Sweet sorghum is a C4 crop possessing high photosynthetic efficiency which can grow in geographical areas with a temperate climate. It contains approximately equal quantities of soluble and insoluble carbohydrates and is a promising substrate for lipid production, as its biomass has a comparatively high C:N ratio of about 60:1 Aim of this work is the evaluation of three oleaginous yeasts (Trichosporon fermentans, Lipomyces starkeyi and Rhodosporidium toruloides) and one fungus (Fusarium oxysporum) concerning their ability to accumulate SCO (yielding biodiesel) when cultivated on enzymatically liquefied sweet sorghum stalks1. Initially experiments were performed with sugar mixtures simulating the carbohydrate content of sweet sorghum. The sugar mixture culture study focused on the effect of nitrogen sources and C:N ratio on the growth and SCO accumulation.
When cultivated on sweet sorghum stalks, the ability of the microorganisms to grow without any addition of external nitrogen source was evaluated. T. fermentans found to have the ability to utilize both carbon and nitrogen content of sweet sorghum and accumulated SCO as high as 2.24 g /100 g dry weight of sorghum stalks at an initial solid concentration of 8.69% w/w. F. oxysporum could also efficiently accumulated SCO as high as 2.20 g /100 g dry material. Finally, in order to increase the final concentration of SCO, higher solids concentrations were applied and the effect of the liquefaction process was evaluated.
1 Matsakas L. and Christakopoulos P. (2013): Optimization of ethanol production from high dry matter liquefied dry sweet sorghum stalks. Biomass and Bioenergy, 51:91-8.