Physicochemical properties and in vitro digestibility of hydrothermal treated Chinese yam (Dioscorea opposita Thunb.) starch and flour.

The objective of this study was to investigate the effects of hydrothermal treatments (heat-moisture treatment (HMT) and annealing (ANN)) on the physicochemical properties and in vitro digestibility of yam starch and yam flour. Hydrothermal treatments decreased the pasting properties of yam starch and yam flour. Compared with yam starch, HMT significantly (p < 0.05) reduced the pasting viscosities of yam flour. Both HMT and ANN caused an increase of the gelatinization temperatures (To, Tp, and Tc) and a decrease of enthalpy (△H). The increasement in ratio of 1047/1022 cm-1 and 995/1022 cm-1 suggested that HMT and ANN resulted in an increase in short-range order. The crystalline pattern of all samples was still A-type, and HMT yam starch exhibited higher crystallinity (26.20%). The most significant inhibition of in vitro digestibility was found in HMT yam flour, with slowly digestible starch and resistant starch contents increasing by 3.73% and 4.40%, respectively. Hydrothermal treatments made the no-starch ingredients in yam flour agglomerate and adhere to starch granules. Confocal laser scanning microscopy showed that the starch being coated or embedded by protein was a possible reason for the differences in physicochemical properties and in vitro digestibility between yam starch and yam flour.