Heat-induced, metal-catalyzed oxidative degradation of quercetin and rutin(quercetin 3-O-rhamnosylglucoside) in aqueous model systems

The oxidative degradation of quercetin and rutin in phosphate buffer soluti ons, pH 8.0, at 97 degrees C, was studied by means of UV-vis spectroscopy a nd reversed-phase high-performance liquid chromatography (HPLC). The effect of the transition metal ions Fe2+ and Cu2+ On degradation rate and brownin g development was also assessed. It was shown that both flavonols are very labile to thermally induced degradation under oxidative conditions. Fe2+ an d Cu2+ caused an increase in the degradation rate, as well as an increase i n browning (A(420)) Significant differences were observed in the degradatio n mechanisms, as implied by HPLC analyses. It is postulated that metal ions promote flavonol oxidation through reactive oxygen species formation, wher eas increases in browning could be ascribed to oxidation and metal-polyphen ol interactions.