Optimization of Extraction Process and Antioxidant and Antibacterial Activities of Total Phenolics from Thalictrum baicalense Turcz

Thalictrum baicalense Turcz (T. baicalense) is a traditional medicinal plant. In this study, response surface methodology was used to optimize the ultrasound-assisted solvent extraction of total phenolics from T. baicalense, and its antioxidant activity, antibacterial activity, and potential antibacterial mechanism were evaluated. The optimal extraction conditions were determined as follows: ultrasonic power 120 W, solid-to-liquid ratio 1:10 (g:mL), extraction time 72 min, temperature 32 °C, and ethanol concentration 49%. Under these conditions, the total phenolic extraction yield reached 15.116 mg gallic acid equivalents per gram of plant powder (mg GAE/g). Antioxidant assays showed that the scavenging rates against 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+), and hydroxyl radicals were 83.41%, 94.69%, and 78.95% at the total phenolic concentrations of 33.33, 20, and 3.85 μg GAE/mL, respectively, and were comparable to those of vitamin C. Antibacterial evaluation revealed that the total phenolic extract exhibited significant inhibitory activity against the Gram-positive bacterium Staphylococcus aureus, with an inhibition rate of 90.34% at a concentration of 570 μg GAE/mL, whereas weaker activity was observed against the Gram-negative bacterium Escherichia coli. Furthermore, crystal violet staining assay and scanning electron microscopy observation suggested that the extract reduced biofilm biomass and caused morphological alterations. In addition, treatment with the extract significantly decreased intracellular ATP levels in both strains, suggesting a possible effect on bacterial energy metabolism. However, these findings do not establish a specific antibiofilm mechanism or comparable efficacy to carbenicillin. Collectively, these findings provide a preliminary scientific basis for the potential application of natural bioactive components from T. baicalense in the fields of antioxidant and antibacterial agents.