Quantitative method for determination of oleocanthal and oleacein in virgin olive oils by liquid chromatography-tandem mass spectrometry

Oleocanthal and oleacein, two key secoiridoid derivatives present in virgin olive oil (VOO), are gaining clinical and nutritional interest thanks to their proved bioactivity; therefore, the determination of both phenols is a growing demanded application to increase the value of VOO. The main problem of previously reported liquid chromatography-based methods for oleocanthal and oleacein measurement is their interaction with water or other polar solvents such as methanol to promote the formation of hemiacetal or acetal derivatives. This interaction can occur during either sample extraction, basically liquid-liquid extraction, and/or chromatographic separation. The aim of this research was to evaluate the suitability of LC-MS/MS for absolute quantitation of oleocanthal and oleacein in VOO. For this purpose, both liquid-liquid extraction and chromatographic separation were studied as potential promoters of acetals and hemiacetals formation from oleocanthal and/or oleacein. The results showed that the use of methanol-water solutions for phenols extraction was not influential on the formation of these artifacts. Acetals and hemiacetals from oleocanthal and/or oleacein were only detected at very low concentrations when methanol gradients under acidic conditions were used for chromatographic separation. With this premise, a protocol based on extraction with acetonitrile and a reverse chromatographic gradient with methanol was established to quantify in absolute terms oleocanthal and oleacein in VOO samples. The resulting protocol was applied to three VOO samples characterized by high, medium, and low levels of these two phenols.