Most of the powdered meat tenderizers sold in grocery stores use papain as the tenderizing agent. Papain is derived from unripe papayas and works in such the same manner as the natural enzymes in meat that help soften connective tissue as the meat is aged. Both are termed proteolytic enzymes because they break down the proteins in muscle fibers and connective tissue into smaller molecules.
Commercial meat tenderizers have a number of shortcomings, though. They are virtually impotent at refrigerator temperatures, only semi-effective at room temperature, and inactivated once the temperature rises above about 150F. Because the papain seldom penetrates deep inside a cut of meat, the cooked food may end up tender (or even mushy) on the surface and tough in its interior. If you increase accessibility to the interior by deeply piercing the meat, as some papain-promoting recipes suggest, your efforts will be counterproductive. Your cooked meat will be tougher than it would be normally because you have created channels through which a lamentable share of juices escape during the cooking process. The store-bought products also tend to be laden with salts and other additives that can impart an unwanted flavor to your finished dish.
Today some slaughterhouses inject a papain solution into an animal shortly before it is to be killed. The papain enters directly into the animal's bloodstream, which carries the tenderizer to muscle tissue throughout the body. While the meat from this animal is cooking, the enzyme is activated (and finally inactivated when the temperature reaches approximately 150F). Although it is true that this tenderizing technique produces meat that has a more uniform texture than meat sprinkled with papain, the flesh still tends to become mushy when cooked because the enzyme destroys too much of the muscle fiber firmness.
** Asian Recipes **