From time to time I meet people who complain about the lack of iron in apples.
Look at what ferruginous apples there used to be. Once you bite it, within a minute it is already dark. Apple iron begins to rust when it comes into contact with air.
Apparently these comrades have no idea how iron rusts.
With such rates of rusting, we would no longer have anything iron left.

Why do apples turn dark when cut? As a rule, this question is answered this way: due to the fact that oxygen in the air oxidizes the iron contained in apples. It is often added that if the apple does not darken after cutting or there is little “rust” on the cut, it means that the apple contains little iron. And that if you pour lemon juice over the cut of an apple, the apple will not darken for a long time, because citric acid will bind iron ions.

It sounds convincing and believable. And yet, all this is completely untrue.

Apples actually contain iron. One apple weighing 100 g contains about 1-2 milligrams of iron - a microscopic amount, completely insufficient to spoil the presentation of the whole fruit. Therefore, by the way, it makes no sense to treat iron deficiency in the body with apples, especially considering that the body absorbs only 1-5% of this tiny amount.

In fact, the mechanism for darkening apples is completely different.

It is known that berries and fruits are rich in antioxidants, which largely determine their benefits for our health. Apples contain a lot of antioxidant substances called polyphenols. In structure, they are chains of molecules of various phenols, which look something like this:

Theaflavin-3-gallate is a polyphenol of plant origin.

(it is known that phenol is a strong poison, but phenol chains are substances with completely different properties and are not at all toxic to humans).

In addition, apples contain polyphenol oxidase enzymes, the task of which, as their name implies, is to oxidize polyphenols.

As a result of the oxidation of polyphenols, quinones are formed. By themselves, they are colorless, but unlike polyphenols, which by their nature interfere with oxidation reactions, quinones, on the contrary, are strong oxidizing agents that, having formed on the surface of an apple cut, begin to interact with everything that gets in their way. As a result, substances are formed that give the apple a rusty color.

Why doesn’t the flesh of a whole apple “rust”? The trick here is that polyphenol oxidase requires oxygen to interact with polyphenols. When the integrity of the apple is damaged, oxygen gains access to the site of action and initiates these processes.

If you treat the cut of an apple with citric acid, you can slow down its darkening. The secret lies in the fact that when acidity increases (chemists say: when pH decreases), the activity of polyphenol oxidases decreases.

What is all this for and what is the point?

The apple is thus protected from pests. The oxidation processes of polyphenols, as you noticed, start only when the apple is damaged. In nature, this happens, for example, if a caterpillar gnaws a fruit. First on the list of apple “defenders” are quinones themselves, which, being strong oxidizing agents, are toxic to microorganisms and fungi. The brown “film” that forms on the damaged surface of the apple heals the damage and protects its flesh from penetration of the damage deeper. And finally, the protective role is played by substances that are formed as a result of oxidation processes. Some of them can greatly spoil the caterpillar’s ​​digestion, while others can make the fruit tasteless to it. Something similar happens when we eat thorns, bird cherry or unripe persimmons - their unpleasant astringent effect is due to the action of tannins, tannins, which also belong to the class of polyphenols and coagulate proteins on the surface of the tongue and mucous membranes to form large “tasteless” molecules.

The rate of formation of the brown film and the intensity of its color are determined by the amount of polyphenols in a given apple variety.

The same mechanism has darkening on the cut of bananas, peaches, unripe walnuts, potatoes, and mushrooms.

The browning of the apple pulp when cut gives it a not particularly appetizing appearance. Therefore, scientists have long wondered how this can be avoided. Apple varieties have already been developed in which the surface of a cut apple does not darken. This was achieved by blocking the genes responsible for the synthesis of polyphenoloxidases.

1. Those who love apples do not have iron deficiency.

Apples, pomegranates and walnuts, which in Soviet times were for some reason proclaimed the basis of hemoglobin nutrition, do not contain much iron. Compare: 100 grams of apples contain up to 2.2 mg of iron, the same amount of almonds - 4.4 mg, apricots - up to 4.9 mg. In addition, iron is absorbed much worse from plant foods (only 3-5 percent) than from animal foods (25-35 percent). Advice to increase the iron content in apples by sticking nails into them is complete nonsense; in this way, apples can only be enriched with pathogenic bacteria.
According to the National Agricultural Library, the iron content in apples is 0.12 mg per 100 grams The average daily requirement for a person is 12 mg of iron. Those. To meet this requirement you need to eat 10 kg of apples!

Verdict: in order for the body to receive enough iron, you need to eat red meat - at least 100 grams 3-4 times a week and offal - 100-150 grams once a week.

2. Red apples provide us with carotene

Carotene is a pigment that gives fruits and vegetables their yellow-orange color. In this sense, the apple is not a competitor to carrots, apricots, or peaches. Yellow apples contain slightly more carotene than red or green apples, but still not much. But with vitamin A, which is synthesized in our body from this substance, an ordinary, non-vegetarian person, as a rule, has no problems: in order not to lack vitamin A, you just need to eat beef or chicken liver several times a month. Vitamin A is one of the few vitamins that our body can accumulate, so its deficiency does not threaten people who eat well and do not have diseases of the small intestine and pancreas.

Verdict: Any orange and yellow fruit is beneficial - including apples.

3. Apples, like all fruits, contain a lot of vitamins

The myth about vitamin-rich vegetables and fruits is so widespread and tenacious that it is unlikely that it will ever be eradicated. This is probably not necessary - we really should eat more fruits. In reality, the situation is like this: vegetables and fruits can boast of real “wealth” in relation to only three substances - vitamin C, carotene and folic acid (vitamin B9). Apples are not the leader in any of the three positions. For example, for someone who wants to top up with their help daily norm vitamin C, you will have to chew 2.5 kilograms of apples. The intestines and tooth enamel will not thank you for this.

Verdict: in order for the body to receive all the vitamins it needs, it needs not only fruits, but also all other food groups - grains, cereals, meat, fish, dairy, etc.

4. “One apple a day will keep your doctor out of work.”
(English proverb)

There is some truth in it: the fiber that apples contain - especially pectin - improves intestinal motility, helps fight constipation, and maintain microflora balance. Having a healthy gut is very important for the immune system. Organic acids contained in apples (and not only them) support intestinal microflora and improve the absorption of food, as do another group of substances present in fruits, including apples - bioflavonoids. But apple lovers are, of course, far from completely free from all health problems.

Verdict: two apples a day is better than none.

5. Apples are the best snack for those who are losing weight

It depends on what kind of apples and what time of day such a snack is arranged. After 17:00, people who are losing weight are not recommended to eat fruit, as this can lead to weight gain. An apple can be a good second breakfast, but even in this case it is better to choose not very sweet varieties and medium-sized fruits. Still, apples are quite sweet things - depending on the variety, they can contain up to 12 percent carbohydrates! Fruits should not be underestimated at all - in recent years, nutritionists and gastroenterologists have become increasingly convinced that the fashion for fruit salads and freshly squeezed juices has played a significant role in the obesity epidemic among Americans.

Verdict: Apple time ends at 5 p.m.

6. It’s better to eat the whole apple, its seeds are very healthy

For people with intestinal diseases, such an experiment can lead to aggravation - the core of the apple, and even the thick peel, irritate the intestines. As for the seeds, they contain hydrocyanic acid - the same one that made many people stop loving apricot kernels. Of course, you won’t be able to get seriously poisoned by the amount contained in apple seeds, but is it worth experimenting? Moreover, there is nothing really useful in them. Iodine is present, but there is much more available methods get it.

Verdict: Eat the apple yourself, give the seeds to the birds.

7. Gnawing on apples is good for your teeth.

Yes and no. Teeth really love solid food; it mechanically cleanses them, and at the same time improves blood supply to the gums. However, teeth do not like sour foods, since acids damage the enamel. Plus, sugar becomes a breeding ground for bacteria. It’s not critical, but the apple will contribute its “two cents” to the collection of risk factors for caries.

Verdict: Apples, especially sour ones, are best eaten with other foods and rinsed your mouth after them.

8. Baked apples are healthier than raw ones

In fact. The baking process cannot but cause some damage to rapidly degrading beneficial substances (for example, vitamin C). However, in a number of parameters, baked apples can really outperform fresh ones. They are better absorbed, there is only more pectin (per 100 g), and the reduced amount of acids makes the dish accessible even to people with problem stomachs. Finally, baked apples, unlike fresh ones, can be a separate, quite satisfying dish.

In winter, many people prefer dried apples, and they can be an excellent alternative to fresh ones - imported or local, but which have lost most of their beneficial substances during long-term storage. You just need to remember that 20 g of apple chips contain the same amount of calories as 100 g of fresh apples.

Use lemon juice. Apples turn brown because the enzyme they contain reacts with oxygen in the air. This process is called oxidation. Lemon juice can prevent oxidation because it contains citric acid, which is an effective antioxidant. You can use freshly squeezed or canned lemon juice. It's best to use this method only on sweet types of apples because the lemon juice will add tartness. You can apply lemon juice to protect apples from oxidation in two ways:

Use salt. Salt is a natural preservative and can effectively protect apples from oxidation. Make a solution at the rate of 1/2 teaspoon of salt per liter of cold water. Place the sliced ​​apples into the solution and let them soak for 3-5 minutes. Remove from water and rinse thoroughly using a colander or sieve. The pieces will not oxidize for some time.

• Don't worry about the fruit tasting salty; as long as you don't use too much salt, don't soak the apple for too long, and rinse it thoroughly afterwards, the flavor of the fruit won't change.

Sliced ​​apples are included in recipes for many dishes - salads, pies, various desserts, etc. And the apple slice itself decorates the table and attracts the attention of guests.

But, unfortunately, apple pieces quickly, in a matter of minutes, darken when cut, losing their appetizing fresh appearance. However, it is not difficult to prevent apples from darkening when cutting: many different methods have been invented for this.

Why does a cut apple turn dark?

As you know, apple pulp contains a lot of iron. The most surprising thing is that this iron in apples is in a quickly digestible state, which is why red apples, which are the richest in this element, are recommended for people with anemia to eat.

But it is iron that causes the darkening of apple slices: iron atoms react with oxygen in the air, forming iron oxide, which gives the pulp its characteristic Brown color. This means that to prevent darkening, you need to prevent the apple juice from coming into contact with air.

Method 1 – lemon juice

To prevent the sliced ​​apples from darkening as long as possible, they are sprayed lemon juice. Both freshly squeezed and canned juice are suitable for this. To evenly coat the slices with juice, you can use a small spray bottle or pastry brush. This method is best suited for sweet varieties of apples, which, when combined with lemon juice, acquire a more refined taste.

If you have sweet and sour apples at your disposal, it is better to prepare a mixture of lemon juice and boiled water, taking no more than a tablespoon of juice per half liter of water. Apple slices are dipped in acidified water, kept in it for about a minute and drained in a colander.

An apple cut after this treatment remains fresh for several hours. Instead of lemon, you can take lime; its juice has the same properties. If you have neither one nor the other, you can use a solution of citric acid by dissolving a teaspoon of powder in a liter of water.

Method 2 – saline solution

Another available preservative is regular table salt. A solution of a teaspoon of salt in a liter of water will also protect the apple slices from darkening. You need to soak them in water with salt for several minutes, and then rinse thoroughly with clean water to wash away the salty taste. It is important here not to over-soak the apples in water so that the salt does not penetrate too deeply into the pulp.

Method 3 – carbonated lemonade

Sweet carbonated drinks always contain citric acid. If you soak apple slices in soda for 3-4 minutes, they will remain fresh and attractive for several hours.

You can rinse the apples after processing or leave a light layer of soda on them, which will add extra flavor and aroma to the slices.

Method 4 – freshener for cut fruits

Some supermarkets sell a special powder to combat the darkening of cut fruits. It consists of a mixture of ascorbic and citric acid, and you can prepare it yourself. Buy glucose tablets with ascorbic acid at the pharmacy, grind them into powder and mix with citric acid. Sprinkle a small amount of the mixture onto the slices and mix well to distribute the powder evenly.

Method 5 - blanching

In order to stop the oxidative process, apples can be blanched, i.e. Place in boiling water for a few minutes. For soft apples, one or two minutes in boiling water is enough, you can hold it a little longer. However, this method is not suitable for sliced ​​apples, which are intended to be served, as the apples will become too soft and slightly change the taste.

But if the slices are used as a pie filling or used as a salad component, blanching will be the best option. After removing the apples from the water, they need to be thrown into a colander and doused with a cold stream, and then the water should be allowed to drain.

Method 6 – cling film

If you cut half a large apple and want to save the other half “for later,” wrap it as tightly as possible in cling film to block air access and put it in the refrigerator. If everything is done correctly, the apple cut will remain fresh for 24 hours.

Instead of cling film, you can use a plastic bag with a zipper. After putting half an apple in it, carefully squeeze out the air and fasten the bag.

Method 7 – rubber band

This method is suitable for those who take a sliced ​​apple with them to school or the office. The washed apple must be cut into slices, removing the core, and then folded these slices together to form a whole apple again.

Now you need to carefully tighten the slices with an elastic band so that they do not fall apart and put them in the bag. After removing the cutter, the slices will be fresh, white and juicy, as if they had just been cut.

The world around us is amazing. And if children understand this easily, then with age they get used to many things and easily forget about it. As a result, the most simple questions a baby can confuse an adult. For example: “Why does an apple turn dark when 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 why an apple turns dark when cut, they hear that this is due to the iron it contains. It is also known from the school chemistry course that iron has a valency (or oxidation state) of +2 and +3. So, in apples it has the first. However, after cutting, it begins to actively come into contact with the air, which contains oxygen. As a result, iron is oxidized to degree +3, thereby forming an oxide. It turns out that the apple simply “rusts”. And the color takes on the appropriate one.

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 really enough to ruin the appearance of a whole fruit? Of course not. In fact, completely different substances are responsible for this. After all, this happens with both pears and bananas. But they don't have that much iron.

The real reasons

So, why does an apple turn dark when cut if it contains virtually no iron? After damage to the fruit, a number of chemical reactions occur, due to which it loses its presentation. But if you trace the entire chain, you can still understand the true reason.

As you know, apples, like any other fruit, are rich in antioxidants. From a chemical point of view, they belong to the group of polyphenols. They have various names, but their essence is the same - it is a combination of different phenols (not to be confused with poison). Of course, this substance itself does not affect the color of the apple in any way, since it is simply colorless. But it also contains the enzyme polyphenol oxidase, 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 apples in huge quantities, and it is a strong oxidizing agent. This is the correct answer to the question of why an apple darkens when cut.

How to fight?

Of course, many people do not like this property of apples. Fruits quickly lose attractive appearance, and even fresh cuts begin to look not very attractive in just a couple of minutes. Chefs have long come up with their own way to combat this disadvantage. To do this, just wipe the cut with lemon peel or sprinkle with lemon juice. Another option is to immerse the fruit in a citric acid solution for 1-2 minutes. As a result, the apple does not darken when cut.

Another option has been invented for apple juice. To do this, it is simply pasteurized for 20-30 minutes at 70-80 degrees. As a result, polyphenol oxidase is destroyed. This means that it is no longer possible to start the oxidation process in principle. Unfortunately, this method is not suitable for whole apples.

Scientific approach

Obviously, by 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, they are believed to be beneficial for the body. And the first thing we managed to achieve was to exclude oxygen from the reaction. To do this, apples are coated with a special wax-like substance (according to the international standard, it is marked E901-E913). However, before eating such fruits, it is advisable to wash off the coating.

But science does not stand still. After all, it has long been known why an apple darkens when cut. The presentation of a new genetically modified variety proved that by removing the oxidizing enzyme, you can simply get “eternal” apples. An excellent solution for supermarkets and restaurants. Moreover, this only required blocking some genes. It is believed that this technology is the most harmless.

When we cut an apple or peel it, it darkens. This process is triggered by the presence of an enzyme in the fruit called polyphenolic oxidase (ascorbic acid oxidase). This enzyme causes browning through the interaction of oxygen and the tannin substance found in apples.

Why does an apple darken when cut: the answer to the question

When a fruit is cut, the cells that are located directly on the cut immediately begin to interact with oxygen. Ascorbic acid oxidase causes the surface of the apple to change color when exposed to oxygen.

The fruit turns brown when exposed to air due to an oxidation process. The peel of an apple protects it from the oxidation process. But as soon as you make a cut on the fruit, its flesh immediately begins to oxidize and within a few minutes the apple turns dark.

It is interesting to know that the rate of oxidation is affected by temperature. For example, if you put a peeled apple in the refrigerator, it will only darken after a few hours or even a day. If you place the fruit in a hot oven, it will turn brown in a few minutes.

By the way, sour varieties darken faster than sweet ones. This is due to the fact that they contain more of the oxidase enzyme. For example, the Granny Smith variety retains a light shade on the cut longer than other varieties.

To prevent apples from darkening when slicing: life hack

If you need to prepare sliced ​​fruit, you are probably wondering how to prevent browning and ensure that the apple retains beautiful colour and juicy appearance.

Vitamin C will come to your aid , it is found in citrus juice. Simply brush the cut side of the apple with orange or lemon juice. Vitamin C prevents the tannin substance from interacting with oxygen, thus preventing browning. Keep in mind that when sprinkled with citrus juice, the apple will be sour.

If you don't want the apples to be sour, sugar syrup will save them from browning. We prepare it according to the standard recipe, then dip into syrup or brush the cut slice with it. This method not only protects against browning, but also gives the fruit a sweet taste.

If you don’t have citrus juice or sugar syrup on hand, citric acid will come to the rescue. Add to cold water 1/4 tsp. citric acid, stir until dissolved, then immerse the fruit for 10 minutes.

Sweet soda - it contains sugar and citric acid, they will prevent oxidation processes. Just sprinkle the cut of the fruit with sweet soda, you don't need to do anything else.

If you take an apple with you

This method is suitable for those cases when you need to take a whole cut apple on a trip, to work or school . We cut it into two halves and take out the core, then put them together again and tie them with a rubber band. We pack it in a bag.

Now you know why the cut of an apple turns dark. If you want to keep it fresh and beautiful, use our simple life hacks.