The "brown stuff" on the apple

Why the apple turned to brown colour?

We always notice that when we peel the apple or cut it into few slices, the apple turned to brown colour. We know that when the apple after being cut became brown colour is because the apple is exposed to the air.

What is the main factor that cause the apple become brown colour after being exposed to the air? Actually, when the flesh of the apple being oxidized in the air, the process is called oxidation. The oxidation of an apple is very similar to the rusting of iron with air. In the oxidation process, the oxygen acts as oxidizing agent.

Besides that, there is a specific enzyme that casues the brown colour appear on the apple which is called polyphenol oxidase (PPO). This enzyme catalyse the o-hydroxylation of monophenols to o-diphenols. PPO enzymes can also catalysed oxidation of o-diphenol to produce o-quinone.

This enzyme can be found in many foods such as breads, chapattis, noodles and so forth. When the cell is broken, the enzyme is released which then reacts with the oxygen in the air and a layer is formed on the outside.

The diagram above has shown the chemical reaction that occurs. In this diagram, we can see that the monophenol reacts with the oxygen in the air, which creates the diphenol. When this chemical reaction is complete, the complex brown polymers are left. So, we can see the "brown stuff" on apple when an apple skin is pierced. The o-quinone reduced the diphenol which in turn is the molecule that is being oxidized. Thus, when an apple is turning brown, actually is the small molecules in the cells are reacting with the oxgen in the air. As a result, a layer of the brwon stuff is forming on the top. But, we no need to worry because it does no make the apple harmful to eat. If you don't want your apple turns to brown colour, what can you do is soak your apple which has been cutting in to the salt water. This can prevent the apple turn to brown colour.