Insights into the reasons for lower digestibility of buckwheat-based foods: The structure-physical properties of starch aggregates

Abstract

To elucidate the lower digestibility of buckwheat starch-based foods, tartary buckwheat starch (TBS) and common buckwheat starch (CBS) were treated by different hydrothermal temperatures, cooling, lyophilization and micronization, and wheat starch (WS) used as reference. The in vitro digestibility, thermodynamic properties, particle-size distribution and texture of starches were measured. According to the structural evolution of starch during the processing, the reasons behind a lower digestibility of buckwheat starch were investigated. At hydrothermal of 25 °C, a significantly higher digestion rate was observed for TBS and CBS as compared to WS, due to smaller granule size of buckwheat starches (BS). At 65 °C, the digestion rate of BS was lower than that of WS, because the more intact crystalline structure was retained in BS due to its higher gelatinization temperature. At 100 °C, in the initial phase, CBS (38.70%) and TBS (53.13%) displayed a lower digestible fraction compared to WS (59.12%), probably as BS had a higher tendency of aggregation during gelatinization-cooling process, thus the BS are more difficult to be micronized. Overall, the formation of denser aggregates during gelatinization-cooling process was proposed to illustrate the relatively lower digestibility of BS.