Development of phenolic-rich fractions from olive mill wastewater by membrane-based operations for application in food industry

Today the valorisation of agro-food wastes and by-products is a challenging opportunity for a sustainable and competitive development of the agro-food industry in agreement with the principles of circular economy [1]. Olive mill wastewater (OMW) generated in the production of extra virgin olive oil poses a significant threat of pollution effect to the environment. On the other hand, it contains a significant phenolic compounds content which can be recovered and valorised for food and nutraceutical applications [2]. This study aimed at investigating the development of polyphenol‐enriched fractions (PEFs) from OMW by using a combination of ultrafiltration (UF) and nanofiltration (NF) membranes. Specifically, OMW was firstly pretreated by UF with a production of a permeate fraction containing 96% of the phenolic compounds of the treated sample. The NF treatment of the UF permeate was investigated by using three thin-film composite membrane in spiral-wound configuration with different molecular weight cut-off (MWCO). The performance of these membranes was evaluated, in selected operating conditions, in terms of productivity and selectivity towards total phenolic compounds (TPC), flavonoids (TFC), hydroxycinnamic acids and flavanols. The obtained PEFs from each NF treatment were also investigated for their antioxidant activity (DPPH, ABTS and FRAP tests). Among the investigated membranes, the Trisep TS40 (from Microdyn Nadir), with a MWCO of 200-300 Da, produced retentate fractions with the highest content of TPC and TFC. Moreover, these fractions exhibited also the highest radical scavenging effect against both ABTS and DPPH test with percentage of inhibition of 96.94 and 92.27%, respectively. In the light of the obtained results the produced PEFs could be considered as a potential source of antioxidants to be applied in several fields, including the food industry, where they could be used for both fortifying and prolonging the shelf life of final products.