Role of Hydrogen Peroxide Produced by Baker's Yeast on Dough Rheology

Baker's yeast, Saccharomyces cerevisiae, has a well-known effect on dough rheology during breadmaking. During a 3-hr fermentation, hydrogen peroxide (H₂O₂) produced by yeast (0.76%, fwb) increased from 1.09 to 2.32 μmol/g of flour. The spread test, a measure of a dough's rheological properties, showed that yeast had an effect on dough rheology similar to that of H₂O₂, an oxidant that makes flour-water dough more elastic. In additional experiments (spread test and H₂O₂ measurement), glucose oxidase, an enzyme that produces H₂O₂, gave results similar to those with yeast. The fact that catalase, an enzyme that destroys H₂O₂, reversed the rheological effect of added H₂O₂ but did not reverse the effect of either yeast or glucose oxidase suggested that either wheat flour contains an inhibitor to catalase or H₂O₂ was not the active component. A series of experiments, including use of defatted flour, remixing, and mixing dough under nitrogen, all indicated that catalase was inhibited by peroxides in the lipid fraction of flour. These results also suggested that H₂O₂ is responsible for the effects of yeast and glucose oxidase on dough.     

Effects of Ferulic Acid and Transglutaminase on Hard Wheat Flour Dough and Bread

The effects of ferulic acid and transglutaminase (TG) on the properties of wheat flour dough and bread were investigated. Ferulic acid and TG were blended with hard wheat flour at levels of 250 and 2,000 ppm of flour weight, respectively. The addition of ferulic acid reduced the mixing time and mixing tolerance. The addition of TG did not obviously affect the mixing properties. Significant effects of ferulic acid plus TG on the rested dough texture were observed for overmixed dough. The maximum resistance (Rmax) of the dough was significantly reduced with the addition of ferulic acid but increased with the addition of TG. The addition of TG with ferulic acid restored the Rmax reduced by ferulic acid alone. The proportion of SDS‐soluble high molecular weight proteins in the dough increased with the addition of ferulic acid and decreased with TG, when assessed with size‐exclusion HPLC fractionation. Although the addition of TG improved the handling properties of the dough made sticky with added ferulic acid, it did not improve the quality of the bread with added ferulic acid as measured by loaf volume and firmness.     

Association of Glutenin Subunit Composition and Dough Rheological Characteristics with Cookie Baking Properties of Soft Wheat Cultivars

The effect of flour type and dough rheology on cookie development during baking was investigated using seven different soft winter wheat cultivars. Electrophoresis was used to determine the hydrolyzing effects of a commercial protease enzyme on gluten protein and to evaluate the relationships between protein composition and baking characteristics. The SDS‐PAGE technique differentiated flour cultivars based on the glutenin subunits pattern. Electrophoresis result showed that the protease degraded the glutenin subunits of flour gluten. Extensional viscosities of cookie dough at all three crosshead speeds were able to discriminate flour cultivar and correlated strongly and negatively to baking performance (P < 0.0001). The cookie doughs exhibited extensional strain hardening behavior and those values significantly correlated to baking characteristics. Of all rheological measurements calculated, dough consistency index exhibited the strongest correlation coefficient with baking parameters. The degradation effects of the protease enzyme resulted in more pronounced improvements on baking characteristics compared with dough rheological properties. Stepwise multiple regression showed that the dough consistency index, the presence or absence of the fourth (44 kDa) subunit in LMW‐GS and the fifth subunit (71 kDa) subunit in HMW‐GS were predominant parameters in predicting cookie baking properties.     

Glucose Oxidase Effects on Gluten and Water Solubles

Hydrogen peroxide was responsible for the improving the effect of glucose oxidase in breadmaking. The mechanism by which H₂O₂ has its effect is not known. The objective of this study was to determine whether the H₂O₂ produced by glucose oxidase affected the gluten proteins or the water-soluble fraction of flour. Glucose oxidase had no effect on gluten protein as measured by protein solubility or the relative viscosity of soluble protein (solubilized using 1.5% w/v SDS). However, glucose oxidase did affect the water-soluble fraction. The sulfhydryl content of the water-soluble fraction extracted from flour or dough decreased in the presence of glucose oxidase. Glucose oxidase also caused oxidative gelation of the water-soluble fraction extracted from flour. However, the viscosity of the water-soluble fraction extracted from fermented doughs containing glucose oxidase decreased when higher levels of glucose oxidase were used (≥5.0 units of glucose oxidase). Glucose oxidase appeared to have the same oxidizing action independent of whether the water-soluble fraction was boiled or not.     

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.     

Factors Associated with Dough Stickiness as Sensed by Attenuated Total Reflectance Infrared Spectroscopy

Attenuated total reflectance (ATR) and Fourier transform infrared (FTIR) spectroscopy have been applied in the characterization of sticky dough surfaces. The characterization provides insight in the chemical distribution of gluten protein, starch, water, and fat during dough kneading. ATR is especially useful for selective sampling of dough surfaces because the depth of penetration of radiation is quite shallow. For dough, it is calculated to be in the order of 0.5–4 μm in the mid‐infrared, ideal for measurements of stickiness effects, where only the dough surface is of interest. To investigate the cohesive and adhesive properties of the individual dough constituents, dough was peeled from the ATR plate to study the material that adhered to it. The infrared spectra obtained indicate that fat and gluten protein appear to be located at the outer sticky dough surfaces, rather than water and starch. In comparison with gluten, the fatty component showed relatively strong adhesive forces to the ATR plate; a high residual fraction was measured after peeling the dough. Gluten proteins display different cohesion and adhesion properties that are strongly dependent on their hydration state. This indicates that the degree of hydration of gluten proteins contributes to the sticky properties of (overkneaded) dough. When analyzing gluten protein in D₂O instead of a dough matrix, more or less similar results were obtained. Significant differences in amide I and amide II intensities were measured for kneaded and stretched gluten protein in comparison to untreated, wet gluten. Besides changes in the vibrational properties of the amide groups, conformational changes in the tertiary protein structure also were observed. It appears that kneading and stretching of dough results in a major decrease in α‐helices content, accompanied by an increase of extended β‐sheet conformations.     

Whey Protein Concentrate Treated with Heat or High Hydrostatic Pressure in Wheat-Based Products

Commercial whey protein concentrate (CWPC) treated with heat or with high hydrostatic pressure (HHP) was incorporated by replacement into wheat flour, and its effects on dough rheology and the quality of cookies, noodles, and bread were evaluated. Wheat flour fortified with heat- or HHP-treated CWPC produced smaller cookies than those fortified with untreated CWPC. Increasing the fortification level of heat- or HHP-treated CWPC from 5 to 10% further decreased cookie diameter. The water absorption for noodle dough decreased by 5% with 10% fortification of untreated CWPC. Both heat- and HHP-treated CWPC increased water absorption from 33% in the control to 35.8%. Incorporation of untreated CWPC decreased the lightness (L*) value of Cantonese noodle dough, while dough fortified with heat- or HHP-treated CWPC had higher L* values compared to those of the control. Yellowness (b*) was improved with incorporation of both untreated and treated CWPC. Cooking loss of Cantonese noodles fortified with untreated or heat- or HHP-treated CWPC was comparable to or lower than that of the control. Incorporation of untreated CWPC increased hardness and cohesiveness of Cantonese noodles. Noodles fortified with heat- or HHP-treated CWPC had similar hardness and were softer than the control and the noodles fortified with untreated CWPC. Wheat flour fortified with 10% untreated CWPC produced wet and sticky bread dough and a small loaf (730 mL). Handling properties of dough were improved and bread volume was increased by 50 mL when heat- or HHP-treated CWPC was incorporated. Incorporation of 10% CWPC increased protein content of bread up to 20.2% and also increased the proportion of essential amino acids.     

Oxido-Reductases and Lipases as Dough-Bleaching Agents

To replace benzoyl peroxide as a bread dough-bleaching agent, pure and commercial oxido-reductases (peroxidases, catalases, glucose oxidases, lipoxygenase, and laccase) were screened based on degradation of β-carotene in a liquid system (5 μg of β-carotene/mL of 0.1M citrate phosphate buffer at pH 5.5 or 6.5) or dough. Peroxidases had the best bleaching activity; some catalases also showed bleaching potential in a liquid system but not in bread dough, suggesting that screening enzymes in liquid media has limited application for dough. In 100 g of flour, combinations of peroxidase (3,000 U), lipase (815–1,630 U), and linoleic acid (0–300 mg) completely bleached bread dough.     

Effect of Damaged Starch and NaCl Level on the Dough Handling Properties of a Canadian Western Red Spring Wheat

The effects of damaged starch and NaCl (1 and 2% w/w [flour weight]) on the dough handling properties of a wheat flour (Triticum asetivum L. ‘Roblin’) were investigated with rheological and textural methods. Damaged starch levels of the base flour and three remilled flours (using reduction rolls with decreasing gap sizes) were 5.42, 6.23, 7.30, and 8.43%. Rheological measurements on the dough showed that the complex modulus increased and the loss tangent (tan δ) decreased with increasing damaged starch levels in the flour, indicating that greater amounts of damaged starch produced stiffer dough. The base flour produced doughs with the highest creep compliance value (J _max), whereas the flour with the most damaged starch deformed the least. Higher levels of salt produced stiffer dough that deformed less, as evident by the higher complex modulus and lower creep compliance, compared with 1% NaCl. Damaged starch overall decreased dough stickiness (N), work of adhesion (N·s), and cohesiveness (mm). Increasing the salt content decreased the stickiness of the doughs. Increasing the damaged starch greatly increased dough extensibility at 1% NaCl. The greater amounts of damaged starch in the remilled flour mitigated some of the negative effects of reducing the salt content on the dough machinability.     

Sulfur,Protein Size Distribution,and Free Amino Acids in Flour Mill Streams and Their Relationship to Dough Rheology and Breadmaking Traits

The aim of this study was to analyze sulfur content, protein size distribution, and free amino acids in flour mill streams (FMS) and their associations to dough rheology and breadmaking traits. Break FMS had higher nitrogen and sulfur quantities than reduction FMS. The third break FMS had the highest nitrogen and sulfur contents among FMS but low bread loaf volume partly due to high ash content. Sulfur quantity had greater or equivalent correlations with dough rheology and breadmaking properties compared with nitrogen quantity when the effect of percent ash content was removed statistically. FMS also showed significant quantitative variation in HMW polymeric proteins of the SDS‐unextractable fraction that had greater association with sulfur content and dough rheology and breadmaking traits than other protein fractions. Asparagine, which is a major amino acid in flour, was found at higher levels in the third break and third reduction FMS. Ratio of nitrogen to sulfur was significantly correlated with asparagine concentration (r = 0.73, α = 0.01). This study indicates that information on sulfur, protein size distribution, and free amino acid is potentially useful in research for more precise blending of FMS in commercial flour mills to meet customer specifications for high quality flour.     

Effect of Physical States of Nonpolar Lipids on Rheology,Ultracentrifugation, and Microstructure of Wheat Flour Dough

In the previous study, we investigated effect of physical state of nonpolar lipids of gluten‐starch model dough. This experiment examined a real wheat flour dough system to assess the role of fat crystals in the breadmaking processes. These experiments were performed with a baking test and an investigation of wheat flour dough through rheological measurements (both large and small deformations), scanning electron microscopy, and ultracentrifugation. As a result, we found that the added oil was absorbed in the gluten structure, causing the aggregation of the gluten, which gave rise to more elastic behavior. In contrast, solid fat seemed to be distributed uniformly between the starch granules in the dough, reducing the friction between the starch granules and facilitating thin gluten gel layers. These properties lead to the lower G′ value and the increased viscous behavior, which yields an increase in loaf volume. In addition, the supposed mechanism behind the large loaf volume described in the previous study was that fat provides a uniform distribution of the dough components, and that the dough can thus expand easily, resulting in a larger loaf volume, which was supported in the wheat flour dough system. In conclusion, we found that thin, expandable gluten films and the uniform dispersion of gluten and starch granules in the dough are prerequisites for attaining better baking performance.     

Rheological Properties of Soft Wheat Flour Doughs: Effect of Salt and Triglycerides

The small deformation rheological properties of wheat flour doughs in relation to their structure and hydration were studied by dynamic mechanical thermal analysis, differential scanning calorimetry, and electron spin resonance. The effect of salt and triglycerides was also examined and compared with results we obtained previously on starch dispersions. Moisture content was adjusted to 48 or 60% (w/w, wb). Samples contained 0–16% NaCl (g/100 g of flour‐water) and 0–18% triolein or lard (g/100 g of flour‐water). The obtained results suggested that starch has an active role in determining the evolution of dough rheological characteristics during heating. The main factors controlling rheological behavior during thermal treatment are the volume fraction and deformability of starch granules. Gluten changes the viscoelasticity of the continuous phase and competes with starch for water. The addition of sodium chloride to flour dispersions shifted the structural disorganization and rigidity increased during heating to higher temperatures. At >7% NaCl, the reverse effect was observed. The mechanism controlling the effect of salt on dough rheological behavior was explained in terms of effect on water properties and on starch structure and hydration. Triglycerides had a lubricant effect (i.e., lowering G′ modulus) on the wheat flour dough system. These effects are of great importance for production and quality of bakery products.     

Improvement of Sorghum-Wheat Composite Dough Rheological Properties and Breadmaking Quality Through Zein Addition

Addition of sorghum flour to wheat flour produces marked negative effects on rheological properties of dough and loaf volume. Although there are notable differences in the chemical composition of sorghum proteins (kafirins) compared with wheat gluten that might imply poor functionality in breadmaking systems, a larger constraint may be the unavailability of kafirins due to encapsulation in protein bodies. In this study, zein, the analogous maize prolamin to kafirin, was used to determine the potential effects of protein-body-free prolamins on dough rheology and baking quality of wheat-sorghum composite flour. Mixograms run at 35°C (above the glass transition temperature of zein) were significantly (P < 0.01) improved with addition of zein. Mixogram peak heights increased while mixing time decreased uniformly with addition of zein. Dough extensibility studies showed an increase in maximum tensile stress, while baking studies showed an increase in loaf volume with increasing amounts of added zein. These data are supported by a previous study showing that, in a model system, zein mixed with starch can form viscoelastic networks, and suggest that kafirin, if made available, could contribute to dough formation.     

Evaluation of a New Viscometer Performance in Predicting the Technological Quality of Soft Wheat Flour

Gluten aggregation properties were investigated by means of the GlutoPeak device, a viscometer recently proposed as a rapid and sensitive test for measurement of wheat flour technological performance. In this study, 62 soft wheat flour samples of different quality and end use were utilized to evaluate if the GlutoPeak parameters could adequately predict chemical and rheological characteristics of soft wheat flour dough, that is, protein content measured by the Kjeldahl method, dough strength measured by a Chopin alveograph, and dough stability and water absorption measured by a Brabender farinograph. Linear correlation analysis showed that most GlutoPeak curve parameters were strongly correlated with protein content, dough strength, and water absorption. The statistical models, obtained by a stepwise multiple regression method, showed the GlutoPeak device to be a promising tool to characterize wheat flour (R_adj² = 0.84 for protein content, R_adj² = 0.71 for dough strength, and R_adj² = 0.67 for water absorption). The rather high accuracy of the prediction models for the three mentioned parameters confirmed that GlutoPeak parameters are well correlated with other frequently used flour quality parameters and are able to describe flour technological performance.     

Changes in Phytate Content in Whole Meal Wheat Dough and Bread Fermented with Phytase‐Active Yeasts

The degradation of inositol hexakisphosphate (IP6) was evaluated in whole meal wheat dough fermented with baker's yeast without phytase activity, different strains of Saccharomyces cerevisiae (L1.12 or L6.06), or Pichia kudriavzevii with extracellular phytase activity to see if the degradation of IP6 in whole meal dough and the corresponding bread could be increased by fermentation with phytase‐active yeasts. The IP6 degradation was measured after the dough was mixed for 19 min, after the completion of fermentation, and in bread after baking. Around 60–70% of the initial value of IP6 in the flour (10.02 mg/g) was reduced in the dough already after mixing, and additionally 10–20% was reduced after fermentation. The highest degradation of IP6 was seen in dough fermented with the phytase‐active yeast strains S. cerevisiae L1.12 and P. kudriavzevii L3.04. Activity of wheat phytase in whole meal wheat dough seems to be the primary source of phytate degradation, and the degradation is considerably higher in this study with a mixing time of 19 min compared with earlier studies. The additional degradation of IP6 by phytase‐active yeasts was not related to their extracellular phytase activities, suggesting that phytases from the yeasts are inhibited differently. Therefore, the highest degradation of IP6 and expected highest mineral bioavailability in whole meal wheat bread can be achieved by use of a phytase‐active yeast strain with less inhibition. The strain S. cerevisiae L1.12 is suitable for this because it was the most effective yeast strain in reducing the amount of IP6 in dough during a short fermentation time.     

Effects of Salt,Polyethylene Glycol,and Water Content on Dough Rheology for Two Red Spring Wheat Varieties

In this research, the relationship between dough rheology and water behavior was investigated in response to two osmotic regulators, salt (NaCl) and polyethylene glycol (PEG), using two Canadian Western Red Spring (CWRS) wheat varieties (Harvest and Pembina). The effects of NaCl (0.5, 1.0, and 1.5 g/100 g of flour) and PEG 400 (2.5, 5.0, and 7.5 g/100 g of flour) on dough rheology (oscillatory and creep) were estimated by using a central composite design. Variation of NaCl showed a significant effect on the phase angle δ, indicating that increasing the NaCl resulted in a more elastic dough. The opposite trend was observed with the addition of PEG. PEG 400 exerted a softening effect owing to plasticization, so that a more compliant liquid‐like dough was produced. The effects of water content (±10% of farinograph absorption) and PEG molar mass on dough rheology and freezable water content were estimated by using a full factorial design. PEGs with different molar mass (400, ≈1,600, and 3,350 g/mol) were added at a concentration of 1 g/100 g of flour. The water content significantly affected all dough rheological attributes, whereas PEG molar mass had no effect. The complex shear modulus (G* ) decreased with increasing water content, and dough creep compliance (J _max) increased. The elastic response of dough, determined as the relative elastic part (J _el) decreased with increasing water content. A high correlation was found between the freezable water content and dough rheological attributes.     

Semicarbazide formation in flour and bread

Azodicarbonamide, an approved food additive, is commonly used as a flour additive and dough conditioner in the United States and Canada. A number of researchers have clearly established a link between the use of azodicarbonamide and semicarbazide contamination in commercial bread products. However, all of these studies have primarily focused on the final baked product and have not extensively investigated the processing and conditions that affect the final semicarbazide levels. In this study, a previously developed method for measuring free semicarbazide in bread was applied to dough samples during the mixing and kneading process. Additionally, flour and bread samples were spiked with biurea or azodicarbonamide to help elucidate semicarbazide formation pathways. The results showed that semicarbazide was not formed as a byproduct of azodicarbonamide decomposition to biurea, which occurs upon the addition of water. Indeed, semicarbazide was not detected after room temperature or elevated temperature dough maturation, but only after baking. It was concluded that although azodicarbonamide is the initial starting material, semicarbazide formation in bread occurs through a stable intermediate, biurea.     

Effect of Salt Reduction on Dough Handling and the Breadmaking Quality of Canadian Western Red Spring Wheat Varieties

The effect of salt (NaCl) on the breadmaking quality of 37 varieties of Canadian Western Red Spring wheat (Triticum aestivum L.) was investigated along with dough stickiness for a 20 variety subset. A principal components analysis indicated that dough development time (DDT), mixing tolerance index (MTI), and stability (STA) were highly correlated. DDT showed an inverse relationship with MTI (r = –0.73) and a positive relationship with STA (r = 0.89). STA was also negatively related to MTI (r = –0.76). A reduction of salt from 2.0 to 1.1% (based on flour weight) was considered from a practical perspective. Each variety responded differently to salt reduction. Obtaining an optimal dough consistency with less salt required less work input and shorter mixing time. Overall, decreasing loaf volume with reducing salt content was observed, although certain varieties produced the opposite effect. This suggests that for a particular flour, depending on the inherent flour strength, there is a level of NaCl that produces an optimum between gluten strength and gas‐holding capacity of the dough, resulting in a loaf with good crumb texture and an even distribution of bubble sizes. A stickiness test was performed on selected varieties to evaluate the dough handling properties at 1.1 and 2.0% salt levels. The overall trend showed an increase in stickiness with a decrease in the salt content; however, certain varieties showed no change.     

Effect of Lipid Oxidation on Dough Bleaching

The effect of lipid composition and oxidation on dough bleaching has been determined. At >2.25% (flour basis), pure linoleic acid was very efficient in degrading β‐carotene in dough, unlike colza, corn, peanut, soy, or sunflower oil, which were mainly characterized by different polyunsaturated fatty acids content. In a very oxidized state, as determined by a peroxide index of >15 meq/kg of oil, sunflower oil (rich in polyunsaturated fatty acids) had a major bleaching activity on β‐carotene when compared with colza oil (less polyunsaturated), especially in combination with long mixing times. A combination of lipase (815 U), slightly oxidized oil (peroxide index of 2–5 meq/kg of oil), and linoleic acid (90 mg/100 g of flour) significantly degraded flour pigments (P < 0.05).     

Retrogradation of Rice Flour Gel and Dough: Plasticization Effects of Some Food Additives

Certain food additives commonly used in flour products also have a plasticization effect on product shelf life regarding retrogradation. Sucrose, sorbitol, glycerol, citric acid, and acetic acid at 25, 25, 25, 0.5, and 0.5%, respectively, were added to two different starch gel systems: slurry (high‐amylose rice flour gel) and dough (waxy rice flour dough). All plasticizers increased gelatinization temperature, decreased enthalpy (ΔH), and promoted a more homogeneous system. Sucrose had the greatest effect on gelatinization increase. Rice dough was more susceptible to plasticizers, resulting in higher moisture content and a more amorphous structure. Retrogradation was highly positively correlated with amylose content, moisture retention, ratio of protons of water/starch, and previous occurrence of retrogradation. Moisture retention was increased in plasticizer‐added samples, especially waxy rice dough. Over a longer storage period, sucrose and sorbitol showed an antiplasticization effect in waxy rice flour dough, but glycerol and acid caused higher retrogradation in high‐amylose rice flour gel.