Abstract: This study was designed to explore the effect of freeze-thaw cycles on the protein oxidation and water holding capacity of yak meat and also to investigate the relationship between the two parameters. Longissimus dorsi samples were collected from the carcass of 3-year-old Gannan yaks, and the changes in pH, thawing loss, cooking loss, pressurized water loss, carbonyl group and total sulfydryl group contents and protein solubility of repeatedly frozen-thawed yak meat were analyzed. The results showed that with an increase in the number of freeze-thaw cycles, pH was significantly decreased as well as water holding capacity (thawing loss, pressurized water loss and cooking loss) were significantly decreased (P < 0.05), the degree of protein oxidation (carbonyl group and total sulfydryl group contents) was significantly increased (P < 0.05), and total, myofibrillar and sarcoplasmic protein solubility were significantly decreased (P < 0.05). pH was significantly correlated with water holding capacity and protein oxidation (P < 0.05). During 7 freeze-thaw cycles, pH decreased at a rate similar to water holding capacity. Moreover, after the fourth cycle, the rate of decrease in water holding capacity was slowed down and the rate of protein oxidation was speeded up. All these results demonstrated that freeze-thaw cycles gave a rise to a significant rise in the degree of protein oxidation and caused a significant reduction of the water holding capacity of yak meat. Therefore, controlling protein oxidation during storage is effective in enhancing the quality of yak meat.

Key words: yak meat, freeze-thaw cycles, water holding capacity, protein oxidation