Extraction–adsorption–desorption process under supercritical condition as a method to concentrate antioxidants from natural sources

Concentrated extracts with antioxidative properties derived from labiatae family herbs were obtained by means of an extraction–adsorption–desorption procedure using supercritical carbon dioxide as solvent. Crude oleoresin, obtained from dried leaves of rosemary (Rosmarinus officinalis) using organic solvents, was used as starting material. Initial content of carnosic acid was 12.1% (w/w). Supercritical extraction of oleoresin followed by an adsorption step with various adsorbents (activated carbon, silica gel, magnesium silicate or activated clays) was carried out. As a result, an extract with low odor, color and aroma was obtained. After adsorption, retained compounds were also recovered in a desorption step under the same supercritical condition but using ethanol as co-solvent. The presence of non-soluble compounds limited the total extract yield to a maximum of 69.2%. As a consequence, only 40% of initial carnosic acid content in crude oleoresin was recovered. Activated carbon proved to be the most effective adsorbent in obtaining the highest value of carnosic acid in extract (29.1 g/100 g extract). In this case, it was possible to obtain an extract 2.4 times more concentrated in carnosic acid than crude oleoresin obtained with organic solvents. Experiments with sunflower crude oil demonstrated that all rosemary extracts increased the stability to oxidation of treated oil. Addition of 200 ppm of extract obtained after adsorption with activated carbon increased the protection factor up to 23% in comparison to the one for non-treated crude oil. This increment was higher than the one using butylated hydroxy toluene (<12%), a synthetic antioxidant of wide commercial use.