Maceration and Liquid-liquid extractions of phenolic compounds and antioxidants from Algerian olive oil mill wastewater

Abstract Purpose Olive oil mill wastewater (OMW) is a major waste stream from the olive oil industry. It is highly polluted due to phenolic compounds. The present study focused on the physicochemical properties of OMW as well as the quantitative and qualitative effects of two methods of extraction (maceration and liquid-liquid extraction) of phenolic compounds. Methods Liquid-liquid extraction and maceration methods were used for the extraction of phenolics. Spectrophotometry and High-Performance Liquid Chromatography-Electrospray Ionization–Mass Spectrometry (HPLC-ESI-MS) were adopted to quantify the phytochemical contents and the phenolic compounds. The antioxidant potentials were evaluated using three assays DPPH, ABTS + and FRAP radical scavenging activities. Results The findings showed that the OMW was an acidic effluent (pH = 5.05) loaded with mineral and organic matter expressed in terms of a high value of electrical conductivity (EC = 13.51 mS/cm). Indeed, the OMW showed high dry matter, chemical oxygen demand (COD) and biological oxygen demand (BOD5). The extract obtained by the maceration method showed the highest yields of total polyphenol, flavonoid, and tannins contents than the liquid-liquid extraction method. The LC-MS results revealed the presence of 16 phenolic compounds in the extract obtained by the maceration method and only 12 phenolic compounds were found in the extract obtained by the second method. Quinic acid was identified as the most abundant compound. Moreover, the macerated extracts possessed the highest antioxidant potential as evidenced by their strong DPPH, ABTS and FRAP radical scavenging activities compared to the liquid-liquid extracts. Conclusions The maceration methods seemed to be the most effective method for extracting phenolic compounds from OMW than liquid-liquid extraction. The OMW constitute a rich source of natural phenolic compounds that could be used as a potential source of natural antioxidants.