Antibacterial and antioxidant potentials of phenolic extracts from olive mill wastewater and their use to enhance the stability of olive oil.

Fresh olive oil mill wastewaters (OMW) were collected in northern Morocco from industrial mills operating with three extraction systems (two [C2] and three-phase [C3] centrifugation decanters and super-pressure system [SP]) during the 2017 growing season. Physicochemical and microbiological characteristics of these effluents were examined. OMW phenolic extracts were prepared and their antibacterial and antioxidant activities were evaluated. Moreover, the improvement of virgin olive oil stability with the addition of OMW phenolic extracts (at 100, 300 and 500 ppm) was investigated. Results from this work confirmed the pollutant load of these effluents characterised by an acidic pH, strong organic content, and considerable amounts of mineral matter. Concerning the microbiological counts, yeasts and moulds were the most abundant. Among the extraction system, C2 displayed OMW with the high levels for all measured parameters, except for the total phenols that were more abundant in C3. For the in vitro bioassays, OMW phenolic extracts showed a promising antibacterial activity against the two studied bacteria. In fact, C2 extract was the most active for inhibiting the bacteria growth, while Escherichia coli (Gram-) was more resistant to bactericidal phenols than Listeria innocua (Gram+). Findings from DPPH and FRAP tests showed a good antiradical potential and an important reducing power capacity and were both concentration-dependent. For the two tests, antioxidant activity of OMW phenolic extracts from C2 was also the most important. The addition of phenolic extracts to virgin olive oil, stocked at 60°C, resulted in lower records for peroxide value, K232 and K270 compared to the control, indicating a good protective effect against oil oxidation. The great antioxidant effect of OMW extracts was at 500 ppm, like that of ascorbic acid. [ABSTRACT FROM AUTHOR]