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     

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.     

Effect of steaming on the rheological characteristics of wheat flour dough

 The effect of steaming on the various rheological characteristics of wheat flour dough was studied. Steaming of flours at atmospheric pressure for 15 min completely denatured the gluten and reduced the water absorption capacity from 58.4% to 45.0%. Even steaming for just 5 min increased the resistance to extension considerably from 500 BU (Brabender Units) to 1000 BU and the ratio figure (resistance to extension/extensibility) from 4.2 to 27.4, indicating stiffening of the dough. The dough made from steamed flour had a higher hardness value of 91.1 N than the dough made from raw wheat flour which had a value of 51.1 N. The pasting characteristics of flour steamed for 15 min measured in a Rapid Visco Analyser showed increased peak viscosity from 218 rapid visco units (RVU) to 257 RVU as well as increased cold paste viscosity from 175 RVU to 200 RVU and increased hot paste viscosity from 94 RVU to 108 RVU for flour steamed for 15 min. Received: 4 August 1998 / Revised version: 23 October 1998     

Degradation of gluten proteins by Fusarium species and their impact on the grain quality of bread wheat

The protein quality of wheat, the most important crop worldwide, is affected by the presence of fungi, mainly those belonging to the Fusarium genus. The aim of this study is to analyze the effects of Fusarium spp. on ground wheat grains quality by measuring gluten strength and quantifying the gliadin/glutenin content. A total of 23 Fusarium spp. isolates and two bread wheat (Triticum aestivum L.) genotypes with contrasting baking quality were used in the investigation. The results of SDS sedimentation test (SDSS) revealed that the presence of Fusarium species significantly affected the gluten strength negatively; while F. pseudograminearum and F. graminearum are the species that predominantly affected the SDSS values. Principal component analysis of gluten composition showed that the effect of Fusarium species on gluten composition depended on the wheat genotypes analyzed. Cluster analysis revealed that all the Fusarium species used as inoculum produced severe effects on grain quality and gluten composition on both the genotypes. In summary, our results showed that the presence of Fusarium spp. impaired storage proteins affecting the wheat dough properties. Therefore, constant monitoring is necessary to reduce the presence of Fusarium in the food chain for reducing the negative potential impact on bread quality.     

Effect of gluten addition and storage time on white pan bread quality: instrumental evaluation

 Continuing an investigation into the different factors affecting the quality of white pan bread and the changes taking place during storage, on the basis of instrumental determinations of firmness using compression and bending tests, this second instalment addresses the influence of adding gluten to the dough. Three types of bread were prepared using three different water contents and three proportions of added gluten each. Firmness was evaluated at 24, 48 and 72 h. Addition of gluten significantly increased flexibility and significantly decreased firmness in the bread at the higher water content levels. It also improved the keeping properties of the bread by slowing the increase in firmness with time; this effect was also higher at the higher water content levels. Received: 4 May 1998     

Detection of wheat adulteration of spelt flour and products by PCR

 To date, no general method to detect wheat [Triticum aestivum vulgare (Vill.) Mackey] adulteration of spelt [T. aestivum spelta (L.) Thell.] exists. Exploiting a published allelic difference in γ-gliadin gene GAG56D, we developed and evaluated three PCR-based methods to determine the proportion of wheat in spelt flour and products. A sensitive wheat-specific PCR system was designed. Moreover, a heterologous internal standard was constructed for quantitative competitive (QC-)PCR. The standard was arbitrarily calibrated to 5% wheat DNA in spelt DNA. A PCR-RFLP system consisting of a GAG56D-specific PCR system with subsequent restriction was used to estimate the relative proportions of wheat and spelt in DNA mixtures. The three methods were successfully applied to seven commercial spelt samples and one self-produced bread. Five and three of the seven samples were found to contain more than 5% and 10% wheat, respectively. One sample appeared to contain no spelt at all. Analyzing the bread crumb with PCR-RFLP, we were able to estimate the wheat content of the flour which was used to produce the bread and thus demonstrated the applicability of PCR-RFLP to quantify processed products. Received: 24 March 2000     

谷朊粉对面包基础粉品质特性的影响

探讨不同添加量的谷朊粉对面包基础粉蛋白质的品质、流变特性及面包烘焙品质的影响。结果表明:谷朊粉可以明显增加面包基础粉的湿面筋含量、沉淀值和蛋白质含量,强化其流变学特性,有效改善面包烘焙品质,增大面包比容和高径比并改善其弹性和硬度。当谷朊粉添加量为10%时,面包烘焙品质最好。     

小麦及其面粉品质对馒头品质的影响

综合分析了小麦与面粉的蛋白质品质、淀粉品质、酶、脂类物质等对馒头品质的影响。     

Effect of extrusion cooking on protein modification in wheat flour

Common soft wheat flour was extruded at three different temperatures and two different moistures. To investigate the dependence of the wheat protein modification on processing conditions, their solubilities in sodium dodecyl sulfate (SDS) were compared with those in SDS+(2-mercaptoethanol) ME. Furthermore, free sulfhydryl groups were detected with Ellmans Reagent and SDS-PAGE was performed under reducing and non-reducing conditions. The solubility values in SDS were greatly reduced after extrusion. The solubility values in SDS+ME were not affected. We therefore concluded that intermolecular cross-linking by disulfide bonding through extrusion cooking had occurred. This result was confirmed by SDS-PAGE under reducing and non-reducing conditions. At low and medium temperatures the solubilities were lower at low moisture; however, more free sulfhydryl groups were detected under these conditions, suggesting that moisture content of the flour has an influence on the way and the nature of the protein polymerization. At the highest thermal energy input at low moisture the solubilities increased again. This was accompanied by an increase of detectable free sulfhydryl groups. This led to the conclusion that disulfide bonds were cleaved at high energy input. The solubility development in 70% ethanol was nearly the same as in SDS. This is seen as a proof that gliadins are highly involved in the protein network formed under extrusion conditions. This finding was also confirmed by the results of SDS-PAGE.     

脱皮对不同筋力小麦粉及其馒头品质的影响

对小麦进行适度脱皮,既能去除粗纤维和表面污染物,还能较好的保留微量营养素.以高筋、中筋和低筋小麦为原料,研究4％脱皮率对不同筋力小麦粉及其馒头品质的影响.结果表明,高筋和低筋小麦脱皮后糊化参数均有所提高,而中筋小麦有所下降;脱皮后,高筋、中筋和低筋小麦粉破损淀粉质量分数分别增加了6.0％、2.6％和4.2％;高筋和低筋...     

Relationship of polymeric proteins and empirical dough rheology with dynamic rheology of dough and gluten from different wheat varieties

Dynamic rheological properties of dough and gluten were studied and related to the empirical rheology (Farinograph) and the protein fractions of different wheat varieties. The relationship between high molecular weight-glutenin subunits (HMW-GS) and dough strength was evaluated. Dynamic rheology of under-, optimum- and over-mixed dough was also related to the farinograph characteristics and the protein fractions. The moduli (G′ and G″) of over- and optimally-mixed dough were significantly correlated with Farinograph characteristics and SDS-unextractable polymeric protein (UPP) content. The temperature-induced rheology of glutens revealed that the differences in G′ and G″ during heating as well as cooling were related to the UPP content. Principal component analysis revealed wide range of differences in the dynamic rheology among the wheat varieties mainly attributed to UPP.     

小麦粉对馒头品质的影响

馒头品质的主要影响因素之一是小麦面粉品质。对小麦粉中的蛋白质含量、蛋白质质量、蛋白质组分及面团的流变学特性,淀粉含量、淀粉组成及小麦淀粉的黏度特性等各因素对馒头品质的影响进行了较为详细的论述。     

Increasing the folate content in Egyptian baladi bread using germinated wheat flour

The main objective of this study was to increase the folate content in Egyptian baladi bread using germinated wheat flour (GWF). The effect of germination temperature and drying conditions on the folate content of wheat grains was studied. Wheat flour was substituted with unsieved and sieved GWF at different levels and the effects on folate content and the rheological properties of dough were determined. Germination of wheat grains resulted in a 3- to 4-fold higher folate content depending on the germination temperature. Maximum folate content (61 μg/100 g dry matter (DM)) occurred at 30 °C. Drying did not affect folate content in germinated grains. After replacement with GWF, folate content in both flour and bread increased 1.5- to 4-fold depending on the level of replacement. Rheological properties of dough were adversely affected by increasing replacement level (as determined by farinograph). While the folate content in bread was as high as 66 μg/100 g DM at complete replacement of flour with sieved GWF, the bread was dark and layers were not separated. After replacement of half of the flour with sieved GWF (50 g/100 g), the baladi bread was acceptable with respect to colour and layer separation. The folate content in this bread was 50 μg/100 g DM, compared with 30 μg/100 g DM in bread without GWF (0 g/100 g).     

Effect of phenolic acids on the rheological properties and proteins of hard wheat flour dough and bread

BACKGROUND: The effects of different phenolic acids on the rheological properties and gluten proteins of hard wheat flour dough and bread were investigated. Caffeic, ferulic, syringic and gallic acids were each blended with hard wheat flour at a concentration of 4.44 µmol L^?1 g^?1 flour. RESULTS: Mixing time and tolerance were reduced with the addition of phenolic acids. The phenolic acids reduced the maximum resistance to extension (R_max) and increased the extensibility of dough, with effects in the following order: gallic < syringic < ferulic < caffeic acid. The effect on R_max was more pronounced in overmixed dough. Loaf volume was most significantly decreased with the addition of caffeic acid. Extraction of sodium dodecyl sulfate‐soluble high‐molecular‐weight proteins was increased in both mixed and fermented doughs by the addition of ferulic and caffeic acids. The order of influence of the phenolic acids on the rheological properties and protein structure of dough and bread was consistent with that of their antioxidant activity. CONCLUSION: The addition of caffeic and ferulic acids reduced R_max and increased the extensibility of hard wheat flour dough by modifying the high‐molecular‐weight gluten, which resulted in decreased bread volume. Copyright © 2011 Society of Chemical Industry     

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     

Gelation of mixed myofibrillar/wheat gluten proteins treated with microbial transglutaminase

Gluten (Glu) and an acid-extracted protein fraction (AF) from wheat flour were mixed (1:1 ratio) with myofibrillar protein (MP) and treated with microbial transglutaminase (MTGase) to observe the effect on heat-induced gelation. Dynamic rheological properties and thermal denaturation patterns of treated samples were measured, respectively, with an oscillatory rheometer and a differential scanning calorimeter. The storage modulus (G′) of control MP sample (no MTGase), with a value of 533 Pa at end of heating (77 °C), was not affected (P > 0.05) by Glu nor by AF. However, mixed protein samples after the MTGase treatment produced higher gel elasticity values that differed (P < 0.05) between samples (1355, 1700 and 1875 Pa at 77 °C for MP, MP/AF, and MP/Glu, respectively). The MP sample underwent three endothermic transitions (peaking at 61.5, 68.0, and 78.5 °C) during thermal scan. The treatment with MTGase and/or addition of Glu or AF tended to lower the temperature for the first transition but raised the temperature for the third transition, suggesting possible interactions of the muscle with non-muscle proteins.     

Incorporation of dairy ingredients into wheat bread: effects on dough rheology and bread quality

 Dairy ingredients are used in breadmaking for their nutritional benefits and functional properties. The effects of the traditionally-used whole and skimmed milk powder, sodium caseinate, casein hydrolysate and three whey protein concentrates on dough rheology and bread quality were studied. Whole and skimmed milk powders improved sensory characteristics. Sodium caseinate and hydrolysed casein displayed beneficial functional properties in breadmaking including low proof time, high volume and low firmness. Both ingredients increased dough height measured with the rheofermentometer. Bread with 2% or 4% sodium caseinate added was rated highly in sensory evaluation. Incorporation of whey protein concentrates generally increased proof time, decreased loaf volume and decreased dough height measured with the rheofermentometer. Received: 6 April 1999 / Revised version: 13 July 1999     

Interactive effects of flour, starter and enzyme on bread dough machinability

 Dough machinability of samples formulated with the enzyme principles glucose-oxidase, lipase, amylase and pentosanase/hemicellulase, and fermented with different microbial starters, was assessed by texture profile analysis and dough stickiness measurements. The individual and interactive effects of flour, enzyme and starter on the primary and secondary mechanical and surface-related parameters were evaluated, and the suitability of enzyme mixtures added to started doughs to improve dough handling characteristics and minimize adhesiveness and stickiness in flours was established. The general improving effect of the mixture of α-amylase, pentosanase and hemicellulase on most dough texture properties is particularly relevant when high-grade and/or sourer-started systems are used, because of their strong effect in decreasing hardness and adhesiveness respectively. Individual additions of glucose-oxidase and lipase cancelled out the excessive stickiness/adhesiveness of started and enzyme-supplemented doughs while the simultaneous presence of glucose-oxidase and lipase improved cohesiveness, chewiness and gumminess. The extent of the effects of this binary combination on dough mechanical characteristics was comparable to that obtained with the ternary mixture of α-amylase, pentosanase and hemicellulase, but avoided the deleterious effect of the latter enzyme combination on stickiness. In well-defined flour-starter systems, the enzyme supplementation of doughs constitutes a useful alternative to chemical improvers for enhancement of dough plasticity. Reveived: 16 February 1998     

Effect of blending of raw and steamed wheat flour on the rheological characteristics of dough

 The blended dough made from raw wheat flour and wheat flour steamed for 15 min at a ratio of 1 : 1, along with minor ingredients (salt, oil) showed reduced farinograph water absorption capacity. The stability of the blended dough with oil was reduced while the mixing tolerance index increased. The inclusion of salt in the blend increased the resistance to extension and also the area under the curve. The hardness and cohesiveness measured by means of texture profile analysis decreased with the inclusion of oil in the blend, while increasing with the addition of salt. The Rapid Visco Analyser used to measure pasting characteristics showed a peak viscosity which increased for the blend with salt, but decreased for that with oil. Similarly, the hot paste viscosity, cold paste viscosity and area under the curve increased for the blend with salt, but decreased for the blend with oil. Received: 5 February 1999 / Revised version: 21 April 1999     

Interactive effects of flour, starter and enzyme on bread dough machinability

 Dough machinability of samples formulated with the enzyme principles glucose-oxidase, lipase, amylase and pentosanase/hemicellulase, and fermented with different microbial starters, was assessed by texture profile analysis and dough stickiness measurements. The individual and interactive effects of flour, enzyme and starter on the primary and secondary mechanical and surface-related parameters were evaluated, and the suitability of enzyme mixtures added to started doughs to improve dough handling characteristics and minimize adhesiveness and stickiness in flours was established. The general improving effect of the mixture of α-amylase, pentosanase and hemicellulase on most dough texture properties is particularly relevant when high-grade and/or sourer-started systems are used, because of their strong effect in decreasing hardness and adhesiveness respectively. Individual additions of glucose-oxidase and lipase cancelled out the excessive stickiness/adhesiveness of started and enzyme-supplemented doughs while the simultaneous presence of glucose-oxidase and lipase improved cohesiveness, chewiness and gumminess. The extent of the effects of this binary combination on dough mechanical characteristics was comparable to that obtained with the ternary mixture of α-amylase, pentosanase and hemicellulase, but avoided the deleterious effect of the latter enzyme combination on stickiness. In well-defined flour-starter systems, the enzyme supplementation of doughs constitutes a useful alternative to chemical improvers for enhancement of dough plasticity. Reveived: 16 February 1998