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
376 The nutrition handbook for food processors Orbital electrons ticles interact with the orbital electrons and are scattered. an orbital electron is removed ng kinetic energy as a secondary electron; in this way an ionised atom/ molecule is left behind and a cascade of secondary electrons causes further ionisation or formation of free radicals Beam handling system (10 Mev electrons) Radioactive source (Co60) Fig. 17.4 Schematic diagram of irradiation facilities: the product to be irradiated has to pass through the irradiation zone; the design details largely depend on the physical prop- erties of the type of radiation used and may be adapted to the packaging and handling requirements of the goods
376 The nutrition handbook for food processors Incident Scattered Ionisation Secondary electron Orbital electrons Fig. 17.3 Principal diagram of ‘ionisation’: whether photon or electron, the incident particles interact with the orbital electrons and are scattered, an orbital electron is removed gaining kinetic energy as a secondary electron; in this way an ionised atom/molecule is left behind and a cascade of secondary electrons causes further ionisation or formation of free radicals. Beam handling system (10 MeV electrons) Radioactive source (Co 60) Irradiated food product 1 6 12 11 10 7 8 9 2 3 Fig. 17.4 Schematic diagram of irradiation facilities: the product to be irradiated has to pass through the irradiation zone; the design details largely depend on the physical properties of the type of radiation used and may be adapted to the packaging and handling requirements of the goods
Irradiation 377 the environment and the workers from the radiation. A tunnel system allows free access for the goods but prevents radiation leakage; fences and detectors prevent unintentional access of anything or anyone when the radiation is on. Machine sources(accelerators) emit the radiation uni-directionally, gamma sources (radioactive isotopes) emit it in all directions. This means that for electron and X-ray processing the goods pass just before the beam exit window and for gamma processing the goods are piled and moved around the source to absorb as much as possible of the emitted energy. When it is not needed a machine source is simply switched off; for radioactive isotopes the frame with the source must be moved to a safe position which is usually a deep water pool. The design of irra- diation facilities is widely standardised; the safety-features are offically approved and authoritative control is well established 17. 4 The effects of irradiation on food There is a vast literature on the effects of ionising radiation on food and food components; for the nutritional aspects of the subject a very few references are sufficient(Diehl, 1995; Molins, 2001). Early textbooks even today are still rele vant(Elias and Cohen, 1977, Josephson and Peterson, 1983)and in later years there has been an updating of details(WHO, 1994) The interaction of ionising radiation with matter takes place by means of a cascade of secondary electrons carrying enough kinetic energy to cause ionia- tion of atoms and molecules and the formation of free radicals besides these direct effects and primary chemical reactions chain reactions of secondary and indirect transitions take place. In systems as complex as food and for biological systems usually high in water content most primary reactive species are formed by the radiolysis of water and the pathways of further reactions largely depend on composition, temperature, dose rate and relative reactivities. Only for a few very simple single-component models have the full pathways of reactions been identified; for highly complex systems a complete picture has not yet been achieved. Nevertheless, some aspects of the picture are beginning to emerge especially with regard to the main components, i.e. carbohydrates, lipids and proteins. The effects of radiation on micronutrients, in particular on vitamins, are complex and are also dependent on overall composition; some macronutrients may protect micronutrients from radiolysis. Minerals and trace elements are not studied because they cannot be affected by radiation processing of food However, the toxicological and nutritional consequences are discussed in further sections of this chapter Biological effects include the beneficial use of irradiation for sprout inhibi ion, ripening delay and insect disinfestation. Microbiological effects include the use of irradiation for the suppression of pathogen microorganisms and the reduc- tion of other, spoilage-causing microorganisms. For both procedures, the princi pal reaction is irreversible radiation damage to the DNA disabling essential functions of the cell. Such DNA changes are irrelevant with regard to food and
the environment and the workers from the radiation. A tunnel system allows free access for the goods but prevents radiation leakage; fences and detectors prevent unintentional access of anything or anyone when the radiation is ‘on’. Machine sources (accelerators) emit the radiation uni-directionally, gamma sources (radioactive isotopes) emit it in all directions. This means that for electron and X-ray processing the goods pass just before the beam exit window and for gamma processing the goods are piled and moved around the source to absorb as much as possible of the emitted energy. When it is not needed a machine source is simply switched off; for radioactive isotopes the frame with the source must be moved to a safe position which is usually a deep water pool. The design of irradiation facilities is widely standardised; the safety-features are offically approved and authoritative control is well established. 17.4 The effects of irradiation on food There is a vast literature on the effects of ionising radiation on food and food components; for the nutritional aspects of the subject a very few references are sufficient (Diehl, 1995; Molins, 2001). Early textbooks even today are still relevant (Elias and Cohen, 1977, Josephson and Peterson, 1983) and in later years there has been an updating of details (WHO, 1994). The interaction of ionising radiation with matter takes place by means of a cascade of secondary electrons carrying enough kinetic energy to cause ionisation of atoms and molecules and the formation of free radicals. Besides these direct effects and primary chemical reactions chain reactions of secondary and indirect transitions take place. In systems as complex as food and for biological systems usually high in water content most primary reactive species are formed by the radiolysis of water and the pathways of further reactions largely depend on composition, temperature, dose rate and relative reactivities. Only for a few very simple single-component models have the full pathways of reactions been identified; for highly complex systems a complete picture has not yet been achieved. Nevertheless, some aspects of the picture are beginning to emerge, especially with regard to the main components, i.e. carbohydrates, lipids and proteins. The effects of radiation on micronutrients, in particular on vitamins, are complex and are also dependent on overall composition; some macronutrients may protect micronutrients from radiolysis. Minerals and trace elements are not studied because they cannot be affected by radiation processing of food. However, the toxicological and nutritional consequences are discussed in further sections of this chapter. Biological effects include the beneficial use of irradiation for sprout inhibition, ripening delay and insect disinfestation. Microbiological effects include the use of irradiation for the suppression of pathogen microorganisms and the reduction of other, spoilage-causing microorganisms. For both procedures, the principal reaction is irreversible radiation damage to the DNA disabling essential functions of the cell. Such DNA changes are irrelevant with regard to food and Irradiation 377
378 The nutrition handbook for food processors nutrition. There was previous concern as to whether irradiation and recycling these irradiated microorganisms could cause mutations that were capable of sur- vival and were more toxic or vigorous as their precursors. It has been shown that this is not the case and that ' no microbiological problems' are introduced World Health Organization, 1981). The storage of irradiated food is important in order to avoid growth of microorganisms or recontamination 17.5 The safety of irradiated food Irradiated food does not become radioactive and this is now accepted even by opponents of the procedure. The limitation of allowable isotope sources to cobalt 60 and caesium-137 and the limitation of the maximum energy of electrons to 10 MeV and of the maximum nominal energy for X-rays(bremsstrahlung or braking radiation) to 5 MeV provides adequate safeguards. Even if the nominal energy for X-rays is increased to 10 MeV the theoretically induced radioactivity would be much less than the natural activity there already is in food due mainly to the presence of potassium-40. Furthermore, it would be very difficult to measure such sparse induced activity in the presence of the natural radioactivity It can be generally stated that the safety record of the radiation processing indus try is slightly higher than that of other branches. There have been only a few acci- scribed procedures that included bridging safety Cllcl , Gion and the reason dents related to radiation exposure or radioactive contamina for all of them was a conscious violation of safety rules or non-adherence to pre From the beginning of systematic studies in the late 1940s it was recognised hat irradiated food needed careful toxicological study before the technology could be applied to food manufacturing and processing. It is useless to question why the word radiation carries such a negative image and causes considerable suspicion, not only among lay persons, but also among many scientists. In such a situation, governments and food control authorities were well advised to restrict the application of the new technology. However, further results have become available and the final judgement has been stated by the World Health Organi- zation (1981)as: ' Irradiation of any commodity. presents no toxicological hazard. This means that governments and authorities are responsible for the con- sequences and recognise the radiation processing of food as safe and as simply one among several other technologies. There have been thorough chemical studies, leading to the principle of ' chemiclearance'and classes of food that are chemically similar have been compared. It was also standard procedure to feed the food under consideration to animals and to look for possible effects on factors such as longevity, reproductive capacity, tumour formation, growth, unusual behaviour, haematological and biochemical indices, chromosomal abnormalities and genetic defects. These studies are very numerous and difficult for the non- specialist to follow; expert reviews are available elsewhere (Diehl, 1995).There have been also several publications reporting negative effects; however, a thor- ough follow-up always revealed deficiencies in the experimental organisation
nutrition. There was previous concern as to whether irradiation and recycling these irradiated microorganisms could cause mutations that were capable of survival and were more toxic or vigorous as their precursors. It has been shown that this is not the case and that ‘no special microbiological problems’ are introduced (World Health Organization, 1981). The storage of irradiated food is important in order to avoid growth of microorganisms or recontamination. 17.5 The safety of irradiated food Irradiated food does not become radioactive and this is now accepted even by opponents of the procedure. The limitation of allowable isotope sources to cobalt- 60 and caesium-137 and the limitation of the maximum energy of electrons to 10 MeV and of the maximum nominal energy for X-rays (bremsstrahlung or braking radiation) to 5 MeV provides adequate safeguards. Even if the nominal energy for X-rays is increased to 10 MeV the theoretically induced radioactivity would be much less than the natural activity there already is in food due mainly to the presence of potassium-40. Furthermore, it would be very difficult to measure such sparse induced activity in the presence of the natural radioactivity. It can be generally stated that the safety record of the radiation processing industry is slightly higher than that of other branches. There have been only a few accidents related to radiation exposure or radioactive contamination and the reason for all of them was a conscious violation of safety rules or non-adherence to prescribed procedures that included bridging safety circuits. From the beginning of systematic studies in the late 1940s it was recognised that irradiated food needed careful toxicological study before the technology could be applied to food manufacturing and processing. It is useless to question why the word ‘radiation’ carries such a negative image and causes considerable suspicion, not only among lay persons, but also among many scientists. In such a situation, governments and food control authorities were well advised to restrict the application of the new technology. However, further results have become available and the final judgement has been stated by the World Health Organization (1981) as: ‘Irradiation of any commodity... presents no toxicological hazard’. This means that governments and authorities are responsible for the consequences and recognise the radiation processing of food as safe and as simply one among several other technologies. There have been thorough chemical studies, leading to the principle of ‘chemiclearance’ and classes of food that are chemically similar have been compared. It was also standard procedure to feed the food under consideration to animals and to look for possible effects on factors such as longevity, reproductive capacity, tumour formation, growth, unusual behaviour, haematological and biochemical indices, chromosomal abnormalities and genetic defects. These studies are very numerous and difficult for the nonspecialist to follow; expert reviews are available elsewhere (Diehl, 1995). There have been also several publications reporting negative effects; however, a thorough follow-up always revealed deficiencies in the experimental organisation or 378 The nutrition handbook for food processors
Irradiation 379 in the final evaluation and validation of the results. This is not the place to discuss such findings as increased polyploidy in malnourished children and the reasons why those experiments have been dismissed by expert bodies; full details and guments can be found elsewhere(Diehl, 1995). It is sufficient to state that the validation of competent expert bodies (World Health Organization, 1981, 1994) always resulted in the 'green light for food irradiation, and finally for any food at any dose(World Health Organization, 1999) 17.6 The nutritional adequacy of irradiated food Most food preservation and decontamination procedures, including irradiation, cause some loss in the nutritional value of foods. Further losses generally occur luring storage and during preparation for consumption(e. g in cooking). The spe ific chemical changes brought about in foods by irradiation include some that alter the nutritional value, but the magnitudes of the changes are small when com pared with those that result from other procedures currently in use. This has led most expert groups to conclude that reduction in the nutritional quality of foods resulting from the widespread use of irradiation is an insignificant part of the total diet as a whole(Elias and CohIn 1977; Advisory Committee on Irradiated and Novel Foods, 1986). One expert group concluded that irradiation of food introduces no special nutritional problems'(World Health Organization, 1981) This conclusion emphasises the word'special, recognising that there might be particular problems with some individual food products. Most expert groups also recommend that the nutrient content of irradiated foods should continue to be monitored while such foods are being introduced A problem with many of the literature reports on the effects of irradiation on food constituents is that the studies have used laboratory 'model experiments, often with pure or relatively pure target substances and irradiated in such media as water or buffers. Whilst these studies are ideal for investigating the chemistry of the radiation-induced changes, it is very difficult to extrapolate from them to the situation in real foods. In real foods, many of the other components present usually in large quantities, interact, quench and otherwise interfere with the reactions of the radiolysis-derived products. Consequently, the magnitude of the changes that occur in specific components in a food matrix is generally much lower than the magnitude of those observed in simpler laboratory studies (Josephson et al, 1979) In general, the nutritional values of the macronutrients in foods(e. g. the car bohydrate, lipid and protein components) are very little affected by ionising radi- ation. Some of the micronutrients, including some vitamins and polyunsaturated atty acids, are more sensitive but their sensitivity is very dependent on the nature of the food. At the l kGy dose level, which is in excess of insect disinfestant applications, virtually no nutrient depletion is usually measurable although there have been reports of rise and fall in ascorbic acid(vitamin C) levels made in con flicting publications. At the 10kGy level, the vitamins ascorbic acid, thiamine
in the final evaluation and validation of the results. This is not the place to discuss such findings as increased polyploidy in malnourished children and the reasons why those experiments have been dismissed by expert bodies; full details and arguments can be found elsewhere (Diehl, 1995). It is sufficient to state that the validation of competent expert bodies (World Health Organization, 1981, 1994) always resulted in the ‘green light’ for food irradiation, and finally for any food at any dose (World Health Organization, 1999). 17.6 The nutritional adequacy of irradiated food Most food preservation and decontamination procedures, including irradiation, cause some loss in the nutritional value of foods. Further losses generally occur during storage and during preparation for consumption (e.g. in cooking). The specific chemical changes brought about in foods by irradiation include some that alter the nutritional value, but the magnitudes of the changes are small when compared with those that result from other procedures currently in use. This has led most expert groups to conclude that reduction in the nutritional quality of foods resulting from the widespread use of irradiation is an insignificant part of the total diet as a whole (Elias and Cohln 1977; Advisory Committee on Irradiated and Novel Foods, 1986). One expert group concluded that ‘irradiation of food . . . introduces no special nutritional problems’ (World Health Organization, 1981). This conclusion emphasises the word ‘special’, recognising that there might be particular problems with some individual food products. Most expert groups also recommend that the nutrient content of irradiated foods should continue to be monitored while such foods are being introduced. A problem with many of the literature reports on the effects of irradiation on food constituents is that the studies have used laboratory ‘model’ experiments, often with pure or relatively pure target substances and irradiated in such media as water or buffers. Whilst these studies are ideal for investigating the chemistry of the radiation-induced changes, it is very difficult to extrapolate from them to the situation in real foods. In real foods, many of the other components present, usually in large quantities, interact, quench and otherwise interfere with the reactions of the radiolysis-derived products. Consequently, the magnitude of the changes that occur in specific components in a food matrix is generally much lower than the magnitude of those observed in simpler laboratory studies (Josephson et al, 1979). In general, the nutritional values of the macronutrients in foods (e.g. the carbohydrate, lipid and protein components) are very little affected by ionising radiation. Some of the micronutrients, including some vitamins and polyunsaturated fatty acids, are more sensitive but their sensitivity is very dependent on the nature of the food. At the 1 kGy dose level, which is in excess of insect disinfestants applications, virtually no nutrient depletion is usually measurable although there have been reports of rise and fall in ascorbic acid (vitamin C) levels made in con- flicting publications. At the 10 kGy level, the vitamins ascorbic acid, thiamine Irradiation 379
380 The nutrition handbook for food processors change but the extent varies considerably and depends on the specific foy a (vitamin B1) and pyridoxine(vitamin B6) are generally the most sensitive to Certain minerals and trace elements are essential for health but their irradia tion at the energies employed in food processing does not result in any change Harris and von Loeseke, 1969) 17. Vitamins Some vitamins are well known for their sensitivity to the effects of ionising radi- ation. Their inactivation (i.e. loss of biological activity) results predominantly from reactions with free radicals and other reactive species generated by the radi- olysis of water in foods. Since these reactive molecules interact with a wide variety of food components, the exact effect of irradiation on a particular vitamin depends not only on the chemical nature of the particular vitamin, but also varies greatly with the nature of the food itself. In vitro studies, in which dilute solu- tions of vitamins have been irradiated, may indicate sensitivities that are never seen in foods, where substantial by competitor molecules usuall occurs( Goldblith, 1955) Reactivity of individual vitamins varies according to their chemical nature World Health Organization, 1994). The most important with respect to food irra- diation, include the water soluble vitamins: ascorbic acid vitamin (vitamin B1); riboflavin(vitamin B2); niacin(vitamin Bs); biotin(vitamin Blo) folic acid (pteroylglutamic acid); pyridoxine(vitamin B&); pantothenic acid cyanocobalamin(vitamin B12); and the fat soluble vitamins: retinol and some of its derivatives(vitamin A); calciferol and some of its derivatives(vitamin D) tocopherols(vitamin E): naphthaquinone derivatives(vitamin K) Among the fat-soluble vitamins the ranking by decreasing sensitivity to radi- ation is: Carotenoids have a similar sensitivity to vitamin A. However, this is no strict order as sensitivity is largely affected by the protective properties of the other main components of a particular food. For this reason, conflicting findings from the published literature are easily explained by the experimental conditions, sometimes using low concentrations of a single vitamin in a solvent which does not resemble a real food. Such findings always need expert interpretation. Among the water-soluble vitamins B,thiamine) is the most sensitive. However, it is notable that radiation-sterilised pork and beef still retains more thiamine than a heat-sterilised equivalent. The most contradictory results have been obtained with vitamin C. One main explanation is whether only ascorbic acid or ascorbic and dehydroascorbic acid was determined, or whether the results are reported as'total vitamin C. Vitamin C is also very sensitive to storage conditions and natural variability might even mask irradiation effects. The following sections discuss tamins
(vitamin B1) and pyridoxine (vitamin B6) are generally the most sensitive to change but the extent varies considerably and depends on the specific food. Certain minerals and trace elements are essential for health but their irradiation at the energies employed in food processing does not result in any change (Harris and von Loeseke, 1969). 17.7 Vitamins Some vitamins are well known for their sensitivity to the effects of ionising radiation. Their inactivation (i.e. loss of biological activity) results predominantly from reactions with free radicals and other reactive species generated by the radiolysis of water in foods. Since these reactive molecules interact with a wide variety of food components, the exact effect of irradiation on a particular vitamin depends not only on the chemical nature of the particular vitamin, but also varies greatly with the nature of the food itself. In vitro studies, in which dilute solutions of vitamins have been irradiated, may indicate sensitivities that are never seen in foods, where substantial ‘quenching’ by competitor molecules usually occurs (Goldblith, 1955). Reactivity of individual vitamins varies according to their chemical nature (World Health Organization, 1994). The most important with respect to food irradiation, include the water soluble vitamins: ascorbic acid (vitamin C); thiamine (vitamin B1); riboflavin (vitamin B2); niacin (vitamin B5); biotin (vitamin B10); folic acid (pteroylglutamic acid); pyridoxine (vitamin B6); pantothenic acid; cyanocobalamin (vitamin B12); and the fat soluble vitamins: retinol and some of its derivatives (vitamin A); calciferol and some of its derivatives (vitamin D); tocopherols (vitamin E); naphthaquinone derivatives (vitamin K). Among the fat-soluble vitamins the ranking by decreasing sensitivity to radiation is: E >> A >> D >> K Carotenoids have a similar sensitivity to vitamin A. However, this is no strict order as sensitivity is largely affected by the protective properties of the other main components of a particular food. For this reason, conflicting findings from the published literature are easily explained by the experimental conditions, sometimes using low concentrations of a single vitamin in a solvent which does not resemble a real food. Such findings always need expert interpretation. Among the water-soluble vitamins B1 (thiamine) is the most sensitive. However, it is notable that radiation-sterilised pork and beef still retains more thiamine than a heat-sterilised equivalent. The most contradictory results have been obtained with vitamin C. One main explanation is whether only ascorbic acid or ascorbic and dehydroascorbic acid was determined, or whether the results are reported as ‘total vitamin C’. Vitamin C is also very sensitive to storage conditions and natural variability might even mask irradiation effects. The following sections discuss particular vitamins. 380 The nutrition handbook for food processors