Antioxidant capacity of quercetin and its glycosides in the presence of β-cyclodextrins: influence of glycosylation on inclusion complexation

In this study, we aimed to investigate the inclusion complexes of the poorly water soluble flavonol, quercetin (QR) and its glycosides quercitrin (QRC) and rutin (RT), formed with beta-cyclodextrin (beta-CD), 2-hydroxyethyl-beta-cyclodextrin (HE-beta-CD), 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD), and methyl-beta-cyclodextrin (M-beta-CD) by using UV-Vis spectrophotometric and spectrofluorometric techniques. The formation constants (K (f) ) of 1:1 stoichiometric inclusion complexes were calculated from Benesi-Hildebrand equation using fluorescence spectroscopic data. Maximum inclusion ability was measured in the case of M-beta-CD for rutin and quercitrin. Among CDs, HP-beta-CD was most effective for complexing quercetin. The glycosylation of flavonoids considerably affects the binding process. The formation constants of flavonoid-CD complexes decrease after glycosylation. The influence of complexation of quercetin, rutin and quercitrin with native and modified beta-CDs on their trolox equivalent antioxidant capacity (TEAC) was studied by the Cupric Ion Reducing Antioxidant Capacity method. It was found that the complexed polyphenols with CDs were much stronger antioxidants than free forms. Antioxidant capacity of HP-beta-CD-complexed QR (compared to that of pure QR) was increased by 7.18 % in methanolic solution. Increase in TEAC for M-beta-CD-complexed RT and M-beta-CD-complexed QRC were measured as 4.30 and 14.8 %, respectively.