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.     

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 investigations of gluten proteins from different wheat species II. Characterization of ω-gliadins

 Flours of different wheat species (common wheats including winter wheat, spring wheat, and wheat rye hybrid, spelt, durum wheat, emmer, and einkorn) were successively extracted with a salt solution and 60% (v/v) aqueous ethanol. The alcohol extracts (gliadins) were separated by reversed-phase HPLC. Six to nine different ω-gliadins were obtained for each wheat sample and were characterized by their relative amounts, the amino acid compositions, the N-terminal amino acid sequences, and the molecular masses. The wheats investigated showed typical differences in the qualitative and quantitative HPLC patterns. The amino acid compositions of all ω-type gliadins revealed significantly higher proportions of glutamine, proline, and phenylalanine compared with other gluten proteins. These three amino acids accounted for 70 to 86% of the total composition. Typical differences in amino acid compositions, N-terminal sequences, and molecular masses allowed a clear differentiation of the proteins into ω5- and ω1,2-type gliadins; the gliadin fractions of emmer and einkorn contained only the ω5-type, but not the ω1,2-type. ω5-Gliadins were characterized by extremely high proportions of glutamine (52–57 mol %) and relatively high proportions of proline (18–21 mol %) and phenylalanine (9–10 mol %). ω1,2-Gliadins had less glutamine (39–45 mol %) and phenylalanine (6–8 mol %), but much more proline (22–31 mol %). ω5-Gliadins of all wheats except emmer could be assigned to the N-terminal sequence variants SRQLSP or SRLLSP; the typical sequence of emmer ω5-gliadins was SMELQT. The N-terminal sequences of ω1,2-gliadins were characterized by two basic variants beginning with KELQSP or ARQLNP. The wheat rye hybrid had additionally components with the sequence RQLNPS known from ω-secalins of rye. The determination of molecular masses by MALDI-TOF mass spectrometry revealed a range of 44,000–55,000 for the ω5-type and a range of 36,000–44,000 for the ω1,2-type. Thus, the actual masses were by far lower than the values derived from SDS-PAGE mobility. Received: 25 May 2000     

The influence of 1B/1R chromosome translocation on gluten protein composition and technological properties of bread wheat

The Austrian bread wheat Amadeus without and with 1BL/1RS translocation and three further translocation genotypes with known HMW subunit compositions were grown under the same environmental conditions. Their flours were characterised by the determination of crude protein content and, partly, by the determination of glutathione and cysteine. Furthermore, the qualitative and quantitative composition of gluten protein types was analysed by a combined extraction and reversed phase HPLC procedure. Dough development time, maximum resistance and extensibility of dough and gluten, and bread volume were determined by means of microscale methods. Protein, glutathione and cysteine contents of flours were only slightly influenced by translocation. The HPLC patterns of gliadins and glutenin subunits showed that translocation caused characteristic changes concerning ω‐gliadins, γ‐gliadins and LMW subunits of glutenin. The amount of ω 1,2‐gliadins was significantly increased and that of LMW subunits decreased. The effect of translocation on the rheological properties of dough and gluten was characterised by a strongly reduced dough development time, reduced maximum resistance and increased extensibility. Bread volume was decreased by about 10%. The amount of glutenin subunits was correlated with dough development time, resistance of dough and gluten, and bread volume to a higher extent (r = 0.79–0.91) than the amount of gliadins (r = 0.52–0.80). Correlation coefficients for LMW subunits were higher (r = 0.82–0.88) than those for HMW subunits (r = 0.35–0.61) when all five wheats were included. Instead, when only translocation lines were considered, HMW subunits (r = 0.89–0.98) were more important than LMW subunits (r = 0.64–0.86). Altogether, the results demonstrate that translocation causes important quantitative as well as qualitative changes in gluten protein composition which can be efficiently determined by reversed phase HPLC. © 2000 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.     

Relationship between gluten strength and pasta firmness in Indian durum wheats

Selected Indian durum wheats including five newly released varieties and seven landraces were studied for their grain quality, gluten strength (sodium dodecyl sulphate‐sedimentation and mixograph) and pasta making properties. Landraces were found to have good grain size, protein content, and gluten strength but they had lower test weight and semolina yield than released varieties. As protein composition affects gluten strength, landraces having combination of low molecular weight (LMW‐GS) with 5, 12, 15 and 19 linked to Gli‐B1 43.5 and high molecular weight (HMW‐GS) 2*, 14 + 15 provide a dough strength comparable with the 7 + 8 and LMW‐GS 2, 4, 6, 12, 15 and 19 (caa) allelic pattern, typically associated with good gluten strength. Landraces have rare combinations of glutenins and gliadins, which are not seen in commercial Indian durums, and in some cases, these rare alleles seem to favour good gluten strength and pasta firmness. Introduction of these alleles through breeding should improve the gluten strength and pasta making properties of Indian durum cultivars.     

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.     

Investigations on the extractability of gluten proteins from wheat bread in comparison with flour

 Immunochemical methods are recommended for the quantitation of small amounts of gluten in food produced for those with coeliac disease. A major problem, however, is the reduced extractability of gliadin, the toxic factor of gluten, with aqueous alcohol, when foods have been heat-processed. A combined extraction/HPLC procedure was used to study the extractability of all gluten protein types from wheat flour and bread under both non-reducing and reducing conditions. Gliadin isolated from wheat flour was used as a reference protein for quantitation. The results indicate that the extractability of gliadin from bread with 60% ethanol under non-reducing conditions is strongly reduced. α- and γ-gliadins are much more affected than ω-gliadins, and less gliadin was extracted from the crust than from the crumb. For a complete extraction of gliadins from bread, reducing conditions and increased temperature are required. However, glutenin subunits are coextracted with the gliadins. This extract can be used for the quantitation of total gluten proteins by RP-HPLC. The recovery of gliadin added to flour before dough-mixing and bread-making is 98%. Received: 16 February 1998     

Investigations on the extractability of gluten proteins from wheat bread in comparison with flour

 Immunochemical methods are recommended for the quantitation of small amounts of gluten in food produced for those with coeliac disease. A major problem, however, is the reduced extractability of gliadin, the toxic factor of gluten, with aqueous alcohol, when foods have been heat-processed. A combined extraction/HPLC procedure was used to study the extractability of all gluten protein types from wheat flour and bread under both non-reducing and reducing conditions. Gliadin isolated from wheat flour was used as a reference protein for quantitation. The results indicate that the extractability of gliadin from bread with 60% ethanol under non-reducing conditions is strongly reduced. α- and γ-gliadins are much more affected than ω-gliadins, and less gliadin was extracted from the crust than from the crumb. For a complete extraction of gliadins from bread, reducing conditions and increased temperature are required. However, glutenin subunits are coextracted with the gliadins. This extract can be used for the quantitation of total gluten proteins by RP-HPLC. The recovery of gliadin added to flour before dough-mixing and bread-making is 98%. Received: 16 February 1998     

Is the calculation of the gluten content by multiplying the prolamin content by a factor of 2 valid?

Presently, the only essential therapy of celiac disease (CD) is the permanent strict withdrawal of gluten from the diet. With respect to gluten containing foods from wheat, rye, barley, and oats, CD patients have to consume surrogates that must be gluten-free according to the “Codex Alimentarius Standard for Gluten-Free Foods”. The recent “Draft Revised Standard” proposes a gluten threshold of 20 mg per kg gluten-free product. For gluten quantitation, the alcohol-soluble prolamins should be extracted and analyzed by an immunochemical method; the amount of gluten is calculated by multiplying the prolamin content by the factor of 2. To investigate, whether this calculation is valid in any case of contamination of gluten-free products by wheat, rye, barley, and oats, wholemeal or white flours from common wheat, spelt, durum wheat, kamut, emmer, einkorn, rye, barley and oats were analyzed for the ratio of prolamins to glutenins (PROL/GLUT) by a combination of extraction and reversed-phase HPLC procedures. Additionally, different industrial wheat starches were analyzed for their prolamin and total gluten content using different extraction and concentration steps followed by gel permeation HPLC. The results for the cereal flours revealed that the ratio PROL/GLUT was generally higher than 1.0 as proposed by the “Draft Revised Standard” and strongly influenced by cereal species and variety. Common wheat showed the lowest ratio (1.5–3.1), followed by oats and spelt (1.7–3.3), barley (1.4–5.0), durum wheat and kamut (3.1–3.4), emmer (3.5–7.6), rye (6.3–8.2), and einkorn (4.0–13.9). In any case, the gluten content of gluten-free products contaminated with CD activating cereals was generally overestimated, when the prolamin content was multiplied by the factor of 2. In extreme cases, e.g., contamination with rye, the overestimation amounted to 72–79%. Completely different PROL/GLUT ratios were found in ten commercial wheat starches ranging from 0.2 to 4.9. Obviously, the quality of wheat cultivars used for starch production and/or different process parameters, e.g., washing steps, influenced the composition of gluten proteins adherent to starch granules. For wheat starch, the calculation of the gluten content by 2 × PROL may either lead to underestimation (−71% at most) or overestimation (+66% at most). In conclusion, this calculation is invalid; therefore, a future task will be the development of immunoassays with antibodies against all types of storage proteins from wheat, rye, barley, and oats.     

In vitro degradation of wheat gluten fractions by <Emphasis Type="Italic">Fusarium graminearum</Emphasis> proteases

Fusarium spp. infection of cereal grain is a common problem, which leads to a dramatic loss of grain quality. The aim of the present study was to investigate the effect of Fusarium infection on the wheat storage protein gluten and its fractions, the gliadins and glutenins, in an in vitro model system. Gluten proteins were digested by F. graminearum proteases for 2, 4, 8 and 24 h, separated by Osborne fractionation and characterised by chromatographic (RP-HPLC) and electrophoretic analysis (SDS-Page). Gluten digestion by F. graminearum proteases showed in comparison with gliadins a preference for the glutenins whereas the HMW subfraction was at most affected. In comparison with a untreated control, the HMW subfraction was degraded of about 97% after 4 h incubation with Fusarium proteases. Separate digestion of gliadin and glutenin underlined the preference for HMW-GS. Analogue to the observed change in the gluten composition, the yield of the proteins extracted changed. A higher amount of glutenin fragments was found in the gliadin extraction solution after digestion and could mask a gliadin destruction at the same time. This observation can contribute to explain the frequently reported reduced glutenin amount parallel to an increase in gliadin quantity after Fusarium infection in grains.     

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.     

Effects of different <Emphasis Type="Italic">Lactobacillus</Emphasis> and <Emphasis Type="Italic">Enterococcus</Emphasis> strains and chemical acidification regarding degradation of gluten proteins during sourdough fermentation

Dough quality and baking performance of wheat dough are significantly affected by the qualitative and quantitative composition of the gluten. Therefore, the degradation was studied of specific fractions of gluten proteins in sourdough as affected by starter cultures. Doughs were fermented for 0, 5, and 24 h at 30 °C after addition of Lactobacillus sakei, L. plantarum, L. sanfranciscensis or Enterococcus faecalis. Chemically acidified doughs were used as controls. All doughs were analyzed quantitatively for their content of albumins, globulins, gliadins, glutenins, and glutenin macropolymer by means of a combined extraction/HPLC procedure. Protein degradation during sourdough fermentation was primarily due to acidic proteases present in flour. While L. sakei, L. plantarum and L. sanfranciscensis were mostly non-proteolytic, E. faecalis clearly contributed to gluten proteolysis. Single gluten protein types were clearly different in their resistance to proteolytic activities of the dough system and E. faecalis, and, in contrast to total glutenins, the amounts of gluten macropolymer were significantly reduced already after 5 h of incubation. When longer fermentation times were applied, gluten was substantially degraded. The strongest decrease was found for the glutenin fraction leading to an increase of alcohol soluble oligomeric proteins in the gliadin fraction. The extent of the decrease of monomeric gliadins was strongest for the γ-type followed by the α- and the ω-types. This indicates that dough properties residing in specific types of gluten fractions can be influenced by the duration of fermentation and the application of proteolytic strains.     

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     

Comparative investigations of gluten proteins from different wheat species

The only commercially available immunoassay for gliadin determination in gluten-free food which has been ring-tested and in use for many years, is a test kit based on monoclonal antibodies against -gliadins. Various studies of the literature have shown that different gliadin standards resulted in different calibration curves, and it has been proposed that the affinity of -gliadins to the monoclonal antibodies varied among wheat varieties. To clarify this fundamental problem, total gliadins and the -gliadins from a winter wheat ("Rektor"), a spring wheat ("CWRS"), a wheat rye hybrid ("Herzog") and varieties of spelt, durum wheat, emmer and einkorn, were isolated and analyzed by means of an enzyme-linked immunoabsorbent assay (ELISA) kit based on antibodies against -gliadins. Additionally, single - and -gliadins of Rektor wheat were studied. The results demonstrated that the calibration curves derived for total gliadins differed, in parts, strongly from that of the kit gliadin standard; only the curves for the durum wheat and spelt gliadins were in congruence with the kit gliadin. Single -gliadins revealed strong differences between and within wheat species and ELISA equivalents had a range from 10 to 220% according to kit gliadin. The affinity of -gliadins was not correlated with the calibration curves of total gliadins. Some of the -gliadins of Rektor wheat showed ELISA equivalents similar to those of -gliadins. Because the proportions of -gliadins in total gliadins were significantly higher than those of -gliadins, the unspecific binding of -gliadins contributed much more to the total affinity of gliadins than the specific binding of -gliadins. -Gliadins, however, did not show any detectable affinity.     

Disulphide bonds in wheat gluten: further cystine peptides from high molecular weight (HMW) and low molecular weight (LMW) subunits of glutenin and from γ-gliadins

Glutenin was prepared from gluten of the wheat variety Rektor by extraction of gliadin with aqueous ethanol. It was cleaved successively into soluble peptides by the enzymes trypsin and thermolysin. Separation of the peptide mixtures was performed by gel permeation chromatography (GPC) on Sephadex G25 and reversed phase high performance liquid chromatography (RP-HPLC) on ODS-Hypersil. Cystine peptides were detected by differential chromatography of the samples prior to and after reduction. After isolation by multi-step RP-HPLC, the cystine peptides were reduced. The resulting cysteine peptides were alkylated with 4-vinylpyridine, separated by RP-HPLC and sequenced by means of the Edman degradation. The isolated cystine peptides represented a considerable portion of the total cysteine in glutenin: four out of seven cysteine residues of HMW subunits, and eight out of nine cysteine residues of LMW subunits are documented by at least one cystine peptide. Most of the peptides corresponded to known sequences of gluten protein components. From the structures of some tryptic peptides, inter- and intramolecular disulphide bonds for HMW subunits of glutenin have been proven. Cystine peptides from the thermolytic digest have been assigned to LMW subunits of glutenin and toγ-gliadins. Other peptides have been closely related to partial sequences of these protein components. The results have allowed several conclusions about the arrangement of intra- and intermolecular disulphide bridges in gluten proteins.     

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.     

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     

Comparison of viscoelastic properties of gluten from spelt and common wheat

Rheological properties of gluten from spelt and common wheat were studied. The mechanical spectra of gluten samples were registered over a frequency range of 0.001–200 rad/s. Retardation tests were performed to keep all measurements within a linear regime. The mechanical spectra were fitted with Cole–Cole functions to calculate the viscoelastic plateau modulus G _N ⁰, the central frequency of the upper dissipative loss peak ω ₀, and the spread parameter n. Steady state compliance J _e ⁰ and Newtonian viscosity η ₀ were determined from the retardation tests results. Recovery data were converted from time to frequency domain using the Kaschta method and combined with dynamic data; this enabled the extension of the gluten mechanical spectra down to 10⁻⁶ rad/s, revealing the lower dissipative peak loss. The width of the viscoelastic plateau τ _m ⁰/τ ₀ was calculated, and substantial qualitative and quantitative differences were found in spelt and common wheat gluten. All differences in gluten rheological properties were related to spelt and common wheat flour baking quality and protein composition.