桑叶活性成分的抑菌作用及稳定性研究

以桑叶为原料，提取多糖、黄酮、生物碱三种活性成分，采用牛津杯法测定活性成分抑菌效果，并研究桑叶黄酮对供试菌的最小抑制浓度（MIC）及抑菌稳定性。结果表明，桑叶多糖对供试菌无抑制作用；桑叶生物碱对大肠杆菌、金黄色葡萄球菌具有抑制作用，抑菌圈直径分别为9.8 mm、13.7 mm；桑叶黄酮对供试菌的抑制效果较好，对金黄色葡萄球菌、大肠杆菌、灰葡萄孢和扩展青霉的最小抑菌浓度分别为5.09 mg/mL、10.18 mg/mL、20.35 mg/mL、20.35 mg/mL；桑叶黄酮在热（40～100 ℃）、紫外照射及酸性（pH 5～7）条件下均有良好的抑菌稳定性。

Antibacterial effect and stability of active components from mulberry leaf

Using mulberry leaf as raw material, the polysaccharides, flavonoids and alkaloids were extracted. The antibacterial effect of active components was determined by Oxford cup method, and the minimal inhibitory concentration(MIC) and antibacterial stability of the flavonoids from mulberry leaf on tested bacteria were studied. The results showed that the polysaccharides from mulberry leaf had no inhibitory effect on the tested bacteria, and the alkaloids from mulberry leaf had inhibitory effect on Escherichia coli and Staphylococcus aureus with the diameter of inhibition zone of 9.8 mm and 13.7 mm, respectively. The flavonoids from mulberry leaf had good inhibitory effect on the tested bacteria, and the MIC on S. aureus, E. coli, Botrytis cinerea and Penicillium expansum was 5.09 mg/ml, 10.18 mg/ml, 20.35 mg/ml and 20.35 mg/ml, respectively. The flavonoids from mulberry leaf had good antibacterial stability under thermal(40-100 ℃), ultraviolet irradiation and acidic conditions(pH 5-7).