牦牛肉成熟过程中肉用品质及结构变化特点

以牦牛肉为研究对象，在宰后1、2、3、4、5、6、7、8d分别测定剪切力、PH值、失水率、钙激活酶（calpains）活性、肌原纤维超微结构，研究牦牛肉成熟过程中肉用品质及结构的变化。结果表明：在0-4℃条件下，牦牛肉的初始pH值为6．12，第4天降到最低点（极限pH值）为5．48；失水率在第4天达到最大值34．38％；Calpains活性呈逐步增高趋势，在第3-4天显著增加；成熟过程中，肌原纤维结构发生了明显的变化，第5天M线和H线消失，Z线破碎情况严重，此变化与嫩度变化特点相吻合。剪切力在第4天达到最大值55．95N，此时肉的嫩度最差，随后剪切力值开始下降，达到食用口感的适宜嫩度范围，牦牛肉完成成熟。

Variations in Quality and Structural Characteristics of Yak Meat during Postmortem Aging

Shear force, pH, water loss rate, calpain activity, myofibril ultrastructure were measured on yak meat at days 1, 2, 3, 4, 5, 6, 7 and 8 after slaughtering to investigate variations in quality and structural characteristics of yak meat during postmortem aging. The initial pH of yak meat was 6.12 at 0-4 ℃, and decreased to its minimum level （extreme pH） 5.48 at day 4 after slaughtering, and the water loss rate reached its maximum level at the same day. The calpaln activity showed a gradual upward trend and a distinct increase at day 3 - 4. Notable variations in myofibril ultrastructure were found during postmortem aging, the M and H lines disappeared, and the Z line was seriously broken at day 5. These variations were consistent with those in the tenderness. Moreover, the highest shear force, 55.95 N, was found at day 4, and yak meat revealed the worst tenderness. The shear force began to decrease at day 5 and the tenderness reached the appropriate range for good palatability. Therefore, yak meat was completely aged.