Comparative Study on the Behavior in Solution and Thermal Character of Starch in Transgenic Potato with AGPase Effects of the Ratio of Purple Sweetpotato Flour on the Properties of Sweetpotato Starch and Starch Noodle Fusion of the Fragments cDNA from Potato Starch Synthases and Construction of the Plant Expression Vector The Effect of Repeated Gelatinization and Retrogradation Treatments on Structure and Physicochemical Properties of Sweet Potato Starches The Study of Correlation Between the Physicochemical Properties of Starch From Different Sweet Potato Varieties and the Quality of Its Starch Noodle