Microwave-assisted extraction and membrane-based separation of biophenols from red wine lees

Winemaking generates huge quantities of waste streams with high added value which can be recycled for the production of innovative products in different market areas. In particular, wine lees contain high concentration of bioactive molecules which can be exploited to obtain extracts or semifinished products of interest for food, nutraceutical and pharmaceutical applications. In agreement with a biorefinery approach applied to winemaking, this work aimed at evaluating the potential of an integrated process, based on a combination of microwave-assisted extraction and membrane-based operations, for the recovery of phenolic compounds from red wine lees before using biomass for energy purposes. Specifically, the hydro-alcoholic extract was clarified by microfiltration (MF) and then processed with three different polymeric membranes: an ultrafiltration (UF) membrane with a molecular weight cut-off (MWCO) of 1,000 Da (Etna 01PP) and two nanofiltration (NF) membranes with MWCO of 150-300 Da (NFT50 and Desal DK). The performance of selected membranes was measured in terms of permeate flux, fouling index and retention of phenolic compounds and sugars. Experimental results indicated that all these parameters are mainly affected by membrane material and pore size. All tested membranes did not show a preferential rejection of phenolic compounds over sugars. Among the selected membranes the NFT50 presented the highest retention towards phenolic compounds allowing to maximize the recovery of these compounds in the retentate fraction.