宰后成熟对牛胴体不同部位显微结构影响

将不同部位肉样真空包装后于4℃条件下成熟72h ，采用石蜡切片苏木精-伊红(HE)染色法、原子力显微镜扫描肌原纤维、环境扫描电镜扫描肌纤维膜、免疫组织化学法及测定剪切力，研究牛胴体不同部位剪切力、宰后成熟过程中肌纤维和肌原纤维裂解程度、肌纤维膜变化及μ-calpain肌纤维定位。结果表明：剪切力：半腱肌＞腹直肌＞背最长肌；牛肉后熟过程中，背最长肌肌纤维、肌原纤维裂解程度最大，腹直肌次之，半腱肌变化较小；肌纤维膜变化不大；μ-calpain主要存在于肌纤维膜和肌浆中，红肌纤维(慢肌)μ-calpain含量高，白肌纤维(快肌)μ-calpain含量低。μ-calpain在牛肉后熟过程中对牛肉嫩化具有重要作用，红肌纤维μ-calpain含量高，白肌纤维μ-calpain含量低，因此，胴体不同部位红肌纤维和白肌纤维的比例是导致其后熟嫩度和显微结构差异较大的一个重要因素。

Effect of Postmortem Aging on Microstructure of Different Beef Muscles

To investigate the effect of postmortem aging on beef microstructure and the underlying mechanism,we herein examined three muscles,namely longissimus dorsi(LD),rectus abdominis(RA),and semitendinosus(ST),from Qinchuan beef carcasses.Meat samples were vacuum packaged and aged at 4 ℃ for 72 h.Subsequently,shear force,paraffin hematoxylin-eosin(HE) staining and atomic force microscopy were used to examine changes in different parts,muscle fiber and myofibril fragmentation.Environmental scanning electron microscopic observations were also performed to examine sarcolemma,and immunohistochemistry was employed to study the localization of μ-calpain in muscle fibers.The results indicated that the shear force of different parts ranked in the following descending order: ST > RA > LD.LD muscle fiber and myofibrils exhibited the most severe fragmentation,and ST fiber showed the least changes during postmortem aging.No significant changes were observed in sarcolemma.Furthermore,μ-calpain was detected mainly in sarcolemma and cytoplasm;high levels of μ-calpain were found in red muscle fiber(slow muscle),whereas white muscle fiber(fast muscle) showed low levels of expression.Therefore,μ-calpain appears to be important for beef tenderization during postmortem aging.In different parts of Qinchuan cattle carcass,the ratio of red to,white muscle fiber could significantly affect microstructural changes in muscle fibers and impovement in beef tenderness during postmortem aging.