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Extracellular modifications to muscle collagen: implications for meat quality.

The extracellular matrix (EMC) of muscle is composed mostly of the protein collagen with lesser quantities of other constituents such as proteoglycans also present. The focus of this brief review is the extracellular modification of collagen, critical to forming a stable matrix, called crosslinking. Enzyme-mediated covalent collagen crosslinks are largely lysine-derived. Their formation is absolutely essential for stabilization of the EMC and a functional muscle. In cooked meat, the presence of crosslinks contribute to the shrinkage and tension development of collagen as it denatures with a subsequent increase in the toughness of meat. Both crosslink and collagen concentrations vary with differing muscle type, producing a wide range of textural differences among muscles. Furthermore, within a given muscle type, a wide range of conditions, often dependent on management choices, influence crosslinking patterns. Although information regarding the chemical structure, specific location, and quantity of collagen crosslinks is available, mechanisms that control and regulate their formation remain elusive. Recent studies, however, suggest a potential role for the proteoglycan decorin in regulating collagen fibrillogenesis, ordering the spatial arrangement of collagen molecules and, thus, influencing crosslinking patterns.