《冷冻食品》（英文第二版） Part 3 Raw material selection.pdf_大学文库

approaching six weeks for some red meat. Even under the best commercial practice (strictly hygienic slaughtering, rapid cooling, vacuum packing and storage at super chill (10.5ºC)) the maximum life that can be achieved in red meat is approximately 20 weeks, however, freezing will extend the storage life of meat to a number of years. In a perfect world, red meat and poultry would be completely free of pathogenic (food poisoning) micro-organisms when produced. However, under normal methods of production pathogen-free meat cannot be guaranteed. For example, salmonella contamination of chilled and frozen poultry carcasses has been significantly reduced in the UK (Fig. 3.1). However, over one-third was still contaminated in 1994.1 While the internal musculature of a healthy mammal or bird is essentially sterile after slaughter, all meat animals carry large numbers of different micro-organisms on their skin/feathers and in their alimentary tract. Only a few types of bacteria directly affect the safety and quality of the finished carcass. Of particular concern are food-borne pathogens such as Campylobacter spp., Clostridium perfringens, Salmonella spp., and pathogenic serotypes of Escherichia coli. The minimum and optimum growth temperatures for some of the pathogens associated with red and poultry meat are shown in Table 3.1. Inevitably, small numbers of pathogens will be present on meat and cooking regimes are designed to eliminate their presence. Most red meat and poultry food poisoning is associated with inadequate cooking or subsequent contamination after cooking and poor cooking and storage. Normally it is the growth of spoilage organisms that has the most important effect in limiting the shelf-life of meat. The spoilage bacteria of meats stored in air under chill conditions include species of Pseudomonas, Brochothrix and Acinetobacter/Moraxella. Varnam and Sutherland state that in general, there is Fig. 3.1 Percentage of chilled and frozen poultry carcasses contaminated with salmonella found in UK surveys carried out in 1979–80 to 1994. 64 Chilled foods

Raw material selection: meat and poultry 65 Table 3.1 Chilled storage life of meat and meat products at different storage temperatures Storage time(days)in temperature range -4.lto-l.1 2.ltos.1°C 5.2to8.2°C Food Mean sd Mean sd Mean sd Mean Bacon 45 20 Beef 40263432 aooe 5086 10 461 18 Rabbi Offal 6 Sausage 10 little difference in the microbial spoilage of beef, lamb, pork and other meat derived from mammals The presence of exudate or 'drip, which accumulates in the container of pre- packaged meat, or in trays or dishes of unwrapped meat, substantially reduces its sales appeal. Drip can be referred to by a number of different names including purge loss,,press loss' and thaw loss' depending on the method of measurement and when it is measured. Drip loss occurs throughout the cold chain and represents a considerable economic loss to the red meat industry Poultry meat is far less prone to drip. The potential for drip loss is inherent in fresh meat and is influenced by many factors. Some of these, including breed diet and physiological history, are inherent in the live animal. Others, such as the rate of chilling, storage temperatures, freezing and thawing, occur during processing. Meat colour can be adversely affected by a variety of factors, including post-mortem handling, chilling, storage and packaging In Australia, CSIRO stated that Toughness is caused by three major factors advancing age of the animal, 'cold shortening '(the muscle fibre contraction at can occur during chilling)and unfavourable meat acidity(pH). 'There is general agreement on the importance of these factors, with many experts adding oking as a fourth equally important influent 3.2 The influence of the live animal Some of the factors that influence the toughness or meat are inherent in the live animal. Church and wood state that it is now well established that it is the properties of the connective tissue proteins, and not the total amount of collagen in meat, that largely determines whether meat is tough or tender. As the animal

little difference in the microbial spoilage of beef, lamb, pork and other meat derived from mammals. The presence of exudate or ‘drip’, which accumulates in the container of prepackaged meat, or in trays or dishes of unwrapped meat, substantially reduces its sales appeal.3 Drip can be referred to by a number of different names including ‘purge loss’, ‘press loss’ and ‘thaw loss’ depending on the method of measurement and when it is measured. Drip loss occurs throughout the cold chain and represents a considerable economic loss to the red meat industry. Poultry meat is far less prone to drip. The potential for drip loss is inherent in fresh meat and is influenced by many factors. Some of these, including breed, diet and physiological history, are inherent in the live animal. Others, such as the rate of chilling, storage temperatures, freezing and thawing, occur during processing. Meat colour can be adversely affected by a variety of factors, including post-mortem handling, chilling, storage and packaging.4 In Australia, CSIRO5 stated that ‘Toughness is caused by three major factors – advancing age of the animal, ‘cold shortening’ (the muscle fibre contraction that can occur during chilling) and unfavourable meat acidity (pH).’ There is general agreement on the importance of these factors, with many experts adding cooking as a fourth equally important influence. 3.2 The influence of the live animal Some of the factors that influence the toughness or meat are inherent in the live animal. Church and Wood4 state that it is now well established that it is the properties of the connective tissue proteins, and not the total amount of collagen in meat, that largely determines whether meat is tough or tender. As the animal Table 3.1 Chilled storage life of meat and meat products at different storage temperatures Storage time (days) in temperature range: 4.1 to 1.1ºC 1 to 2ºC 2.1 to 5.1ºC 5.2 to 8.2ºC Food Mean sd Mean sd Mean sd Mean sd Bacon 45 6 15 3 42 20 Beef 40 26 34 32 10 8 9 9 Lamb 55 20 41 46 28 34 Pork 50 58 22 30 16 16 15 18 Poultry 32 18 17 10 12 11 7 3 Veal 21 10 6 49 49 Rabbit 9 7 13 6 Offal 7 7 6 14 7 Bacon 45 6 15 3 42 20 Sausage 80 43 21 16 36 28 24 10 Raw material selection: meat and poultry 65

66 Chilled foods grows older the number of immature reducible cross-links decreases The mature cross-links result in a toughening of the collagen and this in turn can produce cially significant until a beast is about four years old o probably not commer- tough meat. Increasing connective tissue toughness is e. The pigment concentration in meat which governs its colour is affected by any factors affecting the live animal. These include species -beef, for example, contains substantially more myoglobin than pork; breed and age pigment concentration increases with age; sex- meat from male animals usually contains more pigment than that from female animals; muscle- muscles that do more work contain more myoglobin There are also two specific meat defects; dark, firm, dry(DFD) and pale, soft, exudative(PSE)associated with the live animal that result in poor meat colour DFD meat has a high ultimate pH and oxygen penetration is low. Consequently the oxymyoglobin layer is thin, the purple myoglobin layer shows through, and the meat appears dark In PSe meat the pH falls while the muscle is still warm and partial denaturation of the proteins occurs. An increased amount of light is scattered and part of the pigment oxidised so that the meat appears pale 3.2.1 Between species and breeds In all species the range of storage lives found in the literature is very large (Table 3. 1)and indicate that factors other than species have a pronounced effect on storage life. Overall, species has little effect on the practical storage life of meat. In general, beef tends to lose proportionately more drip than pork and lamb. Unfrozen poultry meat looses little if any drip. Since most of the exudate comes from the cut ends of muscle fibres, small pieces of meat drip more than large intact carcasses. In pigs, especially, there are large differences in drip loss from meat from different breeds and between different muscles. Taylor'showed that there was a substantial difference, up to 2.5 fold, in drip loss between four different breeds of pig(Table 3.2). He also showed that there was a 1.7 to 2.8 fold difference in drip between muscle types(Table 3.3) Although there is a common belief that breed has a major effect on meat quality CSirO state although there are small differences in tenderness due to Table 3. 2 Drip loss after two days storage at ooC, from leg joints from different breeds of pig cooled at different rates Breed Drip loss ( by wt. Slow Wessex X Large White Pietrain 0.6

grows older the number of immature reducible cross-links decreases. The mature cross-links result in a toughening of the collagen and this in turn can produce tough meat. Increasing connective tissue toughness is probably not commercially significant until a beast is about four years old.6 The pigment concentration in meat which governs its colour is affected by many factors affecting the live animal. These include species – beef, for example, contains substantially more myoglobin than pork; breed and age – pigment concentration increases with age; sex – meat from male animals usually contains more pigment than that from female animals; muscle – muscles that do more work contain more myoglobin. There are also two specific meat defects; dark, firm, dry (DFD) and pale, soft, exudative (PSE) associated with the live animal that result in poor meat colour. DFD meat has a high ultimate pH and oxygen penetration is low. Consequently, the oxymyoglobin layer is thin, the purple myoglobin layer shows through, and the meat appears dark. In PSE meat the pH falls while the muscle is still warm and partial denaturation of the proteins occurs. An increased amount of light is scattered and part of the pigment oxidised so that the meat appears pale. 3.2.1 Between species and breeds In all species the range of storage lives found in the literature is very large (Table 3.1) and indicate that factors other than species have a pronounced effect on storage life. Overall, species has little effect on the practical storage life of meat. In general, beef tends to lose proportionately more drip than pork and lamb. Unfrozen poultry meat looses little if any drip. Since most of the exudate comes from the cut ends of muscle fibres, small pieces of meat drip more than large intact carcasses. In pigs, especially, there are large differences in drip loss from meat from different breeds and between different muscles. Taylor7 showed that there was a substantial difference, up to 2.5 fold, in drip loss between four different breeds of pig (Table 3.2). He also showed that there was a 1.7 to 2.8 fold difference in drip between muscle types (Table 3.3). Although there is a common belief that breed has a major effect on meat quality CSIRO8 state ‘although there are small differences in tenderness due to Table 3.2 Drip loss after two days storage at 0ºC, from leg joints from different breeds of pig cooled at different rates Breed Drip loss (% by wt.) Slow Quick Landrace 0.47 0.24 Large White 0.73 0.42 Wessex X Large White 0.97 0.61 Pietrain 1.14 0.62 66 Chilled foods

Raw material selection: meat and poultry 67 Table 3.3 Drip loss after two days storage at 0@C from four muscles from two breeds of pig cooled at different rates Adductor Biceps Combined tendinosus membranous femoris (4 muscles) Pietrain Quick 2.82 4.115.30 Large white 1.04 Slow 1.95 2.323.2 breed, they are slight and currently of no commercial significance to Australian consumers.That said, there are substantial differences in the proportion of acceptable tender meat and toughness between Bos indicus* and Bos taurus* cattle. The proportion of acceptable tender meat has been found to decrease from 100% in Hereford Angus crosses, to 96% in Tarentaise, 93% in Pinzgauer, 86% in Brahman and only 80% in Tsahiwal. Toughness of meat increases as the proportion of Bos indicus increases 3.2.2 Animal to animal variation here is little data on any relationship between animal to animal variation and chilled storage life. However. it is believed to cause wide variations in frozen storage life; differences can be as great as 50% in the freezing of lamb. 2 Differences would appear to be caused by genetic, seasonal or nutritional variation between animals, but there is little reported work to confirm this view Variations were found between the fatty acids and ratio of saturated/unsaturated fatty acids in lambs from New Zealand, America and England. Differences related to sex, geographical area and cut were mainly a reflection of fatness, ith ewes having a greater percentage of body fat than rams. However, differences between areas were found to produce larger variations between animals than sex differences. a number of other trials have detailed differenc between animals There can also be significant differences in texture within Longissimus dorsi shear force values for double muscled Belgium Blue bulls were significantly higher than those of the same breed with normal conformation. Calpain I levels at I h and 24 h post mortem were also much lower. It was suggested that the lower background toughness in the double muscle was compensated for by reduced post mortem proteolytic tenderisation Sex of the animal appears to have little or no influence on tenderness. Huff and Parrish compared the tenderness of meat from 14-month-old bulls and s Bos indicus are tropical and semitropical breeds of cattle primarily Brahman and Bos taurus are temperate breeds such as Hereford or Aberdeen Angus

breed, they are slight and currently of no commercial significance to Australian consumers.’ That said, there are substantial differences in the proportion of acceptable tender meat and toughness between Bos indicus* and Bos taurus* cattle. The proportion of acceptable tender meat has been found to decrease from 100% in Hereford Angus crosses, to 96% in Tarentaise, 93% in Pinzgauer, 86% in Brahman and only 80% in Tsahiwal.9 Toughness of meat increases as the proportion of Bos indicus increases.10 3.2.2 Animal to animal variation There is little data on any relationship between animal to animal variation and chilled storage life. However, it is believed to cause wide variations in frozen storage life; differences can be as great as 50% in the freezing of lamb.11, 12 Differences would appear to be caused by genetic, seasonal or nutritional variation between animals, but there is little reported work to confirm this view. Variations were found between the fatty acids and ratio of saturated/unsaturated fatty acids in lambs from New Zealand, America and England.13 Differences related to sex, geographical area and cut were mainly a reflection of fatness, with ewes having a greater percentage of body fat than rams. However, differences between areas were found to produce larger variations between animals than sex differences. A number of other trials have detailed differences between animals. There can also be significant differences in texture within a breed. Longissimus dorsi shear force values for double muscled Belgium Blue bulls were significantly higher than those of the same breed with normal conformation.14 Calpain I levels at 1 h and 24 h post mortem were also much lower. It was suggested that the lower background toughness in the double muscle was compensated for by reduced post mortem proteolytic tenderisation. Sex of the animal appears to have little or no influence on tenderness. Huff and Parrish15 compared the tenderness of meat from 14-month-old bulls and Table 3.3 Drip loss after two days storage at 0ºC from four muscles from two breeds of pig cooled at different rates Drip (as % muscle weight) Cooling Semi- Semi- Adductor Biceps Combined rate tendinosus membranous femoris (4 muscles) Pietrain Quick 2.82 4.40 5.52 2.69 3.86 Slow 3.99 6.47 6.61 4.11 5.30 Large White Quick 1.69 2.01 2.92 1.04 1.92 Slow 1.95 3.50 5.07 2.32 3.21 * Bos indicus are tropical and semitropical breeds of cattle primarily Brahman and Bos taurus are temperate breeds such as Hereford or Aberdeen Angus. Raw material selection: meat and poultry 67

68 Chilled foods steers, and cows(55 to 108 months old). No differences were found between the tenderness of bulls and steers. Tenderness decreased with the age of the animal Hawrysh et al. reported that beef from bulls may be less tender than that from steers. Sex can have a substantial influence on flavour. For example, cooking the meat from entire male pigs can produce an obnoxious odour known as"boar taint. Problems can also occur with meat from intact males of other species However, they can still be attractive to industry because of their higher rate of growth and lower fat content 3.2.3 Feeding le way in which an animal is fed can influence its quality and storage life. It has been reported that chops from pigs fed on household refuse have half the frozen storage life of those fed on a milk/barley ration. 7, 18 Again, pork from pigs that had been fed materials containing offal had half the practical storage life(Psl)and higher iodine numbers in the fat than that of pigs which had no been fed this type of diet. Conversely, Bailey et al.- did not find differences between meal- and swill-fed pigs after 4 and 9 months at -20oC Rations with large amounts of highly unsaturated fatty acids tend to produce more unstable meat and fat The type of fatty acid composition of ' depot fatin poultry and its stability have been shown to be directly related to the fatty acid composition of ingested fats.1,2 The feeding of fish oils or highly unsaturated vegetable oils(s linseed oil) to poultry is known to produce fishy flavours in the mear uch as The use of vitamin E supplements is recommended for both beef and turke This willresult in delayed onset of discoloration in fresh, ground and frozen beef and in suppression of lipid rancidity, especially in fresh, ground and frozen in cooked beef with turke been shown to improve oxidative stability of cooked and uncooked turkey burgers during six months frozen storage at -20oC25 3.2.4 Variations within an animal Reports of variations in the storage life of different cuts of meat e scarce and primarily deal with dark and light meat. Both Ristic26 and Keshinel et al.27 have found that poultry breast meat stores better than thigh meat. Ristic states that frozen breast meat will store for 16 months while thigh meat can be stored for only 12 months due to its higher fat content. Judge and Aberle- also found that light pork meat stored for a longer time than dark meat. This was thoug to be due to either higher quantities of haem pigments in the dark muscle (which may act as major catalysts of lipid oxidation), or to higher quantities of phospholipids(which are major contributors to oxidised flavour in cooked

steers, and cows (55 to 108 months old). No differences were found between the tenderness of bulls and steers. Tenderness decreased with the age of the animal. Hawrysh et al.16 reported that beef from bulls may be less tender than that from steers. Sex can have a substantial influence on flavour. For example, cooking the meat from entire male pigs can produce an obnoxious odour known as ‘boar taint’. Problems can also occur with meat from intact males of other species. However, they can still be attractive to industry because of their higher rate of growth and lower fat content. 3.2.3 Feeding The way in which an animal is fed can influence its quality and storage life. It has been reported that chops from pigs fed on household refuse have half the frozen storage life of those fed on a milk/barley ration.17, 18 Again, pork from pigs that had been fed materials containing offal had half the practical storage life (PSL) and higher iodine numbers in the fat than that of pigs which had not been fed this type of diet.19 Conversely, Bailey et al.20 did not find any differences between meal- and swill-fed pigs after 4 and 9 months at 20ºC. Rations with large amounts of highly unsaturated fatty acids tend to produce more unstable meat and fat. The type of fatty acid composition of ‘depot fat’ in poultry and its stability have been shown to be directly related to the fatty acid composition of ingested fats.21, 22 The feeding of fish oils or highly unsaturated vegetable oils (such as linseed oil) to poultry is known to produce fishy flavours in the meat.21, 23 The use of vitamin E supplements is recommended for both beef and turkey. This will ‘result in delayed onset of discoloration in fresh, ground and frozen beef and in suppression of lipid rancidity, especially in fresh, ground and frozen beef and less so in cooked beef’. 24 With turkey, vitamin E supplements have been shown to improve oxidative stability of cooked and uncooked turkey burgers during six months frozen storage at 20ºC.25 3.2.4 Variations within an animal Reports of variations in the storage life of different cuts of meat are scarce and primarily deal with dark and light meat. Both Ristic26 and Keshinel et al.27 have found that poultry breast meat stores better than thigh meat. Ristic states that frozen breast meat will store for 16 months while thigh meat can be stored for only 12 months due to its higher fat content. Judge and Aberle28 also found that light pork meat stored for a longer time than dark meat. This was thought to be due to either higher quantities of haem pigments in the dark muscle (which may act as major catalysts of lipid oxidation), or to higher quantities of phospholipids (which are major contributors to oxidised flavour in cooked meat). 68 Chilled foods

Raw material selection: meat and poultry 69 3.3 Pre- and post-slaughter handling 3.3.1 Red meat The way animals are handled and transported before slaughter affects meat quality and its storage life. Increased stress or exhaustion can produce Pse(pale soft and exudative)or dFd(dark firm and dry )meat, which is not recommended for storage, mainly due to its unattractive nature and appearance. Jeremiah and Wilson found that the use of Pse muscle produced low yields after curing and it was concluded that Pse meat was unsuitable for further processing. Experiments designed to determine the effect of treatments immediately before or at the point of slaughter appear to show that they have little effect on meat texture. Exercising pigs before slaughter has been shown to have no effect exture parameters, i.e. muscle shortening and shear force. 30 The use of have a significant effect on the quality of pork y bon dioxide) does not seem to different stunning methods(both electrical and carb Consumers' surroundings fluence their appreciation of tenderness Consumers were more critical of the tenderness of beef steaks cooked in the home than those cooked in restaurants. The Warner-Bratzler force transition level for acceptable steak tenderness was between 4.6 and 5.0 kg in the home and between 4.3 and 5.2 kg in the restaurants Overall, there appears to be little correlation between chilling rates or chilling systems and bacterial numbers after chilling. The microorganisms that usually spoil meat are psychrotrophs; i.e. bacteria capable of growth close to ooC. Only a small proportion of the initial microflora on meat will be psychrotrophs, the majority of microorganisms present are incapable of growth at low temperatures. As storage temperature rises the number of species capable of growth will increase. The growth rate of microorganisms also accelerates with increasing temperature. In the accepted temperature range for chilled meat, -1.5 to C, there can be as much as an eightfold increase in growth rate between the lower and upper temperature. For any particular treatment the maximum chilled storage life will be obtained by holding the meat at -1.5%C. Chilled storage life is halved for each 2-3C rise in temperature Odour and slime cause by the growth of microorganisms will be apparent after approximately 14.5 and 20 days respectively with beef sides stored at 0oC (Fig 3. 2). At 5C the respective times are significantly reduced to 8 and 13 days respectively Rapid chilling reduces drip loss (table 3.2& 3.3). However, chilling has serious effects on the texture of meat if it is carried out rapidly when the meat is still in the pre-rigor condition, that is, before the meat pH has fallen below about 6.2 33 In this state the muscles contain sufficient amounts of the contractile fuel adenosine triphosphate (ATP), for forcible shortening to set in as the temperature falls below 11C, the most severe effect occurring at about 3C This is the so-called cold-shortening' phenomenon, first observed by Locker and Hagyard and its mechanism described by Jeacocke. The meatsets'in shortened state as rigor comes on, and this causes it to become extremely

3.3 Pre- and post-slaughter handling 3.3.1 Red meat The way animals are handled and transported before slaughter affects meat quality and its storage life. Increased stress or exhaustion can produce PSE (pale soft and exudative) or DFD (dark firm and dry) meat, which is not recommended for storage, mainly due to its unattractive nature and appearance. Jeremiah and Wilson29 found that the use of PSE muscle produced low yields after curing and it was concluded that PSE meat was unsuitable for further processing. Experiments designed to determine the effect of treatments immediately before or at the point of slaughter appear to show that they have little effect on meat texture. Exercising pigs before slaughter has been shown to have no effect on texture parameters, i.e. muscle shortening and shear force.30 The use of different stunning methods (both electrical and carbon dioxide) does not seem to have a significant effect on the quality of pork.31 Consumers’ surroundings influence their appreciation of tenderness.32 Consumers were more critical of the tenderness of beef steaks cooked in the home than those cooked in restaurants. The Warner-Bratzler force transition level for acceptable steak tenderness was between 4.6 and 5.0 kg in the home and between 4.3 and 5.2 kg in the restaurants. Overall, there appears to be little correlation between chilling rates or chilling systems and bacterial numbers after chilling. The microorganisms that usually spoil meat are psychrotrophs; i.e. bacteria capable of growth close to 0ºC. Only a small proportion of the initial microflora on meat will be psychrotrophs; the majority of microorganisms present are incapable of growth at low temperatures. As storage temperature rises the number of species capable of growth will increase. The growth rate of microorganisms also accelerates with increasing temperature. In the accepted temperature range for chilled meat, 1.5 to 5ºC, there can be as much as an eightfold increase in growth rate between the lower and upper temperature. For any particular treatment the maximum chilled storage life will be obtained by holding the meat at 1.5ºC. Chilled storage life is halved for each 2–3ºC rise in temperature. Odour and slime cause by the growth of microorganisms will be apparent after approximately 14.5 and 20 days respectively with beef sides stored at 0ºC (Fig. 3.2). At 5ºC the respective times are significantly reduced to 8 and 13 days, respectively. Rapid chilling reduces drip loss (Table 3.2 & 3.3). However, chilling has serious effects on the texture of meat if it is carried out rapidly when the meat is still in the pre-rigor condition, that is, before the meat pH has fallen below about 6.2.33 In this state the muscles contain sufficient amounts of the contractile fuel, adenosine triphosphate (ATP), for forcible shortening to set in as the temperature falls below 11ºC, the most severe effect occurring at about 3ºC. This is the so-called ‘cold-shortening’ phenomenon, first observed by Locker and Hagyard34 and its mechanism described by Jeacocke.35 The meat ‘sets’ in the shortened state as rigor comes on, and this causes it to become extremely Raw material selection: meat and poultry 69

70 Chilled foods 6 20°C 10°C 5°C 0°c Fig. 3.2 Time for odour and slime to develop on beef carcasses at different storage temperatures. tough when it is subsequently cooked. 36 If no cooling is applied and the temperature of the meat is above 25C at completion of rigor then another form of shortening rigor'-or'heat-shortening' will occur Electrical stimulation(ES) of the carcass after slaughter can allow rapic hilling without much of the toughening effect of cold shortening. However, Buts et al.38 reported that in veal ES followed by moderate cooling affected tenderness in an unpredictable way and could result in tougher meat. Electrical stimulation will hasten rigor and cause tenderisation to start earlier at the prevailing higher temperature. In meat from carcasses given high or low voltage stimulation and slow cooling, adequate ageing in beef can be obtained in about half the time of non-stimulated beef This will therefore reduce the requirement nd cost of storage When meat is stored at above freezing temperatures it becomes progressively more tender. This process, known as ageing, conditioning or maturation is traditionally carried out by hanging the carcass for periods of 14 days or longer different times for tenderisation Beef, veal and rabbit age at about the same rate and take about ten days at 1C to achieve 80% of ageing(Table 3.4). Lamb ages slightly faster than beef but more slowly than pork. The ultim depend on the initial'background' tenderness of the meat and the tenderisation that has occurred during chilling. In veal acceptable tenderness can be obtained fter five day ays at IC compared with 10 days for beef. Red colour is more stable at lower temperatures because the rate of oxidation of the pigment decreases. At low temperatures, the solubility of oxygen is greater and oxygen-consuming reactions are slowed down. There is a greater penetration of oxygen into the meat and the meat is redder than at high temperatures The major improvement in tenderness has been shown to occur in less than 14 days. In a study by Martin et al., in which more than 500 animals were examined, it was concluded that for beef carcasses, a period of six days is

tough when it is subsequently cooked.36 If no cooling is applied and the temperature of the meat is above 25ºC at completion of rigor then another form of shortening ‘rigor’ – or ‘heat-shortening’ will occur.37 Electrical stimulation (ES) of the carcass after slaughter can allow rapid chilling without much of the toughening effect of cold shortening. However, Buts et al.38 reported that in veal ES followed by moderate cooling affected tenderness in an unpredictable way and could result in tougher meat. Electrical stimulation will hasten rigor and cause tenderisation to start earlier at the prevailing higher temperature. In meat from carcasses given high or low voltage stimulation and slow cooling, adequate ageing in beef can be obtained in about half the time of non-stimulated beef38 This will therefore reduce the requirement and cost of storage. When meat is stored at above freezing temperatures it becomes progressively more tender. This process, known as ageing, conditioning or maturation is traditionally carried out by hanging the carcass for periods of 14 days or longer. The rate of ageing differs significantly between species and necessitates different times for tenderisation. Beef, veal and rabbit age at about the same rate and take about ten days at 1ºC to achieve 80% of ageing (Table 3.4). Lamb ages slightly faster than beef but more slowly than pork. The ultimate tenderness will depend on the initial ‘background’ tenderness of the meat and the tenderisation that has occurred during chilling. In veal acceptable tenderness can be obtained after five days at 1ºC compared with 10 days for beef. Red colour is more stable at lower temperatures because the rate of oxidation of the pigment decreases. At low temperatures, the solubility of oxygen is greater and oxygen-consuming reactions are slowed down. There is a greater penetration of oxygen into the meat and the meat is redder than at high temperatures. The major improvement in tenderness has been shown to occur in less than 14 days. In a study by Martin et al., 39 in which more than 500 animals were examined, it was concluded that for beef carcasses, a period of six days is Fig. 3.2 Time for odour and slime to develop on beef carcasses at different storage temperatures. 70 Chilled foods

sufficient for a consumer product of satisfactory tenderness. Buchter40 also showed that no significant increase in tenderness occurs after 4–5 days for calves and 8–10 days for young bulls at 4ºC. The ageing process can be accelerated by raising the temperature, and the topic was well studied in the 1940s, 50s and 60s. Ewell41 found that the rate of tenderising more than doubled for each 10ºC rise. Meat from a three-year-old steer requiring ten days at 0ºC to reach the same tenderness as two days at 23ºC. Sleeth et al.42 showed that the tenderness, flavour, aroma and juiciness of beef quarters and ribs aged for 2–3 days at 20ºC were comparable to those aged 12–14 days at 2ºC. Busch et al. demonstrated that steaks from excised muscles held at 16ºC for two days were more tender than those stored at 2ºC for 13 days. The microbiological hazards of high-temperature ageing were well recognised and several investigators used antibiotics and/or irradiation to control bacterial growth.42, 44, 45 Although high-temperature ageing in conjunction with ultraviolet (UV) radiation has been used in the US its use has not expanded owing to its high cost.46 With the use of irradiation gaining more acceptance in the US its use to accelerate ageing in conjunction with modified atmosphere packaging and high-temperature storage has been investigated by Mooha Lee et al.47 Irradiated steaks stored for two days at 30ºC were more tender than unirradiated controls stored at 2ºC for 14 days (Table 3.5). In red meat, there is little evidence of any relationship between chilling rates and frozen storage life. However, there is evidence for a relationship between Table 3.4 Time taken to achieve 50 and 80% ageing at 1ºC for different species8 Time (d) taken to achieve Species 50% 80% Beef 4.3 10.0 Veal 4.1 9.5 Rabbit 4.1 9.5 Lamb 3.3 7.7 Pork 1.8 4.2 Chicken 0.1 0.3 Table 3.5 Shear values for steaks after post mortem ageing Treatment Storage time (d) Unirradiated 2ºC Irradiated 15ºC Irradiated 30ºC 1 4.471.76 4.891.40 4.241.65 2 – 4.810.73 3.441.34 3 – 4.071.03 3.331.21 7 3.621.00 – – 14 3.521.51 – – Raw material selection: meat and poultry 71

72 Chilled foods storage life and the length of time that elapses before freezing occurs. Chilled storage of lamb for one day at ooC prior to freezing can reduce the subsequent storage life by as much as 25% when compared to lamb which has undergone accelerated conditioning and 2 hours storage at 0C. - It has been shown that pork which had been held for seven days deteriorated at a faster rate during rage than carcasses chilled for one and 4s AgeI ing for periods greater than seven days was found by Zeigler" to produce meat with high peroxide and free fatty acid values when stored at.C or -29oC Although shorter ageing times appear to have a beneficial effect on storage life there is obviously a necessity for it to be coupled with accelerated conditioning to prevent any toughening effects. Whilst there has been significant research in such areas as these, little appears to be known about the relationship between the frozen storage life of meat as a raw material and the chilled life of the product in 3.3.2 Poultry After bleeding and death, poultry carcasses are scalded by immersing them in hot water for approximately three minutes. Scalding loosens the feathers so that they can be easily removed. Carcasses can either be soft scalded at 52-53oC or marketed in a chilled state it will be soft scalded and air or spray chilled 2 g hard scalded at 58C Hard scalding removes the cuticles on chicken skin, which gives an unattractive appearance after air chilling. Generally if the poultry is Spray washing is used at numerous points during processing to remove visual contamination. It also has some small role in reducing bacterial contamination The EU Poultry Meat Directive 0 requires poultry to be washed inside and out immediately prior to water chilling. The amount of water to be used (i.e. 1.5 litres for a carcass up to 2.5 kg)is defined in the directive. Water chillers are designed to operate in a counter-current manner to minimise cross-contamination. Th carcasses exit from the chillers at the point where the clean, chilled water enters the system. Again, the Directive defines a minimum water flow through the chiller, i.e. at least one litre per carcass for carcasses up to 2.5 kg in weight Chicken breast muscle ages ten times faster than beef (Table 3.4). He ence geing in poultry carcasses occurs during processing and is usually accomplished before they reach the chiller/freezer. Pool et al. have shown that there were no detectable flavour differences over an 18-month period between turkey that had been frozen immediately and turkey that had been held at +2C for 30 hours 3. 4 Conclusions Even with the best practice, the maximum shelf-life of chilled meat can be measured in weeks. Freezing will extend the storage life of meat to a number of years. If the frozen storage life is not exceeded, freezing and frozen storage of

storage life and the length of time that elapses before freezing occurs. Chilled storage of lamb for one day at 0ºC prior to freezing can reduce the subsequent storage life by as much as 25% when compared to lamb which has undergone accelerated conditioning and 2 hours storage at 0ºC.12 It has been shown that pork which had been held for seven days deteriorated at a faster rate during storage than carcasses chilled for one and three days.48 Ageing for periods greater than seven days was found by Zeigler49 to produce meat with high peroxide and free fatty acid values when stored at 18ºC or 29ºC. Although shorter ageing times appear to have a beneficial effect on storage life there is obviously a necessity for it to be coupled with accelerated conditioning to prevent any toughening effects. Whilst there has been significant research in such areas as these, little appears to be known about the relationship between the frozen storage life of meat as a raw material and the chilled life of the product in which it is used. 3.3.2 Poultry After bleeding and death, poultry carcasses are scalded by immersing them in hot water for approximately three minutes. Scalding loosens the feathers so that they can be easily removed. Carcasses can either be soft scalded at 52–53ºC or hard scalded at 58ºC. Hard scalding removes the cuticles on chicken skin, which gives an unattractive appearance after air chilling. Generally if the poultry is marketed in a chilled state it will be soft scalded and air or spray chilled. Spray washing is used at numerous points during processing to remove visual contamination. It also has some small role in reducing bacterial contamination. The EU Poultry Meat Directive50 requires poultry to be washed inside and out immediately prior to water chilling. The amount of water to be used (i.e. 1.5 litres for a carcass up to 2.5 kg) is defined in the directive. Water chillers are designed to operate in a counter-current manner to minimise cross-contamination. The carcasses exit from the chillers at the point where the clean, chilled water enters the system. Again, the Directive defines a minimum water flow through the chiller, i.e. at least one litre per carcass for carcasses up to 2.5 kg in weight. Chicken breast muscle ages ten times faster than beef (Table 3.4). Hence, ageing in poultry carcasses occurs during processing and is usually accomplished before they reach the chiller/freezer. Pool et al.51 have shown that there were no detectable flavour differences over an 18-month period between turkey that had been frozen immediately and turkey that had been held at +2ºC for 30 hours. 3.4 Conclusions Even with the best practice, the maximum shelf-life of chilled meat can be measured in weeks. Freezing will extend the storage life of meat to a number of years. If the frozen storage life is not exceeded, freezing and frozen storage of 72 Chilled foods