Manipulation of the pre-rigor phase to investigate the significance of proteolysis and sarcomere length in determining the tenderness of bovine M. longissimus dorsi

The objective of this study was to evaluate the importance of proteolysis and sarcomere length in determining the tenderness of bovine M. longissimus dorsi (LD) muscle over a 21-day period. This was done by altering the pre-rigor glycolytic behaviour of hot-boned LD muscles using different early post-mortem temperature regimes. Hot-boned LD muscles (n = 8) were cut in two, randomised, placed in polythene bags and submerged in a water bath set at 5 °C (rapidly chilled) and 15 °C (slowly chilled) for 8 h post-mortem. All muscles were then stored at 2 °C for up to 21 days post-mortem. The temperature regimes altered the glycolytic behaviour of the muscles in the pre-rigor period. The slowly chilled muscles exhibited a faster (P < 0.01) pH fall than rapidly chilled muscles. Cold shortening was induced in rapidly chilled muscles as they had shorter (P < 0.01) sarcomere lengths than slowly chilled muscles up to day 21 post-mortem. Warner Bratzler shear force values (WBSF) deemed cold-shortened muscles as tougher than noncold shortened up to day 14 post-mortem. Both cold-shortened and noncold-shortened muscles tenderised over time to an extent where there was no significant difference in WBSF values by day 21 post-mortem. SDS–PAGE protein profiles indicated that the rate of proteolysis was faster in slowly chilled muscles when compared to rapidly chilled muscles. However by day 21 post-mortem it appeared that rapidly and slowly chilled muscles underwent proteolysis to the same extent.