Can postmortem proteolysis explain tenderness differences in various bovine muscles?

This study investigated the relationship between postmortem proteolysis, muscle pH decline, sarcomere length (SL), intramuscular fat (IMF) and Warner-Bratzler shear force (WBSF) in four bovine muscles (biceps femoris (BF), infraspinatus (IS), longissimus lumborum (LL), psoas major (PM). The WBSF was low in BF, IS and PM, while LL had a higher value (P<0.001), but still considered as tender. The PM had fastest pH decline (P<0.001), ultimate pH was lowest in LL and PM and highest for IS (P<0.001), sarcomeres were longest for PM and shortest for BF and LL (P<0.001), while IS and PM had more IMF than BF and LL (P=0.038). Troponin T degradation was similar in all muscles after 2d postmortem, however after 13d LL had more degradation than IS (P=0.003). The MMP-2 activity increased during storage (P=0.001), while IS had less activity than the other muscles (P=0.022). Although the variation in proteolytic activity could not explain the variation in WBSF, the study provides useful knowledge for the meat industry for optimising processing and storage procedures for different beef muscles.