Structural and functional properties of starches from root tubers of white, yellow, and purple sweet potatoes

Sweet potato is an important starch resource and has different colored root tubers due to different genotype backgrounds. However, it is unclear whether starch properties are related to the color of root tuber. In this study, 3 white, 3 yellow, and 3 purple sweet potato varieties were planted in the same environment. The dry root tubers of white varieties had the highest starch ranging from 61.5 to 67.5% and the lowest soluble sugar ranging from 13.1 to 18.0%, and those of yellow varieties had the lowest starch ranging from 45.8 to 53.1% and the highest soluble sugar ranging from 28.9 to 31.5%. Starches from different varieties had different granule sizes (D[4,3] 12.3-18.1 mu m) and amylose contents (24.1-27.2%), but all exhibited C-A-type crystalline structure. The relative crystallinity ranged from 22.3 to 25.5%, and the IR absorbance ratios of 1045/1022 and 1022/995 cm(-1) ranged from 0.665 to 0.775 and from 0.846 to 0.944, respectively, among 9 varieties. The starches from the same or different colored varieties had differences in swelling power, water solubility, gelatinization temperature, pasting viscosity, and digestion properties. The cluster analysis based on starch property parameters indicated that starch properties of sweet potato had no relationship with the color of root tuber but were determined by the genotype background of variety.