Supercritical carbon dioxide extraction of compounds with pharmaceutical importance from microalgae

Four microalgae (Botryococcus braunii, Chlorella vulgaris, Dunaliella salina, Arthrospira maxima) were object of supercritical CO extraction studies, which were carried out in a flow apparatus at temperatures between 313.1 and 333.1 K and pressures up to 35,0 MPa. The microalga Botryococcus braunii produces extracellular alkadienes. Supercritical extracts obtained at 313.1 K, and pressures of 12.5. 20.0 and 30.0 MPa, were golden and limpid, unlike those obtained with organic solvents. The hydrocarbons of this microalga were selectively extracted and this selectivity increased with pressure. The microalga Chlorella vulgaris is a carotenoid producer of canthaxanthin and astaxanthin. The extraction yields of lipids and carotenoids were compared for whole, crushed and slightly crushed algae at a pressure of 35.0 MPa and a temperature of 328.1 K. The yield of supercritical extraction of carotenoids was also compared at several conditions of pressure and temperature. It increased with pressure at constant temperature, remained practically constant with temperature, at pressures of 27.5 and 35.0 MPa, and decreased with temperature at 20.0 MPa. The third alga studied was the Dunaliella salina. which produces P-carotene in high yield. Natural beta-carotene (cis and trans mixture) from this alga was submitted to supercritical carbon dioxide and it was assessed, at pressures up to 30.0 MPa and temperature of 313.1 K, that both isomers presented higher solubility than the synthetic trans-beta-carotene and that the cis isomer was much more soluble in supercritical CO2 than the trans isomer. Moreover, it was shown that the cis/trans ratio, in the supercritical extracts, increased significantly, relatively to the original one in the microalga, when the Dunaliella was submitted to supercritical CO2. The cyanobacteria Arthrospira (Spirulina) maxima can produce in large amounts the gamma-linolenic acid (GLA), C18:3 omega6. The yield and selectivity of the supercritical extraction, using CO2 and CO2 doped with ethanol, of the lipids and GLA were determined and compared with those obtained with organic solvents. (C) 2003 Elsevier B.V. All rights reserved.