Enhanced production of α-glucosidase inhibitor by a newly isolated strain of Bacillus subtilis B2 using response surface methodology

The strain Bacillus subtilis B2 isolated from a Chinese traditionally fermented food was capable of producing α-glucosidase inhibitor (AGI). On the basis of single-factor experiments, the optimum culture conditions using okara as the substrate were achieved by response surface methodology (RSM). The experimental results lead to the conclusion that the highest yield of AGI was reached at the fermentation time 65.6 h, fermentation temperature 39.0 °C, Okara concentration 4.5% and pH 7.11. A second-order model developed for the production of AGI prediction exhibits a F-value of 15.8 and a high value for the coefficient of determination (R2 = 0.933). Under these conditions, the AGI activity of the broth reached 29.4. In comparison with the highest AGI activity (24.3) obtained at the one-factor-at-a-time fermentation condition, the AGI activity increased by 21%. The AGI in the fermentation broth of B. subtilis B2 was also partially purified and determined by HPLC-ELSD. One of effective AGI, deoxynojirimycin (DNJ) has been proved in the fermentation broth, which indicated that the fermented okara might be considered as one of the promising materials for producing the food-derived DNJ products.

► A new method to obtain DNJ (a strong α-glucosidase inhibitor) by fermentation using Bacillus sbutilis isolated from Meitaoza was provided.
► The cost–effective okara was used as the unique material to produce deoxynojinimycin (DNJ).
► The optimum producing conditions of DNJ was performed using RSM experiment method and the production of DNJ increased by 21% under the optimum conditions.
► The production period of DNJ was only 65.6 h using current fermentation method, which is shorter than that of other reported microorganism and plants.
► B. subtilis B2 was a potential strain employed to produce DNJ-derived foods suitable for diabetes.