Effect of Structural Protein on Tenderness of Beef from Qinchuan Cattle during Postmortem Aging

In order to explore the effects of structural proteins on the quality changes of Longissimus dorsi muscle from Qinchuan cattle during storage, 4D-label free quantification (4D-LFQ) was used to analyze the proteomic changes of beef Longissimus dorsi muscle during different storage periods (0, 2, 4, 6 and 8 days). The changes in shear force, myofibrillar fragmentation index (MFI) and protein content were measured as well. The results showed that the shear force tended to increase and then decrease during the storage period of 8 days (P < 0.01), the increase being greater than the decrease. The MFI showed a significant upward trend with storage time (P < 0.01), increasing by up to 250.81% after 8 days of storage; however, the opposite trend was observed for the total soluble protein content (P < 0.05), decreasing by up to 34.60%. Structural proteins in muscle tissue were degraded with postmortem metabolic changes in muscle tissue, which possibly affected tenderness development and caused a significant decrease in the content of myofibrillar protein (P < 0.05). The content of myofibrillar protein decreased rapidly at first and then slowly, decreasing by 50.56% over the entire storage period. During the first four days, the abundance of four proteins (alpha-actin-1, myosin heavy chain 9, myosin regulatory light chain 2, and myosin regulatory light chain 12B) were changed by regulating the calcium ion-binding and cytoskeletal protein-binding pathways in the development of skeletal muscle tissue. During the 8 days of storage, the abundance of eight proteins (myosin regulatory light chain 2, myosin heavy chain 6, alpha-actin-1, actin, alpha cardiac muscle 1, myosin regulatory light chain 2, troponin Ⅰ 1, troponin Ⅰ 2, and myosin heavy chain 15) was changed by regulating the calcium ion-binding pathway in the development of muscle organ and striated muscle tissue. Moreover, the structural proteins were degraded as a result of the regulation of the physiological state of cells by myosin binding, calcium ion binding, cytoskeletal protein binding myofibrillar assembly, skeletal muscle tissue development, muscle organ development, and striated muscle tissue development, leading to an increase in the MFI, thus improving the tenderness.