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.

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.

  1. The medium in which microorganisms were irradiated was a factor in determining the correct dose of radiation for bacterial inactivation.
  2. Enzymes were more resistant to ionizing radiation than were bacteria.
  3. Irradiation in the frozen state minimized the development of off-flavor in milk and orange juice.

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 be provided through irradiation. However, early sensory evaluation of sterilized (1) irradiated meats described it as having a “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 in Natick, Massachusetts in 1962. The U.S. Army maintained its interest in high-dose irradiation sterilization of meat products. The responsibility for low-dose pasteurization (2) applications development was transferred to the AEC (Atomic Energy 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) was transferred to the U. S. Department of Agriculture (USDA). This agency assigned the responsibility to the Eastern Regional Research 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 food by 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 Energy Commission, industry, universities, and private institutions) including long-term animal feeding studies by 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 on Science and Health.

Regulations for Food Irradiation
The 1958 Food Additive Amendment to the Food, Drug and Cosmetics Act required advance approval from the Food and Drug Administration (FDA) before any particular irradiated food could be sold publicly. At this time, irradiation was legally 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 and wheat flour, and for the inhibition of sprouting in potatoes. In 1983, the FDA approved sterilization of spices with ionizing radiation. Low-dose irradiation can also be used to inhibit sprouting of onions, garlic, and ginger, and to inhibit the ripening of bananas, avocados, mangoes, papayas, and guavas.

Regulatory Highlights — Food Irradiation*

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 they can be used. The U.S. Congress passed legislation, which President Eisenhower signed in 1958. This legislation is 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) approves several 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 Foods Committee.
1980 Joint FAO/IAEA/WHO Expert Committee on (safety/wholesomeness of ) Food Irradiation (JECFI) approves all irradiated 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 kGy and 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 foodborne pathogens. The regulation for irradiation of poultry products from the USDA Food Safety and Inspection Service requires 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 for red meat products to the FDA. A maximum level of 4.5 kGy is proposed for unfrozen red meat, and 7.5 kGy for frozen 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 on Science and Health.
** (1 kGy = 100 kilorads)

In 1985 and 1986, the USDA Food Safety and Inspection Service and the FDA approved the processing regulations for treatment 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 eliminate foodborne pathogens. The regulation for irradiation of poultry products from the USDA Food Safety and Inspection Service requires 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 for processing red meat products (beef, veal, and lamb) to the FDA. A maximum level of 4.5 kGy is proposed for unfrozen red meat, and 7.5 kGy for frozen red meat. Approval of radiation treatment for ground meat products (and other meat items) is expected 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 control of food irradiation (Food Production and Inspection Branch, Agriculture Canada, 1989). Previous to this time, food irradiation 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 are meaningful and specific.

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

To ensure that consumers have the information necessary to choose between irradiated and non-irradiated food, Canada’s food irradiation regulations state that: “Irradiated foods be clearly marked with the international symbol for irradiated foods, and carry a statement to the effect that the food has been irradiated.” When an irradiated food is used as an ingredient constituting 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 in many third world countries, specialized agencies of the United Nations became actively involved in international food irradiation research programs. The illustration, Food Irradiation Facilities Around the World (Loaharanu, 1989), depicts the 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 an average dose of 10 kGy (1 Mrad) [see  Glossary for definitions] or less is wholesome for humans and therefore should be approved without future testing. The table, Partial Listing of Some Countries and Foods Approved for Irradiation in 1988 or 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 Products
Argentina Potatoes, strawberries, onions, garlic
Belgium Potatoes, strawberries, onions, garlic, shallots, paprika, pepper, gum arabic, 78 spices
Bulgaria Potatoes, onions, garlic, grain, dry food concentrates, dried fruits, fresh fruits
Canada Potatoes, onions, wheat flour, poultry, cod and haddock fillets, spices and certain dried vegetables
Finland Spices, herbs, hospital meals
Chile Potatoes, papaya, wheat, chicken, onions, rice, fish products, spices
France Potatoes, onions, garlic, shallots, spices, dried fruits and vegetables
Germany Hospital meals
Israel Potatoes, onions, poultry, 36 spices, fresh fruits and vegetables
Czechoslovakia 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, garlic
South Africa Potatoes, onions, garlic, chicken, papaya, mangoes, strawberries, dried bananas, avocados, beans
Spain Potatoes, onions
Thailand 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, prepared meat products
U.K. Hospital meals
U.S.A. Wheat and wheat flour, potatoes, spices, pork, fresh fruits and vegetables
Yugoslavia Cereals, potatoes, onions, garlic, poultry, dried fruits and vegetables

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