Effect of harvesting processes on the lipid yield and fatty acid profile of the marine microalga Nannochloropsis oculata

The effect of different methods of biomass concentration and salt removal on the lipid yield and fatty acid profile of the marine microalga Nannochloropsis oculata was evaluated. The microalgae were subjected to nine treatments: (1) centrifugation, (2) centrifugation + washing with H2O, (3) centrifugation + washing with ammonium formate, (4) flocculation with NaOH, (5) flocculation with NaOH + washing with H2O, (6) flocculation with NaOH + washing with ammonium formate, (7) flocculation with NaOH and neutralization with HCl, (8) flocculation with NaOH, neutralization with HCl + washing with H2O, and (9) flocculation with NaOH, neutralization with HCl + washing with ammonium formate. Flocculation with the addition of NaOH was effective at concentrating biomass (>90%) but interfered with lipid extraction because it exhibited a lower lipid yield (4.40 ± 0.1%) compared with centrifugation (45.4 ± 0.8%). Moreover, important polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA C20:5) and eicosatetraenoic acid (ETA C20:4), disappeared when NaOH was used. Centrifugation plus washing the biomass with ammonium formate was more effective than other treatments, leading to higher lipid yields, as well as larger amounts of the polyunsaturated fatty acids EPA and ETA. However, it is a very expensive harvesting method. Thus, the main finding of the present study is that microalgae concentration processes can affect lipid and fatty acid extraction in massive microalgae production; therefore, it is necessary to carefully choose the harvest process to be used in large-scale microalgae production.