Comparative susceptibilities to alkali-treatment of A-, B- and C-type starches of Dioscorea zingiberensis, Dioscorea persimilis and Dioscorea opposita

The effect of alkali-treatment for 0, 15, and 30 days at 35 °C on amylose content, morphological properties, crystalline properties, swelling power, solubility, absorbance spectra and in vitro digestibility of starches from Dioscorea zingiberensis, Dioscorea persimilis and Dioscorea opposita were investigated. The amylose content of all the three starches decreased after 15 days of alkaline treatment and then increased after 30 days of alkaline treatment. There were similar changes in relative crystallinity for D. zingiberensis and D. persimilis starches. It was observed that the three starches displayed a reduction trend in swelling power with a significant increase in solubility. Adhesion among some of the starch granules was observed after alkali-treatment for 30 days in D. zingiberensis and D. opposita starches, while D. persimilis starch showed some hollows on the granule surface. The rise in the absorbance ratio of 1047/1035 and 1047/1022 cm−1 from FT-IR was observed during alkali-treatment for D. persimilis and D. opposita starches. Alkali-treatment elevated the in vitro digestibility with resistant starch values climbing up from 50.16% to 64.95% and from 66.14% to 70.74% for D. zingiberensis and D. persimilis starches, respectively, but there was no significant change in resistant starch value for D. opposita starch.