26 Meat refrigeration Table 2.1 Typical time for rigor onset Type of meat Development time Range(h) for rigor(h) 10-20 Source: Offer et al. 1988. the rate of rigor development increases with temperature, like many other metabolic processes. The rate increases three to four times for each 10C rise in this range. As a result of this fall in pH a number of enzymes change their activity ome lose it by changing their three-dimensional structure and some nhance their activity, i. e especially liposomal enzymes which are necessary or the conditioning process(Honikel, 1990). In the course of the break down of energy-rich compounds(shortly before they get used up) the onset of rigor occurs which increases the rigidity of the meat, i.e. the meat tough ens. Conditioning reduces the toughness as the number of rigid longitudi nal and transversal cross-links in the myofibres are reduced by enzymic action(Honikel, 1990) The conditions for the onset and development of rigor have a profound influence on the tenderness, juiciness and water-holding capacity of meats While factors such as species, breed, age, nature of muscle, ante- and post- mortem treatments, and so on all have an influence, temperature is prob- ably the most important Conditions of exhaustion or stress before slaughter can cause changes in the degree of glycolysis producing detrimental effects to the meat. Animals subjected to severe exhaustion shortly before slaughter use up their glyco gen reserves thus less lactic acid is formed pre mucin high pH(6.0-6.5)dark meat, often described as dark, firm and dry(dFD) meat DFD problems an occur in pork, mutton, veal and beef. By convention all pork above pH 6.0/6.2 is classified as DFD meat(Honikel, 1990). Drip losses from DFD meat are less than from normal meat (Offer et aL., 1988) A second cause of shrinkage is protein denaturation In life, muscle pro- teins are stable for many days at 37C and pH7. However, after death the musculature, especially in the interior of the carcass, cools relatively slowl nd becomes acidic. Under this combination of high temperature and low pH, some proteins especially myosin, the principal protein of muscle, slowly denature. If sufficient myosin is denatured, the myofibrils shrink about twice as much as usual and the meat is pale, soft and exudes drip more quickly and in greater amounts than usual Consumers react unfavourably against the unattractive paleness of this pale, soft and exuding(PSe)meatthe rate of rigor development increases with temperature, like many other metabolic processes. The rate increases three to four times for each 10 °C rise in this range. As a result of this fall in pH a number of enzymes change their activity. Some lose it by changing their three-dimensional structure and some enhance their activity, i.e. especially liposomal enzymes which are necessary for the conditioning process (Honikel, 1990). In the course of the break￾down of energy-rich compounds (shortly before they get used up) the onset of rigor occurs which increases the rigidity of the meat, i.e. the meat tough￾ens. Conditioning reduces the toughness as the number of rigid longitudi￾nal and transversal cross-links in the myofibres are reduced by enzymic action (Honikel, 1990). The conditions for the onset and development of rigor have a profound influence on the tenderness, juiciness and water-holding capacity of meats. While factors such as species, breed, age, nature of muscle, ante- and post￾mortem treatments, and so on all have an influence, temperature is prob￾ably the most important. Conditions of exhaustion or stress before slaughter can cause changes in the degree of glycolysis producing detrimental effects to the meat. Animals subjected to severe exhaustion shortly before slaughter use up their glyco￾gen reserves thus less lactic acid is formed producing high pH (6.0–6.5) dark meat, often described as dark, firm and dry (DFD) meat. DFD problems can occur in pork, mutton, veal and beef. By convention all pork above pH 6.0/6.2 is classified as DFD meat (Honikel, 1990). Drip losses from DFD meat are less than from normal meat (Offer et al., 1988). A second cause of shrinkage is protein denaturation. In life, muscle pro￾teins are stable for many days at 37 °C and pH 7. However, after death the musculature, especially in the interior of the carcass, cools relatively slowly and becomes acidic. Under this combination of high temperature and low pH, some proteins especially myosin, the principal protein of muscle, slowly denature. If sufficient myosin is denatured, the myofibrils shrink about twice as much as usual and the meat is pale, soft and exudes drip more quickly and in greater amounts than usual. Consumers react unfavourably against the unattractive paleness of this pale, soft and exuding (PSE) meat. 26 Meat refrigeration Table 2.1 Typical time for rigor onset Type of meat Development time Range (h) for rigor (h) Beef 18 8–30 Lamb 12 10–20 Pork 3 0.6–8 Source: Offer et al., 1988