Muscle fiber type-specific proteome distribution and protease activity in relation to proteolysis trends in beef striploin (M. longissimus lumborum) and tenderloin (M. psoas major)

The muscle fiber type and proteome distributions, protease activity, and protein degradation in bovine M. longissimus lumborum (beef striploin; LL) and M. psoas major (beef tenderloin; PM) were assessed to study muscle type-specific proteolysis. Bovine LL and PM muscle pieces (3 cm thickness) were stored in a refrigerator for 14 days and protein degradation and protease activity were evaluated at 1, 7, and 14 days of storage. Bovine LL included more fast-twitch glycolytic (type IIX) fibers than PM, whereas PM had a higher composition of slow -twitch oxidative (type I) fibers than LL (P < 0.05). Proteome distribution between these two muscles showed muscle fiber type-specificities: LL showed high intensities of proteins responsible for glycolytic metabolism, while PM showed large distribution of mitochondrial proteins. The activity of proteases, mainly calpain, showed different tendencies between the two muscles during 14 days of cold storage, which resulted in different timing of excessive myofibrillar protein breakdown (myosin heavy chains 1 and 2) between the two muscles. These results provided a detailed understanding of the differences in proteolysis by muscle type resulting in proteolysis -induced changes in meat quality during storage.