17 radiation D. A. E. Ehlermann, Federal Research Centre for Nutrition Germany 17.1 ntroduction Genetically modified food has become the object of a heated debate by con sumer activists and replaced irradiation,s leading role as a target. In this debate the term irradiation is frequently confused with radioactive contamination, espe- cially after the Chernobyl accident. The allegation is made that the nuclear indus- try needs food irradiation badly in order to find some use for the waste from nuclear power stations. In addition, the historical involvement of the US Arm in research on food irradiation is used as proof of its link to nuclear weapons and military purposes. However, this chapter on the radiation processing of food by ionising energy, i.e. on food irradiation, highlights the history of the subject which extends over a hundred years. It elaborates the peaceful background, emphasises that radiation processing is a non-nuclear technology and elucidates the physical principles of the interaction between ionising radiation and matter. This basic information is then used to elaborate the beneficial effects of ionising radiation by describing its chemical biological and microbiological action in the food environ These two sections will lead to the radiological and toxicological safety of food processed by ionising radiation. The aim of the Nutrition Handbook for Food Processors is covered in a section on nutritional adequacy and is followed by a section summarising the evaluation of overall safety by national and inter- national expert groups Radiation processing has already found its area of commercial application, governments have approved the process, the food industry is using it and where the irradiated product is available on the market consumers respond favourably Under the WTO-agreement with the associated Codex Alimentarius standard
17 Irradiation D. A. E. Ehlermann, Federal Research Centre for Nutrition, Germany 17.1 Introduction ‘Genetically modified food’ has become the object of a heated debate by consumer activists and replaced irradiation’s leading role as a target. In this debate the term irradiation is frequently confused with radioactive contamination, especially after the Chernobyl accident. The allegation is made that the nuclear industry needs food irradiation badly in order to find some use for the waste from nuclear power stations. In addition, the historical involvement of the US Army in research on food irradiation is used as proof of its link to nuclear weapons and military purposes. However, this chapter on the radiation processing of food by ionising energy, i.e. on food irradiation, highlights the history of the subject which extends over a hundred years. It elaborates the peaceful background, emphasises that radiation processing is a non-nuclear technology and elucidates the physical principles of the interaction between ionising radiation and matter. This basic information is then used to elaborate the beneficial effects of ionising radiation by describing its chemical, biological and microbiological action in the food environment. These two sections will lead to the radiological and toxicological safety of food processed by ionising radiation. The aim of the Nutrition Handbook for Food Processors is covered in a section on nutritional adequacy and is followed by a section summarising the evaluation of overall safety by national and international expert groups. Radiation processing has already found its area of commercial application, governments have approved the process, the food industry is using it and where the irradiated product is available on the market consumers respond favourably. Under the WTO-agreement with the associated Codex Alimentarius standards
372 The nutrition handbook for food processors (1984)and recommended by the WHO*, it is a tool that helps resolve several recent problems of food production, manufacturing and marketing. It can greatly support food safety and environment conservation and therefore serve the con- sumer. In conclusion there is a list of sources of further information: for detailed literature the reader is referred to the monographs referenced. Several concerns have been voiced, for instance about nutritional quality radiolytic products, toxicology, microbiology, occupational safety, environmen- tal side-effects, deception of consumers, consumer acceptance, substitution fo good manufacturing practice, negligent hygienic practice, misuse and increased prices. These are the main arguments of certain consumer organisations against he legal clearance of this technology. They still influence the officials and politi cians who are responsible for the regulation of food technologies. However, with the information available in this chapter readers should be able to make their own formed decisions. References given are restricted to textbooks, monographs and survey or review articles only, but interested readers will use them to lead to more detailed information 17. 2 The history of food irradiation As early as in 1885 and 1886 ionising radiation was discovered and in sub sequent years its bactericidal effects were described. The purpose of the first patent on food irradiation(Appleby and Banks, 1905) was to bring about an improvement in food and its general keeping quality. It was followed by an invention of an ' Apparatus for preserving organic materials by the use of X-rays (Gillett, 1918). However, radiation sources strong enough for industrial exploita tion were not available before the 1950s The following five decades were devoted to the development of this technology to a state where it could be applied both commercially and industrially as well as to an investigation into the health aspects of food treated by ionising radiation. This was done in a world-wide, concerted effort; the US Army and the Us Atomic Energy Commission were involved and stimulated by Eisenhowers initiative ' Atoms for Peace. The academia were led by the Massachusetts Insti- ute of Technology and followed by university and government research estab. lishments in many countries. Details are given by Diehl (1995). Radiation sources, such as radioactive isotopes and machines, became available and were strong enough for treating food at commercial throughput. A radiation process- ing industry developed so that everyday goods could be produced by using ion- ising radiation. Floor-heating pipes, automobile tyres, car parts, electrical wires and cables, shrinkable food packaging, medical disposables(syringes, implants, compresses, bandaging material, blood transfusion equipment)-all are manu- factured using ionising radiation. Even astronauts prefer irradiated food in their diets The WHO Golden Rules for Safe Food Preparation list under Rule 1"Chose foods processed for safety":.. if you have the choice, select fresh or frozen poulty treated with ionizing radiati
(1984) and recommended by the WHO*, it is a tool that helps resolve several recent problems of food production, manufacturing and marketing. It can greatly support food safety and environment conservation and therefore serve the consumer. In conclusion, there is a list of sources of further information; for detailed literature the reader is referred to the monographs referenced. Several concerns have been voiced, for instance about nutritional quality, radiolytic products, toxicology, microbiology, occupational safety, environmental side-effects, deception of consumers, consumer acceptance, substitution for good manufacturing practice, negligent hygienic practice, misuse and increased prices. These are the main arguments of certain consumer organisations against the legal clearance of this technology. They still influence the officials and politicians who are responsible for the regulation of food technologies. However, with the information available in this chapter readers should be able to make their own informed decisions. References given are restricted to textbooks, monographs and survey or review articles only, but interested readers will use them to lead to more detailed information. 17.2 The history of food irradiation As early as in 1885 and 1886 ionising radiation was discovered and in subsequent years its bactericidal effects were described. The purpose of the first patent on food irradiation (Appleby and Banks, 1905) was to bring about an improvement in food and its general keeping quality. It was followed by an invention of an ‘Apparatus for preserving organic materials by the use of X-rays’ (Gillett, 1918). However, radiation sources strong enough for industrial exploitation were not available before the 1950s. The following five decades were devoted to the development of this technology to a state where it could be applied both commercially and industrially as well as to an investigation into the health aspects of food treated by ionising radiation. This was done in a world-wide, concerted effort; the US Army and the US Atomic Energy Commission were involved and stimulated by Eisenhower’s initiative ‘Atoms for Peace’. The academia were led by the Massachusetts Institute of Technology and followed by university and government research establishments in many countries. Details are given by Diehl (1995). Radiation sources, such as radioactive isotopes and machines, became available and were strong enough for treating food at commercial throughput. A radiation processing industry developed so that everyday goods could be produced by using ionising radiation. Floor-heating pipes, automobile tyres, car parts, electrical wires and cables, shrinkable food packaging, medical disposables (syringes, implants, compresses, bandaging material, blood transfusion equipment) – all are manufactured using ionising radiation. Even astronauts prefer irradiated food in their diets. 372 The nutrition handbook for food processors * The WHO Golden Rules for Safe Food Preparation list under ‘Rule 1 “Chose foods processed for safety”: . . . if you have the choice, select fresh or frozen poulty treated with ionizing radiation
Irradiation 373 The world-wide first food irradiation facility became operational in Germany in 1957 for spices, but had to be dismantled in 1959 when Germany banned food irradiation. In 1974 in Japan the Shapiro Potato Irradiator was commissioned and is the oldest food irradiation facility still in operation today. When in 1980 the JECFI made a landmark decision and declared irradiated foods as safe and whole- some for human consumption, it led many governments to permit the radiation processing of food. This did not result in commercial application of the process in all countries. Nevertheless, the total amount of food treated by ionising radi ation is increasing, about 200000 tonne per annum at the time of writing, but is still a very small volume compared to the total amount consumed. However, food irradiation is a niche application, supplementing traditional methods of food processing and serving specific purposes. Two important classes of application, sanitary and phytosanitary, are increas- As recently as 1993, children died tragically after eating undercooked(rare) hamburgers. This was caused by Escherichia coli type O157: H7(EHEC),an emerging pathogen microorganism which is now considered to be ubiquitous There is always the threat of such emerging hazards in modern, industrial food production. Such risks can only be fought by further improvement of good man- ufacturing practices and the application of ' Hazard Analysis and Critical Control Point(HACCP). Adherence to such procedures and improvement of hygienic concepts can only reduce or limit the hazard but never eliminate it. For this reason, supplementary methods, in addition to good practices, help suppress such residual risks to a tolerable, acceptable level. ionising radiation is such a tool, now legal in the USA and helping to make hamburgers, fresh or deep-frozen, far safer for the consumer. Many other pathogen microorganisms are a threat to society, causing death and illness, damages and economic losses. Other ex amples are Campylobacter and Salmonella in poultry n eggs. Listeria in cheese and sprouts. Governments increasingly recognise the value of radiation processing of food in fighting such threats to health and hygiene. The threat to plant production (i.e. phytosanitary aspects) is less widely feared but many areas that are very productive in fruit and vegetables have suppressed several of the original pests. Such areas have strict quarantine controls on imports that might carry insects or pests capable of proliferation. The USA is the leading country in exploitation of ionising radiation for insect elimination: an X-ray facility for treating fruit on Hawaii is now operational and allows for the direct transport of fruit to mainland areas such as California. Also, other countries have strict quarantine regulations; they include Australia, Japan and South Africa where ionising radiation can play a valuable role. Certification systems presently under development will help facilitate international trade. 17.3 The principles of irradiation Processing by ionising radiation is a particular kind of energy transfer: the portion of energy transferred per transaction is high enough to cause ionisation. This kind
The world-wide first food irradiation facility became operational in Germany in 1957 for spices, but had to be dismantled in 1959 when Germany banned food irradiation. In 1974 in Japan the Shapiro Potato Irradiator was commissioned and is the oldest food irradiation facility still in operation today. When in 1980 the JECFI made a landmark decision and declared irradiated foods as safe and wholesome for human consumption, it led many governments to permit the radiation processing of food. This did not result in commercial application of the process in all countries. Nevertheless, the total amount of food treated by ionising radiation is increasing, about 200 000 tonne per annum at the time of writing, but is still a very small volume compared to the total amount consumed. However, food irradiation is a niche application, supplementing traditional methods of food processing and serving specific purposes. Two important classes of application, sanitary and phytosanitary, are increasingly recognised. As recently as 1993, children died tragically after eating undercooked (‘rare’) hamburgers. This was caused by Escherichia coli type O157:H7 (EHEC), an emerging pathogen microorganism which is now considered to be ubiquitous. There is always the threat of such emerging hazards in modern, industrial food production. Such risks can only be fought by further improvement of good manufacturing practices and the application of ‘Hazard Analysis and Critical Control Point (HACCP)’. Adherence to such procedures and improvement of hygienic concepts can only reduce or limit the hazard but never eliminate it. For this reason, supplementary methods, in addition to good practices, help suppress such residual risks to a tolerable, acceptable level. Ionising radiation is such a tool, now legal in the USA and helping to make hamburgers, fresh or deep-frozen, far safer for the consumer. Many other pathogen microorganisms are a threat to society, causing death and illness, damages and economic losses. Other examples are Campylobacter and Salmonella in poultry, Salmonella in eggs, Listeria in cheese and sprouts. Governments increasingly recognise the value of radiation processing of food in fighting such threats to health and hygiene. The threat to plant production (i.e. phytosanitary aspects) is less widely feared but many areas that are very productive in fruit and vegetables have suppressed several of the original pests. Such areas have strict quarantine controls on imports that might carry insects or pests capable of proliferation. The USA is the leading country in exploitation of ionising radiation for insect elimination: an X-ray facility for treating fruit on Hawaii is now operational and allows for the direct transport of fruit to mainland areas such as California. Also, other countries have strict quarantine regulations; they include Australia, Japan and South Africa where ionising radiation can play a valuable role. Certification systems presently under development will help facilitate international trade. 17.3 The principles of irradiation Processing by ionising radiation is a particular kind of energy transfer: the portion of energy transferred per transaction is high enough to cause ionisation. This kind Irradiation 373
374 The nutrition handbook for food processors Table 17.1 Types of particle Particle Description electron An elementary corpuscle carrying one unit of positive or negative electrical harge. The positively charged electron is called a positron pha A charged particle, identical to the nucleus of a helium atom, composed of two neutrons and two protons. It carries two positive elementary units of charge. beta A charged particle, identical to an electron or a positron but emitted from a radioactive nucleus gamma A particle or photon emitted from a radioactive nucleus. Fast-moving charged particles in an electric or magnetic field, usuall enerated by high-energy electrons impinging on a high-atomic-number absorber(e.g. tungsten); also called Rontgen-rays. They are generated by braking radiation(bremsstrahlung) wavelengh 104102100102104104610810-10101210141016 Radio waves Visible light Ultraviolet Cosmic radiation ising radiation Photon energy [ev Fig. 17.1 Range of ctrum): ionising radiation is charac- terised by the ability olecular bonds and to transfer electrons; this energy limit is indicated by the dashed line beginning in the range of ultraviolet light. of radiation was discovered because the emitting radioactive material caused ion- isation in the surrounding air. From the multitude of atomic particles known, only gamma rays from nuclear disintegration and accelerated electrons are useful for food processing(Table 17. 1). Electrons may be converted into X-rays by stop- ping them in a converter or target(Fig. 17. 1). Other particles such as neutrons
of radiation was discovered because the emitting radioactive material caused ionisation in the surrounding air. From the multitude of atomic particles known, only gamma rays from nuclear disintegration and accelerated electrons are useful for food processing (Table 17.1). Electrons may be converted into X-rays by stopping them in a converter or target (Fig. 17.1). Other particles such as neutrons 374 The nutrition handbook for food processors Table 17.1 Types of particle Particle Description electron An elementary corpuscle carrying one unit of positive or negative electrical charge. The positively charged electron is called a positron. alpha A charged particle, identical to the nucleus of a helium atom, composed of two neutrons and two protons. It carries two positive elementary units of charge. beta A charged particle, identical to an electron or a positron but emitted from a radioactive nucleus. gamma A particle or photon emitted from a radioactive nucleus. X Fast-moving charged particles in an electric or magnetic field, usually generated by high-energy electrons impinging on a high-atomic-number absorber (e.g. tungsten); also called Röntgen-rays. They are generated by braking radiation (bremsstrahlung). Wavelength [cm] 104 102 10–2 10–4 10–6 10–8 10–10 10–12 10–14 10–16 100 100 102 104 106 108 1010 Radio waves Infrared Visible light Ultraviolet ionising radiation Photon energy [eV] X-radiation Gamma radiation Cosmic radiation Fig. 17.1 Range of energies (electromagnetic spectrum): ionising radiation is characterised by the ability to split molecular bonds and to transfer electrons; this energy limit is indicated by the vertical, dashed line beginning in the range of ultraviolet light
Irradiation 375 女饭 Fig. 17.2 Interaction with matter(photon versus electron): 1)primary incident radiation 2)Compton electrons caused by photon interaction, 3)secondary electrons and final energy transfer, 4)irradiated medium, 5)finite depth of penetration for electrons. are unsuitable because induced radioactivity is produced. The same may occur at elevated energy levels with electrons and X-rays; for this reason the electron energy is limited to a maximum of 10 MeV and the nominal energy of X-rays is limited to 5 Mev Gamma rays of cobalt-60 have photon energies of 1. 17 V nd 1.33 MeV and cannot induce radioactivity; caesium-137 is not available in commercial quantities but gamma rays of 0.66 MeV are emitted from it. This means that gamma rays from available isotope sources are incapable of inducing radioactivity Whether in the form of particles or as electromagnetic waves, the primary high energy is broken into smaller portions and converted into ashower'of secondary electrons(Fig. 17. 2). These electrons finally interact with other atoms and mol- ecules knocking out electrons from their orbits or transferring them to other positions(Fig. 17.3). This means that an elementary negative charge is removed nd a positively charged atom or molecule, i. e. an ion, is left behind. If an elec tron has been transferred then orbital electrons are no longer paired and free radicals are created. Both ions and free radicals are very reactive, in particular in an aqueous medium such as in food, leading finally to chemical reaction prod ucts that are stable. The effects caused by corpuscular or electromagnetic radia tion are essentially equal; the difference is in the dose distribution along the penetration line into matter. Corpuscles have a definite physical range in matter, they are slowed down by several processes of collision and finally stopped. They have no energy beyond their range. Electromagnetic waves are attenuated expo- nentially and do not have a defined physical range A schematic diagramme of irradiation facilities(Fig. 17. 4)helps to understand the simplicity of the irradiation process: the goods are brought by a transport system into the irradiation cell which essentially is a concrete bunker shielding
are unsuitable because induced radioactivity is produced. The same may occur at elevated energy levels with electrons and X-rays; for this reason the electron energy is limited to a maximum of 10 MeV and the nominal energy of X-rays is limited to 5 MeV. Gamma rays of cobalt-60 have photon energies of 1.17 MeV and 1.33 MeV and cannot induce radioactivity; caesium-137 is not available in commercial quantities but gamma rays of 0.66 MeV are emitted from it. This means that gamma rays from available isotope sources are incapable of inducing radioactivity. Whether in the form of particles or as electromagnetic waves, the primary high energy is broken into smaller portions and converted into a ‘shower’ of secondary electrons (Fig. 17.2). These electrons finally interact with other atoms and molecules knocking out electrons from their orbits or transferring them to other positions (Fig. 17.3). This means that an elementary negative charge is removed and a positively charged atom or molecule, i.e. an ion, is left behind. If an electron has been transferred then orbital electrons are no longer paired and free radicals are created. Both ions and free radicals are very reactive, in particular in an aqueous medium such as in food, leading finally to chemical reaction products that are stable. The effects caused by corpuscular or electromagnetic radiation are essentially equal; the difference is in the dose distribution along the penetration line into matter. Corpuscles have a definite physical range in matter, they are slowed down by several processes of collision and finally stopped. They have no energy beyond their range. Electromagnetic waves are attenuated exponentially and do not have a defined physical range. A schematic diagramme of irradiation facilities (Fig. 17.4) helps to understand the simplicity of the irradiation process: the goods are brought by a transport system into the irradiation cell which essentially is a concrete bunker shielding Irradiation 375 Electrons Photons 5 1 4 3 1 4 3 2 Fig. 17.2 Interaction with matter (photon versus electron): 1) primary incident radiation, 2) Compton electrons caused by photon interaction, 3) secondary electrons and final energy transfer, 4) irradiated medium, 5) finite depth of penetration for electrons