抄録
Quercetin glucosides ingested as components of a foodstuff can be transformed to quercetin, and the quercetin is oxidized by peroxidase in the oral cavity. One objective of this study was the characterization of the oxidation products. Although both salivary peroxidase and myeloperoxidase are contained in whole saliva, salivary peroxidase is mainly involved in the oxidation in the saliva. As the oxidation products, 2,3,5,7,3′,4′-hexahydroxyflavanone-like compound and two isomers of a compound, which was transformed to quercetin and the above flavanone by a HCl/heat-treatment, were isolated. 3,4-Dihydroxybenzoic acid and 2,4,6-trihydroxyphenylglyoxylic acid were also detected in the oxidation products. When dialyzed saliva was used, the salivary peroxidase-dependent oxidation of quercetin and the formation of the oxidation products were partly inhibited by 1 mM thiocyanate which was a substrate for the peroxidase in the oral cavity. The mechanism and the significance of salivary peroxidase-dependent oxidation of quercetin in the oral cavity are discussed.
