Optimization of microbial cell disruption using pressurized CO2 for improving lipid recovery from wet biomass

Microbial cell disruption using pressurized gases (e.g., CO2) is a promising approach to improve the lipid recovery from wet oleaginous microorganisms by eliminating the energy-intensive drying required for conventional methods. In this study, we perform cell disruption of Rhodotorula glutinis using pressurized CH4, N-2, and Ar where we find the efficacy of these gases on cell viability is minimal. Since CO2 is found to be the only viable gas for microbial cell disruption among these four gases, we use a combination of Box-Behnken design and response surface methodology (RSM) to find the optimal cell disruption by tuning different parameters such as pressure (P), temperature (T), exposure time (t), and agitation (a). From RSM, we find 6 log reduction of viable cells at optimized conditions, which corresponds to more than 99% cell death at P=4000kPa, T=296.5K, t=360min, and a=325rpm. Furthermore, from thescanning electron microscope (SEM), we find a complete morphological change in the cell structure when treated with pressurized CO2 compared to the untreated cells. Finally, we find that up to 85% of total lipid can be recovered using optimized pressurized CO2 from wet biomass compared to the untreated wet cells where up to 73% lipid can be recovered.