Optimized Extraction of Antioxidants from Olive Leaves Using Augmented Simplex Centroid Design

The olive tree historically provided economic benefits to the countries in Mediterranean basin as a source of products contributing to health promotion. Some of the health benefits attributed to olive tree leaves are related to phenolic composition. In this study, a 10-point augmented simplex-centroid design was used to formulate a three-component mixture system using water, ethanol, and methanol, adequate for the extraction of phenolics from olive leaves. Phenolic and flavonoid content, antioxidant activity with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), oleuropein, and luteolin7-O-glucoside concentrations were selected as responses. The optimal extraction mixture was: 12.7% water, 14.8% ethanol, and 72.5% methanol. The yields of total phenolic and flavonoid compounds, oleuropein, and luteolin-7-O-glucoside were 163.69 ± 6.35 mg gallic acid g⁻¹, 114.69 ± 3.56 mg rutin g⁻¹, 858.29 µg g⁻¹, and 21.04 µg g⁻¹ dry weight of olive leaves. The antioxidant capacity was 238.71 ± 4.35 mM equivalent Trolox per g⁻¹ dry weight of olive leaves.