Study On Fermentation Of High-activity Natto With Multi-strains

Traditional natto is fermented by Bacillus natto and has a unique flavor.Natto has a variety of nutrition and healthy function.Nattokinase contained in Natto is easily absorbed by the human bodies and has the effect of preventing and controlling the thrombus disease.However,the natto has a smell of ammonia,so that its development in our country was limited.It could not be accepted by some consumers.In this study,the fermentation characteristics of four Bacillus nattos were compared to select the dominant strain with high activity and good growth performance.Natto was fermented by Bacillus natto and Saccharomyces cerevisiae.The activity of nattokinase,the content of volatile basic nitrogen and the sensory score were evaluating indicators for determining the optimal fermentation conditions.A new type of natto with high nattokinase activity and low content of volatile basic nitrogen was prepared to improve the flavor of natto.Natto that fermented by compound strain had more advantages than that fermented by single strain.Finally,natto that fermented by composite strains was dried in different forms,and high-activity natto powder with good flavor was prepared,which provided technical reference for industrial production.The main conclusions were as follows:(1)The number of viable bacteria and nattokinase activity were compared among four Bacillus nattos.We can reach the following conclusions.In solid state fermentation which was carried out at the temperature of 37?,BN10023 has the best fermentation performance.It reaches logarithmic growth stage at about 9 h,and the highest viable count reaches 6.25×108cfu/mL.The highest activity of nattokinase was 2360.5±76.6 U/g.(2)The optimum conditions for solid-state fermentation of natto: The ratio of Bacillus natto and Saccharomyces cerevisiae was 2:1.The fermentation temperature was 33 ?,the fermentation time was 72 h,and the inoculation amount was about 2%.In the optimal fermentation conditions,the average value of the three test was carried out.The sensory score was 87.33.The content of volatile basic nitrogen was 235.04±3.24 mg/100 g.And the activity of nattokinase was about 5032.12±109.31 U/g.(3)The difference between composite fermentation and single strain fermentation was significant(P < 0.01).At the temperature of 33?,the content of volatile basic nitrogen in natto that fermentated by Bacillus natto was 266 ± 4.20 mg/100 g,and the activity ofnattokinase was 2793.83 ± 80.75 U/g.Compared with the single fermentation,the sensory score was increased by 21.01%,the activity of nattokinase was increased by a factor of44.48%,and the ammonia content was reduced by about 11.64%.Natto that fermentated by Saccharomyces cerevisiae and Bacillus natto has less ammonia smell,and was soft.The activity of nattokinase was improved.(4)Vacuum freeze-drying is the most effective way to dry natto.In the condition of-54?,vacuum 5 mtorr(material thickness is 3 mm)drying for 24 h,the loss of nattokinase activity is 19.87%,the content of volatile basic nitrogen was reduced by 17.08%,and the moisture content is 7.42%;Using the air-drying to deal with natto for 7.5 h at 40~60?.the loss of nattokinase activity is 39.61%~68.23%,the content of volatile basic nitrogen was reduced by 39.81%~51.77%,and the moisture content is 3.81%~14%.