Efficient preparation of diacetylated lactonic sophorolipids and their potential for use as antibacterial agents in the agricultural industry

A novel strategy prepares highly pure Di-Ac LSLs with a yield over 77%. • Di-Ac LSLs exhibit potent antibacterial activity against Gram-positive bacteria. • Di-Ac LSLs show significant inhibitory activity against fungal mycelia. • The mechanism involves disruption of cell membranes and inhibition of biofilm formation. Diacetylated lactonic sophorolipids (di-Ac LSLs), the most hydrophobic of the sophorolipids congeners, show great promise as antibacterial agents in a variety of fields. However, their efficient production is challenging. This study proposes a novel strategy for efficiently preparing highly pure di-Ac LSLs from fermented SLs, using oleic acid as a hydrophobic carbon source for the fermentation and isolation processes with crystallization. More than 77% of the di-Ac-LSLs with purity over 95% were obtained through crystallization. The resulting di-Ac-LSLs exhibited significantly superior antibacterial activity against Gram-positive bacteria than crude SLs or ASLs. The minimum inhibitory concentrations (MIC) of di-Ac-LSLs against B. cereus and B. subtilis were as low as in the 8–16 mg/L range. The di-Ac-LSLs acted by disrupting cell membranes and inhibiting the formation of biofilm. They also exhibited remarkable inhibitory activity against fungal mycelium, demonstrating their great potential for use as green and efficient antibacterial agents in agriculture. Download: Download high-res image (142KB) Download: Download full-size image