Abstract: 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.

Key words: cattle, carcass, postmortem aging, different parts, microstructure