Study of oat globulin conformation by Fourier transform infrared spectroscopy.

The conformation of oat globulin dispersions (10% in D2O) under the influence of pH, chaotropic salts, protein structure perturbants, and heating conditions was studied by Fourier transform infrared (FTIR) spectroscopy. The FTIR spectrum of oat globulin showed major bands from 1670 to 1634 cm(-1), corresponding to the four major types of secondary structures, that is, beta-turns, beta-sheets, alpha-helices, and random coils. At extreme acidic and alkaline pH conditions, there were changes in intensity in the bands attributed to beta-sheet structures (1626, 1634, and 1682 cm(-1)), and shifts of the bands to higher or lower wavenumbers, indicating changes in conformation. In the presence of some chaotropic salts, the 1626 and 1634 cm(-1) bands were shifted upward, with a marked decrease in the intensity of the 1634 cm(-1) peak. The addition of several protein structure perturbants led to a slight shift in the alpha-helix/random coil bands and a marked reduction in the beta-sheet peaks, suggesting protein unfolding. Heating under aggregating conditions led to slight shifts in all of the major bands and progressive changes in the intensity of the alpha-helix, beta-sheet, and beta-turn peaks, suggesting protein denaturation. This was accompanied by marked increases in intensity of the two intermolecular beta-sheet bands (1682 and 1624-1626 cm(-1)) associated with the formation of aggregated strands. The IR spectra of soluble and insoluble aggregates showed a redistribution of native and extensively denatured proteins in the two fractions.     

Description of Chemical Changes Implied During Bread Dough Mixing by FT‐ATR Mid‐Infrared Spectroscopy

The aim of the present study was to investigate the ability of mid‐infrared (MIR) spectroscopy to identify physicochemical changes in the French bread dough mixing process. An ATR FT‐MIR spectrometer at 4000–800 cm^–1 was used. The MIR spectra collections recorded during mixing were analyzed after standard normal variate using principal component analysis (PCA) and after second‐derivative treatment. The results were interpreted in terms of chemical changes involved in dough development and more particularly in terms of secondary structural protein changes (amide III). The loading spectrum associated with principal component 1 (PC1) allows three MIR wave number regions of variations (3500–3000, 1700–1200, and 1200–800 cm^–1) to be identified. The loading spectrum associated with PC1 describes an increase in the relative protein band intensities and a decrease in relative water and starch band intensities. The variation during bread dough mixing time of the different amide III bands identified after the second‐derivative show that α‐helical, β‐turn, and β‐sheet structures increase while random coil structure decreases, suggesting that the gluten structure is becoming a more ordered structure. The MIR mixing time identified as being the maximum scores value on the PC1 scores plots was associated with the time at which the dough apparent torque begin to collapse, suggesting that the MIR spectroscopy could monitor bread dough development.     

Comparison of changes in the secondary structure of unheated, heated, and high-pressure-treated beta-lactoglobulin and ovalbumin proteins using fourier transform raman spectroscopy and self-deconvolution

Changes in protein secondary structure and conformation of ovalbumin and beta-lactoglobulin (15% protein w/w) were investigated by Fourier transform Raman spectroscopy and self-deconvolution. The amounts of alpha-helix, beta-sheets, random coil, and beta-turns in native beta-lactoglobulin were 15, 54, 6, and 25%, respectively, and those for ovalbumin (41, 34, 13, and 12%) compared well with published values obtained by X-ray crystallography. The proteins were heated at 90 degrees C for 30 min and high-pressure-treated at 600 MPa for 20 min. Heating increased beta-sheet structures in both proteins at the expense of alpha-helix; for beta-lactoglobulin beta-sheet structures increased from 54 to 70% and for ovalbumin, from 34 to 54%. Random coil increased from 6% in the native protein to 30% in high-pressure-treated beta-lactoglobulin. However, for ovalbumin, the contribution from beta-turns doubled in high-pressure-treated samples, with little change in random coil. Further examination of the deconvoluted amide I band in heated samples revealed several component bands. Bands at 1626 and 1682 cm(-1) for ovalbumin and at 1625 and 1680 cm(-1) for beta-lactoglobulin were observed and are associated with aggregated, intermolecular beta-sheet (beta-aggregation), indicative of heat denaturation. The band seen at 1632-1640 cm(-1) corresponded to intramolecular beta-sheet structures, whereas the band at 1625 cm(-1) is associated with exposed beta-sheets (for example, beta-strands with strong hydrogen bonding that are not part of the core of beta-sheets). In high-pressure-treated samples bands were also observed at 1628 and 1680 cm(-1) for ovalbumin and at 1626 and 1684 cm(-1) for beta-lactoglobulin, suggesting involvement of beta-sheet structures in protein aggregation. Raman bands were observed at 1665-1670 cm(-1) for ovalbumin and at 1663-1675 cm(-1) for beta-lactoglobulin due to random coil structures. The bands at 1650-1660 cm(-1) due to alpha-helices were observed in both heated and high-pressure-treated samples. In addition, in heated samples of both ovalbumin and beta-lactoglobulin, peak intensity increased for beta-sheet in the amide III region, 980-990 cm(-1), and decreased for helix structures (900-960 cm(-1)). In contrast, there was no peak at 1240 cm(-1) (amide III beta-sheet structures) in either high-pressure-treated ovalbumin or beta-lactoglobulin, suggesting that high-pressure denaturation at 600 MPa for 20 min is less extensive than heat denaturation at 90 degrees C for 30 min.     

Analysis of protein structures and interactions in complex food by near-infrared spectroscopy. 1. Gluten powder

The potential of near-infrared (NIR) spectroscopy in detailed food analysis was tested in a model system consisting of gluten powder treated with moisture and heat. Second-derivative transformation and extended multiplicative signal correction were applied for improving the band resolution and removing physical and quantitative spectral variations. Subsequent chemometric analyses gave loading spectra, which were interpreted as spectral effects of altered protein structures, induced by the treatments. Moistening of the gluten powder resulted in shifts and intensity changes in the protein bands, which could be explained by a combination of minor secondary structure changes, water binding, and changed microenvironments of the amino acid side chains. Heat denaturation induced increases at 2209 nm and decreases at 2167-2182 nm, indicating an alpha-helix to beta-sheet transformation, in agreement with the expectations.     

Using synchrotron-based FTIR microspectroscopy to reveal chemical features of feather protein secondary structure: comparison with other feed protein sources

Studying the secondary structure of proteins leads to an understanding of the components that make up a whole protein. An understanding of the structure of the whole protein is often vital to understanding its digestive behavior in animals and nutritive quality. Usually protein secondary structures include alpha-helix and beta-sheet. The percentages of these two structures in protein secondary structures may influence feed protein quality and digestive behavior. Feathers are widely available as a potential protein supplement. They are very high in protein (84%), but the digestibility of the protein is very low (5%). The objective of this study was to use synchrotron-based Fourier transform infrared (FTIR) microspectroscopy to reveal chemical features of feather protein secondary structure within amide I at ultraspatial resolution (pixel size = 10 x 10 microm), in comparison with other protein sources from easily digested feeds such as barley, oat, and wheat tissue at endosperm regions (without destruction of their inherent structure). This experiment was performed at beamline U2B of the Albert Einstein Center for Synchrotron Biosciences at the National Synchrotron Light Source (NSLS) in Brookhaven National Laboratory (BNL), U.S. Dept of Energy (NSLS-BNL, Upton, NY). The results showed that ultraspatially resolved chemical imaging of feed protein secondary structure in terms of beta-sheet to alpha-helix peak height ratio by stepping in pixel-sized increments was obtained. Using synchrotron FTIR microspectroscopy can distinguish structures of protein amide I among the different feed protein sources. The results show that the secondary structure of feather protein differed from those of other feed protein sources in terms of the line-shape and position of amide I. The feather protein amide I peaked at approximately 1630 cm(-1). However, other feed protein sources showed a peak at approximately 1650 cm(-1). By using multicomponent peak modeling, the relatively quantitative amounts of alpha-helix and beta-sheet in protein secondary structure were obtained, which showed that feather contains 88% beta-sheet and 4% alpha-helix, barley contains 17% beta-sheet and 71% alpha-helix, oat contains 2% beta-sheet and 92% alpha-helix, and wheat contains 42% beta-sheet and 50% alpha-helix. The difference in percentage of protein secondary structure may be part of the reason for different feed protein digestive behaviors. These results demonstrate the potential of highly spatially resolved infrared microspectroscopy to reveal feed protein secondary structure. Information from this study by the infrared probing of feed protein secondary structure may be valuable as a guide for feed breeders to improve and maintain protein quality for animal use.     

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。     

Effect of Processing on Functional Properties of Wheat Gluten Prepared by Cold‐Ethanol Displacement of Starch

Functional properties of gluten prepared from wheat flour are altered by separation and drying. Gluten was separated and concentrated by batterlike laboratory methods: development with water, dispersion of the batter with the displacing fluid, and screening to collect the gluten. Two displacing fluids were applied, water or cold ethanol (70% vol or greater, ‐13°C). Both the water‐displaced gluten (W‐gluten) and ethanol‐displaced‐ gluten (CE‐gluten) were freeze‐dried at ‐20°C as a reference. Samples were dried at temperatures up to 100°C using a laboratory, fluidized‐bed drier. Tests of functionality included 1) mixing in a mixograph, 2) mixing in a farinograph, and 3) the baked gluten ball test. Dough‐mixing functionality was assessed for Moro flour (9.2% protein) that was fortified up to 16% total protein with dried gluten. In the mixograph, CE‐gluten (70°C) produced improved dough performance but W‐gluten (70°C) degraded dough performance in proportion to the amount added in fortification. In the microfarinograph, there was a desirable and protein‐proportional increase in stability time for CE‐gluten (70°C) but no effect on stability for W‐gluten (70°C). Baking was evaluated using the baked gluten ball test and the percentage increase in the baked ball volume relative to the unbaked gluten volume (PIBV). PIBV values were as high as 1,310% for freeze‐dried CE‐gluten and as low as 620% for W‐gluten dried at 70°C. PIBV for CE‐gluten was reduced to 77% of the freeze‐dried control by fluid‐bed drying at 70°C. Exposure of CE‐gluten to 100°C air gave a PIBV that was 59% of the reference, but this expansion was still greater than that of W‐gluten dried at 70°C. The highest values of PIBV occurred at the same mixing times as the peak mixograph resistance.     

Structural Modifications of Gluten Proteins in Strong and Weak Wheat Dough During Mixing

The network‐forming attributes of gluten have been investigated for decades, but no study has comprehensively addressed the differences in gluten network evolution between strong and weak wheat types (hard and soft wheat). This study monitored changes in SDS protein extractability, SDS‐accessible thiols, protein surface hydrophobicity, molecular weight distribution, and secondary structural features of proteins during mixing to bring out the molecular determinants of protein network formation in hard and soft wheat dough. Soft wheat flour and dough exhibited greater protein extractability and more accessible thiols than hard wheat flour and dough. The addition of the thiol‐blocking agent N‐ethylmaleimide (NEM) resulted in similar results for protein extractability and accessible thiols in hard and soft wheat samples. Soft wheat dough had greater protein surface hydrophobicity than hard wheat and exhibited a larger decrease in surface hydrophobicity in the presence of NEM. Formation of high‐molecular‐weight (HMW) protein in soft wheat dough was primarily because of formation of disulfides among low‐molecular‐weight (LMW) proteins, as indicated by the absence of changes in protein distribution when NEM was present, whereas in hard wheat dough the LMW fraction formed disulfide interaction with the HMW fraction. Fourier transform infrared spectroscopy indicated formation of β‐sheets in dough from either wheat type at peak mixing torque. Formation of β‐sheets in soft wheat dough appears to be driven by hydrophobic interactions, whereas disulfide linkages stabilize secondary structure elements in hard wheat dough.     

Influence of Gliadin-Rich Subfractions of Glenlea Wheat on the Mixing Characteristics of Wheat Flour

The effect of gliadin-rich subfractions of extra-strong wheat on the mixing properties of Canada Prairie Spring (CPS) wheats and Canada Western Extra Strong Red Spring wheat (CWES) cv. Glenlea was determined by the 2-g mixograph. Thirteen subfractions isolated from the single ethanol extract of Glenlea showed differences in their SDS-PAGE patterns of total proteins, low molecular weight glutenin subunits, the ω-gliadin component, and acid-PAGE electrophoregrams. High molecular weight glutenin subunits were found only in one subfraction isolated by increasing the concentration of ethanol. Subfractions that remained solubilized in the water phase after removal of ethanol from the extract were deficient in ω-gliadins and contained a number of fast-moving protein bands. These fractions caused a significant delay (from 2.64 to 5.41 min and from 5.75 to 8.16 min) in the mixograph peak development of CPS and Glenlea flours, respectively. On the contrary, the water-insoluble subfractions reduced the mixing time requirement (from 2.6 to 1.08 min and from 5.8 to 1.7 min for CPS and Glenlea flours, respectively) and caused a rapid decline in the dough stability as the mixing continued. Both base flours showed an increase in peak height with the addition of ethanol-extractable protein subfractions. Mixograph development time and energy to peak increased with the addition of water-soluble subfractions but decreased with water-insoluble subfractions of the 70% ethanol extract. The band width at peak increased when water-soluble subfraction 6.5 was added to CPS flour but decreased when it was added to Glenlea flour. Removal of ethanol-extractable components from flours resulted in loss of viscoelasticity. Adding subfraction 1.5 back to the flour residue caused a return of this physicochemical attribute. Addition of a nonwater- dispersible subfraction (1.5) to CPS flour or CPS flour residue caused a significant increase in the formation of gluten. Approximately 35–42% of the added gliadins were incorporated into the gluten network of CPS flour and 34–52% into the flour residue.     

Ovalbumin, ovotransferrin, lysozyme: three model proteins for structural modifications at the air-water interface

Structural modifications of ovalbumin, ovotransferrin, and lysozyme at the air-water interface have been investigated using SDS-PAGE, both intrinsic and ANS fluorometry, and circular dichroism experiments. Ovalbumin contact with an interface induced an exposure of aromatic residues, a slight decrease in alpha-helix structures (-1.7%), and an increase in both beta-sheet (+3.4%) and beta-turn (+7.9%) structures. Moreover, these conformational changes led to the formation of insoluble polymers of ovalbumin through intermolecular disulfide bonds. Ovotransferrin contact with an interface led to an increase in its surface hydrophobicity (+30%) and modifications of its secondary structure (-33% of alpha-helices, +96.4% of beta-sheets, +13.2% of beta-turns, and +21.2% of random coils), characteristic of major conformational changes. On the other hand, lysozyme did not undergo any structural modification. These results clearly underscore that at the air-water interface proteins are susceptible to denaturation.     

Effects of Nitrogen and Sulfur Fertilizer on Protein Composition,Mixing Requirements,and Dough Strength of Four Wheat Cultivars

Two field trials using four New Zealand wheat cultivars were undertaken to observe the effects of nitrogen and sulfur fertilization on protein composition, mixing requirements, and dough strength and to compare the results with that observed with a single cultivar, Otane. The results confirmed that adequate sulfur fertilization was necessary to ensure lower dough mixing requirements. The existence of a nexus between mixing requirements and dough strength was confirmed and genotype has significant effects on it. Variation in the content of HMW‐GS in the protein corresponded to changes in dough mixing requirement of Otane. Across the four cultivars, dough mixing requirements (mechanical dough development work input and mixograph development time) and dough strength (Extensigraph resistance to extension) depended on different aspects of protein composition. As the content of polymeric proteins increased, MDD work input increased, but mixograph development time decreased, while the effect on Rmax was small. Rmax, however, was more affected by either the content of small monomerics in the flour or the ratio between HMW‐GS peak area to total gliadin peak area. The ratio of MDD work input to Rmax was largely explained by the gliadin content of the flour. Thus, depending on the genetic background, it should be possible to adjust dough mixing requirements by modifying overall HMW‐GS, LMW‐GS, or gliadin content while maintaining dough strength.     

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.     

Wheat Flour Exposed to Ethanol Yields Dough with Unexpected Properties

Exposure of wheat flour to ethanol solutions followed by slow drying of the ethanol in situ alters the subsequent transformation of the flour into dough. Several types of wheat flour were exposed to small amounts of ethanol solutions so as to be “wetted” but without the appearance of a separate liquid phase. The wet sample was then dried in air. Dough was formed from the treated flour, and its rheological parameters were assessed, including time to peak strength (mixograph and farinograph) and gluten index (glutomatic). Untreated and treated flour and the dough prepared therefrom were assayed using 1D SDS‐PAGE (reducing and unreducing conditions), capillary zone electrophoresis (CZE) applied to 70% leachates with and without sonication, and differential scanning calorimetry. Both gluten index and time to peak increased as a result of the treatment, and the increase was greater for flour or enriched vital gluten with an initially low gluten index than for flour with a relatively high initial index. Endosperm fragmentation following milling of the treated flour was improved by the treatment. Thermal transitions were at lower temperatures following treatment, indicating less structural order and reduced thermal stability. No compositional differences were evident when studied with robust analytical methods. CZE of leached samples (no sonication) revealed lower amounts of accessible or detected proteins following treatment. Conformational changes and new secondary interactions, therefore, appear to cause the effect.     

Raman spectroscopic study of structural changes in Hake (Merluccius merluccius L.) muscle proteins during frozen storage

This paper examines changes in the structure and functionality of fish muscle proteins at frozen storage temperatures known to render very different practical storage lives (-10 and -30 degrees C). Apparent viscosity and dimethylamine (DMA) content showed drastic temperature-related differences during storage. Raman spectroscopy revealed the occurrence of some structural changes involving secondary and tertiary protein structures. The changes in secondary structure were quantified, showing an increase of beta-sheet at the expense of alpha-helix structure. The nuC-H stretching band near 2935 cm(-)(1) increased in intensity, indicating denaturation of the muscle proteins through the exposure of aliphatic hydrophobic groups to the solvent. These structural changes were more pronounced at -10 degrees C but occurred at both storage temperatures, whereas changes in apparent viscosity and DMA only occurred in storage at -10 degrees C. The possible utility of these structural changes for quality assessment is discussed.     

Qualitative Effect of Added Gluten on Dough Properties and Quality of Chinese Steamed Bread

Glutens isolated from 15 soft red winter (SRW) wheat flours were added into a SRW wheat flour to obtain protein levels of 9.6 and 11.3% for determination of the qualitative effect of added gluten on the dough properties and quality of northern‐style Chinese steamed bread (CSB). Sodium dodecyl sulfate sedimentation (SDSS) volume of the gluten source flour exhibited positive relationships with mixograph absorption, midline peak time (MPT), and midline peak value (MPV) of the gluten‐added flours and with surface smoothness, crumb structure, and total score of CSB prepared from the gluten‐added flours regardless of protein content. Positive correlations were also observed between SDSS volume of the gluten source flour and specific volume and stress relaxation score of CSB prepared from the gluten‐added flours of 11.3% protein. The increase in protein content from 9.6 to 11.3% by gluten addition raised mixograph absorption, MPT, and MPV but had no apparent effect on resistance breakdown, dough maximum force for extension, and extensibility, and it increased CSB specific volume and crumb structure score without affecting surface smoothness, stress relaxation, and total score. Mixograph parameters exhibited significant relationships with CSB total score, indicating that they could be effective predictors of the CSB‐making quality of flours.     

Conformational study of globulin from common buckwheat (Fagopyrum esculentum Moench) by Fourier transform infrared spectroscopy and differential scanning calorimetry

Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) were used to study changes in the conformation of globulin from common buckwheat (Fagopyrum esculentum Moench) (BWG) under various environmental conditions. The IR spectrum of the native BWG showed several major bands from 1691 to 1636 cm(-1) in the amide I' region, and the secondary structure composition was estimated as 34.5% beta-sheets, 20.0% beta-turns, 16.0% alpha-helices, and 14.4% random coils. Highly acidic and alkaline pH conditions induced decreases in beta-sheet and alpha-helical contents, as well as in denaturation temperature (Td) and enthalpy of denaturation (DeltaH), as shown in the DSC thermograms. Addition of chaotropic salts (1.0 M) caused progressive decreases in ordered structures and thermal stability following the lyotropic series of anions. The presence of several protein structure perturbants also led to changes in IR band intensities and DSC thermal stabilities, suggesting protein unfolding. Intermolecular antiparallel beta-sheet (1620 and 1681 cm(-1)) band intensities started to increase when BWG was heated to 90 degrees C, suggesting the initiation of protein aggregation. Increasing the time of the preheat treatment (at 100 degrees C) caused progressive increases in Td and pronounced decreases in DeltaH, suggesting partial denaturation and reassociation of protein molecules.     

Effects of water activity and lipid addition on secondary structure of zein in powder systems

The effects of water activity (A(w)) and lipid addition on the secondary structure of powdery zein were investigated using Fourier transform infrared spectroscopy. Two fatty acid esters, i.e., the linolenic and eicosapentaenoic acid ethyl esters (LAE and EPE), were mixed with the zein powder. The powders were stored in the "dry" state (with silica gel) and the "humid" state (A(w) = 0.9). The powdery zein without the lipids was shown to have a high content of the intermolecular hydrogen-bonded beta-sheet in the "dry" state, indicating the presence of protein aggregates. An increase in A(w) induced a decrease in this beta-sheet, concomitant with increases in the alpha-helix and beta-turn structures. The addition of LAE caused decreases in the alpha-helix and intermolecular hydrogen-bonded beta-sheet of zein when the powder was stored in the "humid" state, suggesting the strong interaction of LAE and zein molecules. However, LAE did not affect the secondary structure of zein in the "dry" state. The addition of EPE hardly influenced the secondary structure of zein, irrespective of A(w). These results are discussed in relation to the antioxidative activity of zein in the powder system, which had studied previously.     

Tyrosine cross-links: molecular basis of gluten structure and function

The formation of the large protein structure known as "gluten" during dough-mixing and bread-making processes is extremely complex. It has been established that a specific subset of the proteins comprising gluten, the glutenin subunits, directly affects dough formation and breadmaking quality. Glutenin subunits have no definitive structural differences that can be directly correlated to their ability to form gluten and affect dough formation or breadmaking quality. Many protein structural studies, as well as mixing and baking studies, have postulated that disulfide bonds are present in the gluten structure and contribute to the process of dough formation through the process of disulfide-sulfhydryl exchange. Evidence presented here indicates that tyrosine bonds form in wheat doughs during the processes of mixing and baking, contributing to the structure of the gluten network. The relative contributions of tyrosine bonds and disulfide--sulfhydryl interchange are discussed.     

Genetic Variance for Gluten Strength Contributed by High Molecular Weight Glutenin Proteins

A total of 162 doubled haploid (DH) lines were produced from a cross between Triticum aestivum L. ‘AC Karma’ and line 87E03‐S2B1 to study the genetic contribution of high molecular weight (HMW) glutenin subunits to gluten strength. HMW glutenin subunit composition of each DH line was determined by SDS‐PAGE. The population was grown in the field at one location in 1999 and at three locations in 2000. Gluten strength and dough mixing properties were measured by mixograph test and SDS‐sedimentation test. Variance components were estimated for each measurement to determine the variability contributed by HMW glutenin subunits. Results indicated significant environmental impact on tested mixograph parameters, SDS‐sedimentation volumes and grain and flour protein concentration. Significant main effects of Glu‐1D loci encoded subunits were obtained for mixograph development time, energy to peak, slope after peak, and first minute slope. Lines containing 5+10 combination of subunits had higher values for mixograph development time and energy to peak, while slope after peak and first minute slope were lower as compared with 2+12 containing lines. Low intergenomic interactions were observed for bandwidth energy (BWE), total energy (TEG), and SDS‐sedimentation test, involving B and D genomes only. A portion of the genetic variability for gluten strength was accounted for overexpression of Bx7 subunit originating from the cultivar Glenlea derived line 87E03‐S2B1. There was no significant effect of Glu‐A1 encoded subunits on any of the tested parameters. Estimated genetic variability for gluten strength contributed by Glu‐B1 and Glu‐D1 encoded HMW glutenins was 55% for mixing development time and 51% for energy to peak.     

Disaggregation and reaggregation of gluten proteins by sodium chloride

This study showed that gluten proteins were extracted with distilled water from dough prepared in the presence of NaCl. To elucidate the interrelationship of NaCl and gluten proteins in dough, the extracted proteins were characterized. These proteins were primarily found to be soluble gliadin monomers by N-terminal amino acid sequencing and analytical ultracentrifugation. Extracted proteins were aggregated by the addition of NaCl at concentrations of >10 mM. A decrease in beta-turn structures, which expose tryptophan residues to an aqueous environment in the presence of NaCl, was revealed by Fourier transform infrared analysis and scanning of fluorescence spectra. In addition, cross-linking experiments with disuccinimidyl tartrate showed that a large amount of protein was cross-linked in the dough only in the presence of NaCl. These results suggest that both interactions and distances between proteins were altered by the addition of NaCl.