Effects of Prolylhydroxylase on Postmortem Muscle Glycolysis and Meat Quality of Yaks

In order to study the effects of prolylhydroxylase (PHD) on hypoxia inducible factor-1α (HIF-1α) expression, glycolysis and meat quality in yak muscle during postmortem aging, the Longissimus dorsi muscle of yaks was injected postmortem with dimethyloxaloylglycine (DMOG) or normal saline as a control and evaluated for changes in HIF-1α expression, key glycolytic enzyme activities, glycolysis degree and meat quality after different aging periods. The results showed that HIF-1α expression increased first and then decreased with increasing aging time. However, in the DMOG-treated group, HIF-1α expression was significantly increased during the first 12 h postmortem (P < 0.05), suggesting that inhibition of PHD activity can up-regulate HIF-1α expression. The activity of hexokinase (HK), phosphofructokinase (PFK) and pyruvate kinase (PK) increased first and then decreased with aging time, all of which were significantly higher in the DMOG-treated group than in the control group from 3 to 120 h (P < 0.05). The glycogen content and pH of the DMOG-treated group were significantly lower than those of the control group from 3 to 72 h (P < 0.05), while the lactic acid content was significantly higher than that of the control group (P < 0.05), suggesting that PHD can up-regulate the activity of glycolytic enzymes by mediating HIF-1α expression and consequently accelerate the process of glycolysis. Moreover, the shear force of the DMOG-treated group was significantly higher than that of the control group during 3-72 h (P < 0.05), the L* value was significantly higher than that of the control group during 6-168 h (P < 0.05), and the a* value was significantly higher than that of the control group during the entire aging process (P < 0.05). The muscle fiber diameter and area in the DMOG-treated group were lower than those in the control group, and the gap between muscle fibers was higher but not significantly than that in the control group. These results indicate that PHD affects postmortem meat quality by mediating HIF-1α expression, causing pH changes and consequently changes in shear force and L* value. Nevertheless, the reason for changes in a* value needs to be further explored. In conclusion, PHD can increase the activity of key glycolytic enzymes by up-regulating HIF-1α expression during postmortem aging, thereby accelerating the glycolysis process, resulting in changes in muscle internal environment and ultimately affecting the formation of postmortem meat quality.