Dough Viscoelasticity Research Articles

Roles of dextran, weak acidification and their combination in the quality of wheat bread

Dextran-containing sourdoughs have been widely employed in baking, obtaining products with higher quality instead of adding additives. This study investigated effects of dextran of a high weight-average molecular weight (Mw) and linear structure, sourdough and their combination on wheat bread quality. The underlying mechanism was explored from properties of pasting, amylopectin retrogradation and water distributions of starch systems. Bread characteristic analyses showed that both dextran and weak acidification due to addition of sourdough improved bread quality, especially crumb softness. Dextran decreased moisture migration due to high water-binding capacity. Enhancements of amylose aggregation by weak acidification contributed to retardation of amylopectin recrystallization. A synergy existed between dextran and weak acidification. Dough rheology demonstrated that weak acidification was fundamental for dextran-induced positive dough viscoelasticity. This study indicates a combined anti-firming performance of high Mw dextran and weak acidification, possibly being a promising strategy to prolong shelf life of wheat bread.

Effect of leavening time on LAOS properties of yeasted wheat dough

Wheat dough is subjected to large deformations under realistic processing conditions. The viscoelasticity under large deformations can be hardly captured by traditional small amplitude oscillatory tests. Large amplitude oscillatory shear (LAOS) tests are required for accurate characterization of the nonlinear mechanical response. In this regard, LAOS studies of yeasted wheat dough leavened at different times (0, 30, 60, 90 and 120 min) were carried out in this work, in the strain range from 0.1% to 100% (frequency 2π rad/s). All the dough samples showed a complex rheological response that was characterized by strain stiffening and shear thinning behavior at large strains. FTIR analysis revealed that starch granules were increasingly hydrated and protein molecular configuration was modified by the yeast activity. It was postulated that modifications of the protein secondary structure can be behind the strain stiffening behavior while the suspended starch matrix was associated with the shear thinning behavior. LAOS enabled to disaggregate the viscoelasticity of the wheat dough to assess the nonlinear effects associated with elasticity and energy dissipation mechanisms. Overall, a longer leavening time increased by about 30% the nonlinear mechanical response of wheat dough, an effect probably induced by variations in the secondary structure of wheat proteins and to the gassing of the dough microstructure as consequence of the yeast metabolic activity. The results in this work showed that LAOS is a suitable method for characterization of the nonlinear mechanical response of whet dough, especially for assessing the effect of processing conditions (e.g., leavening time and yeast content).

Molecular characterization and marker development for high molecular weight glutenin subunit 1Dy12** from Yunnan hulled wheat

High molecular weight glutenin subunits (HMW-GSs) play an important role in affecting dough viscoelasticity and extensibility. In this work, the novel HMW-GS gene 1Dy12** in Yunnan hulled wheat was cloned and characterized, and the molecular marker for identifying this gene was developed. SDS-PAGE analysis indicated that the mobility of 1Dy12** was the same as that of 1Dy12. The coding sequence of 1Dy12** was 1953 bp, which was 33 bp less than that of 1Dy12. 1Dy12** possessed 649 amino acid residues and showed a similar molecular structure to the published y-type subunit. It possessed four domains: a signal peptide, a conservative N-terminal domain, a large repetitive domain, and a conservative C-terminal domain. Eight cysteine residues were present in 1Dy12**, which was one more than the conserved number of cysteine residues in the y-type subunit. In vitro SDS-sedimentation tests demonstrated that 1Dy12** could bring higher SDS-sedimentation volumes than those of 1Dy10 or 1Dy12. A set of functional markers for the 1Dy12** gene was developed and validated on 36 bread wheat varieties with different Glu-1 alleles and 48 recombinant inbred lines derived by Yunnan hulled wheat and Yanzhan 1. The markers could effectively distinguish 1Dy12** from other HMW-GS genes and, thus, provide a useful tool for marker-assisted selection in wheat quality improvement programs.

Rice flour physically modified by microwave radiation improves viscoelastic behavior of doughs and its bread-making performance

The physical modification of rice flour by heat-moisture treatment assisted by microwave radiation and its effect on the rheological and pasting properties of gluten-free doughs and the physical quality of their resulting bread was investigated. Two levels of flour initial moisture content, 20% (MW-20%) and 30% (MW-30%) and two levels of its addition (30% and 50%) to the dough were evaluated to assess the potential of the physical treatment to modify dough viscoelasticity and bread-making ability. MW-30% treated rice flour showed the most notable results. It provided enhanced dough viscoelasticity vs the control (100% native rice flour), increasing the dough G1′ modulus up to 69% and 135% for the treated flour additions of 30% and 50% of MW-30% respectively. The treated flour increased the resistance of doughs to deformation and enhanced their elastic behavior and recovery capacity up to 170% when compared to the control dough. The major effects on pasting parameters were also obtained for the doughs formulated with MW-30% flour at the maximum substitution level (50%). It delayed the pasting temperature, decreased the peak, trough and final viscosities with respect to the control dough. Both MW-treated rice flours (MW-20% and MW-30%) led to bread with higher-specific volume, softer crumb and delayed staling. The MW assisted heat moisture treatment of rice flour seems to be a valuable procedure to improve the viscoelastic behavior and bread-making performance of gluten-free doughs.

VISCOELASTIC CHARACTERISTICS OF PART-BAKED BREAD UNDER DIFFERENT PROCESS CONDITIONS

Rheological studies in food have shown chemical changes during their preparation process. In bread making, dough viscoelasticity studies reflect the chemical changes produced by the baking process, which in turn modifies bread volume. The aim of this research was to study the effect of the freezing rate, part-baking and storage time on the viscoelastic properties and specific volume of part-baked bread and the specific volume of bread completely baked. We prepared water-flour dough for viscoelastic evaluations. Formulated dough for part-baked bread was baked for 0, 3 or 6 min, frozen at two freezing rates: slow (0.15°C/min) or fast (1.45°C/min) and stored for 56 days. Every 14 days, par-baked bread frozen samples were thawed for rheological evaluations including: elastic moduli (G´), viscous moduli (G¨) and Tan δ. Another part of the thawed samples was re-baked (complete baked) to complete 10 min and the specific volume of bread was measured. We used a 3x2x5 factorial design experiment. An analysis of variance was carried out with 95% confidence level. The elastic moduli (G’) increased with part-baking time. Part-baking time decreased Tan δ, increasing the elasticity in dough and part-baked bread. Part-baking time decreased gelatinization temperature peak in all frozen storage time. A longer storage time resulted in an increase in the elasticity of dough and part-baked bread. The specific volume of bread increased with part-baking time, however, this parameter decreased with storage time.

Gluten-Free Products for Celiac Susceptible People

The gluten protein of wheat triggers an immunological reaction in some gluten-sensitive people with HLA-DQ2/8 genotypes, which leads to Celiac disease (CD) with symptomatic damage in the small intestinal villi. Glutenin and gliadin are two major components of gluten that are essentially required for developing a strong protein network for providing desired viscoelasticity of dough. Many non-gluten cereals and starches (rice, corn, sorghum, millets, and potato/pea starch) and various gluten replacers (xanthan and guar gum) have been used for retaining the physical-sensorial properties of gluten-free, cereal-based products. This paper reviews the recent advances in the formulation of cereal-based, gluten-free products by utilizing alternate flours, starches, gums, hydrocolloids, enzymes, novel ingredients, and processing techniques. The pseudo cereals amaranth, quinoa, and buckwheat, are promising in gluten-free diet formulation. Genetically-modified wheat is another promising area of research, where successful attempts have been made to silence the gliadin gene of wheat using RNAi techniques. The requirement of quantity and quality for gluten-free packaged foods is increasing consistently at a faster rate than lactose-free and diabetic-friendly foods. More research needs to be focused on cereal-based, gluten-free beverages to provide additional options for CD sufferers.

Enhanced γ-aminobutyric acid accumulation, alleviated componential deterioration and technofunctionality loss of germinated wheat by hypoxia stress

Germination is an effective biofortification strategy to enhance micronutrients of staple grains. The current study targeted at comparing the effects of normoxia and hypoxia on γ-aminobutyric acid (GABA) content and the componential changes underlying the technofunctionality of germinated wheat. Compared with ungerminated wheat, GABA maximumly enhanced by 88.73% and 50.70% in hypoxia- and normoxia-germinated wheat (HGW and NGW), respectively. Hypoxia suppressed the germination degree of wheat, which better preserved the technofunctionality. Compared with NGW, the proteolytic and α-amylase activities were partially inhibited for HGW, resulting in higher protein and starch content. The diminishment of gluten marcopolymers and soluble high-molecular-weight proteins, and conversion of α-helices to β-turns were alleviated in HGW, which contributed to the more viscoelastic dough. Meanwhile, superior pasting and gelation properties were mainly due to suppressed α-amylase activity and more starch content in HGW. The results suggested that HGW flour can be exploited as a functional staple ingredient.

Effects of Fermented Wheat Bran on Flour, Dough, and Steamed Bread Characteristics

Wheat bran is rich in dietary fiber, which improves the flour nutritional content and also endows the flour with a richer flavor. However, a high content of insoluble dietary bran fiber can easily and significantly reduce the processing and edible quality of flour products. This study was conducted to explore ways to decrease the negative effects of adding bran to dough. Basidiomycete strain BS-01 was used to ferment the wheat bran. The surface structure of the bran was examined by scanning electron microscopy, and the fermented bran was incorporated into the wheat flour at various concentrations. The mixed flour farinographic and extensographic characteristics, dough rheological properties, and the specific volume, color, and textural properties of the steamed bread were determined and analyzed. The results suggested that adding an appropriate quantity of fermented bran improves the characteristics of the dough and the quality of the steamed bread compared to those with unfermented bran. The fermented bran effectively decreased the negative impacts exerted on the farinographic and extensographic characteristics of the mixed flour and exerted a positive influence on the dough viscoelasticity and bread specific volume.

Laccase-mediated crosslinking of gluten-free amadumbe flour improves rheological properties

The absence of gluten in gluten-free flours presents a challenge to their application in baking. Enzymatic modification of the protein and polysaccharides may result in a network that mimics gluten. In the current study, the effects of laccase on the rheological properties of amadumbe dough were investigated. Thiol and total phenolic contents of dough decreased by up to 28% and 93%, respectively, as laccase activity was increased (0–3 U/g flour). Both G′ and G″ of laccase-treated dough increased significantly due to laccase-catalysed cross-linking of proteins and polysaccharides esterified with phenolics, as demonstrated by relevant model reactions. Tan δ decreased with increase in laccase activity indicating an increase in the elastic character of the dough. The improvement in dough viscoelasticity may enable the retention of adequate carbon dioxide during proofing and production of more acceptable gluten-free bread.

Effect of extra cysteine residue of new mutant 1Ax1 subunit on the functional properties of common wheat

Subunit pair 1Dx5 + 1Dy10 was recognized as superior subunit combination in wheat and contained an extra repetitive-domain cysteine residue in 1Dx5 that was important for understanding the formation of dough viscoelasticity. In this research, one specific serine codon of the 1Ax1 gene corresponding to the extra cysteine residue of 1Dx5 was substituted by a cysteine codon through site-directed mutagenesis. Four homozygous transgenic lines (T4) expressing the mutant 1Ax1 gene (mut1Ax1) were produced. Their greater dough strength and stability were confirmed by mixograph and were associated with highly increased gluten index, larger amounts of gluten macropolymers, larger size distribution for glutenin macropolymer particles and varied sodium-dodecyl-sulfate sedimentation volumes, compared with those of the one line expressing wild 1Ax1 that had similar expression level of transgene. The contents of β-sheets in dough and disulfide groups in gluten of the mut1Ax1 transgenic lines were significantly increased. The microstructure of dough mixed to peak showed a more continuous gluten matrix in the mutant transgenic lines than the one line mentioned-above. It was concluded that the extra cysteine residue of mutant 1Ax1 subunit plays a positive role in contributing to dough strength and stability of wheat by cross-linking into gluten aggregates through inter-chain disulfide bonds.

Impact of heat moisture treatment and hydration level on physico-chemical and viscoelastic properties of doughs from wheat-barley composite flours

The impact of heat moisture treatment (HMT) on the thermoviscous, viscoelastic and mechanical properties of binary flour matrices (wheat:barley, 60:40, wt:wt) was investigated in untreated and HMT (15% moisture content, 1 h heating time at 120 °C) hydrated samples to assess the potential of HMT to modify dough viscoelasticity and doughmaking functionality in diluted breadmaking wheat matrices. HMT significance was tackled (a) in excess of water, by applying successive cooking and cooling cycles to hydrated samples (14%, w:w), determination of viscometric parameters, and subsequent determination of textural (compression test) and viscoelastic parameters (stress relaxation test) in pasted and gelled hydrated flours, and (b) under water restrictions by assessing the consistency (forward extrusion test), the primary and secondary mechanical properties (Texture Profile Analysis), and the viscoelastic behaviour (stress relaxation test) of untreated and HMT mixed doughs made at different flour hydration levels (63 and 70%). In highly hydrated blends, HMT barley flour provided enhanced viscosity patterns regardless of the presence of native or HMT wheat flour, and harder gels with larger initial stress to reach a defined deformation, particularly in the presence of HMT wheat flour. Under restricted water availability, doughs made at 70% hydration level when compared to their counterparts made at 63% explicited lower stress relaxation curves with higher values for both initial decay rate and extent of the decay, shorter relaxation times and higher percent of stress relaxation, giving softer and more cohesive doughs. The most elastic-like dough blends were those prepared with HMT wheat and barley flours at 63% hydration, while the most viscous-like doughs were those from native flours made at 70% hydration.

Effect of extrusion cooking of sorghum flour on rheology, morphology and heating rate of sorghum–wheat composite dough

Addition of a gluten-free flour such as sorghum has negative impact on the quality of wheat dough for bread making. One of the methods which can be used to promote the quality of sorghum-wheat composite dough is to extrude the sorghum flour before incorporation. In this regard, to produce a dough with appropriate bakery properties sorghum flour was extruded at 110 °C and 160 °C die temperature with 10%, 14% and 18% feed moisture. The effect of extruded sorghum flour incorporation (10%) on rheological (farinography and stress relaxation behavior), morphological and temperature profile of sorghum-wheat composite dough were evaluated. Extrusion cooking altered the sorghum-wheat composite dough properties through partial gelatinization of starch granules. Addition of extruded sorghum flour increased the water absorption and dough development time but it decreased the dough stability. Native sorghum-wheat composite dough showed viscoelastic liquid-like behavior whereas addition of sorghum flour extrudate changed dough to a more viscoelastic solid-like structure. Maxwell model was more appropriate than Peleg model to describe the viscoelasticity of the sorghum-wheat composite dough. Extrusion cooking decreased composite dough elasticity and viscosity. Sorghum extrudate increased the heating rate of composite dough crumb during baking. Addition of extruded sorghum flour formed a non-uniform and less compact dough structure. As a result, dough containing extruded sorghum flour had a good potential for producing a high-yielding bread in a short time of baking.

A rapid extensigraph protocol for measuring dough viscoelasticity and mixing requirement

The extensigraph is particularly useful in characterizing dough viscoelastic properties; however, testing throughput for standard method is low due to the prerequisite for farinograph water absorption, long dough resting and milling to prepare large amounts of flour. Therefore, a rapid extensigraph method was developed that reduced sample size (165 g wheat) for milling and more than tripled throughput. Wheat is milled in Quadrumat Junior mill with a modified sieving system. The resulting flour (100 g) was mixed with a pin mixer at constant water absorption to allow the evaluation of wheat genotypes at the absorption level they are expected to perform. Dough was subsequently stretched by an extensigraph after 15 min of floor time and 30 min resting. Strong correlations for extensigram Rmax (r > 0.93), extensibility (r > 0.64) and area (r > 0.88) were found for the proposed method compared to the standard method. Mixing parameters (time and energy) obtained during dough preparation provided further information about dough strength and mixing requirement. By significantly reducing sample size requirement and increasing testing throughput, this rapid extensigraph method can be widely adopted in milling and baking industry and meets the need for a fast evaluation of dough strength in breeding trials.

Baking Quality of Bread Wheat Cultivars Damaged by Nysius simulans

Wheat grain may be attacked by different insect species. Among them, some Heteroptera species (e.g., Aelia spp. and Eurygaster spp.) reduce wheat breadmaking quality; others, such as Nysius simulans, commonly extract water and nutrients from soy plants. The aim of this study was to assess the effect of N. simulans infestation on breadmaking quality of different bread wheat cultivars. Twelve wheat cultivars (damaged and undamaged by N. simulans) were studied. Infested grain percentage varied between 51 and 78%, depending on cultivar. Protein and gluten quantity and quality were significantly reduced in damaged flours, as shown by gluten index, solvent retention capacity, and SDS sedimentation index. SDS‐PAGE from water‐extractable proteins evidenced an important proteolytic activity in damaged samples. Dough rheological properties showed a reduced dough viscoelasticity in damaged samples. Microbread specific volume changed from 3.26 cm3/g for samples made with undamaged flour to 2.77 cm3/g for bread made with damaged flour. No evidence for modification in starch properties was found. The infestation by N. simulans reduced wheat breadmaking quality in all cultivars studied, as a result of proteolytic activity occurring after dough hydration. Results suggest that the presence of N. simulans should be considered as a factor affecting wheat crops, mainly those located next to soy crop areas, which is the usual host for this insect.

Quality Properties of a Gluten-Free Bread with Buckwheat

ABSTRACTThe demand for gluten-free food due to allergic autoimmune diseases and sensitivity keeps growing. Usually, the treatment is a strictly gluten-free diet. In the absence of gluten, bread making becomes a technological challenge since wheat is the only cereal able to develop a viscoelastic dough. The objective of this research was to develop a gluten-free bread using buckwheat, rice, and cassava flours. Increasing buckwheat flour causes an increase of insoluble fiber, crumb cell circularity, and loaf specific volume. A sensory test showed that buckwheat flour has a positive impact on bread quality.

Effect of Salt and Ethanol Addition on Zein-Starch Dough and Bread Quality.

Development of viscoelastic doughs from non-wheat proteins allows for a wider range of gluten-free products. Little work has been completed to describe mechanisms of zein functionality in food systems. To identify factors responsible for dough development in zein-starch mixtures and their influence on zein bread quality, a mixture of 20% zein-80% maize starch was mixed with water and various reagents. Salts, NaSCN, NaCl, and Na2 SO4 were evaluated at concentrations from 0 to 2M for their influence on the properties of zein-starch dough systems. NaSCN at low concentrations produced softer dough. Ethanol treatments produced softer more workable dough in the absence of salts. Increasing concentrations of NaCl and Na2 SO4 resulted in coalescing of the proteins and no dough formation. The addition of β-ME had minimal softening effects on zein-starch dough. Specific volumes of zein-starch bread increased with decreasing NaCl addition in bread formulations. Likewise, including 5% ethanol (v/v) in the bread formula increased bread quality.

Creep Recovery of Wet Gluten and High‐Molecular‐Weight Glutenin Subunit Composition: Relationship with Viscoelasticity of Dough and Breadmaking Quality of Hard Red Winter Wheat

Effects of high‐molecular‐weight glutenin subunits on viscoelasticity of wet gluten, and its relationships with mixing, extensibility, and breadmaking parameters, were investigated by creep recovery using the Kelvin–Voigt model on 19 hard red winter wheat flours. Gluten samples with Glu‐A1 1 and 2* showed significant differences in retardation time (λ2), whereas subunit 17+18 in Glu‐B1 showed higher elastic moduli (G0, G1, and G2) and viscosity coefficients (η0, η1, and η2) compared with subunits 7+8 and 7+9. Wheats with Glu‐D1 5+10 had higher values of G0, G1, G2, η0, η1, and η2 compared with Glu‐D1 2+12. Gluten samples were on average 5.5, 3.1, and 1.6 times less stiff than dough when comparing G0, G1, and G2, respectively; these differences suggest that the nongluten components have high influence in the instantaneous and first Kelvin–Voigt elements of the model, and they are manifested more quickly compared with gluten components. Higher explanation of variance of loaf volume was found in parameters η2 and G2 (r = 0.57 and 0.58, respectively, P < 0.0001) compared with η1 and G1 (r = 0.45 and 0.56, P < 0.01 and 0.0001, respectively). These findings indicate that large structures formed primarily by crosslinking and agglomeration of glutenins of long chain sizes (second Kelvin–Voigt element) had major effects on quality compared with short chain sizes (first element).

Effect of gelatinized flour fraction on thermal and rheological properties of wheat-based dough and bread.

This work considered gelatinized wheat flour fraction with properties similar to hydrocolloid to enhance the strength of dough network by improving water retention and rheological characteristics. The gelatinized (90 °C) fraction of the wheat flour was incorporated in the dough formulation at different levels (5, 10, and 20% w/w). The effects of the gelatinized flour (GF) fraction on the dough rheology and thermal properties were studied. The incorporation of GF induced a moderate increase of dough viscoelasticity and reduced the freezing and melting enthalpies. On the other hand, the changes in bread textural properties brought by incorporation of GF were insignificant, indicating that the gelatinized fraction acted as a binder that enhanced water trapping in the structure. SEM images showed a more heterogeneous crumb microstructure (e.g., gas cells, porous, etc.) bread prepared using GF. Drying kinetics obtained from TGA indicated that the water diffusivity decreased with the incorporation of GF, which suggested that the bread had a compact microstructure.

Formation of a viscoelastic dough from isolated total zein (α-, β- and γ-zein) using a glacial acetic acid treatment

Only predominantly α-type zein (commercial zein) has been shown to form a viscoelastic dough. In maize zein comprises α-, β-, γ- and δ-zein (total zein). Because glacial acetic acid can fully solubilise zein, its effect was investigated. Dissolving total zein (comprising α-, β-, γ- and δ-zein) in glacial acetic acid and casting a film, enabled a viscoelastic dough to be formed with water above zein's Tg. The dough was stronger and less extensible than commercial zein dough made without film formation. When residual acetic acid was removed from the total zein film, a dough still formed. CLSM showed that the total zein dough fibrils were shorter and less well-aligned than those of commercial zein dough and appeared as particles. Disulphide bond cross-linking was probably responsible, for total zein dough stiffness. FTIR showed that total zein wet doughs and total zein slurry with water were predominantly β-sheet, indicating that β-sheet conformation was not directly responsible for dough formation. It is suggested that acetic acid brings about chemical changes in zein, enabling it to better interact with water molecules, counteracting disulphide bonding effects, allowing total zein to form a dough. This is the first report of viscoelastic dough formation from total zein.

Effects of Quality Improvers and Oat Sourdough on Viscoelasticity of Oat Dough

Effects of Quality Improvers and Oat Sourdough on Viscoelasticity of Oat Dough