F. Békés

Basic Rheology of Bread Dough with Modified Protein Content and Glutenin-to-Gliadin Ratios

ABSTRACT The uniaxial elongational and shear rheology of doughs varying in either the protein content or glutenin-to-gliadin ratio were investigated. Increasing the protein content at constant glutenin-to-gliadin ratio increased the strain-hardening properties of the dough, as shown by increasing elongational rupture viscosity and rupture stress. Glutenin and gliadin had a more complex effect on the elongational properties of the dough. Increased levels of glutenin increased the rupture viscosity but lowered the rupture strain, while elevated gliadin levels lowered the rupture viscosity but increased the rupture strain. These observations provide rheological support for the widely inferred role of gliadin and glutenin in shaping bread dough rheology, namely that gliadin contributes the flow properties, and glutenin contributes the elastic or strength properties. The shear and elongational properties of the doughs were quite different, reflecting the dissimilar natures of these two types of flow. Increasin...

Sequence and properties of HMW subunit 1Bx20 from pasta wheat (Triticum durum) which is associated with poor end use properties.

Abstract.The gene encoding high-molecular-weight (HMW) subunit 1Bx20 was isolated from durum wheat cv. Lira. It encodes a mature protein of 774 amino acid residues with an Mr of 83,913. Comparison with the sequence of subunit 1Bx7 showed over 96% identity, the main difference being the substitution of two cysteine residues in the N-terminal domain of subunit 1Bx7 with tyrosine residues in 1Bx20. Comparison of the structures and stabilities of the two subunits purified from wheat using Fourier-transform infra-red and circular dichroism spectroscopy showed no significant differences. However, incorporation of subunit 1Bx7 into a base flour gave increased dough strength and stability measured by Mixograph analysis, while incorporation of subunit 1Bx20 resulted in small positive or negative effects on the parameters measured. It is concluded that the different effects of the two subunits could relate to the differences in their cysteine contents, thereby affecting the cross-linking and hence properties of the glutenin polymers.

Gluten polypeptides as useful genetic markers of dough quality in Australian wheats

Seed proteins of 28 Australian bread wheat cultivars were analysed by gel electrophoresis to indicate variations in the composition of their gliadins and glutenin polypeptides (both low- and high-molecular-weight). Composition was indicated according to allelic blocks of genes for each protein class and for each chromosome involved. Relationships were studied between gluten-protein alleles, pedigrees and dough properties (in the Extensograph). Overall, gliadins and low-molecular-weight (LMW) subunits of glutenin controlled by group 1 chromosomes showed closest relationships with each other. LMW subunits were most highly correlated with dough resistance and extensibility. Gliadins controlled by chromosomes 6A and 6D also had highly significant relationships to dough resistance and extensibility, respectively. Among high-molecular-weight subunits of glutenin, however, only those controlled by chromosome 1B showed a significant relationship with resistance to dough extension.

Genetic characterisation of dough rheological properties in a wheat doubled haploid population: additive genetic effects and epistatic interactions

Doubled haploid lines (n=160) from a cross between wheat cultivars ‘Cranbrook’ (high dough extensibility) and ‘Halberd’ (low dough extensibility) were grown at three Australian locations. The parents differ at all high- and low-molecular-weight glutenin loci. Dough rheological parameters were measured using small-scale testing procedures, and quantitative trait locus (QTL) mapping procedures were carried out using an existing well-saturated genetic linkage map for this cross. Genetic parameters were estimated using three software packages: QTLCartographer, Epistat and Genstat. Results indicated that environmental factors are a major determinant of dough extensibility across the three trial sites, whereas genotypic factors are the major determinants of dough strength. Composite interval mapping analysis across the 21 linkage groups revealed that as expected, the main additive QTLs for dough rheological properties are located at the high- and low-molecular-weight glutenin loci. A new QTL on chromosome 5A for M-extensibility (a mixograph-estimated measure of extensibility) was detected. Analysis of epistatic interactions revealed that there were significant conditional epistatic interactions related with the additive effects of glutenin loci on dough rheological properties. Therefore, the additive genetic effects of glutenins on dough rheological properties are conditional upon the genetic background of the wheat line. The molecular basis of the interactions with the glutenin loci may be via proteins that modify or alter the gluten protein matrix or variations in the expression level of the glutenin genes. Reverse-phase high performance liquid chromatography analysis of the molar number of individual glutenin subunits across the population showed that certain conditional epistases resulted in increased expression of the affected glutenin. The epistatic interactions detected in this study provide a possible explanation of the variable genetic effects of some glutenins on quality attributes in different genetic backgrounds and provide essential information for the accurate prediction of glutenin related variance in marker-assisted wheat breeding.

Effects of Incorporated Glutenins on Functional Properties of Wheat Dough

ABSTRACT The development of reduction-oxidation methods to open the native gluten polymer, incorporate monomers, and repolymerize the modified polymer, has allowed new types of investigation of the effects of glutenin subunits on dough characters. These methods were used to incorporate bulk high molecular weight glutenin subunits (HMW-GS) and bulk low molecular weight glutenin subunits (LMW-GS) from four cultivars into the parent flours to modify the HMW-GS-to-LMW-GS ratio. In addition, the glutenins from the four cultivars were added to a single base flour of differing glutenin subunit composition. Finally, HMW-GS 7, 8, 5, and 10 were incorporated singly and in pairs into two base flours. The mixing time, peak resistance, maximum resistance to extension, and loaf height increased with increases in HMW-GS-to-LMW-GS ratio. There was a decrease in resistance breakdown observed with increase in HMW-GS-to-LMW-GS ratio. The maximum resistance to extension slightly increased with increases in HMW-GS-to-LMW-GS r...

Gluten protein functionality in wheat flour processing: a review

Gluten protein functionality remains the basis of any understanding of the end-product quality of wheat flours. Information about this functionality has been obtained by both in vivo and in vitro studies. Recent advances include structure/function studies of deletion mutants and transformed genotypes, where the genes incorporated were both naturally occurring genes and genes which have been desired to provide specific structural features. The contributions of these specific changes in structure to the rheology of the resulting doughs allow insight into the underlying physical processes that determine dough and end-product properties.

Characterization and Comparative Analysis of Wheat High Molecular Weight Glutenin Subunits by SDS-PAGE, RP-HPLC, HPCE, and MALDI-TOF-MS

High molecular weight glutenin subunits (HMW-GS) from 60 germplasms including 30 common wheat cultivars and 30 related species were separated and characterized by a suite of separation methods including sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), reversed-phase high-performance liquid chromatography (RP-HPLC), high-performance capillary electrophoresis (HPCE), and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Comparative analysis demonstrated that each methodology has its own advantages and disadvantages. The main drawback of SDS-PAGE was its overestimation of molecular mass and incorrect identification of HMW-GS due to its low resolution. However, it had the advantages of technical simplicity and low requirements of equipment; thus, it is suitable for large-scale and high-throughput HMW-GS screening for breeding programs, especially when the glutenin composition is clear in the breeding material. MALDI-TOF-MS clearly expressed many technical advantages among the four methods evaluated, including high throughput, high resolution, and accuracy; it was, however, associated with high equipment cost, thus preventing many breeding companies from accessing the technology. RP-HPLC and HPCE were found to be intermediate between SDS-PAGE and MALDI-TOF-MS. Both RP-HPLC and HPCE demonstrated higher resolution and reproducibility over SDS-PAGE but lower detection power than MALDI-TOF-MS. Results demonstrated that MALDI-TOF-MS is suitable for analyzing HMW-GS for routine breeding line screening and for identifying new genotypes.

Effects of Gliadin Fractions on Functional Properties of Wheat Dough Depending on Molecular Size and Hydrophobicity

ABSTRACT The effects of α- + β-, γ-, ω- and total gliadins on mixing, extension baking, and techno-functional properties of doughs from hard and soft flours were measured using small-scale techniques. The addition of all gliadin fractions resulted in decreased mixing time, peak resistance, maximum resistance to extension, and loaf height, and in increased resistance breakdown and extensibility. The various gliadin fractions showed differences in functional properties, with γ-gliadin reducing the mixing time and maximum resistance to extension to the greatest extent, ω-gliadin contributing to the greatest reduction in loaf height, and α- + β-gliadins having the least effect on reducing loaf height. The effects of gliadin fractions on loaf height were correlated with molecular mass, and effects on mixing time, maximum resistance to extension, and extensibility were correlated with hydrophobicity.

In Vitro Polymerization of Wheat Glutenin Subunits with Inorganic Oxidizing Agents. I. Comparison of Single-Step and Stepwise Oxidations of High Molecular Weight Glutenin Subunits

ABSTRACT High molecular weight glutenin subunits (HMW-GS) were isolated from wheat flour and polymerized in vitro at pH 3.0 with different oxidizing agents (KBrO3, KIO3, H2O2). An oxidation protocol with single addition of oxidant (single-step oxidation) was compared with a set-up in which the oxidant was added in multiple steps (stepwise oxidation). Changes in size distribution were evaluated with size-exclusion HPLC, multilayer SDS-PAGE, and flow-field flow fractionation (flow-FFF). Flow-FFF is particularly suitable for measuring changes in glutenin size in the very high size ranges. In order of increasing sizes of the resulting polymers, the different oxidizing agents could be ranked as KBrO3 < KIO3 < H2O2. However, none of the oxidation conditions allowed for a complete polymerization of HMW-GS. Interestingly, it was found that high concentrations of KIO3 negatively affect the degree of polymerization. A similar observation was not made with KBrO3 or H2O2. SDS-PAGE showed that y-type HMW-GS particular...

Synergistic and Additive Effects of Three High Molecular Weight Glutenin Subunit Loci. II. Effects on Wheat Dough Functionality and End-Use Quality

ABSTRACT Understanding the relationship between basic and applied rheological parameters and the contribution of wheat flour protein content and composition in defining these parameters requires information on the roles of individual flour protein components. The high molecular weight glutenin subunit (HMW-GS) proteins are major contributors to dough strength and stability. This study focused on eight homozygous wheat lines derived from the bread wheat cvs. Olympic and Gabo with systematic deletions at each of three HMW-GS encoding gene loci, Glu-A1, Glu-B1, and Glu-D1. Flour protein levels were adjusted to a constant 9% by adding starch. Functionality of the flours was characterized by small-scale methods (2-g mixograph, microextension tester). End-use quality was evaluated by 2-g microbaking and 10-g noodle-making procedures. In this sample set, the Glu-D1 HMW-GS (5+10) made a significantly larger contribution to dough properties than HMW-GS coded by Glu-B1 (17+18), while subunit 1 coded by Glu-A1 made ...