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.     

Preparation and properties of thermo-molded bioplastics of glutenin-rich fraction

The present work aims to prepare bioplastics from a glutenin-rich fraction; that is, the gluten residue insoluble in 70% (v/v) ethanol. The influence of reducing agents of sodium bisulfite, sodium sulfite and thioglycolic acid on the properties of the glycerol plasticized doughs and the cross-linked bioplastics were investigated. The results showed that reducing agents can be applied to reduce the Young's modulus of the plasticized dough and to improve the Young's modulus of the cross-linked bioplastics. Moisture absorption, weight loss in water, tensile strength, elongation at break and tensile set were studied to characterize the physical properties of the cross-linked bioplastics.     

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.     

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.     

Rheological and mechanical properties of bioplastics based on gluten- and glutenin-rich fractions

The present work aims to investigate the dynamic rheology at small strains and the equibiaxial extensional deformation at large strain of the glycerol plasticized dough of gluten- and glutenin-rich fractions and their mixture as well as the uniaxial tension deformation behavior of the compression molded bioplastics. The influence of glutenin-to-gluten ratio (GGR) on the rheological properties of the glycerol plasticized doughs and the crosslinked bioplastics were investigated. The results showed that the glutenin dough exhibits higher moduli and lower loss factor and equibiaxial deformability in comparison with the gluten dough. Addition of a glutenin-rich fraction to the gluten dough can improve elasticity at small deformation and extensional deformational stress at large deformations but result in reductions in extensibility of the compression molded bioplastics.     

Rheological and mechanical properties of bioplastics based on gluten- and glutenin-rich fractions

The present work aims to investigate the dynamic rheology at small strains and the equibiaxial extensional deformation at large strain of the glycerol plasticized dough of gluten- and glutenin-rich fractions and their mixture as well as the uniaxial tension deformation behavior of the compression molded bioplastics. The influence of glutenin-to-gluten ratio (GGR) on the rheological properties of the glycerol plasticized doughs and the crosslinked bioplastics were investigated. The results showed that the glutenin dough exhibits higher moduli and lower loss factor and equibiaxial deformability in comparison with the gluten dough. Addition of a glutenin-rich fraction to the gluten dough can improve elasticity at small deformation and extensional deformational stress at large deformations but result in reductions in extensibility of the compression molded bioplastics.     

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.     

Feather meal-based thermoplastics: Methyl vinyl ether/maleic anhydride copolymer improves material properties

The poultry meat processing industry produces large amounts of feather meal, which is traditionally used as lowvalue plant fertilizer or fish nutrient. A higher value application for feather meal is described in this paper - a thermal blending and compression molding method to create compostable composites out of environmentally friendly materials: feather meal, glycerol, and a biodegradable copolymer of methyl vinyl ether and maleic anhydride (MVEMA). The composite’s mechanical, microstructural and chemical characteristics are described. Feather meal plasticized only with glycerol is mechanically fragile, with average tensile strength of 1.7 MPa, Young’s modulus of 296 MPa and strain-at-failure of 0.6 %. With the addition of MVEMA copolymer, feather meal is transformed into a ductile plastic composite, with tensile modulus reduced 2- to 5-fold and strain-at-failure increased 4- to 25-fold. These properties are ideal for creating feather mealbased compostable bioplastics for agricultural and industrial applications.     

Facilitation of α-polylysine in TGase-mediated crosslinking modification for gluten and its effect on properties of gluten films

In this study, α-polylysine was used to enhance the cross-linking effect of TGase on gluten and its effects on properties of gluten films were investigated. The amount of free ammonia released from the cross-linking reaction of gluten induced by TGase at the presence of α-polylysine obviously increased, and more polymers with higher molecular weight were formed from the SDS-PAGE results, which indicated that the TGase-mediated cross-linking reaction ability of gluten was strengthened with the incorporation of α-polylysine. The tensile strength of the films from gluten modified with TGase (20 units/g wheat gluten) and 2% α-polylysine (g/g gluten) for 3 h increased from 4.02 ± 0.09 MPa to 5.28 ± 0.14 MPa, which was more effective than that treated with TGase alone (in which the tensile strength of the films was 4.49 ± 0.10 MPa). The TGase treatment with α-polylysine of gluten improved the water stability of the films much more than that treated with TGase alone. A rougher surface and a more compact cross-section structure were observed by SEM for the films from TGase-α-polylysine treated gluten. The contact angles between the gluten films surface and a water droplet increased because of TGase-mediated cross-linking modification.     

Thermoplastic films from wheat proteins

We show that the wheat proteins gluten, gliadin and glutenin can be compression molded into thermoplastic films with good tensile strength and water stability. Wheat gluten is inexpensive, abundantly available, derived from renewable resource and therefore widely studied for potential thermoplastic applications. However, previous reports on developing thermoplastics from wheat proteins have used high amounts of glycerol (30-40%) and low molding temperature (90-120 °C) resulting in thermoplastics with poor tensile properties and water stability making them unsuitable for most thermoplastic applications. In this research, we have developed thermoplastic films from wheat gluten, gliadin and glutenin using low glycerol concentration (15%) but high molding temperatures (100-150 °C). Our research shows that wheat protein films with good tensile strength (up to 6.7 MPa) and films that were stable in water can be obtained by choosing appropriate compression molding conditions. Among the wheat proteins, wheat gluten has high strength and elongation whereas glutenin with and without starch had high strength and modulus but relatively low elongation. Gliadin imparts good extensibility but decreased the water stability of gluten films. Gliadin films had strength of 2.2 MPa and good elongation of 46% but the films were unstable in water. Although the tensile properties of wheat protein films are inferior compared to synthetic thermoplastic films, the type of wheat proteins and compression molding conditions can be chosen to obtain wheat protein films with properties suitable for various applications.     

Structure and properties of methylcellulose microfiber reinforced wheat gluten based green composites

Environmentally friendly green composites were prepared by conventional blending wheat gluten (WG) as matrix, methylcellulose (MC) microfibers as filler and glycerol as plasticizer followed by compression molding of the mixture at 127 °C to crosslink the matrix. Morphology, dynamic mechanical analysis (DMA), tensile properties (Young’s modulus E, tensile strength σ_b and elongation at break ?_b), and moisture absorption (MA) and weight loss (WL) in water as well as thermogravimetric analysis (TGA) were evaluated in relation to MC content. It was found that addition of MC microfibers can significantly improve E and σ_b of the composite, which is accompanied by rises in glass transition temperatures of the WG matrix. Influences of MC content on the thermal decomposition and gluten solubility (GS) in water are also discussed.     

The impact of redox agents on sugar-snap cookie making

The impact of the oxidants potassium bromate and potassium iodate and the reducing agents L-cysteine, glutathione and sodium metabisulfite on sugar-snap cookie making was investigated. Spread behavior of cookie dough during baking (spread rate, set time and collapse) was monitored and texture properties of the baked cookies were determined. Low levels of redox agents impacted neither dough nor cookie properties. High levels of reducing agents (10,000 ppm on a flour base) significantly decreased set time, and, hence, cookie diameter. They also decreased the degree of collapse, which then, evidently, also increased cookie height. Earlier setting and higher resistance to structural collapse, but also the higher intrinsic break strength of the cookie material when adding high levels of reducing agents could be explained on a molecular level as resulting from earlier and more pronounced gliadin–glutenin cross-linking. In contrast, when high levels of oxidizing agents were added, a postponed setting, a more pronounced collapse and decreased intrinsic cookie break strength were observed. The present work demonstrates the importance of heat-induced gluten polymerization during cookie baking and confirms that free sulfhydryl groups are necessary for the polymerization reactions. A model illustrating the role of gluten cross-linking during cookie making is put forward.     

Characteristics of enzymatic hydrolysis of thermal-treated wheat gluten

Effect of thermal treatment at 50–90 °C on wheat gluten hydrolysis by papain was evaluated in this study. Thermal treatment decreased the amount of sodium dodecyl sulfate (SDS) extractable protein. The treatments at 80 and 90 °C had a strong impact on protein extractability. Thermal treatment for 30 min resulted in a significant reduction in SDS extractable glutenin level in wheat gluten. A significant drop in free sulphydryl level was found in wheat gluten treated at 70 °C for 30 min. It indicated that cross-linking of glutenin through S–S occurred during thermal treatment. The treatments at 70–90 °C led to significant decreases in soluble and nitrogen level, while significant increases in peptide nitrogen amount in the hydrolysates from treated gluten were found. A time-dependent effect was observed for the changes in soluble forms of nitrogen and PN. Thermal treatment resulted in molecular mass distribution change according to gel permeation chromatography analysis. Thermal treatment significantly increased the amount of fractions with molecular mass beyond 10 K (67.2%) in the hydrolysates and greatly decreased the amounts of fractions with MM of 10–5 K and below 5 K in hydrolysates.     

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.     

Composite materials of thermoplastic starch and fibers from the ethanol-water fractionation of bagasse

The aim of this study was to evaluate the potential of the fibrous material obtained from ethanol-water fractionation of bagasse as reinforcement of thermoplastic starches in order to improve their mechanical properties. The composites were elaborated using matrices of corn and cassava starches plasticized with 30 wt% glycerin. The mixtures (0, 5, 10 and 15 wt% bagasse fiber) were elaborated in a rheometer at 150 °C. The mixtures obtained were pressed on a hot plate press at 155 °C. The test specimens were obtained according to ASTM D638. Tensile tests, moisture absorption tests for 24 days (20-23 °C and 53% RH, ASTM E104), and dynamic-mechanical analyses (DMA) in tensile mode were carried out. Images by scanning electron microscopy (SEM) and X-ray diffraction were obtained. Fibers (10 wt% bagasse fiber) increased tensile strength by 44% and 47% compared to corn and cassava starches, respectively. The reinforcement (15 wt% bagasse fiber) increased more than fourfold the elastic modulus on starch matrices. The storage modulus at 30 °C (E_30 °C′) increased as the bagasse fiber content increased, following the trend of tensile elastic modulus. The results indicate that these fibers have potential applications in the development of biodegradable composite materials.     

In vitro release of angiotensin-converting enzyme inhibitors, peroxyl-radical scavengers and antibacterial compounds by enzymatic hydrolysis of glycated gluten

The combined effect of gluten glycation and proteolysis on the release of compounds exhibiting in vitro angiotensin-converting enzyme (ACE) inhibitory, antioxidant and antibacterial activities was investigated. Model systems consisting of wheat gluten and glucose were heated at 120 °C for 45 min, 150 °C for 30 min and 220 °C for 30 min to produce various Maillard reaction products mimicking reactions occurring in bread crusts. Progress of the Maillard reaction was estimated through indirect measurement of Amadori compounds as 2-furoylmethyl-amino acids. Glycation was followed by digestion with Pronase E and ultrafiltration. The anti-hypertensive activity was measured as the ability to inhibit the activity of angiotensin I-converting enzyme involved in hypertension regulation. The Oxygen Radical Absorbance assay was used to measure the peroxyl radical scavenging capacity of the products and their effect on microbial growth of Escherichia coli ATCC 25922 and Staphlococcus aureus ATCC 25923 was also studied. Advanced products of the reaction enhanced the antioxidant and antibacterial properties of gluten hydrolysates and decreased the overall ACE inhibitory activity. Ultrafiltration provided a useful method for separating compounds (< 3000 Da) with ACE inhibitory activity and advanced Maillard reaction products (>3000 Da) which scavenged peroxyl radicals and inhibited the microbial growth.     

Green composites. I. physical properties of ramie fibers for environment-friendly green composites

The surface topography, tensile properties, and thermal properties of ramie fibers were investigated as reinforcement for fully biodegradable and environmental-friendly ‘green’ composites. SEM micrographs of a longitudinal and cross-sectional view of a single ramie fiber showed a fibrillar structure and rough surface with irregular cross-section, which is considered to provide good interfacial adhesion with polymer resin in composites. An average tensile strength, Young’s modulus, and fracture strain of ramie fibers were measured to be 627 MPa, 31.8 GPa, and 2.7 %, respectively. The specific tensile properties of the ramie fiber calculated per unit density were found to be comparable to those of E-glass fibers. Ramie fibers exhibited good thermal stability after aging up to 160°C with no decrease in tensile strength or Young’s modulus. However, at temperatures higher than 160°C the tensile strength decreased significantly and its fracture behavior was also affected. The moisture content of the ramie fiber was 9.9%. These properties make ramie fibers suitable as reinforcement for ‘green’ composites. Also, the green composites can be fabricated at temperatures up to 160°C without reducing the fiber properties.     

Wet-milling Factors of Sorghum and Relationship to Grain Quality

Relationships of grain sorghum quality factors (proximate composition and physical properties) to laboratory wet-milling attributes (fraction yields, protein content of fractions and recovery values) of 24 grain sorghum commercial hybrids were determined. Initial water absorption rate was positively correlated with both starch and gluten recoveries (r>0·45), thus showing the greatest significance among all quality factors. The need to understand fully protein matrix breakdown relative to obtaining optimum separation of components was indicated. Positive correlations of residual protein in starch with density and percent abraded (r>0·45) were observed. Laboratory wet-milling attributes also were correlated among themselves. The highest positive correlations were observed among yield and recovery of starch and gluten (r>0·6). These four parameters had strong negative correlations with fiber/germ yield (r<−0·6). Principal component factor analysis identified five factors (named as matrix-breakdown effect, solids-leaching effect, protein-dispersion effect, protein content of gluten effect, and washing-solids effect) that explained 91% of the total variation among wet-milling attributes.