MEAT TENDERNESS AND THE CALPAIN PROTEOLYTIC SYSTEM IN LONGISSIMUS MUSCLE OF YOUNG BULLS AND STEERS

The objectives of this study were to examine the effects of castration on the calpain proteinase system (mu-calpain, m-calpain, and calpasta tin) activities and meat tenderness. Six each, MARC III bulls and stee rs were slaughtered at approximately 12 mo of age. Longissimus muscle samples were obtained for determining myofibril fragmentation index, W arner-Bratzler shear force, and sensory panel evaluation at 1, 7, and 14 d postmortem, and mu- and m-calpain and calpastatin activities at 2 4 h postmortem. Bulls produced leaner carcasses with lower (P < .05) q uality grades than did steers. Meat from bulls had higher (P < .05) sh ear force values than meat from steers; however, sensory panelists wer e unable (P > .05) to detect differences in tenderness or other sensor y traits between bulls and steers. Activities of mu- and m-calpain wer e not affected (P > .05) by castration; however, calpastatin was highe r (P < .05) in muscles from the bull carcasses. Lower (P < .0 5) myofi bril fragmentation index values indicate that less proteolysis occurre d in muscle from bulls than in muscle from steers during the first 7 d postmortem. Greater calpastatin 24-h activity may be associated with the increased shear force of meat from bulls.