Radio frequency heating of corn flour: Heating rate and uniformity

Non-uniform heating is a major challenge for using radio frequency (RF) heat treatment in pasteurization of low moisture food products. The objective of this study was to evaluate the effect of different electrode gaps, moisture content (MC), bulk density and surrounding materials on RF heating uniformity and rate in corn flour. Additionally, the dielectric and thermal properties of corn flour were determined as affected by MC, temperature (°C), and frequency (MHz). Changes in MC, water activity (a_w) and color in the sample after RF heating were measured to evaluate treatment effect on food quality. A precision LCR meter and a liquid test fixture were used to study DP of the sample at RF frequency ranging from 1 to 30 MHz. The RF heating uniformity and temperature profiles of corn flour as exposed to RF heating were obtained with an infrared camera and a data logger connected to a fiber optic sensor. The DP values increased with increasing MC and temperature, but decreased with frequency. The heating rate increased from 3.5 to 6.8 °C min^− 1 with increasing MC (from 10.4 to 16.7%), but decreased from 12.7 to 5.2 °C min^− 1 with increasing electron gap (from 11 to 15 cm). The corner and edge heating were observed at all layers of the samples for all the distances, and the hottest and the most uniform layer were determined as the middle layer at an electrode gap of 15 cm. Glass petri dish provided better uniformity than those of polyester plastic petri dish. Covering by foam led to more uniform RF heating uniformity in corn flour, and better moisture and a_w distribution. This study provided useful information to develop an effective RF process as an alternative of conventional thermal treatments for pasteurization of low-moisture products.Industrial relevanceThis paper describes a novel methodology based on Radio Frequency heating to pasteurize food powder while maintaining the quality. The study addresses the ever-increasing global demand from consumers for safe food products.     

Investigation of radio frequency heating uniformity of wheat kernels by using the developed computer simulation model

To explore the potential of using radio frequency (RF) energy to control insects or microorganisms in low-moisture granular food crops, wheat kernels were selected as a sample product, and a computer simulation model was developed to study the influence of sample size (wheat kernels filled in plastic container in cuboid shape) and vertical position on RF heating uniformity and to determine the cold and hot spots in the samples. The simulated temperature profile of RF heating was compared with the experimental results to validate the computer model. Temperature uniformity index (TUI) was selected as a criterion to evaluate RF heating uniformity. Results suggested that temperature uniformity of sample depended on sample size and location, where for small sample size, sample placed on either bottom electrode or closed to top electrode would achieve better RF heating uniformity; while for sample in large size, placed in the middle or slightly lower than middle position between the two parallel electrodes achieved better temperature uniformity. Also, a larger sample size had better RF heating uniformity, especially when sample size equaled to the size of the top electrode, indicating that RF energy is more suitable for treating bulk materials. Corner heating was also observed where hot spots located at the corner of samples in cuboid shape, and cold spots depended on sample vertical position. In this study, cold spots were at the center of the top and bottom layers when the sample was placed at the middle position between the two parallel electrodes, at the center of top layer when sample was placed on the bottom electrode, and at the center of bottom layer when sample was placed close to top electrode. Information generated from this study would be essential for developing RF treatment protocol to control insects or microorganisms in low-moisture granular agricultural products.     

添加青麦仁粉对小麦粉特性的影响研究

将青麦仁制成全粉添加在小麦粉中,并对它的理化性质、糊化特性及流变学特性进行研究。结果表明:随着青麦仁粉添加量的增大,混合粉的水分、淀粉、湿面筋含量以及面筋指数下降,灰分、蛋白质、膳食纤维、叶绿素、脂肪含量明显升高;粉质特性表现为面团的稳定时间和粉质质量指数下降,吸水率升高,弱化度升高;拉伸特性显示面团的延伸性、能量以及拉伸阻力显著下降;糊化特性呈现出高峰黏度、最终黏度、低谷黏度、回生值以及衰减值整体都呈下降趋势。     

Computational investigation of the effect of orientation and rotation of shell egg on radio frequency heating rate and uniformity

The objective of this work was to computationally investigate radio frequency (RF) heating rate and uniformity of shell egg as affected by orientation and rotation. To do this, a multiphysics model was developed using COMSOL to simulate RF heating of a vertically oriented non-rotating shell egg. This model was experimentally validated against temperature measurements taken at three different internal locations within the egg. Simulations were then performed using the validated model with both non-rotating and rotating egg for different orientations (vertical and horizontal). Rotation of egg was incorporated into the model by rotating the RF system around the stationary egg instead of rotating the egg. Temperature-dependent material properties of the yolk, albumen and shell within a temperature range of 20 to 70 °C were used in the model. Simulated temperature uniformity index (STUI) values were calculated to evaluate the effect of orientation and rotation on heating uniformity. The results showed that heating was more uniform when shell egg was oriented horizontally rather than vertically. However, rotation did not further improve heating uniformity of the horizontally-oriented egg. Although heating uniformity was improved when the vertically-oriented egg was rotated, concentrated heating around the air cell could not be avoided.     

食品射频灭菌过程加热均匀性调控研究进展

作为一种新型物理灭菌技术,射频(radio frequency, RF)加热具有穿透深度大、传热效率高、无化学残留、适合批量处理等特点,可有效杀灭食品中的致病菌。然而,受物料本身特性参数、射频系统结构、物料周围介质等因素影响,非均匀加热一直是射频灭菌规模化应用面临的主要挑战之一。为进一步明确食品射频灭菌过程均匀性调控的最新研究进展,本文基于射频杀菌的机制及特点,对调控射频加热均匀性的具体措施进行了梳理,包括调控物料介电参数、改变环境介质、优化射频加热系统等,为加热均匀性调控的进一步研究及射频灭菌技术的进一步应用奠定基础。     

Alternaria toxins in Argentinean wheat,bran, and flour

Alternaria species have been reported to infect a wide variety of vegetables, fruits, and cereal crops. Wheat is one of the most consumed cereal worldwide. A sensitive HPLC-DAD methodology was applied to quantify alternariol (AOH), alternariol methyl ether (AME) and tenuazonic acid (TeA) in 65 samples of whole wheat, bran, and flour. The extraction methodology allowed extracting the three toxins simultaneously. Limits of detection in wheat were 3.4, 4.5, and 0.5 µg kg^?1 for AOH, AME and TeA, respectively. For bran, these data were 3.1, 4.5, and 12 µg kg^?1 and for flour 50, 70, and 14 µg kg^?1, respectively. The studied recoveries were higher than 70% and RSD was below 10%. Wheat and bran samples showed low AOH and AME contamination compared to TeA. The averages levels found for TeA in wheat, bran and flour were 19,190, 16,760, and 7360 µg kg^?1, respectively.     

Nutritive value of wheat bran. I. Effects of fine grinding upon bran, and of added bran upon the protein quality of white flour

The addition of bran to a diet based upon white flour, and thereby deficient in lysine, improved the growth rate and food consumption of weanling rats on this diet, partly because of the supplementary effect of the lysine of the bran upon the protein of the flour. The increasing replacement of flour by bran continued to improve growth rate towards an upper value where much of the flour in the diet had been replaced. However, growth rates were still poor, and well below that attainable if flour without bran is supplemented with small amounts of lysine and threonine. Fine grinding of the bran affected neither growth rate nor food intake significantly in a 50 : 50 mixture of bran and flour, but it slightly depressed the apparent digestibility of the nitrogen of the diet.     

麸皮的添加比例对全麦粉流变学特性的影响

研究添加不同比例麸皮对小麦粉流变学特性的影响。以国审强筋品种晋麦92号为原料,进行磨粉制得小麦粉,添加麸皮的比例分别为5%、10%、15%、20%、25%和30%,纯小麦粉和纯麸皮分别作为阴性对照和阳性对照,采用电子粉质仪、电子拉伸仪和全自动吹泡仪等依照GB/T14614—2006、GB/T14615—2006和GB/T14614.4—2005对其进行流变学特性测定。结果表明,随着添加麸皮的比例由30%降低到5%,沉降值、粉质稳定时间和拉伸能量逐渐升高,高吹泡最大压力和Dmax逐渐降低,吹泡曲线长度、吹泡充气指数和吹泡形变能量均呈先降低后升高趋势,拉伸比例和吹泡曲线比值则是先升高后降低。麸皮添加比例为5%～25%的全麦粉均达到中筋乃至中强筋水平,可用于面条或馒头制作。     

麦麸膳食纤维对小麦粉糊化及凝胶质构特性的影响

为研究膳食纤维对淀粉糊化及凝胶质构的影响,本实验以2种不同筋力小麦粉为原料,添加麦麸膳食纤维,5个添加量处理,分析其小麦粉糊化特性、凝胶质构及其微观结构。结果表明:随麦麸膳食纤维添加量的增加,峰值粘度、低谷粘度、稀懈值、最终粘度和回生值等糊化特征参数均呈显著下降趋势,糊化时间和糊化温度的变化不明显,且没有规律性;添加膳食纤维显著降低了糊化凝胶的硬度、粘附性和咀嚼度(p<0.05),而弹性、内聚性和胶粘性未见显著变化;膳食纤维对2种不同筋力小麦粉糊化和凝胶质构特性的影响趋势基本一致;膳食纤维改变了面团和糊化凝胶体系的微观结构,可增加面团的紧致性,但会降低凝胶结构的致密性和均匀性。     

热风辅助射频加热对米糠储藏稳定性的影响

采用热风辅助射频(HA-RF)技术对米糠进行稳定化处理并与挤压处理对比,研究米糠在25、35和45℃下储藏过程中水分含量、水分活度、色度、游离脂肪酸含量和过氧化值的变化,选取关键品质利用其动力学模型来预测货架期.结果表明储藏过程中米糠各项品质变化较慢,而游离脂肪酸含量较为适合作为预测货架期的关键指标,新鲜米糠(FRB)...     

Verification of radio frequency heating uniformity and Sitophilus oryzae control in rough,brown, and milled rice

Radio frequency (RF) heating is considered to be an alternative physical method for disinfesting postharvest agricultural products to replace chemical fumigation due to its inherent dangers on human health and environment. A pilot-scale, 27.12 MHz, 6 kW RF system was used to study the RF heating uniformity and validate the developed RF treatment protocols for disinfesting rough, brown, and milled rice. The results showed that the optimum RF heating uniformity in rough and brown rice was obtained by an appropriate electrode gap of 11 cm with a forced hot air heating at 50 °C, movement of the conveyor with a speed of 12.4 m/h, two mixings, and holding at 50 °C hot air for 5 min. Mortality of adult rice weevils, Sitophilus oryzae (L.), increased with increasing heating temperature and holding time, and reached 100% while RF heating at 50 °C holding in hot air for at least 6 min. There were no significant differences in quality parameters (moisture, protein, water activity, starch, free fatty acid, ash, and color) between RF treatments and untreated controls during storage (P > 0.05). The developed non-chemical alternative RF technology may hold potential for disinfesting rough, brown, and milled rice required by the growing organic market.     

Improvement of radio frequency heating uniformity for millets by changing shape and adding polypropylene blocks

Radio frequency (RF) treatment is a burgeoning method in food processes. RF heating non-uniformity is a main obstacle for industrial implementations and influenced by the geometry of treated materials. In this study, the effect of convex-concavo shapes of the sample top surface and step shapes at the bottom of the rectangular container by adding polypropylene (PP) blocks on the heating uniformity was investigated using a 6 kW, 27.12 MHz free-running oscillator RF system. The results showed that the RF heating uniformity index values of millets decreased with increasing convex degree and decreasing concave degree of the sample top shape. Moreover, adding PP blocks at the bottom of the sample container was a better choice of improving RF heating uniformity owing to the wider adjustable range of sample sizes and better temperature distribution. This study provided a new method to improve the RF heating uniformity by simply changing the shapes of samples in either the top or bottom surface.     

Rheological properties of wheat flour and quality characteristics of pan bread as modified by partial additions of wheat bran or whole grain wheat flour

The use of bran and whole grain flour changes dough rheology and causes difficulties in manufacturing bakery products. The aim of this study was to analyse the influence of substituting refined wheat flour (WF) by wheat bran (WB; 5%, 10%, 20%, 30% and 40%) or whole grain wheat flour (WGWF; 10%, 20%, 30%, 40% and 50%) on dough rheological properties and pan bread quality characteristics. The addition of WB and WGWF increased water absorption and resistance to extension and decreased stability, extensibility and peak viscosity. Effects with WB were more pronounced. The presence of WB or WGWF increased crumb moisture content, firmness and hardness and decreased specific volume of pan bread. It is important to set new farinographic and extensographic standards when using WB and WGWF, allowing for a correct correlation between rheology and quality characteristics of bakery products, as the same standards used for WF are not valid.     

小麦麸皮微波处理对全麦粉面筋品质和流变学特性的影响

目的 探讨小麦麸皮微波处理灭酶对全麦粉面筋品质特性和流变学特性的影响.方法 以中高筋小麦为原料,对麸皮微波处理后再回添到小麦粉中制得全麦粉,设置麸皮水分含量、微波处理时间和麸皮厚度3个变量因素,固定其中2个变量因素,探讨另1个变量因素对全麦粉中面筋特性和流变学特性的影响.结果 麸皮水分含量对湿面筋含量、面筋吸水率、面团...     

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。     

Improving radio frequency heating uniformity using a novel rotator for microorganism control and its effect on physiochemical properties of raisins

In the present study, a novel material rotator was designed to evaluate the possibilities to improve radio frequency (RF) heating uniformity in raisins. The rotator provided a means to rotate materials when subjected to RF heating. The results showed that RF heating uniformity was significantly (p < 0.05) improved with the rotation of raisins. The relative heating uniformity parameter (λ) reduced to less than 15% at rotational speed of 40 and 60 rpm. No significant (p > 0.05) influence on heating rate was observed. Pasteurization experiments showed the total bacterial (4.88 log) count was reduced by 2.55 log CFU/g and the molds (4.83 log) were completely inactivated when raisins were heated to 80 °C and maintained for 10 min, which indicated a great disinfection efficiency of RF heating. Quality evaluation showed the physiochemical property changes of raisins were satisfied with acceptable color and nutrients loss. Therefore, the method used in this experiment could be expanded to develop an effective treatment protocol for controlling microorganisms in raisins.     

Temperature and moisture dependent dielectric properties of legume flour associated with dielectric heating

Dielectric properties data are important in developing thermal treatments using radio frequency (RF) and microwave (MW) energy and are essential in estimating heating uniformity in electromagnetic fields. Dielectric properties of flour samples from four legumes (chickpea, green pea, lentil, and soybean) at four different moisture contents were measured with an open-ended coaxial probe and impedance analyzer at frequencies of 10-1800 MHz and temperatures of 20-90 °C. The dielectric constant and loss factor of the legume samples decreased with increasing frequency but increased with increasing temperature and moisture content. At low frequencies and high temperatures and moisture contents, negative linear correlations were observed between the loss factor and frequency on a log-log plot, which was mainly caused by the ionic conductance. At 1800 MHz, the dielectric properties data could be used to estimate the legume sample density judging from high linear correlations. Loss factors for the four legume samples were similar at 27 MHz, 20 °C and low moisture contents (e.g. <15 g/100 g). At the highest moisture content (e.g. 20 g/100 g) soybean had the highest loss factor at 27 MHz and 20 °C, followed by lentil, green pea, and chickpea. The difference in loss factor among the four legumes did not show clear patterns at 915 MHz. Deep penetration depths at 27 MHz could help in developing large-scale industrial RF treatments for postharvest insect control or other applications that require bulk heating in legumes with acceptable heating uniformity and throughputs.     

Thermogravimetric analysis of water release from wheat flour and wheat bran suspensions

Bran is hygroscopic and competes actively for water with other key components in baked cereal products like starch and gluten. Thermogravimetric analysis (TGA) of flour–water mixtures enriched with bran at different incorporation levels was performed to characterise the release of compartmentalised water. TGA investigations showed that the presence of bran increased compartmentalised water, with the measurement of an increase of total water loss from 58.30 ± 1.93% for flour only systems to 71.80 ± 0.37% in formulations comprising 25% w/w bran. Deconvolution of TGA profiles showed an alteration of the distribution of free and bound water, and its interaction with starch and gluten, within the formulations. TGA profiles showed that water release from bran-enriched flour is a prolonged event with respect to the release from non-enriched flour, which suggests the possibility that bran may interrupt the normal characteristic processes of texture formation that occur in non-enriched products.