Complexation of hydroxytyrosol with β-cyclodextrins. An efficient photoprotection

The complexation of the potent olive oil antioxidant hydroxytyrosol (HT) with commercial β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) in aqueous solutions has been studied for the first time. The 1:1 stoichiometries of the complexes were evidenced by Job’s plot and the association constants were determined by linear regressions from Scott’s method. The geometry of the HT/β-CD complex was elucidated by 2D-ROESY experiments, suggesting insertion of the catechol moiety with the hydroxyalkyl chain directed to the primary rim. The antioxidant activity of encapsulated HT was also evaluated by scavenging of the stable DPPH radical, observing an improvement of the scavenging activity upon increase of the cyclodextrin concentration. Complexation of HT with β-CD also provided a strong photoprotection of the polyphenolic compound upon irradiation with UV (λ=254 nm).