Effect of Membrane Filtration With and Without Enzymatic and Solvent Pretreatment on Recovery of Phenolic Compounds From Olive Mill Wastewater

The olive fruit is rich in phenolic compounds, but only 2% of it remains in the oil and the rest is removed with the olive mill wastewater (OMWW) and pomace. Consequently, the potential for producing phenolic extract from OMWW is substantial. Membrane processing stands as a viable technology for the recovery of phenolic compounds from OMWW. In this study, the extraction of phenolic compounds through membrane processes was carried out employing enzyme and solvent pretreatments for two olive cultivars (Koroneiki and Roghani). The extraction methods were assessed by determining the total polyphenol content, extraction efficiency, and antioxidant activity of the extract. Statistical analysis revealed that the extraction method and its interaction with the cultivar significantly impacted the extraction efficiency, while the effect of the cultivar itself was not significant. Across both cultivars, the enzymatic pretreatment method exhibited the highest extraction efficiency and phenolic compound content. Additionally, it was found that the Koroneiki cultivar had a higher amount of phenolic compounds than the Roghani cultivar. The enzymatic pretreatment achieved the highest extraction efficiency (75.5%) and phenolic content (1631.7 mg/L). The enzymatic pretreatment exhibited a lower value for the radical scavenging activity of the phenolic compound extract, whereas the iron reducing power of the phenolic compound extract was the highest with enzymatic pretreatment. Notably, the extraction method with enzymatic pretreatment exhibited the lowest IC50 and highest reducing power in both cultivars (p < 0.05). The lowest IC50 (51.6 μg/mL) and the highest iron reducing power (87.2 μM Fe II/g) indicated the strongest antioxidant activity in the Koroneiki cultivar. Conclusively, based on these results, the membrane extraction method with enzymatic pretreatment for both cultivars emerges as the most efficient extraction method with the highest antioxidant properties.