Commercially prepared meat tenderizer typically contains a combination of salt and natural enzymes. This powdered substance is sprinkled on meat in order to break down the tough connective tissues and fibres. As these packaged meat tenderizers can also contain many unwanted preservatives, similar results can be produced using specific fruit juices or a meat mallet.
The most common enzyme found in meat tenderizers is papain, which is derived from papayas. Another common enzyme included in these mixtures is bromelain, which is sourced from pineapples. These enzymes tenderise the meat through a process knowing as "forking," where the enzymes penetrate and split the meat fibres and the meat can be cooked almost immediately.
Salt is, in itself, an excellent meat tenderizer. It cannot be sprinkled on meat just prior to cooking, as the enzymes can, as it initially draws out moisture and will result in dry, tough meat. If the meat is sprinkled with a thin layer of salt and left to sit for several hours (or even days), the salt will slowly break down the tough meat fibres and the moisture will be reabsorbed, resulting in tender, juicy meat.
Instead of using a prepackaged powder that contains preservatives along with enzymes extracted from fruits, try using the juice from the fruit (pineapple) or even slices of the fruit itself (papaya) as a marinade, along with salt and spices. Alternatively, try using a meat mallet. It is a kitchen tool similar to a hammer, with spikes on the end, designed to physically break apart the meat fibres to tenderise it.