RESUMEN
Olive tree vegetal materials are considered a powerful source for the isolation of bioactive compounds-mainly phenols and triterpenic acids. However, the high humidity content of them reduces their preservation and extractability to a liquid solvent. Accordingly, a drying step is crucial to homogenize the material and to obtain an efficient extraction. We studied the influence of the drying process on the extraction efficiency of bioactive compounds from olive vegetal material. For this purpose, we evaluated the effects of four drying processes on the solid-liquid extraction of bioactive compounds from two by-products, olive leaves and pomace, and olive fruits harvested from two cultivars, Alfafara and Koroneiki. Infrared-assisted drying (IAD) was the most suited approach to obtain extracts enriched in oleuropein from leaves (28.5 and 22.2% dry weight in Alfafara and Koroneiki, respectively). In the case of pomace, lyophilization and microwave-assisted drying led to extracts concentrated in oleacein and oleuropein aglycone, whereas IAD and oven-drying led to extracts with enhanced contents of hydroxytyrosol glucoside and hydroxytyrosol, respectively. The drying process considerably affected the chemical composition of extracts obtained from fruits. Changes in the composition of the extracts were explained essentially by the drying process conditions using auxiliary energies, temperature, and time, which promoted chemical alterations and increased the extractability of the compounds. Therefore, the drying protocol should be selected depending on the phenolic content and initial raw material.
RESUMEN
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.
