Effects of oleuropein-rich olive leaf extract on the oxidative stability of refined sunflower oil

The aim of this study is to investigate the ability of oleuropein-rich olive leaf extract (OLE) to improve the quality and oxidative stability of sunflower oil subjected to accelerated thermal oxidation. Oleuropein was the major phenolic compound determined by HPLC-DAD with a content ranging from 20.81 to 32.56 mg·g-1 of dry extract (DE). The evaluation of the in vitro antioxidant capacity of OLE showed good scavenging capacity of the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and hydrogen peroxide (H2O2) (1.01 and 0.96 mmol Trolox equivalents (ET·g-1 DE, respectively). The enrichment of sunflower oil with 0.1, 0.25 and 0.5% OLE (w/v) significantly inhibited thermal-induced peroxidation in a dose-dependent fashion. 0.25% OLE was the most effective concentration and showed a significant reduction in peroxide value and conjugated dienes by 61.4 and 17.4%. These results indicate that OLE can be considered a good natural alternative for extending the shelf-life of polyunsaturated vegetable oils.