Physicochemical and structural properties of different colored sweet potato starches

Physicochemical and structural properties of starch from orange- and purple-fleshed sweet potatoes were investigated and compared to those of typical white-fleshed sweet potatoes. Slight differences were found in the proximate composition and amylose content of the starch from colored sweet potatoes. Scanning electron microscopy results showed that the sweet potato starch granules were round and polygonal. The average granule size of the starch isolated from orange-fleshed sweet potatoes was higher than those from white- and purple-fleshed sweet potatoes. X-ray diffraction patterns demonstrated that all the starch samples exhibited C-type crystallinity near A-type. The swelling power and solubility of starch from orange- and purple-fleshed sweet potatoes were greater than those from white sweet potatoes. Differential scanning calorimetry showed that the enthalpy of starch from white sweet potatoes was greater than that of the other types of sweet potato. Starch from different colored sweet potatoes exhibited somewhat different RVA pasting properties. Structural analysis such as molecular size distribution and branch chain length showed minimal structural differences among the starch samples from colored sweet potatoes.