A study of relationships between muscle ultimate pH and meat quality characteristics for M. Longissimus samples from friesian steers, charolais class steers and friesian bulls : a thesis presented in partial fulfilment of the requirements for the degree of Master in Agricultural Science at Massey University, New Zealand
Comparisons of carcass and meat quality characteristics were made between forty Friesian bulls, twenty Friesian steers and nineteen Charolais x Angus cross steers which were grown on mixed pastures and slaughtered at a similar age of approximately 16 to 20 mo. Carcasses were evaluated and dressed under normal commercial conditions and samples of M. longissimus were taken from the right side of each carcass within 90 min of slaughter for meat quality assessments. A comparison of the growth rates of Friesian and Charolais cross steers during the finishing period revealed no significant differences in initial liveweights, final liveweights or overall average daily liveweight gains (p>0.05). Differences in growth patterns indicated that the Friesians grew slightly faster initially while the Charolais cross steers exhibited higher average daily gains at later stages. The Charolais cross steers had significantly greater dressing-out percentages (p<0.001), higher fat depths (p<0.001), shorter carcasses (p<0.001), larger rib-eye areas (P<0.00l) and heavier steaks (p<0.01) than the Friesian steers when compared at a similar carcass weight. The Charolais cross steers had a greater mean meat yield than the Friesian steers of a similar carcass weight, as assessed by the sum of the six major hind-quarter cuts. There were no breed effects on ultimate meat pH, sarcomere length, meat tenderness, meat colour, cooking loss or expressed juice value for meat samples from the two steer groups. Bulls produced leaner carcasses as evidenced by lower fat depth and intramuscular fat levels than steers. At a constant carcass weight, bulls had similar dressing-out percentages to Friesian steers, but the value was significantly lower than that of Charolais cross steers (p<0.001). The bulls possessed the longest carcasses and the largest rib-eye area after adjustments to the same carcass weight. Bull meat had significantly higher ultimate pH values (p<0.01) and a darker colour (p<0.001) than steer meat. Although there were no differences in sarcomere length, tenderness, cooking loss and expressed juice between meat from bulls and steers, bull meat appeared on the basis of shear- force deformation-curve parameters to contain more connective tissue. However, when pH effects were adjusted for by covariance analysis bull meat had a lower WHC and was slightly tougher. There was a significant curvilinear relationship between ultimate pH and meat tenderness with a minimum tenderness at a pH of approximately 6.1. The improved tenderness above this point was associated with improved WHC, while the decrease in meat tenderness from pH 5.4 to 6.1 appeared to be partly due to a significant decrease in sarcomere length. Meat colour darkened markedly with increases in pH values whereas WHC changed very little as pH values increased from 5.4 to 6.2, but was increased sharply with further increases in pH values above 6.2. A comparison was made between the conventional vee-shaped Wamer-Bratzler shear blade and a modified square-blade. The results were closely correlated, but the square-blade always provided clearer initial yield points on the shear deformation curves and higher peak shear force values. All shear parameters (PF, IY, PF-IY and WD) obtained from shear force deformation curves showed significant curvilinear relationships (p<0.001) with ultimate pH. It is concluded that differences in ultimate meat pH can lead to subsequent differences in several important meat quality characteristics. Nevertheless, the effects may sometimes be overshadowed by other factors such as cold-shortening conditions.