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。     

低场脉冲磁共振成像(P-MRI)技术在食品加工中的应用

介绍核磁共振及其成像原理，以及低场脉冲磁共振成像（P—MRI）仪的主要构成。综述了低场P—MRI在食品加工中较有吸引力的几个应用方向：评价果蔬类食品的品质、研究食品中的油脂和水分、测量玻璃态转化温度Tg和研究欧姆加热食品内部的温度分布。说明了低场P-MRI应用在食品科学领域的意义和前景。     

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。     

食品欧姆加热原理及其影响因素

欧姆加热技术不同于传统杀菌技术。它在加工连续流体食品特别是含颗粒食品方面,显示出了巨大的发展潜力。本文介绍了欧姆加热技术的基本原理以及影响欧姆加热食品品质的若干因素。     

液态食品连续欧姆加热的数值模拟

为研究液态食品欧姆加热过程的温度场和速度场分布,实验采用有限元数值计算的方法,对圆柱状加热室中自来水和豆浆的连续欧姆加热过程进行三维稳态数值模拟,分析不同截面加热室速度场和温度场,以及不同流速对加热室的温度分布的影响。加热室中心温度模拟计算结果与参考文献值对比,自来水和豆浆的误差分别为2.32℃和2.65℃,数值模拟很好地预测了自来水和豆浆加热过程中的速度场和温度场。     

欧姆加热技术及其在食品工业中的应用

欧姆加热技术是一种新型的食品工艺,具有许多优点,发展潜力巨大。近年来,欧姆加热技术在食品加工领域中受到了越来越广泛的重视。本文介绍了欧姆加热技术的发展历史、基本原理、特点、影响因素以及在食品工业中的应用和发展前景。     

食品科学的新发展

(接《中国食品学报》Vol.2 No.3 P5)2 新技术范例2.1 欧姆加热在现代工艺中,欧姆加热已经被认为是在工业中应用最发达的工艺之一,它被应用于液体、粒于状态的植物和动物食品的加工,例如蔬菜加工、肉和鱼的加工等。和微波加热不同,欧姆加热温度变化较小,应用过程中只有(0.1—3.0)S/m的最小电流传导率。在典型装置中温度由输入速率和输入能量决定。问题是电化反应导致电极周围出现气泡和走微现象,如果该技术能很好地控制,它引起的营养素损失几乎是最小的,可     

欧姆加热技术在食品加工中的应用进展

欧姆加热是一种新型食品热加工技术,在食品物料的快速均匀加热及提高食品安全性及质量方面有巨大的应用潜力。由于该技术在实际应用中受物料自身电导性、电场强度等因素影响,国内的研究仍处于起步阶段,相较于国外在处理含颗粒食品、含蛋白食品加工的广泛应用,甚至在太空任务中食品加工方面的尝试,存在着较大差距。文中阐述了欧姆加热技术的原理、特点、国内外欧姆加热装备的研发现状及该技术对食品原料中酶、微生物、风味与营养成分等方面的影响,并对该技术在食品加工中的应用现状进行了讨论和总结。     

高新技术在无菌包装中的应用

1 欧姆法加热杀菌技术 欧姆法加热技术在国外已经进入工业应用阶段,一些厂家已生产出可供食品生产厂家应用的欧姆加热器,其优点是可加工粘度较高或颗粒较大的液体食品.颗粒直径可达2.5厘米。目前存在的主要问题是系统的预杀菌仍需采用过热蒸汽。因此,在无菌系统的配置时要配成混合式。2 微波连续灭菌技术 微波灭菌与欧姆加热杀菌的主要区别在于前者采用高     

欧姆加热及其在食品中的应用

欧姆加热是一种新型的加热方式，具有物料升温快、加热均匀、无污染、易操作、加工食品质量好等优点，文章综述欧姆加热的原理，加热特点及其在食品中的应用。     

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.     

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.     

Three-dimensional MRI mapping of microwave induced heating patterns

Summary Magnetic Resonance Imaging (MRI) has been used to map in three dimensions, non-invasively, the complex heating patterns induced by microwave heating. Comparisons with infra-red thermal imaging of the surface heating patterns are demonstrated. The effects of the differential heating properties have been characterized for a model food sample. The potential applications of MRI temperature mapping to optimizing the domestic and industrial use of microwaves for heating of foods is discussed.     

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。     

Influence of temperature,voltage gradient and electrode on ascorbic acid degradation kinetics during ohmic heating of tropical fruit pulp

Vitamin C also known as ascorbic acid is one of the most heat sensitive vitamins. Tropical fruits are a good source of vitamin C, but this vitamin is lost during processing due to high temperature. Ohmic heating is attempted as an alternative technique for the preservation of tropical fruit pulp. The objective of this study was to evaluate the influence of change in temperature, voltage gradient and electrode on vitamin C degradation in the tropical fruit pulps including papaya, sapota and guava, when it is ohmically heated. It was observed that with increase in temperature and voltage gradient, the ascorbic acid content decreased of all the fruit pulp test. Ohmic heating experiment was conducted with two different electrode viz stainless steel and titanium electrode. Ohmic heating experiment when performed with titanium electrode showed better retention of ascorbic acid. A separate experiment was conducted to study the effect of ohmic time on ascorbic acid degradation. Ascorbic acid degradation is also studied during the storage of the ohmic heated pulp. Ascorbic acid content decreased with increase in ohmic heating time and also with increase in storage days.     

Advantages of ohmic cooking in the kilohertz-range - part I: Impact of conductivity and frequency on the heating uniformity of potatoes

The heating uniformity of potato cubes and whole potato tubers was investigated during cooking by ohmic heating (OH) in the low (12 kHz) and high (300 kHz) kHz range. Potatoes were heated in aqueous NaCl solutions with various conductivities (1–5 mS/cm). Conductivities and cell disintegration index of the tissue were determined in dependency of the temperature and the frequency at different points in the tubers. Heating uniformity was characterized by analyzing the temperature profiles with up to four thermocouples and by thermal imaging. Heating behavior of peeled and unpeeled tubers were compared to evaluate the impact of the skin on the OH treatment. For the higher frequency applied, increased electrical conductivities in the potato tissue were observed. At 300 kHz a better heating uniformity, with lower temperature differences within the potato samples compared to OH at 12 kHz was observed. The results provide a better understanding of the effect of high frequency electric fields on the heating uniformity and the conductivity of intact potato tissue.Industrial relevanceOhmic heating (OH) is an alternative heating technology with the potential to reduce processing times and energy consumption. It can overcome limitations in the heat transfer particularly given for large-volume solid foods and provide a uniform heating. However, limited attention has been given to the effects of the product and process parameters on the heating uniformity during OH treatments of solid foods. The present paper highlights the importance of the electrical conductivity and the frequency of the applied electric field on the heating uniformity. The obtained results contribute to the understanding of the interaction of the electric field and the food matrix, which is the basis for the implementation of tailored and targeted processing concepts in the industry.     

The effects of concentration on electrical conductivity of orange juice concentrates during ohmic heating

Ohmic heating is an alternative heating technique, using an electrical current passing through the food product. It can be specially used in pumpable food lines as an alternative heating unit. In this study, orange juice concentrates having 0.20–0.60 mass fraction soluble solids were ohmically heated by using five different voltage gradients (20–60 V/cm). The dependence of electrical conductivity on temperature, voltage gradient and concentration were measured. The ohmic heating system performance coefficients were calculated by using the energies given to the system and taken by the orange juice samples. The mathematical model results, taking system performance coefficients into account, were compared with experimental ones. The predictions of the mathematical model were found to be very accurate.     

Effects of moderate electrothermal treatments on juice yield from cellular tissue

Ohmic and microwave heating were employed to investigate electro-thermal effects on apple juice yield by preheating apple samples to 40 or 50 °C. Cylindrical raw and pretreated samples from fresh apple were wrapped in a non-absorbent cloth and pressed to produce juice. Data on juice yield and applied force were recorded and compared with the raw material. The results showed that apple juice yield was strongly improved by both thermal pretreatments, and pretreated samples showed less resistance during extraction. The thermal effect of ohmic pretreatment on juice yield increased with the pretreatment temperature, while for microwave pretreatment, the low pretreatment temperature resulted in high juice yield. Ohmic heating as a pretreatment increased juice yield and required less input work, compared to microwave heating; thus frequency might play a major role in this effect. The thermal effect difference could be due to increased migration of cellular moisture during ohmic pretreatment. These observations indicate ohmic pretreatment has the potential to enhance juice yield and save energy.