Food irradiation: Irradiation of foodstuffs

The foods are not changed in nutritional value and they are not made dangerous as a result of the irradiation. The high energy ray is absorbed as it passes through food, and gives up its energy.


The food is slightly warmed. Some treated foods may taste slightly different, just as pasteurized milk tastes slightly different from unpasteurized milk. If the food still has living cells, (such as seeds, or shellfish, or potatoes) they will be damaged or killed just as microbes are. This can be a useful effect. For example, it can be used to prolong the shelf life of potatoes by keeping them from sprouting. The energy can induce a few other changes. At levels approved for use on foods, levels of the vitamin thiamine are slightly reduced. This reduction is not enough to result in vitamin deficiency. There are no other significant changes in the amino acid, fatty acid, or vitamin content of food. In fact, the changes induced by irradiation are so minimal that it is not easy to determine whether or not a food has been irradiated.

Irradiated foods need to be stored, handled and cooked in the same way as unirradiated foods. They could still become contaminated with germs during processing after irradiation, if the rules of basic food safety are not followed. Because the irradiated foods have fewer microbes of all sorts, including those that cause spoilage, they may have a longer shelf life before spoiling.

The safety of irradiated foods has been studied by feeding them to animals and to people. These extensive studies include animal feeding studies lasting for several generations in several different species, including mice, rats, and dogs. There is no evidence of adverse health effects in these well-controlled trials. In addition, NASA astronauts eat foods that have been irradiated to the point of sterilization (substantially higher levels of treatment than that approved for general use) when they fly in space. The safety of irradiated foods has been endorsed by the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC) and by the Assistant Secretary of Health, as well as by the U.S. Department of Agriculture (USDA)and the Food and Drug Administration (FDA).

When microbes present in the food are irradiated, the energy from the rays is transferred to the water and other molecules in the microbe. The energy creates transient reactive chemicals that damage the DNA in the microbe, causing defects in the genetic instructions. Unless it can repair this damage, the microbe will die when it grows and tries to duplicate itself. Disease-causing organisms differ in their sensitivity to irradiation, depending on the size of their DNA, the rate at which they can repair damaged DNA, and other factors. It matters if the food is frozen or fresh, as it takes a higher dose to kill microbes in frozen foods.

The size of the DNA "target" in the organism is a major factor. Parasites and insect pests, which have large amounts of DNA, are rapidly killed by extremely low doses of irradiation, with D-values of 0.1 kiloGray or less. It takes more irradiation to kill bacteria, because they have a somewhat smaller DNA, with D-values in the range of 0.3 to 0.7 kiloGray. Some bacteria can form dense hardy spores, which means they enter a compact and inert hibernation state. It takes more irradiation to kill a bacterial spore, with D-values on the order of 2.8 kiloGray. Viruses are the smallest pathogens with that have nucleic acid, and they are in general resistant to irradiation at doses approved for foods. This means that they may have D-values of 10 kG or higher. The prion particles associated with bovine spongiform encephalopathy (BSE, also known as mad cow disease) do not have nucleic acid at all, and so they are not inactivated by irradiation, except at extremely high doses. This means that irradiation will work very well to eliminate parasites and bacteria from food, but will not work to eliminate viruses or prions from food.

At low doses, irradiation could be used on a wide variety of foods to eliminate insect pests, as a replacement for fumigation with toxic chemicals that is routine for many foods now. It can also inhibit the growth of molds, inhibit sprouting, and prolong the shelf life.

At higher doses, irradiation could be used on a variety of different foods to eliminate parasites and bacteria that cause foodborne disease. Many foods can be irradiated effectively, including meat, poultry, grains, and many seafoods, fruits and vegetables. It is likely to have greatest application for raw foods of animal origin that are made by mixing materials from many animals together, such as ground meat or sausage.

However, not all foods are suitable for irradiation. For example, oysters and other raw shellfish can be irradiated, but the shelf life and quality decreases markedly because the live oyster inside the shell is also damaged or killed by the irradiation. Shell eggs can sometimes be contaminated on the insides with Salmonella. However, irradiation causes the egg whites to become milky and more liquid, which means it looks like an older egg, and may not serve as well in some recipes. Alfalfa seeds used in making alfalfa sprouts can sometimes be contaminated with Salmonella.

Using irradiation to eliminate Salmonella from the seeds may require a dose of irradiation that also interferes with the viability of the seeds themselves. Combining irradiation with other strategies to reduce contamination with germs may overcome these limitations.



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