2. Lemon is rich in citric acid, so it is called "citric acid warehouse". Because of its sour taste, it can only be used as a high-grade condiment to prepare drinks, dishes, cosmetics and drugs. Lemon sauce is one of them. Lemon is one of the most medicinal fruits in the world. It is rich in vitamin C, sugar, calcium, phosphorus, iron, vitamin B 1, vitamin B2, nicotinic acid, quinic acid, citric acid, malic acid, hesperidin, naringin and coumarin, high in potassium and low in sodium, which is very beneficial to human body.