Enthalpic Relaxation of Vital and Protease-Treated Wheat Gluten

Commercially available vital wheat gluten was purified with α-amylase and treated with protease in a one-step process. The supernatant of the protease-treated gluten was freeze dried, quench cooled, and aged for 2 weeks and analyzed using differential scanning calorimetry, sodium dodecyl sulfate poly-acrylamide gel electrophoresis, reverse phase high performance liquid chromatography, size exclusion high performance liquid chromatography, capillary zone electrophoresis, and dynamic mechanical analysis. The differential scanning calorimetry profile of the aged (un-purified or un-modified) gluten sample exhibited enthalpic relaxation beneath its glass transition (Tg) indicating molecular relaxation. Samples treated with 0.006 g protease/g gluten showed Tg at 49.11°C with ΔCp = 0.12 (J/°C g). Higher protease levels and longer aging time caused high Tg temperature, ΔCp, and ΔH of enthalpic relaxation. The size exclusion high performance liquid chromatography profile of the protease-treated gluten clearly showed differences in molecular size between the supernatant and the precipitate, while reverse phase high performance liquid chromatography profiles signified more hydrophilic gluten molecules than the control. The small difference in gluten molecular size after protease treatments (0.024 g protease versus 0.032 g) appeared to have a significant effect on the enthalpic relaxation, where the two treatments showed different degrees of enthalpic relation. The capillary zone electrophoresis data confirmed the insignificant difference between 0.024 and 0.032 g protease/g gluten regarding the size to charge ratio. The molecular interactions for protease-treated gluten were much weaker than vital gluten, as indicated by much weaker network and sensitivity to temperature, especially above Tg. The weaker network was evidenced by higher G″ versus G′, which explained the fluid like behavior of the protease-treated gluten.     

Influence of equibiaxial extensional strain on stress relaxation of glycerol plasticised wheat gluten

BACKGROUND: Glycerol plasticised wheat gluten shows advantages for non‐food applications such as biodegradable package films and bioplastics because of their abundant resources, low cost, good biodegradability and suitable mechanical and oxygen barrier properties. The intention of this study was to evaluate to the equibiaxial stress relaxation of 400 g kg^?1 glycerol plasticised gluten at different biaxial strains at room temperature for a better understanding of the processibility. RESULTS: The plasticised gluten shows significant stress relaxation and the spectra span over six decades of time at biaxial strains from 0.03 to 1.51. Plotting the instantaneous modulus against strain reveals strain softening and strain hardening at strains below and above 0.25, respectively. The relaxation modulus as a function of time can be fitted to the Kohlrausch–Williams–Watts equation. CONCLUSION: These results suggest that stress relaxation of plasticised gluten is highly dependent on strain level and biaxial deformation accelerates the network relaxation by widening the distribution of relaxation times. Copyright © 2008 Society of Chemical Industry     

MECHANICAL PROPERTIES OF A CORN STARCH PRODUCT DURING THE POST-FRYING PERIOD

The mechanical properties of the crust and core regions of an immersion-fried corn starch patty containing different amounts of gluten, amylose, and amylopectin were studied after various storage times. Moisture and oil profiles for the different gluten contents were also determined during post-frying storage. The addition of gluten did not affect the hardness of the crust region of the fried samples during storage, but the addition of amylose and amylopectin significantly increased the hardness of the crust. Samples with 5% added amylopectin showed a similar behavior, but in this case the puncture force significantly increased during the first hour of storage and remained constant thereafter. The range of linear viscoelastic behavior for fried corn starch patties in compression was for strains up to 4%. Stress relaxation curves showed that the elasticity of corn starch patties increased with time of storage, but decreased with the addition of gluten. The addition of 5% amylose caused a significant increase in elasticity, whereas with 5% amylopectin, the increase in this variable was less noticeable.     

A composite model for wheat flour dough under large deformation

The mechanical behaviour of dough, gluten and starch were studied in an effort to investigate whether bread dough can be treated as a two phase (starch and gluten) composite material. Mechanical loading tests revealed rate dependent behaviour for both the starch and gluten constituents of dough. There is evidence from cryo-Scanning Electron Microscopy (SEM) that damage in the form of debonding between starch and gluten occurs when the sample is stretched. In addition, a reasonable agreement is seen between the Lodge material model and the compression test data only, indicating again that possibly ‘damage’ is essentially debonding which does not occur under compression, unlike tension and shear loading. A composite finite element model was developed using starch as filler and gluten as matrix. The interface between the starch and gluten was modelled as a cohesive contact interaction. When the interaction of starch and gluten is strong, as indicated for the dough with no damage, the stress-strain curve is always higher than the gluten stress-strain curve under both tension and shear loading. In contrast, when damage is activated in the form of debonding, the dough stress-strain curves under tension are seen to cross over the curves for gluten and therefore leading to lower stress values than in gluten. No damage/debonding occurs under compression when a damage function is used which is in good agreement with the experimental data.     

Effect of gluten content on recrystallisation kinetics and water mobility in wheat starch gels

The effect of gluten on starch retrogradation at 5 °C was studied using ¹H NMR relaxometry. Gels were made from gluten and starch at 27.8 and 38.5% total solids and with gluten comprising either 10, 15 or 20% of the solids. Changes in the transverse relaxation time constant (T₂) were related to water mobility. Mono‐exponential analysis of relaxation curves showed that, in general, gluten retarded starch retrogradation. T₂ values in gluten gels also decreased during storage, but to a much lesser extent. Distributed exponential analysis showed that two distinct regions of T₂ were observed in all samples. During aging, the peak values of both regions shifted to lower values for all gels. Starch gel samples showed the most significant shift, and gluten gels showed the least. The three levels of gluten addition in starch/gluten gels produced similar shifts. For all samples the signal intensity of the less mobile region decreased more dramatically than that of the more mobile region during storage. It was suggested that gluten retards water loss in the granule remnants. Copyright © 2004 Society of Chemical Industry     

面筋蛋白和大米蛋白对鲢鱼鱼糜凝胶特性的影响

面筋蛋白和大米蛋白均可以明显提高鲢鱼鱼糜的凝胶强度和持水性,降低其蒸煮损失率和横向弛豫时间(T_2)。但是与大米蛋白相比,面筋蛋白在改善鲢鱼鱼糜凝胶特性方面效果更加显著。当面筋蛋白添加量为3%时,鱼糜凝胶的破断力、破断距离、凝胶强度和持水性分别为669.0 g、12.2 mm、8 162.0 g·m和89.8%,与对照组(未添加蛋白)相比分别增加了79.8%、37.2%、147.0%、11.6%;而蒸煮损失率为8.51%,与对照组相比降低了19.7%。且此时的凝胶横向弛豫时间T_(23)和T_(24)分别为42.4 ms和156.0 ms。3%的面筋蛋白促使鲢鱼鱼糜凝胶形成十分致密的空间三维网络结构,使其具有较高的凝胶强度和持水性,但是由于面筋蛋白带有浅黄色,所以鱼糜凝胶的白度有轻微下降。     

Gluten Gel and Film Properties in the Presence of Cysteine and Sodium Alginate

ABSTRACT:  Wheat flour has an ability of forming dough by mixing with water, which exhibits a rheological property required for making bread. The major protein is gluten, which is a valuable protein material for food industry. In this study, gluten protein gels and films were formed with cysteine and sodium alginate. Adding cysteine improved gel and film properties (stress relaxation behavior, bending strength). The gel containing 0.01 M cysteine had a longer relaxation time and was more rigid than the gel without cysteine. Although adding sodium alginate to the gluten suspension containing cysteine improved the water-holding ability and homogeneity of the gel network, the film from this gel was more brittle than the gluten film with cysteine alone. Microstructural observations of the gels and films with scanning electron microscopy suggested that water evaporation was more heterogeneous from the gel containing sodium alginate than from the gel with cysteine alone. Fourier transform-infrared (FT-IR) analysis during film formation suggested that the presence of cysteine encourages interaction between gluten molecules and results in intermolecular β-sheet formation in earlier stages than in the no additive condition. FT-IR results also suggested that the combined effect of sodium alginate and cysteine on the protein secondary structure was remarkably different from that of cysteine alone. Our results suggest that addition of a suitable amount of cysteine (0.01 M) and heat treatment to 80 °C during gluten gel and film formation induces a homogenous network in the gel and film by regulating disulfide–sulfide interactions.     

Properties of MTGase treated gluten film

Water barrier and mechanical properties of gluten film affected by the treatment of microbial transglutaminase (MTGase) were evaluated with the water vapor permeability (WVP), magnetic resonance imaging (MRI) T₂ map and mechanical properties of gluten films. The water barrier ability of gluten films was superior to the no film but inferior to the Parafilm^® investigated by MRI T₂ maps in a two-gelatin-gel system. The WVP of gluten film increased, while the tensile force decreased, with increasing in the dosage of MTGase treated. The gluten films were also dyed with Acid Fuchsin and observed by a confocal laser scanning microscopy (CLSM) to localize the proteins in the film. The micrographs showed many pores and inhomogenous gluten network in MTGase treated gluten films. High WVP and weak mechanical properties of MTGase treated gluten films were attributed to the cross-link bonds formation, which created pores and inhomogenous gluten matrix as evidenced by CLSM.     

Effect of processing conditions on some functional characteristics of extrusion‐cooked cassava starch/wheat gluten blends

Extrusion‐cooked blends of cassava starch (CS) and wheat gluten (WG) were studied. The data were analysed using response surface methodology. The results showed the formation of new structures characterised by lower radial expansion (RE) and specific volume (SV) when gluten was added to CS. WG content was the most important variable affecting RE, water absorption index (WAI), water solubility index (WSI), SV and difference in colour (ΔE) of the extruded products, but feed moisture content and barrel temperature also influenced RE. WAI was affected by a significant interaction between WG content and barrel temperature. The extruded products had lower WAI values and higher WSI values than WG‐free products. Heat, high shear rate and high pressure during extrusion cooking caused mechanical destruction or denaturation of the WG and gelatinisation and dextrinisation of the starch components. The extruded blends could have diverse applications. © 2002 Society of Chemical Industry     

MECHANICAL PROPERTIES OF AN IMMERSION FRIED POTATO STARCH-GLUTEN GEL DURING POSTFRYING PERIOD

Moisture profiles in fried samples of potato starch with different gluten contents were determined during postfrying storage. Over time, moisture migrated from the core to the crust of the sample, and the moisture content of the crust region increased. The addition of gluten caused a significant increase in oil uptake in the crust. The initial hardness of the crust significantly decreased as the gluten content increased to 10 and 30%, during the first 30 min of storage. With longer storage time (> 240 min), the crust hardness tended to increase, due to an increase in firmness of the starch sample. This behavior was less pronounced for samples with 10 and 30% gluten. The range of linear viscoelastic behavior (up to 14% strain) was determined from the initial linear zone of the stress-strain curves. Stress relaxation tests were performed in the linear and nonlinear viscoelastic regions, with a strain level of 5% and 40%, respectively. According to stress relaxation curves, samples became less elastic with the addition of gluten and more elastic with the time of storage.     

Rheological and Microstructure Characterization of Composite Dough with Wheat and Mesquite (Prosopis spp) Flours

Rheological behavior and microstructural characteristics of composite dough with wheat and mesquite flours (from Prosopis alba) were analyzed by response surface methodology. A central composite design was applied varying proportions of water (50 to 80 g each 100 g wheat flour) and mesquite flour (0 to 70 each 100 g wheat flour). Texture profile analysis showed that increasing the amount of mesquite flour and decreasing the amount of water led to less cohesive and more resilient doughs. Stress relaxation curves were fitted with a Maxwell model and relaxation times were obtained. These parameters resulted higher for those formulations low in mesquite content and high water levels. Composite dough showed a typical viscoelastic behavior with higher elastic moduli (G’) when mesquite flour ratio in the mixture was increased. ¹H-RMN T2 relaxation assays revealed higher mobility in samples with high amounts of water and minimum level of mesquite. A farinograph was adequate to obtain optimum water amounts and showed that addition of mesquite led to less stable dough respect to control wheat dough. By using confocal laser scanning microscopy with fluorescent probes rhodamine B and fluoresceine isothiocyanate, a poor gluten network development or protein aggregation was observed when water contents were far from optimum.     

添加烤制马铃薯的小麦粉面包加工配方的优化

本文以高筋小麦粉2000 g,添加鸡蛋0.05%、食盐1.50%、白砂糖15%、酵母1.50%、黄油4.00%、奶粉10%为面包的基础配方,通过单因素实验和响应面试验对烤制马铃薯、谷朊粉、改良剂量进行优化,从而得出最佳配方。由响应面结果可知,加入高筋小麦粉质量的25%烤制马铃薯、0.60%改良剂、0.90%谷朊粉,所做出的面包硬度为181.110 g,和预测值180.857 g接近,说明用响应面法优化的工艺可行。     

响应面法优化玉米蛋白挤出工艺

双螺杆挤出改性处理脱脂玉米蛋白粉。以脱脂玉米蛋白粉含水量、挤出温度、螺杆转速为响应因素,可溶性蛋白含量为响应值,采用响应面分析方法,确定脱脂玉米蛋白粉挤出改性的最佳工艺条件。结果表明：物料含水量68%、挤出温度163℃、螺杆转速30Hz(225r/min)时,挤出脱脂玉米蛋白粉中可溶性蛋白含量最高,为3.43%。采用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)测定挤出改性后玉米可溶性蛋白的分子质量分布,结果显示其分子质量介于3500～14300D之间,且主要是分子质量为3500～6500D的多肽。改性后的玉米蛋白粉其理化性质都有了较明显的改善,说明双螺杆挤出改性玉米蛋白粉效果明显,切实可行。     

Baking Performance, Rheology, and Chemical Composition of Wheat Dough and Gluten Affected by Xylanase and Oxidative Enzymes

Baking trials were performed with six wheat doughs prepared with xylanase, peroxidase, or glucose oxidase (GOX), and their combinations. Judging dough properties, baking performance, bread volume, and crumb structure, the dough containing xylanase plus peroxidase performed best. Flow relaxation measurements with doughs indicated that peroxidases introduced new transient linkages, whereas glucose oxidase also introduced cross-links permanent on long time scales. Rheological tests and chemical analysis revealed small differences between control and xylanase and/ or peroxidase containing gluten and more pronounced differences for GOX containing gluten. No evidence was found that xylanase specifically removed arabinoxylans from gluten or that peroxidase catalyzed the formation of covalent bonds between arabinoxylans and gluten proteins.     

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.     

大豆蛋白/谷朊粉复合材料的结构和性能

通过模压成型方法制备了一系列大豆蛋白(SP)/谷朊粉(WGP)复合材料,并研究了复合材料的动态力学性能、热稳定性、力学性能、吸水性能、微观结构和形态。结果表明:红外光谱显示复合材料中大豆蛋白与谷朊粉之间发生氢键作用;扫描电镜和动态力学分析证实,当谷朊粉含量低于28%时,大豆蛋白/谷朊粉复合材料的组织结构均匀,未出现新的损耗峰,表明谷朊粉与大豆蛋白发生共塑化、形成均相体系,且相容性良好;当谷朊粉含量为3.5%时,复合材料的热稳定性提高,并且材料的拉伸强度、断裂伸长率和断裂能分别比非复合材料增大0.33 MPa、31.21%和0.37 kJ/m2,表明复合材料的强度、延伸性、韧性改善;复合材料的2 h吸水率和24 h吸水率均减小,表明谷朊粉的加入显著提高了该材料的抗水性。     

Phenomenological viscoelasticity of some rice starch gels

The applicability of a powerful but still easy to use technique, based on a phenomenological theory of viscoelasticity, for processing and analyzing dynamic mechanical data of some rice gels was investigated. Based on this theory a continuous relaxation spectra was generated by application of Tikhonov regularization procedure on continuous Maxwell model. Interpretation of relaxation spectra in terms of number of peaks, its peak intensity H(λ) and appearance of its main distribution peak and magnitude of equilibrium elasticity modulus (G_e) of continuous Maxwell model was found to appropriately reflect main peculiarities of the viscoelastic behavior of rice starch gels. An increase in number of peaks in the relaxation spectra was observed for starch gels having higher amylose content indicating the creation of more heterogeneous structure. H(λ) and G_e values also increased with increase in amylose content demonstrating a transition of the system to more stable state like a gel.     

Gelation of mixed systems whey protein concentrate–gluten in acidic conditions

Gels of whey protein concentrate (WPC)–gluten were prepared by heating WPC–gluten dispersions (10% whey protein/0–5–10% gluten protein, w/w; pH 3.75 or 4.2). Gels were characterized through solubility assays in different extraction solutions, measures of water-holding capacity (WHC), firmness, elasticity and relaxation time, and light microscopy. Differential scanning calorimetry (DSC) of WPC–gluten dispersions was also performed. Gluten increases the firmness and elasticity of gels, mainly at pH 4.2. The WHC also increases with gluten content, being higher at pH 3.75 than at pH 4.2. Solubility assays indicate that electrostatic forces, hydrophobic and H bindings would be involved in maintaining the gel structure of WPC gels at pH 3.75 and 4.2, whereas in mixed gels of WPC–gluten, the principal forces responsible for the maintenance of the gel structure at these pHs would be hydrophobic and H bindings, and in gels prepared at pH 4.2 also disulfide bonds, but in a minor extent. The presence of gluten shifts the apparent transition temperature for whey protein denaturation towards lower temperatures. Gels with gluten present a smooth network with gaps and a more elastic appearance, as observed by light microscopy.     

热黏合土工布应力松弛力学性能预测模型研究

采用四种力学模型对三种不同类型热黏合土工布的应力松弛力学性能进行拟合研究。结果表明,使用力学模型对热黏合土工布的应力松弛进行预测是可行的,广义麦克斯韦变化模型二对三种试样均具有最佳的拟合效果,拟合能力优于欧林模型,显示了良好的品种适应性和预测能力。     

Laboratory‐scale Dry/Wet‐Milling Process for the Extraction of Starch and Gluten from Wheat

A laboratory‐scale process is presented for the manufacture of starch and gluten from wheat. Main feature of this process is that whole wheat kernels are crushed dry between smooth rolls prior to wet disintegration in excess water in such way that gluten formation is prevented and fibres can be removed by sieving. Centrifugation of the endosperm suspension yields a dough which can be separated into starch and gluten using an established batter process. The results suggest that starch recovery is increased in comparison to a conventional wheat flour process without a concomitant decrease in protein recovery. Although starch purification was omitted, a total starch with a low protein content is obtained. On the other hand, the protein content of the gluten fraction is rather low due to difficulties in removing the starch. Despite this, the effect on dough mechanical properties by the addition of gluten obtained from wet‐milled wheat is comparable to the effect of gluten from flour.