Food irradiation

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June 2015

Irradiation, carried out under conditions of Good Manufacturing Practice, is an effective, widely applicable food processing method judged to be safe on extensive available evidence, that can reduce the risk of food poisoning, control food spoilage and extend the shelf-life of foods without detriment to health and with minimal effect on nutritional or sensory quality. This view has been endorsed by international bodies such as the World Health Organisation, the Food and Agricultural Organisation and Codex Alimentarius.

More than 50 countries have given approval for over 60 products to be irradiated. The USA, China, The Netherlands, Belgium, Brazil, Thailand and Australia are among the leaders in adopting the technology. Currently regulations on food irradiation in the European Union are not fully harmonised. Directive 1999/2/EC establishes a framework for controlling irradiated foods, their labelling and importation, while Directive 1999/3 establishes an initial positive list of foods which may be irradiated and traded freely between Member States. However, this initial positive list has only one food category – dried aromatic herbs, spices and vegetable seasonings. Some countries, such as Belgium, France, The Netherlands and the UK allow other foods to be irradiated, whereas other countries, such as Denmark, Germany and Luxembourg remain opposed. Within the UK seven categories of foods are cleared for irradiation to specified doses. Regulations across the world make provision for labelling to ensure that consumers are fully informed whether foods or ingredients within them have been irradiated.

Food irradiation is slowly gaining consumer acceptance in the US and several other countries but it is slow to gain support within many parts of Europe, including the UK, where the Food Standards Agency (FSA) recommends no extension of application. Many consumers are initially hostile to irradiation but when the process is explained to them they become generally more in favour. There is a role for respected professional bodies to inform consumers of the advantages and limitations of the technology so that they can make informed decisions on buying and eating irradiated foods.

Introduction

Many processing methods have been developed to help prevent food spoilage and improve safety. The traditional methods of preservation, such as drying, smoking and salting have been supplemented with pasteurisation (by heat), canning (commercial sterilisation by heat), refrigeration, freezing and chemical preservatives. Food irradiation is another technology that can be added to this list. It is not new; interest was shown in Germany in 1896 (Stewart, 2004(a)) and it began in the early 1920s, while in the 1950/60s the US Army Natick Soldier Center (NATICK) experimented with both low dose and high dose irradiation for military rations. In the UK, at the same time, the Low Temperature Research Station programme concentrated on low dose pasteurisation (Hannan, R S 1955). Irradiation is extensively used in the medical field for sterilising instruments, dressings, etc.

Food irradiation is the process of exposing food to a carefully controlled amount of energy in the form of high-speed particles or electromagnetic radiation. These occur widely in nature and are included among the energy reaching earth all the time from the sun. While the knowledge of how to produce them originated from research into nuclear energy many years ago, modern methods are available which are straightforward and safe.

The choice of irradiation method will depend on the material needing to be treated. Thus, to treat the surface or a thin layer of a food, one would usually choose beta particles (i.e. electrons). These are easy to produce electronically but they do not have deep penetrating power. To treat a bulky product such as an entire sack of spices, one would choose gamma rays or X-rays.

The energy (otherwise known as ionising radiation) penetrates the food and produces free radicals from the material through which it passes. Free radicals are highly reactive and very short-lived, so short-lived that they cannot be detected in water-containing food almost immediately after it has been irradiated.

Ionising radiation is effective because high-speed electrons, gamma rays and X-rays and the free radicals they produce denature sensitive cell material, importantly DNA (deoxyribonucleic acid), the largest molecule in the nucleus and also RNA (ribonucleic acid). DNA consists of a very long ladder twisted into a double helix. The backbone is composed of sugar and phosphate molecules while the rungs of the ladder are comprised of four nucleotide bases (cytosine, thymine, adenine and guanine), which are joined weakly in the middle by hydrogen bonds. Disruption of these weak hydrogen bonds prevents replication and causes cell death while exerting minimal effects on non-living tissue.

Living organisms deprived of intact DNA or RNA will cease to function. Thus, parasites such as tapeworms and disease-causing microorganisms such as Salmonella species (both of which will occasionally be found in raw food) can be controlled or destroyed by irradiation.

In much the same way, ionising radiation can slow down cell-based processes such as early ripening in fruit, which would lead to premature decay. Likewise, it is effective against insects and moulds, which, if uncontrolled, can destroy grain stocks. Irradiation is thus an effective means of controlling all biological processes, which would render the food supply unpalatable or unsafe (Suresh et al, 2005; Miller, 2005).

The dose of radiation received is commonly measured in grays. One gray corresponds to the absorption of one joule of energy in a mass of one kilogram (1Gy = 1J/kg.) The gray has superseded the older unit - the rad (1Gy = 100 rad). In all but very dry matter, such as bone or shell, small amounts of substances are formed, some of which are highly active but transient free radicals, others of which are useful as markers which can be used to determine whether or not the food has been irradiated. It is the action of the transient free radicals, which accounts for much of the effects (killing pathogenic bacteria, extending shelf-life, etc) of irradiating food.

At no time during the irradiation process does the food come into contact with the radiation source and, by using gamma rays, X-rays up to 5Mev or electron beams up to 10 MeV, it is not possible to induce radioactivity in the food. The length of time the food is exposed to the ionising energy coupled with the strength of the source determine the irradiation dose, measured in grays (Gy) or kilograys (kGy), the food receives (1kGy = 1,000 Gy).

Food Irradiation Applications

A fundamental principle in the use of radiation processing is that irradiation should never be used as a substitute for good manufacturing practices (GMP)

A number of applications for irradiation have been identified, aimed at improving safety and reducing food spoilage. Not all of these are approved in the UK. The application areas include:

  • Low dose (less than 1 kGy) irradiation for insect control (for instance in grain and grain products) where a dose of 150-700 Gy is sufficient.
  • Poultry and poultry products, including mechanically recovered meat, to reduce numbers of Salmonella, Campylobacter and other food poisoning bacteria. Doses of up to 3 kGy (fresh) and up to 7 kGy (frozen) have been recommended. In 2012, the Food and Drink Administration (FDA) extended the maximum dosage for poultry in the USA to 4.5 kGy.
  • Red meats, including particularly hamburger meat, to reduce numbers of E.coli O157:H7 and other food poisoning bacteria. Doses of up to 4.5 kGy (fresh) and up to 7 kGy (frozen) have been recommended. The irradiation of meat in the USA was extended by the FDA in 2012 to cover unrefrigerated meat.
  • Frogs’ legs, especially in Belgium, France, The Netherlands and Finland.
  • Dried herbs and spices to reduce levels of contaminating microorganisms generally and to reduce or eliminate food poisoning bacteria in particular. Doses up to 10 kGy have been recommended. Herbs and spices are the food materials most commonly irradiated. These raw agricultural products, grown and harvested by traditional methods are only processed by mild drying which does not reduce the level of microbes present. Alternative methods to reduce microbial numbers have used chemicals, such as ethylene oxide and methyl bromide that are now considered dangerous to humans and/or the environment. This has led to a large trade in steam flash pasteurised spices, but which can result in flavour losses.
  • Some seafood, in particular warm water shrimp/prawns and other shellfish, to improve their microbiological safety. Doses up to 3 kGy have been recommended. Low doses (<3 kGy) eliminate 90-95% of spoilage organisms, resulting in an improvement in shelf-life and eliminate all vegetative bacterial pathogens. Shrimp in ice have a shelf life of 7 days; treating with 1.5 kGy adds another ten days. 1 kGy eliminates both E.coli and Vibrio spp. in oysters without detracting from their raw quality. 20% of potential oyster consumers said they would be prepared to consume irradiated oysters now that their safety has been significantly enhanced. Oyster meats treated with 2 kGy have a shelf-life of 21 to 28 days under refrigeration, compared to 15 days for their non-irradiated counterpart (Komolprasert, V 2002). The Vibrios, most common in crustaceans and bivalve molluscs (V. vulnificus and V. parahaemolyticus), are very sensitive to irradiation and they are reduced to below detectable levels with a treatment of only 300 Gy. Effective August 16th 2005, the Food and Drug Administration (FDA) in the USA issued a Final Rule allowing irradiation for control of Vibrio and other foodborne pathogens in fresh or frozen molluscan shellfish (oysters, mussels, clams, etc). However, on 14 September 2005 the Center for Food Safety and Public Citizen requested a stay of action and a formal evidentiary public hearing for the purposes of revoking FDA’s Final Rule, putting forward several seemingly cogent arguments, including the potential production of 2-alkylcyclobutanones during the irradiation of certain foods. The 2005 ruling was subsequently confirmed in 2011.
  • Certain fruits and vegetables in order to reduce the numbers of microorganisms, particularly those that cause spoilage. Doses of up to 2 kGy have been recommended. Irradiation has been shown to have minimal effect on flavour, aroma and colour but can have an adverse effect on texture (Komolprasert,V, 2002). Irradiation in combination with modified atmosphere packaging (MAP) exerts a useful synergistic effect (Grant, I.R. and Patterson, M.F., 1991) although this combination processing is not allowed in some countries. Irradiation of onions, garlic, mung beans and tamarind is commercially viable in Thailand. Irradiation is also useful in combating rice weevil (Sirohilus oryzae) and lesser grain borer (Rhyzopertha dominice). It is particularly effective against internal feeders. Only a few species are internal feeders but larvae and pre-emergent pupae present the greatest challenge.
  • The USA approved the use of irradiation of spinach and iceberg lettuce in 2008 on grounds of safety and shelf life extension. This followed several cases of food poisoning attributed to E. coli contamination, including fatalities.
  • Bulbs and tubers, such as potatoes and onions. Doses of less than 1 kGy have been recommended. Potatoes have been irradiated in Japan for over 26 years to prevent sprouting (IAEA 1991), and sweet potatoes are irradiated in Hawaii to control insect infestation (Follett and Weinert, 2012).
  • Cereals, grains and certain fruits, such as papaya and mango as a quarantine measure, to kill insects. Doses of 1 kGy are recommended. In 2010 about 6,000 tonnes of fruits and vegetables were irradiated in Hawaii (Follett and Weinert, 2012). As of 2012, Australia and New Zealand have approved for consumption 10 tropical fruits treated up to 1 kGy for a phytosanitary purposes, and an application was made in 2013 to add tomatoes and capsicums (P. Roberts, personal communication).
  • In South Africa 1,754 tonnes of herbs and spices were irradiated during 2004. The only fruit irradiated is dried mangoes. At retail sale the term radurised is used on the label to denote an irradiated product. The label of a foodstuff which has been treated with ionizing radiation shall carry a written statement indicating the treatment in close proximity to the name of the food. Irradiated or radurised is acceptable. Irradiation doses are not specified, the onus is on the industry / irradiation facility to ensure that the minimum irradiation dose is achieved in order to ensure the required quality and safety of the foodstuff being irradiated Permissions have been granted for the irradiation of meat products (Shirley du Plessis, personal communication).
  • High dose irradiation to produce sterile foods, such as ready meals, for special medical diets, emergency or space diets. These foods are irradiated by doses of 45 kGy to render the foods microbiologically sterile. The irradiation is carried out under frozen conditions to minimise adverse sensory effects. The foods can be subsequently distributed unrefrigerated. Shelf-stable meat dishes have been prepared in South Africa since 1989 for both military and non-military uses (WHO, 1999), but has since been discontinued on cost grounds (Amanda Minnaar, personal communication).
Packaging for Irradiated Food

Since food is often pre-packaged before irradiation to prevent re-contamination, it is possible that irradiation might either affect barrier properties or that radiolytic products formed in the packaging might be absorbed into the product. This topic is covered in “High-dose irradiation: Wholesomeness of food irradiated with doses above 10 kGy” (WHO, 1999). FDA in the USA requires that packaging be evaluated and approved before irradiation. Ionising radiation rarely creates new compounds and generally only serves to augment the size of peak (indicating the increase in quantity of products already present). Any novel compounds are generally of low molecular weight. These possibly already existed in the non-irradiated polymer but are desorbed from the polymer over time. Any product unique to irradiation will only occur at very low levels. A benchmark level of 0.5 ppb for non-carcinogenic compounds has been set; below which level the compounds are considered too insignificant to warrant regulatory concern. The original packaging materials (polyolefins, polystyrene, cellophane, vinylidene chloride copolymers, etc) were approved in 1964.

The evaluation of the suitability of new packaging materials is described in Komolprasert (2007). Consideration should also be given to the suitability of components such as absorbent pads, adhesives and printing inks, especially in minimising the risk of taint from low levels of radiolytic products. In 2001 the FDA determined gamma rays, X-ray and E-beam to be equivalent in terms of types and levels of radiolytic products generated in the packaging materials used in pre-packaged foods before irradiation. Unique chemical markers present in irradiated packaging have not been identified.

International Perspective on Irradiation

More than 100 years of research have gone into the understanding of the safe and effective use of irradiation as a food safety method - more than any other technology used in the food industry today, even canning (Scott Smith and Pillai, 2004). The safety and efficacy of the technology has been repeatedly considered and judged acceptable on available evidence. This has resulted in international bodies including the World Health Organisation (WHO), the Food and Agriculture Organisation (FAO), the International Atomic Energy Agency (IAEA) and Codex Alimentarius commending the process.

A maximum overall average dose of 10 kGy was considered adequate for the majority of food applications. Over 50 countries have given approval for the irradiation of over 60 foods and food products on either a conditional or unconditional basis.

A major stimulus to the adoption of irradiation in the USA occurred in 1993 following an outbreak attributed to E.coli O157:H7 which resulted in four deaths and several hundred victims, many of whom were left with permanent kidney damage - HUS (haemolytic uraemic syndrome). The source was traced to undercooked hamburgers from a single fast food outlet and this led to food safety regulations being revised for the first time in nearly a century. This resulted in 1996, in the promulgation of USDA FSIS 9CFR Pathogen Reduction, HACCP Systems (Final Rule July 25th 1996) which permitted the irradiation of chilled meat up to a maximum dose of 4.5 kGy and frozen meat up to a maximum dose of 7 kGy. Labelling is required, either “irradiated” or “treated with ionising radiation” coupled with the radura symbol illustrated.

A massive recall in 1997 (the largest recall up to that time), which led to a major US food processor implicated going out of business, was also caused by E.coli O157:H7. This incident led to an increase in the use of E-beam irradiation for the treatment of frozen meat patties.

Control of Listeria monocytogenes in prepared foods presented an additional potential use of food irradiation as a food safety measure: between 1998 and 2002 some 56,000 metric tonnes of Ready-to-Eat (RTE) meals were recalled in the USA owing to contamination with Listeria monocytogenes. This very widespread organism which grows well at refrigerator temperatures causes many cases of Listeriosis. 2,500 cases were reported in the USA per annum causing 500 deaths; a mortality rate of some 20%. Many of these cases were attributed to RTE foods. Surveys showed 2.5% of RTE meat products, 1.6% of frankfurters and 5.1% of ham and sliced luncheon meat products to be contaminated (Komolprasert, 2002).

Concerns in the USA regarding E. Coli contamination of other foods have continued to grow, and following an outbreak in 2006 involving fresh spinach, approval was given in 2008 for the irradiation of spinach and iceberg lettuce. Subsequent food poisoning outbreaks from fresh produce (lettuce, sprouted seeds and spinach) have continued to raise interest in irradiation in the USA.

In 2009, the FTSI plant in Florida received a licence to irradiate oysters, primarily to protect against food poisoning from Vibrio vulnificus.

The introduction in the USA of the internet programmes Foodnet and Pulsenet (both of which involve the US Center for Disease Control (CDC); www.cdc.gov) represents a useful step forward in detecting any lapse in food hygiene in the USA. One result has been that food irradiation is being perceived as an important aid in improving food safety.

The National Center for Policy Analysis (2004) carries estimates (advanced by CDC based on Ostherholm et al, 2004) that if half the food at greatest risk consumed in the USA were to be irradiated, food-borne illnesses would decline by 900,000 cases annually and by 352 deaths. The extra cost is estimated at less than 5 cents per pound for the meat and poultry involved. Epidemiological data from Europe are available from several sources such as “The WHO Surveillance Programme for Control of Foodborne Infections and Intoxications in Europe (WHO 2001), the EU “Zoonoses Reports” (EC, 2002) and www.hpa.org.uk.

EU Legislation

EU Legislation

Two Directives (framework Directive 1999/2/EC and implementing Directive 1999/3/EC) were adopted by the EU in 1999. The framework Directive permits irradiation providing it:

  • Is necessary
  • Presents no hazard
  • Is beneficial to consumers
  • Is not used as a substitute for good manufacturing practice

Labelling is required. Irradiated foods must be labelled as either “treated with ionising radiation” or “irradiated”. At present Member States have their own national legislations. The Official Journal of the EU carries a table of Member States’ authorisations of food and food ingredients which may be treated with ionising radiation (OJC 283/5, 24 November 2009). A list of foods and food ingredients authorised for irradiation by EU member states has been published (EC 2003; http://ec.europa.eu/food/food/biosafety/
irradiation/comm_legisl_en.htm
). Member States may also maintain restrictions or bans on irradiated foods, in compliance with the rules of the Treaty, until the completed EU-wide list of products authorised for irradiation comes into force. The Scientific Committee for Foods (SCF) began drawing up an approved list of products to be established under Directive 1999/3/EC, which will replace any national list once it comes into force. At present the initial list contains only dried aromatic herbs, spices and seasonings. Labelling regulations specify no minimum quantity of any ingredient below which irradiation would not need to be declared, i.e. any quantity of irradiated ingredient, however small, would have to be declared.

UK Legislation

In the UK, the Advisory Committee on Novel and Irradiated Foods approved irradiation in 1986 as a safe and satisfactory method of food processing. This opinion was reaffirmed in 1987 after receiving submissions from industry, consumer groups and interested parties. In 1991, the Food (Control of Irradiation) Regulations in the UK cleared 7 categories for irradiation to specified overall average doses: fruits (2.0 kGy), vegetables (1.0 kGy), cereals (1.0 kGy), bulbs and tubers (0.2 kGy), spices and condiments (10 kGy), fish and shellfish (3.0 kGy) and poultry (7.0 kGy). The regulations also make provision for labelling to ensure consumers are fully informed whether foods or any contained ingredients have been irradiated. Under the Food Labelling Regulations (1996), irradiated foods and ingredients have to be identified with the words “irradiated” or “treated with ionising radiation”. Foods prepared under medical supervision (for immunocompromised patients) and products classified as medicines - though they may be taken orally and be available in health food shops, pharmacies, etc, without prescription - are exempt from labelling. Irradiation facilities must meet specified criteria before they can be licensed to process foods. To date, there is only one UK licence, which authorises the irradiation of certain herbs and spices. In 2000, UK legislation was amended to implement the changes introduced by the European Directives.

Following a consultation period in 2009, new Food Irradiation Regulations were drawn up and issued on 31 July 2009 (The Food Irradiation (England) Regulations 2009, (2009 SI 1584), and minor amendments in 2010. Equivalent Regulations were also issued to cover Scotland, Wales and Northern Ireland.

Quality of Irradiated Food

Nutritional Quality of Irradiated Food

Irradiation is very effective against living organisms which contain DNA and/or RNA but does not cause any significant loss of macronutrients. Proteins, fats and carbohydrates undergo little change in nutritional value during irradiation even with doses over 10 kGy, though there may be sensory changes. Similarly, the essential amino acids, essential fatty acids, minerals and trace elements are also unaffected. There can be a decrease in certain vitamins (particularly thiamin) but these are of the same order of magnitude as occurs in other manufacturing processes such as drying or canning (thermal sterilisation). It is calculated that the loss of thiamin in the American diet, due to irradiation of chops and roast pork at 1 kGy would be 1.5%. (Wilkinson and Gould, 1996). More details are given in WHO (1994) and FAO/IAEA/WHO (1999). On the other hand, the niacin content of bread from irradiated flour was 17% more than the non-irradiated control flour (Diehl, 1991). Also, an increase in the niacin content (24%) and riboflavin content (15%) in pork chops after irradiation was reported in another study (Fox et al, 1989).

Sensory Quality of Irradiated Food

The irradiation process is not suitable for all products. Foods with high fat contents, such as fatty fish and some dairy products, develop off-odours and tastes due to the acceleration of rancidity, even at relatively low doses. Loss of firmness can occur with some fruits and vegetables. Foods with a high protein content, such as meat and poultry, can suffer from changes in flavour and odour after irradiation at ambient temperatures but these changes can be reduced by irradiating at chill temperatures and minimised by irradiating at frozen temperatures. For fresh ground beef with a high fat content and for fatty pork products, the maximum dose should not exceed 2.5 kGy to prevent rancidity. Liquid and dry eggs can tolerate doses in excess of 3 kGy, but for shell eggs a 2 kGy dose can cause deterioration of the yolk sac membrane. Milk develops an off-flavour at relatively low doses but various cheese show good tolerance at doses up to 3 kGy (Diehl, J.F., 1983). All these changes are minimised by irradiating at chill or frozen temperatures, and, in addition, many changes can be minimised by careful choice of suitable packaging systems coupled with controlled gas atmospheres.

Detection of Foods that have been Irradiated

The consumers’ ability to make informed choices mainly depends on accurate labelling. Analytical methods that can discriminate between irradiated and non-irradiated foods are therefore required if labelling regulations are to be enforceable. The changes known to occur in irradiated foods are minimal and often similar to those occurring in foods subjected to other processes, which makes the development of sufficiently sensitive tests difficult. In all but very dry matter, such as bone or shell, small amounts of substances are formed, some of which are highly active but transient free radicals, others of which are useful as markers, which can be used to determine whether or not the food has been irradiated. It is the action of the transient fee radicals which accounts for much of the effects (killing pathogenic bacteria, extending shelf-life etc.) of irradiating food.

A range of analytical methods have been successfully developed. These are based on the detection of physical, chemical and microbiological changes that can occur in irradiated food. The most useful and widely used methods include electron spin resonance spectroscopy (ESR), luminescence methods (thermo-luminescence – TL), photo stimulated luminescence (PSL) and the detection of long-chain volatile hydrocarbons and 2-alkylcyclobutanones. The luminescence methods are widely applicable and make use of mineral grains that are present in many foods including herbs, seasonings, spices, fruits, vegetables and shrimp. ESR can be used to detect free radicals captured in the dry parts of foods such as bones, seeds and shells, while methods based on detection of hydrocarbons and 2-alkylcyclobutanones are applicable to foods containing fat, such as meat. These methodologies complement each other and allow discrimination between irradiated and non-irradiated products in a wide variety of foods, although uncertainties in the interpretation of results from different methods can occur. Ten methods have been adopted by the European Committee for Standardisation (CEN) and are available for adoption by national standards bodies, such as the British Standards Institute (BSI) in the UK. All ten of these methods have been adopted by Codex as general methods (CEN, 2009). Concern over illegally irradiated products entering the UK, particularly food supplements, has led to the publication of a Good Practice Guide on compliance with the legislation on the irradiation of food ingredients (Food Standards Agency, 2010).

Safety of Irradiated Food

Decades of research worldwide have shown that irradiation of food is a safe and effective way to kill bacteria in foods and extend its shelf life. Food irradiation has been examined thoroughly by joint committees of the World Health Organization (WHO), the United Nations Food and Agriculture Organization (FAO), by the European Community Scientific Committee for Food, the United States Food and Drug Administration and by a House of Lords committee in the UK.

The toxicity of the 2-alkylcyclobutanone group of radiolytic compounds has been investigated (Burnouf et al.,2002; http://www.iaea.org/programmes/rifa/icgfi/
documents/summary-press.pdf
) and the results assessed by the European Commission (EC) Scientific Committee on Food (SCF), which issued a statement in July 2002 that came to the conclusion it was not appropriate on the basis of these results ‘to make a risk assessment for human health associated with the consumption of 2-alkylcyclobutanones present in fat-containing foods (Stewart, 2004 b). An evaluation of toxicological food safety concerns arising from food irradiation was published in 2004 (IFT, 2004).

In 2011, the European Food Safety Authority reviewed the evidence and reasserted the opinion that food irradiation is safe (EFSA, 2011). It was concluded (i) that there are no microbiological risks for the consumer linked to the use of food irradiation and its consequences on the food microflora, and (ii) that most of the chemical substances formed during irradiation were also formed in food that has been subjected to other processing treatments and that the quantities in which they occur in irradiated food were not significantly higher than those being formed in heat treatments. It was also noted that alkylcyclobutanones had been found in commercial non-irradiated fresh cashew nut and nutmeg samples (Variyar et al., (2008), and could not be classified as unique radiolytic products.

High Dose Irradiation

Foods sterilised by high dose irradiation (>25 kGy) - cold sterilisation as opposed to thermal sterilisation (canning) - have been consumed by astronauts in the NASA space shuttle programme because of their superior quality and variety, compared to foods treated by other preservation technologies. There is a small but increasing demand for sterile products for immunocompromised patients as well as for niche markets, such as the military, campers or disaster victims where a long shelf life at ambient temperatures is required. High dose sterile foods may be prepared under medical supervision for immunocompromised patients without labelling. A research programme on Irradiated Foods for Immuno-compromised Patients is being coordinated by the IAEA, with a target completion date of 2015 (IAEA, 2010).

The current upper limit of 10 kGy is insufficient to achieve sterility. This led a Joint FAO/IAEA/WHO Study Group on High-Dose Irradiation to request the International Consultative Group on Food Irradiation, to petition the Codex Secretariat to remove the upper dose limit of 10 kGy by revising the General Standard. This recommendation was based on the usefulness of effectively eliminating the more resistant spores of proteolytic strains of Clostridium botulinum as well as all vegetative organisms while neither compromising nutritional values nor resulting in any toxicological hazard. This process of cold sterilisation is analogous to canning (thermal sterilisation) the products of which have been safely consumed for well over a century. The conclusion reached by the Joint Study Group was that food irradiated to any dose appropriate to achieve the intended technological objectives is both safe to consume and nutritionally adequate. They also advised that no upper dose limit need be imposed. The Joint Study Group concluded that appropriate steps need to be taken to establish the technological guidelines implied by these conclusions and then to communicate them through Codex Alimentarius standards in order to achieve global standardisation.

The revised Codex General Standard (2003) for Irradiated Foods now reads, “the maximum absorbed dose delivered to a food shall not exceed 10 kGy, except when necessary to achieve a legitimate technological process”. The SCF disagreed with this view and saw inadequate reason to raise the upper limit of 10 kGy. The FDA in the US allows frozen meat for NASA to be irradiated to sterility with a minimum dose of 44 kGy (http://www.cfsan.fda.gov/~dms/opa-fdir.html).

Food Irradiation Worldwide

In 2009, in the region of 380,000 tonnes of food for human consumption and for animal consumption was irradiated. A breakdown across the European Union, the Americas and the Asia Pacific region is given below. (Note: It has been suggested that there is some confusion in publicly accessible information sources in terms of both units used (metric tonnes or imperial tons) and incomplete reporting. This appears to be more the case prior to 2006, and more confidence can be placed on figures post-2006).

European union

Approximately 8,100 tonnes of food for human consumption was irradiated in the EU in 2011 (EU, 2012), and this figure has been generally stable in the period 2007 – 2011. Prior to this period, an estimated quantity of 20,000 tonnes in 2002 had fallen to 15,000 tonnes in 2006 (but see the Note above.) The figures below refer to 2011 unless stated.

  • Belgium irradiated 5030 tonnes (frozen frogs’ legs, poultry, seafood and spices/seasonings were the principal products)
  • The Netherlands irradiated 1573 tonnes (dehydrated vegetables, spices and herbs, poultry, frog parts, egg white and frozen shrimp were the principal products)
  • France irradiated 695 tonnes (poultry, spices and frozen frogs’ legs were the principal products)
  • No food was irradiated in the UK

A survey carried out by the EU in 2011 (EU, 2012) analysed 130 food samples in the UK using CEN analytical methods. The foods comprised items such as dried and fresh herbs and spices, noodles and dehydrated Asian meals, soups and sauces, food supplements and dried fish and seafood. Compliance was found for 117 samples (90%), and non-compliance for 6 samples (4.6%, on the basis of either not being correctly labelled or no evidence that irradiation was carried out in an approved facility. Inconclusive results were found for 7 samples (5.4%). Over the EU as a whole, 5397 samples were analysed, of which 5232 (97%) were compliant, 105 (2%) were non-compliant and 60 (1%) were inclusive.

The Americas

In 2009, around 120,000 tonnes of food for human and animal consumption were irradiated in the USA (Eustice, 2011). An approximate breakdown of this total is 8,000 tonnes of ground beef; 14,000 tonnes of fresh produce; 70-80,000 tonnes of spices (one third of the total annual US production); and 18-20,000 tonnes of pet treats.

In 2010, Mexico exported over 7,500 tonnes of irradiated guavas, mangoes and peppers to the USA.

In Canada, irradiation of potatoes, onions, wheat, flour, whole wheat flour, whole or ground spices, and dehydrated seasoning preparations has been approved, but despite foodborne illness outbreaks associated with Canadian public opinion concerns have inhibited practical applications.

Brazil irradiated 25,000 tonnes of dried products, spices, animal feed and pet products in 2009.

Asia Pacific

China is the largest Asian producer of irradiated foods, with 200,000 tonnes irradiated in 2009, mainly garlic, spices, dried vegetables and cooked meats. In the same year 10,000 tonnes of spices, spice mixes, dried vegetable seasonings and mangoes were irradiated in India. Quantities irradiated in other countries were smaller; 5,300 tonnes of spices, frozen foods and dragon fruit were irradiated in Vietnam, 2,500 tonnes of dried vegetables and spices were irradiated in South Korea, 2,265 tonnes of spices, dehydrated products and frozen shrimps, fish and frog legs in Indonesia and 2,100 tonnes of fermented sausage (nham), spices, herbs, vegetable seasonings, sweet tamarind, mango, mangosteen and longan in Thailand.

In the period 2004 – 2010 the quantity of mango, papaya and litchi irradiated in Australia and imported into New Zealand increased from 256 to 1205 tonnes (Roberts, 2011), and Food Standards Authority Australia New Zealand have approved in 2012 an application to irradiate capsicum and tomato.

Consumer Attitudes to Irradiation

The introduction of irradiated foods has many analogies with the introduction of pasteurisation of milk over a century ago - one of the most significant advances ever made in food safety. The principal allegations advanced against the introduction of thermal pasteurisation of milk and food irradiation (cold pasteurisation) are very similar (Satin, 1996).

Opponents of both thermal pasteurisation of milk and cold pasteurisation of foods by irradiation have claimed that:

  • Nutritional value will be diminished
  • The price will be increased
  • Possibly unsafe
  • Will be used to mask filthy products
  • Legalises the right to sell stale food
  • Is unnecessary
  • Is meddling with nature
  • Will take the ‘life’ out of the product

Many surveys have been carried out (mostly in the USA) to assess consumer attitudes to food irradiation (e.g. Bruhn and Schutz, 1989; Resurreccion et al, 1995; Fox 2002; Nayga et al, 2005). Results have consistently shown that many consumers have misconceptions about the technology and believe that it makes food radioactive. When consumers are given information about the process and a chance to try irradiated products for themselves they are much more likely to accept the technology. Market trials have also met with success.

One of the most successful market trials of irradiated foods was carried out in 1991 in a small food store in Chicago, USA. Clearly labelled irradiated strawberries, oranges and grapefruits outsold their non-irradiated counterparts by a ratio of 9:1. In the following season, irradiated strawberries became the number one seller with the ratio expanding to 20:1 over the non-irradiated product. This positive experience encouraged approximately 60 stores in Indiana, Illinois and Ohio to sell a variety of irradiated foods (Pszczola, 1992).

In one study, the sensory characteristics and consumer acceptance of E-Beam irradiated (at 1, 2 and 3 kGy) RTE meats (frankfurters and diced chicken) were evaluated by a consumer panel of 50. After 18 days of refrigerated storage for the chicken and 32 days for the frankfurters the acceptability of the irradiated products was significantly higher than for the non-irradiated (Johnson et al, 2004). The same authors compared the consumer attitudes towards irradiated foods over the ten years 1993 to 2003. Consumer awareness was no higher in the 2003 study than in 1993 but more consumers were willing to buy more irradiated foods in 2003 than in 1993 (69% and 29% respectively). Consumers in both studies showed more concern over pesticide and animal residues, growth hormones, food additives, bacteria and naturally occurring toxins than irradiation. The slight concern expressed regarding irradiation had decreased significantly among this group. Approximately 76% prefer to buy irradiated pork and 68% prefer to buy irradiated poultry to decrease the possibility of illness from Trichinella and Salmonellae respectively (Johnson et al, 2004).

In another study, 113 consumers who were over 18 and consumed ground beef at least once a month were selected for a trial in Mesa, Arizona to examine the effects of product exposure and consumer education about irradiation. Product exposure was found to exert no effect while educating consumers had the most significant impact on their views of food irradiation. Sensory evaluation showed that consumers could not differentiate between irradiated and non-irradiated ground beef either at the beginning of the study or after three months frozen storage. Groups that received irradiation education were more accepting of the technology and more consumers in these groups changed their perceptions of irradiation in a positive way (Hamilton et al, 2004).

A similar study (Nayga et al., 2005) carried out in 2002 in four Texan towns (Austin, Houston, San Antonio and Waco) involved face-to-face interviews with 484 customers intercepted at random at supermarket entrances. Each respondent was initially asked to say to which of four consumer segments they belonged: “strong buyer”, “interested”,”doubter” or “rejecter”of irradiated foods. They were then presented with two informative statements, the first pertaining to the nature and benefits of food irradiation. The second statement described the two different processes of irradiation (gamma rays and E-Beam) and also involved watching a short video illustrating the E-Beam process. The results are presented in the accompanying table. Males were more inclined to change their view than females and switch towards the segments more likely to purchase irradiated foods.

 

EFFECTS OF CONSUMER EDUCATION ON CONSUMER ATTITUDES STRONG BUYER

INTERESTED

DOUBTER

REJECTER

INITIALLY

8.4%

73.8%

13.9%

3.8%

AFTER FIRST STATEMENT

28.3%

66.6%

3.4%

1.7%

AFTER SECOND

42.2%

54.0%

3.2%

0.6%

 

These results strongly support the thesis that supplying digestible information can be highly effective in shifting consumer attitudes in favour of purchasing irradiated foods.

The participants were also asked about their perception of the Radura symbol:

  • 67.1% considered it an assurance of quality.
  • 5.5% considered it a warning signal and avoided the product.
  • 17.1% indicated it did not affect buying decisions.
  • 10.3% did not recognise the symbol.

Consumer acceptance of irradiated foods in the USA is being reinforced by three key-drives; these being (i) growing public awareness of the risks from bacteria in meat (and other food products), (ii) growing levels of educational media coverage on food irradiation and (iii) fear of bioterrorism on centralised food production. (Deeley, 2002).

The limited number of consumer surveys carried out more recently have continued to reflect the above findings. A study on the effect of an education programme on attitudes of consumers in California (Bhumiratana, 2007) showed that following the programme 60% indicated they would choose irradiated products, and almost 40% said they would pay a premium for irradiated meat; only 3% were opposed to food irradiation. In a survey carried out by the International Food Information Council (IFIC) in 2009, 60% of consumers expressed a positive attitude to food irradiation, with 33% not very favourable or undecided, and 7% not at all favourable. A Canadian survey in 2012 indicated that over half of the consumers would buy irradiated food. In a 2012 publication, Eustice and Bruhn (2012) concluded that “Despite the progress made in the introduction of irradiated foods into the marketplace, many consumers and even highly placed policy-makers around the world are still unaware of the effectiveness, safety, and functional benefits that irradiation can bring to foods. Education and skilled marketing efforts are needed to remedy this lack of awareness.

Professional and Media Recognition

The upsurge in support of food irradiation in the USA has been reflected in Position Statements from a number of professional bodies and media. Bodies such as the American Dietetic Association and American Medical Association support the use of irradiation to enhance the safety and quality of food and see their role as assisting in the education of consumers about the technology. Many sectors of the food industry, such as the Grocery Manufacturers of America, are speaking in favour of food irradiation. The American media has also become increasingly positive towards the technology with newspapers such as the New York Times and the Wall Street Journal running stories in support of the process. In most cases, the main benefit is seen as making food safer to eat.

There is obviously a role for respected professional bodies in informing consumers about the benefits and limitations of food irradiation, so that they can make informed choices.

Supplementation of conventional methods for controlling food pathogens

Food irradiation has a particular role to play where established methods of controlling foodborne pathogens have failed, sometimes resulting in many deaths. In 2011, the Food Standards Agency published a Foodborne Disease Strategy aimed at reducing foodborne disease in the UK (Food Standards Agency, 2011). The programme gives highest priority to reducing illness from Campylobacter (371,000 reported cases in the UK in 2009, mainly from chicken) and from Listeria monocytogenes (low case numbers, but with a 33% fatality level). Whilst these are priority areas, control of foodborne infections caused by E. coli O157 will also be addressed, and illnesses caused by Salmonella and Clostridium perfringens will also be monitored. However, particular concern has been expressed regarding Campylobacter, as the number of cases has been rising steadily since 2004, and it is estimated that 65% of chickens at retail sale are contaminated. In contrast, the incidence of Salmonella has declined during the same period. Control on the farm is important but cannot deliver the same freedom from human pathogens that is provided by irradiation as used within the context of Good Manufacturing Practice.

There are well-publicised advantages of irradiating those foods which are known to harbour a wide variety of human pathogens as a means of reducing the incidence of foodborne illness. Despite this, a meeting of the Consumer Committee of the Food Standards Agency in the UK (held on March 2, 2005; Cons Comm DO30/04), agreed that any moves to encourage more irradiation in the UK at this time should not be supported, and this view continues to prevail.

Key Points to Consider

The steps required to exploit the benefits of irradiation involve standardisation, communication and education. WHO, in collaboration with FAO and IAEA should:

  • Coordinate the preparation of documentation and the drafting of appropriate technical language for adoption of standards by the Codex Alimentarius Commission.
  • Prepare appropriate brochures and documents that integrate food irradiation into existing guidelines and rules governing the safe production, distribution and handling of food (in order to minimise the spread of biological contamination and incidence of foodborne illnesses).
  • Take the lead in advising international agencies and national ministries of health on implementing integrated strategies, including food irradiation, for preventing the international spread of pathogens in food and animal feed, for controlling food borne illnesses and for enhancing the availability of safe and nutritious foods.
  • Organise and participate in appropriate training courses and workshops that educate food regulators and food workers about the role food irradiation could, and should, play as a control measure in the framework of application of the HACCP (Hazard Analysis and Critical Control Point) system.
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The Institute takes every possible care in compiling, preparing and issuing the information contained in IFST Information Statements, but can accept no liability whatsoever in connection with them. Nothing in them should be construed as absolving anyone from complying with legal requirements. They are provided for general information and guidance and to express expert professional interpretation and opinion, on important food-related issues.

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