MEAT TOUGHENING DOES NOT OCCUR WHEN RIGOR SHORTENING IS PREVENTED

The objective of this experiment was to test the hypothesis that meat toughening during the first 24 h postmortem results from sarcomere sho rtening during rigor mortis development. Eleven market-weight lambs we re used to measure changes in shear force of clamped longissimus durin g rigor development. Within 15 min of exsanguination, while attached a t both ends, each longissimus was separated from the vertebrae body an d clamped between three sets of metal plates to prevent muscle shorten ing (six clamped sections per lamb). Five of the clamped sections were placed at -1.1 degrees C for 0, 3, 6, 12, or 24 h. After storage at t heir respective times at -1.1 degrees C, the samples were placed at -3 0 degrees C for 90 min and then at -5 degrees C for 8 d. The sixth sec tion (168-h section) was stored at -1.1 degrees C for the first 24 h, at 4 degrees C for 144 h, and then treated the same as other sampling times. Sections were sampled for pH, sarcomere length, shear force, an d Western blot analyses before and after storage at -5 degrees C. Shea r force values were the same (P >.05) from 0 to 24 h (4.5 kg at 0 h to 4.9 kg at 24 h) then declined(P <.05) to 3.3 kg at 168 h postmortem. As evident by lack of statistical difference in the sarcomere lengths, we were successful in holding the muscle length constant. Western blo t analyses of nebulin, vinculin, and troponin-T indicated that minimum degradation occurred through 12 h, was slightly increased by 24 h, an d was relatively extensive by 168 h postmortem. Although limited prote olysis occurred during storage at -5 degrees C for 8 d, this by itself had no effect on shear force. Results indicate that shear force value s do not increase during rigor development when muscle is prevented fr om shortening; thus, the toughening that occurs during the first 24 h of slaughter is most likely due to sarcomere shortening.