Why doesn't jelly set when fresh pineapple is used?

Basic Problem: Jelly is made from protein, gelatin, this is dissolved in hot water and as it cools, it sets. For a childrens party it was decided to make some fruit jellies, these were made by putting sliced pineapple into the jelly before it set, the following observations were made: oThe jelly set normally when tinned pineapple was added. oWhen fresh, unripe pineapple was used the jelly set but was not as firm. oWhen fresh, …

…reaction other than the enzymes, the control just consists of a disk with the hole cut out, and water in place of a solution. Tinned pineapple: This was set up the same as the other experiments. It is the only real juice used, as it can not be reproduced as a solution. References: Advanced Biology principles and applications, C J Clegg and D G Mackean www.howstuffworks.com Cambridge advanced sciences Mammalian physiology and behaviour