高压脉冲电场处理室内多物理场对微生物灭活作用的研究

发布时间：2018-05-28 16:49

本文选题：高压脉冲电场 + 数值模拟　；参考：《浙江大学》2013年博士论文

【摘要】：液态食品的安全问题历来就受到人们的广泛关注,无论新鲜果蔬汁还是奶制品,甚至是酒精饮品,其产品的品质和安全很大程度上取决于杀菌工序是否可靠。传统的热力杀菌方法在导致微生物失活的过程中,食品受热会发生物理和化学性质的变化,使其色、香、味、组织结构发生改变,营养价值下降,产生各种反应,甚至检测出有毒物质,不仅降低了产品的新鲜度,还严重影响了食品的质量。高压脉冲电场(Pulsed electric field,PEF)技术作为最近几年研究最为热门的非热加工技术之一,不但具有良好的杀菌、钝酶效果,还能最大限度地保持食品的新鲜度,处理过程时间短、温度低,能量消耗少。因而,该技术以其优良的处理效果和低廉的运行费用在液态食品加工领域展示了诱人的应用前景。本文综合利用数值模拟技术、计算流体动力学、微生物计量学、化学计量学和荧光光纤传感技术等诸多领域的知识,研究高压脉冲电场处理室结构参数和处理过程工作参数对于高压脉冲电场技术用于食品中微生物灭活作用的影响。通过建立不同结构的高压脉冲电场杀菌处理室的多物理场耦合模型,分析处理室结构参数对于内部物理场分布规律的影响；研究处理介质的流量和初始温度对于准方波脉冲波形的影响,探索微生物形态特性对于微生物跨膜电势的影响,通过建立杀菌动力学模型分析处理过程工作参数对高压脉冲电场技术处理效率的影响,并通过多物理场耦合模型和杀菌动力学模型的融合,构建基于处理室结构参数和处理过程工作参数的高压脉冲电场技术对微生物作用的定量预测模型,为优化处理室结构参数和优选处理工作参数提供理论依据,为研发具有自主知识产权的工业化大规模高压脉冲电场处理系统提供方法依据,为高压脉冲电场处理技术的推广应用提供一种新的思路,对于提高处理效率和降低生产成本具有深远的现实意义。主要研究内容、结果和结论如下： (1)分析了不同处理室结构对高压脉冲电场处理室内部物理场分布规律的影响。采用数值模拟方法构建了高压脉冲电场处理室的多物理场耦合仿真模型,结果表明：1)平行板型静态处理室中电场强度处处相等,温度随处理时间上升很快。2)同轴型连续式处理室中,电场分布呈现不均匀性,电极间距越小,其电场分布均匀性越好。温度随着轴向距离的增加呈现线性升高,在径向方向上,温度的波动较小。湍流动能随着液体流动方向的轴向距离的增加而减弱,随着电极间距的增加而减弱。3)共场型连续式处理室中,相对电场强度和相对能量输入变化趋势一致,与电极半径和电极间距的比值(r/d)之间存在线性关系,随着r/d值的增大而增大；共场型处理室内部的温度随着物料的流动方向逐渐升高,处理腔二的温度比处理腔一的温度高。在每个处理腔的出口位置,电极和绝缘材料的交界处的物料温度显著上升,出现温度峰值。结果表明：通过建立多物理场耦合模型,可以对高压脉冲电场处理室内部的物理量进行分析,得到电场强度、能量输入和温度升高与处理室结构参数的关系。 (2)分析了层流和湍流状态下优化的绝缘环形状对共场型连续式处理室内部各物理场分布规律的影响。对三种不同绝缘环形状(矩形内嵌式、矩形内嵌倒圆角式和圆弧形内嵌式)的共场型处理室进行仿真,结果表明：1)在层流状态下,绝缘环的内嵌式结构并不能有效地改善处理室内部的处理均匀性,反而会导致电场峰值和温度峰值的产生。2)在湍流状态下,改进后的处理室中电场分布较之原结构得到改善,峰值电场强度减弱,处理室径向的流速相比于层流状态更为均匀。湍流状态对于处理室内温度控制的作用较为明显,与原结构相比有显著提高。3)在两种状态下,相对电场强度和相对能量输入的变化趋势一致,随着内嵌深度和电极半径的比值(i/r)的增大而减小,随着电极半径和电极间距的比值(r/d)的增大而增大。4)在两种状态下,相对温升与电极间距(d)、内嵌深度和电极半径的比值(i/r)及电极半径和电极间距的比值(r/d)都有关。湍流状态下的相对温升拟合度(0.921R20.943)优于层流状态。结果表明：优化的绝缘环结构在湍流状态下能改善处理室内部的物理场分布,并且通过多物理场耦合模型,得到电场强度、能量输入及温度与处理室绝缘环结构参数之间关系。 (3)分析了处理介质的流量和初始温度对于准方波脉冲波形的影响。结果表明：1)通过数值模拟方法得到处理介质的电导率和处理室截面电流值变化趋势一致,随着初始温度的升高,二者逐渐上升,而随着处理介质的流量增大,二者逐渐下降；而脉冲的下降时间随着初始温度的升高而减小,随着处理介质流量的增大而增大。2)建立了处理室等效电阻关于流量和初始温度的函数关系,无论是对单个处理腔的等效电阻还是对两个处理腔的等效并联电阻进行拟合,其决定系数R2均达到0.980以上,RMSE值均小于0.003。3)通过示波器和NI Labview SignalExpress软件采集真实波形与仿真所得结果进行比较。仿真所得的脉冲波形的下降时间与实验所得变化趋势一致,但是,脉冲波形的真实下降时间大于仿真结果。结果表明：通过数值模拟方法,可以建立准方波脉冲波形的下降时间与处理介质流量和初始温度之间的相关性。 (4)分析了不同微生物细胞的形态特性对于高压脉冲电场技术杀菌效果的影响。1)通过数值模拟方法分析了三种微生物细胞(金黄色葡萄球菌、大肠杆菌DH5α和酿酒酵母菌)在高压脉冲电场作用下的跨膜电势,比较其对高强度电场的抵抗能力。结果表明,在同一电场强度下,酿酒酵母菌比大肠杆菌DH5a拥有更大的跨膜电势,金黄色葡萄球菌的跨膜电势最小。2)通过高压脉冲电场技术对三种微生物杀菌实验表明,酿酒酵母菌对高压脉冲电场处理过程的抵抗力最弱,大肠杆菌DH5α次之,金黄色葡萄球菌最强,与跨膜电势的仿真结果一致。3)较大的细胞尺寸可以增加跨膜电势和细胞膜的电场强度,使细胞对于高压脉冲电场处理更为敏感。4)不同的细胞形态对于跨膜电势也有较大影响。杆形细胞的跨膜电势和电场强度均大于拥有相同长径和短径的椭球形细胞。5)随着细胞膜厚度增加,跨膜电势增大非常微小,但是细胞膜的电场强度下降十分明显。结果表明：通过数值模拟方法,可以对不同微生物的跨膜电势进行分析,比较不同微生物对高压脉冲电场处理过程的抵抗力。 (5)分析了高压脉冲电场技术的不同处理工作参数对微生物的致死规律。1)在一定范围的处理强度(电场强度为12-21kV/cm,处理时间为30-180μs)和初始温度(25-35℃)下,研究高压脉冲电场技术对黄酒中酿酒酵母菌的致死作用,得到最大的杀菌效果为5.5个对数级。2)从AFM成像的结果可以看出,经过处理后微生物细胞的数量减少,图像呈现模糊的边界,细胞边缘塌陷,表明高压脉冲电场技术引起了酵母菌细胞膜的破坏。3)采用Log-linear模型、Weibull模型和多元回归模型分别对实验数据进行拟合,通过另一组独立实验分别对根据模型预测得到的杀菌数量和5-D值进行验证,对于杀菌数量的预测,Weibull模型的Af和Bf值分别为1.082和1.019,多元回归模型的Af和Bf值分别为1.152和0.961。对于5-D值的预测,Weibull模型的Af和Bf值分别为1.169和0.996,Log-linear模型的Af和Bf值分别为1.773和1.773。结果表明,Weibull模型和多元回归模型都可用于预测高压脉冲电场技术对黄酒中酿酒酵母的杀菌效果。 (7)探索了将多物理场耦合模型和杀菌动力学模型相结合,构建基于处理室结构参数和处理过程工作参数的高压脉冲电场技术的杀菌效果预测模型的可行性。结果表明：将杀菌物理场和前文所述的多物理场相结合,得到杀菌效果的预测模型,所得到的结果与真实测量所得到的酵母菌的存活数量基本一致。通过所构建的杀菌效果预测模型,提出针对处理室结构参数和处理过程工作参数的优化方法。结果表明：构建基于处理室结构参数和处理过程工作参数的高压脉冲电场技术的杀菌效果预测模型是可行的。
[Abstract]:The safety of liquid food has always been widely concerned. Whether fresh fruit, vegetable, dairy, or even alcoholic beverages, the quality and safety of their products depend largely on the reliability of the sterilization process. The change in nature makes its color, fragrance, taste, structure and structure change, the value of nutrition is reduced, the reaction is produced, and even the toxic substances are detected, which not only reduces the freshness of the products, but also seriously affects the quality of food. The high voltage pulsed electric field (Pulsed electric field, PEF) technology is the most popular non hot processing technology in recent years. One of the techniques, not only has good sterilization, blunt enzyme effect, but also maintains the freshness of food, the processing time is short, the temperature is low, and the energy consumption is low. Therefore, the technology shows the attractive application prospect in the field of liquid food processing with its good treatment effect and low operating cost.
In this paper, the numerical simulation technology is used to calculate the knowledge of fluid dynamics, microbiometrics, chemometrics and fluorescent fiber sensing technology. The effects of the structure parameters and processing parameters of the high voltage pulsed electric field on the inactivation of microbes in food are studied. The multi physical field coupling model of a high voltage pulsed electric field with different structures was established. The influence of the structure parameters on the distribution of the internal physical field was analyzed. The influence of the flow rate and initial temperature of the medium on the quasi square wave pulse waveform was studied, and the influence of the microbiological characteristics on the transmembrane potential of the microorganism was explored. By establishing a germicidal kinetic model to analyze the effect of the working parameters of the processing process on the efficiency of the high voltage pulsed electric field, and through the fusion of the multi physical field coupling model and the germicidal kinetic model, the quantitative prediction of the action of the high pressure pulse electric field based on the structure parameters of the processing chamber and the working parameters of the processing process is constructed. The model provides a theoretical basis for optimizing the structural parameters of the processing chamber and optimizing the processing parameters. It provides a basis for the research and development of the industrial large-scale high voltage pulsed electric field processing system with independent intellectual property rights. It provides a new idea for the popularization and application of high voltage pulsed electric field processing technology, which can improve the processing efficiency and reduce production. The cost has far-reaching practical significance.
The main research contents, results and conclusions are as follows:
(1) the influence of different processing chamber structure on the physical field distribution of high voltage pulsed electric field is analyzed. A multi physical field coupling simulation model of high voltage pulsed electric field processing room is constructed by numerical simulation. The results show that 1) the electric field intensity in the parallel plate static processing chamber is all equal and the temperature rises rapidly with the processing time. .2) the distribution of electric field appears inhomogeneous in a coaxial continuous processing chamber. The smaller the distance of the electrode is, the better the distribution of the electric field is better. The temperature increases linearly with the increase of the axial distance. In the radial direction, the fluctuation of the temperature is smaller. The turbulent kinetic energy decreases with the increase of the axial distance of the liquid flow direction, with the electrode spacing. In the continuous treatment chamber, the relative electric field intensity and the relative energy input change in the continuous treatment chamber, and there is a linear relationship between the ratio of the electrode radius and the ratio of the electrode distance (r/d), which increases with the increase of the r/d value; the temperature of the common field treatment increases with the flow direction of the material, and the treatment cavity is two. The temperature of the cavity is higher than that of the cavity. At the exit position of each processing chamber, the temperature of the material at the junction of the electrode and the insulating material rises significantly, and the temperature peak appears. The results show that the physical and physical amount of the electric field can be analyzed, the intensity of the electric field and the input of the energy can be obtained by the establishment of a multi physical field coupling model. And the relationship between the temperature increase and the structure parameters of the treatment room.
(2) the influence of the shape of the insulated ring under laminar and turbulent flow on the distribution of the physical fields in the interior of the chamber is analyzed. The simulation of the common field processing chamber of three different insulation ring shapes (rectangle inlay, rectangle and arc inlay) is carried out. The results show that 1) in the laminar flow state, the insulation is insulated. The embedded structure of the ring can not effectively improve the treatment uniformity in the treatment of the interior. Instead, it will lead to the generation of the peak and temperature peak of the electric field.2). In the turbulent state, the electric field distribution in the improved treatment room is better than the original structure, the peak electric field intensity is weakened, and the flow velocity in the chamber is more uniform than that of the laminar flow. The effect of the turbulent state on the temperature control is more obvious. Compared with the original structure, it has a significant increase of.3). In the two states, the relative electric field intensity and the relative energy input are in the same trend. With the increase of the ratio of the embedded depth and the radius of the electrode (i/r), the ratio of the electrode radius to the electrode spacing (r/d) increases. In two states, the relative temperature rise and the electrode spacing (d), the ratio of the embedded depth to the electrode radius (i/r) and the ratio of the electrode radius to the electrode spacing (r/d) are all related. The relative temperature rise fitting (0.921R20.943) in the turbulent state (0.921R20.943) is superior to the laminar flow state. The results show that the optimized insulation ring structure can be improved in the turbulent state. The physical field distribution in the interior is dealt with, and the relationship between the electric field strength, the energy input and the temperature of the insulation ring of the treatment chamber is obtained through the multi physical field coupling model.
(3) the influence of the flow rate and initial temperature of the medium on the quasi square wave pulse waveform is analyzed. The results show that: 1) the conductivity of the medium is obtained by the numerical simulation method and the current value of the section of the treatment chamber is the same. With the increase of the initial temperature, the two gradually rises, and with the increase of the flow rate of the treatment medium, the two are gradually increasing. The drop time of the pulse decreases with the increase of the initial temperature. With the increase of the flow rate of the treatment medium, the function of the equivalent resistance of the processing chamber is established on the flow and the initial temperature, which is determined by the equivalent resistance of the single processing chamber or the equivalent resistance of the two lumen. The coefficient R2 is above 0.980 and the RMSE value is less than 0.003.3). The actual waveform obtained by the oscillograph and the NI Labview SignalExpress software is compared with the simulation results. The simulation results are in accordance with the experimental results, but the real descent time of the pulse wave shape is larger than the simulation result. Ming: through numerical simulation, we can establish the correlation between the falling time of quasi square wave pulse and the treatment of medium flow and initial temperature.
(4) the influence of the morphological characteristics of different microorganism cells on the bactericidal effect of high voltage pulsed electric field (.1) was analyzed. Through numerical simulation, the transmembrane potential of three microorganism cells (Staphylococcus aureus, Escherichia coli DH5 alpha and Saccharomyces cerevisiae) under the action of high voltage pulsed electric field was analyzed, and the resistance to high intensity electric field was compared. The results showed that the Saccharomyces cerevisiae had greater transmembrane potential than the Escherichia coli DH5a at the same electric field intensity, and the transmembrane potential of Staphylococcus aureus was least.2). The resistance of Saccharomyces cerevisiae to the treatment of high pressure pulsed electric field was the weakest by high voltage pulsed electric field technique to three microorganism sterilization experiments, and the Escherichia coli D H5 alpha, Staphylococcus aureus is the strongest, which is consistent with the simulation results of the transmembrane potential.3) the larger cell size can increase the transmembrane potential and the electric field intensity of the cell membrane, and make the cells more sensitive to the high voltage pulsed electric field treatment. The different cell morphology also has a greater influence on the transmembrane potential. The transmembrane potential and electric field of the rod shaped cells The strength of the ellipsoidal cell.5 with the same length diameter and short diameter increased with the increase of the thickness of the cell membrane. The increase of the electric potential of the membrane was very small, but the electric field intensity of the cell membrane decreased very obviously. The results showed that the transmembrane potential of different microbes could be analyzed by the numerical simulation method and the high pressure pulse was compared with the different microbes. Resistance in the process of electric field treatment.
(5) the lethal effect of high voltage pulsed electric field technology on Saccharomyces cerevisiae in yellow wine was studied under a certain range of treatment intensity (electric field intensity is 12-21kV/cm, treatment time 30-180 s) and initial temperature (25-35 degrees C), and the maximum sterilization was obtained. The effect is 5.5 logarithmic level.2) from the results of AFM imaging, it can be seen that after processing, the number of microorganism cells is reduced, the image presents a fuzzy boundary, the edge of the cell collapses, indicating that the high voltage pulsed electric field technique causes the destruction of the yeast cell membrane.3) using the Log-linear model, the Weibull model and the multiple regression model respectively. According to the fitting, the number of bactericidal and 5-D values predicted by the model were verified by another group of independent experiments. The Af and Bf values of the Weibull model were 1.082 and 1.019 respectively. The Af and Bf values of the multiple regression models were 1.152 and 0.961., respectively, and the Af and Bf values of the Weibull model respectively. For 1.169 and 0.996, the Af and Bf values of the Log-linear model are 1.773 and 1.773. respectively. The Weibull model and multiple regression model can be used to predict the bactericidal effect of high voltage pulsed electric field technology on the Saccharomyces cerevisiae in yellow wine.
(7) the feasibility of combining the multi physical field coupling model with the germicidal kinetic model is explored to construct the bactericidal effect prediction model of the high voltage pulsed electric field based on the structure parameters of the processing chamber and the working parameters of the processing process. The results show that the bactericidal physical field and the multi physical field described in the previous article are combined to obtain the pre sterilization effect. The results obtained are in accordance with the survival number of the yeast obtained by the real measurement. The optimization method for the structure parameters of the treatment room and the working parameters of the processing process is proposed through the prediction model of the bactericidal effect. The results show that the high pressure pulse based on the parameters of the processing chamber structure and the processing parameters of the process is constructed. It is feasible to predict the germicidal efficacy of the electric field technology.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TS201.3

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