THE RELATIONSHIP BETWEEN EARLY POSTMORTEM PH AND THE TENDERIZATION OFBEEF MUSCLES

The rate of early post-mortem pH fall in bovine muscle was studied to determine its influence on the rate and extent of the tenderisation pr ocess. The pH of M. longissimus dorsi (LD) and M. semimembranosus (SM) muscles of Hereford cross Friesian heifers (n = 127) was taken up to 24 h post mortem. Twenty-four LD and 24 SM muscles were selected accor ding to their rate of pH fall, slow (n = 8), intermediate (n = 8) and fast (n = 8) and were sampled at 2, 7 and 14 days post mortem for sens ory, mechanical, physicochemical and biochemical analysis. Fast glycol ysing LD muscles were rated more tender in sensory analysis and textur e assessment whereas slow glycolysing muscles were considered signific antly tougher (p < 0.001). Fast glycolysing LD had a significantly low er shear force (p < 0.001) at each stage of ageing. Slow glycolysing L D and SM had the highest shear force values. No significant difference was found in intramuscular fat or moisture content between the groups . Slow glycolysing LD muscles had shorter sarcomere lengths at 2 days post mortem. SDS-PAGE electrophoresis patterns showed increased proteo lysis, such as the earlier appearance of the 30 kDa fragment, which is believed to be a goon indicator of tenderness, in fast glycolysing mu scle. These results suggest that the I ate of post-mortem pH fall play s an important role in proteolysis and tenderisation. (C) 1997 Elsevie r Science Ltd.