Abstract
It has been reported that consuming food which contains flavonols is related to the decrease in risks to arteriosclerosis and cancer. One objective of this study was to elucidate the metabolism of quercetin and the glucosides (quercetin 3,4′-diglucoside and quercetin 4′-glucoside) present in onion soup, in the oral cavity. Not only quercetin glucosides but also quercetin were found in whole saliva which was collected 15 min after eating onion soup. Quercetin seemed to be formed by deglucosidation of the glucosides. The concentrations of the flavonols were much higher in sediments than in supernatants of the saliva suggesting that the flavonols bound to components of the sediments like detached epithelial cells. Concentrations of quercetin and the glucosides in the oral cavity decreased as a function of time after the intake. The decreases were mainly due to the washing away from this cavity by saliva. In addition, deglucosidation of quercetin glucosides to quercetin was also assumed to contribute to the decrease in the glucosides and oxidation of quercetin by peroxidase (POX) in saliva to the decrease in quercetin. Based on the data that quercetin was oxidized by POX in saliva in the presence and absence of thiocyanate, it is suggested that quercetin as well as thiocyanate can be a substrate for POX in saliva to scavenge H2O2 in oral cavity.
