Onion contains a lot of flavones. When flavones meet metals such as iron, aluminum and lead, they produce complexes of different colors, such as blue, blue-black, brown and so on. Therefore, when cutting vegetables with an iron knife, or frying onions in an iron pan or aluminum pot, the color of the finished vegetables is dark and not bright.

Dip some dry flour and stir well before frying, which can prevent flavonoids from changing color by direct contact with metals such as iron and aluminum.

Chemical reasons:

It will only be oxidized after high temperature. The oxidized green color is not good for your health. Try not to eat it.

So it is recommended not to eat it.