Microstructure and Composition of Digitaria exilis Stapf (acha): A Potential Crop

Microstructure of the mature caryopsis of Digitaria exilis Stapf was studied by light and scanning electron microscopy and compared to chemical composition. The general structure of the caryopsis was similar to that of other grains, notably the millets. Thin bracts (the palea and lemma) and two glumes encased the caryopsis which consists of the thin, compressed layers of pericarp, testa, and cuticle surrounding the endosperm and embryonic tissues. The endosperm consisted of a single layer of aleurone cells and the starchy endosperm. The aleurone layer was thin over most of the starchy endosperm and thicker at the junction of the embryo and starchy endosperm. Aleurone cells contained lipid droplets and protein bodies. The cell contents of the starchy endosperm consisted of simple, polyhedral starch granules, lipid droplets, and protein bodies. Protein bodies were more abundant toward the periphery, and diminished toward the central portion of the starchy endosperm. Cells in certain regions of the embryo contained few, small, spherical starch granules and an abundance of protein bodies. Protein bodies containing phytic acid inclusions were located in the scutellum of the embryo. Compositional analyses revealed that the grain contained 8.2% protein, 2.1% fat, 0.48% fiber, and 1.4% ash.     

In‐Depth Study of Durum Wheat Grain Tissue Distribution at Milling

The starchy endosperm proportion in durum wheat grain and its ability to be isolated from the peripheral tissues appear as main intrinsic characteristics potentially related to the milling value but still difficult to assess. In this study, several durum wheat samples displaying distinct grading characteristics were analyzed and processed through a pilot mill. The histological composition of grains and milling fractions was monitored by using identified biochemical markers of each wheat grain tissue. Contrasted milling yields of semolina and flour were observed between samples, despite displaying a similar starchy endosperm proportion determined by hand dissection. These yields were related both to differences in the starchy endosperm extraction and to the presence of the aleurone layer, particularly its cellular content. Furthermore, two distinct types of fractionation behavior of the aleurone layer were distinguished depending on the wheat grain sample. Extraction of the envelopes and embryonic axis into semolina and flours were found negligible in comparison with the other tissues.     

FTIR and Raman Signatures of Wheat Grain Peripheral Tissues

Hand‐dissection of mature grains from three common wheat cultivars (Triticum aestivum L.: Caphorn, Crousty, and Recital) and one durum wheat (T. durum Desf., Ardente) was performed to obtain pure samples of aleurone layer, hyaline layer, outer pericarp, and a composite layer made up of testa+inner pericarp. Vibrational spectral signatures were collected on both sides of the layers by ATR‐FTIR and Raman spectroscopy. Spectra were compared with biochemical analysis on the same samples which allowed identification of specific composition patterns in each tissue regardless of the cultivar. Considering the low penetration depth of ATR‐FTIR signal, the cuticles were evidenced on the external sides of outer pericarp, hyaline layer, and testa. Spectra from testa of red and white wheats were clearly distinguished. FTIR spectroscopy, combined with statistical analysis, was successful in identifying the specific spectral signature for each peripheral tissue of wheat grains. In the 1500–800 cm^‐1 spectral region, multivariate models allowed accurate prediction of the histological origin of the pericarp, hyaline, and aleurone layers regardless of the analyzed side, and the testa but with a lower performance.     

Individual contribution of grain outer layers and their cell wall structure to the mechanical properties of wheat bran

The mechanical properties of wheat bran and the contribution of each constitutive tissue on overall bran properties were determined on a hard wheat (cv. Baroudeur) and a soft wheat (cv. Scipion). Manual dissection allowed three different layers to be separated from wheat bran, according to radial and longitudinal grain orientations, which were identified by confocal laser scanning microscopy as outer pericarp, an intermediate strip (comprising inner pericarp, testa, and nucellar tissue), and aleurone layer, respectively. Tissue microstructure and cell wall composition were determined. Submitted to traction tests, whole bran, intermediate, and aleurone layers demonstrated elastoplastic behavior, whereas pericarp exhibited elastic behavior. By longitudinal orientation, pericarp governed 50% bran elasticity (elastic strength and rigidity), whereas, in the opposite orientation, bran elastic properties were mostly influenced by the other tissues. Regardless of test orientation, the linear force required to bran rupture corresponded to the sum of intermediate and aleurone layer strengths. According to radial orientation, the intermediate strip governed bran extensibility, but according to longitudinal orientation, all tissues contributed until bran disruption. Tissues from both wheat cultivars behaved similarly. A structural model of wheat bran layers illustrated the detachment of pericarp from intermediate layer within radial bran strips.     

Effect of Corn Milling Practices on Aleurone Layer Cells and Their Unique Phytosterols

Coarse and fine fiber fractions obtained from the corn wet‐milling processes, with and without steeping chemicals (SO₂ and lactic acid), were evaluated microscopically for structure and analytically for recovery of phytosterol compounds from the fiber oil. Microscopic results showed that wet milling, with and without chemicals during steeping, changed the line of fracture between pericarp and endosperm and therefore affected the recovery of the aleurone layer in coarse (pericarp) and fine (endosperm cellular structure) fiber. Analytical results showed that most of the phytosterols and mainly phytostanols in corn fiber are contributed by the aleurone layer. Hand‐dissection studies were performed to separate the two layers that comprise the wet‐milled coarse fiber, the aleurone, and pericarp layer. Analyses revealed that the aleurone contained 8× more phytosterols than the pericarp.     

Influence of Structural Characteristics of Aleurone Layer on Milling Behavior of Durum Wheat (Triticum durum Desf.)

The structure of the aleurone layer was considered for many years as a potential factor influencing wheat milling efficiency. Eight durum wheat samples of different milling values, including distinct cultivars and harvesting conditions, were employed to investigate the structural characteristics of the aleurone layer through image analysis of kernel sections. Particular attention was paid to tissue thickness and structural irregularity of its interface with the starchy endosperm. Wheat cultivar, agricultural conditions, and location of measurement within the grain had an influence similar to both thickness and irregularity of the aleurone layer. Conversely, grain weight and morphology showed no effect on these parameters. Statistical investigation demonstrated no correlation between structural characteristics and wheat milling behavior. However, the negative correlation between the extraction rate of semolina and starch content in the bran fraction, which was used as an indicator of the endosperm‐aleurone dissociation extent, demonstrated the relevance of the tissue adhesion on milling efficiency.     

Inactive fluorescently labeled xylanase as a novel probe for microscopic analysis of arabinoxylan containing cereal cell walls

A new technique to visualize cereal cell walls by fluorescence microscopy was developed. The novel staining technique is based on an inactive fluorescently labeled xylanase binding to arabinoxylan (AX), an important polysaccharide in grain cell walls in terms of the technological and physiological functionalities of grain. The xylanase probe could stain AX in the seed coat, nucellar epidermis, aleurone layer, and starchy endosperm, but not the highly substituted AX of the pericarp layer. The advantage of this new staining technique over the existing immunolabeling techniques is that the staining procedure is clearly faster and less laborious, and uses a smaller probe that can easily be produced by marking a well characterized enzyme with a fluorescent label. In the future, the here proposed technology can be used to develop probes having specificity also for cell wall components other than AX and thus to study plant cell walls further through fluorescence microscopy.     

Comparative Studies on Composition and Distribution of Phenolic Acids in Cereal Grain Botanical Fractions

The phenolic acid composition and concentration of four manually separated fractions (pericarp, aleurone layer, germ, and endosperm fractions) as well as whole grains of yellow corn, wheat, barley, and oats were analyzed by HPLC‐MS/MS following microwave‐assisted alkaline aqueous extraction. Phenolic acid compositions in whole grains and their fractions were similar, with minor differences among the grain fractions. Significant differences (P < 0.05), however, were observed in phenolic acid concentrations among cereal types, within cereal varieties, and among grain fractions, with yellow corn exhibiting the highest values. The concentrations of p‐coumaric and syringic acid in the pericarp were 10‐ to 15‐fold and 6‐ to 10‐fold higher, respectively, in yellow corn than in wheat, barley, and oats. In the aleurone layer, sinapic and vanillic acids in yellow corn were about 8‐ and 30‐fold more than in wheat. The germ fraction of wheat had 1.8 times more syringic acid than yellow corn germ. Grain fractions, excluding endosperm, had enhanced levels of phenolic acids compared with whole grain. Sinapic acid was more concentrated in the pericarp and germ of wheat, whereas isoferulic acid was concentrated in the germ of purple barley. Syringic and vanillic acids were concentrated in the pericarp and sinapic acid in the aleurone layer of yellow corn. These findings are important in understanding the composition and distribution of phenolic acids, and they act as a guide in identification of grain fractions for use as food ingredients. In addition, yellow corn fractions (aleurone and pericarp) may be potential alternative phenolic‐rich functional food ingredients in grain‐based food products.     

Characterization using Raman microspectroscopy of arabinoxylans in the walls of different cell types during the development of wheat endosperm

The time course and pattern of arabinoxylan deposition in the wheat (Triticum aestivum) endosperm during grain development were studied using Raman spectroscopy. The presence of arabinoxylans (AX) is detected at the beginning of grain filling. At this stage, AX appear more substituted than at the later stages. Feruloylation of AX increases during the grain-filling stage, especially in the case of the aleurone layer. Whatever the stage of grain development, four populations of cells could be defined according to Raman arabinoxylan signatures. In the walls of the aleurone cells, AX appeared to be little substituted and highly esterified with phenolic acids. In the walls of prismatic cells, AX were found to be highly substituted and poorly esterified. Apart from aleurone and prismatic cells, the substitution degree of AX in endosperm was in the same range. Cells in the crease region were distinguished from cells in the starchy endosperm by their lower amount of esterified phenolic compounds.     

玉米应力裂纹的显微分析

观察了３种应力裂纹类型（单裂、双裂、龟裂）玉米的内部显微结构和应力裂纹产生的位置、数量、宽度，分析了应力裂纹在胚乳中扩展的情况以及应力裂纹对胚乳结构产生的影响。裂纹的类型不同，裂纹的形态、数量及大小亦不同。应力裂纹生成在粉质胚乳的中心部位，沿淀粉颗粒的边缘向外扩展。应力裂纹是内部裂纹，只能扩展到种皮附近，接近糊粉层。     

Differences in the Aleurone Layer Fate Between Hard and Soft Common Wheats at Grain Milling

In the milling process, efficient separation between the starchy endosperm and the other grain tissues is a key parameter estimated by ash measurement. Because this separation occurs near the aleurone layer interface, better understanding of this tissue fractionation is critical for a better analysis of the wheat milling behavior. Samples from hard and soft common wheat cultivars that had the same protein content were processed on a pilot mill, and whole grain meals or flour streams were analyzed for ash content. The para‐coumaric acid (p‐CA) and phytic acid flour contents were compared with ash measurement and used as markers of the aleurone cell walls or aleurone cell content, respectively. A greater amount of phytic acid in hard wheat flour compared with soft wheat flour was found and reveals a distinct milling behavior between those wheat classes, mainly at the breaking step. Therefore simple ash content measurement is not sufficient to analyze flour purity. At the reduction stage, quantity of phytic acid increases with the other markers and may result from the overall mechanical resistance of the aleurone tissue. As a consequence, wheat hardness not only determines grain milling behavior but also affects flour composition.     

麦麸结构层粉体的电特性研究

为了确定麦麸结构层粉体静电场分离的可行性,该文以高纯度麦麸糊粉层和外果皮粉体为原料,研究其介电性、导电性和电晕带电特性的差异。结果表明,麦麸粉体的介电常数随频率的增加而降低,最终趋于一致;当频率较低时,外果皮的相对介电常数明显低于糊粉层;当频率为300 MHz时,两者的介电常数之比最大达5.3;麦麸粉体的导电性差,糊粉层粉体的电阻率为2300MΩ/cm,为外果皮电阻率的5倍;经正电晕带电后,糊粉层粉体所获电荷量约为外果皮的1.7倍,具有明显差异;单位质量麦麸粉体所获电荷量随电晕电压的增加而增加,而随麦麸粉体的含水率和粒径的增大而减小。总之,麦麸结构层粉体的介电性、导电性和电晕带电性均存在明显差异,可以利用介电泳和电晕带电后的静电场分离技术对麦麸结构层进行分离纯化。     

Imaging molecular chemistry of Pioneer corn

Synchrotron Fourier transform infrared (FTIR) microspectroscopy as a rapid, direct, and nondestructive analytical technique can explore molecular chemical features of the microstructure of biological samples. The objective of this study was to use synchrotron FTIR microspectroscopy to image the molecular chemistry of corn (cv. Pioneer 39P78) to reveal spatial intensity and distribution of chemical functional groups in corn tissue. This experiment was performed at the U2B station of the National Synchrotron Light Source in Brookhaven National Laboratory (NSLS-BNL, Upton, NY). The Pioneer corn tissue was imaged from the pericarp, seed coat, aleurone, and endosperm under peaks at 1736 (carbonyl C=O ester), 1510 (aromatic compound), 1650 (amide I), 1550 (amide II), 1246 (cellulosic material), 1160 (CHO), 1150 (CHO), 1080 (CHO), 929 (CHO), 860 (CHO), 3350 (OH and NH stretching), 2929 (CH(2) stretching band), and 2885 cm(-1) (CH(3) stretching band). The results showed that with synchrotron FTIR microspectroscopy, the images of the molecular chemistry of Pioneer corn could be generated. Such information on the microstructural-chemical features of grain corn can also be used for corn breeding programs for selecting superior varieties of corn for targeted food and feed purposes and for prediction of corn quality and nutritive value for humans and animals.     

Distribution of Peroxidases in Durum Wheat (Triticum durum)

A biochemical study of the main durum wheat milling fractions (bran, embryo, and semolina) showed that peroxidases (POD) were present in multiple forms in the kernel and appeared to be tissue specific: one form for the embryo, one for the endosperm, one for the subaleuronic layer, and one for the outer layers. Large varietal differences were found regarding both the composition and the POD activity. POD activity, detected by diaminobenzidine, was found mainly in the cell wall of the subaleurone layer and inside some specific, differentiated cells of the embryo. Immuno‐localization with antibodies of durum wheat POD showed the presence of POD in several layers of the pericarp (epidermis) and the seed coat (testa), in the embryo, and also in the endosperm. In this latter tissue, the staining intensity decreased gradually from the outer layers toward the center of the kernel. The localization of POD in durum wheat kernel suggests specific functions for different forms.     

小麦麸皮结构层拉伸力学试样的手工制备方法探讨

制备小麦麸皮结构层试样是开展其机械特性拉伸试验的前提条件。能否利用手工剥离方法实现中间层和糊粉层的完整分离是制备小麦麸皮结构层试样的关键步骤，并形成了“两层说”和“三层说”的观点。该研究结合小麦麸皮结构层试样的制备要求，从小麦麸皮的显微组织结构、几何尺寸特性、实际剥离情况、宏观机械特性和杨氏模量复合法则等方面探讨了手工分离中间层和糊粉层的可行性问题。结果表明：利用手工剥离方法获得完整而纯粹的中间层和糊粉层试样是困难的。同时，明确了“三层说”分离中间层和糊粉层的方法是刮削工艺而不是撕离工艺，导致试样之间互相残留细胞组织，合理解释了两种试样的厚度和机械特性较为接近的原因。基于“两层说”的小麦麸皮结构层拉伸力学试验验证了层合板复合材料混合定律的普适应，表明当前利用“三层说”制备的中间层和糊粉层试样所得的拉伸力学特性参数的准确性不高。以上研究解决了手工分离中间层和糊粉层存在的一些疑惑，为利用小麦麸皮结构层机械特性探究其超微粉碎机理、优化其超微粉碎性能提供指导。     

Site of Origin of Volatile Compounds in Cooked Rice

Volatile compounds emanating from three cultivars of cooked rice milled to different degrees (0, 8, and 30% by weight) were compared to ascertain their site of origin and the effect of pigmentation on synthesis. The cultivars tested were Ilpumbyeo (traditional white rice), Heugjinjubyeo (black pigmented), and Jeogjinjubyeo (red pigmented). In total, 29, 38, and 27 volatile compounds were identified in dehulled, unmilled Ilpumbyeo, Heugjinjubyeo, and Jeogjinjubyeo, respectively. Significant quantitative and qualitative differences were found among the cultivars in their volatile profiles. 2‐Acetyl‐1‐pyrroline, guaiacol, 1‐nonanol, 3‐octen‐2‐one, 1,2‐dimethoxybenzene, pyridine, and pyrrole were found only in Heugjinjubyeo and phenylacetaldehyde only in Jeogjinjubyeo. Removal of the bran, partial endosperm, and pigment qualitatively and quantitatively affected the volatile compounds formed, with certain volatiles higher in unmilled rice (0% milling), indicating the pericarp and aleurone layer (bran) as their primary site of origin. Volatiles emanating from the 8 and 30% milled samples indicated the outer and middle endosperm (8%) and core endosperm (30%) as the primary sites of origin. Therefore, differences in chemical composition with location within the grain appear to account for the quantitative and qualitative variation in volatile synthesis.     

Energy-dispersive x-ray analysis of phytin globoids in aleurone particles of developing rice grains

Abstract

In this study energy-dispersive X-ray analysis was used to discover changes in the composition of phytin globoids in aleurone particles of developing rice grains.

At early milky stage (the 7th to 10th day after flowering) many aleurone particles were observed as electron lucent vacuole-like particles in aleurone cells, some of which contained a small electron-dense inclusion (phytin globoid). The major mineral elements present in phytin globoids were phosphorus (P) and magnesium (Mg). Potassium (K) was also detectable but its concentration was extremely low relative to these two. Calcium (Ca) and zinc (Zn) were found as minor components. At early dough stage (the 17th to 19th day after ftowering) P, Mg and K were observed as the major mineral elements. The composition of mineral elements in phytin globoids tend to be constant in the late staae of ripening. On the other hand, minor elements, i.e. Ca and Zn, were only detectable in the early stage of ripening, suuesting that these elements accumulated in the aleurone particles only during the early stage, and in later stage their accumulation was either complete or at very low levels compared with those of K and Mg. The relative amount of Mg existing in phytin globoid remained roughly constant throughout the ripening periods, while that of K varied.

Energy-dispersive X-ray analysis of phytin globoids in developing rice aleurone particles confirmed that the accumulation of P, Mg and K in rice grains was closely related to the formation of phytin globoids. This analysis suggested further that the mechanism of accumulation of P into aleurone particles was very similar to that of Mg, while that of K differed from both. The results obtained suggested that Ca and Zn might be required in the formation of phytin globoid at the early ripening stage. EDX analysis of a protein body in the starchy endosperm revealed that there was no significant element detectable in an EDX spectrum other than sulfur. This suggests that lamellar concentric structures in protein bodies are not due to phytin.     

Esterases in Barley and Malt

Several esterases from barley and malt have been separated on polyacrylamide gels. The slowest moving bands appear to represent a single enzyme displaying a spread of migration owing to differences in surface charge. During malting, this enzyme, which is located in the starchy endosperm, shifts to a more migratory form. Two other main esterase groups are identified through gel electrophoresis, notably a highly anionic, highly labile enzyme, MW 62,000, located in the aleurone. The slowest and fastest moving bands have been partially purified using salt fractionation and ion‐exchange chromatography. The former, MW 47,000, has strong capability for hydrolyzing acetylxylan and it is speculated that its role in the starchy endosperm is as part of the enzyme system that hydrolyzes the cell walls.     

rDNA cytogenetics and some structural variability in an <Emphasis Type="Italic">Avena barbata</Emphasis> Pott ex Link × <Emphasis Type="Italic">A. sativa</Emphasis> subsp. <Emphasis Type="Italic">nuda</Emphasis> (L.) Gillet et Magne amphiploid after 5-azaC treatment

The paper reports on the study of DNA methylation patterns in chromosomes of an octoploid selection obtained from an amphiploid Avena barbata × Avena sativa ssp. nuda, their alteration and plant structural changes induced by 5-azacytidine (5-azaC) treatment. Subtelomere/telomere regions and some chromosomes remained heavily methylated after this practise. The increased concentration of 5-azaC strengthened the demethylation process. NOR rDNA loci on five and 5S rDNA doubled loci on three pairs of chromosomes were detected. Some 5S loci were colocalised with NORs. The number of active NORs was increased by one homologous pair after demethylation and this was related to minor loci. The NORs were mainly located on A/D genomes. Patterns of nucleoli fusion varied between main and lateral roots and demethylation increased the number of uninucleolar nuclei. Seed germination was inhibited and plant growth decreased under demethylation. 5-azaC also induced distinct anomalies in endosperm development. Extensive parts of the tissue were composed of defected cells or remained empty. Polyploidised clones of starchy or aleurone cells were observed, as were aleurone cells exhibiting new rare phenotypes.