The prime component of connective tissue is the protein collagen. That name derives from the Greek words kolla (glue) and gen (a word appendix signifying "production of"). In everyday English, collagen produces glue or, in this case, gelatin. In a hot, moist environment (boiling water, for instance), collagen can be partially transformed, over a period of time, into gelatin. When this metamorphosis occurs, connective tissue softens and dissolves, making the meat more tender. The second major constituent of connective tissue is elastin.
Unlike the predominant whitish collagen, the yellow-tinged elastin protein does not soften - or at least, not perceptibly - in the dual presence of heat and water.
** Asian Recipes