SUPERCRITICAL CARBON-DIOXIDE EXTRACTION OF EVENING PRIMROSE OIL

The oil extracted from the seeds of Oenothera biennis L. (evening primrose) is a major commercial source of gamma-linolenic acid, a fatty acid having potential therapeutic value in the treatment of several diseases. This fatty acid is prone to oxidation and thermal rearrangement; therefore, the conventional recovery of the oil via mechanical expression and hexane extraction must be carried out under very mild and controlled conditions. In this study, supercritical fluid extraction with carbon dioxide has been employed as an alternative method to recover evening primrose oil (EPO). Extractions were performed over the pressure range of 20-70 MPa and at temperatures from 40 to 60-degrees-C, with a CO2 mass flow rate of 18 g/min. The experimental data permitted the determination of EPO solubility in supercritical CO2 at the tested extraction conditions. Supercritical fluid chromatographic analysis of fractions collected during the extraction showed a subtle shift in the triglyceride composition. Fatty acid methyl ester analysis on similar fractions indicated that the fatty acid content was invariant with respect to extraction time.