Ask a Dietitian

There are many ways to preserve foods, such as freezing, drying, and preservatives. A more modern approach to food preservation is food irradiation. Food irradiation is the process of exposing food to ionizing radiation. Not only does irradiation preserve food by killing harmful bacteria, molds, yeast and insects that could cause spoilage, it also prevents food poisoning by killing disease-inducing bacteria and parasites. Ripening and sprouting in vegetables and fruits is also slowed, prolonging shelf life.

There are three types of radiation allowed: Gamma rays, X-rays, and electron beams. Irradiated foods never become radioactive. Most of the energy just passes through the food, without leaving residue. Food doesn’t come in contact with a radioactive source, and upper limits on acceptable energy levels are quite strict. Not a lot of radiation is actually required to prevent spoilage. One kilogray, the unit for ionizing energy, is generally enough to increase shelf life. Food poisoning prevention requires more, using about 3 kGy to kill Salmonella bacteria. Higher levels are used to kill parasites and insects, while viruses cannot be killed by any acceptable dose of radiation for food. Doses vary with the type of food and the goal of the radiation, be it for storage or disease prevention. Like other methods, food irradiation does not work 100% of the time, so be on the lookout for the usual signs of food spoilage, such as a swollen tin can or mold. If a food looks, smells, or tastes bad, irradiation will not change that or make it less obvious, so there is no fear of being fooled into thinking an irradiated food is okay for consumption when it’s not.

Food irradiation has been approved since the 60’s for onions, potatoes, wheat, flour, whole wheat flour, and whole or ground spices and dehydrated seasonings. Health Canada has proposed adding more foods to this list, such as fresh and frozen ground beef, fresh and frozen poultry, prepackaged fresh, frozen, prepared and dried shrimp and prawns, and mangoes. Foods that have been irradiated have the international irradiation symbol on the package, as well as a written statement that the product has been irradiated. If the product is not packaged, there must be a sign with this information beside the food. Foods containing an irradiated ingredient that is more than 10% of the food must show in the list of ingredients that it has been irradiated.

Many people dislike the idea of consuming irradiated food. So far, the World Health Organization and the Food and Agriculture Organization of the United Nations have recognized food irradiation as a safe way to preserve food and prevent poisoning while maintaining nutritive value. Irradiation does contribute to minor changes in foods, however. Some minor chemical changes, similar to those from cooking, occur, and taste may be slightly altered. None of these changes appear have any adverse effects on human health. However, research is still under way, and it’s possible that irradiation does actually deplete certain vitamins. There is also concern that with the assumption that irradiating food makes it ‘safe’, normal safe food processing procedures may slip. Nevertheless, normal food hygiene procedures are still necessary.

Take Home Message: Food irradiation has been deemed acceptable by many organizations, both national and international. However, when buying irradiated food, you have to maintain your usual standards of preparation and safe storage to prevent spoilage and disease. If you are uncomfortable buying irradiated food, it is possible to avoid it by watching for the symbol on packages. There are many other ways of preserving food and preventing disease, if you prefer.