Bananas go brown, but not usually just at one end
Unripe bananas are green, ripe ones are yellow and overripe bananas are brown. But can you make a banana that’s half brown and half yellow?
Safety: This activity uses a hot stove and boiling water. Ask an adult to help.
When they get old, bananas go brown. They also go brown when they are bruised. But what causes the brownness?
It’s all down to a chemical called polyphenol oxidase (PPO). This chemical oxidises (adds oxygen to) a type of chemical called a phenol. These oxidised phenols then join together with other compounds to make brown colours.
Polyphenol oxidase is normally contained inside certain parts of plant cells. When the cells are damaged, the PPO escapes and starts the browning process. That’s why a bruised banana goes brown, and it’s also what happens in this activity.
There are ways to stop the browning. PPO can’t oxidise anything without oxygen. In this activity, it’s why the banana doesn’t really go brown until it’s out of the water for a while. This exposes the banana to air and the oxygen it contains.
You can also stop the browning by destroying the PPO before it can start oxidising. One way to destroy PPO is to heat it up for several minutes. Why not try boiling a banana for 10 minutes and see if it turns brown?
Browning a banana skin is fun, but there’s also a serious side to all this. Lots of fruit is wasted because it goes brown from a small bruise or from being cut and left in the air. To help fight food waste, CSIRO developed an anti-PPO gene that can prevent browning. It’s currently being used in special Arctic varieties of apples. They’re only available in the Americas for the moment, but maybe sometime soon, you’ll be able to eat some non-browning apple slices!
Read more about CSIRO’s non-browning technology
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29 April, 2022 at 12:29 pm
Interesting post about the banana analogy links to other food science but I am happy to have bruises, birds and bees and fruit that tastes real… it is a sad world that we create science not to waste food when the food could feed millions.