Why do apples change color? As the title suggests, thank you

Apples contain an oxidase, when the apple peels off the skin, the air meets the pulp, and the organic matter in the pulp is oxidized and discolored under the catalysis of oxidation.

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.

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.

Because apples contain iron, when the skin is exposed, the iron oxidizes and changes color!

After the apple is peeled, the phenols in the 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 do this is to rub the skin with salt and wash it off before peeling the apple.

Peel the apples again. Peeled apples like this.

Not only will it not oxidize.

And it can be stored longer than soaking in salt water after shaving.

And there is no saltiness.