Sophorolipid Amine Oxide Production by a Combination of Fermentation Scale-up and Chemical Modification

Production scale-up of high-purity diacetylated C18:1 sophorolipid lactone was demonstrated from lab to pilot scale with the Starmerella bombicola lactone esterase overexpression strain (oe sble) as production organism. The 150 L fermentation using oleic acid and yeast extract, characterized by a titer of 199 g/L and a volumetric productivity of 0.9 g/L·h, was most successful in obtaining a highly pure (>98%) and uniform (96% C18:1 SL lactone) sophorolipid product suitable for chemical derivatization. The fermentation product was subsequently modified to produce sophorolipid amine oxides, which cannot be produced enzymatically. First, the fermentation product was transformed into an intermediate sophorolipid aldehyde via methanolysis and protection of the sugar head through acetylation and ozonolysis. This aldehyde intermediate was then used for the synthesis of the sophorolipid amine oxides via reductive amination, oxidation, and deprotection of the sugar head. The total yield of this synthetic pathway amounts to 18–30%. These compounds constitute a class of innovative sophorolipid derivatives with potential for high added-value applications. The sophorolipid amine oxides have been evaluated for their antimicrobial activity against the Gram-negative bacteria Escherichia coli LMG 8063, Klebsiella pneumoniae LMG 2095, and Pseudomonas aeruginosa PAO1 and the Gram-positive bacteria Staphylococcus aureus ATCC 6538 and Staphylococcus aureus Mu50. The present approach of combining large-scale fermentation and subsequent chemical modification facilitates the creation of a platform of innovative sophorolipid derivatives in adequate quantities, opening the door for novel applications.