1. Flour contains trace amounts of flavonoids. These antioxidant substances are usually almost colorless, but once they are in an alkaline environment, they will show a bright yellow color. Therefore, if the noodles turn yellow after cooking, it is likely that alkali has been added.

2. Yellow noodles have no harmful effect on the human body, but the vitamin content will decrease. Because flour is originally a good source of B vitamins, once alkali is added, these vitamins will be rapidly decomposed and dissolved in alkaline water when heated, and the vitamins will be almost completely lost.