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.     

915MHz和2450MHz下扇贝柱介电特性的研究

利用介电网络分析仪测量温度20~100℃,频率0.3~3GHz下扇贝柱介电常数和介电损耗因数,从而得出扇贝柱在微波加热过程中温度和频率对介电特性的影响。结果表明,温度一定时,介电常数和介电损失因数都是先随着频率增加而降低,随后变化不显著;频率915MHz和2450MHz时,介电常数与温度成负相关,介电损耗因数与温度成正相关。且915MHz和2450MHz下,穿透深度随温度的升高而减小。扇贝柱介电特性的研究为微波杀菌技术的研究提供了理论基础。      

Dielectric Properties of Pumpable Food Materials at 915 MHz

Dielectric properties of pumpable food materials having a potential to be processed using a continuous flow microwave heating system were measured at 915 MHz and in the temperature range of 10–90°C. The products considered in this study were milk and dairy products (ε′: 70.0 to 50.8 and ε″: 14.7 to 41.3), ready to eat puddings (ε′: 69.4 to 52.1 and ε″: 17.2 to 23.8), soy beverages (ε′: 75.4 to 60.8 and ε″: 9.0 to 19.8), and avocado products (ε′: 51.6 to 39.0 and ε″: 17.7 to 67.5). The results showed that the dielectric constant decreased with an increase in temperature and the dielectric loss factor increased with an increase in temperature. Polynomial correlations for the dependence of dielectric properties on temperature were developed. The dielectric properties measured in this study are important parameters for designing a continuous flow microwave heating system for processing pumpable food materials.     

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。      

Effect of Soluble Solids Concentration and Temperature on Thermo-Physical and Rheological Properties of Mango Puree

Thermo-physical and rheological properties of mango pulp were evaluated at different temperatures (20, 40, 60, and 80°C) and total soluble solids concentrations (15, 20, 32, and 40°Brix). Thermal properties were primarily dependent on the moisture content of the sample, and increased with temperature and decreased with soluble solids concentrations. Density showed a reverse trend. Glass transition temperatures increased with an increase in soluble solids concentrations indicating better stability. Empirical models developed for each thermal property as a function of temperature and soluble solids concentrations (R² > 0.90) generally showed better predictions than published models. Mango puree exhibited pseudo-plastic behavior during steady shear measurements, and the power law model well described their flow behavior. Consistency coefficient increased with soluble solids concentrations and decreased with temperature. The flow behavior index ranged between 0.27 and 0.38 but did not show a clear trend either with soluble solids concentrations or temperature. Small amplitude oscillatory shear measurements revealed that mango puree behaved like a weak gel and demonstrated visco-elastic properties.     

不同种类原料肉对婴幼儿肉泥理化性质和体外消化特性的影响

为研究不同种类原料肉对婴幼儿肉泥的影响,本实验以3 种婴幼儿肉泥（牛肉泥、猪肉泥、鸡肉泥）为研究对象,对其营养成分、流变特性及消化情况的差异性进行分析。结果表明：婴幼儿肉泥是一种高蛋白、低脂肪、高水分食品。不同种类肉泥的营养成分含量存在显著性差异（P＜0.05）。其中牛肉泥蛋白质量分数最高（（11.01±0.53）%）,猪肉泥脂肪质量分数最高（（6.19±0.42）%）,鸡肉泥水分质量分数最高（（81.15±0.26）%）。流变学分析结果表明,婴幼儿肉泥呈现出剪切稀化特点,具有弹性成分占主体的弱凝胶特征。表观黏度和储能模量（G’）都呈现出牛肉泥＞猪肉泥＞鸡肉泥。经过胃蛋白酶和胰蛋白酶两步消化后,猪肉泥的消化率高于其他两种肉泥,肉泥的粒径分布范围由最初4.3～550.0 μm范围缩小至1.2～118.0 μm。牛肉泥消化后的中值粒径最小,为（8.15±0.94）μm,猪肉泥和鸡肉泥的粒径无显著差异。总体来说,不同种类原料肉加工而成的婴幼儿肉泥在理化性质和体外消化特性方面存在较大差异。     

全脂乳粉和脱脂乳粉在1kHz～10MHz下的介电特征研究

分别研究了各4种不同品种的全脂乳粉和脱脂乳粉在1kHz～10MHz波段的介电特性。结果发现:随着频率的增加,全脂乳粉和脱脂乳粉的ξ’和ξ″值呈单调递减趋势;全脂乳粉的ξ’和ξ″值都高于脱脂乳粉,相同类型乳粉各品种间的ξ’和ξ″差异不大;全脂乳粉的ξ″值在103～105Hz频率段减小趋势明显,且ξ″值的对数与频率的对数成线性反比关系,而脱脂乳粉无此规律;全脂乳粉和脱脂乳粉的穿透深度Dp随频率的提高而减小,两类乳粉的介电特性差异可能与它们各自的脂肪和乳糖含量有关。     

Physicochemical Properties of Field Pea, Pinto and Navy Bean Starches

Legume starches were compared for physicochemical properties that may explain differences in functional properties. Field pea starch had higher amylose, greater swelling power and solubility, and lower pasting temperatures than pinto and navy bean starches. Scanning electron microscopy (SEM) showed that field pea starch had larger, more irregularly shaped granules and more broken large granules than pinto or navy starches. The most starch damage was observed for field pea. Pinto and navy bean starches had greater resistance to swelling at 60°C than field pea indicating a more strongly bonded micellar network. Higher cold paste viscosity was observed for navy bean and field pea.     

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 and Thermal Conductivity of Marinated Shrimp and Channel Catfish

Peeled shrimp (Peneaus spp.) and channel catfish (Ictalutus punctatus) fillets were either mixed with commercial lemon pepper marinade and vacuum tumbled at 4°C for 30 min or soaked in 2% tripolyphosphate solution overnight. Dielectric constant and loss factor of marinated seafood and the penetration depth of microwaves were functions of temperature. When cooking temperature increased, the dielectric constant increased, while the loss factor and depth of penetration decreased. Because of the large variation in thermal conductivity measured for individual shrimp, no correlation between thermal conductivity and temperature was found. At constant temperature, thermal conductivity of 2% sodium tripolyphosphate-treated shrimp was higher than that of both marinated and nonmarinated shrimp as a result of higher moisture content. However, no difference in thermal conductivity was found between marinated and nonmarinated shrimp or catfish.     

Dielectric properties of sea cucumbers (Stichopus japonicus) and model foods at 915 MHz

Short-time microwave (MW) sterilization is a feasible technology to produce high-quality shelf-stable sea cucumbers (SCs) (Stichopus japonicus). Selection of a model food matching the sea cucumbers in dielectric properties (DPs) is one of the most important steps for developing the MW processing. The test results revealed that rehydrated sea cucumber has much lower relative dielectric loss factor (9.73-5.62) than muscle foods, including salmon fillets and sliced beef, which were reported in the literature. The whey protein gel formulations that had been developed in our laboratory as a tool in heating pattern studies for those products are, therefore, not appropriate for sea cucumber. Adding 1.0% gellan powder sharply reduced the amount of whey protein concentrates needed to form firm gels and significantly lowered the dielectric loss factor. The dielectric properties of the sea cucumbers and model food samples with different formulations were measured using a custom-built temperature controlled test cell and an Agilent 4291B impedance analyzer in the temperature range 20-120 °C. Based on comparison of the measured dielectric properties and the calculated microwave power penetration depths among the sea cucumbers and model foods, appropriate formulation with whey protein concentration 5%, whey protein isolation 3%, gellan gum 1%, d-ribose 0.5% and water 90.5% was chosen as the model food for the sea cucumbers for the purpose of MW processing development.     

Salt-Starch Interactions as Evidenced by Viscosity and Dielectric Property Measurements

Increasing the concentration of salt (NaCl) or starch in a salt-starch solution depressed the dielectric constant and loss factor relative to a pure salt solution, except for the loss factor when no salt was present. The addition of salt to a starch solution increased the viscosity. Both viscosity and dielectric properties were decreased by mechanical agitation and by action of amylase. Above 10% starch the decrease in dielectric loss was abrupt, corresponding to the increase in viscosity. The changes were hypothesized to be due to an interaction between salt and starch, either through direct binding of the salt, or indirectly through the increase in viscosity.     

干酪介电特性与成熟期及成熟度相关性分析

以半硬质契达干酪为研究对象,对同一加工样品在9℃贮存成熟,分别对成熟期0、15、30、45、60、90、120、150、180 d的干酪样品进行了介电特性和成熟度指标的测定,包括干酪样品总氮(total nitrogen,TN)含量、p H 4.6可溶性氮(soluble nitrogen,SN)含量及三氯乙酸(trichloroacetic acid,TCA)溶液中SN含量的测定。测试频率选定为500、915、1 500、2 000 MHz,对测试结果进行了统计分析,建立了干酪介电特性与成熟度指标之间的相关性。结果表明:随着成熟期的延长,干酪水分含量略有减少、水分活度明显降低、p H值先降低后升高、成熟度指数p H 4.6-SN/TN和12%TCA-SN/TN均随成熟期延长而增大;介电常数ε’在所选的测试频率下与成熟期和成熟度指数的变化均呈线性相关关系;介电损耗因数ε’’在所选测试频率范围内,随成熟期的延长和成熟度的增大呈现总体下降趋势,与成熟期和成熟度在500 MHz和915 MHz频率条件下线性相关性极显著(P0.01),而在高频1 500 MHz和2 000 MHz条件下线性相关性不显著;损耗角正切值变化不明显,表明在测试频率范围介电常数ε’和介电损耗因数ε’’的变化方向一致,同时变化幅度相近。     

不同类型蛋白质水溶液的介电特性

为了解不同类型蛋白质水溶液的介电特性,为液态食品的蛋白质掺假提供新的检测方法,本实验采用同轴探头技术,研究了室温25℃、20~4 500 MHz频率范围内不同质量分数(0%~4.63%)的蛋白质(大豆蛋白、乳清蛋白和卵蛋白)水溶液的相对介电常数ε’和介质损耗因数ε"的变化规律。结果表明,随着频率的增大ε’逐渐减小,而ε"先减小后增大;当蛋白质质量分数相同时,大豆和乳清蛋白水溶液的ε’和ε"值均比较接近,与卵蛋白水溶液之间存在明显差异;在特定的频率段内,蛋白质水溶液的ε’(160~600 MHz和1 400~4 500 MHz)和ε"(20~1 400 MHz)与蛋白质质量分数间存在较好的线性相关性,其相关系数分别达到0.90和0.99。研究表明,不同类型和质量分数的蛋白质水溶液介电特性的变化规律不同,这使得基于介电特性检测蛋白饮料中蛋白质的类型及其质量分数成为可能。     

Mechanical Properties of Pear as a Function of Location and Orientation

Abstract

This study provides data on the fundamental mechanical properties of pear tissue and its relationship with specimen orientation and location. The compression tests were performed on Dangshan pear using the Instron Universal Testing Machine. The values of failure stress, failure strain, failure energy, and Young's modulus on the specimen orientation and location in pear were obtained. The four mechanical properties are significantly affected by specimen orientation, latitude, and depth, but not affected by the longitude of the specimen.     

基于介电特性的鸡蛋品种无损鉴别

为更合理有效实现鸡蛋品种分类,研究一种介电特性无损鉴别鸡蛋品种方法。本实验以4组不同品种鸡蛋(江苏镇江洋鸡蛋、江苏镇江草鸡蛋、安徽老南沟草鸡蛋、江苏东台草鸡蛋)为研究对象,采用平行极板法测量4组鸡蛋在10~200 k Hz条件下的介电特性参数,并利用支持向量机(support vector machine,SVM)算法建立鸡蛋品种鉴别分类检测模型。研究不同核函数(线性核函数、多项式核函数、RBF核函数和Sigmoid核函数)、不同参数寻优算法(网格搜索法、遗传算法和粒子群算法)选择对分类模型准确率的影响。结果表明,以线性核函数为SVM核函数、粒子群算法为SVM参数寻优算法时,建立的鸡蛋品种SVM分类模型的性能最优,其训练集正确率为95.83%,测试集正确率为95.83%。利用介电特性无损检测技术结合SVM算法,取得了很好的分类效果,为鸡蛋品种鉴别提供了一种新的快速有效的方法。     

Thermophysical Properties of Clarified Apple Juice as a Function of Concentration and Temperature

Effect of concentration and temperature on thermophysical properties of clarified apple juice was studied. Density, viscosity, specific heat, and thermal conductivity were measured at different conditions, ranging from 20 to 90^oC and 12 to 70^oBrix. Experimental data were related to the corresponding properties of water and compared with the behavior of sugar solutions. The results obtained were used to derive mathematical models and correlations for predicting these properties as a function of both concentration and temperature.     

Dielectric Behaviour of Whole-Grain Wheat with Temperature at 27.12 MHZ: A Novel Use of a Liquid Dielectric Test Fixture for Grains

This paper is a step towards fulfilling the gap seen in temperature dependence of permittivity (?) of grains at radio frequencies. A commercial device especially built for liquids was exploited for the first time in measuring ? of bulk wheat samples at various temperatures. The dielectric constant (?′) of the wheat increased almost linearly with temperature, and varied between 3.82 and 5.95. The loss factor (?″) increased non-linearly with temperature with values between 0.07 and 0.93. Regression models predicted ?′ and ?″ of the wheat with RMSE of 0.14 and 0.034, and R² values of 0.97 and 0.99, respectively.     

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。     

1-MCP对不同成熟度猕猴桃电特性的影响

以适期采收(成熟度Ⅰ,可溶性固形物6.2%)和晚采收(成熟度Ⅱ,可溶性固形物8.8%)的‘海沃德’猕猴桃为试材,研究0.5μL/L 1-MCP处理对在室温(20℃)贮藏条件下果实电特性的影响。结果表明,在1MHz频率下,成熟度Ⅰ的果实复阻抗明显高于成熟度Ⅱ的果实,而且从贮藏7d开始,两成熟度果实复阻抗(Z)值差异达显著水平(P<0.05)。在10kHz频率下,成熟度Ⅰ果实并联等效电容(Cp)值明显高于成熟度Ⅱ的果实,而且从贮藏7d开始,两成熟度果实Cp值差异达显著水平(P<0.05)。在0.1kHz和1MHz电激励频率条件下,随着贮藏时间的延长,1-MCP有抑制果实复阻抗下降的趋势;在10kHz频率条件下,1-MCP处理果Cp值明显高于对照果;但并联等效电感(Lp)和阻抗相角(θ)对成熟度和1-MCP处理的响应不灵敏,不能作为区分成熟度或1-MCP处理的敏感电参数。