Optimisation of Fermentation Process of Aqueous Extract of Sophora japonica and Analysis of Its Antioxidant Activity

To screen the microorganisms used for fermentation to improve the taste of Sophora japonica aqueous extract, optimize its fermentation process, and investigate the effect of fermentation on antioxidant activity. In this study, microorganisms were screened to improve the taste of the aqueous extract of Sophora japonica by using microbiota single-bacteria and mixed-bacteria fermentation techniques, and the optimal fermentation process of Sophora japonica aqueous extract was determined by a one-way combination of Box-Benhnken response surface optimisation test, and changes in antioxidant activity before and after fermentation were detected. The results showed that the optimal bacterial combination for improving the taste of Sophora japonica aqueous extract through fermentation was Lactobacillus suis:Lactobacillus bulgaricus:Streptococcus thermophilus=1:1:1. The optimal fermentation process conditions were: fermentation time of 24 h, inoculation amount of 3%, fermentation temperature of 21 ℃. Under these conditions, the sensory score of the fermentation broth was 79.01 points, and the total flavonoid concentration was 0.3225 mg/mL. The scavenging rate of DPPH radicals by the aqueous extract of Sophora japonica decreased from 86.5% to 67.39% (P<0.001) before fermentation, and the scavenging rate of superoxide anion radicals decreased from 89.22% to 81.10% (P<0.01) before fermentation. The total flavonoid content of the aqueous extract of Sophora japonica increased (0.3225 mg/mL) after fermentation compared with that before fermentation (0.3012 mg/mL) , and the polysaccharide content (1.14 mg/mL) decreased significantly (P<0.05) compared with that before fermentation (1.43 mg/mL). This study obtained a aqueous extract of Sophora japonica with good taste improvement effect, which would provide technical data for the deep development and utilization of Sophora japonica resources and the extension of its industrial chain in the future.