Dielectric Properties of Vegetables and Fruits as a Function of Temperature, Ash, and Moisture Content

ABSTRACT: The dielectric properties of 15 vegetables and fruits were measured at 2450MHz from 5 to 130 °C. Equations were developed as a function of temperature, ash, and either moisture content or water activity, and compared to literature equations. Dielectric constant of vegetables and fruits decreased with temperature and ash content. However, ash was not a factor in the equations produced separately for fruits. Dielectric loss factor changed quadrically with increasing temperature: first decreasing and then increasing. This transition temperature decreased with ash content. Ash increased the dielectric loss factor. Garlic and potato gave unusual results, which could be explained by the behavior of solutions of inulin and potato starch, respectively.     

Characterization and Modeling of Dielectric Properties of Turkey Meat

ABSTRACT: The dielectric properties of turkey meat at water activities of 0.84 to 0.98 were measured at 2450 and 915MHz. Equations were developed as a function of temperature, moisture, water activity, and ash, and compared to literature equations. Unexpected results were: as the water activity decreased or ash increased, the dielectric constant increased with temperature, and dielectric loss factor of reduced moisture samples was determined by moisture not ash. It is theorized that the effect of temperature on dielectric constant is a function of the ratio of bound to free water. Glycerol did not affect the dielectric properties, while lactic acid decreases them by promoting water loss during protein denaturation.     

发育后期苹果的介电特性与理化特性的关系

为了解发育后期苹果的介电特性、生理特性和内部品质的变化规律以及三者之间的关系,采用同轴探头技术测量发育后期3 个月内‘富士’苹果在20～4 500 MHz间的相对介电常数ε’和介质损耗因子ε”,同时测量苹果果实的生理特性（乙烯释放量和呼吸强度）和内部品质（可溶性固形物含量（soluble solids content,SSC）、硬度、pH值和含水率）。结果表明：ε’随频率的增加而减小,ε”在2 000 MHz附近存在极小值;随着果实逐渐发育成熟,ε’和ε”逐渐减小。整个发育后期,果实的SSC和果汁的pH值呈上升趋势,硬度呈下降趋势;乙烯释放高峰出现在2 个呼吸高峰之间。ε’和ε”与SSC、硬度和pH值在特定的频率范围内存在较好的线性相关性。研究说明,苹果的介电特性是生理特性与内部品质的综合反映,根据介电参数值判断苹果的成熟情况以及用单一频率下的介电参数值评价苹果的内部品质均可行。     

Dielectric Properties of Pea Puree at 915 MHz and 2450 MHz as a Function of Temperature

Dielectric properties [dielectric constant (e′) and loss factor (e″)] of 20% (w/w) pea puree with and without fortification of 3.5 mg thiamin/ 100g pea puree at 915 MHz and 2450 MHz were measured from 25 to 125°C by the cavity perturbation techniaue. Thiamin did not affect dielectric properties at ihe concentration studied. The dielectric constant decreased as frequency and temperature increased. The loss factor increased as temperature increased at 915 MHz. However, the relationship between loss factor and temperature was not direct at 2450 MHz due to the contributions of dipolar and ionic losses.     

Dielectric Properties of Pork Muscle

Dielectric properties were measured across a frequency range from 200 MHz to 20 GHz and temperature range from 25 to 85°C for pork meat samples (grouped in four different quality classes). Dielectric properties varied widely with frequency and the loss tangents of different meat quality classes followed different trends. Discriminant analysis indicated that 2400 MHz was most significant (P < 0.05) for separation of the different classes. There were significant changes (P < 0.05) in the dielectric properties within the range of the temperatures corresponding to protein denaturation temperatures. There was clear segregation between the firm and non-exudative (red, firm, and non-exudative; pale, firm, and non-exudative) and the soft and exudative (red, soft, and exudative; pale, soft and exudative) samples. The results showed that dielectric properties could be useful in meat quality classifications.     

Dielectric Properties of a Pregelatinized Bread System at 2450 MHz as a Function of Temperature, Moisture, Salt and Specific Volume

Dielectric properties [dielectric constant (?') and loss factor (?”)] were measured using the transmission line technique. Dielectric constant was independent of salt content while ?” increased when salt was added. Dielectric constant increased when temperature increased from 25 to 60°C then became virtually constant from 60 to 95°C for all samples. Loss factor increased linearly from 25 to 95°C for samples containing 1% salt and decreased linearly when no salt was present. Both ?’ and ?” increased linearly with respect to mass concentration of water (g_water/cm³_sample). Ground bread crumb had lower ?’ and ?” than intact bread when other parameters were kept constant.     

水和盐对猪里脊肉糜介电特性的影响

应用网络分析仪和同轴探头技术,研究室温(25℃)下10～4500MHz 频段内0%～20% 的加水率和0%～4%的加盐率对新鲜猪里脊肉糜射频和微波介电特性的影响。研究结果表明,肉的相对介电常数随着频率的增大而减小;介质损耗因子在约2500MHz 时出现最小值。相同条件下肉的相对介电常数和介质损耗因子随加水率的增加而增大。整个频段内,介质损耗因子随加盐率的增加线性增加,当频率大于约200MHz 时,相对介电常数随含盐量的增加而减小。加水率和加盐率分别对相对介电常数和介质损耗因子有明显的影响,且其间的线性决定系数大于0.98。     

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.     

宣威火腿与金华火腿中游离脂肪酸组成比较分析

以两年宣威火腿和金华火腿为对象,采用气相色谱-质谱联用法(GC-MS)分别对宣威火腿和金华火腿的皮下和肌内脂肪中游离脂肪酸的组成进行分析。结果表明:宣威火腿和金华火腿的肌内脂肪和皮下脂肪中均检测出22种游离脂肪酸,含量较高的脂肪酸为棕榈酸(C16:0)、硬脂酸(C18:0)、油酸(C18:1n9c)与亚油酸(C18:2n6c),且不同火腿及不同部位间的脂肪酸组成含量存在明显差异;金华火腿肌内及皮下脂肪中总游离脂肪酸含量分别为29.24、102.68 μg/mg,分别比宣威火腿高34.58%(p<0.05)、29.09%(p>0.05);宣威火腿和金华火腿肌内脂肪中饱和脂肪酸含量高于不饱和脂肪酸含量,皮下脂肪中不饱和脂肪酸含量高于饱和脂肪酸含量。金华火腿肌内、皮下游离脂肪酸含量均高于宣威火腿相应部位游离脂肪酸含量。     

Dielectric properties of foods: Reported data in the 21st Century and their potential applications

Dielectric properties (DP) are the main parameters that provide information about how materials interact with electromagnetic energy during dielectric heating. These properties have gained great importance and applications for foods that are subjected to novel microwave (MW) or radio frequency (RF) heating treatments. The knowledge of the DP of a determined foodstuff is fundamental in order to understand and model the response of the material to the electromagnetic field, at certain desired frequencies and temperatures. Through the last years, many potential applications of electromagnetic heating for foods have emerged and been published in the literature; however, new uses or research in food products to be treated with MW or RF may be limited due to lack of DP data. This review provides an overall introduction and definition of the DP, factors that affect them, methods for their determination, as it also includes reported DP data for foods after the year 2000. DP values were grouped depending on the nature of foods, such as: 1) fruits and vegetables, 2) flour, dough and bread, 3) nuts, 4) coffee grains, 5) meats, fish and seafood, 6) dairy products, 7) eggs and egg products and 8) liquid fluids. We consider that this paper is a useful reference that contains current and valuable information on the DP of foods, which can be available and used for further developments employing MW or RF heating food technologies.     

The Dielectric Property of Soybean Oil in Deep-Fat Frying and the Effect of Frequency

ABSTRACT: :
Suitability of the dielectric constant for real time and continuous evaluation of frying oil was investigated. Measurements of the dielectric capacitance, in the frequency range 1 kHz to 100 kHz, were made on soybean oil heated at several temperatures (180, 200, 220, and 240 °C) for a few d. Frequency dependence was also measured between 50 Hz and 30 MHz. The dielectric constant of the soybean oil increased with increase in the heating time, and was well correlated with acid value, density, and relative viscosity. Our equipment for measuring capacitance would be available for real time and continuous evaluation of frying oil quality in the food industry.     

Predictive Equations for Dielectric Properties of NaCl, D-sorbitol and Sucrose Solutions and Surimi at 2450 MHz

ABSTRACT: Variation in dielectric properties of aqueous solutions with different concentrations and ratios of NaCl, D-sorbitol, and sucrose were investigated at 21 °C using the open-ended coaxial probe technique at 2450 MHz. Several equations to estimate dielectric properties of mixed or pure solutions were formulated. The equations were tested with other concentrations of solutions and surimi as a food sample containing the solutes. The correlation between the new measured dielectric properties and the calculated values were analyzed using a General Linear Model. The resultant prediction equations are suitable for pure and mixed aqueous solutions of (0 to 6%) NaCl, (0 to 18%) D-sorbitol and (0 to 60%) sucrose. For surimi, only loss factor was successfully predicted.     

中西方干腌火腿风味成分比较及形成机理分析

风味对干腌火腿的质量十分重要 ,它与生产所用原料、生产工艺和参数密切相关。文中比较了金华火腿与欧洲几种著名火腿的风味成分 ,结果显示 ,中西方火腿的风味组成相似 ,醇、醛、酮、酯、含硫化合物、含氮化合物、烷、烯烃类物质是干腌火腿的共有成分 ,但各成分的含量在中西方火腿中存在明显差异 ,金华火腿中烷、烯烃含量最高 ,欧洲的几种火腿中醛类物质含量最高。文中同时分析了干腌火腿中各风味成分的特征和可能的形成机理。     

干腌驴肉火腿加工过程中理化特性的动态变化

为了探究驴肉火腿加工过程中的品质变化及风味的形成规律,对加工过程中7个工艺点(原料期、腌制初期、腌制中期、腌制末期、发酵初期、发酵末期、成熟期)驴肉火腿的理化特性和氧化变质规律进行了研究,以期找到驴肉火腿最佳发酵时间。结果表明,在加工过程中,驴肉火腿pH比较稳定且处于微酸性环境中(6.2~6.6),各工艺点差异不显著(p>0.05);水分含量由72%先显著(p<0.05)下降后趋于平稳在35%,NaCl含量显著(p<0.05)上升在成熟期达到12.39%;TBA值先显著(p<0.05)上升至最大值0.385 mg/kg后缓慢下降最后趋于平稳在0.34 mg/kg且火腿未出现腐败现象,POV显著上升(p<0.05)成熟期达到5.26 meq/kg在国家标准范围内;TVB-N含量呈现稳定上升趋势,在成熟期含量达到85.76mg/100g且能表现出浓郁的特有香味;灰分含量先显著上升(p<0.05)后趋于平稳(p<0.05)。综上所述,驴肉火腿加工过程中理化和氧化特性的变化影响了火腿品质和最终风味的形成且发酵6个月时火腿风味最佳。     

肉鸭火腿肠系列产品的研制

鸭肉经解冻、切块、腌制后进行斩拌,并在斩拌中加入各种调料及改性淀粉(磷酸单酯淀粉),然后经灌肠、蒸煮而生产出不同风味的鸭肉火腿肠系列产品。同时进一步通过正交试验确定去除鸭肉本身腥味的最优添加物配比:白酒1%、姜粉1%、β-环状糊精0·04%,使最终产品在色香味型各方面取得了较好的效果。     

火腿揉制机的建模与火腿的受力分析

我国火腿生产基本通过人工揉制,导致盐分分布不均匀、揉制效果差和产品质量不稳定等。针对HTRZJ火腿揉制机,利用Creo Parametric软件对零部件进行建模及虚拟装配,提供机器实体装配与拆卸的可行性方案。分析火腿在揉制时的受力,通过建立火腿假设模型,对火腿在凸轮与压紧装置共同作用时揉制受力状态进行空间受力分析,得出了火腿的输送喂入条件以达到揉制按摩。为今后火腿揉制机生产装配与试验研究奠定基础。     

基于介电谱无损检测库尔勒香梨的糖度和硬度

为了探索基于介电谱无损检测库尔勒香梨糖度和硬度的可行性,本文采用同轴探头和矢量网络分析仪无损测量了三个来源共168个库尔勒香梨在20~4500 MHz范围内201个频率点下的相对介电常数和介质损耗因子,分析了介电参数的变化规律。基于x-y共生距离的样本划分法分别将112和56个样品划分为校正集与预测集;采用无信息变量消除法和连续投影算法(SPA)分别从全介电谱(FS)中提取出预测糖度的144个和20个特征变量,以及预测硬度的52个和9个特征变量;基于FS和提取的特征变量建立了预测库尔勒香梨糖度和硬度的偏最小二乘、误差反向传播、最小二乘支持向量机和极限学习机(ELM)模型。结果表明:SPA-ELM模型对库尔勒香梨糖度的预测效果最好,其校正相关系数(Rc)和预测相关系数(Rp)分别为0.943和0.876,校正均方根误差和预测均方根误差分别为0.298°Brix和0.330°Brix。所有硬度预测模型的Rc和Rp均小于0.6。研究结果说明,介电谱可用于无损检测库尔勒香梨的糖度,但对硬度的预测效果较差。后期仍需进一步研究介电谱无损检测库尔勒香梨硬度的可行性。     

金华火腿加工过程中的理化特性

以传统金华火腿为原料 ,跟踪测定了火腿加工全过程中半膜肌和股二头肌的水分、NaCl、非蛋白态氮 ,水溶性氮和游离氨基酸含量的变化情况。结果表明 ,半膜肌和股二头肌的水分含量逐渐降低 ;NaCl含量逐步上升 ,水溶性氮的含量在加工过程中先降低后升高 ,非蛋白态氮的含量也逐步上升。各种游离氨基酸随着加工的进行 ,含量逐渐增加 ,尤其是谷氨酸 ,金华火腿主要的鲜味物质 ,在加工过程中含量显著增加。     

Dielectric Properties of Potato Puree in Microwave Frequency Range as Influenced by Concentration and Temperature

Dielectric properties of potato flour-water dispersions (slurry) were measured in the frequency range of 500–2500 MHz by the open-ended coaxial probe method using a network analyzer as a function of concentration (10–25% w/w) and temperature (20–75^oC). Both commercial and laboratory prepared samples of potato flours were used. Results indicated that the dielectric constant (ε′) decreased with temperature and frequency while increased with concentration. The loss factor (ε″) increased with frequency and concentration; however, temperature showed mixed effect. Both ε′ and ε″ data in conventionally used microwave frequencies (915 and 2450 MHz) were studied as function of concentration and temperature for two sample types using a response surface methodology and found to follow 2^nd order polynomial models. Temperature and concentration contributed significantly on dielectric spectra of potato slurry and the sample source had some effect. A change in ε′ and ε″ above 70^oC could be attributed by starch gelatinization. Penetration depth (D_p) decreased with an increase in frequency and non-systematic with temperature. Addition of salt substantially reduced D_p of potato slurry.     

真空醋渍黄瓜品质的介电检测

通过测量醋渍黄瓜的介电特性来衡量其品质并作为一种潜在的非损伤性评价手段。研究采用平行板电极测量了经过不同时间真空醋渍处理的黄瓜于100 kHz~12 MHz的介电特性,同时测量了反映醋渍黄瓜理化品质的参数,如酸度、盐度、亚硝酸盐含量、质构参数。研究结果表明,在整个频率区间,真空醋渍黄瓜的相对介电常数和介电损耗因子都随频率的增加而单调递减,真空醋渍时间与介电参数存在负相关关系。真空醋渍黄瓜的介电参数与盐分和亚硝酸盐含量存在着较好的相关性,然而介电参数与酸度、质构指标之间的相关性不明显。在2.26 MHz和12 MHz频率下,相对介电常数与盐分呈现出良好的线性关系,线性拟合方程的决定系数R2高达0.9813和0.9858;该研究为真空醋渍蔬菜快速检测仪器的开发提供了理论参考。