Why does pineapple break down jello?

Like all protein, gelatin is made up of amino acids, the individual building blocks of live. Gelatin is insoluble in water, but individual amino acids are not, they are soluble. Pineapples, unlike most other fruit, contain an enzyme called bromelain, that breaks up the gelatin into it's amino acid building blocks. read more

The reason pineapple prevents Jell-O from setting is because of its chemistry. Pineapple Enzymes and Collagen Cross-Linking Pineapple contains a chemical called bromelain, which contains two enzymes capable of digesting proteins, which are called proteases. read more

Pineapples, unlike most other fruit, contain an enzyme called bromelain, that breaksup the gelatin into it's amino acid building blocks. Jell-O and other gelatins get their structure from links formed between chains of collagen. read more