Effect of porcine somatotropin and stress susceptibility on the sensory, physical and chemical properties of porcine skeletal muscle

摘要

Forty-eight pigs of three genetically defined phenotypes (stress positive, stress carrier and stress negative) were injected daily with recombinant porcine somatotropin (PST) (4 mg/day) or placebo, and the effects of PST along with stress susceptibility on the sensory, physical, chemical and processing characteristics of pork longissimus and semimembranosus (SM) muscle were observed. Two end-point temperatures (71° and 77°C) were used for sensory analysis of broiled pork chops;PST treatment significantly lowered panel scores for tenderness, juiciness and flavor of broiled pork chops, while stress susceptibility decreased panel scores for tenderness only. PST treatment reduced intramuscular fat and increased moisture in the longissimus muscle, but PSE had no effect on proximate composition. PST treatment and stress susceptibility decreased and increased Hunter L values of chops, respectively. Furthermore, higher end-point temperature of broiled pork chops reduced sensory scores for tenderness and juiciness;PST treatment of animals had no effect on the sensory scores, lipid and protein content, cook yields, or color values of hams. Hams from stress susceptible animals, however, had reduced sensory scores, lower cook yields, and higher Hunter a and b values, and significantly lower lipid content. No interaction between PST treatment and stress classification was observed for any of the measurements;In the second study, the effect of the porcine stress syndrome on the solubility and degradation of sarcoplasmic and myofibrillar/cytoskeletal proteins was investigated. Longissimus dorsi muscle samples were obtained from each of 6 stress positive, 6 stress negative and 5 stress carrier animals 45 minutes post-slaughter and on 1, 3, 5, and 7 days postmortem. Purified myofibrils were prepared for gel electrophoresis, and muscle samples were extracted with phosphate buffers containing KCl or KI. Samples for SDS-PAGE were made from each extraction to observe changes in solubility of individual proteins. Sarcoplasmic and myofibrillar/cytoskeletal protein solubility was significantly lower in muscle samples from stress positive animals and the reduction was uniform among proteins. Postmortem degradation of titin was different in myofibrils purified from stress positive animals in that no increase in the intensity of T[subscript]2 bands at days 5 and 7 was observed. The combination of reduced solubility and degradation of structural constraints may explain the reduced water-holding capacity (WHC) and functionality of PSE muscle.