不同等级兰州百合的电学特性

以不同等级兰州百合为研究对象,在50Hz～1MHz频率范围内,利用平行极板法研究电特性参数与百合等级的关系。结果表明:在同一加载频率下,随百合等级的提高,其相对介电常数和电导增大,复阻抗减小;随频率的增大,复阻抗和相对介电常数均减小,电导增加。因此,复阻抗、相对介电常数和电导可作为判断百合等级的指示参数。并联等效电感、相位角、品质因数和损耗因子则与百合等级的关联性规律不强。     

跌落高度对红地球葡萄介电特性的影响

在频率50Hz¹MHz内,采用平行极板法研究从不同高度跌落并贮藏3d时红地球葡萄的介电参数变化规律。从同一高度跌落后,随加载频率增加红地球葡萄的复阻抗的模和并联等效电容值呈减小趋势,电导值呈增大趋势,损耗因子呈先减小后增大、品质因数呈先增大后减小趋势,且在25kHz时损耗因子和品质因数存在极值。在801MHz内,采用平行极板法研究从不同高度跌落并贮藏3d时红地球葡萄的介电参数变化规律。从同一高度跌落后,随加载频率增加红地球葡萄的复阻抗的模和并联等效电容值呈减小趋势,电导值呈增大趋势,损耗因子呈先减小后增大、品质因数呈先增大后减小趋势,且在25kHz时损耗因子和品质因数存在极值。在80²00 cm的跌落高度内,随跌落高度的增加红地球葡萄复阻抗的模和品质因数呈先增大后减小的趋势,电导、并联等效电容和损耗因子呈先减小后增大的趋势,且120 cm跌落时其复阻抗的模和品质因数最大,电导、并联等效电容和损耗因子最小。综合分析可知,通过葡萄介电参数的变化可反映其所受到的机械损伤程度,且其介电特性与电场频率有很强的相关性。     

常温贮藏时间对红地球葡萄介电特性的影响

以红地球葡萄为研究对象,利用平行极板法,在50 Hz～1 MHz频率内研究了常温贮藏时间对其电特性参数的影响。结果表明:在50 Hz～1 MHz的频率内,随加载频率的增加其复阻抗、并联等效电容值呈减小趋势,电导值呈增大趋势,而损耗因子和品质因数在加载频率为25 KHz时分别达到极小值和极大值。在同一加载频率下,随贮藏时间的延长,红地球葡萄的复阻抗值和品质因数减小,并联等效电容、损耗因子和电导值增大。综合分析可知,常温下贮藏时间对红地球葡萄的电特性参数影响较大,且其电特性参数与电场频率有显著相关性。     

静压力对苹果介电特性和胞内水分的影响

对苹果施加不同大小静压力,同时利用平行板电极法监测其介电参数,用针状电极监测其电阻抗图谱,根据Hayden等效电路模型计算分析了胞内电阻、胞外电阻和细胞内、外液体积分布的变化。结果表明:静压力小于120 N,相对介电常数和损耗因子随静压力的增大而非线性增大,大于120 N后线性增大;同一静压力下,相对介电常数随加载频率增大而变小,损耗因子则在加载频率为20 k Hz时有极小值;随静压力增大,苹果组织胞内电阻增大,胞外电阻在小于120 N阶段基本保持水平,大于120 N后开始增大。在静压力增大至250 N的过程中,细胞外液体积百分比由5.69%增加至9.22%,苹果相对介电常数、损耗因子和细胞外液体积百分比之间呈极显著正相关,相关系数大于0.94,说明细胞外液的体积变化是引起果品介电参数变化的主要原因。本研究有望为果品受压过程中内部生理状态的同步监测研究提供新思路,也将为采用介电特性法快速评价其损伤提供理论指导。     

不同含水率稻谷电学物理量变化规律

为探究高水分稻谷含水率与其电学物理量之间的关系,探索电学物理量在高水分稻谷含水率快速检测方面的可行性,以高水分稻谷(含水率23.14%)为研究对象,利用LCR阻抗测试仪测定信号频率1～8 MHz下不同含水率稻谷的13个电学物理量。结果表明,阻抗的相位角、损耗系数、介电常数和等效并联电容与稻谷含水率具有良好相关性。在1～8 MHz频率范围内,稻谷的阻抗的相位角和损耗系数均随着频率的增加呈先增大后减小趋势,介电常数和等效并联电容均随着频率的增加而增大。1 MHz频率下稻谷的等效并联电容与其含水率具有更好的相关性(R2=0.998)。通过对不同含水率稻谷的电学物理量进行研究,为开发一种利用电学物理量预测稻谷含水率的快速检测技术提供理论基础。     

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。     

低频波段对鸡蛋贮藏期间介电特性的影响

采用平行板电极法测定低频波段(10 Hz~12MHz)区间鸡蛋蛋清和蛋黄在室温贮藏下介电特性与理化品质的关系。结果显示:蛋清和蛋黄的介电参数都随频率的升高而降低,且蛋清均高于蛋黄;不同贮藏时间,相同频率下蛋清的介电常数和损耗因子升高而蛋黄的这两个参数降低;鸡蛋的穿透深度随频率的升高而逐渐减少;蛋清和蛋黄损耗因子与离子传导介电损耗理论计算值的差值与频率的log-log图呈良好的线性关系,且低频段的介电损失主要是由离子传导所致。利用鸡蛋的介电参数,采用PLS方法对其理化品质建立预测模型,蛋清介电常数与哈夫单位、蛋黄介电常数与蛋黄水分的模型决定系数R2分别是0.9640,0.9891,预测标准偏差RMSEP分别是0.9206,0.0653。本研究对于蛋品品质检测仪器的研发提供了参考依据。     

基于微波加热的馒头介电特性的分析与研究

基于一种同轴探头网络分析仪技术和混合方程的途径研究微波加热馒头的介电特性。测量馒头在不同密度下的介电特性值,运用回归分析方法得出介电特性与频率的关系,通过比较馒头介电特性混合方程计算值和测量值,得到Bottcher方程适用于计算馒头的介电常数,Landau and Lifshitz,Looyenga方程用于计算馒头的损耗因子。研究频率范围915~2 450 MHz、含水率范围40.12%~48.50%(w.b.)和温度范围25~100℃下馒头介电特性的变化规律。研究表明:馒头的介电常数随着频率的增加而减小,损耗因子随着频率的增加呈现出先减小后很缓慢增大的趋势;介电常数和损耗因子均随含水率和温度的增加而增加。馒头微波加热的穿透深度随着各影响因素的增加而减小,且在25~100℃温度范围内,915 MHz和2 450 MHz微波加热馒头最大厚度分别不超过12.82 cm和10.62 cm。     

不同留叶数对烤烟新品种NC297生长及产质量的影响

试验研究了不同留叶数对NC297农艺性状、经济性状和内在化学成分等方面的影响。结果表明,随着留叶数的增加,株高、节距呈逐渐增加趋势,茎围呈递减趋势;留叶数20～22片的株型较好;留叶数对中、下部叶片的长宽影响较小,上部叶片则是随着留叶数的增加而减小。随着留叶数的增加产量呈递增趋势,而均价、上等烟比例、中等烟比例则呈递减趋势;以留叶20～22片／株经济性状最好;留叶数22片／株的化学成分比较协调。     

盐渍期间黄瓜理化品质与电学参数的相关性

为了考察盐渍黄瓜的理化品质与电学参数的相关性,采用平行板电极法测量了黄瓜在不同盐渍时期于频率20~12 MHz下的复阻抗Z、相位角θ、并联等效电容Cp、导纳值Y,同时还测量了产品的7个理化指标。结果表明,黄瓜的并联等效电容Cp随盐渍时间的增加而增大,且随频率的增加而减小,并联等效电容Cp与频率的对数坐标呈良好的线性关系(R2=0.982)。在特征频率0.1kHz下,阻抗值Z与可溶性固形物质量分数、坚实度呈显著性正向相关,而与灰分、NaCl质量分数呈显著的负相关,相关系数分别为0.867、0.791,-0.874,-0.974;而相位角θ在0.1 MHz下与水分质量分数有极显著的相关性,相关系数为-0.848;并联等效电容Cp和导纳Y在0.1 kHz下可有效量化氨基酸总量和NaCl质量分数,相关系数分别为-0.848、0.886。研究结论可为腌渍黄瓜产品理化指标的快速检测提供参考。     

DIELECTRIC PROPERTIES of STARCH SOLUTIONS AS INFLUENCED BY TEMPERATURE, CONCENTRATION, FREQUENCY and SALT

Dielectric properties of starch solutions (1 to 4% w/w) were evaluated at temperatures ranging from 20 to 80C at 10, 20 and 30 MHz. the effect of added salt (0.2 and 0.5% w/w) was investigated in relation to changes in trends exhibited by the relative permittivity, loss factor and penetration depth. the relative permittivity ranged from 46 to 308 and 65 to 92 for solutions with and without salt, respectively. the corresponding loss factor ranged 266 to 4133 and 9 to 266, respectively. Temperature, frequency, concentration and their interactions had different levels of significance on the dielectric properties of starch solutions. Salt enhanced the relative permittivity, and its effect conformed to the anomalous dispersion phenomenon. the loss factor increased with increasing temperature and salt content, and penetration depths associated with salt‐enriched samples were low compared to samples without salt. Generally, the effects of temperature, frequency, concentration and salt on the dielectric properties of starch solutions were attributed to the complex interaction between conductivity, density, moisture content, loss angle and starch rheological properties. Excellent correlations were developed that could be used for estimating the dielectric properties of starch solutions with and without salt.     

基于介电特性的菜籽油品质快速检测技术研究

采用自制平行电极板检测菜籽油加热及储存过程中电容、电感及阻抗3个介电特征值的变化,并用国家标准方法分析酸值、过氧化值、碘值、羰基价及皂化值5个品质指标,然后建立菜籽油品质指标与介电特性参数之间的相关性。结果表明,在设定的加热温度和储存时间下,菜籽油的介电特性参数电容、阻抗及电感值,分别与其品质指标过氧化值、酸值及羰基价之间具有显著的相关关系。建立了每个介电特性参数(电容、阻抗及电感值)与菜籽油品质指标(过氧化值、酸值及羰基价)、温度及储藏时间的回归方程。菜籽油品质指标实际测量值与计算值的误差均在允许范围内,建议通过测定菜籽油的介电特性值(电容、阻抗及电感值)来直接计算品质指标过氧化值、酸值及羰基价。     

不同电极结构对冷却鸡胸肉阻抗特征值响应效果的影响

采用针式电极和片式电极测量冷却鸡胸肉的阻抗幅值和相位角,研究测量方向和测试样品厚度与鸡胸肉阻抗特征值的关系;通过主成分分析得分图和DI值相结合的方法评价两种电极对鸡胸肉阻抗特征值区分辨别的能力;再对采用针式电极获得的鸡胸肉阻抗谱进行定量的方差分析,用统计方法确定针式电极对测试样品厚度变化的响应能力。结果表明:垂直于鸡胸肉肌纤维方向测量的阻抗幅值大于平行于肌纤维方向的阻抗幅值,符合生物组织的各向异性;同一频率下测试样品厚度40 mm时的阻抗幅值高于测试样品厚度20 mm时的阻抗幅值;针式电极对不同测量方向阻抗特征值的区分效果好,辨别值DI=85.47%;使用针式电极测得鸡胸肉样品从低频到高频的阻抗特征值的差值转换来区分不同样品厚度具有统计学上的显著意义（P<0.05）。通过针式电极垂直于鸡胸肉肌纤维方向测量阻抗特征值的准确性高,可以为后续采用电阻抗技术实现鸡胸肉在线快速检测提供参考。     

损伤对猕猴桃果实电特性的影响

以猕猴桃品种“海沃德”果实为材料,采后果实经50cm高处自由落体碰伤处理,利用日置智能LCR测试仪测定了果实的6个电参数(复阻抗Z、并联等效电容Cp、并联等效电感Lp、损耗系数D、电导G、阻抗相角θ)在6个电场频率(100、158、251、398、631kHz和1MHz)条件下的变化,以及随着贮藏时间的延长各电参数的变化。结果表明：在(25±1)℃条件下,随着电激频率的增加,无论损伤果还是对照果,Z、Lp均呈逐渐减小的变化趋势,Cp、G呈逐渐增加的变化趋势,D呈现先上升后下降的变化趋势,θ呈现先下降后上升的变化趋势。损伤果采后Z在6个电激频率条件下都显著低于对照果,所以Z可作为区分其损伤与否的敏感电参数。在100kHz和251kHz两个电激频率条件下,损伤果采后D值显著高于对照果,所以在这两个特征频率条件下D可作为区分“海沃德”猕猴桃果实损伤与否的敏感电参数。     

阻抗法快速分析牛奶中的菌落总数

以电导、总阻抗、双电层电容、培养介质电容、阻抗角作为检测参数,比较含初始菌数不同的阻抗测试管的阻抗变化率曲线,结果阻抗角不适于作为阻抗法快速分析牛奶中菌落总数的检测参数。将检出时间DT值和平板计数法得到的菌落总数的对数值lgC用SAS做线性回归,结果电导、总阻抗、双电层电容之间存在线性相关。用Δ=lg(C0/CSPC)=lg(C0)-lg(CSPC)值分析阻抗法的检测误差,结果由电导、总阻抗作为检测参数得到的菌落总数值符合实际情况。用阻抗法快速分析牛奶中的菌落总数时,分析FPR、FNR随DTTH的变化趋势,DTTH值分别选440min(电导和总阻抗)和410min(双电层电容)。     

冻融对木质化鸡胸肉品质的影响

以中度木质化鸡胸肉为研究对象，测定冻融过程中木质化鸡胸肉的基本品质指标和阻抗特性，并进行主成分分析，根据Cole-Cole方程拟合得到阻抗等效参数，研究冻融对木质化鸡胸肉食用品质和电阻抗的影响。结果表明：反复冻融后木质化鸡胸肉红度值下降，黄度值呈上升趋势，保水性变差，整体品质降低；在0.06～200.00 kHz频率范围内，新鲜木质化鸡胸肉和解冻木质化鸡胸肉的阻抗幅值均随着频率上升呈现下降趋势，新鲜木质化鸡胸肉的阻抗幅值高于冷冻木质化鸡胸肉，多次冻融处理后木质化鸡胸肉的阻抗幅值明显降低；木质化鸡胸肉的相位角绝对值随着频率上升呈现下降趋势，低频段新鲜木质化鸡胸肉的相位角绝对值低于冷冻木质化鸡胸肉，高频段新鲜木质化鸡胸肉的相位角绝对值高于冷冻木质化鸡胸肉；利用主成分分析对不同冻融次数木质化鸡胸肉的原始阻抗数据和品质数据进行降维处理，新鲜肉、冻融1 次和冻融多次样品之间区分明显，中低频段的阻抗幅值和相位角变量与亮度值和剪切力呈正相关关系，不同冻融次数木质化鸡胸肉的阻抗参数与品质参数有一定相关性。     

Analysis of radio frequency (RF) power distribution in dry food materials

The objectives of this research were to investigate the influence of various factors on radio frequency (RF) power distribution in dry food materials, placed in a 12 kW, 27.12 MHz parallel plate RF system, using a validated finite element computer model. The factors investigated were sample size, shape, relative position between the RF electrodes, and dielectric properties (DPs) of the sample and the surrounding medium. Effects of electrode gap and top electrode configuration on the RF power distribution behavior of the sample were also studied. The RF power uniformity in the samples was compared using RF power density uniformity index (PUI). Simulated results showed that the RF power uniformity in cuboid shaped samples, placed on the bottom electrode, first decreased and then increased with the increase in sample size. The sample shape and its vertical position between the fixed gap parallel plate electrodes also affected the RF power distribution and uniformity. A cuboid sample had higher RF power densities at the edges, while an ellipsoid had higher power densities in the center parts. Simulated results showed that the smaller values of DPs resulted in better RF power uniformities in the samples. Reducing the electrode gap improved the RF power uniformity of the sample. While studying the influence of the top electrode configuration on the RF power distribution and uniformity, the results showed that optimum RF power uniformity in a particular sample size could be achieved with a particular top electrode bending position and angle. The results are useful in understanding complex RF heating, designing and scaling up of efficient RF systems.     

Objective measurements of pork quality: Evaluation of various techniques

Research has been undertaken in which various methods for meat quality evaluation were compared. The measures used were pH (by homogenization and by combined electrode), light scattering conductivity, dielectric loss factor and colour. A very low incidence of PSE (Pale, Soft, Exudative) and DFD (Dark, Firm, Dry) cases was observed and the correlation between pH, as measured by homogenization and by combined electrode, did not appear to be completely satisfactory. Dielectric loss factor, as measured by the MS tester, seems to be specifically suited for PSE diagnosis. On the other hand, higher values of light scattering and conductivity measured at 24 h post mortem, are found to be linked to the rate of pH fall, even outside the range for PSE. Colour measurements, especially of the parameters L(?), a(?) and hue angle, have given interesting information. In fact, meat could be classified by colour intensity (a(?), psychometric chroma), by type of colour (hue angle) and by exudative phenomena (L(?)). No marked effects of rearing techniques have been observed, whereas the genetic background appears to influence some colour parameters. Slaughter conditions, on the other hand, could affect markedly all the meat quality parameters measured in this research.     

Effect of dimensions and geometry of co-field and co-linear pulsed electric field treatment chambers on electric field strength and energy utilisation

Approximations of the electric field strength and specific energy input of continuous pulsed electric field (PEF) systems often assume parallel plate configurations. However, it is known that actual electric field strengths and specific energy inputs can be significantly different from this simplistic approach. A systematic study of more than 150 dimensions and various insulator geometries of pilot-scale PEF treatment chambers with co-linear electrode configuration was performed. A reduction of the inner diameter of the insulator and its shape changes the distribution and (average) intensity of the electric field. Both, the average electric field strength of the PEF treatment zone and the actual specific energy input, were significantly lower than the expected values derived from dividing the applied voltage by the electrode gap. The difference between theoretical and actual values generally increased with increasing electrode radius and decreasing electrode gap. The relative ratios of theoretical electric field strength or specific energy input to actual (average) electric field strength or specific energy input showed a linear dependency on the ratio of electrode radius and gap. The determined relationships of specific energy input and treatment chamber dimensions and geometry were experimentally validated in four different PEF treatment chambers.