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。      

Modeling the Dielectric Properties of Ham as a Function of Temperature and Composition

ABSTRACT The dielectric properties of 19 different ham samples with different moisture (38.2% to 68.9%) and ash contents (1.78% to 6.80%) were measured at −35 to 70 °C at 2450MHz. Equations were developed as a function of temperature, moisture, and ash, and compared to literature equations. The dielectric constant decreased with ash content and increased with moisture content. It increased instead of decreasing with temperature. The dielectric loss factor increased with moisture content for moisture contents lower than 60.7%, then decreased for higher moisture contents. Ash content and temperature increased dielectric loss factor. Frozen samples had low dielectric activity that was increased by ash content above −20 to −10 °C.     

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.     

Temperature Profiles Within Milk after Heating in a Continuous-flow Tubular Microwave System Operating at 915 MHz

ABSTRACT: Milk with different fat contents (0, 1, 2, 4%, and chocolate milk) were heated in a specially designed continuous-flow microwave applicator operating at 915 MHz. The nominal power was 5 kW and the flow rates were 2.0 and 3.0 L/min to attain laminar flow. Temperature profiles at the exit of the applicator were measured. The results showed that the average increases in temperature were similar to one another, being 42 °C at 2.0 L/ min and 29 °C at 3.0 L/min. Differences between the lowest and highest temperatures were 3.7 and 3.0 °C, respectively. The temperature profiles illustrated that slightly higher temperatures were achieved within segments flowing close to the center of the tube.     

番茄浆料的流变特性

对不同浓度的番茄浆料在30～60℃时的流变学性质进行了研究.结果显示,番茄浆料为假塑体系,屈服应力值的范围比较宽(40～140Pa).通过回归分析得到数学模型K=K0exp(Ea/RT)和K=Aexp(BC).可以分别用来描述温度和浓度对番茄浆料稠度系数的影响.利用这些方程,可以预测实际加工过程中不同温度和不同浓度条件下番茄浆料的粘度.     

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.     

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.     

Effect of Chitosan Nanoparticles and Pectin Content on Mechanical Properties and Water Vapor Permeability of Banana Puree Films

Abstract: Puree prepared from over‐ripe peeled bananas was used as raw material for films processing in a laboratory padder. Pectin and glycerol as plasticizer were added in small concentrations and chitosan nanoparticles (88.79 ± 0.42 nm medium size) incorporated at 0.2% (dry weight basis) as reinforcement material. The mechanical properties, water vapor transmission, thermal stability, and scanning electron microscopy of fractured film surfaces were characterized. Both pectin and glycerol demonstrated an important role in promoting elongation and film handability as was expected. The incorporation of nanoparticles promoted noticeable improvement of the mechanical properties and acted in reducing the water vapor permeation rate, by 21% for films processed with pectin and up to 38% for films processed without pectin, when compared to the control (puree films with no pectin and nanoparticles additions). Microscopic observation revealed a denser matrix when nanoparticles are incorporated into the films. Practical Application: The development of films from fruit purees head to a new strategy for plastic processing from natural resources. The over‐ripe or even waste banana can be adequately prepared for batch films processed with reasonable mechanical and barrier properties, suitable for applications in the food segment. The addition of small fractions of chitosan nanoparticles, form nanocomposites enhancing mechanical and thermal stability broadening potential film applications.     

Green Pea and Garlic Puree Model Food Development for Thermal Pasteurization Process Quality Evaluation

Development and selection of model foods is a critical part of microwave thermal process development, simulation validation, and optimization. Previously developed model foods for pasteurization process evaluation utilized Maillard reaction products as the time–temperature integrators, which resulted in similar temperature sensitivity among the models. The aim of this research was to develop additional model foods based on different time–temperature integrators, determine their dielectric properties and color change kinetics, and validate the optimal model food in hot water and microwave‐assisted pasteurization processes. Color, quantified using a^* value, was selected as the time–temperature indicator for green pea and garlic puree model foods. Results showed 915 MHz microwaves had a greater penetration depth into the green pea model food than the garlic. a^* value reaction rates for the green pea model were approximately 4 times slower than in the garlic model food; slower reaction rates were preferred for the application of model food in this study, that is quality evaluation for a target process of 90 °C for 10 min at the cold spot. Pasteurization validation used the green pea model food and results showed that there were quantifiable differences between the color of the unheated control, hot water pasteurization, and microwave‐assisted thermal pasteurization system. Both model foods developed in this research could be utilized for quality assessment and optimization of various thermal pasteurization processes.     

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。     

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.     

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。     

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.     

Effect of Temperature (−5 to 130 °C) and Fiber Direction on the Dielectric Properties of Beef Semitendinosus at Radio Frequency and Microwave Frequencies

ABSTRACT:  The dielectric properties must be defined to design efficient radio frequency (RF) and microwave (MW) processes by the food manufacturers. The objective of this study was to understand how frequency, temperature, and muscle fiber orientation influence the dielectric properties. The eye of round ( Semitendinosus ) muscle was selected because it contains large, relatively uniform muscle cells with similar muscle fiber orientation and relatively uniform chemical composition throughout the tissue. Dielectric properties were measured using an open-ended coaxial probe technique at 27, 915, and 1800 MHz and temperatures between −5 and 130 °C. Power penetration depth was calculated. Since many commercially prepared, thermally processed, ready-to-eat entrees are made with frozen meat, dielectric property measurements were started from −5 °C. The dielectric constant and dielectric loss factors were often higher for muscle with the muscle fiber measured in a parallel orientation to the probe compared to samples of the same treatment (for example, fresh or frozen) in a perpendicular tissue orientation at the same frequency and temperature. Dielectric constant and loss values for frozen beef tended to be higher than fresh beef at the same temperature and frequency. Tissue orientation appeared to have a greater effect on dielectric loss values at lower frequencies. Penetration depth tended to be greater when the direction of propagation was perpendicular to the muscle fiber.     

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.