EARLY POSTMORTEM CONDITIONS AND THE CALPAIN CALPASTATIN SYSTEM IN RELATION TO TENDERNESS OF DOUBLE-MUSCLED BEEF/

Early post mortem temperature, pH, sarcomere length, colour, water hol ding capacity, calpain/calpastatin activities and myofibrillar protein concentrations (semi-quantative SDS-PAGE), measured at different time s post mortem on 153 double-muscled Belgian Blue White bulls, were rel ated to shear force (SF) measurements. The M. longissimus thoracis ten derised up to 8 days post mortem. SF was slightly correlated with temp erature at 3 h post mortem (r=0.20, p=0.015), but not with pH early po st mortem. Higher ultimate pH values measured at 24 h post mortem were related to darker meat, lower cooking losses and shorter sarcomere le ngths. Sarcomere length was significantly related to SF, even after 12 days of ageing, suggesting that proteolytic activity was not able to overcome shortening. Up to 12 days post mortem, calpastatin and m-calp ain activities were significantly correlated with SF suggesting a cons iderable role of calpains in meat tenderization of double-muscled Belg ian Blue White bulls, although at 24 h post mortem, mu-calpain could n o longer be detected Titin, nebulin, filamin and troponin-T were degra ded during the ageing period. Troponin-T was degraded by 80% between d ay 1 and 8. At 8 days post mortem its concentration was significantly correlated with 30 kDa (r=0.63, p=0.00), shear force (r=0.39, p=0.00), calpastatin activity at I day post mortem (r=0.29, p=0.001) and with the m-calpain/calpastatin activity ratio at I day post mortem (r=-0.43 , p=0.00). (C) 1997 Elsevier Science Ltd.