New Method for the Extraction of Single-Cell Oils from Wet Oleaginous Microbial Biomass: Efficiency, Oil Characterisation and Energy Assessment

Abstract

Culture medium composition and an efficient lipid extraction process have the largest impact on the cost of industrial production of microbial single-cell oil (SCO). In this study, SCO from the yeast Rhodosporidium thoruloides grown in sugarcane medium was successfully produced in a 1 m3 bioreactor. Biomass was concentrated by sedimentation and the acid-hydrolysed cells were extracted using a recurrent extraction (RE) and a newly-proposed wet extraction (WE) process. RE consisted of Soxhlet extraction of dry hydrolysed biomass with different solvents: hexane, chloroform and chloroform/methanol (2:1). The WE process consisted of the extraction of wet hydrolysed biomass with the same solvents. The highest lipid yields (m/m) were achieved by hexane in RE and chloroform in WE. The chloroform WE extract presented similar density, saponification number, iodine value, moisture and acid value as that from RE with hexane, but much lower peroxide content. The fatty acid methyl ester compositions of WE and RE extracts were also very similar. An energy–cost analysis showed that WE used only 13% of the energy used in RE. Moreover, an energy conservation analysis showed that approx. 65% of the energy from molasses was effectively transformed into microbial lipids. The low energy requirement, the high efficiency and the characteristics of the resulting bio-oil achieved by WE evidence the potential of the proposed methodology for use on an industrial scale.