ABSTRACT
The Fischer-Tropsch reaction water, which contains C2 to C5 monocarboxylic acids, generated as a co-product of the Sasol industrial oil-from-coal process, constitutes a potential cheap carbon substrate for the production of gamma-linolenic acid (GLA) by selced Mucor species. Three strains of Mucor were each grown in an air-lift reactor operated in a fed-batch, pH-stat mode under N-limitation with a mixture of C2 to C5 monocarboxylic acids as both pH titrant and carbon source. The production of GLA from this substrate was evaluated. Growth typically resulted in the rapid assimilation of acetic, n-butyric and n-valeric acids. Although propionic, iso-butyric and iso-valeric acids were assimilated to varying degrees, these acids accumulated in the culture. Mucor circinelloides CBS 203.28 gave the best results in that it assimilated 36% to 100% of each acid, had a biomass yield coefficient of 0.3 (calculated on acids utilized), and contained 28% crude oil, 84% of which comprised neutral lipids with a GLA content of 14.4%, giving 33 mg GLA/g biomass. GLA accumulation coincided with a decrease in the stearic-acid content of the neutral-lipid fraction. The results were comparable with previous results obtained with acetic acid and glucose as sole carbon sources, demonstrating the feasibility of producing GLA from the above mixture of organic acids.