食品通电加热技术的研究进展

综述了国内外关于食品通电加热技术的理论与应用研究的现状 ,并对通电加热技术的开发及应用前景做了展望     

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。     

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、     

液态食品连续通电加热的加热速率与温度分布

利用自行研制的小型液态食品通电加热装置研究了自来水在连续通电加热过程中的温度分布。实验结果表明,该系统能实现液态食品的连续加热。整个加热过程可分为三个阶段,在加热初始阶段各加热室的加热速率随电场强度的降低而减小：加热室的平均温度与装置长度呈线形关系;在同一极板表面中心处和0．5R处的温度基本相同;加热室极板表面出现了轻微“过热”现象。     

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。     

通电加热在食品加工中的应用

介绍了通电加热的基本原理、特点、通电加热设备及通电加热在杀菌、肉制品和豆腐以及解冻等食品加工中的应用,并对通电加热的应用前景进行了分析.     

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。      

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。     

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     

A microwave and ohmic combination heater for uniform heating of liquid-particle food mixtures

Microwave and ohmic combination heating was proposed to improve the uniformity of thermal processing of particulate foods. Thermal patterns of a liquid-particle mixture in a small test cell were studied using both experimental and simulation approaches. Carrot cubes (10 mm × 10 mm × 10 mm) and 0.1% NaCl salt solution were used as model foods. The temperature distribution of solid and liquid phases was examined using individual and combination heating methods. Under ohmic heating, the liquid was heated faster by 18.9 °C after 250 s. The heating rate of a carrot cube was faster than liquid under microwave heating and temperature rise of carrot was approximately 11.2 °C higher than that of solution after heating of 70 s. Samples experienced different heating patterns over time during the combination heating. Carrot samples showed a thermal lead initially when heated under microwave and the trend reversed during the second stage when ohmic heating was applied. Liquid-particle temperature difference was reduced as the combination heating proceeded, and came to be less than 2 °C at the end. Results obtained from simulation showed similar patterns and all prediction data agreed well with the experimental data. The prediction errors for sample temperatures ranged from 5.7% to 11.6%. The results provided better understanding for designing a continuous flow combination heater that can produce uniform temperature of solid-liquid mixtures. PRACTICAL APPLICATION: If successful, this combination heating technique will find its way to effective aseptic or sterile processing of low acid multiphase foods containing large particulates (such as soups with meatballs or vegetables) that has not been a commercial reality in the United States.     

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。     

苹果法的欧姆加热研究

研究了苹果汁的欧姆加热规律及其对果汁品质的影响,考察了温度(T)和可溶性固形物(SS)含量对电导率σ的影响,以及电场强度(E)、可溶性固形物(SS)和加热体积(液高 h)对加热速率的影响、同时考察了欧姆加热对果汁糖度、pH、透光率等的影响.结果表明,苹果汁的电导率随温度的升高而增大,且呈线性关系,随着可溶性固形物含量的增加,苹果汁的电导率和加热速率都是先增大然后减小,在26°Bx左右时最大.苹果汁的加热速率随电场强度的增加而增大,而在相同电场强度下,液高对加热速率没有影响.并且,欧姆加热对果汁品质影响很小,因此极具开发前景.     

含绝缘体物料的欧姆加热过程模拟

欧姆加热利用食品物料本身的电阻抗来产生热量,是一种内加热方式,与传统加热方式相比,具有快速均匀的加热特点。但食品往往不是一个均匀体系,不同部位的电导率的差异也会造成欧姆加热升温的不均匀性,研究不均匀体系欧姆加热时的温度分布对于欧姆加热技术的开发利用有重要意义。本文利用有限元方法,模拟了含有绝缘体的物料的欧姆加热过程,并用实验进行了验证。结果表明,有限元模型能够很好地模拟欧姆加热过程,整个加热过程中,模拟预测的温度与实验测得温度接近,最大差值为8K。同时运用有限元模型模拟了绝缘体的位置和方位对温度场的影响,绝缘体在物料中的位置和方位影响物料中电流密度的分布,温度场最高点位置始终出现在电流密度最高的区域,而最低点与电流的加热作用和物料间的热传导作用有关。     

Product formulation for ohmic heating: blanching as a pretreatment method to improve uniformity in heating of solid-liquid food mixtures

ABSTRACT:  The electrical conductivity of food components is critical to ohmic heating. Food components of different electrical conductivities heat at different rates. While equal electrical conductivities of all phases are desirable, real food products may behave differently. In the present study involving chicken chow mein consisting of a sauce and different solid components, celery, water chestnuts, mushrooms, bean sprouts, and chicken, it was observed that the sauce was more conductive than all solid components over the measured temperature range. To improve heating uniformity, a blanching method was developed to increase the ionic content of the solid components. By blanching different solid components in a highly conductive sauce at 100 °C for different lengths of time, it was possible to adjust their conductivity to that of the sauce. Chicken chow mein samples containing blanched particulates were compared with untreated samples with respect to ohmic heating uniformity at 60 Hz up to 140 °C. All components of the treated product containing blanched solids heated more uniformly than untreated product. In sensory tests, 3 different formulations of the blanched product showed good quality attributes and overall acceptability, demonstrating the practical feasibility of the blanching protocol.     

Electrical conductivity and physical properties of surimi-potato starch under ohmic heating

ABSTRACT:  Electrical conductivities of Alaska pollock surimi mixed with native and pregelled potato starch at different concentrations (0%, 3%, and 9%) were measured at different moisture contents (75% and 81%) using a multifrequency ohmic heating system. Surimi-starch paste was tested up to 80 °C at frequencies from 55 Hz to 20 KHz and at alternating currents of 4.3 and 15.5 V/cm voltage gradient. Electrical conductivity increased when moisture content, applied frequency, and applied voltage increased, but decreased when starch concentration increased. Electrical conductivity was correlated linearly with temperature ( R ²≈ 0.99). Electrical conductivity pattern (magnitude) changed when temperature increased, which was clearly seen after 55 °C in the native potato starch system, especially at high concentration. This confirms that starch gelatinization that occurred during heating affects the electrical conductivity. Whiteness and texture properties decreased with an increase of starch concentration and a decrease of moisture content.     

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。     

蛋清、蛋黄溶液的通电加热特性研究

研究了温度、蛋清、蛋黄浓度和电压对蛋清溶液和蛋黄溶液的电导率的影响;研究了蛋清、蛋黄浓度和电压对蛋清溶液、蛋黄溶液加热速率的影响。结果表明,蛋清溶液、蛋黄溶液的电导率随温度、蛋清和蛋黄浓度和电压的增高而增大,且电导率与温度呈线性关系;加热速率随蛋清和蛋黄浓度和电压的增高而加快,且温度与时间呈指数关系。     

通电加热下频率、温度对草鱼鱼块和鱼皮电导率的影响

为探索通电加热作为淡水鱼类加工方式的可行性,以草鱼为研究对象,采用LCR测量仪,测定了经50 Hz,20 V交流电加热后,草鱼鱼块(并联、串联)、碎鱼肉、带皮鱼块样品在10~80℃温度范围、50~20 k Hz频率范围内的阻抗值,并计算样品电导率。实验结果表明,三种样品(并联及串联鱼块、碎鱼肉)的电导率均呈现出随频率增大而增大、随温度升高而升高的趋势,其中,受鱼块内部膜方向的影响,并联、串联样品电导率有显著差异(p<0.05);碎鱼肉样品消除了鱼肉内部膜的影响,其电导率值介于并联、串联样品之间。带皮鱼块样品由于鱼皮的存在,比起其他样品有不同的电导率值,鱼皮平行于电流放置时电导率值高于鱼皮垂直电流放置的值。