Studies On The Quality Of Calpain3 And Its Function During Adeing Time

Tenderness is one of the most important factors of beef quality. During aging time, tenderization of different muscles in an individual carcass is variable, and this intramuscular variation is possibly influenced by many factors, such as sarcomere length, connective tissue, and sensitivity of muscle structural proteins to proteolysis. In mammals, inconsistency and variability in meat texture have been identified as two of the major problems that face the meat industry, especially in beef industry. By far, most scientists consider calpains as the major enzyme in beef tendrness, and focus on calpainl and calpain2. Calpain3, a skeletal muscle-specific calpain, has attracted much attention because its gene mutation is responsible for limb-girdle muscular dystrophy type 2A. Isolation of the intact 94KDa enzyme has been different to achieve due to its rapid autolysis, and uncertainty has arisen over its Ca²⁺ dependence for activity.This thesis is consisted of three chapters.Chapterl.The relationship between CAPN3 mRNA expression and the concentration of calcium: the objective of this chapter was to study the relationship between calpain3 mRNA expression in m. longisimus thoraciset lumborum and concentration of calcium. RT-PCR and optical density ananlysis indicated that calpain3 mRNA expression was not significant affected by the concentration of calcium.Chapter2. Isolation of Calpain3 and characterization of its autolysis: Isolation of the intact 94KDa enzyme has been different to achieve due to its rapid autolysis, and uncertainty has arisen over its Ca²⁺ dependence for activity. In the present of Ca²⁺, calpain3 cleaved itself into several fragments, indicated that the autolysis of calpain3 was dependent of the concentration of Ca²⁺. In the studty, we also find that the autolysis of calpain3 proceeded in four consecutives steps:89 KDa, 68 KDa and 58 KDa fragment were produced as intermediates before a stable 55 KDa fragment appeared.Chapter3. Autolysis of Calpain3 and its effect on meat tenderization during post-mortem ageing: we determined the temporal changes of calpain3 in the bovine m.longissimus thoraciset lumborum during post-mortem ageing. And found that there was strong reletionship between the kinetics of shear force and myofibrillar fragmentation index. We found that calpain3 was completely autolyzed in 24 hours after slaughtered. Thus, it was indicated during post-mortem ageing that calpain3 was degraded by itself or other enemy, and don't effect the tenderness of meat through hydrolyze muscle framework protein.