If you cut or peel an apple and then leave it on a plate for some time, the flesh will turn brown. Many people believe this happens because apples contain a lot of iron, which, as is commonly known, rusts when oxidized. They think the iron in apples reacts similarly when exposed to oxygen. But that’s not the case.
There is indeed iron in apples — 100 g of pulp contains approximately 0.12 mg, which, by the way, is relatively little. Moreover, it is not absorbed very efficiently from plant-based foods. If you want to increase the content of this microelement in your body (and it is necessary for the production of hemoglobin), you should primarily focus on eating meat, fish, eggs, as well as spinach, cabbage, and other green leafy vegetables.
The apple doesn’t turn brown because of iron but due to an enzyme called polyphenol oxidase. When the fruit is cut or bruised, oxygen enters the damaged tissue. The polyphenol oxidase in the chloroplasts reacts with it and oxidizes the phenolic compounds present in the flesh. This results in the formation of so-called o-quinones, which then interact with amino acids or proteins, leading to the production of melanin—a brown pigment.
This process is not unique to apples; it also occurs in pears, bananas, and eggplants. Additionally, polyphenol oxidase is responsible for the brown color of black tea, coffee, and cocoa.
To prevent an apple from browning, you can blanch it, which means scalding it with hot water. This neutralizes the polyphenol oxidase, further proving that apples don’t brown due to iron. After all, if they were truly “rusting,” contact with water would accelerate the process, not stop it. You can also drizzle the apple with lemon or pineapple juice—the acids in these juices slow down the reaction between oxygen and polyphenol oxidase.
Incidentally, there is a genetically modified variety of apple called Arctic that never browns. It has had the polyphenol oxidase enzyme production blocked. Arctic apples taste the same and have the same nutritional value as regular apples, so their appeal is more aesthetic.
