Relationships between ultimate pH and antioxidant enzyme activities and gene expression in pork loins

Ultimate pH (pH_u ) is a major determinant factor of meat quality. In this study, we investigated the effects of pH_u on the muscle antioxidant capacity, and the relationship between pH_u and muscle antioxidant capacity of pigs. A total of 137 pigs from three pig breeds with the same feeding condition were slaughtered and used to measure the pH_u , superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), total antioxidant capacity (T-AOC), and malondialdehyde (MDA) content, and gene expression of SOD1 and GPX4. Loins from 137 pigs of three breeds were classified based on pH_u into three groups: low (L-pH: ≤5.50), intermediate (I-pH: 5.51-5.90), and high (H-pH: ≥5.91). A majority of loins (47.5%-52%) were classified into the intermediate group. The results suggested that the pH_u value was correlated with the activity of SOD, GSH-PX, T-AOC, and MDA, and gene expression of SOD1 and GPX4 in all pigs. In addition, our results also indicated a linear relationship between the pH_u value and antioxidant traits. The pH_u value accounted for 23%-40% of the variation in the antioxidant traits. These results suggested that increased pH_u reduce the lipid peroxidation, and also indicated that pHu may be a key factor explaining the variation in the activity of antioxidant enzymes and gene expression in pork loins.