Food irradiation

Food irradiation^[1] is the process of exposing food to ionizing radiation in order to destroy microorganisms, bacteria, viruses, or insects that might be present in the food. 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 micro-organisms 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 speciality 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 world wide. ^{[2] [3] [4]}

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Processing of food by ionizing radiation

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 kilograys 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. ^[1]

Furthermore, insect pests can be sterilized using irradiation at relatively low doses^[5]. 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. The United Nations Food and Agricultural Organization (FAO) has passed a motion to commit member states to implement irradiation technology for their national phytosanitary programs; the General assembly of the International Atomic Energy Agency (IAEA) has urged to make wider use of the irradiation technology; the World Health Organization (WHO) has complained that food irradiation is not available to those who need it most because of reluctance and opposition in some developed countries. And the USDA has made a number of bi-lateral agreements with developing countries to facilitate the imports of exotic fruits and to simplify the quarantine procedures.

Currently, the European Union has regulated processing of food by ionizing radiation in specific directives since 1999; the situation is easily explored and the several documents and reports are accessible.^[6] The 'implementing' directive contains a 'positive list' only permitting irradiation of dried aromatic herbs, spices, and vegetable seasonings^[7]. However, any Member State is permitted to maintain previously granted clearances or to add new clearance as granted in other Member States, in the case the EC's Scientific Committee on Food (SCF) has given a positive vote for the respective application. Presently, six Member States (Belgium, France, Italy, Netherlands, Poland, United Kingdom) have adopted such provisions.^[8]

Because of the 'Single Market' of the EC, any food--even if irradiated--must be allowed to be marketed in any other Member State even if a general ban of food irradiation prevails, under the condition that the food has been irradiated legally in the state of origin. Furthermore, imports into the EC are possible from third countries if the irradiation facility had been inspected and licensed by the EC and the treatment is legal within the EC or some Member state^[9] . The Scientific Committee on Food (SCF) of the EC has given a positive vote on eight categories of food to be irradiated^[10]. However, in a compromise between the European Parliament and the European Commission, only dried aromatic herbs, spices, and vegetable seasonings can be found in the positive list. The European Commission was due to provide a final draft for the positive list by the end of 2000; however, this failed because of a veto from Germany and a few other Member States. In 1992^[11] and in 1998^[12] the SCF voted positive on a number of irradiation applications which had been allowed in some Member States before the EC Directives came into force, in order to enable those Member States to maintain the national authorizations. In 2003 (at the occasion when Codex Alimentarius was about to remove any upper dose limit for food irradiation) the SCF adopted a 'revised opinion'^[13] which in fact is just a re-confirmation and endorsement of the 1986-opinion. The cancellation of the upper dose limit is denied, and before the actual list of individual items or food classes (as in the opinions expressed in 1986, 1992 and 1998) is expanded, new individual studies into the toxicology of each of such food and for each of the proposed dose ranges is requested. After 2003 the SCF has been replaced by the new European Food Safety Authority (EFSA), which not yet has voted on processing food by ionizing radiation.

Other countries including New Zealand, Australia, Thailand, India, and Mexico have permitted the irradiation of fresh fruits for fruit fly quarantine purposes amongst others. Other countries as Pakistan and Brazil have adopted the Codex Alimentarius Standard on Irradiated Food without any reservation or restriction, ie. any food to any dose.

Radiation absorbed dose

'Dose' is the physical quantity governing radiation processing of food and the beneficial effects to be achieved.

Unit of measure for irradiation dose

The dose of radiation is measured in the SI unit known as Gray (Gy). One Gray (Gy) dose of radiation is equal to 1 joule of energy absorbed per kg of food material. In radiation processing of foods, the doses are generally measured in kGy (1000 Gy).

Dosimetry

The measurement of radiation dose is referred to as dosimetry and it involves exposing dosimeters jointly with the treated food item.^[14][15] Dosimeters are small components attached to the irradiated product made of materials that when exposed to ionizing radiation change specific measureable physical attributes to a degree that can be correllated to the dose received. Modern dosimeters are made of a range of materials such as alanine pellets, perspex blocks, radiochromic films, as well as special solutions and other materials. These dosimeters are used in combination with specialized read out devices. Standards that describe calibration and operation for radiation dosimetry are maintained by the American Society for Testing and Materials (ASTM international) and are also available as ISO/ASTM standards.^[16]

Applications

On the basis of the dose of radiation the application is generally divided into three main categories as detailed under:

Low Dose Applications (up to 1 kGy)

• Sprout inhibition in bulbs and tubers 0.03-0.15 kGy
• Delay in fruit ripening 0.25-0.75 kGy
• Insect disinfestation including, quarantine treatment and elimination of food borne parasites 0.07-1.00 kGy

Medium Dose Applications (1 kGy to 10 kGy)

• Reduction of spoilage microbes to improve shelf-life of meat, poultry and seafoods under refrigeration 1.50-3.00 kGy
• Elimination of pathogenic microbes in fresh and frozen meat, poultry and seafoods 3.00-7.00 kGy
• Reducing number of microorganisms in spices to improve hygenic quality 10.00 kGy

High Dose Applications (above 10 kGy)

• Sterilisation of packaged meat, poultry and their products which are shelf stable without refrigeration. 25.00-70.00 kGy
• Sterilisation of Hospital diets 25.00-70.00 kGy
• Product improvement as increased juice yield or improved re-hydration

It is important to note that these doses are above those currently permitted for these food items by the FDA and other regulators around the world. The Codex Alimentarius Standard on Irradiated Food does not specify any upper dose limit.^[17][18] NASA is authorized to sterilize food for Astronauts at doses of 44 kGy as a notable exception^{[citation needed]}.

Irradiation treatments are also sometimes classified as radappertization,radicidation and radurization

Technologies

Electron irradiation

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 irradiation

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^[19]. 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 this is achieved by substantial 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. Other uncommonly used designs feature dry storage by providing movable shields that reduce 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 further shielding is required for such designs.

X-ray irradiation

Similar to gamma radiation, X-rays are photon radiation of a wide energy spectrum and an alternative to isotope based irradiation systems. X-rays are generated by colliding accelerated electrons 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. Like most other types of facilities, X-ray systems rely on concrete shields to protect the environment and workers from radiation.

Irradiated foods in the market place

Current U.S. market

Many U.S. supermarkets carry irradiated food products today ranging from fresh tropical fruit from Hawaii or Florida,^[20] dehydrated spices^[21] and ground meat products.^[22][23] Certain supermarkets like Whole Foods Market prefer not to carry irradiated products for reasons of consumer perception.^[24]

International and other national markets

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General economic aspects

(to be expanded) [former chapter on economics]

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 disinfestation 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.^[25] Irradiation is a capital-intensive technology requiring a substantial initial investment, ranging from $1 million to $5 million. In the case of large research or contract irradiation facilities, major capital costs include a radiation source (cobalt-60), hardware (irradiator, totes and conveyors, control systems, and other auxiliary equipment), land (1 to 1.5 acres), radiation shield, and warehouse. Operating costs include salaries (for fixed and variable labor), utilities, maintenance, taxes/insurance, cobalt-60 replenishment, general utilities, and miscellaneous operating costs^[26][27]

Treatment costs vary as a function of dose and facility usage. Low dose applications such as disinfestation of fruit range between $US 0.01/lbs and $US 0.08/lbs while higher dose applications can cost as much as $US 0.20 / lbs.^[27]

Consumer perception

Some older studies suggest that majority of the public questions the safety of irradiated foods, and if given a choice, will not buy foods that have been irradiated.^[28] More recent consumer attitude and markets studies worldwide, however, indicate consumers today will tend to accept irradiated food. Major studies in the United States indicate the number of consumers concerned about the safety of irradiated food has decreased in the last 10 years and continues to be less than the number of those concerned about pesticide residues, microbiological contamination, and live insects in their food. Where ever irradiated food has reached the market, it has found a sufficient number of consumers to buy it. A number of marketing tests has proven, that consumers as soon as they are allowed to try the real irradiated food item and are informed about the technology and the purpose of the treatment are willing to buy. The number of people reporting no concerns about irradiated food is among the lowest for food issues, comparable to that of people with no concern about food additives and preservatives.^[29]

The globalized food supply

Opponents of food irradiation sometimes state that large-scale irradiation would increase processing, transportation, and handling times for fruits and vegetables thus contributing to a negative ecological balance compared to locally grown foods.

Labeling and Terminology Issues

Labeling laws differ from country to country. While Codex Alimentarius represents the global standard in particular under the WTO-agreement, member states are free to convert those standards into national regulations. With regard to labelling of irradiated food detailed rules are published at CODEX-STAN - 1 (2005) labelling of prepacked food^[30]

The provisions are that any 'first generation' product must be labelled 'irradiated' as any product derived directly from an irradiated raw material; for ingredients the provision is that even the last molecule of an irradiated ingredient must be listed with the ingredients even in cases where the unirradiated ingredient will not appear on the label. The RADURA-logo is optional; several countries use a graphical version which differs from the Codex-version.

In the US as in many other countries irradiated food must be labeled as "Treated with irradiation" or "Treated by radiation" and require the usage of the Radura symbol at the point of sale. 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 affected 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 in the US; other countries follow the Codex Alimentarius provision to label irradiated ingredients down to the last molecule (cf. EU).

FDA is currently proposing a rule that in some cases would allow certain irradiated foods to be marketed without any labeling at all. Under the new rules, only those irradiated foods in which the irradiation causes a material change in the food, or a material change in the consequences that may result from the use of the food, would bear the Radura symbol and the term "irradiated", or a derivative thereof, in conjunction with explicit language describing the change in the food or its conditions of use. In the same rule FDA is proposing to permit a firm to use the terms "electronically pasteurized" or "cold pasteurized" in lieu of "irradiated", provided it notifies the agency that the irradiation process being used meets the criteria specified for use of the term "pasteurized".^[31]

Food irradiation is sometimes referred to as 'cold pasteurization'^[32] or 'electronic pasteurization'^[33] because ionizing radiation used to sterilize the food does not heat the food to high temperatures during the process, as in heat-pasteurization (at a typical dose of 10 kGy, food that is physically equivalent to water would warm by about 2.5 °C). 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.

Enforcement of labelling

There are analytical methods available to detect the usage of irradiation on food items in the marketplace.^[34][35][36] This is understood as a tool for government authorities to enforce existing labeling standards and to bolster consumer confidence. The European Union is particularly strict in enforcing irradiation labeling requiring its member countries to perform tests on a cross section of food items in the market-place and to report to the European Commission; the results are published annually in the OJ of the European Communities.^[37]

Safety aspects

Safety, security and wholesomeness aspects

Hundreds of animal feeding studies of irradiated food, including multigenerational studies, have been performed since 1950.^[38] Endpoints investigated have included subchronic and chronic changes in metabolism, histopathology, and function of most systems; reproductive effects; growth; teratogenicity; and mutagenicity. Because a large number of studies has been performed, some have demonstrated adverse effects of irradiation, but no consistent pattern has emerged.^[38] Independent reviews of the scientific evidence by a series of expert committees, involving the UN Food and Agriculture Organization (FAO), the International Atomic Energy Agency (IAEA), the World Health Organization (WHO) and the International Consultative Group on Food Irradiation (ICGFI), as well as the FDA have concluded in general that irradiation of foods is safe.^[39][40][41]

Some consumer advocacy groups like Public Citizen or Food and Water Watch maintain that the safety of irradiated food is not proven and strongly oppose the use of the technology.^[42][43]

Irradiation to cover up poor food quality

Concerns have sometimes been expressed by public interest groups and public health experts that irradiation, as a non-preventive measure, might disguise or otherwise divert attention away from poor working conditions, sanitation, and poor food-handling procedures that lead to contamination in the first place.^[44] However, similar or even identical concerns had been expressed when the heat-pasteurization of milk had become compulsory; in the contrary to such fears, dairy operations and hygiene have been improved until today.

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. Furthermore, while food irradiation can in some cases maintain the quality of certain perishable food for a longer period of time, it can not undo spoilage effects that occur prior to irradiation. Irradiation can therefore not be successfully used to mask quality issues other than pathogens. Under a HACCP-concept (Hazard Analysis and Critical Control Point) radiation processing can serve and contribute as an ultimate CCP (Critical Control Point).

Worker safety and impact on the environment

Experience over more than 40 years in the field of radiation processing has shown that such technology is generally safely used.^[45] The steady improvement in the design of such facilities and careful selection and training of operators have contributed to a very good safety record. Nevertheless, there have been instances, as in Italy in 1975, in Norway in 1982 and in El Salvador in 1989, when safety systems have been circumvented and serious radiological accidents involving workers at the facilities have ensued.^[45] The safety of irradiation facilities is regulated by the United Nations International Atomic Energy Agency and monitored by the different national Nuclear Regulatory Commissions. The incidents that have occurred in the past are documented by the agency and thoroughly analyzed to determine root cause and improvement potential. Such improvements are then mandated to retrofit existing facilities and future design.

National and international regulations on the levels and types of energy used to irradiate food generally set standards that prevent the possibility of inducing radioactivity in treated foods. Care must be taken not to expose the operators and the environment to radiation. Interlocks and safeguards are mandated to minimize this risk. Nevertheless there have been radiation related deaths and injury amongst workers of such facilities, many of them caused by the operators themselves overriding the interlocks.^[45]

An incident in Decatur, Georgia where water soluble caesium-137 leaked into the source storage pool requiring NRC intervention^[46] has led to near elimination of this radioisotope; it has been replaced by the more costly, non-water soluble cobalt-60.

Alternatives

Other methods to reduce different pathogens in food include heat-pasteurization, Ultra-high temperature processing, UV radiation, Ozone or fumigation with ethylene oxide.

Insect pests can also be eliminated by fumigation with methyl bromide or aluminum phosphine, vapour heat, forced hot air, hot water dipping, or cold treatment. However, the Mango weevil sitting in the stone of the fruit can only be reached by ionizing radiation.

Other methods to extend shelf life of food items include modified atmosphere packaging, carbon monoxide, dehydration, vacuum packaging, freezing and flash freezing as well as chemical additives. However, such methods are not effective for products already deep-frozen where only ionizing radiation can penetrate the product (without re-thawing).

Some people argue that the best alternative to food irradiation to reduce pathogens is in good agricultural practices. For example, farmers and processing plants should improve sanitation practices, water used for irrigation and processing should be regularly tested for E. coli, and production plants should be routinely inspected. Concentrated animal feeding operations near farmland where produce is grown should be regulated. However, such methods as also practised in organic farming can only reduce the extend of the load with microorganisms of all kind; a residual flora including pathogen germs will always persist; and processing by ionizing radiation could be the ultimate measure (as a CCP under a HACCP-concept) to practically eliminate such risks.

See also

• Deinococcus radiodurans
• Food labeling regulations
• Food and cooking hygiene
• Irradiated mail

Recommended further reading

• World Health Organization publications:
  • Food irradiation — A technique for preserving and improving the safety of Food, WHO, Geneva, 1988
  • Wholesomeness of irradiated food, WHO, Geneva, Technical Report Series no. 659, 1981
  • Safety and nutritional adequacy of irradiated food, WHO, Geneva, 1994
  • High-dose irradiation: Wholesomeness of food irradiated with doses above 10 kGy, WHO, Geneva, 1999, Technical Report Series no. 890
  • WHO Statement on 2-Dodecylcyclobutanone and Related Compounds
• 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.H. and Fan, X. (eds.), Food Irradiation Research and Technology, Blackwell Publishing, Ames, IA, 2006

References

• Food Irradiation Processing Alliance FIPA represents the irradiation service industry, manufacturers of food irradiators and suppliers of cobalt-60 sources.

• U.S. Food Irradiation FAQ, Food and Water Watch
• Irradiation Fact Sheet, Center for Food Safety
• Facts about Food Irradiation, a series of 14 fact sheets, International Consultative Group on Food Irradiation, International Atomic Energy Agency, Vienna, 1991 (English)
• Bibliography on Food Irradiation, Federal Research Centre for Nutrition and Food, Karlsruhe, Germany (English)
• Should we irradiate fruit and vegetables? Dateline NBC investigation
• Irradiation FAQ provided by Phytosan S.A. de C.V. of Mexico (English)