Effect of oxygen mass transfer coefficient (kLa) on surfactin production by Bacillus subtilis ATCC 21332

Abstract Surfactin is one of the most effective biosurfactants available and has several interesting properties. However, the high cost and low yield associated with surfactin production have been major drawbacks preventing its wider industrial application. The use of intensive stirring and aeration, in order to increase surfactin synthesis, can cause excessive foaming, resulting in low levels of biosurfactant production inside the bioreactor. Therefore, the aim of this study was to evaluate the influence of the oxygen mass transfer coefficient (kLa) on surfactin productivity in a bioreactor integrated with a foam collector using low aeration rates. The experiments were carried out at 32°C, using a mineral salts medium containing 10 g/L of glucose, at constant pH 7.0. The results showed that the best surfactin production performance was achieved at kLa = 21.88 h− 1 (with 0.3 vvm aeration and 250 rpm stirring), which resulted in a maximum productivity of 14.1 mg/L.h and a maximum surfactin concentration of 443.1 mg/L in the foam. Despite loss of the culture broth through the exhaust air line, a very high surfactin concentration was reached in the foam phase, which can facilitate downstream processing and purification of the product. Besides, the best results regarding surfactin enrichment and recovery were obtained by using low aeration rate combined with high agitation rate.