1a.Objectives (from AD-416):
1. Develop a semi-automated protocol for measuring sarcomere length using image analysis of micrographs obtained from powdered muscle tissue.
2. Determine the relative contribution of sarcomere length and postmortem proteolysis to breed effects on beef tenderness.
3. Determine which myofibrillar protein provides the best index of overall postmortem proteolysis
1b.Approach (from AD-416):
Objective 1. The standard laser diffraction method of sarcomere length measurement will be compared to a protocol for obtaining high quality micrographs of powdered muscle tissue allowing images of sarcomeres to be captured for image analysis measurement of sarcomere length on 100 longissimus samples ranging widely in tenderness. Objective 2. Slice shear force will be determined on longissimus from 1000 carcasses of steers sired by bulls from each of the 16 most prevalent beef breeds in the U.S. beef herd. Sarcomere length and degradation of the cytoskeletal protein desmin using western blotting will be measured on each sample. Objective 3. Carcasses (n = 30) will be selected to be variable in tenderness. Five muscles (longissimus lumborum, semimembranosus, biceps femoris, vastus lateralis, semitendinosus) will be obtained from each carcass and cut into five steaks which will be aged until 2, 5, 7, 14, and 28 d postmortem. Steaks will be cooked and slice shear force determined to assess tenderness and postmortem proteolysis will be determined by western blotting.
For objective 1, data were collected by two technicians in duplicate for both standard laser diffraction and for image analysis of powdered muscle methods of sarcomere length measurement. No differences were detected in accuracy, repeatability, or time required for sarcomere length measurement from the two methods. For objective 2, slice shear force, which is an objective assessment of tenderness, was determined for top loin steaks obtained from the carcasses of 800 beef steers. Steers were sired by bulls sampled from the most common U.S. beef breeds. Following slice shear force determination, two biochemical traits related to tenderness were assessed on the remnants of the cooked steak. It was determined that variation among sires for both postmortem proteolysis and sarcomere length contributed to variation among sires in tenderness. Thus, there may be merit to identifying sources of genetic variation in both of these components of tenderness. For objective 3, data collection is ongoing.