A little on enzymes:

Bromelain, the mixture of enzymes found in fresh pineapples contains protease (or proteolytic enzymes) which breaks proteins into short protein chains or peptides. Since jello or gelatin is made of collagen, which is a type of protein, the protease in the pineapple breaks the proteins down preventing the gelatin from solidifying. However, when  fresh pineapples are heated above 70 Celsius the enzymes denature, so cooked pineapples have no effect on the gelatin.

Other fresh fruits such as papaya, mango, guava, and kiwi also have protease enzymes which affect gelatin the same way as pineapples.

So when you want fruits in your gelatin desserts use canned fruits! The heating during the canning process will prohibit the enzymes from affecting the gelling of the gelatin.

🙂