Comparison between extraction of lipids and fatty acids from microalgal biomass

Seven solvent mixtures have been used to extract the lipid fraction of lyophilized biomass of Isochrysis galbana . Six of them were composed of biocompatible solvents. Each method was carried out under relaxed operating conditions (i.e., one hour at room temperature) with extraction in a nitrogen atmosphere to prevent autooxidation and degradation of polyunsaturated fatty acids (PUFAs). Apart from the well‐established Bligh and Dyer method [ Can. J. Biochem. Physiol. 37 :911 (1959)] (Cl 3 CH/MeOH/H 2 O, 1∶2∶0.8, vol/vol/vol), which rendered the highest yield of lipids (93.8%), ethanol (96%) and hexane/ethanol (96%), 1∶2.5 vol/vol produced the best results (84.4 and 79.6%, respectively). To obtain free fatty acids, KOH was added to the solvent mixtures used to extract the total lipids, except for Cl 3 CH/MeOH/H 2 O, and direct saponification was carried out at 60°C for 1 h or at room temperature for 8 h. The highest yields obtained by direct saponicification were 81% with hexane/ethanol (96%), 1∶2.5, vol/vol and 79.8% with ethanol (96%). Partial yields of the main n ‐3 PUFAs found in I. galbana , stearidonic acid (SA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were calculated for both extraction methods. For lipid extraction with ethanol (96%), yields of 91, 82 and 83% were obtained for SA, EPA and DHA, respectively. When direct saponification was used, hexane/ethanol (96%; 1∶2.5, vol/vol) produced the best yields of (91, 79 and 69% for SA, EPA and DHA, respectively).