Method for preparing freeze-dried powder containing bacillus natto and nattokinase

The present invention relates to freeze-dried powder containing bacillus natto and nattokinase and a preparation method thereof, the process of which comprises that: firstly, culture medium is confected and sterilized, wherein, the culture medium components with the weight percentage are 8 percent to 15 percent of soybean flour, 1 percent to 5 percent of sucrose, 0.4 percent to 0.6 percent of NaCl and the water with the rest quantity, the pH value of which is 6.8 to 7.2; secondly, the bacillus natto is inoculated, and the inoculation quantity is 2 percent to 8 percent; thirdly, the bacillus natto after the inoculation is cultured and fermented for 20 to 28 hours under the temperature of 36 DEG C to 38 DEG C; fourthly, fermentation liquid is frozen and dried in vacuum, the glycerin with 1 percent to 7 percent of the weight of the fermentation liquid is used protecting agent to be added into the fermentation liquid, which is frozen under the temperature of subzero 18 DEG C in advance to be frozen and dried in vacuum for 12 to 20 hours and then is resolved under the temperature lower than 30 DEG C. The method has low cost and is in favor of the industrial production. Under the precondition of maintaining the nattokinase activity, the freeze-dried process also holds other nutrient component in the bacillus natto and the fermentation liquid, which reduces the nattokinase purification cost.