冰温贮藏对宰后肌肉成熟进程的影响

Effects of Controlled Freezing Point Storage on Aging from Muscle to Meat

【目的】动物被屠宰后,经过僵直、成熟等一系列复杂的生理生化反应完成从肌肉到食用肉的转变。温度对这一过程和肉品品质具有重要影响,成熟与肉质也存在密切关系。本试验以探究冰温条件下肌肉成熟进程为目标,确定冰温对成熟进程的影响,为调控肌肉成熟进程提供理论基础。【方法】选取无角陶赛特公羊背最长肌在冰温和冷藏条件下成熟,采用试剂盒测定糖酵解产物、糖酵解关键酶活力,采用酪蛋白酶源分析法测定钙蛋白酶活力,并结合肌原纤维小片化指数分析肌原纤维蛋白降解的变化规律。【结果】宰后p H达到极限值后逐渐增加,冷藏组(2—4℃)、冰温组(-1—-2℃)分别于宰后3 d、7 d达到极限p H,两组极限p H差异不显著。肌糖原含量先降低后稳定,成熟过程中冷藏组与冰温组肌糖原含量差异不显著。乳酸含量先蓄积后稳定最后降解,宰后2、6、12和24 h冷藏组乳酸含量显著高于冰温组。丙酮酸激酶活力先降低后稳定,宰后2 h、24 h冰温组丙酮酸激酶活力显著高于冷藏组。乳酸脱氢酶活力先增加后降低最后稳定,宰后6 h、12 h、24 h和5 d冷藏组乳酸脱氢酶活力显著高于冰温组。μ-钙蛋白酶活力先增加后降低,宰后12 h、24 h、5 d、7 d冰温组μ-钙蛋白酶活力显著高于冷藏组。宰后肌原纤维小片化指数逐渐增加,宰后6 h、12 h、3 d、5 d、7 d和9 d冷藏组肌原纤维小片化指数显著高于冰温组。【结论】与冷藏相比,冰温对肌糖原含量和极限p H影响不显著,但可以使肌糖原达到最低值的时间延长2 d左右,乳酸达到最高值的时间延长1 d左右;冰温可上调丙酮酸激酶活力,下调乳酸脱氢酶活力,显著延长μ-钙蛋白酶存活时间。冰温可延缓宰后肌肉糖酵解进程1—2 d,延迟肌肉成熟。

[Objective] The conversion from muscle to meat after slaughter includes rigor, aging and a series of complicated changes. Temperature is very important for this process and the quality of meat. Aging process also affects meat quality. The objective of this study was to investigate the process of glycolysis in controlled freezing point storage and provide theoretical basis for regulating the speed of aging. [ Method ] The longissimus of Poll Dorset rams were stored at controlled freezing point （-1-2℃） and refrigeration （2-4℃） for 9 days. The products of glycolysis and glycolytic activity of key enzyme were analyzed by the corresponding kit. The degradation of myofibrillar protein during post-mortem were analyzed by myofibrillar fragmentation index, combining with the activity ofcalpain which were analyzed by casein enzyme analysis. [Result] The pH value of the refrigeration and controlled freezing point groups were decreased to the minimum value at 3 d and 7 d, respectively, and then increased gradually. The difference of the minimum value of the two groups were not significant. The content of glycogen decreased and then had no significant changes. There were no significant difference between the two groups during post-mortem. The contents of lactic acid were increased and then became stable, followed by degradation, and the lactic acid content of refrigeration was significantly higher than controlled freezing point at 2 h, 6 h, 12 h, 24 h post-mortem. Pyruvate kinase activity reduced before they were stable, and the pyruvate kinase activity of controlled freezing point was significantly higher than refrigeration at 2 h, 24 h post-mortem. Lactate dehydrogenase activity was first increased and then decreased before becoming stable. The lactate dehydrogenase activity of samples in refrigeration was significantly higher than in controlled freezing point storage at 6 h, 12 h, 24 h, 5 d post-mortem. The activity of μ-calpain was increased first and then decreased, μ-calpain activity of controlled freezing point was significantly higher than refrigeration at 12 h, 24 h, 5 d, 7 d post-mortem. Myofibrillar fragmentation index increased gradually, and myofibrillar fragmentation index of refrigeration was significantly higher than controlled freezing point at 6 h, 12 h, 3 d, 5 d, 7 d, 9 d post-mortem. [Conclusion] Compared with refrigeration, there was no significant difference in glycolysis content and minimum pH value between the two groups, but the controlled freezing point delayed the glycogen degradation about 2 d and the lactic acid accumulation about 1 d. Controlled freezing point could impact the decrease of pyruvate kinase activity and the increase of lactic dehydrogenase activity. In addition, controlled freezing point could also weaken the inactivation of μ-calpain. Controlled freeing point could delay glycolysis process about 1-2 days, so it can delay the aging of muscle.