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

Abstract

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±1.6mg 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±1.6mg/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±1.1mg/L).

Keywords: Carotenoids; Eicosapentaenoic acid; Lipids; Mixotrophic culture; Nannochloropsis oculata; Polyunsaturated fatty acids.