Relationship between Mitochondrial Oxidative Phosphorylation and Color Stability of Tan Sheep Meat during Postmortem Storage

In order to elucidate the relationship between the oxidative phosphorylation and the color stability of Tan sheep meat during postmortem storage, the changes in the color stability and oxidative phosphorylation of the Longissimus dorsi of 6-month-old Tan sheep were determined after 0, 1, 2, 3, 4, 6 and 8 days of postmortem storage at 4 ℃. The results showed that L*, a* and b* values increased first and then decreased during 0–8 days of storage (P < 0.05), and so did R₆₃₀/R₅₈₀ ratio (P < 0.05). The relative content of metmyoglobin (MetMb) showed a decreasing and then increasing trend (P < 0.05), whereas the relative content of oxymyoglobin (OxyMb) exhibited the opposite trend (P < 0.05), and the relative content of deoxymyoglobin (DeoMb) showed a decreasing trend (P < 0.05). Mitochondrial membrane permeability significantly increased (P < 0.05), and mitochondrial membrane potential significantly decreased (P < 0.05). The activity of mitochondrial complex Ⅰ, Ⅱ, Ⅲ and Ⅳ significantly decreased (P < 0.05), while the activity of complex Ⅴ significantly increased (P < 0.05). Reactive oxygen species (ROS) levels significantly increased (P < 0.05). The activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) significantly decreased (P < 0.05). Catalase (CAT) activity first increased and then decreased (P < 0.05). The contents of ATP, ADP and AMP significantly decreased (P < 0.05). The relative contents of MetMb, OxyMb and DeoMb and meat color parameters were significantly correlated with oxidative phosphorylation. The above results indicate that the failure of endogenous antioxidant enzymes in Tan sheep meat during postmortem storage led to excessive ROS production in myocytes, which damaged the integrity of mitochondria, and then affected the activities of enzymes related to mitochondrial oxidative phosphorylation and consequently the activity of MetMb reductase in myocytes, which resulted in the failure of MetMb reduction, thereby leading to deterioration of the color stability of Tan sheep meat.