Efficient production of acidic sophorolipid from rapeseed oil by Candida bombicola

Owing to the high surface activity and good biological activity, sophorolipid (SL) has been considered as one of the most promising biosurfactants in recent years. Among all of the structures of SL, acid-type SL has gained increasing attention and application in the areas of bioremediation and daily chemical industry owing to its excellent foamability and water solubility. However, few studies focused on acid-type SL biological production have been reported. In this study, acid-type SL production by the yeast Candida bombicola ATCC 22214 was comprehensively evaluated and optimized. Under the optimal medium composition and fermentation conditions, the yield of SL in the shake flask reached 68.8 g L⁻¹, in which acid-type SL accounted for 70%. With subsequent scale-up to a 5 L bioreactor, the yield of SL using fed-batch fermentation strategy reached 131.2 g L⁻¹, and the acid-type SL accounted for 84.7%. To the best of our knowledge, the yield of acid-type SL in this study is the highest reported currently. In addition, the SL mixture (containing 84% acid-type SL) produced by C. bombicola ATCC 22214 had better surface activity, emulsification properties and environmental stability than current commercial SL products. This study provided a promising microbial chassis and fermentation strategy for commercial production of acid-type SL.