Optimisation of organic solvent-free polyphenol extraction from Hypericum triquetrifolium Turra using Box-Behnken experimental design and kinetics

Hypericum triquetrifolium Turra 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. triquetrifolium Turra 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 degrees C provided very satisfactory extraction yield in total polyphenols (54.83 mg gallic acid equivalents per g of dry weight), which was significantly higher than that attained with water (17.3 %). 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.