Arachidonic acid production by Mortierella alpina MA2-2: Optimization of combined nitrogen sources in the culture medium using mixture design

Abstract

Arachidonic acid (ARA) is an omega-6 fatty acid that is essential for human nutrition. Commercial production of ARA by fermentation is of great interest, as it is present in relatively low levels in breast milk. The production of ARA by the fungus Mortierella alpina is affected by the types of nitrogen available in the culture medium as well as the carbon to nitrogen (C:N) ratio. In this study, the C:N ratio and combined nitrogen sources were investigated for optimal production of biomass, lipids, ARA content and concentrations by M. alpina MA2–2. Results showed that a C:N ratio of 15 could increase biomass, lipid content and ARA concentration by a 1.49, 1.50 and 1.99 fold-increase, respectively. After screening experiments, peptone, yeast extract, sodium nitrate (NaNO₃) and monosodium glutamate (MSG) were selected for closer study using mixture design to determine the optimal combination of nitrogen sources for maximizing ARA concentration. The combination of yeast extract and sodium nitrate was the most effective for producing ARA, resulting in 17.67 ± 0.16 g L⁻¹ biomass, 32.7 ± 0.02 % lipids, and 39.33 ± 2.10 % ARA content (2270 ± 100.9 mg L⁻¹ ARA concentration), corresponding to 1.21, 1.90, 1.32 and 3.05 fold-increases, respectively. This study demonstrates that a significant improvement in total lipid accumulation and ARA concentration can be achieved by combining a complex organic nitrogen source with a lower level of inorganic nitrogen in the culture medium.