Astaxanthin from the Yeast Phaffia rhodozyma. Supercritical Carbon Dioxide and Organic Solvents Extraction

Supercritical carbon dioxide extraction of astaxanthin from Phaffia rodozyma was carried out, for several experimental conditions, using a semi-continuous apparatus. The yeast was previously freeze-dried and ground with a ball mill. The effects of the pressure (200 and 300 bar), temperature (40, 50 and 60?C) and supercritical solvent superficial velocities of 1.2 and 2.4 cm min, as well as the use of ethanol, as co-solvent (10 mol %), on the extraction efficiency were assessed. Organic solvent extractions, using acetone, dimethyl sulfoxide (DMSO) and a mixture of methanol and dichloromethane, were also carried out on whole and ground cells. The extraction with acetone of astaxanthin from ground Phaffia led to the highest yield. Supercritical extraction was compared with the organic extraction, and the highest recovery (75%) was achieved at the pressure of 300 bar, the temperature of 40?C and using ethanol as co-solvent. The lowest recovery of supercritical extraction was obtained at the pressure of 200 bar and the temperature of 50?C, without co-solvent. Moreover, the extraction yield increased with the pressure at constant temperature. On the contrary, the increase f temperature at constant pressure led to a decrease of the yield at 200 bar and to a slight decrease at 300 bar. Furthermore, the yield decreased with the flow rate.