Browning of the chopped apple can be minimized by:
- A.using table sugar.
- B.preserving in a container.
- C.using lemon juice.
- D.using milk of magnesia.
Correct answer
Explanation
The correct answer is C, using lemon juice. Lemon juice is acidic and rich in vitamin C, which together slow the enzyme reaction that browns cut apple.
When an apple is cut, the enzyme polyphenol oxidase in its cells meets oxygen in the air and oxidises the fruit's phenolic compounds into brown pigments (melanins). Lemon juice lowers the pH, which slows the enzyme, and its ascorbic acid (vitamin C) is an antioxidant that reduces the coloured products back before they build up. That is why cut fruit for salads is often sprinkled with lemon juice.
A is wrong because table sugar does not stop the enzyme or the oxidation in any useful way.
B is wrong because an ordinary container still holds air, so browning goes on.
D is wrong because milk of magnesia (magnesium hydroxide) is a base; raising the pH does not stop the enzyme and can speed browning.
Exam tip: browning of cut fruit = polyphenol oxidase + oxygen; acid and vitamin C (lemon juice) slow it.
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