果蔬导热系数的测试

果蔬类产品大多具有含水率高的特点,用常规的方法难以测定其导热系数。采用探针法测量了几种果蔬的导热系数,证明了该方法测量时间短,测量过程中试样温升小,测试结果可以准确反映被测物料的实际状态。文中介绍了探针法测量果蔬导热系数的基本原理、测试系统和数据处理方法。     

苹果汁导热系数影响因素的实验研究

由于目前对果汁热物性参数基础研究比较缺乏，本文采用微热探针法测试系统对3～50℃温度范围内不同浓度苹果汁的导热系数进行了系统测试。结果表明，苹果汁的温度和浓度对其导热系数具有显著影响。在相同温度条件下，苹果汁的导热系数与其浓度呈高度线性负相关；相同浓度的苹果汁导热系数与其温度呈高度线性正相关，并得出了苹果汁导热系数关于浓度和温度的二元数学模型，为果汁加工业的相关研究提供了科学依据。     

谷物层内部非稳态温度场的有限元解

利用求解微分方程的边值问题和泛函求极值问题的等价性,进行了谷物干燥过程中谷物层内部非稳态温度场的有限元解尝试。对热传导偏微分方程的泛函形式进行有限元离散、求极值、形成有限元方程的过程。为预测谷物干燥过程中谷层内部温度场随时间的变化情况提供了有效途径。同时进行了实验验证,结果基本吻合。在无人工送风的情况下,流入表层热量的测定和谷物导热系数的选择是影响预测精度的主要因素。该项研究为更复杂情况的模拟打下了基础。     

日光温室栽培基质有效导热系数预测模型

栽培基质为固流两相组成的多组分材料,其导热系数是日光温室热环境营造过程中重要的热参数之一,在温室地面热量的传输中起着重要的作用。为了预测日光温室生产中栽培基质的有效导热系数,以珍珠岩、蛭石、炉渣、河沙、椰糠、泥炭及腐熟牛粪与花生壳8种常用单一基质为研究对象,首先利用干燥与饱和状态下基质有效导热系数的测试结果,通过复合材料有效特性混合模型的反向计算,确定了8种单一基质的固相导热系数,得到珍珠岩、蛭石、炉渣、河沙、椰糠、泥炭及腐熟牛粪与花生壳的固相导热系数分别为0.058、0.139、0.252、0.817、0.148、0.518、0.262及0.066 W/(m·K);其次,利用复配基质有效导热系数的实测结果,通过复合材料有效特性混合模型的正向与反向计算,明确了组成固相的各组分呈并联关系排列,并确定了复配基质中固相导热系数与基质各组分体积比例的关联;进一步将复配基质在不同饱和度下的有效导热系数实测值与基于6种复合材料导热系数模型理论计算值进行比较。结果表明：并联模型适用于复配基质有效导热系数的理论计算,构建了日光温室栽培基质有效导热系数的预测模型。采用实际生产中常用的4种育苗和栽培基质在不同饱和度下的有效导热系数对所建模型进行检验,模型预测值和实测值的平均相对偏差范围为0.42%～1.76%。基于并联模型构建的有效导热系数预测模型能够较为准确的计算日光温室栽培基质在不同饱和度下的有效导热系数。     

超高压增大食品物料的导热系数

食品物料在超高压下的导热系数是研究超高压加工过程中传热与温度变化的必要参数,但有关超高压下食品物料的导热系数数据和测量方法还十分缺乏。该文基于线热源法设计了适用于超高压力环境下食品物料导热系数的测量探针和聚甲醛样品容器,利用1.5%琼脂凝胶对热探针在25℃不同压力下(0.1~400 MPa)进行标定试验,结果表明测量值与纯水导热系数的参考值非常接近且呈良好的线性相关关系(R2=0.9997),据此得到探针的标定系数为0.9944。在25℃测量了蛋清、蛋黄、火腿肠和奶油在0.1~400 MPa压力下的导热系数值。结果发现:在25℃条件下,超高压下食品物料的导热系数较常压下均有一定程度的增大(最大达到28%),且有随压力增大而增大的趋势;一定压力条件下,食品物料的导热系数随着含水量的增大而增大。建立了25℃条件食品物料在一定压力范围内(0.1~400 MPa)导热系数预测的经验公式,对研究的几种食品物料拟合得到的方程回归系数在0.91以上。     

热敏电阻法测量胡萝卜及马铃薯的热物性

热物性参数的测定对于农产品加工及储藏过程中的数学模拟计算非常重要。在分析微珠状热敏电阻传热模型的基础上,在室温对标准样品(乙二醇、乙醇、氯化钙的水溶液)的热物性进行测定,结果显示,导热系数及热扩散系数的测量值与推荐值之间无显著性差异(p>0.05);热敏电阻法与热探针法对比测定胡萝卜及马铃薯两种农产品的导热系数,结果显示两种方法之间无显著性差异(p>0.05);热敏电阻法与常规计算对比测定胡萝卜及马铃薯两种农产品的热扩散系数,结果显示两种方法之间无显著性差异(p>0.05)。热敏电阻法能够用于小直径农产品热物性的测量。     

茶叶导热系数的研究

对六种不同形状和制法的茶叶的导热系数用线性热源法作了测定和研究。这种方法可以在物料的密度和比热未知的条件下,迅速取得物料导热系数的资料。研究结果表明,茶叶的导热系数为0.0362～0.0486W/m·k,相当于工程隔热材料的热特性;因此,在茶叶加工中必须重视对流给热的作用。在同等密度条件下,茶叶的导热系数与含水率呈正相关;在含水率相同条件下,茶叶的导热系数随容重的增加而提高。茶叶的形状、含水率和揉捻紧度不同,其导热系数不同。红碎茶的导热系数高于条形茶,发酵茶的导热系数高于不发酵茶。各种茶叶的茶汤导热系数与水接近。试验采用的线性热源结构简单、应用方便、样品容易制作并且测定迅速,还可在现场取样测定,便于进行动态跟踪研究。     

不同化学改性方法提高玉米芯骨料混凝土的性能

玉米芯具有较低的导热系数,可以作为天然的保温材料,用于混凝土砌块中。然而,由于玉米芯的多孔结构,导致玉米芯骨料混凝土的抗压强度偏低,亟需进行改性。为了推广玉米芯的规模化利用,该研究以玉米芯为原料改善混凝土砌块的性能,通过红外光谱、拉曼光谱和扫描电镜等测试手段,探讨了3种不同改性技术对玉米芯骨料混凝土水化产物化学键、分子结构、界面过渡区微观结构、抗压强度和导热系数的影响。结果表明：与环氧树脂改性相比,陶粒法改性和裹浆法改性不仅增加了玉米芯骨料混凝土界面过渡区的水化硅酸钙凝胶含量,同时也降低了界面过渡区的厚度,优化了混凝土砌块的微观结构、提高了混凝土砌块的抗压强度、降低了混凝土砌块的导热系数。其中,陶粒法改性技术的效果尤为明显。界面过渡区厚度水化硅酸钙特征峰大小顺序分别为陶粒法改性、裹浆法改性、环氧树脂改性。经过陶粒法改性、裹浆法改性和环氧树脂改性后,玉米芯骨料混凝土的界面过渡区厚度分别为无明显界面过渡区、55～66 μm和93～101 μm之间。和未改性玉米芯骨料混凝土相比,掺30 %陶粒法改性玉米芯骨料混凝土的抗压强度的导热系数分别降低了51.5%和32.2%。当掺入不超过15%的改性玉米芯骨料时,混凝土砌块满足国家标准GB/T8239-2014中对抗压强度的要求。为了改善玉米芯骨料混凝土砌块的综合性能,建议掺入不超过15%的陶粒法改性玉米芯骨料。这项研究结果为玉米芯在混凝土砌块中的大规模利用提供了依据,同时也为进一步改善混凝土砌块的相关性能提供了参考。     

温度和粉碎粒度对不同能量饲料原料热物理特性的影响

为探究常见能量饲料原料在不同温度、不同粉碎粒度下的热物理特性差异,该文以4种谷物(玉米、小麦、大麦和高粱)和4种加工副产品(小麦麸、木薯渣、甜菜渣和米糠)原料为研究对象,分别粉碎过孔径1.5、2.0和2.5 mm筛片,得到3种不同粉碎粒度的粉料,利用差示扫描量热法(differential scanning calorimetry,DSC)和线热源法分别测定了不同粉料在25～100℃范围内的比热和导热率,通过计算得到相应的导温系数,分析了温度、粉碎粒度对原料热特性的影响以及不同原料之间的热特性差异,并建立了热特性参数关于温度的回归预测模型。结果显示:8种原料粉碎过1.5 mm筛孔的粉料比热、导热率和导温系数随温度的升高分别在1.580～2.671 kJ/(kg·K),0.054～0.362 W/(m·K)和6.694×10~(-8)～23.254×10~(-8) m~2/s范围内变化。整体上,原料的热特性均随温度的升高而呈线性或非线性上升趋势。不同粉碎粒度的同一原料,在相同温度下的比热差异均不显著(P0.05);随着粒度的增大,粉料的导热率和导温系数均有逐渐下降的趋势。4种谷物的比热与温度之间呈线性关系;小麦麸、木薯渣和米糠的比热可用温度的三次多项式表示;而甜菜渣的比热与温度呈二次关系。4种谷物和甜菜渣在3种粒度下的导热率均可用温度的三次多项式表示,而小麦麸、木薯渣和米糠的导热率则可用温度的二次多项式表示。小麦麸和米糠的导温系数与温度呈二次关系,其余6种原料的导温系数则可用温度的三次多项式表示。研究结果可为配合颗粒饲料配方变换所需的调质、制粒等热加工过程的工艺参数的调整、优化提供理论依据。     

可逆热致变色竹塑复合材料的温度与光响应及热学性能

为更进一步了解可逆热致变色竹塑复合材料所具有的特性,该论文对可逆变色竹塑复合材的温度与光响应及热学性能进行研究,主要包括：环境温度对变色时间的影响、变色复合材料的曝晒试验（测试环境温度与曝晒装置内的温度）、试样表面的反射率、导热系数等。研究结果表明：变色竹塑复合材料在较高的环境温度下竹塑复合材料的变色响应时间较短,如WTB1在45、50、55、60、65℃的变色时间分别为256.11、146.18、82.78、69.16、45.06 s;曝晒试验的结果表明颜色影响试验箱内温度,添加钛白粉可降低曝晒装置内的温度;在12:00时,WTB1、WTB2、WTB3、WTB4、WTR1、WTR2与环境的温差分别为14.3、12.8、15.3、11.3、15.3、11.3℃。可逆变色竹塑材料的导热系数随着温度的升高而增大,WTB2在15、30、45、60℃下的导热系数分别为0.098、0.099、0.103、0.107 W/(m K),WTB1（未添加钛白粉）表面自由能和接触角分别为67.3°、41.50 MJ/m2,而WTB2（添加钛白粉）的表面自由能和接触角分别为74.6°、37.52 MJ/m2;各种试样的反射率存在差异,添加钛白粉提高了材料的表面反射率,颜色是影响太阳反射率的重要因素之一。研究结果为该材料的实际应用提供数据支持。     

Oat Grain Density Measurement by Sand Displacement and Analysis of Physical Components of Test Weight

Test weight or bulk density of oats (Avena sativa L.) has a major influence on the monetary value of oat grain. We hypothesize that test weight can be attributed to grain density and packing efficiency. We have measured oat grain volume and density by a sand‐displacement method and derived the packing factor for six oat cultivars grown in three environments. Volumes of individual grains were 31–38 mm³ and were highly correlated with grain mass. Grain densities were 0.96–1.03 g/cm³. Packing efficiency, defined as the space proportion occupied by the grains, was 53–55%. Regression analysis suggested that 78% of the variation in test weight could be attributed to grain density. Size fractionation of grain by sieving and analysis by digital image analysis indicated that smaller grains within an oat sample packed more efficiently than larger grains and larger grains in a sample were less dense than the smaller grains. Analysis of oat grain components indicated groat densities were ≈1.29 g/cm³ and hull densities were ≈0.69 g/cm³. The difference in densities between groat and hull provide a physical basis for the recognized relationship between groat percentage and test weight.     

Detection of Fragments from Internal Insects in Wheat Samples Using a Laboratory Entoleter

A simple, rapid method that uses a small mechanical rotary device (entoleter) was developed for estimating insect fragment counts in flour caused by hidden, internal‐feeding insects in whole grains of hard red winter and soft red winter wheat. Known counts of preemergent adults, pupae, and larvae of lesser grain borers and rice weevils were blended with 500 g samples of uninfested wheat. The entoleter impeller speed was adjusted based on grain hardness and moisture content to obtain about ≈98% intact and ≈2–2.5% broken kernels in an uninfested sample. The entoleter flung the wheat kernels against a surrounding steel ring. Approximately 70–90% of the insect‐infested kernels, being weaker, released internal insect pieces upon impact. The broken kernels were sieved with number 10 and number 20 sieves to obtain large‐sieved and small‐sieved fractions, respectively. Insect pieces in sieved fractions were counted. The insect piece counts were correlated with the estimated flour fragments (R² = 0.94). The entoleter method can distinguish samples of grain containing 0, 25, or 75 fragments in 50 g of flour, with greater than 95% confidence. The method can be performed in approximately 5 min per 500 g sample and could potentially be a cost‐effective method that grain handlers can use to inspect wheat loads for detecting insect damage and estimating insect fragments in flour.     

不同样本尺度和分区方案的粮食产量空间化及误差修正

粮食产量数据空间化有助于粮食产量数据与其他自然、人文数据进行综合分析,但空间化过程中必然会产生误差。该文按照3种分区方案(全国不分区、全国分为7个区以及按省分区),选择3种尺度上(县级、地市级和公里网格)的总产及平均产量数据(即4种样本:县级粮食总产、县级平均粮食产量、地市级粮食总产、地市级平均粮食产量)分别为因变量,以对应的3种农田类型(水田、水浇地、旱地)面积数据为自变量,利用多元线性回归分析方法,得到15种空间化模型。采用两阶段误差分析方法,选取2个模型误差评价因子和5个空间化结果误差评价因子,对模型和空间化结果进行误差分析。结果表明:1)空间化过程中,模型精度与空间化结果的精度存在不一致性;2)对于采用同一样本的模型(常数项为0)而言,空间化结果精度随着分区方案的细化先提高再降低,而对于采用同一样本的模型(常数项非0)而言,空间化结果精度随着分区方案的细化而降低;3)在全国不分区和分为7个区2种情况下,空间化结果精度随着分析样本尺度的细化(从地市级到县级再到公里网格)先提高后降低。根据上述分析结果,最终以县级粮食总产为样本、常数项为0、全国分7个区建模的方案实现全国粮食产量数据空间化,并通过修正,得到2005年中国粮食产量公里网格分布图。该研究弥补了粮食产量空间化误差分析的不足,探寻了不同样本尺度和分区方案与空间化误差的关系,提高了空间化精度,同时对其他类型的社会经济统计数据空间化研究具有一定的参考价值。     

基于近红外光谱的灌浆期玉米籽粒水分小样本定量分析

玉米灌浆期含水率测定是考种育种的重要指标。为了节约样本且快速准确测定灌浆期玉米水分,该文应用近红外光谱技术,提出了基于小样本条件下的自举算法(Bootstrap)与基于x-y距离结合的样本划分方法(SPXY,sample set partitioning based on joint x-y distances)相结合的样本优化方法的偏最小二乘(PLS,partial least square)水分定量分析模型Bootstrap-SPXY-PLS模型。试验结果表明,当Bootstrap重抽样本次数等于500,样本数量大于等于10时,模型的性能稳定,并且随着样本数量增加,重抽样本次数相对减少;样本数量为10和50时,全谱Bootstrap-SPXY-PLS模型的预测均方根误差(RMSEP,root-mean-square error of prediction)均值分别为0.38%和0.40%,预测相关系数(correlation coefficients of prediction)分别为0.975 1和0.968 5,决定系数R~2分别为0.999 9和0.993 6;基于竞争性自适应重加权采样算法(CARS,competitive adaptive reweighed sampling)波长变量筛选后的CARS-Bootstrap-SPXY-PLS模型的预测均方根误差RMSEP均值分别为0.36%和0.35%,预测相关系数分别为0.973 6和0.975 0,模型决定系数R~2分别为0.924 5和0.918 0。因此,全谱Bootstrap-SPXY-PLS模型和CARS-Bootstrap-SPXY-PLS模型均具有稳定的预测能力,为玉米育种时灌浆期种子水分测定提供了一种稳定、高效的方法。     

Assessment of Heat-Damaged Wheat Kernels Using Near-Infrared Spectroscopy

Heat damage is a serious problem frequently associated with wet harvests because of improper storage of damp grain or artificial drying of moist grain at high temperatures. Heat damage causes protein denaturation and reduces processing quality. The current visual method for assessing heat damage is subjective and based on color change. Denatured protein related to heat damage does not always cause a color change in kernels. The objective of this research was to evaluate the use of nearinfrared (NIR) reflectance spectroscopy to identify heat-damaged wheat kernels. A diode-array NIR spectrometer, which measured reflectance spectra (log (1/R)) from 400 to 1,700 nm, was used to differentiate single kernels of heat-damaged and undamaged wheats. Results showed that light scattering was the major contributor to the spectral characteristics of heat-damaged kernels. For partial least squares (PLS) models, the NIR wavelength region of 750–1,700 nm provided the highest classification accuracy (100%) for both cross-validation of the calibration sample set and prediction of the test sample set. The visible wavelength region (400–750 nm) gave the lowest classification accuracy. For two-wavelength models, the average of correct classification for the classification sample set was >97%. The average of correct classification for the test sample set was generally >96% using two-wavelength models. Although the classification accuracies of two-wavelength models were lower than those of the PLS models, they may meet the requirements for industry and grain inspection applications.     

牛肉大理石花纹图像特征信息提取及自动分级方法

为了解决牛肉大理石花纹在人工分级中准确率和效率低的问题,该文基于计算机视觉和图像处理技术提出一种实用的牛肉大理石花纹自动评估和分级方法。通过图像解析,利用所提出的分级算法实现牛肉大理石花纹的快速提取,并计算反映大理石花纹丰富程度的10个特征参数。使用特征参数建立主成分回归模型,对牛肉大理石花纹等级进行预测,预测相关系数Rv=0.88,预测标准差SEP=0.56。校正时模型总体的回判正确率为97.0%,验证时总体的判别正确率为91.2%。在此基础上,开发了大理石花纹自动分级软件系统和硬件装置,并且在该试验室前期研制的样机上进行了试验,验证了算法的运算速度和准确率。结果表明,所提出的分级方法的检测速度和精度均能够满足企业中对牛肉大理石花纹分级的要求。     

Microwave drying for safe storage and improved nutritional quality of green gram seed (Vigna radiata)

The present study describes the effect of the microwave-heating method on disinfestations and physico characteristics, viz., grain size, grain hardness, and nutritional quality, of the stored green gram seed. It has been observed that the use of the microwave-heating method not only prolongs the storage duration of the green gram seed but also enhances its nutritional quality. The effect of independent parameters, viz., microwave power level and time of exposure, on the moisture content, insect mortality, color, and antinutrient factor (phyic acid) was optimized using response surface methodology (RSM), with the optimized value for power of 808 W and time at 80 s. The optimally treated green gram seed has 8.9% moisture, 99.5% insect mortality, 2.22 Δa* (green color of seed), and 591.79 mg/100 g of antinutrient factor (phytic acid). The grain size (geometric mean diameter, D(m)) of the control (untreated) sample was 3.75 mm, and that of the microwave-treated sample using optimum conditions was 3.99 mm. The grain hardness of the control sample was 3.31 kg, and that of the microwave-treated sample using optimum conditions was 1.305 kg. In vitro protein digestibility (IVPD) of the control (untreated) sample was 83 ± 0.289%, and that of the microwave-treated sample using optimum conditions was 85 ± 0.296%. These values are significantly difference (p < 0.05). The mineral elements studied were Zn, Fe, Mg, Mn, Cu, K, Ca, and Na. The microwave treatment resulted in a non-significant (p < 0.05) effect for Mg, Mn, Cu, K, and Na but a significant (p < 0.05) effect for Zn, Ca, and Fe. The results indicate that the microwave heating not only increases the insect mortality but also reduces the moisture content and antinutritional factor (phytic acid), while the natural green color of the seed is not affected much. This study provides a novel and environmentally safe technique and increase in the nutritive quality.     

高大平房仓储粮品质变化与储粮环境的关系

采用多点随机抽样法对高大平房仓储粮品质变化与储粮环境的关系进行了研究。结果表明,温度和粮食水分是决定粮食储藏状况的主导因素,低水分储粮和低温储粮对提高储粮稳定性具有重要作用;仓内湿度与粮食陈化之间没有明显的相关关系,不是影响粮食品质的直接因素;另外,害虫为害对粮食品质的影响也不可忽视。     

Dispersing sandy soil for the measurement of particle size distributions using optical laser diffraction

Despite the speed and accuracy of particle size distribution measurement by optical laser diffraction instruments, the dispersion of the sample, especially of soil aggregates, remains time-consuming. The Malvern Instruments obscuration measurement was used to calculate the dispersion ratio as an indicator of soil disaggregation. It enabled rapid and direct comparison between measurements made using different amounts of soil, dispersed using different fluids and dispersion methods. The dispersion ratio was necessary to select the most suitable media and method of dispersion for the soil samples and was useful for identifying grain breakage and flocculation. A standard for size distribution measurements involved a soil sample suspended in tap water and dispersed using ultrasonic action for 3 min. Reproducibility of grain size distribution measurements on the Malvern laser sizer showed that variation caused by resampling was greater than variation in the optical measurement provided that the measurement sweeps for the instrument were appropriately set. Blending size distributions for material measured using two different focal lenses was problematic. It is suggested that the laser light source Coulter LS-100 may be a more suitable instrument when many sample measurements are required.     

Solvolysis procedures for the determination of bound residues of the mycotoxin deoxynivalenol in fusarium species infected grain of two winter wheat cultivars preinfected with barley yellow dwarf virus

A trichloroacetic acid treatment at 140 degrees C for 40 min was successfully established as a suitable solvolysis procedure for the recovery of bound deoxynivalenol or its derivatives in Fusarium-infected plants. Deoxynivalenol itself was not decomposed in the procedure. The derivative 15-acetyl-deoxynivalenol was chosen as a model compound for setting free deoxynivalenol in an acid-catalyzed deesterification reaction, developing the method. This is the first report using a trichloroacetic acid solvolysis procedure as a sample incubation step to free bound deoxynivalenol and determine free from bound deoxynivalenol in the sample. Between 13 and 63% of the total deoxynivalenol consisted of nonextractable deoxynivalenol. Deoxynivalenol contents in grain of the susceptible cultivar "Agent" infected with Fusarium spp. were 12-24 times higher when compared to those for the corresponding moderately resistant cultivar "Petrus". The highest deoxynivalenol amounts were determined in grain infected with Fusarium spp. as well as simultaneously infected with BYDV. This solvolysis procedure may be of importance for distinguishing between resistant and susceptible plants and their ability to immobilize (bound) mycotoxins as a plant defense mechanism.