PRERIGOR AND POSTRIGOR CHANGES IN TENDERNESS OF OVINE LONGISSIMUS MUSCLE

A novel approach was used to measure the tenderness of prerigor ovine longissimus thoracis et lumborum by avoiding the confounding effects o f heat-induced shortening resulting from cooking prerigor meat. The ob jective was to determine the tenderness of the muscle at the time of s laughter and to monitor changes in tenderness during rigor development and postmortem aging. Nine Romanov and 12 Finnsheep rams were slaught ered at 49.3 kg live weight. Samples of longissimus thoracis et lumbor um were removed at 0, 3, 6, 9, 12, 24, 72, or 336 h after exsanguinati on. Five of the eight sample times were represented in each carcass an d all carcasses were sampled at 0, 12, and 24 h. Prerigor muscle sampl es (0, 3, 6, 9, and 12 h) were clamped between two metal plates before excision to prevent shortening. The samples were frozen at -30 degree s C then stored at -5 degrees C for 10 d to allow glycolysis to procee d to completion, and thus ultimate pH and complete rigor mortis were a ttained. The longissimus thoracis et lumborum was then cut into chops and cooked and shear force was determined. Sarcomere length decreased through 24 h postmortem, then increased slightly through 336 h postmor tem. Warner-Bratzler shear force values were 5.1 kg at 0 and 3 h, incr eased to 8.3 kg from 3 to 9 h, and then declined to 3.1 kg from 24 to 336 h postmortem. These data imply that longissimus thoracis et lumbor um at slaughter is intermediate in tenderness, rigor shortening toughe ns the meat, and proteolysis tenderizes the meat, resulting in more te nder meat after 14 d of aging than at slaughter.