Intramuscular variations of proteome and muscle fiber type distribution in semimembranosus and semitendinosus muscles associated with pork quality.

Proteome analysis was performed to understand intramuscular variations in muscle fiber distribution in semimembranosus (SM) and semitendinosus (ST) muscles associated with pork quality. Fifteen SM and ST muscles were separated into dark and light portions. The relative area of oxidative fiber was higher (P < .0001) in dark portion than that in light portion, while glycolytic fiber types were distributed primarily (P < .01) in light portions regardless of muscle types. Myosin-1, myosin-4, troponin complex (fast), myosin light chains, and metabolic enzymes responsible for fast-twitch glycolytic types were overexpressed in light portions (P < .05). However, myosin-2, myosin-7, myoglobin, and mitochondrial oxidative metabolic enzymes were closely related to slow-twitch oxidative fibers. These resulted in high pH, redness, and tenderness but low lightness and drip loss of pork quality. In conclusion, differentially expressed muscle proteins are associated with fiber type (oxidative vs. glycolytic) distribution, resulting in intramuscular variations of pork quality.