Food Irradiation: The treatment of foods with ionizing radiation

Kim M. Morehouse, Ph.D., Research Chemist
U.S. Food and Drug Administration
Center for Food Safety and Applied Nutrition
Office of Premarket Approval

{As published in Food Testing & Analysis, June/July 1998 edition (Vol. 4, No. 3, Pages 9, 32, 35)}

Food irradiation is a means of food preservation that has been in development since the early part of the twentieth century. If applied properly, irradiation can be an effective way to reduce the incidence of foodborne disease and treat a variety of potential problems in our food supply. It is capable of improving the safety and quality of many foods, and extending their shelf-life. Irradiation, however, is not a cure-all process. It is not necessarily suitable for every food, and it cannot reverse spoilage that has already occurred.

Foods are treated with ionizing radiation to accomplish many different goals. This food processing technology can improve the safety of food through the reduction of pathogenic bacteria and other microorganisms and parasites that cause foodborne diseases. Irradiation also inactivates food spoilage organisms, including bacteria, molds, and yeasts. It can be effective in lengthening the shelf-life of fresh fruits and vegetables by decreasing the normal biological changes associated with growth and maturation processes, such as ripening or sprouting.

During the irradiation process, food is exposed to the ionizing energy source in such a way that a precise and specific dose is absorbed. In food irradiation, the dose is the amount of radiation absorbed by the food. It is not the same as the level of energy transmitted from the radiation source. The absorbed dose is controlled by the intensity of the radiation source and the length of time the food is exposed. The SI unit used to describe the dose, or amount of absorbed radiation, is the gray (Gy). One gray is defined as one joule of absorbed energy per kilogram.

In practice, the dose used varies according to the type of food and the desired effect. Treatment levels can be grouped into three general categories:

• "Low" dose, up to 1 kGy, is used to delay physiological processes, such as, ripening or sprouting of fresh fruits and vegetables, and to control insects and parasites in foods.

• "Medium" dose, 1-10 kGy, is used to reduce spoilage and pathogenic microorganisms on various foods, to improve technological properties of food, such as reduce cooking times for dehydrated vegetables, and to extend the shelf-life of many foods.

• "High" dose, greater than 10 kGy, is used for the sterilization of meat, poultry, seafood, and other prepared foods in combination with mild heating to inactivate enzymes, and for the disinfection of certain foods or ingredients, such as spices and enzyme preparations.

The amount of radiation listed for these categories is approximate, and in some cases, a lower or higher dose may be suitable to achieve the desired effect. The foods that have current approval by the U.S. Food and Drug Administration (FDA) to be treated with ionizing radiation are provided in Table I.