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.