Study On Rapid Detection The Aerobic Plate Count In Milk By The Impedance Method

The aerobic bacterial count is an important indicator of microbiological detection of milk, and its rapid detection can instruct employed people to adopt appropriate manufacturing procedure, ensuring the quality and the safety of dairy products. There are many superiorities of impedance method, such as rapid detection, easy to operate, cost-effective of single detection. Therefore, the objective of this research was to explore the potential utilization of the impedance method in rapid detection the aerobic bacterial count of milk through the following aspects:1) the change pattern of the conductance (G), the total impedance (Z), the double-layer capacitance (Cs), the medium capacitance (Cp), and the impedance angle (θ) during the impedance detection and the equivalent circuit; 2)the influence of temperature, frequency on curves of G, Z, Cs, Cp,θchange rate;3) the practical value of the impedance method in the rapid detection the aerobic bacterial count of milk.The main research findings were summarized as follows:1. The value of G, Cs increased, the value of Z, Cp,θdecreased during impedance detection. Cs is the most sensitive to the change of the impedance characteristic of culture medium, its amplitude of the change rate was the biggest, while Cp was the smallest. The total impedance contained the conductance which didn't vary with frequency, the conductance varied with frequency, and the imaginary component of impedance varied with frequency. The equivalent circuit of the process of impedance detection could be the constant phase angle element (CPE) serried with the resistance (R), the calculation formula of Z, Z=11.423+1.3704×104×(2×π×f)-0.7767×cos((?))-j1.3704×104×(2×π×f)-0.7767×sin((?))·2. The temperature affected the value of G, Z, Cs, Cp and the detection time (DT) of impedance detection. There was linear relationship between impedance parameters and the temperature, the value of G, Cs, Cp increased, the value of Z decreased, while the temperature increased. The growth of microorganism would be inhibited when the temperature was too high or too low. However, when the temperature was among suitable growth range of micro-organism, the higher the temperature the shorter the DT. As a result, the suitable temperature range of rapid detection the aerobic bacterial count by the impedance was 30 to 40℃。 3. The influence of frequency on curves of G, Z, Cs, Cpchange rate was different-the curves of G, Z change rate were almost not affected, while high frequency severely affected the Cs, Cp. Therefore, while G. Z was chose as parameter, the suitable frequency range was 100Hz-1MHz。the suitable frequency range of Cs was 100Hz-100KHz.4. When G, Z, Cs was chosen as the detection parameters, there was linear correlation between the value of DT and the logarithmic value of the aerobic bacterial count by the plate count method (1gCSPC). Furthermore, the result was more consistent when G or Z was chosen as detection parameter.In conclusion, rapid detection the aerobic bacterial count of milk could be conducted at 40℃,1 KHz. The corresponding detection time DTTH was 440min, 440min,400min, respectively, while G, Z or Cs was chosen as parameter to rapidly detect the microorganism quality of milk.