Journal
JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY
Volume 55, Issue 20, Pages 8088-8094Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jf0709698
Keywords
phase solubility; nuclear magnetic resonance; differential scanning calorimetry; oleuropein; olive leaves; inclusion complex; natural antioxidants
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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 enclothermic 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-CID 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 (similar to 300 M-1), and an increase of the aqueous solubility by similar to 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-CID that involves deep insertion of the dihydroxyphenethyl moiety inside the cavity from its secondary side.
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