《食品加工营养手册》参考资料（英文版）17 Irradiation

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 par￾ticles 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 prop￾erties 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 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 ionisa￾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￾tion, 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 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 sur￾vival 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 indus￾try is slightly higher than that of other branches. There have been only a few acci￾dents 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 pre￾scribed 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 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 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 spe￾cific 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 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 car￾bohydrate, lipid and protein components) are very little affected by ionising radi￾ation. 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