Study on the Optimum Extraction Conditions and Antibacterial Activities in Vitro of Total Flavonoids from Grape Leaves

The optimum extraction process of total flavonoids from grape leaves and their antibacterial activities in vitro were investigated. Total flavonoids were extracted by Soxhlet extraction. The content of total flavonoids in grape leaves was determined with aluminum nitrate chromogenic Spectrophotometry. The antibacterial activity was determined by K-B and agar diffusion method. The antibacterial test was done respectively by Escherichia coli, Staphylococcus aureus, Candida albicans, Bacillus subtilis, and choosing Staphylococcus aureus as the indicator organisms for the most obvious antibacterial effect. The single-factor test and orthogonal test taken the extraction rate of total flavonoids and the diameter of inhibition zone as index. Linear regression with concentration and absorbance of rutin standard solution, the regression equation was Y = 0.3295X + 0.0012 (R2= 0.995), and the linear range was 0.4 similar to 2.0mg/mL. The content and extraction rate of total flavonoids in grape leaves were calculated according to the regression equation. Magnitude order of the effect of the four factors on the extraction rate and the antibacterial activities of total flavonoids in grape leaves was : extraction temperature> the concentration of ethanol> reflux time> ratio of material to liquid. The optimum extraction conditions were determined as follows: the concentration of ethanol (90%), ratio of material to liquid (1: 40), extraction temperature (80 degrees C), the extraction time (3.5h). The average extraction rate of total flavonoids in grape leaves under the optimum extraction conditions was 7.16%. Total flavonoids in grape leaves had a significant antibacterial effect on Staphylococcus aureus and Escherichia coli, and the effect on Staphylococcus aureus was the most obvious, but on Bacillus subtilis was not very remarkble.