Metabolites of dietary quercetin: Profile, isolation, identification, and antioxidant capacity

The study of the profile, isolation and antioxidant capacity of pig quercetin metabolites after onion dry skin intake was performed. Onion dry skin contain very high content of quercetin, which occurred mainly in aglycone form (87%). Urine was collected from seventeen pigs before and within 2-6 hours after intake of onion dry skin providing quercetin. Quercetin metabolites profile was analyzed by HPLC-MS/MS. Upon quercetin intake, quercetin was absorbed and occurred in pig urine in methylated, glucuronided, sulfated and combined derivatives. Among 12 quercetin metabolites identified, quercetin monoglucuronides were predominant. Quercetin metabolites were isolated and purified by Amberlite XAD-16 column chromatography and on HPLC C18 semi-preparative column. Quercetin metabolites mixture showed higher radical-scavenging activities compared to native quercetin derivatives of onion skin. Results indicated that the profile of quercetin metabolites in pig reflects that in a humans. Moreover, quercetin metabolites present in systemic circulation after quercetin intake still acted as antioxidants.