Levan production using Bacillus subtilis natto cells immobilized on alginate
The immobilization of B. subtilis natto Takahashi on alginate matrix was attempted for repeated production of levan. Factors that influence the stability of the immobilized-cell beads and the levan production in the process of fermentation were also investigated. The levan production and the stability of immobilized beads were greatly affected by the sucrose concentration, medium pH, metal ions and agitation speed. When the immobilized cells was cultivated in the optimal conditions, high levan production (70.6 g/L) was obtained after 3 d of fermentation and no damaged beads were observed. In the repetitive cultivation, the supplement of organic nitrogen source and control of initial pH was critical for high levan production. Immobilized cells on alginate beads were reused in five successive reaction cycles (each cycle 72 h) without any loss of biocatalytic activity and 9 cycles with 72% residual activity.