－20℃下鳙鱼肉中组织蛋白酶B及L对其肌纤维微结构及持水力的影响
Effects of cathepsin B and L on myofibrillar microstructure and water holding capacity of bighead carp (Aristichthys nobilis) fillets stored at -20℃

以鳙鱼肉为研究对象，测定-20℃下鳙鱼肉的肌原纤维、肌浆中的组织蛋白酶B及组织蛋白酶B+L活性、肌原纤维蛋白及肌浆蛋白的SDS PAGE条带以及扫描电镜和透射电镜下的肌原纤维显微结构、质构、持水力（汁液损失及LF-NMR数据）随贮藏时间的变化。结果显示：鳙鱼片在-20℃下冻藏不同时间后再解冻，其组织蛋白酶仍具有较高的活性，肌球蛋白重链、肌动蛋白、肌钙蛋白T及原肌球蛋白随着冻藏时间的延长而降解，且出现了有可能是组织蛋白酶L酶解产物的20 ku肌浆蛋白条带。扫描电镜及透射电镜的结果显示，在冻藏112 d，肌纤维遭到了严重破坏，肌节中的A带及I带已经不能被清楚地辨别出来，M线几乎消失，同时鳙鱼肉的硬度及弹性随冻藏时间延长而大幅下降。鳙鱼肉的汁液损失、水分的T21、T22、P22均随着冻藏时间延长而显著上升，水分的P21随冻藏时间延长而显著下降。研究结果表明，鳙鱼肉在冻藏过程中，组织蛋白酶B及B+L参与了肌原纤维蛋白及肌浆蛋白的降解，从而破坏了鱼肉肌纤维微结构的完整，并造成了鳙鱼肉质构及持水力的劣化。
The changes of cathepsin activity in myofibrils and sarcoplasm,degradation of myofibrillar and sarcoplasmic protein by SDS PAGE,myofibrillar microstructure by scanning electron microscopy (SEM) and transmission electron microscopy (TEM),instrumental texture,water holding capacity (WHC) by drip loss and LF NMR for bighead carp fillets were measured during -20℃ storage.The results showed that the cathpsins were still active for thawed fillets stored at -20℃.The degradation of myosin,actin,troponin T and tropomyosin were observed.A 20 ku sarcoplasmic protein band which might be a proteolysis product of cathepsin L was found.The results of SEM and TEM showed that the muscle fibers were severely damaged at 112 d,which expressed by indistinguishable A band and I band in the sarcomere and almost disappeared M line.The hardness and elasticity of the fish were significantly decreased.The drip loss and T21,T22 and P22 of fillets increased,but P21 decreased significantly with the extension of frozen storage time.Overall the proteolysis of cathepsins on myofibrillar and sarcoplasmic protein during frozen storage led to the great destruction of integrity of myofibrillar microstructure and weakeness of fish texture and WHC