Apple is rich in iron, so if the pulp is left in the air for a while, it will undergo oxidation reaction and form iron oxide, which is yellow. Everyone has seen rust. If it is oxidized for a long time, or if the apple is broken and placed, it will turn into a red rust color. The white pulp turns reddish brown in the blink of an eye, is it still a little magical?
Of course, the discoloration of apples is not only caused by iron. Both apples and pears contain phenols. When the apples or pears are half eaten, the phenols in pulp cells will combine with oxygen in the air under the action of enzymes to form quinones, that is, oxidative discoloration reaction. The longer it is left, the more quinones there are, and the darker the color will be, gradually changing from khaki to reddish brown.
In fact, not only apples and pears, but also many vegetables and fruits will have this phenomenon. For example, potatoes, eggplant and even blackened lotus roots are all caused by oxidation. However, although the color has changed after oxidation, and the nutrients have been lost, it can still be eaten, but the taste has become very different. Therefore, it is recommended that peeled and cut vegetables and fruits should be used or cooked as soon as possible.
Isn't nature amazing? It gives us a lot of food, gives us a lot of surprises, and there are many very interesting phenomena. Oxidation is actually only the most common phenomenon. If you can't finish eating the fruit after cutting it for a while, you can pack it with plastic wrap and put it in the refrigerator to minimize air contact, which can also delay oxidation.