Why do cut fruits and vegetables change color?

Why do cut fruits and vegetables change color?

Some fruits and vegetables will change color after being cut, which is related to their composition. Fruit, water chestnut and lotus root all contain a substance called tannic acid. When the iron knife comes into contact with tannic acid, it will produce a black substance called iron tannic acid. After the skin of the fruit is knocked off, it will change color after a long time. This is because fruit also contains a substance called oxidase. When it comes into contact with oxygen in the air, it will produce a new substance, which will discolor the fruit.