Effect of supercritical CO2 extraction on the recovery of bioactive lipids and pigments from pretreated Nannochloropsis gaditana biomass

Nannochloropsis gaditana microalgae is a rich source of bioactive components, such as lipids and pigments, however their production is limited due to the complexity of the extraction process and the resistance of the cell wall. The aim of this study was to evaluate the extraction of bioactive compounds from N. gaditana using supercritical fluid extraction (SFE) with CO₂, which was compared with a conventional solvent extraction. The effect of biomass pretreatment with freeze/thaw cycles followed by ultrasounds before SFE or conventional extraction was evaluated, showing differences in extraction yields. Although the lipid extract obtained by SFE was low (1.63% dry weight of biomass), the application of the pretreatment substantially increased the yield (8.51%). Scanning electron microscopy images showed that freeze/thaw cycles plus ultrasounds damaged the cell structure favoring the release of bioactive components outside the cell. Eicosapentaenoic acid (EPA, 20:5 n-3) was the most abundant fatty acid (FA) followed by cis-9 16:1 and 16:0 in all extracts. The highest EPA levels were achieved by SFE with pretreated biomass (37.58% of total FA). These extracts also showed the most nutritionally suitable FA profile. SFE application increased the total carotenoid and chlorophyll contents, reaching values of 21.18 and 60.23 mg/g extract, respectively. The combination of co-solvents with different polarity (ethyl acetate and ethanol) during SFE proved to be useful for a more complete extraction of the different components. Our findings support SFE as a sustainable alternative technique to produce molecules with recognized biological value from microalgae pretreated biomass.