A method for preparing a purple sweet potato concentrate that is free from starch, rich in anthocyanins, phenolic compounds, minerals, and soluble dietary fiber with low viscosity, attractive color, and with natural sweetness is presented. The method first prepares and liquefies the purple sweet potatoes and fixes the colorization by adjusting the pH value. Next, amylase and an enzyme complex of hemicellulase, pectinase, cellulase, glucoamylase and protease are added in sequence under conditions effective to produce the juice with the above mentioned properties. The juice is then centrifuged and membrane-filtered to produce a purified purple sweet potato juice which is vacuum-concentrated to yield a purple sweet potato concentrate. Purple sweet potato powder can be obtained by vacuum drying the sediment and concentrate mixture.
