. . . And Diminish Toughness

Uncontrolled enzyme activity also tenderizes meat. Enzymes called calpains mainly weaken the supporting proteins that hold the contracting filaments in place. Others called cathepsins break apart a variety of proteins, including the contracting filaments and the supporting molecules. The cathepsins also weaken the collagen in connective tissue, by breaking some of the strong cross-links between mature collagen fibers. This has two important effects: it causes more collagen to dissolve into gelatin during cooking, thus making the meat more tender and succulent; and it reduces the squeezing pressure that the connective tissue exerts during heating, which means that the meat loses less moisture during cooking.