The application of foaming for the recovery of Surfactin from B. subtilis ATCC 21332 cultures

Foaming, a proficient method for the recovery of surface active solutes from dilute solutions, was successfully applied for the concentration of the lipopeptide biosurfactant Surfactin from B. subtilis ATCC 21332 cell culture broths. Foaming was only partially successful in concentrating Surfactin when applied as a separate semi-batch unit downstream of the cell culture stage. Surfactin partitioned strongly into the foam during the latter stages of the semi-batch process, where enrichments of over 50 could be obtained. However, simultaneous high enrichments and recoveries of Surfactin could not be obtained as the majority of Surfactin (around 70% of the total recovered) was produced at a low concentration during the early stages of foaming. Foam fractionation was considered for both cell free and cell containing broths; the presence of cells increased the foamability of the solution and therefore yielded more dilute Surfactin preparations. More favourable recovery and enrichment of Surfactin occurred when foaming was integrated with the cell culture stage. The use of low stirrer speeds was essential in producing foam at a controlled rate. By collecting fractions of the foam produced between 10 and 30 hours, from systems stirred at 166 and 146 rpm, a highly concentrated Surfactin extract could be obtained. The Surfactin concentration in the foam was 1.22 and 1.67 g l−1 respectively, which represented enrichments and percent recoveries of over 60. This study points to the utility of foaming as a method for the recovery of surface-active fermentation products, particularly when used in an integrated production/recovery system.