Why do apples turn brown?

+97 votes
asked Mar 12, 2015 in Food & Drink by cortiss (550 points)
I was eating an apple, and it was starting to change to brown before I could even finish it. Is it okay to eat nonetheless? What makes apples turn brown?

3 Answers

+27 votes
answered Mar 18, 2015 by B (1,060 points)

enzyme that will react with the phenols and oxygen also contained in the apple. The reaction between the two forms what is essentially rust on the fruit. When this fruit is bruised or cut, the cells are damaged and oxygen reacts with the apple’s enzyme and turn brown.

There are many ways to slow this process, such as cooking the fruit, adding lemon juice to reduce the pH on the apple’s surface, or adding preservative substances such as sulfur dioxide. Another way to stop the fruit from browning is to reduce the amount of oxygen, by vacuum sealing it or submerging it in water. However, the rate of browning will be increased if you use cutlery that has some amount of corrosion, as found with some types of steel knives, as there are more iron salts to speed up the reaction.

Also, it is safe to eat the brown part.

Reference:

http://scienceline.ucsb.edu/getkey.php?key=64

+9 votes
answered Mar 20, 2015 by selam (1,220 points)
Why do apples turn brown? This is because when you cut an apple, the inside of the fruit is exposed to oxygen. Apple contains iron, and iron will turn brown after exposing in oxygen. It’s fine to eat them like this; I do it all the time. They’re not as good, but my mom insists they’re still healthy.
+5 votes
answered Mar 14, 2015 by Sofie (780 points)
The apple’s color has nothing to do with iron. If that were true, you could eat apples to help with anemia.

The apple’s oxidation is not related to iron. But the other person was correct when they mentioned polyphenol oxidase, the enzyme contained in apples.

The enzyme is a highly responsive compound that must be preserved in vacuole-like organelles, and helps produce sugar as the fruit ripens.

Another misleading idea: the enzyme being oxidized by air exposure. In fact, there are two things happening: when you cut the apple, the enzyme is released into the exposed cells, which make contact with the polyphenols in the cytoplasm. Then, the enzyme mixes the phenols with the oxygen in the air. The result is a brown ring of carbon, not iron.

When an apple is dropped and then cut, it is brown even though it hasn’t been exposed to oxygen. The air contained within the apple has ample oxygen to complete that process.

Acids, heat, and high amounts of salt and sugar can inhibit the enzyme from functioning, which is why green apples aren’t as easily oxidized.

Water blocks oxygen from reaching the reaction site, which also stops the reaction.
Welcome to Instant Answer, where you can ask questions and receive answers from other members of the community.
...