Trends in skeletal muscle biology and the understanding of toughness in beef

This review focuses on recent developments in the field of muscle biology t hat reflect on the problem of toughness in beef. Meat science has shown tha t post-mortem processing can make a large contribution to beef tenderness. However live-animal factors such as growth path and genotype also influence the toughness of beef either directly or indirectly through interactions w ith processing technologies. This review sets out to integrate recent devel opments in the field of meat science into a mechanistic overview of toughne ss, while still highlighting the biology of some important contributors. Th ese contributors are discussed at several levels of order between the molec ular and the whole animal. The myofibrillar component of muscle is identifi ed as the major contributor to initial toughness particularly through the e ffects of variation in sarcomere length. Muscle fibre-types whilst importan t to the growth and development of the animal are yet to be linked convinci ngly with toughness. Connective tissue is seen to play a dominant role in t he sensation of toughness in muscles where its content is high. In muscles that are generally used for table beef, the contribution of connective tiss ue is less significant. In either case its contribution to measurable tough ness cannot be easily separated from that of the myofibrillar component and the review discusses various levels of interaction between these 2 major c omponents of beef. The review covers aspects of muscle ultrastructure as fa r as they are pertinent to the problem of beef toughness. In particular it deals with current knowledge of post-mortem metabolism of muscle and the de gradation of costameric structures. Molecules are considered that are likel y to propagate tensional forces from sarcomeres across the sarcolemma to th e extracellular molecules of the endomysium. While much of the research aro und these molecules has not been performed by meat scientists, the insights developed are likely to be important to our understanding of beef toughnes s. Technological approaches to the objective measurement of toughness are d iscussed, as well as recent developments in the field. The review takes an integrative approach to features of the life of the bov ine that might impact on the toughness of beef derived from its carcass. Fe atures of the animal's pre-slaughter experience, including stress and physi cal activity, have been shown to influence markedly the toughness of beef t hrough mechanisms that are described at the tissue level. Features of the g rowth path that the animal followed during its development have also recent ly been shown to significantly reduce the toughness of beef and properties of the connective tissue component have been implicated. Areas of strategic research are identified that, in the author's opinion, will facilitate com mercial-scale improvements in the tenderness of beef.