Production of protein-rich extracts from disrupted microalgae cells: Impact of solvent treatment and lyophilization

This study investigated the preparation of protein-rich extracts from different microalgae by purification and minimal processing approaches (less-refinement) by studying separately the effects of (i) (nonaqueous) solvent-precipitation, (ii) lyophilization, and (iii) (nonaqueous) solvent-washing of lyophilized fractions. Cells were disrupted by high pressure homogenization (180 MPa, 25 degrees C) and increasing number of passes. Cells were resistant to cell disruption in following order: Phaeodactylum tricornutum < Chlorella sorokiniana < Chlorella vulgaris < Nannochloropsis oceanica. Dispersions of disrupted microalgae were separated into water-soluble-protein and water-insoluble-protein fractions by centrifugation and powdered extracts were prepared from both fractions. Solvent-precipitation produced extracts with the highest protein content except for the insoluble protein fractions of Phaeodactylum tricornutum, and low overall pigment content. Highest protein contents were observed for extracts of Chlorella sorokiniana with contents of 49.9 +/- 1.1 wt% (solvent-precipitated soluble-protein extract) and 56.5 +/- 1.2 wt% (solvent-precipitated insoluble-protein extract) (N x 5). Less-refined lyophilized extracts had protein contents from 18.5 +/- 0.3 wt% to 46.6 +/- 0.4 wt% (N x 5) without solvent consumption but pigments were not separated. Finally, mainly polar solvents facilitated an increase in protein content and only slight changes in color were obtained during solvent-washing of lyophilized extracts.