Study On Fermentation Of Whole Soybean Milk By Bacillus Subtilis Natto And Lactobacillus

Soybean products fermented by Bacillus subtilis natto usually have poor flavor and the products are almost the same. The traditional process of soybean generally produces a large number of okara, which could easily lead to pollution. To solve the two problems, a new soymilk with good flavor using whole soybean milk as the main raw material, fermented by Bacillus subtilis natto and Lactobacillus was made. The Lactobacillus could improve the flavor of soymilk fermentated by Bacillus subtilis natto. Bacillus subtilis natto could hydrolyze polysaccharides and protein, and promote the growth of Lactobacillus in soymilk,which could provide a new idea for the development of fermented whole soybean milk and natto products.First, Lactobacillus which could grow well with Bacillus subtilis natto and produce good flavor in the soymilk with low extent of post acidfication was chosen in this paper. By comparing viable counts, acid-producing velocity, sensory evaluation and pH changes during refrigeration, the Hanson commercial use Lactobacillus was selected to ferment soymilk with Bacillus subtilis natto.Next, the method for preparing whole soybean milk was optimized. Research was performed on bean water ratio milling soybeans, homogeneous conditions By single factor experiments, whole soybean milk preparation method was determined: bean water ratio milling soybeans was 1:8, condition of homogenization was homogenizing 2 times under 30 MPa.Then, the effects of different inoculation method and ventilation on the quality of the fermented soymilk were researched. The determined process was that soymilk was inoculated with Bacillus subtilis natto and fermented in the shaker firstly, then the soymilk was inoculated with Lactobacillus and fermented staticly. With the method, both the Lactobacillus and Bacillus subtilis natto could grow well in the soymilk, and the soymilk had higher protein hydrolysis degree and sensory score.Fermentation process conditions were optimized by orthogonal experiments. With the protein hydrolysis degree and sensory scores as indexes, this paper optimized the conditions of Bacillus subtilis natto fermentation. The optimum conditions were: fermentation time 10 h,shaking speed 120 rpm and fermentation temperature 37°C. With titratable acidity and sensory evaluation as indexes, this paper optimized the conditions of Lactobacillus fermentation.The results showed that the optimum conditions were: fermentation temperature 43°C,fermentation time 7 h, addition of sucrose 7%.The sensory score was 8.8 by the fermentation process conditions above.Fermentation process analysis found that the protein hydrolysis degree of soymilk was11.01%, and the viable counts of Bacillus subtilis natto and Lactobacillus were 8.21lg(CFU/mL) and 9.76 lg(CFU/mL) seperately. Fermentation process analysis found that Bacillus subtilis natto could hydrolyze polysaccharide and protein in soymilk, promote the growth of Lactobacillus in soymilk. Lactobacillus fermentation could reduce undesirable volatile substances from Bacillus subtilis natto fermentation and soymilk. After fermentation,2-ethyl-3, 6-dimethyl pyrazine and trimethyl oxazole couldn’t be dectected and the proportion of 2-pentyl furan decreased from 7.02% to 3.06%. The Lactobacillus could also increase the proportion of volatile substances in the esters, aldehydes, ketones and alcohols, which contributed to the improvement of flavor.Finally, the quality of fermented soymilk was evaluated. The content of crude protein in soymilk increased from the of 3.89 g/100 mL(pre-fermentation)to 4.08 g/100 mL. The content of crude fat decreased from 2.10 g/100 mL(pre-fermentation) to 1.82 g/100 mL. During the fermentation, the total free amino acid in the soymilk increased and the composition of the amino acid also changed. The content of 10 kinds of amino acids increased. DPPH and ABTS clearance rate in fermented soymilk was 29.19% and 34.76%, which indicates that fermentation might increase vitro antioxidant capacity in the soymilk. ACE inhibition rate was 38.6%, which may help control high blood pressure. Since the fermented soymilk pH was too low, the activity of natto kinase fell rapidly and at the end of fermentation the enzyme activity was only 320.7 U/mL. The stability of soymilk quality was well at 4°C storage.