The idea for this experiment came from Dr Nicole McDonald - thank you!
This experiment is a good one to do on a night you want to have dessert with dinner. This experiment demonstrates how some special chemicals which are in all living things, enzymes, act to change whats around them. Enzymes are a biological molecule which help to speed up other chemical reactions that take place inside cells. Sometimes they make reactions go faster by helping to "process" some of the chemicals involved in the reactions.
Pineapples are a special kind of plant because they contain one certain enzyme called BROMELAIN. Only plants from the bromeliad family (spiky leaved plants which grow in the ground or on trees) make this enzyme. Bromelain digests protein - it helps to break the big protein molecules up into little pieces, and can be used to tenderise meat. Sometimes pineapple makes people's tongue sore which is actually the bromelain trying to tenderise your tongue!!
Jelly contains Gelatin. This is what binds together to turn the water into a jiggling wobbling jelly! Gelatin is made up of different proteins, and when it is mixed with water the very long molecules all tangle together trapping water in between them and forming the jelly. If you add some bromelain though, the long protein molecules will be chopped to pieces and wont be able to tangle together.
The interesting part of this experiment is that if you cook the pineapple first (which they do before canning it), the bromelain is inactivated! So you can add canned pineapple to your jelly without impacting the gelatin.
To do this enzyme experiment you will need:
Fresh pineapple
Tinned pineapple
Jelly
Step 1: Line up 3 bowls. Make up the jelly according to the instructions on the packet and pour some into each of the 3 bowls.
Step 2: Add the pineapple! To one bowl add a few pieces of the tinned pineapple, to the second add a few pieces of fresh pineapple and leave the third as your control with no pineapple in it.
Step 3: Pop it in the fridge and wait...
Step 4: See how the jelly with no pineapple set, the jelly with the tinned pineapple set and the jelly with the fresh pineapple didn't set! No matter what you do, you wont get it to set - the bromelain has chopped the gelatin up into little pieces and they just wont work.