Optical, rheological, thermal, and microstructural elucidation of rutin enrichment in Tartary buckwheat flour by hydrothermal treatments.

Tartary buckwheat grains were subjected to hydrothermal treatments (steaming/boiling/autoclaving) whose effects on rutin enrichment in the buckwheat flour by rutin migration from the bran fraction were investigated in terms of optical, rheological, thermal, and microstructural properties. The highest amount of rutin was observed in the bran out of the native milling fractions (hull, bran, and flour). The hydrothermal treatments however increased the level of rutin in the flour, even showing a higher level of rutin than the bran in the autoclaved sample. Furthermore, rutin in the hydrothermally-treated flours was not degraded into quercetin by mixing with water. Scanning electron microscopic images demonstrated that the granules of buckwheat starch round in shape and grouped in lumps were disrupted by the hydrothermal treatments. The rutin contents of the buckwheat flour samples were linearly well-correlated with their pasting profiles (peak viscosity), colors (L and b values), and thermal parameters (gelatinization enthalpy and temperature).