The influence of low temperature, type of muscle and electrical stimulation on the course of rigor mortis, ageing and tenderness of beef muscles.

The course of rigor mortis, ageing and tenderness have been evaluated for two beef muscles, M. semimembranosus (SM) and M. longissimus dorsi (LD), when entering rigor at constant temperatures in the cold-shortening region (1, 4, 7 and 10°C). The influence of electrical stimulation (ES) was also examined. Post-mortem changes were registered by shortening and isometric tension and by following the decline of pH, ATP and creatine phosphate. The effect of ageing on tenderness was recorded by measuring shear-force (2, 8 and 15 days post mortem) and the sensory properties were assessed 15 days post mortem. It was found that shortening increased with decreasing temperature, resulting in decreased tenderness. Tenderness for LD, but not for SM, was improved by ES at 1 and 4°C, whereas ES did not give rise to any decrease in the degree of shortening during rigor mortis development. This suggests that ES influences tenderization more than it prevents cold-shortening. The samples with a pre-rigor mortis temperature of 1°C could not be tenderized, when stored up to 15 days, whereas this was the case for the muscles entering rigor mortis at the other higher temperatures. The results show that under the conditions used in this study, the course of rigor mortis is more important for the ultimate tenderness than the course of ageing.