通电加热中电场强度对猪肉电导率的影响

利用通电加热装置对猪肉进行了通电加热装置,比较了不同电场强度对试样加热速率和电导率的影响,结果显示在其它条件一定的情况下,电场强度越大试样的加热速率就越快;电场强度的不同对试样的电导率略有影响,但影响不大。     

乳酸菌降解猪血培养基中亚硝酸盐的研究

对添加猪血的培养基中乳酸菌降解亚硝酸盐的情况进行了研究。其结果为：亚硝酸盐降解量与培养液的pH值呈负相关，pH值下降速度越快，亚硝酸盐的降解速度也越快。乳酸杆菌产酸能力强于球菌，使环境pH值快速下降，导致发酵后期乳酸菌对亚硝酸盐的降解能力上杆菌大于球菌。发酵液酸度越大，pH值越小，亚硝酸盐降解作用越显著。     

乳酸菌降解猪血培养基中亚硝酸盐的研究

对添加猪血的培养基中，乳酸菌降解亚硝酸盐的情况进行了研究。其结果为：亚硝酸盐降解量与培养液的pH值呈负相关，pH值下降速度越快，亚硝酸盐的降解速度也越快。乳酸杆菌产酸能力强于球菌，使环境pH值快速下降，导致发酵后期乳酸菌对亚硝酸盐的降解能力，杆菌大于球菌。发酵液酸度越大pH值越小，亚硝酸盐降解作用越显著。     

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。     

含颗粒液态食品通电加热加工特性及影响因子

通电加热技术不同于传统杀菌加工技术 ,它在加工连续流体食品特别是含颗粒食品方面 ,显示出了巨大的优越性及发展潜力。文中介绍了含颗粒液态食品通电加热加工特性及影响通电加热食品品质的若干因素。     

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。     

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。     

基于通电加热技术的猪皮胨凝胶工艺

利用猪皮为主要原料,采用通电加热的方法研制出皮胨凝胶。文中主要研究了:(1)以不同食盐添加量、不同电压条件下对皮胨汤汁加热速率和电导率的影响;通电加热制成的皮胨凝胶与传统工艺制作而成的皮胨凝胶在物理特性及成胨微观结构方面的比较;并在实验的基础上进行了猪皮胨凝胶通电加热技术的深层次数据挖掘。结果表明:随着食盐浓度的升高及电压强度的增强,皮胨汤汁加热速率越快,即皮胨凝结速度越快;(2)通电加热技术制作的皮胨凝胶其弹性、韧性、滑爽程度优于传统工艺制作而成的皮胨凝胶,且其保水性和强度都得到了提高。     

通电加热过程中食品物料电导率的研究进展

介绍了通电加热的基本原理及其特点 ,重点分析和探讨了通电加热过程中食品物料电导率的研究现状 ,展望了食品物料电导率的研究方向     

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。     

Evaluation of key parameters during construction and operation of an ohmic heating apparatus

This study aimed to design, build and validate an ohmic heating apparatus in bench scale and evaluate its performance on liquid food processing. The equipment developed showed adequate performance, monitoring data and heating products satisfactorily. Three ohmic cells were developed and tested in the device. When acerola and blueberry pulps were heated in the ohmic heater, a nonlinear behavior of electrical conductivity with temperature was observed. This behavior is associated with bubble formation caused by water boiling due to temperature gradients inside the cells. This phenomenon is influenced by a number of factors, such as solids content, electric field strength, ohmic cell size and agitation. Two of the ohmic cells developed, when placed on agitating devices, are suitable for a uniform heat treatment of liquid foods. The ohmic heating apparatus developed is adequate to conduct studies to better understand this technology and its applications on food processing.Industrial relevanceThe apparatus of ohmic heating for liquid foods designed and tested in this work can be used to evaluate fundamental parameters, such as electrical conductivity of the product, heating time and process homogeneity. It also provides a tool to monitor processing effects on the quality of end products in order to find the best conditions for a continuous ohmic heating process in an industrial scale.     

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.     

DIFFUSION OF BEET DYE DURING ELECTRICAL AND CONVENTIONAL HEATING AT STEADY‐STATE TEMPERATURE1

Ohmic heating has been shown to alter mass transfer properties of fruit and vegetable tissue. Diffusion of beet dye from beetroot tissue into a fluid was studied during conventional and ohmic heating as a function of steady‐state temperature. The volume of beet dye diffusing into solution during ohmic heating was enhanced with respect to conventional heating at 42C and 58C, but not at 72C. This can be explained by examining the differences in electrical conductivity of beet tissue at these temperatures during conventional and ohmic heating. At 42 and 58C, the electrical conductivity of beet tissue heated ohmically is higher than the electrical conductivity of beet tissue heated conventionally. At 72C, the electrical conductivities of beet tissue during conventional and ohmic heating are equal. The extent of diffusion in the ohmic case is also positively correlated with applied voltage. These results suggest that food processes involving mass transfer can be enhanced by choosing conditions in which the electrical conductivity of a sample under ohmic conditions is maximized.     

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.     

Changes in the electrical conductivity of foods during ohmic heating

Ohmic heating is a food processing operation in which heat is internally generated within foods by the passage of alternating electric current. The process enables solid particles to heat as fast as liquids, thus making it possible to use High Temperature Short Time sterilization techniques on particulate foods. Ohmic heating rates are critically dependent on the electrical conductivities of the foods being processed, about which little information is available. This paper reports experiments to determine the changes in electrical conductivity which occur during ohmic heating of some common foods. A number of effects which occur during conventional heating, such as starch transition, melting of fats and cell structure changes, are shown to affect the electrical conductivity. In some cases the presence of an electric field induces enhanced diffusion of cell fluids in the food which increases the rate of change of conductivity with temperature above that found by conventional heating. Preheating is found to increase the electrical conductivity of some foods, making them acceptable for ohmic processing.     

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。     

Ohmic Heating: Concept and Applications—A Review

Ohmic heating, also known as Joule heating, electrical resistance heating, and direct electrical resistance heating, is a process of heating the food by passing electric current. In ohmic heating the energy is dissipated directly into the food. Electrical conductivity is a key parameter in the design of an effective ohmic heater. A large number of potential applications exist for ohmic heating, including blanching, evaporation, dehydration, fermentation, sterilization, pasteurization, and heating of foods. Beyond heating, applied electric field under ohmic heating causes electroporation of cell membranes, which increase extraction rates, and reduce gelatinization temperature and enthalpy. Ohmic heating results in faster heating of food along with maintenance of color and nutritional value of food. Water absorption index, water solubility index, thermal properties, and pasting properties are altered with the application of ohmic heating. Ohmic heating results in pre-gelatinized starches, which reduce energy requirement during processing. But its higher initial cost, lack of its applications in foods containing fats and oils, and less awareness limit its use.     

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。