| Chinese bayberry (Myrica rubra (Lour.) Sieb.et Zucc.) is a traditional fruit with high nutritional value and health value. Now, people are paying more attention to its antibacterial effects and anti-dysentery effects. The bayberry fruit contains lots of potential antibacterial substances, such as polyphenols and flavonoids. The development of antibacterial agents from bayberry fruit can make full use of this resource and its natural product can meet the food safety increasing demand.Firstly, we extract effective antimicrobial substances in bayberry fruit by water, ethanol, acetone and ethyl acetate. Then the antibacterial properties of extracts to 14 species of Gram-positive bacterium and Gram-negative bacterium have been evaluated. The bacterium include Staphylococcus aureus ,β-hemolytic streptococcus, Shigella dysenteriae and Salmonella typhi, which can lead to diarrhea normally. The result shows that the water extraction has most powerful antibacterial activities. The minimum inhibitory concentration (MIC) values of the water extract were also determined. The contents of flavonoids in 4 extracts were obviously different at level of p<0.05, but the contents of tannins and organic acids were more similar at the same level.The growth curves of the bacterium in artificial intestinal fluid and the broth medium were compared by both turbidity method and viable counting method. The result showed that the antimicrobial activity of the water extract in broth medium is better than that in artificial intestinal fluid. Based on the results of the contents of tannins and organic acids, it suggested that the main antibacterial activity was from tannins and organic acids and the digestive enzyme such as glycosidase and protease in the artificial intestinal fluid can impact upon the active compounds in the extract, and reduce its antibacterial activity.We choose ethanol, chloroform, petroleum ether, ethyl ether and ethyl acetate as the solvents to further pure and separate the water extract by solvent-grading method. And test antibacterial activities of different grading samples by using Staphylococcus aureus as the representative bacteria. It can be concluded that, form the result, ethanol, chloroform, petroleum can remove carbohydrates, protein, lipid, waxiness, and some other non-active cnmponds. Ethyl ether and ethyl acetate can be used as degrading solvents to separate the complex polyphenols with different polarities. The antibacterial effect test result of the degrading samples shows that: Ethyl ether degrading sample does not contain antibacterial compounds, and no non-polar polyphenols exist in the water extract; the ethyl acetate and residual water degrading samples are obviously show antibacterial activities. It can be concluded that the polyphenols in the extract are middle-polar and polar polyphenols. In addition, in the test, we also found that ethyl acetate grading sample appears increase antibacterial activity along with the ethanol solution purifies time extension.We use single factor method and orthogonal experimental design to optimize the ethanol purification test. The result shows that the purification time of ethanol is the most significant parameter, and the ethanol experimental conditions are: purification time 24h, concentration 90% and temperature 25℃.The structures of water grading sample and ethyl acetate grading sample are examined by ultraviolet scan spectrometry and UPLC-DAD-ESI-MS. The major component in water grading sample is cyanidin-3-glucoside, in ethyl acetate grading sample are cyanidin-3-glucoside, Bayberry flavonoid deoxy hexa-carbon glycoside, quercetin-3-O-glucosidase and quercetin deoxy hexa-carbon glycoside, and the content of cyanidin-3-glucoside in ethyl acetate grading sample is much less than that in water grading sample. We presume the main antibacterial compounds in ethyl acetate grading sample is cyanidin-3-glucoside, bayberry flavonoid deoxy hexa-carbon glycoside, quercetin-3-O-glucosidase and quercetin deoxyhexa-carbon glycoside.
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