Supercritical antisolvent precipitation as a green technology to fractionate an Origanum majorana extract: Relationship between fractions cellular antioxidant activity and phytochemical composition.

Abstract

The aim of this work was to determine the optimal conditions to fractionate a marjoram extract using supercritical antisolvent precipitation (SAS) technology in order to improve its antioxidant activity. This activity was evaluated using a cellular antioxidant assay (CAA) and compared to a chemical method (ABTS). After extract fractionation, most of the phenolics were recovered in the precipitate, except for the less polar ones that were found in the separators, along with essential oil components, non-volatile terpenes and fatty acids. Precipitate fractions obtained at 40 °C and 20–25 MPa showed the best TEAC values (1.7 mmol Trolox/g extract). Nevertheless, no precipitate fraction exerted better CAA than the unfractionated extract. This activity was related to the presence of arbutin and rosmarinic acid in their composition. In contrast, separators showed a low TEAC value (0.3 mmol Trolox/g), but a higher cellular antioxidant activity, especially fractions obtained at 15–20 MPa and 40–50 °C. This enhanced antioxidant activity was mainly attributed to the presence of ursolic acid, sterubin, menthol, sabinene hydrate and terpineol, compounds with a less polar character that therefore could cross more easily the cell membrane and exert their antioxidant activity inside the cells. Thus, separator fractions obtained at 20 MPa and 40 °C increased a 30% the CAA value respect to UAE extract and could be used for designing nutraceuticals or functional foods with cellular antioxidant activity. Precipitate fractions, at these extraction conditions, also showed an increase in TEAC value (40%) and could be employed as natural antioxidants in food formulations.