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Food Irradiation
Food Irradiation
Food irradiation is a technology for controlling spoilage and eliminating food-borne pathogens, such as salmonella. 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 they rely on to destroy the microbes. While conventional pasteurization relies on heat, irradiation relies on the energy of ionizing radiation. The FDA emphasizes that no preservation method is a substitute for safe food handling procedures.
On this page :
- How is food irradiated?
- What are the sources of radiation used?
- Cobalt 60 Gamma Sources
- Electron Beam Facilities
- X-Ray Facilities
- What is the radiation dose to the food?
- How does irradiation kill bacteria?
- References
How is food irradiated?
Bulk or packaged food passes through a radiation chamber on a conveyor belt. The food does not come into contact with radioactive materials, but instead passes through a radiation beam, like a large flashlight.
The type of food and the specific purpose of the irradiation determine the amount of radiation, or dose, necessary to process a particular product. The speed of the belt helps control the radiation dose delivered to the food by controlling the exposure time. The actual dose is measured by dosimeters within the food containers.
Cobalt-60 is the most commonly used radionuclide for food irradiation. However, there are also large cesium-137 irradiators and the Army has also used spent fuel rods for irradiation.
What are the sources of radiation used?
The food irradiation process uses three types of ionizing radiation sources:
Cobalt 60 Gamma Sources
Cobalt-60 emits ionizing radiation in the form of intense gamma rays. "Gamma facilities" store it in stainless steel capsules (like "pencils" of cobalt), in underwater tanks. Cobalt-60 has several advantages:
- up to 95% of its emitted energy is available for use
- penetrates deeply
- yields substantial uniformity of the dose in the food product
- decays to non-radioactive nickel
- considered to pose low risk to the environment.
However, its 5.3-year half-life offers disadvantages:
- cobalt-60 "pencils" require frequent replenishment
- treatment of the food is relatively slow.
Cesium-137 is a gamma source that is also used for irradiation. Cesium-137 has a less penetrating gamma beam and a longer half-life, making it more suitable under certain circumstances.
Electron Beam Generators
Electron beam facilities generate e-beams with an electron beam linear accelerator. (It works on the same principle as a television tube.) The electrons are concentrated and accelerated to 99% of the speed of light and energies of up to 10 MeV.
Because e-beams are generated electrically, they offer certain advantages:
- they can be turned on only as needed
- they do not require replenishment of the source as does cobalt-60
- there is no radioactive waste
E-beam technology also has disadvantages:
- shallow depth of penetration
- e-beams must be converted to x-rays to penetrate large items such as carcasses
- high electric power consumption
- complexity, and potentially high maintenance
X-Ray Accelerators
X-ray facilities use an electron beam accelerator to target electrons on a metal plate. Although some energy is absorbed, the rest is converted to X-rays. Like gamma rays, X-rays are penetrating, and can be used on food boxes 15 inches thick or more. This allows food to be processed in a shipping container.
X-rays offer the advantage of high penetration, but share the other e-beam technology disadvantages.
What is the radiation dose to the food?
Radiation doses vary for different foodstuffs. For the vast majority of foods, the limit is less than 10 kiloGray. The U.S. Food and Drug Administration (FDA) sets radiation dose limits for specific food types:
| Food Type | Dose (kiloGrays) |
|---|---|
| fruit | 1 |
| poultry | 3 |
| spices, seasonings | 30 |
The dose limit for spices and seasons is higher, because they are consumed in very small quantities.
How does irradiation kill bacteria?
When ionizing radiation strikes bacteria and other microbes, its high energy breaks chemical bonds in molecules that are vital for cell growth and integrity. As a result, the microbes die, or can no longer multiply causing illness or spoilage.Breaking chemical bonds with radiation is known as radiolysis.
References
- Center for Consumer Research at the University of California-Davis
- Iowa State University Food Safety Research Project
