Papaya, especially the leaves and unripe fruit, has been used for centuries to tenderize meats. It contains a protein-digesting enzyme - papain - that breaks down muscle and connective proteins in meat. If that doesn't make your mouth water, yes, pineapples, figs, and certain fungi also produce such flesh-eating enzymes.

So all of them can be somewhat effective in tenderizing meat. But the complaint lodged against these (and all commercial meat tenderizers) is that they only do their work on the outside of the meat, where they may do such a good job that it's slimy, leaving the inside as tough as ever.

Also, because they're so busy consuming the meat you just paid for, they reduce the meat's ability to hold moisture, so it dries out faster.

So mushy outside, tough inside, and dry over all - not exactly the result you are looking for, is it? As Harold McGee, author of On Food & Cooking, says, "In general, there are at present no really satisfactory ways of tenderizing meat chemically."

Sorry for the bad news.