This study aimed to determine the effect of frozen-then-chilled storage on free Ca²⁺, proteolytic enzyme activity of calpains and the proteasome, water-holding capacity and shear force of porcine longissimus thoracis et lumborum muscle. Pork loins were subjected to either chilled storage at 2 ± 1 °C for 1, 2, 4, 6 and 9 days, or frozen-then chilled storage (−20 ± 1 °C for 1 week followed by thawing overnight). Free Ca²⁺ increased with chilled storage in the non-frozen group. Frozen-then-chilled storage increased free Ca²⁺ concentration, followed by a faster decrease of calpain-1 activity and activation of around 50% of calpain-2. Proteasome activity was reduced by around 40% following freezing-thawing. Purge loss increased and water-holding capacity of myofibrils decreased in the frozen-thawed group, suggesting considerable denaturation of myofibrillar proteins. Shear force was not affected by freezing-thawing, and we speculate that the tenderizing effect of calpain activation was counteracted by loss of proteasome activity and substantial exudate loss.

本研究旨在确定冷冻后冷藏对猪长脊柱及腰部肌肉的游离Ca ²⁺，钙蛋白酶的蛋白水解酶活性以及蛋白酶体，保水能力和剪切力的影响。将猪里脊肉在2±1°C下冷藏1、2、4、6和9天，或冷冻后冷藏（-20±1°C 1周，然后融化过夜）。在非冷冻组中，随着冷藏的进行，游离Ca ^2+的含量增加。冷冻后冷藏可增加游离钙²⁺浓度升高，随后钙蛋白酶1活性下降更快，钙蛋白酶2活化约50％。冻融后蛋白酶体活性降低了约40％。在冻融组中，吹扫损失增加，肌原纤维的保水能力降低，表明肌原纤维蛋白大量变性。剪切力不受冻融的影响，我们推测蛋白酶蛋白酶活性的丧失和大量渗出液的丧失抵消了钙蛋白酶激活的嫩化作用。