Why do peeled apples turn yellow after being left for a while

was oxidized. When the apple is peeled or cut and left for a while, the color of the cut surface will change from light to dark and finally dark brown.

The discoloration reaction occurs mainly due to the presence of phenolic compounds in these plants. For example: polyphenols, catechols, etc.

Phenolic compounds are easily oxidized to quinones, that is, they change color and turn yellow, and the color gradually deepens with the increase of the amount of reaction, and finally turns dark brown. The oxidation reaction occurs due to the contact with oxygen in the air and the release of phenol oxidase in the cell.

Phenolic oxidase exists in organelles and cannot come into contact with phenolic compounds until the tissue is damaged, and oxygen in the air cannot enter, so no oxidative discoloration reaction occurs. When the cell tissue is damaged, phenol oxidase is released to contact with phenolic compounds, catalyzing the oxidation of phenolic compounds, coupled with the action of oxygen in the air, a discoloration reaction will occur. Among them, polyphenols can be directly oxidized to quinones and change color.

Catechol molecules, on the other hand, polymerize under the action of phenol oxidase. Two catechol molecules are linked together to form catechol dimers, which in turn can be joined in pairs to form tetramers. The individual catechol molecules and their dimers and tetramers are all colorless, but catechol tetramers can form multimers, which are purple.

So the more polymers are formed, the darker the color of the incision surface will be.

It is oxidized to produce alcohol (ethanol).

You don't eat and are eaten by the air.

Whether the apple is cut or the skin is peeled, the problem of discoloration can easily occur as long as the apple flesh is exposed to the air. This is because apples contain some phenolic substances that, under the action of enzymes, can easily oxidize with the air to produce new substances. The appearance of this substance causes the apple flesh to begin to change color.

Peeled apples are exposed to air, so they undergo an "oxidation" reaction. The specific reaction can be shown in the figure below, that is, some phenolic substances will react with oxygen under the catalytic action of PPO to form quinones - the so-called PPO is phenol enzyme (polyphenol oxidase), and this quinone substances gather together to react to form melanin. These melanin pigments are responsible for the yellowing of apples.

Please click Enter a description.

Please click Enter a description.

If the apples are peeled and stored for a longer period of time, the color of the apples will be darker because the oxidation reaction time of apples will be longer, which will not only cause the apples to change color but also affect the nutrients in the apples, especially a type of methanol and malic acid, which will make the apples sour, taste bad, and may eventually go bad, so apples should be consumed as soon as possible after peeling.

Please click Enter a description.

Please click Enter a description.

Extended Information: How do you keep apples peeled overnight? First of all, apples need to be soaked in cold water for a period of time, not too long, and then quickly put the apples into the cold compartment of the refrigerator, which can effectively ensure the freshness of the apples and reduce the possibility of oxidation of the apple pulp.

Apples must be eaten in time after peeling, otherwise, apples will not only spoil, but also affect the nutritional value of apples. And to prevent apples from turning yellow, it's as simple as letting this catalyst fail. As for enzymes, anyone who has studied high school biology knows that it is actually a protein, so it is very sensitive to the reaction environment.

As long as the pH level of the apple's surface changes even slightly, the enzyme will not work. So to prevent apples from discoloring, you can simply apply soda (alkaline) or lemonade (acidic) to the surface of apples. The picture below shows what an apple smeared with soda and lemonade looks like after a day, and as you can see, there is almost no discoloration.

Of course, the process of yellowing apples itself does not produce substances harmful to the human body, but apples exposed to the air for a long time will cause the apples' moisture to evaporate, decay, etc., so eat the cut apples quickly and don't leave them for too long.

Please click Enter a description.

Please click Enter a description.

Why do apples turn yellow when they are cut.

When apples are peeled, the phenols in plant cells are oxidized with the air under the action of phenols, producing a large amount of quinones. The new quinones can cause plant cells to turn brown rapidly, a change called enzymatic browning of food. So apples will change color after peeling and leaving them for a while.

Can you still eat apples when they are yellow.

Apples can be eaten when they turn yellow.

Apples are indeed easy to turn yellow, many people will find that some places have begun to turn yellow while eating, apples are yellow because of the oxidation reaction between the oxidase in the apple and the oxygen in the air, so it will change color, but the apple at this time does not produce toxic substances.

How long can you not eat apples when they are cut.

From a nutritional point of view, it is best to eat the cut apples on the same day and not until the next day.

If the cut apples are peeled, diced, soaked in salt water and refrigerated, half of the nutrients will be lost after eating them the next day. In half of the cases, the larger the area of the cut fruit that comes into contact with the air, the more nutrients are lost, and the taste deteriorates.

1.In the process of growth and development, if the apple does not get relatively sufficient nutrients and water, it is likely to lead to the lack of nutrients in the apple, making the apple yellow, and if the potassium in the soil is too high, it may also make the apple yellow.

2.If the apples continue to be in a hot state in the autumn, then the apples are likely to enter the ripening period early, but if the growers still pick the apples at the normal time, it is likely to cause the problem of yellowing of the apples.

3.Apples are a kind of food that is easy to be oxidized, because apples contain some phenolic substances, which are particularly easy to oxidize with oxygen in the air under the action of enzymes, and will produce a substance called kun, which is likely to make apples yellow, so usually after we peel apples, apples will slowly begin to turn yellow.

Peeled apples tend to turn yellow because the vitamin C in apples is oxidized and deteriorated by oxygen in the air.

Peeled apples tend to turn yellow because when the skin of the apple is peeled off, it has no protective effect. And some of the fructose in apple pulp is easily oxidized. So it's easy to turn yellow.

Peeled apples are easy to turn yellow, mainly because there is no outer protective layer after the apple is bloody, and the same is true for apples that peel any fruit in the air that will turn yellow. If you want the best apples, not yellowing, the best way is to wrap them in plastic wrap, which can effectively prevent the apples from yellowing.

Because it will oxidize when it encounters oxygen, it will turn yellow after oxidation, so this is very normal, and after oxidation, the original apple will be oxidized.

Peeled apples turn yellow because the flesh of the apples loses the protection of the skin and is oxidized in the air after peeling.

After the apple is peeled, the skin will be lost, so that the pulp will be oxidized with oxygen in the air and will turn yellow and black, the fundamental reason is because there is, oxygen is aerobic oxidation, if you shave the apple and put it in the water, because there is less oxygen in the water, it will turn yellow and black, if it is placed in a vacuum, it will not turn yellow and black, because there is no oxygen in the vacuum.

Peeled apples are easy to turn yellow, this is mainly because Xiao good apples are exposed to the air and are easy to be oxidized by the air, in fact, similar phenomena are not only in apples, just like our peeled potatoes, there will also be similar phenomena, which are a common phenomenon and reaction in this kind of fruits and vegetables.

Without the protection of the peel, oxidation occurs when the pulp comes into contact with the air, so apples are prone to yellowing! If you don't want to eat the peeled apples directly, or if you don't finish them all at once, you can seal them with plastic wrap so that the apples don't turn yellow! Without the protection of the peel, oxidation occurs when the pulp comes into contact with the air, so apples are prone to yellowing!

If you don't want to eat the peeled apples directly, or if you don't finish them all at once, you can seal them with plastic wrap so that the apples don't turn yellow!

In fact, after you peel the apple, the inside will be easy to yellow, which means that you have actually begun to oxidize.

Peeled apples are easy to turn yellow because apples are prone to oxidation when they come into contact with air after peeling, just like us, if they are not well protected, they will become senile.

Reason for discoloration: Although the fruit is picked, but its internal metabolic activities have not stopped, various enzymes are still "working", when they are peeled or peeled, a polyphenolic chemical contained in their body——— tannins, will be under the action of enzymes, and the oxygen in the air will have a chemical reaction to produce quinone compounds, and the color of the food will also turn brown. Losses:

The first is the sensory influence, the color and taste of the food are not as good as before the discoloration, which affects the desire to eat; The second is that the nutritional value is affected, and it is conceivable that when the "discoloration" reaction is underway, some other nutrients will also be oxidized, with vitamin C being the most severely lost. Prevention: Apples are easy to change color after cutting or peeling, and they will not change color if they are soaked in lemonade.

Be careful that the lemonade should not be very strong. It is also fine to soak in salt water, but the apples will be a little soft after soaking, so it is best to soak them in lemonade.

Oxidized.

Apple flesh contains an organic substance called tannin. It comes into contact with the knife used to peel apples, resulting in a black iron tannins that coats the surface. Apples also contain an oxidase, which is catalyzed by the oxidase when air meets the pulp.

However, the discolored apple flesh does not affect consumption. Other nutrients do not oxidize in the air and can still be used by the body.

Soaking apples in salt water will not change color because the oxidase enzyme becomes inactive.

This is because the iron in the apple comes into contact with the air and oxidizes.

1. When the apple is peeled, the phenolic substances in the plant cells will be oxidized with the air under the action of phenolase, producing a large number of version quinones. Neonatal quinones can cause plant cells to turn brown rapidly, a change called enzymatic browning of food. So apples will change color after peeling and leaving them for a while.

Not only apples, pears and some vegetables.

2. This is also the case (such as potatoes, eggplants, etc.). This browning affects the appearance of the food, reducing the nutrient content of the outer layer, but it is still edible. If the apple is left for a long time after peeling, the oxidative decomposition of plant cells in the air is intensified, the nutrients in the outer layer of the apple are decomposed more, and the pectin substances are further decomposed into pectin acid and methanol under the action of enzymes, making the flesh loose, moist, discolored, tasteless, and even rotten and deteriorated.

If you don't eat it for a long time, it will oxidize.

The reason why apples turn yellow when cut is because the cut area has an oxidation reaction with the air.

In fact, this is because there are phenolic compounds in apples, such as polyphenols, catechols, etc., these phenolic compounds are easily oxidized into quinones, that is, these discoloration reactions occur, with the extension of time, the amount of reaction will gradually increase, and the corresponding color will gradually deepen, and the oxidation reaction refers to the release of phenol oxidase after contact with oxygen in the air.

When the apple is not cut, the phenol oxidase cannot come into contact with the phenolic compounds, so there is no oxidative discoloration reaction, and when the apple is cut, the phenol oxidase in the cell is released, and then there is contact with the phenolic compounds, which catalyzes the oxidation of the phenolic compounds, and then the color change reaction occurs.

The polyphenols in apples can usually be directly oxidized to quinones to produce discoloration, while catechols are polymerized under the action of phenol oxidase, for example, two catechol molecules will be linked together to form catechol dimers, and then dimers can be combined in pairs to form tetramers, and catechol molecules and dimers and tetramers are colorless, but tetramers can be resynthesized into polymers, and the polymers are purple, so when there are more and more polymers, The area that is cut will become darker and darker.

However, it is important to understand that after apples change color and yellow, the content of vitamin C will decrease, and if you want to prevent the discoloration of cut apples, you can soak cut apples in lightly salted water.

Apples themselves have high nutritional value, contain a variety of minerals and vitamins, and are also rich in calcium, which can help metabolize excess salt in the body, and the nutrients in apples are very soluble and very easy to be absorbed by the body. The magnesium, pectin, vitamin C, etc. in apples can help remove toxins from the body and make ** more moist and shiny.