ARS | Publication request: SARCOMERE LENGTH INFLUENCES IN VITRO CALPAIN-INDUCED PROTEOLYSIS OF BEEF MYOFIBRILS

Submitted to: American Meat Science Association Conference Reciprocal Proceedings
Publication Type: Abstract
Publication Acceptance Date: April 24, 2006
Publication Date: June 16, 2006
Citation: Weaver, A.D., Bowker, B.C., Gerrard, D.E. 2006. Sarcomere length influences in vitro calpain-induced proteolysis of beef myofibrils [abstract]. American Meat Science Association Reciprocal Meat Conference Proceedings. Paper No. 16P. June 18-21, 2006, Champaign, Illinois.

Technical Abstract: The objective of this study was to determine the influence of sarcomere length on the extent of postmortem proteolysis and beef tenderness. First a model was developed to evaluate the effect of sarcomere length on tenderness, utilizing Warner-Bratzler shear force. Bovine semitendinosus and psoas major muscles were excised within 30 minutes postmortem and muscle strips were dissected along the long axis of the muscle, parallel to fiber orientation. Strips were either clamped onto adjustable supports and stretched to increase sarcomere length or chilled in an ice slurry to induce short sarcomeres lengths. At 36 h postmortem samples were removed for Warner-Bratzler shear force analysis and myofibril isolation. Purified myofibrils were subjected to phase-contrast microscopy for sarcomere length determination. Results indicate a significant correlation (R2=.84) between sarcomere length and cooked Warner-Bratzler shear force. Utilizing this model, bovine semitendinosus muscles were processed to generate long and short sarcomere lengths to study their effect on the degradation of Troponin-T. Myofibrils were isolated and western blot analysis of Troponin-T was conducted to analyze the effect of calpain digestion on isolated myofibrils. Exogenous '-calpain was added to myofibrils and the extent of Troponin-T degradation was monitored at 0, 2, 15, 60, 120 min, 1 d and 2d. As anticipated, sarcomere length was shorter in muscle strips exposed to ice slurry conditions as compared to those held in a stretched state during the development of rigor mortis (1.55 vs 2.57 'm). Warner-Bratzler shear force was greater (P<0.0001) in the shortened samples than in the stretched muscle samples (15.9 vs 5.9 kg). Western blot analysis of Troponin-T indicated an enhanced rate of proteolysis in the stretched samples as compared to shortened samples. Disappearance of the intact Troponin-T complex and the appearance of a 30 kDa polypeptide were greater in myofibrils with long sarcomere lengths. These data suggest myofibrils with shorter sarcomere lengths undergo delayed postmortem degradation of Troponin-T and subsequent tenderization. Overall these data show the significance of sarcomere length in predicting meat shear force values. In addition, sarcomere length influences the rate of postmortem degradation of Troponin-T. Further studies are necessary to determine the effect of sarcomere length on the degradation of other key myofibrillar proteins. Together, these studies may lead to advanced tenderness prediction technologies and improved consistency of beef products.