Study on Antibacterial Effects of Purple,Yellow and White-skinned Onions

Onion （Allium cepa L.） is a common biennial herb,and contains allicin compounds which can kill harmful microorganism.The antibacterial effects of raw and mature onion juice of purple,yellow and white-skinned onions at different concentrations on Escherichia coli （E.coli） and Staphylococcus aureus （S.aureus） were studied.There were differences among the antibacterial effects of raw and mature onion juice of purple,yellow and white-skinned onions at different concentrations.What was more,the antibacterial effects of raw onion juice were better than those of the mature one.The antibacterial effects of high concentration onion juice were better than those of the low one.The content of the total flavonoids in raw purple onion was higher than that in mature onion,and reached extremely significant levels in 50%,75% and 100%,respectively.Through comparison,it was found that onion juice of purple-skinned had the best suppression effects on S.aureus （gram-positive bacterium） and E.coli （gram-negative bacterium）,and gram-positive bacterium had better suppression effects than gram-negative bacterium.It wound provide the basis about bioactive function and antibacterial drugs.