Improving Hydroxytyrosol Derivatives Content in Virgin Olive Oil using Ultrasound-assisted Maceration with Olive Leaf Extract

Background: Olive oil is rich in monounsaturated fatty acids and is an essential Mediterranean diet component. Many of its health benefits are associated with the presence of phenolic compounds. Several strategies for the enhancement of the phenolic content and, more specifically, the concentration of hydroxytyrosol derivatives in olive oils have been proposed, as extra virgin olive oil (EVOO) of high phenolic content is preferred by health-conscious consumers. Methods: The supplementation of EVOO with hydroxytyrosol derivatives from olive leaf extract was performed with the employment of ultrasound-assisted maceration at different concentration levels (2 g·L^-1 oil and 4 g·L^-1 oil), temperatures (20 and 40°C), and maceration times (20 and 40 min). The phenolic contents of enriched EVOOs were determined by spectrophotometric and HPLC methods. In addition, the effect of supplementation on the physicochemical parameters of EVOOs, namely acidity and extinction coefficients (K232 and K270), was also studied. Results: The addition of extract slightly increased the acidity values and extinction coefficients of the samples, and at the same time, it significantly improved their phenolic composition. The use of appropriate ultrasound-assisted maceration parameters (addition of olive leaf extract at a concentration level of 2 g L^-1 at 20°C for 20 min) provided EVOO with acceptable values for total acidity (<0.8%), K232 (<2.5), and K270 (<0.22), high contents of total phenolics and flavonoids, and improved hydroxytyrosol derivative contents. Conclusion: The enrichment of EVOO with leaf extract is a promising strategy to enhance its content in hydroxytyrosol derivatives, providing premium EVOOs with respect to their bioactive composition.