Effect of Ultrasound and Vacuum-Assisted Extraction on the Quality and Bioactive Properties of Olive Oil

Abstract

In this study, the effects of sonication, which can be in combination with malaxation or as an alternative to malaxation, on the chemical properties, bioactive compounds, and fatty acid composition of olive oil, as well as oil contents of olives, were investigated. The oil contents of olives were not affected by the vacuum, whereas an increase in the sonication time enhanced the oil contents of the samples. The malaxation process was necessary to obtain high chlorophyll and carotenoid contents, and the process under vacuum increased their amounts. The highest free acidity (8.96%), peroxide (2.75 meq O₂/kg), K₂₃₂ (2.47), and K₂₇₀ (0.49) values were observed in olive oils that were malaxed for 30 min under ambient conditions. The total phenolic content (303.10 mg/L), antioxidant activity (0.73 µmol/mL by 2,2-diphenyl-1-picrylhydrazyl [DPPH] and 4.33 µmol/mL by iron(III) reducing antioxidant [FRAP]), hydroxytyrosol (211.60 mg/L), and tyrosol (220.72 mg/L) concentrations of olive oil significantly increased with malaxation + sonication application under vacuum for 10 min. Malaxation environment and time caused significant differences in the amounts of oleic and palmitic acids. It was observed that vacuum application increased the α-tocopherol content of oils and the most effective process was malaxation + sonication.

Practical Applications: The conventional malaxation process caused the highest peroxide and K values of the oils. The processes carried out under vacuum environment decreased the free acidity and K values of the oils. Thereby, the applied processes have a positive effect on oil quality. It was observed that vacuum application increased the total phenolic content, antioxidant activity, hydroxytyrosol, tyrosol, and tocopherol content of oils and the most effective process was malaxation + sonication. Accordingly, the combination of malaxation + sonication under vacuum is recommended for olive oil extraction.