The surrounding world is amazing. And if children understand this easily, with age they get used to many things and safely forget about it. As a result, the simplest questions a child can put an adult at a dead end. For example: "Why does the apple darken at the cut?" This process is very multifaceted, but not as simple as it seems at first glance. After all, different apples darken in different ways, and some do not darken at all.
Most often, when asked about whythe apple darkens on the cut, they hear that this is due to the iron contained in it. It is also known from the course of school chemistry that iron has a valence (or oxidation state) of +2 and +3. So, in apples it has the first degree of oxidation. However, after cutting, it begins to actively contact with air, which contains oxygen. As a result, iron is oxidized to +3, thereby forming an oxide. It turns out that the apple just "rusts". And the color takes the corresponding one.
However, any chemist knows that this is not so. In an apple weighing about 150-160 grams contains only 3-4 mg of iron. Is this enough to spoil the appearance of the whole fruit? Of course not. In fact, absolutely other substances are responsible for this. After all, this happens with pears and bananas. But they do not have as much iron.
The real reasons
So, why does the apple darken at the cut, if in italmost no iron? After damage to the fruit, a whole series of chemical reactions takes place, because of which it loses its marketing appearance. But if you follow the whole chain, you can still understand the true reason.
As you know, apples, like any other fruit,rich in antioxidants. From the point of view of chemistry, they are referred to the group of polyphenols. They have different names, but the essence of them is one - this is a mix of different phenols (not to be confused with poison). Of course, this substance in itself does not affect the color of the apple, since it is simply colorless. But it still contains an enzyme of polyphenol oxidase, which after any damage begins to actively interact with polyphenols. The main catalyst for the reaction is oxygen. And as a result, in the apples in a huge amount of quinone is formed, and he - a strong oxidizer. This is the correct answer to the question of why the apple darkens at the cut.
How to fight?
Of course, this property of apples is not to many people's liking. Fruits quickly lose an attractive appearance, and even a fresh cut in just a couple of minutes begins to look not very attractive. Cooks have long come up with a way to combat this shortcoming. To do this, it is sufficient to rub the cut with lemon peel or sprinkle with lemon juice. Another option is to drop fruit for 1-2 minutes in a solution of citric acid. As a result, the apple does not darken at the cut.
For apple juice invented another option. For this, it is simply pasteurized for 20-30 minutes at 70-80 degrees. As a result, polyphenol oxidase is destroyed. So, it is already impossible to start the oxidation process in principle. For whole apples such a method, unfortunately, does not fit.
Obviously, by removing one of the three componentsreaction, you can make sure that apples do not darken. Unfortunately, it is impossible to get rid of polyphenols. In addition, it is believed that they are useful for the body. And the first thing that was achieved is to exclude oxygen from the reaction. To do this, apples are covered with a special substance, similar to wax (according to the international standard it is labeled E901-E913). However, before consuming such fruits in food, the coating should be washed off.
But science does not stand still. After all, it has long been known why the apple darkens at the cut. Presentation of the new genetically modified variety has proved that by removing enzyme-oxidizer, you can get just "eternal" apples. An excellent solution for supermarkets and restaurants. Moreover, it only required blocking some genes for this. It is believed that this technology is most harmless.