Science Questions

Do bananas brown faster in the fridge?

Mon, 24th Oct 2011

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Question

Shelley asked:

Do bananas brown faster in the fridge?

Answer

Emily - Well itís a good question and the answer is that they will brown faster in the fridge.  Itís mainly due to the formation of ice crystals, so if you put your banana in the fridge, the ice crystals grow, and they actually rupture the cells of the banana skin. This releases an enzyme called polyphenol oxidase and as the name suggests it acts to oxygenate phenols, which have a ring-like structure, into quinones, and these quinones can then all join together or polymerise and produce a black, brown, or red pigment called polyphenol and this is what gives it the brown colour. So, if you have your banana in the fridge, this will occur and you'll get a brown banana.  But another interesting thing about bananas is that if you have them in the fruit bowl, they'll release ethene and this will make the other fruits in the bowl ripen faster because itís a ripening hormone.

Chris -   So, the question is though, if this is a chemical reaction making this brown pigment, if you slow down the reaction by lowering the temperature, then it should happen more slowly, therefore, going in the fridge should make the bananas go black slower?

Emily -   I can see why you're thinking that but actually, itís more the rupturing of the cells.  So if you have a banana on your table, the cells are going to be intact, the enzymes contained, and the reaction is not happening at all whereas if you put in the fridge, the enzyme is released and the reaction can happen Ė although yes, it might happen slower.

 

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