Abstract:

The conditions for ultrasound-assisted extraction of ursolic acid from Fructus Mume were optimized by response
surface methodology (RSM). Based on the results of single-factor tests, three factors including ethanol concentration, solidto-
liquid ratio and extraction time were identified as main variables that affect extraction efficiency. Optimization of the
three factors was performed using extraction efficiency of ursolic acid as the response. Besides, the antibacterial effect
of ursolic acid on Escherichia coli was studied. The optimum extraction conditions were determined as follows: ethanol
concentration, 71%; solid-to-liquid ratio, 3:44 (g/mL); and extraction time, 2.5 h. Under these conditions, the yield of ursolic
acid was (12.61 ± 0.13) mg/g. The antibacterial test showed that the minimal inhibition concentration of ursolic acid against
E. coli was 0.25 mg/mL. After treatment with 0.5 mg/mL ursolic acid, the cell wall and membrane permeability of E. coli
was increased and the contents of protein, nucleic acid materials, Ca2+ and total leakage were enhanced by 29, 2.5, 8 and 1.8
folds compared to control, respectively. The scanning electron microscopic observation of E. coli showed that the cells were
obviously destroyed or broken, indicating that ursolic acid has inhibitory effect on the growth of E. coli. The study can lay
the theoretical basis for the application of ursolic acid and Fructus Mume in the future.

Key words: Fructus Mume, ursolic acid, response surface methodology, Escherichia coli, antibacterial effect