Human plasma protein binding of water soluble flavonoids extracted from citrus peels

Abstract

The human plasma protein binding of water soluble flavonoids in the peels of five spices of citrus fruits was studied by ultrafiltration combined with HPLC. The flavonoids were extracted separately by hot and cold water, and higher total flavonoid contents were detected in the former extracts than the latter ones. All the extracts show significant scavenging abilities to both ABTS and DPPH free radicals, which indicates the health benefits of the water extracts of citrus fruits peels. For DPPH radical, the IC50 values of hot extract follow as Navel orange (NO)≈Mandarin orange (MO)< Lemon (LE)< Lo tangerine (LO)< Pomelo (PO), while the rank is NO< PO<LE≈MO<LO for ABTS radical. The HPLC results reveal that the kinds and contents of the flavonoids detected in the extracts are different among the species. MO extract has the most neohesperidin dihydrochalcone of 118.76 μmol/L and quercetrin of 211.81 μmol/L of which are much more than the rest extracts. Pomelo extract has the most plentiful flavonoids of naringin with a concentration of 303.28 μmol/L. The high contents of myricetrin and dihydromyricetin which both are potent free radical scavengers may explain the highest free radical scavenging activity of the NO extract. The plasma binding rates decrease with the increasing concentrations of flavonoids, and the flavonoids having plenty hydroxyl groups on both A ring and B ring of the molecular skeleton have relative higher plasma binding rates. In addition, the plasma binding rates of flavonoids with saturated C3–C4 bond decrease significantly with the increasing concentrations.