Real-time dynamic analysis with low-field nuclear magnetic resonance of residual oil and sophorolipids concentrations in the fermentation process of Starmerella bombicola.

The yeast Starmerella bombicola is known to produce sophorolipids (SLs) by fermentation method. In the fermentative production of SLs, at least three phases i.e. hydrophilic phase of glucose, ions and acidic-form SLs; hydrophobic phase of oil and lactone-form SLs; solid phase of cell biomass and SLs crystals are present in the broth. Therefore, a rapid and real-time detection of residual oil and SLs can provide valuable information in the regulation and optimization of the process to better produce SLs effectively. Looking into the importance, in this study, a rapid, accurate and precise method to quantify the concentrations of oil and SLs using low-field nuclear magnetic resonance (LF-NMR) was developed. Compared to the traditional weighing method, all the parameters for the evaluation of accuracy, precision and relative recovery presented better performances. Moreover, the proposed LF-NMR method could completely avoid using organic solvents that are commonly employed in the weighing method, besides shortening the pre-treatment and detection times from 24 h to just <20 min. Finally, LF-NMR method has been successfully used to monitor residual oil and SLs during the fermentation of Starmerella bombicola to obtain SLs and it has been observed that the production of SLs would be effectively improved by appropriately controlling the concentration of oil in terms of titer, productivity and yield.