Why does lemon juice prevent browning?
Show answer & explanation
Answer: Acid lowers pH stopping enzymes
Coats fruit blocking oxygen — Wrong. Liquid can reduce oxygen contact, but the primary mechanism is chemical—citric acid lowers pH, denaturing polyphenol oxidase enzyme.
Acid lowers pH stopping enzymes ✓ — Correct! Enzymatic browning (apples, avocados) requires polyphenol oxidase enzyme to work at specific pH (~6-7). Lemon juice is acidic (pH ~2), which lowers the fruit's pH below the enzyme's best range, denaturing it and stopping oxidation. The enzyme can't function in acidic conditions!
Sugar content preserves fruit — Wrong. Lemon juice has minimal sugar. The anti-browning effect comes from citric acid denaturing the enzyme that causes oxidation.