[Polyphenolic antioxidants in fruit juice. Urinary excretion and effects on biological markers for antioxidative...

This intervention study was designed as cross-over (four women, one man) with three doses of black currant/apple (1:1) juice (750, 1000, and 1500 mL) for one week corresponding to an intake of 4.8, 6.4, and 9.6 mg quercetin per day. Urinary excretion of quercetin increased significantly with dose and with time. The fraction excreted in urine was constant 0.29-0.47%. Plasma quercetin did not change with juice intervention. Plasma ascorbate increased during intervention due to ascorbate from the juice. Total plasma malondialdehyde decreased with time during 1500 mL juice intervention. Plasma protein 2-adipic semialdehyde residues, increased with time and dose, and glutathione peroxidase increased with juice dose, whereas other selected markers of oxidative status did not change. These effects might be related to several components of the juice and cannot be attributed solely to its quercetin content.