Abstract:The major aim of this study was to investigate the changes in the levels of phosphorylation of sarcoplasmic proteins with respect to the postmortem ageing time in mutton with different levels of tenderness. Longissimus muscle samples of 40 sheep were collected at 0.5, 1, 4, 12, and 24 h postmortem, and were divided into two groups (high-level-of-tenderness and low-level-of-tenderness) based on the shear force and myofibrillar fragmentation index (MFI) at 24 h postmortem. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was combined with fluorescence staining in order to analyze the level of phosphorylation of sarcoplasmic proteins. The results of these analyses indicated that groups with different degrees of tenderness and postmortem times showed significantly different levels of sarcoplasmic protein phosphorylation within 24 h (postmortem). The highest levels of protein phosphorylation in the low-level-of-tenderness and high-level-of-tenderness groups were observed at 4 and 12 h postmortem, respectively. In addition, the global levels of sarcoplasmic protein phosphorylation observed in the low-level-of-tenderness group at 0.5, 1, and 4 h postmortem were significantly higher than those observed in the high-level-of-tenderness group. Therefore, the level of sarcoplasmic protein phosphorylation was significantly affected by the varying degrees of tenderness and the different postmortem times (P < 0.05); moreover, it was theorized that protein phosphorylation influences rigor mortis in postmortem muscles through glycolysis, thereby affecting muscle tenderness.
