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.     

Effect of hydrostatic pressure and temperature on the chemical and functional properties of wheat gluten: Studies on gluten, gliadin and glutenin

The effect of hydrostatic pressure (0.1–800 MPa) in combination with various temperatures (30–80 °C) on the chemical and physical properties of wheat gluten, gliadin and glutenin was studied. Chemical changes of proteins were determined by extraction, reversed-phase high-performance liquid chromatography (HPLC), sodium dodecylsulphate (SDS) polyacrylamide gel electrophoresis (PAGE), circular dichroism (CD) spectroscopy, thiol measurement and studies on disulphide bonds. Rheological changes were measured by extension tests and dynamic stress rheometry. Treatment of gluten with low pressure (200 MPa) and temperature (30 °C) increased the proportion of the ethanol-soluble fraction (ESF) and decreased gluten strength. The enhancement of both pressure and temperature provoked a strong reduction of the ESF and the thiol content of gluten. Within gliadin types, cysteine containing α- and γ-gliadins, but not cysteine-free ω-gliadins were sensitive to pressure and were transferred to the ethanol-insoluble fraction. Disulphide peptides isolated from treated gluten confirmed that cleavage and rearrangement of disulphide bonds were involved in pressure-induced reactions. Increased pressure and temperature induced a significant strengthening of gluten, and under extreme conditions (e.g. 800 MPa, 60 °C), gluten cohesivity was lost. Isolated gliadin and glutenin reacted differently: solubility, HPLC and SDS-PAGE patterns of gliadin having a very low thiol content were not influenced by pressure and heat treatment; only conformational changes were detected by CD spectroscopy. In contrast, the properties of isolated glutenin having a relatively high thiol content were strongly affected by high pressure and temperature, similar to the effects on total gluten.     

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.     

Morphology and mechanical properties of thermo-molded bioplastics based on glycerol-plasticized wheat gliadins

Glycerol-plasticized wheat gliadin bioplastics were prepared through thermo-molding method. The effect of glycerol content on the morphology and the mechanical properties of wheat gliadin bioplastics was studied. Morphology, tensile properties (tensile strength and elongation at break), dynamic mechanical properties and rheological properties were evaluated in relation to glycerol content. Experimental results reveal that the morphology, the glass transition temperatures (T_g) of both the gliadin-rich and the glycerol-rich domains and the tensile properties are closely linked to the glycerol content. The time–temperature superposition (TTS) fails to be applied to the dynamic loss modulus G″ (all temperatures) and the dynamic storage modulus G′ (above 80 °C) of wheat gliadin bioplastics.     

Improved physicochemical and structural properties of wheat gluten with konjac glucomannan

Konjac glucomannan (KGM), a dietary fiber, can be used to improve the quality of flour products. In this study, the effects of KGM at different concentrations on the water distribution, morphological, textural, thermal, and structural properties of wheat gluten were studied. KGM improved the physicochemical and structural properties of wheat gluten by changing the water holding capacity, secondary structure, and free sulfhydryl and disulfide bond contents. Scanning electron microscopy confirmed that KGM can evenly fill the network structure, affecting gluten network development. KGM exhibited no effect on moisture content; however, KGM decreased water mobility in wheat gluten. The increased thermal denaturation temperature indicates that KGM can improve the thermal stability of wheat gluten. Sharp changes in texture profile analysis (TPA) parameters were observed around 5% KGM, and elasticity and cohesiveness were optimal after the addition of 4% KGM. In addition, the secondary structure analysis indicated that α-helix and β-sheet structures increased. The addition of 5% KGM increased the content of disulfide bonds by 2.57-fold. Overall, the changes in gluten structure and properties suggest that wheat gluten could be improved the stability, functionality and water holding capacity of gluten by adding KGM.     

Preparation and properties of wheat gluten based bioplastics with fish scale

The objective of this study was to prepare the wheat gluten based bioplastics with fish scale (FS) through compression molding. The tensile strength of the wheat gluten/FS composites (the range of 6.5–7.5 MPa) was higher than that of the neat wheat gluten-based bioplastic (3.40 MPa). There was a good dispersion of the fish scale powder embedded within the wheat gluten matrix. Dynamic mechanical analysis results showed that the tan delta max peak height and storage modulus of the wheat gluten-based bioplasic was reduced by adding the fish scale. Moreover, the addition of the fish scale caused a weight loss and the surface of the wheat gluten based bioplastic after 120 h of accelerated weathering were differed from the neat wheat gluten based bioplastic. These results may help to find a new applications for fish scale waste to control the degradation rate of a wheat gluten based bioplastic in the agricultural field.     

Effect of hydrostatic pressure and temperature on the chemical and functional properties of wheat gluten II. Studies on the influence of additives

Cysteine, N-ethylmaleinimide, radical scavengers, various salts or urea were added to wheat gluten. After treatment at increasing pressure (0.1–800 MPa) and temperature (30–80 °C) the resulting material was analysed by micro-extension tests and an extraction/HPLC method to measure protein solubility. Furthermore, cysteine was added to isolated gliadin and glutenin prior to high-pressure treatment and protein solubility was determined. The resistance to extension of gluten strongly increased and the solubility of gliadin in aqueous ethanol decreased with increasing pressure and temperature. As compared to experiments without additive the observed effects were much stronger. Isolated gliadin turned largely insoluble in aqueous ethanol when cysteine was added prior to high-pressure treatment. The S-rich α- and γ-gliadins were much more strongly affected than the S-poor ω-gliadins pointing to a disulphide related mechanism. Monomeric gliadin components were completely recovered after reduction of the aggregates with dithioerythritol. In contrast, samples without free thiol groups such as isolated gliadins or with SH groups, which had been blocked by N-ethylmaleinimide, were hardly affected by high-pressure treatment. The addition of radical scavengers to gluten showed no effect in comparison to the control experiment, indicating that a radical mechanism of the high-pressure effect can be excluded. The observed effects can be explained by thiol-/disulphide interchange reactions, which require the presence of free thiol groups in the sample. The addition of salts and urea showed that unfolding of the protein due to weakening of interprotein hydrogen bonds is strongest for ions with a high radius (e.g. thiocyanate). This leads to weakening of gluten at ambient pressure but it facilitates high pressure induced reactions, e.g. of disulphide bonds.     

Effect of temperature, time and wheat gluten moisture content on wheat gluten network formation during thermomolding

A plastic-like material can be obtained by thermomolding wheat gluten protein which consists of glutenin and gliadin. We studied the effect of molding temperature (130-170 °C), molding time (5-25 min) and initial wheat gluten moisture content (5.6-18.0%) on the gluten network. Almost no glutenins were extractable after thermomolding irrespective of the molding conditions. At the lowest molding temperature, the extractable gliadin content decreased with increasing molding times and moisture contents. This effect was more pronounced for the α- and γ-gliadins than for the ω-gliadins. Protein extractabilities under reducing conditions revealed that, at this molding temperature, the cross-linking was predominantly based on disulfide bonds. At higher molding temperatures, also non-disulfide bonds contributed to the gluten network. Decreasing cystine contents and increasing free sulfhydryl and dehydroalanine (DHA) contents with increasing molding temperatures and times revealed the occurrence of β-elimination reactions during thermomolding. Under the experimental conditions, the DHA derived cross-link lanthionine (LAN) was detected in all gluten samples thermomolded at 150 and 170 °C. LAN was also formed at 130 °C for gluten samples containing 18.0% moisture. Degradation was observed at 150 °C for samples thermomolded from gluten with 18.0% moisture content or thermomolded at 170 °C for all moisture contents.     

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.     

Influence of reducing agents on properties of thermo-molded wheat gluten bioplastics

The present work aims to study the influence of reducing agents of sodium bisulfite, sodium sulfite and thioglycolic acid on the equibiaxial extensional deformation of glycerol plasticized wheat gluten and the properties of gluten bioplastics thermo-molded at 125 °C. Moisture absorption, weight loss and water uptake, uniaxial tensile properties (Young's modulus, tensile strength, elongation at break and tensile set), and morphology observations were performed to characterize the physical properties of the thermo-molded gluten bioplastics. The results showed that reducing agents facilitated the viscous flow and restrained the elastic recovery of the plasticized gluten while not hindering the crosslinking reaction of gluten proteins during thermo-molding. On the contrary, reducing agents do not significantly influence moisture absorption, Young's modulus, tensile strength and the morphology of the gluten bioplastics thermo-molded at 125 °C. It is shown that reducing agents are highly effective for tailoring the flow viscosity of the plasticized gluten dough and the mechanical properties of thermo-molded gluten bioplastics.     

Effect of temperature variation during grain filling on wheat gluten resistance

The objective was to investigate effects of natural variation in temperature during grain filling on wheat (Triticum aestivum L) gluten quality. Seventeen field trials with four different varieties were conducted during the years 2005–2008. Temperature records were obtained from automatic weather stations located near the field trial sites. The period from heading to yellow ripeness was divided into 20 sub-phases of equal thermal time units, and a last sub-phase comprising the seven days after yellow ripeness. Partial Least Squares Regression was used to relate the temperature records of the different sub-phases to gluten quality analysed by the Kieffer Extensibility test and the SDS sedimentation test.     

Improvement on functional properties of wheat gluten by enzymatic hydrolysis and ultrafiltration

Four fractions (100-, 50-, 20-K and permeate) from a proteolytic hydrolysate (DH=2.8%) of wheat gluten were separated using size fractionation on ultrafiltration membranes with molecular weight cut-offs of 100, 50 and 20 kDa and their functional properties evaluated. Proteolysis led to a significant (P<0.05) increase in solubility of gluten fractions at pHs between 2–10 and a shift of the pI value from 6–7 to 5. The solubilities of 100-K, 50-K, 20-K and permeate fractions were significantly (P<0.05) improved compared with the untreated control and the hydrolysate. The 50-K fraction was superior to other three fractions for emulsion activity index between pH 2 and 10. The most stable foam was given by the 100-K fraction which showed 65.8% of initial foam while the control sample gave only 23% of foam, after 60 min resting. Foam stability decreased as the molecular mass of hydrolysate fractions decreased. Furthermore, after proteolysis, the surface hydrophobicity (H₀) of gluten increased significantly (P<0.05) compared with the control except for the permeate fraction. The highest value of H₀ was given by the 100-K fraction, followed by the 50-K, 20-K and permeate fractions. In addition, proteolysis resulted in a decrease in the storage modulus of gels.     

Similarities and differences in secondary structure of viscoelastic polymers of maize α-zein and wheat gluten proteins

The secondary structure of a dough-like zein polymer was compared to the structure present in a wheat viscoelastic system using FT-IR spectroscopy. When zein was mixed at 35 °C, which is above its glass transition temperature (T_g), changes in its secondary structure suggested that the protein loses its native structure, mainly composed of α-helices (68%), and a viscoelastic system is formed by a structural rearrangement that favors β-sheet structures. This rearrangement is very similar to the structural changes observed in gluten viscoelastic polymers. Upon removal of shear stress, the zein polymer showed a rapid decrease in the proportion of β-sheet structures (from 48% to 28% after the first 3 min) in favor of unordered structures. At the same time, the viscoelasticity of the polymer decreased rapidly. In contrast, gluten, in a similar viscoelastic system and held at the same temperature, showed a fairly constant high content of β-sheet structures (49%) coinciding with the slow relaxation time typical of gluten networks after the removal of shear. We speculate that the addition of a protein capable of causing extensive and stable β-sheet formation in the zein–starch viscoelastic polymer could increase the stability and relaxation time of the zein system and, thereby, create the possibility of a zein dough with similar functionality to a wheat viscoelastic system.     

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.     

Interaction of water unextractable solids and xylanase with gluten protein: effect of wheat cultivar

A previously proposed explanation for the change in gluten properties on addition of pentosans to doughs was based on data for only one wheat cultivar. Using three wheat cultivars, Scipion, Soissons and Amazon, differing in technological quality from weak to strong we have obtained results that support the previous explanation. In addition to standard techniques for characterizing gluten and glutenin macropolymer (GMP) yield, composition and properties, a new technique (particle size analysis) was applied that provides further detail on GMP particle size distribution. For each of the three wheat cultivars the effect of WUS and xylanase on gluten and GMP yield, composition and properties followed the trend previously observed. However, WUS and xylanase affected gluten yield and properties more strongly for Scipion and Soissons than for Amazon. Amazon flour contains more protein and less pentosans. The analysis of GMP particles demonstrates that the volume surface average particle diameter D_3,2 of GMP particles from Amazon wheat is larger than those from Scipion and Soissons. Amazon has the ability to form larger and stickier particles. These factors may explain why the effects of pentosans and xylanase on gluten yield and properties are smaller for this wheat.     

麦茬复种饲料油菜的播种量对其生长性状的影响

通过田间小区试验，研究在麦茬复种条件下，不同播量的油菜株高、鲜重、干重、叶面积指数和净同化率的动态变化规律。结果表明，麦茬复种油菜地上生物产量的累积规律为幼苗期缓慢，蕾薹期最快，开花后减缓，基本符合“S”型生长曲线。高密播种能极显著提高复种油菜地上部干重、鲜重及其日生长量，以播量11.5kg/hm2处理为最优。增加播种量能明显提高复种油菜叶面积指数以及群体同化率。不同播种密度下，油菜生长期与其生长指标数学方程拟合为：干重y = k/(1+ae-bx)，叶面积指数y = a+bx+cx2，其它指标均为y = a+bx+cx2+ dx3，其拟合度均达极显著性水平。     

Thermal transitions of the amorphous polymers in wheat straw

The thermal transitions of the amorphous polymers in wheat straw were investigated using dynamic mechanical thermal analysis (DMTA). The study included both natural and solvent extracted wheat straw, in moist (8-9% water content) and dry conditions, and was compared to spruce samples. Under these conditions two transitions arising from the glass transition of lignin and hemicelluloses have been identified. Key transitions attributed to softening of lignin were found at 53, 63 and 91 °C for moist samples of wheat straw, extracted straw and spruce, respectively. Transitions for hemicelluloses were determined at 2, −1 and 5 °C, respectively. Differences are likely due to different compositions of lignin and hemicelluloses from straw and spruce and structural differences between the raw materials. The high wax content in wheat straw resulted in a transition at about 40 °C which was absent in solvent extracted wheat straw samples and spruce. This specific transition was further investigated and confirmed by differential scanning calorimetry (DSC) of extracted wheat straw wax. Information about the thermal transitions is of great importance for the utilization of wheat straw in pelletizing, briquetting and fiber board manufacturing.     

Intrinsic influence of various plasticizers on functional properties and reactivity of wheat gluten thermoplastic materials

Various compounds, differing in their chemical functions, number of functional group and degree of hydrophobicity, were tested as wheat gluten plasticizers in a thermoplastic process. A low melting point and a moderate hydrophobicity were found to be critical characteristics of a good wheat gluten plasticizer. The influence of five selected plasticizers (water, glycerol, 1,4-butanediol, lactic and octanoic acids) on functional properties of the wheat gluten network was investigated. Dried gluten was used to avoid any plasticization due to hydration water (usually around 10% for commercial gluten). The influence of plasticizer properties and content was studied by dynamic mechanical thermal analysis, size exclusion-high performance liquid chromatography, tensile and water swelling tests. The plasticizing effect, at the same molar content, was found to be identical for water, glycerol and 1,4-butanediol. Lactic and octanoic acids were found to have higher and lower plasticizing effects, respectively. Mechanical properties were mainly related to the thermoplastic state of the materials. Water and lactic acid were found to confer smaller and larger extensibilities, respectively, to gluten materials. Thermo-mechanical reactivity also depended on plasticizer properties. Gluten aggregation, normally induced by heating, was prevented by the acidic environment produced by lactic acid. Water swelling behaviour was found to depend on the hydrophobicity of the plasticizer used, on the degree of gluten crosslinking and on the pH of the gluten-plasticizer blend.     

Effect of wheat bran and enzyme addition on dough functional performance and phytic acid levels in bread

Effects of bran concentration, bran particle size distribution, and enzyme addition – fungal phytase, fungal alpha-amylase – on the mixing and fermentative behaviour of wheat dough and on the amount of phytic acid remaining in bread have been investigated using a factorial design of samples 2⁴. Bran concentration and bran particle size significantly affected all Farinograph parameters, whereas enzyme effects were particularly observed on both the water absorption of the flour and the parameters characterizing the overmixing. Water absorption was maximized in doughs with higher fine bran addition and/or in doughs with no enzymes, and was minimized in blends containing coarse added bran and alpha-amylase and/or alpha-amylase and phytase. alpha-Amylase addition had a significant positive effect on dough development and gassing power parameters during proofing. At low bran addition, phytate hydrolysis takes place to a greater extent than at high bran addition levels. Combination of bran with amylolytic and phytate-degrading enzymes could be advisable for overcoming the detrimental effect of bran on the mineral availability (phytase) or on the technological performance of doughs (alpha-amylase).     

Effect of lipases on the surface properties of wheat straw

Surface characteristics of untreated and lipase-treated wheat straw (WS) have been investigated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and SEM–Energy dispersive X-ray spectroscopy (SEM–EDX). Static contact angle of WS surface was determined by the pendant drop method. The WS thermal stability was also investigated using the thermogravimetric analysis (TGA). It was shown that the lipases from Candida cylindracea insignificantly changed the chemical group, microscopic morphology, and wettability of the WS inner surface. However, FTIR showed the lipases could effectively remove the hydrophobic lipophilic extractives and silica from the outer surface of untreated WS, and increased the hydroxyl group content in the outer surface. SEM images also exhibited the lipases stripped off the dense hydrophobic layer on the WS outer surface with the help of shear force. SEM–EDX analysis showed that the lipase treatment reduced Si content on the WS outer surface from 12.44 to 1.33%. The water contact angle of the WS outer surface decreased from 92.7° to 65.2° after lipase treatment, which indicated that the wettability of the lipase-treated WS outer surface was equivalent to that of the inner surface with a water contact angle of about 63°. Lipase-treated and untreated WS had a similar thermal stability. Therefore, the lipase treatment was one of the potential methods to improve the wettability of natural fibers in composite material processing. Comparative testing of particleboards produced from the whole WS untreated and treated by the lipases is under way to evaluate the overall effects of the lipase treatment on the improvement in their mechanic performances.