Microstructure Of Gluten Research Articles

Honey induces changes in the molecular structure and microstructure of gluten in wheat-rye sourdoughs.

Chemical oxidizers and redox enzymes have traditionally been used to enhance the quality of baked goods. However, consumers now seek natural and clean-label ingredients, avoiding those with chemical-sounding names. Honey, a natural source of glucose oxidase (GOX), represents a promising alternative to purified enzymes for baking purposes. This study aimed to evaluate the effect of honey on the molecular structure and microstructure of gluten proteins in sourdough fermented by different lactic acid bacteria (LAB) strains. Four wheat-rye (1:1) sourdoughs were prepared, each supplemented with honey and inoculated with a different LAB strain. Additionally, two uninoculated doughs, one with honey (honey dough) and the other without (control dough), were prepared under identical conditions. Electronic paramagnetic resonance spectroscopy revealed the presence of hydrogen peroxide in honey solutions, indicating its role as an active source of GOX. Raman spectroscopy showed that honey addition altered the molecular structure of gluten by increasing the proportion of random coils at the expense of α-helix structures. This change is likely attributed to the competition between honey sugars and gluten proteins for water molecules in this system. Moreover, honey led to a decrease in the free sulfhydryl content of gluten compared to the control dough, suggesting an increase in disulfide crosslinking points. These enhanced protein-protein interactions were observed in scanning electron microscopy micrographs as a coarse gluten network composed of interconnected strands and fibrils. All LAB strains exhibited optimal acidification (pH < 4.3) in honey-supplemented sourdoughs, promoting the hydrolysis of gluten proteins into smaller fragments. Overall, honey-supplemented sourdoughs showed a gradual increase in the β-sheet content while decreasing the proportion of random coils over time. This trend suggests that the polypeptide fragments interacted through interchain hydrogen bonds, leading to a more ordered structure, which likely contributes to providing dough with good baking aptitude.

Atomic force microscopy, deformation-recovery and numerical study of wheat dough

Experimental and numerical modelling work related to microstructure and deformation of starch, gluten and wheat dough was presented. Atomic force microscopy analyses through force spectroscopy on starch samples showed elastic behaviour of both dried and reconstituted wet starch granules, where wet starch was shown to be more cohesive than dried starch. Deformation-recovery test over time under compression mode showed almost complete recovery to original sample height of gluten, whereas only a slight recovery was observed for dough. Finite element modelling was then commenced to simulate gluten deformation-recovery and starch-gluten dough deformation. The gluten geometry used for the starch-gluten dough model was obtained from cryo-SEM image from the previous work before the starch geometry was then included. The interface between the starch and gluten model was defined using viscoelastic cohesive zone elements. The modelling results suggested significant influence of gluten cellular structure towards starch-gluten dough integrity. In addition, the results from the current work further supported the previous report of the starch-gluten interfacial behaviour using viscoelastic cohesive zone model.

Effects of electrostatic field-assisted freezing on the functional properties and aggregation behavior of gluten

Changes in gluten during the freezing process could cause a deterioration in dough quality, which would be solved by electrostatic field treatment. This paper investigated the effects of electrostatic field assisted freezing (EFAF) on the functional properties, structural characteristics and aggregation behavior of gluten. The results showed that EFAF improved the functional properties of gluten with enhanced water holding, emulsifying and foaming properties. When the electrostatic field was applied, the α-helix content and g-g-g conformation of gluten proteins increased with a maximum of 27.50 % and 40.05 %, respectively, which were significantly different from the control (P < 0.05). The degree of depolymerization of gluten macromolecules decreased when the electrostatic field was applied, and was obtained to be the lowest at 600 V with 5.71 %, which was significantly different from that without applied electrostatic field (P < 0.05). After EFAF, AFM analysis showed a more intact glutenin chain structure and smaller particle size of the gliadin. These results indicated that EFAF improved the functional properties of gluten proteins by the mechanism of slowing down the depolymerization of gluten macromolecules, maintaining the chain structure of gluten, stabilizing the intramolecular disulfide bonds of gliadin, and stabilizing the microstructure of gluten.

Structural characteristics variations of dough incorporated with long-chain inulin modified by phosphorylation

In the study, long-chain inulin (FXL) was modified by phosphorylation (PFXL) to obtain new characteristics for improving the quality of dough. The secondary structure, disulfide bond content, surface hydrophobicity, and microstructure of gluten in dough, as well as the emulsification properties of gluten, were investigated. The results showed that the PFXL could affect the gluten structure through hydrogen bonding interactions and hydrophobic interactions, thus increasing the contents of β-sheets structure, α-helices structure and the disulfide bond, and decreasing the surface hydrophobicity of the dough. And the emulsification activity and stability of gluten were also improved. A more stable and ordered gluten network structure was promoted to form mainly through a liquid lamellar film formed by PFXL. Generally, the phosphorylation modification for FXL is an effective alternative to increasing the additive amount of dietary fiber in the dough and improving its quality.

Effect of fermentation on structural properties and antioxidant activity of wheat gluten by Bacillus subtilis.

Bacillus subtilis has been extensively studied for its ability to inhibit the growth of harmful microorganisms and its high protease activity. In this study, Bacillus subtilis was used to ferment gluten and assess the effects of the fermentation process on the physicochemical, microstructure and antioxidant properties of gluten. The results of Fourier infrared spectroscopy (FT-IR) and circular chromatography (CD) showed a significant decrease in the content of α-helix structures and a significant increase in the content of β-sheet structures in gluten after fermentation (p < 0.05). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that glutenin was degraded into small molecular peptides with a molecular weight of less than 26 kDa after 24 h of fermentation; meanwhile, the fermentation process significantly increased the free amino acid content of the samples (p < 0.05), reaching 1923.38 μg/mL at 120 h of fermentation, which was 39.46 times higher than that at 24 h of fermentation (p < 0.05). In addition, the fermented back gluten has higher free radical scavenging activity and iron reduction capacity. Therefore, fermented gluten may be used as a functional food to alleviate oxidative stress. This study provides a reference for the high-value application of gluten.

Using electric field to modify wet gluten as meat analogue material: A comparative study between pulsed and direct current electric fields

To assess the efficacy of electric field (EF) on vegetable protein juice-holding and texturisation as a low denaturation processing means, the impacts of pulsed (PEF) and low direct current (DCEF) electric field on the water- (WHC) and oil-holding capacity (OHC), microstructure, texture and physical structure of wheat gluten were investigated using wet gluten dough. The results showed that the PEF and DCEF affected the WHC and OHC significantly. The PEF seemed not to affect the textural properties so severely although significant differences appeared in hardness, chewiness, gumminess, and cohesiveness; there were no significant differences either in springiness or in resilience. The DCEF had a stronger impact on all the textural indices. Scanning electronic microscopy suggested that the PEF caused smaller and uniform micropores and the DCEF derivated more continuous and compact microstructure. Fourier transform infrared spectrometry demonstrated that EF significantly altered the composition proportion of the secondary structure. A slight blue shifts of UV spectra, a red shift of fluorescence spectra, and an increased surface hydrophobicity of gluten could be observed after EF treatment. X-ray diffractometry demonstrated that the EF significantly made the physical structure of wet gluten compacter. The results suggested that EF is promising in vegetable protein texturisation.

Effect of freeze‐thaw cycles at different temperatures on the properties of gluten proteins in unfermented dough

AbstractBackground and ObjectivesThe present study investigated the effects of different freezing temperatures and different freeze‐thaw cycles on the physical, chemical, functional, and structural properties of gluten protein. The water‐holding capacity, rheological properties, water distribution, microstructure, and secondary structure were measured.FindingsWith the same number of freeze‐thaw cycles, the water‐holding capacity of gluten was higher at low temperature, and the viscoelasticity and binding water content increased slightly with decreasing temperature. At −30°C and −24°C, the microstructure of gluten protein was more uniform and relatively intact. Lower temperatures significantly decreased the ratio of α‐helix and β‐turns and significantly increased the ratio of β‐sheets. At the same temperature, the water‐holding capacity, bound water content, and viscoelasticity of the freeze‐thaw cycle gradually decreased with the increase in the number of freeze‐thaw cycles. Compared to the first freeze‐thaw cycle (F1), the holes in the microstructure of gluten in the fifth freeze‐thaw cycle (F5) were larger and fractured.ConclusionsIncreasing the number of freeze‐thaw cycles damaged the properties of gluten protein, and lower temperatures were more conducive to maintaining the stability of gluten properties.Significance and NoveltyThis study revealed the changes in gluten protein quality during storage at −6°C, −12°C, −18°C, −24°C, and −30°C and different numbers of freeze‐thaw cycles. The results provide a theoretical basis for the quality management and control of frozen dough during storage and transportation.

Impact of xanthan gum on gluten microstructure and bread quality during the freeze-thaw storage

Xanthan gum (XG) is commonly used as a hydrocolloid in frozen dough to improve the texture and the sense quality of the products. The effects of XG on the molecular weight, secondary structure, microstructure of gluten and bread quality during freeze-thaw storage were studied. As results showed, XG and gluten formed more compact complexs through electrostatic interactions, which relieved the destruction of side chain molecules for gluten. XG protected the molecular weight of gluten proteins from 2 × 106 Da–108 Da. FTIR showed that XG-gluten mixtures had more α-helices (28.98%) and less intermolecular β-sheets (9.45%) compared with gluten. The secondary structure of XG-gluten remains unchanged under freeze-thaw treatment from 0 to 60 days. However, when the time reached 120 days, there was a decrease in α-helices (11.85%) and β-turns (6.28%) accompanied an increase by β-sheets (19.13%). CLSM revealed that XG gradually migrated to the centre with moisture after freeze-thaw storage, thereby protecting the gluten network. So the bread, prepared from XG-gluten mixtures, possessed superior colour, volume and visible pore proportion than bread without XG. Overall, the freeze-thaw stability of the gluten was enhance by XG under freeze-thaw treatment from 0 to 90 days.

Effect of Highland Barley on Rheological Properties, Textural Properties and Starch Digestibility of Chinese Steamed Bread.

Highland barley has a different composition and structure to other crops. It has higher contents of total polyphenol (TPC), total flavonoid (TFC) and β-glucan, which can be supplemented to improve the nutrition of wheat-flour-based food. In this study, the flours of three different grain-colored highland barley varieties Beiqing 6 (BQ), Dulihuang (DLH), and Heilaoya (HLY), were added to Jimai60 (JM, a wheat variety with medium gluten) wheat flour at different substitution levels to investigate their effects on the unextractable polymeric protein (UPP) content, micro-structure, rheological properties and mixing properties of dough, and the color, texture, flavor, and in vitro digestion of Chinese steam bread (CSB). The results showed that the moderate substitution of highland barley (20%) increased the UPP%, optimized the micro-structure of gluten, and improved its rheological properties by increasing dough viscoelasticity. The CSBs made from the composite flours exhibited a similar specific volume, cohesiveness, springiness and resilience to wheat CSB, while the firmness of composite CSBs (particularly JM-HLY-20) was delayed during storage. Importantly, the addition of highland barley increased the contents of TPC, TFC and β-glucan, but decreased the in vitro starch digestibility of CSBs. A sensory evaluation showed that JM-HLY CSB was the most preferable. Taken together, highland barley can be used as a fine supplement to food products, with health-promoting properties.

Effect of phosphate salts on the gluten network structure and quality of wheat noodles

The effects of three phosphate salts (PS) on the secondary structure, microstructure of gluten, rheological properties of dough and water status of noodles were investigated to determine the mechanisms underlying the changes in the quality of noodles. Changes in the secondary structure detected were the increased number of β-sheet and decreased number of random coil structures. PS reduced the content of free sulfhydryl (SH) and increased the content of disulfide (SS) bonds. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicated that the band density of the high molecular regions of the gluten was reduced. The results showed that adding PS induced a more compact microstructure and improved the G′ and G′′ values of the dough. After adding PS, the water-solids interaction in noodles was enhanced by the decreased water mobility. It was concluded that PS promoted the water holding capacity of the noodles and strengthened the gluten network.

Addition of Aegilops geniculata 1Ug chromosome improves the dough rheological properties by changing the composition and micro-structure of gluten

Aegilops geniculata, a relative of common wheat, has many useful traits for the improvements of wheat varieties. The wheat-Ae. geniculata disomic addition lines (DALs) carrying prior traits need to be characterized for wheat varieties improvement. We currently found that CS-1Ug (Chinese Spring-Ae. geniculata 1Ug DAL) possessed improved dough rheological properties than CS (Chinese Spring) did, and investigated the reasons of those rheological changes in dough. The results showed that CS-1Ug carries a novel high-molecular-weight glutenin subunit (HMW-GS), a substitute for Dx2 from CS, which led to the changes in the relative proportion of individual HMW-GS in total HMW-GSs. Changes in gluten composition improved the stability and elasticity of dough by promoting the accumulation of unextractable polymeric protein, and optimizing the micro-structure of the gluten. The current study provides basic information on CS-1Ug used as a potential resource for future wheat quality breeding.

Analysis of microstructure and texture of gluten‐ and lactose‐free cereal bars, produced with different hydrocolloids and drying temperatures and no‐added sugar

A gluten- and lactose-free cereal bar with no-added sugar, suitable for lactose intolerants and for celiac people was developed. The cereal bar was formulated with extruded rice, oat flakes, flaxseeds, sesame, sunflower lecithin, hydrocolloids, maltodextrin, mannitol, maltitol syrup, and sodium chloride. The effect of three different hydrocolloids (locust bean gum, pectin, and carboxymethyl cellulose), and processing temperature on microstructure, moisture content, Aw, texture, and sensory properties of cereal bars was assessed by an L9 orthogonal experimental design based on Taguchi methods. Results indicated that Aw and moisture content were not affected by the type or levels of the hydrocolloids studied, but decreased with the increase in drying temperature. Hardness and fracturability values increased with temperature increase. From the Scanning Electron Microscopy analysis, it was concluded that increasing processing temperature provides a more uniform microstructure of cereal bars. The application of the Taguchi method, allowed identifying the temperature as being the factor of greater influence on the characteristics of the cereal bars. In addition, according to this method, the optimum formulation is 0.05% locust bean gum and 0.1% pectin with 70°C as the optimum processing temperature. Practical applications Organizations responsible for public health throughout the world are increasingly concerned with the feeding of populations, and great efforts are made to promote the adoption of nutritious and balanced diet in order to decrease the occurrence of the chronic diseases constantly related to inadequate diets. Cereal bars were introduced over a decade ago as a “healthy” alternative confectionery, and became a convenience food, as they can be easily consumed, do not require any preparation and are a source of essential nutrients, such as vitamins, minerals, fibers, proteins, and complex carbohydrates. The effect of the combination of different levels (0%, 0.05%, and 0.1% wt/wt) of locust bean gum, pectin, and carboxymethyl cellulose, and three drying temperatures (20°C, 60°C and 70°C), on microstructure, sensory, and texture properties of the cereal bars was analyzed. Results obtained with this work showed that it is possible to produce a gluten- and lactose-free cereal bar with no-added sugar, suitable for lactose intolerants and for celiac people. This can be achieved by taking advantage of the synergy between two hydrocolloids in different concentrations to improve the hardness of the cereal bar. Also, with the help of an experimental design based on Taguchi method it was possible to find out the optimum formulation and processing temperature of the cereal bars. In this work, the results show that the temperature also has a great influence, with 70°C being the most suitable to promote greater hardness.

Effect of Maillard reaction conditions on the solubility and molecular properties of wheat gluten-maltose conjugates.

In this experiment, the conjugation reaction between gluten and maltose via Maillard reaction under dry‐heated condition was studied. The process conditions for the preparation of protein–maltose conjugates with optimum solubility were optimized by using Box‐Behnken model. The conjugation reaction and the structure changes of the protein–maltose conjugates were confirmed by infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results showed that the process conditions for the preparation of protein–maltose conjugates with optimum solubility were as follows: temperature 50.72°C, time 1.92 days, and gluten/maltose (W/W) 267.36%. The infrared spectroscopy showed that the structure of the modified protein had a very obvious change, including the decrease in β‐fold and β‐turn and the increase in α‐helix at a certain degree. But the conjugation reaction has little effect on the irregular coiled structure. The scanning electron microscopy showed that the microstructure of gluten is small grainy, but gluten–maltose conjugate looks sheet with bigger volume.

The overexpression of high-molecular-weight glutenin subunit Bx7 improves the dough rheological properties by altering secondary and micro-structures of wheat gluten.

Bread wheat (Triticum aestivum L.) is one of the crucial cereals consumed by human beings and wheat gluten, the natural macromolecules, mainly determines the processing quality of wheat dough. The high-molecular-weight glutenin subunits (HMW-GSs) of gluten proteins are recognized as one of the main components regulating the rheological properties of dough. The overexpressed Bx7 subunit (Bx7OE) has been reported to improve wheat quality and rheological properties of dough, however its effect on secondary and micro- structures of gluten is still unclear. In this study, we evaluated the composition of main storage proteins in wheat grains of two near-isogenic lines and studied the effect of Bx7 subunit expression level on the secondary structures of gluten and micro-structure of gluten during dough mixing process. Results showed the protein content, HMW-GSs proportion in total glutenins and free sulfhydryl content increased in the flour of HMW-Bx7OE wheat line, and the accumulation of unextractable polymeric protein during grain filling stage accelerated. It was found that the content of β-sheets in secondary structures of gluten increased and a more compact micro-structure of gluten network formed in the dough. Protein network analysis characterized and quantified the alterations in the gluten micro-structure. In the process of dough mixing, protein area, total protein length, number of junctions and branching rate reach the peak at dough development time, which was consistent with Chopin mixing profile. Interestingly, during dough mixing, the above-mentioned parameters of HMW-Bx7OE showed less changes than those of HMW-Bx7 wheat line, indicating Bx7OE improved the dough stability during mixing. To conclude, Bx7OE alters the secondary and micro- structures of gluten and thus improves the mixing and rheological properties of wheat dough.

Effect of baked wheat germ on gluten protein network in steamed bread dough

SummaryThe effect of baked wheat germ (BWG) on the gluten network structure in steam bread dough was investigated. The secondary structure, free sulphydryl (‐SH) content, disulphide (‐SS‐) bonds content and microstructure of gluten were analysed to evaluate gluten structural changes. The addition of different amounts of BWG (0, 2, 4, 6, 8, 10, and 12%) in dough resulted in decreased content of α‐helix and β‐sheet structures, but increased random coils, which indicated that a disordered structure was formed. The presence of BWG increased the ‐SH content but decreased the ‐SS‐ bonds content, which indicated fracture of disulfide bonds. Confocal laser scanning microscopy (CLSM) analysis indicated that steamed bread dough containing BWG had larger‐sized gas cell and granules of starch separated by the protein matrix, which weakened the gluten network structure. These changes may inevitably affect the viscoelastic properties of steamed bread dough.

Hydration, water distribution and microstructure of gluten during freeze thaw process: Role of a high molecular weight dextran produced by Weissella confusa QS813

The effect of exopolysaccharide (EPS) produced by Weissella confusa QS813 on the hydration, water distribution, rheology and microstructure of wheat gluten during freeze–thaw cycles (FTC) was investigated. Addition of EPS increased the water content of fresh gluten and delayed the dehydration of gluten during FTC. Low field-nuclear magnetic resonance showed that the presence of EPS reduced the mobility of both confined and bulk water in the fresh gluten matrix. Proton distribution changes in gluten during FTC indicated that deterioration of the gluten network was attributable to ice recrystallization of capillary confined water and bulk water. The presence of EPS effectively reduced the release of bulk water and retarded the redistribution of confined water induced by FTC. Dynamic oscillatory studies indicated that the presence of EPS induced a softening effect on the fresh gluten. FTC significantly decreased the rheological parameters, storage modulus (G′) and loss modulus (G″), of all gluten samples. Gluten with higher concentrations of EPS (above 0.5%) exhibited a delayed decrease in G′ and G″ and maintained a constant tanδ value after FTC. Laser scanning confocal microscope and scanning electron microscope revealed that EPS maintained the structural integrity of gluten during FTC, suggesting an inhibitory effect on the recrystallization of ice crystals. These results in the present study indicated that the bacterial dextran is a promising cryoprotectant for the frozen dough industry.

The influence of night warming treatment on the micro-structure of gluten in two wheat cultivars

Bread wheat (Triticum aestivum L.) is one of the important cereals for human life. As people pursue higher quality of life, the requirements of improving the quality of wheat flour also increase accordingly. Global warming exhibits asymmetrically, that is, the warming rate during the night is significantly greater than that during the day. However, the effect of moderate warming on the quality formation of wheat is still unclear. In this study, night warming treatment was carried out at the grain filling stage to clarify the effects of night warming on the accumulation of UPP% (percentage of SDS-unextractable polymeric protein) and micro-structure of wheat gluten, with a strong gluten wheat cultivar Xinong979 and a plain gluten wheat cultivar Tam107 as materials. Results showed that night warming treatment significantly increased the protein content in the grains of the two varieties, accelerated the accumulation rate of UPP%, made the micro-structure of wheat dough more compact and dense and increased the flour processing quality. Quantitative analysis of protein networks showed night warming increased junction density, total protein length and lacunarity of micro-structure of dough in both varieties. Night warming treatment in this study helped the two varieties demonstrate better quality traits in both wheat grain and dough.

Effects of HMW-GS at Glu-B1 locus on the polymerization of glutenin during grain development and on the secondary and micro-structures of gluten in wheat (Triticum aestivum L.)

The viscoelastic properties of wheat dough are due mainly to the structure of gluten and interactions within the protein complex. We determined the effects of high-molecular-weight glutenin subunit (HMW-GS) on the polymerization of glutenin during grain development and on the secondary and micro-structures of gluten, using Xinong1718 and its four near-isogenic lines (NILs). The polymerization of glutenin was monitored based on the percentage of unextractable polymeric protein (%UPP). Xi1718-3 with the superior allele Bx17 + By18 exhibited a rapid increase in %UPP five days earlier than the other lines with variations at Glu-B1, thereby obtained the highest %UPP at maturity. The secondary structures, such as the proportion of β-sheets and the α-helix/β-sheet ratio differed significantly among the NILs. The micro-structure of gluten in NILs varied in terms of the pore size distribution and cross-linkage patterns. Significant correlations were found between %UPP with the β-sheet content and α-helix/β-sheet ratio, so these secondary structures could also be used as indicators of wheat flour quality.

Influence of high-molecular-weight glutenin subunit composition at Glu-A1 and Glu-D1 loci on secondary and micro structures of gluten in wheat (Triticum aestivum L.)

As one of critical gluten proteins, high-molecular-weight glutenin subunits (HMW-GS) mainly affect the rheological behaviour of wheat dough. The influence of HMW-GS variations at the Glu-A1 and Glu-D1 loci on both secondary and micro structures of gluten and rheological properties of wheat dough was investigated in this study. Results showed that the Amide I bands of the three near-isogenic lines (NILs) shifted slightly, but the secondary structures differed significantly. The micro structure of gluten in NIL 4 (Ax null) showed bigger apertures and less connection, compared to that in Xinong 1330 (Ax1). The micro structure of gluten in NIL 5 (Dx5+Dy10) showed more compact than that in Xinong 1330 (Dx2+Dy12). Correlation analysis demonstrated that the content of β-sheets and disulfide bonds in gluten has a significant relationship with dough properties. The secondary structures of native gluten are suggested to be used as predictors of wheat quality.

Influence of high-molecular-weight glutenin subunit composition at Glu-B1 locus on secondary and micro structures of gluten in wheat (Triticum aestivum L.)

Glutenin is one of the critical gluten proteins that affect the processing quality of wheat dough. High-molecular-weight glutenin subunits (HMW-GS) affect rheological behavior of wheat dough. This research demonstrated the effects of four variations of HMW-GS composition at the Glu-B1 locus on secondary and micro structures of gluten and rheological properties of wheat dough, using the bread wheat Xinong 1330 and its three near-isogenic lines (NILs). Results indicated that the Amide I bands of the four wheat lines shifted slightly, but the secondary structure, such as content of α-helices, β-sheets, disulfide bands, tryptophan bands and tyrosine bands, differed significantly among the four NILs. The micro structure of gluten in NIL 2 (Bx14+By15) and NIL 3 (Bx17+By18) showed more cross linkage, with two contrasting patterns. Correlation analysis demonstrated that the content of β-sheets and disulfide bonds has a significant relationship with dough stability, which suggests that the secondary structures could be used as predictors of wheat quality.