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, N₂, 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 = 4000 kPa, T = 296.5 K, t = 360 min, and a = 325 rpm. Furthermore, from the scanning 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.