A combination of aqueous extraction and polymeric membranes as sustainable process for the recovery of polyphenols from olive mill solid wastes

Polyamide commercial membranes in flat-sheet configuration and with molecular weight cut-off (MWCO) in the range of ultrafiltration (UF)-nanofiltration (NF) membranes were tested for the recovery of phenolic compounds from clarified olive mill solid waste (OMSW) aqueous extracts. The performance of selected membranes was evaluated in terms of productivity (permeate flux) and selectivity towards biologically active compounds (as phenolic compounds, flavanols and hydroxycinnamic acids derivatives) and total antioxidant activity (TAA) as a function of transmembrane pressure (TMP). NF membranes produced higher permeate fluxes and lower fouling index in comparison with UF membranes. Retention of bioactive compounds resulted also significantly higher for NF membranes than for UF membranes. In particular, membranes with MWCO in the range 150-500 Da showed rejection towards flavanols and hydroxycinnamic acid derivatives of about 100%; on the other hand, the rejection towards TAA and total polyphenols was of about 90% and 72% %, respectively. Therefore, NF retentate fractions appear of practical interest for the production of food additives and food supplements due to their high antioxidant activity.