食品物料的电导率及其影响因素

本文阐述了食品物料电导率的定义及其电导率对通电加热的影响;分析讨论了影响食品物料电导率的因素,展望了食品物料电导率的研究方向。     

液态食品通电加热速度与电导率的关系

通过对液态食品 (液体食品、亲水性胶体食品和含颗粒液态食品 )通电加热速度与电导率的试验研究 ,得出食品物料的电导率是影响加热速度的主要因素 ,电导率越大 ,通电加热速度越快 ;食品的 pH值对加热速度也有一定的影响 ,pH值越小 ,酸性越强 ,电导率越大 ,加热速度越快。     

通电加热技术在食品中的应用研究动态

通电加热是利用食品物料本身的电阻抗来产生热量的加热技术,是一种内加热方法。与其他加热方式相比,具有加热快速、均匀的特点。文章介绍了通电加热装置的主要组成,总结了电导率的影响因素,概述了通电加热过程中食品的温度分布模拟,归纳整理出通电加热在热烫、脱水、蒸发、发酵、提取、解冻、灭菌等方面的应用,并对食品通电加热技术的应用前景进行了展望。     

食品的电导率以及通电加热技术的探讨

电导率是食品的电物性之一,其主要应用为食品的通电加热,本文阐述了食品电导率的概念,并对食品通电加热技术的发展进行了分析和探讨。     

液体食品连续通电加热系统的实验研究

设计制作了一小型液体食品连续通电加热系统,并用电 导率为1074μS／cm(水温25.4℃)的自来水对其进行了实 验研究。初步实验结果表明,该系统能实现液体物料的连 续加热,并且实验测得液体食品在流动状态下的电导率 与静态时的变化规律相同。     

食品的通电加热技术研究

从食品热加工手段玫手,追溯了食品通电加热的历史沿革,阐述了食品通电加热的基本原理及相关的数学模型如电场、温度的分布以及发热量等。讨论了食品的电导率、温度、组成、形状等影响通电加热的因素;论述了实施通电加热的工艺设计的重要参数及系统设计的总体要求;阐述了通电加热在食品加工工业中的特点。应用范围、现状及其发展前景关的工艺设计的重要参数及系统设计的总体要求;阐述了通电加热在食品加工业中的特点、应用范围、     

猪肉在接触式通电加热和浸泡式通电加热中的电导率比较

利用接触式和浸泡式通电加热实验装置对猪肉进行了通电加热,比较了两种通电加热方式对猪肉电导率的影响,结果显示:两种通电加热方式中猪肉的电导率曲线(随温度的变化曲线)基本相同,在60℃以上时,接触式通电加热中猪肉的电导率略高于浸泡式通电加热中的电导率。     

液态食品连续通电加热的温度场研究

利用自行研制的小型液态食品连续通电加热装置研究了自来水和豆浆在连续通电加热过程中加热室的温度场。实验结果表明:自来水和豆浆连续通电加热时各加热室平均温度变化类似,豆浆的加热速率大于自来水的加热速率;同一极板上,中心处和1/2R处的温度基本相同;加热时加热室上极板表面温度出现了波动,且豆浆的波动幅度大于自来水的波动幅度;自来水和豆浆连续通电加热室极板表面均出现了“过热”现象,且豆浆的过热现象较严重。实验结果对于解决通电加热过程中极板附近物料的“过热”现象,研制实用化的液态食品连续通电加热装置具有一定指导意义。     

液态食品连续通电加热的试验研究

设计制作了一套可拆卸式液态食品连续通电加热系统,研究了连续通电加热时豆浆的温度和电导率。结果表明,豆浆的升温过程可分三个阶段,第一阶段升温迅速,温度与时间呈指数关系;第二阶段升温缓慢,温度与时间呈对数关系;第三阶段温度保持不变,温度和电导率呈线性关系。加热时出现了豆浆在极板表面的黏附,黏附与极板表面的腐蚀有关。试验结果对研制实用化的小型通电加热系统有一定指导意义。     

淀粉溶液的通电加热研究

本文研究了食盐浓度、淀粉浓度和电压对淀粉溶液的电导率和通电加热速率的影响;研究了通电加热对淀粉糊化特性的影响。结果表明:淀粉溶液在通电加热过程中,加热速率和电导率随食盐浓度的增大而增大;随电压的升高而增大;随淀粉浓度的增大而减小。而电导率在达到糊化温度之前随温度的升高而增大,在糊化温度之后随温度的升高而降低。淀粉溶液在通电加热时其糊化特性无明显变化。     

食品通电加热技术及其装备的研发与应用

通电加热技术是食品工程中的一门新兴技术,本文介绍了通电加热技术的基本原理和特点,讨论了通电加热及其装备在杀菌、肉制品加工、淀粉糊化中的应用,指出了通电加热技术研究中存在的问题并对通电加热技术的应用前景进行了分析。     

欧姆加热及其在食品加工中的应用

综述了欧姆加热的原理和特点，讨论了欧姆加热在食品的杀菌、解冻、漂烫和淀粉糊化中的应用，并指出了其在研究和应用中存在的问题，并对其应用前景进行了分析。     

CHANGES IN ELECTRICAL CONDUCTIVITY OF SELECTED VEGETABLES DURING MULTIPLE THERMAL TREATMENTS1

Electrical conductivity (σ) is the most important parameter in ohmic heating. Although data exist on its changes during ohmic heating, limited information is available about preheated foods. In this study, the conductivity changes of raw vegetable samples (potato, carrot, and yam) in cyclic ohmic heating and samples preheated by conventional heating prior to ohmic heating were investigated. In cyclic ohmic heating, cylindrical vegetable samples were subjected to three repeated cycles of ohmic heating (40 V/cm, 60Hz) to 80C, and cooling to 25C. Fresh samples were also preheated by conventional heating to 80C, then subjected to ohmic heating for comparison. Specific heats changed by cycles, although moisture content remained constant in all cases. The results show that in cyclic ohmic heating, the heating rate increased by cycles. Samples preheated by either conventional or ohmic heating showed a higher heating rate than raw materials. Electrical conductivity data during ohmic heating showed that preheated vegetables have higher conductivities than fresh ones, and a tendency of increase by cycles was found.     

欧姆加热对嗜酸耐热菌的杀灭作用研究

本实验探讨了欧姆加热对嗜酸耐热菌的杀灭作用。利用自行设计的批式欧姆加热装置,对苹果汁中嗜酸耐热菌进行处理,分析了欧姆加热的电压、pH值、时间及加热体积等对杀菌效果的影响,并利用扫描电镜观察微生物细胞壁膜结构的变化,利用电导率仪和紫外吸收分光光度计测定菌悬液的成分变化。结果表明欧姆加热可以有效的杀灭苹果汁中的嗜酸耐热菌,杀菌率随电压、加热体积的升高而增大,随pH值的降低而增大。通过环境扫描电镜可观察到嗜酸耐热菌的表面出现凹陷和破损,电导率仪和紫外吸收分光光度计测定细胞内容物的溢出,据此推测欧姆加热造成了嗜酸耐热菌的"电穿孔"。     

大米通电加热特性的研究

研究了大米的通电加热工艺,并研究了大米通电加热后微观结构的变化,并与传统的加热方式进行了比较。结果表明大米经浸泡12h后,通电加热蒸煮20min口感最佳,通电加热蒸煮的米粒口感明显好于电炉加热。通电加热后的米粒微观结构与电炉加热的米粒微观结构有明显差异,通电加热的米粒糊化程度高于电炉加热。     

欧姆加热技术在肉品工业中的应用

欧姆加热作为一种新型的食品加工技术,具有加热速度快、加热均匀、消耗能量少等优点,成为近几年研究的热点。目前,欧姆加热主要运用于加工液态和颗粒流体食品,肉品的欧姆加热还处于起步阶段。本文介绍了欧姆加热的原理、肉品欧姆加热的研究热点问题及欧姆加热在食品中的其它应用。     

Simulation and verification of ohmic heating in static heater using MRI temperature mapping

Mathematical modeling of ohmic heating of liquid-particulate mixtures allows insight into the heating behavior, but model verification that uses only a selected number of points in an ohmic heating system is inadequate because of the unknown temperature distribution within the heated food materials, including the locations of hot and cold spots. In this study, ohmic heating of liquid-particulate mixtures was simulated using the finite-element analysis with the commercial software FEMLAB, and the model predictions were verified against temperature maps obtained using magnetic resonance imaging (MRI). A factor ignored by the previous modeling works, the electricity-to-heat conversion efficiency, was considered in the model, resulting in an improved model performance. The electrical conductivity and its temperature dependence for all the materials used in the simulation were determined under consistent electric field strength as the simulated ohmic heating processes. Other factors/parameters affecting model prediction, such as the boundary conditions and heat transfer coefficients, were also determined in situ for an accurate parametric input. The model predictions yielded good agreement with the MRI temperature maps. Results showed that the electrical conductivity of the materials is the most critical factor causing heating rate variations between the particulate phase and the liquid phase. The heating rate variations could be overcome by adjusting the electrical conductivity of the food materials before ohmic heating. This modeling procedure can be used for designing and controlling ohmic heating processes to ensure thermal sterilization and safety of ohmically heated food products.     

Pulsed Ohmic Heating–A Novel Technique for Minimization of Electrochemical Reactions During Processing

Minimization of electrochemical reactions during ohmic heating would be desirable. This study examines a pulsed ohmic heating technique to determine its effect on electrochemical reactions. Effects of pulse parameters, such as frequency, pulse width, and delay time were studied, in comparison with conventional (60 Hz, sine wave) ohmic heating using various electrode materials. Analyses of electrode corrosion, hydrogen gas generation, and pH change of the heating media were performed. The results suggest that pulsed ohmic heating is capable of significantly (P < 0.05) reducing the electrochemical reactions of stainless steel, titanium, and platinized‐titanium electrodes, compared with conventional 60 Hz ohmic heating. The importance of allowing enough delay time for discharge of the electrical double layers after each pulse input is emphasized.