Post-mortem changes in beef : comparison of muscles

The characteristic conversion of muscle to meat that occurs post-mortem arises due to a series of biochemical and biophysical changes that are initiated upon death. Dransfield (1993) has presented a model which quantifies these changes and attempts to predict this increase in muscle tenderness post-mortem. To identify if this proposed model can predict the differences in muscle tenderness among muscles of different contractile type, four muscles (Longissimus doris, Psoas major, Sternocephalicus and diaphragm) were assessed for rate of pH and temperature decline and levels of proteolytic enzymes µ-calpain, m-calpain and their natural inhibitor calpastatin. Greater muscle tenderness was observed in fast twitch muscle which also exhibited the greater rate and extent of pH decline post-mortem. This increase muscle tenderness was associated with a higher calpain/calpastratin ratio and more rapid activation of the proteolytic calpains. Therefore this investigation has revealed that the differences in meat tenderness which exist between muscles are associated with predicted differnces in the calpain-calpastatin proteolytic system.