Introduction Trends in food spoilage and sa ther than falling, year by year(e.g. Foods deteriorate as a result of phys hanges, the activities of enzymes and of micro- r approximately doubled between 1983 organisms (Table I). In addition, post-harvest losses in the UK, with substantial economic consequences occur due to insect pests. The activities of micro-( Roberts and Sockett, 1994). In developing countries, rganisms are by far the most important quantitatively, food poisoning remains one of the major causes of ading to enormous levels of spoilage(Table II). Losses morbidity and mortality. Control measures are evidently of commodity foods, particularly in the less-well- failing or, at least, not making the progress that we developed countries of the world, are estimated to should expect in the final decade of this millennium exceed 50% for fruits and vegetables and 10% for cereal New approaches to the effective elimination of the most ains and legumes (Anon, 1993). Deterioration in important of the food poisoning micro-organisms from olour, taste and texture of foods is catalyzed by the relatively small number of most frequently contami- endogenous enzymes, and undesirable physiological nated foods are urgently needed. changes, such as ripening and sprouting, degrade food Food preservation technologies The presence of certain micro-organisms in foods The major food preservation technologies, which lead to food poisoning by infection or, if the micro- employed to counteract the deleterious effects of micro multip Food, to intoxication organisms in foods, mostly act by inhibiting or delaying some instances (Table II). Unfortunately heir growth rather than by inactivating them(Table If) developed countries, despite public awareness of food For example, the d, low pH, salts, su poisoning risks, the numbers of food ing cases are preservatives, etc, all act essentially by inhibition. Many Table I Quality loss reactions of foods(adapted from Gould, 1989). Chemical Enzymic Microbiological Mass transfer. movement of low Oxidative rancidity Lipolytic rancidity Multiplication of spoilage MW components micro-organisms Drying, loss of succulence, caking Loss of colour Proteolysis and other Hydration, loss of crisp textures Non-enzymic browning Enzymic browning Multiplication of toxin Loss of nutrients Freeze-induced damag
Introduction Trends in food spoilage and safety Foods deteriorate as a result of physical and chemical changes, the activities of enzymes and of microorganisms (Table I). In addition, post-harvest losses occur due to insect pests. The activities of microorganisms are by far the most important quantitatively, leading to enormous levels of spoilage (Table 11). Losses of commodity foods, particularly in the less-welldeveloped countries of the world, are estimated to exceed 50% for fruits and vegetables and 10% for cereal grains and legumes (Anon, 1993). Deterioration in colour, taste and texture of foods is catalyzed' by endogenous enzymes, and undesirable physiological changes, such as ripening and sprouting, degrade food quality. The presence of certain micro-organisms in foods may lead to food poisoning by infection or, if the microorganisms have multiplied in a food, to intoxication, in some instances (Table 11). Unfortunately, in many developed countries, despite public awareness of food poisoning risks, the numbers of food poisoning cases are rising, rather than falling, year by year (e.g. reported cases of disease caused by Salmonella and Campylobader approximately doubled between 1983 and 1993, in the UK, with substantial economic consequences (Roberts and Sockett, 1994)). In developing countries, food poisoning remains one of the major causes of morbidity and mortality. Control measures are evidently failing or, at least, not making the progress that we should expect in the final decade of this millennium. New approaches to the effective elimination of the most important of the food poisoning micro-organisms from the relatively small number of most frequently contaminated foods are urgently needed. Food preservation technologies The major food preservation technologies, which are employed to counteract the deleterious effects of microorganisms in foods, mostly act by inhibiting or delaying their growth rather than by inactivating them (Table 111). For example, the use of cold, low pH, salts, sugars, preservatives, etc., all act essentially by inhibition. Many Table I Quality loss reactions of foods (adapted from Gould, 1989). Physical Chemical Enzymic Microbiological Mass transfer, movement of low Oxidative rancidity Lipolytic rancidity Multiplication of spoilage MW components micro-organisms Drying, loss of succulence, caking Loss of colour Proteolysis and other enzyme activities organisms Presence of infectious microHydration, loss of crisp textures Non-enzymic browning Enzymic browning Multiplication of toxinogenic Loss of flavours Freeze-induced damage micro-organisms Loss of nutrients 1
2 Introduction Table II Microbial food spoilage and food poisoning Table III Food preservation techniques(updated from Gould, 1989 Problems Examples Mode of action Preservation technique Excretion of majot Lactic and acids of growth etabolic products rbon dioxide Reduced water activity conserving with added lability of nutrients in Secretion of enzyme ipass, proteases, cellulases, etc. ausing flavour and texture changes Removal of oxygen from vacuum Biomass slime, haze, mould colonies, etc. Presence sf infectious salmonella, Campy Addition of acids, directly or by multiplication of Staphylococcus aureus, Clostridium Increased ethanol levels by botulinum fermentation fortification release in Addition of preservatives including have been proposed in recent years in reactio Inactivation consumers'requirements for less severely proce sterilize, by hot air, water or high m: by newer met more natural, additive-free foods, also act by inhibition luding microwaves and electrical (e.g. 'modified atmosphere packaging, use of naturally- (ohmic) methods occurring antimicrobials; Dillon and Board, 1994) lonizing radiation to in Since the major underlying cause of microbial food spoilage and food poisoning is ultimately the presence of rgan 以 the micro-organisms in the foods in the first place, it Ultraviolet radiation to inactivate follows that inactivation techniques are ideally prefera 0-organisms in water or on the ble to inhibitory ones. Heat is the only food preservation surfaces of foods and packaging chnique which is used on a large scale, that acts primarily by inactivation High-intensity visible laser and a problem with inactivation techniques, such as high erature processing, has been that they often tend to sms in water and on surfaces e unacceptable damage in the quality of food Application of ultra-high roducts. For this reason, procedures that minimize heat duced damage are being pursued, e.g. rotary retorting, crowave heating, ohmic heating, etc, for pasteuriza- of ultrasound with mild on and sterilization. Also, essentially non-thermal echniques are being explored and some are already sonication) ing exploited on a small scale, e.g. enzymic tech Addition of bad ques such as the addition of lysozyme, other enzymes nd naturally-occurring antimicrobials to foods; physical natural antimic techniques such as the application of ultra-high pressure, elec ed with mild heat and slightly rmosonication')(Table Ill These 'emerging'techniques are novel and scientif- Ionizing radiation ically challenging but few of them are widely employ Food irradiation is the use of ionizing radiation to As yet, one of the most effective altematives to heat for increase food storage life, reduce post-harvest food he inactivation of micro-organisms Is zing losses and eliminate food poisoning micro-organisms The effectiveness of ionizing radiation, its penetrating
2 Introduction Table I1 Microbial food spoilage and food poisoning problems (adapted from Gould, 1989). Problems Examples Food spoilage Excretion of major metabolic products Excretion of minor metabolic products Secretion of enzymes Biomass Food poisoning Presence of infectious micro-organisms Multiplication of toxinogenic microorganisms Lactic and acetic acids causing souring; gases (carbon dioxide, hydrogen) causing blowing. Low odour threshold compounds (amines, esters, thiols) causing offodours, discolouration. Lipases, proteases, cellulases, etc., causing flavour and texture changes. Visible presence of micro-organisms (slime, haze, mould colonies, etc.) Salmonella, Campylobacter; Listeria. Staphylococcus aureus, Clostridium botulinum. of the new developments, which have come into use or have been proposed in recent years in reaction to consumers’ requirements for less severely processed, more natural, additive-free foods, also act by inhibition (e.g. ‘modified atmosphere packaging’, use of naturallyoccurring antimicrobials; Dillon and Board, 1994). Since the major underlying cause of microbial food spoilage and food poisoning is ultimately the presence of the micro-organisms in the foods in the first place, it follows that inactivation techniques are ideally preferable to inhibitory ones. Heat is the only food preservation technique, which is used on a large scale, that acts primarily by inactivation. A problem with inactivation techniques, such as hightemperature processing, has been that they often tend to produce unacceptable damage in the quality of food products. For this reason, procedures that minimize heatinduced damage are being pursued, e.g. rotary retorting, microwave heating, ohmic heating, etc., for pasteurization and sterilization. Also, essentially non-thermal techniques are being explored and some are already being exploited on a small scale, e.g. enzymic techniques such as the addition of lysozyme, other enzymes and naturally-occurring antimicrobials to foods; physical techniques such as the application of ultra-high pressure, high-voltage electric discharges (‘electroporation’), ultrasonics combined with mild heat and slightly raised pressure (‘manothermosonication’) (Table 111, Gould, 1995). These ‘emerging’ techniques are novel and scientifically challenging but few of them are widely employed. As yet, one of the most effective alternatives to heat for the inactivation of micro-organisms is ionizing radiation. Table 111 Food preservation techniques (updated from Gould, 1989). Mode of action Preservation technique Inhibition or slowing of growth freezing. Lowered temperature by chilling, Reduced water activity achieved by drying, curing with added salts, conserving with added sugars. Restricted availability of nutrients in water-in-oil emulsions. Removal of oxygen from vacuum packs. Increased carbon dioxide, in ‘modified atmosphere’ packs. Addition of acids, directly or by fermentation. Increased ethanol levels by fermentation, fortification, release in packs from sachets. Addition of preservatives including naturally-occurring antimicrobials. Inactivation Heat, to blanch, pasteurize or sterilize, by hot air, water or highpressure steam; by newer methods including microwaves and electrical (ohmic) methods. Ionizing radiation to inactivate pathogenic or spoilage microorganisms in foods. Ultraviolet radiation to inactivate micro-organisms in water or on the surfaces of foods and packaging materials. High-intensity visible laser and noncoherent light to inactivate microorganisms in water and on surfaces. Application of ultra-high pressure Application of high-voltage electric discharges. Application of ultrasound with mild heat and pressure (manothermosonication). Addition of bacteriolytic (e.g. lysozyme) and other enzymes and natural antimicrobials. Acid dips and sprays for carcase decontamination. Ionizing radiation Food irradiation is the use of ionizing radiation to increase food storage life, reduce post-harvest food losses and eliminate food poisoning micro-organisms. The effectiveness of ionizing radiation, its penetrating
Introduction 3 power and its straightforward kinetics make it much the extensive losses that now occur. Food irradiation mpler, in practice, to use than heat. It does bring about could fulfil these requirements for some foods if wider serious organoleptic changes in some foods, but very understanding and acceptance of the treatment could be tle change in others. In this respect, it is analogous to most of the other means of food preservation that alter the quality attributes of different foods to some extent. References The toxicological aspects of food irradiation have Anon(1993)Report and recommendations of a working en studied more extensively than for any group, in Cost-benefit Aspects of Food irradiation reservation technique. As a result of these studies, the Processing Proceedings of an IAEA/FAO/WHO xicological safety and wholesomeness'of foods irradiated up to specified doses, have been judged to Codex Alimentarius Commission(1984) Codex general satisfactory and to introduce no special or nutritiona standard for irradiated foods and recommended inter problems(WHO, 1981). This has led to acceptance by national code of practice for the operation of radiation 30 governments of a Codex General Standard for facilities used for the treatment of foods Codex Irradiated Foods (Codex Alimentarius Commission Alimentarius volume Xv lst edition. Food and 984)and to approval by 37 countries of over 40 foods Agriculture Organization of the United Nations/world or groups of foods for consumption. Currently, full-scale Health Organization, Rom plementation is inhibited by issues concerning eco- Dillon, V.M. and Board, RG.(eds)(1994) Natural nomic viability and the levels of consumer acceptance of Antimicrobial Systems and Food Preservation, CAB the process(Lagunas-Solar, 1995) International, Wallingford, Oxon Gould, Gw.(1989) Introduction, in Mechanisms of Conclusions Action of Food Preservation Procedures, (ed. G w Substantial advances have been made in understanding Gould) Elsevier Applied Science, London, pp 1-10 the basis of efficacy of food irradiation for the reduction Gould, G.w.(ed )(1995) New Methods of Food of food spoilage and for the improvement in food safety Preservation. Blackie Academic and Professional However, although a surge in application was expected n in the use of food irradiation has been Lagunas-Solar, MC.(1995) Radi rocessing of slow. without doubt, a major reason for this has been the foods: an overview of scientific current reluctance by consumers in many countries to accept that status, Journal of Food Protect (2),186-92 the process is satisfactorily safe, in spite of the extensive Roberts, J.A. and Sockett, PN. (1994)The socio scientific evidence that now exists economic impact of human Salmonella enteritidis safely supplement the use of heat, and other more severe biology, 21, 117-29 reservation procedures, for the improvement of food WHo(1981)Report of a Joint FAO/WHO/AEA Expe Comm life of commodity foods are necessary in order to reduce World Health Organization
Introduction 3 the extensive losses that now occur. Food irradiation could fulfil these requirements for some foods if wider understanding and acceptance of the treatment could be achieved. power and its straightforward kinetics make it much simpler, in practice, to use than heat. It does bring about serious organoleptic changes in some foods, but very little change in others. In this respect, it is analogous to most of the other means of food preservation that alter the quality attributes of different foods to some extent. The toxicological aspects of food irradiation have been studied more extensively than for any other food preservation technique. As a result of these studies, the toxicological safety and ‘wholesomeness’ of foods, irradiated up to specified doses, have been judged to be satisfactory and to introduce no special or nutritional problems (WHO, 1981). This has led to acceptance by 130 governments of a Codex General Standard for Irradiated Foods (Codex Alimentarius Commission, 1984) and to approval by 37 countries of over 40 foods or groups of foods for consumption. Currently, full-scale implementation is inhibited by issues concerning economic viability and the levels of consumer acceptance of the process (Lagunas-Solar, 1995). Conclusions Substantial advances have been made in understanding the basis of efficacy of food irradiation for the reduction of food spoilage and for the improvement in food safety. However, although a surge in application was expected, the expansion in the use of food irradiation has been slow. Without doubt, a major reason for this has been the reluctance by consumers in many countries to accept that the process is satisfactorily safe, in spite of the extensive scientific evidence that now exists. New inactivation techniques are urgently needed to safely supplement the use of heat, and other more severe preservation procedures, for the improvement of food quality and safety. New techniques to extend the storage life of commodity foods are necessary in order to reduce References Anon (1993) Report and recommendations of a working group, in Cost-benefit Aspects of Food Irradiation Processing, Proceedings of an IAEA/FAO/WHO International Symposium, Aix-en-Provence, p. 48 1. Codex Alimentarius Commission (1984) Codex general standard for irradiated foods and recommended international code of practice for the operation of radiation facilities used for the treatment of foods, Codex Alimentarius Volume Xv 1st edition, Food and Agriculture Organization of the United Nations/Wor€d Health Organization, Rome. Dillon, V.M. and Board, R.G. (eds) (1994) Natural Antimicrobial Systems and Food Preservation, CAB International, Wallingford, Oxon. Gould, G.W. (1989) Introduction, in Mechanisms of Action of Food Preservation Procedures, (ed. G.W. Gould) Elsevier Applied Science, London, pp. 1-10, Gould, G.W. (ed.) (1995) New Methods of Food Preservation, Blackie Academic and Professional, Glasgow. Lagunas-Solar, M.C. ( 1995) Radiation processing of foods: an overview of scientific principles and current status, Journal of Food Protection, 58(2), 186-92. Roberts, J.A. and Sockett, P.N. (1994) The socioeconomic impact of human Salmonella enteritidis infection, International Journal of Food Microbiology, 21, 117-29. WHO (1981) Report of a Joint FAO/WHO/IAEA Expert Committee, WHO Technical Report Series, No. 659, World Health Organization
