EFFECT OF POSTMORTEM CONDITIONS ON CERTAIN CHEMICAL, MORPHOLOGICAL AND ORGANOLEPTIC PROPERTIES OF BOVINE MUSCLE

Paired sides from U.S. Choice grade beef were aged immediately after slaughter at 2 and 16°C. Samples were removed from longissimus and semitendinosus at slaughter and at 1, 3 and 7 days postmortem for ATPase assay, phase microscopy, shear and organoleptic evaluation. Rib steaks from sides aged at 16°C for 1‐day postmortem were as tender as steaks from sides aged at 2°C for 7 days postmortem. Flavor development of rib steaks also was more rapid at 16°C than at 2°C. Tenderness of semitendinosus steaks was improved by aging sides at 16°C; the difference in improvement of tenderness of semitendinosus, however, was not as great between 2°nd 16° as it was for rib steaks. Ca ++ , Mg ++ and EGTA‐modified ATPase activity of myofibrils from both muscles increased with postmortem time, with myofibrils from muscles held at 16°C having slightly higher ATPase activity than myofibrils from muscles held at 2° Increased EGTA‐modified ATPase activity was indicative of loss of calcium sensitivity of the myofibril. Sarcomeres of myofibrils from longissimus were longer at 1‐day postmortem than those from at‐death longissimus and they remained essentially unchanged during the remainder of postmortem aging; however, tenderness improved at 16°C for 1 day and at 2°C for 3 days. Also greater fragmentation of myofibrils from longissimus postmortem aged at 16°C for 1 day and at 2°C for 3 days was observed, suggesting that the rate of myofibril fragmentation is an important factor in tenderization.