Development And Evaluation Of Total Bacteria And Coliform Detection Plates

In recent years people pays more and more attention to the food safety.Looking for a suitable microbial detection method is particularly important.In this study,the film-carrier structure was designed by referencing the widely used commercialized test plates.The basic structure and performance of the test plate were optimized and the culture medium formula was modified to obtain the total bacterial colonies count plate and the the coliform count plate.And the performance of the test plate was evaluated.By comparing the performance of different medium,the ingredients of culture medium for colony total test plate and coliform test plate were finally determined.The medium component of the total bacterial colonies count plate include 1.25 g/L glucose,0.025 g/L tween 80,6.25 g/L peptone and 1.25 g/L yeast.The medium component of the coliform count plate include 3 g/L yeast extract,5 g/L lactose,7 g/L sodium chloride,3.4 g/L dipotassium phosphate,1 g/L potassium dihydrogen phosphate and 15 g/L peptone.The production method of the plate was finally determined as follows:(1)The culture medium was prepared based on the optimized method.Chromogenic agent,gelling agent were adde and thoroughly mixied;(2)Two different non-wovens were impregnated with the medium containing cold-water-soluble gelatinizer for 3min.The 0.45?m nylon filter membrane was impregnated with the medium without cold-water-soluble gelatinizer.The different layers were assembled as follows:the thinner non-woven fabric being placed on the lower layer,the thicker one placed on the thinner one,the nylon filter placed on the top.The main structure was dried at the temperature of 55? for 4-6 hours;(3)The 3mm washer was set as the bottom.the three layers of non-wovens and nylon filter membrane mentioned above were set as the middle layer.The 4.5mm washer was set as the upper layer.The main structure of the test plate was finally constructed,which was a"sandwich" structure formed by three layers.(4)The test plate was finished by adhering the main structure to the material and covering with the 0.6mm thickn PET sheet.(5)The plate was put into a aluminum packaging bag and sterilized by irradiation on the dose of 15 KGy.The performance of the prepared test plate was evaluated by comparison with national standared method.The testing time of the total bacterial colonies count plate is about 20 hours.The result of the accuracy experimental test showed that accordance with national standared method is 103.56%.The colony forming is greater than the national standard method.The testing time of the coliform count plate is about 24 hours.The result of the accuracy experimental test showed that accordance with national standared method is 70.16%.The colony detection rate is less than the national standard method.But the specificity of the test plate is good,only coliform bacteria could grow on the plate.