Study On The Detective Method Of Coliform Bacteria In Tea

Our country's food sanitation microorganism standard system is mainly composed of colony counts, coliform bacteria and pathogenic bacteria. Coliform bacteria refers to the aerobic or the optional anaerobic gram-negative non-spore bacillus that can produce acid and gas through lactose fermentation at 37℃in 24h.As the indicator offecal pollution,Coliform bacteria is part of bacteria colony counts, and it also has close correlation with the enteric pathogenic bacteria. Therefore the coliform bacteria occupies a important position in food microbiology index system.As a traditional advantage agricultural product of our country,tea is not only the domestic sale staple commodity, but also the traditional export product of our country. However,recently the exports of Chinese tea are facing serious "green barriers",particularly Europe,US and Japan continuously establish more strict and extensive standards. Our country has not listed the harmful microorganism as the compulsory index in the tea standard systems yet,but European Union, America,Canada and Japan have tried to examine the index. Russia has a request of examining the yellow aspergillus and the mold(<1000cfu/g) in Chinese tea. According to the test results of Chinese tea by the United States and Japan,the main harmful microorganism are E.coli, Salmonella,and other intestinal bacterias. Both the E.coli and the yellow aspergillus have been detected from our country's tea. The tea production and marketing units and relevant administrative departments should pay the attention to this phenomenon.This author uses green tea,flower tea,Pu'er tea and Kang brick tea as the research object, investigates the bacteria colony counts and the growth regularity of E.coli in tea. The author also does the preliminary investigate on the contamination of coliform bacteria and compares several detection methods on tea;In this foundation,the detective method of coliform bacteria has been discussed that adapts to tea. And then,this paper has analyzed and evaluated the method. Finally, the coliform bacterias of tea have been appraised preliminarily. We draw the following conclusions eventually.(1)The bacteria colony counts of tea ranges from2000-200000cfu/ml,and the contamination degree of different kinds of tea is:packaging green teabrick tea> packaging green tea>buking green tea. The comparison of several methods indicateses that LST method is more suitable for the detection of tea than two other methods,but LST method still need to be improved.(3) The best culture medium for the decedtion of coliform bacteria is LST+0.3%Tuwen,the fermentation time is 36h.Meanwhile,the LST+0.3%Tuwen culture medium plays a decisive role in the detection of coliform bacteria. the accordant ratio is about 90% between the result of the substrate(LST+0.3%Tuwen)fermenting and final result. This reaches the detective purpose for one step completely.Furthermore, we have researched on how to repair coliform bacteria of tea. The best repair time is 1.5h with the substrate of nutrient agar.To sum up,the research finds a new method to detect coliform bacteria in tea:repair coliform bacteria of tea for 1.5h with nutrient agar medium—to inoculate 1ml tea soup into LST+0.3%Tuwen medium to ferment for 36h—to observe whether the gas is produced—to look up the stable MPN.Through analysing and evaluating the new method,we find the method has the trait of high sensitivity and specificity of detecting coliform bacteria of tea.(4)In the end,the dominant coliform bacteria in tea are Klebsiella III, Klebsiella IV, Escherichia II and Escherichia IV.