Abstract
Natto is a popular food because it contains a variety of active compounds, including nattokinase. Previously, we discovered that fermenting natto with the combination of Bacillus subtilis GUTU09 and Bifidobacterium animalis subsp. lactis BZ25 resulted in a dramatically better sensory and functional quality of natto. The current study further explored the effects of different fermentation parameters on the quality of natto fermented with Bacillus subtilis GUTU09 and Bifidobacterium BZ25, using Plackett–Burman design and response surface methodology. Fermentation temperature, time, and inoculation amount significantly affected the sensory and functional qualities of natto fermented with mixed bacteria. The optimal conditions were obtained as follows: soybean 50 g/250 mL, triangle container, 1% sucrose, Bacillus subtilis GUTU09 to Bifidobacterium BZ25 ratio of 1:1, inoculation 7%, fermentation temperature 35.5 °C, and fermentation time 24 h. Under these conditions, nattokinase activity, free amino nitrogen content, and sensory score were increased compared to those before optimization. They were 144.83 ± 2.66 FU/g, 7.02 ± 0.69 mg/Kg and 82.43 ± 5.40, respectively. The plate thrombolytic area and nattokinase activity both increased significantly as fermentation time was increased, indicating that the natto exhibited strong thrombolytic action. Hence, mixed-bacteria fermentation improves the taste, flavor, nattokinase activity, and thrombolysis of natto. This research set the groundwork for the ultimate manufacturing of natto with high nattokinase activity and free amino nitrogen content, as well as good sensory and thrombolytic properties.
Highlights
The Bacillus subtilis GUTU09 (B9) and Bifidobacterium animalis subsp. lactis BZ25 were strains with excellent performance screened by our laboratory from Guizhou local characteristic food [9,10]
Effect of NaCl on Natto would become almost depleted in the solid fermentation of soybean, and this favored the growth of the Bifidobacterium and inhibited the strictly aerobic Bacillus strain
When the inoculation concentration was less than 6% or higher than 8%, nattokinase activity, free amino nitrogen, and ratios were 2:1, 1:1, and 1:2, there was no significant change in pH (p > 0.05)
Summary
People’s living standards have gradually risen in recent years, and the incidence of thrombosis in blood arteries has increased year after year [1]. The prevalence of cardiovascular and cerebrovascular diseases has skyrocketed. The importance of healthy products and foods in the prevention of cardio-cerebrovascular diseases has grown. A natural fermentation enzyme known as nattokinase has been a prominent study issue among those nutritious foods. Natto is a soybean that has a distinct flavor and texture, which is made by fermenting soybeans with Bacillus subtilis.
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