Food irradiation

Food irradiation is the process of exposing food to ionizing radiation in order to disinfest, sterilize, or preserve food. It is, like most technology involving ionizing radiation, the subject of some controversy regarding its safety. Irradiation is used on other things as well, such as medical hardware. Largely to avoid consumer fear of the term "radiation", it is often called cold pasteurization to emphasize its similarity to the process of pasteurization. Ie. treatment of solid food by ionizing radiation can provide an effect similar to heat pasteurization of liquid food as milk.

Food irradiation

By irradiating food, depending on the dose, some or all of the microbes and insects present are killed. This prolongs the life of the food in cases where microbial spoilage is the limiting factor in shelf life. Some foods (e.g., herbs and spices) are irradiated at such high doses (5 kilograys or more) that they are partially sterilized. It has also been shown that irradiation can delay the ripening or sprouting of fruits and vegetables and replace the need for pesticides. Irradiation may also create new chemicals in food that are unique to this process - chemicals that would not be created by cooking or other standard food processing techniques.

The United Nations Environmental Program passed the Montreal Protocol on Substances that deplete the Ozone Layer banning amongst other substances all non-critical uses of methyl bromide, the most common fumigant for post-harvest quarantine treatment of fruit. Although in theory still permitted for quarantine applications, prices of the fumigant have increased dramatically as a consequence. Some governments and corporations think that irradiation is a legitimate replacement for such fumigants and in consequence some large agricultural nations of the world are currently building irradiation facilities for fresh fruit, although the food industry has been slow to adopt this technology on any large scale.

The United States Department of Agriculture has approved irradiation technology as an alternative treatment for fruits and vegetables that are considered hosts to a number of fruit flies and seed weevils. The United Nations Food and Agricultural Organization (FAO) have passed a motion to support this step committing the member states to implement this technology for their national phytosanitary programs.

Processes

While the term irradiation pertains to all forms of treating food products with ionizing radiation, specific types of radiation treatments are used in the food industry today.

Radurization

Radurization is the process of pasteurization by the use of radiation. It primarily used to treat foods that have a high moisture content and a high pH. The microbes that are targeted are mainly spoilage organisms. Meat and fish are the foods for which this process is mainly used. For dryer, acidic foods, yeasts and molds can be denatured. The treatment dose for radurization is approximately 1 kGy.

Radicidation

The process of radicidation is used to eliminate pathogens. This process kills vegetative cells only, meaning that it will not kill spores. Also, certain radiation-resistant vegetative cells can survive, including some strains of the bacterium Salmonella which have been found to be radiation-resistant. Refrigeration is required for the product post-treatment. The dose for radicidation ranges from 2.5 - 5.0 kGy. At this level some physical and chemical changes may be detected, depending on the type of food. For example, leafy vegetables such as lettuce are more sensitive to irradiation than foods with a tougher consistency.

Radappertization

Radappertization involves treating the product to levels of radiation of approximately 30 kGy. This high level of radiation kills all vegetative cells and also destroys spores from organisms such as Clostridium botulinum. Such levels are generally deemed sufficient for clinical sterility, but not usually employed on food items. Based on recommendations of the International Consultative Group on Food Irradiation that was formed by the joint FAO/IAEA division many national legislation limit applicable doses to 10kGy for many food items.

Technologies

Electron beam irradiation

Electron beam irradiation uses electrons accelerated in an electric field to a velocity close to the speed of light. International and national regulations limit the energy of the beam to guarantee that no induced radioactivity occurs. Electrons have cross-sections many times larger than photons, so that they do not penetrate the product beyond a few inches, making it necessary to treat fruit and vegetables individually; on the other hand, treatment times are only a few seconds. Electron facilities rely on substantial concrete shields to protect workers and the environment from radiation exposure.

Gamma radiation

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 very few cases cesium 137. It is the most cost-effective technology and is preferred by many processors because the good penetration enables administering treatment to entire industrial pallets or totes, greatly reducing the need for material handling. A pallet or tote is typically exposed for several minutes depending on dose. The environment is protected by a large concrete shield. With most designs the radioisotope can be lowered into a water storage pool in order to allow maintenance personnel to enter the radiation shield. In this mode the water in the pool absorbs practically all radiation providing a safe working environment for plant personnel. Other not commonly used designs feature dry storage by providing movable shields that eliminate radiation levels in areas of the irradiation chamber.

One variant of gamma irradiators keeps the cobalt 60 under water at all times and lowers the product to be irradiated under water in hermetic bells. No shielding is required for such designs.

X-Ray irradiation

Similar to gamma radiation, x-rays are a substitute for the former. These systems 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 require a great deal of electrical energy when operating, and exposure times are longer than with gamma rays. Like most other types of facilities, X-Ray systems rely on concrete shields to protect the environment from radiation.

Public perception

The effects of food irradiation have been studied for over 60 years. Under certain circumstances some research suggests that irradiation forms new chemicals in food, some of which are uniquely radiolytic products. However, the levels of these compounds produced in irradiated foods have been deemed too low to present a meaningful risk to consumers. At very high doses, e.g. >6 kilogray, irradiation can reduce the vitamins and other essential nutrients; and negatively impact the flavor, odor and texture of food. At the doses typically used in irradiation treatment of food, e.g. <3.5 kilogray, these changes appear minimal. Independent scientific research on the subject has been extensive leading to endorsement of food irradiation by the US Food and Drug Administration, the United States Department of Agriculture and the U.N. World Health Organization as a safe, effective process.

Concerns have been expressed by public health groups that irradiation, by killing all bacteria in food, can serve to disguise poor food-handling procedures that could lead to other kinds of contamination. However, processors of irradiated food are subject to all existing regulations, inspections and potential penalties regarding plant safety and sanitization, including fines, recalls and criminal prosecutions.

Others are concerned with the safety of irradiation plants and accidents that have occurred previously. The three recorded accidents on file at the IAEA in the history of irradiation facilities in the world were suffered by individual employees who entered the radiation chamber, disabling all available safety measures.

Based on the intrinsic inability of the techniques used for food irradiation to induce radioactivity into the targets it is impossible for an irradiation facility to release radioactive material into the environment with the processed items. Any problems that might occur are therefore contained in the radiation zone of the installation. Radioactive sources used in irradiators are thermally hot, and the repeated cycling of the source in and out of the shielding pool can cause thermal shocks that may eventually cause breakage of the cladding around the radioactive materials. Although this risk has been eliminated by modern source configuration, this is not commonly a major problem as by far the most common isotope employed is cobalt 60 which is not water soluble making a clean-up relatively simple. An irradiator in the Atlanta, Georgia area, however, had to be closed after the storage pool became radioactive after a leak of the water-soluble Cesium 137 isotope sources. As a result, the US NRC has banned cesium 137 for in water storage. These concerns do not apply to electron beam, or x-ray irradiators or the most common cobalt 60 facilities, in which the radiation is gone as soon as the source is switched off or in the case of cobalt 60 stored in water.

Activist websites frequently quote the unknown cancer risk of radiolytic byproducts such as 2-dodecylcyclobutanone or 2DCB as a source of concern citing mainly the work of Henry Delincee and Beatrice-Luise Pool Zobel. On several occasions has Dr. Delincee clarified that he does not agree with the interpretation of such activists^*." target="_blank" >Furthermore it has been established by the World Health Organization that sufficient research has been conducted to conclude that "based on the current scientific evidence, including the long-term feeding studies, 2-DCB and 2-alkylcyclobutanones in general do not appear to pose a health risk to consumers."triglycerides excluding many foods commonly irradiated from such concerns altogether. FDA has asked for repeated and conclusive testing of mutagenicity of 2DCBs in irradiated meat and the study performed by Sommers, C.H. and published in October 2005 under the title "Toxicology Testing of the Unique Radiolytic Product 2-Dodecylcyclobutanone" concluding that "No 2-DCB induced mutagenesis was observed in any of the test systems, both with and without exogenous metabolic activation" confirming previous findings [http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=185057" target="_blank" >^*.

Labeling

Labeling laws differ from country to country. In the US as in many other countries labeling regulations require the usage of the Radura symbol at the point of sale together with usage of the word "irradiated" or "treated by irradiation". However, the meaning of the label is not consistent. The amount of irradiation used can vary and since there are no published standards, the amount of pathogens effected by irradiation can be variable as well. In addition, there are no regulations regarding the levels of pathogen reduction that must be achieved. Food that is processed as an ingredient by a restaurant or food processor is exempt from the labeling requirement.

Economics

Widespread food irradiation is credited for some economic benefits. 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 distance.

Critics point out that the greatest food losses occur in warm, moist, lesser-developed countries, where the capital is lacking for existing storage technologies such as refrigeration, and other atmospheric controls. It might therefore be questionable if the most affected countries possess the resources to employ this technology. According to the IAEA registry, however, more and more facilities are licenced in such regions.

Food irradiation does not provide a convenient total solution to food safety, it is in fact one alternative in a variety of food processing techniques; Furthermore irradiation can not undo the effects of spoilage that has already occurred prior to treatment. Most national regulations therefore do not permit a decrease in hygienic standards in food handling if product is to be irradiated, but rather demand the same high quality prior to treatment. Food irradiation therefore can add to the complexity and cost of food processing if it does not replace any more costly alternative process. It should also be noted that irradiation does not prevent re-infestation or contamination of a product if exposed to the pathogen after treatment.

Insect pests can have a devastating effect on crop production. They can also transmit diseases that destroy crops and kill livestock and people. But, heavy reliance on pesticides raises environmental concerns and problems of pest adaptation and resistance. Hence, in many countries, minimizing insecticide use through the application of environmentally friendly and cost effective irradiation techniques has been given a priority.

Alternatives

There are many alternative methods of food preservation, such as Ultra-high temperature processing, Vacuum Packing and Flash freezing however none can be so uniformly applied to such a wide range of foods as irradiation. Critics have stated that changes in Western dietary habits, and a seasonal availability of fresh produce could eliminate the need for irradiation.

Irradiation is sometimes used to facilitate the long distance shipments of food that, as with most other food, may contain bacteria which could eventually cause spoilage if the food is not sold quickly. In that sense it is feared by some critics that irradiation may negatively contribute in the effects of globalization claiming that a local and seasonal production may be a more effective, safer approach toward food safety.

References

Sipher, A.T. Food Irradiation: An FDA Report. FDA Papers, Oct. 1968
Delincee, H. and Pool-Zobel, B. Genotoxic properties of 2-dodecylcyclobutanone, a compound formed on irradiation of food containing fat. Radiation Physics and Chemistry
WHO Statement on 2-Dodecylcyclobutanone and Related Compounds

Sommers, C.H. 2005. Toxicology Testing Of The Unique Radiolytic Product 2-Dodecylcyclobutanone

Diehl, J.F., Safety of irradiated food, Marcel Dekker, N.Y., 1995 (2. ed.)

Satin, M., Food irradiation, Technomic, Lancaster, 1993 (2. ed.)

Urbain, W.M., Food irradiation, Academic Press, Orlando, 1986

Molins, R. (ed.), Food irradiation - Principles and applications, Wiley Interscience, N.Y., 2001

Sommers, C. and Fan, X. (eds.), Food irradiation Research and technology, Blackwell Publishing, Ames, 2006 (in print)

WHO-publications:

anon., Food irradiation - A technique for preserving and improving the safety of Food, WHO, Genf, 1988 anon., Wholesomeness of irradiated food, WHO, Genf, Technical Report Series no. 659, 1981

anon., Safety and nutritional adequacy of irradiated food, WHO, Genf, 1994

anon., High-dose irradiation: Wholesomeness of food irradiated with doses above 10 kGy, WHO, Genf, 1999, Technical Report Series no. 890