Why Do Apples Turn Brown?
Have you ever bitten into an apple, set it down for a few moments, and found that it has turned brown? This is caused by an enzyme (polyphenol oxidase and catechol oxidase are two common examples) that reacts with oxygen in the air and an iron or copper cofactor in the fruit. A cofactor is a component that is necessary for a certain enzymatic reactions to happen. The fruit starts to oxidize, when electrons are lost to another molecule (in this case the air), and the food turns brown. In other words, it’s like edible rust on your food!
Oxidation can be prevented or slowed down by not allowing oxygen to get to the surface of the fruit. To accomplish this, you can cook the food, which destroys the enzyme. It is also possible to prevent browning without cooking by covering the fruit (preventing air from reaching the fruit), or by lowering the pH on the surface, making it more acidic.
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