Why do peeled apples change color?

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 in these plants. For example:

Polyphenols, catechols, etc. That is, the color change reaction turns yellow, and as the amount of reaction increases, the color gradually deepens, and finally turns dark brown. The oxidation reaction occurs due to the contact with oxygen in the air and the release in the cells.

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. When apples change color, the amount of vitamin C will decrease, affecting the nutritional value. To prevent the apple from changing color after cutting, the best way to keep it out of contact with the air is to soak the apple in salt water.

Let the cut apples not change color, the cut apples will quickly dull in color, affecting the appearance, is there any magic trick to change? It's as simple as dripping lemon juice on the cut side of the apple, which not only does not change color, but also retains the original flavor. In addition, some fruits that are easy to change color can also be treated in this way, and the effect is excellent!

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.

This is also the case for apples and pears, as well as some vegetables (such as potatoes and eggplants). 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.

The best way to prevent this is to rub the skin with salt before peeling the apples, then wash them off, and then peel the apples again, so that the peeled apples will not oxidize, and they will last longer than soaking them in salt water after peeling, and they will not have a salty taste. <>

In fact, apples can be eaten after peeling and changing color, although the taste is a little different from the product, except for the loss of nutrients, there is no unhealthy substance, so you can still eat with confidence, if you really feel awkward, you can go to another layer of skin, the flesh inside is still fresh. Apple flesh contains an organic substance that tannins. When peeling with a knife, the tannin in the apple flesh reacts with the iron of the blade to produce a black ferric tannin that covers the surface of the apple.

In addition to tannic acid, apples also contain an oxidase enzyme. When the skin of the apple is peeled, the air meets the pulp, and under the catalysis of oxidase, the organic matter in the pulp is oxidized and discolored, so the peeled apple also changes color. <>

Because oxidation takes place in the air.

The reason is that the apple flesh itself contains the organic substance of tannin, and when you peel the apple with a knife, the tannin substance in the apple flesh reacts with the iron substance in the knife, and a black iron tannin appears on the surface of the apple flesh. Moreover, it is also because of the oxidation that occurs in the air. The apple itself contains oxidase, and after peeling, the apple flesh is exposed to the air, which makes the oxidase in the apple flesh change, so this is the reason why the apple will change color after peeling.

1.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.

2.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.

How do you peel apples and keep them 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.