Encapsulation of complex extracts in β-cyclodextrin: An application to propolis ethanolic extract

Propolis ethanolic extracts (PE) are rather complicated mixtures of bioactive compounds belonging to several chemical classes. The potential use of beta-cyclodextrin (beta-CD) cavity for the incorporation of specific PE components, aiming to increase their solubility in water, was studied in a Greek propolis, which was rich in polyphenols and terpenes. The PE/beta-CD inclusion complexes were prepared by sonication of PE suspensions in aqueous solutions of beta-CD, followed by filtration and freeze-drying. The aqueous solubility of PE in the presence of beta-CD was studied by the construction of solubility diagrams and by determining the fraction of PE constituents that was dissolved in water. Encapsulation efficiencies were found to be higher (9.4-23.3%) for relatively small aromatic molecules like cinnamic and benzoic acid derivatives and lower for terpenic acids (5.0-6.7%), anthraquinones (3.6-8.4%) and flavonoids (4.0-10.7%). The respective in vitro solubilities in simulated gastric fluid followed an opposite trend, being lower for the relatively small aromatic molecules. It is concluded that the encapsulation in beta-CD may increase the solubility of PE constituents in a manner related to their structure, while the amount of substances released will depend both on their chemical properties and on their relative abundance in the matrix.