Study on the physicochemical indicators and activity of medicinal black beans fermentation with Bacillus subtilis.

In order to reveal the changing patterns of physicochemical indexes, active substances and microbial growth during liquid fermentation of medicinal black beans by Bacillus subtilis, the changes of microbial growth curves, pH, proteins, polysaccharides, reducing sugars, total phenolics, total flavonoids and isoflavone of black beans were determined during the fermentation process. Compared to black bean water extracts, the antioxidant ability of medicinal black bean ferments were comprehensively evaluated by DPPH and ABTS radical scavenging assay and zebrafish embryonic ROS scavenging assay. The results showed that Bacillus subtilis entered the logarithmic growth stage after being cultured for 8 h and the pH of black bean ferments increased rapidly from 8~28 h stage. The protein content of the ferments firstly exhibited a decrease from 6.44 mg/mL to 5.66 mg/mL and increased constantly to 5.99 mg/mL accompanied by the proliferation and metabolism of the microorganisms. The polysaccharide content of the ferments decrxeased rapidly from 913.03 mg/L to 105.85 mg/L at the period of 0~24 h and then slowly decreased to 100.01 mg/L. The reducing sugar content increased from 0.44 mg/mL to a peak of 4.38 mg/mL and then rapidly decreased and finally leveled off. The levels of total phenols and total flavonoids of black beans were greatly enriched by Bacillus subtilis, especially the total phenols increased from 238.22 mg/L to 736.61 mg/L with an elevation of 209.21% and the total flavonoids increased from 172.22 mg/L to 495.30 mg/L with a maximum promotion of 187.60%. Seven soy isoflavone glycosyl groups were all hydrolyzed into three soy aglycones including daidzein, glycitein and genistein which were obviously accumulated, especially the content of genistein was up to (530.07 ± 0.66) μg/g. The results of antioxidant activity assay showed that 10% medicinal black bean ferments had 99.42% DPPH radical scavenging rate and 100.06% ABTS radical scavenging rate, respectively. Whereas the scavenging rates of the two free radicals in 10% black bean aqueous extract were only 70.81% and 41.89%. Finally in the results of 24 hpf zebrafish embryos ROS scavenging assay, the black bean fermentation at amount of 0.01%, 0.1% and 1% all exhibited higher ROS scavenging rates than black bean water extracts in a dose-dependent relationship. [ABSTRACT FROM AUTHOR]