Encapsulation of Olive Leaf Extract in β-Cyclodextrin

Abstract

Olive leaf extract, rich in oleuropein, formed an inclusion complex with beta-cyclodextrin (beta-CD) upon mixing of the components in aqueous media and subsequent freeze-drying. Inclusion complex formation was confirmed by differential scanning calorimetry (DSC). DSC thermograms indicated that the endothermic peaks of both the olive leaf extract and the physical mixture of olive leaf extract with beta-CD, attributed to the melting of crystals of the extract, were absent in DSC thermogram of inclusion complex. Moreover, DSC studies under oxidative conditions indicated that the complex of olive leaf extract with beta-CD was protected against oxidation, since it remained intact at temperatures where the free olive leaf extract was oxidized. Phase solubility studies afforded A L type diagrams, 1:1 complex stoichiometry, a moderate binding constant ( approximately 300 M (-1)), and an increase of the aqueous solubility by approximately 50%. The formation of the inclusion complex was also confirmed by nuclear magnetic resonance (NMR) studies of beta-CD solutions in the presence of both pure oleuropein and olive leaf extract. The NMR data have established the formation of a 1:1 complex with beta-CD that involves deep insertion of the dihydroxyphenethyl moiety inside the cavity from its secondary side.