Raw sweet potatoes are green: this is a sign of germination. The green ones on sweet potatoes can be eaten as long as they are removed and cooked, and there will be no poisoning symptoms. After the sweet potato turns green, it not only tastes bad, but also loses its edible value because of the massive loss of nutrition and water. Sweet potato is a nutritious food and can also be used as a diet therapy for many diseases. If the skin is brown or black, it can't be eaten because it is polluted by Alternaria alternata. The toxin discharged by Alternaria alternata contains sweet potato ketone and sweet potato ketone alcohol, which makes sweet potato hard and bitter and highly toxic to human liver. Although this toxin is boiled and baked, its biological activity will not be destroyed.

The cooked sweet potato turns green: it is the browning of starch. Sweet potato contains oxidase, which will change color when exposed to oxygen, and starch will turn black when exposed to iron, so it will appear green. This discoloration does not affect eating. Before use, make sure that the ingredients are not polluted, rotted or deteriorated.