不同冻融次数下牦牛肉蛋白质氧化与保水性的关系

探讨不同冻融次数下牦牛肉中的蛋白质氧化对其保水性的影响。选取3?岁左右的甘南牦牛背最长肌，经过7?次冻融循环，分别测定样品的pH值、解冻损失率、蒸煮损失率、加压失水率、羰基含量、巯基含量以及蛋白质溶解度。结果表明，随着冻融次数的增加，pH值显著降低（P＜0.05），解冻损失率、加压失水率和蒸煮损失率反映的保水性也显著降低（P＜0.05），羰基、巯基含量反映的蛋白质氧化程度显著增加（P＜0.05），蛋白质溶解度中全蛋白、肌原纤维蛋白以及肌浆蛋白均呈现显著下降（P＜0.05）。pH值、保水性和蛋白质氧化之间相关性显著（P＜0.05），在7?次冻融过程中，pH值下降速率趋势与保水性下降速率趋势一致，并且后期保水性下降速率减缓的同时蛋白质氧化速率上升。表明多次冻融循环会引起牦牛肉蛋白质氧化程度显著升高，造成保水性显著下降，贮运体系中通过有效地控制蛋白质氧化可以更好地提高牦牛肉品质。

Relationship between Protein Oxidation and Water Holding Capacity of Yak Meat under Freeze-Thaw Cycles

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.