food irradiation food irradiation food irradiation (sometimes radurization or radurisation) 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 (preservation) by effectively destroying organisms responsible for spoilage and foodborne illness, inhibits sprouting or ripening, and is a means of controlling insects and invasive pests. cobalt-60 irradiation facility is used to test irradiation as a tool to ensure food safety. the international radura logo, used to show a food has been treated with ionizing radiation. a portable, trailer-mounted food irradiation machine, c. 1968 in the us, consumer perception of foods treated with irradiation is more negative than those processed by other means. the u.s. food and drug administration (fda), the world health organization (who), the centers for disease control and prevention (cdc), and u.s. department of agriculture (usda) have performed studies that confirm irradiation to be safe. in order for a food to be irradiated in the us, 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 (e.g. potato, onion, and garlic) 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 (less than 1000 gy). 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 efficiency illustration of the different radiation technologies (electron beam, x-ray, gamma rays) further information: irradiation, radiation chemistry, and induced radioactivity the target material is exposed to a radiation source that is separated from the target material. the radiation source supplies energetic particles or waves. as these waves/particles enter the target material they collide with other particles. 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. around the sites of these collisions chemical bonds are broken, creating short lived radicals (e.g. the hydroxyl radical, the hydrogen atom and solvated electrons). 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 (sensory and chemical) 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 power levels that are incapable of causing significant induced radioactivity are used for food irradiation. in the united states this limit is deemed to be 4 mega electron volts for electron beams and x-ray sources – cobalt-60 or caesium-137 sources are never energetic enough to be of concern. particles below this energy can never be strong 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(gy or j/kg). 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 (dosimetry) involves exposing one or more dosimeters along with the target material. for purposes of legislation doses are divided into low (up to 1 kgy), medium (1 kgy to 10 kgy), and high-dose applications (above 10 kgy). 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 (doses of 44 kgy) and food for hospital patients. the ratio of the maximum dose permitted at the outer edge (dmax) to the minimum limit to achieve processing conditions (dmin) determines the uniformity of dose distribution. this ratio determines how uniform the irradiation process is. applications of food irradiation application dose (kgy) low dose (up to 1 kgy) inhibit sprouting (potatoes, onions, yams, garlic) 0.06 - 0.2 delay in ripening (strawberries, potatoes) 0.5 - 1.0 prevent insect infestation (grains, cereals, coffee beans, spices, dried nuts, dried fruits, dried fish, mangoes, papayas) 0.15 - 1.0 parasite control and inactivation (tape worm, trichina) 0.3 - 1.0 medium dose (1 kgy to 10 kgy) extend shelf-life of raw and fresh fish, seafood, fresh produce 1.0 - 5.5 extend shelf-life of refrigerated and frozen meat products 4.5 - 7.0 reduce risk of pathogenic and spoilage microbes (meat, seafood, spices, and poultry) 1.0 - 7.0 increased juice yield, reduction in cooking time of dried vegetables 3.0 - 7.0 high dose (above 10 kgy) enzymes (dehydrated) 10.0 sterilization of spices, dry vegetable seasonings 30.0 max sterilization of packaging material 10.0 - 25.0 sterilization of foods (nasa and hospitals) 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 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. research on minimally processed vegetables watercress (nasturtium officinale) is a rapidly growing aquatic or semi aquatic perennial plant. because chemical agents do not provide efficient microbial reductions, watercress has been tested with gamma irradiation treatment in order to improve both safety and the shelf life of the product. it is traditionally used on horticultural products to prevent sprouting and post-packaging contamination, delay post-harvest ripening, maturation and senescence. public perceptions some who advocate against food irradiation argue the long term health effects and safety of irradiated food cannot be scientifically proven, however there have been hundreds of animal feeding studies of irradiated food performed since 1950 endpoints include subchronic and chronic changes in metabolism, histopathology, function of most organs, reproductive effects, growth, teratogenicity, and mutagenicity. industrial process up to the point where the food is processed by irradiation, the food is processed in the same way as all other food. packaging for some forms of treatment, packaging is used to ensure the food stuffs never come in contact with radioactive substances and prevent re-contamination of the final product. food processors and manufacturers today struggle with using affordable, efficient packaging materials for irradiation based processing. the implementation of irradiation on prepackaged foods has been found to impact foods by inducing specific chemical alterations to the food packaging material that migrates into the food. cross-linking in various plastics can lead to physical and chemical modifications that can increase the overall molecular weight. on the other hand, chain scission is fragmentation of polymer chains that leads to a molecular weight reduction. treatment to treat the food, it is exposed to a radioactive source for a set period of time to achieve a desired dose. radiation may be emitted by a radioactive substance, or by x-ray and electron beam accelerators. special precautions are taken to ensure the food stuffs never come in contact with the radioactive substances and that the personnel and the environment are protected from exposure radiation. irradiation treatments are typically classified by dose (high, medium, and low), but are sometimes classified by the effects of the treatment (radappertization, radicidation and radurization). food irradiation is sometimes referred to as "cold pasteurization" or "electronic pasteurization" because ionizing the food does not heat the food to high temperatures during the process, and the effect is similar to heat pasteurization. the term "cold pasteurization" is controversial because the term may be used to disguise the fact the food has been irradiated and pasteurization and irradiation are fundamentally different processes. gamma irradiation gamma irradiation is produced from the radioisotopes cobalt-60 and caesium-137, which are produced by neutron irradiation of cobalt-59 (the only stable isotope of cobalt) and as a nuclear fission product, respectively. cobalt-60 is the most common source of gamma rays for food irradiation in commercial scale facilities as it is water insoluble and hence has little risk of environmental contamination by leakage into the water systems. as for transportation of the radiation source, cobalt-60 is transported in special trucks that prevent release of radiation and meet standards mentioned in the regulations for safe transport of radioactive materials of the international atomic energy act. the special trucks must meet high safety standards and pass extensive tests to be approved to ship radiation sources. conversely, caesium-137, is water-soluble and poses a risk of environmental contamination. insufficient quantities are available for large scale commercial use as the vast majority of caesium-137 produced in nuclear reactors is not extracted from spent nuclear fuel. an incident where water-soluble caesium-137 leaked into the source storage pool requiring nrc intervention has led to near elimination of this radioisotope. cobalt-60 stored in gamma irradiation machine gamma irradiation is widely used due to its high penetration depth and dose uniformity, allowing for large-scale applications with high through puts. additionally, gamma irradiation is significantly less expensive than using an x-ray source. in most designs, the radioisotope, contained in stainless steel pencils, is stored in a water-filled storage pool which absorbs the radiation energy when not in use. for treatment, the source is lifted out of the storage tank, and product contained in totes is passed around the pencils to achieve required processing. treatment costs vary as a function of dose and facility usage. a pallet or tote is typically exposed for several minutes to hours depending on dose. low-dose applications such as disinfestation of fruit range between us$0.01/lbs and us$0.08/lbs