Morphology, structure and in vitro digestibility of starches isolated from Ipomoea batatas (L.) Lam. by alkali and ethanol methods.

The tubers of Ipomoea batatas was one of the main sources of starch. This work aimed to assess the effect of extraction methods (alkali method and ethanol method) on the structural and physicochemical properties of Ipomoea batatas starches. The amylose content ranged from 10.18% to 13.35% for starches and from 5.63% to 7.61% for flours compared with isolated starches. I. batatas flours possessed greater water-binding capacity than their starches, but the difference was not significant. Scanning electron micrographs revealed that the I. batatas flour granules were attached to surrounding small particles and fragments, which gathered to form oval clusters. The starches all showed typical C-type X-ray diffraction patterns with the flours' CB-type. The predicted glycaemic index was relatively low, ranging from 59.30 to 79.88 for flour, which is available for functional food. Principal component analysis showed that the three principal components explained 90.71% of the total variation. The flours and starches were divided into three groups according to their properties. Most starches isolated with the ethanol method received higher scores than those isolated with the alkali method. It is possible to conclude that the isolation method exerted a marked effect on the starch properties and on in vitro starch digestibility.