Food irradiation
Food irradiation is the process of exposing food and food packaging to ionizing radiation, such as from gamma rays, x-rays, or electron beams. Food irradiation improves food safety and extends product shelf life by effectively destroying organisms responsible for spoilage and foodborne illness, inhibits sprouting or ripening, and is a means of controlling insects and invasive pests.
In the United States, consumer perception of foods treated with irradiation is more negative than those processed by other means. The U.S. Food and Drug Administration, the World Health Organization, the Centers for Disease Control and Prevention, and U.S. Department of Agriculture have performed studies that confirm irradiation to be safe. In order for a food to be irradiated in the U.S., the FDA will still require that the specific food be thoroughly tested for irradiation safety.
Food irradiation is permitted in over 60 countries, and about 500,000 metric tons of food are processed annually worldwide. The regulations for how food is to be irradiated, as well as the foods allowed to be irradiated, vary greatly from country to country. In Austria, Germany, and many other countries of the European Union only dried herbs, spices, and seasonings can be processed with irradiation and only at a specific dose, while in Brazil all foods are allowed at any dose.
Uses
Irradiation is used to reduce or eliminate pests and the risk of food-borne illnesses as well as prevent or slow spoilage and plant maturation or sprouting. Depending on the dose, some or all of the organisms, microorganisms, bacteria, and viruses present are destroyed, slowed, or rendered incapable of reproduction. When targeting bacteria, most foods are irradiated to significantly reduce the number of active microbes, not to sterilize all microbes in the product. Irradiation cannot return spoiled or over-ripe food to a fresh state. If this food was processed by irradiation, further spoilage would cease and ripening would slow, yet the irradiation would not destroy the toxins or repair the texture, color, or taste of the food.Irradiation slows the speed at which enzymes change the food. By reducing or removing spoilage organisms and slowing ripening and sprouting irradiation is used to reduce the amount of food that goes bad between harvest and final use. Shelf-stable products are created by irradiating foods in sealed packages, as irradiation reduces chance of spoilage, the packaging prevents re-contamination of the final product. Foods that can tolerate the higher doses of radiation required to do so can be sterilized. This is useful for people at high risk of infection in hospitals as well as situations where proper food storage is not feasible, such as rations for astronauts.
Pests such as insects have been transported to new habitats through the trade in fresh produce and significantly affected agricultural production and the environment once they established themselves. To reduce this threat and enable trade across quarantine boundaries, food is irradiated using a technique called phytosanitary irradiation. Phytosanitary irradiation sterilizes the pests preventing breeding by treating the produce with low doses of irradiation. The higher doses required to destroy pests are not used due to either affecting the look or taste, or cannot be tolerated by fresh produce.
Process
The target material is exposed an external source of radiation. The radiation source supplies energetic particles or electromagnetic waves. These particles or waves collide with material in the target. The higher the likelihood of these collisions over a distance are, the lower the penetration depth of the irradiation process is as the energy is more quickly depleted.These collisions break chemical bonds, creating short lived radicals. These radicals cause further [|chemical changes] by bonding with and or stripping particles from nearby molecules. When collisions occur in cells, cell division is often suppressed, halting or slowing the processes that cause the food to mature.
When the process damages DNA or RNA, effective reproduction becomes unlikely halting the population growth of viruses and organisms. The distribution of the dose of radiation varies from the food surface and the interior as it is absorbed as it moves through food and depends on the energy and density of the food and the type of radiation used.
Better quality
Irradiation leaves a product with qualities that are more similar to unprocessed food than any preservation method that can achieve a similar degree of preservation.Not radioactive
Irradiated food does not become radioactive; only particle energies that are incapable of causing significant induced radioactivity are used for food irradiation. In the United States this limit is 4 mega electron volts for electron beams and x-ray sources—cobalt-60 or caesium-137 sources are never energetic enough to induce radioactivity. Particles below this energy can never be energetic enough to modify the nucleus of the targeted atom in the food, regardless of how many particles hit the target material, and so radioactivity can not be induced.Dosimetry
The radiation absorbed dose is the amount energy absorbed per unit weight of the target material. Dose is used because, when the same substance is given the same dose, similar changes are observed in the target material. Dosimeters are used to measure dose, and are small components that, when exposed to ionizing radiation, change measurable physical attributes to a degree that can be correlated to the dose received. Measuring dose involves exposing one or more dosimeters along with the target material.For purposes of legislation doses are divided into low, medium, and high-dose applications. High-dose applications are above those currently permitted in the US for commercial food items by the FDA and other regulators around the world, though these doses are approved for non commercial applications, such as sterilizing frozen meat for NASA astronauts and food for hospital patients.
The ratio of the maximum dose permitted at the outer edge to the minimum limit to achieve processing conditions determines the uniformity of dose distribution. This ratio determines how uniform the irradiation process is.
| Application | Dose | |
| Low dose | Inhibit sprouting | 0.06 - 0.2 |
| Low dose | Delay in ripening | 0.5 - 1.0 |
| Low dose | Prevent insect infestation | 0.15 - 1.0 |
| Low dose | Parasite control and inactivation | 0.3 - 1.0 |
| Medium dose | Extend shelf-life of raw and fresh fish, seafood, fresh produce | 1.0 - 5.5 |
| Medium dose | Extend shelf-life of refrigerated and frozen meat products | 4.5 - 7.0 |
| Medium dose | Reduce risk of pathogenic and spoilage microbes | 1.0 - 7.0 |
| Medium dose | Increased juice yield, reduction in cooking time of dried vegetables | 3.0 - 7.0 |
| High dose | Enzymes | 10.0 |
| High dose | Sterilization of spices, dry vegetable seasonings | 30.0 max |
| High dose | Sterilization of packaging material | 10.0 - 25.0 |
| High dose | Sterilization of foods | 44.0 |
Chemical changes
As ionising radiation passes through food, it creates a trail of chemical transformations due to radiolysis effects. Irradiation does not make foods radioactive, change food chemistry, compromise nutrient contents, or change the taste, texture, or appearance of food.Food quality
of food by ionizing radiation is a safe and efficient process for elimination of pathogenic bacteria. Ionizing radiation treatment can be applied to either raw materials or ready to eat foods, with some countries, like the United States, imposing limitations on its use.Assessed rigorously over several decades, irradiation in commercial amounts to treat food has no negative impact on the sensory qualities and nutrient content of foods.