THE CONTRIBUTION OF pH TOWARDS ENDOPEPTIDASE ACTIVITY AND SMALL HEAT SHOCK PROTEIN DISTRIBUTION IN BEEF AND ITS ROLE WITH ACHIEVED TENDERNESS

摘要

IntroductionThe contribution of cathepsins and calpains to the tenderising process has been investigated in much detail over the past two decades (Koohmaraie and Geesink, 2006; Sentandreu et al., 2002). However questions remain as to why the rate of meat tenderisation is so variable in red meat. One reason for this variability is ultimate pH (pHu). High pHu (pHu> 6.3) throughout the ageing process will provide a good environment for calpain activity whereas normal meat (pHu < 5.7) provides an optimum environment for cathepsin activity. Intermediate (Int) and high pH (pHu > 5.7) beef is frequently observed in New Zealand due to a pasture-fed production system (low calorie diet) combined with pre-slaughter stress resulting in high and variable meat tenderness (Lowe et al., 2004). The role of small heat shock proteins (sHSP) in the conversion of muscle to meat has also proved an enigma to meat science (Aubry et al., 2006). Several proteome studies have identified sHSP like alpha β-crystallin (aβC) and HSP27 are upregulated in postmortem meat (Bouley et al., 2004; Hwang et al., 2005; Sayd et al., 2006). Others have speculated that HSP must have a role in controlling the processes of meat tenderness and quality (Herrera-Mendez et al., 2006; Ouali et al., 2006). This study aimed to characterise the behaviour of these molecular chaperones in postmortem beef muscle and determine if they contribute to beef tenderness.