THE ROLE OF ENDOGENOUS PROTEASES IN THE TENDERIZATION OF FAST GLYCOLYZING MUSCLE

The activities of lysosomal cathepsins and the calpain-calpastatin sys tem were measured to determine their involvement in the more rapid ten derisation of fast glycolysing muscle. The rate of pH fall of M. longi ssimus dorsi (LD) of Hereford cross Friesian heifers (n = 52, Experime nt 1, n = 36, Experiment 2) was measured. Muscles were selected accord ing to their rate of glycolysis; slow and fast (n = 16, Experiment 1, n = 10, Experiment 2). Fast glycolysing muscles were rated more tender in sensory analysis and had a lower shear force than slow glycolysing muscles. Slow glycolysing muscles had shorter sarcomere lengths. Low pH conditions in fast glycolysing muscle correlated with the enhanced release of cathepsins B and L from lysosomes. Calpain I activity was h igher and calpastatin activity was lower in fast glycolysing muscle ea rly post mortem. SDS-PAGE electrophoresis patterns showed increased pr oteolysis, such as the earlier appearance of the 30 kDa fragment in fa st glycolysing muscle. Transmission Electron Microscopy (TEM) results showed a greater degree of ultrastructural breakdown early post mortem in fast glycolysing muscle. The results suggest that the increase in tenderness in muscles that undergo fast glycolysis early post mortem m ay be caused by proteolysis by released lysosomal cathepsins and calpa in I uninhibited by calpastatin. (C) 1997 Elsevier Science Ltd. All ri ghts reserved.