What makes an apple turn brown?

Answer 1

OXIDATION

Fresh cut apples turn brown when iron-containing chemicals inside apple cells react with oxygen in the air. We see this every day when iron objects rust, or when scabs on cuts turn brown.

The chemical reaction is called "oxidation", and the enzyme that regulates oxidation in apples is called "polyphenol oxidase" (PPO), also known as "tyrosinase".


HOW APPLE CELLS GET EXPOSED TO OXYGEN

There are millions of tiny cells inside each apple. One way apple cells get exposed to oxygen is by cutting the apple open. This damages the wall that protects each cell and exposes its contents to oxygen in the air.

Bruised apples also exhibit oxidation. When an apple gets damaged--as might happen if it were dropped--many of the cell walls inside the apple get broken. This enables the contents of those cells to flow freely inside the apple, where they react with air that is also inside the apple (apples are 80% air--that's why they float).

WAYS TO KEEP YOUR APPLES FROM GOING BROWN

* Use anti-oxidants such as lemon juice, which are high in citric acid. In commercial processing, sulphur dioxide is used.
* Remove the air from your apples. This is why vacuum-packed canned foods stay fresh so long.
* Remove water from your apples (called "dehydration"). Polyphenol oxidase--and just about everything else that can spoil food--needs water to work.
* Use clean, high-quality cooking utensils. Iron salts found on steel cooking utensils corroded by organic acids can act as potent catalysts to oxidation by producing per-oxides and super-oxides.
* Cook your apples. Heat "denatures" (changes & weakens) polyphenol oxidase.
* Eat your apples quickly...before they have time to go brown!

Interestingly, in humans tyrosinase is important because it helps create melanin, which causes tanning. A lack of tyrosinase may lead to a condition known as 'albinism'.

Answer 2

If you are cooking it, it is called "carmelization". The sugars in the apple are reacting with the heat. If you cut an apple and it is exposed to air, it is, contrary to popular belief, not oxidation. The bacteria are exposed to the apple, because the skin is what keeps the apple protected. The exposure to air helps the bacteria breath, the only oxidation involved is the bacteria getting the air they need. The bacteria will feast on the abundance of sugars in the apple, and the brown is the eaten parts, lined with, er, bacteria "poo". I hope that I helped!

Answer 3

Like rust, apples go through a chemical reaction called oxidation. In other words, when you cut the apple, and damage the cell walls, the iron containing chemicals in the apple react to the oxygen in the air.

A good way to keep cut apples from rusting is to use lemon juice....or so I've heard.

Answer 4

Oxygen reacting with chemicals in the apple. YOu can prevent it by adding some lemon juice.

Answer 5

Exposure to air. If you put it in a bag with a lemon slice, the acid from the lemon will help to prevent that.

Answer 6

Anaerobic glycolysis... its lunchtime for the microbes. Organic things rot.

Answer 7

That's a good question!

Answer 8

oxygen in the air

Answer 9

the air

Answer 10

Yeah it might be correct