Histological Studies of Post‐Mortem Changes in Sarcomere Length as Related to Bovine Muscle Tenderness

SUMMARY The effect of post-mortem muscle contraction on ultimate tenderness was studied in muscles of 12 beef animals of similar weight and grade. State of contraction was determined by measurement of sarcomere lengths. Longissimus dorsi and semimembranosus muscles were observed. Histological samples removed at various intervals post-mortem were treated with ethylenediaminetetraacetate (EDTA) to prevent further contraction. A phase-contrast microscope was used to observe muscle fibers, and sareomeres were measured with a filar micrometer. Muscle contraction patterns of each animal were plotted through a 7-day aging period. State of contraction after 7 days appeared to have a greater influence on subsequent (7 days) tenderness than did state of contraction at time of maximum rigor mortis. Although contraction did not seem to be the factor most responsible for final tenderness, it did appear to have a significant influence. Considerable lengthening of sarcomeres normally occurred during the aging period. Semimembranosus muscles routinely contracted less than longissimus dorsi muscles during rigor mortis, and were more relaxed after 7 days of aging. Semimembranosus muscles were consistently less tender than longissimus dorsi muscles at slaughter, but the reverse was usually true after 7 days.