Efficient purification of sophorolipids via chemical modifications coupled with extractions and their potential applications as antibacterial agents

Efficient synthesis and purification of sophorolipids produced by fermentation into ester and free acid derivatives has attracted significant interest as these compounds have many potential specific applications. In this study, the ester and free acid derivatives of sophorolipids were prepared via chemical modifications, and the purification via a series of stepwise extractions was optimized. Acidic type sophorolipids (SL-COOH) was readily obtained by hydrolysis of sophorolipids isolated from fermentation broth, while the lactonic sophorolipids (SL-ester) can be prepared by the esterification of SL-COOH. Then, a series of newly developed stepwise extractions using optimized solvent systems recovered more than 50% of the SL-COOH and about 80% of the SL-ester with high purity, respectively. Both modified SLs have great surface activities, can reduce the surface tension to 40–43 mN/m with critical micellar concentrations ranged from 50 to 120 mg/L. More importantly, SL-ester presented excellent antibacterial activity against B. subtilis and Moesziomyces sp ., and the inhibition efficiency reached over 96% and 83% at concentration of 1 g/L, was much better than that by natural SLs and SL-COOH. Such chemical modifications followed by the newly developed purification would be conducive to the practical applications of sophorolipids in several fields, especially as antibacterial agents.