Study On The Technology Of Fermenting Low Ammonia Flavored Natto With Multi-Strains

Natto is a fermented food with a long history made by fermenting soybeans with Bacillus natto.It has rich nutritional value and powerful health care functions.Its unique biologically active substance,nattokinase,has strong fibrinolytic activity,good biological safety,and is beneficial to the prevention of various cardiovascular diseases.Most natto fermentation products on the Chinese market have low nattokinase activity,and most domestic studies focus on the optimization of single-bacteria fermentation process,and there are few studies on the preparation of natto by double-bacterium mixed fermentation.Therefore,it is very necessary to deeply study and explore the process of fermentation of natto by double bacteria,and to develop new ideas for improving the activity of nattokinase and the flavor of natto.In this thesis,9 strains of Bacillus natto were isolated and purified,separated by spreading on a coated plate,observation of colony morphology and hydrolysis circle selection,plus 1 purchased strain,a total of 10 strains.Physiological and biochemical experiments were carried out on 10 strains,and the activated seed liquid was selected to be coated on starch medium and casein medium with a suitable gradient.Based on the results of physiological and biochemical experiments and the ratio of colony diameters(C/H)of the hydrolyzed loops of the culture medium as indicators,4 strains were removed,and 6strains were identified as Bacillus natto,numbered N₁,N₂,N₃,N₄,N₅,N₆.The growth activity and the enzyme activity of natto fermentation of strains N₃ and N₅ are superior to other strains.The enzyme activity of strain N₃ to ferment natto is 218.5U/g,and the enzyme activity of strain N₅ to ferment natto is 352.3U/g.In order to improve the fermentation of natto with two enzymes,the two strains N₃and N₅ with good vigor and high enzyme production capacity were selected,and the most suitable process conditions for the fermentation of natto with two strains were obtained through single factor and orthogonal experiments:strains The ratio(N₅:N₃)is 4:1,the inoculation amount is 8%,the fermentation time is 25h,and the fermentation temperature is 35?.The content of volatile base nitrogen is 205.2mg/100g,the activity of nattokinase is 481.8U/g,which is much higher than that of natto fermented by single bacteria.The experiment shows that using two strains of Bacillus natto to jointly ferment and optimize the fermentation process can improve the enzyme activity of natto to a certain extent.In order to reduce the content of volatile base nitrogen in natto,improve the sensory evaluation score,and without reducing the enzyme activity,the selected strain N₅ and yeast S₁ were used for natto-yeast complex fermentation natto experiment.From the single factor and orthogonal experiments,the most suitable process conditions for mixed fermentation of natto can be obtained:the ratio of strains(N₅:S₁)is 3:1,the inoculation amount is 4%,the fermentation time is 45h,and the fermentation temperature is 35?.The enzyme activity of natto is 341.25U/g,the volatile base nitrogen content is 198.66mg/100g,and the sensory evaluation score is 85.71,under the above conditions.Compared with natto fermented by single bacteria,the mixed bacteria can reduce the ammonia smell of natto without reducing the enzyme activity.The product natto is also accompanied by a light wine flavor and excellent sensory quality.The experiment shows that yeast has a certain effect on removing the unpleasant odor in natto,but the process is not yet perfect.Research on the use of yeast or other food fermentation strains to remove the unpleasant odor in natto can continue to be deepened.