β-Cyclodextrin complexation of extracts of olive leaves obtained by pressurized liquid extraction

Abstract

The aim of this work was to investigate different methods of complexation of extracts of olive leaves (EOL) with β-cyclodextrin (β-CD) and to verify how EOL, in its free form and as inclusion complex, behaves as an antioxidant in olive oil. The extracts were obtained by pressurized liquid extraction at 343 K and ∼1 × 104 kPa with ethanol as solvent. Oleuropein represented approximately 75% of the total phenols whose content determined by Folin-Ciocalteu was ∼0.12 kg GAE kg−1, while the IC50 of the dry EOL was 0.043 kg m−3. The antioxidant capacity of the extract determined by the ABTS method was 0.12 kg TEAC kg-1 dry weight. The dry powder extracts were used as guest to form inclusion compounds with β-CD by involving the methods of physical mixture (PM), kneading (KN), PM and KN assisted by supercritical CO2 as complexation medium. Free EOL, free β-CD and EOL/β-CD complexes were characterized in terms of spectral properties by 1H NMR, FT-IR and XRD, and morphology by SEM. Unambiguous interactions between hydrogen atoms in the free EOL and in the host, reduction of relaxation times in the formed complexes, and area under absorption bands in the EOL/β-CD complexes that were significantly smaller than the ones of pure EOL were the results that more markedly supported effective complexation from these analyses. Recorded data of induction time revealed that free EOL, but mainly the formed EOL/β-CD complexes, when used as additives to an olive oil may increase its oxidative stability.