Hydrothermal conditioning of oleaginous yeast cells to enable recovery of lipids as potential drop-in fuel precursors

Authors: BANERJEE, SHIVALI - University Of Illinois; Dien, Bruce; SINGH, VIJAY - University Of Illinois

Submitted to: Journal of Cleaner Production
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2024
Publication Date: 8/16/2024
Citation: Banerjee, S., Dien, B.S., Singh, V. 2024. Hydrothermal conditioning of oleaginous yeast cells to enable recovery of lipids as potential drop-in fuel precursors. Journal of Cleaner Production. https://doi.org/10.1186/s13068-024-02561-x.
DOI: https://doi.org/10.1186/s13068-024-02561-x

Interpretive Summary: There is an unmet market demand for biological oils for use in making chemicals and fuels. For example, bio-oils can be used to manufacture a blend for jet fuel that reduces green house gas emissions. Airline carriers are promoting production of sustainable aviation fuel (SAF) in order to meet their ambitious environmental targets. This will be a major challenge for agriculture given that the U.S. consumes 1.5 million barrels of jet fuel each day. One potential source of these oils are growing yeast that naturally produce and store these oils as droplets in their cells. Yeast used by ARS researchers typically contain 50% of their weight in oil. However, getting the oil out is challenging because these yeast have tough cell walls. Working with collaborators, we have found that simply heating the yeast at 121C followed by standard solvent extraction is sufficient for recovering all of the available oil. This method is expected to be convenient to implement industrially because it just involves heating the cells in a tank. The results are expected to be of most interest for the corn fermentation industry because of their current interest in producing SAF and expertise in growing yeast.

Technical Abstract: Lipids produced using oleaginous yeasts is an emerging feedstock to manufacture commercially valuable oleochemicals ranging from pharmaceuticals to lipid-derived biofuels. Biodiesel and sustainable aviation fuel (SAF) are two markets that can be served by yeast derived lipids. Production of lipids using yeast is a multistep procedure that requires yeast cultivation and harvesting, recovery of the lipids, and chemical conversion of the lipids to the biofuels. Lipid recovery is a technically challenging step because it requires cell lysis and solvent extraction. In this study, thermal pretreatment has been explored as a method for lysing the cell wall of the oleaginous yeast Rhodotorula toruloides prior to lipid extraction. Hydrothermal pretreatment for 60 min. at 121°C with a dry cell weight of 7% (w/v) in the yeast slurry led to a recovery of 84.6±3.2% (w/w) of the total lipids. The conventional sonication and acid-assisted thermal cell lysis led to a lipid recovery yield of 99.8±0.03% (w/w) and 109.5±1.9% (w/w), respectively. The fatty acid profiles of the hydrothermally pretreated cells and freeze-dried control were the same, suggesting that the thermal lysis of the cells did not degrade the lipids. This work demonstrates that hydrothermal pretreatment of yeast cell slurry at 121°C for 60 min. is a robust and green method for cell conditioning for extracting intracellular microbial lipids for biofuel production and provides a baseline for further scale-up and process integration.