Supercritical extraction of astaxanthin from H. pluvialis using ethanol-modified CO2. Experiments and modeling

Haematoccocus pluvialis is the main natural source of astaxanthin. Extraction with SuperCritical (SC) carbon dioxide (CO2) is an interesting choice for astaxanthin recovery because the medium-to-high yield, high selectivity for high-value compounds, and avoidance of thermal damage to labile bioactive compounds. In the case of heavy and/polar compounds such as astaxanthin, yield can be increased using GRAS polar cosolvents or modifiers such as ethanol. For this reason SC CO2 extraction was carried out at 313-343 K and 30-55 MPa using pure or ethanol-modified (4 or 8% v/v) CO2. Response surface analysis showed a positive effect of pressure and mild negative effect of temperature in the astaxanthin recovery. Besides, added ethanol improves astaxanthin recovery but up to a maximal using 4.5% (v/v). The model of Sovova (2006) fitted well experimental data for astaxanthin extraction using pure and ethanol-modified CO2 under selected experimental conditions. Best-fitting model parameters suggest that improvement in astaxanthin recovery when adding ethanol is due to its large positive effect on mass transfer within unbroken H. pluvialis cysts rather than in the solubility in SC CO2 or solute partition between SC CO2 and pretreated cysts.