Small heat shock proteins and toughness in intermediate pHu beef

Bull M. longissimus dorsi (n = 94) categorised into high (n = 28), intermediate (n = 14) and low (n = 52) ultimate pH (pH(u)) were aged at -1.5 degrees C for 28 days. Shear force was higher and more variable (p < 0.05) in intermediate pH(u) samples during ageing. Titin, filamin and desmin degradation was also less extensive in intermediate pH(u) samples compared to the other two pH categories. The extent of the decline of HSP20, HSP27 and alpha beta-crystallin concentrations during post mortem ageing was pH(u) related such that high pH(u) meat maintained the highest concentration of small heat shock proteins followed by intermediate and low pH(u) meat. mu-Calpain autolysis was slowest in intermediate pH(u) and cathepsin B activities remained consistently low during ageing in this group (p < 0.05). Meat toughness in the intermediate pH(u) group may be attributed to the combination of a larger pool of sHSP with a sub-optimal cathepsin B activity and intermediary mu-calpain activities. (c) 2013 Elsevier Ltd. All rights reserved.