Yu Wang

and 2 more

A simpler and more efficient method for preparing sophorolipids (SLs) facilitates the application of SLs. In this study, a new preparation method for SLs named SLs-WpH was designed firstly: the SLs in fermentation broth were separated by sedimentation in a separatory funnel, then dissolved in distilled water by adjusting the pH to 6-7 and centrifuged to remove the yeast brought in the sedimentation process, and the supernatant was vacuum freeze-dried. Secondly, the purity, composition, and antimicrobial activity of SLs-WpH were compared with the other two types SLs purified by ethanol and ethyl acetate (SLs-EtOH, SLs-EAC) in order to evaluate the feasibility of this preparation process. The purity of SLs-WpH was between that of SLs-EtOH and SLs-EAC and there was no difference in the composition, mainly lactonic SLs by TLC and HPLC analysis. SLs-WpH showed broad-spectrum antimicrobial activity against bacteria, fungi and actinomyces. In addition, both the diameter of the inhibition zone (15 to 18 mm) against Staphylococcus aureus and the mycelium inhibition rate (70 to 78%) against Phytophthora infestans were not significantly different among these three types SLs; SLs-WpH had better inhibitory effect against Streptomyces scab and S. bottropensis with MICs of 32 μg mL-1 than the other two types with MICs ≥64 μg mL-1, which is the first reported that SLs had inhibitory activity against actinomyces. The results of this study indicated that the new preparation process of SLs is feasible and SLs have great application potential in the prevention of potato common scabs caused by pathogenic Streptomyces.