Encapsulation of Hypericum perforatum (St John's wort) methanolic extract in β-cyclodextrin

Methanolic extracts of Hypericum perforatum (HP) grown in Northern Greece were consistently rich in total polyphenols – reaching 71.9±6.8g gallic acid equivalent (GAE)/100g (N=6) as assayed by Folin Ciocalteu reagent. Among the individual polyphenols identified and quantified by GC/MS in the form of their trimethylsilylethers, epicatechin, catechin and quercetin predominated comprising 94.3±3.2% (N=6) of the determined polyphenols, while their respective concentrations were 118.9±20.6, 8.7±1.4 and 5.8±0.8mg/g extract. Among anthocyanins – determined by HPLC – malvidine was present at 1.96±0.2mg/g.

We examined the possibility of encapsulating the HP extract in β-cyclodextrin (β-CD) by freeze-drying. The formation of the inclusion complexes between β-CD and constituents of HP extract was confirmed by differential scanning calorimetry (DSC); endothermic peaks corresponding to the melting of extract constituents were present in DSC thermograms of pure extract, but were absent in thermograms of the encapsulated extract. A confirmation of inclusion was additionally provided by DSC run under oxidative conditions, indicating that the encapsulated form of the extract is protected towards oxidation, as it remained intact even at high temperatures (300°C). Nuclear magnetic resonance (NMR) studies of aqueous β-CD solutions in the presence of the HP extract showed definite cavity inclusion, as well. Furthermore, the GC/MS determination of catechins and quercetin in methanol solutions obtained from the extraction of mixtures containing pure HP extract and its inclusion complex at several ratios, confirmed the formation of the inclusion complexes.