Postmortem proteolysis and its indicators vary within bovine muscles: Novel insights in muscles that differ in their contractile, metabolic, and connective tissue properties

This study assessed postmortem proteolysis over 14 d in bovine Masseter (MS), Longissimus thoracis (LT), and Cutaneous trunci (CT) muscles. First, the metabolic, contractile, and connective tissue properties were characterized to establish their intrinsic differences. The MS contained the highest levels of oxidative markers and myosin heavy chain-I (MyHC-I), whereas the CT possessed the greatest glycolytic capacity, MyHC-IIx, and connective tissue proteins (P < 0.05). The LT had intermediate metabolic characteristics, a heterogeneous mixture of MyHC isoforms, and the lowest amount of connective tissue proteins (P < 0.05), confirming the muscles' intrinsic divergence. Proteolytic analysis revealed increased desmin and slow troponin-T (TT-slow) degradation, with a higher 110 kDa band intensity in the MS than in the CT (P < 0.05). In comparison, the CT exhibited greater TT-fast degradation and higher 30 kDa fragment intensity (P < 0.05). The LT demonstrated the greatest overall proteolysis, indicated by increased TT-fast and TT-slow degradation and the highest intensity of the 30 kDa band (P < 0.05). This is likely due to protease activity, as the LT and MS exhibited more calpain-1 autolysis and less calpastatin abundance than the CT (P < 0.05). However, caspase-3 activity was highest in the MS and lowest in the LT. A principal component analysis incorporating proteolytic indicators further demonstrated the distinct proteolytic profiles in the three muscles. Overall, findings suggest that the progression of postmortem proteolysis is muscle-specific and that a single proteolytic indicator does not sufficiently describe proteolysis when comparing muscles differing in contractile and metabolic properties.