Concentration of Bioactive Phenolic Compounds in Olive Mill Wastewaters by Direct Contact Membrane Distillation

Olive mill wastewater (OMW), generated as a by‐product of olive oil production, is con‐ sidered one of the most polluting effluents produced by the agro‐food industry, due to its high concentration of organic matter and nutrients. However, OMW is rich in several polyphenols, rep‐ resenting compounds with remarkable biological properties. This study aimed to analyze the chem‐ ical profile as well as the antioxidant and anti‐obesity properties of concentrated fractions obtained from microfiltered OMW treated by direct contact membrane distillation (DCMD). Ultra‐high per‐ formance liquid chromatography (UHPLC) analyses were applied to quantify some phenols se‐ lected as phytochemical markers. Moreover, ‐Amylase, ‐glucosidase, and lipase inhibitory activ‐ ity were investigated together with the antioxidant activity by means of assays, namely ‐carotene bleaching, 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulphonic) acid (ABTS) diammonium salts, 2,2‐ diphenyl‐1‐picrylhydrazyl (DPPH) assay, and Ferric Reducing Activity Power (FRAP) tests. MD retentate—which has content of about five times greater of hydroxytyrosol and verbascoside and about 7 times greater of oleuropein than the feed—was more active as an antioxidant in all applied assays. Of interest is the result obtained in the DPPH test (an inhibitory concentration 50% (IC50) of 9.8 g/mL in comparison to the feed (IC50 of 97.2 g/mL)) and in the ABTS assay (an IC50 of 0.4 g/mL in comparison to the feed (IC50 of 1.2 g/mL)