Comparative investigations of gluten proteins from different wheat species I. Qualitative and quantitative composition of gluten protein types

In contrast to the hexaploid common (bread) wheat, little information is available on the qualitative and quantitative compositions of gluten proteins from other cultivated wheat species. Therefore, representatives of hexaploid spelt, tetraploid durum wheat and emmer, and diploid einkorn were compared with three classes of common wheat (winter wheat, spring wheat, wheat rye hybrid). The flours were extracted to yield total endosperm proteins and the gluten protein fractions (gliadins and glutenin subunits). The extracts were characterised using sodium dodecyl sulfate polyacrylamide gel electrophoresis and reversed-phase HPLC; both methods revealed that gluten protein groups and types known from common wheat (ω-, α-, γ-gliadins, HMW and LMW subunits of glutenin) were present in all species. The HPLC platterns of gliadins and glutenin subunits from species with the same genome composition (common wheat/spelt or durum wheat/emmer) were related, and those of einkorn quite different. According to the quantities determined by reversed-phase HPLC, α-gliadins were predominant in most cases, followed by γ-gliadins and LMW subunits; ω-gliadins and HMW subunits were generally minor components. Common wheats were characterised by the highest proportions of total glutenins and HMW subunits, which are known to be important for breadmaking quality. Moreover, the lower ratio of gliadins to glutenins was typical. Emmer had the lowest proportions of total glutenins and of HMW and LMW subunits, together with einkorn the highest proportion of α-gliadins, and, by far, the highest ratio of gliadins to glutenins. The values for spelt and durum wheat were mostly in a medium range between common wheats, emmer, and einkorn, respectively. Amongst common wheats, spring wheat was characterised by more balanced quantities of α- and γ-gliadins, and wheat rye hybrid by the highest proportions of ω-gliadins. Received: 26 November 1999     

The influence of nitrogen fertilisation on quantities and proportions of different protein types in wheat flour

The flours of 13 wheat varieties grown at different levels of nitrogen fertilisation were characterised by the quantitative determination of flour protein groups and gluten protein types using a combined extraction/HPLC procedure. The results demonstrate that the quantities of albumins and globulins were scarcely influenced by different nitrogen fertilisation, whereas those of gluten proteins (gliadins, glutenins) were strongly influenced. The effect on gliadins was more pronounced than on glutenins, as well as the effect on major protein types (α-gliadins, γ-gliadins, LMW subunits of glutenin) in comparison with minor types (ω-gliadins, HMW subunits of glutenin). The proportions of hydrophilic proteins (ω-gliadins, HMW subunits of glutenin) were increased by high levels of nitrogen and those of hydrophobic proteins (γ-gliadin, LMW subunits of glutenin) were decreased. The degree of the effects on both quantities and proportions of flour protein groups and gluten protein types was strongly dependent on the variety. © 1998 SCI.     

The polypeptide composition,structural properties and antioxidant capacity of gluten proteins of diverse bread and durum wheat varieties,and their relationship to the rheological performance of dough

The aim of this study was to compare five bread and five durum wheat genotypes for gliadins and glutenins profiles, the concentration of free sulphhydryl groups and disulphide bonds, antioxidant capacity of gluten proteins and their bread‐making performance. On average, bread wheat had significantly higher concentration of total sulphur‐rich (S‐rich) and sulphur‐poor (S‐poor) subunits of gliadins, as well as total low molecular weight (LMW) and high molecular weight (HMW) subunits of glutenins than durum wheat. However, durum wheat had higher concentration of S‐rich γ‐gliadins and S‐poor D‐LMW‐glutenins, but did not possess S‐poor ω‐gliadins. The concentration of disulphide bonds and total cysteine was higher in the durum gluten than that in the bread gluten, as well as antioxidant capacity (on average 90.6 vs. 85.9 mmol Trolox Eq kg^?1, respectively). In contrast to the bread wheat, the concentration of HMW‐glutenins was negatively associated with extensibility, as well as resistance to extension in durum wheat flour dough.     

Comparative proteome analysis of glutenin synthesis and accumulation in developing grains between superior and poor quality bread wheat cultivars

BACKGROUND: Wheat glutenins are the major determinants of wheat quality. In this study, grains at the development stage from three wheat cultivars (Jimai 20, Jin 411 and Zhoumai 16) with different bread‐making quality were harvested based on thermal times from 150 °C_d to 750 °C_d, and were used to investigate glutenin accumulation patterns and their relationships with wheat quality. RESULTS: High and low molecular weight glutenin subunits (HMW‐GSs and LMW‐GSs) were synthesised concurrently. No obvious correlations between HMW/LMW glutenin ratios and dough property were observed. Accumulation levels of HMW‐GSs and LMW‐GSs as well as 1Bx13 + 1By16 and 1Dx4 + 1Dy12 subunits were higher in superior gluten quality cultivar Jimain 20 than in poor quality cultivar Jing 411 and Zhoumai 16. According to the results of two‐dimensional gel electrophoresis, six types of accumulation patterns in LMW‐GSs were identified and classified. The possible relationships between individual LMW‐GSs and gluten quality were established. CONCLUSION: The high accumulation level of HMW‐GSs and LMW‐GSs as well as 1Bx13 + 1By16 and 1Dx4 + 1Dy12 subunits contributed to the superior gluten quality of Jimai 20. Two highly expressed and 16 specifically expressed LMW glutenin subunits in Jimain 20 had positive effects on dough quality, while 17 specifically expressed subunits in Zhoumai 16 and Jing 411 appeared to have negative effects on gluten quality. Copyright © 2011 Society of Chemical Industry     

Chemistry of gluten proteins

Gluten proteins play a key role in determining the unique baking quality of wheat by conferring water absorption capacity, cohesivity, viscosity and elasticity on dough. Gluten proteins can be divided into two main fractions according to their solubility in aqueous alcohols: the soluble gliadins and the insoluble glutenins. Both fractions consist of numerous, partially closely related protein components characterized by high glutamine and proline contents. Gliadins are mainly monomeric proteins with molecular weights (MWs) around 28,000-55,000 and can be classified according to their different primary structures into the alpha/beta-, gamma- and omega-type. Disulphide bonds are either absent or present as intrachain crosslinks. The glutenin fraction comprises aggregated proteins linked by interchain disulphide bonds; they have a varying size ranging from about 500,000 to more than 10 million. After reduction of disulphide bonds, the resulting glutenin subunits show a solubility in aqueous alcohols similar to gliadins. Based on primary structure, glutenin subunits have been divided into the high-molecular-weight (HMW) subunits (MW=67,000-88,000) and low-molecular-weight (LMW) subunits (MW=32,000-35,000). Each gluten protein type consists or two or three different structural domains; one of them contains unique repetitive sequences rich in glutamine and proline. Native glutenins are composed of a backbone formed by HMW subunit polymers and of LMW subunit polymers branched off from HMW subunits. Non-covalent bonds such as hydrogen bonds, ionic bonds and hydrophobic bonds are important for the aggregation of gliadins and glutenins and implicate structure and physical properties of dough.     

EFFECT OF COMPOSITION OF GLUTHNIN SUBFRACTIONS ON RHEOLOGICAL PROPERTIES OF WHEAT

Gluten extracted from defatted flours of cv. Aubaine (extra‐strong), Hereward (strong) and Riband (weak) was separated into five different fractions (R2 to R6) by sequential centrifugation and addition of sodium chloride. A seven‐minute mixing time was used to carry out fractionation on the basis of depolymerization of glutenin macropolymers (GMP). Depolymerization of GMP occurred at much higher rates in dough of the weak cultivar compared to the strong and extra‐strong cultivars. Polypeptide compositions of different ghttenin fractions were determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis under reduced and non‐reduced conditions, followed by densitometric scanning of stained patterns. The amount of HMW‐glutenin subunits decreased and LMW‐glutenin subunits increased correspondingly in each cultivar with the fractionation from R₂ to R₆. The rheological behavior of the fractions was analyzed by small deformation rheological tests (strain sweep and frequency tests). The high molecular weight fraction (R₂) from extra‐strong wheat had a higher vahte of G' and a lower tan δ value as compared to strong and weak bread‐making wheats. The moduli of HMW glutenin fractions (R2 and R3) were frequency independent and promoted the network properties, whereas moduli of LMW glutenin fractions were frequency dependent and gave rise to a plasticizing effect. Therefore, it was concluded from the present studies that HMW‐glutenin subunits are not the only factors governing good bread‐making quality but their proportions in relation to low molecular weight glutenin subunits is equally important in sinking a balance between viscous and elastic properties essential for bread making performance.     

Relationship between glutenin subunit composition and gluten strength measurements in durum wheat

Durum breeders use a range of techniques in the development of new cultivars. An important selection criterion is the rheological properties of semolina dough and durum wheat breeders use this criterion in the development of new cultivars using a range of techniques. Because of the need to process large numbers of genotypes encountered in breeding programs, methods that are inexpensive, rapid, require small amounts of sample and that correlate with semolina quality are desirable. Using breeding material, this study investigated the relationship between the glutenin subunit composition and two traditional tests of gluten strength, gluten index (GI) and mixograph. Two sample sets of durum wheat breeding lines and cultivars, one grown in Canada (n = 229) and the other grown in Australia (n = 139) were analysed for GI, mixograph and both high molecular weight (HMW) and low molecular weight (LMW) glutenin subunits by SDS‐PAGE. Nine different HMW and 14 different LMW allelic combinations were found. In the Canadian set, the most frequent LMW alleles were aaa, bba, caa and cfa while in the Australian set, caa was predominant. For the HMW subunits, the most common allelic groups were Glu‐A1c/Glu‐B1d (null, 6 + 8) and Glu‐A1c/Glu‐B1b (null, 7 + 8) with fewer numbers of Glu‐A1c/Glu‐B1e (null, 20) in both sample sets. LMW subunits were more important contributors to gluten strength than HMW subunits with the rank for higher GI according to the LMW allele (Canadian set) being caa = aaa > bba and aaa > cfa while HMW subunits 6 + 8 = 7 + 8 > 20. Similarly, using the mixograph, strength ranking for the LMW alleles was aaa > cfa = bba and HMW subunit 20 gave poorer rheological properties. For some samples with a good LMW allelic group a low GI was observed and vice versa. Further characterisation of the protein composition in these samples showed the GI results could be explained by polymeric/monomeric (P/M), glutenin/gliadin (Glu/Gli) and HMW/LMW ratios or the proportion of unextractable polymeric protein. © Crown in the right of the State of New South Wales, Australia; and for the Department of Agriculture and Agri‐Food, Government of Canada, © Minister of Public Works and Government Services Canada 2005. Published for SCI by John Wiley & Sons, Ltd.     

Role of gluten and its components in influencing durum wheat dough properties and spaghetti cooking quality

Protein is an important component of grain which affects the technological properties of durum wheat. It is known that the amount and composition of protein can influence dough rheology and pasta quality but the influence of the major classes of protein is not well documented. The influence of the various gluten components on dough and pasta properties was investigated. The protein composition of durum semolina was altered by either adding gluten fractions to a base semolina or preparing reconstituted flours with varying protein composition. The effects on semolina dough rheology and spaghetti texture were measured. Published methods to isolate relatively pure quantities (gram amounts) of glutenin, gliadin, high molecular and low molecular weight glutenin subunits were evaluated and modified procedures were adopted. Reconstituted flours with additional glutenin increased dough strength while additional gliadin and LMW‐GS decreased strength. These changes did not impact on spaghetti texture. Results from using the addition of protein fractions to a base semolina showed that gluten and glutenin addition increased the dough strength of a weak base semolina while gliadin addition weakened the base dough further. Addition of HMW‐GS greatly increased dough strength of the base while addition of LMW‐GS greatly reduced dough strength. Again, these affects were not translated into firmer pasta. Copyright © 2007 Society of Chemical Industry     

Wheat gluten: high molecular weight glutenin subunits--structure, genetics, and relation to dough elasticity

ABSTRACT:  Gluten proteins, representing the major protein fraction of the starchy endosperm, are predominantly responsible for the unique position of wheat amongst cereals. These form a continuous proteinaceous matrix in the cells of the mature dry grain and form a continuous viscoelastic network during the mixing process of dough development. These viscoelastic properties underline the utilization of wheat to prepare bread and other wheat flour based foodstuffs. One group of gluten proteins is glutenin, which consists of high molecular weight (HMW) and low molecular weight (LMW) subunits. The HMW glutenin subunits (HMW-GS) are particularly important for determining dough elasticity. The common wheat possesses 3 to 5 HMW subunits encoded at the Glu-1 loci on the long arms of group 1 chromosomes (1A, 1B, and 1D). The presence of certain HMW subunits is positively correlated with good bread-making quality. Glutamine-rich repetitive sequences that comprise the central part of the HMW subunits are actually responsible for the elastic properties due to extensive arrays of interchain hydrogen bonds. Genetic engineering can be used to manipulate the amount and composition of the HMW subunits, leading to either increased dough strength or more drastic changes in gluten structure and properties.     

Genetic Variation in Glutenin Protein Composition of Aestivum and Durum Wheat Cultivars and Its Relationship with Dough Quality

Genetic variability of high molecular weight glutenin subunits and low molecular weight glutenin subunits composition at the Glu-1 loci in Triticum aestivum L., and T. durum L., wheat was studied using sodium dodecyl sulfate polyacrylamide gel electrophoresis and polymerase chain reaction based markers. The end use quality of wheat is mainly influenced by the composition of glutenin protein. Aestivum cultivar GW-273 showed highest gluten index (94.4%) and sedimentation value (61 mL). GW-273 and GW-322 showed highest Glu-1 score of 10 out of 10, indicating superior dough quality for bread making. Results from glutenin protein separation using electrophoresis revealed that selected Indian wheat cultivars were abundant in high molecular weight glutenin subunits AxNull allele, which is responsible for poor quality. Gene specific polymerase chain reaction using high molecular weight glutenin subunits and low molecular weight glutenin subunits primers showed Dx5 and Dy10 in only two cultivars GW-273 and GW-322, which is responsible for good dough quality. Sequencing of high molecular weight glutenin subunits Dx5 gene fragment showed four cysteine at the N-terminal end. Cysteine residues are helpful in intermolecular disulfide bond formation among different glutenin and gliadins proteins leading to good elasticity of dough.     

Quantitative and Qualitative Assessment of Wheat Gluten Proteins and their Contribution to Instant Noodle Quality

This study was carried out to examine the effect of quantity and quality of wheat gluten proteins on the quality attributes of instant fried noodles. Dough development time, dough stability, SDS sedimentation volume, gluten index and Resistance to extension/Extensibility (R/E) ratio were found to be positively correlated with glutenin content, whereas negatively associated with the quantity of gliadin sub-fractions. Medium strong flours were found most suitable for noodle preparation. The weaker flours from cultivars HW 2004 and C 306 having HMW-GS composition of Null, 2+12 and 20 alleles expressed at Glu-A1, B1 and D1, respectively could not withstand sheeting, resulted in rough surface and high breakage of noodles. The best noodle cultivars DBW 16 and WH 542 had 5+10 glutenin subunits at Glu-D1, however, differed in subunits expressed at Glu-A1 and Glu-B1 loci. Oil uptake and cooking time of noodles varied considerably from 15.4 to 22.7% and 2.0 to 4.0 min, respectively. Oil uptake in noodles was positively correlated with dough softening, however, all the parameters related to gluten quality and strength were negatively associated with the oil uptake. Cooking time of instant noodles was found to be highly associated with protein content (R² = 0.778) of flour, gluten quality and strength. Hardness or firmness of cooked noodles was found to be significantly linked with SDS sedimentation volume (R² = 0.725), gluten index (R² = 0.610), glutenin content (R² = 0.619), gliadin content (R² = ?0.567), R/E ratio (R² = 0.532) and gliadins/glutenins (R² = ?0.605) ratio.     

Comparative quality analysis of gluten strength and the relationship with high molecular weight glutenin subunits of 6 Tunisian durum wheat genotypes

Six Tunisian durum wheat genotypes (4 landraces and 2 improved) were evaluated for protein content, gluten strength, rheological characteristics, and HMW-GS patterns using a LabChip system. Variance analysis identified genotypic variation. The landraces Azizi, Mahmoudi, Chili, and Arbi exhibited the highest protein concentrations and gluten contents, and best dough tenacity and extensibility values. The Mahmoudi and Chili varieties had the highest protein contents (17.06 and 17.32% dry mass, respectively). Arbi and Chili had the highest gluten contents (60.88 and 60.59%, respectively). Azizi, Mahmoudi, and Chili were characterized by higher dough tenacity, lower dough extensibility, and a greater alveograph configuration ratio P/L. The high molecular weight glutenin subunits 6+8 (Azizi and Mahmoudi) and 7+15 (Chili), coded by the Glu-B1 locus, improved gluten strength and viscoelastic dough properties. Calculated HMW to LMW-GS ratios were within a narrow range of 0.17–0.29. Some genotypes have potential to be used as parents in breeding programs.     

Effect of glutens of different quality on dough characteristics and breadmaking performance

Glutens of different quality were extracted from commercial flours of distinct breadmaking performance and employed as improvers at a level of 1 g/100 g. The same flours used as a source of gluten were employed for testing the gluten effect. Flours were characterized by farinographic and alveographic assays and their protein profile was determined by SDS-PAGE. Rheology of each dough without and with gluten addition was studied by empirical and fundamental assays. Breadmaking performance was evaluated by loaf volume measurements and crumb texture.Though protein content was similar for all flours (11 g/100 g), dough exhibited different breadmaking characteristics which could be related to a different gliadin/glutenin proportion and a different protein profile. The weakest flour lacked two glutenin subunits (83 and 64.5 kDa) and showed a lower number of bands of gliadins respect to the other ones. Adding any of the three types of gluten to the weakest flour resulted in an increase of farinographic stability. The medium and inferior quality flours showed an increase in dough elasticity when the strongest gluten was added. In breadmaking assays the medium quality flour and its mixtures with gluten showed the highest specific volumes.     

Studies on the protein composition and baking quality of einkorn lines

White flours from 23 einkorn breeding lines (assortment 1) and wholemeal flours from 24 einkorn lines (assortment 2) were investigated for their qualitative and quantitative protein compositions by means of a combined extraction/HPLC procedure. The HPLC patterns of the gliadin fractions enabled the differentiation of most einkorn samples. The absence of a group of γ-gliadins at the beginning of the γ-gliadin elution region was unique for einkorn compared to all other wheat species. Differences in the patterns of γ-gliadins allowed the classification of einkorns into four groups; a further subdivision of these groups was possible by the number of ω5-gliadins and the different patterns of α-gliadins and low-molecular-weight glutenin subunits. The total gluten protein (gliadins + glutenins) contents of einkorn flours were similar to or even higher than those of common wheat and spelt. Typical for einkorn flours was the extreme excess of gliadins over glutenins with ω5-gliadins being most abundant and high-molecular-weight glutenin subunits being extremely rare. Micro-tests on the mixing properties and baking performance of assortment 2 flours revealed remarkable differences. Dough development time was negatively correlated with the ratio of gliadins to glutenins and positively with the content of glutenins; bread volume was mainly dependent on the content of glutenins. In conclusion, the determination of the quantitative gluten protein compositions offers a reliable indication of the expected baking quality during the early stages of breeding.     

Importance of amounts and proportions of high molecular weight subunits of glutenin for wheat quality

 High molecular weight (HMW) subunits of wheat glutenin are generally considered to play a key role in gluten formation and structure, and to be closely related to wheat quality. Though quantities of HMW subunits in flour have been proposed to be as important for wheat quality as their structures, only few quantitative data are available in the literature. Therefore, two assortments of wheat consisting of 13 international and 16 German cultivars were analyzed for their contents and proportions of single HMW subunits using an extraction and HPLC procedure on a micro-scale. The results were compared with quantitative data from the literature that were obtained by sodium dodecylsulfate polyacrylamide gel electrophoresis combined with densitometry or by reversed-phase HPLC combined with UV detection. The quantitative analyses demonstrated that the contents of HMW subunits varied within a broad range dependent on genotype and growing conditions. The proportions of subunits within a given subunit combination, however, varied only within a small range. Generally, subunits 2, 5, 7, 10 and 12 were major components and subunits 1, 2*, 6, 8 and 9 were minor components. The levels of HMW subunits were highly correlated to dough development time, maximum resistance of dough and gluten, and bread volume. Among HMW subunits the x-type components (subunits 1–7) were much more important than the y-type components (subunits 8–12). In particular, the presence of subunit 5 (which has an additional cysteine residue) and of subunit 7 (which occurs in the greatest amounts) contributed to high wheat quality. Received: 22 June 1999     

Functional and multiple end‐use characterisation of Canadian wheat using a reconstituted dough system

Three Canadian wheat cultivars representing the Canada Western Red Spring, Canada Western Extra Strong and Canada Prairie Spring classes, varying in protein content yet containing similar high‐molecular‐weight glutenin subunits, were evaluated for dough functionality and multiple end‐use properties. The effect of protein content on dough properties and end‐product quality was also studied. Gluten, starch and water‐soluble components were extracted from the flours and reconstituted to make up three samples for each variety to match the protein content of the three parent flours. Empirical and dynamic dough rheological properties, baking (bread and tortilla) performance and noodle‐making properties of the flours were determined using small‐scale techniques. Results indicated that protein content had a significant effect on rheological and end‐use quality of wheat flours. Increase in protein content (of the reconstituted dough) increased mixograph peak height (r = 0.761), peak width, maximum resistance to extension and end‐product quality characteristics such as loaf volume (r = 0.906), noodle firmness and cutting force and decreased storage and loss moduli. Reconstituted flours from the three varieties at the same protein content also showed significant differences in mixing time, mixograph peak height, maximum resistance to extension, composite fineness of pan bread, tortilla diameter, cooked noodle hardness, gumminess and dynamic viscosity of dough. This study indicates that a simple reconstituted dough system can provide an unambiguous assignment of the quantitative and qualitative effects of dough components on dough properties. It has the advantages that any aspect of flour composition can be manipulated and details of the relation between composition and functional behaviour can be obtained for any end‐product. Copyright © 2003 Crown in the right of Canada. Published by Society of Chemical Industry     

Hearth bread baking quality of durum wheat varying in protein composition and physical dough properties

Thirty durum wheat genotypes from ten countries of origin were grown in field plots for two consecutive years. Three of the genotypes were γ‐gliadin 42 types and the remainder were γ‐gliadin 45 types. Among the γ‐gliadin 45 types, six high‐molecular‐weight glutenin subunit (HMW‐GS) patterns were identified: 6 + 8, 7 + 8, 7 + 16, 14 + 15, 20 and 2*, 20. All the γ‐gliadin 42 genotypes contained low amounts of unextractable polymeric protein (UPP) and exhibited low gluten index values and weak gluten properties. The γ‐gliadin 45 genotypes exhibited a wide range of UPP, gluten index and dough strength. HMW‐GS 20 genotypes were generally weak, whereas HMW‐GS 6 + 8 and 7 + 8 genotypes were generally strong. When baked by a lean formulation, long‐fermentation straight‐dough hearth bread process, the durum wheat genotypes exhibited a wide range of baking quality. Loaf volume and bread attributes were strongly correlated with UPP and gluten index. Some of the genotypes exhibited bread attributes and loaf volume equal or slightly superior to those of a high‐quality bread wheat flour. However, even the strongest durum wheat genotypes exhibited inferior fermentation tolerance to the bread wheat flour, as seen by a requirement for lower baking absorption during dough handling and more fragile dough properties when entering the oven. Among the HMW‐GS groups, HMW‐GS 7 + 8 and 6 + 8 exhibited the best and HMW‐GS 20 the poorest baking quality. Farinograph, alveograph and small‐scale extensigraph properties demonstrated that a combination of dough elasticity and extensibility was needed for superior durum wheat baking performance. Copyright © 2007 Society of Chemical Industry     

Effects of amounts of HMW glutenin subunits determined by capillary electrophoresis on technological properties in wheat doubled haploids

BACKGROUND: Knowledge of the types and amounts of individual HMW glutenin subunits (HMW-GS) is important for predicting technological quality. In this study, 228 wheat doubled haploids were compared in respect of HMW-GS composition, seed protein content, flour yield, rheological properties of dough, and loaf properties. The quantitative and qualitative composition of particular HMW-GS was determined by CE. The relative amounts of x-type and y-type subunits encoded by individual Glu-1 loci were considered. RESULTS: The results show that the amounts of some pairs x + y of HMW-GS are correlated with technological properties. The importance of quantities of particular pairs of HMW-GS for technological values depends on allele compositions in all the Glu-1 loci. Positive correlation was found between the amount of subunits Ax1, Ax2*, Bx7 + By8 or Dx5 + Dy10 and loaf volume (r = 0.215–0.618, P < 0.05). The influence of an increasing amount of Ax1 was positively correlated with dough softening (r = 0.451, P < 0.01) and negatively with dough development time (r = − 0.209, P < 0.05) and stability (r = − 0.351, P < 0.01), whereas for subunit Ax2* these associations were opposite. CONCLUSION: The results confirm the occurrence of epistatic interactions between alleles of Glu-1 loci. The effects of amounts of HMW subunits on bread-making quality should be considered only within glutenin subunit compositions. Copyright © 2008 Society of Chemical Industry     

Pilot scale preparation of wheat gluten protein fractions: II. Technological properties of the fractions

Fractions differing in prolamin compositions were obtained on a pilot scale when wheat gluten proteins were separated by differential extraction in dilute acetic acid. The soluble fractions were enriched in gliadins and the insoluble ones were richer in glutenins. The effects of the gluten fractions on the technological properties of wheat flours were investigated using an alveographic test and a comparison was made with gluten-added flours. Gliadin-rich fractions increased the extensibility of the dough and reduced its resistance to deformation. On the other hand, glutenin-rich fractions had an opposite effect and increased the dough resistance more than that of equally-concentrated whole gluten. The magnitude of the effects was strongly related to the gliadin and glutenin contents of the fractions. Prediction of technological effects is thus possible using composition analyses based on protein extractibility or size-exclusion chromatography. Finally, the improving effects of the gliadin-rich and of the glutenin-rich fractions were observed at different stages of the breadmaking process.     

Studies on the distribution and binding of endogenous glutathione in wheat dough and gluten. II. Binding sites of endogenous glutathione in glutenins

For the identification of the binding sites of glutathione (GS) in glutenins, flour of the wheat cultivar " Canadian Western Red Spring " was mixed with water containing ³⁵S-labelled reduced GS as a tracer. The resulting dough was washed in a Glutomatic, and, in order to remove gliadins, the gluten obtained was extracted with 70% aqueous ethanol adjusted to pH 5.5 with acetic acid. The residual proteins (glutenins) were hydrolyzed with thermolysin, and the hydrolysate was separated by gel permeation chromatography on Sephadex G25 and by several steps of reversed-phase HPLC on C₁₈ silica gel. The major radioactive disulphide peptides identified by scintillation analysis were collected and analysed for their amino acid sequences. Twenty-five peptides linked to GS could be assigned to known sequences of gluten proteins. Most peptides (16) were derived from low molecular weight (LMW) subunits of glutenin. Among these, 13 peptides contained the cysteine residue C^b*, which is present in the repetitive sequence region of LMW subunits and which has been postulated to form intermolecular disulphide bonds. This peptide type represented 45% of the total radioactivity of isolated peptides. Three further peptides from LMW subunits representing 46% of radioactivity included cysteine C^x, which has also been proposed to form intermolecular disulphide bonds. Four peptides with 3.2% of radioactivity could be assigned to high molecular weight subunits (cysteines C^b, C^d, C^e, C^y) and four peptides (3.0% of radioactivity) to glutenin-bound %-gliadins (C^b*, C^w, C^z). One peptide (3.3% of radioactivity) corresponded to cysteine C^c from %-gliadins or LMW subunits. Altogether the cysteine residues in glutenins, which are usually linked by intermolecular disulphide bonds, contributed up to 95% of total radioactivity. The results obtained are in accordance with the effect of reduced GS on the rheological properties of dough, namely the weakening of dough by depolymerization of glutenin polymers via specific cleavage of intermolecular disulphide bonds.