kGy), and c is the thermal capacity of the material in joules per gram per degree Celsius (J/g/°C). Examples of thermal capacities and temperature rises during irradiation of several common materials are shown in Table 2.1 (Cleland and others. 2003a). Absorbed dose requirements for various industrial irradiation processes

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Table 2.1. Examples of Thermal Capacities in J/g/°C and Temperature Rises in °C/kGy in Several Common Materials Material

Thermal Capacity

Temperature Rise

4.19 2.30 1.05 0.90 0.38

0.24 0.43 0.95 1.11 2.63

Water Polyethylene Polytetrafluoroethylene Aluminum Copper

cover a wide range from 0.1 kGy to 1000 kGy. Most of these processes need less than 100 kGy, while many need less than 10 kGy and some need less than 1 kGy. The temperature rises during irradiation of fresh foods, which have high water contents, are negligible because of the relatively low dose requirements, which seldom exceed a few kilograys. Gamma-Ray Facilities More than 200 gamma-ray facilities are being used for various industrial applications, mainly for sterilizing medical devices and for food irradiation. Gamma rays from cobalt-60 and cesium-137 are allowed by the U.S. Food and Drug Administration and by international standards for food irradiation (CFR 1986; Codex 2003). However, Cs-137 is seldom used because large Cs-137 sources are not readily available.The main commercial suppliers of encapsulated Co-60 sources are located in Canada and the UK (MDS Nordion 2005; PURIDEC 2002). Co-60 is a man-made radionuclide. It can be activated by placing metallic slugs of stable Co-59 in a nuclear power reactor.The absorption of a neutron, which was released by the fission of U-235, changes Co-59 to Co-60. It emits two gamma rays simultaneously with energies of 1.17 and 1.33 million electron volts (MeV). It also emits low-energy beta rays (electrons) with a maximum energy of 0.32 MeV. Co-60 has a half-life of 5.26 years, so the activity decays by 12.35% per year.The total activity in the irradiation facility is replenished by adding new sources every year. Older sources are usually kept in the facility for up to 4 half lives or about 20 years before being replaced. The emitted gamma-ray power from 1 megacurie (MCi) of Co-60 can be calculated as follows: P = 1 x 106 x 3.7 x 1010 x 2.5 x 106 x 1.6 x 10-19

(5)

P = 14.8 x 103 J/s or 14.8 kW

(6)

Gamma Ray, Electron Beam, and X-ray Technologies

Figure 2.1.

15

Photograph of an MDS Nordion Co-60 pencil.

where 1 ⫻ 106 is the source strength in curies, 3.7 ⫻ 1010 is the number of becquerels (Bq) per curie (1 Bq means 1 disintegration per second), 2.5 ⫻ 106 is the combined energy of the two gamma rays in electron volts (eV), and 1.6 ⫻ 10-19 is the conversion factor from electron volts to joules (J).About 9% of the gamma ray power is absorbed internally in an encapsulated Co-60 source, so the emitted power is about 14.8 x 0.91 = 13.5 kW per MCi (Jarrett 1982). Most Co-60 sources are in the form of pencils with a length of 452 mm (17.8 in) and a diameter of 11.1 mm (0.44 in). The nickel-plated cobalt slugs are doubly encapsulated in zircaloy tubes as shown in Figure 2.1 (MDS Nordion 2005).The activity in one pencil can be 14.25 kilocuries (kCi) or 527 terabecquerels (TBq).The pencils are loaded into flat, vertical racks as shown in Figure 2.2.These racks are lowered into deep water-filled pools when personnel need to enter the treatment room. They are raised above the pool water to irradiate product containers passing by the source rack on a conveyor. The treatment room is surrounded by a thick concrete shield, which protects operating personnel from the gamma radiation when the source rack is in the raised position.

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Figure 2.2.

Food Irradiation Research and Technology

Photograph of an MDS Nordion Co-60 source rack.

A drawing of the MDS Nordion Pallet™ irradiator for large pallet loads of low-density packages is shown in Figure 2.3.The power absorption efficiency and the dose uniformity are enhanced by passing product loads at two levels on both sides of the source rack. This design is called a panoramic irradiator.With a source loading of 3 MCi, this type of irradiator can process nearly 30 metric tonnes per hour with a product density

Gamma Ray, Electron Beam, and X-ray Technologies

Figure 2.3.

17

Drawing of an MDS Nordion Pallet™ Co-60 irradiator.

of 0.3 g/cm3 and a minimum dose of 2 kGy. Other types of irradiators may have up to 5 MCi. A drawing of the MDS Nordion Centurion™ gamma-ray facility for treating thinner packages of high-density products is shown in Figure 2.4.The source rack is raised and turned to a horizontal position so that product packages can pass above and below the rack. This conveyor arrangement facilitates automatic transfer of single layers of packages from external pallets to the conveyor before treatment and then back to the original pallets.The tops and bottoms of the packages are presented to the source rack without turning them over. A drawing of the Gray*Star Genesis™ gamma-ray facility, which irradiates products under water, is shown in Figure 2.5.The package containers are closed at the top but open at the bottom.Water is kept out of the containers by injecting air with increasing pressure as they are lowered into the pool.The absorbed dose is determined by the dwell time of the containers, which are placed first on one side and then the other side of the source rack. The rack is never raised above the pool, so there is no need for a concrete shield above ground.This arrangement is called a selfcontained irradiator.The total source loading may be up to 1 MCi of Co60 (Gray*Star 2005). The absorbed dose in materials irradiated with gamma rays decreases exponentially with increasing depth.The tenth value layer (depth to decrease the intensity by a factor of 1/10) in water with a large area rack of Co-60 sources is about 31 cm (Cleland and Pageau 1987).The penetration is inversely proportional to the average material density.With an average

18

Figure 2.4.

Food Irradiation Research and Technology

Drawing of an MDS Nordion Centurion™ Co-60 irradiator.

density of 0.3 grams per cubic centimeter (g/cm3), which might be the highest density for most packages of medical devices, the tenth value layer would be about 1 meter (m).With a product load thickness equal to the tenth value layer, a dose uniformity ratio (DUR = Dmax/Dmin) of about 1.6 could be obtained with treatment from opposite sides.This calculated value for a large area absorber would be increased slightly by edge effects in product loads of finite size.

Gamma Ray, Electron Beam, and X-ray Technologies

Figure 2.5.

19

Drawing of a Gray*Star Genesis™ Co-60 irradiator.

Electron Beam Facilities Accelerated electrons with energies up to 10 MeV are allowed by the U.S. Food and Drug Administration and by the international standards for food irradiation (CFR 1986; Codex 2003).This energy limit was recommended to avoid inducing radioactive nuclides in the food (WHO 1981).The penetration of an electron beam increases in proportion to the electron energy, so it is advantageous to use energies of at least 5 MeV for packages of foods, which may have average densities up to 0.8 g/cm3. Lower elec-

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Food Irradiation Research and Technology

Figure 2.6. Electron beam depth-dose distributions in water, from Monte Carlo calculations.

tron energies can be used for irradiating grains and fluids because their thicknesses can be controlled to match the penetration of the electron beam. The depth-dose distributions in water for electron energies between 5 MeV and 12 MeV are shown in Figure 2.6 (Cleland and others 2003b). Electron penetration in water is nearly the same as in polyethylene because of their similarity in atomic composition (Cleland and others. 2002). For treatment from one side with 10 MeV electrons, the thickness where the exit dose equals the entrance dose is about 3.7 centimeters (cm) (1.5 in), after subtracting the equivalent thicknesses of the electron beam window (40 microns of titanium) and the air space (15 cm) between the window and the water. For treatment from opposite sides with 10 MeV electrons, the thickness can be increased to about 8.6 cm (3.4 in).Then the dose in the middle would be the same as the entrance and exit doses. This thickness is enough to irradiate most retail packages of fresh meat, except for whole turkeys.

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Absorbed Dose vs. Beam Current The absorbed dose in materials irradiated with high-energy electron beams can be expressed by the following equation: D(x) = K(x) Fi I T / A

(7)

where D(x) is the dose in kGy at the depth x, I is the emitted beam current of the electron accelerator in milliamperes (mA),T is the treatment time in minutes (min), and A is the area of the irradiated material in square meters (m2). Fi is a dimensionless factor, which accounts for the fraction of beam current that is intercepted by the material. In practice, this fraction depends on the size and shape of the object and the way it is oriented on the product conveyor. In an industrial process for treating wide flat sheets of material, Fi may be as high as 0.90. K(x) is called the area processing coefficient. It is equal to 6 times the energy deposition per electron per unit area density at the depth x where the dose is specified. Its value can be obtained by Monte Carlo calculations (ASTM 2002a; ASTM 2002b). The surface value of the energy deposition per electron is 1.83 MeV-cm2/g for water irradiated with 10 MeV electrons, so K(0) is 6 x 1.83 = 11.0 kilogray square meter per millampere minute (kGy-mA/ma-min) (Cleland and others. 2003b). Rearranging Equation (7) gives the area processing rate (Cleland and others. 2002;ASTM 2002a). A / T = K(x) Fi I / D(x)

(8)

This relationship can also be called a unity rule because the area processing rate is 1 m2/min with a beam current of 1 mA and a surface dose of 10 kGy (1 Mrad).This rule applies when the product of K(x) and Fi is about 10. Even though these values do not correspond to most industrial processes, this unity rule is easy to remember and provides a basis for quickly estimating actual area processing rates by scaling with the appropriate values of Fi, I, and D(x). Electron Beam Technologies More than 1,000 industrial electron beam (EB) accelerators are now used for a variety of irradiation processes, mainly for treating plastic and rubber products to improve their qualities, and for sterilizing single-use medical devices. Only a few of these machines are being used for food irradiation, but this application is still in its infancy. It now has the advantage

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Food Irradiation Research and Technology

of being based on reliable equipment technologies that have been evolving since the 1950s for other applications. Several different methods are used to produce high-energy, high-power electron beams.These include constant-potential, direct-current systems, microwave linear accelerators (linacs), and radio-frequency, resonant cavity systems (Scharf 1986; Abramyan 1988; Cleland 1992; Cleland and Parks 2003c).The choice of a type of accelerator for a particular application is usually based on the process requirements for electron energy and average beam power. Constant-Potential Accelerators This category includes equipment with maximum electron energies as high as 5 MeV and as low as 0.1 MeV. Accelerators with energies below 0.3 MeV can be used for treating grains and powders and for sterilizing surfaces of packaging materials (Nablo and others 1998; Berejka and others 2004; Morisseau and Malcolm 2004; ESI 2005; AEB 2005; Linac Technologies 2005). Accelerators with higher energies up to 5 MeV are capable of treating retail packages of food.These types of equipment are made in the United States, Japan, France, Russia, and China. Systems in the higher energy range above 0.3 MeV are described briefly below. A simplified diagram of a high-energy, constant-potential accelerator is shown in Figure 2.7. The operation is similar to that of a television picture tube or a computer monitor, except that the voltage is much higher. Low-energy electrons are emitted from a heated cathode connected to the negative terminal of a high-voltage power supply. They are accelerated by the strong electric field in a long, evacuated beam tube that consists of many metallic dynodes separated by glass rings. External highvoltage resistors are connected between the dynodes to establish a uniform electric field along the tube axis.This prevents sparks from occurring inside the tube.After the narrow beam of electrons has been accelerated, it is scanned back and forth along a thin metallic “window” at ground potential. Then the beam emerges into the air to irradiate products on a conveyor. The accelerators in this category use similar acceleration tubes. The main differences are found in the methods used to generate the very high potentials that are needed to irradiate thick materials and products. Most high-voltage, constant-potential generators utilize cascaded rectifier systems to convert alternating current (ac) to direct current (dc) power. However, different methods are used to couple the input ac power to the multiple rectifiers, which are connected in series to produce successively higher dc potentials. There are four basic power coupling methods, which can be classed as

Gamma Ray, Electron Beam, and X-ray Technologies

Figure 2.7.

23

Diagram of a constant-potential, scanned-beam electron accelerator.

inductive or capacitive, series or parallel systems (Abramyan 1988). Insulating Core Transformers™ (ICT) made by Wasik Associates in the USA (Wasik Associates 2005) and Vivirad in France (Vivirad S.A. 2005) are inductive, series-coupled systems. The largest ICTs can provide up to 100 kW of electron beam power at 3 MeV. The Electron TransformerRectifier™ (ELV) accelerators made by the Budker Institute of Nuclear Physics in Russia are inductive, parallel-coupled systems (BINP 2005).The largest ELVs can provide up to 90 kW of electron beam power at 2.5 MeV (Salimov and others 2000). Electron Processing Systems™ (EPS) made by Nissin High Voltage in Japan use capacitive, series-coupled generators. These systems are also called Cockcroft-Walton accelerators, because they have evolved from the primitive accelerator that was used to produce the first man-made nuclear reaction more than 75 years ago.The largest EPS can provide up to 150 kW of electron beam power at 5 MeV (Uehara and others 1993; Nissin Electric Co. 2005). The Dynamitron™ accelerators made by IBA

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Food Irradiation Research and Technology

Figure 2.8. Photograph of an IBA-RDI Dynamitron™ 5 MeV constant-potential electron accelerator.

E-Beam X-Ray Solutions in the USA (Galloway and others 2004; IBA 2005; RDI 2005) and similar equipment made in China (Liang and others 1993) are capacitive, parallel-coupled systems.The largest IBA-RDI Dynamitrons can provide up to 300 kW of electron beam power at 5 MeV. A photograph of this type of accelerator is shown in Figure 2.8.The rectifiers and the acceleration tube are located inside the cylindrical array of coupling electrodes. A drawing of an electron beam processing facility with a 5 MeV Dynamitron is shown in Figure 2.9. Microwave Linear Accelerators Microwave linear accelerators (linacs) can induce high kinetic energies in electron beams without using high-voltage dc generators.The accelerating structure consists of a linear array of many small, evacuated, copper cavities. Strong ac electric fields are generated inside these resonant cavities by injecting high frequency power from a klystron microwave amplifier. Linacs with beam power ratings below 25 kW operate at the S-band frequency, 3000 megahertz (MHz). A few larger

Gamma Ray, Electron Beam, and X-ray Technologies

Figure 2.9. facility.

25

Drawing of an IBA-RDI Dynamitron™ 5 MeV electron beam processing

systems with higher beam power ratings operate at the L-band frequency, 1300 MHz. Low-energy electrons are emitted from a heated cathode at one end of the structure and gain energy while passing through each cavity. Overall energy gains of several MeV per meter can be obtained with a peak power dissipation of several megawatts. The klystron is operated with short, repetitive pulses to avoid overheating the system and to reduce the average electron beam current and power. Linacs are seldom used in the energy range below 5 MeV because they cannot provide as much beam current and power as constant-potential accelerators.Their main advantage is the ability to provide higher electron energies to irradiate thicker products. There are several suppliers of industrial linacs for radiation processing. Mevex Corporation in Canada provides S-band systems in the 5 MeV to 10 MeV range with modest beam power ratings of 5 kW to 10 kW (Mevex Corporation 2005). Linac Technologies S.A. in France provides Circe™ Sband systems with higher beam power ratings up to 20 kW at 10 MeV

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Food Irradiation Research and Technology

Figure 2.10. Photograph of an Iotron Industries Canada IMPELA™ 10 MeV L-band microwave linear electron accelerator (linac).

(Linac Technologies 2005). Titan Scan in the United States provides similar systems (Titan Scan Technologies 2005). Titan has also produced a prototype 5 MeV L-band system with more than 75 kW of beam power. Iotron Industries Canada Inc. offers L-band systems, which can provide 60 kW at 10 MeV. This design was developed by Atomic Energy of Canada Ltd (Hare 1990; Iotron Industries Canada 2005). A photograph of their IMPELA™ linac is shown in Figure 2.10.There are several other linac suppliers in Japan (Kamino 1998), Russia (NIIEFA 2005), and China (Liang and others 1993). Radio-Frequency Accelerators Medium-energy electron beams can be produced by passing the beam once through a single large resonant cavity.These systems operate in the radio frequency (RF) range of about 110 MHz and are energized with triode tubes, which are more efficient than klystrons.The Budker Institute of Nuclear Physics has produced several models of these ILU™ systems

Gamma Ray, Electron Beam, and X-ray Technologies

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Figure 2.11. Illustration of the electron beam paths in a six-pass IBA Rhodotron™ radio-frequency (RF) electron accelerator.

(BINP 2005). Model ILU-8 can provide 20 kW of beam power in the 0.6 MeV to 1.0 MeV range; Model ILU-6M can provide 40 kW of beam power in the 1.0 MeV to 2.0 MeV range; and Model ILU-10 can provide 50 kW of beam power in the 2.5 MeV to 4.0 MeV range (Auslender and Meshkov 1990). Higher electron energies can be produced with a single large resonant cavity by passing the electrons several times through the same cavity. The Rhodotron™ accelerators developed by IBA give an energy gain of 1 MeV per pass. They can achieve up to 10 MeV by passing the beam through a coaxial cavity 10 times (Defrise and others 1995). Lower energies can also be obtained by extracting the beam after fewer passes. An illustration of the beam paths is shown in Figure 2.11.Three Rhodotron models have beam power ratings of 35 kW, 80 kW, and 200 kW at 10 MeV (IBA 2005). A photograph of the lower half of a 200 kW cavity is shown in Figure 2.12. The beam apertures and the beam deflecting magnets can be seen around the middle of the cavity. A more powerful model with six passes has 100 mA of beam current or 500 kW of beam power at 5 MeV

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Food Irradiation Research and Technology

Figure 2.12. Photograph of the lower half of a ten-pass IBA Rhodotron™ RF cavity for a 10 MeV, 200 kW electron accelerator.

and 700 kW at 7 MeV (Abs and others 2004).These high beam power ratings can provide substantial X-ray processing capability, even though the efficiency for X-ray generation is relatively low. The cavity of this accelerator resonates at a frequency of 107.5 MHz. Because of its large diameter (2 meters) and the relatively low energy gain per pass, a Rhodotron cavity can be energized in the continuous wave (CW) mode with an RF power dissipation of about 100 kW. In contrast to a pulsed linac, the electron beam can be scanned rapidly, like a dc beam. This enables the use of high beam power and high conveyor speeds for low-dose applications with high throughput rates. Rhodotron beam scanners can be equipped with special magnets to eliminate beam divergence. This feature gives more uniform dose distributions in packages with different sizes, which have different spacings from the beam window of the accelerator.

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Table 2.2. Comparisons of Basic Properties of Radiation Processing with HighEnergy X-rays at 5 MeV, 7.5 MeV, and 10 MeV in Water Maximum X-Ray Energy (MeV)

X-ray Emission Efficiency (%)

Tenth Value Layer in Water (cm)

Optimum Thickness Two-Sided (cm)

Dose Uniformity Ratio (Dmax/Dmin)

10.0 7.5 5.0 Co-60

16.2 13.3 8.2 Gamma Rays

49.0 44.3 39.0 31.0

43 38 34 28

1.54 1.54 1.54 1.75

X-Ray Facilities X-rays (bremsstrahlung) with energies up to 5 MeV are allowed by the U.S. Food and Drug Administration and by international standards for food irradiation (CFR 1986; Codex 2003). The 5 MeV energy limit was originally approved by the USFDA in response to a petition from RDI (CFR 1964). Later it was recommended by a Joint FAO/IAEA/WHO Expert Committee (WHO 1981). Still later, another IAEA consultant’s meeting recommended increasing the X-ray energy limit to 7.5 MeV (ICGFI 1995; IAEA 2002).This higher value was recently approved by the USFDA in response to a petition from IBA (CFR 2004). X-rays are emitted when energetic electrons strike any material.The efficiency for converting electron beam power to emitted X-ray power increases with the atomic number of the target material and the electron energy. Increasing the energy also improves the X-ray penetration and allows the treatment of thicker packages or heavier products, such as fresh foods.These improvements are indicated by the data given in Table 2.2, which were obtained by Monte Carlo simulations (Meissner and others 2000). Nevertheless the penetration, even with 7.5 MeV X-rays, is still not sufficient to irradiate full pallet loads of fresh foods from opposite sides with acceptable dose uniformity. The Palletron™ system, patented by MDS Nordion and licensed by IBA, provides a solution to this problem (Kotler and Borsa 2003). The drawing in Figure 2.13 illustrates the Palletron concept. Single pallets are irradiated from the side while they are rotating in front of a tall Xray target.When the load density is higher than 0.5 g/cm3, the dose uniformity ratio (DUR) can still be too high because of the X-ray attenuation in the middle of the load. However, the DUR can be improved by placing thick steel collimators on both sides of the scanning X-ray

30

Figure 2.13.

Food Irradiation Research and Technology

Illustration of the Palletron™ rotational X-ray irradiation system.

beam.This reduces the dose near the outside without reducing the minimum dose in the middle of the load.The optimum spacing of the collimators depends on the load density. The treatment of single pallets simplifies the scheduling of products with different densities and different dose requirements. The data presented in Figure 2.14, calculated by Monte Carlo simulation, shows that a DUR below 1.4 can be obtained with product densities up to 0.8 g/cm3, a pallet footprint of 100 cm ⫻ 120 cm, and a pallet height of 180 cm, using either 5 MeV or 7.5 MeV X-rays. The data presented in Figure 2.15, also calculated by Monte Carlo simulation, shows that increasing the maximum X-ray energy from 5 MeV to 7.5 MeV would nearly double the throughput rate with the same electron beam power. The X-ray throughput rate would be about 50 tons per hour with 700 kW of electron beam power at 7.5 MeV, a minimum dose of 2 kGy in the density range from 0.5 g/cm3 to 0.8 g/cm3, and allowing a pallet transfer time of 20 seconds (Stichelbaut and others 2002; Stichelbaut and others 2004).The layout of an X-ray irradiation facility equipped with a Palletron system is shown in Figure 2.16.

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Figure 2.14. Dose uniformity ratio vs. product density with the Palletron™ rotational X-ray irradiator at 5 MeV and 7.5 MeV.

Conclusion Gamma ray, electron beam and X-ray sources are used for a variety of industrial processes. Irradiation of food is a small but growing part of the radiation processing industry. Ongoing developments in radiation sources and processing facilities are increasing their capacity, productivity, and reliability. These mature technologies are able to support a substantial increase in the availability of irradiated food.

Figure 2.15. Hourly throughput rate vs. product density with the Palletron™ rotational X-ray irradiator at 5 MeV and 7.5 MeV.

Figure 2.16.

Layout of a Palletron™ rotational X-ray irradiation facility.

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References Abramyan EA. 1988. Industrial Electron Accelerators and Applications. New York: Hemisphere Publishing Corporation, Harper & Row. 302 p. Abs M, Jongen Y, Poncelet E, Bol J. 2004.The IBA Rhodotron TT1000:A Very High Power EBeam Accelerator. Radiat Phys Chem 71(1-2):287–290. AEB. 2005.Advanced Electron Beams.Web site, www.advancedelectronbeams.com, tel 978 658 8600, mail 10 Upton Drive,Wilmington, MA 01887, USA. ASTM. 2002a. ISO/ASTM 51649:2002(E). Standard Practice for Dosimetry in an Electron Beam Facility for Radiation Processing at Energies Between 300 keV and 25 MeV. Annual Book of ASTM Standards, 12.02,ASTM International, 100 Barr Harbor Drive, PO Box C700,West Conshohocken, Pennsylvania 19428. ASTM. 2002b. ASTM E 2232-02. Standard Guide for Selection and Use of Mathematical Methods for Calculating Absorbed Dose in Radiation Processing Applications. Annual Book of ASTM Standards, 12.02, ASTM International, 100 Barr Harbor Drive, PO Box C700,West Conshohocken, Pennsylvania 19428. ASTM. 2003. ASTM E 2303-03. Standard Guide for Absorbed-Dose Mapping in Radiation Processing Facilities. Annual Book of ASTM Standards, 12.02, ASTM International, 100 Barr Harbor Drive, PO Box C700,West Conshohocken, Pennsylvania 19428. ASTM. 2004. Standards on Dosimetry for Radiation Processing, 2nd Edition, Sept 2004. ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, Pennsylvania 19428. 350 p. Auslender VL,Meshkov IN.1990.Powerful Single-Cavity RF Accelerators and Their Use in the Industrial Radiation Chemical Processing Lines. Radiat Phys Chem 35(4-6):627–631. Berejka AJ, Avnery T, Carlson C. 2004. Modular Low-Voltage Electron Beams. Radiat Phys Chem 71(1-2):301–305. BINP. 2005. Budker Institute of Nuclear Physics.Web site, www.inp.nsk.su, tel 383 3 39 47 60, mail Acad. Lavrentiev Prospect 11, 630090 Novosibirsk, Russia. CFR. 1964. Radiation and Radiation Sources Intended for Use in the Production, Processing, and Handling of Food. X-Radiation for Processing Food. Commissioner of Food and Drugs, Department of Health, Education, and Welfare, 21 CFR Part 121 Subpart G, Docket No. 64-13057. Fed Reg, Dec 19, 1964:18056. CFR. 1986. Irradiation in the Production, Processing and Handling of Food, Final Rule. Food and Drug Administration, Department of Health and Human Services, 21 CFR Part 179, Docket No. 81N-0004. Fed Reg 51(75):13376–13399. CFR. 2004. Irradiation in the Production, Processing and Handling of Food, Final Rule. Food and Drug Administration, Department of Health and Human Services, 21 CFR Part 179, Docket No. 2003F-0088. Fed Reg 69(246):76844–76847. Cleland MR, Pageau GM. 1987. Comparisons of X-ray and Gamma Ray Sources for Industrial Irradiation Processes. Nucl Inst Meth Phys Res B24/25:967–972. Cleland, MR. 1992. High Power Electron Accelerators for Industrial Radiation Processing. Chapter 3, In: Eds.A. Singh and J. Silverman. Radiation Processing of Polymers. Munich, Carl Hanser Verlag. New York, Oxford University Press. 23–49. Cleland M, Galloway R, Genin F, Lindholm M. 2002. The Use of Dose and Charge Distributions in Electron Beam Processing. Radiat Phys Chem 63(3-6):729–733. Cleland MR, Parks LA, Cheng S. 2003a. Applications for Radiation Processing of Materials. Proceedings of IRaP 2002, 5th International Symposium on Ionizing Radiation and Polymers. Nucl Inst Meth Phys Res B: Beam Interactions with Materials and Atoms 208:66–73.

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Cleland MR, Lisanti TR, Galloway RA. 2003b. Equations Relating Theoretical Electron Range Values to Incident Electron Energies for Water and Polystyrene. RDI-IBA TIS 1556. IBA E-Beam X-Ray Solutions, 151 Heartland Blvd, Edgewood, New York 11717. Cleland MR, Parks LA. 2003c. Medium and High-Energy Electron Beam Radiation Processing Equipment for Commercial Applications. Proceedings of IRaP 2002, 5th International Symposium on Ionizing Radiation and Polymers. Nucl Inst Meth Phys Res B: Beam Interactions with Materials and Atoms 208:74–89. Codex. 2003. Codex General Standard for Irradiated Foods (CODEX STAN 106-1983, Rev. 1-2003. 2 p.) and Recommended International Code of Practice for the Radiation Processing of Food (CAC/RCP 19-1979, Rev. 2-2003. 7 p.). Codex Alimentarius Commission, Food and Agriculture Organization and World Health Organization,Viale delle Terme di Caracalla, 00100 Rome, Italy. Defrise D,Abs M, Genin F, Jongen Y. 1995.Technical Status of the First Industrial Unit of the 10 MeV, 100 kW Rhodotron. Radiat Phys Chem 46(4-6):473–476. ESI. 2005. Energy Sciences Inc. Web site, www.ebeam.com, tel 978 694 9000, mail 42 Industrial Way,Wilmington, MA 01887, USA. Galloway RA, Lisanti TR, Cleland MR. 2004.A New 5 MeV-300 kW Dynamitron for Radiation Processing. Radiat Phys Chem 71(1-2): 551–553. Gray*Star. 2005. web site, www.graystarinc.com, tel 973 398 3331, mail 200 Valley Road, Suite 103, Mt.Arlington, NJ 07856, U.S.A. Hare GE. 1990. IMPELA Electron Accelerators for Industrial Radiation Processing. Radiat Phys Chem 35(4-6):619–626. IAEA. 2002. Natural and Induced Radioactivity in Food. IAEA-TECDOC-1287, ISSN 10114289, International Atomic Energy Agency, Wagramer Strasse 5, PO Box 100, A-1400 Vienna,Austria. 136 p. IBA 2005. Web site, www.iba-worldwide.com, tel 32 10 47 58 92, mail Chemin du Cyclotron 3, 1348 Louvain-la-Neuve, Belgium. ICGFI. 1995. The Development of X-Ray Machines for Food Irradiation. Proceedings of a Consultant’s Meeting, Oct 16–18, 1995. International Consultative Group on Food Irradiation (ICGFI), International Atomic Energy Agency, Wagramer Strasse 5, P.O. Box 100,A-1400 Vienna,Austria. 17 p. Iotron Industries Canada Inc. 2005.Web site, www.iotron.com, tel 604 945 8838, mail 1425 Kebet Way, Port Coquitlam, British Columbia, Canada V3C 6L3. Jarrett RD, Sr. 1982. Isotope (Gamma) Radiation Sources. Chapter 6, In: Eds, E.S. Josephson and M.S. Peterson. Preservation of Food by Ionizing Radiation,Vol. I. Boca Raton, Florida 33431: CRC Press. 137–163. Kamino Y.1998.10 MeV 25 kW Industrial Electron Linac.Radiat Phys Chem 52(1-6):469–473. Kotler J, Borsa J. 2003; MDS Nordion, assigned to MDS (Canada) Inc., Kanata, Canada. Product Irradiator for Optimizing Dose Uniformity in Products. Patent Descriptor, United States Patent No. US 6,504,898 B1. Date issued, January 7, 2003. Liang X, Qian J, Zhai X, Wang D, Zhu X. 1993. Development and Application of Electron Accelerators for Radiation Processing in China. Radiat Phys Chem 42(1-3):519–523. Linac Technologies S.A. 2005.Web site, www.linactechnologies.com, tel 33 1 69 35 24 00, mail 16 rue Nicolas Appert, 91400 Orsay, France. McLaughlin WL, Boyd AW, Chadwick KH, McDonald JC, Miller A. 1989. Dosimetry for Radiation Processing. New York, NY:Taylor and Francis. 251 p. MDS Nordion. 2005. Web site, www.mds.nordion.com, tel 613 592 2790, mail 447 March Road, Ottawa, ON K2K 1X8, Canada. Meissner J,Abs M, Cleland MR, Herer AS, Jongen Y, Kuntz F, Strasser A. 2000. X-Ray Treatment at 5 MeV and Above. Radiat Phys Chem 57(3-6):647–651.

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Mevex Corporation. 2005. Web site, www.mevex.com, tel 613 831 2664, mail 108 Willowlea Road, P.O. Box 1778, West Carleton Industrial Park, Stittsville, Ontario, K2S 1B4, Canada. Morisseau D, Malcolm F. 2004. SterStar System: Continuous Sterile Transfer by E-Beam. Radiat Phys Chem 71(1-2):555–558. Nablo SV, Wood JC, Jr, Desrosiers MF, Nagy VY. 1998. A Fluidized Bed Process for Electron Sterilization of Powders. Radiat Phys Chem 52(1-6):479–485. NIIEFA. 2005.The D.V. Efremov Scientific Research Institute of Electrophysical Apparatus. Web site, www.niiefa.spb.su, mail 3 Doroga na Metallostroy, Promzona “Metallostroy”, St. Petersburg 196641, Russia. Nissin Electric Co. 2005. Web site, www.nissin.co.jp, tel 81 75 864 8849, mail 47 UmezuTakase-cho, Ukyo-ku, Kyoto 615-8686, Japan. PURIDEC Irradiation Technologies. 2002.Web site, www.puridec.co.uk, tel 44 1494 77444, mail 6 Chiltern Court,Asheridge Road, CHESHAM, Buckinghamshire, England HP5 2PX. RDI. 2005. Radiation Dynamics Inc.Web site, www.e-beam-rdi.com, tel 631 254 6800, mail 151 Heartland Boulevard, Edgewood, New York 11717, U.S.A. Salimov RA, Cherepkov VG, Golubenko JI, Krainov GS, Korabelnikov BM, Kuznetsov SA, Kuksanov NK, Malinin AB, Nemytov PI, Petrov SE, Prudnikov VV, Fadeev SN, Veis ME. 2000. D.C. High Power Electron Accelerators of ELV-Series: Status, Development, Applications. Radiat Phys Chem 57(3-6):661–665. Scharf,Waldemar. 1986. Particle Accelerators and Their Uses, Part 1 Accelerator Design, Part 2 Applications of Accelerators, New York, NY: Harwood Academic Publishers. 1050 p. Stichelbaut F, Bol J, Cleland MR, Gregoire O, Herer AS, Jongen Y, Mullier B, Rose G, Vander Donckt M. 2002. The Palletron: A High Dose Uniformity Pallet Irradiator with X-Rays. American Institute of Physics (AIP) Conference Proceedings 680:891–894. Stichelbaut F, Bol J, Cleland MR, Gregoire O, Herer AS, Jongen Y, Mullier B. 2004. The Palletron:A High-Dose Uniformity Pallet Irradiator with X-Rays. Radiat Phys Chem 71(12):291–295. Titan Scan Technologies. 2005.Web site, www.titanscan.com, tel 858 812 6500, mail 9020 Activity Road, Suite D, San Diego, CA 92126, U.S.A. Uehara S,Taniguchi S, Kashiwagi M, Mizusawa K, Sakamoto I, Hoshi Y,Tomita K. 1993.A 5 MV 30 mA EB/X-Ray Processing System. Radiat Phys Chem 42(1-3):515–518. Vivirad S.A. 2005.Web site, www.vivirad.com, tel 33 3 88 69 13 25, mail 23 Rue Principale, 67117 Handschuheim (Strasbourg), France. Wasik Associates. 2005. Web site, www.wasik.com, tel 978-454-9787, mail 29 Diana Lane, Dracut, MA 01826, U.S.A. WHO. 1981.Wholesomeness of Irradiated Food. Report of a Joint FAO/IAEA/WHO Expert Committee, World Health Organization, Technical Report Series 659, Geneva, Switzerland. 33 p.

Food Irradiation: Research and Technology Edited by Christopher H. Sommers, Xuetong Fan Copyright © Blackwell Publishing and the Institute of Food Technologists 2006

Chapter 3 REGULATION OF IRRADIATED FOODS AND PACKAGING George H. Pauli, Ph.D.

Introduction I would like to take this opportunity to discuss the process that FDA follows in the regulation of irradiated foods and irradiated food packaging. I have found that people who have not been intimately involved in the process often assume what is required and therefore may not understand the reasons for FDA actions.An overview of FDA’s activities prior to 1986 has been previously published (Pauli and Takeguchi, 1986). First, FDA’s premarket approval authority for irradiated foods and packaging derives from the Food Additives Amendment of 1958. In that legislation, the definition of a food additive reads, in part, as follows: Any substance the intended use of which results or may reasonably be expected to result, directly or indirectly, in its becoming a component or otherwise affecting the characteristics of any food (including any substance intended for use in producing, manufacturing, packing, processing, preparing, treating, packaging, transporting, or holding food; including any source of radiation intended for any such use) . . . (emphasis added). Although there are exceptions to this definition, use of a source of radiation to treat food always requires approval. Section 402(a)(7) of the Federal Food, Drug, and Cosmetic Act reads: A food shall be deemed to be adulterated—if it has been intentionally subject to radiation, unless the use of radiation was in conformity with a regulation or exemption pursuant to section 409. 37

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Section 409 provides the general safety and procedural rules for approving use of all food additives, including a source of radiation. Approving regulations may be promulgated by proposal and comment rulemaking initiated by FDA, or by a petition submitted by an interested party that is announced by a filing notice and decided upon by a final regulation. Generally, petitions are the more efficient route to a regulation because: (1) they focus on specific applications of sufficient interest to someone to cause them to prepare documentation of safety; and (2) because FDA can simply publish a notice of filing rather than a proposed rule describing the basis for issuing a regulation and solicitation of comments. Although FDA considers comments addressed to a petitioned action announced in a notice of filing, and although this may complicate the effort, it is less labor intensive to FDA than the proposal route. Importantly, a petition places an action on FDA’s agenda whereas many competing goals are considered before FDA decides to issue a proposal. As of July 2004, FDA had eight active petitions on its agenda. The subjects of the petitions and the petitioners are as follows: Subject

Petitioner

Reduce microorganisms on fresh or frozen molluscan shellfish

National Fisheries Institute and Louisiana Dept. of Agriculture and Forestry USDA/FSIS

Control microorganisms on non-chilled meat food products (“hot-boned” meat) Raise dose and change packaging requirements for poultry Control pathogens in multiple ingredient foods Control pathogens in crustaceans Control microbial contamination on dietary supplements Use of X-rays generated from machine sources at energies not to exceed 7.5 MeV1 Use of sterilizing doses for shelf stable foods

USDA/FSIS Food Irradiation Coalition/NFPA National Fisheries Institute Steris Corporation IBA (Now Sterigenics International, Inc.) IBA (Now Sterigenics International, Inc.)

Most of these petitions have been with FDA for a considerable time. This is disappointing because FDA places a priority on food additive petitions intended to provide technology for controlling pathogens. Because FDA considers the status of a petition to be confidential until a decision is reached (except for communication with the petitioner to

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resolve important issues), the absence of information can lead to unwarranted speculation. Because of the long time, and because some of the reason for delay is now public information, I thought it would be helpful to discuss the essence of a petition review in the context of the petition from the Food Irradiation Coalition/NFPA. The first thing we do when we receive a petition is to determine the scope of the petition. Specifically, we try to determine what the regulation would say if we approved the petition.Although this determination is fundamental, it is often more difficult than it seems, because a petitioner may know what it wants to have approved, but putting it into words may go far beyond the petitioner’s intent and may raise difficult issues in which it has little or no interest. An approving regulation is generic—applicable to everyone, not just the petitioner. Therefore, the petitioner’s intent is not as important as what a regulation would allow. After the scope is known, we look to see whether there could be any safety questions that had not been directly and completely addressed by previous decisions. This may result from new information or expanded scope. We look to see how the petitioner has addressed such issues. We ask whether anything else in the published literature or FDA files may be relevant to such issues. Finally, we determine whether any comments have been submitted to the Docket for the petition and, if so, we evaluate whether the comments have met the burden for supporting the action they request, just as we evaluate whether the petitioner has met the burden of safety demonstration with its petition. I will now use the petition mentioned above to discuss how this is done. The petition, received in 1999, is quite broad in scope. We exchanged correspondence with the petitioner several times to clarify what all would be covered.After publishing a notice of filing, in general terms, we discovered that our notice was too narrow and published a second, amended notice to ensure that the public had been notified of everything under consideration. Previous decisions by FDA on irradiated foods had generally been for raw agricultural commodities or single-ingredient foods.This petition addressed previously processed foods that would have the variety of ingredients we see on an ingredient list.Also, previous decisions pertained to foods containing minimal amounts of carbohydrate, except for those foods that were irradiated only at a very low dose, or that were an insignificant amount in the diet.Thus, we needed to address the question of the effects of irradiation on common food ingredients as well as the effect on carbohydrates. Our chemistry reviewer examined published literature on irradiation of high-carbohydrate foods (Diehl, 1982). Among other things, he found a reference to an unpublished report of furan in ir-

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radiated apple juice but not in heat-processed juice (Dubois and others, 1966).After obtaining a copy of the report, he concluded that the identification of furan was neither well supported nor quantified. However, because furan was listed on the U.S. Department of Health and Human Services 8th Report On Carcinogens in 1998 and remains listed today in the 11th Report (USHHS, 2005), we concluded that we had to understand the consequence of this finding more completely. To follow up on this report, our chemist irradiated apple juice and verified that the authors were correct; low levels of furan were produced when apple juice was irradiated (Morehouse, 2001).To obtain more information, FDA began a collaborative effort with the petitioner to determine whether furan was limited to fruit juice or whether there were broader ramifications. Reports were identified with non-quantified amounts of furan in heat-processed, but not irradiated, foods.Thus, we extended the effort to look at other processed foods. In sum, we discovered that furan appears to occur more commonly in foods than previously thought. Importantly, it appears to be formed through a variety of mechanisms from several precursors.Three mechanisms that have been elucidated include thermal degradation of carbohydrates, thermal oxidation of lipids, and decomposition of ascorbic acid or its derivatives (FDA, 2004). Levels found in heat-processed foods purchased in the supermarket generally contained higher levels than those found in irradiated foods2 (FDA,2004).FDA announced these findings on May 10, 2004, with a call for data on the occurrence of furan in foods, mechanisms of furan formation, and mechanisms of furan toxicity, and discussed their significance at a Food Advisory Committee meeting on June 8, 2004. Information on this issue is posted on FDA’s Web site at http://www.cfsan.fda.gov/~lrd/pestadd.html.We continue to evaluate the significance of furan. Because of the focus on foods currently on the market, the research on irradiated foods has not been completed sufficiently at this time for publication. I mentioned earlier that we also evaluate comments received. Because we have not reached a final decision, I cannot discuss what our decision will be.The comments are public, however and, as of July 2004, generally fall into the following six categories: (1) the commenters disagree with specific conclusions in a 1999 book on high dose food irradiation issued by the World Health Organization; (2) the commenters express concern about 2-alkylcyclobutanones produced when fat is irradiated; (3) the commenters believe irradiation will increase the levels of trans-fats; (4) the commenters were concerned with reports of polyploidy reported in India in the 1970s; (5) the commenters were concerned with the ratio of reports of mutagenicity compared to those that report no mutagenicity; (6) the commenters believe that more research is needed.

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It is also worth noting that although FDA’s decisions on irradiated food become effective when published, those who believe that FDA erred may file objections within 30 days of a decision and request an evidentiary hearing. FDA has received objections to its decisions on irradiated eggs, irradiated seeds, and radiation systems used to inspect cargo. Finally, as with all its food additive approvals, FDA decisions are based on conditions of use.When FDA reviews the safety of packaging, it considers the type of food in the package (dry, aqueous, oily) and the temperature permitted for food contact. FDA considers that irradiating a package with food inside is a condition that needs explicit review. Although various approvals were issued several decades ago, there has been little in the approval agenda in recent years. FDA is now authorized to evaluate safety via a 120-day notification process, making the petition process for packaging a remnant of the past.At present, FDA has no effective notifications for irradiated packaging. FDA has been working on guidance in this area but nothing has been issued.

Notes 1.This petition was approved on December 23, 2004. 2. Importantly, although quantifiable amounts have been identified in heat-processed foods, irradiated foods currently on the market (which have not been heat-processed) do not appear to contain sufficient furan to be quantified (limit of quantitation is 2–5 ppb depending of the food type).

References Pauli, G.H., and Takeguchi, C. A. 1986. Irradiation of Foods - An FDA Perspective, Food Reviews International,Vol. 2, 79–107. Diehl, J.F. 1982. Radiolytic Effects in Foods, in Preservation of Food by Ionizing Radiation, Edward S. Josephson and Martin S. Peterson, ed. CRC Press, Inc., Boca Raton, Florida Dubois, P., Zenz, H. Stehlic, G., and Kaindl, 1966.Analysis of the volatile components in irradiated apple and grape juices, Seibersdorf Project Report SPR-8. U.S. Department of Health and Human Services, 11th Report On Carcinogens, (2005) http://ntp.niehs.nih.gov/index.cfm?objectid=32BA9724-F1F6-975E-7FCE50709CB4C932. Morehouse, K., Personal communication (2001) Transcript of June 8, 2004 FAC meeting at: http://www.fda.gov/ohrms/dockets/ac/04/transcripts/204-4045t2b-02.htm Exploratory Data on Furan in Food, FDA. 2004. (updated 2005) http://www.cfsan.fda.gov/ ~dms/furandat.html.

Food Irradiation: Research and Technology Edited by Christopher H. Sommers, Xuetong Fan Copyright © Blackwell Publishing and the Institute of Food Technologists 2006

Chapter 4 TOXICOLOGICAL SAFETY OF IRRADIATED FOODS Christopher H. Sommers, Henry Delincée, J. Scott Smith, and Eric Marchioni

Introduction Generation of cancers in animals requires the mutation or deletion of oncogenes or tumor suppressor genes, resulting in a loss of heterozygosity at those allele locations. Mutation (point mutations or frame-shift mutations) and deletion of genes can be induced by exposure of cells to genotoxic chemicals or can occur naturally as part of the cellular DNA repair and replication process (Ames and Gold 1990). Many consumers are simply unaware that foods contain carcinogens, either natural or artificial, and cause cancer. A very small subset of naturally occurring carcinogens in foods include compounds such as benzene and formaldehyde (Smith and Pillai 2004; Fan and Thayer 2002). A number of studies have confirmed the mutagenicity of cooked meats and their fats, and the formation of nitrosamines as part of the meat curing and cooking process (Knekt and others 1999).Tumor promoters present in cooked meat and poultry include oxidization products of fats and oils, heme, and cholesterol (Van der Meer-van Kraaij and others 2005; Yang and others 1998; Tseng 1996).Alcohol is known to induce the formation of tumors in the gastrointestinal tract of rodents (Mufti 1998). It was recently found that high-temperature frying and baking of starch-containing foods results in the formation of acrylamide, a suspected human carcinogen (Friedman 2003). Furan, a carcinogen in animals, is formed in foods as a result of thermal processing (Perez-Locas and Yaylayan 2004). Compounds used in the pickling, salting, and smoking processes are associated with gastro-intestinal cancers in humans (Weisburger and Jones 1990). Discussions pertaining to food irradiation 43

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therefore have to be placed in context with the risks associated with consumption of irradiated foods versus foods processed using technologies and additives that are known to cause cancer in animals and humans.

Food Irradiation Food irradiation is perhaps the single most studied food processing technology for toxicological safety in the history of food preservation. Studies pertaining to the safety and nutritional adequacy of irradiated foods date back to the 1950s and were frequently associated with the use of radiation to sterilize foods. Hundreds of short-term and long-term safety studies led to the approval of one or more foods for irradiation by presently more than sixty countries.These studies are thoroughly reviewed in The Safety and Nutritional Adequacy of Irradiated Foods, published by the World Health Organization (WHO 1994). In the United States, the Food and Drug Administration reviewed the available studies for the quality of experimental design, rigor, and statistical validity before approving irradiation of a variety of food products including grain, fruits and vegetables, spices and dried herbs, meat and poultry, and eggs for human consumption (Federal Register 2005; WHO 1994).The vast majority of the studies failed to find adverse effects associated with consumption of or exposure to irradiated foods. Not surprisingly, a small number of studies produced equivocal results pertaining to the safety of irradiated foods. However, in-depth review of those studies determined that they were deficient in experimental design, used insufficient numbers of test subjects for proper statistical analysis, or suffered from experimenter error (WHO 1994). The preferred method for assessing the toxicological safety of irradiated foods has been long-term feeding studies in animals, often for multiple generations. Toxicologists prefer to use animals for these types of evaluations, as opposed to using people or their children, for obvious reasons. Swallow (1991) reported that animals used for toxicological research, fed diets of radiation-sterilized foods for 40 generations, suffered no ill effects from consumption of irradiated foods. Thayer and others (1987) reported that rodents fed diets of radiation-sterilized chicken meat (45–68 kGy) did not suffer an increased risk of cancer or birth defects. The same study also failed to find adverse affects associated with long-term consumption of irradiated meat in beagle dogs. De Knechtvan Eekelen and others (1971, 1972) conducted single- and multiplegeneration feeding studies in rats without finding adverse effects due to consumption of the irradiated chicken diet. Poling and others (1955) re-

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ported no evidence of changes in survival, histopathology, or reproduction in three generations of rats fed radiation-sterilized ground beef. Feeding studies in animals have been very consistent in the lack of adverse effects associated with long-term consumption of irradiated foods.

Benzene, Formaldehyde and Amines The presence of several compounds, most notably benzene and toluene, has generated some concerns about the safety of irradiated foods. It was originally thought that trace amounts of benzene were formed in irradiated foods and that this was a unique situation. It is currently thought that benzene and toluene are produced from the oxidative/radiolytic cleavage of phenylalanine.They have been reported in irradiated beef (Merritt and others 1978; Nam and others 2003), though in the 5–60 ppb range. Benzene and its derivatives are not typically found in raw food products, but it appears that thermal treatments do produce trace amounts in some cooked products. Matiella and Hsieh (1991) identified benzene derivatives in scrambled eggs, whereas McNeal and others (1993) reported the presence of benzene in butter, eggs, meat, and certain fruits with levels ranging from 0.5 ppb in butter to 500–1900 ppb in eggs.Angelini and others (1975) evaluated volatile compounds in fresh and irradiated haddock and found benzene and toluene in all samples with larger quantities present in the irradiated ones. In 1979 the Federation of American Societies for Experimental Biology evaluated 65 compounds found in irradiated beef and noted that small amounts of benzene could be detected in both irradiated (56 kGy) and untreated beef (Chinn 1979a). Gamma and electron-irradiated beef contained about 18–19 ppb, which was reduced to 15 ppb upon cooking. On the other hand, the thermally-sterilized and frozen controls contained no detectable benzene, but on cooking the levels were approximately 2–3 ppb.They concluded that such small amounts of benzene did not constitute a significant risk. Health Canada (Bureau of Chemical Safety), in a recent evaluation (2002) of an application for irradiated ground beef, has estimated that approximately 3 ppb of benzene would be formed in irradiated beef at the typical dose ranges (1.5–4.5 kGy) and concluded that it is of insignificant health risk. Formaldehyde and malonaldehyde are probably formed in most foods containing carbohydrates (Dauphin and Saint Lebe 1977). Usually the formed formaldehyde is very reactive and will readily form covalent links with proteins and other constituents.Thus, unless the food item is low in

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protein or contains a considerable amount of water, it would not be present. Fan (2003) has shown that formaldehyde can be generated from solutions of fructose, glucose, and sucrose. Significant amounts were also observed in both pasteurized and fresh irradiated apple juice (Fan and Thayer 2002). Lee and others (1973) observed slight increases in formaldehyde amounts in irradiated Irish Cobbler potatoes at doses of 1.5 kGy. Irradiation has been suggested as a way to control nitrosamine formation in cured meat products such as bacon (Fiddler and others 1985). Ahn and others (2004), using water solutions, have shown that the nitrosamines, nitrosodimethylamine, and nitrosopyrrolidine were significantly reduced by gamma irradiation in addition to residual nitrite levels. However, the reduction was not apparent unless the irradiation dose was 10 kGy or higher, an unrealistically high dose. Similar results were observed when using irradiated cooked pork sausage where doses of 5 or 10 kGy reduced residual nitrite levels and nitrosodimethylamine and nitrosopyrrolidine (Ahn 2004).Thus it appears that irradiation can destroy preformed nitrosamines directly or, by limiting residual nitrite or reactive nitrogen compounds, can inhibit the formation upon cooking. Use of irradiation to reduce other toxic nitrogenous compounds, the biogenic amines, has been evaluated in fermented soybean paste. Irradiation of the paste prior to fermentation did not produce any differences compared to controls.After fermentation for 12 weeks, there were significantly lower amounts of histamine, putrescine, tryptamine, and spermidine in the treated samples, suggesting that irradiation may have altered the microflora to one not conducive to biogenic amine formation (Kim and others 2003). Levels of the biogenic amines putrescine, tryptamine, spermine, and spermidine were reduced in pepperoni subjected to gamma irradiation (5–20 kGy) prior to storage (4° C, 4 wk), again suggesting reduction in bacterial numbers (Kim and others 2005).

Formation and Levels of 2-ACBs in Foods Particular attention has been drawn to a special class of cyclic compounds being formed on irradiation of lipids.A wealth of radiolytic products are formed on irradiation of, for example, triglycerides, among them fatty acids, hydrocarbons, aldehydes, ketones, esters, and dimeric and polymeric components (Nawar 1978, 1986; Stewart 2001), but to date one class of components, the 2-alkylcyclobutanones (2-ACBs), is of particular interest. This new class of cyclic components was reported more than 30 years ago (LeTellier and Nawar 1972) to be formed on irradiation

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Figure 4.1. Formation of 2-ACB on irradiation of a triglyceride (LeTellier and Nawar 1972; Nawar 1978, 1986; see also Stewart 2001).

of pure saturated triglycerides containing C6, C8, C10, C12, C14, C16, and C18 fatty acids with a high dose (60 kGy under vacuum). These compounds were identified as the 2-alkylcyclobutanones of the same carbon number as the precursor fatty acid. It has been proposed that these compounds may result from cleavage of the acyl-oxy bond via the formation of a six-membered ring intermediate (Figure 4.1). 2-Dodecylcyclobutanone (2-dDCB) derived from palmitic acid (C16) was also identified in an irradiated synthetic phospholipid, that is, dipalmitoyl-phosphatidyl-ethanolamine, which had been treated with a very high radiation dose (500 kGy under air) (Handel and Nawar 1981). It was, however, not before 1990 that a 2-ACB was identified in irradiated food. Stevenson and others (1990) reported the detection of 2-dDCB in chicken irradiated at a dose of 5 kGy. Subsequent work indicated that the 2-ACBs are radiation specific because they are not detected in raw, cooked, frozen, freeze-dried, spoiled chicken, thermally sterilized chicken stored at room temperature for 12–13 years, or chicken exposed to modified atmospheres (Boyd and others 1991; Crone and others 1992a, b; Stevenson and others 1993). In another approach Ndiaye and others (1999a) treated an aqueous suspension of a synthetic mixture of pure saturated triglycerides (C10, C12, C14, C16 and C18) with microwaves (20 min at 750 W, 2450 MHz),

48 Table 4.1.

Food Irradiation Research and Technology Radiation-Induced Formation of 2-ACBs from Their Precursor Fatty Acids

Fatty Acid

2-alkylcyclobutanone

C 10:0

Capric acid

C 12:0

Lauric acid

C 14:0

Myristic acid

C 16:0

Palmitic acid

C 16:1

Palmitoleic acid

C 18:0

Stearic acid

C 18:1

Oleic acid

C 18:2

Linoleic acid

C 18:2

Linolenic acid

2-hexyl-cyclobutanone (2-HCB) 2-octyl-cyclobutanone (2-OCB) 2-decyl-cyclobutanone (2-DCB) 2-dodecyl-cyclobutanone (2-dDCB) 2-(dodec-5⬘-enyl)-cyclobutanone (2-dDeCB) 2-tetradecyl-cyclobutanone (2-tDCB) 2-(tetradec-5⬘-enyl)-cyclobutanone (2-tDeCB) 2-(tetradeca-5⬘,8⬘-dienyl)-cyclobutanone (2-tD2eCB) 2-(tetradeca-5⬘,8⬘,11⬘-trienyl)-cyclobutanone (2-tD3eCB)

with heat in a convection oven (30 min at 150° C), with UV irradiation (60 min with ␭ 240–280 nm), with high pressure (60 min with 6000 bar) and with ultrasound (5 min at 455 W, 20 kHz) and were unable to detect any 2-ACBs. However, if the triglyceride solution was irradiated, all the corresponding 2-ACBs could be identified.Thus every fatty acid gives rise to its own 2-ACB (Table 4.1). To date, 2-ACBs have not been identified in nonirradiated foods.An exotic occurrence may be the possible presence of 2-methylcyclobutanone in Hevea brasiliensis (Nishimura and others 1977).These authors speculated that the cyclization of isoprene components after sonication could lead to the cyclobutanone structure, but as mentioned previously, when saturated triglycerides were treated with sonication, no 2-ACBs could be detected (Ndiaye and others 1999a).This seems to support the hypothesis that 2-ACBs may be radiation specific, thus being “Unique Radiolytic Products.” However, the possibility also exists that available detection methods of 2-ACBs are just not sensitive enough, so the amount possibly present also in non-irradiated foods is at the moment below the detection limit of the analytical methods (Ndiaye and others 1999a). The occurrence of 2-ACBs in many irradiated foodstuffs has now been confirmed in meat (beef, pork, lamb), poultry (chicken, mechanically re-

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covered poultry meat), liquid whole egg, cheese (Camembert, Brie, or cheese made from sheep’s milk), seafood (prawns), fish (sardine, trout, salmon), fruit (mango, papaya, avocado), nut (peanut), seeds (perilla), and cereals (rice) (see references in EN 1785:2003). 2-dDCB could be also identified in foods irradiated at very low doses (0.05–0.1 kGy) such as onions, garlic, rice, or cowpeas (Horvatovich and others 2002a; Ndiaye 1998; Ndiaye and others 1999b). The levels of 2-ACBs seem to vary in different foods. Of course, this depends on the fat content of the food, its fatty acid composition, and the dose of radiation. Also, the irradiation temperature plays a role, less 2ACBs being formed in frozen foodstuffs. Generally a linear dose dependency of the formation of 2-ACBs has been observed (Stevenson 1992, 1994; Stevenson and others 1993; Crone and others 1992a, b; Ndiaye and others 1999a; Stewart and others 2000; Park and others 2001;Tanabe and others 2001; Gadgil and others 2002; Burnouf and others 2002). Mostly, the level of 2-ACBs is given per gram of fat and is reflective of the fatty acid composition of the meat. For chicken meat, values between 0.15 and 0.75 μg 2-dDCB / g lipid / kGy have been reported (Stevenson and others 1992, 1993, 1996; Boyd and others 1991; Crone and others 1992a, b, 1993; Meier and others 1996; Stewart and others 2001;Tanabe and others 2001), whereas values for 2-tDCB were about 0.05–0.1 μg / g lipid / kGy.The levels in pork meat varied from 0.13–0.21 μg 2-dDCB / g lipid / kGy and 0.12–0.27 μg 2-tDCB / g lipid / kGy (Stevenson 1994, 1996; Stewart and others 2001; Park and others 2001). For beef the reported 2-dDCB yield was about 0.1–0.18 μg / g lipid / kGy, and for 2-tDCB it amounted to be ~ 0.14 μg / g lipid / kGy (Stevenson 1994; Gadgil and others 2002). A systematic approach was taken by Ndiaye and others (1999a), who related the amount of 2-ACBs to the precursor fatty acid. For several foodstuffs (cheese, sardine, trout, beef, and poultry meat) irradiated between 0.1 and 3.1 kGy, the yield of saturated 2-ACBs was reported to be between 1.0 and 1.6, in average 1.3 ± 0.2 nmol / mmol precursor fatty acid / kGy.This indicated that the amount of 2-ACBs (in this case, saturated 2ACBs) formed is relatively independent of the food or food matrix and mostly reflects the amount of precursor fatty acid.This was confirmed by Burnouf and others (2002), who irradiated various types of foods, that is, milk powder, hazelnuts, chicken, beef, goose liver, cocoa, ground beef patties, smoked salmon, frog legs, chicken quenelles, salmon, avocado, liquid whole egg, and noticed that in general similar yields expressed in nmol 2-ACBs / mmol precursor fatty acid / kGy were obtained, although some variation was obvious.This variation could possibly be ascribed to different positions of the fatty acids in the triglycerides (Stevenson 1994). In a

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recent study Horvatovich and others (2005) reported that the formation of saturated 2-ACBs (2-dDCB, 2-tDCB) in chicken, liquid whole egg, and avocado was 1.4 ± 0.4 nmol / mmol precursor fatty acid / kGy. For the formation of mono-unsaturated 2-ACBs (cis-2-dDeCB, cis-2-tDeCB) from the same foods, a slightly lower value of 0.9 ± 0.3 nmol / mmol precursor fatty acid / kGy was found, although this value was found not to be significantly different from the value for the saturated 2-ACBs (Horvatovich and others 2005). In a study with pure triacylglycerides (C16, C18, C18:1, C18:2, C18:3) and the corresponding authentic fatty acids, different radioproduction yields were reported (Kim and others 2004), with the highest levels of 2-ACBs being observed for the saturated triglycerides. In food with mixed triglycerides and usually low amounts of free fatty acids, phospholipids, sterols and other fat components, the radioproduction levels seem to vary only slightly (Ndiaye and others 1999a; Burnouf and others 2002; Horvatovich and others 2005).Therefore, if the fat composition of the food sample is known, the levels of 2-ACBs can be roughly predicted. Considering the edible fat containing only triglycerides and restricting this rough calculation only to the four most common fatty acids in food, namely palmitic acid, stearic acid, oleic acid, and linoleic acid, and taking into account the most recent formation factors of Horvatovich and others (2005) of 1.4 nmol for the saturated 2-ACBs and 0.9 nmol for the unsaturated 2-ACBs per mmol precursor fatty acid per kGy—as a first approximation the formation factor of the di-unsaturated 2-ACB from linoleic acid is set to be similar to that of the mono-unsaturated 2-ACB from oleic acid—the prediction leads to the following yields: for chicken meat containing about 12.5% edible fat with a composition of approx. 21% palmitic acid, 6% stearic acid, 32% oleic acid, and 25% linoleic acid, which has been irradiated at the maximum dose of 3 kGy, levels of 2ACBs amounts to about 11 μg 2-dDCB, 3 μg 2-tDCB, 10 μg 2-tDeCB, and 8 μg 2-tD2eCB per 100 g of fresh irradiated (3 kGy) chicken. For beef, for example, ground beef patties containing a maximum of 23% fat with a fatty acid composition of approx. 27% palmitic acid, 15% stearic acid, 43% oleic acid, and 3.8% linoleic acid, a similar calculation arrives at 36 μg 2-dDCB, 20 μg 2-tDCB, 37 μg 2-tDeCB, and 3 μg 2-tD2eCB per 100 g of fresh irradiated (maximum dose 4.5 kGy) beef. If a 20% loss in 2-ACBs after cooking (Crone and others 1992a) is anticipated and the actual mean intake of poultry (as given by Health Canada 2003) is about 62.1 g poultry per day, this intake would provide 0.08 μg 2-dDCB + 0.02 μg 2-tDCB + 0.08 μg 2-tDeCB + 0.06 μg 2-tD2eCB per kg body weight (kg bw) per day.This makes a total intake due to irradiated poultry of about 0.24 μg 2-ACBs / kg bw / day.

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Similar for beef with a daily intake of 23.2 g (Health Canada 2003), the consumption of irradiated beef would result in an intake of 0.10 μg 2dDCB + 0.06 μg 2-tDCB + 0.10 μg 2-tDeCB + 0.01 μg 2-tD2eCB per kg body weight per day. The total intake of 2-ACBs due to irradiated beef would thus amount to 0.27 μg 2-ACBs / kg bw / day. The daily intake by irradiated beef and poultry results in a value of 0.51 μg 2-ACBs / kg bw / day. Of course it should be taken into account that not all beef and poultry at present is being irradiated, and this can also not be expected in the near future. Only a very low percentage of beef and poultry is presently irradiated.The rough calculation shows a conservative value, which, however, could increase if higher radiation doses used for sterilization were to be applied and if other irradiated fatcontaining foodstuffs with considerable amounts of 2-ACBs would be consumed. This calculated daily intake of roughly 0.5 μg 2-ACBs / kg bw may be compared with the estimated uptake of acrylamide by, for example, fried food such as french-fried potatoes or potato crisps, the average value for the general population reported by the WHO (2002) being about ~ 0.3–0.8 μg acrylamide / kg bw / day. However, the toxicology database of acrylamide contains much information, whereas knowledge about the toxicological properties of 2-ACBs is still scarce.Already during the evaluation of the health aspects of certain compounds found in irradiated beef in the 1970s by FASEB, it was mentioned that metabolic and toxicological studies of the 2-ACBs presumably present in beef would be desirable (Chinn 1979b). At that time, 2-ACBs had not yet been identified in food, but only in triglycerides irradiated at high doses (60 kGy). The total daily intake of roughly 40 μg 2-ACBs per person per day surpasses the recently discussed threshold of toxicological concern (TTC) of 1.5 μg / person / day (Barlow and others 2001), which is used by the U.S. FDA for reviewing components of food contact materials with low exposures. So it may be prudent to collect more knowledge on the toxicological and metabolic properties of 2-ACBs in order to quantify a possible risk—albeit minimal. Knowledge about the metabolism of 2-ACBs is very restricted. Only one study about the fate of 2-ACBs in rats has been published (Horvatovich and others 2002b). Rats received a drinking fluid containing 0.005% 2-tDCB or 2-tDeCB daily for four months.The 2-ACBs could be identified in very low amounts in the adipose tissues of the rats (10-5 times the total quantity consumed). Less than 1% of the 2-ACBs ingested daily were excreted in the faeces. These results indicate that 2-ACBs are probably largely metabolized.Thus, further metabolic studies are desirable.

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Food Irradiation Research and Technology

Toxicological Safety of 2-ACBs Although the toxicological safety of irradiated meat and poultry has been studied extensively, far less data is available pertaining to the genotoxic potential of 2-ACBs, the chemicals that are formed by the radiolysis of triglycerides, phospholipids, and fatty acids. Controversy over the genotoxicity of the 2-ACBs started following the publication of preliminary data by Delincée and Pool-Zobel (1998) in which 2-dDCB at concentrations of 0.30–1.25 mg / ml in in vitro experiments induced DNA strand breakage in primary human and rodent colon cells using the Comet Assay.The authors’ study cautioned against interpretation of the results to infer that irradiated foods were carcinogenic and instead called for more study on the issue of 2-ACB genotoxicity (Delincée and Pool-Zobel 1998). The Comet Assay, although used extensively as a screening assay, has not been validated for the detection of weak genotoxins and can produce false-positive results due to the chromosome degradation that occurs as a result of non-genotoxic cell death (Health Canada 2003; Tice and others 2000). A retest of multiple 2-ACBs in the Comet Assay, in human HT-29 and HT-29 cl 19A cells at concentrations up to 400 μM, failed to detect significant levels of DNA strand breakage (Burnouf and others 2002). The genotoxicity of 2-ACBs was also studied in two human cell lines, HeLa and HT-29, using an alkaline unwinding procedure to quantify DNA strand breaks and Fpg-sensitive sites following the procedure proposed by Hartwig and others (1996). The frequencies of both DNA strand breaks and oxidative DNA modifications served as sensitive indicators of DNA damage.The results obtained thus far demonstrate that all of the test compounds that were investigated (2-tDCB, 2-tDeCB, 2-dDCB and 2-DCB) have cytotoxic effects in both cell lines at concentrations ⱖ100 μM.All of the 2-ACBs were also shown to induce oxidative DNA damage. In the case of 2-tDCB and 2-tDeCB, DNA damage occurred only at concentrations that were already highly cytotoxic, such that considerable fractions of the cells were no longer viable.The situation was different with 2-dDCB and 2-DCB, where oxidative DNA damage occurred at non-cytotoxic concentrations, making these results more relevant to the toxicological assessment (Burnouf and others 2002; Marchioni and others, 2004). Several 2-ACBs including 2-dDCB have also been tested in the Salmonella Mutagenicity Test (SMT), with no induction of mutations due to exposure to 2-ACBs using TA97, TA98, and TA100 tester strains being detected (Burnouf and others 2002). Other laboratories have focused their efforts on 2-dDCB, a prevalent 2-ACB in ground beef formed by the radiolysis of palmitic acid.Two studies investigated the ability of 2-dDCB to induce mutagenesis in the bacterial reverse mutation assays, with and

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without exogenous metabolic activation (Sommers 2003; Sommers and Schiestl 2004). No increase in the formation of mutants was observed in the SMT or the E.coli TRP Assay using tester strains WP2 [pKM101],WP2 uvrA [pKM101], TA98, TA100, TA1535, and 1537, which were in agreement with results published by Burnouf and others (2002). Gadgil and Smith (2004) also investigated the ability of 2-dDCB to induce mutations in the SMT using tester strains TA97,TA98,TA100,TA102, and TA1535, and failed to detect an increase in the formation of mutants as a result of 2dDCB exposures up to 1 mg / plate.Three laboratories have now failed to detect an increase in mutagenesis as a result of exposure to 2-dDCB, or multiple 2-ACBs, in the widely used and validated SMT and E. coli TRP Assays. In forward mutagenesis assays, an entire gene is a target for mutagenesis, as opposed to single nucleotide changes that are detected in the bacterial reversion tests. 5-Fluorouracil (5-FU)-resistant mutants in E. coli or Salmonella are formed when a null mutation is fixed within the DNA sequence of the 0.551 kb uracil-phosphoribosyltransferase gene, which would normally convert 5-FU to a toxic metabolite within the bacterium (Skopek and Thilly 1983). Sommers and Mackay (2005) failed to detect an increase in the formation of 5-FU mutants in E. coli following exposure to 1 mg / ml 5-FU, with or without exogenous metabolic activation. Gene expression profiling has also been used extensively for determination of genotoxic potential and is capable of identifying many genotoxins that are not detectable using bacterial reverse mutation assays. Transcription of RNA from the DNA damage-inducible UmuDC, RecA, DinD, and Nfo DNA genes of E. coli has been shown to increase following exposure to genotoxins (Orser and others 1995a, b). 2-dDCB was not able to induce gene expression from any of those gene promoters, as measured by increased ␤-galactosidase activity levels, at concentrations up to 1 mg / mL in E. coli SF1 containing each of the aforementioned promoter/␤-galactosidase reporter constructs, with or without exogenous metabolic activation (Sommers and Mackay 2005). This is in contrast to other carcinogens routinely present in foods including formaldehyde, dimethylnitrosamine, and aflatoxin B1 as shown by Orser and others (1995a, b). The Microtox™ system uses the bioluminescent marine microorganism Vibrio fisheri to measure the acute toxicity of chemicals or environmental samples, and has been commercially available since the 1980s as a primary toxicity screen. Gadgil and Smith (2004) examined the cytotoxicity of 2-dDCB in the Microtox Assay in order to make a comparative analysis between 2-dDCB and common GRAS food additives including the carbonyl compounds cyclohexanone and 2-nonenal. In the Gadgil

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Food Irradiation Research and Technology

and Smith (2004) study the EC50 values, the test compound concentrations that produced a 50% decrease in bioluminescence, were 21.7 ppm for 2-dDCB, 37.4 ppm for cyclohexanone, and 1.65 ppm for nonenal.The authors concluded that the acute toxicity of 2-dDCB was between that of carbonyl group containing GRAS food additives cyclohexanone and 2nonenal in the Microtox Assay.These results are conflicting with those of Burnouf and others (2002), who in growth inhibition studies with Salmonella typhimurium bacteria found clear cytotoxic effects for several 2-ACBs, particularly for 2-DCB. The toxic dose (37% survival) of 2dDCB was about 40 μM, but that of 2-DCB was only 4 μM (Marchioni and others 2004). In addition to tests in bacteria, 2-dDCB has also been tested for the ability to induce rearrangement of chromosomes in eukaryotic cells. The Yeast (Saccharomyces cerevisiae) DEL Assay measures a compound’s ability to cause genomic rearrangements, induced by DNA strand breakage, by restoration of a nonfunctional duplication of the his3 gene to functionality (HIS3+) by intrachromosomal (DEL) recombination (Sommers and Schiestl 2004).The assay does not produce false positives due to cell death because only recombination events in live cells are selected for. This is unlike the Comet Assay, which detects only the DNA strand break, not the actual genetic endpoint. Concentrations up to 5 mg / ml of 2-dDCB, which reduced cell viability to 28%, failed to induce genomic rearrangements in the Yeast DEL Assay (Sommers and Schiestl 2004). In contrast, carcinogens commonly present in food such as benzene and formaldehyde each induce increases in intrachromosomal recombination in the yeast-based test (Sommers and others, 1995).Very recent experiments using Comet Assay to measure DNA strand breaks and 24-color-Fluorescence-In-Situ-Hybridization to estimate chromosomal abnormalities indicated that 2-dDCB had a genotoxic potential and caused chromosomal aberrations in human colon cells (Knoll and others 2005).

2-ACBs and Tumor Promotion There have been very few studies on the ability of highly purified 2-ACBs to induce tumors in animals. Raul and others (2002) investigated the ability of 2-tDeCB and 2-tDCB to induce pre-neoplastic lesions (aberrant crypt foci) and tumors in the colons of Wistar rats. In that study, rats were fed 1% ethanol in water, or fed 1.6 mg/day 2-ACBs (about 6 mg / kg bw) dissolved in water that contained 1% ethanol as the 2-ACB solvent. The rats in each group were injected (intra-peritoneal) at weeks 2 and 3 with carcinogen azoxymethane (15 mg / kg bw), which induces pre-

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neoplastic lesions (ACFs) and tumors in the colons of rodents.The animals were sacrificed at 3 and 6 months and the colons examined for the total number of aberrant crypt foci, the number of crypts per foci, and actual tumor formation. Only a small number of rats, six per group, were used in the study. For each of the test groups, the number of ACF/cm in the distal colon were similar, with no difference in the total number of ACFs being evident. However, a statistically significant, but less than twofold, increase in the number of aberrant crypts per foci was observed in the 2-tDeCBtreated rats after six months, but not after three months.After six months, the total number of tumors in the colon was threefold higher in the 2-ACBtreated animals than in the AOM controls.The colons of four of six AOMcontrol rats exhibited only one small tumor (~6 mm3). Multiple tumors were observed in four and three of six animals treated with 2-tDCB or 2-tDeCB, respectively, whereas medium (6 < S < 25 mm3) and larger (>25 mm3) tumors were detected only in 2-ACB-treated animals. The possibility that one or more of the 2-ACBs at pharmacological doses could be tumor promoters prompted the authors to recommend further research into the tumor promotion phenomenon. Additional in vivo studies, using larger numbers of animals, with 2-ACBs incorporated into the feed of animals as opposed to drinking water, that use multiple 2-ACB concentrations are clearly warranted in order to more accurately assess the tumor-promoting potential of the 2-ACBs.

Diet and Tumor Promotion Although the tumor-promoting potential of the 2-ACBs has not been fully elucidated, the increases in the number of aberrant crypts and tumors in 2-ACB treated animals that received large doses of the carcinogen azoxymethane and the tumor promoter ethanol would not be totally unexpected. Raul and others (2002) speculated that the increase in the number of aberrant crypts observed in their study might be due to the interaction of the fatty acid derivatives with the epithelial cells of the colon.The impact of high levels of dietary fat and the risk of chronic disease, including colon cancer, have been well documented (Weisburger 1997). Udilova and others (2003) found that dietary oil components can induce oxidative stress, lipid peroxidation in membranes, cytotoxicity, and enhanced risk of colon cancer through regenerative cell proliferation. Oxidized beef fat has been shown to induce the formation of colon tumors in rodents (Yang and others 1998). Other colon tumor promoters found in meat and poultry products include oxidized heme, cholesterol, and cholic acid (Van der Meer-van Kraaij and others 2005; Yang and

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others 1998; Tseng 1996). Consumption of high concentrations of fat and fat derivatives causes formation of tumors in the colons of rodents. It is not surprising, therefore, that large doses of purified 2-ACBs might induce formation of tumors in the colons of rodents.

Conclusions Cancer in animals and humans has been associated with many factors including excessive consumption of fried, smoked, and barbecued meats and fish, pickled foods, and alcohol. Carcinogens such as formaldehyde, furan, acrylamide, nitrosamines, and benzene are naturally occurring in many foods, or formed as a result of thermal processing.Tumor promoters present (at milligram and gram quantities) in meat include lipids and oxidized lipids, hemes, and cholesterol. Because levels of 2-ACBs are present in sufficient (albeit μg) quantities to be considered an indirect food additive, assessment of their toxicological potential should be a priority in the science of food irradiation. It should also be recommended that any toxicological risk assessment pertaining to the 2-ACBs should be in the context of the total human diet and the potential benefit of food irradiation in reducing illnesses, hospitalizations, and deaths associated with foodborne illness. Paracelsus, the fifteenth-century philosopher and scientist, observed that all substances are poisons; it is only a matter of dose. Although it is almost impossible to prove the absolute safety of any food or food processing technology, it is difficult to conceive—considering the toxicological database—that radiation-pasteurized foods, including meat and poultry, pose a significant risk to human health when consumed as part of a healthful, well-balanced diet. This is true especially when compared to other, “more established” food processing and preservation methodologies that have been directly associated with the formation of cancers in animals and humans.

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Berglin EH, Carlsson J. 1986. Effect of hydrogen sulfide on the mutagenicity of hydrogen peroxide in Salmonella typhimurium TA102. Mutat Res 175:5–9. Barlow SM, Kozianowski G, Würtzen G, Schlatter J. 2001. Threshold of toxicological concern for chemical substances present in the diet. Food Chem Tox 39:893–905. Boyd DR, Crone AVJ, Hamilton JTG, Hand MV, Stevenson MH, Stevenson PJ. 1991. Synthesis, characterization, and potential use of 2-dodecylcyclobutanone as a marker for irradiated chicken. J Agric Food Chem 39:789–792. Burnouf D, Delincée H, Hartwig A, Marchioni E, Miesch M, Raul F,Werner D. 2002. Etude toxicologique transfrontalière destinée à évaluer le risque encouru lors de la consommation d’aliments gras ionisés. Toxikologische Untersuchung zur Risikobewertung beim Verzehr von bestrahlten fetthaltigen Lebensmitteln. Eine französisch-deutsche Studie im Grenzraum Oberrhein. Rapport final / Schlussbericht INTERREG II. Projet / Projekt No. 3.171. Marchioni E, Delincée H, Editors. Bundesforschungsanstalt für Ernährung, Karlsruhe, BFE-R—02-02.pp.1-198. Chinn HI. 1979a. Evaluation of the health aspects of certain compounds found in irradiated beef. I. Further toxicological considerations of volatile products. Federation of American Societies for Experimental Biology, Life Sciences Research Office, Bethesda, MD. Contract Rep. No. DAMD 17-76-C-6055, pp. 1–29. Chinn HI. 1979b. Evaluation of the health aspects of certain compounds found in irradiated beef. II. Possible radiolytic compounds. Federation of American Societies for Experimental Biology, Life Sciences Research Office, Bethesda, MD. Contract Rep. No. DAMD 17-76-C-6055, pp. 1–42. Crone AVJ, Hamilton JTG, Stevenson MH. 1992a. Effect of storage and cooking on the dose response of 2-dodecylcyclobutanone, a potential marker for irradiated chicken. J Sci Food Agric 58:249–252. Crone AVJ, Hamilton JTG, Stevenson MH. 1992b. Detection of 2-dodecylcyclobutanone in radiation-sterilized chicken meat stored for several years. Int J Food Sci Technol 27:691–696. Crone AVJ, Hand MV, Hamilton JTG, Sharma ND, Boyd DR, Stevenson MH. 1993. Synthesis, Characterisation and Use of 2-Tetradecylcyclobutanone Together with Other Cyclobutanones as Markers for Irradiated Liquid Whole Egg. J Sci Food Agric. 62:361–367. Dauphin J, Saint Lebe LR. 1977. Radiation chemistry of carbohydrates. Pp.131-195, In Radiation Chemistry of Major Food Components (PS Alias, AJ Cohen, Editors), Elsevier,Amsterdam. Delincée H, Pool-Zobel BL 1998. Genotoxic properties of 2-dodecylcyclobutanone, a compound formed on irradiation of food containing fat. Radiat Phys Chem 52:39–42. Delincée H, Pool-Zobel BL, Rechkemmer G 1999. Genotoxizität von 2-Dodecylcylobutanon. Pp. 262–269, In Lebensmittelbestrahlung (M Knörr, DAE Ehlermann, H Delincée, Editors), 5. Deutsche Tagung, Karlsruhe, Berichte der Bundesforschungsanstalt für Ernährung. 1112 Nov. 1998; BFE-R—99-01. EN 1785. 2003. Foodstuffs—detection of irradiated food containing fat—Gas chromatographic / mass spectrometric analysis of 2-alkylcyclobutanones, (revised version, supersedes EN 1785:1996). European Committee for Standardization, Brussels. Fan X,Thayer DW. 2002. Formation of malonaldehyde, formaldehyde, and acetaldehyde in apple juice induced by ionizing radiation. J Food Sci 67:2523–2528. Fan X. 2003. Ionizing radiation induces formation of malondialdehyde, formaldehyde, and acetaldehyde from carbohydrates and organic acid. J Agric Food Chem. 51(20): 5946–5949. Federal Register. 2005. Irradiation in the Production, Processing, and Handling of Food [Docket No. 1999F-4372] 21 CFR Part 199. Federal Register 70(175) 48057–49073.

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Fiddler W, Pensabene W, Gates RA, Jenkins RK,Wierbicki E. 1985. Observations on the use of gamma irradiation to control nitrosamine formation in bacon. Food Irradiation Processing: Proceedings International Symposium Food Irradiation Processing. Washington, D.C., 4–8 March, 1985, pp. 238–239. Friedman M. 2003. Chemistry, biochemistry, and safety of acrylamide.A review. J Agric Food Chem. 51(16):4504–4526. Gadgil P, Smith JS. 2004. Mutagenicity and acute toxicity evaluation of 2-dodecylcyclobutanone. J. Food Sci. 69:713–716. Gadgil P, Hachmeister KA, Smith JS, Kropf DH. 2002. 2-Alkylcyclobutanones as irradiation dose indicators in irradiated ground beef patties. J Agric Food Chem. 50:5746–5759. Handel AP, Nawar WW. 1981. Radiolytic Compounds from Mono-, Di- and Triacylglycerols. Radiat Res 86:428–436. Hartwig A, Dally H, Schlepegrell R. 1996. Sensitive analysis of oxidative DNA damage in mammalian cells: Use of the bacterial Fpg protein in combination with alkaline unwinding.Toxicol Lett. 88:85–90. Health Canada. 2002. Irradiation of ground beef: Summary of submission process. October, 29. Food Directorate, Food Products and Health Branch, Ottawa, www.hc-sc.gc.ca/foodaliment/fpi-ipa/e-gbeef_submission.pdf. Health Canada. 2003. Evaluation of the significance of 2-dodecylcyclobutanone and other alkylcyclobutanones. Pp. 1–7. http://www.hc-sc.gc.ca/food-aliment/fpi-ipa/e-cyclobutanone.html.Accessed September 2004. Horvatovich P, Miesch M, Hasselmann C, Marchioni E. 2002a. Supercritical fluid extraction for the detection of 2-dodecylcyclobutanone in low dose irradiated plant foods. J Chromatogr A 968:251–255. Horvatovich P, Raul F, Burnouf D, Delincée H, Hartwig A, Werner D, Marchioni E. 2002b. Detection of 2-alkylcyclobutanones, markers for irradiated foods, in adipose tissues of animals fed with these substances. J Food Protect 65:1610–1613. Horvatovich P, Miesch M, Hasselmann C, Delincée H, Marchioni E. 2005. Determination of mono-unsaturated alkyl side-chain 2-alkylcyclobutanones in irradiated foods. J Agric Food Chem, 53:5836-5841. Kim JH,Ahn HJ, Kim DH, JoC,Yook HS, Park HJ, Byun MW 2003. Irradiation effects on biogenic amines in Korean fermented soybean paste during fermentation. J Food Sci 68:80–84. Kim KS, Lee JM, Seo HY, Kim JH, Song HP, Byun MW, Kwon JH. 2004. Radiolytic products of irradiated authentic fatty acids and triacylglycerides. Radiat Phys Chem 71:45–49. Kim JK,Ahn HJ, Lee JW, Park JP, Ryu GH, Kang IJ, Byun MW. 2005. Effects of gamma irradiation on the biogenic amines in pepperoni with different packaging conditions. Food Chem 89:199–205. Knecht-van Eekelen A de, Mueller HC van den,Til HP, Groot AP de. 1971. Multi-generation study in rats with radiation-pasteurized chicken. Rept. R3622. Central Inst. For Nutrition and Food Research. Zeist,The Netherlands. Knecht-van Eekelen A de, Feron VJ,Til HP, Groot AP de. 1972. Chronic (two year) feeding study in rats with radiation-pasteurized chicken. Rept. R3773. Central Inst. For Nutrition and Food Research. Zeist,The Netherlands. Knekt P, Jarvinen R, Dich J, Hakulinen T. 1999. Risk of colorectal and other gastro-intestinal cancers after exposure to nitrate, nitrite and N-nitroso compounds: A follow-up study. Int. J Cancer. 80:852–856. Knoll N,Weise A, Glei M, Claussen U, Marian B, Pool-Zobel BL. 2005. 2-Dodecylcyclobutanone, a radiolytic product of palmitic acid, causes DNA strand breaks and chromosomal aber-

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rations in human colon adenoma cells. Naunyn-Schmiedeberg’s Arch Pharmacol. 371, Suppl. 1, R 131. Lee MS, Kim HL, Jeong, JB. 1973. Effects of ionizing radiation on development of wound periderm, solanine content, and the formation of carbonyl compounds in potato tubers. Korean J Food Sci Technol. 5:65–69. LeTellier PR, Nawar WW. 1972. 2-Alkylcyclobutanones from radiolysis of triglycerides. Lipids 1:75–76. Levin DE, Marnett L,Ames BN. 1984. Spontaneous and mutagen induced deletions: Mechanistic studies in Salmonella tester strain TA102. Proc Natl Acad Sci (U.S.A.) 81:4457–4461. Mufti SI. 1998.Alcohol-stimulated promotion of tumors in the gastrointestinal tract. Cancer Detect Prev. 22(3):195–203. Marchioni E, Raul F, Burnouf D, Miesch M, Delincée H, Hartwig A, Werner D. 2004. Toxicological study on 2-alkylcyclobutanones—results of a collaborative study. Radiat Phys Chem. 71:145–148. Matiella JE, Hsieh TCY. 1991.Volatile compounds in scrambled eggs. J Food Sci 56:387–390, 426. McNeal TP, Nyman PJ, Diachenko GW, Hollifield HC. 1993. Survey of benzene in foods by using headspace concentration techniques and capillary gas chromatography. J AOAC Int 76:1213–1219. Meier W,Artho A, Nägeli P. 1996. Detection of Irradiation of Fat-containing Foods by On-line LC-GC-MS of Alkylcyclobutanones. Mitt Geb Lebensm Hyg 87:118–122. Merritt Jr C,Angelini P, Graham R A. 1978. Effect of radiation parameters on the formation of radiolysis products in meat and meat substances. J Agric Food Chem 26:29–35. Nam KC, Min BR, Park KS, Lee SC,Ahn DU. 2003. Effects of ascorbic acid and antioxidants on the lipid oxidation and volatiles of irradiated ground beef. J Food Sci 68:1680–1685. Nawar WW. 1978. Reaction mechanisms in the radiolysis of fats: A review. J Agric Food Chem 26:21–25. Nawar WW. 1986.Volatiles from food irradiation. Food Reviews Intern 21:45–78. Ndiaye B. 1998. Les 2-Alkylcyclobutanones, molecules indicatrices d’un traitement ionisant des aliments. PhD Thesis, University Louis Pasteur Strasbourg. Ndiaye B, Jamet G, Miesch M, Hasselmann C, Marchioni E. 1999a. 2-Alkylcyclobutanones as markers for irradiated foodstuffs II.The CEN (European Committee for Standardization) method: Field of application and limit of utilization. Radiat Phys Chem 55:437–445. Ndiaye B, Horvatovich P, Miesch M, Hasselmann C, Marchioni E. 1999b. 2-Alkylcyclobutanones as markers for irradiated foodstuffs. III. Improvement of the field of application on the EN 1785 method by using silver ion chromatography. J Chromatogr A 858:109–115. Nishimura H, Philp RP, Calvin M. 1977. Lipids of Hevea brasiliensis and Euphorbia coerulescens. Phytochemistry 16:1048–1049. Orser CS, Foong FC, Capaldi SR, Nalezny J, Mackay W, Benjamin M, Farr SB. 1995a. Use of prokaryotic stress promoters as indicators of the mechanisms of toxicity. In Vitro Toxicol 8 (1):71–85. Orser CS, Capaldi S, Morse R, Schnieder BJ, Nalezny J, Farr SB 1995b. Utility of cell wall mutants in the Pro-Tox bacterial stress gene assay. Xenometrix, Inc. 2860 Wilderness Place, Boulder, CO, 80301, U.S.A. Park ER, Kim EA, Kim KS. 2001. Detection of radiation-induced hydrocarbons and 2alkylcyclobutanones from irradiated pork. Food Sci Biotechnol 10:84–89. Perez-Locas C,Yaylayan VA. 2004. Origin and mechanistic pathways of formation of the parent furan—a food toxicant. J Agric Food Chem. 52:6830–6836.

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Poling CE, Warner WD, Humburg FR, Reber EF, Urbain WM, Rice EE. 1955. Growth, reproduction, survival and histopathology of rats fed beef irradiated with electrons. Food Res 20:193–214. Raul F, Gossé F, Delincée H, Hartwig A, Marchioni E, Miesch M,Werner D, Burnouf D. 2002. Food-borne radiolytic compounds (2-Alkylcyclobutanones) may promote experimental colon carcinogenesis. Nutr Cancer 44:188–191. Reyns KM, Diels AM, Michiels CW. 2004. Generation of bactericidal and mutagenic components by pulsed electric field treatment. Int J Food Microbiol 93(2):165–173. Skopek TR, Thilly WG. 1983. Rate of induced forward mutation at 3 genetic loci in Salmonella typhimurium. Mutat Res 108:45–56. Smith CM, Koch WH, Franklin SB, Foster PL, Cebula TA, Eisenstadt E. 1990. Sequence analysis and mapping of the Salmonella typhimurium LT2 umuDC operon. J Bacteriol 172:4964–4978. Smith JS, and Pillai S. 2004. Irradiation and food safety. Food Technology 58 (11):48–55. Sommers CH, Mackay WJ, Nalezny J, Gee P, Benjamin M, Farr SB. 1995. Induction of DEL recombination in the yeast Saccharomyces cerevisiae using a microtiter plate format. In Vitro Toxicol 11:37–47. Sommers CH. 2003. 2-Dodecylcyclobutanone does not induce mutations in the Escherichia coli tryptophan reverse mutation assay. J Ag Food Chem 51:6367–6370. Sommers CH, Schiestl RH. 2004. 2-Dodecylcyclobutanone does not induce mutations in the Salmonella Mutagenicity Test or intrachromosomal recombination in Saccharomyces cerevisiae. J Food Prot 67:1293–1298. Sommers CH, Mackay WM. 2005. 2-Dodeclycyclobutanone does not induce formation of 5fluorouracil resistant mutants or increase expression of DNA damage inducible genes in Escherichia coli. J Food Sci 70:254–256. Stevenson MH, Crone AVJ, Hamilton JTG. 1990. Irradiation detection. Nature 344:202–203. Stevenson MH. 1992. Progress in the identification of irradiated foods. Trends Food Sci Technol 3:257–262. Stevenson MH. 1994. Identification of Irradiated Foods. Food Technol 48:141–144. Stevenson MH, Crone AVJ, Hamilton JTG, McMurray CH. 1993.The use of 2-dodecylcyclobutanone for the identification of irradiated chicken meat and eggs. Radiat Phys Chem 42:363–366. Stevenson MH. 1996.Validation of the Cyclobutanone Protocol for Detection of Irradiated Lipid Containing Foods by Interlaboratory Trial, McMurray CH, Stewart EM, Gray R, Pearce J (Eds.). In Detection Methods for Irradiated Foods–Current Status. Pp. 269–284. Royal Society of Chemistry, Cambridge, UK. Stewart EM. 2001. Food Irradiation Chemistry. Molins RA (Ed.). In Food Irradiation: Principles and Applications. Pp. 37–76. J.Wiley & Sons, New York. Stewart EM, McRoberts WC, Hamilton JTG, Graham WD. 2001. Isolation of lipid and 2alkylcyclobutanones from irradiated foods by supercritical fluid extraction. J AOAC Int 84:976–986. Stewart EM, Moore S, Graham WD, McRoberts WC, Hamilton JTG. 2000. 2-Alkylcyclobutanones as markers for the detection of irradiated mango, papaya, Camembert cheese and salmon meat. J Sci Food Agric 80:121–130. Swallow AJ. 1991. Wholesomeness and safety of irradiated foods. Friedman, M. Editor. In Nutritional and toxicological consequences of food processing. Pp. 11–31. Plenum Press, NY, NY, U.S.A. Tanabe H, Goto M, Miyahara M. 2001. Detection of irradiated chicken by 2-alkylcyclobutanone analysis. Food Irrad Japan 36:26–32.

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Thayer DW, Christopher JP, Campbell LA, Ronning DC, Dahlgren RR, Thompson GM, Wierbicki E. 1987. Toxicology studies of irradiation-sterilized chicken. J Food Prot 50:278–288. Tice RR, Agerell E, Anderson D, Burlison B, Hartmann A, Kobayashi H, Miyamae Y, Rojas E, Ryu JC, Sasaki YF. 2000. Single cell gel/comet assay; guidelines for in vitro and in vivo genetic toxicology testing. Environ Mol Mutagen 35(3):206–221. Tran TT, Medline A, Bruce WR. 1996. Insulin promotion of colon tumors in rats. Cancer Epidemiol Biomarkers Prevent 5:1013–1015. Tseng TH, Hsu JD, Chu CY,Wang CJ. 1996. Promotion of colon carcinogenesis through increasing lipid peroxidation induced in rats by a high cholesterol diet. Cancer Lttrs 100:81–87. Udilova N, Jurek D, Marian B, Gille L, Schulte-Hermann R, Nohl H. 2003. Induction of lipid peroxidation in biomembranes by dietary oil components. Food Chem. Toxicol. 41:1481–1489. U.S. Food and Drug Administration. 1997. Irradiation in the production, processing and handling of food. Final Rule. Federal Register 62 (232):64107–64121. Van der Meer-van Kraaij C, Kramer E, Jonker-Termont D, Katan MB, van der Meer R, Keijer J. 2005. Differential gene expression in rat colon by dietary heme and calcium. Carcinogenesis 26:73–79. Weisburger JH. 1997. Dietary fat and the risk of chronic disease: Mechanistic insights from experimental studies. J Amer Dietetic Assoc 97: 16–23. Weisburger JH, Jones RC. 1990. Prevention of formation of important mutagens/carcinogens in the human food chain. Basic Life Sci 52:105–118. World Health Organization. 1994. In Safety and nutritional adequacy of irradiated food. World Health Organization. Geneva, Switzerland, p. 81–107. World Health Organization. 2002. Health implications of acrylamide in foods. Report of a joint FAO/WHO consultation.World Health Organization. Geneva, Switzerland, Chapter 5, p.7-12. Yang CM, Kendall CWC, Stamp D, Medline AM,Archer MC, Bruce WR. 1998.Thermally oxidized dietary fat and colon carcinogenesis in rodents. Nutr Cancer 30:69–73.

Food Irradiation: Research and Technology Edited by Christopher H. Sommers, Xuetong Fan Copyright © Blackwell Publishing and the Institute of Food Technologists 2006

Chapter 5 CONSUMER ACCEPTANCE AND MARKETING OF IRRADIATED FOODS Ronald F. Eustice and Christine M. Bruhn

Introduction Many innovations, even those with obvious advantages, require a lengthy period of time between when they become available and when they are widely accepted (Rogers 1983). Technologies such as pasteurization, immunization, and chlorination are now considered by health experts to be “pillars of public health,” yet each of these lifesaving innovations was met with suspicion and resistance when first introduced. Louis Pasteur discovered that bacteria could be eliminated by heating during the 1850s.This process became known as pasteurization and was highly controversial at that time. As late as the 1930s, many in the dairy industry resisted widespread use of pasteurization. One of multiple concerns expressed was that the promotion of pasteurized milk would cast a negative shadow over the nonpasteurized product and force milk handlers to install “expensive” equipment to pasteurize milk. During the 1920s, the U.S. dairy industry and insurance companies were promoting so-called certified raw milk as a more acceptable alternative to pasteurization (Metropolitan Life 1923). It was only through the insistence of medical and scientific groups that the dairy industry abandoned its “good milk” versus “bad milk” concerns and embraced pasteurization as a lifesaving technology that would help to make all milk safe. Pasteurization took nearly 70 years to be fully accepted in the United States, and the arguments against it were almost identical to those used today against food irradiation (Hall and Trout 1968).Among some 70 concerns raised by the critics of pasteurization were the following: 63

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• • • • •

“We must not meddle with nature.” “This process changes the properties of the food.” “Dangerous substances could be formed.” “This process could be carelessly done and accidents could happen.” “Pasteurization will increase the price of the product.We have a direct and prompt food distribution system.” • “It is not necessary.” None of these doomsday predictions turned out to be true; however, the campaign against pasteurization, including resistance from dairy producers and processors, significantly delayed its introduction, with the effect that thousands of people suffered chronic illness, developed longterm health consequences, or died. The question of legal responsibility for inflicting this suffering was never explored.

Resistance to “New” Technology Although food irradiation, sometimes called “cold pasteurization,” has been described as the “most extensively studied food processing technology in the history of humankind” and is endorsed or supported by virtually all medical and scientific organizations (see Table 5.1), the process is still considered a relatively “new” technology. It is human nature to resist change and to fear the “unknown.” Exploration of the “new world” was stifled by critics who believed the earth was flat. Arguments against constructive change take many forms. University of Houston economics professor and noted author Thomas R. DeGregori says,“One common argument against change is the search for a risk less alternative” (DeGreggori 2002). DeGregori says,“Every change has its risks; some real, others imagined.Whether a change is political, scientific, or technological, a simple assertion of risk should not in and of itself be an argument against that change.We must measure the benefits of change against the risks of not changing.” Christopher Columbus and other explorers faced a multitude of risks, but their ships did not drop off the edge of the earth. Impossible demands for a zero-risk society are often made by those who wish to maintain the status quo and convince others that the risks outweigh benefits.Those who choose to believe that the earth is flat despite overwhelming scientific evidence to the contrary have every right to do so. In a free society, proponents of the “Flat Earth Theory” have a right to their own set of opinions, but those opinions do not alter the fact that the earth is demonstrably and unequivocally spherical.

Table 5.1.

List of Organizations That Approve or Endorse Irradiation

American Council on Science and Health American Dietetic Association American Farm Bureau Federation American Feed Industry Association American Meat Institute American Medical Association American Veterinary Medical Association Animal Health Institute Apple Processors Association Centers for Disease Control & Prevention Chocolate Manufacturers Association Codex Alimentarius Council for Agricultural Science and Technology Florida Fruit and Vegetable Association Food and Drug Administration Food Distributors International Food and Agriculture Organization (FAO) Grocery Manufacturers of America Health Physics Society Institute of Food Science & Technology Institute of Food Technologists International Atomic Energy Agency International Food Information Council (IFIC) The Mayo Clinic Millers' National Federation National Confectioners' Association National Cattlemen's Beef Association National Food Processors Association National Fisheries Institute National Meat Association National Food Processors Association National Turkey Federation National Pork Producers Council Northwest Horticulture Association Produce Marketing Association Scientific Committee of the European Union United Egg Association United Fresh Fruit & Vegetable Association United Egg Producers United Kingdom Institute of Food Science & Technology United States Chamber of Commerce U.S. Department of Agriculture Western Growers Association World Health Organization (WHO)

65

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Risks versus Benefits DeGregori says,“If we examine the many changes over the past century— changes that have reduced infant and child mortality by more than 90%, have given Americans nearly 30 years of added life expectancy, have recently caused an even more rapid growth in disability-free years of life, and have allowed comparable or greater advances in other countries— we will find that all those changes carried risks.” Technologies such as chlorination of water, pasteurization of milk, synthetic fertilizers, chemical pesticides, modern medicine, genetically enhanced organisms, immunization, and irradiation, to name a few, all faced and continue to face various levels of opposition. Most cities use chlorine to purify their water, most parents want their children immunized against dreaded diseases, and very few people would consider drinking unpasteurized (raw) milk because of the known risks. Yet these lifesaving technologies all have their risks. Chlorine is toxic, and immunization can sometimes cause the disease it was intended to prevent. Pasteurized milk tastes different than milk straight from the cow, can be recontaminated, and will spoil if not refrigerated. By comparison, the risks of irradiation, if there are any, are “unknown” because after years of study, scientists haven’t found any (Wisconsin State Journal Editorial Board 2003). Weigh that against the known risks of contracting bacterial illnesses from the consumption of food that harbors unseen pathogens.

World’s Safest Food Supply, But Not Safe Enough The meat and poultry industry’s surveillance and intervention efforts have reduced, but not eliminated, microbial contamination of meat and poultry carcasses (CDC 2000; USDA FSIS 2003). Steve Kay, Editor and Publisher of Cattle Buyers Weekly, estimates that between 1993 and 2003, the 10 largest beef-processing companies spent more than $400 million on new equipment and added $250 million to their operating costs to fight E. coli O157:H7. Kay calculates that the overall cost of E. coli O157:H7 to the beef industry since 1993 is $2.8 billion and rising (Kay 2003). Despite these efforts, consumers continue to experience preventable illnesses and deaths caused by microbial contamination of foods. Traditional safety measures have the primary role in ensuring the safety of our meat supply, but they will not eliminate all contamination, particularly in a meat-processing environment. The U.S. Department of Agriculture’s (USDA) Food Safety and Inspection Service determined that

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the contamination level for E. coli O157:H7 in ground beef was 0.17% in 2004 compared to 0.30% in 2003, 0.78% in 2002, 0.84% in 2001, and 0.86% in 2000 (USDA 2005). Although this downward trend is very encouraging, it is imperative that the meat industry further enhance efforts to provide the public with the protection they expect and deserve against foodborne illness. Because the U.S. produces about 8 billion pounds of ground beef annually, even this exceedingly low percentage of contamination means production of an estimated 12 to 15 million pounds of E. coli O157:H7– contaminated ground beef each year (Roybal 2003). Based on these numbers, nearly two of every 1,000 hamburger patties produced in the U.S. contain bacterial pathogens when they leave the manufacturing plant. If that contaminated ground beef is not properly cooked to 160 degrees Fahrenheit (71 degrees Centigrade), it can cause serious injury or death. Furthermore, pathogens that may be on the meat could potentially contaminate other foods in the kitchen. If the product were irradiated, the pathogens would be destroyed before entering the home or foodservice kitchen. What would be the public response if a Detroit automaker sold a line of vehicles while fully aware that 0.17% of those vehicles had a production defect that each year could potentially lead to thousands of injuries and scores of deaths among its customers? The situation becomes more serious when we consider recent research by FDA/FSIS that shows that although some 60% of households have a meat thermometer, only 6% of consumers report using it often or always (Cates, 2002). Research at Utah State University further confirms this data (Anderson and others, 2004).The study, completed in 2003 and published in the Journal of the American Dietetic Association, showed that only five of 99 participants used a thermometer to determine doneness of meat, poultry, or seafood and only six of those who owned a thermometer reported using it often/always. Nearly half of study participants reported not knowing the recommended cooking temperature for chicken (43%) and ground beef (44%).

Irradiation: A Powerful and Effective Tool to Improve Food Safety Although irradiation cannot prevent primary contamination, it is the most effective tool available to significantly reduce or eliminate harmful bacteria in raw product and make sure that contaminated ground beef does not reach the marketplace.At doses that are commonly used to ir-

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radiate ground beef, we can expect the following levels of pathogen reduction: E. coli O157:H7 99.99% to 99.9999% Salmonella 99% to 99.9% Listeria 99.9% to 99.99% Food irradiation has the potential to dramatically decrease the incidence of foodborne disease and has earned virtually unanimous support or approval from international and national medical, scientific, and public health organizations, as well as food processors and related industry groups. Dr. Robert Tauxe of the U.S. Centers for Disease Control and Prevention estimates that if 50% of poultry, ground beef, pork, and processed meats in the United States was irradiated, the potential benefit of the irradiation would be a 25% reduction in the morbidity and mortality rate caused by these infections. This estimated net benefit is substantial; the measure could prevent nearly 900,000 cases of infection, 8,500 hospitalizations, more than 6,000 catastrophic illnesses, and 350 deaths each year (Tauxe 2001). Given the probable number of unreported and undetected foodborne illnesses, this reduction is likely to be even greater (Table 5.2). The globalization of trade in food and agricultural commodities and the increasing demand for food safety and security from “Farm to Fork” represent new challenges to the food industry (Satin 2003). Morton Satin, former Chief of Food and Agro-Industries, FAO, Rome, Italy, describes the dismantling of national barriers to trade as opportunities for greater efficiencies in economic growth, but says that as free trade increases, foodborne disease organisms cross international borders with relative impunity. Satin says,“Pathogens journey along with finished food products, raw agricultural commodities, handlers, travellers, and hidden insects. When one considers that these organisms travel with the tiniest particles of dust carried in the wind and are easily swept along international waterways, it is apparent that even the most rigorous quarantine procedures cannot prevent the movement of foodborne pathogens between countries. Routine use of irradiation of fruits, vegetables, and raw meat at border crossings should be seriously considered as an intervention strategy.”

Consumer Acceptance of Irradiated Foods So, if irradiation is such a great idea, where can we buy irradiated foods? Why aren’t supermarket shelves full of irradiated meat and produce? Why aren’t restaurants serving irradiated hamburgers and poultry as a routine

Consumer Acceptance and Marketing of Irradiated Foods Table 5.2. Pathogen

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Food Irradiation: Potential Annual Public Health Benefits by Specific

Pathogen

Prevented Cases

Prevented Hospitalizations

E. coli O157:H7 and other STEC 23,000 Campylobacter 500,000 Salmonella 330,000 Listeria 625 Toxoplasma 28,000

700 2,600 4,000 575 625

Total

8,500

881,625

Prevented Major Complications

Prevented Deaths

250 HUS cases 250 GBS cases 6,000 RA cases 60 miscarriages 100-1,000 cases Cong. toxo 6,660 major illnesses

20 25 140 125 94 404

R.Tauxe, CDC. 2001.

part of doing business? When will state health departments recommend that all ground beef and poultry served in hospitals, day care centers, and nursing homes be irradiated? When will school boards that would never consider serving raw milk in school cafeterias demand that all ground beef and poultry served to students be precooked or irradiated? Although irradiated fruits, vegetables, and poultry have been available commercially on a limited basis since the early 1990s, the introduction of irradiated ground beef in Minnesota during May 2000 significantly increased awareness and interest in the technology.According to Jim Jones, Food Tech Services, Mulberry, FL, approximately 18 to 20 million pounds of irradiated ground beef and poultry were marketed in the United States during 2004. Jones also estimates that some 2 million pounds of irradiated fruits and vegetables, mainly mango, papaya and guava, are sold annually by U.S. retailers. Spices have been commercially irradiated since 1986.Approximately one-third of the commercial spices consumed in the United States, some 175,000,000 lbs, are irradiated annually according to John Masefield, Executive Advisor of Steris IsoMedix Services, Mentor, OH. Yet, despite widespread media attention from food recalls, serious illness, and death, food irradiation technology remains underutilized and often misunderstood. Acceptance of irradiation has been slowed by several factors (Osterholm and Norgan 2004). First, the term “irradiation” is sometimes confusing or alarming to consumers because of its perceived association with radioactivity. Second, the causes, incidence, and prevention of foodborne disease are poorly understood by the general public.Third, health professionals and the media are largely unaware of the benefits of food irradia-

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tion. Finally, an anti-irradiation campaign has been conducted by certain activist groups because of their beliefs about food production issues, nuclear power, international trade, and industrialization, as well as the introduction of technologies.

Education: The Key to Consumer Acceptance What is preventing the technology from gaining widespread consumer acceptance? Numerous consumer studies clearly show that when given a choice and even a small amount of accurate information, consumers are not only willing to buy irradiated foods but also often prefer them over food treated by conventional means.A variety of market research studies conducted over the past two decades repeatedly demonstrate that 80–90% of consumers will choose irradiated products over nonirradiated after they hear the facts and understand the benefits. In a 1995-1996 University of California, Davis, study, interest in buying irradiated foods among California and Indiana consumers increased from 57% to 82% after seeing a 10-minute video describing irradiation. A 1995 study at Kansas State University showed that more than 80% of 229 respondents would purchase irradiated instead of nonirradiated poultry if both were offered at the same price.Thirty percent were prepared to pay a 10% premium for irradiated chicken, and 15% indicated a willingness to pay a 20% premium. A 2001 study funded by the Cattlemen’s Beef Board (CBB) (National Cattleman’s Beef Association 2002) showed that consumer acceptance of irradiated ground beef is growing.The study, which measured consumer perceptions about irradiated ground beef, revealed a sizeable potential market for the product. Researchers found that a person’s acceptance of irradiated beef was greatly influenced by initial perceptions. Four consumer segments were identified: strong buyers (27% of the test group), interested (34%), doubters (24%), and rejecters (15%). The first three were identified as potential markets for irradiated ground beef, and the study suggested that by implementing consumer education programs and continuing product quality research, the market for irradiated ground beef should continue to grow. Nearly all the “strong buyers” were ready to buy irradiated ground beef before the study, more likely to buy it after trying it, and willing to pay 10 cents a pound more for it.The “rejecter” segment snubbed placebo ground beef patties—nonirradiated burgers that were labeled as irradiated in the study—as often as the irradiated patties. The study said that no amount of information would convince this group, which generally rejects any new product.

Consumer Acceptance and Marketing of Irradiated Foods

Figure 5.1. 2003).

71

Consumer willingness to buy and pay for irradiated ground beef (Aiew

A spring 2002 study by Texas A & M University (TAMU) (Aiew and others 2003) investigated Texas consumers’ knowledge and acceptance of food irradiation and the effects of information about food irradiation on consumer acceptance and willingness to pay for irradiated ground beef (Figure 5.1). Before the presentation of any information in the TAMU study, about half of the respondents indicated a willingness to purchase irradiated ground beef.After receiving information about food irradiation, 88.5% of the respondents were willing purchasers. Even more (94.12%) indicated a willingness to buy irradiated ground beef after a second set of information on food irradiation was presented. The willingness-to-buy percentages in the Texas A & M study appear higher than estimates from the FoodNet Population Survey (1998-1999) conducted by the Centers for Disease Control and Prevention (CDC). The CDC also estimate that at least half of consumers will buy irradiated food, if given a choice between irradiated and nonirradiated; also, if consumers are first educated about irradiation, about 80% will buy irradiated products. Scientists at the University of Georgia conducted a survey to determine current consumer attitudes toward irradiation after consuming irradiated ready-to-eat poultry meat products and to evaluate differences in consumer acceptance, if any, over a 10-year period (1993 versus 2003) (Johnson and others 2004). Surveys were completed by 50 consumers in

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the metro-Atlanta area. More than twice as many consumers were willing to buy irradiated products in 2003 than in 1993 (69% and 29%, respectively).The majority (66%) of the respondents were aware of irradiation; among these, 71% indicated that they were either “somewhat informed” or “had heard about irradiation, but do not know much about it.” Consumers in both studies expressed more concern for pesticide and animal residues, growth hormones, food additives, bacteria, and naturally occurring toxins than irradiation. Consumers expressed slight concern regarding irradiation; however, this concern had decreased significantly over the past 10 years. Approximately 76% preferred to buy irradiated pork and 68% preferred to buy irradiated poultry to decrease the probability of illness from Trichinella and Salmonella, respectively. The University of Georgia study also found that a fourth (24–25%) of all consumers said they would buy more beef, poultry, and pork if these were irradiated and labeled.This figure reflects an 80–85% increase, over the 10-year period, in the number of consumers who would buy more poultry and beef, respectively. Many (41–45%) respondents said they would pay a 1–5% premium for irradiated products, with a few more going as high as 6–10%. A 2003 study by Jefferson Davis Associates (2003) showed that 68% of 396 respondents in six Midwestern states were aware of irradiation and 78% considered irradiated ground beef a “good thing.” The results of dozens of studies at leading universities consistently show that information about the nature and benefits of irradiation is a major factor affecting consumers’ perception of and attitudes toward irradiated foods.The findings reflect the importance of educating the public about the hazards of foodborne pathogens and the potential benefits of consuming irradiated foods. Studies consistently show that information plays an important role in consumer buying decisions, and consumers are generally receptive to irradiated foods when the benefits of irradiation are explained. Negative information about the process can reduce demand for irradiated foods, but that negative information can be honestly and effectively countered.

Effect of Unfavorable Information Fox and others (2001) describe how consumers respond to the presence of unfavorable information about food irradiation. In a choice experiment, 87 consumers were given a typical pork sandwich and asked to bid in a repeated auction for an upgrade to an irradiated pork sandwich. Participants were required to consume either the typical or the irradiated pork

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at the end of the experiment, and the auction was nonhypothetical—that is, the winner was required to pay for the upgrade to the irradiated pork. For the first five of a total of 10 rounds in the auction, participants were provided with a description of irradiation based on Food and Drug Administration information. Based on that description, approximately 60% of participants bid some amount to upgrade from a typical to an irradiated pork sandwich. The same participants were then provided with either a favorable or unfavorable description of irradiation, or both simultaneously.The favorable description (from the American Council on Science and Health) emphasized the benefits and safety of the process and its contribution to controlling foodborne illness.The unfavorable description (from Food & Water, Inc. a Vermont-based anti-irradiation advocacy group) noted that irradiation produced carcinogens called radiolytic products, that it caused vitamin losses, that it would eliminate warning signs of botulin toxin, and that the use of radioactive materials would put workers and nearby communities at risk. As expected, the favorable description alone resulted in more bids to upgrade to irradiated pork and the unfavorable description alone caused bids to decrease.When given only the favorable description, close to 90% of the participants bid for the upgrade to the irradiated product. Among those who were given only the unfavorable description, the proportion bidding for irradiated pork fell from 60% to 10–15%. But the disappointing result was that when subjects were provided with both sets of information, the effect of negative information dominated that of the positive and the proportion bidding for irradiated pork fell by approximately 20 percentage points. In fact, of 50 subjects who received both descriptions, only one subsequently submitted a higher bid to obtain an irradiated pork sandwich.

Can Unfavorable Information Be Counteracted? The results above demonstrate how negative information tends to dominate positive information and illustrates the need to honestly and aggressively counter false claims. Assuming that consumers will be exposed to unfavorable information about irradiation, this suggests that it is not sufficient for industry to promote food irradiation only on its own merits; it will also need to counter the claims made by opponents. The question then, is whether the anti-irradiation message can be effectively countered— that is, whether consumers, once exposed to anti-irradiation propaganda, can be reassured about the technology. To address that question, investigators conducted experiments in

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which consumers could purchase irradiated or nonirradiated chicken breasts. In the experiments (Shogren and others 1999; Fox 2002; Fox and others 2001), 96 consumers were provided with a U.S. Dept. of Agriculture brochure describing the food irradiation process and then asked to make a purchase choice between irradiated or nonirradiated (typical) chicken breasts. When all subjects had made their decision, they purchased and paid for the product they had chosen—and 79% purchased irradiated chicken. The participants were then provided with a copy of the unfavorable description of irradiation used in the earlier experiment and asked whether, if allowed, they would make a different purchase decision—and the proportion choosing irradiated chicken fell to 43%. Investigators were then interested to find out whether the negative claims could be countered and if confidence in the irradiated product could be restored.To counter the negative information, investigators used a televised report on food irradiation hosted by John Stossel of ABC News for the 20/20 news program.The report, entitled “The Power of Fear,”first broadcast on December 13, 1991, focused on protests at a food irradiation facility in Florida. Stossel interviewed the plant’s developer and representatives of Food & Water, Inc. who were leading the protest.The report concluded that food irradiation was a safe process, and Stossel indicated that, given the choice, he would actually prefer irradiated to nonirradiated meat. Furthermore, the report concluded that many of the claims made by Food & Water, Inc. were at best misleading or based on irrelevant science. Following the video segment, the investigators emphasized to the participants that (1) irradiated foods do not become radioactive; (2) radiolytic products, similar to those produced by irradiation, were also produced when foods were grilled or fried; (3) no studies had shown a connection between food irradiation and cancer or birth defects; (4) vitamin losses were insignificant and lower than those found in processes such as canning or freezing; (5) irradiation at approved doses did not sterilize food and spoilage warning signs were not lost; (6) there were no links between food irradiation and nuclear weapons or nuclear power; and (7) irradiation had been used to sterilize medical devices and consumer products for several decades with no problems related to the use or transportation of radioactive materials. Once again, investigators asked consumers to indicate what their purchase decision would be if they were allowed to repeat it—and 82% said they would choose irradiated chicken. These results illustrate that although the anti-irradiation message is powerful, it can be effectively counteracted and confidence in the safety of the irradiation process can be restored.

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Effects of Gender, Income, and Children Studies examining the effects of demographics on decisions to purchase irradiated food have found some consistent results. Typically, they find that females are more concerned about irradiation than males and, in most but not all cases, that individuals with more formal education are more accepting of the technology. Regarding the effects of age and income, results are mixed and generally not statistically significant (Lusk and others 1999). To determine the effect of gender, household income, and the presence of children, Fox and others examined results from two studies. First, the set of experiments referred to above in which consumers were exposed in sequence to positive, negative, and again positive information was examined, and the consumers were classified into different categories. Second, the results from a mail survey in which respondents made similar, albeit hypothetical, choices about purchasing irradiated chicken were examined. First, consistent with the results of other studies, males were more likely to be classified as proponents of irradiation. Second, the presence of children under 18 is associated with opposition to irradiation. Frenzen and others (2001) also reported a negative impact associated with the presence of children (under age 5), but their result was not statistically significant at the traditionally reported levels. Most studies find higher education associated with more favorable attitudes toward irradiation. It is worth noting that the effect of more education in the Kansas study showed more highly educated consumers more likely to be either “opponents” or “proponents” and less likely to be classified as “undecided.”This result is intuitively appealing because one does not generally associate opposition to technology with less education, and it may also explain why other studies do not always find a consistent linear impact for education. Finally, age of the respondent has no effect on classification, and, as expected, the higher the perceived risk from nonirradiated chicken, the more likely one is to be a proponent of irradiation.

Barriers to Acceptance The most significant obstacle to increased consumer acceptance of irradiated foods may well be the lack of availability in the marketplace.A survey of retail and foodservice beef purchasers was conducted in January and February 2004 by the National Cattlemen’s Beef Association to meas-

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ure awareness of, and attitudes toward, irradiation technology among foodservice and retail establishments that do and do not offer irradiated beef, measure the willingness to offer irradiated ground beef among those that do not offer it, identify barriers/issues to offering irradiated ground beef including researchable knowledge gaps, and both identify successful retailers and determine which practices help them sell this product (National Cattlemen’s Beef Association, 2004). The study showed that about four in 10 knowledgeable past users and nonusers of irradiated ground beef reported lack of availability as the main reason for not offering irradiated ground beef to their customers. This same study showed that respondents were relatively positive about purchasing irradiated ground beef. Almost half of past users were very (14%) or somewhat (33%) likely to purchase the product within the next year, and more than a fourth of the knowledgeable nonusers were very (4%) or somewhat (23%) likely to do so. In addition, a majority of the current purchasers (58%) indicated they would increase the amount of irradiated ground beef they would buy (versus 23% intending to decrease the amount).These data show a growing rather than a shrinking market.

The “Minnesota Model” of Consumer Acceptance Studies clearly show that an overwhelming majority of educated consumers will buy and in many cases prefer irradiated food products.These studies also point out a growing need to educate the public about the benefits of irradiation. The educational effort that began in Minnesota during the fall of 1997 has helped pave the way toward the successful introduction of irradiated ground beef and other foods not only in the United States but also a growing number of foreign countries. Following the largest recall of ground beef in history, Minnesota health experts, beef industry officials, and educators began to present consumers, opinion leaders, and others with facts and solid science about irradiation through a series of educational activities, product sampling demonstrations, information workshops, press releases, and media interviews. For example, in 1998, when John Glenn flew into outer space on Shuttle Discovery to help research how weightlessness affects the body of an older person, the Minnesota Beef Council sent out a press release calling attention to the fact that NASA has served irradiated foods in space since 1972. A team of experts from the Minnesota Department of Health, the University of Minnesota, and the food industry were quick to hold the critics accountable by challenging misinformation, half truths, and dis-

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torted information about irradiation through letters to the editor, opinion pieces, and media interviews. No opportunity was missed to serve samples of irradiated ground beef and inform the public about the benefits of food irradiation. More than 500,000 samples of irradiated ground beef have been served to consumers at various events in Minnesota and 30 other states since 1999.An Irradiated Ground Beef Education Initiative was conducted by the American National Cattlewomen during 2003 and 2004. The project involved product sampling and educational activities at women’s expos, food shows and other events to increase the knowledge of irradiated ground beef. More than 260,000 consumers/influencers were reached at 61 events in 20 states. Survey results were obtained from over 7,000 respondents and showed the following: • The majority of respondents (74% of 4,668) correctly said that irradiation does not eliminate the necessity for safe food handling practices. • The overwhelming majority (87% of 4,603) of respondents correctly stated that irradiation does not change the nutritional value of ground beef. • Ninety percent of 4,463 respondents correctly said that irradiation raises the food safety level of ground beef. • An unexpected finding was that almost half of respondents (46% of 4,728) did not know the proper cooking temperature for ground beef. • About 98 percent of respondents (3,286 out of a total of 3,347) at 25 events tabulated rated the taste of the irradiated ground beef samples with a positive score.The most frequent response was Good (1,382), followed by Great (335),Tasty/Very Good (186), and Excellent (168).A neutral score was given by 48 respondents (1.4%) with 22 respondents rating the product as Average. Negative evaluations were given by 25 individuals (0.7%).The average score was 8.2 on a 10-point scale. These informal taste tests combined with research at the University of Minnesota (Vickers and Wang 1999) have clearly demonstrated that irradiated ground beef is just as flavorful as typical, nonirradiated ground beef. A survey conducted at the 2001 Minnesota State Fair showed that only 39 percent of 201 participants would buy irradiated ground beef without sampling it first.After tasting the irradiated ground beef at the state fair, 89 percent said they would be willing to purchase irradiated ground beef.The importance of education, product sampling, and public/private partnerships is further confirmed by the previously mentioned Jefferson Davis Associates study (Shogren and others 1999) showing that 85% of

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Figure 5.2.

Food Irradiation Research and Technology

Overall appeal of irradiated beef concept (Jefferson Davis Associates, Inc.).

Minnesota respondents consider irradiated ground beef a “good thing,” compared to 78% overall (Figure 5.2). Irradiation education continues to be a major focus of a cooperative effort among the Minnesota Department of Health, the Minnesota Beef Research & Promotion Council, and ground beef manufacturers.Today, irradiated ground beef is readily available at most Minnesota supermarkets and many convenience stores, via home delivery and through mail order.

Marketing of Irradiated Ground Beef Louis Pasteur said,“To those who devote their lives to science, nothing can give more happiness than making discoveries, but their cups of joy are full only when the results of their studies find practical applications.” Pasteur did not live long enough to realize the magnitude of the impact resulting from his efforts. Neither did Marie Curie, whose landmark research on radiant energy and radiation earned her a Nobel Prize in 1904 and set the stage for the use of irradiation of food and medical products (Waltar 2004). In May 2000 Huisken Meats of Sauk Rapids, Minnesota, became the first ground beef processor in the nation to market irradiated ground beef when irradiated frozen ground beef patties were offered in 84 supermar-

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kets in the Twin Cities of Minneapolis/St. Paul, Minnesota. Schwan’s, Inc., a nation-wide foodservice provider through home delivery, quickly followed Huisken’s lead when it started marketing irradiated ground beef a few weeks later. Omaha Steaks of Nebraska has successfully marketed irradiated ground beef through mail order since 2000.Today, all noncooked ground beef offered by Schwan’s, Omaha Steaks, and several others is irradiated.Auburndale, Florida–based Colorado Boxed Beef offers frozen irradiated beef patties at about 1,000 supermarkets on the East Coast. In November 2004, a Cedar Rapids, Iowa–based company introduced irradiated fresh ground beef with extended shelf life at a number of convenience stores in Iowa and Illinois. In early 2005, it was estimated that irradiated ground beef (mostly frozen) was available in some 2,500 to 3,500 supermarkets and convenience stores. Rochester, New York–based Wegmans, with 68 supermarkets in New York, New Jersey, Pennsylvania, and Virginia, is a strong believer in the irradiation process and is one of the most visible marketers of irradiated ground beef.Although Wegmans takes every measure to ensure that all its ground beef products are safe, the retailer views irradiation as a value-adding process that offers the consumer an additional layer of food safety protection. Retailers throughout the United States have continued to show considerable interest in Wegmans’ successful marketing of irradiated ground beef.

A Defining Moment in Food Safety The successful commercial introduction of irradiated ground beef and poultry in supermarkets has gone largely unnoticed. According to food safety expert Morton Satin, when irradiated ground beef was introduced, consumers gained a reasonable expectation of buying products that offered much greater food safety and lower risk. As a consequence, untreated ground beef acquired the character legally defining a product having a built-in defect (Osterholm and Norgan 2004). Satin cites the American Legal Institute’s Third Restatement of the Law, Torts: Products Liability, adopted in 1998, which states in section 2, “Categories of Product Defect”: A product is defective when, at the time of sale or distribution, it contains a manufacturing defect . . . .A product: a) contains a manufacturing defect when the product departs from its intended design even though all possible care was exercised in the preparation and marketing of the product.

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Is it Farm to Fork, or Turf to Tort? Lawsuits and the threat of litigation as a result of recalls and sickness from E. coli 0157:H7, Salmonella, Listeria, and other pathogens will be a significant factor that will drive more retailers, restaurant chains, and manufacturers toward the use of irradiation (Eustice 2004).The financial liability for selling, using, lending, or simply having unsafe products on your premises rests with the business marketing the product.“If they sell it, they’re liable, period,” says Frances Zollers, a professor in the law and public policy department of the Whitman School of Management at Syracuse University in New York (Henricks 2005). For a victim, one case of foodborne illness is one too many. For a manufacturer, one recall is one too many. For a school district, one sick or dead child is a tragedy. For everyone but the attorneys prosecuting the case, one lawsuit is a nightmare! Faced with liability from selling contaminated products that can legally be defined as “defective,” the food industry will have to weigh the cost of using irradiation against the cost of product recalls, lawsuits, loss of brand equity, or even bankruptcy caused by such contaminated products (Satin 2003; Loaharanu 2003).

Conclusion No one single intervention can provide 100% assurance of the safety of a food product.That is why meat and poultry processing plants use a multiple barrier (hurdle) approach utilizing several types of interventions such as thermal processes combined with chemical and antimicrobial treatment to achieve pathogen reduction. These technologies have successfully reduced, but not eliminated, the amount of harmful bacteria in ground beef. Food irradiation does not eliminate the need for established, safe food-handling and cooking practices, but when used in combination with other technologies including an effective Hazard Analysis Critical Control Points (HACCP) program, irradiation becomes a highly effective

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and viable sanitary and phytosanitary treatment for food and agricultural products. Irradiation is one of the most effective interventions available because it significantly reduces the dangers of primary and crosscontamination without compromising nutritional or sensory attributes. The number of U.S. supermarkets that offer irradiated food at retail is significant and growing. Despite the progress made in the introduction of irradiated foods into the marketplace, many consumers and even highly placed policy-makers around the world are still unaware of the effectiveness, safety, and functional benefits that irradiation can bring to foods. Education and skilled marketing efforts are needed to remedy this lack of awareness. Morton Satin says, “Pathogens do not follow political imperatives or moral philosophies—they simply want to remain biologically active. Strategies to control them, which are based on political ideals or mythinformation, will not be effective. If we want to get rid of pathogens, we have to destroy them before they harm us. Food irradiation is one of the safest and most effective ways to do this.An international coordinated effort to develop effective knowledge transfer mechanisms to provide accurate information on food irradiation to policymakers, industry, consumers and trade groups is vital to meet today’s food safety needs” (Satin 2003). During the twentieth century, life expectancy in the United States increased from 47 to 77 years (CDC 2004). Many public health experts attribute this dramatic increase to the “pillars” of public health: pasteurization, immunization, and chlorination. Some of these same experts predict that food irradiation will become the fourth pillar of public health.Time will tell whether this prediction is correct.

References Aiew,W, Rudolfo, N, and Nichols, J. 2003.The Promise of Food Irradiation:Will Consumers Accept It? CHOICES. (Third Quarter 2003):31–34. Anderson, J, Schuster, T, Hansen, KE, Levy, AS, Volk, A. 2004. A Camera View of Consumer Food Handling Behaviors. Journal of American Dietetic Association: February 2004. Cates, S. 2002. Reported Safe Handling Practices: Cooking (FDA/FSIS Food Safety Survey2001). Changes in Consumer Knowledge, Behavior, and Confidence Since 1996 PR/HACCP Final Rule. Thinking Globally—Working Locally: A Conference on Food Safety Education, Orlando, FL, September 18, 2002. CDC. 2000. CDC Foodborne Outbreak Response and Surveillance Unit. Foodborne diseases outbreaks due to bacterial etiologies. (Accessed at: http://www.cdc.gov/foodborneoutbreaks/us_outb/fbo2000/bacterial00.htm.) CDC. 2004. National Center for Health Statistics, Centers for Disease Control and Prevention. Health: United States 2004 (Accessed on January 29, 2005 at: http://www.cdc. gov/nchs/data/hus/hus04trend.pdf#027)

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Consumer Reports. 2003. Of birds and bacteria. (Accessed on February 8, 2005 at: http://www.consumerreports.org/main/detailv2.jsp?CONTENT%3C%3Ecnt_id=29779 7&FOLDER%3C%3Efolder_id=162689) DeGregori, TR. 2002. Zero Risk Fiction. New York, NY: American Council on Science and Health. Eustice, RF. 2004.The Market for Irradiated Meat; Survey Reveals Lack of Knowledge: Meat & Seafood Merchandising. Lenexa, KS:Vance Publishing. p. 18–19. Fox, JA, Bruhn, CM, and Sapp, S. 2001. Consumer Acceptance of Irradiated Meats. In: Interdisciplinary Food Safety Research, Elsa Murano and Neil Hooker, eds. Boca Raton, FL: CRC Press. p. 139–158. Fox, JA. 2002. Influences on Purchases of Irradiated Foods. Food Technology 56 (11): 34–37. Hall, CW and Trout, GM. 1968. Objections to Pasteurization. In: Milk Pasteurization. Westport, Connecticut:The AVI Publishing Company. p. 5–8. Henricks, M. 2005. Risky Business; Before a Defective Product Becomes Your Downfall, Learn to Protect Yourself. In: Entrepeneur Magazine (March 2005) p. 32. Jefferson Davis Associates. 2003. Consumer Awareness of and Attitudes toward Irradiated Ground Beef. Presented to Mitec Advanced Technologies. Cedar Rapids, IA. 1–7. Johnson, A, Estes, RA, Jinru, C, and Resurreccion, AVA. 2004. Consumer Attitudes toward Irradiated Food: 2003 vs. 1993. Food Protection Trends 24(6): 408–418. Kay, S. 2003. Cattle Buyers Weekly. Meat & Poultry 49.2. Loaharanu, P. 2003. Irradiated Foods; Fifth Edition. American Council on Science and Health; New York. Lusk, JL, Fox, JA, McIlvain, CL. 1999. Consumer Acceptance of Irradiated Meat. Food Technology. 53(3):56–59. Metropolitan Life Insurance Company. 1923. All about Milk. New York: Metropolitan Life Insurance Company. p. 1–24. National Cattlemen’s Beef Association. 2002. Irradiation: Consumer Perceptions. On behalf of Cattlemen’s Beef Board, Centennial, Co. (Accessed on July 18, 2005 at: http://www. beefusa.org/uDocs/irradiation.pdf.) National Cattlemen’s Beef Association. 2004. Irradiation Beef Industry Study. National Cattlemen’s Beef Association on behalf of Cattlemen’s Beef Board, Centennial, Co. (Accessed July 18, 2005 at: http://www.beef.org/uDocs/Executive%20Summary %20Beef%20Industry%20Irradiation.pdf.) Osterholm, MT, Norgan, AP. 2004. The Role of Irradiation in Food Safety. New England Journal of Medicine, 2004 350(28):1898–1901 (Perspectives). Rogers, EM. 1983. Diffusion of Innovations, 3rd Edition. New York:The Free Press. Roybal, J. 2003. Beef industry logs successful week in E.coli O157:H7 battle. BEEF Magazine’s Cow-Calf Weekly. (Accessed September 30, 2003, at http://enews.primediabusiness.com/enews/beef/cowcalf_ weekly/current - a030926_4) Satin, M. 2003. Future Outlook: International Food Safety and the Role of Irradiation. International Meeting on Radiation Processing, Chicago, IL. Shogren, JF, Fox, JA, Hayes, DJ, and Roosen, J. 1999. Observed Choices for Food Safety in Retail, Survey and Auction Markets. American Journal of Agricultural Economics 81(5):1192–1199. Tauxe, RV. 2001. Food Safety and Irradiation: Protecting the Public from Foodborne Infections. Presentation from the 2000 Emerging Infectious Diseases Conference in Atlanta, Georgia. Emerging Infectious Disease 7(3): 516–521. Wisconsin State Journal Editorial Board. 2003. Let Irradiation Improve Safety Of School Food. Wisconsin State Journal, Madison. May 1, 2003.

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USDA FSIS. 2003. Food Safety and Inspection Service. 2003 recall cases. (Accessed at: http://www.fsis.usda.gov/OA/recalls/rec_actv.htm#2003) USDA FSIS. 2005. Press Release: FSIS Ground Beef Sampling Shows Substantial E. coli O157:H7 Decline In 2004. (Accessed at: http://www.fsis.usda.gov/News_&_Events/ NR_022805_01/index.asp on February 28, 2005) Vickers, Z, and Wang, J. 1999. Acceptability of Irradiated Fresh Ground Beef Patties; Influence of Information and Product Identification. University of Minnesota. Waltar, AE. 2004. Radiation and Modern Life, Fulfilling Marie Curie’s Dream. Amherst, NY: Prometheus Books.

Food Irradiation: Research and Technology Edited by Christopher H. Sommers, Xuetong Fan Copyright © Blackwell Publishing and the Institute of Food Technologists 2006

Chapter 6 DETECTION OF IRRADIATED FOODS Eric Marchioni, Ph.D.

Introduction The action of ionizing radiation on food results in the formation of free radicals and radiolytic products that are predominantly not radiation specific. It was thus not astonishing that after many years of research before the nineties, it was still not possible to identify any specific radiolytic product that could be used to establish a universal analytical method for the detection of irradiated food. Moreover, the radiation process, when performed at usual absorbed doses (less than 10 kGy), involves many fewer chemical modifications than other treatments such as heating or storage. Indeed, the absorption of the maximal allowed dose for food irradiation (10 kGy) leads only to a temperature rise limited to 2.4° C.This observation pleads certainly in favor of the safety of radiation processing, but represents a major disadvantage when one seeks to identify such a process while studying physical or chemical modifications in the foodstuff itself. As a result of two concerted actions conducted and funded by the Community Bureau of Reference (Raffi and others 1993) and by the International Atomic Energy Agency (McMurray and others 1996) at the beginning of the nineties, no fewer than fifteen analytical methods for the detection of irradiated food were developed, of which ten were standardized by the European Committee for Standardization (CEN). Six of them are reference methods and are based on the analysis of primary radiolytic products, by electron spin resonance spectroscopy (ESR) (Anonymous 1996c, d; 2000a), and by thermoluminescence (Anonymous 1996e), or on the analysis of secondary radiolytic products from fatty acids, namely volatile hydrocarbons (Anonymous 1996a) and 2-alkylcyclobutanones (Anonymous 1996b). The four other methods resulting from these concerted efforts are less specific than the reference methods but are never85

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theless of interest because they are easier to carry out, less expensive, and less time-consuming than the reference ones and could thus be used as screening methods to establish a suspicion of irradiation treatment. It is recommended that any positive result obtained by such screening methods be confirmed using a standardized reference method. These screening methods consist in photo-stimulated luminescence (P.S.L.) (Anonymous 2000b), single gel micro-electrophoresis (Anonymous 2000c), bacteriological methods D.E.F.T./A.P.C. (Direct Epifluorescence Filter Technique/Aerobic Plate Count) (Anonymous 2000d) and L.A.L./ G.N.B. (Limulus Amoebocyte Lysate/Gram Negative Bacteria) (Anonymous 2004).The scope of all these methods is indicated in Table 6.1. Several bibliographical studies concerning the detection of irradiated food were already published (Hasselmann and Marchioni 1991; Delincée 1991; Raffi and others 1993; McMurray and others 1996).This chapter is a résumé of these various studies while insisting particularly on the methods selected and standardized by CEN, which have now been adopted by the Codex Alimentarius as General Codex Methods and which can be regarded today as being foolproof and effective. According to the chronological appearance of radiolytic products or changes observed in the food matrix, the methods for food irradiation detection can be classified according to the following two categories.

Free Radicals and Electronic Excited States ESR Spectroscopy Food having a dry or rigid matrix, or presenting certain dry or rigid parts, is able to trap free radicals or excited states of electrons for a period of time that can be much longer than the lifetime of the food itself.Thus, irradiated meat with bones (poultry, beef, pork, and so on), fish with bones, scales, or teeth, eggs with shells, shellfish, fruits with achenes, nuts with shells, dry fruits containing crystalline sugars, and some seeds and spices can be analyzed by electron spin resonance spectroscopy. It is a nondestructive analytical method that allows the detection of free radicals in matter. It consists in subjecting a test sample to the simultaneous action of a magnetic field (intended to direct the magnetic moments—spins— of the matter, and thus those of the free radicals) and of an electromagnetic microwave of very high frequency (approx. 9 GHz).When the value of the imposed magnetic field allows the spins of the radicals to be directed so that their transition energy becomes identical to that of the incident electromagnetic microwave, the energy of the latter is absorbed.

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Chemical methods

NF EN 13 783 D.E.F.T.-A.P.C.

Microorganism

Herbs and spices

(d)

(e)

Gram Negative Bacterium Fresh or frozen poultry meat

NF EN 14 569 L.A.L.-G.N.B.

Microbiological methods

(b) (c)

(a)

Screening Methods

(b) NF EN 1 784 NF EN 1 785 (c) Gas chromatography (d) Volatile hydrocarbon 2-Alkylcyclobutanone (e) Food containing fat

(a)

Reference Methods

Silicate and other mineral Food containing mineral debris, e.g. silicates

NF EN 13 751 P.S.L.

Food containing DNA

NF EN 13 784 Single gel microelectrophoresis DNA

Physical method Biochemical method

NF EN 1 788 NF EN 1 787 NF EN 1 786 NF EN 13 708 Thermoluminescence Electron spin resonance spectroscopy Silicate mineral Crystalline cellulose Bone, tooth, scale Crystalline sugar Food containing Food containing Food containing Food containing silicate minerals cellulose bones sugars

Physical methods

Table 6.1. Selected C.E.N. Methods for the Detection of Irradiated Food: (a) Type of Methods; (b) C.E.N. Classification; (c) Analytical Methods; (d) Compound to Be Analyzed; and (e) Application Field of the Method.

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Figure 6.1. ESR spectra 1) nonirradiated; 2) irradiated from samples of (a) 5 kGy irradiated poultry bones, (b) achenes extracted from 3 kGy irradiated strawberries, and (c) 5 kGy irradiated figs.

The derivative representation of this absorption, according to the value of the magnetic field, gives the ESR spectrum (Fig. 6.1). The application of this analytical method is simple, consisting of drying a food sample (water prevents the ESR analysis because of the O-H dipole, which absorbs the microwave energy) under reduced pressure at 50°C max in order to avoid modifying the food composition (sugars) and the recombination of the radicals, and to record the ESR absorption spectrum. Of course, the presence of radicals in food is not radiation specific (radicals are also produced by heating or crushing, and a low amplitude symmetric ESR absorption signal is also present in nonirradiated bone samples). Nevertheless, observing the shapes of the spectra recorded in case of irradiated samples, as well as their gyromagnetic factors, causes analysts to consider some ESR signals to be radiation specific. It is now widely recognized that the presence of ESR signals (as described below) is radiation specific, but the absence of such ESR signals (except in case of mammal bones) never constitutes proof that the food has not been irradiated. The spectrum presented in Figure 6.1a can be observed in irradiated food containing bones, fishbones, cuticles, teeth, or egg shells. It consists of an intense radiation-specific asymmetrical signal (A and B, g=2.002 g=1.998) superimposed upon a symmetrical endogenous signal (C, g=2.005) of much lower amplitude also present in nonirradiated bone samples (the beginning of this signal is presented in Figure 6.1a by the arrow S). It corresponds (Bacquet and others 1981) to an extremely stable

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CO2⭈– radical trapped in the lattices of hydroxyapatite [Ca10(PO4)6(OH)2] which constitutes approximately 60% of the bone composition. Measuring the ESR signals induced in animal bones is not really new. It has already been used for accidental post-irradiation dosimetry (Rossi and others 2000) and for dating bones and shells (Takano and Fukao 1994). Detection of irradiated fish and meat samples is generally possible above a minimal detectable dose of 0.5 kGy, lower than those used for commercial applications for this kind of food product. Identification remains possible up to 12 months after irradiation (Anonymous 1996c). The ESR signal represented in Figure 6.1b is obtained with irradiated food containing crystalline cellulose. It is a hyperfine triplet centered at g=2.004 and superimposed on an intense central nonradiation-specific singlet C belonging to lignin (Deighton and others 1993).This singlet has a similar g factor and is sensitive to radiation but also to drying processes (deJesus and others 1996). From the triplet ESR lines that are induced by irradiation, only the two outermost peaks A and B (g=2.020 and g=1.985, ⌬H~6mT) can be used in the case of very dry plant products such as paprika powder or dry fruit components (achenes, pips, shells, stalks, or stones) (Raffi and Agnel 1989) but also in citrus fruit skins, skin components and stalks (Tabner and Tabner 1994) and fruit cell walls (deJesus and others 1999; Delincée and Soika 2002). The multicomponent ESR signal in Figure 6.1c may be observed in some dry fruits containing crystalline sugars (raisins, mangoes, papayas) (Raffi and others 1992).As various mono- and disaccharides may widely be dominant in fruit samples, different ESR spectra, centered at g=2.003, could be produced after irradiation (Anonymous 2000a).They consist in intense and easily detectable multiplets that can be identified provided that the moisture has been correctly eliminated during sample preparation. Such nonirradiated foods containing crystalline sugars do not give out any ESR signal. Today, these three analytical ESR methods are CEN and Codex standards used by various EU Member States and also other countries all over the world to exercise control over the international trade of irradiated foods. Luminescence The absorption of ionizing radiation by matter induces the formation of electronic excited states. If the matter has a crystalline structure, the excited charge carriers can remain trapped in the crystalline lattice defects for several years. Heat stimulation (50°C to 500°C depending to the depth of the trap) releases a part of this stored energy in the form of detectable light. A thermoluminescence reader measures the amount of

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light that is emitted during controlled heating.This observation is already in use for radiation dosimetry including clinical applications, archaeological and geological age determination, mineral prospecting of uranium sources, study of meteorites and lunar material, or solid-state defect structure analysis.The use of thermoluminescence as a detection method for irradiated food first consisted in analyzing directly a few mg of the whole food sample (spices) with a commercial TL reader. In 1989 Sanderson reported that the origin of luminescence of spices is due to “extraneous inorganic matter.”The food is indeed almost always contaminated by very small quantities of silicate minerals, mainly quartz and feldspar (Soika 2000), which come either from the action of the wind (fruits with dust) or from the contact with soil (plants and spices with sand) or with the seabed (shells and shellfish with sand). The standardized CEN method (Anonymous 1996e) for the detection by thermoluminescence of food containing silicate minerals consists of water ultrasound-assisted extraction of the mineral impurities, separation of the silicate minerals from the organic fraction, and an analysis of the purified minerals by thermoluminescence. An irradiated foodstuff (Fig. 6.2) results in a sharp peak, approximately at 220°C, whereas nonirradiated food does not give out any TL signal at this temperature. Only some low signals caused by natural radioactivity appear beyond 350°C. Because mineral impurities are common to many food products, this method of analysis has wide applications.That is why this technique of detection is largely used in food control laboratories. Unfortunately, the equipment has no other application in an analytical food laboratory. A novel approach to this method was suggested by Sanderson and others (1996). These authors proposed to release the trapped charge carriers from their excited energy level using infrared pulsed laser beam excitation, which allows an examination of inorganic systems in the presence of organic matter. This technique is original because the energy carried by the emitted luminescence photon is higher than that of the laser excitation.This rare anti-Stokes property is highly radiation specific because the energy conservation principle lays down that the quantum energy differences between stimulation and luminescence are balanced by the energy stored in the form of trapped charge carriers.Therefore, nonirradiated samples are unable to participate in these transitions.The synchronous detection of the luminescence with the pulsation of the excitation laser light enhances the signal-to-background ratios, thus increasing detection sensitivity. Moreover, no preparation of the sample is necessary and the equipment appears as a simple box fitted with a drawer in which the food to analyze is introduced in a disposable petri dish.This fast and simple method was standardized by CEN (Anonymous 2000b). It is al-

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Figure 6.2. Thermoluminescence glow curves of silicate minerals extracted from a sample of dehydrated asparagus powder; (a) 8 kGy irradiated sample and (b) nonirradiated sample.

ready screening method is used in official national food control laboratories but also in several food industries and central buying offices. The radicals induced in foods by radiation processing can also be detected by indirect methods such as luminescence. The chemiluminescence consists of an emission of light consecutive to a chemical reaction. During rehydration of some irradiated dry foods, the radical recombination allows such light emission. This luminescence can be amplified by the use of additives such as Luminol or Lucigenine.This method was extensively studied by German authors (Bögl and Heide 1985) and was submitted for interlaboratory tests. However, it has a very poor reproducibility (Delincée 1987) and was not standardized by CEN.

Analysis of Stable Radiolytic Products After being induced in the food matrix, free radicals and excited states of the matter (extremely reactive chemical species of very short lifetime, ex-

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cept in the case of dry or/and rigid food) react with the food components, giving rise to a great number of chemical reactions and resulting in radiolytic products. In order to be detected in a foodstuff, the stability of these compounds must be comparable to the shelf-life of the food. Radiolytic Products from Proteins Detection of o-, m- and p-tyrosines, produced during radiolysis of food containing phenylalanine, was proposed by Simic and others (1983) who thought that o-tyrosine was a unique radiolytic product (U.R.P.). However, it was later shown by other authors (Hasselmann and Laustriat 1973; Hart and others 1988) that this molecule was also present in nonirradiated food and could also be formed by photolysis. Hein and others (1999) showed that o-tyrosine was indeed a natural product and thus could not be used as a food irradiation detection test except, of course, if a maximal threshold of o-tyrosine present in the food could be defined, a threshold above which the food is regarded as having been irradiated. In any case this method was never validated by blind tests or by interlaboratory analyses. Volatile Compounds The chromatograms of volatile food extracts (spices) present numerous peaks.The comparison (Hasselmann and others 1986; Swallow 1988) of such chromatograms from irradiated and nonirradiated food extracts highlights the presence or absence of peaks or the variation of some peak intensities. However, it was established that the profiling of these chromatograms depends also upon the origin of the analyzed spice and upon its treatments. Therefore a discrepancy between two chromatograms cannot be attributed to radiation treatment. Radiolytic Products from Carbohydrates The radiolysis of pure aqueous carbohydrate solutions is well described in the relevant literature (VonSonntag 1987). But the radiolysis of carbohydrates in food is much more complex.The process results in acids and carbonyl groups. Molecular weight or methylation degree changes leading to modifications of the viscosity of food extracts were also reported (Farkas and others 1990). But almost all the methods of detection based on the study of the carbohydrates radiolytic breakdown products were disappointing (Delincée and Ehlermann 1989), because the products observed were not radiation specific. Moreover, the variability of the radi-

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olytic product concentrations or of the food viscosity, depending on the food itself (origin, state of ripening, and conditions of culture and storage), was much higher than the variability that could be caused by the radiation process alone. Only the ESR analysis (Anonymous 2000a) as described at the beginning of this chapter allows an unambiguous detection of irradiated food containing crystalline sugars (dry fruits). Radiolytic Products from Nucleic Acids The presence of DNA in almost all food could be the basis of a universal method of detection of irradiated food. But the food DNA analysis is complex due to the low concentration of these fragile macromolecules.They quickly degrade when stored at temperatures above 0° C because of the nucleases present in the cells.This reduces the application field of this investigation to fresh or frozen food. Detection of chemical modifications of the bases was proposed by Pfeilsticker and Lucas (1987). These authors proposed a detection test based on the fluorescence analysis of thymine glycol, a thymine radioderivative.This work never could be confirmed by other laboratories because the production of this molecule is very dependent on the matrix of the studied food. Another very interesting study consists in an immunological detection of dihydrothymidine produced in absence of oxygen (radiation processing consumes oxygen dissolved in the cell) from thymidine (Williams and others 1994; Tyreman and others 2004). The fast and elegant method suggested by these authors was, however, not confirmed by other laboratories and no blind test was carried out to validate it. An original approach was proposed by Marchioni and others (1992). The suggested protocol is based on the morphological modifications of the mitochondrial DNA (mtDNA), which is protected against autolysis by the mitochondrial wall.The test thus remains applicable throughout the shelf life of food (in the fresh or frozen state). A low dose of irradiation (< 100 Gy) causes single strand breaks, which in turn transforms the native supercoiled mtDNA into an open circular mtDNA.An increase in the absorbed dose leads to the disappearance of the supercoiled shape, the multiplication of open circular mtDNA, and the appearance of linear shaped mtDNA. These three shapes may easily be separated by using agarose gel electrophoresis. Unfortunately, no other laboratory continued these studies, and the protocol suggested (quite long and complex) is not yet in use for the detection of irradiated food. The most successful approach was proposed by Östling (1988). This author proposed an extraction of the cells by a simple shaking in a buffer

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Figure 6.3. Electrophoretic pattern of single cells extracted from (a) nonirradiated and (b) 1.5 kGy irradiated poultry meat (H. Delincée).

solution.The cellular suspension, mixed with low-melt agarose, is coated on a microscope slide and subjected to short (2 min) electrophoresis.The cells whose DNA have a high molecular weight (unaltered DNA) will just migrate a little bit into the gel (Fig. 6.3a).The cells extracted from irradiated food have short DNA (because of strand breaks) and will migrate over longer distances (Fig. 6.3b). Electrophoretic pattern of such cells appears as comets whose heads are represented by the cell and the tails consist of the low molecular-weight DNA.The higher the absorbed dose, the longer the tail of the comet. This simple and fast method does not require any expensive equipment and can be used to analyze fresh or frozen foods. It is now a CEN standard (Anonymous 2000c), already used by several food control laboratories as a detection method of irradiated food. Radiolytic Products from Lipids Lipid radiolysis has been extensively studied (Nawar 1986, 1994) because the radiolytic breakdown products of edible fats (hydrocarbons, aldehydes, ketones, esters, peroxides, oxisterols, and so on) were suspected to degrade the flavor of irradiated food.As of now, only two analytical methods on lipids appear to be really interesting for the detection of irradiated food. The radiolysis of a fatty acid Cn:m (n = carbon atoms, m = double bounds) leads mainly, due to side chain breakage (␣ and ß position of the carbonyl group), to the formation of volatile hydrocarbons of formulas Cn-1:m and Cn-2:m+1, and of 2-alkylcyclobutanones, with a Cn-4 alkyl chain in position 2 of the four-carbon ring (Fig. 6.4 and Table 6.2). The presence of volatile hydrocarbons in a food, easily identified by gas chromatography with flame ionization detection, is not radiation spe-

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Figure 6.4. Radiation-specific breakages on the triglyceride molecule. (a) Cn-1:m hydrocarbon, (b) Cn-2:m+1, 1-unsaturated hydrocarbon, (c) 2-alkylcyclobutanone.

Table 6.2. fatty acids.

Radiolytic hydrocarbons and 2-alkylcyclobutanones from major food

Precursor fatty acid Palmitic (C16:0)

Stearic (C18:0)

Oleic (C18:1)

Hydrocarbon Pentadecane (C15:0) 1-Tetradecene (C14:1) Heptadecane (C17:0) 1-Hexadecene (C16:1) 8-Heptadecene (C17:1) 1,7-Hexadecadiene (C16:2)

2-Alkylcyclobutanone 2-Dodecylcyclobutanone (2-dDCB) 2-Tetradecylcyclobutanone (2-tDCB) 2-(Tetradec-5⬘-enyl)cyclobutanone (2-tDeCB)

cific, but the appearance in the chromatogram of a hydrocarbon couple Cn-1:m/Cn-2:m+1 for each corresponding fatty acid Cn:m establishes beyond doubt that the food analyzed has been irradiated (Fig. 6.5). The 2-alkylcyclobutanones are, until proof for the contrary is available, the first chemical compounds specifically formed by irradiation (Ndiaye 1999a).Their presence, corresponding to specific fatty acids (the 2-dodecylcyclobutanone, 2-tetradecylcyclobutanone, and cis 2-tetradec5’-enyl-cyclobutanone radio induced respectively from palmitic, stearic, and oleic acid) characterized by mass spectrometry after separation by gas chromatography (Fig. 6.6), thus is an unquestionable proof of a radiation process on the food analyzed (Stevenson 1990). The protocols proposed for the detection of hydrocarbons and 2-

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Figure 6.5. Chromatogram of volatile hydrocarbons extracted from 5 kGy irradiated milk powder (C14:1 and C15:0 induced from C16:0 palmitic acid, C16:1 and C17:0 induced from C18:0 stearic acid and C16:2, and C17:1 induced from C18:1 oleic acid).

alkylcyclobutanones are, in fact, very similar (Soxhlet extraction, SPE purification of the extracts on a Florisil column and separation by gas chromatography, with mass-selective detection in the case of the analysis of the 2-alkylcyclobutanones). The two standard protocols are applicable to food whose triglyceride content is not negligible (> 1g%), provided that the absorbed dose of radiation is not too weak (> 0.5 kGy) (Ndiaye 1999a). The chemical stability of volatile hydrocarbons and of 2-alkylcyclobutanones in food is quite good, and the moderate losses observed during storage do not reduce the validity of the two methods, which are now CEN standards (Anonymous 1996a,b).The application field of these methods is thus potentially very large. These standards have nevertheless the twofold disadvantage of being time consuming (1.5 to 2 days), partly owing to the use of a 6 h Soxhlet extraction, and quite expensive on account of the need for a large quantity of Florisil in the solid phase extraction needed to purify the extracts obtained (retention of the lipids). Horvatovich and others (2000) proposed the use of selective supercritical carbon dioxide extraction to reduce the duration of analysis (down to 3 hours) and to avoid the costly Florisil clean-up step. These authors succeeded in detecting and quantifying the two radiation-sensitive markers (hydrocarbons and 2-alkylcyclobutanones) in one single protocol.

Modification of Macroscopic Physico-Biological Parameters of the Food After being induced in the food matrix, some stable radiolytic products may change macroscopic physico-biological parameters of the food.

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Figure 6.6. Chromatogram of 2-alkylcyclobutanones extracted from 5 kGy irradiated milk powder (2-HCB induced from capric acid, 2-OCB induced from lauric acid, 2-DCB induced from myristic acid, 2-dDCB induced from palmitic acid, and 2-tDCB induced from stearic acid).

Gas Evolution A very simple method for the detection of irradiated dry and frozen foods was proposed by Furuta and others (1995) and improved by Roberts and others (1996) and by Delincée (1996). It consists of the release by fast heating of low-molecular gases produced on irradiating food components (lipid, water, protein, sugars, and so on) and trapped in the matrix of the dry or frozen food.These gases (H2, CO, H2S, NH3) can be very easily detected by multiple gas sensors even several months (dry grains) or years (frozen food) after the treatment. Unfortunately, this method was not used by other scientific teams and has never been validated. Cellular Wall Modifications Radiolytic products induced by radiation treatment may modify the physical properties of the food subjected to a radiation process.The electric impedance of fish (Ehlermann 1972) and potatoes (Hayashi and others 1993) may be modified after irradiation and was proposed as a test for food irradiation detection. However, it was shown by these authors that the measurements were not reliable because the variations of impedance, measured from one food to another, were more important than those that were due to the radiation process itself. Other physical properties of foods, such as their viscosity, capacity to rehydrate (dehydrated spices), membrane permeability, melting point, and so on, were also studied but unfortunately without any real success. Once again, the variability of the results due to the food itself (variety, origin, conservation, physical state, and so on) was always higher than the modifications induced by the radiation treatment of the food.

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Bacteriological Modifications Generally, the objective of radiation processing is the lowering of bacterial bioburden and the elimination of pathogenic flora. It was thus to be expected that scientists proposed microbiological methods to detect irradiated food. Two of these methods were subjected to interlaboratory analyses and standardized by the CEN (Anonymous 2000d, 2004). After a radiation treatment, the dead bacteria can still be detected either by microscopic fluorescence observation (Direct Epifluorescence Filter Technique or DEFT) or by immunological analysis of the endotoxins contained in the Gram negative bacteria (Limulus Amoebocyte Lysate test or LAL), whereas the viable bacteria can be enumerated by an Aerobic Plate Count (respectively APC or GNB). The total number of dead and viable microorganisms, including nonviable cells (very often higher than 104CFU.g–1), is compared with the number of viable microorganisms (very weak after an radiation treatment).When the difference between the total number of microorganisms (viable and nonviable) and the number of viable microorganisms is above or about 3 to 4 log units, the sample may be identified as having been irradiated. Of course, this method is not radiation specific, because the same result may be obtained after heating, fumigation or use of bactericidal agents. However, it allows a cheap and quick screening of food likely to be irradiated. Germination Inhibition Last, the radiolytic products can have consequences that are easy to detect on the evolution of food. It is well-known that the radiation treatments are used to inhibit germination of the bulbs and tubers. Kawamura and others (1996a) proposed a test for the detection of irradiated citrus fruits based on the germination inhibition of their seeds. This simple method (but very long because four days are necessary for the seed to germinate) was validated by an interlaboratory test (Kawamura and others 1996b) but never standardized, and then never used by the official food control laboratories.

Irradiated Ingredients and Low-Dose Irradiated Plants The European Directive 1999/2/EC (Anonymous 1999) makes it mandatory in all EU Member States to mention on the labels whether a food has been irradiated or contains irradiated ingredients irrespective of the in-

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clusion rate.The detection of irradiated foods, when sold as items, does not pose any major analytical problems because 10 standardized protocols have been published by CEN.The situation is not the same when the detection of an irradiated ingredient included in low amounts in a nonirradiated food is to be considered.The radiolytic products will be diluted to such low concentrations in the food matrix that they will not be detectable anymore because of the insufficient sensitivity and specificity of the currently available detection methods. Ndiaye and others (1999b) proposed the use of silver chromatography to enhance the selectivity and the sensitivity of the 2-alkylcyclobutanone method. Horvatovich and others (2002) proposed a modified highly sensitive SFE method. Both improvements allowed the detection of irradiated, mechanically recovered poultry meat in precooked meals, but also of a very low dose (0.05 to 0.1 kGy) treatment for insect disinfestation of cereals and leguminous plants (rice, avocados, cowpeas). Marchioni and others (2003) proposed an enzymatic hydrolysis, carried out at 55° C, for the extraction of silicate minerals and bone fragments present in precooked meals and cheeses containing very low levels of irradiated spices and/or mechanically recovered poultry meats (MRM) or fish.When followed by a purification of the extracts using an aqueous solution of sodium polytungstate, the extraction method made it possible to detect very low inclusions of irradiated spices (0.05% wt:wt by thermoluminescence) or irradiated MRM (0.5% wt:wt by ESR) included in various meals (cheeses and precooked meals). Even for food containing the two ingredients, it was possible to detect and identify them simultaneously.

Conclusion It is thus clear that detection of irradiated food (regarded as extremely difficult 10 years ago) is now possible thanks to standardized analytical methods used in food-control laboratories. The six reference methods adopted by the European Committee for Standardization allow the detection of the radiation treatment in the majority of foods likely to be irradiated. The four other methods (also adopted by the European Committee for Standardization), simple to implement and inexpensive, but whose applicability is restricted and specificity is lower, are used as screening methods. However, in spite of the 5,000 food samples analyzed in 2002 within the Northern Europe food control laboratories, only 2.7% were detected as not correctly labelled (1.4% if dietary supplements are excuded). Therefore, one could question the usefulness of the analytical, human,

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and financial efforts to set up protocols for food irradiation detection, and therefore for the control of food treated by a technology that poses only very few risks but numerous benefits for human health. References Anonymous. 1996a. Foodstuffs. Detection of irradiated food containing fat. Gas chromatographic analysis of hydrocarbons. EN 1784. Brussels (Belgium): European Committee for Standardization. 22 p. Anonymous. 1996b. Foodstuffs. Detection of irradiated food containing fat. Gas chromatographic/Mass spectrometric analysis of 2-alkylcyclobutanones. EN 1785. Brussels (Belgium): European Committee for Standardization. 14 p. Anonymous. 1996c. Foodstuffs. Detection of irradiated food containing bone. Method by ESR spectroscopy. EN 1786. Brussels (Belgium): European Committee for Standardization. 12 p. Anonymous. 1996d. Foodstuffs. Detection of irradiated food containing cellulose by ESR spectroscopy. EN 1787. Brussels (Belgium): European Committee for Standardization. 11 p. Anonymous. 1996e. Foodstuffs. Detection of irradiated food from which silicate minerals can be isolated. Method by thermoluminescence. EN 1788. Brussels (Belgium): European Committee for Standardization. 20 p. Anonymous. 1999. Directive 1999/2/EC of the European Parliament and of the Council of 22 February 1999 on the approximation of the laws of the Member States concerning foods and food ingredients treated with ionizing radiation. L66/16. Brussels (Belgium): The Official Journal of the European Communities 13 March 1999. p 16–25. Anonymous. 2000a. Foodstuffs. Detection of irradiated food containing crystalline sugar by ESR spectroscopy. EN 13708. Brussels (Belgium): European Committee for Standardization. 9 p. Anonymous. 2000b. Foodstuffs. Detection of irradiated food using photostimulated luminescence. EN 13751. Brussels (Belgium): European Committee for Standardization. 12 p. Anonymous. 2000c. Foodstuffs. DNA comet assay for the detection of irradiated foodstuffs—Screening method. EN 13784. Brussels (Belgium): European Committee for Standardization. 17 p. Anonymous. 2000d. Foodstuffs. Detection of irradiated food using Direct Epifluorescence Filter Technique/Aerobic Plate Count (DEFT/APC)—Screening method. EN 13783. Brussels (Belgium): European Committee for Standardization. 17 p. Anonymous. 2004. Foodstuffs. Microbiological screening method for irradiated food using LAL/GNB procedures. EN 14569. Brussels (Belgium): European Committee for Standardization. 16 p. Bacquet G,Truong VQ,Vignoles M,Trombe JC, Bonel G. 1981. ESR of carbon dioxide radical anion in x-irradiated tooth enamel and A-type carbonated apatite. Calcif Tissue Int. 33:105–109. Bögl KW, Heide L. 1985. Chemiluminescence measurements as an identification method for gamma-irradiated foodstuffs. Radiat Phys Chem. 25:173–185. Deighton N, Glidewell SM, Goodmann BA, Morisson IM. 1993. Electron paramagnetic resonance of gamma-irradiated cellulose and lignocellulosic material. Int J Food Sci Technol. 28:45–55.

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Delincée H. 1987. Ist die Bestrahlung von Gewürzen durch Chemiluminescenz nachweisbar? Fleischwirtschaft. 67:1410–1418. Delincée H, Ehlermann DAE. 1989. Recent advances in the identification of irradiated food. Radiat Phys Chem. 34:877–890. Delincée H. 1991.Analytical detection methods for irradiated foods—a review of the current literature, IAEA Tecdoc 587.Vienna (Austria): IAEA. 172 p. Delincée H. 1996.A rapid and simple screening test to identify irradiated food using multiple gas sensors. In: McMurray CH, Stewart EM, Gray R, Pearce J, Editors. Detection Methods for Irradiated Foods—Current Status. Cambridge (United Kingdom):The Royal Society of Chemistry. p. 326–330. Delincée H, Soika C. 2002. Improvement of the ESR detection of irradiated food containing cellulose employing a simple extraction method. Radiat Phys Chem 63:437–441. Ehlermann DAE. 1972. The possible identification of an irradiation treatment of fish by means of electrical (ac) resistance measurement. J Food Sci 37:501. Farkas J, Koncz A, Sharif MM. 1990. Identification of irradiated dry ingredients on the basis of starch damage. Radiat Phys Chem 35:324–328. Furuta M, Dohmaru T, Katayama T, Toratani H, Takeda A. 1995. Retention of radiolytic CO gas in irradiated pepper grains and irradiation detection of spices and dry grains with the level of stocked gas. J Agric Food Chem 43:2130–2133. Hart RJ,White JA, Reid WJ. 1988. Occurrence of o-tyrosine in nonirradiated foods. Int J Food Sci Technol 23:643–647. Hasselmann C, Laustriat G. 1973. Photochimie des acides aminés aromatiques en solution—I. DL-Phenylalanine, DL-Tyrosine et L-Dopa. Photochem Photobiol 17:275–294. Hasselmann C, Grimm L, Saint-Lèbe L. 1986. Mise en évidence de l’irradiation des aliments par des méthodes physico-chimiques. Med Nut 22:121–126. Hasselmann C, Marchioni E. 1991. Physicochemical methods for the detection of food irradiation. In: S Thorne, ed. Food Irradiation.Amsterdam (The Netherlands): Elsevier Appl Sci 129–168. Hayashi T,Todoriki S, Otobe K. 1993.Applicability of impedance measuring method to the detection of irradiated treatment of potatoes. Nippon Shokuhin Kogyo Gakkaishi 40: 378–384. Hein WG, Simat TJ, Steinhart H. 1999. Nachweis der ␥-Bestrahlung von Nordseegarnelen über nicht proteingebundenes o-Tyrosin. In Knörr M, Ehlermann DAE, Delincée H, Eds. Lebensmittelbestrahlung -5. Deutsche Tagung-. Karlsruhe (Germany): Berichte der Bundesforshunganstahlt für Ernährung. BFE-R-99-01. p. 148–152. Horvatovich P, Miesch M, Hasselmann C, Marchioni E. 2000. Supercritical fluid extraction of hydrocarbons and 2-alkylcyclobutanones for the detection of irradiated foodstuffs. J Chromatogr A 897:259–268. Horvatovich P, Miesch M, Hasselmann C, Marchioni E. 2002. Supercritical fluid extraction for the detection of 2-dodecylcyclobutanone in low dose irradiated plant foods. J Chromatogr A 968:251–255. deJesus EFO, Rossi AM, Lopes RT. 1996. Influence of sample treatment on ESR signal of irradiated citrus.Appl Radiat Isot 47:1647–1653. deJesus EFO, Rossi AM, Lopes RT. 1999.An ESR study on identification of gamma-irradiated kiwi, papaya and tomato using fruit pulp. Int J Food Sci Technol 34:173–178. Kawamura Y, Murayama M, Uchiyama S, Saito Y. 1996a. Development of half-embryo test and germination test for detection of irradiated fruits and grains. In: McMurray CH, Stewart EM, Gray R, Pearce J, Eds. Detection Methods for Irradiated Foods—Current Status. Cambridge (United Kingdom):The Royal Society of Chemistry. p. 383–391.

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Kawamura Y, Sugita T,Yamada T, Saito Y. 1996b. Half-embryo test for identification of irradiated citrus fruit: collaborative study. Radiat Phys Chem 48:665–668. Marchioni E,Tousch M, Zumsteeg V, Kuntz F, Hasselmann C. 1992.Alterations of mitochondrial DNA: A method for the detection of irradiated beef liver. Radiat Phys Chem 40:485–488. Marchioni E, Horvatovich P, Ndiaye B, Miesch M, Hasselmann C. 2003. Detection of low amount of irradiated ingredients in non-irradiated precooked meals. Radiat Phys Chem 63:447–450. McMurray CH, Stewart EM, Gray R, Pearce J. 1996. Detection Methods for Irradiated Foods—Current Status. Cambridge (United Kingdom):The Royal Society of Chemistry. 431 p. Nawar WW. 1986.Volatiles from food irradiation. Food Rev Int 21:45–78. Nawar WW. 1994. Progress in the detection of irradiated foods by measurement of lipidderived volatiles. In: McMurray CH, Stewart EM, Gray R, Pearce J, Eds. Detection Methods for Irradiated Foods—Current Status. Cambridge (United Kingdom):The Royal Society of Chemistry. p 241–248. Ndiaye B, Jamet G, Miesch M, Hasselmann C, Marchioni E. 1999a. 2-Alkylcyclobutanones as markers for irradiated foodstuffs. II.The CEN (European Committee for Standardization) method: Field of application and limit of utilization. Radiat Phys Chem 55:437–445. Ndiaye B, Horvatovich P,Miesch M,Hasselmann C,Marchioni E.1999b.2-Alkylcyclobutanones as markers for irradiated foodstuffs: III. Improvement of the field of application on the EN 1785 method by using silver ion chromatography. J Chromatogr A 858:109–115. Östling O. 1988. Radiation induced DNA strand breaks in single cells. In: Bögl KW, Regulla DF, Suess MJ, Editors. Health Impact, Identification, and Dosimetry of Irradiated Foods, Report of a WHO working group. ISH 125. Neuherberg (Germany): Bundesgesundheitsamt. P. 305–307. Pfeilsticker K, Lucas J. 1987. Die fluorimetrische Bestimmung von Thyminglycol in Lebensmitteln (biologischem Material)—der Thyminglycolgehalt als Kriterium für eine Behandlung mit ionisierenden Strahlen.Angew Chem 99:341–342. Raffi J,Agnel JP. 1989. Electron spin resonance identification of irradiated fruits. Radiat Phys Chem 34:891–894. Raffi J, Stevenson MH, Kent M,Thiery JM, Belliardo JJ. 1992. European intercomparison on electron spin resonance identification of irradiated foodstuffs. Int J Food Sci Technol 27:111–124. Raffi J, Delincée H, Marchioni E, Hasselmann C, Sjöberg AM, Leonardi M, Kent M, Bögl KW, Schreiber G, Stevenson H, Meier W. 1993. Concerted action of the Community Bureau of Reference on the Methods of Identification of Irradiated Foods, EUR 15261 EN, Brussels (Belgium): BCR. 119 p. Roberts PB, Chambers DM, Brailsford GW. 1996. Gas evolution as a rapid screening method for detection of irradiated foods. In: McMurray CH, Stewart EM, Gray R, Pearce J, Eds. Detection Methods for Irradiated Foods—Current Status. Cambridge (United Kingdom):The Royal Society of Chemistry. p 331–334. Rossi AM,Wafcheck CC, de Jesus EF, Pelegrini F. 2000. Electron spin resonance dosimetry of teeth of Goiânia radiation accident victims.Appl Radiat Isot 52:1297–1303. Sanderson DCW, Slater C, Cairns KJ. 1989.Thermoluminescence of foods: Origins and implications for detecting irradiation. Radiat Phys Chem 34:915–924. Sanderson DCW, Carmichael LA, Spencer JQ, Naylor JD. 1996. Luminescence detection of shellfish. In: McMurray CH, Stewart EM, Gray R, Pearce J, Eds. Detection Methods for Irradiated Foods—Current Status. Cambridge (United Kingdom): The Royal Society of Chemistry. P. 139–148.

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Simic MG, Dizdaroglu M, DeGraff E. 1983. Radiation chemistry. Extravaganza or an integral component of radiation processing of food. Radiat Phys Chem 22:233–239. Soika C, Delincée H. 2000.Thermoluminescence analysis for detection of irradiated food— Luminescence characteristics of minerals for different type of radiation and radiation doses. Lebensm-Wiss u-Technol 33:431–439. Stevenson MH, Crone AVJ, Hamilton JTG. 1990. Irradiation detection. Nature 344:202–203. Swallow AJ. 1988. Some approaches based on radiation chemistry for identifying irradiated food. In: Bögl KW, Regulla DF, Suess MJ, Eds. Health Impact, Identification, and Dosimetry of Irradiated Foods, Report of a WHO working group. ISH 125. Neuherberg (Germany): Bundesgesundheitsamt. P. 128–138. Tabner BJ, Tabner VA. 1994. Electron spin resonance spectra of ␥-irradiated citrus fruits skins, skin components and stalks. Int J Food Sci Technol 29:143–152. Takano M, Fukao Y. 1994. ESR dating of Pleistocene fossil shells of the Atsumi group, Central Honshu, Japan: On the discrepancy in TD value among different ESR peaks.Appl Radiat Isot 45:49–56. VonSonntag C. 1987.The Chemical Basis of Radiation Biology. London (United Kingdom): Taylor and Francis. 515 p. Tyreman AL, Bonwick GA, Smith CJ, Coleman RC, Beaumont PC, Williams JHH. 2004. Detection of irradiated food by immunoassay-development and optimisation of an ELISA for dihydrothymidine in irradiated prawns. Int J Food Sci Technol 39:533–540. Williams JHH, Tyreman AL, Deeble DJ, Jones M, Smith CJ, Christiansen JF, Beaumont PC. 1994. Immunochemical detection of modified DNA bases in irradiated food. In: McMurray CH, Stewart EM, Gray R, Pearce J, Eds. Detection Methods for Irradiated Foods—Current Status. Cambridge (United Kingdom):The Royal Society of Chemistry. P. 367–374.

Food Irradiation: Research and Technology Edited by Christopher H. Sommers, Xuetong Fan Copyright © Blackwell Publishing and the Institute of Food Technologists 2006

Chapter 7 DOSIMETRY FOR FOOD PROCESSING AND RESEARCH APPLICATIONS Kishor Mehta, Ph.D., and Kevin O’Hara

Importance of Dosimetry Food products may be treated with ionizing radiation for various purposes including insect disinfestation, growth inhibition, control of parasites, and shelf-life extension. Food irradiation specifications usually include an upper-dose limit to avoid product and product packaging degradation and lower-dose limit to ensure the intended beneficial effect. For food processing, the upper-dose limit is set for good irradiation practice and not from a food safety viewpoint (IAEA 2002). Much research and experimentation are carried out to set these dose limits suitable for the food product and the process under consideration. Due to the farreaching influence of the outcome of these experiments, it is imperative that the dose measurements are very accurate to arrive at a reliable set of dose limits for the process (ISO/ASTM 2004a).These dose limits are then often prescribed by regulations, where again proper dosimetry helps to verify compliance with these regulations at a commercial facility, as well as with national and international standards. Dosimetry is an integral part of both research and radiation-processing applications. It is important, therefore, that dosimetry personnel have some basic understanding of the radiation physics and chemistry of dosimetry.This chapter deals mainly with the application of dosimetry in food processing (for both commercial processing and radiation research); for those who are interested, references to the chemistry and physics of radiation dosimetry are given throughout the chapter. As a minimum requirement, food-processing personnel involved with dosimetry should have relevant experience and training.

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There are fundamental requirements for dosimetry in the process of conducting research on the irradiation of food and agricultural products that are based on good scientific practices. Radiation research for food often involves the establishment of the quantitative relationship between the absorbed dose and the relevant radiation-induced effects in these products.This effect in the food product is often measured with state-ofthe-art analytical equipment, but the absorbed dose to induce that effect is sometimes treated with less importance.The measurement and reporting of absorbed dose should be treated with equal importance, as with the measurement of these effects.

Introduction Proper dosimetry depends on the user’s ability to measure the absorbed dose to the food product, on the ability to determine the absorbed-dose distribution throughout the food product, and on the ability to perform routine dosimetry during processing or research. In the case of research, the delivery of the desired absorbed dose to the food product under known and validated conditions also requires good dosimetry.The accurate measurement of the dose distribution gives confidence that the maximum absorbed dose (Dmax) and minimum absorbed dose (Dmin) have indeed been measured. The principal objective of dosimetry in research is the determination of dose to achieve a desired effect. However, it is also necessary to establish baseline data in experimental design and to determine the dose distribution in the research sample. Because absorbed dose is the quantity that relates directly to the radiation-induced effect, the need for accurate dose measurement cannot be overestimated. In radiation processing, the overexposure or underexposure of the food product may have economic and legal consequences. In radiation research, the consequence is that incorrect conclusions are reached. Radiation-processing applications include operational qualification (such as irradiator dose mapping), process qualification (such as product dose mapping) and routine process control (such as routine product dosimetry for product release). For both research and radiation-processing applications, dosimetry measurements should be part of an overall quality assurance program. The dosimetry procedures should be based on internationally recognized practices such as those of International Organization for Standardization (ISO), European Committee for Standardization (CEN), and American Society for Testing and Materials, International (ASTM).

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Some Fundamentals of Dosimetry The measurement of absorbed dose involves a chemical or physical dosimeter whose well-defined and established radiation-induced effect is measured (for example, by spectrometers or spectrophotometers) and related to absorbed dose via the dosimetry system’s calibration curve. Several types of dosimetry systems are used in food irradiation (for example, liquids, plastic, radiochromic or alanine films, or pellets). For all of the dosimetry systems mentioned in this chapter, ISO/ASTM standards exist on their use; in addition, ISO/ASTM gives guidance on the selection and calibration of an appropriate dosimetry system (ISO/ASTM 2004b). Absorbed Dose In the irradiation of food products for processing or research, the emphasis is on “absorbed dose”and is defined as the quantity of ionizing radiation energy imparted per unit mass of a specified material. The SI unit of absorbed dose is the gray (Gy), where 1 Gy equals 1 J/kg.The absorbed-dose range of interest in food irradiation varies significantly and is generally categorized as low, medium, and high as defined in Table 7.1 (IAEA 2002). For food irradiation applications, water is usually considered the reference material and dose generally refers to “dose to water.” The vast majority of dosimeters available for food applications are considered waterequivalent in composition (for example, polymethylmethacrylate [PMMA] and radiochromic film). Dosimetry System A dosimetry system is used for determining absorbed dose and consists of dosimeters, measurement instruments, and procedures for the system’s use.A dosimeter is a device that, when irradiated, exhibits a quantifiable change in some property that can be related to absorbed dose using measurement instrumentation. In addition, reference standards are often considered to be part of a dosimetry system. These reference standards could include absorbance and wavelength standards for instrument calibration or instrument performance checks. Selection and Characterization of a Dosimetry System Types of Dosimetry Systems Dosimetry systems are classified based on their intrinsic accuracy and applications into one of four categories: primary-standard dosimeters,

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Table 7.1. Low, Medium, and High Dose Ranges for Food Processing and Research (IAEA 2002) Dose Range (Low, Medium, or High) Low Low Low

Low Low Medium Medium

High

High

Irradiation Application Sprout inhibition (for example, potatoes, onions, garlic, yams) Delay in ripening (for example, strawberries, potatoes) Insect disinfestation (for example, insects in grains, cereals, coffee beans, spices, dried fruits, dried nuts, dried fish products, mangoes and papayas) Quarantine security (against, for example, tephretid fruit flies in fruits and vegetables) Inactivation of pathogenic parasites (for example, tape worm and trichina in meat) Reduction in food spoilage causing microorganisms Improve the hygienic quality of food by inactivating foodborne pathogenic bacteria and parasites Pathogenic organism reduction in dried spices, herbs and other dried vegetable seasonings Sterilization to extend the shelf life of precooked food products in hermetically sealed containers

Typical Dose or Dose Range (Gy) 20 to 150 10 to 1,000 20 to 1,000

150 300 to 1,000 1,000 to 10,000 1,000 to 8,000

10,000 to 30,000

25,000 to 75,000

reference-standard dosimeters, transfer-standard dosimeters, and routine (or working) dosimeters (ISO/ASTM 2004b). Primary-standard dosimeters enable an absolute measurement of absorbed dose and are maintained and operated by national laboratories (for example, NIST and NPL). There are two types of primary-standard dosimeters: ionization chambers and calorimeters (ISO/ASTM 2004b). Reference-standard dosimeters are dosimeters of high metrological quality that can be used as reference standards to calibrate other dosimeters. They must have a radiation response that is accurately measurable and has a well-defined relationship with the dose. Commonly used reference-standard dosimeters include Fricke, ceric-cerous, dichromate, ethanol-chlorobenzene (ECB), and alanine dosimeters (ISO/ASTM 2004b). Transfer-standard dosimeters are used for transferring dose informa-

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tion from an accredited laboratory to an irradiation facility or a research laboratory.These dosimeters are normally reference-standard dosimeters that have characteristics meeting the requirements of the particular application. For example, they have to be transported from one place to another; there is also a time delay between the irradiation and their analysis (ISO/ASTM 2004b). Routine (or working) dosimeters are used for dose mapping and for process monitoring for quality control.They are often calibrated against reference- or transfer-standard dosimeters.Alternatively, the calibration of the routine dosimeter should be verified under actual conditions of use using a reference- or transfer-standard dosimeter. Commonly used routine dosimeters include PMMA and radiochromic dosimeters (ISO/ASTM 2004b). The Selection of an Appropriate Dosimeter As mentioned earlier, dosimetry is an essential part of radiation processing, especially for achieving a reliable process and thus a quality end product. A dosimetry system should be carefully selected in the early planning stages of the irradiation project. Selection is based on understanding the dosimetry requirements of the process and matching them to the characteristics of the dosimetry system.A dosimetry system for research applications may be different than the system that is suitable for commercial processing. The criteria for selection of a suitable dosimeter (and dosimetry system) may differ between a routine dosimeter and reference-standard dosimeter and are technical or operational in nature.The following list of criteria is not exhaustive, but examples are given to illustrate why certain attributes are important (ISO/ASTM 2004b and IAEA 2002). Suitable dose range for the applications: Food irradiation dose ranges vary from low dose levels (10 Gy to 1 kGy) to medium dose levels (1 kGy to 10 kGy) to high dose levels (10 kGy to 100 kGy).The user may wish to use one dosimeter to span the entire range of applications, but doing so may not be possible. More than one system may be required at the facility. Figure 7.1 gives the useful dose ranges for a number of common dosimetry systems suitable for food irradiation (ISO/ASTM 2004b and IAEA 2002). Post-irradiation change in dosimeter response: The time required for dosimeter’s response to develop following irradiation will vary from dosimeter type to dosimeter type. In the case in which irradiated product is released for use based on dosimetry results, this may be very important, but for some research applications may not be important.

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Figure 7.1.

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Useful dose range for various dosimeters (ISO ASTM/2004b).

Ruggedness of the dosimeter: For example, resistance to damage during normal routine handling could be critical. Many dosimeters may be supplied in a protective cover. Ease of system use: The form of a dosimeter ranges from a thin film, to a glass ampoule, to a pellet, to an optically transparent piece, and differs considerably in the method of handling, readout and general use. Stability of dosimeter response both before and after irradiation is important, as well as the ability to correct for influence quantities. In addition, the readout methods vary from UV/visible spectrophotometry to EPR spectroscopy to potentiometric techniques.All dosimetry systems require good laboratory practice, but ease of use should be considered. Capital investment: Initial capital investment and ongoing operational cost of the system, including dosimeters, measurement instruments, and labor, will vary from system to system. Dose mapping: The size of the dosimeter and its ability to measure dose gradients are important considerations. Significant dose gradients will likely exist at the interface between materials of different density (for example, near the bone-tissue interface in the cavity of a chicken or near the surface of a nectarine pit). It is important to use dosimeters that are capable of measuring these variations. For example, a film dosimeter is small relative to distances over which the dose gradient is significant.

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Type of irradiation facility and source: Different types of irradiation facilities may produce gamma rays, electrons or x-radiation (bremsstrahlung) with energies ranging from 0.1 MeV to 10 MeV. Some dosimetry systems may not be suitable for electrons and photons or low-energy radiation. Dosimetry System Characterization Before a dosimetry system is used, it should be characterized.The characterization consists of calibration, estimate of overall uncertainty, determination of batch homogeneity, establishment of traceability, and understanding of the effect of influence quantities on the dosimeter’s response. Similar to any other measurement system, a dosimetry system must be calibrated before being used.Three methods of dosimetry system calibration are described in detail in ISO/ASTM 51261 (2004b) and NPL Report CIRM 29 (1999). Uncertainty in the measured absorbed dose will differ significantly among dosimetry systems. Indeed, the knowledge about desired level of overall (or total) uncertainty for a specific food application will help to select an appropriate dosimetry system for that application. ISO/ASTM Guide 51707 (2004c) and NPL Report CIRM 29 (1999) describe possible sources of uncertainty in dosimetry and offer procedures for estimating the uncertainties. Regardless of the application (research or commercial), an estimate of uncertainty should accompany the measured and reported dose value (Mehta 2002).Typically, overall uncertainty in dose for reference-standard dosimeters should be better than 5% (at the 95% confidence level) and for routine dosimeters should be better than 8% (at the 95% confidence level). ISO/ASTM Guide 51707 (2004c) uses an uncertainty methodology adopted by ISO in 1995, which is different from the way uncertainty has been traditionally expressed in terms of “precision” and “bias.” Batch homogeneity represents the extent of variability of the dosimeter’s response for a given batch of dosimeters. How well does a calibration accurately represent the dosimetry system, including the entire batch of dosimeters? An indication of batch homogeneity is derived during the dosimetry system calibration.The procedure for estimating batch homogeneity is described in IAEA 2002. A measured dose value is called traceable when it can be related to recognized standards, usually national or international standards within acceptable limits. Traceability is a prerequisite for radiation-processing dosimetry and is also recommended for food research dosimetry (IAEA 2002).

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The reality of absorbed dose measurement is that the response of the dosimeter is affected by influence quantities that may not be within the control of the food processing or research facility. Such influence quantities include irradiation and storage temperature of dosimeters, dosimeter humidity, absorbed-dose rate, and radiation energy spectrum. It is important to understand how these influence quantities affect the response of the dosimeters, as well as the interpretation of dose and the estimate of uncertainty (ISO/ASTM 2004c). The effects of influence quantities may introduce significant uncertainties if the conditions during calibration differ from those during routine use.These effects must be evaluated.

The Use of a Dosimetry System Numerous ISO/ASTM standard practices and guidelines have been written on the use of specific dosimetry systems.These standards include the recommended instrumentation performance check, calibration techniques (including irradiation), storage and handling guidelines, dosimeter analysis techniques, dosimeter characterization (including postirradiation characterization), and documentation requirements. Another important consideration in the use of a dosimetry system is that, ideally, the presence of the dosimeter does not appreciably disturb the photon and electron energy spectrum in the volume where the dosimeter is located. Ideally, the dosimeter’s effective atomic number is similar to that of the irradiated material. For dose measurement in a hydrogenous material (for example, fruit, meat, poultry, or vegetable), a dosimeter of low-atomic number is useful (for example, aqueous solutions, PMMA, radiochromic thin film, alanine).

Dosimetry in Food Research Research on the effectiveness of irradiation of food products to achieve a defined benefit may involve different experimental parameters from one test to another. For example, the dose necessary for fruit disinfestation is much lower than the dose required for the bacterial inactivation in meat. In addition, the type of irradiation source may be different from facility to facility.The radiation-induced effect may also depend on other factors, for example, the absorbed-dose rate and energy of the radiation. Indeed, the radiation-induced effect may be different for two specimens that received the same absorbed dose but under different conditions.The radiation-induced effect in the food product depends on a large number

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of factors that may be physical, physiological, or chemical. Also, several environmental factors (for example, irradiation and analysis temperature of dosimeters, and moisture content in the food) may affect the radiation response of dosimeters; these should be documented. In research, an experiment is often designed to irradiate the specimen uniformly, but in practice, a variation in absorbed dose will exist throughout the specimen. Absorbed-dose mapping is performed to determine this variability—for example, the magnitude and location of Dmax and Dmin for a set of defined experimental parameters. One of the principal objectives in experimental design is to establish baseline data for evaluating the effectiveness and reproducibility of the experiment. Dosimetry is part of this experimental design. Proper dosimetry will allow the researcher to differentiate absorbed-dose variations that are expected under normal experimental conditions. Most important, dosimetry allows the researcher to measure absorbed-dose distributions in the irradiated specimen and to associate the absorbed dose with the radiation-induced effect. Documented experimental procedures ensure a reproducible dose distribution in the irradiated food, and allow other scientists to repeat the experiment. In research, dose mapping may involve the measurement of absorbeddose distribution through a single fruit, or box of fruit. This is achieved by placing dosimeters throughout the volume of interest, including the surface and within the volume. Even if the researcher is certain of the resultant dose distribution, the initial experiments should consist of a very thorough placement of dosimeters. Data from previous experiments can provide useful information for determining the number and location for these dosimeters.After the distribution is accurately determined, including the reproducibility of the measurements, dosimeter placement at and near zones of Dmax and Dmin is warranted for subsequent irradiations. In some applications, the irradiated food product may experience pronounced dose gradients on the surface or within the volume. Smalldimension dosimeters (for example, radiochromic film) may be used to measure these gradients. In the case when there is a large difference between dose extremes, it may be difficult to associate an absorbeddose level with an induced effect, unless that induced effect is relatively constant. A number of factors will affect the absorbed-dose distribution: sourceto-product distance; primary radiation scattered from experimental apparatus into the volume of interest; composition of the product packaging; and containment. Experimental set-ups that yield complex dose distributions or significant dose variation should be avoided. After the absorbed-dose distribution has been established for a given

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experimental set-up, the routine measurement of absorbed dose continues (ISO/ASTM 2004a).This measurement is often at a reference-dose location and does not require continued extensive dosimetry unless experimental conditions are changed with a resultant change in the dose distribution. Changes that could impact the dose distribution include changes in the radiation source or a significant alteration in the food geometry or packaging material. Theoretical calculations may also be used to determine absorbed-dose distribution in the irradiated food, and complement absorbed-dose measurement (ASTM 2004a). Calculations may also be used to evaluate the impact of changes in the experimental set-up, and to help optimize the set-up.

Dosimetry at a Commercial Facility General The dosimetry system selected for research may not be necessarily most suitable at the commercial facility.Thus it may be necessary to go through the selection process based on the criteria listed earlier. A second measurement instrument as a back-up is recommended for the selected routine dosimetry system. Some large irradiation facilities also have a referencestandard dosimetry system. Dosimetry plays a key role for two major activities at a commercial facility: • process validation, which includes characterization and maintenance of the irradiator, and the radiation process itself, and • routine process control, which includes those activities that control the process during routine operation and that gather evidence/information to show that this routine operation was under control. Process Validation Process validation is used to show that the entire process is under control.This involves establishing documented evidence that provides a high degree of assurance that a specific process will consistently produce a product that meets its predetermined specifications and quality characteristics.The best and most convenient method of documenting such evidence is through reliable dosimetry. The framework of such a process validation program includes:

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• operational qualification • process qualification Each of these activities is briefly described below, including the demands each puts on the dosimetry system. It is essential that validation is maintained through relevant activities carried out at regular intervals. Operational Qualification The commissioning and the subsequent operational qualification are the responsibility of the facility owner/operator. Operational qualification includes testing, calibrating, and characterizing the equipment at the facility, including the source and its ancillary control system, the conveyor system, any weighing equipment, and the dosimetry system(s) in use at the facility.These tasks are carried out after the commissioning of the facility and are repeated at regular intervals and whenever changes are introduced that may significantly affect dose or dose distribution in the irradiated products. Dosimetry is an important element in qualifying an irradiation facility, especially in establishing baseline data for evaluating facility effectiveness, predictability, and reproducibility for the range of conditions of operation. For example, dosimetry is used: • for irradiator dose mapping (measuring absorbed-dose distributions in reference materials with reference irradiation geometry) • for characterizing the facility, including establishing relationships between absorbed dose and operating parameters of the facility These procedures are described in ISO/ASTM Practice 51204 (2004d) for gamma-ray facilities and in ISO/ASTM Practice 51431 (2004e) for electron and x-ray facilities.These activities are also described briefly here. Irradiator Dose Mapping In a commercial irradiation facility, product may be transported through the radiation field using different methods (for example, tote box, carrier, or on a pallet). For simplicity in the following discussion, this method is referred to as a carrier. To determine the capability of an irradiator, it is important to locate the regions of Dmax and Dmin and their values within such a carrier, which is achieved by measuring a threedimensional dose distribution (dose mapping) in a carrier filled with a homogeneous reference material.For this purpose, a reference material may be selected that has composition and density close to food product

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that would be irradiated at the facility. Options are bulk feed ingredients that are relatively inexpensive; for example, rolled barley (density ~ 0.4 g/cm3), dehydrated alfalfa (~ 0.5 g/cm3), and whole corn (~ 0.7 g/cm3). Such dose mapping requires placing a sufficient number of dosimeters throughout the carrier in a systematic grid form; however, placing more dosimeters in the region where dose is expected to be extreme, based on general knowledge or previous experience with similar irradiators or from theoretical calculations. Dosimeters should be selected depending on the irradiation geometry; the size of the dosimeters should be such that they can spatially resolve the dose variation expected in the carrier. For example, thin film dosimeters are essential for an electron facility because of high dose gradients. For dose mapping, precision is more important than accuracy, because only dose variation is required.Thus it may be necessary to choose a dosimetry system that is different from the one used for process control during routine production.An acceptable way to refer to the uniformity of dose in the carrier is “dose uniformity ratio, DUR,” defined as the ratio of Dmax and Dmin. Figure 7.2 shows a typical

Figure 7.2. An example of the Dmax and Dmin locations in product for a two-pass gamma ray facility (IAEA 2002).

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Figure 7.3. An example of the Dmax and Dmin locations in product for an electron beam irradiation facility after one pass (IAEA 2002).

irradiation geometry for a rectangular product carrier for a gamma-ray facility, where hatching indicates the probable regions of Dmax and Dmin after the second pass. Figure 7.3 shows a typical irradiation geometry for an electron facility, where hatching indicates the probable regions of Dmax and Dmin for a rectangular carrier following a one-sided irradiation. Characterization of the Facility An irradiation facility is thoroughly characterized before it is used for commercial purposes (Cavaco and others 1991; Kovács and others 1998). Characterization includes the determination of the relationships between absorbed dose (or dose rate) and those process parameters that affect the dose in the product, over the full operational range of the parameters. These parameters include source strength and source arrangement, conveyor speed or dwell time, multi-pass mode, irradiation geometry, and bulk density of product. For an accelerator facility (both for electron and x-ray mode), there are also other parameters that are important, such as electron beam current,beam energy,beam spot,and scan width and scan frequency. Gamma-ray facility: The dose delivered to the food product depends strongly on either the selected dwell time or conveyor speed, which is most frequently used to control dose to the product. Dose rate also depends on the bulk density of the product; to deliver the same dose to a

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product, it would take longer time as the bulk density increases.These relationships should be established during operational qualification; this understanding is of practical help for the operation of the facility, and especially during process qualification. For this purpose, real products or simulated products (such as reference materials) may be used.The bulk density of the simulated products should be chosen to cover a range of values that are expected to be irradiated at the facility.The dosimeters are placed, by preference, at locations where minimum dose is expected (as determined during irradiator dose mapping).The data should then be analyzed using regression analysis to obtain the relationships between the variables. Accelerator facility: Characterization of an accelerator irradiator would also include measuring the mean energy of the electron beam, beam spot profile, and scan width (ISO/ASTM 2004f); information about the last two parameters helps to assure that the dose is uniformly delivered on the surface of a product carrier. For these two parameters, it is very convenient to use a strip or a large sheet of dosimetric film material. The penetration of the electrons depends on the beam energy (and on the composition and density of the product); thus, the beam energy is practically measured by determining the variation of dose with depth (depth-dose distribution) along the beam axis in a reference material. Figure 7.4 shows a typical depth-dose distribution that is generally measured by exposing either several thin film dosimeters at different depths in stack geometry or a strip of dosimetric material in a wedge (ISO/ASTM 2004f).The reference material is generally low atomic number material, such as polystyrene, water, graphite, or aluminum.The range parameters, namely optimum thickness (Ropt), half-value depth (R50), and halfentrance depth (R50e), may be used for designing a suitable carrier, while parameters R50 and practical range (Rp) can be used for estimation of mean electron beam energy and the most probable electron beam energy based on mathematical relationships (ISO/ASTM 2004f; ICRU 1984). Process Qualification The goal of the irradiation process is to deliver dose to every part of the product that is between the two prescribed dose limits.These limits are established based on research results and are generally stipulated by regulators. The objective of process qualification is therefore to determine the values of all key process parameters (including timer setting, conveyor speed, and the characteristics of the product carrier, such as arrangement of product within) that will satisfy these dose specifications (and others, if any, such as temperature control for frozen food) with a

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Figure 7.4. Typical (idealized) depth-dose distribution for a 10MeV electron beam in homogeneous material composed of low-atomic number elements.The peak-to-surface dose ratio depends on the energy of the incident electron beam. For definitions of Ropt, R50, R50e, and Rp, refer to ISO/ASTM 51649 (2004f). Reprinted with permission of ISO/ASTM 2004f, copyright ISO/ASTM International.

high degree of confidence.This is achieved by measuring the dose distribution for the product in a specific product carrier with a specific product arrangement and is referred to as “product dose mapping.” Product Dose Mapping The objective of product dose mapping is to determine the locations and values of Dmax and Dmin in the carrier that is under consideration; these values are then compared against the dose limits. First, the detailed dose distribution is measured for one carrier—generally requiring 50 to 100 dosimeters depending on the degree of product homogeneity (Polonia and others 1998). For products with voids or nonuniform products (such as whole chicken), dosimeters should be placed at locations where discontinuities in composition or density may affect the regions of Dmax and Dmin (Miller and Batsberg 1981). Initially, the process parameters may be selected on a trial basis, based on past experience and operational

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qualification data. After irradiation, the dosimeters are removed, with careful noting of the position of each. The dosimeters are analyzed and the dose values determined. Dmax and Dmin are identified (ASTM 2004b) and the DUR value calculated.The objective is to achieve DUR value less than the ratio between the prescribed dose limits. If that is not the case, one or more process parameters need to be adjusted to decrease DUR following some of the methods described next. • For gamma-ray facilities: • extend the source beyond the boundaries of the product (source overlap) • move the carrier past the source at several different levels (product overlap) • use attenuators or compensating dummy • irradiate from two or four sides, or rotate the carrier during irradiation, and • increase the source-to-product distance • For electron facilities: • change the beam characteristics, for example, by optimizing the electron beam energy • use attenuators, scatterers, or reflectors • use double-sided irradiation depending on the bulk density, thickness, and heterogeneity of the product • arrange baffles to control product flow through the irradiation zone in the case of bulk-flow irradiators (for both types of facilities) If the DUR is still not acceptable, rearrangement of the product within the product carrier or alteration of its size may be necessary. Verification process The distribution of absorbed dose within the product depends on many factors, such as plant design, type of product, and energy and type of radiation. These factors will not normally vary during a given radiation process. However, due to the statistical nature of the radiation process, there are fluctuations in the values of some of the process parameters affecting the dose distribution (McLaughlin and others 1989; Biramontri and others 1989; Mehta 1992). In practice, variability is unavoidable in any radiation process due to several effects, including: • variation in the bulk density or product configuration between carriers • variation of dosimeters in placement, that is, dosimeters are not placed exactly at identical locations in different carriers

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• statistical fluctuations of some of the process parameters during irradiation • uncertainty associated with the dosimetry system The extent of this variability may be measured by randomly selecting a number of nominally identical carriers, n, where n is between 3 and 10. Several dosimeters are placed in each carrier in the expected zones of Dmax and Dmin, as identified during the product dose mapping exercise. These carriers are then irradiated together or sequentially, keeping all the process parameters nominally constant. Dmax and Dmin will vary due to the factors discussed above.These n values are expected to follow a normal (Gaussian) distribution characterized by two parameters, the mean value and the standard deviation. The standard deviations for Dmax and Dmin may not have the same value. These two standard deviations are then used to set “target doses” as discussed below.This exercise is sometimes referred to as “verification process.” Target Doses To ensure that the measured dose in the product during routine production is within the two specified dose limits in the presence of this variability, the operator sets the process parameters (such as dwell time or conveyor speed) so as to deliver a dose between two more restrictive limits.Thus, the lower dose limit is adjusted upward (higher value) while the upper dose limit is adjusted downward (lower value). These new dose limits are sometimes referred to as target doses.Their actual values depend on the values of the standard deviations determined above, and the economics of the process under consideration (Mehta 1992; IAEA 2002). These revised “dose limits” (or target doses) sometimes place severe restrictions on the process, which can be alleviated by reducing the process variability, for example by selecting a dosimetry system with a reduced uncertainty (that is, with higher precision and accuracy). Reference Monitoring Location For some radiation processes, the position of Dmin is inside the product carrier and not on the surface; hence, placement of dosimeters at these positions for process control during routine irradiation (see below) might be impossible without taking apart the carrier. For such cases, a convenient reference-monitoring location should be selected on the surface of the carrier, or outside but close to the carrier, for routine process control. The essential requirement during process qualification is that the relationships between the dose at this alternative reference location and the dose extremes be established, shown to be reproducible, and documented.

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Routine Process Control To assure that the process is being correctly administered, that is, all product is receiving dose within the specified range, certain process control procedures are in place at the irradiation facility.The following are principal elements in process control: • • • •

monitoring of all key process parameters routine product dosimetry product control product release and certification

Process Parameters All key process parameters that affect dose in the product are controlled and monitored (IAEA 2002). In a well-designed irradiation facility, these parameters are monitored from a control console and recorded automatically and continuously. Modern information technology has contributed significantly toward reliable control and recording of relevant parameters (Gibson and Levesque 2000; Comben and Stephens 2000). Routine Product Dosimetry One of the fundamental elements of process control is routine dosimetry.To allow the facility operator to certify the dose received by the product, routine dosimetry of each and every production run is essential (IAEA 2002).This provides a system that relevant authorities worldwide can rely on to ensure that imported food products have been treated according to the legal requirements. Dosimetry data may also be required in the event of mechanical failures and operational anomalies. For a gamma-ray facility operating in a continuous mode (for example, a shuffle-dwell system in which a single carrier cannot be removed independently from the irradiation chamber), it is recommended that there is always at least one product carrier inside the irradiator that contains one dosimeter or a dosimeter set. For a dosimeter set consisting of more than one dosimeter, the average value is taken as the dose at that location.Also, one dosimeter or a dosimeter set should be placed on the first and the last carrier of the production run.When operating in a batch mode, routine dosimeters should be placed on several carriers that are evenly distributed throughout the batch to generate statistically meaningful data. For incremental-dose systems, in which a single carrier can be removed independently from the irradiation chamber, it is recommended that one dosimeter or one dosimeter set be placed on each carrier.This is to minimize the loss of product in the event of a serious failure during the

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process. For an electron facility, there should always be one dosimeter set at the start of a production run. For long runs, one dosimeter or one dosimeter set should also be placed near the middle of the run and at the end of the run, and at other intervals as appropriate (Mehta and others 1993; Cabalfin and others 1991). In general, more frequent placement of dosimeters during a production run could result in less product rejection in the case of operational uncertainty or failure. Routine dosimeters should be placed either at the location of minimum dose or at the reference monitoring locations identified during process qualification. After the process, the dosimeters should be read and the corresponding dose values determined and compared against the values determined during process qualification. For process control, the accuracy of the measured absorbed dose is of essence. For reliable measurements, it is important to handle the dosimeters before, during, and after irradiation in controlled environment as specified in the facility’s operating procedures or in the manufacturer’s instructions. Product Control Plant design and administrative procedures should ensure that it is impossible to mix irradiated and nonirradiated product. In a well-designed irradiation facility, the areas for storing nonirradiated product are physically isolated from the areas where treated product is stored or handled. This also simplifies the product inventory control procedures. In some applications, radiation-sensitive (sometimes referred to as go/ no-go) indicators (which change color upon irradiation) may be used to show that a product has been exposed to a radiation source (ISO/ASTM 2004g). This practice does not, however, replace the routine product dosimetry discussed above because these are only qualitative indicators of irradiation. In addition, the color change is not always stable after irradiation and may in fact be affected by light or heat.Thus, indicators are useful only within the irradiation facility where these conditions are controlled. It must be emphasized that although these indicators can conveniently be used to assist in product inventory control, they must never be used to replace other inventory control procedures. Product Release and Certification Proper facility operation and adherence to process control procedures require records and documentation. Such records are necessary for the purpose of auditing by a customer or of inspection by an authority.These are reviewed by authorized individuals and maintained in the process documentation.Typically, these records should include (IAEA 2002):

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• information on calibration and maintenance of equipment and instrumentation used to control and measure dose delivered to the food product • all dosimetry data for process qualification, product absorbed-dose mapping, and routine product processing (including uncertainty in the dose values) • values of all process parameters affecting absorbed dose in the food product • product description and loading pattern in the carrier • date the product is processed, the name of the operator, and any special conditions of the irradiator that can affect dose to the product (such as process interruption) • copy of the shipping documents and of the certificate of irradiation Prior to the release of the irradiated food product for use, dosimetry data and recorded values of the key process parameters are examined to verify compliance with specifications. For each production run, the dose delivered to the product should be certified.

References ASTM. 2004b. Guide for Absorbed-Dose Mapping in Radiation Processing Facilities, E2302, Annual book of ASTM standards,Vol. 12.021,American Society for Testing and Materials International,West Conshohocken, PA, U.S.A. ASTM. 2004a. Standard Guide for Selection and Use of Mathematical Methods for Calculating Absorbed Dose in Radiation Processing Applications, E2232,Annual book of ASTM standards, Vol. 12.02, American Society for Testing and Materials International, West Conshohocken, PA, U.S.A. Biramontri, S.,Thongmitr,W.,Wanitsoksombut,W. 1989. Dosimetry for commissioning and quality control in the irradiation of onions.Appl. Radiat. Isot. 40:349–354 Cabalfin, E.G., Lanuza, L.G., Solomon, H.M. 1991. Process control and dosimetry in a multipurpose irradiation facility. Radiat. Phys. Chem. 55:781–784. Cavaco, M.C., Almeida, J.C., Andrade, M.E., Kovács, A., 1991. Dosimetry commissioning for an industrial cobalt-60 gamma radiation facility.Appl. Radiat. Isot. 42:1185–1188 Comben, M., Stephens, P. 2000. Irradiation plant control upgrades and parametric release. Radiat. Phys. Chem. 57:577–580. Gibson,W.H., Levesque, D. 2000. How gamma processing systems are benefiting from the latest advances in information technology. Radiat. Phys. Chem. 57: 581–585. IAEA. 2002. Dosimetry for food irradiation, TRS No. 409, International Atomic Energy Agency,Vienna. ICRU. 1984. Radiation dosimetry: Electron beams with energies between 1 and 50 MeV, ICRU Report 35, International Commission on Radiation Units and Measurements, Washington, D.C. ISO/ASTM. 2004d. Practice for Dosimetry in Gamma Irradiation Facilities for Food Processing, 51204, Annual book of ASTM standards, Vol. 12.02, American Society for Testing and Materials International,West Conshohocken, PA, U.S.A.

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ISO/ASTM. 2004b. Standard Guide for Selection and Calibration of Dosimetry Systems for Radiation Processing, 51261, Annual book of ASTM standards, Vol. 12.02, American Society for Testing and Materials International,West Conshohocken, PA, U.S.A. ISO/ASTM. 2004e. Practice for Dosimetry in Electron and Bremsstrahlung Irradiation Facilities for Food Processing, 51431, Annual book of ASTM standards, Vol. 12.02, American Society for Testing and Materials International, West Conshohocken, PA, U.S.A. ISO/ASTM. 2004g. Guide for Use of Radiation-Sensitive Indicators, 51539, Annual book of ASTM standards, Vol. 12.02, American Society for Testing and Materials International, West Conshohocken, PA, U.S.A. ISO/ASTM. 2004f. Practice for Dosimetry in an Electron-Beam Facility for Radiation Processing at Energies between 300 keV and 25 MeV, 51649,Annual book of ASTM standards, Vol. 12.02, American Society for Testing and Materials International, West Conshohocken, PA, U.S.A. ISO/ASTM. 2004c. Standard Guide for Estimating Uncertainties in Dosimetry for Radiation Processing, 51707, Annual book of ASTM standards, Vol. 12.02, American Society for Testing and Materials International,West Conshohocken, PA, U.S.A. ISO/ASTM. 2004a. Guide for Dosimetry in Radiation Research on Food and Agricultural Products, 51900, Annual book of ASTM standards, Vol. 12.02, American Society for Testing and Materials International,West Conshohocken, PA, U.S.A. Kovács,A., Moussa,A., Othman, I.,Alnaal, K. 1998. Dosimetry commissioning of the gamma irradiation facility ‘ROBO’. Radiat. Phys. Chem. 52:585–589 McLaughlin,W.L., Boyd,A.W., Chadwick, K.H., McDonald, J.C., Miller,A. 1989. Dosimetry for radiation processing. New York:Taylor and Francis. Mehta, K. 1992. Process qualification for electron-beam sterilization. Medical Device and Diagnostic Industry, June: 122–134. Mehta, K., Kovács,A., Miller,A. 1993. Dosimetry for quality assurance in electron-beam sterilization of medical devices. Medical Device Technology,April: 24–29. Mehta, K. 2002. Dosimetry uncertainty in radiation processing. Radiation Protection and Environment,Vol 25, No.2, 59–65. NPL. 1999. (National Physical Laboratory) Report CIRM 29, Guidelines for the Calibration of Dosimeters for Use in Radiation Processing,August 1999. Miller, A., Batsberg Pedersen, W. 1981. Dose distribution in electron irradiated plastic tubing. Radiat. Phys. Chem. 18:967–973. Polonia, I., Portugal, L.,Andrade, M.E. 1998. Dose mapping of dried figs treated by gammaradiation. Radiat. Phys. Chem. 52:569–573.

Notes 1. The Annual book of ASTM standards, Vol. 12.02 is published annually by ASTM International, although each standard is only updated about every five years.The reader is encouraged to seek the current version of the relevant ISO/ASTM or ASTM standard (www.astm.org).

Food Irradiation: Research and Technology Edited by Christopher H. Sommers, Xuetong Fan Copyright © Blackwell Publishing and the Institute of Food Technologists 2006

Chapter 8 MECHANISMS AND PREVENTION OF QUALITY CHANGES IN MEAT BY IRRADIATION Doug U. Ahn and E.J. Lee

Introduction Since the U.S.Army Medical Department began to assess irradiated food in 1955, many researchers have studied the safety of irradiated foods, and the World Health Organization (WHO) announced that irradiation of foods at 99% efficacy (Follett and Armstrong 2004) and potentially could be combined with poor host status, inspection, field control, and other mitigation procedures to give a high level of quarantine security.

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Maximum pest limit is another approach to quarantine security that focuses on survival rather than mortality and is closely related to the alternative treatment efficacy approach (Baker et al. 1990; Mangan et al. 1997). It is defined as the maximum number of insects that can be present in a consignment imported during a specified time at a specified location (Baker et al. 1990).A minimum sample size for inspection is determined from an estimate of the level of pest infestation, the efficacy of the postharvest treatment, and the maximum lot size assembled per day at a location.This level of inspection is predicted to detect infestation levels greater than the maximum level of permissible infestation with a certain probability and confidence limits (Baker et al. 1990).

Generic Treatments A “generic” quarantine treatment is one that provides quarantine security for a broad group of pests. From a regulatory standpoint, “generic” can also refer to a treatment for a pest on all commodities it infests.A generic treatment for a group of insects could be applied at many taxonomic levels, for example, to all Diptera (flies), or to flies in the family Tephritidae (fruit flies), or to tephritid fruit flies in the genus Bactrocera. Irradiation is the ideal technology for developing generic treatments because it is effective against most insects and mites at dose levels that do not affect the quality of most commodities. Before a generic treatment can be recommended, information is needed on effective irradiation doses for a wide range of insects within the taxon. Initially, development of the generic dose concept has focused on tephritid fruit flies.The International Consultative Group on Food Irradiation (ICGFI) was the first group to formalize a recommendation for generic irradiation treatments (ICGFI 1991). In 1986, based on irradiation data for several tephritid fruit fly species and a limited number of other insect pests, they proposed a dose of 150 Gy for fruit flies and 300 Gy for other insects.Adoption of the 150 Gy dose for fruit flies was stymied by research suggesting that three tephritid fruit fly species in Hawaii required higher irradiation doses to prevent adult emergence from infested fruit (Seo et al. 1973). Based on the data presented by Seo et al. (1973), USDA-Animal Plant Health Inspection Service (APHIS) approved irradiation doses of 210, 225, and 250 Gy for the melon fly, Mediterranean fruit fly, and oriental fruit fly, respectively, for exporting fruits and vegetables from Hawaii (Federal Register 1997).The majority of economically important tephritid fruit flies come from four genera—Anastrepha, Bactrocera, Ceratitis, and Rhagoletis, and irradiation studies have been con-

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ducted with species in each of these genera. Although results from various irradiation studies with fruit flies have not always been consistent (reviewed by Burditt 1994, 1996; Rigney 1989; Hallman and Loaharanu 2002), the preponderance of evidence suggested that all the species in these genera could be controlled by doses at or below 150 Gy. Recently, Follett and Armstrong (2004) demonstrated that irradiation doses of 100, 125, and 150 Gy controlled C. capitata, B. dorsalis, and B. cucurbitae, respectively, which supported lowering the dose for Hawaii’s fruit flies and acceptance of the proposed 150 Gy generic dose for tephritids. A proposed rule from USDA-APHIS is in preparation, recommending a generic dose of 150 Gy for all tephritid fruit flies. This will be the first widespread use of a generic phytosanitary treatment for any pest group or treatment type. The generic dose concept has been applied on a limited scale to irradiation treatment for fruits exported from Hawaii to the U.S. mainland. In 2001, the USDA-APHIS convened a meeting to establish treatment protocols for a new commercial irradiation facility (Hawaii Pride LLC) in Hawaii, and approved generic irradiation doses of 250 Gy for any species of Tephritidae (fruit flies) and Thysanoptera (thrips); and 400 Gy for any species of Coccidae (soft scales), Pseudococcidae (mealybugs), and immature Lepidoptera (moths) infesting eight fruits being exported to the U.S mainland. In this case, the doses for nonfruit fly pests were established based on information from studies in Japan and Hawaii on a limited number of species within each taxa (Follett and Armstrong 2004). This was the first time USDA-APHIS recommended a generic irradiation dose for any group of insects, albeit on a limited scale and only for certain Hawaii fruits. New Zealand is preparing a rule to allow import of tropical fruits from Australia using generic irradiation treatments of 150 Gy for fruit flies, 250 Gy for other insects, and 300 Gy for mites (Corcoran and Waddell 2003). Broad application of the generic irradiation concept to other taxa at the family or order level would be beneficial to promote trade in agricultural commodities and provide a treatment alternative for infested consignments arriving in importing countries. An International Database of Insect Disinfestation and Sterilization (IDIDAS 2003) under development by the International Atomic Energy Agency contains information on many Coleoptera (79 species, mainly curculionids) and Lepidoptera (72 species, mainly pyralids and tortricids); however, the majority of the studies referenced were not designed for quarantine purposes and lack the necessary large-scale tests. Information for other important regulatory arthropod groups such as Thysanoptera, Hemiptera, and Acari is limited. The “high-dose” approach is a variation of the generic dose concept.

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With this approach, a dose is set in excess of that believed to be required to control the pests associated with the commodity. For example, sweet potato growers in Hawaii are unable to ship sweet potatoes to California and the U.S. mainland without a quarantine treatment because of the presence of three regulatory pests, West Indian sweet potato weevil, Euscepes postfasciatus (Coleoptera: Curculionidae), sweet potato vine borer, Omphisa anastomosalis (Lepidoptera: Pyralidae), and sweet potato weevil, Cylas formicarius elegantulus (Coleoptera: Curculionidae). An irradiation treatment of 400 Gy for sweet potatoes was approved based on preliminary data for the pests (Follett 2003) and data from IDIDAS and the irradiation literature on curculionid and pyralid pests suggesting this dose would be adequate.This provisional irradiation treatment was published as a final rule in the Federal Register on February 18, 2004 (Federal Register 2004). This was the first time APHIS considered the high-dose approach for controlling a pest complex before research is completed to confirm a lower dose. Before generic treatments can be recommended for a wider range of insects and on a broader scale, information from coordinated research projects and large-scale tests is needed on effective irradiation doses for key pests and under-represented taxa. The most radiotolerant insect species tested to date is the Angoumois grain moth, which successfully reproduced at 500 Gy but not at 600 Gy (Ignatowicz 2004).Theoretically, this dose could be set as a generic treatment for all insects; however, a limiting factor for the practical use of a generic treatment at 600 Gy is the 1,000 Gy (1 kGy) maximum allowed dose for fresh produce set by the Food and Drug Administration.With typical dose uniformity ratios of 1.5–3.0 at commercial irradiation facilities, treatment to achieve a minimum absorbed dose of 600 Gy without exceeding 1 kGy would be difficult. Also, doses above 600 Gy adversely affect the organoleptic properties of many fresh fruits and vegetables (Kader 1986; Morris and Jessup 1994).A generic irradiation dose of 400 Gy for arthropods is supported by available data of Lepidoptera pupae and adults, and mites are excluded.

Regulatory Aspects of Irradiation The establishment of national regulations for the use of irradiation as a phytosanitary treatment began in 1930 with a failed proposal to use Xrays for treating fruit exported from Formosa (Koidsumi 1930). Seven decades later, the International Plant Protection Convention (IPPC) adopted an international standard for the use of irradiation as a phytosanitary treatment (IPPC 2003a).The evolution of irradiation as a phytosani-

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tary treatment from its disappointing start to international success was marked by a long history of national, regional, and international initiatives and several watershed events (discussed below), including the official acceptance of irradiation as a “safe” treatment and the establishment of a regulatory and policy framework by the United States for the implementation of irradiation as a phytosanitary treatment. Codex Alimentarius (Codex), the international organization responsible for establishing harmonized standards for food safety, adopted its Codex General Standard for Irradiated Food (CAC/RS 106-1979) in 1979. Although the standard does not specifically apply to phytosanitary treatments, it was the first international standard for irradiated food, and many phytosanitary treatments are for food commodities. The standard was subsequently revised in 1983 following the recommendations of the joint FAO-IAEA-WHO Expert Committee, and again in 2003 based on additional research indicating that the maximum absorbed dose could exceed 10 kGy when necessary to achieve a legitimate technological purpose (Codex 2003). Associated with the General Standard is the Codex Recommended International Code of Practice for the Operation of Irradiation Facilities. This was significant because it represented the first internationally harmonized guidelines on how to measure absorbed dose. It also describes relevant parameters in facilities; dosimetry and process control; good radiation processing practice; and product and inventory control (Codex 1984). The Code includes two annexes:Annex A is related to dosimetry, indicating how to calculate the overall average adsorbed dose and explaining the concept of limiting dose values, routine dosimetry, and process control;Annex B gives some examples of technological conditions for the irradiation of certain items. Mango is one of the examples. It is noted that mangoes may be irradiated for three objectives: (1) control of insects, (2) to improve quality (extend shelf life), and (3) to reduce microbial load using up to 1 kGy as an average dose. It is significant that the Code focused on mangoes because the chemical treatment of mangoes became a serious political issue in 1982 after the U.S. Environmental Protection Agency (EPA) announced a ban on the use of ethylene dibromide (EDB) because it was demonstrated to be a carcinogen (Ruckelshaus 1984). EDB was popular and widely used as a phytosanitary treatment at the time. The ban forced phytosanitary officials to seek alternative treatments for many commodities that were routinely treated for import and export, especially tropical fruits. Political pressures and growing interest in the commercialization of irradiation for the treatment of food in the United States spurred the

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Food and Drug Administration (FDA) to open the regulatory door in 1986 by publishing 21 CFR 179.26, “Irradiation in the Production, Processing and Handling of Food.” Among other things, this regulation authorized the use of irradiation up to 1 kGy for the disinfestation of arthropod pests in food, the use of up to 8 kGy for the control of microbial pathogens on seeds for sprouting, and up to 30 kGy for the microbial disinfestation of spices.This rule cleared the regulatory path for the USDA to authorize irradiation as a phytosanitary treatment on commodities for consumption. European authorities have historically been among the most reluctant to accept irradiation as a treatment for foods, but also among the most active in supporting research on the safety of irradiation. Concerns are principally focused on health risks to food processing workers, possible long-term effects of consuming irradiated food (especially for children), and fears that food producers and processors will be less motivated to use good manufacturing practice to ensure the wholesomeness of food if they are able to rely on irradiation treatment to produce clean products.A very limited list of herbs, spices, and seasonings is currently authorized from approved facilities with mandatory labeling requirements. In 2001, the European Commission suggested that this list be considered complete and recommended further research on the effects of consuming irradiated food and identifying alternative treatments rather than expanding the possibilities for irradiation (European Commission 2001). A similar situation occurs with Japan, where the use of nuclear technologies of any kind is perhaps more sensitive than for other countries for historical reasons.As do the Europeans, the Japanese allow and use irradiation for the treatment of food on a very limited and highly restricted basis.To date, the only phytosanitary treatment reported by Japan is for potatoes. A small proportion of Japan’s potato production is treated for sprout inhibition (Furuta 2004).

USDA Regulations The USDA had decided as early as 1966 that 150 Gy was the minimum dose to prevent adult emergence of three fruit flies: oriental fruit fly, Bactrocera dorsalis; Mediterranean fruit fly, Ceratitis capitata; and melon fruit fly, Bactrocera curcubitae; associated with papaya from Hawaii (Balock et al. 1966). In 1989, soon after FDA’s regulations went into effect, the Animal and Plant Health Inspection Service (APHIS), the USDA agency responsible for promulgating regulations dealing with quarantine treat-

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ments, published the first rule to allow the use of irradiation as a phytosanitary treatment.The rule specified a treatment of 150 Gy in order to ship fresh papaya from Hawaii to the mainland, Guam, Puerto Rico, and the Virgin Islands (Hawaii was later changed to 250 Gy). Despite being limited to a specific commodity, origin, and domestic program (and despite the fact that no fruit was immediately shipped due to the lack of a treatment facility in Hawaii), this minor domestic regulation had major global impacts as a result of the regulatory and policy implications it represented for the phytosanitary community. By publication of this rule, the United States made clear its acceptance of irradiation as both a safe and effective phytosanitary treatment and, for the first time, APHIS approved a treatment that dealt with a complex of pests (fruit flies) rather than a single pest.At the same time,APHIS recognized the legitimacy of a nonmortality treatment (the required response was “inability to fly”) and the possibility of detecting and accepting “live” quarantine pests in treated shipments (USDA-APHIS 1989). Regulatory interest in irradiation peaked again in 1992 when the fumigant methyl bromide (MB) was listed in the Montreal Protocol as one of the substances that causes depletion of the ozone layer. The Montreal Protocol is an international treaty for the regulation of ozone-depleting substances in the atmosphere (EPA 1993). At the Meeting of the Parties to the Montreal Protocol held September 1997 in Montreal, Canada, it was agreed that the production of MB should be phased out by a certain percentage each year beginning in 1999. Developed countries were expected to phase it out completely by 2005 and developing countries by 2015 (EPA 1996). Although the Montreal Protocol makes an exception for the use of MB as a quarantine treatment, the overall reduction in production of the fumigant over time has caused cost increases and reduced the availability of the compound with the net effect of making it increasingly less practical.The effect is not as immediate as was the ban on EDB, but the repercussions are just as significant because MB is also popular and widely used as a phytosanitary treatment for both food and nonfood items (for example, cut flowers and wood products). After 1995, rapidly increasing global trade pressures and the possible loss of methyl bromide as a fumigant for regulatory pest treatments made it imperative for practical treatment options to be explored. Unfortunately, the perception of public reluctance to accept irradiation and the relatively high initial costs associated with changing to irradiation as a preferred treatment technology made it less desirable than lower-cost alternatives.At the same time, technological advances, greater experience, and a growing body of research indicated that irradiation had increas-

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ingly greater potential as a treatment, or as an alternative treatment, for many quarantine pest problems. It is in this light that APHIS decided in 1996 to expand its regulatory framework addressing irradiation treatment, develop comprehensive policy statements, and begin encouraging international harmonization while also updating its own treatments and approving new ones. In a Policy Notice of 1996 titled “The Application of Irradiation to Phytosanitary Problems,”APHIS listed key positions and procedures, defined terms, offered research protocols, and proposed generic doses for nine fruit fly pests (USDA-APHIS 1996). In response to a petition from Hawaii, APHIS further expanded its authorization in 1997 to add the possibility of treating fresh papaya, lychees, and carambolas from Hawaii at 250 Gy (Moy and Wong 2002).An irradiation dose of 250 Gy rather than 150 Gy was established after review of the data in Seo et al. (1973). Following this,APHIS also approved the irradiation of sweet potato (Follett, in press) and other commodities from Hawaii. Fruits and vegetables from Hawaii that are currently authorized for irradiation treatment include abiu, atemoya, bell pepper, carambola, litchi, longan, eggplant, mango, papaya, pineapple (other than smooth Cayenne), rambutan, sapodilla, Italian squash, sweet potato, and tomato (Federal Register 2002; Follett 2004). Consistent with its Policy Notice, APHIS supplemented its authorizations for exports from Hawaii with regulations to also allow foreign imports by publishing a rule on Irradiation as a Phytosanitary Treatment for Imported Fresh Fruits and Vegetables (7 CFR 319.305). This regulation sets out specific standards for irradiation treatment to provide protection against 11 species of fruit flies and the mango seed weevil. Included also in this regulation are provisions that require the exporting country to establish Framework Equivalency Work Plans with APHIS demonstrating that the exporting country accepts irradiated commodities for import. Current plans are to continue expanding regulatory authorizations for the use of irradiation as a phytosanitary treatment based on additional research and experience (Pers. Comm 2005). Data currently under review offers possibilities for significant refinement of existing treatments and would make some new treatments available, including doses of 150 Gy for all tephritid fruit flies (Follett and Armstrong 2004), 300 Gy for the false red spider mite (Brevipalpus chilensis), 200 Gy for codling moth (Cydia pomonella), 250 Gy for koa seedworm (Cryptophlebia illepida), 250 Gy for litchi fruit moth (Cryptophlebia ombrodelta), 200 Gy for oriental fruit moth (Grapholita molesta), 92 Gy for plum curculio (Conotrachelus nenaphur), and 150 Gy for sweet potato weevil (Cylas formicarius elegantulus).

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Regional and International Harmonization The North American Plant Protection Organization (NAPPO), the regional organization responsible for setting phytosanitary standards recognized under the North American Free Trade Agreement (NAFTA), formally recognized the effectiveness of irradiation as a broad-spectrum quarantine treatment for fresh fruits and vegetables in 1989. In addition to NAPPO, other regional plant protection organizations that operate within the framework of the IPPC, including the European and Mediterranean Plant Protection Organization (EPPO), the Asia and the Pacific Plant Protection Commission (APPPC), the Comite de Sanidad Vegetal del Cono Sur (COSAVE), and the Organismo Internacional Regional de Sanidad Agropecuaria (OIRSA), endorsed irradiation as a quarantine treatment for fresh horticultural products at the Technical Consultation of Regional Plant Protection Organizations held in San Salvador in 1992 (FAO 1992). At the NAPPO Annual Meeting in 1994, a roundtable discussion was organized on “The Application of Irradiation to Phytosanitary Problems.” NAPPO delegates from Canada, Mexico, and the United States provided enough encouragement for the NAPPO Executive Committee to agree on an initiative to elaborate a regional standard.The policies put forward by APHIS in 1996 provided the framework for the development of “Guidelines for the Use of Irradiation as a Phytosanitary Treatment” that was adopted as a NAPPO standard (NAPPO 1997).This marked a significant step forward in international harmonization and became the springboard for creation of an international standard (IPPC 2003a). Since 1993, the IPPC has prepared international standards for phytosanitary measures designed to promote international harmonization and facilitate safe trade by avoiding the use of unjustified measures as barriers. Standards adopted by the IPPC must be observed by members of the World Trade Organization according to the Agreement on the Application of Sanitary and Phytosanitary Measures (the WTO-SPS Agreement). Governments must provide a technical justification (generally a risk assessment) for measures that are inconsistent with international standard or for measures put in place in the absence of a standard (WHO 1994). The Interim Commission on Phytosanitary Measures (ICPM), governing body of the IPPC, considered the global application of irradiation as a phytosanitary measure at its Third Session in 2001.A decision was made to create a working group with the purpose of developing an international standard for irradiation as a phytosanitary treatment, which was officially adopted in April 2003 (IPPC 2001; IPPC 2003b).The IPPC standard (International Standards for Phytosanitary Measures [ISPM] No. 18 Guidelines for the use of irradiation as a phytosanitary measure) describes

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specific procedures for the application of ionizing radiation as a phytosanitary treatment for regulated pests or articles. The document is organized like other IPPC standards, with sections including an introduction, scope, references, definitions and abbreviations, and an outline of requirements preceding the general and technical requirements. In addition, the standard includes an appendix providing scientific information on absorbed dose ranges for certain pest groups and another appendix providing guidance on undertaking research to develop irradiation treatments for regulated pests (IPPC 2003a).

Trade The establishment of the NAPPO standard in 1997 opened new possibilities for the use of irradiation in trade between Mexico and the United States. Mexico has great potential because of the high volume of fruit and vegetable exports requiring phytosanitary treatments. Mexico also has trained personnel and significant experience with irradiation treatments. What may be more important is that Mexico already has a regulatory framework in place for sanitary and phytosanitary treatments that allow food to be irradiated for consumption and for importation (Verdejo 1997). In 1998, a meeting was organized in Mexico to evaluate the capability of the country to initiate export markets for irradiated fruits and vegetables.Although it was recognized that Mexico had substantial potential for the export of irradiated fruits, especially mango, the producers opted instead to continue with treatments such as hot water dip that required a much lower initial investment in equipment and had no controversial implications for consumers. This attitude is changing, and Mexico is currently engaged in constructing new irradiation treatment facilities and pursuing necessary agreements with APHIS for the export of irradiated foods (Pers. Comm. 2004). The United States has opened the door for shipments of irradiated commodities from not only Mexico but also all countries. Several countries, including Brazil, Colombia, and Thailand, are pursuing Framework Equivalency Work Plans with APHIS in order to initiate bilateral trade in products irradiated for phytosanitary purposes (Pers. Comm. 2005). Based on the progressive regulatory directions established by the United States after 1980, many countries began to also consider legislation or regulations for irradiated food. Approximately 40 countries currently have regulations pertaining to irradiation as a treatment for food products and are treating or accepting treatment for at least one irradi-

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ated commodity (see Table 9.3). Although a large number of countries have approved irradiation as a treatment for food, few have large-scale commercial operations.This is due partly to regulatory barriers and partly to the lack of facilities and markets. Also, ensuring adequate throughput can be a substantial challenge given the seasonality of many agricultural products. The situation is slightly less complicated with nonfood treatments. Commodities such as wood products, cut flowers, and bird seed that may also require phytosanitary treatments are not subject to the same degree of regulation associated with food products.As a result, regulatory frameTable 9.3. Countries

Foods and Food Products Authorized for Irradiation for Selected

Country Algeria Argentina Australia

Bangladesh Belgium Brazil Canada Czech Republic Chile China

Croatia Cuba Denmark Ecuador Egypt Finland

Examples of Food Products Authorized or Treated with Irradiation Potatoes Spices and dried vegetables, garlic, egg products, and dehydrated bovine serum Breadfruit, carambola, custard apple, longan, litchi, mango, mangosteen, papaya and rambutan, herbs, spices, and herbal infusions Potatoes, onions, dried fish Feed for laboratory animals, spices, frozen frog legs, shrimp, aromatic herbs and teas, dehydrated vegetables Spices, dehydrated vegetables, fruits, vegetables, grain Potatoes, onions, wheat flour and whole wheat flour, spices and dehydrated seasonings, mango Spices Spices and condiments, dried vegetables, frozen food, potatoes, poultry meat Spices, pepper, condiments and seasoning, dried fruits, nuts and preserved fruit, cooked meat foods of livestock and poultry, fresh fruits and vegetables, frozen packaged meat of livestock and poultry, grains, beans and bean products, garlic spice, dehydrated vegetables, others Various tea herbs, chamomile, mixed spices, dry cauliflower and broccoli, paprika, liquid egg yolk, dry beef noodles Potatoes, onions, beans Spices Banana flour, spices, animal feed, raw jelly, honey, tea herbs Fresh bulbs, tuber crops, dried garlic, dried onion, herbs and spices Spices (continued)

Table 9.3. Foods and Food Products Authorized for Irradiation for Selected Countries (continued) Country

Examples of Food Products Authorized or Treated with Irradiation

France

Laboratory animal food, spices,Arabic gum, dehydrated vegetables, cereal, poultry (frozen de-boned chicken), frog legs, shrimp, dried fruit and vegetables, rice flour, strawberries, bovine serum Germany Spices Ghana Yam, maize Hungary Spices, onions, wine cork, enzymes India Pulses, dried seafood, fresh seafood, frozen seafood, spices and dry vegetables, seasonings Indonesia Frozen seafood products (including frog legs), cacao powder, spices, food packaging, rice Iran Spices, dried fruits, nuts Iraq Spices Israel Spices, condiments, dry ingredients Italy Spices Japan Potato Republic of Korea Potato, onions, garlic, chestnuts, mushrooms (fresh and dried), spices, dried meat, red pepper, paste powder, soy sauce powder, starch for condiments, dried vegetables, yeast-enzyme products, aloe powder, ginseng products, mushrooms (fresh & dried), spices, dried meat, shellfish powder, soybean paste powder, starch for condiments, dried vegetables, dried yeast and enzyme products, aloe powder, ginseng products, sterile meals Malaysia Spices Mexico Spices, dried vegetables, chili, dried meat Moroco Spices Netherlands Spices, frozen products, poultry, dehydrated vegetables, egg powder, packaging material New Zealand Breadfruit, carambola, custard apple, longan, litchi, mango, mangosteen, papaya, rambutan, herbs, spices and herbal infusions Norway Spices Pakistan Potatoes Peru Spices, condiments, dehydrated products, medical herbs, flours, food supplements Philippines Spices (onion powder, garlic powder, cayenne powder, ground black pepper, Spanish paprika, dehydrated chives, ground anise, instant gravy, sausage seasoning, minced onion), frozen fruits (avocado, mango, macapuno, durian, ube, atis, buco, cheese, fruit cocktail), Solo papaya, Carabao mango, Cavendish banana

162

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Table 9.3. Foods and Food Products Authorized for Irradiation for Selected Countries (continued) Country Poland Portugal South Africa

Syria Thailand Turkey

Ukraine United Kingdom United States Vietnam Yugoslavia

Examples of Food Products Authorized or Treated with Irradiation Spices, dried mushrooms, medical herbs Spices Cereal, dairy products, dehydrated foods, dehydrated vegetables, dried fruit, egg products, fish, fresh vegetables, garlic, health preparations, honey products, marinade, royal jelly, shelf-stable foods, soya mixtures, spices and herbs,Torulite yeast, vegetable powder Chicken, cocoa beans, condiments, dates, fresh fish, dried fish products, mango, onions, licorice, spices Fermented pork sausage, sweet tamarind, spices, onions, enzymes Spices, dried seasonings and herbs, dried vegetables, meat and meat products, frozen fish and seafood, frozen frog legs, dried fruits Spices Spices Spices, chicken, beef, fish, fresh fruits and vegetables, meals Spices Spices

Source: ICGFI, 1997–2002; Loaharanu, 1997

works for these treatments do not address health and safety concerns but rather emphasize the efficacy of the treatment, and the integrity of the treatment process and facility. The evolution of regulatory frameworks for the adoption and implementation of irradiation as a phytosanitary treatment has been marked by numerous successes around the world. In the past, regulatory uncertainties have heightened anxiety among investors and producers who were already concerned about potential problems with public acceptance despite extensive information about the safety and effectiveness of irradiation.Today, the world has an international standard as a global reference point for the use of irradiation as a phytosanitary treatment, and the United States has put in place a regulatory framework demonstrating full acceptance of the technology.The uncertainties associated with potential regulatory barriers are substantially reduced, and the path is clear to realizing the full potential of irradiation as a phytosanitary treatment.

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References Ahmed M. 2001. Infestation of stored grains, pulses, dried fruits and nuts, and other dried foods. p. 77–112. In: Food Irradiation: Principles and Applications, RA Molins, ed. John Wiley & Sons, Inc., New York. Alpen, EN. 1998. Radiation Biophysics.Academic Press, San Diego, CA. Baker,AC. 1939.The basis for treatment of products where fruit flies are involved as a condition for entry into the United States. U.S. Department of Agriculture Circular No. 551. Baker RT, Cowley JM, Harte DS, Frampton ER. 1990. Development of a maximum pest limit for fruit flies (Diptera: Tephritidae) in produce imported into New Zealand. J Econ Entomol 83:13–17. Balock, JW, Burditt AK Jr., Christenson LD. 1966. Effects of gamma radiation on various stages of three fruit fly species. J Econ Entomol 56:42–46. Batchelor TA. 1989. Potential use of biochemical data in the development of radiationbased insect disinfestations treatments for fresh commodities. PhD dissertation, University of California, Davis , CA. Burditt,AK. 1994. Irradiation, p. 101–117. In: J. L. Sharp and G. J. Hallman, eds., Quarantine Treatments for Pests of Food Plants.Westview Press, Boulder, Colorado. Burditt,AK. 1996. Irradiation as a quarantine treatment against fruit flies. p. 479–484. In: B. McPheron and G. Steck, eds., Fruit Fly Pests: A World Assessment of their Biology and Management. St. Lucie Press, Delray Beach, Florida. Bustos ME, Enkerlin W, Reyes J,Toledo J. 2004. Irradiation of mangoes as a postharvest treatment for fruit flies (Diptera:Tephritidae). J Econ Entomol 97:286–292. Castro D, Espinosa DJ,Vargas M. 2004. Ionizing radiation as a quarantine treatment for controlling Brevipalpus chilensis (Acarina:Tenuipalpidae) in Thompson seedless grapes, p. 143–53. In: Irradiation as a Phytosanitary Treatment of Food and Agricultural Commodities. IAEA Techdoc 1427,Vienna,Austria. Codex. 1984. Codex Recommended International Code of Practice for the Operation of Radiation Facilities used for the Treatment of Foods (CAC/RCP 10-1979, Rev 1). Codex Alimentarius Commission,Vol. XV, Geneva. Codex. 2003. Codex General Standard for Irradiated Foods, Codex Stan 106-1983, Rev. 12003. Codex Alimentarius Commission. FAO, Rome. Corcoran RJ,Waddell BC. 2003. Ionizing Energy Treatments for Quarantine Disinfestation. Horticulture Australia Limited. Couey HM, Chew V. 1986. Confidence limits and sample size in quarantine research. J Econ Entomol 79:887–890. Diehl JF. 2001. Achievements in Food Irradiation during the 20th Century, p. 1–7. In: Irradiation for Food Safety and Quality, P. Loaharanu and P.H.Thomas, eds. Proceedings of FAO/IAEA/WHO International Conference on Ensuring the Safety and Quality of Food through Radiation Processing.Technomic Publishing, Lancaster, PA. Ducoff HS. 1972. Causes of cell death in irradiated adult insects. Biol Rev 47:211240. EPA. 1993. Protection of Stratospheric Ozone: Final Rule. Federal Register 58 (236): 65018–65082. EPA. 1996. Revocation of Pesticide Food Additive Regulations: Final Rule. Federal Register 61 (57):11994–11999. European Commission. 2001. Commission communication on foods and food ingredients authorized for treatment with ionizing radiation in the Community [COM (2001) 4722002/2008 (COS)]. European Commission, Brussels.

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Hallman GJ. 1998. Ionizing radiation quarantine treatments. An Soc Entomol Brasil 27: 313–323. Hallman GJ. 2001. Irradiation as a quarantine treatment. P. 113–130. In: Food Irradiation: Principles and Applications, R. Molins, ed. John Wiley & Sons, New York. Hallman GJ. 2003. Ionizing irradiation quarantine treatment against plum curculio (Coleoptera: Curculionidae). J Econ Entomol 96:1399–1404. Hallman GJ. 2004. Ionizing irradiation quarantine treatment against oriental fruit moth (Lepidoptera: Tortricidae) in ambient and hypoxic atmospheres. J Econ Entomol 97:824–827. Hallman GJ. 2004. Irradiation disinfestation of apple maggot (Diptera: Tephritidae) in hypoxic and low-temperature storage. J Econ Entomol 97:1245–1248. Hallman GJ, Martinez LR. 2001. Ionizing irradiation quarantine treatment against Mexican fruit fly in citrus. Postharvest Biol Technol 23:71–77. Hallman GJ, Loaharanu P. 2002. Generic ionizing radiation quarantine treatments against fruit flies (Diptera:Tephritidae) proposed. J Econ Entomol 95:893–901. Hara AH,Yalemar JA, Jang EB, Moy JH. 2002. Irradiation as a possible quarantine treatment for green scale Coccus viridis (Green) (Homoptera: Coccidae). Postharvest Biol Technol 25:349–358. Heather NW. 1992. Review of irradiation as a quarantine treatment for insects other than fruit flies. P. 203–18. In: Use of irradiation as a quarantine treatment of food and agricultural commodities. International Atomic energy Agency,Vienna,Austria. Heather NW. 2004. Generalized quarantine disinfestation research protocol. P. 171–178. In: Irradiation as a Phytosanitary Treatment of Food and Agricultural Commodities. IAEA Techdoc 1427,Vienna,Austria. Heather NW, Corcoran RJ, Banos C. 1991. Disinfestation of mangoes with gamma irradiation against two Australian fruit flies. J Econ Entomol 84:1304–1307. IDIDAS. 2003. International Database on Insect Disinfestation and Sterilization. Web site: www-ididas.ieae.org/ididas/. International Atomic Energy Agency,Vienna. ICGFI (International Consultative Group on Food Irradiation). 1991. Irradiation as a quarantine treatment of fresh fruits and vegetables. ICGFI Document No. 13. International Atomic Energy Agency,Vienna,Austria. ICGFI 1997–2002. Status Reports on Food Irradiation by Member Countries of the International Consultative Group on Food Irradiation (ICGFI) 1997–2002. International Atomic Energy Agency,Vienna. Ignatowicz S. 2004. Irradiation as an alternative to methyl bromide fumigation of agricultural commodities infested with quarantine stored product pests. P. 51–66. In: Irradiation as a Phytosanitary Treatment of Food and Agricultural Commodities. IAEA Techdoc 1427,Vienna,Austria International Plant Protection Convention (IPPC). 2001. Report of the Third Session of the Interim Commission on Phytosanitary Measures.April, 2001. FAO, Rome. International Plant Protection Convention (IPPC). 2003a. International Standards for Phytosanitary Measures (ISPM) No. 18, Guidelines for the use of irradiation as a phytosanitary measure.April. 2003. FAO, Rome. International Plant Protection Convention (IPPC). 2003b. Report of the Fifth Session of the Interim Commission on Phytosanitary Measures.April, 2003. FAO, Rome. Jang, EB, Moffitt H. 1994. Systems approaches to achieving quarantine security. P. 225–237. In: J. L. Sharp and G. J. Hallman, eds., Quarantine Treatments for Pests of Food Plants. Westview Press, Boulder, Colorado. Kader, AA. 1986. Potential applications of ionizing radiation in postharvest handling of fresh fruits and vegetables. Food Technol 40:117–121.

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Kaneshiro, KY, Ohta AT, Kurihara JS, Kanegawa KM, Nagamine LR. 1985. Gammaradiation treatment for disinfestations of the medfly in thirty-five varieties of California-grown fruits. P. 98–110. In: J. Moy, ed., Radiation Disinfestation of Food and Agricultural Products. Hawaii Institute for Tropical Agriculture and Human Resources, Honolulu, HI. Koidsumi K. 1930. Qualitative studies on the lethal actions of X rays upon certain insects. J Soc Trop Agric Taiwan 7:243. Komson, P, Smitasiri E, Lapasatukul C, Unahawutti U, Nonthachai S, Sukkaseam S,Tantidham K, Sutantawong M. 1992. Use of radiation in an export plant quarantine programme. P. 117–132. In: Use of irradiation as quarantine treatment of food and agricultural commodities. International Atomic Energy Agency,Vienna,Austria. Koval, TM. 1994. Intrinsic stress resistance of cultured lepidopteran cells. P. 157–185. In: Insect Cell Biotechnology, K. Marmarorosh and A. McIntosh, eds. CRC Press, Boca Raton, Florida, U.S.A. Landolt PJ, Chambers DL, Chew V. 1984.Alternative to the use of probit 9 mortality as a criterion for quarantine treatments of fruit fly (Diptera:Tephritidae) infested fruit. J Econ Entomol 77:285–287. Loaharanu P. 1997.“International Developments of Food Irradiation,” Memorias Seminario Nacional, Aceptacion y Comercio de Alimentos Irradiados. 27–29 October, 1997. Instituto Nacional de Investigaciones Nucleares.Toluca, Mexico, p. 1–8. Mangan, RL, Frampton ER,Thomas DB, Moreno DS. 1997.Application of the maximum pest limit concept to quarantine security standards for the Mexican fruit fly (Diptera: Tephritidae). J Econ Entomol 90:1433–1440. Mansour M, Mohamad F. 2004. Gamma irradiation as a phytosanitary measure for exported Syrian fresh fruit. p. 19–36. In: Irradiation as a Phytosanitary Treatment of Food and Agricultural Commodities. IAEA Techdoc 1427,Vienna. Morris SC, Jessup AJ. 1994. Irradiation. P. 163–190. In: R. E. Paull and J. W. Armstrong, eds., Insect Pests and Fresh Horticultural Products: Treatments and Responses. CAB International,Wallingford, UK. Moy JH, Wong L. 2002.The efficacy and progress in using radiation as a quarantine treatment of tropical fruits—a case study in Hawaii. Rad Phys Chem 63:397–401. NAPPO 1997. Guidelines for the Use of Irradiation as a Phytosanitary Treatment. NAPPO Regional Standard for Phytosanitary Measures (archive). NAPPO, Ottawa. Nation,JL, Burditt AK. 1994. Irradiation. P. 85–102. In: Insect Pests and Fresh Horticultural Products: Treatments and Responses. Paull, RE, Armstrong, JW eds. CAB International Wallingford, UK. Personal communication(s). 2005. Paul Gadh, Treatment Specialist with USDA-APHIS Plant Protection and Quarantine, Phytosanitary Issues Management Staff. Riverdale, MD. Personal communication. 2004. Dr. Javier Trujillo Arriaga, Director en Jefe, Servicio Nacional de Sanidad, Inocuidad y Calidad Agroalimentaria (SENASICA). May, 2004. Mexico City, Mexico. Powell, MR. 2003. Modeling the response of the Mediterranean fruit fly (Diptera: Tephritidae) to cold treatment. J. Econ Entomol 96:300–310. Rigney, CJ. 1989. Radiation-disinfestation of fresh fruit. P. 425–434. In:A. S. Robinson and G. Hooper, eds., World crop pests, 3B: Fruit Flies, their Biology, Natural Enemies, and Control, Elsevier,Amsterdam. Rigney CJ,Wills PA. 1985. Efficacy of gamma irradiation as a quarantine treatment against Queensland fruit fly. P. 116–120. In: Radiation disinfestations of food and agricultural products, J. H. Moy, ed. University of Hawaii at Manoa, Honolulu, Hawaii.

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Robertson JL, Preisler HK. 1992. Pesticide Bioassays with Arthropods. CRC Press, Boca Raton, Florida. Ruckelshaus WD. 1984. Ethylene dibromide, amendment of notice of intent to cancel registration of pesticide products containing ethylene. Federal Register 49: 14182–14185. Seo ST, Kobayashi RM, Chambers DL, Dollar DM, Hanaoka M. 1974. Hawaiian fruit flies in papaya, bell pepper, and eggplant: quarantine treatment with gamma irradiation. J Econ Entomol 66:937–939. Sproul AN. 1976. Disinfestation of Western Australian Granny Smith apples by cold treatment against the egg and larval stages of the Mediterranean fruit fly (Ceratitis capitata [Wied.]) Austral J Exp Agric Anim Husb 16:280–285. Tilton EW, Brower JH. 1983. Radiation effects on arthropods. P. 269-316. In: Preservation of Food by ionizing Radiation,Vol. 2, E.S. Josephson and M.S. Peterson, eds. pp. CRC Press Inc., Boca Raton, FL. Toledo J, Liedo P, Bustos EM. 2003. Gamma irradiation as a guava treatment for guavas infested with larvae of Anastrepha striata Schiner (Diptera: Tephritidae). Folia Entomologia Mexicana 42:371–379. USDA-APHIS. 1989. Use of irradiation as a quarantine treatment for fresh fruits of papaya from Hawaii. Federal Register 54(4):387–392. USDA-APHIS. 1996. The application of irradiation to phytosanitary problems (Notice of Policy). Federal Register 61(95):24433–24439. USDA-APHIS. 2002. Irradiation Phytosanitary Treatment of Imported Fruits and Vegetables Final Rule. Federal Register Vol. 67 No 205:65016–65029. Vail PV, Tebbetts JS, Mackey BE, Curtis CE. 1993. Quarantine treatments: a biological approach to decision making for selected hosts of codling moth (Lepidoptera: Tortricidae). J Econ Entomol 86:70–75. Verdejo S Maricela. 1997. Irradiacion de Alimentos, Legislacion Vigente. P. 133–137. In: Memorias Seminario Nacional,Aceptacion y Comercio de Alimentos Irradiados. 27–29 October, 1997. Instituto Nacional de Investigaciones Nucleares.Toluca, Mexico. Whyte CF, Baker RT, Cowley JM, Hart DS. 1994. A quantitative method for calculating the probability of pest establishment from imported plants and plant products, as a part of pest risk assessment. N. Z. Plant Protection Centre Publications No. 4, Auckland, New Zealand. WHO (World Health Organization). 1981. Wholesomeness of irradiated food. Technical Report Series No. 659.WHO. Geneva. WHO (World Health Organization). 1994. Agreement on the application of sanitary and phytosanitary measures. GATT Uruguay Round Agreements.World Trade Organization, Geneva.

Food Irradiation: Research and Technology Edited by Christopher H. Sommers, Xuetong Fan Copyright © Blackwell Publishing and the Institute of Food Technologists 2006

Chapter 10 LOW-DOSE IRRADIATION OF FRESH AND FRESH-CUT PRODUCE: SAFETY, SENSORY,AND SHELF LIFE Brendan A. Niemira and Xuetong Fan

Introduction With consumption of fresh and fresh-cut produce increasing in the United States, and market globalization becoming a more important factor, has come greater concern over produce-associated foodborne illness (Thayer and Rajkowski 1999). From an epidemiological standpoint, foodborne illness outbreaks in the United States associated with contaminated fruits, vegetables, salads, and juices have risen from fewer than 20 throughout the 1970s to more than 100 in the 1990s (Sivapalasingam and others 2004). New tools to ensure the safety of fresh and fresh-cut produce are required; low-dose irradiation is one of the more promising of these. Vegetables were among the first experimental subjects in studies of physiological response to irradiation (Guilleminot 1908; Miege and Coupe 1914).The first studies with irradiated produce typically used relatively high doses and were intended to achieve reductions in spoilage bacteria and fungi equivalent to thermal pasteurization (Diehl 1995).This research helped to define sterilization doses for commensal and spoilage organisms. However, these doses frequently exceeded the maximum radiation tolerances of vegetable commodities tested, resulting in loss of quality (Howard and Buescher 1989; Prakash and others 2000b). For this reason, irradiation was historically regarded as less suited to application to produce (Maxie and Abdel-Kader 1966; Yu and others 1996; Osterholm and Potter 1997). However, more recent research with lower radiation 169

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doses, that is, less than 3 kiloGray (10 kGy = 1 Mrad), has suggested a role for irradiation as one of several “hurdles” in fruit and vegetable processing (Thayer and Rajkowski 1999; Smith and Pillai 2004; Niemira and Deschenes 2005).This approach is of particular value with regard to the elimination of human pathogens from produce.The role of contaminated produce in foodborne illness is a subject of increasing concern due to changes in consumption patterns associated with minimally processed fruits, vegetables, and juices (NACMCF 1999; Sivapalasingam and others 2004). It bears reiterating that foods treated with ionizing radiation have consistently been shown to be wholesome and nutritious (WHO 1999; Smith and Pillai 2004).

Produce Microbiology and Irradiation Treatment Phytopathogenic and human pathogenic bacteria may be internalized in fruits and vegetables, beyond the reach of surface sanitizers (Takeuchi and Frank 2000; Burnett and Beuchat 2002).The penetrability and subsurface antimicrobial efficacy of irradiation suggest that it can play an important role in the sanitization of produce. Of the three types of ionizing radiation commonly employed, electron beam (e-beam) is less penetrating than photon sources (x-rays or gamma rays), with maximal penetration of 6–7 cm for the former vs. 20–24 cm for the latter in foods of approximately unit density (1g/cc) (Niemira and Deschenes 2005). With either technology, irregular or asymmetric treatment results in uneven irradiation, with some parts of the product receiving a higher dose than others. Excessive variation in treatment can lead to undesirable sensory damage (dose too high) or lack of antimicrobial or phytosanitary efficacy (dose too low). Computer simulations suggest that, for irregularly shaped produce such as apples treated with the less penetrating e-beam, the ratio of the highest dose delivered to the lowest dose delivered (the Max/Min ratio) can be as high as 3.0 (Brescia and others 2003). It is thus readily shown that fruits and vegetables, with their irregular shapes and variations of density, present a complex challenge for effective, uniform treatment with e-beam irradiation. Fresh produce may be irradiated for a number of purposes, including inhibition of sprouting, delay of ripening, disinfestation (elimination or sterilization of insect pests), and reduction of microbial load. The doses required for effective reduction of microbial load (typically at least 0.5 kGy or greater) are higher than that required for the other major purposes (typically less than 0.3 kGy) and thus will exert the largest effect on produce quality and shelf life (Farkas and others 1997).The most im-

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portant effect of irradiation in the treatment of produce, therefore, is reduction of microbial load, with the intended target of the intervention either spoilage phytopathogens or contaminating human pathogens (Thayer and Rajkowski 1999; Niemira and Deschenes 2005).The primary means of preserving fresh produce in the supply chain connecting producer and consumer are refrigeration and modified atmosphere packaging (Sumner and Peters 1997; Niemira and others 2005). The nature of fresh produce, that is, living tissue that respires, metabolizes, ripens, and so forth, makes it relatively sensitive to ionizing radiation. Improper or excessive treatment can lead to changes in firmness, aroma, color or taste (Yu and others 1996; Mahrouz and others 2004) or delayed effects on phytoplane microbial ecology (Howard and Buescher 1989; Al-Kahtani and others 2000; Prakash and others 2000a). Irradiated fresh produce, as with all irradiated foods, must adhere to the basic rules of good manufacturing practice for preservation of quality and food safety. Fungi and viruses are typically more resistant to radiation than are bacteria. D10 values, that is, the amount of radiation necessary to achieve a 90% (1-log) reduction, are in the range of 1 to 3 kGy for fungi (Narvaiz and others 1992; El-Samahay and others 2000; Niemira and Deschenes 2005) and somewhat higher for viruses (Howard and Buescher 1989;Yu and others 1996; Monk and others 1994).The doses required to achieve meaningful population reductions of fungal and viral contaminants (that is, 3–5 log10) typically result in loss of sensorial quality of fresh and freshcut produce. Low-dose irradiation has been shown to suppress, but not eliminate, some phytopathogenic fungi responsible for storage losses (Niemira and Deschenes 2005). In contrast, the D10 for pathogenic bacteria on produce ranges from 0.2–0.8 kGy (Foley and others 2002; Niemira and others 2002; Niemira 2003; Martins and others 2004); this degree of sensitivity would allow a 5 log10 reduction with doses between 1 and 4 kGy, a more achievable level of treatment. Irradiation is therefore clearly best suited to control of bacterial pathogens, as opposed to viral or fungal pathogens.

Irradiation to Enhance Microbial Safety of Produce Fresh and fresh-cut produce have been implicated in instances of foodborne illness with increasing frequency in recent years (Sivapalasingam and others 2004). Methods to sanitize these products so as to improve their safety have been improving, but the physical nature of fruits and vegetables presents serious challenges to conventional means of removing or inactivating pathogenic bacteria. Plant parts such as leaves, stems,

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fruits, and roots typically support 103–106 colony-forming units (cfu) per gram of plant tissue (Sumner and Peters 1997; Mercier and Lindow 2000). Sanitization of produce has traditionally meant surface treatment; however, an improved understanding of how bacteria inhabit the surface and internal spaces of fruits and vegetables is resulting in new concerns over the efficacy of traditional antimicrobial measures. Internalization of Bacteria Bacteria have recently been shown to enter fruits and vegetables through natural openings such as stomata, stem scar, calyx, and so forth, or via abiotic wounds and/or phytopathogenic penetrations; once internalized, bacteria can survive within the produce for days or weeks (Takeuchi and Frank 2000; Riordan and others 2000). Bacteria may migrate naturally, or they may be drawn in with contaminated water by improper washing steps (Penteado and others 2004). Bacteria internalized within produce occupy cell junctions and intracellluar spaces at least 50 microns deep (Auty and others 2005) and are therefore beyond the reach of chemical sanitizers (Fett 2000; Niemira and others 2005). These require mechanisms that are more penetrating; although this has traditionally meant heat treatments (Gorny 2005), the heat-sensitive nature of fresh produce limits this approach and prompts examination of irradiation as an alternative. Biofilms The de facto life habitat for phytoplane bacteria is as a biofilm, a complex community of many bacterial species bound to the plant surface in a durable exopolysaccharide matrix (Carmichael and others 1999; Fett 2000). Human pathogens such as E. coli and Salmonella are known to form durable biofilms on industrial surfaces (Dewanti and Wong 1995; Korber and others 1997). Of concern for food safety, the protective nature of bacterial biofilms has been repeatedly demonstrated to reduce the efficacy of antimicrobial measures such as ozone, chlorine, and hydrogen peroxide, frequently by orders of magnitude (Stewart and others 2004). Unattached L. monocytogenes cells were reduced by 8.29 log10 cfu by treatment with 0.25 ppm ozone for 3 min.This treatment resulted in only a 1.48 log10 cfu reduction for biofilm-associated L. monocytogenes (Robbins and others 2005).That study showed that a 16⫻ concentration (4.00 ppm) was required to achieve comparable reductions for the biofilm (8.07 log10 cfu). In contrast, a recent study of three Salmonella isolates has shown that biofilm-associated bacteria are as sensitive as or

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more sensitive to irradiation than planktonic bacteria (Niemira and Solomon 2005).This finding suggests that the penetrating nature of ionizing radiation may make it uniquely suited to the problem of internalized, biofilm-associated, or otherwise protected pathogens on or in produce. Post-Irradiation Recovery and Regrowth As an antimicrobial process, the reduction of pathogen populations is the primary goal of irradiation; however, pathogen regrowth in storage following irradiation due to reduced interspecies competition is a known phenomenon. Palekar and others (2004) examined cut cantaloupe pieces and determined that a chlorine wash (200 ppm sodium hypochlorite) combined with e-beam irradiation to 1.4 kGy led to a lasting suppression of the aerobic microflora during the 21 d storage period. A lower radiation dose, or a treatment that used a water wash, led to significant regrowth of the microflora. On studies of inoculated endive leaves, L. monocytogenes was observed to regrow in storage following a dose equivalent to a 99% (2 log10) reduction, that is, 0.42kGy (Niemira and others 2003). After this moderate dose, the pathogen eventually regrew to equal or exceed the level seen in the untreated control. However, a higher dose of 0.84 kGy, calibrated to achieve a 4 log10 reduction, suppressed the pathogen throughout the 19 d of the storage period.A later study using modified atmosphere packaging (MAP) confirmed the capacity of L. monocytogenes to regrow after relatively mild doses of irradiation, sufficient to achieve 1-3 log10 reductions (Niemira and others 2004). A reduced-O2, enhanced-CO2 packaging scheme effectively suppressed this capacity and prevented the pathogen from regrowing. Treatment Parameters for Irradiation of Produce A dose of 1.0 kGy reduced total aerobic plate count and L. monocytogenes on pre-cut bell pepper by approximately 4 log10 cfu/g; storage (4 d) at abuse temperatures (10 or 15° C) led to regrowth, but refrigeration temperature (4° C) suppressed regrowth of the pathogen, preserving the initial efficacy of the treatment (Farkas and others 1997). E. coli and L. monocytogenes were effectively eliminated (>5 logs) from diced celery by 1.0 kGy (Prakash and others 2000b). Peeled, ready-to-use carrots that were treated with 1 kGy showed aerobic plate counts reduced by 4 log10 cfu when packed in air, and 4.5 log10 reduction when packed under modified atmosphere (Lafortune and others 2005).The use of an edible coating in combination with irradiation improved the keeping quality of the carrot pieces in that study.Total aerobic counts were reduced by ~3 logs

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Food Irradiation Research and Technology

on iceberg lettuce by 0.19 kGy (Hagenmaier and Baker 1997), by ~1.5 logs on romaine lettuce by 0.35 kGy (Prakash and others 2000a) and ~2 logs on shredded carrot by 0.45 kGy (Hagenmaier and Baker 1998) by irradiation and storage under MAP. Thus, it can readily be seen that optimized combinations of antimicrobial treatments will serve to improve the applicability of irradiation to a wider range of vegetable products. Rajkowski and Thayer (2000) obtained D10 values for E. coli O157:H7 of 0.34, 0.27 and 0.26 kGy on radish, alfalfa, and broccoli sprouts, respectively. D10 values obtained for Salmonella on radish sprouts in that study were dependent on the provenance of the isolates, that is, the type of food product from which they were derived: 0.54 kGy (meat sources) in contrast to 0.46 kGy (vegetable sources). D10 values obtained by Bari and others (2004) for cocktails of E. coli O157:H7 and Salmonella were approximately 0.3 kGy for both pathogens when tested on radish sprouts, roughly comparable to those of Rajkowski and Thayer (2000). However, when tested on mung bean sprouts, the D10 values of E. coli O157:H7 (0.18kGy) and Salmonella (0.16kGy) cocktails were markedly lower. Goularte and others (2004) obtained somewhat different D10 values on shredded iceberg lettuce for E. coli O157:H7 (~0.11 kGy) and Salmonella (~0.2 kGy).The sensitivity of the irradiation process to factors such as the provenance of the experimental isolate(s), the suspending medium, and treatment conditions indicates that, before irradiation can be implemented within any given commercial context, validation of the protocol using commercially applicable factors (dose, conditions, product, processing time, and so on) is a necessary step. Influence of Plant Variety The specific variety of fruit or vegetable has been shown to have a significant effect on the response to irradiation. This has been shown in regards to sensory responses, including loss of color, firmness, aroma, and so on, for a number of types of produce: iceberg lettuce (Hagenmaier and Baker 1997) as opposed to romaine lettuce (Prakash and others 2000a); the potato varieties Ajax vs. Diamant (Al-Kahtani and others 2000); and blueberry cultivars Climax (Miller and others 1994) vs. Sharpblue (Miller and others 1995) vs. Brightwell and Tifblue (Miller and McDonald 1996). The differences among varieties can also result in significant differences in the D10 for associated pathogens. A series of studies determined the D10 for E. coli O157:H7, Salmonella and L. monocytogenes on four lettuce varieties: red leaf, green leaf, Iceberg, and Boston. These studies found evidence for variety- and pathogen-specific influence on radiation sensitivity (Table 10.1).These complex and poorly understood factors in-

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Low-Dose Irradiation of Fresh and Fresh-Cut Produce Table 10.1.

Radiation D10 Values for Pathogens on Four Lettuce Varieties D10 values (kGy) on lettuce types1

Pathogen E. coli O157:H72 Salmonella3 L. monocytogenes3

Red leaf

Green leaf

Boston

Iceberg

0.119a 0.23a 0.19a

0.123a 0.31b 0.19a

0.140b 0.24a 0.19a

0.136b 0.25a 0.20a

1D 10

values in each row followed by the same letter are not significantly different (Analysis of covariance, P 0.9) was observed and the degradation rate constant was 0.009 min⫺1. The radiolytic products of NDMA and NPYR dissolved in dichloromethane were identified by gas chromatography and mass spectrometry. The major radiolytic components of NDMA were ethyl acetate and 2-dimethyl propanol, and those of NPYR were 2butanone and 2-methyl-6-propylpiperidine (Ahn and others 2003a).

Biogenic Amines (BAs) Reduction Biogenic amines (BAs) are found in many kinds of fermented foods during aging, fermentation, and storage. BAs are formed by the action of mi-

Potential Applications of Ionizing Radiation

253

Table 15.1. Monitoring of Residual Nitrite Levels (ppm) of Sausage Prepared with 150 ppm Sodium Nitrite in Different Packaging and Irradiation Doses during Processing and Storage Storage Periods (Week)

Processingc 0

1

2

3

4

Irradiation Dose (kGy)

Packaging

Aerobic Vacuum SEMb Aerobic Vacuum SEMb Aerobic Vacuum SEMb Aerobic Vacuum SEMb Aerobic Vacuum SEMb

0

5

10

20

SEMa

122.7

122.7

122.7

122.7

1.98

81.2adxe 66.8ay 1.01 80.5a 74.8a 0.98 85.8a 79.3a 2.83 79.5a 66.7a 1.29 55.7ax 40.1ay 0.82

73.2ab 64.0a 1.76 73.4b 63.2ab 4.48 77.7bx 69.9by 0.88 73.7bx 54.5by 1.08 48.0bx 34.4aby 1.01

64.5bx 57.6by 0.64 65.5c 57.6b 3.34 71.8b 66.7b 1.43 65.2cx 47.4cy 0.60 44.3cx 32.2by 0.80

54.6c 45.6c 2.62 62.6dx 49.0by 0.60 62.1cx 49.0cy 1.95 57.4dx 41.5dy 0.54 39.2d 24.2c 2.53

2.25 0.79 0.69 3.97 1.67 2.12 1.08 1.46 0.85 1.91

a

Standard errors of the mean (n = 8). Standard errors of the mean (n = 4). c Nitrite level was analyzed immediately after emulsification. d Different letters (a–d) within a same row differ significantly (P