Detecting The Quality Of Raw Milk With The Homemade Impedance Tester

As the basic material of milk manufacture, the quality control of raw milk is the substantial step in the whole quality control. If this step occurs problems, no matter how advanced the next control method is and how strict the control instrument is, we will only get half the result with twice the effort. Milk is a kind of well-fed food. These nutrition is extremely good for microbe's growth and reproduction. Therefore, detect raw milk's aerobic bacterial count is one of the most important indexes of milk quality's detection. The traditional method of detecting aerobic bacterial count is agar counting which operate fussily, need 48 hours'detect time and count with naked eye can be easily influenced by environmental factors and influence economic efficiency of milk manufacture. In this thesis, basic research has been done about detecting aerobic bacterial count in the raw milk with homemade impedance detector. Introduce homemade impedance detector's work principle, tester's configuration and test parameter's enactment; analyse the effect of the sample's cubage, raw milk's protein content, fat content and aerobic bacterial count on detect result of impedance detector; do research about the change rule of aerobic bacterial count and detect time in raw milk; detect the time when raw milk's resistance and electromotive force achieve threshold, combine linearity regress theory and method, build linearity regress mathematical model and standard curve of aerobic bacterial count and detect time; make contrast experiment with impedance detector and the method of agar counting to detect aerobic bacterial count in raw milk, make compare analysis to the two results. The main conclusion as follows:(1)The homemade impedance tester is used to detect the bacterial totall of the milk which is placed different days in the room. Checking the electromotive force and resistance of the sample milk get DT1 and DT2. The conclusion as follow: 1) With the milk's bacterial total increasing, the DT1 which checking the electromotive force gets is reduced gradually. The reason is that if the cow milk is polluted by the bacteria, along with oxygenic being consumed an the reductive metabolizable production coming out, the redox force is fallen down gradually. So along with the bacterial total of the cow's milk increasing, its metabolism quickens gradually, the electromotive force reduces more quickly, the time when the value is reached is more short.2) With the milk's bacterial total increasing, the DT2 which checking the electromotive force gets is reduced gradually. The reason is that when the bacteria reproduce ,the nutrition element (for example the lactose, the protein, the fattiness) of the raw milk, the big molecule substances is coverted to the small molecule substances (lact-salt or ammonia). The milk's resistance gets reduced. So along with the bacterial total of the cow's milk increasing, its metabolism quickens gradually, the resistance reduces more quickly, the time when the value is reached is more short.(2)The variety of lactose,fattiness,protein's content in the raw milk is no influence for the detected results. The DT's error is between±0.03-±0.07h. The reasons as follow:1) They aren't quite sterilized, so they are likely to take bacterial. Or when the milk is shared, it is polluted outside. Consequently, the DT become short.2) When the milk is being detected, it is mixed other bacteria, or disturbed from environment(for example the tremble, too high sound). These are the reasons that the error come out.(3) The standard curvilinear is set up and validate experimentantion, the conclusion as follow:1) The research indicates that the detect time DT received by testing sample milk's resistance and electromotive force with impedance detector is shortened gradually as the aerobic bacterial count increased, that is the high aerobic bacterial count is, the smaller DT is.2) The research indicate that according to the principle of electric impedance detect method, test the electromotive force and resistance in sample milk and receive detect time DT1, make regression analysis with these received data, build standard curve and the regression equation is y? = 10.3671?0.6924x. Make hypothetic test of significance to regression equation and regression coefficients using F detect method, the results are all marked. Receive correlation coefficient r1= -0.9590, that is the relation of aerobic bacterial count and DT1 is high negative correlation.3) The research indicates that according to the principle of electric impedance detect method, test the electromotive force and resistance in sample milk and receive detect time DT2, make regression analysis with these received data, build standard curve and the regression equation is y? = 10.2728?0.6745x. Make hypothetic test of significance to regression equation and regression coefficients using F detect method, the results are all marked. Receive correlation coefficient r2= -0.9481, that is the relation of aerobic bacterial count and DT2 is high negative correlation.4) The research indicates that by the 7 parallel test of three quantitative level, validate the two above regression equation, make hypothetic test by t detect method, the result shows that the aerobic bacterial count detected by the two methods is the same as detected by the method of agar counting. The innovation of this thesis is:Using homemade impedance detector to detect aerobic bacterial count in the raw milk;Using homemade impedance detector to test electromotive force and resistance in raw milk, build two standard curves.