Relationships Between Gluten Rheological Properties and Hearth Loaf Characteristics

The rheological properties of fresh gluten in small amplitude oscillation in shear (SAOS) and creep recovery after short application of stress was related to the hearth breadbaking performance of wheat flours using the multivariate statistics partial least squares (PLS) regression. The picture was completed by dough mixing and extensional properties, flour protein size distribution determined by SE‐HPLC, and high molecular weight glutenin subunit (HMW‐GS) composition. The sample set comprised 20 wheat cultivars grown at two different levels of nitrogen fertilizer in one location. Flours yielding stiffer and more elastic glutens, with higher elastic and viscous moduli (G′ and G″) and lower tan δ values in SAOS, gave doughs that were better able to retain their shape during proving and baking, resulting in breads of high form ratios. Creep recovery measurements after short application of stress showed that glutens from flours of good breadmaking quality had high relative elastic recovery. The nitrogen fertilizer level affected the protein size distribution by an increase in monomeric proteins (gliadins), which gave glutens of higher tan δ and flatter bread loaves (lower form ratio).     

Characterization of Functional Properties of Gluten Proteins in Spelt Cultivars Using Rheological and Quality Factor Measurements

Wet glutens of 27 European spelt (Triticum aestivum ssp. spelta (L.) Thell.) cultivars were examined using fundamental rheological methods (oscillatory and creep tests) in conjunction with the determination of moisture contents of these glutens and the wet gluten contents of the flours. Furthermore, SDS sedimentation volumes were determined. A special baking test for spelt was developed that encompassed the characteristic elements used in the production of traditional German spelt speciality breads. Various significant correlations between gluten properties and baking results were found for three sets of spelt cultivars obtained from different demographic locations and years of harvest. Furthermore, the relationship between baking results (response) and gluten properties (predictors) could be modeled quite well with the help of multiple linear regression analysis. Radar charts used to profile the gluten properties of a particular cultivar showed a great amount of diversity within the spelt material, but there were also similarities between several cultivars. The differences between spelt cultivars should be taken into account when characterizing spelt in general terms or when comparing spelt and modern wheat.     

Rheological Properties of Vital Wheat Gluten Suspensions

Flour and doughs represent rheologically complex materials whose properties are dependent on many factors including processing conditions. To avoid some of the problems associated with the rheological characterization of dough, we have initiated a study focused on the rheological properties of one of the major components of dough, vital wheat gluten. Suspensions of vital wheat gluten were prepared with concentrations of 225–325 mg/mL.The moduli of the gluten suspensions was 0.2 Pa at 225 mg/mL to 37 Pa at 325 mg/mL. At <250 mg/mL, the gluten suspensions exhibited fluidlike behavior. The crossover frequency, (G′[ω] = G″[ω]) shifted slightly from 0.5 rad/sec at 225 mg/mL to 0.9 rad/sec at 250 mg/mL. At >300 mg/mL, the gluten suspensions exhibited solidlike behavior. The crossover frequencies were independent of concentration and equal to 100 rad/sec. At <250 mg/mL, the high‐frequency behavior of moduli were proportional to ω^3/4, as expected for a semiflexible coil. At >300 mg/mL, the high‐frequency behavior of moduli were proportional to ω^1/2, indicating a flexible coil. These results suggest vital wheat gluten suspensions undergo a structural change between 250 and 300 mg/mL.     

Comparison of Small and Large Deformation Rheological Properties of Wheat Dough and Gluten

The rheological properties of dough and gluten are important for end‐use quality of flour but there is a lack of knowledge of the relationships between fundamental and empirical tests and how they relate to flour composition and gluten quality. Dough and gluten from six breadmaking wheat qualities were subjected to a range of rheological tests. Fundamental (small‐deformation) rheological characterizations (dynamic oscillatory shear and creep recovery) were performed on gluten to avoid the nonlinear influence of the starch component, whereas large deformation tests were conducted on both dough and gluten. A number of variables from the various curves were considered and subjected to a principal component analysis (PCA) to get an overview of relationships between the various variables. The first component represented variability in protein quality, associated with elasticity and tenacity in large deformation (large positive loadings for resistance to extension and initial slope of dough and gluten extension curves recorded by the SMS/Kieffer dough and gluten extensibility rig, and the tenacity and strain hardening index of dough measured by the Dobraszczyk/Roberts dough inflation system), the elastic character of the hydrated gluten proteins (large positive loading for elastic modulus [G′], large negative loadings for tan δ and steady state compliance [J_e⁰]), the presence of high molecular weight glutenin subunits (HMW‐GS) 5+10 vs. 2+12, and a size distribution of glutenin polymers shifted toward the high‐end range. The second principal component was associated with flour protein content. Certain rheological data were influenced by protein content in addition to protein quality (area under dough extension curves and dough inflation curves [W]). The approach made it possible to bridge the gap between fundamental rheological properties, empirical measurements of physical properties, protein composition, and size distribution. The interpretation of this study gave indications of the molecular basis for differences in breadmaking performance.     

Wheat gluten used as a clarifying agent of red wines.

Bovine spongiform encephalopathy caused a situation of crisis leading the public and winemakers to lose their confidence in the use of gelatin as a fining agent and to reject animal proteins in general. Therefore, we started the search for a substitute for gelatin and egg protein by comparing gluten with these fining treatments currently used. This study concerned the fining of a Burgundy red wine (Rully, Controlled Appellation). For 6 g/hL, enzymatically hydrolyzed glutens (EHG) gave better efficiencies than deamidated glutens. The efficiency of the egg proteins treatment was situated between those of the hydrolyzed glutens and deamidated glutens. For 12 and 18 g/hL, turbidities of the wine treated by five glutens were 67 to 86% less than that of the control wine. Better results were obtained with egg proteins for short kinetics particularly. Wine fining with gluten was always better than gelatin treatments. The differences between the five glutens became very small when the dose incorporated in the wine increased. The volumes of lees generated by fining with gluten are situated between the values obtained with egg proteins and gelatin. After fining, immunodetection with gluten polyclonal antibodies failed to detect residual deamidated gluten.     

Effects of Transglutaminase Enzyme on Fundamental Rheological Properties of Sound and Bug‐Damaged Wheat Flour Doughs

Transglutaminase (TG) catalyzes the formation of nondisulfide covalent crosslinks between peptide‐bound glutaminyl residues and ∊‐amino groups of lysine residues in proteins. Crosslinks among wheat gluten proteins by TG are of particular interest because of their high glutamine content. Depolymerization of wheat gluten proteins by proteolytic enzymes associated with bug damage causes rapid deterioration of dough properties and bread quality. The aim of the present study was to investigate the possibility of using TG to regain gluten strength adversely affected by wheat bug proteases. A heavily bug‐damaged (Eurygaster spp.) wheat flour was blended with sound cv. Augusta or cv. Sharpshooter flours. Dynamic rheological measurements, involving a frequency sweep at a fixed shear stress, were performed after 0, 30, and 60 min of incubation on doughs made from sound or blended flour samples. The complex moduli (G* values) of Augusta and Sharpshooter doughs blended with 10% bug‐damaged flour decreased significantly after 30 min of incubation. These dough samples were extremely soft and sticky and impossible to handle for testing purposes after 60 min of incubation. To test the possibility of using TG to counteract the hydrolyzing effect of bug proteases on gluten proteins, TG was added to the flour blends. The G* values of TG‐treated sound Augusta or Sharpshooter doughs increased significantly after 60 min of incubation. The G* values of the Augusta or Sharpshooter doughs blended with bug‐damaged flour increased significantly rather than decreased after 30 and 60 min of incubation when TG was included in the dough formulation. This indicates that the TG enzyme substantially rebuilds structure of dough hydrolyzed by wheat bug protease enzymes.     

Quantitative and Qualitative Role of Added Gluten on White Salted Noodles

A commercial gluten and glutens isolated from four soft and four hard wheat flours were incorporated into a hard and a soft white flour by replacement to directly determine the quantitative and qualitative role of gluten proteins in making noodles. Gluten incorporation (6%) decreased water absorption of noodle dough by 3%, shortened the length of the dough sheet by 15 and 18%, and increased the thickness of the dough sheet by 18 and 20% in soft and hard wheat flour, respectively. Noodles imbibed less water and imbibed water more slowly during cooking with gluten incorporation, which resulted in a 3‐min increase in cooking time for both soft and hard wheat noodles. Despite the extended cooking time of 3 min, noodles incorporated with 6% gluten exhibited decreases in cooking loss by 15% in soft wheat. In hard wheat flour, cooking loss of noodles was lowest with 2% incorporation of gluten. Tensile strength of fresh and cooked noodles, as well as hardness of cooked noodles, increased linearly with increase in gluten incorporation, regardless of cooking time and storage time after cooking. While hardness of cooked noodles either increased or showed no changes during storage for 4 hr, tensile strength of noodles decreased. There were large variations in hardness and tensile strength of cooked noodles incorporated with glutens isolated from eight different flours. Noodles incorporated with soft wheat glutens exhibited greater hardness and tensile strength than noodles with hard wheat glutens. Tensile strength of cooked noodles incorporated with eight different glutens negatively correlated with SDS sedimentation volume of wheat flours from which the glutens were isolated.     

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.     

Effects of Temperature on Sorption of Water by Wheat Gluten Determined Using Deuterium Nuclear Magnetic Resonance

The effects of lipids and residual starch components of wheat flour gluten on gluten hydration properties were investigated using nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) techniques. Whole or native, lipid-free, starch-free, and lipid- and starch-free gluten samples were prepared from wheat (Triticum aestivum) cv. Mercia. ²H NMR relaxation on gluten samples hydrated with deuterium oxide (D₂O) was measured over a 278–363 K temperature range. FTIR spectra were recorded in dry and fully hydrated material. Transverse relaxation (T₂) results indicated that all four gluten samples were hydrophilic in nature. There was little difference in relaxation behavior of whole and lipid-free gluten samples. T₂ values and populations of the relaxation components were very similar in each. The FTIR spectra of both samples showed an increase in extended β-sheet secondary structures on hydration. These results suggest that lipid binding in gluten, if it occurs, has little effect on wheat gluten properties. Adding starch to the gluten matrix results in an increase in water sorption on heating that may be attributed to the effects of starch gelation. However, the whole water uptake of the gluten cannot be accounted for by the contribution of the residual starch, as estimated by the effects of added starch. Extraction of residual starch required solubilization of the protein, including breaking of the disulfide bonds. This process altered the gluten structure and properties. Light microscope investigation showed that glutens with residual starch extracted were unable to form fibrillar strands on hydration. NMR and FTIR results showed greater water sorption in both samples with extracted starch than in the unextracted samples.     

Effect of Mixing Time on Gluten Recovered by Ultracentrifugation Studied by Microscopy and Rheological Measurements

The effect of mixing time on gluten formation was studied for four commercial flour mixtures. The gluten phase was separated from dough using a nondestructive ultracentrifugation method. Small deformation dynamic rheological measurements and light and scanning electron microscopy were used. The recovered gluten was relatively pure with a small amount of starch granules embedded. The protein matrix observed by microscopy became smoother with prolonged mixing. No effect of overmixing was observed on the storage modulus (G′) of gluten for any of the flours. The amount of water in gluten increased from optimum to over‐mixing for most of the flours. Increased water content during prolonged mixing was not related to an effect on G′. The Standard flour resulted in the highest water content of gluten, which increased considerably with mixing time. The Strong flour had the lowest G′ of dough, a high G′ of gluten, and no increase in gluten water content from optimum to over‐mixing. The Durum flour did not show gluten development and breakdown similar to the other flours. The differences in gluten protein network formation during dough mixing are genetically determined and depend on the flour type.     

Effects of Transglutaminase on Rheology,Microstructure, and Baking Properties of Frozen Dough

The improving effects of transglutaminase (TGase) were investigated on the frozen dough system and its breadmaking quality. Rheological properties and microstructure of fresh and frozen doughs were measured using a Rapid Visco‐Analyser (RVA), dynamic rheometer, and scanning electron microscopy (SEM). The frozen doughs with three storage periods (1, 3, and 5 weeks at –18°C) were studied at three levels (0.5, 1.0, and 1.5%) of TGase. As the amount of TGase increased, hot pasting peak viscosity and final viscosity from the RVA decreased, but breakdown value increased. The TGase content showed a positive correlation with both storage modulus G′ (elastic modulus) and the loss modulus G″ (viscous modulus): G′ was higher than G″ at any given frequency. The SEM micrographs showed that TGase strengthened the gluten network of fresh, unfrozen dough. After five weeks of frozen storage at –18°C, the gluten structure in the control dough appeared less continuous, more disrupted, and separated from the starch granules, while the dough containing 0.5% TGase showed less fractured gluten network. Addition of TGase increased specific volume of bread significantly (P < 0.05) with softer bread texture. Even after the five weeks of frozen storage, bread volume from dough with 1.5% TGase was similar to that of the fresh control bread (P < 0.05). The improving effects of TGase on frozen dough were likely the result of the ability of TGase to polymerize proteins to stabilize the gluten structure embedded by starch granules in frozen doughs.     

Effect of Transglutaminase on Properties of Glutenin Macropolymer and Dough Rheology

The effect of transglutaminase (TG) on glutenin macropolymer (GMP) properties could help to understand changes in bread quality. The aim of the present study was to analyze modifications in GMP and dough properties caused by TG addition. Transglutaminase introduced cross‐links to gluten proteins, mainly high molecular weight glutenins. This effect modified the protein structure and markedly increased dough strength. These changes in the structure of glutenins increased SDS solubility and decreased GMP content and GMP storage modulus. However, TG increased GMP particle size, notably at higher doses. TG affected rheological characteristics of dough in that increasing TG doses decreased tan δ, and increased G'. In all the studies conducted, the TG increased GMP polymer size, but contrary to what was expected, this increase did not involve an increase in GMP content. These results confirmed the effect of TG on dough quality and the great differences found with different TG doses.     

Effects of Micronization on Protein and Rheological Properties of Spring Wheat

This research investigated the effects of micronization, at different moisture levels, on the chemical and rheological properties of wheat. A set of tests designed to analyze protein fraction characteristics and rheological behaviors were conducted on samples from four wheat cultivars (AC Karma, AC Barrie, Glenlea, and Kanata). After being subjected to infrared radiation at three moisture levels (as‐is, 16%, and 22%), the seeds were milled to produce straight‐grade flour. The protein fractionation test revealed significant decreases (P ≤ 0.01) in both monomeric proteins (from 54% of total protein in the control to 37% in the tempered micronized sample) and soluble glutenins (9.4–2.5%). There was a strong negative correlation (r = ‐0.98) between the percentages of monomeric proteins and insoluble glutenins. Total extractable proteins of micronized samples tempered to 22% moisture decreased 43.5% when compared with nonmicronized control samples using size‐exclusion HPLC (SE‐HPLC). Micronization had a significant effect on gluten properties, as seen from a decrease in water absorption (P ≤ 0.01) and dough development time (P ≤ 0.01). Results showed that micronization at 100 ± 5°C had detrimental effects on wheat flour gluten functionality, including a decrease in protein solubility and impairment of rheological properties. These phenomena could be due to the formation of both hydrophobic and disulfide bonds in wheat during micronization.     

Surface Properties of Gluten Investigated by a Fluorescence Approach

The surface properties of glutens isolated from a durum wheat cultivar (Capeiti) and two bread wheats (Riband and Hereward) were investigated using intrinsic and extrinsic fluorescence. Intrinsic fluorescence decreased on increasing protein concentration and increased after urea addition. The extrinsic fluorescence was evaluated by a titration with 8‐anilino‐1‐naphthalene sulphonate (ANS), an hydrophobic probe. The saturating concentration for ANS and its dissociation constant (Kd) were determined. The hydrophobicity of durum and bread wheat gluten showed a different behavior increasing the protein concentration: Capeiti was not influenced, but there was a change on the gluten surface for Riband and Hereward. The significance in understanding gluten structure and the relevance of the surface properties are discussed.     

Influence of Degree of Protein Aggregation on Mass Transport Through Wheat Gluten Membranes and Their Digestibility—An In Vitro Study

The influence of the network structure of wheat gluten on the barrier properties against enzymes was investigated in vitro. The changes in the network structure were introduced by different temperature treatments. The modifications were assessed with solubility studies of wheat gluten proteins in sodium dodecyl sulfate (SDS). The physical barrier properties of wheat gluten membranes were investigated with transport studies examining the transfer of a model protein with no enzymatic activity (BSA) through gluten membranes. The protein network was an effective barrier for BSA, although lightly cross‐linked films were mechanically instable. Membrane breaks occurred in function of the cross‐linking density (percentage of SDS‐insoluble proteins) after only 24 hr for lightly cross‐linked films (≈30% SDS‐insoluble proteins), while highly cross‐linked membranes (≈80% SDS‐insoluble protein) were tight up to more than 33 days. The digestion experiments of the gluten films with pepsin showed that the hydrolysis of wheat gluten films with >72% of SDS‐insoluble protein was significantly retarded. In conclusion, technological treatments to increase the cross‐linking density of gluten have the potential to slow the digestion of cereal‐based foodstuff and to reduce the degradation rate of composite biomaterials.     

Temperature‐Induced Changes in the Dynamic Rheological Behavior and Size Distribution of Polymeric Proteins for Glutens from Wheat Near‐Isogenic Lines Differing in HMW Glutenin Subunit Composition

Viscoelasticity of hydrated gluten depends on composition of HMW gluten subunits (GS), size distribution of glutenin polymers, and proteinprotein interactions. Glutens extracted from four near‐isogenic lines with differing HMW‐GS were analyzed. Rheological properties were studied by dynamic assay in shear. Size distribution of prolamins was determined by sequential extraction and size‐exclusion HPLC. Assays performed at 20°C confirmed that viscoelasticity was determined by large glutenin polymers. The abundance of large glutenin polymers depended on the HMW‐GS composition of the lines. Difference of functionality linked to subunit structure was highlighted by comparing the behaviors of the 1A/1B null and 1A/1D null lines. Glutens were submitted to heating and cooling cycles, with or without an SH‐blocking agent (N‐ethylmaleimide [NEMI]). At 20–40°C, no irreversible changes of the mechanical properties occurred. Thermal treatment affected chain mobility, and possibly H bonds, but not the chemical structure of the network. At >40°C, irreversible rheological changes were observed without NEMI. Irreversibility was mainly due to chemical modifications affecting the polymer size distribution through SH‐SS exchange reactions. The sensitivity of gluten to temperature depended on subunit composition.     

Influence of Sodium Caseinate and Whey Protein on Baking Properties and Rheology of Frozen Dough

Dairy ingredients are added to bakery products to increase nutritional and functional properties. Sodium caseinate (SC) and whey protein concentrate (WPC) were incorporated into frozen dough. WPC was subjected to heat treatment (WPCHT) to eliminate undesirable weakening of the gluten network. 2% SC or 4% SC decreased proof time, increased loaf volume, and improved texture. Effects of adding 4% SC on baking quality were similar to adding ascorbic acid (AA) and diacetyl tartaric acid esters of monoglycerides (DATEM). WPC increased proof time, decreased volume, and negatively affected texture. Heat treatment of WPC improved baking performance. Bread with WPCHT had volume similar to that of the control without dairy ingredients. Adding 4% SC decreased resistance to extension (R_5cm measured with the extensigraph), while adding 4% WPC increased extensibility. Dynamic oscillation testing determined the effects of the ingredients on fundamental rheological properties. WPC decreased storage modulus (G′) and loss modulus (G″), while heat treatment of WPC increased G′ and G″. Confocal laser scanning microscopy (CLSM) showed that milk proteins affect frozen dough ultrastructure. Frozen doughs with SC had an enhanced gluten network compared with the control, while untreated WPC appeared to interfere with the gluten network.     

Celiac-related properties of chemically and enzymatically modified gluten proteins

The effects of chemical (acid-heating treatment) and enzymatic (microbial transglutaminase, TGase) modification (deamidation) of gluten proteins on their physicochemical and celiac disease-related properties were studied. Ammonia release, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and sample solubility analyses were employed to check the extent of gluten modification. Among different treatments achieved, the acid-heating treatment performed at 90 degrees C for 3 h induced gluten deamidation, paralleling an increase of gluten solubility without relevant proteolysis. Changes in the immunoreactivity of celiac IgA anti-gliadin antibodies (AGAs) to modified gluten proteins were detected by using a competitive indirect enzyme-linked immunosorbent assay method. Chemical deamidation by acid-heating treatment of gluten lowered IgA-AGA immunoreactivity. IgA-AGA immunoreactivity to gliadins was increased when they were submitted to TGase-catalyzed deamidation. The acid-heating treatment of gluten reduced its cytotoxic activity on human colon adenocarcinoma LoVo cell line. These results showed that chemical deamidation of gluten may be envisaged as a way to lower the potential risk for celiac people due to widespread use of gluten as a food additive.     

Properties of deamidated gluten films enzymatically cross-linked

Films were prepared at neutral pH from deamidated gluten by casting with or without enzymatic treatment by transglutaminase in the presence of various concentrations of diamines added to the film-forming solution. Variation in the glycerol/deamidated gluten ratio from 0.2 to 0.5 had a major effect on the film mechanical properties, which is characteristic of a plasticizing effect. A ratio of 0.35, producing a tensile strength of 1.14 +/- 0.12 MPa and an elongation at break of 376 +/- 62%, was chosen for most of the enzymatic modifications. The action of transglutaminase with or without the addition of external diamines induced a simultaneous increase in tensile strength and elongation at break of the films but tended to decrease the contact angle between the film surface and a water droplet. The presence of diamines in the film solution affected the elongation at break more than the tensile strength of the films. These diamines, able to react at their two extremities, probably acted as spacers between gluten proteins. The decrease in solubility was related to the formation of high molecular weight polymers in the film. The film properties were unaffected by the type of diamine added as secondary substrate in the transglutaminase reaction.     

The Combination of Rhizopus chinensis Lipase and Transglutaminase Affects the Rheology and Glutenin Macropolymer Properties of Frozen Dough

The combination of Rhizopus chinensis lipase (RCL) and transglutaminase (TG) was previously reported to improve the quality of frozen dough bread. In this study, the effects of RCL, TG, and their combination on the modification of glutenin macropolymer (GMP) and rheological properties of dough during frozen storage were investigated. Frozen storage changed both GMP and rheology properties of dough. TG treatment significantly decreased the ratio of high‐molecular‐weight glutenin subunits to low‐molecular‐weight glutenin subunits and GMP content in fresh dough, and GMP particle size increased. The effect of RCL on GMP properties was not significant, but its combination with TG dramatically increased the proportion of the larger particles and weighted average volume (D_4.3) in GMP. The treatment with the enzyme combination could have inhibited the depolymerization of GMP, which slowed down the decrease rate of some parameters such as GMP content, proportion of larger particles, D_4.3, and release of free amino and thiol groups during frozen storage. The modification of GMP properties by enzyme treatment weakened the effect of the freezing process on rheological properties of dough, especially TG treatment and its combination with RCL. Correlation between GMP particle size and dough properties (dough tensile force and elastic modulus) after freezing and enzyme treatment were confirmed.