Flos Sophorae Immaturus extracts: Effects of different extraction solvents on antioxidant, antimicrobial activities and active ingredients

Flos Sophorae immaturus (FSI), the flower bud of the leguminous plant Sophora japonica L., is a traditional medicinal herb widely used for blood pressure reduction and as a food source. The composition and concentration of metabolites in FSI can vary with the use of different extraction solvents, making it crucial to assess an effective extraction solvent with high bioactivity. This study aims to evaluate the effects of five extraction solvents - water, EtOH (ethanol), MeOH (methanol), AcOH (acetic acid), and EA (ethyl acetate) – applied to FSI. The functional role of FSI in antioxidant and antimicrobial properties was explored. Additionally, we analyzed the differences in bioactive components of FSI extracts from the five solvents using Ultra-High Performance Liquid Chromatography- Q Exactive-Mass Spectrometry (UHPLC-QE-MS). Results indicate that AcOH yielded the highest extraction rate (51.34 ± 0.38 %), while EA had the lowest yield (6.07 ± 0.17 %). The total flavonoid content (TFC), total antioxidant capacity (T-AOC), and DPPH radical scavenging ability of the MeOH extract were significantly higher than those of other solvent extracts (P < 0.05). The impact of different solvents on total phenolic content (TPC) and ·OH radical scavenging rate of FSI extracts followed a similar trend, with AcOH > MeOH > EtOH > water > EA. UHPLC-QE-MS analysis revealed differences in composition and content of the extracts among the five solvents, mainly in flavonoids, alkaloids, terpenes, vitamins, steroids, and lignans. EtOH and EA extracts exhibited inhibitory effects on Escherichia coli and Staphylococcus aureus, showing a dependence on mass and concentration. None of the extracts were inhibitory against Aspergillus niger and Saccharomyces cerevisiae. Overall, MeOH and AcOH extracts of FSI displayed higher yields and stronger antioxidant activity, while EtOH and EA extracts showed greater antibacterial capabilities compared to other solvents. These findings may contribute to further research on the commercial prospects of FSI in the food and pharmaceutical industries.