DETERMINANTS OF TENDERIZATION IN BEEF LONGISSIMUS-DORSI AND TRICEPS BRACHII MUSCLES

Tenderisation of bovine Mm. longissimus dorsi and triceps brachii and factors impacting tenderisation were studied. Mm. longissimus dorsi and triceps brachii of 12 Friesian-Holstein cows (age 3-11 years; 212-349 kg carcass weight) were sampled at various times post mortem (p.m.) for determination of pH, temperature, fibre type and morphology, connective tissue distribution, SDS-PAGE of myofibrillar proteins, Warner-Bratzler shear force, sarcomere length and osmolality. The stretched position of the M. triceps brachii (sarcomere length 2.35 +/- 0.24 mu m) resulted in a relatively low shear force at 1 day p.m. (6.2 +/- 0.9 kg/cm(2)) with further storage having little additional effect. M. longissimus dorsi entered rigor in a more contracted state (sarcomere length 1.65 +/- 0.11 mu m), resulting in a relatively high shear force at 1 day p.m. (10.3 +/- 2.3). Stepwise linear regression was used to calculate the best 1- to 3-variable equations for shear force of M. longissimus dorsi at 1, 7 and 14 days p.m. and the decrease in shear force between 1 and 14 days p.m. Shear force at 1 day p.m. appeared to be determined mainly by the speed of pH- and temperature-decline. Proteolysis of myofibrillar proteins and animal age appeared to be the main determinants for shear force at 7 and 14 days p.m. The average surface area of type I fibers could explain part of the variation in the decrease in shear force between 1 and 14 days p.m.