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Title: Sarcomere length influences postmortem proteolysis of excised bovine semitendinosus muscle

item Bowker, Brian

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2008
Publication Date: 4/11/2008
Citation: Weaver, A., Bowker, B.C., Gerrard, D. 2008. Sarcomere length influences postmortem proteolysis of excised bovine semitendinosus muscle. Journal of Animal Science. 86(8):1925-1932.

Interpretive Summary: By showing that postmortem degradation of the troponin protein is different in stretched versus shortened beef semitendinosus muscle, this study indicates that sarcomere length and muscle shortening influence the postmortem proteolysis associated with the aging tenderization of beef.

Technical Abstract: The interaction between sarcomere length and postmortem proteolysis as related to meat tenderness is not clear. The extent of thick and thin filament overlap alters actomyosin binding and may alter substrate availability during aging-induced tenderization. The objective of this study was to determine the influence of sarcomere length on proteolytic degradation in beef. Strips from bovine semitendinosus were either stretched 40 percent and restrained, or allowed to shorten unrestrained in an ice bath. After rigor completion, 0.6 cm cross-sections were fabricated and randomly assigned to 2, 4, 7 or 10 d aging treatments. Myofibrils were isolated for sarcomere length determination. Samples were collected and frozen for shear force analysis and muscle proteins were extracted for SDS-PAGE and western blotting analyses to determine troponin T (TnT) proteolysis. Sarcomere length was greater (P<0.01) in stretched muscle samples compared to shortened samples (2.57 um vs. 1.43 um, respectively). Correspondingly, shear force values were greater (P<0.05) in shortened samples than stretched samples. Western blots revealed the presence of three major intact TnT bands that diminished with time postmortem and four bands (TnT degradation products) that accumulated during postmortem storage. Quantification of intact TnT showed increased (P<0.05) proteolysis at 4 and 7 d postmortem in samples with long sarcomeres. By 10 d only traces of the highest molecular weight intact TnT band were evident in both shortened and stretched samples suggesting this TnT band may be more susceptible to proteolysis than other intact TnT bands. Degradation products of TnT appeared earlier postmortem in samples with long sarcomeres. The 30 kDa TnT fragment appeared after 7 d postmortem storage in samples with long sarcomeres but not until 10 d in muscle containing short sarcomeres. Collectively, these data show that postmortem TnT proteolysis is sarcomere length-dependent and suggest that thick and thin filament overlap may influence the postmortem aging process in beef.