Optimisation and comparative kinetics study of polyphenol extraction from olive leaves (Olea europaea) using heated water/glycerol mixtures

Olive leaves consist a residual food-processing material, rich in biologically functional polyphenolic phytochemicals. The efficient recovery of polyphenols from this material has been the subject of several studies, yet the methodologies proposed may suffer serious shortcomings due to increased cost and/or solvent toxicity. The aim of the present study was the investigation on the efficiency of heated water/glycerol mixtures in extracting polyphenols from dried olive leaves and its critical comparison with previously optimised methodologies. Glycerol concentration and extraction time were optimised using response surface methodology, while comparative assessment of the extraction efficiency between water/glycerol and water/ethanol mixtures was carried out using kinetics. The results showed that a mixture of 9.3% (w/v) aqueous glycerol at 80 degrees C provided very satisfactory extraction yield in total polyphenols (51.91 mg gallic acid equivalents per g of dry weight), which was higher than that attained with 60% (v/v) aqueous ethanol, at pH 2 and 24 degrees C. Liquid chromatography-mass spectroscopy analysis showed that the polyphenolic profile of water/glycerol mixture was significantly different than that of water/ ethanol mixture, a sound evidence of differentiated selectivity. (C) 2014 Elsevier B.V. All rights reserved.