Centuries Ago, native people in the tropical climate of Central America accomplished tenderization by boiling meat with unripe Papaya fruit or by wrapping meat with the leaves of the Papaya plant. What they didn't know was that they were witnesses to a chemical reaction of one of the most efficient tenderizers known today, Papain.
Papain is a protein-cleaving enzyme derived from papaya and certain other plants. Enzymes are complex molecules produced in living organisms to catalyze (speed up) chemical reactions within the cell. Papain cuts the protein chains in the fibrils and also in the connective tissue, disrupting the structural integrity of the muscle fiber, and tenderizing the meat. Papain also has a mild, soothing effect on the stomach and aids in protein digestion.
Courtesy of tenderizemeat