The bioavailability of quercetin in pigs depends on the glycoside moiety and on dietary factors.

Recent investigations suggest that the bioavailability of quercetin depends on the glycoside moiety of the quercetin glycosides present in the diet. In this study, we compared the oral bioavailability of quercetin from quercetin aglycone and two different quercetin glycosides in pigs. Pigs were equipped with permanent catheters in the jugular and portal veins. After consumption of a test meal containing the respective compounds, blood samples were drawn repeatedly over a period of 24 h and analyzed by HPLC. In a first set of experiments, pigs received a single oral dose of 148 micromol/kg body (equivalent to 50 mg/kg) provided as quercetin aglycone, quercetin-3-O-glucoside (Q3G) or quercetin-3-O-glucorhamnoside (rutin) as part of their diet. The main metabolite in plasma was always conjugated quercetin, whereas free quercetin was not detected in either the jugular or the portal blood. For Q3G and rutin, the relative total bioavailability of quercetin (i.e., conjugated quercetin and conjugated methylethers of quercetin) was 148% (P = 0.07) and 23% (P < 0.05), respectively, compared with quercetin aglycone. In another experiment with a dose of 29.6 micro mol/kg (equivalent to 10 mg/kg), the relative total bioavailability of Q3G was 167% compared with the aglycone (P < 0.05). Bioavailability of Q3G was significantly higher when the test meal was ground beef rather than the standard ration. Our results indicate that the bioavailability of quercetin from quercetin glycosides is determined by a complex interdependence between the chemical form of the flavonols and dietary factors.