The use of nanofiltration membranes for the fractionation of polyphenols from grape pomace extracts

Filtration experiments in batch concentration mode (with recycling of the retentate stream) of grape pomace extract were performed in laboratory filtration membrane equipment by using nine commercial nanofiltration (NF) membranes with an approximate molecular weight cut-off (MWCO) of 1000‒150 Da. The filtration experiments of the selected pomace extract were performed by modifying the most important operating variables: transmembrane pressure, tangential velocity, temperature, and the nature and MWCO of the membranes. The evolution of the cumulative permeate volumes and permeate fluxes with processing time was analyzed till a volume reduction factor (VRF) of 10 was reached. The effect of the mentioned operating conditions was discussed. The effectiveness of the filtration treatments was determined by the evaluation of the rejection coefficients for several families of polyphenols. Membranes possessing MWCO between 1000 and 500 Da were able to quantitatively recover polymeric proanthocyanidins in the concentrate stream and separate them from phenols that passed through the membrane into the permeate stream. On the other hand, the 600 to 300 Da membranes could also be used for the fractionation of monomeric phenolic families. The membranes were able to partially remove the anthocyanin fragments of phenolic acid derivatives and flavonols in the concentrate stream and at the same time.