Optimisation of the extraction of pomegranate (Punica granatum) husk phenolics using water/ethanol solvent systems and response surface methodology

Pomegranate (Punica granatum (Linn.)) husk is an agri-food residual material, particularly rich in polyphenolic phytochemicals. An experimental setup based on a 23-full factorial central composite design was implemented with the aim to optimising recovery of polyphenol extraction from pomegranate husks, using ethanol/water/citric acid as the extracting medium. The factors considered were (i) the pH of the medium, (ii) the ethanol concentration and (iii) the extraction time. Optimal extraction afforded extracts exceptionally enriched in total polyphenols, with the yield being 324.9 mg gallic acid equivalents per g of dry weight. Liquid chromatography-electrospray ionisation mass spectrometry of the optimally obtained extract revealed that the principal phytochemicals recovered were punicalins A and B and ellagic acid.