This is a fun and easy experiment that demonstrated the properties of enzymes.
You need a fresh pineapple (canned with not work) with the skin removed, three bowls, and a box of Jello gelatin.
Crush the pineapple in a blender until you have a fairly smooth but pulpy mixture. Place one tablespoon of the pineapple into the first bowl labeled, "Fresh pineapple." Label a second bowl, "Heated pineapple" and set it aside.
Prepare the Jello as directed on the package. Pour it into the three bowls leaving a little room in the Heated Pineapple bowl (I needed a fourth bowl because mine were small.)
Cook the rest of the pineapple on the stove for 5 minutes, stirring constantly. It will boil, which is fine; just keep stirring it. When done add 1 tablespoon of the cooked pineapple to the bowl labeled, "Heated pineapple" and stir thoroughly.
Place the bowls in the refrigerator for 4 hours. What happened?
The bowl with the fresh pineapple did not harden into Jello while the bowl with the heated pineapple did. Pineapple contains an enzyme that breaks down protein, and gelatin is protein. Heating the enzyme destroys it allowing the Jello to harden.
Canned pineapple cannot be used because it is heated before it is canned.
This experiment will work with papaya as well. The enzyme in papaya is called papain and is so potent that it is the active ingredient in prescription debriding ointments. My Blue Goo Cracked Heel ointment I get at Walmart also has papain in it, but not for long. As of November 4, 2008 the FDA has banned papain from all over-the-counter products. I better stock up now and make sure I don't rub my eyes after applying it to my feet.