Purple sweet potato is rich in red pigment,is an important source of new pigment. Its main component is acylation anthocyanins,with a clear anti-oxidation.The red pigment extracted from it, color bright, suitable for a variety of acidic foods. In acidic conditions, it shows red, in the neutral conditions, it shows purple, in the Alkaline conditions, it appears blue. Soluble in water, acetic acid, ethanol, not soluble in oils and fats.