Effect of postmortem pH on the physical, biochemical, and sensory characteristics of bovine longissimus thoracis et lumborum muscle.

Abstract

From a large feeding trial study consisting of 299 bulls and steers, 15 carcasses exhibited stress-related syndromes manifested by atypical color and pH which were then selected for subsequent analysis. Samples of longissimus thoracis et lumborum muscle with postmortem pH in the range of 5.5-6.9 were subjected to a 14-day aging period at 2°C. Sensory panel tenderness, connective tissue, juiciness, and flavor intensity of high pH (6.4-6.9) meat were significantly different (p < .05) from samples of intermediate pH(6.0-6.1) as well as normal pH (5.5). Muscles at pH 6.0-6.1 were the toughest samples. This was confirmed by Warner-Bratzler shear force (WBSF), residual force, and myofibril fragmentation index. Palatability attributes of normal pH (5.5) samples were significantly different (p < .05) from dark-cutting beef in terms of tenderness and flavor and at the high pH extreme. The increase in WBSF at pH 6.0-6.1, lack of extensive degradation of muscle proteins, and the decreased sarcomere length resulted in tougher meat than low or high pH muscles. Sodium dodecyl-sulfate polyacrylamide gel electrophoresis of meat at the high pH extreme (6.7-6.9) revealed that the breakdown of troponin-T to 30 kD was complete while at intermediate pH (6.0-6.1) was incomplete. In addition, the appearance of a 'doublet' on high-molecular-weight resolution gels may also account for the greater tenderness experienced by sensory panelists.