Apples turn brown because of a chemical reaction called “oxidation” , which is caused by oxygen from the air. Oxygen is one of the most reactive substances known. Apples are rich in iron, which is present in all their cells. Oxygen from the air reacts with the iron in the apple cells, forming iron oxides, This is just like the rust that forms on the surface of iron objects. An enzyme called polyphenol oxidase (that’s present in these cells) increase the rate of chemical reaction, that is, helps make this
reaction go faster. The oxidized layer (brown color) formed is just to provides some protection against foreign bodies that may affect the exposed apple cells.
There’s no harm in eating an apple that has turned brown, for the iron oxide will not affect you. Meanwhile, if you are to prepare
apple juice. The iron oxide
gives it the special golden-brown colour, and it’s a tastier way to consume an apple!