【正文】 However, other factors such as geics, muscle type, processing practices, and preslaughter stressors have also been recognized to impact the biochemical processes during rigor and the development of conditions such as PSE and dry, firm, and dark (DFD) meat (van Hoof, 1979。 1997。 Woelfel et al., 1998。 C (Offer, 1991). ?Geic improvements in poultry have also influenced carcass temperatures during processing. ?Selection in the poultry industry has resulted in heavier carcasses and thicker muscles, leading to increased time to reduce the internal musculature temperature, thus decreasing chilling rates and consequently increasing the exposure of carcasses to elevated temperatures (Rathgeber et al. (1999). ?Dransfield and Sosnicki (1999) suggested that the potential detrimental PSElike effect of fast growing, heavily muscled lines could partially be offset by increasing the rate of carcass cooling. ? Preslaughter Factors ?The effects of preslaugher stressors and their influence on meat quality have been well documented in the beef and swine industries. ?In poultry, broilers and turkeys exposed to adverse conditions before slaughter frequently produce meat with characteristics analogous to PSE in pork. ?McKee and Sams (1998) reported that breast meat from heat stressed turkeys exhibited lower initial and ultimate postmortem pH and higher rates of postmortem pH decline when pared to nonstressed birds. ?The meat harvested from heat stressed birds exhibited characteristics similar to PSE suggesting that seasonal stress might be a factor in the development of PSE by accelerating postmortem metabolism and biochemical processes in the muscle. ?In general terms, fasting prior to slaughter is known to deplete glycogen stores resulting in meat with higher ultimate pH and dark color. The opposite effect has been observed in cattle fed up to the point of slaughter, resulting in higher glycogen stores, lower ultimate pH and paler meat. ?WismerPedersen (1959) reported that meat from pigs fed two pounds of sugar three to four hours prior to slaughter exhibited higher glycogen content, lower ultimate pH, and paler meat. However, meat from sugarfed pigs exhibited a more uniform color when pared to meat from control pigs. ?In contrast to other species, fasted broilers have been observed to have higher glycogen stores than broilers fed with a diet supplemented with sugar(Mellor et al., 1958). ?Meat from sugarfed broilers was more tender than meat from their control counterparts. However other meat quality traits were not evaluated. PSEPale, Soft and Exudative Meat ? Ludvigsen (1954) described for the first time a condition in swine that he termed muscle degeneration. The condition was characterized by postmortem development of a pale color, soft texture, and considerable exudation from the muscle surface. This condition has bee known as PSE. ? PSE affects between 5 to 20% of pig carcasses. Extensive research has indicated that the condition has a geic basis and has been directly related to porcine stress syndrome (PSS) and malignant hyperthermia (Mitchell and Heffron, 1982。 C during processing exhibit rapid rates of glycolysis and a premature onset of rigor mortis (de Femery and Pool, 1960). ?Temperatures as high as 55176。 C resulted in a 20fold increase in protein denaturation. ?Khan (1971) reported that elevated carcass temperatures accelerated glycolysis and toughened breast meat, while low temperatures delayed glycolysis without toughening. ?In meattype chickens, rigor mortis is particularly rapid in parison to red meat species and is usually plete within 2 to 3 hours postmortem (Grey et al., 1974: Grey and Jones, 1977). ?Broiler carcasses exposed to temperatures between 37176。 Offer and Knight, 1988). ? Tenderness, juiciness, firmness, and appearance of meat improve as the content of water in the muscle increases, leading to an improvement in quality and economical value. Factors affecting Water Holding Capacity ? Lactic acid production and the resultant decline in pH after death results in protein denaturation, loss of protein solubility and in an overall reduction of reactive groups available for water binding on muscle proteins ? Another important factor affecting WHC is the lack of space between the myofibrillar proteins that results by the accumulation of actinomyosin plexes as energy sources are depleted in the muscle. ?As rigor mortis progresses, divalent cations such as Mg++ and Ca++ in the sarcoplasm bind to the reactive groups on adjacent protein chains, reducing the electrostatic repulsion between the negatively charged groups that maintain them apart. ?This reaction draws adjacent protein chains closer, reducing the space available for water to be retained intramuscularly and increasing the amount of water expelled to the extracellular space. Factors Affecting Meat Quality ? Biochemical Changes ?After slaughter, biochemical changes occur in the conversion of muscle to meat. The normal development of these biochemical changes will determine final meat quality. ?Rigor mortis development is crucial in the process of muscle death and is essential to proper meat quality. ?As an animal dies due to asphyxia resulting from bleeding, musc