Study on supercritical extraction of lipids and enrichment of DHA from oil-rich microalgae

The present study aims to isolate the lipids from microalgae by supercritical CO₂ (SC-CO₂) extraction followed by a further enrichment of crude lipids to produce high-purity docosahexenoic acid (DHA) by an urea complexation method. Our systematic approach indicates the optimum conditions of supercritical CO₂ extraction were obtained as follows: 35 MPa, 40 °C, ethanol (95%, v/v) as the co-solvent, and the mass ratio of material to co-solvent 1:1. Under these conditions, 33.9% of lipid yield and 27.5% of DHA content were achieved. Despite the relatively low lipid yield, supercritical CO₂ extraction has exhibited many advantages over the Soxhlet extraction for the DHA enrichment such as high DHA purity and superb product quality. Furthermore, urea complexation method on DHA enrichment considerably increased the DHA purity from 29.7% to 60.4% with an enrichment ratio of 60.6%, under the optimum complexation conditions of urea/fatty acid 2:1, complexation time 8 h, and the complexation temperature of −10 °C.