Effect of ethanol addition on the physicochemical, structural and in vitro digestive properties of Tartary buckwheat starch-quercetin/ rutin complexes

The effects of ethanol on the physicochemical, structural and in vitro digestive properties of Tartary buckwheat starch-quercetin/rutin complexes (e-TBSQ and e-TBSR) were investigated. Ethanol restricted the gelatinization of Tartary buckwheat starch (TBS), which resulted an increase in Delta H, G' and G" as well as a decrease in apparent viscosity of e-TBSQ and e-TBSR. The particle size, scanning electron microscopy and X-ray diffraction results showed that ethanol influenced the morphological structure of TBS granules and the starch crystalline structure in e-TBSQ and e-TBSR changed from B-type to V-type when the ethanol concentration was 25%. Saturation transfer difference-nuclear magnetic resonance results revealed that ethanol weakened the binding ability of quercetin/rutin to TBS in e-TBSQ and e-TBSR, leading to a change in the binding site on the quercetin structural unit. The residual ungelatinized TBS granules in e-TBSQ and e-TBSR induced a high slowly digestible starch content, and thus displayed a "resistant-to-digestion".