System optimization of an embedding protocol to immobilize cells from Candida bombicola to improve the efficiency of sophorolipids production

This study introduces the implication of immobilization technology in the fermentation process of sophorolipids (SLs) production by Candida bombicola. Firstly, an evaluation system was established for the performance of embedding immobilization and subsequently applied to guide the optimization of operating conditions for sodium alginate immobilization. Correspondingly, the SLs titer increased from 11.4 g/L to 14.6 g/L. Secondly, polyvinyl alcohol was introduced for composite embedding to improve the stability of immobilized beads. Then exogenous addition of 1.5% diatomite further enhanced the fermentation performance of immobilized cells, thereby increasing the SLs titer to 35.9 g/L, which was 2.1 times higher than the original immobilized cells method. Finally, the immobilized cells were tested for three repeated batches of SLs fermentation. Compared to the free cells fermentation, the SLs productivity and substrate conversion rate were increased by 35.5% and 9.1%, respectively. The obtained results showed high potential for application on an industrial scale.