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).