Optimization of Bacillus Subtilis Natto Immobilization Process on Alginate – Chitosan Complex and Its Application for Nattokinase Fermentation

Nattokinase is a potent fibrinolytic enzyme with the potential for fighting cardiovascular diseases. In this study, Bacillus subtilis natto were immobilized in the alginate – chitosan complex for fermentation of nattokinase enzyme. Six factors affecting the efficiency of immobilization cells were screened by Plackett – Burman design including: concentration of alginate, concentration of chitosan, pH of chitosan, concentration of CaCl2, added cells density, shaking time after supplementing chitosan. Results of optimization have identified two factors affecting the efficiency of cell immobilization. They are concentration of alginate (2.5%) and added cells density (approximately 5.86 million colonies per milliliter). With these two factors optimized and others kept at the normal level, immobilization efficiency reached 90.73%. After Bacillus subtilis natto had been immobilized by optimization of parameters, we conducted application for fermenting nattokinase. For 24 hours of fermentation, nattokinase enzyme activity reached 71.80 ± 0.19 FU/ml. Immobilized Bacillus subtilis natto cells were reused 6 times and on the 6 th time of reuse, nattokinase enzyme activity only decreased 2.7% in compared with the 1 st reuse.