Why do apples turn brown?
Show answer & explanation
Answer: Oxygen causes oxidation
Oxygen causes oxidation ✓ — Correct! When apple cells are damaged (cutting/bruising), enzyme polyphenol oxidase (PPO) is exposed to oxygen. PPO catalyzes oxidation of phenolic compounds to quinones—brown pigments (enzymatic browning). Prevents: lemon juice (acid denatures enzyme), cold (slows reaction), airtight storage. Same process browns potatoes, bananas, avocados!
Sugar caramelizes quickly — Wrong. Caramelization requires high heat. Apple browning is enzymatic oxidation—enzymes react with oxygen creating brown compounds.
Vitamins leak out and stain — Wrong. Vitamins don't cause browning. The brown color comes from enzymatic oxidation—enzymes in the apple react with oxygen to create brown pigments.