Effects of dietary α-lipoic acid on glycolysis of postmortem muscle

The effects of dietary α-lipoic acid (α-LA) on the pH value, AMP-activated protein kinase (AMPK) activation, and the activities of glycogen phosphorylase and pyruvate kinase in postmortem muscle were investigated. Eighteen C57BL/6J mice were fed diets containing 0%, 0.5%, and 1.0% α-LA. At the end of 2-week feeding trial, the mice were killed and longissimus muscles were sampled at 0-, 1-, and 24-h postmortem for pH determination and enzyme assay. The results showed that dietary α-LA treatment significantly slowed down the decrease of pH values in postmortem muscle. The ultimate pH values in postmortem muscle of mice receiving 0.5% and 1.0% α-LA treatments were 6.40 and 6.63, respectively, significantly higher than that (6.21) of no α-LA treatment (p < 0.05). AMPK was activated at the early postmortem stage. Dietary α-LA can suppress the activation of AMPK in postmortem muscle. At 1- and 24-h postmortem, activities of AMPK were much lower in postmortem muscle of mice receiving 0.5% and 1.0% α-LA treatments than that with no α-LA treatment. Between these two dietary α-LA treatments, however, no difference in AMPK activity was observed, indicating that 0.5% dietary α-LA is enough to suppress AMPK in postmortem muscle. Similar to AMPK, glycogen phosphorylase activity was higher in the treatment without dietary α-LA than those with 0.5% and 1.0% dietary α-LA supplements. No difference in the activity of glycogen phosphorylase was observed between the 0.5% and 1.0% dietary α-LA treatments. Dietary α-LA had no significant influence on the activity of pyruvate kinase in postmortem muscle. All these results indicate that AMPK plays a role in glycolysis in postmortem muscle. Dietary α-LA supplementation can suppress the activation of AMPK in postmortem muscle, down-regulate the activity of glycogen phosphorylase, resulting in a higher ultimate pH values in postmortem muscle. Therefore, dietary α-LA supplementation is a potential way to reduce the incidence of pale, soft, exudative (PSE) meat.