Effects of electrical stimulation on post-mortem changes in the activities of two Ca dependent neutral proteinases and their inhibitor in beef muscle

Post-mortem changes in the activities of two calcium-dependent neutral proteinases and their inhibitor were studied in electrically stimulated and control beef Longissimus dorsi muscles. During meat conditioning in control muscles the activity of the high-calcium-requiring proteinase (mmCa ANP) was not affected while a decrease in the activities of the low-calcium-requiring proteinase (μmCa ANP) was observed. After electrical stimulation, the mmCa ANP activity was only slightly decreased, but the μmCa ANP and the inhibitor activities were drastically affected. An 80% decrease in μmCa ANP activity was observed 4 h post electrical stimulation. The post-mortem changes seem to be closely related to the post-mortem pH fall. If the Ca-requiring neutral proteinases are involved in the meat ageing mechanism, it eems that the μmCa ANP is more likely to cause most of the post-mortem changes in the myofibrillar proteins, taking into account the low level of intracellular calcium. But as its activity is drastically reduced during the rigor mortis process, most of the effect of μmCa ANP could occur at the very beginning of the post-mortem changes.