Small Heat Shock Proteins and Tenderness in Intermediate pHu Beef

摘要

This study tested the hypothesis that toughness and inconsistent tenderness in intermediate ultimate pH (pH_u) beef is due to the protective function of small heat shock proteins (sHSP) combined with the low proteolytic activities in this pH_u group. M. longissimus dorsi from 94 bulls were categorised into high (pH > 6.2, n = 28), intermediate (pH 5.8 - 6.19, n = 14) and low (pH < 5.79, n = 52) pH_u and aged for up to 28 days post mortem at -1.5°C. Cathepsin B, μ-calpain, HSP20, HSP27 and αβ-crystallin levels were determined on a subset from each pH_u group at 0, 1, 2, 7, 14 and 28 days post mortem. Shear force was measured for all samples from 1 day post mortem. Intermediate pH_u samples were generally tougher and more variable in tenderness compared with high and low pH_u samples. sHSP levels decreased with pH_u and time post mortem. μ-Calpain activity - as indicated by autolysis - was highest and occurred earlier in high pH_u samples. The greater and less variable tenderness of the high and low pH_u samples could be due to the elevated activities of calpains and cathepsin B, respectively. The low level and high variability in tenderness of intermediate pH_u samples could be attributed to the combination of a larger pool of active sHSP with the sub-optimal cathepsin B and intermediary μ-calpain activities in this pH_u group.