Glutathione affects rheology and water distribution of wheat dough by changing gluten conformation and protein depolymerisation

The effects of reduced glutathione (GSH) on dough rheology, water state and distribution, gluten conformation, and protein molecular weight distribution were investigated. Addition of GSH (0.02−0.04%) resulted in a more viscous and less elastic dough with decreased G′ and increased tanδ values, which suggested decreased cross-links in gluten network and a weakened dough structure. The molecular weight of proteins was reduced by the GSH-induced cleavage of intermolecular disulphide bonds. Fourier transform infrared spectroscopy showed a high fraction of β-sheet formation at the expense of α-helix and β-turns, indicating a destabilised secondary structure and protein depolymerisation. GSH increased water release from the gluten network in dough resulting in an increase in freezable water content and caused water redistributed from bound water to weakly bound water. This study provided insights into correlation between wheat dough rheological properties and gluten structure influenced by GSH.     

Effect of baked wheat germ on gluten protein network in steamed bread dough

The effect of baked wheat germ (BWG) on the gluten network structure in steam bread dough was investigated. The secondary structure, free sulphydryl (-SH) content, disulphide (-SS-) bonds content and microstructure of gluten were analysed to evaluate gluten structural changes. The addition of different amounts of BWG (0, 2, 4, 6, 8, 10, and 12%) in dough resulted in decreased content of α-helix and β-sheet structures, but increased random coils, which indicated that a disordered structure was formed. The presence of BWG increased the -SH content but decreased the -SS- bonds content, which indicated fracture of disulfide bonds. Confocal laser scanning microscopy (CLSM) analysis indicated that steamed bread dough containing BWG had larger-sized gas cell and granules of starch separated by the protein matrix, which weakened the gluten network structure. These changes may inevitably affect the viscoelastic properties of steamed bread dough.     

Impact of arabinoxylan with different molecular weight on the thermo‐mechanical,rheological, water mobility and microstructural characteristics of wheat dough

The aim of this study was to investigate the effects of arabinoxylan with different molecular weight on the wheat dough thermo‐mechanical, rheological, microstructural and water mobility properties. Arabinoxylan was extracted from wheat bran and hydrolysed by endo‐1,4‐β‐xylanase (EC 3.2.1.8 from Trichoderma reesei, 10 000 U g^?1) for 2 min (AX_M) and 10 min (AX_L), respectively. The addition of hydrolysed arabinoxylan AX_L increased the stability time, decreased the setback value of wheat dough and enhanced the values of storage modulus (G′) and loss modulus (G″), while unhydrolysed arabinoxylan (AX_H) reduced these values. Meanwhile, unhydrolysed arabinoxylan increased T₂ relaxation time while hydrolysed arabinoxylan AX_L decreased T₂₁ and T₂₂. Confocal laser scanning microscope (CLSM) results showed that the addition of hydrolysed arabinoxylan AX_L promoted the formation of a more compact and continuous protein network in wheat dough. These results revealed that compared with high molecular weight arabinoxylan, hydrolysed arabinoxylan could improve the rheological properties and processing properties of wheat dough by enhancing the interaction among water molecules, starch and gluten in wheat dough.     

不同谷物麸皮对面团流变学特性及面筋蛋白结构的影响

本实验选用小麦麸皮、黑小麦麸皮、燕麦麸皮为原材料,探究在高添加量(质量分数30%)情况下不同谷物麸皮对面团流变学特性、面筋蛋白组成及结构的影响。结果表明,谷物麸皮含有丰富的膳食纤维,麸皮的加入使面团的吸水率、黏度崩解值显著增加,回生值显著降低,面团的形成时间、稳定时间虽与麸皮种类有关,但整体均呈上升趋势;添加麸皮的面筋蛋白中麦谷蛋白与麦醇溶蛋白比例增加了24.7%~73.0%、二硫键含量显著下降了26.0%~35.5%;面筋蛋白中的二级结构以β-折叠为主,小麦麸皮和黑小麦麸皮的加入使得面筋蛋白中的β-转角结构向β-折叠结构转化;扫描电子显微镜图显示麸皮的加入破坏了面筋蛋白原本均匀致密的微观结构。综上所述,谷物麸皮的加入改变了面筋蛋白的组成及二级结构,这些变化可能是导致面团流变学特性及面制品品质下降的原因。     

Effects of japonica rice flour on the mesoscopic and microscopic properties of wheat dough protein

The aim of this study was to study the effects of twelve varieties of japonica rice flour on the gluten protein composition and structure of wheat dough. Experimental results indicated that the addition of japonica rice flour significantly decreased the α-helix structure in the gluten protein sample, but increased the random coil content, indicating that the protein secondary structure became more disordered. The ratio of α-helix/β-sheet structures in the dough supplemented with different varieties of japonica rice flour was decreased, contributing to improved dough stability. Increasing the proportion of japonica rice flour from 10% to 40% significantly decreased the sulfhydryl content of the mixed flour dough. However, the total sulfhydryl content was only positively correlated with the amount of Longdao 19 japonica rice flour, reaching a maximum of 25.34 mol g⁻¹ at 40% japonica rice flour. The gluten structure of mixed flour dough typically forms a porous three-dimensional network, with the Longdao 19, 20, 23 and 25, Longjing 31 and Mudanjiang 31 japonica rice flours leading to improved gluten protein networks. In summary, the supplementation of standard wheat flour with japonica rice flour can alter dough properties and gluten structure.     

Incorporation of several additives into gluten free breads: Effect on dough properties and bread quality

The objective of this work was to assess the effect of emulsifiers, hydrocolloids and enzymes on gluten-free dough rheology and thermal properties and bread quality, while relating dough properties parameters to bread technological quality. Breads were based on rice flour, cassava starch and full-fat active soy flour, with 65% or 75% (flour-starch basis) of water incorporation. Additives used were emulsifiers (diacetyl tartaric acid ester of monoglycerides – DATEM and sodium stearoyl lactylate – SSL), enzymes (glucose oxidase and α-amylase) and hydrocolloids (xanthan gum, carboxymethylcellulose, alginate and carrageenan). Results showed that additive incorporation modified dough behavior, evidenced by different calorimetric and rheological properties. Besides, the electrophoretic pattern of dough extracted proteins changed with glucose oxidase addition. These modifications resulted in breads with different characteristics, such as specific volume, firmness and firming rate, and crumb structure. Nonetheless, they did not necessarily show better quality parameters than the control bread. The control dough displayed good performance for obtaining gluten-free breads of acceptable volume, crumb structure and, principally, with lower hardening rate during storage. Contrary to widespread opinion, this work shows that the presence of additives is not essential for gluten-free bread production. This fact provides new perspectives to the gluten free market at the moment of selecting raw materials and technological parameters, reducing production costs and facilitating gluten free products development.     

Effect of wheat bran dietary fibre on the rheological properties of dough during fermentation and Chinese steamed bread quality

The effects of wheat bran dietary fibre (WBDF) on the rheological properties of dough during fermentation and quality of Chinese steamed bun (CSB) were investigated. The study revealed that with the increase of the content of WBDF, the dough extensibility and time at which gas starts to escape from the dough significantly decreased but the dough firmness significantly increased (P < 0.05). The elastic modulus and viscous modulus showed an upward trend, probably due to the increased molecular weight of the viscoelastic body resulting from the presence of WBDF. Additionally, by changing the quality of the gluten network, the specific volume and L^* value significantly decreased from 2.52 to 1.31 mL g⁻¹, and from 87 to 51, respectively, these adverse effects on CSBs could be moderated by the fermentation process.     

揉面过程中面团面筋蛋白结构的变化

研究了手工揉面过程中面团面筋蛋白结构的变化。结果表明:揉面过程中,揉面初期(2 min)面团游离巯基下降10.69%,二硫键增加4.48%,随后缓慢增长或下降;氢键显著增多(P<0.05),疏水作用力显著下降(P<0.05);二级结构中的无规则卷曲初始骤降56.52%,β-折叠初始增加32.34%,随后小幅增长或下降,α-螺旋和β-转角无明显变化;面筋蛋白、麦醇溶蛋白、麦谷蛋白的SDS可萃取率均有不同程度下降;B/C-LMW-GS峰面积分别增加4.56%,2.61%,4.11%,6.73%,3.18%,0.81%,α-麦醇溶蛋白亚基峰面积分别降低22.42%,10.87%,11.59%,12.87%,9.22%,4.35%。手工揉面促进了面筋蛋白的交联聚合反应,使其蛋白构象朝着更为有序和稳定方向发展,进而增强了面团的黏弹性。     

水分对冷冻小麦面团质构及面筋蛋白二级结构的影响

应用质构分析仪和傅里叶变换红外光谱仪测定小麦面团质构特性和微观结构(面筋蛋白二级结构),分析不同加水量对冷冻和未冷冻面团品质的影响。结果表明:加水量和冷冻对小麦面团的质构特性和面筋蛋白二级结构影响显著。随着加水量的增加,冷冻后小麦面团与未冷冻相比硬度增加、黏性升高、内聚性下降、弹性降低,而对面团的回复性影响很小。经冷冻后面团面筋蛋白的二级结构β-折叠和α-螺旋的相对含量增加,β-转角的相对含量降低,使面筋蛋白的网状结构趋于稳定。以上结果可以说明水分可能是影响冷冻面团品质的一个重要因素,也为进一步揭示加水量在小麦冷冻面团中的作用机理提供了重要的研究参考。     

Water dynamics in white bread and starch gels as affected by water and gluten content

Three levels of water (180, 220 and 260 g/345 g flour) and three levels of gluten (giving 11.2, 13.0 and 14.2 g protein/100 g flour) were used to study the effects of water and gluten on water mobility in white bread using ¹H nuclear magnetic resonance (NMR) relaxometry. Changes in the transverse relaxation time (T₂) were related to water mobility. The three water levels resulted in three different moisture contents in the finished bread (0.55-0.77 g H₂O/g solids). Distributed exponential analysis showed two distinct regions of T₂ (30-600 μs and 1-60 ms), associated with multiple domains of water in the bread crumb. There was no significant difference in peak T₂ values with different gluten content, but significant differences were observed with different moisture content. The results suggested that the mobility of water associated with starch decreased dramatically because of gelatinization. To further investigate the effect of gluten on starch gelatinization, NMR measurements were made directly on model systems containing starch and various gluten amounts. The starch-gluten gels had higher T₂ values than pure starch gels, indicating less swelling of starch granules and absorption of water. This was attributed to less water available to starch in the presence of gluten.     

Highly viscous dough-forming properties of marama protein

Marama bean is an indigenous southern African oilseed legume with an unusual protein composition. Hence, its rheological properties were studied. Marama protein formed a highly viscous and extensible dough when compared to soya and gluten. With a dough of 38% moisture, marama protein extensibility was very high (304% of its original length), twice that of gluten and soya, and this increased considerably (>3-fold) when the moisture content was increased to 45%. With added peroxidase, the storage modulus (G′) of marama protein dough increased with time, suggesting the formation of new and strong protein networks. Dityrosine crosslinks were detected in the doughs. Marama protein showed a single transition with a denaturation temperature higher than soya glycinin. Marama protein was more hydrophobic and contained more β-sheet structure than did soya. Thus, the highly viscous and extensible rheological behaviour of marama protein is probably related to its high β-sheet conformation, hydrophobic interactions and tyrosine crosslinks.     

Optimization of hydrocolloid addition to improve wheat bread dough functionality: a response surface methodology study

Effects of high ester pectin+α-amylase+sucrose (GNFZ), a high ester pectin+sucrose (BIG), xanthan gum (XANTHAN) and hydroxypropylmethylcellulose (HPMC) on wheat dough performance have been studied. Effects of hydrocolloids added singly and in association at different levels, on the investigated rheological, mechanical and thermal parameters have been evaluated by response-surface methodology. Optimum hydrocolloid formulations for white wheat bread are recommended.Positive linear and negative quadratic significant effects of GNFZ were observed on both the gluten index (GI) and the energy of dissociation of the amylose–lipid complex (ΔH_x). Optimized dosage of 1.36 g GNFZ/100 g flour, d.b. (maximum of the respective response surface plot) led to maximized values for both GI and ΔH_x, described as good indicators and predictors of the quality of fresh and stored formulated breads to be obtained. The strengthening effect of high ester pectin was reinforced by the negative quadratic effect of GNFZ on gluten extensibility, the positive effect of GNFZ/HPMC on the resistance to extension of gluten, and the negative synergistic effect of the pair BIG/HPMC on dough extensibility. XANTHAN when added singly induced desirable increase in dough resistance to extension, and the incorporation of the pair XANTHAN/GNFZ into dough formula is recommended because of the reduction of the induced degree of softening during mixing (farinograph) of GNFZ formulated doughs. A dosage of 0.109 g XANTHAN/100 g flour annulate the softening effect of GNFZ when added at an optimized dose of 1. 36 g GNFZ/100 g flour. Caution should be applied when added XANTHAN in presence of BIG because of the decrease in the extent of amylose–lipid complexation. Addition of HPMC at a level <1/>1 moderate/enhance, respectively, the effect of GNFZ on the resistance to extension of the gluten, and the water binding capability of BIG, and in this respect the incorporation of the cellulose derivative is encouraged at a dose dependent on the required effect.     

牡丹花蕊蛋白对面团和面筋蛋白特性的影响

为实现牡丹花蕊资源化利用,以大豆分离蛋白为参照,研究牡丹花蕊蛋白对面团和面筋蛋白质构、动态流变学特性、二硫键、表面微观结构和二级结构的影响。结果表明,牡丹花蕊蛋白能够明显提高面团的硬度、黏着性和咀嚼性,添加量低于6%时效果优于大豆分离蛋白。添加花蕊蛋白提高了面团的储能模量与损耗模量,使得面团黏弹性增加。牡丹花蕊蛋白对面筋蛋白网络结构形成的影响与大豆分离蛋白基本一致,添加量为6%时,扫描电镜显示面筋蛋白气孔数量多且孔洞深,网络结构致密;面筋蛋白二级结构中,相对稳定的α-螺旋+β-折叠占比达到最大值59.32%,与空白组相比二硫键含量提高了89%。牡丹花蕊蛋白能够有效促进面筋蛋白网络结构的形成,提高面团的品质,可用于对黏弹性要求较高的面制品生产。     

Wheat bran dietary fibre-induced changes in gluten aggregation and conformation in a dough system

This study was conducted to determine the effect of wheat bran dietary fibre (WBDF) on aggregation and conformational changes of gluten in fermented and unfermented dough systems. The results revealed that WBDF has an advantage in maintaining the content of glutenin macropolymer (GMP) in the fermentation process. The analysis of the molecular weight distribution showed decreased content of larger polymeric proteins (LPPs). At the same WBDF level, after fermentation, the content of larger polymeric proteins (SPPs) increased, likely due to the polymerisation of the gliadins. Additionally, fluorescence spectroscopy and surface hydrophobicity analysis revealed that, in fermented dough, with the increase of WBDF content, the protein hydrophobicity significantly increased from 6.56 to 9.43 (P < 0.05). Hydrophobic interactions contributed to the macromolecular unfolding and/or aggregation of gluten. Also, WBDF may induce changes in dough properties by inducing conformational changes in the gluten protein.     

Combined effects of freezing rate, storage temperature and time on bread dough and baking properties

This study compares the effects of freezing temperature and rate as well as storage temperature and time on the quality of frozen dough. Yeasted bread dough was frozen using four freezing rates (19-69 °C/h), then stored at −10, −20, −30, or −35 °C for up to 180 days. Dough strength diminished with longer storage time and higher storage temperatures. Cryo-SEM showed that dough stored at −30 and −35 °C had the least damaged gluten network. NMR studies showed that more rapidly frozen dough, and that stored at lower temperatures had lower transverse relaxation (T₂) times (9-10 ms). However, dough stored at −20 °C displayed the highest yeast activity among samples. Bread loaf volume decreased with storage time, and bread made from dough stored at −20 °C showed the highest loaf volume. Breads produced from −30 and −35 °C stored dough displayed less change in the texture profile during storage as well as less change in T₂ values. Response surface analysis showed that optimal properties occurred at freezing rates of around 19-41 °C/h and storage temperatures of −15 to −20 °C.     

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     

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.     

The role of gluten in a pound cake system: A model approach based on gluten–starch blends

In order to evaluate the role of gluten in cake-making, gluten–starch (GS) blends with different ratios of gluten to starch were tested in a research pound cake formula. The viscosities of batters made from commercial GS blends in the otherwise standardised formula increased with their gluten content. High viscosities during heating provide the batters with the capacity to retain expanding air nuclei, and thereby led to desired product volumes. In line with the above, increasing gluten levels in the cake recipes led to a more extended oven spring period. Cakes with a starch content exceeding 92.5% in the GS blend suffered from substantial collapse during cooling. They had a coarse crumb with a solid gummy layer at the bottom. Image analysis showed statistical differences in numbers of cells per cm², cell to total area ratio and mean cell area (p < 0.05). Both density and mean cell area were related to gluten level. Moreover, mean cell area and cell to total area ratio were the highest for cakes with the lowest density and highest gluten levels. Relative sodium dodecyl sulfate (SDS, 2.0%) buffer (pH 6.8) extractabilities of protein from cakes baked with the different GS blends decreased with gluten content and were strongly correlated with the intensity of collapse. Taken together, the results teach that protein gives the cakes resistance to collapse, resulting in desirable volumes and an optimal grain structure with uniform cell distribution.     

Inhibitory activity towards human α‐amylase in wheat flour and gluten

Wheat α‐amylase inhibitors (AI) have been targeted as potential triggers of noncoeliac gluten or wheat sensitivity (NCGS). The aim of this study was to determine AI activity towards α‐amylase from human source in wheat cultivars. Contrary to barley, buckwheat, or oats, high level of AI activity was found in wheat and, to a lesser extent, rye. AI activity (mean IC₅₀ = 137 μg mL^?1) did not vary with respect to ancient or recently developed wheat cultivars. Vital wheat gluten had very high and heat‐stable AI activity (mean IC₅₀ = 23 μg mL^?1), higher than wheat starch (?10 000 μg mL^?1) or acarbose (40 μg mL^?1), a medication for the management of hyperglycaemia and potentially causing digestive disorders due to the accumulation of undigested carbohydrates in the intestine. Data suggest that eating raw wheat gluten, flour or dough could pose a health risk.     

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.