射频杀菌条件下黑胡椒颗粒中沙门氏菌的替代菌研究

为探究热杀菌过程中屎肠球菌NRRL B-2354作为沙门氏菌ATCC 14028替代菌的可行性,通过等温实验测定黑胡椒颗粒中屎肠球菌NRRL B-2354和沙门氏菌ATCC 14028的耐热性参数,并对黑胡椒颗粒（A_w=0.65）开展射频杀菌实验验证。等温实验结果表明,黑胡椒颗粒中屎肠球菌的耐热性高于沙门氏菌。射频杀菌实验中,将2 g接种微生物的黑胡椒颗粒真空包装后置于45 g黑胡椒中心位置,在40.68 MHz射频场中加热15 min,黑胡椒颗粒中沙门氏菌的减少量相较于屎肠球菌更多,证明在射频加热中屎肠球菌的耐热性高于沙门氏菌,可作为黑胡椒颗粒杀菌过程中沙门氏菌的合适替代菌。     

基于微波加热的馒头介电特性的分析与研究

基于一种同轴探头网络分析仪技术和混合方程的途径研究微波加热馒头的介电特性。测量馒头在不同密度下的介电特性值,运用回归分析方法得出介电特性与频率的关系,通过比较馒头介电特性混合方程计算值和测量值,得到Bottcher方程适用于计算馒头的介电常数,Landau and Lifshitz,Looyenga方程用于计算馒头的损耗因子。研究频率范围915~2 450 MHz、含水率范围40.12%~48.50%(w.b.)和温度范围25~100℃下馒头介电特性的变化规律。研究表明:馒头的介电常数随着频率的增加而减小,损耗因子随着频率的增加呈现出先减小后很缓慢增大的趋势;介电常数和损耗因子均随含水率和温度的增加而增加。馒头微波加热的穿透深度随着各影响因素的增加而减小,且在25~100℃温度范围内,915 MHz和2 450 MHz微波加热馒头最大厚度分别不超过12.82 cm和10.62 cm。     

影响食品射频/微波介电特性的因素及影响机理分析

了解食品的射频- 微波介电特性,对于充分利用电磁能加热食品及研发食品成分传感器具有重要意义。为了给国内食品射频- 微波介电特性领域的研究提供借鉴,本文在介绍常用食品介电特性参数和介电极化机理的基础上,综述电信号的频率、食品温度、主要成分(水、盐和脂肪)以及容积密度对食品物料射频- 微波介电特性的影响规律,分析影响机理,并指出今后的研究方向。     

马铃薯淀粉的微波和射频韧化处理特性研究

该文研究了介电淀粉韧化处理方法，对比分析了微波(microwave, MW)和射频(radio frequency, RF)2种介质加热条件对马铃薯淀粉的颗粒形态、微观结构、热特性、黏度特性及颗粒大小分布的影响。结果表明，RF加热使淀粉表面粗糙糊化。介电加热后X射线衍射图谱没有变化，但结晶度较未处理的马铃薯淀粉有所降低。经RF加热后的马铃薯淀粉体积直径大于经MW加热后的体积直径。介电加热与未处理的马铃薯淀粉相比，淀粉的热焓值、起始温度、峰值温度和终止温度显著降低。未处理马铃薯淀粉的崩解值和峰值黏度均大于介电加热的淀粉。MW加热淀粉的膨胀度大于RF加热。介电加热淀粉在贮藏期间的透光率低于未处理的马铃薯淀粉。     

频率、温度和含水率对白果粉介电特性的影响研究

以白果粉为研究对象,利用网络分析仪研究频率(1~1000)MHz、温度(30~80)℃和含水率11.6%~31.6%(w.b.)范围内,被压缩的白果粉的相对介电常数ε′和介电损耗因子ε′′随频率、温度和含水率变化的影响;计算了射频穿透深度并分析频率、含水率和温度对其影响,运用回归分析方法得出介电特性与温度及含水率的理论方程。研究表明,白果粉的介电特性与其含水率和温度,以及频率密切相关。白果粉的介电特性随着其含水率和温度的增大而增加,随频率的增加而减小。处于较低的射频频率时介电常数和损耗因子比处于较高频率下的变化更加明显;穿透深度随着频率,样品含水率和温度的增加而减小。研究结果对了解白果粉的介电特性以及白果粉的干燥及保存有重要的指导意义。     

915MHz和2450MHz频率下温度和盐溶液浸渍对青鱼介电特性的影响

采用同轴探针法测定了频率915、2450MHz,温度范围10～90℃下,经浓度1％、2％、3％、4％食盐溶液浸渍的生鲜青鱼鱼片和预加热青鱼鱼片的介电特性值,并应用DSC测定了样品肌动蛋白和肌球蛋白的热变性温度.考察了温度、频率、水分含量、食盐溶液浸渍和蛋白质热变性对样品介电常数、介电损失率和穿透深度的影响.结果显示,浸渍盐溶液的渗透使得样品介电行为在一定程度上接近于相应盐浓度的浸渍溶液.浸渍对样品介电常数影响较小,而对介电损失率变化较大.随温度的上升,因加热过程中蛋白质的热变性引起样品水分的流失,导致生鲜样品的介电常数值的减小趋势明显大于预加热样品.而经浸渍的生鲜样品的介电损失率增大趋势明显大于预加热样品,并随浸渍溶液含盐量增大而增大.应用二项式方程得出介电特性的回归预测方程.     

微波加热过程中圆柱型包装食品的温度分布研究

从实验和理论上考察介电特性(介电常数、介电损失率)对圆柱型食品温度分布形态形成的影响。实验中以凝胶琼脂为实验样品,通过对样品添加NaCl来改变样品的介电特性,采用液晶感温片测得样品直径面的温度分布。结果表明,添加NaCl可提高样品的表面加热性,使样品的温度分布高温区由中心部向着项角部转移。为了从理论上对该现象加以描述,采用数学模型对样品中的温度分布进行了计算,结果表明,计算值与实验值有着良好的一致性。     

香草胡椒味鸡腿排的研制

香草胡椒味鸡腿排是在传统风味的基础上,添加了香草粉和黑胡椒碎。试验以鸡腿排通过添加香草粉和黑胡椒碎,研究不同配比对鸡腿排风味的影响。结果表明:当香草粉用罗勒粉与迷迭香以7∶3的比例混合,50目黑胡椒碎和30目黑胡椒碎以3∶2的比例混合使用时,产品风味浓郁,口感鲜嫩。     

基于介电特性的菜籽油品质快速检测技术研究

采用自制平行电极板检测菜籽油加热及储存过程中电容、电感及阻抗3个介电特征值的变化,并用国家标准方法分析酸值、过氧化值、碘值、羰基价及皂化值5个品质指标,然后建立菜籽油品质指标与介电特性参数之间的相关性。结果表明,在设定的加热温度和储存时间下,菜籽油的介电特性参数电容、阻抗及电感值,分别与其品质指标过氧化值、酸值及羰基价之间具有显著的相关关系。建立了每个介电特性参数(电容、阻抗及电感值)与菜籽油品质指标(过氧化值、酸值及羰基价)、温度及储藏时间的回归方程。菜籽油品质指标实际测量值与计算值的误差均在允许范围内,建议通过测定菜籽油的介电特性值(电容、阻抗及电感值)来直接计算品质指标过氧化值、酸值及羰基价。     

吸湿性多孔材料介电特性表征

微波加热干燥吸湿性多孔材料相比于传统干燥方法大大缩短了干燥时间。然而,微波干燥过程中出现的加热不均匀等问题严重限制了微波加热干燥吸湿性多孔材料应用的发展。上述问题主要是由于微波干燥过程中吸湿性多孔材料的介电特性的精确描述缺少可以实际应用的理论。文章在总结多孔材料介电特性描述理论的基础上,综合考虑吸湿性多孔材料内部微观结构,并把多孔材料中不同类型的水和颗粒形状与吸湿性多孔材料介电特性联系起来,提出适应于微波加热干燥吸湿性多孔材料多物理场计算的材料介电特性表征理论。     

射频解冻过程中食品加热均匀性影响因素的研究进展

射频加热(radio frequency, RF)技术作为一种新兴加热技术，是一种高效、低能耗的可替代传统加热的热处理方法。该方法在提高工业效率的同时又可保证食品的质量安全性及品质，可满足食品工业中的解冻以及其他加工需求，在食品工业中具有越来越大的应用潜力和发展前景。但解冻过程中存在的“边缘效应”等加热不均匀问题仍是制约该技术的一个瓶颈。本研究对射频解冻及其原理进行了介绍，并总结了影响解冻过程中加热均匀性等问题的因素，包括电磁场、射频功率、电极电压及间隙、食品的介电特性等，以期为射频解冻技术的研究及改善加热均匀性等未来研究发展方向提供参考。     

Radio Frequency Dielectric Properties of Bulk Canola Seeds under Different Temperatures,Moisture Contents,and Frequencies for Feasibility of Radio Frequency Disinfestation

The parallel capacitances and resistances of the bulk canola seeds were measured to determine the dielectric properties of canola seeds using a radio frequency dielectric fixture at different levels of temperature (30–80°C) and moisture content (5–11% w.b.), over the frequency range of 5 to 30 MHz. The dielectric constant (ε′) increased from 3.82 to 7.85 with increasing temperature and decreasing frequency regardless of the seed moisture contents. The dielectric loss factors (ε”) of the bulk seeds increased with increasing temperature and moisture content and decreased with frequency, ranging between 0.11 and 13.0. The penetration depth of the electromagnetic power in the bulk seeds varied from 1.30 to 48.0 m depending upon temperature, frequency, and moisture content. The distinct correlation of sensitivity of dielectric properties with moisture content was not observed except for that of penetration depth. The dielectric properties of the bulk canola seeds were higher than those of other oil seeds at various moisture contents; it might be affected by relatively higher linolenic acid content among other fatty acids. The large difference of the dielectric loss factors of insect pests cf. those of canola seeds showed potential for radio frequency disinfestation based on selective heating of insect pests in the canola seeds. The dielectric properties determined can be used for simulating temperature distribution within the bulk canola seeds during the radio frequency process.     

胡萝卜、辣椒干燥过程中的介电特性与其理化品质的关系研究

为研究北方特色蔬菜的介电特性与其主要品质:糖度、水分、色泽、硬度之间的数学关系。本研究采用矢量网络分析仪测量干燥过程中胡萝卜、辣椒在0~3 500 MHz范围内275个频率点下的相对介电常数和介质损耗因子,并测量了干燥过程中胡萝卜、辣椒的可溶性固形物含量、水分、色泽和硬度等参数。结果表明,介电特性与其理化品质之间均存在着显著的相关性。研究结果为利用介电常数检测干燥过程中蔬菜的理化品质奠定了基础,同时也为研发蔬菜理化性质的快速无损检测技术提供了理论依据。     

A novel strategy for improving radio frequency heating uniformity of dry food products using computational modeling

This study attempted to quantify effects of dielectric properties (DPs) and densities of a surrounding container and treated food products on heating uniformity in a 6 kW, 27.12 MHz parallel plate radio frequency (RF) system. A computer simulation model was established with finite element-based commercial software, COMSOL Multiphysics®, and experiments with 1.5 kg soybean flour packed in a rectangular polystyrene container were performed to validate the developed model. Surface temperature distributions of soybean flour in three different horizontal layers were obtained with an infrared camera, and temperature–time histories at two representative locations inside the container were monitored with two optical fiber sensors. The uniformity index (UI) was used as a criterion to evaluate the RF heating uniformity within food products. Results showed that the RF heating uniformity in food samples was clearly influenced by DPs and density of the surrounding container. UI was the lowest when the surrounding container dielectric constant was in a comparable range of the sample's, with the loss factor values of surrounding container lying between 0.01–0.1% of the sample's. The optimum RF heating uniformity in food products could be achieved with a smaller density value of the surrounding container. The correlations of DPs and density between surrounding container and food products derived from the validated simulation model could provide valuable information and strategy to improve the RF heating uniformity in low moisture foods for insect or microbial control. Thus, the established strategy can further be used for developing effective industrial-scale RF treatment protocols after optimization of this process by the food industry.Industrial relevanceAlthough the most important characteristic of radio frequency (RF) treatments is fast and volumetric heating generated by dipole rotation and ionic conduction, edge over-heating is still a major problem for foods heated in rectangular containers. The validated model was used to study the effects of dielectric properties and density of sample and surrounding container on sample uniformity index. Simulated results illustrated that the RF heating uniformity could be improved when the dielectric constant and density of surrounding container and sample were in accordance with the established relationships. The established strategy may provide valuable optimized methods to ensure RF heating uniformity in industrial applications.     

Radio frequency heating of foods: principles, applications and related properties--a review

Radio frequency (RF) heating is a promising technology for food applications because of the associated rapid and uniform heat distribution, large penetration depth and lower energy consumption. Radio frequency heating has been successfully applied for drying, baking and thawing of frozen meat and in meat processing. However, its use in continuous pasteurization and sterilization of foods is rather limited. During RF heating, heat is generated within the product due to molecular friction resulting from oscillating molecules and ions caused by the applied alternating electric field. RF heating is influenced principally by the dielectric properties of the product when other conditions are kept constant. This review deals with the current status of RF heating applications in food processing, as well as product and system specific factors that influence the RF heating. It is evident that frequency level, temperature and properties of food, such as viscosity, water content and chemical composition affect the dielectric properties and thus the RF heating of foods. Therefore, these parameters should be taken into account when designing a radio frequency heating system for foods.     

Characterization of 50-ohm radio frequency heating of bulk canola seeds (Brassica napus. L) in a tubular applicator with parallel electrodes and post-treatment quality

A pilot-scale 50-ohm (Ω) radio frequency (RF) heating system was used to determine the temperature distribution of bulk canola seeds (Brassica napus L.), 9% moisture content (MC) wet-basis (w.b.) in a tubular applicator with parallel electrodes. Non-uniformity of the temperature distribution of bulk canola was observed during the RF heating process of the canola seeds. The hottest spot was observed at the front side of the tubular cavity of the applicator adjacent to the hot electrode. T_avg of the canola seeds was 38 °C, 42.2 °C, and 40 °C at 3 kW, 5 kW, and 7 kW respectively. Temperature distribution was relatively uniform in the back zone (0.287, 0.433, and 0.278 for 3 kW, 5 kW, and 7 kW respectively). The physicochemical properties of canola seeds changed significantly after 50-ohm RF heating at various end temperatures and power levels.Industrial relevance textRadio frequency heating is an emerging technology and has immense potential in food grains, pulses, and oilseeds processing. The radio frequency heating can be used for disinfestation of insects, drying, and removal of anti-nutritional compounds in stored food grains, pulses, and oilseeds. Radio frequency heating is based on dielectric heating principle thus allowing selective and volumetric heating. The radio frequency waves have wavelengths ranging from 1 mm to about 100 km with a frequency of 3 kHz to about 300 GHz, the penetration depth is comparatively higher than microwaves, which has wavelengths ranging from 1 mm to about 1 m with frequencies between 300 MHz and 300 GHz. Thus, radio waves penetrate larger volume objects compared to microwaves. This research investigated a 50-ohm radio frequency heating system with a through field parallel plate type applicator to observe the temperature distribution throughout the bulk canola at different power levels. Understanding the characteristics of 50-ohm radio frequency heating of bulk canola seeds at different power levels can help design effective heating processes involved in canola seeds storage and handling.     

射频烘干机在染纱生产中的应用

射频烘干机是介电技术在烘干领域的应用。此技术在加热时具有选择性，即产生的热量与实际水量成正比，而吸收的能量取决于存在的水量，因而能够使织物均匀烘干，为下道工序提供最佳处理效果。     

Disinfestation of insect pests in stored agricultural materials using microwave and radio frequency heating: A review

This article provides a comprehensive review of the disinfestation of insects in stored agricultural materials using radio frequency (RF) and microwave (MW) heating. It covers RF and MW disinfestation principles; measurement methods and effects of the operating parameters on dielectric properties; comparison between RF and MW and their effect on the mortality of different insects, quality of the host materials after disinfestation, and heating uniformity; and disinfestation economics. This review shows that RF and MW disinfestation are useful without affecting the quality of the host materials. However, RF heating is being preferred over MW heating for its higher selective heating characteristic.