How to keep a cut apple from browning. We answer questions. Why does an apple turn dark when cut? What to do to prevent apples from turning brown
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 simplest questions from a child 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 different names, but their essence is the same - they are 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 their attractive appearance, and even freshly cut fruits 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 darkens.
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 its beautiful color 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 1/4 tsp to cold water. 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.
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 slicing: 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 cuts: 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 sprinkled with 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, since 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 sliced apples with them to school or the office. The washed apple needs to be cut into slices, removing the core, and then folded into these slices 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 simplest questions from a child 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 different names, but their essence is the same - they are 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 their attractive appearance, and even freshly cut fruits 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.
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.
Use carbonated drinks. Carbonated drinks containing citric acid can also prevent apples from browning. Lemonades infused with lemon or lime and ginger ale are the most popular options for soaking apple slices.
Use fruit freshener. It is a powdered mixture of citric and ascorbic acid that is specially formulated to prevent fruits from browning. The manufacturer claims that the product will protect fruit for up to 8 hours. You can find the powder in the canned food section of most grocery stores.
Blanch the apples. You can blanch the apple pieces to prevent them from browning. Blanching disables the enzymes in the apple and prevents it from reacting with oxygen in the air. Simply place the apples in a pan of boiling water for about 5 minutes, then remove and rinse with cold water.
Wrap in plastic wrap. This is a very simple way to prevent apples from oxidizing; simply wrap the cut piece in plastic wrap. This method helps, since the film protects the apple from air penetration, and therefore from oxidation. Try to wrap the apple as tightly as possible, without creases in the plastic wrap where it meets the cut on the fruit.
- This method is best used with half an apple rather than slices, as it will be easier for you to wrap one piece in cling film.
- Remember, if air remains under the film, the apple will begin to oxidize. Since it is quite difficult to completely remove air from under the film, this method is not the most effective.
Many housewives know that cutting apples in advance is problematic - they can lose their original attractive appearance. What can you do to prevent apples from turning dark? How to work around this problem. Let's figure it out - the tips have been tested by experienced chefs.
A way to prevent green fruit from changing color
When exposed to air, cut apples quickly begin to darken. To prevent this from happening, before you start cutting apples, pour water into any bowl and squeeze lemon juice into it. For 2 glasses of water – 2 tbsp. spoons of freshly squeezed lemon juice. Cut the apples into as many pieces as you need for the recipe. Place each slice immediately into prepared water with lemon juice. Before cooking, drain the apples in a colander.
Apple peels contain many beneficial substances. If previously no one thought about whether to peel apples or not, now, when apples are treated with various chemicals on top, this question has become a problem.
The choice here is up to each of us. If someone is willing to risk receiving a dose of chemicals from the skin of apples at the same time as a dose of nutrients, then the peel does not need to be peeled. If someone is not ready to take such a risk, then the peel should be peeled. However, in both cases, the apples need to be washed well.
Unfortunately, when preparing purees, compotes, preserves, jams and even apple juices, apples lose a huge amount of nutrients. It has been proven that only 10% polyphenols and 3% catechins remain in apple juice. However, if you put a whole apple in a blender, the resulting juice will retain all the beneficial substances. Unfortunately, this method of preparing apple juice is not used in industry. Therefore, it is better to cook it at home.