Tocopherol speciation as first screening for the assessment of extra virgin olive oil quality by reversed-phase high-performance liquid chromatography/fluorescence detector

Abstract

A method based on reversed-phase high-performance liquid chromatography with fluorescence detector has been developed for the determination of tocopherols in vegetable oils. Oils were diluted in acetonitrile/tetrahydrofuran (THF) and injected directly onto HyPurity C 18 column. Methanol and THF (90:10) mixture was used as a mobile phase. Tocopherols were detected by fluorescence detector. The method had good limit of detection (LOD) (7 ng/g for α-tocopherol and 6 ng/g for β-, γ- and δ-tocopherols) and reproducibility (CV% < 2.8%). The method was applied to the determination of α-, (β+γ)- and δ-tocopherols in extra virgin olive oil (EVOO), sunflower, high oleic sunflower oil (HOSO), hazelnut, soy, corn, peanut and almond oil. A new parameter, the ratio of α-/(β+γ)-tocopherol concentration (named α/β tocopherol ratio), in these vegetable oils was systematically assessed and proposed as a first screening marker of the authenticity of EVOO by studying EVOO/sunflower, EVOO/hazelnut and EVOO/peanut mixtures. The use of δ-tocopherol as adulteration marker was also discussed.