Optimizing the production of docosahexaenoic fatty acid by Crypthecodinium cohnii and reduction in process cost by using a dark fermentation effluent

Abstract

Recovery of omega-3 fatty acids (FAs) from microalgae constitutes a valuable alternative to fish oil, and offers the ability to isolate a single ω-3 FA, instead of a mixture. In the framework of the concept of circular economy and sustainability, in the current work, an alternative carbon source was used as feed for oleaginous microalga Crypthecodinium cohnii cultivation and, consequently, production of the omega-3 FA, docosahexaenoic acid (DHA). The conditions that improve DHA production in a fed-batch culture of C. cohnii, using an organic acid-rich liquid fraction of dark fermented biowaste as feed, were studied and optimized. The process was mathematically approached focusing on a proper Design of Experiments (DoE) method coupled with Response Surface Methodology (RSM). The temperature of 23 °C and the use of yeast extract (YE) as initial nitrogen source favored the amount of DHA recovered. In addition, the increase of the volatile FA (VFA) concentration of the feed enhanced the recovered cell biomass. In order to propose a final fermentation protocol with industrial potential and evaluate the annual total cost for the production of DHA, fermentation process was scaled-up and economically evaluated through cost analysis. The increase of bioreactor size from 1 to 20 m3 leads to a significant decrease in the cost of produced DHA while leveling at higher capacities.