Natural Antioxidant Potential of Olive Leaves for Stabilizing Edible Oils: A Chemometric Study

Among the by-products of the olive industry, olive leaves are the most abundant, yet their high content of bioactive compounds remains largely underexploited. Their valorization offers good opportunities in various fields, including food conservation. Our work aims to evaluate the performance of olive leaf extracts of ‘cv Picholine Marocaine’ as a natural additive for improving the oxidative stability of various edible vegetable oils, including sunflower, soybean, and olive oils, obtained from three extraction technologies: wo-Phase (2P), Three-Phase (3P), and Super-Pressure (SP) extraction systems. The aqueous extraction of bioactive compounds was performed using the Soxhlet instrument. Three concentrations of leaf extracts, 200, 400, and 800 ppm, were added to the studied vegetable oils. A physicochemical characterization, including free acidity (FA), peroxide value (PV), extinction coefficients (K232 and K270), chlorophyll content (Chl), carotenoid content (Cart), fatty acid composition, antioxidant activity (AA), total phenolic compounds (TPCs), and total flavonoid content (TFC), were monitored for six months. Combined analysis of variance reveals that treatment with additives, storage time, and their interaction had highly significant effects (p ≤ 0.001) on almost all investigated parameters. Moreover, storage time was the most important factor influencing the dependent variables. The results of our mean comparison show a significant improvement of the investigated parameters, PV, K₂₃₂, K₂₇₀, TPC, and TFC, following the incorporation of 400 and 800 ppm leaf extract. In contrast, no significant effect (p ≥ 0.05) was observed on the fatty acid composition of the vegetable oils. Robust simple regression was highlighted between the concentration of leaf extract and both TPC and pigment contents. Principal component analysis confirmed the ANOVA results and clustered the enriched olive oils in correlation with the low values of oxidation indices. In conclusion, olive leaves provide a potential by-product to enhance the oxidative stability of vegetable oils.