| MadSci Network: Biochemistry |
You're right: your wife has proven through experimentation that the kiwi fruit, or Chinese gooseberry (Actinidia chinensis), contains something that prevents the gelatin from setting! Kiwi, like many tropical fruits including pineapples and papayas, contains a strong enzyme that digests proteins called a protease (pro-tee-ace). The protease specifically found in kiwis is actinidain, which is a member of the papain family of cysteine endopeptidases. As a biochemist, I thought of two (not terribly plausible) solutions to making kiwi jello. You could add some cystatin to the mix - cystatin is a protein found in soya beans and egg whites that inhibits papains - although finding food-grade cystatin may be difficult. Or, you could try adding baking soda to the mix - actinidain requires an acidic pH (~5) to function, so raising the pH to around 8 should deactivate the protease - as well as making the jello taste slightly bitter. I couldn't find any references to the heat stability of actinidain, so I don't know whether cooking the kiwis prior to adding them would help, but it might be worth a try. As a cook, I would prefer trying this last approach. If nothing else, you could always resort to "kiwi-flavored" jello and add a different fruit.
Good luck with your experiments!
Mike Onken, MadSci moderator
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