Optimisation of polyphenol extraction from Hypericum perforatum (St. John's Wort) using aqueous glycerol and response surface methodology

•Polyphenol extraction from Hypericum perforatum.•Use of aqueous glycerol and response surface methodology optimisation.•Process assessment using extraction kinetics.•Liquid chromatography-diode array–mass spectrometry characterisation of major polyphenols.

Hypericum perforatum is a plant rich in biologically functional polyphenolic phytochemicals. The efficient recovery of polyphenols from this material has not been previously investigated in depth, in terms of establishing an environmentally benign and cost effective process that would aim at producing extracts enriched in polyphenolic compounds. The objective of the present study was the examination of the efficiency of water/glycerol mixtures in extracting polyphenols from dried aerial parts of H. perforatum and its critical comparison with water. Extraction temperature and time were optimised using response surface methodology, while comparative assessment of the extraction efficiency between water/glycerol and water was carried out using kinetics. The results showed that 10% (w/v) aqueous glycerol at 70 °C provided very satisfactory extraction yield in total polyphenols (89.9 mg GAE g−1 dw), which was significantly higher than that attained with water. Similar results were drawn for the reducing power, in concurrence with the polyphenolic concentration. Liquid chromatography–mass spectrometry analysis showed that the polyphenolic profile of water/glycerol extract was composed by polar substances, such as chlorogenic acids and quercetin glycosides.

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