Food irradiation preserves meat, produce, and seasonings with high-energy gamma rays to improve product safety and shelf life. Spices, seasonings, potatoes, fresh fruits and vegetables, and meats and poultry may be irradiated.
This method of preservation prevents growth of food poisoning bacteria, destroys parasite, and delays ripening of fruits and vegetables. Food irradiation could be used to reduce or replace chemical preservatives used in food. More than 40 years of research on food irradiation has established that foods exposed to low-levels or irradiations are safe and wholesome, and they retain high quality.
Further applications include sprout inhibition, delay of ripening, increase of juice yield, and improvement of re-hydration. Irradiation is a more general term of deliberate exposure of materials to radiation to achieve a technical goal (in this context 'ionizing radiation' is implied). As such it is also used on non-food items, such as medical hardware, plastics, tubes for gas-pipelines, hoses for floor-heating, shrink-foils for food packaging, automobile parts, wires and cables (isolation), tires, and even gemstones. Compared to the amount of food irradiated, the volume of those every-day applications is huge but not noticed by the consumer.
The genuine effect of processing food by ionizing radiation relates to damages to the DNA, the basic genetic information for life. Microorganisms can no longer proliferate and continue their malignant or pathogen activities. Spoilage causing microorganisms cannot continue their activities. Insects do not survive or become incapable of proliferation. Plants cannot continue the natural ripening or aging process. All these effects are beneficial to the consumer and the food industry, likewise.
It should be noted that the amount of energy imparted for effective food irradiation is low compared to cooking the same; even at a typical dose of 10 kGy most food, which is (with regard to warming) physically equivalent to water, would warm by only about 2.5 °C.
The specialty of processing food by ionizing radiation is the fact, that the energy density per atomic transition is very high; it can cleave molecules and induce ionization (hence the name), which cannot be achieved by mere heating. This is the reason for new beneficial effects, however at the same time, for new concerns. The treatment of solid food by ionizing radiation can provide an effect similar to heat pasteurization of liquids, such as milk. However, the use of the term, cold pasteurization, to describe irradiated foods is controversial, because pasteurization and irradiation are fundamentally different processes, although the intended end results can in some cases be similar.
Food irradiation is currently permitted by over 40 countries and volumes are estimated to exceed 500 000 metric tons annually worldwide.
Nutritious Value and Safety of Irradiated Foods
Irradiated foods are wholesome and nutritious. All known methods of food processing and even storing food at room temperature for a few hours after harvesting can lower the content of some nutrients, such as vitamins. At low doses of radiation, nutrient losses are either not measurable or, if they can be measured, are not significant. At the higher doses used to extend shelf-life or control harmful bacteria, nutritional losses are less than or about the same as cooking and freezing.
Radioactivity in foods can occur by two routes: contamination of foods with radioactive substances or by penetration of energy into the nuclei of the atoms that make up the food.
The irradiation process involves passing food through an irradiation field; however, the food itself never contacts a radioactive substance. Also, the ionizing radiation used by irradiators is not strong enough to disintegrate the nucleus of even one atom of a food molecule.
Irradiation, at the levels normally used in food processing, destroys most, but not necessarily every single microorganism present; it does not sterilize the food.
As with any food, consumers must take appropriate precautions, such as refrigeration and proper handling and cooking, to make sure that potentially harmful organisms do not present a problem.
After treatment, the surviving disease-causing and food spoilage organisms may start to multiply again if the food is not properly handled. The disease-causing organisms in irradiated food are just as dangerous, but not more so, as the same organisms in non-irradiated food.
One concern has been that irradiation does not kill the bacteria that causes botulism. However, studies also have shown that in both irradiated and non-irradiated food, spoilage organisms will grow and alert consumers to spoilage before botulism-causing bacteria can produce toxin.
Federal government and other scientists reviewed several hundred studies on the effects of food irradiation before reaching conclusions about the general safety of the treatment. In order to make recommendations specifically about poultry irradiation, U.S. Food and Drug Administration scientists reviewed findings form additional relevant studies.
Independent scientific committees in Denmark, Sweden, United Kingdom and Canada also have reaffirmed the safety of food irradiation. In addition, food irradiation has received official international endorsement from the World Health Organizations and the International Atomic Energy Agency.
Chemical Changes in Irradiated Foods
Yes, irradiation does produce chemical changes in foods. These substances, called "radio-lytic products", may sound mysterious, but they are not. Scientists in making safety assessments of irradiated foods have scrutinized them. Any kind of treatment causes chemical changes in food. For instance, heat treatment, or cooking, produces chemicals that could be called "thermolytic products." Scientists find the changes in food created by irradiation minor to those created by cooking. The products created by cooking are so significant that consumers can smell and taste them, whereas only a chemist with extremely sensitive lab equipment may be able to detect radio lytic products.
Irradiated Technology in Application
By irradiating food, depending on the dose, some or all of the harmful bacteria and other pathogens present are killed. This prolongs the shelf life of the food in cases where microbial spoilage is the limiting factor. Some foods (e.g., herbs and spices) are irradiated at sufficient doses (five kilo grays or more) to reduce the microbial counts by several orders of magnitude; such ingredients will not carry over spoilage or pathogen microorganisms into the final product. It has also been shown that irradiation can delay the ripening of fruits or the sprouting of vegetables.
Furthermore, insect pests can be sterilized using irradiation at relatively low doses. In consequence, the United States Department of Agriculture has approved the use of low-level irradiation as an alternative treatment to pesticides for fruits and vegetables that are considered hosts to a number of insect pests, including fruit flies and seed weevils; US FDA has cleared among a number of other applications the treatment of hamburger patties to eliminate the residual risk of a contamination by a virulent E. coli.
Besides the benefits irradiating foods, the technology is used on cancer treatment and many other purposes, including: performing security checks on hand luggage at airports, making tires more durable, sterilizing manure for gardens, making non-stick cookware coatings, purifying wool, sterilizing medical products like surgical gloves And destroying bacteria in cosmetics.
Also, concerns regarding living in proximity to an irradiator should not be alarmed. The use and transportation of radioactive materials, including the facilities in which they are used and the equipment in those facilities, is closely monitored by the Nuclear Regulatory Commission, state agencies and the Department of Transportation.
The radioactive material itself is sealed within two layers of metal that prevent corrosion and oxidation. When shipped, it is placed within brick layers of lead that prevent gamma rays from escaping.
Facilities include many safety features to prevent both environmental and worker exposure. For example, when radioactive cobalt is in the storage position in an irradiator, it is under water and otherwise shielded. The irradiator is operated by remote control, and many other protections are required to prevent workers form entering the irradiation enclosure.
Requirements to perform Food Irradiation
Two things are needed for the irradiation process
A source of radiant energy, and
A way to confine that energy. For food irradiation, the sources are radioisotopes (radioactive materials) and machines that produce high-energy beams.
Specially constructed containers or compartments are used to confine the beams so personnel won't be exposed. Radioisotopes are used in medical research and therapy in many hospitals and universities. They require careful handling, tracking, and disposal. Machines that produce high-energy beams offer greater flexibility. For example, they can be turned on and off unlike the constant emission of gamma rays from radioisotopes.
Irradiation is a cold process. It does not significantly increase the temperature or change the physical or sensory characteristics of most foods. An irradiated apple, for example, will still be crisp and juicy. Fresh or frozen meat can be irradiated without cooking it. During irradiation, the energy waves affect unwanted organisms but are not retained in the food. Similarly, food cooked in a microwave oven, or teeth and bones that have been X-rayed do not retain those energy waves.
Major Application Areas
However, irradiation cannot be used with all foods. It causes undesirable flavor changes in dairy products, for example, and it causes tissue softening in some fruits, such as peaches and nectarines.
Irradiation is most useful in four areas.
Irradiation can be used to destroy or inactivate organ-isms that cause spoilage and decomposition, thereby extending the shelf life of foods. It is an energy-efficient food preservation method that has several advantages over traditional canning. The resulting products are closer to the fresh state in texture, flavor, and color. Using irradiation to preserve foods requires no additional liquid, nor does it cause the loss of natural juices. Both large and small containers can be used and food can be irradiated after being packaged or frozen.
Foods that are sterilized by irradiation can be stored for years without refrigeration just like canned (heat sterilized) foods. With irradiation it will be possible to develop new shelf-stable products. Sterilized food is useful in hospitals for patients with severely impaired immune systems, such as some patients with cancer or AIDS. These foods can be used by the military and for space flights.
Control sprouting, ripening, and insect damage
In this role, irradiation offers an alternative to chemi-cals for use with potatoes, tropical and citrus fruits, grains, spices, and seasonings. However, since no residue is left in the food, irradiation does not protect against reinfestation like insect sprays and fumigants do.
Control food borne illness
Irradiation can be used to effectively eliminate those pathogens that cause food borne illness, such as Salmonella.
All methods used to process and preserve foods have benefits and limitations.
Opponents of irradiation worry that these radiolytic products are hazardous. Biochemical and biomedical tests have not been able to identify any health problems or ill effects associated with tested radiolytic compounds.
Electron irradiation uses electrons accelerated in an electric field to a velocity close to the speed of light. Electrons are particulate radiation and have cross section many times larger than photons, so that they do not penetrate the product beyond a few inches depending on product density. Electron facilities rely on substantial concrete shields to protect workers and the environment from radiation exposure.
Gamma radiation is radiation of photons in the gamma part of the spectrum. The radiation is obtained through the use of radioisotopes, generally Cobalt-60 or, in theory, Cesium-137. Cesium-137 is recovered during the refinement of spent nuclear fuel. Because this technology - except for military applications - is not commercially available, insufficient quantities of it are available on the global isotope markets for use in large scale, commercial irradiators. Presently, Cesium-137 is used only in small hospital units to treat blood before transfusion to prevent Graft-versus-host disease.
Food irradiation using Cobalt-60 is the preferred method by most processors, because the better penetration enables administering treatment to entire industrial pallets or totes, reducing the need for material handling. A pallet or tote is typically exposed for several minutes depending on dose. Radioactive material must be monitored and carefully stored to shield workers and the environment from its gamma rays. During operation substantial concrete shields achieve this. 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. Other uncommonly used designs feature dry storage by providing movable shields that reduce radiation levels in areas of the irradiation chamber.
Similar to gamma radiation, X-rays are photon radiation of a wide energy spectrum and an alternative to isotope based irradiation systems. Colliding accelerated electrons generate X-rays with a dense material (target) such as Tantalum or Tungsten in a process known as bremsstrahlung-conversion. X-ray irradiators are scalable and have good penetration, with the added benefit of using an electronic source that stops radiating when switched off. They also permit very good dose uniformity. However, these systems generally have low energetic efficiency during the conversion of electron energy to photon radiation requiring much more electrical energy than other systems and longer exposure times than those required by gamma rays or electron beams.
Irradiated Foods in the Market Today
Some foods, particularly fruits and vegetables, are naturally restricted from sale on the global market, unless they are irradiated to prolong quality for transportation. Less spoilage at the receiving end means fewer discards, lowering the unit cost. Irradiation has also been used to reduce bacteria counts in seafood that is shipped over long distances. Because irradiation can reduce or even eliminate pest infestations, it has opened the markets for previously prohibited items, such as mangoes from India that otherwise have a risk of carrying certain insects and pathogens with them into the importing country. On Hawaii a dedicated irradiator serves for insect disinfestations before transfer to mainland USA, and a second facility is under construction. Insect pests can have a devastating effect on crop production. They can also transmit diseases that destroy crops and kill livestock and people. Heavy reliance on pesticides raises environmental concerns and problems of pest adaptation and resistance. As a result, many countries are seeking to minimize insecticide use through irradiation techniques.
Such benefits are offset by the cost of this rather capital intensive technology. The actual cost of food irradiation is influenced by dose requirements, the food's tolerance of radiation, handling conditions (i.e., packaging and stacking requirements), construction costs, financing arrangements, and other variables particular to the situation. Irradiation is a capital-intensive technology requiring a substantial initial investment, ranging from $1 million to $5 million.
Until recently, only irradiated dried spices and enzymes were marketed in the United States. In January 1992, irradiated Florida strawberries were sold at a North Miami supermarket. Sales of irradiated products are ongoing in several grocery stores. Poultry irradiation began commercially in 1993.
Irradiation of food has been approved in 37 countries for more than 40 products. The largest marketers of irradiated food are Belgium and France (each country irradiates about 10,000 tons of food per year), and the Netherlands (which irradiates bout 20,000 tons per year).
Irradiated food cannot be recognized by sight, smell, taste, or feel. Irradiated foods will be labeled with a logo, along with the words "Treated with Radiation", or "Treated by Irradiation."
Irradiation can be compared to Pasteurization
As in the heat pasteurization of milk, the irradiation process greatly reduces but does not eliminate all bacteria. Irradiated poultry, for example, still requires refrigeration, but would be safe longer than untreated poultry. Strawberries that have been irradiated will last two to three weeks in the refrigerator compared to only a few days for untreated berries.
Type of Irradiated Food and Its Effects
Irradiation has been approved for many uses in about 36 countries, but only a few applications are presently used because of consumer concern and because the facilities are expensive to build. In the United States, the Food and Drug Administration (FDA) has approved irradiation for eliminating insects from wheat, potatoes, flour, spices, tea, fruits And vegetables. Irradiation also can be used to control sprouting and ripening. Approval was given in 1985 to use irradiation on pork to control trichinosis. Using irradiation to control Salmonella and other harmful bacteria in chicken, turkey, and other fresh and frozen uncooked poultry was approved in May 1990.
|Type of food
|Effect of Irradiation
Destroys pathogenic fish organisms, such as Salmonella, Campylobacter and Trichinae
|Delays spoilage; retards mold growth; reduces number of microorganisms
|Controls insect vegetables, infestation dehydrated fruit, spices and seasonings
Onions, carrots, potatoes, garlic, ginger
Bananas, mangos,papayas, guavas, other non-citrus fruits
Delays ripening avocados, natural juices.
Reduces rehydration time