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

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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, ripe pineapple was used, the jelly did not set at all

But why?

The reason the jelly is not setting is due to protease, which is breaking down the protein in the jelly, protease is an enzyme, and its rate of activity is affected by many things, such as temperature and concentration.

Theoretical investigation.
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It is a hydrophilic biopolymer and the reason it is broken down is because the peptide bonds between the amino acids are being hydrolysed. Gelatin is in the majority composed of the amino acids glycine, praline, and hydroxyproline. When boiling water is added to the gelatin the weak bonds are broken by the energy the hot water supplies, The helical structure falls apart, and you are left with free polypeptide chains floating about in solution. the polypeptide chains begin to re-associate and reform the tight triple helix structure. However, the chilling process is slow, and the individual strands have been widely dispersed by mixing, so the helices aren't perfectly formed. In some places, there are gaps in the helix, and in others, there is just a tangled web of polypeptide chains. When the gelatine solution is chilled, water is trapped inside these gaps and pockets between chains. This is what causes the mixture to become solid. When the enzyme comes in contact with the gelatine it breaks down the peptide bonds between the amino acids in the gelatine chain by hydrolysing them this causes the helical structure to break down and the water to be taken in leaving you with a solution of broken chains of gelatine. The enzyme itself I have concluded to be an endo-peptidase as it breaks down bonds between acid residues in the interior of proteins.

Tinned pineapple, why does it have no effect on the gelatine?

Because it is the

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