Tetradesmus obliquus microalgae: solvent extraction of lipids under different process conditions

Abstract

Microalgal lipids exhibit physical-chemical characteristics similar to vegetable oils, representing alternative sources of long-chain fatty acids for food supplements.However, separating intracellular lipids from microalgae biomass is still challenging due to downstream processing technology limitations that depend on the particular microalgal species and its cultivation conditions. Thus, this work evaluated a multistep process for lipid extraction from Tetradesmus obliquus biomass instead of conventional single extraction methods to improve the lipid yield. The wet biomass was freeze-dried, the cells of the dried biomass were disrupted in a ball mill, and the milled biomass was suspended in water to obtain solid contents of 5 % and 10 % w v -1 . Lipids were extracted from the aqueous suspension using the ethanol polar solvent and the hexane apolar solvent with ethanol:hexane ratios of 1:1, 1:2, and 3:5 v v -1 . Tests were also carried out on the deproteinized biomass to evaluate the effect of proteins on emulsion formation since deproteinization can avoid emulsion formation. Thus, lipid downstream processing could be designed without an emulsion removal stage. The biomass was deproteinized before lipid extraction with NaOH at pH 10.The highest lipid content was verified for the 1:2 ethanol:hexane ratio, in which up to 42 % of the total lipids were extracted from the biomass. With the 3:5 ratio, the organic and aqueous phases emulsified due to the presence of lipoproteins, which hindered the lipid extraction process. Under the studied conditions, no increase in lipid extraction yield was observed with increases in the solid content or biomass deproteinization.