宰后僵直及成熟过程中羊背最长肌理化性质的变化

动物宰后从肌肉到肉品经过僵直、成熟等一系列复杂的生理生化反应。僵直及成熟过程的研究可为肉品质改善及肉制品加工提供理论依据。选取杂交公羊(小尾寒羊×北京本地羊)双侧背最长肌在4℃成熟0.5、2.0、6.0、12.0、24.0、48.0、72.0、120.0、168.0 h,测定不同时间的pH值、剪切力、肌节长度、ATP含量、肌原纤维小片化指数(myofibril fragmentation index,MFI)、钙蛋白酶活力。结果表明:宰后成熟过程中,pH值先下降后逐渐趋于稳定,从第24小时后变化不显著(P0.05);剪切力先上升后下降,在第24小时达到最大值;肌节长度在宰后先缩短后逐渐变长,且在第48小时缩至最短;ATP含量先上升后下降,48 h后趋于稳定;μ-钙蛋白酶80 kD大亚基在宰后24 h基本降解完全,其降解的78 kD大亚基在第48小时降解完全;肌间线蛋白和肌钙蛋白T作为μ-钙蛋白酶的降解底物,在成熟过程中发生降解,第168小时几乎观察不到完整的蛋白条带;随着宰后时间的延长,羊背最长肌从第2小时开始僵直,到第24小时程度达到最大,从第48小时开始解僵,解僵后肉的嫩度逐渐改善。

Changes of Physicochemical Characteristics of Lamb longissimus dorsi Muscle during Rigor Development and Aging

The carcass undergoes a series of complicated physiological and biochemical processes driving the muscle to meat conversion after slaughter. Studying rigor development and postmortem aging is expected to provide theoretical supports for meat quality improvement and processing. Six crossbred rams (Small-tailed Han sheep × Beijing native sheep breed) were slaughtered, and both longissimus dorsi muscles (n = 12) from each carcass were excised and stored at 4 ℃ for 0.5, 2.0, 6.0, 12.0, 24.0, 48.0, 72.0, 120.0 and 168.0 h to determine pH, ATP content, sarcomere length, shear force, myofibril fragmentation index (MFI), protein degradation and μ-calpain activity. During the conversion of muscle to meat, pH initially decreased and then remained not changed significantly at 24 h postmortem (P > 0.05). Shear force first increased until reaching a maximum value at 24 h after slaughter and then decreased. Sarcomere length was first shortened until reaching a minimum value at 48 h and then extended gradually. ATP content was initially increased, then decreased and finally tended to be stable. The 80 kD subunit of μ-calpain degraded almost completely disappeared at 24 h, and a 78 kD subunit was formed firstly and then degraded completely at 48 h after slaughter. Desmin and troponin T as the substrates of μ-calpain were degraded during ageing and intact proteins were scarcely be observed at 168 h. In conclusion, the development of rigor mortis in longissimus dorsi started at 2 h postmortem and reached a peak at 24 h, and it began to disappear at 48 h. The meat tenderness was improved greatly after the complete disappearance of rigor mortis.