Effect of rigor temperature on muscle shortening and tenderisation of restrained and unrestrained beef m. longissimus thoracicus et lumborum.

Pairs of muscularis longissimus thoracicus et lumborum (LTL) from young bulls were removed within 1h of slaughter. Small portions of the muscles were placed in a rigormeter to continously follow the isometric tension and isotonic shortening developed, at constant temperatures of 15, 20, 25, 30 and 35°C, as the muscle went into rigor. The bulk LTL was placed in water baths at the same temperature. One of the bulk pairs was tightly restrained by wrapping, to reduce muscle shortening, the other was unrestrained free to shorten. For the bulk samples, shear values were measured using a Warner-Bratzler instrument (1, 7 and 14 days post mortem), and sensory attributes were measured using a sensory panel (7 and 14 days post mortem). Minimum tension and shortening occurred at 15°C. The activation energy for the muscle shortening process was larger than for the isometric tension process. This indicates that the isometric tension data, collected during rigor, does not solely reflect muscle shortening. Thus, a counteracting process that decreases the tension response, most likely ageing is simultaneously detected. Meat that went into rigor at 15°C had least shortening and was always more tender than meat going into rigor at higher temperatures. For meat entering rigor at temperatures higher than 15°C, restraining of the muscle by wrapping, significantly (p<0.05) decreased the amount of muscle shortening and resulted in an improved meat tenderness (p<0.001). It was also observed that at rigor temperatures higher than 15°C the meat tenderness is affected negatively by a reduced ageing capacity. It therefore appears that muscle shortening and enzyme activity both affect tenderness and that both are highly affected by rigor temperature and have the greatest beneficial effect at a rigor temperature of 15°C.