Abstract: To investigate the effect of cytochrome c (Cyt-c) redox state during postmortem aging on the water-holding capacity and tenderness of Tan sheep meat, hindleg muscles were allocated into two groups: a treatment group and a control group, which were injected with 100 μmol/L N,N,N’,N’-tetramethyl-p-phenylenediamine dihydrochloride (TMPD) and 0.8% saline, respectively. Changes in the Cyt-c redox state, apoptosis rate, water-holding capacity, and tenderness of Tan sheep meat wet-aged for different periods (0, 6, 12, 24, 48, 96, and 192 h) postmortem were determined. The results showed that in the control group, the level of mitochondrial reactive oxygen species (ROS), mitochondrial permeability transition pore (MPTP) openness and myofibril fragmentation index (MFI) increased significantly with postmortem aging time (P < 0.05). The pH and caspase-9 activity showed a decreasing and then increasing trend. Both ATP content and mitochondrial membrane potential decreased significantly (P < 0.05). The Cyt-c redox level, cytosolic Cyt-c content, caspase-3 activity, shear force, centrifugal loss, and cooking loss all increased initially and then decreased. Meanwhile, throughout the entire aging process, the ATP content, early ROS levels, oxidative damage indicators, Cyt-c content and apoptosis rate in the treatment group were significantly lower than those in the control group (P < 0.05), whereas the Cyt-c redox level, shear force, cooking loss and centrifugal loss showed the opposite trend. Notably, the cytosolic Cyt-c content in the treatment group was significantly lower than that in the control group at the early postmortem stage, but significantly higher than that in the control group at the late stage (P < 0.05). In conclusion, the redox state of Cyt-c during postmortem aging influenced apoptosis, water-holding capacity, and tenderness in Tan sheep meat. Reduced Cyt-c was less likely to be released into the cytoplasm, thereby decreasing the activity of caspase-9 and caspase-3 and lowering the apoptotic rate. Consequently, myofibrillar protein degradation was slowed, leading to increased cooking loss and centrifugation loss, decreased MFI, and elevated shear force, which were unfavorable for meat tenderness and water-holding capacity.

Key words: Tan sheep; cytochrome c redox state; apoptosis; water retention; tenderness