Why do apples turn brown?
Apples turn brown when their cut flesh is exposed to oxygen. An enzyme called polyphenol oxidase reacts with compounds in the apple, producing brown pigments.
Inside an apple's cells, the enzyme and natural chemicals called polyphenols are kept apart. When you cut or bite an apple, cells break open and the enzyme comes into contact with the polyphenols and oxygen in the air. This chemical reaction, called enzymatic browning, creates brown pigments similar to melanin.
Browning does not mean the apple is spoiled or unsafe to eat, though it can change the taste and texture slightly. The same reaction happens in bananas, potatoes, pears and avocados. Some apple varieties brown more slowly than others.
How to slow browning
Coating cut apples with lemon juice works because its acid and vitamin C slow the enzyme. Soaking slices in salt water or honey water also helps, as does keeping them cold. A genetically modified apple called the Arctic apple was developed to resist browning by reducing the enzyme.
Did You Know?
Enzymatic browning is useful in some foods. It helps give tea, coffee, cocoa and raisins their color and flavor.