Postmortem Changes in Muscle Extracellular Matrix Proteins

It has long been recognized that meat tenderness is related to both the components inside the muscle fibers (predominantly the myofibril) and the connective tissues surrounding the fibers (predominantly collagen). It has also been shown that the tenderness of meat increases with time of storage postmortem. Most work attempting to determine the mechanism of this postmortem tenderization has concentrated on the changes that occur in the myofibril that pack the muscle cell fiber. Although this part of muscle clearly has a major role in meat tenderness, the components of the extracellular matrix may play a previously unrecognized role as well. In this review I plan to summarize briefly the properties of the different components of the muscle extracellular matrix, their macroscopic, microscopic, and ultra structural locations; potential proteases and their inhibitors which might play a role in possible degradation processes, and current information about postmortem changes in these molecules and structures. The literature on the extracellular matrix is vast; most of it relates to matrix material in nonmuscle tissues. I will not attempt to cover all this material, but will try to provide references to key reviews. The reader is referred to the excellent book by Bailey and Light (1989) and the reviews by Light (1987), Bailey (1989), and McCormick (1989) for more extensive background material which includes a meat perspective.