Relationship between proteolytic changes and tenderness in prerigor lacticacid marinated beef

A meat tenderising procedure involving injection of a lactic acid solution into prerigor muscle was investigated using beef M pectoralis profundus. Th e distribution of lysosomal enzymes in subcellular fractions, densities of myofibrillar protein bands after SDS-PAGE and shear force were measured in non-injected, 0.5 M and 1.0 M lactic-acid-injected samples during a 21 days ageing period. The activities of cathepsin B + L and beta-glucuronidase in the soluble fraction increased with level of lactic acid and with time pos t-mortem (P < 0.001). Lactic acid and storage decreased densities of SDS-PA GE bands migrating at the position of myosin heavy chain (MHC) and alpha-ac tinin and increased densities of a 150 kDa band (P < 0.01). SDS-PAGE of iso lated perimysium cleaved with CNBr showed proteolytic cleavage of collagen after prolonged storage. Lactic acid injection significantly reduced shear force (P < 0.001). The cathepsin B + L activity in the soluble fraction cor related to shear force (r = -0.8), the degradation of MHC and alpha-actinin (r = -0.88 and -0.90) and the generation of the 150 kDa fragment (r = 0.90 ) but not to the generation of a 31 kDa fragment (r = 0.05). A major part o f the tenderness improvement after lactic acid injection was complete at 24 h post-mortem, and was therefore due to a rapid process, eg pa-induced swe lling of the muscle structure. The data on enzyme activities and protein de gradation, however, suggested that the action of lysosomal cathepsins also contributed to textural changes. (C) 1999 Society of Chemical Industry.