4. What causes the change in color of the potatoes and apples

When you eat apples or bananas, or when peeling potatoes or eggplant, the color of the fruit and vegetables becomes brown and sometimes "changes to black color, the reason is due to oxidation of phenolic compounds in the fruit under the action of an enzyme called polyphenol oxidase

Explanation:

The actual mechanism that causes browning in apples and potatoes involves an enzyme called polyphenol oxidase, also known as tyrosinase.

The enzyme then has access to oxygen in the air and it does its thing, turning the fruit brown.

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