Impact of water content on the solubilisation of arabinoxylan during xylanase treatment of wheat bran

Arabinoxylan (AX) has a major impact on the functional properties of wheat bran, and it has been shown that technological properties of bran can be improved by using endoxylanases. Enzymatic treatments are typically conducted at high water content. However, in industrial applications, low water content may be advantageous, especially when targeting dry end products. The aim of the study was to examine the impact of water content, ranging from 20 to 90%, on the efficiency of endoxylanase treatment of wheat bran. Interestingly, AX solubilisation was highest at the water contents of 40 and 90%. At water contents 50–80%, AX solubilisation was lower than at 40 and 90%. Furthermore, at low water content, less depolymerisation was detected. At water content of 40%, the bran-water mixture was transformed from powder-like into compact mass. Probably the compact consistency of the material enhanced AX solubilisation by increased breakdown of bran cell walls due to shear forces or via enhanced enzyme binding to the substrate. The results show that solubilisation of bran AX can also be efficiently performed at low water content.     

Quality of shear fractionated wheat gluten – Comparison to commercial vital wheat gluten

The functional properties of gluten obtained with a shear-induced separation process, recently proposed by Peighambardoust et al. (2008), are compared with a commercially available vital wheat gluten. Two tests were performed. First, a relatively strong wheat flour, Soissons, was enriched with gluten protein. The resulting dough was then evaluated on its kneading performance. Second, a weak flour, Kolibri, was enriched to evaluate the baking properties. The wheat flour enriched with gluten protein obtained via the shear-induced separation process (SCG) showed comparable to improved gluten functionality relative to commercial available vital wheat gluten protein (CVWG). The differences in functionality cannot be directly related to the composition as analyzed with SE-HPLC, because the composition of the gluten materials was rather comparable. The differences in functionality may therefore be related to the different drying techniques used or to the inherent mildness of the shear-induced separation technique.     

The effect of gluten on the retrogradation of wheat starch

The retrogradation of amylopectin in a wheat starch and a wheat starch/gluten (10:1) blend prepared by extrusion and containing 34% water (wet weight basis) was studied using X-ray diffraction, differential scanning calorimetry and NMR relaxometry during storage at constant water content and temperature (25 °C). For both samples, amylopectin ‘fully’ retrograded after 2–3 days storage, i.e. the different parameters monitored with time to follow the retrogradation had reached their maximum value, and crystallised predominantly into the A polymorph. Under the experimental conditions used, there was no evidence of any significant effects of the presence of gluten on the kinetics, extent or polymorphism of amylopectin retrogradation.     

Debranning of wheat prior to milling reduces xylanase but not xylanase inhibitor activities in wholemeal and flour

Debranning of wheat to remove the outer 7% of the kernel, prior to grinding or milling reduced xylanase activity in wheat wholemeal and wheat endosperm flour by up to 80 and 60%, respectively, whereas there was no significant reduction of xylanase inhibiting activity. Flours obtained after debranning and milling showed no major differences in moisture content, whereas ash content decreased and protein and arabinoxylan content decreased slightly with increasing debranning degree. Part of the xylanase activity in the flour was lost on addition of Triticum aestivum xylanase inhibitor (TAXI). Since TAXI specifically inhibits glycosyl hydrolase family 11 xylanases and since endogenous cereal xylanases belong exclusively to family 10, part of the xylanase activity in the flour is most likely of microbial origin. Debranning also significantly reduced alpha-amylase activities in wheat wholemeal and wheat flour. Debranning prior to milling can, therefore, impact on flour functionality.     

Effect of hydrostatic pressure and temperature on the chemical and functional properties of wheat gluten III. Studies on gluten films

Numerous gluten preparations were produced by the variation of pressure and temperature. Optimal conditions for the production of gluten films on a laboratory-scale were by suspending of gluten (1 g) in a mixture of ethanol (3 mL), glycerol (0.5 g) and conc. formic acid (10 mL), casting and drying at 40 °C. Small-scale laboratory methods for the production of gluten films by casting and moulding were developed. Film strips obtained were examined by micro-extension tests, which resulted in curves similar to extensigrams for dough and gluten and allowed the determination of the resistance to extension, extensibility and elasticity. The results demonstrated that pressure treatment of gluten in combination with variable cultivars, temperature, process parameters and additives, allow the production of films with a wide range of rheological properties – from soft and smooth to strong and hard rubber like. Finally, it was demonstrated that the addition of fibres to gluten enhanced the stability of films. Thus, high pressure treatment allows a selective modification of gluten as raw material for film production. In comparison with conventional plastic films, gluten films have considerable advantages, because they can be produced from renewable plants and they are readily biodegradable.     

Influence of high solid concentrations on enzymatic wheat gluten hydrolysis and resulting functional properties

Enzymatic hydrolysis at increased solid concentrations is beneficial with regard to energy and water consumption. This study examines the influence of the solid concentration on the enzymatic hydrolysis of wheat gluten and the resulting functional properties of the hydrolysate. Wheat gluten was mildly hydrolyzed at a solid concentration varying from 10% to 60% to degrees of hydrolysis (DH%) ranging from 3.2% to 10.2%. The gluten was susceptible to hydrolysis at all solid concentrations but the hydrolysis rate was influenced by increasing solid concentrations. Size-exclusion high-performance liquid chromatography revealed an increase in the ratio of peptides with a molecular mass >25 kDa for solid concentrations of 40% and 60%. The water solubility increased on hydrolysis and was independent of the solid concentration during proteolysis. The foam stability was not influenced by the solid concentration at low DH%. At DH% higher than 8%, high solid concentrations increased the foam stability, which might be related to the presence of more peptides with a molecular mass >25 kDa. In addition, we found increased reactor productivity. The results show the potential of hydrolyzing wheat gluten at high solid concentrations, which could lead to large savings for water and energy when applied industrially.     

Introgression of transgenes into a commercial cultivar confirms differential effects of HMW subunits 1Ax1 and 1Dx5 on gluten properties

Transgenes encoding the HMW subunits 1Ax1 and 1Dx5 have been transferred from “model” wheat lines into the commercial French bread wheat cultivar Soissons, using three backcrosses. Five pairs of BC3 expressing and null lines were isolated from each cross and multiplied to provide grain for functionality studies. Analysis of white flour samples confirmed the expression of the transgenes. SE-HPLC and Reomixer studies showed that the two transgenes had differential effects on dough functional properties. Thus, subunit 1Dx5 resulted in detrimental effects on dough development which were associated with decreased extractability of large glutenin polymers. In contrast, lines expressing subunit 1Ax1 contained increased proportions of extractable large glutenin polymers with three lines showing higher torque at similar mixing times (i.e. increased dough strength). This confirms the results obtained with the model wheat lines and shows that the 1Ax1 transgene can be used to increase dough strength in commercial cultivars.     

Dynamic water vapour sorption in gluten and starch films

Water sorption of gluten and wheat starch films as a function of water activity was studied using gravimetric step-change sorption experiments. Films of different thicknesses were used with the aim to vary the characteristic diffusion time and to get insights in the contribution of the polymer-chain rearrangement in the sorption behaviour. It is shown that both starch and gluten are in the glassy state for a water activity a_w below 0.9. From comparison of the dynamical sorption curves with a Fickian diffusion model, it is shown that water diffusion in gluten films seems Fickian for a_w < 0.7, and non-Fickian for a_w > 0.7, while for starch films, non-Fickian sorption behaviour is observed for a_w > 0.1. The results show that polymer-chain rearrangement and the stress built up in the matrix play an important role in the sorption dynamics of these films. Even when the material is in the glassy state matrix relaxation phenomena play a role in the sorption behaviour of starch and gluten.     

Influence of sulphur fertilisation on quantities and proportions of gluten protein types in wheat flour

Although different supplies of sulphur (S) during wheat growth are known to influence the quantitative composition of gluten proteins in flour, an effect on the amount and on the proportions of single protein types has yet not been determined. Therefore, wholemeal flours of the spring wheat ‘Star’ grown on two different soils and at four different levels of S fertilisation (0, 40, 80, 160 mg S per container) were analysed in detail using an extraction/HPLC procedure. The results demonstrated that the amount of total gluten proteins as well as of the crude protein content of flour was little influenced, whereas amounts and proportions of single protein types were strongly affected by the different S fertilisation. The changes were clearly dependent on the Cys and Met content of each protein type. The amount of S-free ω-gliadins increased drastically, and that of S-poor high-molecular-weight (HMW) glutenin subunits increased moderately in the case of S deficiency. In contrast, the amounts of S-rich γ-gliadins and low-molecular-weight (LMW) glutenin subunits decreased significantly, whereas the amount of α-gliadins was reduced only slightly. S deficiency resulted in a remarkable shift of protein proportions. The gliadin/glutenin ratio increased distinctly; ω-gliadins became major components, and γ-gliadins minor components, whereas the ratio of HMW to LMW glutenin subunits was well-balanced.     

Effect of lipid incorporation on functional properties of wheat gluten based edible films

Wheat gluten is an inexpensive protein derived from mill industries with good film forming properties, which allows producing semipermeable membranes able to slow down water migration in foods.The first objective of this study was to evaluate the effects of the incorporation of a lipid phase (25 wt%, dry basis) in wheat gluten on the functional properties of the film, such water sorption, surface hydrophilicity, water barrier properties, mechanical properties and thermal properties. The second one was to asses if such incorporation was able to reduce the water sensitivity of film mechanical properties.Findings clearly showed that the incorporation of a lipid phase was able to decrease the water sorption, water affinity (hydrophilicity) and water transfer (≈2 times) of wheat gluten films. Moreover, mechanical properties are also affected by the lipid addition with a decrease in rigidity and, at high a_w, an increase in extensibility. However, the sensitivity of the mechanical properties to water was not modified. Lastly, DSC (Differential Scanning Calorimetry) analysis proved that changes in mechanical properties of films as a function of hydration state were the consequence of glass transition depletion, which allowed them to turn from a glassy-like behavior to a rubber-like behavior.     

Enriching novel Glu-Ax alleles and significantly strengthening gluten properties of common wheat through wide hybridization with wild emmer

Two hybrids, BAd7-209 and BAd7-210, were obtained by wide hybridization between wild emmer D97 and weak gluten cultivar CN16. They had a genetic background of common wheat, resulting from continuous selfing over nine times. These hybrids were better than CN16 in dough quality and processing quality tests. BAd7-210 was better than medium gluten wheat cultivar MM37, and BAd7-209 was far better than moderate to strong gluten wheat cultivar SM482. Through chromosome engineering, BAd7-210 possessed the 1Ax2.2 of male D97, and BAd7-209 had the 1Ax1.2 which was caused by complex variation because of cross-parents’ genomic asymmetry. The open reading frames (ORFs) of two novel active Glu-Ax alleles 1Ax2.2 and 1Ax1.2 were 2496 bp and 2514 bp, encoding 830 and 836 amino acid residues, respectively. The 1Ax1.2 was the second longest Glu-Ax gene discovered to date, and it had two deletions and one insertion besides many single nucleotide polymorphisms (SNPs) compared with the 1Ax2.2 and 1Ax1. The longer polypeptide of 1Ax1.2 should explain why BAd7-209 has better processing quality than BAd7-210. Therefore, wild emmer could be effectively utilized to enrich the 1Ax alleles of common wheat through direct cross transferring and generating novel allele variation, which could significantly enhance the gluten strength.     

Trends in wheat technology and modification of gluten proteins for dietary treatment of coeliac disease patients

Coeliac disease (CD) is a long-life intolerance to gluten proteins, with prevalence of 1–2% worldwide and health consequences if not treated. Currently, the treatment is the dietary gluten withdrawal, but commercial gluten-free foodstuffs present undesirable properties. Therefore, attempts are being made to modify the immunogenic sequences of gluten to avoid recognition by the immune system and to prepare safe and acceptable foods. These include long-time fermentation by sourdough and enzymic modification. The present article reviews our current knowledge of the pathogenesis of CD and the advantages and limitations of the current approaches to gluten modification and to develop safer foods for CD patients.     

Large deformation stress relaxation and compression-recovery of gluten representing different wheat classes

Despite the great variety of physicochemical and rheological tests available for measuring wheat flour, dough and gluten quality, the US wheat marketing system still relies primarily on wheat kernel hardness and growing season to categorize cultivars. To better understand and differentiate wheat cultivars of the same class, the tensile strength, and stress relaxation behavior of gluten from 15 wheat cultivars was measured and compared to other available physicochemical parameters, including but not limited to protein content, glutenin macropolymer content (GMP) and bread loaf volume. In addition, a novel gluten compression–relaxation (Gluten CORE) instrument was used to measure the degree of elastic recovery of gluten for 15 common US wheat cultivars. Gluten strength ranged from 0.04 to 0.43 N at 500% extension, while the degree of recovery ranged from 5 to 78%. Measuring gluten strength clearly differentiated cultivars within a wheat class; nonetheless it was not a good predictor of baking quality on its own in terms of bread volume. Gluten strength was highly correlated with mixograph mixing times (r = 0.879) and degree of recovery (r = 0.855), suggesting that dough development time was influenced by gluten strength and that the CORE instrument was a suitable alternative to tensile testing, since it is less time intensive and less laborious to use.     

Temperature variations during grain filling obtained in growth tunnel experiments and its influence on protein content,polymer build-up and gluten viscoelastic properties in wheat

The aim of this study was to investigate effects of temperature during grain filling on gluten quality characteristics at a lower to moderate temperature range. Experiments with two wheat varieties grown in field covered by polypropylene tunnels during grain filling were performed in two seasons. Mean day temperature differences achieved within the tunnel were approximately 2–2.5 °C from the open to the closed end. There were significant effects of temperature on grain maturity time, thousand grain weight and protein content. The resistance to stretching of the gluten doughs increased with the increasing day temperatures. This was reflected in the proportion of unextractable polymeric proteins (UPP). The results suggest that increases in temperature within this temperature range affect the polymerization of polymeric proteins, giving higher molecular weights, and hence increased Rmax and stronger gluten. The two varieties differed in their response to temperature. In addition, there were seasonal variations in gluten functionality that may be associated with fluctuations in day temperatures between the seasons.     

Impact of late-season N fertilisation strategies on the gluten content and composition of high protein wheat grown under humid Mediterranean conditions

The rise in high protein common wheat in humid Mediterranean areas has determined a need to compare specific and effective nitrogen (N) fertilisation protocols in order to increase their end-use value. The aim of the work was to assess the impact of late-season N fertilisation strategies on grain yield and protein content (GPC), gluten fraction composition, and rheological traits. Different applications and types of fertiliser (soil applied ammonium nitrate, soil applied urea, foliar applied urea and a foliar applied commercial fertiliser) were distributed at the same rate (30 kg N ha⁻¹) in a field experiment in NW Italy, during three growing seasons. A control without any late-season N fertilisation was also considered. All the treatments received 130 kg N ha⁻¹ as ammonium nitrate (AN), which was split between tillering and the beginning of the stem elongation growth stages.None of the compared late-season N fertilisations significantly affected canopy greenness and stay green duration during the grain filling period, or the grain yield, test weight, and thousand kernel weight, although the foliar application significantly increased foliage burning (+9.8%). The late application of N consistently increased GPC (+1.1%) and dough strength (W, +21%) in the different growing seasons. The type of fertilisation strategies clearly affected the gluten content and rheological parameters: AN was more effective than urea as a soil top-dressed applied fertiliser in increasing W (+10%), as a result of a higher rise in the GPC content (+0.5%) and extensibility (L, +11%). The foliar application at anthesis, at the same N rate, led to a comparable GPC and W with those of the soil top-dressed granular fertiliser. Only a weak effect of granular urea on y/x type HMW was observed for the gluten composition. Conversely, a notable influence of year was observed (i.e. GS/Glia and y/x type HMW), which in turn resulted in a significant impact on W and P and on the aggregation time and aggregation energy.This study offers a further contribution to the improvement of specific N fertilisation strategies in order to enhance the wheat quality according to its end-use value.     

Migration of gluten under shear flow as a novel mechanism for separating wheat flour into gluten and starch

This paper describes a novel principle for the separation of wheat flour into starch and gluten in a concentrated medium. The process is based on the use of simple shear flow in a cone-and-cone device. The separation takes place in two steps. Initially, local segregation of gluten and starch phases occurs, leading to formation of macroscopically visible gluten patches distributed throughout the dough. This local segregation can be understood by considering the dough as a visco-elastic matrix containing an inert filler (starch). Further shearing leads to aggregation of those patches and migration (large-scale separation) towards the apex of the cone. As a result, the wheat dough is separated into a protein-poor fraction, containing less than 4% protein, and a protein-rich fraction containing almost 50% protein on a dry weight basis. However, under the process conditions used, upon a very long shearing, a redistribution of the aggregated gluten structures in the starch phase was observed, demonstrating a processing limit for the separation performance. Compared to traditional processing, the separation process presented shows opportunities for producing high quality gluten accompanied with significant water savings. Considering the fact that simple shear flow in steady rate is less harmful to gluten quality, such a separation process could benefit gluten quality.     

Variation in the levels of the different xylanase inhibitors in grain and flour of 20 French wheat cultivars

A xylanase from Aspergillus aculeatus (glycoside hydrolase family 10), uninhibited by TAXI, and a xylanase from Bacillus subtilis (family 11), uninhibited by XIP-I, were selected to quantify the respective apparent levels of XIP-I and TAXI inhibitors, in flours and grains of 20 wheat varieties. The apparent TAXI amount ranged from 0.05 to 0.19 mg/g in flour (mean: 0.11 mg/g) and from 0.07 to 0.2 mg/g in grain (mean: 0.14 mg/g). The range observed for XIP-I was 0.12–0.6 mg/g in flour (mean 0.32 mg/g), and 0.21–0.56 mg/g in grain (mean: 0.41 mg/g). The inhibition profile of the xylanase from A. aculeatus by a crude inhibitor preparation suggested the presence of an additional component in wheat flour, responsible for an increase in inhibition.     

The effect of sodium chloride on gluten network formation and rheology

Gluten samples were obtained from two wheat flours with different levels of total protein in the presence or absence of sodium chloride (2% flour base). The dynamic oscillation rheology, large extensional deformation, confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM) and chemical analysis of disulfide bond linkages and the ratio of polymeric glutenins and monomeric gliadins were used to investigate the effect of salt on the structure and rheological properties of gluten. CLSM and TEM images showed that NaCl caused the gluten to form fibrous structure. The presence of NaCl increased non-covalent interactions and β-sheet structure, measured by FTIR, in gluten proteins. The gluten matrix formed with salt resulted in higher tan δ values corresponding to a less elastic network when measured using oscillatory rheometry. Large deformation extensional measurements showed that the maximum force to fracture were lower for the gluten samples prepared in the presence of NaCl. The results from this study indicate that changes in the solvent quality due to the presence of NaCl during dough mixing result in different molecular conformation and network structure of gluten proteins which contributed to the differences in the rheological properties.     

Influence of processing temperature on the water vapour transport properties of wheat gluten based agromaterials

The influence of processing conditions (thermoforming temperature) on water vapour transport properties (permeability, sorption and diffusion) of wheat gluten-based films was studied in relation to structural properties (cross-linking degree of the wheat gluten matrix). Increasing temperature from 80 °C to 120 °C led to a significant decrease in material swelling in high moisture environment and a WVP reduction mainly due to a decrease in diffusivity but without important effect on the moisture sorption isotherms. This was attributed to a higher cross-linking degree of protein network for film thermoformed at 120 °C, with a limited mobility and less possibilities of rearrangement in high moisture conditions.     

Modification of gluten by methionine binding to prepare wheat bread with reduced reactivity to serum IgA of celiac disease patients

Celiac disease (CD) is caused by ingestion of wheat gluten proteins, due to immune response to proline- and glutamine-rich sequences. In this study, for reduction of the immune recognition, gluten proteins were enzymatically modified by binding methionine to the amino lateral groups of glutamine residues. Additionally, a bread-making process with modified gluten was assayed. The methionine binding was monitored by measuring the alpha-amino group disappearance and reduction of celiac IgA immunoreactivity. The best methionine binding was after 60 min reaction at pH 10, inducing a reduced to null IgA immunoreactivity to prolamins extracted from modified gluten. The bread prepared with modified gluten had lower specific volume (3.86 cm³/g) than the control wheat bread (4.52 cm³/g) but higher than those reported for gluten-free loaves. The preserved functionality of gluten proteins will make it feasible to apply this kind of modification in different wheat-based foodstuffs like the assayed bread in this study.