【作者】 张爱萍；

【导师】 刘东红；

【作者基本信息】 浙江大学 ， 食品科学， 2011， 硕士

【摘要】 菌落总数是牛奶微生物学检测中一项重要的指标,实现其快速检测可以快速确定牛奶的品质,指导企业的质量管理人员选取合适的加工工艺参数,对保障产品的质量和安全有着积极意义。阻抗法进行微生物检测具有快速、操作简便、单次检测成本低的优点,可应用于牛奶中菌落总数的快速分析。本文主要从以下三个方面探索阻抗法在快速检测牛奶中菌落总数中的应用：1)检测过程中各阻抗参数(电导G,总阻抗Z,双电层电容值Cs,培养介质电容Cp,阻抗角θ)的变化规律及阻抗检测过程中的等效电路；2)检测温度、频率对G、Z、Cs、Cp、θ的变化率曲线的影响；3)阻抗法快速检测牛奶中菌落总数的实际应用价值。实验结果表明：1.在用阻抗法快速检测牛奶中的菌落总数过程中,G、Cs值增大,Z、Cp、θ值减小。在这个过程中,Cs对培养介质阻抗特性的改变最为敏感,其变化率幅值最大,Cp最小。双电极系统测得的总阻抗包含不随频率变化的电导、随频率呈指数变化的电导和随频率呈指数变化的阻抗虚部这三项。阻抗法检测过程中的等效电路可认为是常相位角元件CPE与电阻R的串联。Z值的计算公式：2.检测温度对G、Z、Cs、Cp值和阻抗检测的检出时间(DT)都有影响。G、Z、Cs、Cp值随温度的升高呈线性变化：G、Cs、Cp值线性增大,Z值则线性减小。温度过高或过低都会抑制微生物的生长繁殖,但在微生物适宜生长温度范围内,增加温度可以缩短DT值。得到,阻抗法快速检测牛奶中的菌落总数的适宜温度范围为30-40℃。3.检测频率对G、Z、Cs、Cp的变化率曲线影响不同,对于G、Z基本没有影响,高频对Cs、Cp有很大的影响。得到G、Z作为阻抗法检测参数,其检测频率范围为100Hz～1MHz,Cs检测频率范围为100Hz～100KHz。4.G、Z、Cs作为检测参数得到的检出时间DT跟菌落总数的对数值(lg CSPC)存在线性相关,可作为阻抗法的检测参数,其中以G、Z作为检测参数得到的检测结果与实际更符。综上所述,可以选择40℃、1KHz作为检测条件,在以G、Z、Cs作为阻抗法的检测参数快速分析牛奶的微生物品质时,其对应的检测时间DTTH分别为440min、440min、400min。更多还原

【Abstract】 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.更多还原