Novel protein fibers from wheat gluten

Protein fibers with mechanical properties similar to those of wool and better than those of soyprotein and zein fibers have been produced from 100% wheat gluten. Wheat gluten is a low cost, abundantly available, and renewable resource suitable for fiber production. A simple production method has been developed to obtain high-quality wheat gluten fibers, and the structure and properties of the fibers have been studied. Wheat gluten fibers have breaking tenacity of about 115 MPa, breaking elongation of 23%, and a Young's modulus of 5 GPa, similar to those of wool. Wheat gluten fibers have better tensile properties than soyprotein- and casein-based biomaterials. In addition, the wheat gluten fibers have resistance similar to that of PLA fibers to water in weak alkaline and slightly lower resistance in weak acidic conditions at high temperatures.     

Mechanical properties and network structure of wheat gluten foams

This Article reports the influence of the protein network structure on the mechanical properties of foams produced from commercial wheat gluten using freeze-drying. Foams were produced from alkaline aqueous solutions at various gluten concentrations with or without glycerol, modified with bacterial cellulose nanosized fibers, or both. The results showed that 20 wt % glycerol was sufficient for plasticization, yielding foams with low modulus and high strain recovery. It was found that when fibers were mixed into the foams, a small but insignificant increase in elastic modulus was achieved, and the foam structure became more homogeneous. SEM indicated that the compatibility between the fibers and the matrix was good, with fibers acting as bridges in the cell walls. IR spectroscopy and SE-HPLC revealed a relatively low degree of aggregation, which was highest in the presence of glycerol. Confocal laser scanning microscopy revealed distinct differences in HMW-glutenin subunits and gliadin distributions for all of the different samples.     

Structure and morphology of wheat gluten films: from polymeric protein aggregates toward superstructure arrangements

Evaluation of structure and morphology of extruded wheat gluten (WG) films showed WG protein assemblies elucidated on a range of length scales from nano (4.4 ? and 9 to 10 ?, up to 70 ?) to micro (10 μm). The presence of NaOH in WG films induced a tetragonal structure with unit cell parameters, a = 51.85 ? and c = 40.65 ?, whereas NH(4)OH resulted in a bidimensional hexagonal close-packed (HCP) structure with a lattice parameter of 70 ?. In the WG films with NH(4)OH, a highly polymerized protein pattern with intimately mixed glutenins and gliadins bounded through SH/SS interchange reactions was found. A large content of β-sheet structures was also found in these films, and the film structure was oriented in the extrusion direction. In conclusion, this study highlights complexities of the supramolecular structures and conformations of wheat gluten polymeric proteins in biofilms not previously reported for biobased materials.     

Transport and tensile properties of compression-molded wheat gluten films

Mechanical and transport properties were assessed on wheat gluten films with a glycerol content of 25-40%, prepared by compression molding for 5-15 min at temperatures between 90 and 130 degrees C. Effects of storing the films up to 24 days, in 0 and 50% relative humidity (RH), were assessed by tensile measurements. The films were analyzed with respect to methanol zero-concentration diffusivity, oxygen permeability (OP), water vapor permeability (WVP), Cobb60 and sodium dodecyl sulfate (SDS) solubility coupled with sonication. The SDS solubility and methanol diffusivity were lower at the higher molding temperature. Higher glycerol content resulted in higher OP (90-95% RH), WVP, and Cobb60 values, due to the plasticizing and hygroscopic effects. Higher glycerol contents gave a lower fracture stress, lower Young's modulus, lower fracture strain, and less strain hardening. The mold time had less effect on the mechanical properties than mold temperature and glycerol content. The fracture stress and Young's modulus increased and the fracture strain decreased with decreasing moisture content.     

强筋与弱筋小麦籽粒蛋白质组分与加工品质对灌浆期弱光的响应

选用强筋小麦品种济麦20和弱筋小麦品种山农1391,在大田试验条件下,分别于籽粒灌浆前期(花后6—9 d)、中期(花后16—19 d)和后期(花后26—29 d)对小麦进行弱光照处理,研究了籽粒产量、蛋白质组分及加工品质的变化。灌浆期弱光显著降低小麦籽粒产量,灌浆中期对济麦20和灌浆后期对山农1391的产量降幅最大。弱光处理后,籽粒氮素积累量及氮素收获指数减少。但弱光使籽粒蛋白质含量显著升高,其中灌浆中期弱光升幅最大,原因可能是由于其粒重降低造成的。弱光对可溶性谷蛋白无显著影响,但增加不溶性谷蛋白含量,使谷蛋白聚合指数显著升高,面团形成时间和稳定时间亦升高,籽粒灌浆中、后期弱光对上述指标的影响较前期大。灌浆期短暂的弱光照对改善强筋小麦粉质仪参数有利,但使弱筋小麦变劣;并均伴随籽粒产量的显著降低这一不利影响。     

Distribution of gluten proteins in bread wheat (Triticum aestivum) grain

Background and Aims

Gluten proteins are the major storage protein fraction in the mature wheat grain. They are restricted to the starchy endosperm, which forms white flour on milling, and interact during grain development to form large polymers which form a continuous proteinaceous network when flour is mixed with water to give dough. This network confers viscosity and elasticity to the dough, enabling the production of leavened products. The starchy endosperm is not a homogeneous tissue and quantitative and qualitative gradients exist for the major components: protein, starch and cell wall polysaccharides. Gradients in protein content and composition are the most evident and are of particular interest because of the major role played by the gluten proteins in determining grain processing quality.

Methods

Protein gradients in the starchy endosperm were investigated using antibodies for specific gluten protein types for immunolocalization in developing grains and for western blot analysis of protein extracts from flour fractions obtained by sequential abrasion (pearling) to prepare tissue layers.

Key Results

Differential patterns of distribution were found for the high-molecular-weight subunits of glutenin (HMW-GS) and γ-gliadins when compared with the low-molecular-weight subunits of glutenin (LMW-GS), ω- and α-gliadins. The first two types of gluten protein are more abundant in the inner endosperm layers and the latter more abundant in the subaleurone. Immunolocalization also showed that segregation of gluten proteins occurs both between and within protein bodies during protein deposition and may still be retained in the mature grain.

Conclusions

Quantitative and qualitative gradients in gluten protein composition are established during grain development. These gradients may be due to the origin of subaleurone cells, which unlike other starchy endosperm cells derive from the re-differentiation of aleurone cells, but could also result from the action of specific regulatory signals produced by the maternal tissue on specific domains of the gluten protein gene promoters.     

Recent advances in the genetics underlying wheat grain protein content and grain protein deviation in hexaploid wheat

Wheat is one of the most important global crops and selection for better performance has been ongoing since ancient times. As a quantitative trait controlled by the interplay of several genomic loci and under the strong influence of the environment, grain protein content (GPC) is of major interest in breeding programs. Here, we review the most recent contributions to the genetics underlying wheat GPC and grain protein deviation (GPD, representing the relationship between grain protein content and yield), together with the performance of genomic prediction models characterizing these traits. A total of 364 significant loci related to GPC and GPD are positioned on the hexaploid wheat genome, highlighting genomic regions where significant independent QTL overlap, with special focus on two regions located on chromosomes 3A and 5A. Some of the corresponding homoeologous sequences co-locate with significant independent QTL reported on the B and D subgenomes. Overlapping independent QTL from different studies are indicative of genomic regions exhibiting stability across environments and genotypes, with promising candidates for improving grain quality.     

Mapping of main and epistatic effect QTLs associated to grain protein and gluten strength using a RIL population of durum wheat

Quality, specifically protein content and gluten strength are among the main objectives of a durum wheat breeding program. The aim of this work was to validate quantitative trait loci (QTLs) associated with grain protein content (GPC) and gluten strength measured by SDS sedimentation volume (SV) and to find additional QTLs expressed in Argentinean environments. Also, epistatic QTL and QTL x environmental interactions were analyzed. A mapping population of 93 RILs derived from the cross UC1113 x Kofa showing extreme values in gluten quality was used. Phenotypic data were collected along six environments (three locations, two years). Main effect QTLs associated with GPC were found in equivalent positions in two environments on chromosomes 3BS (R² = 21.0-21.6%) and 7BL (R² = 12.1-13%), and in one environment on chromosomes 1BS, 2AL, 2BS, 3BL, 4AL, 5AS, 5BL and 7AS. The most important and stable QTL affecting SV was located on chromosome 1BL (Glu-B1) consistently detected over the six environments (R² = 20.9- 54.2%). Additional QTLs were found in three environments on chromosomes 6AL (R² = 6.4-12.5%), and in two environments on chromosomes 6BL (R² = 11.5-12.1%), 7AS (R² = 8.2-10.2%) and 4BS (R² = 11–16.4%). In addition, pleiotropic effects were found affecting grain yield, test weight, thousand-kernel- weight and days to heading in some of these QTLs. Epistatic QTLs and QTL x environment interactions were found for both quality traits, mostly for GPC. The flanking markers of the QTLs detected in this work could be efficient tools to select superior genotypes for the mentioned traits.     

Aging properties of films of plasticized vital wheat gluten cast from acidic and basic solutions

In order to understand the mechanisms behind the undesired aging of films based on vital wheat gluten plasticized with glycerol, films cast from water/ethanol solutions were investigated. The effect of pH was studied by casting from solutions at pH 4 and pH 11. The films were aged for 120 days at 50% relative humidity and 23 degrees C, and the tensile properties and oxygen and water vapor permeabilities were measured as a function of aging time. The changes in the protein structure were determined by infrared spectroscopy and size-exclusion and reverse-phase high-performance liquid chromatography, and the film structure was revealed by optical and scanning electron microscopy. The pH 11 film was mechanically more stable with time than the pH 4 film, the latter being initially very ductile but turning brittle toward the end of the aging period. The protein solubility and infrared spectroscopy measurements indicated that the protein structure of the pH 4 film was initially significantly less polymerized/aggregated than that of the pH 11 film. The polymerization of the pH 4 film increased during storage but it did not reach the degree of aggregation of the pH 11 film. Reverse-phase chromatography indicated that the pH 11 films were to some extent deamidated and that this increased with aging. At the same time a large fraction of the aged pH 11 film was unaffected by reducing agents, suggesting that a time-induced isopeptide cross-linking had occurred. This isopeptide formation did not, however, change the overall degree of aggregation and consequently the mechanical properties of the film. During aging, the pH 4 films lost more mass than the pH 11 films mainly due to migration of glycerol but also due to some loss of volatile mass. Scanning electron and optical microscopy showed that the pH 11 film was more uniform in thickness and that the film structure was more homogeneous than that of the pH 4 film. The oxygen permeability was also lower for the pH 11 film. The fact that the pH 4 film experienced a larger and more rapid change in its mechanical properties with time than the pH 11 film, as a consequence of a greater loss of plasticizer, was presumably due to its initial lower degree of protein aggregation/polymerization. Consequently, the cross-link density achieved at pH 4 was too low to effectively retain volatiles and glycerol within the matrix.     

The dynamics of protein body formation in developing wheat grain

Wheat is a major source of protein in the diets of humans and livestock but we know little about the mechanisms that determine the patterns of protein synthesis in the developing endosperm. We have used a combination of enrichment with ¹⁵N glutamine and NanoSIMS imaging to establish that the substrate required for protein synthesis is transported radially from its point of entrance in the endosperm cavity across the starchy endosperm tissues, before becoming concentrated in the cells immediately below the aleurone layer. This transport occurs continuously during grain development but may be slower in the later stages. Although older starchy endosperm cells tend to contain larger protein deposits formed by the fusion of small protein bodies, small highly enriched protein bodies may also be present in the same cells. This shows a continuous process of protein body initiation, in both older and younger starchy endosperm cells and in all regions of the tissue. Immunolabeling with specific antibodies shows that the patterns of enrichment are not related to the contents of gluten proteins in the protein bodies. In addition to providing new information on the dynamics of protein deposition, the study demonstrates the wider utility of NanoSIMS and isotope labelling for studying complex developmental processes in plant tissues.     

Viscoelastic properties of wheat gluten in a molecular dynamics study

Wheat (Triticum spp.) gluten consists mainly of intrinsincally disordered storage proteins (glutenins and gliadins) that can form megadalton-sized networks. These networks are responsible for the unique viscoelastic properties of wheat dough and affect the quality of bread. These properties have not yet been studied by molecular level simulations. Here, we use a newly developed α-C-based coarse-grained model to study ∼ 4000-residue systems. The corresponding time-dependent properties are studied through shear and axial deformations. We measure the response force to the deformation, the number of entanglements and cavities, the mobility of residues, the number of the inter-chain bonds, etc. Glutenins are shown to influence the mechanics of gluten much more than gliadins. Our simulations are consistent with the existing ideas about gluten elasticity and emphasize the role of entanglements and hydrogen bonding. We also demonstrate that the storage proteins in maize and rice lead to weaker elasticity which points to the unique properties of wheat gluten.     

Opioid peptides derived from wheat gluten: their isolation and characterization.

Four opioid peptides were isolated from the enzymatic digest of wheat gluten. Their structures were Gly-Tyr-Tyr-Pro-Thr, Gly-Tyr-Tyr-Pro,Tyr-Gly-Gly-Trp-Leu and Tyr-Gly-Gly-Trp, which were named gluten exorphins A5, A4, B5 and B4, respectively. The gluten exorphin A5 sequence was found at 15 sites in the primary structure of the high molecular weight glutenin and was highly specific for delta-receptors. The structure-activity relationships of gluten exorphins A were unique in that the presence of Gly at their N-termini increased their activities. Gluten exorphin B5, which corresponds to [Trp4,Leu5]enkephalin, showed the most potent activity among these peptides. Its IC50 values were 0.05 microM and 0.017 microM, respectively, on the GPI and the MVD assays.     

Genetic architecture of grain protein content in wheat

Studies on identification and localization of quantitative traits for grain protein content (QGpc-loci) on chromosomes in Triticum aestivum and Triticum durum are reviewed. Association of QGpc with various traits of morphology, physiology, adaptation and tolerance to abiotic and biotic stress is shown. Genetic and environmental QGpc contexts that should be taken into account when using molecular markers in breeding for the grain protein content are considered.     

Mechanism of heat and shear mediated aggregation of wheat gluten protein upon mixing

Changes in wheat gluten network structure upon mixing were studied from the biochemical analyses of gluten/glycerol blends mixed at 100 rpm with increasing times (up to 30 min) and temperatures of regulation (40, 60, and 80 degrees C). Whereas mixing induced protein solubility loss, the reduction of disulfide bonds restored protein extractability. But disulfide bond reduction became less efficient in promoting gluten extractability as mixing severity increased. This feature is consistent with the formation of a three-dimensional protein network stabilized by the formation of an increasing number of interchain disulfide bonds. Mixing induced a transient increase in free thiol groups while total thiol-equivalent groups dropped continuously. The changes were attributed to a shear-mediated scission of gluten disulfide bonds followed by oxidation of the thiyl radical moieties. Upon mixing, gluten solubility loss showed an Arrhenius-type temperature dependence with activation energy of 33.7 kJ.mol-1 instead of the more than 100 kJ.mol-1 reported for heat-induced gluten protein solubility loss. To explain this discrepancy, we postulated that during mixing, the disulfide interchange reactions are mediated by thiyl radicals in place of free thiol groups. A general model accounting for shear and temperature effects on gluten network structure is proposed.     

Genetic architecture of grain protein content in wheat

Studies on identification and localization of quantitative traits for grain protein content (QGpc-loci) on chromosomes in Triticum aestivum and Triticum durum are reviewed. Association of QGpc with various traits of morphology, physiology, adaptation and tolerance to abiotic and biotic stressors is shown. Genetic and environmental QGpc contexts that should be taken into account when using molecular markers in breeding for the grain protein content are considered.