Evaluation of methodologies for lipid extraction from Lipomyces starkeyi and Rhodosporidium toruloides

Single cell oils (SCOs) have been explored as potential raw material for biodiesel production. Oleaginous yeasts, such as Rhodosporidium sp. and Lipomyces sp., are good candidates as SCOs producers. However, yeast cells are covered with a rigid cell wall which hinders the lipid extraction. Furthermore, the lipid extractability differs according to the species and lipid composition of the yeast. There is little literature available on which methodology is more suitable for each oleaginous yeast species. The most adequate methodology for extracting lipids from intact cells of Rhodosporidium toruloides CCT 0783 and Lipomyces starkeyi CBS 1807 were therefore identified in this project. The microorganisms were cultivated in bioreactors for 95 hours in a cultivation media using xylose as a carbon source and yeast extract and ammonium sulfate as nitrogen sources (C:N ratio equal to 116) and pH 5.5. The final biomass was 13.6 g/L for R. toruloides and 23.6 g/L for L. starkeyi. Lipid extractions were conducted in duplicates using hexane or different combinations of chloroform and methanol as described by Folch et al. (1957), Bligh and Dyer (1959), Pedersen (1962). For both yeast the Folch methodology resulted in higher lipid contents (mass of lipids/dry cell biomass): 42% for R. toruloides and 47% for L. starkeyi, followed by Pedersen’s (28% and 38%, respectively), Bligh and Dyer (23% and 7%, respectively) and hexane (3% and 6%, respectively).