Comparison of lipid droplet extraction from cell wall-deficient Chlamydomonas reinhardtii with pulsed electric fields or osmotic shock

Microalgal lipid droplets (LDs) are promising sources of pre-emulsified triacylglycerols (TAGs) and can be extracted aqueously due to their hydrophilicity. To develop more sustainable extraction processes, pulsed electric fields (PEF) and osmotic shock (OS) with NaCl were compared as treatments before aqueous LD extraction from a cell wall-deficient microalga Chlamydomonas reinhardtii. The highest LD extraction yields were 54% (0.6 g L^-1) using OS and 42% (0.5 g L^-1) with PEF. Both treatments were most effective with cells from the late stationary phase of growth. LD extracts from both processes exhibited a TAG composition similar to the original biomass. LDs recovered after PEF appeared native (diameters from 1.4 to 2.0 μm), whereas OS caused LD coalescence (diameters from 1.9 to 2.6 μm). Both methods co-extracted nitrogenous compounds, while OS also co-extracted chlorophyll. OS and PEF for aqueous LD extraction provide greener alternatives to the widespread extraction of lipid using organic solvents.