Why do apple slices turn brown

Curiosities: Why do apple slices turn brown? October 20, Share via Facebook. Share via Twitter. Share via Linked In. PPO—a mixture of monophenol oxidase and catechol oxidase enzymes—is present in nearly all plant tissues and can also be found in bacteria, animals and fungi. In fact, browning by PPO is not always an undesirable reaction; the familiar brown color of tea, coffee and cocoa is developed by PPO enzymatic browning during product processing.

Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. Get smart. Sign up for our email newsletter. Sign Up. This works because there is a compound in honey that stops the enzyme responsible for oxidation. Additionally, this is one of the methods that will not unpleasantly alter the apple's taste.

If you want to take the submersion method up a notch, you can add a little bit of citrus or pineapple juice to the water. What do these juices have in common? They contain citric acid, which slows the chemical reaction and prevents browning. But there are actually a few ways to use juice in order prevent browning: 1 you can add two tablespoons of juice to water and submerge the apple slices, 2 you could submerge the apples into juice, or 3 you can simply squeeze lemon, lime, or orange directly onto the surface of the cut apple.

The only downside of using this method is that the juice will impart a little bit of flavor onto the apple—so pick your favorite. Then, keep them in the fridge.