滩羊肉宰后成熟期间ATPase活力变化对微观结构及保水性的影响

为研究宰后成熟期间ATPase活力变化对滩羊肉微观结构以及保水性的影响，以6 月龄滩羊背最长肌（Longissimus dorsi）为研究对象，分析其4 ℃成熟0、1、2、4、8 d时Na＋-K＋-ATPase、Ca2＋-ATPase、Caspase-3活力以及肌肉微观结构、pH值与滴水损失率的变化情况。结果表明：随成熟时间延长，Na＋-K＋-ATPase与Ca2＋-ATPase活力先升高后降低，成熟1 d时达到最大值；Caspase-3活力先升高后降低，成熟2 d时达到最大值；滴水损失率先升高后降低，pH值先降低后有所回升；总蛋白、低盐溶性蛋白及高盐溶性蛋白质量浓度均逐渐减少，水溶性蛋白质量浓度成熟2 d后显著降低（P＜0.05）；成熟至8 d时，肌原纤维断裂，肌纤维之间、肌束之间、肌纤维及肌膜之间形成间隙，Z线断裂，H带消失；相关性分析结果表明Na＋-K＋-ATPase活力与各指标均呈极显著相关性（P＜0.01），Ca2＋-ATPase活力与pH值、Na＋-K＋-ATPase及Caspase-3活力均呈极显著相关性（P＜0.01）。结论：滩羊肉宰后成熟过程中Na＋-K＋-ATPase与Ca2＋-ATPase活力变化可能促使下游Caspase-3激活，Caspase-3水解结构蛋白可能导致肌肉组织在不同部位形成间隙，在重力作用下肌肉中的水分流入间隙中，引起滩羊肉滴水损失升高，保水性变差。

Effect of ATPase Activity on Microstructure and Water-Holding Capacity of Tan Sheep Meat during Postmortem Aging

This study aimed to clarify the changes in ATPase activity and its effect on the microstructure and water-holding capacity (WHC) of Tan sheep meat during postmortem aging. The Longissimus dorsi muscle of Tan sheep slaughtered at 6 months of age was aged at 4 ℃ and evaluated for the activities of Na+-K+-ATPase, Ca2+-ATPase and caspase-3, microstructure, pH and drip loss rate after 0, 1, 2, 4 and 8 days. Results showed that the activities of Na+-K+-ATPase and Ca2+-ATPase increased initially and subsequently decreased with aging time, peaking at day 1. The activity of caspase-3 and drip loss increased with aging time up to 2 days and then decreased. In contrast, the opposite trend was observed for muscle pH. The contents of total proteins, low-salt soluble proteins, and high-salt soluble proteins continuously decreased with aging time. The content of water soluble proteins significantly decreased after day 2 (P < 0.05). On day 8, the myofibrils were broken, and gaps between myofibers, between muscle fiber bundles, and between myofibers and sarcolemma appeared; the Z lines were broken, and the H bands disappeared. Correlation analysis indicated that the activity of Na+-K+-ATPase was correlated with all other parameters (P < 0.01) and the activity of Ca2+-ATPase was significantly correlated with muscle pH and the activities of Na+-K+-ATPase and caspase-3 (P < 0.01). Overall, during postmortem aging, the variations in the activities of Na+-K+-ATPase and Ca2+-ATPase can lead to downstream caspase-3 activation to hydrolyze cytoskeleton proteins, resulting in the formation of gaps at different muscle sites. The water in muscle flows into the formed gaps due to gravity, causing an increase in the drip loss and a decrease in the WHC of Tan sheep meat.