Why do apples turn brown when cut?
Show answer & explanation
Answer: Enzymatic oxidation reaction
Moisture evaporates changing color — Wrong. Evaporation doesn't cause browning—oxygen exposure does. Enzyme PPO catalyzes reaction between phenols and O₂.
Enzymatic oxidation reaction ✓ — Correct! Enzymatic browning! Apples brown because: (1) Cutting damages cells—releases enzyme polyphenol oxidase (PPO). (2) PPO exposed to oxygen in air. (3) Catalyzes oxidation—phenolic compounds → quinones. (4) Quinones polymerize → melanins (brown pigments). (5) Natural protection—forms barrier (wounds). Prevent: lemon juice (citric acid denatures PPO), salt water, refrigeration (slows enzyme). Also: bananas, potatoes, avocados. Not harmful—just appearance!
Light breaks down apple cells — Wrong. Light isn't the cause—oxygen exposure is. PPO enzyme catalyzes reaction between oxygen and phenolic compounds in cut apple.
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