Recovery of phenolic compounds from by-products of the winemaking chain by ultra and nano-filtration membranes

The winemaking process generates different types of waste and by-products such as grape pomace, grape stems, wine lees and wastewater. Although these residues are mainly produced in the harvest period, they are distributed throughout the year causing environmental problems if they are not properly disposed of. Among wastes, wine lees and grape pomaces constitute a valuable source of bioactive compounds, especially phenolic compounds, with potential uses as food additives, nutraceuticals, and/or cosmeceuticals. For this reason, the winemaking industry is geared towards innovative and sustainable waste management systems, with an increasing demand for recycling or valorization strategies which deal with the principles of the Circular Economy. The coupling of membranes and other physical-chemical treatment appears to be a promising research domain in this field. In this work ultra- and nano-filtration laboratory-made flat-sheet membranes were investigated for the recovery of phenolic compounds from wine lees and red grape pomace extracts. The membrane performance was measured in terms of productivity, fouling index, cleaning efficiency and rejection coefficients towards total phenolics content, antioxidant activity, proanthocyanidins, glucose and fructose. UF and NF membranes were effective in separating target compounds from wine lees rejecting more than 92% of polysaccharides, with polyphenols preferentially permeating through the membrane. Concentrated fractions with high antioxidant activity can be produced through a combination of UF and NF processes in a sequential design. Among the prepared membranes, a specific NF membrane provided the best results in terms of separation between sugars and phenolic compounds of wine lees, with low rejections for glucose and fructose (19% and 12%, respectively) and high rejections for total phenolics content and proanthocyanidins (73% and 92%, respectively). This membrane exhibited also high productivity, with permeate flux of about 50.58 L/m2h (at 20 bar and 25 °C) and low fouling index.