FURTHER INVESTIGATIONS INTO THE RELATIONSHIP BETWEEN ULTIMATE PH AND TENDERNESS FOR BEEF SAMPLES FROM BULLS AND STEERS

Samples of longissimus dorsi muscle from 150 cattle comprising Friesian hulls and steers and Charolais X Angus cross steers, were used to investigate the nature of the relationship between ultimate pH and beef tenderness under conditions where cold-shortening was avoided. A modified Warner-Bratzler (WB) shear machine with a square- rather than a vee-blade enabled several aspects of tenderness to be evaluated, including peak force (PF), initial yield force (IY), PF-IY, and an index of total work done. The two steer groups differed little in meat quality characteristics, but, in terms of six major hindquarter cuts, the Charolais cross group yielded 14.3% more meat per unit live weight, due to a combination of a superior dressing-out percent and a higher cutability. Relative to Friesian steers, the bulls produced beef with a higher ultimate pH (P < 0.001), and after adjustment to a common pH, the bull beef was tougher for all WB parameters except PF-IY Cooking loss was higher for beef from bulls after adjustment for pH. Although reduced by pH adjustment, beef from bulls remained significantly darker than that from steers (P < 0.05) based on reflectance measurements. Maximum toughness in terms of PF, IY, and work index was at an ultimate pH of 6.0-6.1, but the peak was much less clear for PF-IY The decline in tenderness with an increase in ultimate pH to 6.2 was associated with a decrease in sarcomere length. This result supports a previous suggestion that shortening explains, at least in part, the lower average tenderness at intermediate pH values.