Proteome basis for the biological variations in color and tenderness of longissimus thoracis muscle from beef cattle differing in growth rate and feeding regime

The proteome basis for the biological variations in color and tenderness of longissimus thoracis muscle from 'A Angus (Bos taurus taurus) x 'A Nellore (Bos taurus indicus) crossbred steers was evaluated in a completely randomized experimental design consisting of four treatments (n = 9 per treatment): 1) feedlot finished, high growth rate (FH); 2) feedlot finished, low growth rate (FL); 3) pasture finished, high growth rate (PH); and 4) pasture finished, low growth rate (PL). The following comparisons were made to evaluate the effects of finishing systems and growth rates on muscle proteome: 1) FH x PL; 2) FL x PH; 3) FH x FL; and 4) PH x PL. Sixteen protein spots were differentially abundant among these comparisons (P < 0.05), which were distinguished in two major clusters, energy metabolism-and muscle structure-related proteins that impacted glycolysis, carbon metabolism, amino acid biosynthesis and muscle contraction pathways (FDR < 0.05). For FH x PL comparison, triosephosphate isomerase (TPI), phosphoglucomutase-1 (PGM1) and phosphoglycerate kinase 1 (PGK1) were overabundant in FH beef whereas troponin T (TNNT3), alpha-actin (ACTA1) and myosin regulatory light chain 2 (MYLPF) were overabundant in PL beef. For the FL x PH comparison, PGM1, phosphoglycerate mutase 2 (PGAM2) and annexin 2 (ANXA2) were overabundant in PH beef. For the FH x FL comparison, AMP deaminase (AMPD1) and serum albumin (ALB) were overabundant in FH beef whereas glycogen phosphorylase (PYGM) was overabundant in FL beef. For the PH x PL comparison, myoglobin (MB) was overabundant in PH beef whereas PYGM and MYLPF were overabundant in PL beef. In non-aged beef, L* was positively correlated with PGM1 (r = 0.54) while tenderness was negatively correlated with PGAM2 (r =-0.74) and ANXA2 (r =-0.60). In 7-d aged beef, color attributes (L*, a* and b*) were positively correlated with PGM1 (r = 0.67, 0.64 and 0.64, respectively) while tenderness was negatively correlated with TNNT3 (r =-0.57), PGK1 (r =-0.52) and MYLPF (r =-0.66). Therefore, finishing systems and growth rate affected the muscle proteome profile, which was related to beef color and tenderness. Additionally, these results suggest potential biomarkers for beef color (PGM1 and PGAM2) and tenderness (ANXA2, MYLPF, PGK1 and TNNT3).