Screening Of Natto Strain And The Developing Of A New Flavor Natto Food

As a traditional fermentation food,natto has many active substances,such as nattokinase,vitamin,dietary fiber and so on,which are beneficial to human's health.Modern medical research showed that eating natto have the function of preventing disease and other health care functions.Although natto have many health functions such as promoting thrombolysis and regulating intestinal tract,because of the special ammonia smell which produced in fermentation period,it can not be accepted by the majority of consumers in China,as a result its promotion and development in the Chinese market is limited.Therefore,this research aiming at to develop a new flavored natto food and improve the flavor of natto,which can match Chinese people's preference better.In this paper,the original bacillus natto strain ware isolated from five commercially available natto products,which has a high activity of nattokinase.And then,the original strain was treated by UV mutagenesis,through preliminary screening and secondary screening,a best strain was obtained,which has a higher enzyme production capacity and a better genetic stability,and it was named ND10-5 according to the sreening test batch number and strain number.After obtained the best strain,it takes the total volatile basic nitrogen(TVB-N)content and the nattokinase(NK)activity as the indexs.Firstly,mixed strains fermentation was used to reduce the unique smell of natto,and the proportion of mixed strains is Bacillus natto and Saccharomyces cerevisiae 3:1.Secondly,single factor experiment and response surface method were used to optimize the fermentation condition of natto,the best natto fermentation condition of water content,oybean thickness,sterilization time,inoculation amount,fermentation temperature,and fermentation time is 60%,3 cm,3 min,6%,35 ?,28 h.According to the best fermentation condition,the nattokinase activity is the maximum 1473.37 U/g,which is increased 39.1% than original strain,as well as the content of total volatile basic nitrogen is 102.01 mg/100 g,reduced 38.4% than optimization before.In order to further improve the flavor and texture of ND10-5,the flavor of fermented natto was adjusted without affecting the activity of nattokinase and sensory evaluation of natto.Finally,it is determined that adding 4% glucose and 4% pepper before sterilization,2% salt at after-ripening,and after-ripening for 1 d,under that condition,the activity of nattokinase is 1453.27 U/g,and the sensory evaluation is 98,natto has a better quality.Considering the taste preferences and needs of Chinese consumers,the seasoningpacket has been developed,which optimized by single factor test and orthogonal test,and the formula is mustard sauce 17%,vinegar 5%,sodium glutamate 2%,thirteen-spices 3.5%.In order to extend the preservation time of ND10-5's natto,trehalose was selected as the protectant to the maximum extent without affecting the activity of nattokinase and sensory score.It was found that 3% trehalose could effectively protect the activity of nattokinase during-20 ? and 4 ? cold storage.The retention rate of nattokinase activity was 90.4%after 30 days of-20 ?.The activity retention rate of nattokinase was 83% after 14 days storage at 4 ?,which significantly delayed the loss of nattokinase and prolonged the preservation time of fresh natto.