Tenderness of beefm. longissimus lumborumat normal and intermediate ultimate pH before and after a period of ageing

Abstract

Beef tenderness, in terms of WarnerBratzler shear force values, was measured following ageing periods of 1 or 20 days for samples of m. longissimus lumborum from pairs of steers or heifers (n = 38) with the two members of each pair being from the same mob. One sample of each pair had an intermediate ultimate pH (pHult;.2) and the other a normal pHult (<5.6). Samples of the intermediate pHult group had the expected lower cooking losses and darker colour (lower L*, a*, and b* values). In contrast to previous studies where intermediate pHult has been associated with tougher beef, however, the two groups did not differ in shear-force values, sarcomere length, or in myofibrillar fragility as measured by a filtration method or by image analysis. Samples for this study were removed from carcasses after rigor mortis had set in, which may have accounted for the sarcomere lengths being longer than in previous studies. It is suggested that the failure to detect a pHult effect on shear force values may have been because skeletal attachments prevented any pHult effect on sarcomere length. If this was the case, the problem of intermediate pHult toughness may be over-emphasised when muscle samples are removed from the carcass in the prerigor state. No evidence was found of a lower fragility of myofibrils at intermediate pH values.