Statistical optimization of arachidonic acid synthesis by Mortierella alpina CBS 754.68 in a solid-state fermenter

Arachidonic acid (ARA) is an omega-6 fatty acid that plays a major role in human health. The present study optimizes the production of ARA by the soil fungus Mortierella alpina CBS 754.68 on oil cakes. In the first step, the best substrate was chosen from four oil cakes, namely soybean, sunflower, olive, and colza oil cakes, of which sunflower oil cake showed the highest yield. In the next step, screening tests were performed using the Plackett-Burman design. Seven variables (substrate particle size, moisture content, time, temperature, yeast extract, glucose, and glutamate) were investigated (each taking values of +1 and -1). Among these variables, time, temperature, and substrate particle size significantly affected ARA production (p < .05), so they were further investigated in the optimization step. The optimal fermentation time, temperature, and substrate particle size calculated by response surface methodology were 8.75 days, 18.5°C, and 1.3 mm-1.7 mm, respectively. Under these conditions, M. alpina was predicted to produce 4.19 mg of ARA/g dry weight of substrate (DWS). The actual yield, determined in evaluation tests, was 4.48 ± 0.16 mg ARA/g DWS, which shows the accuracy of the model. In the final step, the effect of the aeration rate on producing ARA was investigated in a packed-bed solid-state fermenter under the determined optimal conditions. In this stage, the highest ARA yield was 10.13 ± 0.26 mg/g DWS, approximately double that of the optimization step, and this confirms that aeration increases ARA production by M. alpina.