food irradiation today[2]

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Food Irradiation Today http://www.hi-tm.com/Documents/Irrad.html 1 of 20 4/29/2006 3:01 PM FOOD IRRADIATION TODAY by O.P. Snyder and D.M. Poland Copyright 1995 Hospitality Institute of Technology and Management St. Paul, MInnesota Introduction Irradiation of food is the use of ionizing radiations from radioactive isotopes of cobalt or cesium or from accelerators that produce controlled amounts of beta rays or x-rays on food. The food does not become radioactive. Research over the past 40 years has shown that irradiation can be used: to destroy insects and parasites in grains, dried beans, dried fruits and vegetables, and meat and seafood; to inhibit sprouting in crops such as potatoes and onions; to delay ripening of fresh fruits and vegetables; and to decrease the numbers of microorganisms in foods. Hence, the incidence of foodborne illness and disease can be decreased and the shelf life of food can be extended. History The discovery of x-rays by W.K. Roentgen in 1895 and the discovery of radioactive substances by H. Becquerel in 1896 led to intense research of the biological effects of these "radiations." Initially, most of the irradiations made use of x-rays, which are produced when electrons from an electron accelerator are stopped in materials. These early investigations laid the foundation for food irradiation (Brynjolfsson, 1989). Ionizing radiation was found to be lethal to living organisms soon after its discovery. The use of this lethality to control spoilage and other organisms that contaminate foods was demonstrated in the early decades of the 20th century. However, no commercial development of this use occurred then, due to the inability to obtain ionizing radiation in quantities needed and at costs that could be afforded (Urbain, 1989). In the mid 1940s, the interest in food irradiation was renewed when it was suggested that electron accelerators could be used to preserve food. However, the accelerators in those days were rather costly and too unreliable for industrial application. From 1940 through 1953, exploratory research in food irradiation in the United States was sponsored by the Department of the Army, the Atomic Energy Commission, and private industry (Thayer, 1986). Early research in the late 1940s and early 1950s investigated the potential of 5 different types of radiation (ultraviolet light, x-rays, electrons, neutrons, and alpha particles) for food preservation. Researchers concluded at that time that only cathode ray radiation (electrons) had the necessary characteristics of efficiency, safety, and practicality. They considered x-rays to be impractical because of the very low conversion efficiency from electron to x-ray that was possible at that time. Ultraviolet light and alpha particles were considered to be impractical because of their limited ability to penetrate matter. Neutrons exhibited great penetration and were very effective in the destruction or inactivation of bacteria, but were considered inappropriate for use because of the potential for inducing radioactivity in food. In the 1940s, as described by Urbain (1989), sources of proper kinds of ionizing radiation became available. The first sources were machines that produced high energy electron beams of up to 24 million electron volts. This energy was sufficient to penetrate and sterilize a 6-inch No. 10 can of food when electron beams were "fired" from both sides of the can. Also in this same decade, man-made radionuclides such as Cobalt-60 and Cesium-137 (which in their radioactive decay emit gamma rays) became available through the development of atomic energy. The availability of these sources stimulated research in food irradiation aimed at the development of a commercial process. Proctor and Goldblith (1951) concluded that food could be sterilized by ionizing radiation. They reported a number of important observations. The medium in which microorganisms were irradiated was a factor in determining the correct dose of radiation for bacterial inactivation. 1. Enzymes were more resistant to ionizing radiation than were bacteria. 2. Irradiation in the frozen state minimized the development of off-flavor in milk and orange juice. 3. Most in-depth studies in food irradiation since 1952 have been government sponsored. Because of military interest in this type of food processing, much of the early research was done to sterilize food by the Quartermaster Corps of the U.S. Army at the Food and Container Institute in Chicago, Illinois because of its need to provide high-quality, shelf-stable field rations for troops. The Army Quartermaster Corps concluded early on that wholesome, economical, shelf-stable field rations could

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Food Irradiation Today http://www.hi-tm.com/Documents/Irrad.html

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FOOD IRRADIATION TODAY

by O.P. Snyder and D.M. PolandCopyright 1995

Hospitality Institute of Technology and Management St. Paul, MInnesota

Introduction Irradiation of food is the use of ionizing radiations from radioactive isotopes of cobalt or cesium or from accelerators thatproduce controlled amounts of beta rays or x-rays on food. The food does not become radioactive. Research over the past40 years has shown that irradiation can be used: to destroy insects and parasites in grains, dried beans, dried fruits andvegetables, and meat and seafood; to inhibit sprouting in crops such as potatoes and onions; to delay ripening of fresh fruitsand vegetables; and to decrease the numbers of microorganisms in foods. Hence, the incidence of foodborne illness anddisease can be decreased and the shelf life of food can be extended.

History The discovery of x-rays by W.K. Roentgen in 1895 and the discovery of radioactive substances by H. Becquerel in 1896led to intense research of the biological effects of these "radiations." Initially, most of the irradiations made use of x-rays,which are produced when electrons from an electron accelerator are stopped in materials. These early investigations laid thefoundation for food irradiation (Brynjolfsson, 1989). Ionizing radiation was found to be lethal to living organisms soonafter its discovery. The use of this lethality to control spoilage and other organisms that contaminate foods wasdemonstrated in the early decades of the 20th century. However, no commercial development of this use occurred then, dueto the inability to obtain ionizing radiation in quantities needed and at costs that could be afforded (Urbain, 1989).

In the mid 1940s, the interest in food irradiation was renewed when it was suggested that electron accelerators could beused to preserve food. However, the accelerators in those days were rather costly and too unreliable for industrialapplication. From 1940 through 1953, exploratory research in food irradiation in the United States was sponsored by theDepartment of the Army, the Atomic Energy Commission, and private industry (Thayer, 1986). Early research in the late1940s and early 1950s investigated the potential of 5 different types of radiation (ultraviolet light, x-rays, electrons,neutrons, and alpha particles) for food preservation. Researchers concluded at that time that only cathode ray radiation(electrons) had the necessary characteristics of efficiency, safety, and practicality. They considered x-rays to be impracticalbecause of the very low conversion efficiency from electron to x-ray that was possible at that time. Ultraviolet light andalpha particles were considered to be impractical because of their limited ability to penetrate matter. Neutrons exhibitedgreat penetration and were very effective in the destruction or inactivation of bacteria, but were considered inappropriatefor use because of the potential for inducing radioactivity in food.

In the 1940s, as described by Urbain (1989), sources of proper kinds of ionizing radiation became available. The firstsources were machines that produced high energy electron beams of up to 24 million electron volts. This energy wassufficient to penetrate and sterilize a 6-inch No. 10 can of food when electron beams were "fired" from both sides of thecan. Also in this same decade, man-made radionuclides such as Cobalt-60 and Cesium-137 (which in their radioactivedecay emit gamma rays) became available through the development of atomic energy. The availability of these sourcesstimulated research in food irradiation aimed at the development of a commercial process.

Proctor and Goldblith (1951) concluded that food could be sterilized by ionizing radiation. They reported a number ofimportant observations.

The medium in which microorganisms were irradiated was a factor in determining the correct dose of radiation forbacterial inactivation.

1.

Enzymes were more resistant to ionizing radiation than were bacteria.2.Irradiation in the frozen state minimized the development of off-flavor in milk and orange juice.3.

Most in-depth studies in food irradiation since 1952 have been government sponsored. Because of military interest in thistype of food processing, much of the early research was done to sterilize food by the Quartermaster Corps of the U.S. Armyat the Food and Container Institute in Chicago, Illinois because of its need to provide high-quality, shelf-stable field rationsfor troops. The Army Quartermaster Corps concluded early on that wholesome, economical, shelf-stable field rations could

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be provided through irradiation. However, early sensory evaluation of sterilized (1) irradiated meats described it as havinga "wet dog aroma." The development of off-flavors and aromas in meats was solved by freezing meat to -22ºC (-30ºF). [(1) The reduction of spores of proteolytic A and B strains of Clostridium botulinum by 10-12]

Research was continued by the U.S. Army when a food irradiation facility was built at the Army's research laboratories inNatick, Massachusetts in 1962. The U.S. Army maintained its interest in high-dose irradiation sterilization of meatproducts. The responsibility for low-dose pasteurization (2) applications development was transferred to the AEC (AtomicEnergy Commission). The Army sponsored studies for the development of shelf-stable bacon, ham, pork, beef, hamburger,corned beef, pork sausage, codfish cakes, and shrimp. In 1980, the residual Army food irradiation program (chicken) wastransferred to the U. S. Department of Agriculture (USDA). This agency assigned the responsibility to the Eastern RegionalResearch Center, Philadelphia, Pennsylvania (Skala, 1986). [(2) Pasteurization is best defined as reducing the existing numbers of vegetative pathogenic cells to an undetectable level,less than 1/gram. Since the maximum load of vegetative pathogens such as Salmonella spp. is on the order of 103/gram,this is the standard that is usually used.]

Food Irradiation: Some Major Milestones*

1895 Von Roentgen discovers x-rays.

1896 Becquerel discovers radioactivity. Minsch publishes proposal to use ionizing radiation to preserve foodby destroying microorganisms.

1904 Prescott publishes studies at MIT on bactericidal effects of ionizing radiation. 1905 U.S. and British patents issued for use of ionizing radiation to kill bacteria in foods. 1905 to 1920 Much research conducted on the physical, chemical, and biological effects of ionizing radiation.

1921 USDA researcher Schwartz publishes studies on the lethal effect of x-rays on Trichinella spiralis in raw pork.

1923 First published results of animal feeding studies to evaluate the wholesomeness of irradiated foods. 1930 French patent issued for the use of ionizing radiation to preserve foods. 1943 MIT group, under U.S. Army contract, demonstrates the feasibility of preserving ground beef by x-rays.

Late 1940s and early 1950s

Beginning of era of food irradiation development by U.S. Government (among Atomic EnergyCommission, industry, universities, and private institutions) including long-term animal feeding studiesby U.S. Army and Swift and Company.

1950 Beginning of food irradiation program by England and numerous other countries. * Adapted from American Council on Science and Health. 1988. Irradiated Food (Third edition). American Council onScience and Health.

Regulations for Food Irradiation The 1958 Food Additive Amendment to the Food, Drug and Cosmetics Act required advance approval from the Food andDrug Administration (FDA) before any particular irradiated food could be sold publicly. At this time, irradiation waslegally defined as an additive, not a process (IFT Expert Panel, 1983).

The FDA, in 1963 and 1964, approved the use of low-dose ionizing radiation for bacon, for killing insects in wheat andwheat flour, and for the inhibition of sprouting in potatoes. In 1983, the FDA approved sterilization of spices with ionizingradiation. Low-dose irradiation can also be used to inhibit sprouting of onions, garlic, and ginger, and to inhibit the ripeningof bananas, avocados, mangoes, papayas, and guavas.

Regulatory Highlights -- Food Irradiation*

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1958

The Food, Drug and Cosmetic Act is amended, directing that food irradiation be evaluated as a food additive,not as a physical process. All new food additives, including radiation, must be approved by the FDA before theycan be used. The U.S. Congress passed legislation, which President Eisenhower signed in 1958. This legislationis still the law of the land.

1958 to 1959 U.S.S.R. approves potato and grain irradiation.

1960 Canada approves potato irradiation. 1963 to 1964 U.S. FDA approves irradiated bacon, wheat, and wheat flour and potatoes.

1964 to 1967 U.S. FDA approves flexible packaging material for food containers during irradiation processing.

1976 Joint FAO/IAEA/WHO Expert Committee on (safety/wholesomeness of ) Food Irradiation (JECFI) approvesseveral irradiated foods and recommends that food irradiation be classified as a physical process.

1979 U.S. FDA Bureau of Foods (Center for Food Safety and Applied Nutrition) forms internal Irradiated FoodsCommittee.

1980 Joint FAO/IAEA/WHO Expert Committee on (safety/wholesomeness of ) Food Irradiation (JECFI) approves allirradiated foods treated with a maximum average dose of 10 kGy**.

1983 U.S. FDA and Canadian Health and Welfare Department approve sterilization of spices with irradiation.

1985 U.S. FDA approves irradiation pasteurization of pork to control trichinosis (with a minimum dose of 0.3 kGyand a maximum of 1.0 kGy of ionizing radiation).

1986 U.S. FDA approves irradiation of fruits and vegetables and other foods up to 1 kGy.

1990 to 1992

The U.S. government announced approval of ionizing radiation treatments of poultry to eliminate foodbornepathogens. The regulation for irradiation of poultry products from the USDA Food Safety and Inspection Servicerequires minimum and maximum doses of 1.5 and 3.0 kGy, respectively.

1994 The Food Safety and Inspection Service of the USDA has indicated dosages of ionizing radiation treatments forred meat products to the FDA. A maximum level of 4.5 kGy is proposed for unfrozen red meat, and 7.5 kGy forfrozen red meat. Approval of radiation treatment for red meat products is expected early in 1995.

* Adapted from American Council on Science and Health. 1988. Irradiated Food (Third edition). American Council onScience and Health. ** (1 kGy = 100 kilorads)

In 1985 and 1986, the USDA Food Safety and Inspection Service and the FDA approved the processing regulations fortreatment of pork meat and products with a minimum dose of 0.3 kGy and a maximum of 1.0 kGy (1 kGy = 100 kilorads)of ionizing radiation to control Trichinella spiralis.

From 1990 through 1992, the U.S. government announced approval of ionizing radiation treatments of poultry to eliminatefoodborne pathogens. The regulation for irradiation of poultry products from the USDA Food Safety and Inspection Servicerequires minimum and maximum doses of 1.5 and 3.0 kGy respectively.

Most recently, the Food Safety and Inspection Service of the USDA has indicated acceptable levels of ionizing radiation forprocessing red meat products (beef, veal, and lamb) to the FDA. A maximum level of 4.5 kGy is proposed for unfrozen redmeat, and 7.5 kGy for frozen red meat. Approval of radiation treatment for ground meat products (and other meat items) isexpected early in 1995.

Canadian Regulations On March 23, 1989, Food and Drug Regulations of Canada were amended to create a new division for the specific controlof food irradiation (Food Production and Inspection Branch, Agriculture Canada, 1989). Previous to this time, foodirradiation had been regulated for more than 20 years under food additive provisions of Division 16. The new division,Division 26 is called Food Irradiation. It recognizes food irradiation as a process and contains regulations that aremeaningful and specific.

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The new regulations define "ionizing radiation" and control the sources used in the process; set out requirements forrecord-keeping, thereby strengthening inspection and compliance programs; and detail the pre-clearance requirements to bemet before regulatory consideration is given to any additional or extended uses of food irradiation or changes in radiationsources or dosages. Canada agrees with the Codex Alimentarius Commission, which in 1983 took the position that foodsirradiated below 10 kGy present no toxicological hazard.

To ensure that consumers have the information necessary to choose between irradiated and non-irradiated food, Canada'sfood irradiation regulations state that: "Irradiated foods be clearly marked with the international symbol for irradiatedfoods, and carry a statement to the effect that the food has been irradiated." When an irradiated food is used as an ingredientconstituting 10% or more of a finished product, it must be described as "irradiated" in the ingredient list.

International Trade Work on food irradiation has spread to other countries throughout the world. Because of the lack of research facilities inmany third world countries, specialized agencies of the United Nations became actively involved in international foodirradiation research programs. The illustration, Food Irradiation Facilities Around the World (Loaharanu, 1989), depictsthe number and location of food irradiation facilities throughout the world.

In 1981, the Joint Expert Committee on Wholesomeness of Irradiated Foods convened by the World Health Organization(WHO) reviewed all food safety information regarding irradiated foods. They concluded that any food irradiated to anaverage dose of 10 kGy (1 Mrad) [see Glossary for definitions] or less is wholesome for humans and therefore should beapproved without future testing. The table, Partial Listing of Some Countries and Foods Approved for Irradiation in 1988or Earlier, highlights 19 countries and some foods that have been approved for irradiation through 1988 in those countries.

Partial Listing of Some Countries and Foods Approved for Irradiation in 1988 or Earlier* Country Food ProductsArgentina Potatoes, strawberries, onions, garlicBelgium Potatoes, strawberries, onions, garlic, shallots, paprika, pepper, gum arabic, 78 spicesBulgaria Potatoes, onions, garlic, grain, dry food concentrates, dried fruits, fresh fruitsCanada Potatoes, onions, wheat flour, poultry, cod and haddock fillets, spices and certain dried vegetablesFinland Spices, herbs, hospital mealsChile Potatoes, papaya, wheat, chicken, onions, rice, fish products, spicesFrance Potatoes, onions, garlic, shallots, spices, dried fruits and vegetablesGermany Hospital mealsIsrael Potatoes, onions, poultry, 36 spices, fresh fruits and vegetablesCzechoslovakia Potatoes, onions, mushrooms

The Netherlands

Asparagus, cocoa beans, strawberries, mushrooms, hospital meals, potatoes, shrimp, onions, poultry,soup greens, fish fillets, frozen frog legs, rice and ground rice products, rye bread, spices, endive,powdered batter mix

Philippines Potatoes, onions, garlicSouth Africa Potatoes, onions, garlic, chicken, papaya, mangoes, strawberries, dried bananas, avocados, beansSpain Potatoes, onionsThailand Potatoes, onions, garlic, dates, wheat, rice, fish, chicken

U.S.S.R. Potatoes, grain, fresh and dried fruits and vegetables, dry food concentrates, poultry, onions, preparedmeat products

U.K. Hospital mealsU.S.A. Wheat and wheat flour, potatoes, spices, pork, fresh fruits and vegetablesYugoslavia Cereals, potatoes, onions, garlic, poultry, dried fruits and vegetables

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* Adapted from American Council on Science and Health. 1988. Irradiated Food (Third edition). American Council onScience and Health. As taken from List of Clearances as of March 22, 1988 for Use of Ionizing Energy on Foods.International Atomic Energy Agency Supplement to Food Irradiation Newsletter. 12(1): 2-15.

There is a need to standardize regulations regarding food irradiation throughout the world. Harmonizing national regulations regarding food irradiation will facilitate international trade (Loaharanu, 1989). The upsurge in the interest infood irradiation by national authorities and industry may be attributed to:

1. Increasing concern over foodborne diseases and uses of certain chemicals in food.1.2. High post-harvest food losses from infestation, contamination, and microbial spoilage.2.3. Stringent regulations related to quality and quarantine in international trade in food products.3.

Defining Ionizing Radiation Used For Food Irradiation Energy exists in the form of waves and is defined by its wavelength. As the wavelength gets shorter, the energy of the waveincreases. The example of the electromagnetic spectrum as adapted from Frazer and Westhoff (1988) identifies the kindsof energy that exist . Electric power, radio and television, microwaves (radar) and light have longer wavelengths and lower energies. They causemolecules to move but cannot structurally change the atoms in those molecules. Ionizing radiation (gamma rays, x-rays)has a very short wavelength and higher energy, high enough to change atoms by knocking off an electron from them toform an ion, but not high enough to split atoms and cause exposed sources to become radioactive. Therefore, the sources ofradiation allowed for food processing (Cobalt-60, Cesium-137, accelerated electrons and x-rays) cannot make foodradioactive.

Electron beam irradiation. High-voltage electron beams (accelerated electrons) generated from linear accelerators are analternative to radioisotope generators (Best, 1989). They lack the penetration depth of gamma irradiation (about 0.5 cm.)per 1,000,000 electron volts (MeV) of energy, however, they require much shorter exposure times (seconds vs. hours forgamma irradiation) to be effective. Electron beam irradiation is currently being used to disinfest grain at 1.4 MeV at a grainloading facility in Odessa, Russia, and to pasteurize frozen mechanically separated meat products with 10 MeV at aprocessing facility in France. Irradiation research facilities at Iowa State University's Meat Irradiation Technology Centerfeatures a 10 MeV linear accelerator than can switch from electrons to x-ray beams.

X-rays generated when electrons from an electron beam bombard a heavy metal target such as tungsten, have a greaterpenetration depth but are less desirable because of the low energy conversion efficiency of electrons to x-rays.

Gamma rays used for irradiation processing of food are radioactive fission products of Cobalt-60 and Cesium-137.Gamma rays have good penetration, as do x-rays. With "cross-firing", they can easily deliver a uniform (less than 25%overdose) of energy to a 6-inch No. 10 can of food.

Cobalt-60 is not a waste product from the nuclear industry. It is specifically manufactured for use in radiotherapy,sterilization of medical products, and the irradiation of food. Cesium-137 is one of the fission products contained in usedfuel rods. It must be extracted in reprocessing plants before it can be used as a radiation source. Currently, almost allradiation facilities in the world use Cobalt-60 rather than Cesium-137 (WHO, 1987).

Comparison of gamma rays, x-rays and cathode rays. Gamma rays, x-rays, and electron beams are equally effective insterilization for equal quantities of energy absorbed. The greatest drawback at present to the use of x-rays in foodpreservation is the low efficiency and consequent high cost of their production. For this reason, most research hasconcentrated on the use of gamma photons and electron beams. Gamma rays have a maximum of 10 to 25% utilizationefficiency, while the maximal efficiency of electrons from electron beam generators ranges between 40 and 80%(depending on the shape of the irradiated material). Radioactive sources of gamma rays (Cobalt-60 or Cesium-137) decaysteadily and hence weaken with time, which is another cost. They must be constantly replenished.

The use of electrons from electron beam generators presents fewer health problems than the use of gamma rays, sinceelectron beams are directional and less penetrating, can be turned off for repair or maintenance work, and present no hazardof radioactive materials after a fire, explosion, or other catastrophe. Gamma rays are emitted in all directions, arepenetrating, are continuously emitted, and come from radioactive sources. Gamma rays require more shielding to protectworkers.

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The one overriding requirement for an energy source to be employed in food irradiation is that the energy levels must bebelow those that could possibly cause the food to become radioactive. After that requirement is met, sources are consideredon the basis of their practical and economic feasibility. Machine sources must produce radiation with relatively simpletechnology. Isotopes must be sufficiently long lived and emit penetrating radiation (Jones, 1992).

Effects on Microorganisms Lethality due to ionizing radiation, as proposed by the target theory, occurs when the irradiated microorganisms aredestroyed by the passage of an ionizing particle or quantum of energy through, or in close proximity to, a sensitive portionof the cell. This direct "hit" on the target causes ionization in this sensitive region of the organism or cell and subsequentdeath. It is also assumed that much of the germicidal effect results from the ionization of the surroundings, especially water,to yield free radicals, some of which may be oxidizing or reducing and therefore helpful in the destruction of the organisms.This effect is reduced if food is irradiated in the frozen state. Irradiation may also cause mutations in the organisms present.

Bacterial spores are more resistant to ionizing radiation than are vegetative cells. Gram-positive bacteria are more resistantthan gram-negative bacteria. The resistance of yeasts and molds varies considerably, but some are more resistant than mostbacteria.

According to Frazier and Westhoff (1988), the bactericidal efficacy of a given dose of irradiation depends on the following:

The kind and species of the organism. [See the table, Approximate Killing Doses of Ionizing Radiations in Kilorays(kGy) ]

1.

The numbers of organisms (or spores) originally present. The more organisms there are, the less effective a givendose will be.

2.

The composition of the food. Some constituents [e.g., proteins, catalase, and reducing substances (nitrites, sulfites,and sulfhydryl compounds)] may be protective. Compounds that combine with the SH groups would be sensitizing.

3.

The presence or absence of oxygen. The effect of free oxygen varies with the organism, ranging from no effect tosensitization of the organism. Undesirable "side reactions" are likely to be intensified in the presence of oxygen andto be less frequent in a vacuum.

4.

The physical state of the food during irradiation. Both moisture content and temperature affect different organisms indifferent ways.

5.

The condition of the organisms. Age, temperature of growth and sporulation, and state (vegetative or spore) mayaffect the sensitivity of the organisms.

6.

Approximate Killing Doses of Ionizing Radiations in Kilorays (kGy)*

Organism Approximate lethal dose (kGy)Insects 0.22 to 0.93 Viruses 10 teo 40 Yeasts (fermentative) 4 to 9 Yeasts (film) 3.7 to 18 Molds (with spores 1.3 to 11Bacteria (cells of pathogens):

Mycobacterium tuberculosis Staphylococcus aureus Cornybacterium diphtheriae Salmonella spp.

1.41.4 to 7.0

4.23.7 to 4.8

Bacteria (cells of saprophytes): Gram-negative:

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Escherichia coli Pseudomonas aeruginosa Pseudomonas fluorescens Enterobacter aerogenes

1.0 to 2.31.6 to 2.31.2 to 2.31.4 to 1.8

Gram-positive

Lactobacillus spp. Streptococcus faecalis Leuconostoc dextranicum Sarcina lutea

0.23 to 0.381.7 to 8.8

0.93.7

Bacterial spores: Bacillus subtillus Bacillus coagulans Clostridium botulinum (A) Clostridium botulinum (E) Clostridium perfringens Putrefactive anaerobe 3679 Bacillus stearothermophilus

12 to 1810

19 to 3715 to 18

3.123 to 5010 to 17

* Adapted from Frazier, W.C., and Westhoff, D.C. 1988. Chapter 10. Preservation by radiation. In Food Microbiology(Fourth edition). McGraw-Hill. New York, NY.

Importance of Surviving Bacteria in Low-dose Irradiated Food It is common knowledge that some microorganisms grow in foods and cause them to "spoil" or deteriorate in quality beforethey are eaten or discarded. The growth of these microorganisms also inhibits the growth of some pathogenicmicroorganisms. Therefore, there must be some "spoilage survivors" to inhibit the outgrowth of pathogens from survivingspores. For example, radiation survival curves were determined for 7 strains of Enterococcus faecium, 10 strains of Enterococcus faecalis, and 8 strains of the proteolytic variety of E. faecalis (Huhtanen, 1990). The D values (i.e., the dosesgiving 90% reduction of viable counts) ranged from 5.0 to 47 kGy for E. faecium strains, 3.5 to 21 kGy for the E. faecalisstrains, and 3.0 to 4.5 kGy for the proteolytic variants of E. faecalis strains. The survival curves were linear for most strainsbut some exhibited non-linear trends. The results of this study indicate useful radiation resistant strains of group Dstreptococci, which may find application in low-dose irradiated foods for preventing toxin formation by pathogenicmicroorganisms such as Clostridium botulinum in bacon and other foods.

Uses of Food Irradiation Ionizing radiation can be used to process food. Its effect on the food is dependent on the dose level (amount) of irradiationto which the food has been subjected. High-dose levels of irradiation (20 to more than 70 kGy) can be used to sterilizefoods by eliminating all vegetative microorganisms and spores in the food. Very low doses of irradiation (less than 0.1kGy) can be used to inhibit sprouting in potatoes, onions and garlic.

Low doses have also been shown to be as effective as pesticide fumigants for deinfesting grain products prior to shipmentand storage, and for reducing microbial and insect contamination on fresh fruits and vegetables. For example, grapefruitgrown in Mexico, Central America, and South America frequently are infested with larvae of the Mexican fruit fly,Anastrepha ludens. To prevent entry of this insect into the United States, grapefruits must be quarantined and treated withethylene dibromide. A study reported that 20 grays for 0.25, 0.5, 1.0, or 100 minutes reduced adult emergence of Mexicanfruit flies from larvae by more than 99% (Lester and Wolfenbarger, 1990). Therefore, once a quarantine security treatmentfor the Mexican fruit fly is established, a low irradiation dose rate can be used to reduce adult emergence and should impartlittle damage to grapefruit peel tissue.

Not all fresh produce is suitable for irradiation. The shelf life of mushrooms, potatoes, tomatoes, onions, mangoes, papayas,bananas, apricots, strawberries, and figs can be extended with low-dose irradiation with no loss in quality. However, thequality of some foods (some citrus fruits, avocados, pears, cantaloupes, and plums) is actually degraded by irradiation.

Pasteurizing doses of irradiation can kill or reduce the populations of both food spoilage and pathogenic microorganisms infood. For example, Salmonella spp. and Campylobacter jejuni can be eliminated from poultry, and trichinae from pork(ACSH, 1988). Escherichia coli O157:H7, Salmonella, C. jejuni, Listeria monocytogenes, and Staphylococcus aureus can

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be eliminated in uncooked ground beef (Beuchat et al., 1993).

Different doses (levels) of radiation are used for different purposes as shown in the table Applications of Food Irradiationbelow.

Applications of Food Irradiation*

Type of Food Radiation Dose in kGy Effect of Treatment

Meat, poultry, fish, shellfish, some vegetables, baked goods,prepared foods

20 to 71 Sterilization. Treated products can be stored at room temperaturewithout spoilage. Treated products are safe for hospital patients whorequire microbiologically sterile diets.

Spices and other seasonings Up to a maximum of 30

Reduces number of microorganisms and insects. Replaces chemicalsused for this purpose.

Meat, poultry, fish 0.1 to 10 Delays spoilage by reducing the number of microorganisms in thefresh, refrigerated product. Kills some types of food poisoning bacteriaand renders harmless disease-causing parasites (e.g., trichinae).

Strawberries and some other fruits 1 to 5 Extends shelf life by delaying mold growth.

Grain, fruit, vegetables, and other foods subject to insectinfestation

0.1 to 2 Kills insects or prevents them from reproducing. Could partiallyreplace post-harvest fumigants used for this purpose.

Bananas, avocados, mangoes, papayas, guavas, and certainother non-citrus fruits

1.0 maximum Delays ripening.

Potatoes, onions, garlic, ginger 0.05 to 0.15 Inhibits sprouting. Grain, dehydrated vegetables, other foods Various doses Desirable changes (e.g., reduced rehydration times).

* Adapted from American Council on Science and Health. 1988. Irradiated Food (Third edition). American Council onScience and Health.

Irradiated foods are used by astronauts during space travel. In a review of the use of irradiated foods, Karel (1989) statedthat, "On earth, food irradiation will most likely be used in combination with other preservation techniques. In space, howirradiation will be used will depend on the length of the voyage."

Effect of Ionizing Radiation on Nutrients in Food When foods are exposed to ionizing radiation under conditions envisioned for commercial application, no significantimpairment in the nutritional quality of protein, lipid and carbohydrate constituents was observed (Josephson et al., 1979).Irradiation is no more destructive to vitamins than other food preservation methods (ACSH, 1988).

It was noted that there were small losses of vitamin E and thiamin. According to Thayer et al., (1993a) thiamin in pork isnot significantly affected by the FDA-approved maximum radiation dose to control Trichinella, but at larger doses, it is significantly affected. Protection of nutrients is improved by holding the food at low temperature during irradiation and byreducing or excluding free oxygen from the radiation environment. This is accomplished by irradiating vacuum-packagedfoods at temperatures below 0°C (32°F).

The effect of irradiation on retention of vitamin E (alpha tocopherol) in chicken breasts was determined when the chickenbreasts were irradiated in air with a Cesium-137 source at 0, 1, 3, 5.6, and 10 kGy at 0° to 2°C (32.0° to 35.6°F). The freshmuscle tissue was saponified and the total tocopherols were isolated and quantitated using normal phase high performanceliquid chromatography with a fluorescence detector. Gamma irradiation of the chicken resulted in a decrease in alphatocopherol with increasing dose. At 3 kGy and 2°C, the radiation level approved by the FDA to process poultry, there was a

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6% reduction in alpha tocopherol level. No significant changes were observed for gamma tocopherol (Lakritz and Thayer,1994).

Free radical scavengers were tested for their ability to reduce the loss of thiamin and riboflavin in buffered solutions and inpork during gamma irradiation. In aqueous solution, the tested compounds were twice as effective for the protection ofriboflavin as for the protection of thiamin. The presence of nitrous oxide doubled the rates of loss for thiamin and riboflavinin solution, indicating a predominance of reactions with hydroxyl radicals. In buffered solutions, niacin was not affected bygamma radiation unless either thiamin or riboflavin was present, in which case, the niacin was destroyed rather than theother vitamin. Ascorbate, cysteine, and quinoid reductants were demonstrated to be naturally present in sufficient quantitiesto account for the lower rates of loss of thiamin and riboflavin observed during irradiation of pork meat, as compared toirradiation in buffered solution (Fox et al., 1992).

A study was made of thiamin content of the skeletal muscles and livers of pork, chicken, and beef after gamma irradiation.Gamma irradiation from a Cesium-137 source was used to irradiate the samples with doses of 0, 1.5, 3, 6, and 10 kGy at2°C (35.6°F). Samples were also titrated with dichlorophenoindophenol to determine the reducing capacity of the tissue.The rate of loss of thiamin upon irradiation was found to be about 3 times as fast in skeletal muscle as in liver and to be afunction of the reducing capacity of the tissues, the loss decreasing with increasing reductant titer. For the same amount ofthiamin loss, liver could be irradiated to 3 times the dose as could muscle (Fox et al., 1993).

Wholesomeness of Irradiated Foods The World Health Organization (WHO) (as cited by Lee, 1994) released the following updated policy statement onSeptember 23, 1992: "Irradiated food produced under established Good Manufacturing Practices is to be considered safeand nutritionally adequate because:

The process of irradiation will not introduce changes in the composition of the food which, from a toxicologicalpoint of view would impose an adverse effect on human health.

1.

The process of irradiation will not introduce changes in the microflora of the food which would increase themicrobiological risk to the consumer.

2.

The process of irradiation will not introduce nutrient losses in the composition of the food which, from a nutritionalpoint of view, would impose an adverse effect on the nutritional status of individuals or populations."

3.

Review of data and concerns raised during the Food and Drug Administration and Food Safety Inspection Service of theUSDA approval process for irradiation of poultry indicates that properly processed irradiated foods are wholesome. Neithershort nor multi-generation animal feeding studies have produced evidence of toxicological effects in mammals due to theiringestion of irradiated foods (Thayer, 1994c).

In a feeding trial in China, 21 male and 22 female volunteers consumed 62 to 71% of their total caloric intake as irradiatedfoods for 15 weeks (Chi et al., 1986). The diet included rice irradiated to 0.37 kGy and stored for 3 months; rice irradiatedto 0.4 kGy and stored for 2 weeks; meat products such as pork sausage irradiated to 8 kGy and stored at room temperaturefor 2 weeks; and 14 different vegetables irradiated to 3 kGy and stored at room temperature for 3 days. A double-blinddesign was used and included measurement of total caloric intake, monthly biochemical and physical exams and sensoryevaluations of the food. The diet was well received, and there were no adverse findings associated with the consumption ofthe irradiated foods.

Bhaskaram and Sadasivan (1975) reported that children suffering from kwashiorkor developed a 1.8% incidence ofpolyploidy (3) after being fed irradiated wheat. It was also reported that there was 0% polyploidy in controls and a testgroup of children after the removal of the treated diet, even though polyploidy is not unusual in human populations. Expertsand governmental agencies (The Government of India; FDA; IFT Expert Panel on Food Safety and Nutrition; WHO/FAO).looking at the safety of food irradiation have discredited this study because of its inconsistencies. [(3) Polyploidy describes cells, tissues, or individuals in which there are 3 or more sets of chromosomes.]

There is a concern that ionizing radiation creates free radicals, and that they may be present in the food at the time ofingestion. Free radicals are also formed when food is fried, baked, ground, and dried. More free radicals are created duringthe toasting of bread than through ionizing radiation. In foods with a high moisture content, free radicals disappear within afraction of a second; in dry foods, the free radicals are much more stable and do not dissipate as quickly (ACSH, 1988;Jones, 1992).

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The assessment of the safety for human consumption of irradiated foodstuffs has involved basically four aspects (Elias,1989).

Radiological safety1.Microbiological safety2.Nutritional adequacy3.Toxicological safety4.

After reviewing an extensive amount of data on animal feeding studies conducted at several laboratories as well as theradiation chemistry data, the Joint FAO/IAEA/WHO Expert Committee in 1981 concluded that irradiated foods are safeand wholesome (Brynjolfsson, 1985). The committee's main conclusions were that the irradiation of any food commodityup to an overall average dose of 10 kGy presents no toxicological hazard; hence, toxicological testing of foods so treated isno longer required. The irradiation of foods up to an overall average dose of 10 kGy introduces no special nutritional ormicrobiological problems.

Recent Support for the Irradiation of Foods in the United States In an editorial commentary in the Journal of the American Medical Association, Dupont (1992) discussed the potential fortransmission of bacterial enteropathogens (Salmonella, Shigella, Campylobacter, Vibrios) through food vehicles destinedfor human consumption. It was recommended that the microbiological safety of food in the United States be improvedthrough the use of irradiation. Future health hazards could be reduced if this technique is employed widely for certainhigh-risk items, including poultry potentially contaminated with Salmonella and Campylobacter.

The Assistant Secretary for Health, Director, U.S. Public Health Service, Dr. Phillip R. Lee pointed out the importance ofusing irradiation to prevent foodborne illness in another recent issue of the Journal of the American Medical Association(Lee, 1994). "Foodborne illness is one of the largest preventable public health problems in the United States. Studies by theCenters for Disease Control and Prevention show that foodborne diseases caused by pathogenic bacteria, such asSalmonella, Campylobacter, E. coli, and by Vibrio, Trichinella, tapeworms, and other parasites, cause an estimated 9000deaths and from 6.5 million to 81 million cases of diarrheal disease annually. Unfortunately, it has taken a crisis to raiseconsumer, industry, and lawmakers' awareness. Media scrutiny about salmonella in poultry and the highly publicizeddeaths of four children and severe illness of 600 people linked to E. coli-tainted hamburger have raised serious questionsabout food safety."

"There is a need and responsibility for U.S. Public Health Service to use what is known to protect and improve the health ofthe public. Each modern food-processing advance -- pasteurization, canning, freezing -- produced criticism. Food radiationis no different." (Lee, 1994).

The Wall Street Journal noted that: "Irradiating beef may help save lives, but the meat industry is still waiting for the greenlight" (Gibson, 1994). Agriculture scientists report that small doses of irradiation could wipe out "nearly 100%" of the E. coli strain in beef, and has been shown to sterilize meat and produce against practically all bacteria that cause spoilage. Yet,the Department of Agriculture is holding back because of the concern that the public might link beef irradiation with thegovernment radiation experiments of the 1950s. Proponents of Beef Irradiation include: The National Food Processors Association, the American Medical Association, the World Health Organization, and the American Meat Institute. All saybeef irradiation will help reduce deaths from E. coli.

In December, 1993, the American Medical Association (AMA) endorsed food irradiation as "a safe and effective processthat increases the safety of food when applied according to governing regulations." The AMA also affirms the principle that"the demonstration of safety requires evidence of a reasonable certainty that no harm will result, but does not require proofbeyond any possible doubt [i.e., 'zero' risk does not exist]" (Marsden, 1994).

An article in the Washington Times (Fumento, 1994) reported that irradiation will give food producers another line ofdefense in preventing foodborne illness, and to prevent its use is to deny them a valuable tool in protecting public health.The U.S. Secretary of Agriculture asked the Food and Drug Administration to approve the use of irradiation on beef. Thereare many activists who oppose the use of radiation for food. "Instead of using irradiation to enhance food safety, opponentssay the answer is increased government regulation, especially increasing the size of the government's meat inspection force.At this time, the government employs only about 8,000 inspectors, including supervisors, for about 32 million head ofslaughtered cattle annually." However, "inspectors cannot see bacteria and other spoilage organisms and no microbiologicaltests currently exist that would make it practical to perform routine laboratory analysis on raw meat." (Fumento, 1994)

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Gallager and Kwittken (1994) reported conclusions of an E. coli O157:H7 Consensus Development Conference sponsoredby the American Gastroenterological Association Foundation. "Protection of the public's health requires the immediateimplementation of currently recognized scientific technology for ensuring food safety. An emphasis should be placed onscience-based monitoring and verification of the nation's slaughter plant operations. The current inspection-based systemshould be replaced by a science-based risk assessment process with government verification." The 14-member nonadvocatepanel was comprised of professionals and public representatives from gastroenterology, epidemiology, public health,microbiology, food science, industry and consumer affairs. Speakers included scientific investigators, governmentrepresentatives, industry officials, and consumers. One of the major recommendations made was as follows: "Irradiationpasteurization is a safe and effective intervention strategy, especially in ground beef and should be implemented as soon aspossible."

Effect of Ionizing Radiation of Meats Various parasites cause human illnesses with medical costs and productivity and disability losses totaling billions of dollarsannually. Food is an important vehicle for some of these parasitic diseases. In the United States, congenital toxoplasmosisis estimated to cost up to $5.3 x 109 annually. Half of the incidence of toxoplasmosis can be attributed to food sources.Irradiation of fresh pork could decrease cases of congenital toxoplasmosis. Similarly, other parasitic diseases (Cyticerci, Anisakindinae, Trichinella spiralis, and Giardia lamblia) could be reduced by irradiating beef, pork or fish (Roberts andMurrel, 1993).

Research completed in 1993 for the American Meat Institute Foundation found that very low doses of irradiation aresufficient to kill a host of harmful bacteria in frozen, boxed hamburger patties. The dosage equivalent to that approved forpoultry (1 to 3 kGy) is ample and this amount of radiation can be used for this purpose when irradiation is approved forbeef. Research was conducted at the Center for Food Safety and Quality Enhancement, University of Georgia incollaboration with Vindicator, Inc., Mulberry, Florida. Experiments were done to determine the D kGy of E. coli O157:H7, Salmonella, C. jejuni, L. monocytogenes, and S. aureus in uncooked ground beef (Beuchat et al. 1993). The influence of 2levels of fat (8 to 14% and 27 to 28%) and temperature (frozen [-17° to -15°C (1.4° to 5.0°F)] and refrigerated [-3° to 5°C(26.6° to 41.0°F)] during gamma irradiation (Cobalt-60) was studied. Cells of all test pathogens were in the stationaryphase of growth when inoculated into ground beef before subjecting it to 7 target irradiation doses ranging from 0 to 3.0kGy.

The use of ionizing (gamma) radiation can be used as an alternative to thermal processes for the preservation of food.Thayer et al. (1986) reviewed research studies of the uses of ionizing radiation to extend the safety of processed meats.Radiation research studies of meat products included: bacon, ham, frankfurters, corned beef and pork sausage, and beef,chicken and pork. Beef, chicken and pork were organoleptically acceptable after irradiation in vacuo at -30°C (+/-10°C)[-22.0°F ()18°F)]. 12D doses for the process were 4.12, 4.27, and 4.37 Mrad for beef, chicken, and pork loin, respectively.It was also reported that while sublethal radiation doses enhance the safety and storage life of raw beef, chicken, and pork,it may actually increase the spoilage rate in cured meat products.

Gamma radiation doses of 0.26 kGy and 0.36 kGy, administered in vacuo at 0°C (32°F), destroyed 90% of log-phase andstationary-phase colony forming units (CFU) of S. aureus, respectively, in mechanically deboned chicken meat (MDCM).Samples inoculated with 103.9 CFU/g of S. aureus were treated with gamma radiation in vacuo at 0°C (32°F) and then heldfor 20 hours at 35°C (95.0°F) (abusive storage). Enterotoxin was not detected in irradiated MDCM. A predictive equationwas developed for the response of S. aureus in MDCM to radiation dose and irradiation temperature (Thayer and Boyd,1992).

Treating fresh or frozen meats with ionizing radiation is an effective method to reduce or eliminate several of the foodbornehuman pathogens such as Salmonella, Campylobacter, Listeria, Trichinella, and Yersinia. It is possible to produce high-quality, shelf-stable commercially sterile meats. Irradiation dose, processing temperature, and packaging conditionsstrongly influence the results of irradiation treatments on both microbiological and nutritional quality of meat. These factorsare especially important when irradiating fresh non-frozen meats. Radiation doses up to 3.0 kGy have little effect on thevitamin content, enzyme activity, and structure of refrigerated non-frozen chicken meat, but have very substantial effects onfoodborne pathogens (Thayer et al., 1993a).

E. coli O157:H7 had a significantly higher D value when irradiated at -17° to -15°C (1.4° to 5.0°F), compared to treatmentat 3° to 5°C (37.4° to 41.0°F) At a given temperature, the level of fat in beef did not have an effect on D values. Salmonellabehaved similarly to E. coli O157:H7 in low fat beef, but temperature had no effect on D values when the pathogen wasirradiated in high-fat beef. Significantly higher D values were calculated for C. jejuni in frozen compared to refrigerated low-fat beef. The pathogen was more resistant to irradiation in low-fat beef when treatment was done at -17° to -15°C

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(-1.4° to 5.0°F). Neither the level of fat nor the treatment temperature significantly affected the D values for L. monocytogenes and S. aureus. Considering all combinations of fat level and treatment temperature, the ranges of D values(kGy) were, in ascending order of irradiation resistance:

Campylobacter jejuni 0.175 to 0.235 kGy Escherichia coli O157:H7 0.241 to 0.307 kGy

Staphylococcus aureus 0.435 to 0.453 kGy Listeria monocytogenes 0.507 to 0.610 kGy

Salmonella 0.618 to 0.800 kGy

Thayer and Boyd (1994b) reported a study of the sensitivity of E. coli O157:H7 suspended in beef or mechanically debonedchicken meat (MDCM) to gamma irradiation and also to determine the influence of processing parameter such asatmosphere or temperature on that sensitivity. Undercooked and raw meat has been linked to outbreaks of hemorrhagicdiarrhea due to the presence of E. coli O157:H7; therefore, treatment with ionizing radiation was investigated as a potentialmethod for the elimination of this organism. Response-surface methods were used to study the effects of irradiation dose (0to 2.0 kGy), temperature [-20° to +20°C (-4.0° to 68.0°F)], and atmosphere (air and vacuum) on E. coli O157:H7 inmechanically deboned chicken meat. Differences in irradiation dose and temperature significantly affected the results. 90%of the viable E. coli in chicken meat was eliminated by doses of 0.27 kGy at +5°C (41.0°F) and 0.42 kGy at -5°C (23.0°F).Small but significant differences in radiation resistance by E. coli were found when finely ground lean beef rather thanchicken was the substrate. Unlike non-irradiated samples, no measurable verotoxin was found in finely ground lean beefthat had been inoculated with 104.8 CFU E. coli O157:H7 per gram, irradiated at a minimum dose of 1.5 kGy, andtemperature abused at 35°C (95.0°F) for 20 hours. The authors concluded that radiation is an effective method to controlthis foodborne pathogen.

Research from the USDA, Agricultural Research Service which defines the effect of atmosphere and irradiationtemperature on control of the foodborne pathogens (Aeromonas, Listeria, Salmonella, and Staphylococcus) was reviewed by Thayer (1993d). Results indicate that both the temperature and atmosphere during irradiation of meats are important,and that these pathogens can be greatly reduced in population by radiation doses of 3 kGy or less.

Vacuum-packaged ground fresh pork samples absorbed gamma radiation doses of 0, 0.57, 3.76, 5.52, or 7.25 kGy at 2°C(35.6°F). Samples were analyzed after 1, 7, 14, 21, 28, or 35 days storage at 2°C (35.6°F) for presence and number ofaerobic and anaerobic mesophiles and endospore formers and aerobic psychrotrophs. Conventional plate counts did notdetect surviving microflora in any sample that received an absorbed dose of 1.91 kGy or higher, even after refrigeratedstorage for up to 35 days. The microflora in the control were predominantly Gram-positive for the first 21 days; however,Serratia predominated at 28 and 35 days. Staphylococcus, Micrococcus, and other yeast species predominated in samplesthat received 0.57 kGy (Thayer, 1993e).

The gamma radiation resistance of 5 enterotoxic and 1 emetic isolate of Bacillus cereus vegetative cells and endosporeswas tested in mechanically deboned chicken meat (MDCM) ground turkey breast, ground beef round, ground pork loin, andbeef gravy. The D values for B. cereus were 0.184, 0.431, and 2.56 kGy for logarithmic-phase cells, stationary-phase cells,and endospores at 5°C (41.0°F) on MDCM, respectively. Neither the presence nor absence of air during irradiationsignificantly affected radiation resistance of vegetative cells or endospores of B. cereus when present on MDCM. Irradiation temperature [-20° to +20°C (-4.0° to 68.0°F)] did affect the radiation resistance of stationary-phase vegetativecells, and to a limited extent that of spores on MDCM. Impedance studies indicated that surviving vegetative cells wereseverely injured by radiation. A dose of 7.5 kGy at 5°C (41.0°F) was required to eliminate a challenge of

4.6 x 103 B. cereus from temperature-abused MDCM [24 hours at 30°C (86.0°F)]. The radiation resistance of a mixture ofendospores of 6 strains to gamma radiation was 2.78 kGy in ground beef round, ground pork loin, and beef gravy, but 1.91kGy in turkey and MDCM. The results indicate that irradiation of meat or poultry can provide significant protection fromvegetative cells but not from endospores of B. cereus (Thayer and Boyd, 1994a).

The effects of water content, activity, NaCl, and sucrose content on the survival of Salmonella typhimurium on irradiatedMDCM and ground pork loin were investigated. The effects of NaCl and sucrose concentration were investigated byadding various amounts to MDCM or ground pork loin with NaCl solutions with various degrees of saturation. The effects

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of water content were investigated by rehydrating freeze-dried ground pork loin with different quantities of water.Inoculated samples were irradiated at 5°C (41.0°F) in vacuo to doses up to 6.0 kGy. The survival of S. typhimurium was effected by water content, water activity, and NaCl content, but not by sucrose content. The failure of sucrose to providethe same protection for S. typhimurium in meat against radiation argues against reduced water activity being a primarymechanism of protection. The results indicate that the survival of foodborne pathogens on irradiated meat with reducedwater content or increased NaCl levels may be greater than expected (Thayer et al., 1994b).

Longissimus dorsi from beef, pork, and lamb, and turkey breast and leg meats were inoculated with E. coli O157:H7, L. monocytogenes, Salmonella spp. and S. aureus, and the gamma radiation resistance of the pathogens were determinedunder identical conditions. At a temperature of 5°C (41.0°F), the respective radiation D value for the mixture of E. coliO157:H7 and L. monocytogenes was not affected by the suspending meat. The D value for a mixture of Salmonella spp. was significantly lower on pork than on beef, lamb, turkey breast, and turkey leg meats. The D value for S. aureus was significantly lower on lamb and MDCM than on the other meats. All values were, nevertheless, within the ranges expectedfor these pathogens (Thayer et al., 1994d).

Research has demonstrated that ionizing radiation can inactivate parasites, eliminate or greatly reduce the populations ofmicrobial pathogens, and extend the shelf life while preserving the desired nutritional and sensory properties of refrigeratedpoultry and red meat. Foodborne pathogens can be greatly reduced in population and sometimes completely eliminatedfrom foods by low doses of ionizing radiation. The shelf life of poultry, pork, and beef can be significantly extended bytreatment with ionizing radiation. Combination treatments with vacuum packaging or modified atmosphere packaging andionizing radiation have produced better than predicted results. Additional research is needed on the combined processes(Thayer, 1993c).

The American Meat Institute (AMI) is actively involved in the investigation of viable pathogen-preventing technologieswhich can be applied to the meat and poultry industry. Irradiation is one of those technologies and it is one that hasgathered support from governments and scientists worldwide (Marsden, 1994). In AMI's view, reducing pathogens in thefood supply and preventing foodborne illness will demand a multi-faceted, farm-to-table approach. While irradiation maybe helpful, it alone will not solve public health problems related to foodborne pathogens.

Labeling FDA requires labeling if the entire product or major ingredient has been irradiated (ACSH, 1988). The current version ofthe FDA low-dose irradiation rule requires that the retail label consist of the internationally agreed-upon symbol (International Food Irradiation Symbol), and the phrases "treated with radiation" or "treated by irradiation."

Irradiated spices in foods are considered minor ingredients and do not require labeling in combination products (Pszczola,1990).

Schutz et al. (1989) reported a nationwide study on the influence of label statements on the perception of quality, safety,and willingness to buy. The label statements used were "Irradiated to control microorganisms", "Irradiated for quarantinecontrol", "Irradiated to extend shelf life", and "Irradiated to control spoilage". Consumers thought the products bearing thelabel "Irradiated to extend shelf life", and "Irradiated to control spoilage" would stay fresh longer. They also responded thata food with a label "Irradiated to control microorganisms" was an indication of higher quality than a non-irradiated food.People thought it would probably be safer and more expensive than the non-irradiated counterpart; about 50% said theywould like to buy the product.

Consumer Acceptance Irradiated foods carry a value-added perception of safety among consumers in both the Netherlands and South Africa,where irradiation is in commercial use. However, in the United States, consumers' acceptance of irradiated foods is beingdemonstrated slowly.

Bruhn and Schutz (1989) reported a study concerning consumer acceptance or rejection of irradiated food products.Rejecters are opposed to irradiation for personal beliefs, such as the desire to eat only natural, unprocessed, or "organic"foods. About 5 to 10% of the population are irradiation rejecters. About half of the population are undecided. These peopleare unsure in their knowledge and understanding of the irradiation technology. Their concerns include food's safety, qualityand nutritional value. The acceptors, estimated to be from 25 to 30% of the population, believe they understand the processof irradiation and accept that irradiated foods are safe and nutritious. Accepting consumers trust the FDA and foodmanufacturers. To be acceptable, irradiation must offer to the consumer an advantage. This advantage could be higherquality, greater safety, longer shelf life, wide product availability, or lower cost.

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All consumers wanted irradiated products labeled for various reasons. Some, so they can avoid them, while others wantedirradiated products labeled so they could choose them and realize the advantage they thought the process could offer.Others simply wanted to know what they were buying. Some people believe that non-labeling implies that informationabout the product is hidden.

The authors (Bruhn and Schutz, 1989) concluded that consumers need to be educated and informed. Information may notreduce consumer concern, but it allows choice to be based on fact, rather than suspicion. Consumer attitude and marketingstudies show that, given information about irradiation, the majority of consumers will choose irradiated foods. Othersobject to irradiation and will never select it. The opportunity for choice in the marketplace should exist. "The eventualutilization of this technology will depend upon the safety of alternative technologies, industry's perception of potentialsuccess, responsible media coverage, and consumer information."

Clarke and Riley (1993) reported that consumers lack knowledge, but support irradiation once they understand it. A studyconducted by The Gallup Organization (1993) confirms that the more consumers know about food irradiation, the morelikely they are to desire it for destroying bacteria in poultry, pork, beef and seafood. Although 73% of Americans haveheard about food irradiation, only 24% claim to have any knowledge of the process. After the benefits of irradiation areexplained and endorsements from health organizations are mentioned, over half (54%) of those interviewed say they wouldpurchase irradiated meat rather than non-irradiated meat. Further, 60% said they would be willing to pay a 5% premium forirradiated hamburger. Men and those who had experienced foodborne illnesses are most accepting of irradiated foods.

Consumers generally do not understand the food safety benefits of most food preservation technologies, includingpasteurization, canning, and freezing. In a simulated supermarket setting study conducted by the University of Georgia andreported by Clarke and Riley (1993), 50% of consumers tested, chose irradiated ground beef over regular ground beef.After all consumers tested learned more about the irradiation process and how it affects raw meats, those choosingirradiated beef increased to 70% of the sample size (Clarke and Riley, 1993).

There is the perception that the public, reacting to a distrust of anything even remotely related to nuclear energy, will neverbuy or accept irradiated food. In response to this perception of consumer fear, no industry has been willing to sell irradiatedfood until recently (Conley, 1992). Consumers are not likely to demand food irradiation because they do not know enoughabout it, but they are demanding safer food. Food safety is an area of consumer, industry, and government concern.Irradiation of meat, poultry, fruits, and vegetables at appropriate levels could control many organisms that cause foodborneillness and product spoilage. Thus, food irradiation could be a viable process that could improve safety and extend shelflife.

Market tests in Florida indicate consumer acceptance of irradiated mangoes, papayas, apples, and strawberries. A 1988study conducted by a USDA Economic Research Service economist and a University of Florida professor found thatconsumers are willing to pay more for a safer product and would buy irradiated chicken (Conley, 1992).

Anti-food Radiation Activists However, there are anti-food radiation activists. Food and Water, an anti-irradiation group based in Marshfield, Vermont, isleading a nationwide campaign to keep food irradiation from winning public acceptance (Katzenstein, 1992). Other groupsthat look upon food irradiation with suspicion include Ralph Nader's Public Citizen Consortium and Michael Jacobsen'sCenter for Science in the Public Interest. At this time, some supermarket chains and grocery retailers are reluctant to offerirradiated foods for sale, fearing customer boycotts.

Consumer Education and Responsible Information Concerning Food Irradiation Education is the key. Proponents of food irradiation firmly believe that these foods will be accepted when offered for sale.But it will not be easy. If half the population is undecided about the process, and studies show that information andeducation can increase consumer acceptance, why are massive amounts of information unavailable? The answer is that theindustry, not wanting to appear prejudiced and fearing reprisals from interest groups, has been reluctant to produceconsumer-oriented materials. The federal government thus far has taken the position that, while the process is safe andshould be available to the industry and consumers, the government should not be viewed as a proponent of the process. Asa result, there is very little consumer-oriented material available about irradiated food or the process. Into this void stepactivist groups, some of which provide information and material than can increase fear of irradiated food products.

Responsible government should provide information to help consumers make educated choices, not choices based onlimited information and fear tactics. Conley (1992) advocates that the FSIS and the National Agricultural Library incooperation with other food-related agencies such as the FDA should provide education materials to consumers regarding

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food irradiation.

Food Irradiation Standards Food irradiation will be successful only if regulators, industry, and consumers agree that it is safe and effective.Appropriate control and inspection procedures are important aspects of that agreement. ASTM (American Society forTesting Materials) standards are being developed using "Codes of Good Irradiation Practice" developed by theInternational Consultative Group on Food Irradiation (ICGFI). This will facilitate acceptance of irradiated foods ininternational trade (Derr, 1993).

Commercialization of the Food Irradiation Process Decisions by food processors to invest (or not to invest) in radiation processing depends on many factors (Hall, 1989).Some of these rarely receive much attention in discussions of the subject. In the Netherlands, commercial food irradiation isroutinely applied to a broad range of products; however, nowhere else has food irradiation achieved this goal. Regulatoryand safety aspects of the process, equipment and cost factors, and obtaining consumer acceptance are factors which havecontributed to the slowness of commercialization of food irradiation in the United States.

When deciding whether or not to develop a food irradiation process, the processor must ask:

Will irradiation serve my particular needs?1.How much will it cost?2.Is it safe for consumers, customers, employees?3.What regulations will apply, how much trouble will they be, and what will they cost me?4.What public relations aspects, including community attitudes, will I need to address? What will I have to do addressthem? How much will it cost?

5.

What will consumers of my product think? How will they react? How can I find out in advance?6.What liability questions are involved?7.

In the Codex General Standard for Irradiated Foods (Codex Alimentarius Commission, 1984), it is required that:

Radiation treatment of foods shall be carried out in facilities licensed and registered for this purpose by a competentnational authority.

1.

The facilities shall be designed to meet the requirements of safety, efficacy and good hygienic practices of foodprocessing.

2.

The facilities shall be staffed by adequate, trained and competent personnel.3.Control of the process within the facility shall include the keeping of adequate records including quantitativedosimetry.

4.

Premises and records shall be open to inspection by appropriate national authorities. (In the United States, theauthorities would include the Nuclear Regulatory Commission, the FDA and the USDA.)

5.

The Codex General Standard for Irradiated Foods also states, in the section on hygiene of irradiated foods andtechnological requirements that:

The food should comply with the provisions of Recommended International Code of Practice—General Principles ofFood Hygiene and, where appropriate, with the Recommended International Code of Hygienic Practices of theCodex Alimentarius relative to a particular food.

1.

The irradiation of food is justified only when it fulfills a technological need or where it serves a food hygienepurpose, and should not be used as substitute for Good Manufacturing Practices.

2.

Summary Irradiation can provide considerable advantages as summarized by Urbain (1989). Irradiation:

Preserves food to a varying extent as determined by the treatment. Food irradiation is particularly effective incontrolling foodborne spoilage microorganisms. All organisms present in the food can be inactivated to securelong-term preservation, or a fraction of them can be inactivated to secure limited extension of product life. Meats,seafood, fruits, vegetables, cereal grains, and legumes are some of the foods than can be preserved.

1.

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Decontaminates food of pathogenic bacteria, yeast, molds, and insects. This decontamination can improve thehygienic quality of the foods and prevent the potential health hazards. Meats and seafood can be decontaminated ofbacteria and parasites; cereal grains, legumes, fruits, and dried fish of insects; spices and vegetable seasonings ofbacteria and insects.

2.

Controls maturation, senescence, and sprouting of fresh fruits and vegetables.3.Alters chemical composition for quality improvement. The chemical composition of cereal grains and legumes canbe altered so as to improve their quality. This is regulated by the dose (i.e., amount of radiation absorbed by thefood).

4.

Produces no toxic residues in foods. This is accomplished by limiting the energy level of the radiation employed,and also be selecting the type of radiation. The lethal action of ionizing radiation on living organisms was traced toalteration of the DNA molecule. Products formed in foods by irradiation were identified and determined to be of notoxicological significance to the consumer of irradiated foods.

5.

Maintains full nutritive value of foods. Studies have shown no changes in macronutrients and only insignificant onesin the micronutrients (vitamins). Irradiated foods were shown to be wholesome.

6.

Maintains sensory quality. Knowledge of radiation chemistry has guided the development of means to preventundesired sensory changes. An example of this is the irradiation of meats in the frozen rather than unfrozen state inorder to avoid a flavor change.

7.

The World Health Organization (WHO) (1987) summarizes advantages of the irradiation technique over conventional foodprocessing methods in this manner:

Foods can be treated after packaging.1.Irradiation processing permits the conservation of foods in the fresh state.2.Perishable foods can be kept longer without noticeable quality loss.3.The cost of irradiation and the low energy requirements compare favorably with conventional food processingmethods. Irradiation treatment up to the prescribed dose leave no residue; changes in nutritional value (i.e., loss ofsome vitamins) are comparable with those produced by other processes and during storage.

4.

Foods processed under prescribed conditions for irradiation do not in any way become radioactive, a fact that manypeople do not understand.

5.

Nationally syndicated columnist, Jane Brody (1995) recently compared public outcry against irradiation of foods to theprotests registered against the pasteurization of milk. A century ago, "myth-mongering opponents" kept the pasteurizationof milk from commercial use for over 50 years. Brody goes on to state that:

"Unfortunately, irrational fears about irradiation too often stand in the way of rational consideration of its benefits andrealistic consideration of its risks when it is used to treat some foods that people eat.

"Several marketing surveys have shown that when consumers learn more about the process and its uses in food, acceptanceof the theory and practice of irradiating food rises markedly. .....Everyone agrees that the nation's food supply needscleaning up so that consumers can be spared the costly, debilitating and sometimes deadly illnesses and the enormouswaste associated with foods that spoil before they can be eaten and the potential hazards of pesticides now used to controlspoilage and insect contamination."

In closing, it can be stated that food irradiation is not a miracle process that can convert spoiled food into high-quality food.It is equally true that not all foods are suitable for radiation treatment, just as not all foods are suitable for canning, freezing,drying, etc.

Food irradiation has two main benefits to the health and well-being of humans: the destruction of certain foodbornepathogens, thus making the food safer; and prolongation of the shelf life of food by killing pests and delaying thedeterioration process, thus increasing food supply.

Glossary*

Electron radiation. Streams or beams of electrons accelerated to energies of up to 10 MeV. There are a number ofmachine sources available for electron radiation.

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Gray (Gy). The unit (or level) of energy absorbed by a food from ionizing radiation as it passes through in processing. 1 Gray (Gy) = 100 rads 1,000 Gy = 1 Kilogray (kGy)

X-rays. Electromagnetic radiation of a wide variety of short wavelengths. They are usually produced by a machine inwhich a beam of fast electrons in a high vacuum bombards a metallic target. X-rays are sometimes called "Roentgen rays",after their discoverer, Lord von Roentgen.

Gamma Radiation. Electromagnetic radiation of very short wavelength, of the same nature as "short" x-rays. Gamma raysare emitted by isotopes of such elements as cobalt and cesium as they disintegrate spontaneously.

Rad. Another name or unit for "radiation energy absorbed" by food being processes with radiation. 1,000 rads = 1 Kilorad = 10 Grays 1,000,000 rads = 1 Mrad = 10 kGy (The rad has been superseded by the Gray.)

* Adapted from: Institute of Food Technologists' Expert Panel on Food Safety and Nutrition. 1983. Radiation preservationof Foods. A scientific status summary. Food Technol. 37(2): 55-60.

Abbreviations FAO = United Nations Food and Agriculture Organization WHO = World Health Organization IAEA = International Atomic Energy Agency FSIS = Food Safety and Inspection Service, USDA

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