Ultrasound-induced oxidation of flavonoids.

Ultrasound-induced oxidation of some flavonoids was detected by UV spectral analysis. From among twenty seven compounds investigated only flavonol aglycones and their 7-glycosides, but not 3-glycosides, flavones, catechins and flavanones were found to be oxidized with opening of the ring C. The products of quercetin oxidation were identical with those obtained during slow aerial oxidation of the compound in neutral solution. The oxidation products were deprived of the oxido-reductive properties of native flavonoids. Neither they reduced cytochrome c, nor inhibited lipid oxidation nor scavenged superoxide anions.