Study On The Fermentation Technology And Antioxidant Activity Of Common Vetch Natto

Natto is a kind of nutrient-rich micro-ecological food.In recent years,it has been popular due to its thrombolysis,cancer prevention,lowering blood pressure and other functions.The common vetch has been used as green manure and forage for a long time.The development of common vetch as natto product can make better use of the resources and nutritional value of common vetch,and improve the diversity of natto products in the market.In this paper,common vetch was used as raw material to ferment natto and explored its fermentation process and antioxidant activity.The main research contents of this paper are as follows:(1)Bacillus natto was isolated and extracted from commercially available natto.Based on the ratio of hydrolytic circle produced by the strain on casein plate culture medium to its own colony diameter,NT-3 with the largest ratio was selected as the subsequent experimental fermentation strain,and the ratio was 2.94.Physiological,biochemical experiments and molecular biology identification of strain NT-3 were carried out.After comparison,it was found that NT-3 was consistent with the characteristics of Bacillus subtilis.The strain was preserved for subsequent fermentation.(2)Common vetch was used as raw material to produce common vetch natto by fermentation with NT-3 strain.The single factor method and response surface optimization method were used to explore the fermentation process of common vetch natto.This work explored the determination of nattokinase activity by folin-phenol method.The correlation between folin-phenol method and UV spectrophotometry for the determination of enzyme activity was established.It was found that there was a good correlation between the two methods,and the correlation equation was Y=0.0023x+16.349,R~2=0.9929.Using the integrated score of the sum of the protease activity score and the sensory score as an indicator,the fermentation conditions were optimized by using three-factor three-level experiments.The best results was obtained:the inoculum amount was 3.1%,the fermentation temperature was 36.8?,the fermentation time was 26.7h.Under these conditions,the activity of nattokinase was314.06U/m L and the sensory score was 40.9,which was better than the result of single factor.The optimum reaction temperature of nattokinase was 40?.The optimum reaction p H of nattokinase was 8.(3)In order to explore the difference between common vetch natto and other natto,the key properties of common vetch natto was compared with traditional natto(soybean natto)and new natto(black bean natto and chickpea natto).The protein content of common vetch natto,soybean natto,black bean natto and chickpea natto were determined by the Coomassie brilliant blue method,which were 14.91±1.35%,14.75±0.60%,5.88±0.75%and 18.41±0.66%,respectively.The content of total phenols and proanthocyanidins of common vetch natto was higher than that of black bean natto and chickpea natto,the content of total flavonoids was higher than that of soybean natto and black bean natto.(4)The antioxidant capacity of four kinds of natto showed that the free radical scavenging capacity of four kinds of natto increased with the increase of substrate concentration.The antioxidant activity of common vetch was better.In the DPPH free radical scavenging experiment,the scavenging capacity of the four kinds of natto was sorted as:common vetch natto>black bean natto>chickpea natto>soybean natto.In the ABTS free radical scavenging experiment,the scavenging capacity of the four kinds of natto was sorted as:common vetch natto>black bean natto>soybean natto>chickpea natto.In the superoxide anion radical scavenging experiment,the scavenging capacity of the four kinds of natto was sorted as:common vetch natto>soybean natto>chickpea natto>black bean natto.Under the same mass concentration,the reducing power of the four kinds of natto was sorted as:common vetch natto>black bean natto>soybean natto>chickpea natto.In the hydroxyl radical scavenging experiment,the scavenging capacity of the four kinds of natto was sorted as:soybean natto>black bean natto>chickpea natto>common vetch natto.