Optimization of Oxygen Supply Control During the Fermentation of Sophorolipids Synthesis from Alkane as Substrate

Sophorolipid (SL) is one of the most promising biosurfactants widely used in cosmetics, petroleum, pharmaceutical and other industrial fields. In this study, n-hexadecane was used as a hydrophobic substrate to investigate the effect of different oxygen supply levels on SLs synthesis. Through integrated analyses of metabolic flux distribution and key enzyme activities during the fermentation process, it was found that the oxygen supply level significantly affected the syntheses of fatty acids and hydroxyl fatty acids, and, simultaneously, caused significant changes in the utilization of glucose and alkanes. The on-line physiological parameter respiratory quotient (R_Q) well dictated the changes of intracellular metabolic flux, which could act as a key process parameter to regulate cell metabolism. Finally, by enabling an appropriate oxygen supply level during the synthesis period of SLs, the utilization rate of the relatively expensive alkane substrate could be optimized, and the related power input reduced, thus improving the production economy. The results of this study could be extended to the study of other hydrophobic substrates such as rapeseed oil and oleic acid for SLs fermentation, and provided a theoretical basis for the control of industrial-scale SLs fermentation process.