A membrane-assisted green strategy for purifying bioactive compounds from extracted white wine lees

This work was aimed at investigating the recovery of wine-derived bioactive compounds from white wine lees through a combination of hydroalcoholic extraction and membrane-based operations, as a potential alternative for winery wastewater treatment and valorisation. Hydroalcoholic extracts obtained in selected conditions of solid-liquid ratio, extraction time and working temperature (1:10, 25 % and 32 ± 2 °C, respectively) were previously clarified by ultrafiltration (UF) in order to produce a clarified solution free of suspended solids and colloidal substances. The concentration of bioactive compounds from the clarified extract was investigated by using three different spiral-wound NF membranes with molecular weight cut-off (MWCO) in the range of 200-1000 Da (TS40, XN45 and NP010, all from Microdyn-Nadir); their performance was analysed in terms of productivity, fouling index and retention towards target compounds (polyphenols, flavonoids, sugars) and antioxidant activity. Low molecular weight polyphenols (i.e. gallic acid, catechin, vanillic acid, epicatechin and caffeic acid) were highly rejected by the selected membranes despite their difference in MWCO; on the other hand, the rejection index for total phenolic content (TPC), flavonoids and glucose was in agreement with the MWCO. The TS40 membrane, with a lowest cut-off (200-300 Da), showed the highest rejection for flavonoids (100 %) and rejections for total phenolic compounds of 85 % resulting in concentrated fractions containing 1.7 g of gallic acid equivalents per liter (GAE/L); most of the components analysed in the retentate samples showed a concentration factor of approximately 3.5 in agreement with the weight reduction factor of the NF process. The analysis of fouling mechanisms according to the Hermia's model revealed that the cake filtration mechanism was the predominant one for all selected NF membranes.