Medium and process optimizations for Euglena gracilis with high biomass production enriched with protein

Axenic Euglena cultures were grown under different LED conditions, medium compositions, and durations of cultivation to identify the factors involved in tuning Euglena biomass quality, especially protein and paramylon contents. Compositional analysis suggests that paramylon and protein concentrations in biomass can be tuned to different extents depending on medium and process conditions, including medium compositions, glucose concentrations, and illuminations of various LED spectra. Through the optimization of these parameters, the biomass productivities under specified conditions reached ~50–68 g/L. The protein-rich (>50 % dry basis) Euglena cultures can be produced with higher biomass productivities (38 g/L) under mixotrophic conditions with the presence of white and red LED lights and the modified medium composition. The cell morphology studies of Euglena cultures under various cultivation conditions indicate the correlation of slender cell-shape to the cell feature of high-protein contents in the biomass. The fresh cellular volumes and dry weights of paramylon-rich round-shaped cells were also estimated to be 5–9 times higher than those of protein-rich slender-shaped cells. The present study demonstrates an effective method to produce high-protein Euglena biomass with higher productivity in a shorter time.