Biochemical and functional properties of wheat gliadins: a review

Wheat gliadin hydrolysates based nano-micelles for hydrophobic naringin: Structure characterization, interaction, and in vivo digestion

In this study, enzymatic hydrolysis was used to fabricate wheat gliadin hydrolysates (WGHs) for the encapsulation and protection of naringin. The exposure of hydrophilic amino acids decreased the critical micelle concentration (from 0.53 ± 0.02 mg/mL to 0.35 ± 0.03 mg/mL) and improved solubility, which provided amphiphilic conditions for the delivery of naringin. The hydrolysates with a degree of hydrolysis (DH) of 9 % had the strongest binding affinity with naringin, and exhibited the smallest particle size (113.7 ± 1.1 nm) and the highest encapsulation rate (83.2 ± 1.3 %). The storage, heat and photochemical stability of naringin were improved via the encapsulation of micelles. Furthermore, the micelles made up of hydrolysates with a DH of 12 % significantly enhanced the bioavailability of naringin (from 19.4 ± 4.3 % to 46.8 ± 1.4 %). Our experiment provides theoretical support for the utilization of delivery systems based on water-insoluble proteins.

Investigating the interaction mechanism between gliadin and lysozyme through multispectroscopic analysis and molecular dynamic simulations

The development of stable nanocomplexes based on gliadin and other biopolymers shows potential applications as delivery vehicles in the food industry. However, there is limited study specifically targeting the gliadin-lysozyme system, and their underlying interaction mechanism remains poorly understood. Therefore, the objective of this study was to investigate the binding mechanism between gliadin and lysozyme using a combination of multispectroscopic methods and molecular dynamic simulations. Stable gliadin-lysozyme complex nanoparticles were prepared using an anti-solvent precipitation method with a gliadin-to-lysozyme mass ratio of 2:1 and pH 4.0. The characteristic changes in the UV-visible spectrum of gliadin induced by lysozyme confirmed the complex formation. The analyses of fluorescence, FT-IR spectra, and dissociation tests demonstrated the indispensability of hydrophobic, electrostatic, and hydrogen bonding interactions in the preparation of the composites. Scanning electron microscopy revealed that the surface morphology of the nanoparticles changed from smooth and spherical to rough and irregular with the addition of lysozyme. Furthermore, molecular dynamic simulations suggested that lysozyme bound to the hydrophobic region of gliadin and hydrogen bonding was crucial for the stability of the complex. These findings contribute to the advancement of gliadin-lysozyme complex nanoparticles as an efficient delivery system for encapsulating bioactive compounds in food industry.

Interaction of wheat bran dietary fiber-gluten protein affects dough product: A critical review

Wheat bran dietary fiber (WBDF) is an emerging food additive used for improving the nutritional value of dough products, albeit its adverse effects cannot be ignored. The dilution effect, mechanical shear effect, competitive water absorption, and steric hindrance of WBDF, as well as the non-covalent binding between WBDF and gluten protein, are considered the key mechanisms underlying the WBDF-gluten protein interaction. However, current studies on the interaction are mostly limited to the impact of the interaction on gluten protein and are rarely focused on the quality of products. Therefore, the effects of the interaction on the structural characteristics and aggregation behavior of gluten protein and multiple involved mechanisms are discussed in this review. On this basis, these changes are systematically related to the gluten network structure, dough properties, and product quality. Mitigation measures corresponding to negative impacts also need to be elaborated to guide and standardize the production and development of dough products containing WBDF.

Effects of Aegilops longissima chromosome 1Sl on wheat bread-making quality in two types of translocation lines

KEY MESSAGE

Two wheat-Ae. longissima translocation chromosomes (1BS·1SlL and 1SlS·1BL) were transferred into three commercial wheat varieties, and the new advanced lines showed improved bread-making quality compared to their recurrent parents. Aegilops longissima chromosome 1Sl encodes specific types of gluten subunits that may positively affect wheat bread-making quality. The most effective method of introducing 1Sl chromosomal fragments containing the target genes into wheat is chromosome translocation. Here, a wheat-Ae. longissima 1BS·1SlL translocation line was developed using molecular marker-assisted chromosome engineering. Two types of translocation chromosomes developed in a previous study, 1BS·1SlL and 1SlS·1BL, were introduced into three commercial wheat varieties (Ningchun4, Ningchun50, and Westonia) via backcrossing with marker-assisted selection. Advanced translocation lines were confirmed through chromosome in situ hybridization and genotyping by target sequencing using the wheat 40 K system. Bread-making quality was found to be improved in the two types of advanced translocation lines compared to the corresponding recurrent parents. Furthermore, 1SlS·1BL translocation lines displayed better bread-making quality than 1BS·1SlL translocation lines in each genetic background. Further analysis revealed that high molecular weight glutenin subunit (HMW-GS) contents and expression levels of genes encoding low molecular weight glutenin subunits (LMW-GSs) were increased in 1SlS·1BL translocation lines. Gliadin and gluten-related transcription factors were also upregulated in the grains of the two types of advanced translocation lines compared to the recurrent parents. This study clarifies the impacts of specific glutenin subunits on bread-making quality and provides novel germplasm resources for further improvement of wheat quality through molecular breeding.

Insight into Organization of Gliadin and Glutenin Extracted from Gluten Modified by Phenolic Acids

The changes in the secondary structure of individual gluten protein fractions (gliadin and glutenin) caused by the supplementation of model dough with eight phenolic acids were analysed. Gliadins and glutenins were extracted from gluten samples obtained from overmixed dough. The changes in the gliadin secondary structure depended on the amount of phenolic acid added to the dough. Higher acid concentrations (0.1% and 0.2%) led to a significant reduction in the amount of α-helices and to the formation of aggregates, non-ordered secondary structures, and antiparallel β-sheets. After the addition of acids at a lower concentration (0.05%), the disaggregation of pseudo-β-sheet structures and the formation of β-turns, hydrogen-bonded β-turns, and antiparallel β-sheets were detected. In the case of glutenin, most of the phenolic acids induced the formation of intermolecular hydrogen bonds between the polypeptide chains, leading to glutenin aggregation. When phenolic acids were added at a concentration of 0.05%, the process of protein folding and regular secondary structure formation was also observed. In this system, antiparallel β-sheets and β-turns were created at the expense of pseudo-β-sheets.

Periodic changes in chain lengths distribution parameters of wheat starch during endosperm development

This study analyzed the molecular structure of developing wheat endosperm starch at different stages after anthesis (DAA) using chain length distribution analysis by size exclusion chromatography (SEC) and fluorophore-assisted carbohydrate electrophoresis. Our results revealed periodic changes in the content of both amylose and amylopectin fractions. Specifically, the content of amylose chains with a degree of polymerization (DP) > 100 significantly decreased from 5 to 10 DAA (28% to 21%) and from 15 to 20 DAA (29% to 26%), but increased between 10 and 15 DAA (21% to 29%) and 20 to 25 DAA (30.0% to 33%). Conversely, the content of short amylopectin chains with DP ≤ 32 showed the opposite trend. Interestingly, mRNA expression levels of key starch biosynthesis genes did not exhibit periodic changes. These findings contribute to our understanding of starch biosynthesis and provide important insights for the development of starch-based products.

Gliadin and glutenin genomes and their effects on the technological aspect of wheat-based products

Wheat is the most important crops worldwide, providing about one-fifth of the daily protein and calories for human consumption. The quality of cereal-based products is principally governed by the genetic basis of gluten (glutenin and gliadin proteins), which exists in a wide range of variable alleles and is controlled by clusters of genes. There are certain limitations associated with gluten characteristics, which can be genetically manipulated. The present review aimed to investigate the correlation between the genetic characteristics of gluten protein components and wheat-based product's quality. According to various references, Glu-B1d (6 + 8), Glu-B1h (14 + 15) and Glu-B1b (7 + 8) are related to higher gluten strength and pasta quality, while, subunits Dx2 + Dy12 and Dx5 + Dy10, are usually present at the Glu-D1 locus in bread wheat, resulted in lower cooked firmness in pasta. Moreover, introducing Gli-D1/Glu-D3 and Glu-D1 loci into durum wheat genomes, causing to provide the maximum values of gluten index in pasta products. 1Dx5 + 1Dy10 alleles determine the level of increase in dough's consistency, elasticity, viscosity, and extensibility quality of baking and appropriate bread loaf volume, while 1Dx2 + 1Dy12 as the alleles associated with poor baking quality, being more suitable for soft wheat/pastry end uses. Bx7, Bx7OE, 1Bx17 + 1By18, 1Bx13 + 1By16, Bx7 + By9 and 1Bx7 + 1By8 at Glu-B1alleles and 1Ax2* found on Glu-A1, augmented dough strength and has positive effects on consistency, extensibility, viscosity, and elasticity of bread dough. Breeding programs by genome editing have made gluten a promoting component for improving cereal-based products.

An elite γ-gliadin allele improves end-use quality in wheat

Gluten is composed of glutenins and gliadins and determines the viscoelastic properties of dough and end-use quality in wheat (Triticum aestivum L.). Gliadins are important for wheat end-use traits, but the contribution of individual gliadin genes is unclear, since gliadins are encoded by a complex, multigenic family, including many pseudogenes. We used CRISPR/Cas9-mediated gene editing and map-based cloning to investigate the contribution of the γ-gliadin genes annotated in the wheat cultivar 'Fielder', showing that Gli-γ1-1D and Gli-γ2-1B account for most of the γ-gliadin accumulation. The impaired activity of only two γ-gliadin genes in knockout mutants improved end-use quality and reduced gluten epitopes associated with celiac disease (CD). Furthermore, we identified an elite haplotype of Gli-γ1-1D linked to higher end-use quality in a wheat germplasm collection and developed a molecular marker for this allele for marker-assisted selection. Our findings provide information and tools for biotechnology-based and classical breeding programs aimed at improving wheat end-use quality.

Effect of Wheat Gluten and Peanut Protein Ratio on the Moisture Distribution and Textural Quality of High-Moisture Extruded Meat Analogs from an Extruder Response Perspective

Wheat gluten (WG) and peanut protein powder (PPP) mixtures were extruded at high moisture to investigate the potential application of this mixture in meat analog production. Multiple factors, including the water absorption index (WAI), water solubility index (WSI), rheological properties of the mixed raw materials, die pressure, torque and specific mechanical energy (SME) during high moisture extrusion, texture properties, color, water distribution, and water activity of extrudates were analyzed to determine the relationships among the raw material characteristics, extruder response parameters, and extrudate quality. At a WG ratio of 50%, the extrudates have the lowest hardness (2.76 kg), the highest springiness (0.95), and a fibrous degree of up to 1.75. The addition of WG caused a significant rightward shift in the relaxation time of hydrogen protons in the extrudates, representing increased water mobility and water activity. A ratio of 50:50 gave the smallest total color difference (ΔE) (about 18.12). When the added amount of WG was 50% or less, it improved the lightness and reduced the ΔE compared to >50% WG. Therefore, clarifying the relationship among raw material characteristics, extruder response parameters, and extruded product quality is helpful in the systematic understanding and regulation of the fiber textural process of binary protein meat analogs.

Preparation and Characterization of Gluten/SDS/Chitosan Composite Hydrogel Based on Hydrophobic and Electrostatic Interactions

Gluten is a natural byproduct derived from wheat starch, possessing ideal biocompatibility. However, its poor mechanical properties and heterogeneous structure are not suitable for cell adhesion in biomedical applications. To resolve the issues, we prepare novel gluten (G)/sodium lauryl sulfate (SDS)/chitosan (CS) composite hydrogels by electrostatic and hydrophobic interactions. Specifically, gluten is modified by SDS to give it a negatively charged surface, and then it conjugates with positively charged chitosan to form the hydrogel. In addition, the composite formative process, surface morphology, secondary network structure, rheological property, thermal stability, and cytotoxicity are investigated. Moreover, this work demonstrates that the change can occur in surface hydrophobicity caused by the pH-eading influence of hydrogen bonds and polypeptide chains. Meanwhile, the reversible non-covalent bonding in the networks is beneficial to improving the stability of the hydrogels, which shows a prominent prospect in biomedical engineering.

Composition and functional properties of hemp seed protein isolates from various hemp cultivars

Hemp seed protein isolates (HPI) were extracted from seven commercial hemp cultivars, a Cornell breeding line, and a commercial hemp heart product, and their composition and functional properties were investigated. HPI contained different ratios of edestin, vicilin, and albumin proteins, which affected protein solubility and functionality. Higher protein solubility was associated with cultivars that contained more vicilin and albumin, which influenced the subsequent functional properties of HPI. Significant differences in water holding capacity (0.83-1.05 g water/g protein isolate), oil holding capacity (1.28-1.81 g oil/g protein isolate), foam capacity (52.9%-84.9%), and foam stability (68.1%-89.4%) were observed across HPI. The Cornell hemp breeding line exhibited the highest protein solubility at pH 7.0 and was uniquely capable of forming an emulsion. The relationship identified between hemp seed protein composition and functionality, in conjunction with the demonstration of an on-going hemp breeding line, suggest that continued, targeted development of hemp cultivars can improve its seed protein functional properties for ingredient utilization in plant-based foods.

Impacts of Sourdough Technology on the Availability of Celiac Peptides from Wheat α- and γ-Gliadins: In Silico Approach

Celiac peptide-generating α- and γ-gliadins consist of a disordered N-terminal domain extended by an α-helical-folded C-terminal domain. Celiac peptides, primarily located along the disordered part of α- and γ-gliadin molecules, are nicely exposed and directly accessible to proteolytic enzymes occurring in the gastric (pepsin) and intestinal (trypsin, chymotrypsin) fluids. More than half of the potential celiac peptides identified so far in gliadins exhibit cleavage sites for pepsin. However, celiac peptides proteolytically truncated by one or two amino acid residues could apparently retain some activity toward HLA-DQ2 and HLA-DQ8 receptors in docking experiments. Together with the uncleaved peptides, these still active partially degraded CD peptides account for the incapacity of the digestion process to inactivate CD peptides from gluten proteins. In contrast, sourdough fermentation processes involve other proteolytic enzymes susceptible to the deep degradation of celiac peptides. In particular, sourdough supplemented by fungal prolyl endoproteases enhances the degrading capacities of the sourdough fermentation process toward celiac peptides. Nevertheless, since tiny amounts of celiac peptides sufficient to trigger deleterious effects on CD people can persist in sourdough-treated bread and food products, it is advisable to avoid consumption of sourdough-treated food products for people suffering from celiac disease. As an alternative, applying the supplemented sourdough process to genetically modified low gluten or celiac-safe wheat lines should result in food products that are safer for susceptible and CD people.

Empirical and Theoretical Bases of Good Steamed Bread Production

Chinese steamed bread (CSB) is a main staple food in China, accounting for 40% of wheat flour usage in China. Due to its health benefits, CSB is gaining popularity across the world. In this review, the effects of gluten proteins (particularly glutenins and gliadins) on the quality of CSB are summarized from the literature. Requirements of appropriate rheological parameters in different studies are compared and discussed. Along with the increasing demand for frozen storage food, there are obvious increases in the research on the dynamics of gluten proteins in frozen dough. This review also summarizes the factors influencing the deterioration of CSB dough quality during frozen storage as well as effective measures to mitigate the negative effects.

High-Moisture Shear Processes: Molecular Changes of Wheat Gluten and Potential Plant-Based Proteins for Its Replacement

Nowadays, a growing offering of plant-based meat alternatives is available in the food market. Technologically, these products are produced through high-moisture shear technology. Process settings and material composition have a significant impact on the physicochemical characteristics of the final products. Throughout the process, the unfolded protein chains may be reduced, or associate in larger structures, creating rearrangement and cross-linking during the cooling stage. Generally, soy and pea proteins are the most used ingredients in plant-based meat analogues. Nevertheless, these proteins have shown poorer results with respect to the typical fibrousness and juiciness found in real meat. To address this limitation, wheat gluten is often incorporated into the formulations. This literature review highlights the key role of wheat gluten in creating products with higher anisotropy. The generation of new disulfide bonds after the addition of wheat gluten is critical to achieve the sought-after fibrous texture, whereas its incompatibility with the other protein phase present in the system is critical for the structuring process. However, allergenicity problems related to wheat gluten require alternatives, hence an evaluation of underutilized plant-based proteins has been carried out to identify those that potentially can imitate wheat gluten behavior during high-moisture shear processing.

Protein-based nanomaterials: a new tool for targeted drug delivery

Protein nanomaterials are well-defined, hollow protein nanoparticles comprised of virus capsids, virus-like particles, ferritin, heat shock proteins, chaperonins and many more. Protein-based nanomaterials are formed by the self-assembly of protein subunits and have numerous desired properties as drug-delivery vehicles, including being optimally sized for endocytosis, nontoxic, biocompatible, biodegradable and functionalized at three separate interfaces (external, internal and intersubunit). As a result, protein nanomaterials have been intensively investigated as functional entities in bionanotechnology, including drug delivery, nanoreactors and templates for organic and inorganic nanomaterials. Several variables influence efficient administration, particularly active targeting, cellular uptake, the kinetics of the release and systemic elimination. This review examines the wide range of medicines, loading/release processes, targeted therapies and treatment effectiveness.

Challenges and opportunities for proteomics and the improvement of bread wheat quality

Wheat remains a critical global food source, pressured by climate change and the need to maximize yield, improve processing and nutritional quality and ensure safety. An enormous amount of research has been conducted to understand gluten protein composition and structure in relation to end-use quality, yet progress has become stagnant. This is mainly due to the need and inability to biochemically characterize the intact functional glutenin polymer in order to correlate to quality, necessitating reduction to monomeric subunits and a loss of contextual information. While some individual gluten proteins might have a positive or negative influence on gluten quality, it is the sum total of these proteins, their relative and absolute expression, their sub-cellular trafficking, the amount and size of glutenin polymers, and ratios between gluten protein classes that define viscoelasticity of gluten. The sub-cellular trafficking of gluten proteins during seed maturation is still not completely clear and there is evidence of dual pathways and therefore different destinations for proteins, either constitutively or temporally. The trafficking of proteins is also unclear in endosperm cells as they undergo programmed cell death; Golgi disappear around 12 DPA but protein filling continues at least to 25 DPA. Modulation of the timing of cellular events will invariably affect protein deposition and therefore gluten strength and function. Existing and emerging proteomics technologies such as proteoform profiling and top-down proteomics offer new tools to study gluten protein composition as a whole system and identify compositional patterns that can modify gluten structure with improved functionality.

Grain Transcriptome Dynamics Induced by Heat in Commercial and Traditional Bread Wheat Genotypes

High temperature (HT) events have negative impact on wheat grains yield and quality. Transcriptome profiles of wheat developing grains of commercial genotypes (Antequera and Bancal) and landraces (Ardito and Magueija) submitted to heatwave-like treatments during grain filling were evaluated. Landraces showed significantly more differentially expressed genes (DEGs) and presented more similar responses than commercial genotypes. DEGs were more associated with transcription and RNA and protein synthesis in Antequera and with metabolism alterations in Bancal and landraces. Landraces upregulated genes encoding proteins already described as HT responsive, like heat shock proteins and cupins. Apart from the genes encoding HSP, two other genes were upregulated in all genotypes, one encoding for Adenylate kinase, essential for the cellular homeostasis, and the other for ferritin, recently related with increased tolerance to several abiotic stress in Arabidopsis. Moreover, a NAC transcription factor involved in plant development, known to be a negative regulator of starch synthesis and grain yield, was found to be upregulated in both commercial varieties and downregulated in Magueija landrace. The detected diversity of molecular processes involved in heat response of commercial and traditional genotypes contribute to understand the importance of genetic diversity and relevant pathways to cope with these extreme events.

Characterization of Glutenin Genes in Bread Wheat by Third-Generation RNA Sequencing and the Development of a Glu-1Dx5 Marker Specific for the Extra Cysteine Residue

High-molecular-weight glutenin subunits (HMW-GS) and low-molecular-weight glutenin subunits (LMW-GS) in a mature grain play important roles in the formation of a glutenin macropolymer and gluten quality. To characterize the expressed glutenin genes of the bread wheat variety Xinmai 26 during seed development, a total of 18 full-length transcripts were obtained by the newly emerged third-generation RNA sequencing of the PacBio Sequel II platform, including 5 transcripts of HMW-GS genes and 13 transcripts of LMW-GS genes (8 intact genes and 5 pseudogenes). Combined with the patterns of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), allelic types of the obtained glutenin genes were, respectively, determined, wherein molecular characterization deduced by transcript1528 (1Dx5) and transcript907 (Glu-A3c) indicated their great influence on dough quality. In addition, a specific functional marker dCAPS5 was developed for the single-nucleotide substitution at position 353 of the 1Dx5 subunit, which was further intensively compared with the other proposed markers to efficiently utilize the 1Dx5 subunit with the extra cysteine residue. This study provides an efficient method to accurately identify and utilize glutenin genes in bread wheat, which is helpful in understanding the contributions of glutenin genes to wheat quality.

Moderate heat enhances gliadin-proanthocyanidin interactions

Understanding wheat gliadin-proanthocyanidin (PA) interactions would be useful to systematically control foams and gels, create novel textures, and reduce inflammatory reactions. This work aimed to determine the effects of heat (50-90 °C) on gliadin-proanthocyanidin (PA) interactions. Gliadin-PA mixtures were heated for 30 min in aqueous ethanol, and resulting morphology, fluorescence, and MW distribution were analyzed. Atomic force microscopy showed that PA greatly increased gliadin particle size, especially with heat. PA significantly quenched gliadin's tryptophan fluorescence. Further fluorescence data analysis indicated that PA interacted with gliadins through static quenching, primarily via hydrophobic interactions, and that 75 °C treatment yielded the greatest gliadin-PA interactions, likely because the proteins unraveled and exposed residues for interaction. PA appeared to interact mostly with ω-gliadins, based on their absence in the SDS-PAGE gel. Though it has been overshadowed in previous studies by non-covalent interactions, staining of quinoproteins indicated that PA covalently cross-linked gliadins at pH ∼ 6.

Versatile wheat gluten: functional properties and application in the food-related industry

Gluten is a key component that allows wheat flour to form a dough, and it is also a byproduct of the production of wheat starch. As a commercial product, wheat gluten is increasingly used in the food-related industry because of its versatile functional properties and wide range of sources. Wheat gluten is manufactured industrially on a large scale through the Martin process and batter process and variants thereof. Gliadin and glutenin impart cohesiveness and elasticity properties, respectively, to wheat gluten. The formation of gluten networks and polymers depends mainly on covalent bonds (disulfide bonds) and noncovalent bonds (ionic bonds, hydrogen bonds, and hydrophobic interactions). The multifunctional properties (viscoelasticity, gelation, foamability, etc.) of wheat gluten are shown by rehydration and other processing techniques. Wheat gluten has been widely used in wheat-based products, food auxiliary agents, food packaging, encapsulation and release of food functional ingredients, food adsorption and heat insulation materials, special purpose foods, and versatile applications. In the future, wheat gluten protein will be used as an important raw material to participate in the development and preparation of various food and degradable materials, and the application potential of wheat gluten in food-related industries will be massive. This review summarizes the main manufacturing processes, composition, and structure of gluten protein, and the various functional properties that support its application in the food and related industries.

Gliadin interacted with tea polyphenols: potential application and action mechanism

The effect of tea polyphenols (TPs) on noodles quality was investigated, and the interaction mechanism between catechins and gliadins was explored. With TPs addition, noodles showed the significant changes in physicochemical and sensory properties. The water absorption, tensile strength and elasticity increased by 1.35%, 4.98%, 28.51% with 0.5% of TPs, and then decreased with the increasing of TPs. According to the determinations of surface hydrophobicity, spatial structure, thermal properties, amidogen and sulfhydryl content, the structure and properties of gliadin were affected by catechins. Esterified catechins tended to disrupt gliadin structures and non-esterified catechins polymerised gliadin molecules. Furthermore, molecular docking results indicated that catechins interacted with gliadin mainly by hydrogen bonds and hydrophobic action. The reactivity of catechins with gliadin was in the sequence as: epigallocatechin gallate > epicatechin gallate > epigallocatechin > epicatechin, which was based on the account of gallate and B-ring hydroxyl number discrepancy. All results suggested that catechins affected greatly on gliadin, and TPs were potentially used to improve the quality of flour products.

Insights from multi-spectroscopic analysis and molecular modeling to understand the structure-affinity relationship and the interaction mechanism of flavonoids with gliadin

Gliadin, as a main component of wheat storage protein, is used as a drug encapsulation and delivery system owing to its specific characteristics. Flavonoids are regarded as active natural products with a variety of pharmacological effects. In this study, an integrated method including UV-vis, fluorescence, and FT-IR spectroscopy and molecular modelling was applied to explore the structure-affinity relationship and the interaction nature between a library of flavonoids and gliadin. The characteristic UV-vis spectral changes of gliadin mediated by flavonoids with absorption bands at 218 and 278 nm demonstrated the existence of an interaction depending on generating the ground-state complexes. Fluorescence quenching results showed that the intrinsic fluorescence of gliadin could be effectively quenched by flavonoids coupled with the formation of flavonoid-gliadin complexes through the static quenching mechanism. The structure-affinity relationship revealed the critical structural elements associated with the binding affinity on gliadin and underlined the favorable substituents at the specific positions of flavonoid skeletons leading to a stronger binding potency. From the analysis of synchronous fluorescence spectra, flavonoids could cause the conformation change of gliadin and impact the microenvironment around TYR and TRP residues. Moreover, the ANS fluorescent probe assay suggested that these flavonoids also influenced the surface hydrophobicity of glaidin based on the further exposure or blocking of hydrophobic domains. Molecular modelling was subsequently performed and illustrated the proposed binding conformation of flavonoids on gliadin. Combined with the FT-IR spectra, these results further confirmed the important role of hydrophobic interactions and hydrogen bonds in their binding process.

Comparative study of the effects of ultrasonic power on the structure and functional properties of gliadin in wheat and green wheat

The impact of different ultrasonic power on the structure and functional properties of wheat gliadin (WG) and green wheat gliadin (GG) was investigated and compared. Ultrasound had no obvious effect on subunit composition and bands of WG and GG, and there were more small molecular weight bands in GG. The results of Fourier transform-infrared spectroscopy, intrinsic fluorescence spectroscopy, and scanning electron microscopy analyses demonstrated that ultrasonic treatment had a significant effect on the structure of WG and GG, inducing the transformation from order structure to disorder structure. The dispersion and uniformity were better at 400 and 300 W, respectively. Under proper ultrasonic treatment, the particle size of WG and GG was significantly reduced, and the free sulfhydryl groups and surface hydrophobicity were significantly increased (p < 0.05). Furthermore, the functional properties of WG and GG such as solubility, emulsification properties, water holding and oil holding properties, thermal stability, and digestibility were enhanced. The better functional properties of WG and GG were obtained at 400 and 300 W, respectively. These results indicated that ultrasonic treatment with appropriate power was a valuable method for improving functional characteristics of WG and GG. PRACTICAL APPLICATION: Ultrasonic treatment could cause structural changes of wheat gliadin (WG) and green wheat gliadin (GG), and their functional properties are improved under appropriate power. This study compares the effects of ultrasound on WG and GG, and the results will provide theoretical guidance for the development of GG in the food industry.

Promoter DNA hypermethylation of TaGli-γ-2.1 positively regulates gluten strength in bread wheat

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TaGli-γ-2.1 belonged to a subgroup of γ-gliadin multigene family.

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TaGli-γ-2.1 was a negative regulatory factor in gluten strength.

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Methylation of pTaGli-γ-2.1 played a key role in regulating TaGli-γ-2.1 expression.

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Lower γ-gliadin content followed with hypermethylation of pTaGli-γ-2.1.

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Decreasing TaGli-γ-2.1 expression could be used to improve gluten strength in wheat breeding.

Introduction

Gliadins are the major components of gluten proteins with vital roles on properties of end-use wheat product and health-relate quality of wheat. However, the function and regulation mechanisms of γ-gliadin genes remain unclear.

Objectives

Dissect the effect of DNA methylation in the promoter of γ-gliadin gene on its expression level and gluten strength of wheat.

Methods

The prokaryotic expression and reduction–oxidation reactions were performed to identify the effect of TaGli-γ-2.1 on dough strength. Bisulfite analysis and 5-Aza-2′-deoxycytidine treatment were used to verify the regulation of TaGli-γ-2.1 expression by pTaGli-γ-2.1 methylation. The content of gluten proteins composition was measured by RP-HPLC, and the gluten strength was measured by Gluten Index and Farinograph.

Results

TaGli-γ-2.1 was classified into a subgroup of γ-gliadin multigene family and was preferentially expressed in the later period of grain filling. Addition of TaGli-γ-2.1 protein fragment into strong gluten wheat flour significantly decreased the stability time. Hypermethylation of three CG loci of pTaGli-γ-2.1 conferred to lower TaGli-γ-2.1 expression. Treatment with 5-Aza-2′-deoxycytidine in seeds of strong gluten wheat varieties increased the expression levels of TaGli-γ-2.1. Furthermore, the accumulations of gliadin and γ-gliadin were significantly decreased in hypermethylated wheat varieties, corresponding with the increasing of gluten index and dough stability time.

Conclusion

Epigenetic modification of pTaGli-γ-2.1 affected gluten strength by modulating the proportion of gluten proteins. Hypermethylation of pTaGli-γ-2.1 is a novel genetic resource for enhancing gluten strength in wheat quality breeding.

Comparative evaluation of gliadins from four extraction protocols using advanced analytical techniques

Gliadin, a major component of gluten, is known to trigger celiac disease; therefore, its extraction is important to study its properties as well as its presence in gluten-free products. Four gliadin extraction procedures Osborne (1924), Weiss (1993), Wallace (1989) and DuPont (2005), were investigated on six wheat cultivars using advanced analytical techniques such as dynamic light scattering (DLS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Higher zeta potential of extracted gliadin was observed in DuPont (23.53-27), followed by Weiss (16.17-20.80), Osborne (16.17-20.13), and Wallace (14.60-19.47). Particle Z-average size (15.74-184.83 nm) was found to have an inverse relationship with the Polydispersity index (0.17-184.83). The surface morphological structure of TEM studies revealed the compact globular particle arrangement of gliadin, besides rod-shaped arrangement, was also found in DuPont and Wallace extracted gliadin. XRD pattern of gliadin exposed the crystalline domain at 44.1°, 37.8°, and 10.4° diffraction peaks. The d-spacing obtained from XRD and TEM-SAED analysis supports the presence of crystalline domains in gliadin apart from the amorphous domain. The insight obtained from this work will provide a better understanding of morphology and other properties of the same protein extracted with different extraction procedures.

Rapid spectroscopic method for quantifying gluten concentration as a potential biomarker to test adulteration of green banana flour

The demand for gluten-free banana flour has led manufactures to enforce strict measures for quality control. A need has arisen for the development of more sensitive and reliable methods to test the quality of green banana flour (GBF). The objective of this study was to develop rapid visible to near-infrared (Vis-NIR) based spectroscopic models to detect gluten concentration, as a biomarker to detect wheat flour adulteration in green banana flour (GBF). Spectroscopic data were acquired using a desktop (FOSS®) Vis-NIR spectroscopy ranging from 400 to 2500 nm of the electromagnetic spectrum. The spectral and reference data were submitted to principal component analysis (PCA) and partial least squares regression (PLSR) for the development of gluten adulteration detection models. Calibration models were constructed based on a full cross-validation approach, consisting of 51 samples for the calibration set and 21 samples for the test set. PCA scores plot discriminated gluten adulterated and unadulterated GBF samples with 100% accuracy for the first two principal components (PCs). The optimal prediction model was obtained after a combination of baseline (offset and baseline linear correlation) and standard normal variate (SNV) pre-processing technique. This model showed a 94% coefficient of determination of cross-validation (R²_cv) and prediction (R²_p); root mean square error of cross-validation (RMSECV) of 3.7 mg/kg, root mean square error of prediction (RMSEP) of 3.9 mg/kg; and RPD value of 4. This work has demonstrated that Vis-NIRS method is a robust and feasible technology that may be used to ensure the safety of banana flour and that this product stays gluten-free by providing good and reliable gluten detection and quantification prediction models.

Characterization of gliadin, secalin and hordein fractions using analytical techniques

Prolamins, alcohol soluble storage proteins of the Triticeae tribe of Gramineae family, are known as gliadin, secalin and hordein in wheat, rye and barley respectively. Prolamins were extracted from fifteen cultivars using DuPont protocol to study their physiochemical, morphological and structural characteristics. SDS-PAGE of prolamins showed well resolved low molecular weight proteins with significant amount of albumin and globulin as cross-contaminant. The β-sheet (32.72–37.41%) and β-turn (30.36–37.91%) were found higher in gliadins, while α-helix (20.32–28.95%) and random coil (9.05–10.28%) in hordeins. The high colloidal stability as depicted by zeta-potential was observed in gliadins (23.5–27.0 mV) followed secalins (11.2–16.6 mV) and hordeins (4.1–7.8 mV). Surface morphology by SEM illustrated the globular particle arrangement in gliadins, sheet like arrangement in secalins and stacked flaky particle arrangement in hordeins fraction. TEM studies showed that secalin and hordein fractions were globular in shape while gliadins in addition to globular structure also possessed rod-shaped particle arrangement. XRD pattern of prolamin fractions showed the ordered crystalline domain at 2θ values of 44.1°, 37.8° and 10.4°. The extracted prolamins fractions showed amorphous as well as crystalline structures as revealed by XRD and TEM analysis. Space saving hexagonal molecular symmetry was also observed in TEM molecular arrangement of prolamins which has profound application in development of plant-based polymers and fibres.

Effective Degradation of Gluten and Its Fragments by Gluten-Specific Peptidases: A Review on Application for the Treatment of Patients with Gluten Sensitivity

To date, there is no effective treatment for celiac disease (CD, gluten enteropathy), an autoimmune disease caused by gluten-containing food. Celiac patients are supported by a strict gluten-free diet (GFD). However, in some cases GFD does not negate gluten-induced symptoms. Many patients with CD, despite following such a diet, retain symptoms of active disease due to high sensitivity even to traces of gluten. In addition, strict adherence to GFD reduces the quality of life of patients, as often it is difficult to maintain in a professional or social environment. Various pharmacological treatments are being developed to complement GFD. One promising treatment is enzyme therapy, involving the intake of peptidases with food to digest immunogenic gluten peptides that are resistant to hydrolysis due to a high prevalence of proline and glutamine amino acids. This narrative review considers the features of the main proline/glutamine-rich proteins of cereals and the conditions that cause the symptoms of CD. In addition, we evaluate information about peptidases from various sources that can effectively break down these proteins and their immunogenic peptides, and analyze data on their activity and preliminary clinical trials. Thus far, the data suggest that enzyme therapy alone is not sufficient for the treatment of CD but can be used as a pharmacological supplement to GFD.

Post-translational cleavage of HMW-GS Dy10 allele improves the cookie-making quality in common wheat (Triticum aestivum)

Wheat is a major staple food crop worldwide because of the unique properties of wheat flour. High molecular weight glutenin subunits (HMW-GSs), which are among the most critical determinants of wheat flour quality, are responsible for the formation of glutenin polymeric structures via interchain disulfide bonds. We herein describe the identification of a new HMW-GS Dy10 allele (Dy10-m619SN). The amino acid substitution (serine-to-asparagine) encoded in this allele resulted in a partial post-translational cleavage that produced two new peptides. These new peptides disrupted the interactions among gluten proteins because of the associated changes to the number of available cysteine residues for interchain disulfide bonds. Consequently, Dy10-m619SN expression decreased the size of glutenin polymers and weakened glutens, which resulted in wheat dough with improved cookie-making quality, without changes to the glutenin-to-gliadin ratio. In this study, we clarified the post-translational processing of HMW-GSs and revealed a new genetic resource useful for wheat breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-021-01238-9.

Characterization of Bacillus cereus AFA01 Capable of Degrading Gluten and Celiac-Immunotoxic Peptides

Wheat gluten elicits a pro-inflammatory immune response in patients with celiac disease. The only effective therapy for this disease is a life-long gluten-free diet. Gluten detoxification using glutenases is an alternative approach. A key step is to identify useful glutenases or glutenase-producing organisms. This study investigated the gluten-degrading activity of three Bacillus cereus strains using gluten, gliadin, and highly immunotoxic 33- and 13-mer gliadin peptides. The strain AFA01 was grown on four culture media for obtaining the optimum gluten degradation. Complete genome sequencing was performed to predict genes of enzymes with potential glutenase activity. The results showed that the three B. cereus strains can hydrolyze gluten, immunotoxic peptides, and gliadin even at pH 2.0. AFA01 was the most effective strain in degrading the 33-mer peptide into fractions containing less than nine amino acid residues, the minimum peptide to induce celiac responses. Moreover, growth on starch casein broth promoted AFA01 to degrade immunotoxic peptides. PepP, PepX, and PepI may be responsible for the hydrolysis of immunotoxic peptides. On the basis of the potential of gluten degradation, AFA01 or its derived enzymes may be the best option for further research regarding the elimination of gluten toxicity.

Solvent Retention Capacity and Gluten Protein Composition of Durum Wheat Flour as Influenced by Drought and Heat Stress

Drought and temperature stress can cause considerable gluten protein accumulation changes during grain-filling, resulting in variations in wheat quality. The contribution of functional polymeric components of flour to its overall functionality and quality can be measured using solvent retention capacity (SRC). The aim of this study was to determine the effect of moderate and severe drought and heat stress on SRC and swelling index of glutenin (SIG) in six durum wheat cultivars with the same glutenin subunit composition and its relation with gluten protein fractions from size exclusion high performance liquid chromatography. Distilled water, sodium carbonate and sucrose SRC reacted similarly to stress conditions, with moderate heat causing the lowest values. Lactic acid SRC and SIG reacted similarly, where severe heat stress highly significantly increased the values. SIG was significantly correlated with sodium dodecyl sulphate sedimentation (SDSS) and flour protein content (FPC) under all conditions. Lactic acid SRC was highly correlated with FPC under optimal and moderate heat stress and with SDSS under moderate drought and severe heat. SIG was negatively correlated with low molecular weight glutenins under optimal and drought conditions, and combined for all treatments. The relationship between SRC and gluten proteins was inconsistent under different stress conditions.

Research on the influences of two alcohol soluble glutenins on the retrogradation of wheat amylopectin/amylose

Two alcohol soluble glutenins (ASGLUs) were extracted from gluten and further separated by column chromatography. The ASGLUs with Mw lower than 20,000 (ASGLU 1) and Mw higher than 70,000 (ASGLU 2) show the total amino acid contents of 86.71 g/100 g and 62.847 g/100 g respectively. Both of them are rich in Glu (45.574% and 43.224%) and Pro (15.447% and 16.370%) while poor in cys-s, met and lys (less than 1%). When wheat amylopectin/amylose retrogrades with those ASGLUs, the retrogradation rate of amylopectin with ASGLU 1 enhances significantly. UV-Vis, X-ray diffraction, FT-IR, DSC, CD and solid ¹³C NMR suggest that the double helixes of amylopectin short-chain branching are unwound during gelatinization. The hydrogen bonds of ASGLU 1 between amide and carbonyl oxygen are destroyed, meanwhile, β-sheets are unfolded. During retrogradation, ASGLU 1 with less steric hindrance gets into the crevice of amylopectin and combines with the short-chain branching by hydrogen bond. The retrogradation dynamics show that the nucleation type of amylopectin-ASGLU 1 changes from instantaneous to rod-like growth during the process of retrogradation. β-sheet of ASGLU 1 changes to β-turn and random conformations at the meantime. The results provide a key targeting to control retrogradation of dough.

Development of polyoxyethylene (2) oleyl ether-gliadin nanoparticles: Characterization and in vitro cytotoxicity

Natural polymers have been widely investigated as materials for the delivery of active compounds as a consequence of their biocompatibility, low-cost and the opportunity they furnish to obtain micro- and nanostructures. In this investigation, commercial wheat gliadin was used as raw material with the aim of obtaining a vegetal protein-based nanoformulation to be used for various applications. The influence of non-ionic and anionic surfactants on the physico-chemical properties of gliadin nanoparticles was evaluated in order to propose a suitable candidate able to stabilize the colloidal structure. The use of Super Refined polyoxyethylene (2) oleyl ether gave the best results, promoting the formation of spherical-shaped nanosystems with a narrow size distribution. The oleyl ether-based emulsifier prevented the destabilization of the colloidal systems when pH- and temperature-dependent stress was applied. A freeze-dried formulation was obtained when mannose was used as a cryoprotectant. Polyoxyethylene (2) oleyl ether-stabilized nanosystems were shown to retain and release both hydrophilic and lipophilic model compounds in a controlled manner. The cytotoxicity of the surfactant-free and polyoxyethylene (2) oleyl ether-stabilized gliadin based nanosystems was assessed on human cells, both normal and tumoural, in order to investigate the concentrations of particles that can be used during in vitro experiments. Polyoxyethylene (2) oleyl ether-stabilized gliadin-based nanosystems are promising carriers for the delivery of several active compounds.

Engineered Nanotopography on the Microfibers of 3D-Printed PCL Scaffolds to Modulate Cellular Responses and Establish an In Vitro Tumor Model

Scaffold-based three-dimensional (3D) cell culture systems have gained increased interest in cell biology, tissue engineering, and drug screening fields as a replacement of two-dimensional (2D) monolayer cell culture and as a way to provide biomimetic extracellular matrix environments. In this study, microscale fibrous scaffolds were fabricated via electrohydrodynamic printing, and nanoscale features were created on the fiber surface by simply leaching gliadin of poly(ε-caprolactone) (PCL)/gliadin composites in ethanol solution. The microstructure of the printed scaffolds could be precisely controlled by printing parameters, and the surface nanotopography of the printed fiber could be tuned by varying the PCL/gliadin ratios. By seeding mouse embryonic fibroblast (NIH/3T3) cells and human nonsmall cell lung cancer (A549) cells on the printed scaffolds, the cellular responses showed that the fiber nanotopography on printed scaffolds efficiently favored cell adhesion, migration, proliferation, and tissue formation. Quantitative analysis of the transcript expression levels of A549 cells seeded on nanoporous scaffolds further revealed the upregulation of integrin-β1, focal adhesion kinase, Ki-67, E-cadherin, and epithelial growth factor receptors over what was observed in the cells grown on the pure PCL scaffold. Furthermore, a significant difference was found in the relevant biomarker expression on the developed scaffolds compared with that in the monolayer culture, demonstrating the potential of cancer cell-seeded scaffolds as 3D in vitro tumor models for cancer research and drug screening.

Heteroalleles in Common Wheat: Multiple Differences between Allelic Variants of the Gli-B1 Locus

The Gli-B1-encoded γ-gliadins and non-coding γ-gliadin DNA sequences for 15 different alleles of common wheat have been compared using seven tests: electrophoretic mobility (EM) and molecular weight (MW) of the encoded major γ-gliadin, restriction fragment length polymorphism patterns (RFLPs) (three different markers), Gli-B1-γ-gliadin-pseudogene known SNP markers (Single nucleotide polymorphisms) and sequencing the pseudogene GAG56B. It was discovered that encoded γ-gliadins, with contrasting EM, had similar MWs. However, seven allelic variants (designated from I to VII) differed among them in the other six tests: I (alleles Gli-B1i, k, m, o), II (Gli-B1n, q, s), III (Gli-B1b), IV (Gli-B1e, f, g), V (Gli-B1h), VI (Gli-B1d) and VII (Gli-B1a). Allele Gli-B1c (variant VIII) was identical to the alleles from group IV in four of the tests. Some tests might show a fine difference between alleles belonging to the same variant. Our results attest in favor of the independent origin of at least seven variants at the Gli-B1 locus that might originate from deeply diverged genotypes of the donor(s) of the B genome in hexaploid wheat and therefore might be called “heteroallelic”. The donor’s particularities at the Gli-B1 locus might be conserved since that time and decisively contribute to the current high genetic diversity of common wheat.

Effects of Physical and Chemical Factors on the Structure of Gluten, Gliadins and Glutenins as Studied with Spectroscopic Methods

This review presents applications of spectroscopic methods, infrared and Raman spectroscopies in the studies of the structure of gluten network and gluten proteins (gliadins and glutenins). Both methods provide complimentary information on the secondary and tertiary structure of the proteins including analysis of amide I and III bands, conformation of disulphide bridges, behaviour of tyrosine and tryptophan residues, and water populations. Changes in the gluten structure can be studied as an effect of dough mixing in different conditions (e.g., hydration level, temperature), dough freezing and frozen storage as well as addition of different compounds to the dough (e.g., dough improvers, dietary fibre preparations, polysaccharides and polyphenols). Additionally, effect of above mentioned factors can be determined in a common wheat dough, model dough (prepared from reconstituted flour containing only wheat starch and wheat gluten), gluten dough (lack of starch), and in gliadins and glutenins. The samples were studied in the hydrated state, in the form of powder, film or in solution. Analysis of the studies presented in this review indicates that an adequate amount of water is a critical factor affecting gluten structure.

Effect of fats and oils on pasting and textural properties of wheat flour

Effects of fats and oils on pasting and textural properties of soft and hard wheat flours were investigated. Fats and oils significantly diminished peak viscosity, trough, breakdown, setback, final viscosity and escalated the pasting temperature. Effects on pasting properties were found more noticeable for soft wheat flour. Pasting properties of soft and hard wheat flour were significantly affected by coconut oil and hydrogenated fat. Texture analyser results divulged that fats and oils decreased the flour gel hardness, adhesiveness, gumminess and chewiness of flour gel of both varieties, whereas gel springiness was improved. Textural properties of wheat flour gels of both soft and hard wheat varieties were influenced most extensively by groundnut oil.

Diversity in Grain, Flour, Amino Acid Composition, Protein Profiling, and Proportion of Total Flour Proteins of Different Wheat Cultivars of North India

Wheat cultivars grown at three different locations in North India were assessed for their variability in kernel and flour characteristics. Protein and the wet and dry gluten contents of the flour varied significantly (p ≤ 0.05) from 9.32 to 12.60%, 23.46 to 43.04%, and from 8.28 to 15.00%, respectively. Wheat varieties exhibited moderate sodium dodecyl sulfate (SDS) sedimentation and solvent retention values. Flour showed a significant (p ≤ 0.05) difference in the amino acid composition. Lysine, having the lowest chemical score, was the first most limiting amino acid in all wheat varieties. The variability of total flour proteins determined by SDS-PAGE showed polymorphism both in the number and intensity of bands, particularly in the molecular weight range of 35.1-42.8 kDa corresponding to the α-, β-, and γ-gliadin/low-molecular-weight glutenin subunit (LMW-GS) region. Pearson's correlation established between the various grain and flour parameters showed a significant correlation, which can result in better end product use.