Compressive Strength of Wheat Endosperm: Comparison of Endosperm Bricks to the Single Kernel Characterization System

The three major classes of endosperm texture (grain hardness) of soft and hard common, and durum wheat represent and define one of the leading determinants of the milling and end‐use quality of wheat. Although these three genetic classes are directly related to the Hardness locus and puroindoline gene function, much less is known about the kernel‐to‐kernel variation within pure varietal grain lots. Measurement of this variation is of considerable interest. The objective of this research was to compare kernel texture as determined by compression failure testing using endosperm bricks with results of whole‐kernel hardness obtained with the Single Kernel Characterization System 4100 hardness index (SKCS HI). In general terms, the variation obtained with the SKCS HI was of similar magnitude to that obtained using failure strain and failure energy of endosperm brick compression. Objective comparisons included frequency distribution plots, normalized frequency distribution plots, ANOVA model R², and coefficients of variation. Results indicated that compression testing and SKCS HI similarly captured the main features of texture classes but also reflected notable differences in texture properties among and within soft, hard, and durum classes. Neither brick compression testing nor the SKCS HI may be reasonably expected to correctly classify all individual kernels as to genetic texture class. However, modest improvements in correct classification rate or, more importantly, better classification related to end‐use quality may still be achievable.     

Collaborative Analysis of Wheat Endosperm Compressive Material Properties

The objective measurement of cereal endosperm texture, for wheat (Triticum spp. L.) in particular, is relevant to the milling, processing, and utilization of grain. The objective of this study was to evaluate the interlaboratory results of compression failure testing of wheat endosperm specimens of defined geometry. Parallelepipeds (bricks) and cylinders were prepared from individual soft and hard near‐isogenic wheat kernels and compressed in two orientations (parallel and perpendicular to the long brush‐to‐germ axis). Compression curves were used to derive failure stress, failure strain, work density (area under the curve), and Young's modulus. In all five laboratories, the ability to delineate hard from soft wheat endosperm material properties was quite high. Four laboratories compressed endosperm bricks in the same orientation, on edge; texture class (soft vs. hard) was consistently the greatest source of variation in analysis of variance models (F‐values from 417 to 1401, Young's modulus and failure stress, respectively). Failure stress was found to be the best overall means of measuring the difference in what is known in the vernacular as wheat hardness. Across laboratories, the absolute measures of all four material properties ranged on the order of about two‐ to threefold from low to high, although within a laboratory, results were highly consistent. Laboratory by texture class interaction was deemed to be of minor importance. Brick size and moisture content within the ranges tested were not major sources of variation, and cylinders prepared from endosperm produced results similar to those obtained from bricks. The results suggested that wheat endosperm might express some level of anisotropic behavior, as specimens compressed in the kernel orientation parallel to the long axis failed at lower strain and stress values, with lower work density, when compared with kernel orientation perpendicular to the long axis. A key feature of interlaboratory variation was identified as being instrument rigidity, a subject of ongoing research. In conclusion, the preparation of endosperm specimens of defined size and shape, in combination with compression failure testing at low moisture content (<18%), is useful for objectively delineating the phenomenon known as hardness. The study presented here will advance our ability to objectively measure cereal grain texture and the material properties of endosperm.     

Influence of Instrument Rigidity and Specimen Geometry on Calculations of Compressive Strength Properties of Wheat Endosperm

Endosperm texture is one of the most important quality features in wheat; it defines milling energy requirements and end‐use suitability. From an engineering perspective, texture can be quantified by measuring the physical property of the resistance force to crushing of precisely machined specimens of endosperm. In such procedures, cylindrical or parallelepiped blocks are crushed under a constant rate of strain, in which values are reported of maximum stress, strain at maximum stress, Young's modulus, and the energy of compression to the point of maximum stress. Generally overlooked, however, is the instrument itself, which can significantly affect the apparent values of the latter three properties. Because no instrument is infinitely rigid, departures between apparent and actual strength properties occur. In this study, the physical principles for compressive strength measurement with respect to corrections for instrument rigidity are developed. Results show that the departures are exacerbated in specimens of small slenderness ratio and elevated hardness. This issue is demonstrated in a small collaborative study involving three laboratories and three instruments with low, intermediate, and high rigidity. Specimens were prepared from wheat kernels from hard and soft near‐isogenic lines derived from the cultivar Alpowa. For strain at maximum stress, the implementation of a correction for instrument rigidity reduced the range across laboratories from 6.03–47.7% (before correction) to 4.49–7.35% (after correction) for the hard genotype, and the corresponding ranges for the soft genotype were 3.29–18.6% and 2.07–6.01%, respectively. For Young's modulus, instrument rigidity correction resulted in a tenfold correction for the hard genotype measured on the least rigid instrument, going from 0.21 GPa (before) to 4.9 GPa (after). Likewise, with this instrument, the imparted energy density to maximum stress was reduced from an average apparent value of 23 MJ/m³ (before) to 3.8 MJ/m³ (after). Because of these large differences between apparent and actual values for these physical‐strength properties, it is recommended that future strength property measurements should account for instrument rigidity by implementation of the correction procedure described herein.     

糯性胚乳小麦的选育

在自然界,大多数禾谷类作物,如玉米、水稻、高梁、粟、黍子等,都存在糯性类型.但是由于普通小麦是异源六倍体作物,在它的染色体7AS、4AS和7DS 上各有一个基因,即Wx-A1、Wx-B1 和Wx-D1控制Wx蛋白(淀粉粒束缚淀粉合成酶),Wx蛋白与直链淀粉的合成有关.当三个位点基因全部缺失或不表达时不能合成直链淀粉,只有支链淀粉、自然界不存在三个Wx基因同时缺失的小麦.所以迄今为止尚未发现自然界存在的糯性小麦.小麦面粉中直链淀粉含量是决定面条品质的一个重要因素.本研究以"两个部分糯性"材料作亲本,并结合花粉染色、籽粒剖面染色、SDS-PAGE电泳等手段,在杂种后代中选出了若干糯性小麦品系,定名为"农大糯麦"系列.     

Pbf启动子在小麦离体胚乳中的特性分析

为了探明胚乳特异启动子的调控活性，对小麦醇溶蛋白盒结合因子基因（pbf）的启动子序列进行了5´、3´和中间缺失片段-GUS基因嵌合体载体（pbf.a-d）的构建，并在小麦离体胚乳中转化。GUS瞬间表达活性检测和功能缺失试验表明：pbf 的-2510- -1bp全长序列能够在小麦离体胚乳中表现活性，而5´ 端-2510bp- -670bp以及3´端-1288bp- -1bp序列的缺失则使启动子在胚乳中丧失了活性；中间序列-2160bp- -689bp的缺失使GUS的表达强度明显降低。文中对pbf启动子序列中存在的重要基序种类和数量以及基序对启动子表达调控活性的作用也给予了初步分析。本文对小麦胚乳发育状态及GUS瞬间表达体系等对pbf启动子活性检测的影响也作了探讨。     

N‐Terminal Amino Acid Sequence Analysis of Endosperm Proteins in Japanese Hexaploid Wheat

Semidry electroblotting is convenient and allows a rapid and efficient protein transfer from two‐dimensional polyacrylamide gel electrophoresis (2D‐PAGE) gels onto sequencer stable supports for protein microsequence analysis in a gas‐phase sequencer. Using this technique, I determined the amino acid sequences of the endosperm proteins in Japanese hexaploid commercial wheats (Triticum aestivum). Based on sequence determination of the Japanese hexaploid wheats, the endosperm protein could be easily characterized. Wheat endosperm protein, extracted in the presence of 2‐mercaptoethanol and SDS, fractionated into many protein polypeptides using 2D‐PAGE under dissociating conditions. These components were grouped into HMW glutenin subunits, α‐, β‐ or γ‐gliadins, and novel protein polypeptides by using the N‐terminal amino acid sequences. The novel endosperm protein polypeptides were detected, and two new types of N‐terminal amino acid sequences have been found for protein poly‐peptides. These polypeptides have much faster electrophoresis mobility during 2D‐PAGE and are therefore probably a much smaller size than any other peptides of endosperm protein groups found in hexaploid wheat. Ten protein polypeptides have been purified from cultivars of Japanese wheat. Some differences in the contents of amino acids for four protein polypeptide spots were apparent in Japanese wheat.     

Endosperm Structural Changes in Wheat During Drying of Maturing Caryopses

A transmission electron microscopic (TEM) study was conducted on maturing wheat to determine the sequences of events involved during the drying of preripe starchy endosperm. Field‐grown hard red winter wheat Karl and soft red winter wheat Clark were harvested at 21 days after flowering (DAF) and air‐dried in the spike at 20°C for 2, 4, 8, 12, 24, 48, and 96 hr and until completely air‐dried (7 days). Fresh samples of Karl and Clark were also harvested and prepared immediately for microscopy. Both wheat cultivars underwent similar changes during drying. Few changes were observed during the first 8 hr of drying. By 12 hr after the start of drying, the rough endoplasmic reticulum (RER) was distended and circularized. Protein bodies were irregular in shape and small autophagic vacuoles were found in the cytoplasm. An amorphous material was first observed in areas of the cytoplasm after 24 hr of drying. RER was typically associated with those regions. Endosperm tissue looked nearly mature after 48 hr of drying. Artificially induced senescence caused by harvesting wheat spikes prematurely caused the endosperm tissue to undergo a number of changes that resulted in the tissue looking normal when compared with wheat that was not prematurely harvested. This suggests that the wheat plant has great capacity to develop normally when subjected to environmental stresses. The methods used in this study can be used to investigate endosperm structural changes caused by adverse environmental stress.     

Rapid Size‐Exclusion Chromatography Analysis of Molecular Size Distribution for Wheat Endosperm Protein

A quick method for the separation of the main size classes of wheat endosperm proteins using size‐exclusion HPLC is presented. Separations achieved in a 10‐min run showed high correlation with the reference method of our laboratory (35‐min) using the same type of column. The clear separation obtained allows a quick analytical determination of important parameters such as the proportion of the main classes of wheat endosperm protein, the glutenin‐to‐gliadin ratio, and the percentage of unextractable (SDS‐soluble with sonication) polymeric protein, all of which have been closely correlated with breadmaking quality parameters. The improved method offers the advantages of better utilization of valuable resources such as HPLC equipment, quicker analysis of large sample sets, and collection of eluted fractions.     

黄麻纤维加筋崩岗岩土的无侧限抗压强度研究

为深入了解黄麻纤维加筋崩岗岩土在增强崩岗抗压强度和提高其稳定性的作用机理,采用两因素随机区组设计试验研究了筋土复合体的应力-应变及无侧限抗压强度特性,探讨了黄麻纤维不同数量、不同分布方式下的筋土抗压强度。结果表明:崩岗的四层土体分别具有不同的最优加筋条件,即黄麻纤维数量和分布方式不同,且四层土体最优加筋条件下的无侧限抗压强度分别较未加筋土样提高7.97%、19.24%、15.35%、42.88%。最优加筋条件下淀粉处理黄麻纤维的研究表明:纤维经过淀粉处理养护不同时间后,四层筋土复合体的抗压强度与养护时间达到了显著相关,分别在养护时间的7、7、5、3d后达到最大,分别提高14.45%、15.07%、8.90%、8.07%。崩岗侵蚀预防和治理时分层修复的新思路将为崩岗区侵蚀防治工作的开展提供重要的科学依据。     

Mechanical and Physicochemical Characterization of Vitreous and Mealy Durum Wheat Endosperm

The mechanical, physical, and biochemical characteristics of mealy and vitreous endosperm were investigated. Endosperm were obtained from four durum wheat cultivars grown under different nitrogen fertilization designs. The textural properties and the density of the endosperm were measured on hand‐shaped parallelepiped endosperm samples. Endosperm protein content and composition and also gliadin composition were investigated by HPLC. Mechanical tests showed that mealy and vitreous endosperm differed in hardness and vitreousness. Vitreousness increased with nitrogen fertilization supply whereas there was no variation among the different cultivars. Hardness seemed to be linked to genotype and insensitive to nitrogen supply. From this result, we concluded that hardness and vitreousness are not related. Endosperm protein content and gliadin‐to‐glutenin ratio were related to nitrogen supply and increased especially when nitrogen supply was applied at flowering. At the same time, endosperm vitreousness increased. Further biochemical analyses were performed on 270 kernels, mealy or vitreous, hand‐picked from 148 different crops. Results showed that protein content of vitreous endosperm exceeded 9.7% in >90% of the cases. The glia/glu ratio was a less accurate predictor of kernel vitreousness, indicating that, by itself, it cannot account for the change in kernel vitreousness. Endosperm vitreous texture would rise above a threshold content of 9.7% protein within the endosperm.     

Molecular Structure and Organization of Starch Granules from Developing Wheat Endosperm

Wheat starches isolated from seeds harvested between 7 and 49 days after anthesis (DAA) were fractionated into large (>8 μm) and small (<8 μm) granules and studied for starch structure and architecture. Starch granules at 7 DAA possessed unimodal size distribution, whereas it was bimodal at later maturity stages. The apparent amylose fraction of starch granules at early maturity (7 and 14 DAA) consisted of intermediate‐type materials, whereas starch at later maturity stages (28 and 49 DAA) contained branched amylose. Wide‐angle X‐ray scattering (WAXS) revealed a well‐developed polymorphic structure already at 7 DAA. Although the presence of a small proportion of B‐type crystallites mixed with A‐type crystallites was observed in the X‐ray diffractogram of starches at early maturation (7 and 14 DAA), it was masked by the A‐type crystallites at later maturity stages. However, the large granules had a higher proportion of B‐type crystallites and lower relative crystallinity (RC) than their small‐granule counterpart. The iodine absorption properties of the starch granules demonstrated different levels of mobility of the starch polymers at different stages of maturity and the mobility of more glucan polymers in the large granule population compared with the small granules at the same maturity stage. Iodine did not change the characteristic A‐type crystalline pattern of starch, but it increased RC. Changes in peak width at half height based on WAXS data further suggested the possible interaction of iodine with amylopectin intercluster chain segments and branch chains in formation of inclusion complexes.     

Separation and Characterization of A- and B-Type Starch Granules in Wheat Endosperm

Mature wheat (Triticum aestivum L.) endosperm contains two types of starch granules: large A-type and small B-type. Two methods, microsieving or centrifugal sedimentation through aqueous solutions of sucrose, maltose, or Percoll were used to separate A- and B-type starch granules. Microsieving could not completely separate the two types of starch granules, while centrifuging through maltose and sucrose solutions gave a homogenous population for B-type starch granules only. Centrifuging through two Percoll solutions (70 and 100%, v/v) produced purified populations of both the A- and B-type starch granules. Analysis of starch granule size distribution in the purified A- and B-type granule populations and in the whole-starch granule population obtained directly from wheat endosperm confirmed that the purified A- and B-type starch granule populations represented their counterparts in mature wheat endosperm. Centrifugations through two Percoll solutions were used to purify A- and B-type starch granule populations from six wheat cultivars. The amylose concentrations and gelatinization properties of these populations were analyzed. All of the A-type starch granules contained higher amylose concentrations and had higher gelatinization enthalpies than did B-type starch granules. Although A- and B-type starch granules started to gelatinize at a similar temperature, B-type starch granules had higher gelatinization peak and completion temperatures than did A-type starch granules     

混掺小麦秸秆对不同土壤育苗砖蒸发的影响

育苗砖能为植物营造一个良好的生长环境,引导植物根系的发育和生长,且苗的移栽不受时间限制。对红黏土、黄绵土、山地白土和黑麻土分别添加0%,5%,8%和10%的小麦秸秆后制得育苗砖,并对其进行蒸发试验。在相同土壤下测得它们蒸发量大小顺序为:混掺0%小麦秸秆的育苗砖>混掺5%小麦秸秆的育苗砖>混掺8%小麦秸秆的育苗砖>混掺10%小麦秸秆的育苗砖。结果表明,混掺小麦秸秆对育苗砖蒸发影响显著,而且秸秆混掺比例越大蒸发量越小,故添加秸秆可有效减少育苗砖的蒸发损失。混掺相同比例小麦秸秆的不同土壤育苗砖,蒸发量大小顺序为:红黏土育苗砖>黑麻土育苗砖>山地白土育苗砖>黄绵土育苗砖。综合分析来看,混掺10%小麦秸秆的黄绵土育苗砖蒸发损失最小。     

Hydration Dynamics of Durum Wheat Endosperm as Studied by Magnetic Resonance Imaging and Soaking Experiments

The precise knowledge of the kinetics of water transport in durum wheat endosperm is a prerequisite for the optimization of wheat processing techniques like pasta dough mixing on a fundamental basis. Pieces of endosperm were cylindrically cut, prepared from durum wheat kernels, and used to study the water uptake by applying a gravimetric method and magnetic resonance imaging (MRI). The total water uptake of endosperm cylinders at different soaking times was determined by gravimetric soaking experiments and revealed a swelling limit of ≈40 g/100 g wb after 60 min. With these results it was possible to estimate an apparent diffusion coefficient of water in durum endosperm by using numerical simulation based on a diffusion model (D_25°C ~ 0.76 × 10^–10 m²/sec). MRI was used to quantify the water distribution in the endosperm cylinders over time at excess and limited water conditions. The calibration of MRI for the quantification of local and time‐dependent water contents was successful by correlating the spin‐spin relaxation time (T₂) with the water content of calibration samples at intermediate moisture levels (19–45 g/100 g wb). Water content maps were generated and showed the kinetics of water distribution inside the endosperm cylinders up to equilibrium conditions. The water uptake of the endosperm cylinders over time, as measured by MRI, fitted well to the water uptake as determined gravimetrically in soaking tests, which validated the applied MRI calibration and measurement procedures. The results allow the quantitative prediction of water transport properties of durum wheat endosperm during moistening procedures.     

养护龄期对改良膨胀土无侧限抗压强度试验的影响

以湖北省宜昌市某公路膨胀土为研究对象,分别采用不同掺量的石灰、水泥、粉煤灰、风化砂对膨胀土进行改良。在经过7,14和28d标准条件养生后,进行无侧限抗压强度试验。试验结果表明,上述4种材料均能有效地提高改良膨胀土的无侧限抗压强度,在最初的14d内,水泥改良膨胀土的强度增长较为明显,后期随着养护龄期的增长,无侧限抗压强度增长速率较缓慢;石灰改良膨胀土的无侧限抗压强度值随着养护龄期的增加,一直保持近似直线形的增长趋势;粉煤灰改良膨胀土的无侧限抗压强度亦随着养护龄期的增长而呈直线增长,但其值小于石灰改良膨胀土;养护龄期对风化砂改良膨胀土的无侧限抗压强度影响很小。     

黄麻纤维加筋条件对崩岗岩土无侧限抗压强度的影响

借鉴剑麻等天然纤维加筋土的研究成果,初步确定包括加筋长度、加筋率、加筋位置3种因素的崩岗岩土黄麻纤维加筋条件,通过无侧限抗压强度试验和正交试验设计方法,选出崩岗不同层次土体的最优加筋条件为红土层01:加筋长度为15mm,加筋率为0.35%,加筋位置为整体加筋;红土层02:加筋长度为15mm,加筋率为0.25%,加筋位置为上部加筋;砂土层03:加筋长度为15mm,加筋率为0.35%,加筋位置为整体加筋;碎屑层04:加筋长度为15mm,加筋率为0.30%,加筋位置为下部加筋。通过对比黄麻纤维加筋土和未加筋土的应力应变特性,结果表明:在最优加筋条件下崩岗4层土体的无侧限抗压强度比未加筋土体分别提高了27.81%,29.73%,23.26%,39.58%;未加筋土无侧限抗压强度与加筋土无侧限抗压强度存在线性回归关系(R~2=0.977 9);同时黄麻纤维加筋还限制了土体的横向变形。研究成果为利用生物材料改良崩岗岩土力学性质,提高崩岗稳定性提供科学依据。     

干湿循环对崩岗不同层次土体无侧限抗压强度的影响

针对发育于花岗岩出露区的崩岗土体易受干湿循环影响导致大量崩壁失稳等问题,通过开展一系列室内无侧限抗压强度试验,研究崩岗不同层次土体在干湿循环作用下无侧限抗压强度的变化规律,并且建立了在崩岗不同层次土体深度比和干湿循环次数共同影响下的无侧限抗压强度模型。结果表明:表土层、红土层、斑纹层、碎屑层在第1次干湿循环后无侧限抗压强度衰减幅度最大,分别为26%,15%,40%和49%;在第2~4次干湿循环后无侧限抗压强度衰减幅度逐渐减小;在第5次干湿循环后无侧限抗压强度基本保持不变;随着干湿循环次数的增加,崩岗不同层次土体无侧限抗压强度总体表现为表土层红土层斑纹层碎屑层;在不同干湿循环次数下,崩岗不同层次土体的应力—应变曲线总体上呈应变软化型且应变为2%时达到峰值,但红土层在3次干湿循环时的应力—应变关系曲线局部波动性较强;无侧限抗压强度模型中预测值与实测值之间具有显著(R2=0.91)的相关关系,该模型在预测干湿循环对通城地区崩岗不同层次土体无侧限抗压强度影响中具有较高的应用价值。     

Relationship of Dough Extensibility to Dough Strength in a Spring Wheat Cross

A negative relationship between dough strength and dough extensibility would pose a problem for breeding hard wheats, as both dough strength and dough extensibility are desirable. We derived 77 recombinant inbred lines (RIL) from a cross between hard red spring wheat cultivars McNeal and Thatcher. McNeal produces flour with stronger dough and lower extensibility than does Thatcher. RIL were evaluated for strength‐related properties using mixograph analysis and extensibility parameters using the Kieffer attachment to the TA.XT2 texture analyzer. Additionally, the RIL were test baked. Measurements using the mixograph and the Kieffer attachment were highly heritable. Maximum dough extensibility (Ext_max) was negatively correlated with resistance to extension (R_max) (r = ‐0.74) and with mixograph tolerance (r = ‐0.45). Loaf volume was correlated with both R_max (r = 0.42) and area under the extensigraph curve (r = 0.44) based on partial correlation analysis adjusted for protein differences. Ext_max was negatively correlated with loaf volume (r = ‐0.26). The McNeal allele for polymorphism at the Gli1‐B1 locus on chromosome 1BS caused high dough‐mixing tolerance and low dough extensibility. Our results suggest that traditional selection criteria in hard red spring wheat, including tolerance to dough mixing and high loaf volume, may result in reduced dough extensibility.