Exploiting microalgae as a source of essential fatty acids by supercritical fluid extraction of lipids: Comparison between Scenedesmus obliquus, Chlorella protothecoides and Nannochloropsis salina

•Supercritical carbon dioxide extraction of lipids from Scenedesmus obliquus, Chlorella protothecoides and Nannochloropsis salina.•Comparative Soxhlet extraction of lipids.•Effect of the extraction method, SCCO2 parameters and microalgae species on α-linolenic content and fatty acid profile.•Application of mathematical models to simulate extraction curves.•Correlation of the experimental solubility data.

Supercritical CO2 extraction from microalgae is applied with the aim of obtaining an oil rich in α-linolenic (ALA) essential fatty acid and with a low ω6:ω3 ratio. The maximum extraction yield is obtained at 60 °C and 30 MPa with 0.4 kg/h of CO2 and 5% of co-solvent (ethanol). When the effect of pressure, temperature and density on the supercritical extraction yield and solubility are studied, the thermodynamic cross-over is found at a pressure close to 30 MPa, while the extraction cross-over occurs at around 25 MPa. The experimental solubility data are correlated by literature empirical models. Mathematical models developed by Sovová are applied to describe the experimental extraction curves. Soxhlet extraction of lipids is also carried out, obtaining a similar fatty acids profile but proving to be less selective than SCCO2 method. Among the three species of microalgae examined, results show that Scenedesmus obliquus oil is richer in ω-3 fatty acids and ALA than Chlorella protothecoides and Nannochloropsis salina lipids. The effect of the extraction parameters on ALA content and the fatty acid profile is also analysed, concluding that the ω-3 percentage is favoured by lower temperatures, lower pressures and shorter extraction times.

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