Recovery of surfactin from fermentation broths by a hybrid salting-out and membrane filtration process

Surfactin biosurfactant was produced by fermentation method with culture of Bacillus subtilis ATCC 21332. Downstream processing for surfactin recovery by ammonium sulfate salting-out, ultrafiltration (UF), nanofiltration (NF), and their hybrid process was studied. Experiments were performed at different initial concentrations of surfactin (210–3620 mg/L), the concentrations of added ammonium sulfate (0–46%, w/v) and micelle-destabilizing solvent ethanol (0–44%, v/v), and membrane molecular-weight cut-off (MWCO, 1–300 kDa) were investigated. When 23% (w/v) ammonium sulfate and 33% (v/v) ethanol were added to the broths, it was shown that surfactin micelles could be efficiently destroyed and other protein macromolecules could be removed. On the other hand, the UF membrane with MWCO less than 100 kDa was found to be suitable for the retention of surfactin micelles, and the NF membrane with a MWCO less than 1 kDa was found to be suitable for the retention of surfactin monomers. Finally, the hybrid salting-out and membrane filtration (UF or NF) process was proposed and tested. Comparisons among these single and hybrid processes demonstrated that the hybrid process not only enhanced the recovery yield but also improved the purity of surfactin.