Food Irradiation

Food irradiation is a food safety technology that can eliminate disease-causing germs from foods. Like pasteurization of milk, and pressure-cooking of canned foods, treating food with ionizing radiation can kill bacteria that would otherwise cause food borne disease. The process can also control insects and parasites, reduce spoilage, and inhibit ripening and sprouting. (5) The effects of irradiation on the food and on animals and people eating irradiated food have been studied extensively. These studies show that when irradiation is used on foods, as approved, that disease-causing germs are reduced or eliminated. The food does not become radioactive, dangerous substances do not appear in the foods, and the nutrition al value of the food is essentially unchanged. (1)

Raw meat and poultry treated with irradiation could eliminate bacteria common for these foods, such as E. coli, Salmonella, and Campylobacter. Irradiating prepared, ready- to -eat meats such as hot dogs and deli meats, may eliminate the risk of Listeria. Additionally, Cyclosporine parasites and bacteria such as Shigella and Salmonella from fresh produce could be removed. There is also potential benefit for dry foods that are stored for long times and transported over great distances, like spices and grains. (1)

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 to control the radiation dose delivered to the food by controlling the exposure time. (2) About 170 industrial cobalt-60 irradiators and hundreds of electron accelerators , around the world, have been processing a variety of goods. (4)

Three different irradiation technologies exist, using different kinds of rays: gamma rays, electron beams, and x-rays.

Gamma rays can penetrate foods to a depth of several feet. Radioactive substances emit gamma rays all the time. Cobalt-60 emits gamma rays. When not in use, the radioactive "source" is stored in stainless steel capsules, in underwater tanks, which absorbs the radiation harmlessly and completely. (2) To irradiate food or some other products, the source is pulled up out of the water in to a chamber with massive concrete walls that keep and rays from escaping. Medical products or foods to be irradiated are brought into the chamber, and are exposed to the rays for a defined period of time. After it is used, the source is returned to the water tank. (1)

Electron beams are propelled out of an electron gun with streams of high-energy electrons. This electron gun is a larger version of the device in the back of a TV tube that propels electrons into the TV screen at the front of the tube, making it light up. No radioactivity is involved from this. Electron beams have a shallow depth of penetration only to a depth of about 3 cm or just over an inch. (1)

The newest technology is X-ray irradiation. The X-ray machine is a more powerful version of the machines used in many hospitals and dental offices to take X-ray pictures. 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 the gamma rays, X-rays are able to penetrate deeply and can be used on food boxes 15 inches thick or more. (2)

The dose of irradiation is usually measured in a unit called the Gray (Gy). This is a measure of the amount of energy transferred to food, microbe or other substance being irradiated. To kill Salmonella, fresh chicken can be irradiated at up to 4.5 kiloGrays, which is about 7 million times more irradiation than a single chest X-ray. The killing effect on microbes is measured in D-values. One D-value is the amount of irradiation needed to kill 90% of that organism. For example, it takes 0.3 kiloGrays to kill 90% of E. coli O157, so the D-value of E. coli is 0.3 kGy. (1)

Irradiation kills bacteria by the process of radiolysis. This process involves breaking chemical bonds, with radiation. 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. (2)

There is controversy by some people who argue the actual benefits of food irradiation. These arguments reveal that taste is sacrificed and food is damaged because of the breaking up of molecules and creating free radicals. The free radicals kill some bacteria, but they also bounce around in the food, damage vitamins and enzymes, and combine with existing chemicals (like pesticides) in the food to form new chemicals, called unique

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