Pressurized fluid extraction of polyunsaturated fatty acids from the microalga Nannochloropsis oculata

Microalgae are the primary producers of economically valuable polyunsaturated fatty acids (PUFAs) and can be used as a resource for biorefining. In this respect, these high-value products may support the economical viable energy recovery from microalgae. The extraction of PUFA-containing lipids from Nannochloropsis oculata, a marine species rich in eicosapentaenoic acid (EPA), was tested with a commercially available pressurized fluid extraction technique (PFE, traded as Accelerated Solvent Extraction (ASE®)) in our study. Solvents, which are suitable for an application in the food and pharmaceuticals industry, were used (n-hexane, n-hexane/propan-2-ol (2:1 vol.%), ethanol 96 vol.%) to test the quantitative effect of solvent polarity on the gravimetric extraction yield, total fatty acid and EPA yield. The highest extraction yield resulted from ethanol extraction (36 ± 4 mass%), compared to low yields from n-hexane extraction (6.1 ± 0.3 mass%). A maximum fatty acid yield of 16.7 ± 0.6 mass% was determined for the biomass extracted with the green solvent ethanol. The EPA yield of 3.7 ± 0.1 mass% with the use of ethanol indicates that EPA production from N. oculata is economically beneficial, referring to prognosis from literature. The remaining biomass may eventually be used for energy recovery and other applications within a biorefinery concept.

Graphical abstractGravimetric extraction yield, total fatty acid (Σ FA), total polyunsaturated fatty acid (PUFA) and total eicosapentaenoic acid (EPA) content based on microalgae lipid extract and biomass input (“yield”) in mass%. Data from Accelerated Solvent Extraction (ASE®) tests with n-hexane, a n-hexane/propan-2-ol mixture (2:1 vol.%) and ethanol (96 vol.%) at 60 °C and 10–12 MPa with 5 extraction cycles and 10 min static extraction time each. Freeze-dried and ground (1 mm) microalgae Nannochloropsis oculata was used for the tests.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Pressurized fluid extraction of PUFA-containing microalgal lipids (N. oculata). ► Solvents suit food industry. ► Best results in terms of PUFA-yields achieved with most polar solvent. ► Achieved EPA-yield is economically beneficial (according to literature data).