The world around is amazing. And if children understand this easily, then with age they get used to many things and safely forget about it. As a result, the simplest questions of the baby can confuse the adult. For example: "Why does an apple darken on a 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.
Debunking Myths
Most often, when asked about why an apple darkens at a cut, they hear that this is due to the iron contained in it. It is also known from school chemistry that iron has a valency (or oxidation state) of +2 and +3. So, in apples, it has a first oxidation state. However, after cutting, it begins to actively come into contact with air, which contains oxygen. As a result, iron is oxidized to the degree of +3, thereby forming an oxide. It turns out that the apple just “rusts”. And the color takes appropriate.
However, any chemist knows that this is not so. One apple weighing about 150-160 grams contains only 3-4 mg of iron. Is this amount enough to spoil the appearance of the whole fruit? Of course not. In fact, completely different substances are responsible for this. After all, this happens with pears and bananas. But they do not have such an amount of iron.
True reasons
So, why does an apple darken on a slice if there is practically no iron in it? After damage to the fruit, a number of chemical reactions take place, due to which it loses its presentation. But if you trace the whole chain, you can still understand the true reason.
As you know, apples, like any other fruit, are rich in antioxidants. From the point of view of chemistry, they belong to the group of polyphenols. They have different names, but they have one essence - a compound 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 the polyphenol oxidase enzyme, which, after any damage, begins to actively interact with polyphenols. The main catalyst for the reaction is oxygen. And as a result, quinone is formed in large quantities in apples, and it is a strong oxidizing agent. This is the correct answer to the question of why the apple darkens on the cut.
How to fight?
Of course, many people don’t like this property of apples. Fruits quickly lose their 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 their own way to deal with this shortcoming. To do this, just wipe the slice with a lemon peel or sprinkle with lemon juice. Another option is to lower the fruits for 1-2 minutes in a solution of citric acid. As a result, the apple does not darken on the cut.
For apple juice, another option has been invented. To do 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. Unfortunately, this method is not suitable for whole apples.
Scientific approach
Obviously, removing one of the three components of the reaction, you can ensure that the 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 was to exclude oxygen from the reaction. To do this, apples are coated with a special substance similar to wax (according to the international standard, it is labeled E901-E913). However, before eating such fruits in food, it is desirable to wash off the coating.
But science does not stand still. After all, it has long been known why an apple darkens on a cut. The presentation of the new genetically modified variety proved that by removing the enzyme oxidizing agent, you can get just "eternal" apples. A great solution for supermarkets and restaurants. Moreover, for this it was only necessary to block some genes. It is believed that this technology is the most harmless.