Selective Production and Characterization of Levan by Bacillus subtilis (Natto) Takahashi

To meet the industrial need of an efficient microbial method for increased levan production, Bacillus subtilis (natto) Takahashi, a commercial natto starter for preparing fermented soybeans (natto), was used to produce levan. After cultivation for 21 h, 40-50 mg of levan mL(-1) was produced in medium containing 20% (w/w) sucrose, which was approximately 50% yield on available fructose. The product consisted of two fractions with different molecular masses (1794 and 11 kDa), which were easily separated by fractionation using an ethanol gradient. The products were well characterized by GPC, 13C NMR, and 1H NMR. The various sugars and concentrations, initial pH, fermentation temperature, and agitation speed affected the levan production by B. subtilis (natto) Takahashi. Takahashi strain is the most efficient levan-producing strain among all of the B. subtilis strains tested and, as previously reported, it produced the highest yield of levan in the least time (21 h) under the common cultivation condition.