Production of eicosapentaenoic acid by Nannochloropsis oculata: Effects of carbon dioxide and glycerol

•Glycerol had significant effects on metabolism of Nannochloropsis oculata.•Glycerol enhanced the lipid fraction in biomass but reduced the chlorophyll content.•Mixotrophy increased the percentage of saturated fatty acids in the lipids.•Eicosapentaenoic acid (EPA) level in broth depended strongly on growth conditions.•Mixotrophic growth with intermittent CO2 supply achieved a high EPA concentration.

The marine microalga Nannochloropsis oculata is a potential source of eicosapentaenoic acid (EPA, C20:5n3) and carotenoids for use in functional foods and nutraceuticals. Mixotrophic culture of N. oculata using glycerol was examined as a possible way of increasing the biomass and metabolite productivity relative to a pure photoautotrophic culture in modified f/2 medium. The effect of CO2 supply was also tested. EPA production in semi-continuous culture with and without glycerol and CO2 was evaluated. The effects of glycerol supplementation and light/dark cycling on the production of the biomass and EPA are reported for cultures conducted at a constant pH controlled using CO2. Consumption of glycerol was small, but its effects were significant. Glycerol enhanced the lipid content of the biomass but reduced the chlorophyll a content. Mixotrophic cultivation favored the production of lipids with a high percentage of saturated fatty acids that are generally desired in oils for making biodiesel. EPA concentration (5.3 ± 0.6 to 27.5 ± 1.6 mg EPA/L) in N. oculata cultures depended strongly on growth conditions. The highest EPA concentration occurred in non-aerated mixotrophic culture with intermittent CO2 supply without pH control. This EPA concentration (= 27.5 ± 1.6 mg/L) was comparable to that obtained in semi-continuous culture without glycerol and pH control, and aerated with CO2 enriched air during the light period (= 23.6 ± 1.1 mg/L).