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.     

Characteristics and Protein Subunit Composition of Flour Mill Streams from Different Commercial Wheat Classes and Their Relationship to White Salted Noodle Quality

Proximate characteristics and protein compositions of selected commercial flour streams of three Australian and two U.S. wheats were investigated to evaluate their effects on the quality of white salted noodles. Wheat proteins of flour mill streams were fractionated into salt‐soluble proteins, sodium dodecyl sulfate (SDS)‐soluble proteins, and SDS‐insoluble proteins with a sequential extraction procedure. SDS‐soluble proteins treated by sonication were subsequently separated by nonreducing SDS polyacrylamide gel electrophoresis (SDS‐PAGE). There was a substantial amount of variation in distributions of protein content and protein composition between break and reduction mill streams. SDS‐insoluble proteins related strongly to differences in protein quantity and quality of flour mill streams. The soluble protein extracted by SDS buffer included smaller glutenin aggregates (SDS‐soluble glutenin) and monomeric proteins, mainly gliadin (α‐, β‐, γ‐, and ω‐types) and albumin and globulin. SDS‐soluble proteins of different flour mill streams had similar protein subunit composition but different proportions of the protein subunit groups. Noodle brightness (L) decreased and redness (a) increased with increased SDS‐insoluble protein and decreased monomeric gliadin. Noodle cooking loss and cooking weight gain decreased with increased glutenin aggregate (SDS‐soluble glutenin and SDS‐insoluble glutenin) and decreased monomeric gliadin. Noodle hardness, springiness, cohesiveness, gumminess, chewiness, tensile strength, breaking length, and area under the tensile strength versus breaking length curve increased with increased glutenin aggregate. Monomeric gliadin contributed differently to texture qualities of cooked noodles from glutenin aggregate. Monomeric albumin and globulin were not related to noodle color attributes (except redness), noodle cooking quality, and texture qualities of cooked noodles. The results suggested that variation in protein composition of flour mill streams was strongly associated with noodle qualities.     

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.     

Studies on Effects of Microbial Transglutaminase on Gluten Proteins of Wheat. I. Biochemical Analysis

The enzyme transglutaminase (TG) is known to have beneficial effects on breadmaking. However, only limited information is available on the structural changes of gluten proteins caused by TG treatment. The effect of TG has, therefore, been systematically studied by means of model peptides, suspensions of wheat flours and doughs. The treatment of synthetic peptides mimicking amino acid sequences of HMW subunits of glutenin with TG results in isopeptide bonds between glutamine and lysine residues. To study the effect on gluten proteins, different amounts of TG (0 to 900 mg enzyme protein per kg) were dissolved in a buffer and added to wheat flour. The flour suspensions were incubated and centrifuged and the residues were successively extracted with water, a salt solution, 60% aqueous ethanol (gliadin fraction) and SDS solution including a reducing agent (glutenin fraction). The characterization of the fractions by amino acid analysis, SDS‐PAGE, gel permeation HPLC and reversed‐phase HPLC has indicated that the quantity of extractable gliadins decreases by increasing TG amounts. Among gliadins, the ω5‐type was affected to the greatest extent by the reduction of extractability, followed by the ω1,2‐, α‐ and γ‐types. The oligomeric portion of the gliadin fractions (HMW gliadin) was strongly reduced when flour was treated with 450 and 900 mg TG per kg of flour, respectively. In the first instance, the quantity of the glutenin fractions increased by the treatment of flour with 90 and 450 mg TG per kg of flour, and significantly decreased by the treatment of flour with 900 mg TG per kg of flour. Parallel to an increase in TG concentration, the amounts of glutenin‐bound ω‐gliadins and HMW subunits were strongly reduced, whereas the LMW subunits reached a maximal amount after treatment with 450 mg TG per kg of flour. The insoluble residue was almost free of protein when flour was treated with lower amounts of TG. Higher amounts led to a great increase of protein in the residues. The effects of TG on doughs were similar to those of flour suspensions, but less strongly pronounced probably due to the lower water content of the dough system. Sequence analysis of peptides from a thermolytic digest of the insoluble residue revealed that HMW subunits of glutenin and α‐gliadins were predominantly involved in cross‐links formed by TG treatment.     

Dynamic viscoelastic and tensile properties of gluten and glutenin gels of common wheats of different strength

Dynamic viscoelastic properties at 25 degrees C of gluten and glutenin gels were obtained from Canadian common wheats of different strengths. The relaxation spectra showed a maximum intensity at a characteristic relaxation time (tau). The relaxation modulus associated with this maximum was taken as the strength of the glutenin or gluten gel transient network (G(tau)). The ratio of G(tau) for glutenin and gluten gels from the same cultivar ranged from 5.6 for an extra strong cultivar to 51.1 for a soft wheat. This gives indirect evidence that the gliadin fraction weakens the glutenin gel network more in weaker cultivars. In addition, the fact that both glutenin and gluten gels showed extensive stress relaxation coupled with the fact that addition of l-cysteine to a gluten gel eliminated the network structure at 25 degrees C and resulted in a power law stress relaxation spectrum suggests that the transient network in gluten is a reversible network. This power law relaxation pattern was not seen here for an entangled polymer melt (poly(dimethylsiloxane)). It was also found here that the viscosity of the gluten gel (G(tau) x tau) trended best with the tensile stress build-up in a uniaxial tensile test of gluten gels. Together, these results indicate that both network strength and relaxation times should be considered in characterizing the linear viscoelastic properties of hydrated cereal proteins.     

Wheat Gluten Polymer Structures: The Impact of Genotype,Environment, and Processing on Their Functionality in Various Applications

For a number of applications, gluten protein polymer structures are of the highest importance in determining end‐use properties. The present article focuses on gluten protein structures in the wheat grain, genotype‐ and environment‐related changes, protein structures in various applications, and their impact on quality. Protein structures in mature wheat grain or flour are strongly related to end‐use properties, although influenced by genetic and environment interactions. Nitrogen availability during wheat development and genetically determined plant development rhythm are the most important parameters determining the gluten protein polymer structure, although temperature during plant development interacts with the impact of the mentioned parameters. Glutenin subunits are the main proteins incorporated in the gluten protein polymer in extracted wheat flour. During dough mixing, gliadins are also incorporated through disulfide‐sulfhydryl exchange reactions. Gluten protein polymer size and complexity in the mature grain and changes during dough formation are important for breadmaking quality. When using the gluten proteins to produce plastics, additional proteins are incorporated in the polymer through disulfide‐sulfhydryl exchange, sulfhydryl oxidation, β‐eliminations with lanthionine formation, and isopeptide formation. In promising materials, the protein polymer structure is changed toward β‐sheet structures of both intermolecular and extended type and a hexagonal close‐packed structure is found. Increased understanding of gluten protein polymer structures is extremely important to improve functionality and end‐use quality of wheat‐ and gluten‐based products.     

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.     

Relationship Between the Qualitative and Quantitative Compositions of Gluten Protein Types and Technological Properties of Synthetic Hexaploid Wheat Derived from Triticum durum and Aegilops tauschii

The contribution of the diploid wheat species Aegilops tauschii (Coss.) Schmall to the technological properties of bread wheat (Triticum aestivum L.) was previously studied by the investigation of synthetic hexaploids derived from tetraploid durum wheat (T. turgidum L.) and three diploid Ae. tauschii lines. The results indicated that bread volume, gluten index, SDS‐sedimentation volume, and maximum resistance of gluten were significantly influenced by the Ae. tauschii lines. To determine the relationship between technological properties and qualitative and quantitative compositions of gluten proteins, the flours of parental and synthetic lines were extracted using a modified Osborne fractionation. Gliadin and glutenin fractions were then characterized by reversed‐phase (RP) HPLC on C₈ silica gel. The HPLC patterns revealed typical differences between synthetic and parental lines. The gliadin patterns of three synthetic lines and the glutenin patterns of two synthetic lines were more similar to that of the diploid Ae. tauschii parents involved in the hybrids. In the glutenin pattern of one synthetic line, characteristics from both Ae. tauschii and the durum wheat parents were observed. The amount of total gliadin and gliadin types of the synthetic lines was mostly intermediate between those of the durum and Ae. tauschii parents. The amounts of total glutenin and glutenin types (HMW and LMW subunits) of the synthetic lines were generally higher than those of the parental lines, and the ratio of gliadins to glutenins was significantly decreased. High positive correlations were found between the amount of total glutenins, HMW, and LMW subunits and bread volume, maximum resistance and extension area of gluten, and SDS‐sedimentation volume. The ratio of gliadins to glutenin subunits had a strong negative influence on these properties. The protein content of the flours and the amount of total gluten proteins were not correlated with any of the technological properties. Results on the relationship between biochemical characteristics and the breadmaking properties indicated that wheat prebreeding would benefit from studies on protein types and quantification in the choice of parents. In addition, the potential of the diploid Ae. tauschii for improvement of breadmaking quality should be further exploited.     

Effect of the Molecular Weight Distribution of Glutenin Protein from an Extra‐Strong Wheat Flour on Rheological and Breadmaking Properties Through Reconstitution Studies

Ten glutenin fractions were separated by sequential extraction of wheat gluten protein with dilute hydrochloric acid from defatted glutenin‐rich wheat gluten of the Canadian hard red spring wheat (HRSW) cultivar Glenlea. The molecular weight distribution (MWD) of 10 different soluble glutenin fractions was examined by multistacking SDS‐PAGE under nonreduced conditions. Also, the subunit composition of the different glutenin fractions was determined by SDS‐PAGE under reduced conditions. The MWD of the fractions (especially HMW glutenins) varied from fraction to fraction. From early to later fractions, the MWD shifted from low to high. The early extracted fractions contained more LMW glutenin subunits (LMW‐GS) and less HMW glutenin subunits (HMW‐GS). The later extracted fractions and the residue fraction contained much more HMW‐GS (2*, 5, and 7 subunits) than the early extracted fractions. The trend in the amounts of 2*, 5, and 7 subunits in each fraction from low to high matched the extraction solvent sequence containing from lower to higher levels of HCl. The influence of glutenin protein fractions from the extra‐strong mixing cultivar, Glenlea, on the breadmaking quality of the weak HRSW, McVey, was assessed by enriching (by 1%) the McVey base flour with isolated glutenin protein fractions from Glenlea. The mixograph peak development times and loaf volumes of enriched flour were measured in an optimized baking test. The results indicated that the higher content in Glenlea glutenin of HMW‐GS with higher molecular weight, such as 2*, 5, and 7, seem to be the critical factor responsible for the strong mixing properties of Glenlea. Our results confirmed that subunit 7 occurred in the highest quantity of all the HMW‐GS. Therefore, it seems that the greater the content of larger molecular weight glutenin subunits, the larger the glutenin polymers and the stronger the flour.     

Intercultivar Variation in the Quantity of Monomeric Proteins,Soluble and Insoluble Glutenin,and Residue Protein in Wheat Flour and Relationships to Breadmaking Quality

A new fractionation procedure based on differential solubility was applied to wheat flour proteins to evaluate the relationship between protein fractions and functionality for breadmaking. Flour was initially extracted with 50% 1-propanol. Monomeric proteins (mainly gliadins) and soluble glutenin contained in the 50% propanol soluble extract were fractionated by selective precipitation of the glutenin by increasing the concentration of 1-propanol to 70%; monomeric proteins remain in the supernatant. Insoluble glutenin in the 50% propanol insoluble residue was extracted using 50% 1-propanol containing 1% dithiothreitol (DTT) at 60°C. Protein in the final residue was extracted using SDS with or without DTT. It comprised mainly Glu-1D high molecular weight glutenin subunits and nongluten polypeptides. For seven Canadian cultivars of diverse breadmaking quality, there was relatively little variation in the percentage of flour protein corresponding to monomeric proteins (48–52%) and residue protein (14–18%). In contrast, intercultivar variation in soluble and insoluble glutenin was substantial, with contents of 10–20% and 12–28% of flour protein, respectively. Soluble and insoluble glutenin were also highly correlated with physical dough properties, accounting for 83–95% of the variation of individual dough rheological parameters (except dough extensibility), and ≈ 74% of the variation in loaf volume. In contrast, monomeric and residue protein fractions were poorly associated with breadmaking quality. However, among the four protein fractions, only residue protein was significantly correlated (r = -0.79) with dough extensibility. The flour sample with the highest and lowest concentrations of insoluble and soluble glutenin, respectively, as well as marginally the lowest concentrations of monomeric and residue proteins was Glenlea, a cultivar of the Canada Western Extra Strong Red Spring wheat class which characteristically possesses distinctly strong dough mixing properties.     

水氮耦合对强筋冬小麦子粒蛋白质和淀粉品质的影响

在高肥力条件下,研究水氮耦合对小麦子粒产量、蛋白质含量及组成、蛋白质质量、淀粉含量及组成和淀粉品质的影响。结果表明,无论施氮与否,灌水均显著提高小麦子粒产量,同时显著降低子粒粗蛋白、单体蛋白及湿面筋含量;但不同灌水量间(W1、W2、W3)差异不显著。在低灌水频次(W0、W1)条件下,施氮具有明显的增产效应;而高灌水频次(W2、W3),施氮的增产效应不显著。随着灌水次数增加,谷蛋白总量保持稳定,而谷蛋白组分产生了显著的变化,其中可溶性谷蛋白含量呈上升趋势,不溶性谷蛋白含量和谷蛋白聚合指数呈下降趋势,粉质仪参数(形成时间和稳定时间)也呈下降趋势。小麦子粒蛋白质含量及组分和子粒品质均因施氮(N.168.kg/hm2)而有不同程度的提高,其中非面筋蛋白(清蛋白和球蛋白)的增加幅度高于面筋蛋白(醇溶蛋白和谷蛋白),可溶性谷蛋白增加幅度高于不溶性谷蛋白,即降低了谷蛋白聚合指数。水氮对子粒的淀粉含量及其组成的影响存在明显的交互效应。在不施氮肥条件下,随灌水次数增加,支链淀粉和总淀粉含量呈上升趋势;施氮条件下,各灌水处理(W1、W2、W3)的总淀粉和支链淀粉含量均显著高于不灌水处理(W0),但各灌水处理间差异不显著。随灌水次数增加,直链淀粉含量和直/支比均呈下降趋势,黏度仪指标(峰值黏度、稀值、最终黏度和反弹值)均呈上升趋势。施氮在低灌水频次(W0、W1)条件下促进支链淀粉的合成,同时降低直链淀粉含量和直/支比;高灌水频次(W2、W3)条件下则相反。     

Influence of Starch and Gluten Characteristics on Rheological Properties of Wheat Flour Gel at Small and Large Deformation

Starch and gluten were isolated from 10 wheat cultivars or lines with varied amylose content. The rheological properties of 30% wheat flour gel, starch gel, and the gel of isolated gluten mixed with common starch were determined in dynamic mechanical testing under shear deformation, creep‐recovery, and compression tests under uniaxial compression. Variation of wheat samples measured as storage shear modulus (G′), loss shear modulus (G″), and loss tangent (tan δ = G″/G′) was similar between flour and starch gels and correlated significantly between flour and starch gel. The proportion of acetic acid soluble glutenin exhibited a significant relationship with tan δ of gluten‐starch mixture gel. The small difference in amylose content strongly affected the rheological parameters of flour gels in creep‐recovery measurement. Wheat flour gel with lower amylose content showed higher creep and recovery compliance that corresponded to the trend in starch gel. Compressive force of flour gel at 50 and 95% strain correlated significantly with that of starch gel. Gel mixed with the isolated gluten from waxy wheat lines appeared to have a weaker gel structure in dynamic viscoelasticity, creep‐recovery, and compression tests. Starch properties of were primarily responsible for rheological changes in wheat flour gel.     

New Insights Into the Role of Gluten on Durum Pasta Quality Using Reconstitution Method

The effects of varying the gluten composition at constant protein, protein content at constant composition, and glutenin‐to‐gliadin (glu/gli) ratio on durum semolina rheological properties and the quality of the spaghetti derived from these doughs was investigated using the reconstitution method. Reconstituted flours were built up from a common durum starch and water‐soluble fraction but with varying gluten types from a range of wheats at both 12 and 9% total protein. A 10‐g mixograph and microextensigraph properties were affected by the source of the gluten, which was related to glutenin composition and polymeric molecular weight distribution. Cooked pasta firmness was highly correlated to mixograph development time (MDDT). Furthermore, varying the protein content (9–20%) showed an increase in mixograph peak resistance (PR) with no effect on extensigraph Rmax. Pasta firmness increased and stickiness decreased with increasing protein content. In another experiment, the glutenin and gliadin fractions isolated from durum wheat were added to the respective base semolina to investigate the effect of varying the glu/gli ratio by 1.3–1.6 fold. Increasing the ratio increased MDDT but had no effect on PR and resistance breakdown. Variable effects were obtained for spaghetti firmness. The information obtained should prove useful to durum breeders by providing further evidence for the importance of protein to pasta quality.     

Relationship between endogenous protein disulfide isomerase family proteins and glutenin macropolymer

The effects of endogenous protein disulfide isomerase (PDI) family proteins on the properties of gluten proteins in dough during breadmaking were determined using bacitracin, an inhibitor of PDI. Bread loaf volume in the presence of bacitracin was increased to 118% of that in the absence of bacitracin. The addition of bacitracin caused a decrease in the extension tolerance of the dough. The amount of sodium dodecyl sulfate (SDS)-insoluble glutenin macropolymer (GMP) in dough decreased to approximately 70% of that in flour during the 20 min of mixing for doughmaking. The addition of bacitracin to dough caused a dramatic GMP decrease, corresponding to ～20-30% of that in flour during the 20 min of mixing. The decrease in GMP was compensated by an increase in SDS-soluble glutenin polymer. Taken together, these results suggest that the endogenous PDI family proteins in flour suppress the depolymerization of GMP during dough mixing.     

施氮水平对小麦子粒蛋白质组分和加工品质的影响

选用两个优质小麦品种烟农15号和济麦19号,研究了施氮水平对小麦子粒蛋白质组分和加工品质的影响。田间试验设4个施氮水平,即N.0、120、240和360.kg/hm2。结果表明,施用氮肥对子粒发育前期清蛋白和球蛋白含量有明显的提高效应,但随子粒灌浆充实,这种效应逐渐削弱,到成熟期,施氮处理虽能提高子粒清蛋白和球蛋白的含量,但不同施氮水平间无明显差异。施用氮肥还能显著地提高子粒醇溶蛋白和麦谷蛋白的含量,尤其是子粒麦谷蛋白的含量,使子粒麦谷蛋白/醇溶蛋白比值提高。试验还表明,施用氮肥能明显提高子粒湿面筋含量,延长面团形成时间、面团稳定时间和断裂时间。综合分析看出,子粒醇溶蛋白和麦谷蛋白的含量以及麦谷蛋白/醇溶蛋白比值是影响小麦加工品质的重要因素,可以作为小麦品质育种中亲本及后代材料的选择、评价和优质栽培技术评价的依据。     

Characterization of Glutenin Protein Fractions from Sequential Extraction of Hard Red Spring Wheats of Different Breadmaking Quality

Gluten proteins from two cultivars of hard red spring (HRS) wheat with good and poor breadmaking quality were fractionated into 13 fractions by sequential extraction with dilute hydrochloric acid. Each subfraction was characterized by multistacking (MS) SDS‐PAGE under nonreducing conditions, followed by imaging densitometry. The glutenin polymers from the origins of MS‐SDS‐PAGE were analyzed by SDSP‐PAGE under reducing conditions to determine the composition of high and low molecular weight subunits. The results showed that fractions differed significantly in glutenin‐to‐gliadin ratios and in the size distribution of glutenin polymers. The earlier precipitated fractions were composed of more gliadins but fewer glutenin polymers. However, the glutenin polymers gradually increased in their relative quantities with the residue having the largest glutenin‐to‐gliadin ratio. The size distribution of glutenin polymers differed significantly from early precipitated to later fractions. The relative quantities of glutenin aggregates at the 4% origins increased significantly. The ratio of high molecular weight (HMW) to low molecular weight (LMW) glutenin subunits increased significantly from early to intermediate fractions. Between the two cultivars, significant differences were found in the ratio of HMW to LMW glutenin subunits and quantity of SDS insoluble glutenin polymers in the residue fraction with the better breadmaking quality cultivar ND706 having a greater ratio than the cultivar Sharp. It was concluded that the size distribution of glutenin polymers played an important role in determining the differences in breadmaking quality between the good and poor HRS wheat cultivars.     

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.     

不同追施氮肥处理对冬小麦产量和品质的影响

以不同品质类型的2个小麦品种为试验材料,采用2因素随机区组设计,研究了不同品种和氮肥追施处理对产量和品质的影响.结果表明,在底肥量和追肥总量相同的条件下,适当增加开花期追施氮肥的比例有利于提高产量,处理间差异显著,品种间产量差异不显著;不同追肥处理对总蛋白含量影响不显著,但对清蛋白、醇溶蛋白和谷蛋白含量影响显著;追肥处...     

Quantitative Determination of Gluten Protein Types in Wheat Flour by Reversed-Phase High-Performance Liquid Chromatography

A combined extraction-HPLC procedure was developed on a microscale to determine the amounts of the different gluten protein types (ω5-, ω1,2-, α- and γ-gliadins; high molecular weight [HMW] and low molecular weight [LMW] glutenin subunits) in wheat flour. After preextraction of albumins and globulins from flour (100 mg) with a salt solution (2 × 1.0 mL), extraction of gliadins was achieved with 60% aqueous ethanol (3 × 0.5 mL). Subsequently, the glutenin subunits were extracted under nitrogen and at 60°C with 50% aqueous 1-propanol containing Tris-HCl (0.05 mol/L, pH 7.5), urea (2 mol/L) and dithioerythritol (1%). The separation and quantitative determination of gliadins and glutenin subunits was then performed by reversed-phase HPLC on C₈ silica gel at 50°C using a gradient of increasing acetonitrile concentration in the presence of 0.1% trifluoroacetic acid. The flow rate was 1.0 mL/min, and the detection wavelength was 210 nm. Temperature and flow rate were modified for the quantitation of single underivatized HMW subunits. To determine the absolute amounts of protein types, different protein standards (gliadin, LMW and HMW subunits, bovine serum albumin) with known protein contents were compared to HPLC absorbance areas. The calibration curves were almost identical and linear over a broad range (20–220 μg). This extraction-HPLC procedure allows an accurate, reproducible, sensitive, and relatively fast quantitative determination of all gluten protein types in wheat flour, and can be applied to quality evaluation of cereals as raw materials or in processed products.     

Effect of the Coenzymes NAD(P)(H) in Straight‐Dough Breadmaking on Protein Properties and Loaf Volume

The nicotinamide adenine dinucleotide coenzymes [NAD(P)(H)] are strong redox agents naturally present in wheat flour, and are indispensable cofactors in many redox reactions. Hence, it is not inconceivable that they affect gluten cross‐linking during breadmaking. We investigated the effect of increasing concentrations of NAD(P)(H) on gluten cross‐linking, dough properties, and bread volume using two flours of different breadmaking quality. Separate addition of the four nicotinamide coenzymes did not significantly affect mixograph properties. While addition of NAD⁺ hardly affected bread volume, supplementation with NADP(H) and NADH significantly decreased loaf volumes of breads made using flour of high breadmaking quality. Wheat flour incubation with NAD(P)H under anaerobic conditions increased wheat flour thiol content, while NAD(P)⁺ increased the extractability in SDS‐containing medium of the protein of the strong breadmaking flour. Based on the results, it was hypothesized that at least three reactions, competing for NAD(P)(H), occur during breadmaking that determine the final effect on protein, dough, and loaf properties. Next to coenzyme hydrolysis, the experiments pointed to coenzyme oxidation and NAD(P)(H) dependent redox reactions affecting protein properties.