Leucine and Valine Improve Pork Tenderness by Driving Myofiber Transition, Optimizing Lipid Profiles and Enhancing Antioxidant Defense

Pork tenderness is a critical quality trait. Pork with divergent shear force (n = 10, 20 pigs in total) revealed a positive association between tenderness and branched-chain amino acid (BCAA) concentrations. Therefore, large white pigs (initial body weight 100.88 kg) were fed a control diet or diets supplemented with 1% leucine (Leu) or valine (Val) (n = 6, 18 pigs in total). Compared with the control, Leu or Val significantly reduced shear force, intramuscular fat, myofiber diameter, and cross-sectional area (p < 0.05). These interventions were associated with a potential shift in myofiber type, indicated by upregulated MyHC I and IIa and downregulated MyHC IIb and IIx (p < 0.05). The supplemented groups showed lower SFA content and an n-6/n-3 ratio, alongside enriched MUFA and n-3 PUFA content (p < 0.05). Antioxidant capacity significantly improved across muscle, liver, and serum, evidenced by elevated T-AOC, T-SOD, GSH-Px, and CAT and reduced MDA levels (p < 0.05). Lipid metabolism and antioxidant genes were also significantly upregulated (p < 0.05). Overall, Leu and Val may improve pork tenderness and nutritional value, which appear to be associated with the modulation of myofiber type, lipid metabolism, and antioxidative status, offering a potential nutritional strategy for producing high-quality pork.