The Caspase System: a Potential Role in Muscle Proteolysis and Meat Quality?

Meat quality is the generic term used to describe the properties and perceptions of meat which are generally considered to be colour, flavour, texture, tenderness and juiciness (Maltin et al., 2003), with tenderness considered as one of the most important traits (Miller et al., 2001). Meat tenderisation occurs primarily from the weakening of the myofibrillar structure in muscle fibres via the actions of proteolytic enzymes (Sentandreu et al., 2001). There are several proteolytic systems that could have a potential role in postmortem proteolysis and meat tenderisation, including the cathepsins, the multicatalytic protease (or proteasome) and calpains. The contribution of cathepsins to meat tenderisation is no longer considered to be a strong candidate as they are contained within the lysosomes and appear not to have access to the myofibrillar structure at critical stages of the post-mortem proteolysis period (Hopkins and Taylor, 2004). There is also little association between cathepsin activity and the variation in tenderness in meat (Whipple et al., 1990). Although the proteasome is found at relatively high levels in skeletal muscle and is well established as having a role in muscle function, it is thought that it does not contribute to meat tenderisation as it is unable to cleave myofibrillar proteins to generate a similar pattern to that seen in situ during the conditioning period (Taylor et al., 1995). Calpains are probably the most extensively studied protease family with regard to meat science and it is widely accepted that calpain-mediated proteolysis does play a major role in the process of meat tenderisation (Sentandreu et al., 2001). Although there is considerable evidence to support the role of the calpain system in the postmortem conditioning period and the development of meat tenderness, it has been suggested that the calpain system cannot be solely responsible for all the biochemical and structural changes that take place, and therefore other proteolytic systems must be involved (Jiang, 1998). Recently, several reviewers have reexamined the role of proteolytic systems in postmortem proteolysis and meat tenderisation and have proposed that the caspase family of proteases could be activated postmortem and influence the rate of tenderisation (Sentandreu et al., 2001; Herrera-Mendez et al., 2006; Ouali et al., 2006).