Effect and Mechanism of Energy Substances, pH and Myofibril Fragmentation Index on Beef Tenderness of Qinchuan Cattle during Postmortem Ageing

In order to explore the mechanism of the tenderness change of the longissimus dorsa muscle of Qinchuan cattle during postmortem ageing, this study measured the changes in energy substances, pH and myofibril fragmentation index (MFI) during storage up to eight days, and it explored the effect of proteomic changes on beef tenderness by four-dimensional label-free quantification (4D-LFQ). It was found that the shear force value increased first and then decreased with storage time, reaching a maximum value of (157.94 ± 2.53) N on the 4^th day, indicating the worst tenderness; however, the opposite trend was observed for the pH, reaching a minimum value of 5.37 ± 0.03 on this day. The contents of the energy substances ATP, AMP and NADH showed a decreasing trend with storage time, and the decrease was the most significant from days zero to two, while the reverse trend was observed for MFI. Totally 11 differential proteins related to the tenderness were identified through correlation analysis. Among them, ATP5F1D, ATP5F1C, NDUFB5, NDUFA6, and SUCG1 regulated the changes in ATP content and pH by participating in the glycolysis process, causing muscle fiber cross-linking, muscle stiffness, and ultimately leading to decreased tenderness; PPP3R1, CAMK2D, HNRNPK, PSMD13, and CTSD regulated muscle cell apoptosis and proteolysis by participating in the muscle fiber membrane, the membrane protein complexes, the organelle inner membranes, and the calcium signaling pathway, resulting in an increase in MFI and ultimately contributing to improve beef tenderness.