Quantitative Assessment of Gas Cell Development During the Proofing of Dough by Magnetic Resonance Imaging and Image Analysis

The structure of bread crumb is an important factor in consumer acceptance of bakery products. The noninvasive monitoring of the gas cell formation during the proofing of dough can aid in understanding the mechanisms governing the crumb appearance in the baked product. The development of gas cells during the proofing of dough was monitored in a noninvasive manner using magnetic resonance imaging (MRI) at 4.7‐T. The acquired MRI time series were analyzed quantitatively using image analysis (IA) techniques. The effects of both kneading temperature and mechanical damage by molding were studied. When additional rheological stress was introduced during molding, a more heterogeneous (coarse) gas cell size distribution was observed, and the dough had a smaller specific volume (as measured by MRI). These characteristics were preserved in the bread crumb structure after baking. The fast‐deformation during molding also resulted in an isotropic growth of the dough during proofing, whereas slow‐deformation during molding resulted in anisotropic growth. This can be related to a better conservation of stress in the dough under a moderate molding operation. A higher temperature during kneading also resulted in a coarser distribution of the gas cells and a smaller MRI specific dough volume. No effect of kneading temperature on the growth anisotropy could be detected, however. This indicates that temperature has a smaller effect on the conservation of stress in the dough than molding. The current work illustrates the capability of MRI/IA for understanding and predicting the influence of food processing parameters on consumer‐relevant features in a food product (bread).     

Demixing in Wheat Doughs—Its Influence on Dough and Gluten Rheology

Reshaping of relaxed wheat doughs leads to an increase in firmness that significantly changes the results of rheological measurements involving large uniaxial deformations of the dough, whereas the gluten properties remain unaffected. Microscopic investigations reveal that directly after kneading, starch and gluten are thoroughly mixed. However, the shaping procedure of a relaxed dough or shear-flow during rheological measurements cause a separation of gluten and starch. The dilatant behavior of the starch granules and the capacity of gluten to aggregate account for the observed dough-hardening.     

A New Method to Study Simple Shear Processing of Wheat Gluten‐Starch Mixtures

This article introduces a new method that uses a shearing device to study the effect of simple shear on the overall properties of pasta‐like products made from commercial wheat gluten‐starch (GS) blends. The shear‐processed GS samples had a lower cooking loss (CL) and a higher swelling index (SI) than unprocessed materials, suggesting the presence of a gluten phase surrounding starch granules. Pictures of dough micro‐structure by confocal scanning laser microscopy (CSLM) showed the distribution of proteins in the shear‐processed samples. This study revealed that simple shear processing could result in a product with relevant cooking properties as compared with those of commercial pasta. Increasing gluten content in GS mixtures led to a decrease in CL and an increase in maximum cutting stress of processed samples, whereas no clear correlation was found for SI values of sheared products. It was concluded that the new shearing device is unique in its capability to study the effect of pure shear deformation on dough development and properties at mechanical energy and shear stress levels relevant to industrial processing techniques like pasta extrusion.     

Effect of Physical State of Nonpolar Lipids on Rheology and Microstructure of Gluten‐Starch and Wheat Flour Doughs

To clarify the effects of solid fat and liquid oil on dough in more detail in a simpler system, gluten‐starch doughs with different gluten contents were investigated. The results from rheological measurements indicate that dough with a higher starch content has less resistance to strain and dough with a lower starch content has a rubber‐like structure. The effects of the physical state of nonpolar lipids such as fat and oil on gluten‐starch doughs and wheat flour doughs were investigated using rheological measurements and scanning electron microscopy. Fat‐containing dough had more gas cells and a very smooth gluten gel surface with few holes, which may provide higher tolerance to strain. Moreover, the fat seemed to uniformly distribute the gluten gel between the starch granules in the dough, which reduced the friction between starch granules and led to a lower storage modulus. A mechanism governing the effect of fats on loaf volume is proposed based on the phenomena observed in the fat‐containing dough.     

基于低场核磁和差示量热扫描的面条面团水分状态研究

为了解低水分面条面团中水分的存在状态,明确真空度及和面时间对水分状态的影响,该研究以3个小麦品种（济麦20、宁春4号、济麦22）磨制的面粉为材料,采用真空和面制作低水分面条面团（含水率35%）,采用低场核磁共振技术（LF-NMR,low-field nuclear magnetic resonance）和差示量热扫描（DSC,differential scanning calorimetry）2种技术,测定不同真空度（0、0.06、0.09 MPa）和搅拌时间（4、8、12 min）下面团中水分的形态和分布,并进一步分析2种技术测定水分形态结果的相关性。结果表明,在低水分面条面团中,水分主要以弱结合水形态存在。不同品种的小麦粉面团的水分形态及分布存在差异,强筋小麦粉（济麦20）制作面团的水分自由度较低。真空和面（0.06 MPa）可以促进水分与面筋蛋白的相互作用,降低面团中水分子流动性,促进水分结构化;而非真空或过高真空度均会导致面团中水分自由度增加。济麦20、济麦22小麦粉和面时间为8 min时,面团水分流动性较低;而宁春4号小麦粉面团在4 min时,水分自由度较低;继续搅拌,深层结合水减少、弱结合水增多。LF-NMR和DSC测得面团水分状态的结果具有一致性。LF-NMR测得的弱结合水峰面积百分比与DSC测得的可冻结水百分比具有相同的变化趋势（r=0.695）,且深层结合水峰面积百分比与非冻结水百分比具有相同的变化趋势（r=0.564）。研究结果为认识制面过程中水分的作用,优化和面工艺和调整产品特性提供参考。     

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.     

Stress Relaxation Behavior of Wheat Dough,Gluten, and Gluten Protein Fractions

Relaxation behavior was measured for dough, gluten and gluten protein fractions obtained from the U.K. biscuitmaking flour, Riband, and the U.K. breadmaking flour, Hereward. The relaxation spectrum, in which relaxation times (τ) are related to polymer molecular size, for dough showed a broad molecular size distribution, with two relaxation processes: a major peak at short times and a second peak at times longer than 10 sec, which is thought to correspond to network structure, and which may be attributed to entanglements and physical cross‐links of polymers. Relaxation spectra of glutens were similar to those for the corresponding doughs from both flours. Hereward gluten clearly showed a much more pronounced second peak in relaxation spectrum and higher relaxation modulus than Riband gluten at the same water content. In the gluten protein fractions, gliadin and acetic acid soluble glutenin only showed the first relaxation process, but gel protein clearly showed both the first and second relaxation processes. The results show that the relaxation properties of dough depend on its gluten protein and that gel protein is responsible for the network structure for dough and gluten.     

小麦粉面团形成过程水分状态及其比例变化

为揭示小麦粉面团形成过程水分状态和比例、面团结构的变化,以及这种变化与粉质仪和拉伸仪表征的质量特性之间的关系;认识面团形成过程表征筋力强弱的物质基础和变化机理。选用中筋(宁春4号)和强筋(师栾02-1)小麦品种为试验材料,利用低场核磁共振技术测定粉质仪和面过程、拉伸仪醒发拉伸过程不同时间点面团水分状态和比例的变化;利用红外显微成像技术分析面团形成过程不同取样点蛋白质和淀粉的分布及结构变化。结果表明,面粉原料中主要为弱结合水。面粉在粉质仪加水搅拌形成面团后,水分状态和比例发生显著变化,面团中的水可以分为强结合水(T_(21))、弱结合水(T_(22))和自由水(T_(23))。面团搅拌形成过程中,中筋小麦品种宁春4号面团中的强结合水比例显著降低;师栾02-1的强结合水的弛豫时间在和面终点消失,弱结合水的弛豫时间显著延长,而自由水的比例显著增加(P0.05)。强筋小麦粉强结合水的保持时间较长。拉伸过程加盐和不加盐对同一取样点、同一种水分状态之间的水分弛豫时间和比例无显著影响;宁春4号自由水的弛豫时间在加盐和不加盐处理时都显著缩短(P0.05)。湿面筋含量高、筋力较强面团的蛋白质网络结构致密。粉质仪和面过程强结合水和弱结合水弛豫时间和比例的变化,与面筋含量和强度有关。该结论可为面制品加工过程和面工艺选择与优化等方面提供一定的理论参考。     

Macromolecular and Micronutrient Profiles of Sprouted Chickpeas to Be Used for Integrating Cereal‐Based Food

Pulse flour may be used to improve nutritional traits of gluten and gluten‐free formulations in traditional food such as bread or pasta. However, owing to some intrinsic nutritional, textural, and sensory properties, the use of pulses as ingredients for production of enriched food remains limited. In this study, we investigated the modification in macromolecules and micronutrients in industrial‐scale flour from partially sprouted chickpeas to define its possible use as an ingredient in cereal‐based foods. Controlled sprouting resulted in significant decrease of antinutritional compounds (e.g., phytic acid and serine protease inhibitors) and in an increase of free minerals and vitamins. Sprouting also affected the overall structural organization of proteins (such as aggregate formation) and their thiol/disulfide balance, and it promoted release of peptides. All of these had a positive effect on dough mixing properties, in particular for dough development. Formulations with enrichment in sprouted chickpea flour (wheat/chickpea ratio = 100:20) were tested also as for their dough leavening properties, which improved with respect to flour from nonsprouted chickpeas. Taking into account the modifications induced by partial sprouting on an industrial scale, we can conclude that sprouted chickpea flour represents an interesting ingredient for production of enriched cereal‐based food with better nutritional and rheological characteristics.     

Gluten Structural Evolution During Pasta Processing of Refined and Whole Wheat Pasta from Hard White Winter Wheat: The Influence of Mixing,Drying, and Cooking

An attempt was made to evaluate gluten structural changes in refined and whole wheat pasta from hard white winter wheat to elucidate the impact of whole wheat components on the formation and structure of the gluten network in pasta. Attenuated total reflectance–FTIR spectroscopy was used to track gluten secondary structure through most of the major steps in pasta processing: raw material, mixing, drying, and cooking. Protein solubility, accessible thiols, and SDS‐PAGE data were also collected to provide additional information on the nature of protein interactions and network composition. Few secondary structural differences were observed between refined and whole wheat flours from hard white wheat. However, mixing induced a significant shift to β‐sheet structures in refined dough that was not equally matched by whole wheat dough. Drying under both high temperature, short time (HT) and low temperature, long time (LT) conditions resulted in a reversion to structural distributions similar to those for flour in both pastas. However, greater protein denaturation in HT samples was indicated by lower protein solubility also in the presence of denaturants and disulfide reducing agents. Cooking generated a substantial increase in β‐sheet structures for both pasta systems. This structure was greatest in refined and LT samples. Thiol accessibility data indicate the presence of a highly aggregated, compact gluten network in refined pasta, mostly driven by hydrophobic association. Conversely, the network in whole wheat pasta was more loosely associated and dependent on disulfide bonding, both of which fit well with the secondary structural data.     

Extrusion of Wheat Gluten Plasticized with Glycerol: Influence of Process Conditions on Flow Behavior,Rheological Properties,and Molecular Size Distribution

Gluten-glycerol dough was extruded under a variety of processing conditions using a corotating self-wiping twin-screw extruder. Influence of feed rate, screw speed, and barrel temperature on processing parameters (die pressure, product temperature, residence time, specific energy) were examined. Use of flow modeling was successful for describing the evolution of the main flow parameters during processing. Rheological properties of extruded samples exhibited network-like behavior and were characterized and modeled by Cole-Cole distributions. Changes in molecular sizes of proteins during extrusion were measured by chromatography and appeared to be correlated to molecular size between network strands, as derived from the rheological properties of the materials obtained. Depending on operating conditions, extrudates presented very different surface aspects, ranging from very smooth-surfaced extrudates with high swell to completely broken extrudates. The results indicated that extrudate breakup was caused by increasing network density, and some gliadins may have acted as cross-linking agents. Increasing network density resulted in decreasing mobility of polymeric chains, and “protein melt” may no longer have been able to support the strain experienced during extrusion through the die. Increasing network density was reflected in increased plateau modulus and molecular size of protein aggregates. Increasing network structure appeared to be induced by the severity of the thermomechanical treatment, as indicated by specific mechanical energy input and maximum temperature reached.     

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.     

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.     

Contribution of Hydrophobic Soluble Gluten Proteins,Fractionated by Hydrophobic Interaction Chromatography in Highly Acetylated Agarose,to Dough Rheological Properties

Hydrophobic interaction chromatography with highly acetylated agarose in 1‐mL columns was used to fractionate gliadins and acid‐soluble glutenins. Proteins were eluted in two fractions, the first with acetate buffer (pH 3.6) containing 35% propanol, and the second with Tris buffer in 8M urea. The proportion of eluted protein in the second fraction was called the surface hydrophobicity index. The study included 20 wheat samples of different baking qualities. Multiple regression analysis using the general linear model combined with the stepwise technique was used to relate the surface hydrophobicity index of soluble gluten proteins to specific dough rheological characteristics. Surface hydrophobicity index of gliadins and acetic acid soluble glutenins explained part of the variability of swelling index, extensibility, and work of deformation (dough strength) measured with the alveograph, and part of the farinograph water absorption variability, but showed no relationship to dough mixing characteristics. Hydrophobic soluble gluten proteins fractionated by hydrophobic interaction chromatography (HIC) explained a part of the variability of dough rheological properties.     

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.     

Determination of secondary structural changes in gluten proteins during mixing using Fourier transform horizontal attenuated total reflectance spectroscopy

Fourier transform horizontal attenuated total reflectance (FT-HATR) was used to examine changes in the secondary structure of gluten proteins in a flour-water dough system during mixing. Midinfrared spectra of mixed dough revealed changes in four bands in the amide III region associated with secondary structure in proteins: 1317 (alpha-helix), 1285 (beta-turn), 1265 (random coil), and 1242 cm (-1) (beta-sheet). The largest band, which also showed the greatest change in second derivative band area (SDBA) during mixing, was located at 1242 cm (-1). The bands at 1317 and 1285 cm (-1) also showed an increase in SDBA over time. Conversely, the band at 1265 cm (-1) showed a corresponding decrease over time as the doughs were mixed. All bands reached an optimum corresponding to the minimum mobility of the dough as determined by the mixograph. Increases in alpha-helix, beta-turn, and beta-sheet secondary structures during mixing suggest that the dough proteins assume a more ordered conformation. These results demonstrate that it is possible, using infrared spectroscopic techniques, to relate the rheological behavior of developing dough in a mixograph directly to changes in the structure of the gluten protein system.     

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.     

Impact of Bran Addition on Water Properties and Gluten Secondary Structure in Wheat Flour Doughs Studied by Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy

The aim of this work was to elucidate the underlying physical mechanism(s) by which bran influences whole grain dough properties by monitoring the state of water and gluten secondary structure in wheat flour and bran doughs containing 35–50% moisture and 0–10% added bran. The system was studied with attenuated total reflectance (ATR) FTIR spectroscopy. Comparison of the OH stretch band of water in flour dough with that in H₂O‐D₂O mixtures having the same water content revealed the formation of two distinct water populations in flour dough corresponding to IR absorption frequencies at 3,600 and 3,200 cm^–1. The band intensity at 3,200 cm^–1, which is related to water bound to the dough matrix, decreased and shifted to lower frequencies with increasing moisture content of the dough. Addition of bran to the dough caused redistribution of water in the flour and bran dough system, as evidenced by shifts in OH stretch frequency in the 3,200 cm^–1 region to higher frequencies and a reduction in monomeric water (free water). This water redistribution affected the secondary structure of gluten in the dough, as evidenced by changes in the second‐derivative ATR‐FTIR difference spectra in the amide I region. Bran addition caused an increase in β‐sheet content and a decrease in β‐turn (β‐spiral) content. However, this bran‐induced transconformational change in gluten was more significant in the 2137 flour dough than in Overley flour dough. This study revealed that when bran is added to flour dough, water redistribution among dough components promotes partial dehydration of gluten and collapse of β‐spirals into β‐sheet structures. This transconformational change may be the physical basis for the poor quality of bread containing added bran.     

Osmotic Properties of Gluten

A model for dough is proposed in which the distribution of water between hydrated gluten and starch paste explains a number of practical observations such as 1) the extreme sensitivity of the consistency of dough to the amount of water in the recipe, and 2) the fact that working of the material results in an increase in consistency. The model assumes dough to be a composite material consisting of a starch paste and gluten filaments. During kneading, the starch granule paste in dough dries to become a phase with a yield stress as a result of the uptake of water by the stretching gluten filaments. This study focused on one particular aspect of this model: the osmotic properties of gluten during stretching. The results suggest that gluten can be hydrated more efficiently in the stretched state than in an unstretched conformation. Gluten hydration tends to change slowly over a period of weeks, which is accompanied by water expulsion or uptake, depending on the osmotic properties of the solvent. The rate of change does not seem to depend very much on pH and osmotic pressure for the current experimental conditions. The level of hydration of relaxed gluten depends strongly on pH, as expected. The experiments allow the construction of an osmotic pressure versus gluten concentration diagram over the range 4.6 < pH < 5.8. The level of hydration of the gluten is consistent with the proposed model for dough.     

Effect of Transglutaminase,Citrate Buffer,and Temperature on a Soft Wheat Flour Dough System

Transglutaminase (TGase) can improve the functional characteristics of proteins by introducing covalent bonds inter‐ or intrachains. Temperature and pH interfere with the protein structure and the catalytic activity of enzymes. Because these three factors can act synergistically, TGase, citrate buffer, and temperature were evaluated for their effects on the rheological and chemical changes in low‐protein wheat flour dough. Dough strength, measured by microextension test, significantly increased with increasing levels of TGase (8 U/g of protein), with changes in pH of the citrate buffer (pH 6.5), and by the effect of interaction between these factors. The same trend was observed in the size‐exclusion HPLC measurements, indicating that these two parameters have the effect of increasing gluten protein aggregation. Temperature had a significant effect on dough extension, measured by microextension test. The changes in secondary structure of gluten protein were investigated by FTIR second‐derivative spectra (amide I region, 1,600–1,700 cm⁻¹) and showed an increase in β‐sheet structures initiated by TGase, citrate buffer pH, and their interaction.