Food irradiation involves exposing food products to a radiant energy source such as gamma rays, x-rays, or electron beams within a shielded facility. Food irradiation is a process applied to certain foods chiefly to obtain the following results:
- Reduce disease-causing microbes and food-borne pathogens, such as salmonella;
- Extend food shelf life;
- Avoid the use of insecticides that may involve risk to human health;
- Prevent post-harvest losses by inhibiting sprouting in root, tuber, and bulb crops; and
- Provide a briefer quarantine treatment of imported food that allows shipment of riper, more valuable fruits.
The result is similar to conventional pasteurization and is often called "cold pasteurization" or "irradiation pasteurization". Like pasteurization, irradiation kills bacteria and other pathogens that could otherwise result in spoilage or food poisoning. The fundamental difference between the two methods is the source of the energy relied upon to destroy the microbes. While conventional pasteurization relies on heat, irradiation relies on the energy of ionizing radiation. Consumers should note that the preservation method is a substitute for safe food handling procedures.
The food irradiation process
The process exposes food to gamma rays from radioactive cobalt-60, or electron beams and x-rays from accelerator machines. During the process, prepackaged food is moved by conveyor into a thick-walled room housing the irradiator—pencil-like rods of cobalt-60. The food is exposed to the radioactive material for 15 to 45 minutes, depending on the food. The fact that food is prepackaged eliminates the possibility that bacteria could be introduced after being irradiated. When the process is completed, the rods of cobalt-60 are retracted into a pool of water, which acts as a radiation barrier. The cobalt-60 and electron-beam processes both use ionizing radiation to kill bacteria in food. The same process has been used to sterilize medical devices, bandages, condoms, tampons, contact lens solutions and food for astronauts.
The amount of radiation energy used or needed for a particular application varies depending on the food and the reason for irradiating. Typically, to increase shelf life or to prevent spoilage a low dose of irradiation is required, only one kilogray (kGy) of absorbed energy. To prevent food poisoning, the dose will depend on the type of bacteria being targeted and the type of food. An absorbed dose of up to 3 kGy is usually sufficient to kill Salmonella in fresh chicken. Generally, it takes higher levels of radiation to kill parasites and insects. Viruses, for the most part, are not destroyed by the irradiation levels that are suitable for use in foods.
Safety and health issues
Irradiated food never contacts any radiation sources, so it never has the opportunity to become radioactive. If a radioactive source is used, it is contained in a dense metal apparatus (or in the case of a cobalt-60 irradiator, stainless steel tubes) that allows the radiation to be emitted in a controlled manner, similar to a lightbulb. If high-energy electrons or x-rays are used, all radiation is generated electrically and there is no radiation or radioactivity at all when the process is switched off. When the radiation is “on” (just as when the lightbulb is on) food passes through the radiation field (the area illuminated by the bulb) and is treated or irradiated. When the radiation beam is turned off (just as when lightbulb is off) the irradiation stops. This radiation cannot cause food to become radioactive, just as a dental x-ray does not cause a person to become radioactive.
Food irradiation has been studied more than any other food preservation process. Comparisons of the nutritional value of irradiated food with nonirradiated food reveal little difference. Processing food by traditional means, such as cooking or canning, causes chemical changes within the food. Radiation can also cause some minor chemical changes within the food. Food that is irradiated at regulated doses may lose some nutritional value, including vitamins, but the loss is not considered significant in terms of the entire diet. The food-irradiation process can be tailored to give the proper amount of radiation to each kind of food to obtain the desired pathogen reduction while maintaining nutritional value. No studies to date have shown that consuming irradiated food is harmful to humans. In short, food irradiation is safe and, by killing dangerous microbes, it makes the food supply much safer than use of nonirradiated foods. Irradiation kills E. coli and salmonella (two of the more common bacteria in meat) at least 99% of the time.
Irradiated foods should still be handled and prepared like nonirradiated foods. For instance, ground beef should be prepared and cooked to the recommended temperature of 160 degrees Fahrenheit. After cooking, follow standard procedures for refrigerating leftovers. Microbes are greatly reduced with irradiation but food can still be infected during storage and preparation.
Food irradiators utilizing radiation sources or high-energy x-rays and electron beams are strictly regulated by federal and/or state licensing agencies that provide health and safety guidelines for employees and the general public. In the U.S., products currently approved for irradiation by the Food and Drug Administration are the following (with the purpose for irradiation in parentheses):
- Wheat and wheat flour (disinfestation of insects)
- White potatoes (inhibit sprouting and extend shelf life)
- Spices, herbs, and dry vegetable seasonings (disinfestation of insects and decontamination)
- Pork carcasses or fresh, nonheat-processed cuts (control of Trichinella spiralis and/or microorganisms)
- Fruit (delay of maturation and disinfestation of insects)
- Fresh vegetables (disinfestation of insects)
- Fresh or frozen poultry (control of microorganisms, particularly salmonella)
- Fresh, frozen, or chilled red meat (control of E. coli and salmonella)
- Animal and pet food (control of salmonella)
Nutritional Quality of Irradiated Foods
Irradiation does effect on the nutritional attributes of food, but so too do other forms of food treatment and preparation, such as heating an freezing. According the U.S. Center for Disease Control, "An overwhelming body of scientific evidence demonstrates that irradiation does not harm the nutritional value of food, nor does it make the food unsafe to eat. Just as for the pasteurization of milk, it will be most effective when irradiation is coupled to careful sanitation programs. Consumer confidence will depend on making food clean first, and then using irradiation or pasteurization to make it safe."
Regulation of food irradiation
The 1958 Food Additives Amendment to the U.S.Federal Food, Drug, and Cosmetic Act defined ionizing radiation as a food additive, rather than a process, even though from a physics point of view nothing but energy is added. This Act mandates the Food and Drug Administration (FDA) to regulate food irradiation. As part of its approval, FDA requires that irradiated foods include labeling with either the statement "treated with radiation" or "treated by irradiation" and the international symbol for irradiation, the radura. Irradiation labeling requirements apply only to foods sold in stores. For example, irradiated spices or fresh strawberries should be labeled. When used as ingredients in other foods, however, the label of the other food does not need to describe these ingredients as irradiated. Irradiation labeling also does not apply to restaurant foods.
The green “radura” symbol is internationally recognized as an indication of irradiated food and is displayed on foods offered for sale to the public.
- Food Irradiation, U.S. Environmental Protection Agency.
- Consumer Attitudes Toward Food Irradiation, Conducted by Axiom Research Company for the International Food Information Council.
Disclaimer: This article contains information that was originally published by the Health Physics Society. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the Health Physics Society should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.