Lipid Extraction from the Wet Microalgal Biomass of Nannochloropsis gaditana using Pressurized Liquids
Natalia Castejón and Francisco Javier Señoráns*
Healthy-Lipids Group, Seccion Dept. Ciencias de la Alimentación, Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid, Spain. 
 *Email: javier.senorans@uam.es

Microalgae are the primary producers of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids in the marine environment, therefore they are considered to be a promising alternative source of omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs). Lipid extraction directly from the wet microalgae, without a drying or lyophilization process, could reduce significantly the cost of the extraction process. Moreover, the lipid extraction methods used for microalgae are based on organic solvents (chloroform/methanol) with the disadvantage that these solvents are toxic. Nannochloropsis gaditana is a cultivated algae with an important content of triglycerides and polar lipids. This work presents the use of Pressurized Liquid Extraction (PLE) to extract efficiently the lipid compounds of Nannochloropsis gaditana wet biomass with less toxic solvents than traditionally used and to isolate the omega-3 rich triglycerides. Different extraction solvents and their mixtures were evaluated to extract the lipid fraction of Nannochloropsis gaditana concentrated biomass with 27% of microalga. The optimal extraction method using PLE was achieved by sequential extraction with different solvents to fractionate the algal lipids. After a first extraction with water at 90°C, algae was extracted with 5% ethanol in water at 90°C and finally two consecutive extractions with hexane/ethanol (3:1).  At these conditions, a lipid extract yield of 13.12% was obtained, only slightly minor than using the same method with chloroform/methanol (2:1) (15.75%). Lipid extract obtained with hexane/ethanol (3:1) was composed of triglycerides (21.88%) enriched in 37.3% of EPA, while using chloroform/methanol (2:1) was 15.0% of triglycerides enriched in 36.9% of EPA. In conclusion, results showed that the proposed extraction method using PLE is a clean and direct alternative to fractionate lipid compounds enriched in omega-3 EPA from Nannochloropsis gaditana wet biomass avoiding toxic and aggressive solvents.