Integrated biorefinery process for production of sophorolipids from corn straw

Sophorolipids (SLs) are biosurfactants composed by a dimeric carbohydrate sophorose linked to a hydroxyl group of a fatty acid, and they have a great potential for commercial using in different industrial sectors due to their superior environmental compatibility combined with excellent functional properties. In this study, hydrolysate of corn straw cellulose was used as a hydrophilic carbon substrate to produce sophorolipids with Starmerella bombicola ATCC 22214. The two-step method was employed for detoxification of corn straw hydrolysate, and the process of detoxification was optimized. The yield of sophorolipids obtained using the detoxified hydrolysate medium was 2.07 fold higher than that obtained using undetoxified hydrolysate. In addition, the optimal conditions for the production of sophorolipids were as follows: the hydrophobic carbon source was 6 % (w/v) oleic acid, the nitrogen source was 0.45 % (w/v) ammonium nitrate, the metal ions was 0.075 % (w/v) Fe2+ ions, and the pH of the fermentation broth was 3.0. The yield of lactonic sophorolipid and total sophorolipid following 7 days of fermentation reached a maximum of 6.16 g/l and 27.45 g/l, respectively. These results demonstrate the biorefinery of corn straw to produce SLs is a kind of utilization method with industrialization potential, which can realize the high-value comprehensive utilization of corn straw.