The calpain system and postmortem tenderization in ovine meat from callipyge and normal phenotypes

In an attempt to further our understanding of the relationship between the calpain system and postmortem tenderization, three muscles [biceps femoris (BF), infraspinatus (IS), and longissimus (LD)] from normal (N = 6) and callipyge (N = 6) sheep were studied. Callipyge is a genetic phenomenon where carriers of the callipyge gene present a hypertrophy of pelvic and torso muscles, such that BF and LD are affected while IS is not. It has been observed characteristically that calpastatin and m-calpain activities are increased in muscles of animals affected by the callipyge phenotype. Soluble calpain and calpastatin, and myofibril-bound μ-calpain activities, and myofibrillar fragmentation index (MFI) were determined at death, 1d, 3d and 10d postmortem. Sarcomere length was determined at 1d and 10d postmortem. Shear force of the longissimus muscle was determined at 1d, 3d and 10d postmortem. Western blots for calpastatin, μ-calpain, desmin, nebulin, titin, troponin-T and α-actinin were performed to follow the degradation pattern of those proteins. The calpastatin and m-calpain activities were more than two-fold greater in BF and LD muscles from callipyge than in the same muscles from normal animals. Calpastatin activities in infraspinatus muscle from normal animals were higher than in the other two muscles of this phenotype. Soluble μ-calpain activities were higher at death for normal phenotype in BF and IS muscles and it decreased rapidly during postmortem storage. However, the rate of this decrease in that activity was faster in normal than in callipyge phenotype. Myofibrils contained calcium dependent protease activity and this activity was inhibited by cysteine proteases inhibitors and by calpastatin to some degree. There was no difference in the myofibril-calcium dependent protease activity between phenotypes at any time postmortem, presenting lower activity at death. The magnitude of protein degradation and tenderization were assessed by MFI and shear force, respectively. Neither the MFI nor shear force changed appreciably during storage of the callipyge affected muscles. Calpastatin level seems to determine the rate of postmortem tenderization