Microwave and Radio Frequency Processing

SCOPE OF DELIVERABLES: The use of microwave and radio frequencies to heat food for commercial pasteurization and sterilization in order to enhance microbial safety is discussed here. Although not under FDA regulations, use of microwave technology to enhance microbial food safety in the home is also discussed briefly. Mechanisms of heating food and destroying pathogens, and the validation of industrial processes are also discussed, followed by conjecture on handling deviations during industrial processing. This document summarizes information obtained through published literature and personal contacts with industry, academia, and government. Although radio frequency is covered whenever possible, very little information on radio frequency heating for commercial pasteurization or sterilization of food is available in the published literature and no commercial facility for this purpose could be located. The microbial inactivation mechanisms of radio frequency heating are also quite similar to those of microwave heating. Thus, this document refers mostly to microwave processing with the implicit assumption that the principles are generally applicable to radio frequency. Specific information on radio frequency is included whenever available.     

Sterilization of Foodstuffs Using Radio Frequency Heating

ABSTRACT: A study was conducted with a pilot-scale sterilization system based on 27-MHz radio frequency (RF) energy to investigate the effectiveness in shortening process time and in improving quality for foods sealed in 6-pound military-ration polymeric trays. Chemical marker M-1 was used to evaluate heating uniformity in 20% whey protein gels as a model food, and macaroni and cheese was processed to assess the influence of RF process on product quality. With the RF system, a lethality ( F ₀= 10 min) was achieved in both model food and macaroni and cheese within 30 min with relative uniform heating, compared to a 90 min conventional retort process that delivered a similar lethality.     

射频处理八角粉杀菌工艺

利用作者所在实验室团队自主研发的射频设备探究了射频处理对八角粉的杀菌效果。结果表明,随射频(27.12 MHz)处理时间的增加,样品的温度不断增大,微生物致死率也显著增加。射频处理八角粉7 min,在最大限度保证样品质量的条件下可使样品中的微生物降低1.74 lg CFU/g。但是,RF处理样品加热的非均匀性一直是制约射频技术发展的关键问题。利用4个装有相同质量八角粉(37 g)的聚乙烯塑料袋(140 mm×100 mm)对称重叠在一起组成的模型来研究射频加热的均匀性。研究结果表明,样品内部和中心的温度明显高于表面温度,RF处理结合间歇的翻转可显著提高射频加热的均匀性。射频技术是一种很有前景的低水分活度食品新型杀菌技术。     

Continuous Flow Radio Frequency Heating of Water and Carboxymethylcellulose Solutions

Tap water and 1% CMC solutions were heated in a 40.68 MHz, 30 kW continuous flow radio frequency unit. Temperatures at different vertical and radial locations were monitored by fiber optic probes during batch heating of tap water and 1% CMC solution. Temperatures at different locations were similar during batch heating of tap water, while a significant temperature difference was observed for 1% CMC solutions, with the temperature close to the wall being higher than that at the center. Similar trends were observed during continuous heating of tap water and 1% CMC solutions, with T_wall > T_R/2 > T_center for the latter. The observations were a result of different dielectric properties of these 2 fluids, as well as the fluid flow characteristics during continuous heating.     

无线电波加热提高狭鳕鱼糜的解冻效率

应用传统的方法解冻鱼糜耗时长,为了加快冷冻鱼糜的解冻速率并保持鱼糜的品质,本实验以狭鳕鱼糜为研究对象,比较了空气解冻、流水解冻、无线电波直接加热和无线电波间歇加热4种解冻方式对冷冻狭鳕鱼糜解冻效率和品质的影响。结果表明:空气解冻和流水解冻过程中狭鳕鱼糜温度分布较为均匀。无线电波解冻过程中鱼糜边角部位会出现局部过热现象,采用无线电波间歇式加热能有效延缓鱼糜表面温度的过快升高。无线电波加热解冻速度快,仅需4.6 min就可以使狭鳕鱼糜的中心温度达到1.8℃。应用无线电波间歇加热后的狭鳕鱼糜的持水力为78.8%,白度值为61.7,无线电波加热在一定程度上能增加狭鳕鱼糜的弹性和抑制微生物的生长繁殖,解冻后的狭鳕鱼糜菌落总数仅为4.9×103 CFU/g。采用无线电波间歇式加热的物料温度分布均匀性较好,解冻效率高,又能最大限度地保持冷冻食品的品质,是一种极具潜力的解冻方式。     

无线射频识别技术在食品生产流通中的应用

本文介绍了无线射频识别技术的基本工作原理和系统组成,概述了无线射频识别技术在食品的跟踪与溯源、品质监控、生产过程优化、防伪等方面的应用,结合现状分析该技术存在问题以及今后发展趋势.     

Effects of Radio Frequency Heating Treatment on Structure Changes of Soy Protein Isolate for Protein Modification

The effects of radio frequency (RF) heating treatments with different final temperatures (70, 80, and 90 °C) and electrode gaps (120, 160, and 200 mm) on the structural characteristics of soy protein isolate (SPI) dispersion were investigated. The results showed that RF heating significantly influenced free sulfhydryl groups and surface hydrophobicity of SPI. Free sulfhydryl groups increased with the increase of final temperature. The hydrophobicity of the RF-heated sample was higher than the original SPI without RF treatment. The highest hydrophobicity of the RF-heated SPI was found with electrode gap of 200 mm at 90 °C. RF heating treatment resulted in the reduction of ultraviolet absorption of SPI indicating the change of three-dimensional positions of soy protein but did not modify the protein primary structure of SPI. The Fourier transform infrared spectroscopy showed that hydration of SPI was decreased by RF heating. The self-reassembly from random coil structure to β-sheet structure suggested that RF heating treatment can change the secondary structure of soy protein to be more orderly.

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多酚氧化酶的射频加热灭活效果及动力学分析

为了阐述多酚氧化酶(PPO)射频加热对灭活规律,本文研究了板间距和溶酶磷酸盐缓冲液电导率对加热速度及酶灭活效果的影响,进行了酶灭活动力学模型研究。结果表明:极板间距和电导率影响射频加热速度,极板间距越大升温越慢,电导率为0.1 S/m时,升温速度最快。在极板间距120 mm,电导率0.1 S/m时,射频加热105 s,PPO的灭活率为91.88%。对酶灭活的动力学曲线分别用一级动力学模型、Weibull模型和Log-Logistic模型进行拟合。通过对模型的拟合评价参数即精确因子Af、偏差因子Bf、根平均方差RMSE和决定系数R2进行比较,PPO的灭活动力学曲线不符合一级反应动力学模型,Weibull和Log-Logistic模型都能较好的拟合PPO失活曲线。通过衡量三种模型的预测值和实测值的一致性,Log-Logistic模型能最好地拟合射频加热条件下多酚氧化酶的失活曲线。     

Effects of Hot Air-assisted Radio Frequency Heating on Quality and Shelf-life of Roasted Peanuts

Roasting is a critical step in processing peanut snack foods. The conventional roasting using hot air ovens has drawbacks of low production rate, poor product quality, and high energy cost. This study investigated the feasibility of using hot air-assisted radio frequency (RF) to roast dried salted peanuts. Physicochemical properties, volatile compounds, and sensory quality of the roasted peanuts were determined. The quality changes and shelf-life of vacuum-packaged roast peanuts stored under an accelerated shelf-life testing (ASLT) trial conducted at 20 and 50 °C were also evaluated. After 45 min roasting, moisture content of the salted peanuts reduced from initial 7.7 to 3.1 % and acid and peroxide values were 0.26?±?0.02 mg/g and 2.46?±?0.10 meq/kg, respectively, all in the levels associating with good quality of roasted peanuts. Sensory evaluation further validated the good quality of the roasted peanuts. Totally, 69 volatile compounds were identified in the roasted peanuts, in which 3 new volatiles were produced after about 13 weeks of storage. During the storage, relative concentrations of the favorable volatile compounds (mainly pyrazines and furan compounds) decreased in a certain degree, while the relative concentrations of some undesirable flavor compounds increased. The roasted peanuts had 31 weeks of shelf-life based on the industrial standard on the peroxide value. This study demonstrated that hot air-assisted RF roasting can produce high-quality roasted peanuts with prolonged shelf-life, thus, a new technology for the peanut roasting industry.     

印刷技术在无线电频率识别中崭露头角

在最近的几年当中，无线电频率识别（RFID）技术发展显著。在这个时段之前，缺少生产标准和支持不同RFID应用的基础结构使这一创新的技术起点受到质疑。     

微波干燥均匀性研究进展

微波干燥技术及其设备已在轻化工业、食品与农产品加工业等行业得到广泛应用。然而微波加热不均匀性已成为微波干燥技术在生产实际应用过程中的瓶颈。本文就目前国内外关于微波干燥均匀性的研究现状进行较全面的分析和归纳,并对这一问题进行展望。     

卷烟制丝加料工序均匀性的评价与控制

为量化研究卷烟制丝加料工序的均匀性,运用同时蒸馏萃取-气质联用选择离子扫描技术,对卷烟制丝加料工序中添加的乙基麦芽酚进行分离分析,建立了一套回收率高、重复性好的分析方法;并以乙基麦芽酚为考察指标,应用所建立的分析方法,对改造前后加料系统的均匀性进行了系统的研究.结果表明,调整加料系统后,均匀性效果明显提高,检测数据的标准偏差由26.821下降至15.020,加料精度提高了44%;并对改造效果进行验证,检测数据的标准偏差为14.428,说明调整效果较好.     

Critical Heating Point for Thermal Processing of Mussels in Cans

Heating curves for different locations inside cans of mussels brine, placed in vertical, horizontal and inclined positions, were experimentally determined. Temperature profiles were fitted the response of a second order system to a step input. The location of the slowest heating point was established by comparison of the time constants. The critical heating point was found to be on the axis at one eighth the height of the cans when they were in a vertical position.     

基于图像处理的烟片加料均匀性评价方法

为量化评价加料工序单张烟片料液分布和加料过程均匀性,应用数字图像处理技术对料液附着点分布图像进行处理,建立了基于图像处理的烟片加料均匀性评价方法,采用料液分布变异系数表征单张烟片料液分布均匀性,采用烟片间料液附着量变异系数表征加料过程均匀性。验证结果表明:基于图像处理的加料均匀性评价方法检测结果,与采用YC/T 353—2010行业标准检测结果具有相同趋势,检测结果可有效表征整体加料过程的改善或劣化程度。      

Developing Hot Air-Assisted Radio Frequency Drying for In-shell Macadamia Nuts

Dehydration reduces water activity and extends shelf life of perishable agricultural products. The purpose of this research was to study the application of radio frequency (RF) energy in dehydration of in-shell Macadamia nuts and shorten the lengthy process times needed in conventional hot air drying operations. A pilot scale 27.12-MHz and 6-kW RF system was used to determine the operational parameters, the drying curve, and the quality attributes of the processed nuts. The results showed that an electrode gap of 15.5 cm and a hot air temperature of 50 °C provided an acceptable heating rate and stable sample temperatures, and were used for further drying tests. The drying curves showed an exponential decay and required 750 and 360 min to achieve the final moisture content of 0.030 kg water/kg dry solid (3.0 % dry basis) in whole nuts in hot air drying and RF heating/hot air combined drying, respectively. The drying kinetics of the nuts were described well by the Page model for hot air drying, but a logarithmic model was more suited for RF/hot air drying. Peroxide value and free fatty acid increased with the drying time both for hot air and RF drying but remained within acceptable range required by the nut industry. The RF process shows potential to provide rapid, uniform, and quality-acceptable drying technology for the nut industry.     

纺织空调变频多风机系统送风均匀性设计分析

文章应用流体力学原理及设计方法,结合多风机送风原理和车间对均匀送风的要求,分析影响变频多风机送风效果的因素。     

卷烟加工过程中烟丝掺配均匀性影响因素分析及改进

为改善批次内烟丝实际掺配效果,保障最小单元各组分含量均匀一致,以瞬时精度为指标,对加工过程中影响烟丝实际混合效果的各种因素进行了分析,并对叶丝干燥后的筛分装置和配比秤进行了改进.在筛分装置的振筛上方设计安装了松散装置,以优化叶丝结构,提高叶丝松散度;在配比秤落料处设计安装了匀料装置,以解决堵料和物料流的连续性问题.结果表明:①烟丝的松散度和瞬时流量的均匀性、稳定性是影响烟支内各组分含量一致性的关键因素;②改进后烟丝瞬时掺配精度由1.84％降低到1.09％,烟支内各组分实际含量偏差由1.30％降低到0.79％.提高了烟丝松散性,避免了烟丝结团和堵料,有效提升了卷烟品质的加工精度和过程控制能力.     

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.