A while ago I posted about using kiwi juice to tenderize meat. I also noted that pineapple also has a protease enzyme, bromelain, that will tenderize meat. It does this by breaking down the proteins in the meat and therefore breaking the cellular structure.
One thing I did not mention is that the bromelain also does its wonders on your tongue if you eat the pinapple, especially more green. I cut up a beautiful pineapple the other day and was happily munching away when my tongue started to tingle and felt burnt! Turns out the bromelain was also breaking down the proteins on my tongue...fortunately, the surface of our tongues is replenished almost daily so the effects are not long lasting but in future I think I will eat my pineapple with something a but more creamy such as yogurt to help coat my tongue from the effects. I have read that truly ripe from the tree pineapples do not have the same effect as the amount of bromelain is reduced as the pineapple ripens.
One downside of the protein attack is that you cannot put raw pineapple in gelatin since it will break down the gelatin (which is a protein). The canned pineapple would work since it is usually cooked and will have inactivated the bromelain (need to try this experiment). To make pineapple jelly, you would need to use pectin not gelatin.
Pineapple strawberry jelly
Dickson, S R and Bickerstaff, G F Pineapple bromelain and protein hydrolysis. Journal of Biological Education 25, 164–166 (1991)