Home Science CommunicationOutreach & engagement Dark stories from the kitchen – melanin in fruit

Dark stories from the kitchen – melanin in fruit

by Eva Amsen
School visit

 explaining pigmentation with bananas.

A few weeks ago I gave a talk at a grade 8 class about my research. The long molecular biological explanation was out of their league, so instead I had them produce melanin using bananas. We showed that melanin needs oxygen to be formed: If you scratch in a nice yellow banana peel with a pencil, just breaking the surface of the skin, you’ll see brown appear within minutes. That’s melanin! You can try this at home, and eat the banana right afterward. The banana itself is fine, because you only damaged the skin, but if you leave it, it will rot faster than an unscratched banana.

One of the students asked me why this doesn’t happen if you cut your own skin. After all, human skin produces melanin too. The difference is that human skin is not airtight: it lets oxygen through, and melanin can always be produced in there. The banana has an airtight outer layer, so no melanin is formed until you break that layer, either by scratching it or by just letting the banana sit there for a few days (brown spots…)

We also showed that lemon juice inhibits melanin formation by cutting an apple in half and rubbing one half with lemon juice, but not the other half. The apple takes longer than the banana to turn brown, but after an hour you can see the difference between lemoned and unlemoned. Thanks to the lovely people at AskMe I figured out that I had to use a red apple for this experiment to work best.

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