EFFECTS OF POSTMORTEM AGING TIME, ANIMAL AGE, AND SEX ON DEGRADATION OF TITIN AND NEBULIN IN BOVINE LONGISSIMUS MUSCLE

This study was conducted to determine degradation of the giant myofibr illar proteins titin and nebulin in postmortem aged beef, with known t enderness values, from animals differing in sex (steers vs bulls) and age (cows vs steers and bulls). Ten bulls and 10 steers (both groups w ere approximately 14 mo old) and 10 cows (44 to 108 mo old) were slaug htered. Longissimus muscle samples were removed for determination of W arner-Bratzler shear force, sensory panel tenderness evaluation, and S DS-PAGE analysis at 3, 7, 14, and 28 d postmortem. The SDS-PAGE analys is of titin and nebulin revealed that titin often migrated as three cl osely-spaced bands (T-1, T-1-2, T-2, in increasing order of migration) in 3-d postmortem samples. With increasing time postmortem, intact ti tin (T-1) decreased and degraded titin (T-2) increased in all samples. Within a class (i.e., steers, bulls, or cows) the rate of conversion of T-1 to T-2 was slower in the less-tender samples. The T-1 to T-2 co nversion postmortem was slower in the intact males (bulls) than in the castrated males (steers). The T-1 to T-2 conversion postmortem also w as slower in the older animals (cows) in comparison to the younger ste ers, but not in comparison to the younger bulls. Nebulin was degraded by 3 d postmortem in tender samples from steers, but some nebulin rema ined in the less-tender 3-d samples from steers and in all of the 3-d samples from bulls and older animals (cows). Intact nebulin was absent in all 7-d samples, regardless of the class of animal. Our results su ggest that titin and nebulin are degraded at faster rates in more tend er beef samples within each of the three classes of animals examined. The rate of degradation seems to differ when sex and age classificatio ns are compared.