Food irradiation is a process of treating a food to a specific dosage of ionizing radiation for a predefined length of time. This process slows or halts spoilage that is due to the growth of pathogens. Food irradiation is currently permitted by over 50 countries, and the volume of food treated is estimated to exceed 500,000 metric tons annually worldwide. Irradiated food is sold in regular stores, often in specially marked packages .
Radura Logo
The Radura logo, required by U.S. Food and Drug Administration regulations to show a food has been treated with ionizing radiation
By irradiating food, depending on the dose, some or all of the microorganisms, bacteria, viruses, and insects present are killed. This prolongs the shelf-life of the food in cases where pathogenic spoilage is the limiting factor. Some foods, e.g., herbs and spices, are irradiated at sufficient doses (five kilograys or more) to reduce the microbial counts by several orders of magnitude. Such ingredients do not carry spoilage or pathogen microorganisms into the final product. It has also been shown that irradiation can delay the ripening of fruits and the sprouting of vegetables.
Food irradiation using cobalt-60 is the preferred method by most processors. This is because the deep penetration of gamma rays allows for the treatment of entire industrial pallets or totes at once, which reduces the need for material handling. A pallet or tote is typically exposed for several minutes to several hours, depending on the dose. Radioactive material must be monitored and carefully stored to shield workers and the environment from its gamma rays. During operation this is achieved using concrete shields. With most designs the radioisotope can be lowered into a water-filled source storage pool to allow maintenance personnel to enter the radiation shield. In this mode the water in the pool absorbs the radiation.
X-ray irradiators are considered an alternative to isotope-based irradiation systems. X-rays are generated by colliding accelerated electrons with a dense material (the target), such as tantalum or tungsten, in a process known as bremsstrahlung-conversion. X-ray irradiators are scalable and have deep penetration comparable to Co-60, with the added benefit that the electronic source stops radiating when switched off. They also permit dose uniformity, but these systems generally have low energetic efficiency during the conversion of electron energy to photon radiation, so they require much more electrical energy than other systems. X-ray systems also rely on concrete shields to protect the environment and workers from radiation.
Irradiated food does not become radioactive, since the particles that transmit radiation are not themselves radioactive. Still, there is some controversy in the application of irradiation due to its novelty, the association with the nuclear industry, and the potential for the chemical changes to be different than the chemical changes due to heating food (since ionizing radiation produces a higher energy transfer per collision than conventional radiant heat).