Research paperSystematic development of a two-stage fed-batch process for lipid accumulation in Rhodotorula glutinis

- An industrial relevant process of oleaginous Rhodotorula glutinis was developed.
- The fast and robust process ensures 106 ± 2 g L−1 biomass with 63 ± 6% lipid content.
- The optimal C/N ratio for an economic and sufficient lipid production was 50.
- A lipid detection assay based on fluorescent Nile Red was established.
- For the first time glycerol formation in R. glutinis was investigated and discussed.

The application of oleaginous yeast cells as feed supplement, for instance in aqua culture, can be a meaningful alternative for fish meal and oil additives. Therefore, a two-stage fed-batch process split into growth and lipogenesis phase was systematically developed to enrich the oleaginous yeast Rhodotorula glutinis Rh-00301 with high amounts of lipids at industrial relevant biomasses. Thereby, the different carbon sources glucose, sucrose and glycerol were investigated concerning their abilities to serve as a suited raw material for growth and/or lipid accumulation. With the background of economic efficiency C/N ratios of 40, 50 and 70 were investigated as well. It became apparent that glycerol is an improper carbon source most likely because of the passive diffusion of this compound caused by absence of active transporters. The opposite was observed for sucrose, which is the main carbon source in molasses. Finally, an industrially applicable process was successfully established that ensures biomasses of 106 ± 2 g L−1 combined with an attractive lipid content of 63 ± 6% and a high lipid-substrate yield (YL/S) of 0.18 ± 0.02 g g−1 in a short period of time (84 h). Furthermore, during these studies a non-negligible formation of the by-product glycerol was detected. This characteristic of R. glutinis is discussed related to other oleaginous yeasts, where glycerol formation is absent. Nevertheless, due to modifications in the feeding procedure, the formation of glycerol could have been reduced but not avoided.