The effect of sodium chloride on gluten network formation and rheology

Gluten samples were obtained from two wheat flours with different levels of total protein in the presence or absence of sodium chloride (2% flour base). The dynamic oscillation rheology, large extensional deformation, confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM) and chemical analysis of disulfide bond linkages and the ratio of polymeric glutenins and monomeric gliadins were used to investigate the effect of salt on the structure and rheological properties of gluten. CLSM and TEM images showed that NaCl caused the gluten to form fibrous structure. The presence of NaCl increased non-covalent interactions and β-sheet structure, measured by FTIR, in gluten proteins. The gluten matrix formed with salt resulted in higher tan δ values corresponding to a less elastic network when measured using oscillatory rheometry. Large deformation extensional measurements showed that the maximum force to fracture were lower for the gluten samples prepared in the presence of NaCl. The results from this study indicate that changes in the solvent quality due to the presence of NaCl during dough mixing result in different molecular conformation and network structure of gluten proteins which contributed to the differences in the rheological properties.     

Effect of barley and oat flour types and sourdoughs on dough rheology and bread quality of composite wheat bread

The potential of sourdough to improve bread quality of barley and oat enriched wheat breads may depend on the characteristics of the added flour (cereal type, variety, extraction rate). We compared the effect of different barley flours and oat bran (substitution level 40%), unfermented and as sourdoughs (20% of total flour), on composite wheat dough and bread characteristics by combining empirical rheological analyses (DoughLab, SMS/Kieffer Dough and Gluten Extensibility Rig) with small-scale baking of hearth loaves. Whole grain barley flour sourdough increased resistance to extension (Rmax) of the dough and improved the form ratio of hearth loaves compared to unfermented whole grain barley flour. However, sourdough showed little effect on the breads prepared with sifted barley flour or oat bran. The breads made with oat bran showed highest bread volume, lowest crumb firmness and highest β-glucan calcofluor weight average molecular weight (MW). The heat treatment of oat bran inactivated endogenous enzymes resulting in less β-glucan degradation. High MW β-glucans will increase the viscosity of the doughs water phase, which in turn may stabilise gas cells and may therefore be the reason for the higher bread volume of the oat bran breads observed in our study.     

Composition and surface properties of dough liquor

The composition and surface properties of dough liquor isolated by ultracentrifugation have been characterised. Addition of ascorbate had no effect and salts only a limited effect, on the yield, protein content and composition of the dough liquor. Fourier transform infrared spectroscopy (FT-IR) revealed the presence of proteins, lipids, starch oligosaccharides together with the non-starch polysaccharide, arabinoxylan. At high dilution the dough liquor air:water interface was dominated by protein, with surface tensions of around 55 mN/m and high surface elasticity. As the concentration was increased, surface tensions dropped to around 40 mN/m for undiluted dough liquor. This was accompanied by the interface becoming less elastic, and indicated that dough liquor lipids were interacting and disrupting the protein films in concentrated dough liquor. Dough liquors from de-fatted flours remained elastic and gave surface tension values of around 50–55 mN/m even at low dilution, indicating that removal of the lipids gave rise to a purely protein stabilised interface. Addition of salt to the dough had the greatest effect on the surface properties, both reducing surface tension and reducing surface elasticity, probably because the charge screening effect of the salt improved the dispersion of lipids in the dough liquor, thus enabling it to disrupt the protein films more effectively. These results indicate that the aqueous phase of bread doughs lining the gas cells would give rise to a mixed protein:lipid interface. Such interfaces are unstable, and would contribute to the instability of the foam structure of risen dough. In addition they show that dough ingredients may modify gas cell stability (and hence may affect crumb structure), by altering the composition and properties of the aqueous phase of doughs.     

Effect of barley flour addition on the physico-chemical properties of dough and structure of bread

The effects of different percentages of barley flour (i.e. 0–25%) in wheat flours on the physico-chemical properties and structure of dough and bread were investigated. As the percentage of barley flour in mixed flour was increased, its protein and gluten contents decreased whereas the ash content and enzyme activity increased. The rheological characteristics of the four dough mixes were studied using Farinograph, Extensograph and Alveograph. The water absorption (p < 0.01) and stability (p < 0.05) decreased significantly as the percentage of barley flour increased, while no changes were observed in the extensibility and maximum heights. Significant differences were observed in the structural and physical properties as well as in the image analysis of breads. With the increase in the percentage of barley flour, the crumb apparent density decreased (p < 0.1) whereas the porosity (i.e., fraction to total volume) increased (p < 0.1). Overall, the shape and pore structure at 10% barley flour (W90B10) were similar to the pure wheat flour bread, while addition at 15 and 25% of barley flour (W85B15 and W75B25) showed more non-uniform and larger pores.     

Nonlinear,time-dependent shear flow behaviour,and shear-induced effects in wheat flour dough rheology

Retardation test, step-shear rate experiments, low-amplitude and large-amplitude dynamic measurements have been combined to study the nonlinear and time-dependent viscosity of dough and shear-induced effects of flow on dough structure. Despite large quantitative differences in linear viscoelastic constants, doughs from different flours or with different water contents display the same type of flow behaviour. Shear-induced structural changes cause flow to shift from a high viscosity steady-state regime to a low viscosity one. The process, irreversible, is responsible for the time-dependent character of dough viscosity and seems to be controlled by the mechanical energy absorbed. Nevertheless, the two steady-state viscosities follow the same shear-thinning flow curve, fitted by a Cross equation with an exponent close to 1; the Newtonian plateau is approached at very low shear rate values. Viscosity data obtained on different doughs yield a unique flow master curve in reduced coordinates. Shear-induced structural changes cause also the linear viscoelastic plateau modulus of dough to decrease; this progressive weakening of the network structure is irreversible and seems governed by the accumulated strain. These characteristics of dough rheology are discussed with reference to the behaviour of concentrated suspensions.     

Dough thermo-mechanical properties: influence of sodium chloride, mixing time and equipment

Thermo-mechanical properties of doughs prepared from common wheat flour were investigated under different kneading conditions and with different amounts of sodium chloride. Dynamic mechanical thermal analysis showed that high-speed mixing and the addition of salt to dough slowed heat-induced reactions such as starch gelatinisation and protein coagulation. The effect of dough mixing technology was more significant than the amount of sodium chloride in modifying dough rheological characteristics.     

Rheological properties of pasta dough during pasta extrusion: Effect of moisture and dough formulation

A study was conducted to investigate the effect of dough formulation and hydration level on the rheological properties of pasta dough during pasta extrusion. Semolina 100%, whole wheat 100%, and the following mixtures semolina-whole wheat (49:51), semolina-flaxseed flour (90:10), whole wheat-flaxseed flour (90:10), and semolina-whole wheat-flaxseed flour (39:51:10) were the formulations used for the experiments. Dough was hydrated at 30, 32, and 34% moisture content. Pasta was extruded with a capillary and a semi-commercial pasta extruder to determine the apparent viscosity of the dough during extrusion conditions and its relationship to the behavior of the dough during pasta processing. Results showed that non-traditional pasta dough behaved like a shear thinning fluid that can be described by the Power Law model. Increased hydration levels and/or presence of flaxseed flour on the dough formulation decreased the apparent viscosity of the dough, which correlated with extrusion pressure, mechanical energy, and specific mechanical energy that were required to extrude the dough in the pasta extruder. The strong correlations found between the apparent viscosity of the dough and the pasta extrusion parameters indicates the possibility of using a capillary rheometer to determine the appropriate hydration level of ingredient formulations before extruding with a pasta press.     

Flour constituent interactions and their influence on dough rheology and quality of semi-sweet biscuits: A mixture design approach with reconstituted blends of gluten, water-solubles and starch fractions

The aim of this study was to identify the biochemical parameters that alter the soft wheat flour functionality for biscuit-making quality. A 9-point simplex centroid was used to investigate the effect of varying the ratios of gluten, water-solubles and starch-fractions isolated from three different flour grades (patent, middle-cut and clear flours) which exhibited a wide range of compositional and functionality characteristics on the dough rheological behaviour and the semi-sweet biscuit quality parameters. The amounts of soluble and insoluble proteins and pentosans as well as the endogenous lipids in each flour fraction were quantified. Dough consistency, elongational viscosity, hardness, half-relaxation time, relaxation rate constant, cohesiveness and springiness as well as biscuit density, firmness, tearing force and spatial frequency for the different flour fraction combinations were also assessed. Regression models have been developed to predict the responses of the rheological attributes of the dough as well as the biscuit quality characteristics to the compositional changes of the flour blends; in addition to the main linear terms (concentration of starch, gluten and water-solubles isolated from the different flour grades), significant interaction terms were identified which cannot be neglected in any prediction scheme for the dough and biscuit properties. Contour plots were drawn in an effort to better understand the overall property responses of the dough and biscuits. Significant relationships among certain dough rheological parameters and biscuit characteristics were found, implying a functional role for the total, soluble and insoluble proteins, pentosans and lipids in biscuit making.     

Effect of the addition of extruded wheat flours on dough rheology and bread quality

Extruded wheat flours, due to their increased water absorption capacity, constitute an opportunity to increase bread output in bakery production. However extrusion may modify dough and bread characteristics. The aim of this study was to investigate the effect of the substitution of 5% of the wheat flour by extruded wheat flour (produced with different time-temperature extrusion treatments) on dough mixing, handling and fermentation behaviour and bread volume, shape, texture and colour. The RVA curves indicate that extrusion intensity increases with increasing temperature or water content. Water absorption capacity rises with increasing treatment intensity, but dough stability tends to decrease. Adding extruded flours decreases dough extensibility but increases tenacity and gas production. Differences in dough structure were observed on photomicrography, though there were no clear differences in bread quality. These results indicate that it is possible to obtain adequate dough and bread characteristics using dough with 5% extruded wheat flour.     

Grain of high digestible,high lysine (HDHL) sorghum contains kafirins which enhance the protein network of composite dough and bread

The aim of this study was to determine whether protein body-free kafirins in high digestibility, high-lysine (HDHL) sorghum flour can participate as viscoelastic proteins in sorghum-wheat composite dough and bread. Dough extensibility tests revealed that maximum resistance to extension (g) and time to dough breakage (sec) at 35 °C for HDHL sorghum-wheat composite doughs were substantially greater (p < 0.01) than for normal sorghum-wheat composite doughs at 30 and 60% substitution levels. Functional changes in HDHL kafirin occurred upon exceeding its T_g. Normal sorghum showed a clear decrease in strain hardening at 60% substitution, whereas HDHL sorghum maintained a level similar to wheat dough. Significantly higher loaf volumes resulted for HDHL sorghum-wheat composites compared to normal sorghum-wheat composites at substitution levels above 30% and up to 56%, with the largest difference at 42%. HDHL sorghum-wheat composite bread exhibited lower hardness values, lower compressibility and higher springiness than normal sorghum-wheat composite bread. Finally, HDHL sorghum flour mixed with 18% vital wheat gluten produced viscoelastic dough while normal sorghum did not. These results clearly show that kafirin in HDHL sorghum flour contributes to the formation of an improved protein network with viscoelastic properties that leads to better quality composite doughs and breads.     

Effect of fat level,mixing pressure and temperature on dough expansion capacity during proving

In this work the effect of fat content on dough aeration during proving was investigated using dynamic dough density measurements. Doughs of three different fat levels (0%, 0.04% and 0.2% flour basis) were mixed under various pressures using a Tweedy mixer and proved at five different temperatures (30, 35, 40, 45 and 50 °C) in the dynamic dough density system. The dough expansion capacity and the time of the gas loss of each dough sample were measured and related to fat level, mixing pressure and proving temperature.     

Effect of wheat dietary fibres on bread dough development and rheological properties

Several fractions of wheat fibres were isolated from starchy endosperm, aleurone layer and bran, and characterized for their hydration properties and arabinoxylans (AX) content. The influence of their addition, up to 10%, to standard flour was studied through mixing tests, and rheological tests at small and large deformations. The effect of insoluble AX on dough development was accounted for by their capacity to retain water, whatever their origin and percentage of addition. The addition of insoluble AX increased the viscoelastic plateau modulus. The addition of soluble and insoluble AX to the dough did not modify the overall dough flow behaviour in shear, characterized by a Newtonian plateau at low shear rates followed by shear-thinning behaviour at larger shear rates. This behaviour could be fitted by the Cross model. The addition of water soluble AX modified the Newtonian viscosity value. Conversely, the addition of insoluble ones increased dough consistency, probably through a filler-like effect in the dough matrix.     

Effect of heat on rheology of gluten fractions from flours with different bread-making quality

Flours from wheat varieties of differing bread-making quality were fractionated using a sequential salt precipitation technique. The gluten fractions in the different varieties varied in the proportion of HMW, LMW glutenins and gliadins. Their rheological behaviour was examined using constant strain (2%) small deformation oscillation tests over frequencies ranging from 0.005 to 10 Hz, before and after heating at 90 °C. The fractions containing a higher proportion of HMW glutenins were associated with a predominantly elastic character, whereas fractions containing mostly gliadins exhibited a viscous-like behaviour. The frequency dependent rheological behaviour of fractions containing HMW proteins was less susceptible to heat, and their elastic character was maintained after heating, whereas the rheology of intermediate fractions and fractions containing mostly gliadins was more susceptible to heating, indicating a rapid change from viscous to elastic behaviour after heating.     

Effect of temperature, time and wheat gluten moisture content on wheat gluten network formation during thermomolding

A plastic-like material can be obtained by thermomolding wheat gluten protein which consists of glutenin and gliadin. We studied the effect of molding temperature (130-170 °C), molding time (5-25 min) and initial wheat gluten moisture content (5.6-18.0%) on the gluten network. Almost no glutenins were extractable after thermomolding irrespective of the molding conditions. At the lowest molding temperature, the extractable gliadin content decreased with increasing molding times and moisture contents. This effect was more pronounced for the α- and γ-gliadins than for the ω-gliadins. Protein extractabilities under reducing conditions revealed that, at this molding temperature, the cross-linking was predominantly based on disulfide bonds. At higher molding temperatures, also non-disulfide bonds contributed to the gluten network. Decreasing cystine contents and increasing free sulfhydryl and dehydroalanine (DHA) contents with increasing molding temperatures and times revealed the occurrence of β-elimination reactions during thermomolding. Under the experimental conditions, the DHA derived cross-link lanthionine (LAN) was detected in all gluten samples thermomolded at 150 and 170 °C. LAN was also formed at 130 °C for gluten samples containing 18.0% moisture. Degradation was observed at 150 °C for samples thermomolded from gluten with 18.0% moisture content or thermomolded at 170 °C for all moisture contents.     

Effect of glutathione on wheat dough properties and bread quality

Reduced glutathione (GSH), released from lysed yeast cells, is well-known for weakening dough structure. However, its influence on bread texture and staling has not yet been completely elucidated. Herein, this study aims at assessing the effects of GSH on dough properties and bread quality, especially bread staling, using Rheofermentometer analysis, texture profile analysis (TPA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and low-field nuclear magnetic resonance (LF-NMR). The results revealed that GSH substantially decreased the dough height and gas-retention capacity during fermentation. The weakened dough structure was attributed to GSH-induced disulfide bond cleavage in gluten proteins and the depolymerization of glutenin polymers. The addition of 0.005%–0.01% GSH resulted in acceptable bread quality. However, bread supplemented with 0.015%–0.03% of GSH exhibited a coarser and more open crumb microstructure, as well as high level of hardness and low resilience during aging. GSH promoted crumb water loss and drove the water shift from the immobilized to the bound state. The DSC and XRD analyses further confirmed that GSH promoted starch retrogradation and recrystallization. These results suggest that apart from the gluten structure, GSH also altered gluten−starch interactions and water redistribution, ultimately decreasing bread quality and accelerating bread staling.     

Dough quality of bread wheat lacking α-gliadins with celiac disease epitopes and addition of celiac-safe avenins to improve dough quality

Celiac disease is a T-cell mediated immune response in the small intestine of genetically susceptible individuals caused by ingested gluten proteins from wheat, rye, and barley. In the allohexaploid bread wheat (Triticum aestivum), gluten proteins are encoded by multigene loci present on the homoeologous chromosomes 1 and 6 of the three homoeologous genomes A, B, and D. The effect of deleting individual gluten loci was analyzed in a set of deletion lines of T. aestivum cv. Chinese Spring with regard to the level of T-cell stimulatory epitopes (Glia-α9 and Glia-α20) and to technological properties of the dough including mixing, stress relaxation, and extensibility.     

Effect of glucose oxidase,transglutaminase, and pentosanase on wheat proteins: Relationship with dough properties and bread-making quality

Glucose oxidase (Gox), transglutaminase (TG), and pentosanase (Pn) were investigated for their effect on bread quality. The changes introduced in wheat protein by the action of these enzymes were analysed to explain dough behaviour. Gox treatment decreased free sulphydryl groups (SHf), increased glutenin macropolymer contents, and modified the electrophoretic pattern of protein fractions. Gox modified mainly albumin, globulin, and glutenin, forming large protein aggregates. These modifications explained the high strength of the dough and the low bread specific volume of samples with Gox. TG treatment modified solubility in SDS of protein and decreased glutenin macropolymer content. However, it formed large protein aggregates. The new cross-linking bonds introduced by this enzyme were different to S–S bonds and, consequently, the dough was less extensible and showed high resistance. Pn treatment increased water soluble pentosan content. Moreover, in these samples a tendency to increase SHf content was observed. In addition, Pn increased protein solubility in isopropanol, which indicates that the reduction of pentosans size decreases steric impediment of insoluble pentosans, thus increasing interaction among protein and making their extraction easier. These changes at the microscopic level allowed explaining the formation of softer dough and the production of higher specific volume in breads with Pn.     

Characterization of two 1D-encoded ω-gliadin subunits closely related to dough strength and pan bread-making quality in common wheat (Triticum aestivum L.)

Gliadin proteins of 113 common or bread wheat (Triticum aestivum L.) cultivars and advanced lines from China and other countries, were analyzed by high performance capillary electrophoresis (HPCE) and reversed-phase high performance liquid chromatography (RP-HPLC). A major protein peak migrating at 3 min by HPCE and eluting at about 20 min by RP-HPLC was identified in the ω-gliadin region. It was present in cultivars with good pan bread-making quality, whereas most cultivars with poor bread-making quality lacked this protein peak. Quality testing and statistical analysis showed that this ω-gliadin peak was significantly related to dough strength, loaf volume and loaf score. It was separated into two apparent protein components by one-dimensional SDS-PAGE and two-dimensional electrophoresis (2-DE). According to their relative mobilities on the gels, the proteins were designated ω-15 and ω-16, and their accurate molecular masses (42590.5 Da for ω-15 and 41684.1 Da for ω-16) were determined by MALDI-TOF-MS. The ω-15 and ω-16 gliadins possessed the N-terminal amino acid sequences of ARELNPSNKELQQQQ and KELQSPQQQF, and therefore they belonged to 1D-encoded ω-2 type and ω-1 type gliadins, respectively. Both gliadin subunits were always present together among the 86 cultivars analyzed, suggesting that they were encoded by two closely linked genes at Gli-D1 locus. The accumulative characteristics of gliadins during grain development indicated possible additive quantitative effects of ω-15+16 on dough strength. The ω-15 and ω-16 gliadins could be used as valuable genetic markers for wheat quality improvement.     

Surface properties and locations of gluten proteins and lipids revealed using confocal scanning laser microscopy in bread dough

Surface properties of gluten proteins were measured in a dilation test and in compression and expansion tests. The results showed that monomeric gliadin was highly surface active, but polymer glutenin had almost no surface activity. The locations of those proteins in bread dough were investigated using confocal scanning laser microscopy and compared with polar and nonpolar lipids. Added gluten proteins participated in the formation of the film or the matrix, surrounding and separating individual gas cells in bread dough. Gliadin was found in the bulk of dough and gas ‘cell walls’. Glutenin was found only in the bulk dough. Polar lipids were present in the protein matrix and in gas ‘cell walls’, as well as at the surface of some particles, which appeared to be starch granules. However, nonpolar lipid mainly occurred on the surface of particles, which may be starch granules and small lipid droplets. It is suggested that the locations of gluten proteins in bread dough depends on their surface properties. Polar lipid participates the formation of gluten protein matrix and gas ‘cell walls’. Nonpolar lipids may have an effect on the rheological properties by associating with starch granule surfaces and may form lipid droplets.