Food Irradiation

Andrew Ladd
March 9, 2011

Submitted as coursework for Physics 241, Stanford University, Winter 2011


Every year in the United States there are an estimated 76 million cases of foodborne illness. [1] The resultant 325,000 hospitalizations and 5,000 deaths places per year creates an annual economic burden of roughly $6.7 billion from bacterial infections alone. [1,2] Pathogenic bacteria such as Salmonella, Campylobacter, Escherichia coli, and Vibrio are common contaminants in food and frequent culprits of foodborne disease. [3] While irradiation has proven an effective means of preventing foodborne illness, it is infrequently used in the United States. Ten percent of herbs and spices and less than 0.002 percent of meat, poultry, fruit, and vegetables are irradiated before being sold. [1]

Irradiation is based on a similar principle as pasteurization, a technique used on 99 percent of fresh milk in the United States to minimize the risk of foodborne disease. [2] In pasteurization, the amount of pathogens in a liquid is critically reduced through heating, all without altering the liquid. Irradiation achieves the same effect as pasteurization, killing pathogenic organisms present in the raw food using ionizing radiation. [1,2] Nonpathogenic organisms may survive, eventually causing the food to spoil but not posing a threat to human health. [1]

Gamma Irradiation Kills Pathogens

For the treatment of food, the United States Food and Drug Administration (FDA) permits the use of the following sources of ionizing radiation: X-rays up to 5 meV, electron beams under 10 meV, and gamma rays from the natural decay of cobalt-60 or cesium-137. [4] Both radionuclides are produced in commercial nuclear reactors. [2] Cobalt-60 and cesium-137 have half lives of 5.27 and 30.1 years respectively, appropriately long for commercial installation in food irradiation facilities. Cobalt-60 emits two gamma rays with energies of 1.17 and 1.33 MeV, whereas cesium-137 first beta decays to barium-137m, a metastable nuclear isomer that emits gamma rays with energy of 0.66 MeV. The FDA regulates three categories of radiation: less than 1 kGy is used to extend shelf life and disinfect food, 1-10 kGy is utilized for pasteurizing meat and poultry, and greater than 10 kGy is for sterilizing food products. [1]

The process of irradiation is simple. Radioactive pellets of cobalt-60 or cesium-137 are kept in water when the sources are not in use; the water absorbs all of the ionizing radiation. [4] To irradiate food, the radioactive source is removed from water and food is passed through its radiation field. As gamma rays are deeply penetrating, foods can even be treated in bulk on shipping pallets. [2] The high energy rays directly damage the DNA of living organisms on the food. Pathogens are either killed or their reproduction is inhibited, protecting consumers from potential illnesses. [2]

Misconceptions and Shortcomings of Irradiation

The negative connotations associated with radioactive materials and ionizing radiation can make food irradiation alarming to consumers. [5] The food industry is rather reluctant to more widely employ irradiation techniques in fear that consumers will not accept irradiated food. However, 80 to 90 percent of surveyed consumers, after being educated about irradiation and the dangers of foodborne pathogens, claimed to be comfortable buying irradiated food in the future. [2,4] Contrary to popular belief, irradiated food does not become radioactive, and the FDA has confirmed that the nutritional quality of irradiated food is not diminished. [5] While some insignificant changes to the quality of vitamins might occur during irradiation, consumers should note that traditional methods of cooking introduce substantial chemical changes to food. [2] In fact, differences in nutritional content after food irradiation are fewer than those caused by the commonly accepted techniques of pasteurization and canning. [2] It should be remembered that the electric generation of X-rays and electron beams may also be used to irradiate food, eliminating the concerns over the use of radioactive material. [1]

Although the aforementioned consumer concerns are erroneous or exaggerated, irradiation is certainly not a magic bullet for food safety. Within the limits imposed by the FDA, irradiation will not inactivate viruses, prions, or microbial toxins. Additionally, irradiation does not have a persistent effect; contamination after irradiation has been performed is a possibility. [3] In certain cases, irradiation has been known to discolor food and alter odors and flavors. Freezing food before irradiation usually solves these problems, but not all foods are amenable to freezing. [3] In fact, some foods are best not irradiated at all; a variety of fruits, vegetables, and dairy products experience a significant degradation of shelf life once irradiated, and irradiation wilts sprouts and leafy vegetables. [1,5]

© Andrew Ladd. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] M. Osterholm et al., "The Role of Irradiation in Food Safety," The New England Journal of Medicine 18, 1898 (2004).

[2] R. Tauxe, "Food Safety and Irradiation: Protecting the Public from Foodborne Infections," Emerging Infectious Diseases 7, 515 (2001).

[3] J. Farkas, "Irradiation as a Method for Decontaminating Food," International Journal of Food Microbiology 44, 189 (1998).

[4] D. Thayer et al., "Radiation Pasteurization of Food," Council for Agricultural Science and Technology 7, 1 (1996).

[5] M. Osterholm et al., "Iradiation Pasteurization of Solid Foods: Taking Food Safety to the Next Level," Emerging Infectious Diseases 3, 575 (1997).