Simultaneous quantitative analysis of quercetin and rutin in Tartary buckwheat flour by Raman spectroscopy and partial least square regression

Structurally similar molecules, such as rutin and quercetin, were simultaneously characterized by Raman spectroscopy and multivariable analysis. The Raman spectra of quercetin and rutin in ethanol solutions at several concentrations were measured to develop the partial least square (PLS) model. The predicted concentrations obtained by the Raman and PLS analyses agreed with the actual concentrations. Thereafter, this method was applied to analyze Tartary buckwheat flour, which contains rutin and quercetin. Two Tartary buckwheat flour samples were employed: one was washed with water prior to extraction with ethanol, whereas the other was not washed. The prepared samples were extracted by ethanol using a Soxhlet, and the concentrations of quercetin and rutin were determined by Raman spectroscopy and PLS regression. Only quercetin was detected in the sample washed with water at a concentration of 2.31 × 10−4 mol/L. Conversely, only rutin was detected in the unwashed sample in a concentration of 4.49 × 10−4 mol/L. These concentrations were almost identical to those obtained using high-performance liquid chromatography. The difference in the results was attributed to the presence of a hydrolysis enzyme. The rutin in the Tartary buckwheat sample pretreated with water was hydrolyzed into quercetin and rutinose by the hydrolysis enzyme.