EFFECTS OF DOUBLE-MUSCLING ON CARCASS QUALITY, BEEF TENDERNESS AND MYOFIBRILLAR PROTEIN-DEGRADATION IN BELGIAN BLUE WHITE BULLS

Carcass properties and meat quality characteristics of 32 Belgian Blue White double-muscled bulls (DM) were compared with those of 59 bulls of the same breed with normal conformation (N). DM showed superior car cass quality as revealed in increased dressing percentage, meat produc tion yield, conformation grade, muscle/fat and muscle/bone ratios (all P < 0.001). Longissimus dorsi (LD) shear force values, drip and cooki ng losses at 8 days post mortem (pm) were significantly higher (P < 0. 001) for DM, whereas sarcomere lengths were not different. Calpain 1 a nd calpastatin levels at 1 h and 24 h pm were tremendously decreased i n DM as were also cathepsin B and L levels at 1 and 8 days pm (P < 0.0 01). As evident from semi-quantitative SDS-PAGE, these differences wer e accompanied by higher titin and lower 30 kDa levels (P < 0.001) in D M. Troponin-t levels were not different, but very low. Intramuscular c ollagen content was significantly lower in DM (P < 0.001). This sugges ts that lower background toughness in DM was compensated for by reduce d postmortem proteolytic tenderization. Discrepancy with literature re ports regarding tenderness of DM might be related to the extreme muscu larity of the Belgian Blue White breed, compared to other DM breeds. T he results also suggest that reduced protein turnover might be involve d in the muscle hypertrophy phenomenon within this breed, because of l ikely reduced levels of calpains and cathepsins in living DM animals.