Study of the microstructure of durum wheat endosperm using X-ray micro-computed tomography

Durum wheat grains are used for producing food, such as pasta or couscous. The grain mechanical properties which are linked to its internal micro-structure (i.e. endosperm porosity) are known to determine its ability to produce semolina during milling. The proportion of grains having porous endosperm in a batch appears therefore as a critical quality factor for the durum wheat value chain. Our objective was to investigate the ability of X-ray micro-tomography (μCT) method to describe the porous or vitreous counterpart structures in the endosperm of durum wheat grains. We selected two different durum wheat samples displaying vitreous or partially porous endosperms. The grains were analyzed using μCT at two pixel sizes (1 μm or 7 μm). The μCT data collected at 7 μm pixel size were used for qualitative classification of grains according to apparent distribution curve of the porosity parameters. Analysis of μCT images at 1 μm pixel size allowed us to propose pore size classification in the vitreous and porous parts of the endosperm in three durum wheat grain. Results are used to better describe the durum-wheat endosperm microstructure, but requires long scanning periods.     

Fracture Mechanics of Vitreous and Mealy Wheat Endosperm

The concepts of fracture mechanics have been applied to quantify the fracture behaviour of vitreous and mealy wheat endosperm in a single wheat cultivar. Two new techniques were developed and used to measure fracture toughness (energy per unit area of fracture) of individual grains: (1) load cycling of a notched grain; and (2) instrumented microtome cutting. The load cycling method gave average fracture toughness values for vitreous endosperm of 130 ± 42 J/m² and 50 ± 12 J/m² for mealy endosperm. Fracture toughness measured using the instrumented microtome gave values of 159 ± 7·4 J/m² for vitreous endosperm and 44 ± 4·6 J/m² for mealy endosperm. The results are consistent with the hypothesis that vitreous endosperm has stronger starch-protein matrix bonding than mealy endosperm. The effect of changing grain moisture on cutting fracture properties was investigated. As moisture decreased, values of fracture toughness increased for both mealy and vitreous endosperms at the same rate down to 11% moisture content, below which fracture toughness increased more rapidly for vitreous than for mealy endosperm. Intra-grain fracture toughness was also investigated by cutting successive sections across individual wheat grains. These showed a decrease in cutting force from the outside of the grain towards the centre, and then an increase near the crease. The critical particle size at which a transition from brittle to ductile failure occurs was calculated, giving predicted values of 1·2 mm for vitreous endosperm and 0·9 mm for mealy endosperm at 15% moisture content. This shows that vitreous endosperm undergoes more ductile deformation during deformation than does mealy endosperm, and that larger particle sizes are predicted for vitreous endosperm as a result of milling.     

授高油玉米花粉对普通玉米子粒胚乳细胞增殖及灌浆特性的影响

以高油115为授粉者,与2个普通玉米杂交种进行杂交,用Richards模型拟合胚乳细胞增殖过程和子粒灌浆过程,以胚和胚乳的贡献率、胚乳细胞增殖参数、子粒灌浆参数和子粒的充实状况来评价授高油玉米花粉对普通玉米粒重的影响。结果表明,授高油玉米花粉后普通玉米粒重有增有减,主要原因是胚乳重量的增加或减少所致。增产组合(ND108×HOC115)与自交相比粒重增加的部分中胚乳的贡献率为70.51%;减产组合(LY20×HOC115)与自交相比粒重降低的部分中胚乳的贡献率为-85.46%。增产组合(ND108×HOC115)起始分裂势(R_o)增加、最大增殖速率(G_max)升高、胚乳细胞增殖速率最大时胚乳细胞数(W_max)增多、平均增殖速率(G_average)增加、胚乳细胞活跃分裂期(D)缩短;减产组合(LY20×HOC115)则表现出相反的趋势。通过增加胚乳细胞数量和提高胚乳质量是进一步提高授高油玉米花粉后普通玉米产量的根本途径。     

Endosperm Texture in Wheat

One of the fundamental means of classifying wheat is through its endosperm texture. It impacts significantly on the milling process affecting among other things flour particle size and milling yield. Hardness in wheat is largely controlled by genetic factors but it can be affected by the environment and factors such as moisture, lipid, and pentosan content. The principal genetic locus controlling endosperm texture in wheat, Ha, is located on the chromosome 5D. At this locus several genes, notably the puroindolines, have been identified. Puroindolines are the major components of the 15 kDa protein band associated with starch granules that is more abundant in soft wheats than in hard. Recently the puroindolines have been shown to enhance grain hardness in rice. In this review we discuss the structure of hard and soft wheat endosperm with particular emphasis on when differences in endosperm texture can be detected in the developing seed. The role of the environment and other factors that may affect the endosperm texture is also examined together with the role of the puroindoline genes at theHa locus. Finally, we compare endosperm hardness in wheat and in barley.     

Variability in dehydrodiferulic acid composition of durum wheat (Triticum durum Desf.) and distribution in milling fractions

The dehydrodiferulic acid content of different common and durum wheat grains and milling fractions was determined by an HPLC procedure. The 8-O-4′, 5–8′ benzofuran, 5–8′ and 5-5′ dehydrodimers were identified in all samples studied and occurred in decreasing relative amounts, respectively. Durum wheats were twice as concentrated in dimers as common wheats. An important genetic variation for dehydrodiferulic acid content was shown within durum wheat grains, whereas the agronomic conditions had no effect. There was 10 to 20 times more dehydrodiferulic acids in external layers (aleurone, bran) than in the starchy endosperm of durum wheat grains. The content and composition in dimers of the inner endosperm did not vary according to genotypes and cultivation conditions. The ratio of dehydrodimers to monomers of ferulic acid which represented an index of dimerisation, was 1·6 times higher in the external layers of the grain than in the endosperm. No relation was found, however, between the degree of ferulic acid dimerisation and the milling behaviour of durum wheat grains.     

施氮量对两个粒型小麦品种籽粒胚乳细胞增殖及糖含量的影响

为了解小麦胚乳细胞增殖、糖代谢在粒型间的差异及氮营养的调控效应,2009-2010年度以大粒型品种郑育麦9987和小粒型品种郑麦004为材料,研究了施氮量对小麦籽粒胚乳细胞增殖、细胞壁转化酶活性及糖含量的影响。结果表明,郑育麦9987胚乳细胞数(11.92×105)较郑麦004(10.73×105)多11.1%。施氮量影响籽粒胚乳细胞数,其中郑育麦9987低氮处理(150kg·hm-2)的胚乳细胞数目较高氮处理(300kg·hm-2)增加29.1%,而郑麦004则表现为高氮处理较低氮处理增加44.7%。两品种籽粒细胞壁转化酶活性均于花后5~8d达到峰值,花后20d则降到较低水平;籽粒可溶性糖和蔗糖含量均随灌浆进程整体呈先上升后下降趋势,在花后25d有一个小波峰。增施氮肥可增加籽粒细胞壁转化酶活性,提高后期籽粒可溶性糖和蔗糖含量。表明增施氮肥有利于小麦籽粒胚乳细胞增殖、光合产物的积累与运转,从而提高了粒重。     

Influence of solar drying and storage conditions on microstructure,crack propagation and nano-hardness of paddy and wheat

The influence of hybrid solar drying (HSD) and storage conditions on microstructure, crack propagation, nano-hardness and milling indices of paddy and wheat grains were investigated. Milling yield and head rice yield of dried paddy was 71.48% and 72.42%, which was further increased by 1–1.26% and 3.12–4.65%, respectively. Flour yield from dried wheat was found to be 77.30% and was reduced by 3.5–7.7% after 180 days of storage. Maximum nano-hardness of 0.15 ± 0.02 GPa was obtained for rice stored at 5 °C, whereas, for wheat, nano-hardness, elastic modulus, and peak load values gradually reduced with a storage time of 180 days. Micro-X ray computed tomography images revealed the pore size of paddy and wheat samples to be in the range of 0.01–0.8 mm³. Micrographs showed a compact paddy surface, whereas wheat endosperm witnessed cell disruption and agglomeration.     

Genetic and Agronomic Variation in Arabinoxylan and Ferulic Acid Contents of Durum Wheat (Triticum durumL.) Grain and Its Milling Fractions

Total arabinoxylan (AXt), water-extractable arabinoxylan (WeAX) and ferulic acid (FA) from five cultivars of durum wheat (Triticum durumL.), grown under four different agronomic conditions, were measured. Among the varieties analysed, AXt, WeAX and FA contents ranged between 4·07%–6·02%, 0·37%–0·56% and 0·784 mg/g–7·98 mg/g, respectively. High genetic and agronomic variability was detected for AXt, WeAX and FA. AXt and FA increased sharply in milling products for extraction rates above 60%. FA was quantified in durum wheat milling fractions. High concentrations of FA esterified to cell-wall arabinoxylans were found in the aleurone layer (69% of total FA), germ and seedcoat (26·6% of total FA). Only trace amounts were detected in the starchy endosperm (1·4% of total FA). A highly significant correlation appeared between AXt and FA contents.     

Wheat endosperm cell walls: Spatial heterogeneity of polysaccharide structure and composition using micro-scale enzymatic fingerprinting and FT-IR microspectroscopy

Micro-scale enzymatic fingerprinting and FT-IR microspectroscopy were used to investigate changes of polysaccharide structure and composition in cell walls from wheat endosperm. These methods were applied to transverse and longitudinal sections of wheat grains harvested at maturity and 270°D. Principal component analysis treatment of the data revealed marked differences in the (1,3)-(1,4)-beta-glucans (BG)/arabinoxylans (AX) ratio and in the structure of AX depending on both cell position in the grain and stage of development. Cell walls close to the germ were enriched in BG in both developing and mature grain. AX in developing grain were characterized by a higher proportion of di-substitution by arabinose as compared to mature grain AX. In addition, AX in mature grains exhibited a different structure depending on prismatic or central origin of cell walls in the grain. These results indicated a high spatial and temporal control of the biosynthesis of AX and BG in wheat endosperm.     

Evaluation of roller milling potential of amaranth grains

In the present study roller milling potential of amaranth grains was evaluated. The conditioning moisture influenced the millability of the amaranth grain. The results showed that the coarse seed coat (CSC) fraction increased from 12.91 to 38.33% with increase in conditioning moisture of the grains from 11 to 18.5%. The nutrients were more concentrated in the CSC fraction, while flour (FL) fraction showed low protein, ash, fat and dietary fiber contents. As the grain moisture content was increased from 11.0 to 15.5%, the yield of flour decreased with improvement in the brightness values. CSC showed higher values for redness and yellowness and lower values for brightness compared to other milled fractions. CSC had the highest water and oil holding capacities with the values of 410 g/100 g and 215 g/100 g respectively. The swelling power was also higher for CSC and fine seed coat (FSC) fractions. Among milled fractions, highest pasting temperature of 75.9 °C and peak viscosity of 212 BU was recorded for CSC and FL fractions respectively. These results showed that the roller mill can be used for milling amaranth grains to produce fractions rich in nutrients with unique functional properties.     

Localisation of iron in wheat grain using high resolution secondary ion mass spectrometry

Insufficient iron (Fe) is one of the most prevalent micronutrient deficiencies in humans, with billions of people affected. Cereal grains are an important source of Fe for humans but the bioavailability of Fe in cereals is generally low. Information regarding the cellular and sub-cellular localisation of Fe in wheat grain will aid optimising nutrient delivery for human health. In this study high resolution secondary ion mass spectrometry (NanoSIMS) was used to map the distribution of Fe in the aleurone layer and in the endosperm of immature wheat grain. Iron was shown to be localised strongly in the phytin globoids in the aleurone cells and to a lesser extent in the cytoplasm around the starch granules in the endosperm.     

改进压痕加载曲线法测定小麦籽粒各组分硬度及其仿真验证

为检验谷物籽粒压痕加载曲线法优化改进后对单个谷物籽粒硬度的测定效果,应用改进的压痕加载曲线法对小麦品种西旱2号籽粒各组分(胚、胚乳、麦皮)的硬度进行测定和分析。结果表明,含水率为15.6%的小麦籽粒各组分中麦皮硬度最大,硬度值为38.52~42.48 MPa,胚乳硬度次之(21.94~22.76MPa),胚的硬度最小(10.64~11.96 MPa)。运用有限元法建立小麦籽粒各组分的力学模型,证实改进压痕加载曲线硬度检测方法对小麦籽粒各组分硬度值的测定具有可行性,准确性较高。     

氮密互作对淮北砂姜黑土区冬小麦冠层光合特性和产量的影响

为筛选出适合淮北平原砂姜黑土区小麦稳产高产栽培的氮密配置,在大田条件下以安农0711(AN0711)和烟农19(YN19)为试验材料,采用裂区设计,设置150×10~4、210×10~4、270×10~4和330×10~4株·hm~(-2)4个种植密度(分别用D1～D4代表),以及135、180、225和270 kg·hm~(-2)4个施氮水平(分别用N1～N4代表),分析了氮密互作对冬小麦冠层结构、光合特性和籽粒产量的影响。结果表明,氮密互作可改善小麦冠层结构,显著影响冠层光合特性。旗叶净光合速率和叶绿素相对含量随着种植密度的增加而降低,而随着施氮量的增加而增加,但施氮量超过225 kg·hm~(-2)时变化均不显著。随着种植密度和施氮量的增加,叶面积指数和冠层截获光合有效辐射显著提高,且在孕穗期和开花期均以D4N4处理最大,灌浆中期均以D3N3处理最大。氮密对籽粒产量有显著的互作效应。在D3N3处理下AN0711和YN19的冠层光合能力和籽粒产量均最高,其中产量分别达到7 866.67和7 400.00 kg·hm~(-2)。在本试验条件下,适宜的种植密度和施氮量分别为270×10~4株·hm~(-2)和225 kg·hm~(-2)。     

测墒补灌条件下施氮量对小麦干物质积累转运和产量的影响

为筛选测墒补灌节水条件下实现小麦高产和氮素高效利用的最优施氮量,以小麦品种烟农1212为材料,在拔节期和开花期将0~40 cm土层土壤相对含水量补灌至70%条件下,设置0、120、180和240 kg·hm^-2施氮量处理（分别用N0、N1、N2和N3代表）,分析施氮量对测墒补灌小麦旗叶光合特性、干物质积累与转运和氮素利用率的影响。结果表明,N2处理下小麦花后7~28 d旗叶光合性能显著高于N0和N1处理,但施氮量增至N3时光合性能无显著变化。N2处理的营养器官花前贮藏干物质在花后向籽粒的转运量显著高于其他处理;花后光合同化物积累量显著高于N0和N1处理,但与N3处理无显著差异。成熟期N2处理干物质在籽粒中的分配比例较N0和N1处理分别高5.00和2.86个百分点。N2处理的籽粒灌浆持续时间和活跃灌浆期长,最大灌浆速率下粒重高,籽粒产量较N0和N1处理分别高41.01%和22.44%,且氮肥农学效率最高,氮肥偏生产力较高。综合考虑,180 kg·hm^-2施氮量为测墒补灌节水条件下最佳施氮量。     

立体匀播和密度对冬小麦光合、干物质积累分配及产量的影响

为给小麦立体匀播栽培推广提供理论依据,选用小麦品种新冬22号和新冬46号为供试材料,采用裂区设计,主区种植方式设立体匀播和常规条播2个处理,副区种植密度设150万株·hm~(-2)(D_(150))、225万株·hm~(-2)(D_(225))、300万株·hm~(-2)(D_(300))和375万株·hm~(-2)(D_(375))4个处理,研究了种植方式和密度对冬小麦光合、干物质积累与分配、产量及其构成因素的影响。结果表明,与常规条播比较,立体匀播方式下小麦群体生育后期中、下部叶的LAI、SPAD值和净光合速率显著提高;植株重、干物质转运量、干物质转运效率和干物质转运对籽粒产量贡献率增大,而植株成熟期营养器官干物质分配率降低;随着种植密度增大,茎鞘干物质分配率上升,叶片干物质分配率减小,而颖壳及穗轴、籽粒干物质分配率则无显著变化。与常规条播相比,立体匀播方式下新冬22号和新冬46号主茎穗粒重平均降低7.95%和4.43%,而分蘖穗粒重平均提高11.54%和5.06%,穗数显著提高(17.31%和17.68%),产量提高6.40%和9.84%,以D_(225)处理产量最高;穗粒数分别降低2.23%和1.71%,千粒重分别降低4.38%和4.54%。由此可知,立体匀播方式提高了小麦群体生育后期中、下部叶片叶面积指数和净光合速率,增大了植株干物质积累量,促进了营养器官干物质向分蘖穗籽粒中转运,并主要通过增加群体穗数和分蘖穗穗粒重提高产量;最佳的种植密度为225万株·hm~(-2)。     

Changes in common wheat grain milling behavior and tissue mechanical properties following ozone treatment

Ozone treatment (10 g/kg) of common wheat grains with a new patented process, Oxygreen^®, used before milling was found to significantly reduce (by 10–20%) the required energy at breaking stage whatever the grain hardness and without changes in the flour yield. Detailed study of each of the milling steps undertaken on a hard type cultivar showed that both the breaking and the reduction energy were decreased. Reduction of the coarse bran yield was also observed concomitantly with an increase in the yield of white shorts. Biochemical characterization of the milling fractions pointed out changes in technological flour properties as starch damage reduction, aleurone content enrichment and increase of insoluble glutenin polymers. Measurement of wheat grain tissue mechanical properties showed that ozone treatment leads to reduction of the aleurone layer extensibility and affects the local endosperm resistance to rupture. These data as well as the direct effect of ozone oxidation on biochemical compounds could explain the observed changes in milling energy, bran and shorts yield and flour composition.     

Milling efficiency of triticale grain for commercial flour production

Triticale is a high yielding cereal grain, however low milling yields have discouraged its utilisation as a wheat alternative in processed flour products. This research investigated the role of hardness, grain size and tempering moisture on milling yields in modern triticale genotypes which do not exhibit shrivelled grain morphology. Replicate samples of three triticale varieties grown in two environments with a bread wheat standard were milled at five moisture contents. Both milling yield and ash content increased with decreasing tempering moisture in all genotypes. Triticale milling yield was between 7.1% and 10.1% less than wheat when tempered between 11% and 15% moisture respectively. The very hard textured triticale exhibited extremely low milling yield, similar to durum wheat. The ratio of ash in flour compared to bran was greater in triticale and the ash content of triticale flour could not be reduced to the level of wheat by alteration of tempering moisture. Surface area of larger triticale grain may also influence ideal tempering moisture, however further investigation is required. Milling yields and flour protein content in triticale can be improved by tempering triticale to lower moisture content, provided high ash content is not considered unfavourable in the final product.     

离体穗培养条件下C、N供给对小麦穗粒数、粒重及蛋白质含量的影响

为探究C、N供给时期和供给水平对小麦籽粒建成及蛋白质含量的影响,以冬小麦品种济麦22为材料,采用离体穗培养的方法,设置了三个蔗糖浓度(C1:20 g·L-1;C2:40 g·L-1;C3:80 g·L-1)和四个硝酸铵水平(N1:0.57g·L-1;N2:1.14g·L-1;N3:2.28 g·L-1;N4:4.56g...     

Wheat class identification using monochrome images

Wheat class identification by bulk sample analysis using a machine vision method would be helpful for automation of grain handling, binning and shipping operations in grain elevators. A machine vision system with a monochrome camera was used to identify eight western Canadian wheat classes at four moisture levels (11%, 14%, 17% and 20% wet basis) by bulk sample analysis (n=100 images for each group of samples). Grayscale images (1024×768 pixels) of the grain bulk were captured by the monochrome camera, and stored on a data acquisition system. Algorithms were developed to extract 32 textural features automatically from the grayscale images. The mean gray values of the western Canadian wheat classes ranged between 106 and 143, and it was the highest for Canada Prairie Spring Red and the lowest for Canada Western Extra Strong and Canada Western Red Winter. The mean gray values of the wheat samples were significantly higher at 17% moisture content and lower at 11% moisture content among the tested moisture levels (α=0.05). The overall classification accuracies of a quadratic discriminant function were 93.8%, 92.5%, 92.0% and 94.4% when the wheat classes were at 11%, 14%, 17% and 20% moisture contents, respectively. Similarly, the accuracies of a linear discriminant function were 96.1%, 95.0%, 95.4% and 96.3% at 11%, 14%, 17% and 20% moisture contents, respectively. When the wheat classes were identified irrespective of moisture levels (images of the four moisture level grains in each class were mixed together), the accuracy was 89.8% and 85.4% for quadratic and linear discriminant functions, respectively. A monochrome image analysis system has the potential to use for online identification of classes in wheat handling facilities. However, further research is required to determine the performance of the developed method for impurities in bulk grain such as foreign material and dockage.     

Analysis of the milling reduction of bread wheat farina: Physical and biochemical characterisation

The reduction of coarse farina during milling from five representative hard and soft French bread wheat cultivars was followed step by step. Particle size distribution of the milled products and energy required to dissociate wheat farina revealed large differences between cultivars. A grinding index (required energy to produce 1 kg of flour), K′, corresponding to the energy necessary to obtain a given amount of flour, was found to be related with both grain hardness and vitreousness. Analysis of particle size distribution suggested a major influence of hardness in the production of fine particles <50 μm during the reduction process. On the other hand, vitreousness appeared to impact on the extent of coarse particle size reduction. Differences in farina reduction behaviour of the wheats analysed were related to their endosperm mechanical properties as determined by compression tests and structural characteristics as measured by Hg intrusion porosity. Vitreousness appeared to affect the endosperm extensibility and degree of porosity. The profile of the different lipid and protein classes in the reduction products of two cultivars showing opposite behaviour as well as different PINA/PINB ratio were determined. The results suggest that the most resistant parts of the grain are enriched in glycolipids, whereas phospholipids appear associated with the most friable parts, at least in the soft wheat grains tested.