Effect of Moisture Content on Viscoelastic Properties of Hydrated Gliadin

The effect of moisture content on the linear viscoelastic properties of gliadin hydrated to 30 and 40% moisture content [gliadin(30%) and gliadin(40%), respectively] was determined. These two moisture contents bracketed the equilibrium moisture content of gliadin, which was 37.6%. Time‐temperature‐superposition was used to develop master curves of the elastic modulus (G′), viscous modulus (G″), dynamic viscosity (η′), and tan δ (G″/G′) from isothermal frequency sweep data obtained at 25–80°C. Smooth master curves were obtained for all of the viscoelastic functions for both gliadins. G′ and G″ showed a power law dependency on frequency (with G″ > G′) for frequencies <0.1 rad/sec for gliadin(30%) and <1 rad/sec for gliadin(40%). The low‐frequency‐limiting slopes on log‐log coordinates for G′ and G″ were 0.700 and 0.646 for gliadin(30%), respectively. Corresponding values were 0.658 and 0.614 for gliadin(40%). G′ crossed over G″ at a frequency of ≈0.3 rad/sec for gliadin(30%), while G′ and G″ for gliadin(40%) only became congruent at higher frequencies. Both gliadin samples showed appreciable frequency dependence of η′ over the entire frequency range, while η′ was greater for gliadin(30%) than for gliadin(40%) at all frequencies, but especially at the lowest frequencies. Tan δ increased gradually from a value of ≈1 at 0.1 rad/sec to ≈2 at the lowest frequency of 0.0002 rad/sec for both gliadins, but tan δ decreased rapidly for gliadin(30%) for frequencies >0.1 rad/sec. Thus, the main difference between gliadin(30%) and gliadin(40%) was that elastic effects (G′ > G″ and decreased tan δ were more prominent for gliadin(30%) at the higher frequencies. In addition, the frequency dependence of G′, G″, η′, and tan δ for the two gliadin samples was compared directly with two samples of poly(dimethylsiloxane) (PDMS) a linear silicone‐based entangled polymer with molecular weights (MW) of 140,000 and 385,000. The substantial differences in the magnitude and overall patterns of the frequency dependence of the viscoelastic functions between the gliadin and PDMS samples was attributed to the dominant effect that noncovalent secondary associations apparently have on the linear viscoelasticity of the gliadins. The energy of activation for flow (determined from the temperature dependence of the shift factors) for the gliadin samples for the range 25–45°C was higher than is typical for entangled linear polymer melts. The activation energy decreased for temperatures greater than ≈60°C for gliadin(30%) and ≈50°C for gliadin(40%). Thus, hydrated gliadin cannot be considered to be a simple viscoelastic liquid.     

缓苏过程中玉米颗粒内部水分分布的数学模拟

在平面直角坐标下,利用有限元方法,对玉米颗粒在缓苏过程中的含水量变化进行了数学模拟。玉米颗粒在75℃的热风温度下干燥2小时,然后进行密闭保温缓苏,结果表明:随着缓苏时间的增加,玉米颗粒中心部位的含水量缓慢下降,表面的含水量增加较快,只有次中间部位的含水量变化较小。在玉米颗粒内部,粉质胚乳的平均含水量呈下降的趋势,而角质胚乳和胚的平均含水量是增加的。     

Effect of Varying Protein Content and Glutenin-to-Gliadin Ratio on the Functional Properties of Wheat Dough

Gluten, starch, lipids, and water-soluble material were separated from seven wheat samples with a range of protein contents and breadmaking quality. The isolated glutens were further partitioned into gliadin- and gluteninrich fractions using pH precipitation. Protein content and glutenin-togliadin ratio were systematically altered by blending these fractions into the original flours in calculated amounts. Mixing properties, extension-tester parameters, and baking performance of composite flours were determined using small-scale techniques. Results of dough testing with blends of constant glutenin-to-gliadin ratio showed increases in the mixing time, mixograph peak resistance, maximum resistance to extension, extensibility, and loaf volume as the protein content increased. At constant protein content, increases in glutenin-to-gliadin ratio were associated with increases in mixing time, mixograph peak resistance, maximum resistance to extension, and loaf volume, and with decreases in extensibility. Thus, total protein content and glutenin-to-gliadin ratio independently affected dough and baking properties. The results have allowed the separation of the effects of flour protein quantity and composition on breadmaking properties.     

Removing Moisture Effect on Soil Reflectance Properties: A Case Study of Clay Content Prediction

Visible, near-infrared and shortwave-infrared (VNIR-SWIR) spectroscopy is an efficient approach for predicting soil properties because it reduces the time and cost of analyses. However, its advantages are hampered by the presence of soil moisture, which masks the major spectral absorptions of the soil and distorts the overall spectral shape. Hence, developing a procedure that skips the drying process for soil properties assessment directly from wet soil samples could save invaluable time. The goal of this study was twofold:proposing two approaches, partial least squares (PLS) and nearest neighbor spectral correction (NNSC), for dry spectral prediction and utilizing those spectra to demonstrate the ability to predict soil clay content. For these purposes, we measured 830 samples taken from eight common soil types in Israel that were sampled at 66 different locations. The dry spectrum accuracy was measured using the spectral angle mapper (SAM) and the average sum of deviations squared (ASDS), which resulted in low prediction errors of less than 8% and 14%, respectively. Later, our hypothesis was tested using the predicted dry soil spectra to predict the clay content, which resulted in R² of 0.69 and 0.58 in the PLS and NNSC methods, respectively. Finally, our results were compared to those obtained by external parameter orthogonalization (EPO) and direct standardization (DS). This study demonstrates the ability to evaluate the dry spectral fingerprint of a wet soil sample, which can be utilized in various pedological aspects such as soil monitoring, soil classification, and soil properties assessment.     

Effect of Moisture Content at Harvest and Degree of Milling (Based on Surface Lipid Content) on the Texture Properties of Cooked Long-Grain Rice

The effects of the degree of milling (based on surface lipids content [SLC]) on cooked rice physicochemical properties were investigated. Head rice yield (HRY), protein, and SLC decreased with increasing milling, while the percent of bran removed and whiteness increased. Results showed that SLC significantly (P < 0.05) affected milled as well as cooked rice properties across cultivar, moisture content (MC) at harvest, and location (Stuttgart, AR, and Essex, MO). Cooked rice firmness ranged from 90.12 to 111.26 N after milling to various degrees (SLC). The decrease in cooked rice firmness with increasing milling was attributed to the lowering of total proteins and SLC. Cooked rice water uptake increased with increasing degree of milling. Water uptake by the kernel during cooking dictated the cooked rice firmness. The increase in cooked rice stickiness with increasing degree of milling was attributed to an increase in starch leaching during cooking because of the greater starch granule swelling associated with a greater water uptake.     

土壤容重和含水量对耕作阻力的影响

土壤容重和含水量是影响机具耕作阻力和能量消耗的主要因素。为了研究它们之间的数量关系,在田间将土壤容重和含水量分别在１．１～１．７ｇ／ｃｍ^３和１１％～１９％的范围内取三个水平,进行靴式开沟器耕作阻力的正交试验。用改进的五轮仪测试开沟器的工作阻力和开沟深度,土壤容重和含水量,采用容重环法实行定点测试。试验数据用改进的Ｍａｒｑｕａｒｄｔ法,通过ＴＳＰ统计软件进行回归分析,得到了土壤耕作阻力－容重－含水量数学模型,并具有较高的拟合精度,可以用于分析评价不同土壤容重和含水量条件下拖拉机的牵引效率和能量消耗。     

Effect of Moisture Content and Temperature on Respiration Rate of Rice

One cause of yellowing or stackburn of rice may be elevated respiration rates caused by storage at either high moisture content (MC) or temperature. The effect of MC and temperature on the respiration rate of Oryza sativa L. ‘Bengal’ and ‘Cypress’ rice harvested in the fall of 1998 was investigated. For respiration rate measurement of rough rice at different temperatures, rice samples at high, medium, and low MC were sealed in quart jars and equilibrated to temperatures of 20–80°C. The respiration rate was quantified by measuring the rate of CO₂ accumulation in the free air space. To determine the effect of MC on respiration rate, rough rice was tested at 12–25% MC. Respiration was greatly affected by MC and temperature. The response of respiration to temperature was dependent on MC and varied between rice cultivars. Respiration rates increased as MC increased from ≈15 to 25%. Maximum respiration was at 50°C when MC was high (20–25%). At 15% MC, respiration increased from 20 to 70°C, while respiration of 12% MC rice, although very low, appeared to increase up to 80°C. A model was developed from this data to predict the respiration rate of rice over the MC range tested.     

针型电容法测量谷物含水率的研究

采用针型电容传感器和测量电路,并采取减小介质损耗的有效措施,研制了测量谷物含水率的针型电容法。实验结果表明,在谷物含水率与输出电压间具有良好的线性关系。该方法具有较高灵敏度、稳定性和良好的动态特性,完全可以满足谷物含水率的测量要求,为谷物含水率的准确、快速和在线测量提供了一种有效的方法。     

在线测量谷物含水率的声学方法

研究了一种测量谷物含水率的声学方法,为实现谷物含水率的在线测量提出了新的途径。通过试验研究,分析得到了流动麦粒碰撞噪声声压与含水率在13～20kHz频率区间的数学关系。在此研究基础上设计的测量系统对京411小麦和农大60玉米进行了实测。试验数据表明,该方法测量精度高、测量重复性好,具有良好的开发应用前景。     

滴灌条件下土壤平均含水率计算方法研究

为寻找适合滴灌农田土壤平均含水率的计算方法,在裸地和大田试验研究的基础上选用单点平均、三点平均等5种方法分别计算了滴灌条件下平均土壤含水率,并以积分法为标准,对其他4种方法进行评价。结果表明,3点取样,采用面积加权平均法计算各层土壤的平均含水率,然后在垂直方向上采用积分中值定理求平均值的方法计算结果更接近真实值,误差最小,可利用该方法计算滴灌农田土壤平均含水率。     

Effects of Product Temperature and Moisture Content on Viscoelastic Properties of Glutinous Rice Extrudates

The viscoelastic properties of glutinous rice flour extruded at moisture contents of 45–55% and barrel temperatures of 75–95°C have been investigated using a small amplitude oscillatory rheometer. High moisture contents (50 and 55%) resulted in product temperatures 3–5°C lower than the barrel temperatures. It appeared that the moisture content was a key element in influencing the value of G′ and tan δ. Raising product temperature reduced the difference in G′ caused by the moisture content. When the product temperature was >85°C, the extrudates yielded a similar degree of gelatinization despite the difference in moisture content. Meanwhile, both G′ and G″ decreased due to the disintegration of starch granules. The relationship between the energy input, measured as specific mechanical energy, and the viscoelastic properties was also assessed.     

Effect of Steeping Treatment on Pasting and Thermal Properties of Sorghum Starches

Chemical treatments in wet milling could improve the physico‐chemical properties of starch isolated from high‐tannin sorghums. Sorghums Chirimaugute (medium‐tannin), DC‐75 (high‐tannin), and SV2 (tannin‐free) were steeped in water, dilute HCl (0.9%, v/v), formaldehyde (0.05%, v/v), and NaOH (0.3%, w/v) solutions before wet milling and starch separation. Pasting, textural, and thermal properties of starch were determined. Steeping in NaOH resulted in starches with higher peak viscosity (PV), cool paste viscosity (CPV), and setback than when water, HCl, and formaldehyde were used. The time to PV (P_time) and PV temperature (P_temp) were markedly reduced by treatment with NaOH. NaOH could have caused a degree of pregelatinization. HCl treatment gave starches with higher P_temp and P _time, presumably due to delayed granule swelling. Gel hardness was largely determined by the starch amylase content. The low hardness of DC‐75 starch gels was slightly improved in NaOH‐treated grains. Gelatinization temperatures of sorghum starches were generally low, regardless of steeping treatment. Starch from NaOH‐treated grain generally had slightly higher gelatinization temperatures than when water, HCl, or HCHO was used. Chemical treatments during steeping of sorghum grains greatly affected starch properties. Dilute alkali steeping during wet milling could be used to improve properties of starch isolated from tannin‐containing sorghums.     

Effect of Moisture Content on the Viscoelastic Properties of Individual Wheat Kernels Evaluated by the Uniaxial Compression Test Under Small Strain

Wheat product quality is related to its physicochemical properties and to the viscoelastic properties of the kernel. The aim of this work was to evaluate the viscoelastic properties of individual wheat kernels using the uniaxial compression test under small strain (3%) to create experimental conditions that allow the use of the elasticity theory to explain the wheat kernel viscoelasticity and its relationships to physicochemical characteristics, such as weight tests, size, and ash and protein contents. The following viscoelastic properties of the kernels of hard and soft wheat cultivars at two different moisture contents (original and tempered at 15%) were evaluated: total work (W_t), elastic work (W_e), plastic work (W_p), and modulus of elasticity (E). There was a significant decrease in W_t as the moisture content increased. In the soft wheat Saturno, W_t decreased 80% (from 0.217 to 0.044 N·mm) as the moisture content increased. Individual wheat kernels at their original moisture content showed higher W_e than under the tempered condition. W_p increased as the moisture content increased. E decreased as the moisture content increased. The soft wheat Saturno showed the highest decline (54.9%) in E (from 14.18 to 6.39 MPa) as the moisture content increased. There were significant negative relationships between the viscoelastic properties and the 1,000‐kernel weight and kernel thickness. The uniaxial compression test under small strain can be applied to evaluate the viscoelastic properties of individual wheat kernels from different classes and cultivars.     

Effect of Corn Moisture on the Properties of Pet Food Extrudates

Corn moisture (9.5–13.5%) was significantly correlated to extrudate properties, even though water was added at the extruder to compensate for the differences in moisture. Water addition was more effective at the preconditioner than at the extruder, and longer retention preconditioner improved expansion. Water added to the pet food formula apparently was absorbed by the other formula ingredients and not the corn. Controlling the specific mechanical energy did not compensate for differences in corn moisture.     

Effect of Particle Size and Moisture Content on Viscosity of Fish Feed

A model was developed for the influence of particle size on the extrusion of a fish feed and the physical characteristics of the extrudates evaluated. The study was conducted using factorial experiments in a fractional replication design for four variables with three levels, and one‐third of the replicates (3⁴ factorial in 27 units) were examined in a laboratory extruder. The torque‐screw speed measurement was used to develop a viscosity model equation that considered different shear rates, product temperature, initial moisture content, and particle size. When particle size decreased, the apparent viscosity became smaller. The barrel pressure was important in producing extrudate with a uniform volume over the range of processing conditions tested because it had a strong correlation with the volumetric expansion. The material with lower moisture and larger particles caused the specific mechanical energy to increase. The viscosity model developed in this study can be applied to the development of large‐scale extrusion models that determine the effect of particle size on the feed material extrudates.     

初始含水率对崩岗土体抗拉特性的影响

针对花岗岩发育的崩岗土体崩壁失稳等问题,通过单轴抗拉试验,研究了湖北通城地区不同初始含水率的崩岗土体抗拉强度特性。结果表明:初始含水率对崩岗土壤抗拉强度影响明显。土壤抗拉强度特征曲线为单峰型,表土层、红土层和红砂过渡层抗拉特征曲线在含水率W_C(24.4%)附近出现抗拉强度峰值,而砂土层在W_C(25.8%)出现抗拉强度峰值。崩岗不同层次土壤轴向拉伸长和径向收缩长随初始含水率呈现正相关关系,且土壤轴向拉伸率和径向收缩率与初始含水率拟合出相关系数较高的线性函数关系(除砂土层的径向收缩率与初始含水率呈指数函数关系)。低(18%～22%)、中(22%～30%)、高(30%～饱和)3种初始含水率区间下崩岗土壤持水机制分别为土壤毛细管持水机制、团粒水桥联结持水机制与团粒持水机制。研究结果可为崩岗科学防治提供一定的科学依据。     

Effect of Ferulic Acid and Catechin on Sorghum and Maize Starch Pasting Properties

The effects of ferulic acid and catechin on starch pasting properties were studied as part of an investigation into the structure and functionality of phenolics in starch‐based products. Commercial maize starch, starches from sorghum cultivars (SV2, Chirimaugute, and DC‐75), and the phenolic compounds ferulic acid and catechin were used in the investigation. Pasting properties were measured using rapid viscosity analysis. Ferulic acid and catechin (up to 100 mg each) were added to maize or sorghum starch (3 g, 14% mb) in suspensions containing 10.32% dry solid content. Addition of catechin resulted in pink‐colored pastes, whereas ferulic acid had no effect on paste color. Ferulic acid and catechin decreased hot paste viscosity (HPV), final viscosity, and setback viscosity of maize and sorghum starch pastes, but had no influence on the peak viscosity (PV) of the former. Both phenolics increased breakdown viscosity. Ferulic acid had greater influence on HPV, final viscosity, breakdown, and setback than catechin. Addition of catechin under acidic conditions (pH 3) decreased HPV, final viscosity, and setback of maize starch, but alkaline conditions (pH 11) slightly increased setback. Both acidic and alkaline conditions resulted in increased breakdown. Investigations on model‐system interactions between ferulic acid or catechin and starch demonstrated that phenolic type and pH level both significantly influence starch pasting properties, with ferulic acid producing a more pronounced effect than catechin. The significance of these interactions is important, especially in food matrices where phenolics are to be added as functional food ingredients.     

前期含水量对机械压实土壤结构特征的影响

使用美国MT865履带式拖拉机对东北典型黑土区耕地土壤进行1,3,8,13次的积累压实试验,通过对土壤硬度、广义土壤结构指数的测定及计算·并结合土壤三相的二维三系图对比分析了不同前期含水量条件下土壤机械压实特征.结果表明:由于表层0-10 cm含水量的不同.相对高含水量的土壤剖面受机械压实的影响范围 较低含水量时深10 cm,且各个层次的土壤硬度增量的变化趋势也相对低含水量时滞后10 cm,从初次碾压开始就体现了积累压实作用,在其压实影响范围内硬度与对照相比提高了22.58%～753.85%;而低含水量的土壤则具有相对较强的抗机械压实的能力,同时发现,在土壤承受能力范围内,适当的压实可以有效调节土壤三相,改善土壤结构;秸秆还田不仅具有传统的蓄水保墒、培肥改土的效用,还可以缓解作业机械对土壤的压实.