why does cut apple turn brown?

1. When the apple is cut,PPO will receive a lot of oxygen

2. Thus the PPO will rapidly oxidize phenolic compounds naturally present in the apple tissues to o-quinones.

3. O-quinones then produce the well documented brown colour by reacting to form compounds with amino acids or proteins or they self-assemble to male polymers.

4. Apple contain polyphenol oxidase enzymes (PPO) in the chloplast.