The Research On The Uncertainty Of The Lactic Acid Bacteria In The Dairy Production And The Technology Of Milk Preservation

This study detected actic acid bacteria number in dairy products according to the standards of GB4789.1-2010and analyze the source of uncertainty of there measurements. All tests were performed by the same laboratory personnel, and each sample was controlled with a parallel sample and a blank sample. When evaluate uncertainty of actic acid bacteria number, all test results were transferred to logarithm so as to reduce the errors and improve the accuracy. This study evaluated uncertainty of lactic acid bacteria by using the method of merging sample standard deviation. Our results showed that uncertainty of the number of lactic acid bacteria is logarithm of the measurements±0.039. Confidence interval of actic acid bacteria number was6.2×107≤X≤7.5×107cfu/g. These results may help to improve microbial detection and the counting accuracy and precision in dairy products.Nisin is a antibacterial polypeptide substances extracted in raw streptococcus materials after ferment. Nisin is an efficient,non-toxic and natural preservative,which is an only bacteriocin that can be used as a preservative in food. This study analyzed its impact on the total bacteria in raw milk, when Nisin was used as a biological preservative in dairy products. The total bacteria number was analyzed at different time points at cold temperature (4℃) and room temperature (20℃) in raw milk which contained0(control),100,200and500mg/L Nisin repectively. Compared to the control group, the total number of colonies with addition of Nisin in raw milk was significantly reduced, and with the increasing of Nisin concentration, the inhibitory effect of Nisin increased. In addition, temperature and storage time were another two important factors related to proliferation rate of bacteria in raw milk. Proliferation rate of bacteria at4℃was significantly slow than at20℃. With the extension of storage time, Nisin can not inhibited rapid proliferation of bacteria gradually. This study showed that addition of500mg/L Nisin at4℃can effectively inhibit the growth of aerobic bacterial count in raw milk. Thus we concluded that in the low-temperature preservation environment, addition of high concentrations of Nisin can improve the preservation of dairy product in a certain storage period.