Intramuscular connective tissue and its role in meat quality.

The amount, spatial distribution and composition of the connective tissue within muscle vary with muscle position in the carcase and with animal age. This has long been recognised to influence the tenderness of cooked meat. This paper builds upon some historical perspectives with a review of some recent clarifications of the biological function of intramuscular connective tissue (IMCT) and of its contribution to meat texture, which is clearly multifactorial. The perimysial component of IMCT varies most in amount between muscles and is also the IMCT structure most involved in defining the mechanical integrity of cooked meat. The distribution of perimysium defines muscle fascicle size (muscle "grain" size), which is also still regarded as an indicator of tenderness. Postmortem conditioning of meat has consistently been shown to reduce the strength of intramuscular connective tissue in the raw state, but with equal consistency, this has been shown not to affect the toughness of cooked meat. Cooking increases IMCT strength in the range 20-50 °C and decreases its contribution at higher temperatures and longer cooking times. Crosslinking of collagen in older animals is generally considered to result in tougher meat, although definitive links between mature crosslink content and cooked meat toughness have been difficult to prove. In the last quarter-century, IMCT has been increasingly viewed as a "background" contributor to meat texture, which is difficult to change. However, the large variation in perimysial content of muscles in one animal represents an incredible range of expression. This appears to be firmly fixed to the functional properties of different muscles. In particular, it is hypothesised that definition of muscle fascicle size and shape by the bounding perimysium is related to the need for sub-sections of the whole muscle to slip past each other in the normal contractile function of the tissue. Despite this, the amounts and composition of IMCT can be manipulated by animal nutrition and exercise, and factors affecting the turnover of IMCT may especially be a future target for manipulation of meat texture.