The interaction between pH and temperature decline early postmortem on the calpain system and objective tenderness in electrically stimulated beef longissimus dorsi muscle.

The study investigated the effects of pH and temperature decline early postmortem (pm) on calpains and calpastatin activities and objective tenderness in M. longissimus thoracis et lumborum. A total of 40 sides were used to generate a range of pH and temperature declines, by different stimulation treatments (i.e. low voltage stimulation applied for either 10 or 40 s 3 min pm), and chilling treatments (fast or slow). Both rapid glycolysis, or a slow chilling regime significantly reduced μ-calpain level at 4 h pm (P< 0.001 and P< 0.05, respectively). There were significant interactions between pH and temperature at 1.5 h pm on μ-calpain and calpastatin activities at 24 h pm (P< 0.05). Rapid glycolysis resulted in lower shear force and compression measurements at day 1, although because of low ageing rates, an intermediate pH decline (i.e. pH 5.9-6.2 at 1.5 h pm) resulted in the most tender meat after 14 days ageing. Higher shear forces in the slow glycolysing sides appeared to be associated with the later activation of tenderising process, as well as physical shortening. The optimum pH decline early pm varied with days ageing, with an intermediate pH decline resulting in the lower shear forces for meat aged for 14 days.