Fumaric acid production by Rhyzopus oryzae in presence of n-dodecane as oxygen-vector

Abstract

The production of fumaric acid by Rhyzopus oryzae has been investigated for two fermentation systems, namely batch and fed-batch fermentations. In both cases, n-dodecane has been added into the broth at various concentrations, this hydrocarbon acting as oxygen-vector, increasing the DO level and oxygen transfer rate. Higher oxygen concentration could lead to the inhibitory phenomenon, which is more pronounced at n-dodecane concentration over 10 % vol. For this reason, the highest fumaric acid concentration was reached for 5% vol. n-dodecane. The fed-batch system allowed to reaching higher concentrations of fumaric acid, regardless of n-dodecane volumetric fraction. Compared to the batch system, the productivity was for 1.2–1.4 times higher, the most important increase corresponding to 10 and 15 % vol. hydrocarbon, while the least important for 0 and 5% vol. hydrocarbon. The values of kLa for fed-batch regime were considerably lower compared to those recorded for batch fermentation, due to the cumulative effects of higher viscosity (highest rate of biomass accumulation) and smaller size of fungal pellets. On the basis of the experimental results, it was concluded that the optimum concentration level of n-dodecane for acid production in both fermentation systems is 5% vol.