New Zealand Journal of Agricultural Research abstracts

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Tenderness of beef m. longissimus lumborum at normal and intermediate ultimate pH before and after a period of ageing

R. W. Purchas

Institute of Food, Nutrition and Human Health
Massey University
Palmerston North, New Zealand
email: r.purchas@massey.ac.nz

Abstract  Beef tenderness, in terms of Warner-Bratzler 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; 5.7-6.2) 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.

Keywords  beef; tenderness; ultimate pH; ageing

A03062; Received 20 October 2003; accepted 14 April 2004; Online publication date 17 August 2004
New Zealand Journal of Agricultural Research, 2004, Vol. 47: 299-305
0028-8233/04/4703-0299 © The Royal Society of New Zealand 2004

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