Viscoelastic characterization of glutenins in wheat kernels measured by creep tests

The effect of high and low molecular weight glutenin subunits on viscoelastic properties of wheat kernels was investigated using creep tests with generalized Kelvin–Voigt model (r² ≈ 0.94; P < 0.0001). Glu-A1, Glu-B1 and Glu-D1 affected the creep coefficients in Glu-1 loci. Regarding LMW-GS, the locus Glu-A3 had highest influence on creep followed by Glu-B3; Glu-D3 did not showed differences. In general, the modulus of elasticity E₀ ≈ 242 MPa and viscosity was μ₀ ≈ 1.6 × 10⁷ MPa·s. Higher elastic moduli and viscosity were found in HMW-GS and LMW-GS of good quality compared to the poor quality performance genotypic groups. Samples with subunit Glu-A1 null presented lower elastic modulus and viscosity compared to Glu-A1 1 and 2^∗. Glu-B1 13 + 16 presented higher elastic modulus and viscosity, which is associated with good quality performance. The elastic moduli, especially E₀ were positively correlated with SDS-volume and rheological properties. This methodology can be applied to few kernels is easy, rapid, and nondestructive.     

Lesser known sources of protein in some Nigerian peasant diets

The proximate mineral composition and indispensable amino acid pattern were determined for samples of Snail (Vivapara quadrata), periwinkle (Littorina littorea), crayfish (Palamonetes varians) and some locally smoked fresh water fish (Pisces spp.).The crude protein contents of smoked fish, crayfish, snail and periwinkle were 75·31, 74·84, 65·29 and 60·93% dry matter, respectively. These values were 56·9, 54·9, 35·2 and 26·1%, respectively higher than that of whole hen's egg. All the samples, except snail, also had higher ash values. Whole hen's egg, however, contained more crude fat (40·23%) and gross energy (34·74 Kj/g) than the test samples.The minerals calcium and phosphorus were higher in the test samples than in whole hen's egg. Samples analysed contained higher amounts of tryptophan than whole hen's egg and, with the exception of snail, the samples also contained more lysine. The test samples have high chemical scores ($\text{A}\text{E}$ ratios). Comparison has also been made of the indispensable amino acid patterns of these samples with those of cow's milk, human milk and the FAO (1957) provisional pattern.     

Thermal and rheological properties of tapioca starch gels with and without xanthan gum under cold storage

Changes in the thermal and rheological properties of tapioca starch (TS) with and without xanthan gum (Xan) (total polysaccharide concentration = 25% w/w) were investigated using a differential scanning calorimeter, Rheolograph Gel and Texture Analyser. The gelatinization temperatures of TS shifted to higher values with the Xan concentration. Xan enhanced the retrogradation of TS during the initial stage of storage but retarded the process for a further storage time at 5 °C. The onset temperature of all reheated TS/Xan gels decreased with increasing storage time indicating thermally unstable structure formation after a longer storage time. Storage Young’s moduli (E′) of the TS and TS/Xan gels stored at 5 °C increased with increasing storage time. The E′ values became more temperature dependent with storage time due to the weak cross-linkage of amylopectin molecules in the gels but became less dependent in the system containing Xan. TS/Xan gels kept for 14 days showed lower Young’s moduli than TS gels from the compression test confirming retardation of the retrogradation process by Xan. The results suggested that Xan could retard the retrogradation of TS gels for longer storage times.     

Impact of combined ascorbic acid/CaCl2, hydrogen peroxide and ultraviolet light treatments on structure,rheological properties and texture of fresh-cut pear (William var.)

This work aimed to evaluate and correlate rheological properties (dynamic oscillatory, creep/recovery and double compression tests), texture (sensory evaluation) and structure (optical and transmission electron microscopy observations) of fresh-cut pear as affected by ascorbic acid/CaCl₂ dipping, hydrogen peroxide and short-wave ultraviolet light radiation (UV-C). All pear samples showed a solid behavior (G′ > G’’), but both dynamic moduli decreased in response to the treatments. For treated tissues, the instantaneous elastic (J₀) and the retarded (J₁, J₂) compliances increased, while the steady-state viscosity (η_N) and all mechanical parameters decreased. PLS regression models revealed that texture could be well explained by rheological properties. Deformability modulus (E_d) was positively correlated to sensory fracturability and hardness and negatively correlated to juiciness. J₀, J₁ and J₂ were negatively related to sensory hardness. Compression and creep parameters evidenced changes in structure (mainly rupture of membranes, degradation of middle lamella and cell walls) of surface tissues.     

Textural changes of Canestrello Pugliese cheese measured during storage

The changes in the fundamental textural properties of the Canestrello Pugliese cheese, during ripening, were studied, accounting for the internal and external portions of the cheese. The cheese was ripened at 12–14 °C and 80% relative humidity and analyzed at 0, 15, 30, 45, 60, 95, and 120 days to determine the moisture content, water activity (A_w), pH values and some fundamental-mechanical and dynamic-mechanical properties such as the elastic modulus (E_c), storage modulus (G′), loss modulus (G″) and relaxation times distribution curve. Significant differences in the moisture content, A_w, pH and the elastic modulus were observed for the inside and outside portions of the investigated cheese. In particular, for the first 60 days of ripening the elastic modulus of the outer region was higher than that of the inner region. As the ripening process approached the end of the fourth month the contrary was true. Moreover, results show that, above all the pH and A_w play a major role in determining the mechanical properties of the Canestrello Pugliese cheese during ripening.     

Compaction and relaxation characteristics of single compacts produced from distiller’s spent grain

Compaction and relaxation characteristics of densified distiller’s spent grain compacts produced at different levels of compressive pressure (60.3–135.7 MPa), initial moisture content (15%, 20% and 25% wb) and soluble content (15% and 30%) were analyzed during the study. The compaction levels used in this study caused up to a 4% wb reduction in the moisture of compacts in comparison to their initial moisture. The density of compacts was analyzed to determine the compaction characteristics of distiller’s spent grain using Jones model. Analysis of the Jones model showed that there was a significant (P = 0.004) decrease in compressibility with an increase in soluble content from 0% to 30%. The distiller’s spent grain compacts were subjected to relaxation tests and the relaxation data obtained were normalized and analyzed to determine the asymptotic modulus (E_A) of the compacts. The asymptotic modulus was used as a measure of rigidity of the compacts. Distiller’s spent grain compact produced with a compressive force of 135.7 MPa and initial moisture of 25% wb possessed the highest E_A value.     

Comparison of Transparent Gels with Turbid Gels Prepared from Egg White: Creep Analysis of Gels

Egg white from which the precipitate occurring during dialysis against water had been removed gave a transparent gel on heating at lower salt concentrations and pH 3.54. The addition of NaCl or a shift of pH from 3.54 to 4.50 brought about the turbid gels. Creep analyses of these transparent and turbid gels were done using a four-element mechanical model. The instantaneous elastic modulus, E₀, Newtonian modulus, ηn and retarded viscoelastic moduli, E₁ and η₁ increased with NaCl up to 125 mM and then decreased with increase in NaCl concentration at pH 3.54. At 125 mM NaCl and pH 3.54, a translucent gel was obtained. E₀ and η₁ decreased with the temperature of the gel, while E₁ and η₁did not change depending of temperature.     

Acid gelation of low acyl gellan gum relevant to self-structuring in the human stomach

The aim of this study was to investigate the in vitro acid-induced gelation of low acyl gellan gum. Various metabolically relevant pH environments and hydrocolloid concentrations were investigated. These resulted in very different acid structures, which were characterised by texture analysis, with Young’s and bulk moduli and work of failure being reported. The structures of the acid gels were shown to depend upon the pH and hydrocolloid concentration (c) used during their production, with a maximum in gel strength between pH 3 and 4. Both the Young’s and bulk moduli data suggest that there is a critical concentration for gelation to occur, and both parameter values displayed a gradual increase (which appears to be lower than a c² dependency) as the gellan concentration was increased.     

Dynamic rheological properties and bread‐making qualities of wheat gluten: effects of urea and dithiothreitol

Controlled stress rheometry differentiated glutens from the cultivars under study into ‘extra‐strong’, strong and weak on the basis of their elastic and viscous moduli measured in the linear domain. The mechanical spectra of different glutens revealed no qualitative differences, but exhibited large quantitative differences in the magnitude of the dynamic measurements, ie elastic modulus, G′, viscous modulus, G″, and loss tangent, tanδ. Both covalent and non‐covalent interactions appeared to contribute to these differences. However, disulfide cross‐links proved to be especially important determinants of differences in the elastic characteristics of the glutens. The present study indicated that dynamic rheological parameters of glutens were related to their bread‐making performance, as evidenced by the significant correlations between the dynamic moduli of the glutens and loaf volume. Copyright © 2004 Society of Chemical Industry     

Fatty acid composition of egg yolk phospholipid fractions following feed supplementation of Lohmann Brown hens with humic-fat preparations

The effect of feed supplementation with humic-fat preparations on the fatty acid composition of egg yolk phospholipid fractions was studied. The Lohmann Brown was the experimental hen strain and two feeding mixtures were applied – the standard feed and the mixture supplemented with humic-fat preparations. The fatty acid profile of yolk lipids was significantly affected (P = .05) by the supplementation of feed and total increase of n-3 polyunsaturated fatty acids (PUFA) was established. A different distribution of n-3 PUFA in egg yolk lipid fractions was observed: α-linolenic acid (18:3) was found in the triacylglycerol fraction, whereas docosahexaenoic acid (22:6) was detected in the phospholipid fractions. Supplementation of the hen’s diet with humic-fat preparations resulted in the production of n-3 enriched eggs with decreased n-6/n-3 ratio in all phospholipid fractions in comparison to the eggs from the control group.     

Creep of wood under a large span of loads in constant and varying environments

Theoretical study was made on the basis of experimental data that were obtained under both linear and nonlinear load magnitudes as presented in a previous paper. Creep compliances and the nonlinear strees functiong were determined for wood specimens of different elastic moduli. It was observed that they both were larger for wood of smaller elastic modulus. A model was proposed which gives satisfactory decriptions of the creep behaviour of wood under a large range of loading magnitude in complex varying environment. The values and the dependence on some important quantities of the mechano-sorptive coefficients used in the model were determined. The coefficients, which may be regarded as a measure of the intensity of the mechano-sorptive effect, increased with the rise of the load magnitude as well as with the fall of elastic modulus.     

Activation energy measurements in rheological analysis of cheese

Activation energy of flow (E_a) between 30 and 44 °C was calculated from temperature sweeps of cheeses with contrasting characteristics to determine its usefulness in predicting rheological behavior upon heating. Cheddar, Colby, whole milk Mozzarella, low-moisture part-skim Mozzarella, Parmesan, soft goat, and Queso Fresco cheeses were heated from 22 to 70 °C, and E_a was calculated from the resulting Arrhenius plots. Protein and moisture content were highly correlated with E_a. The E_a values for goat cheese and Queso Fresco, which did not flow when heated, were between 30 and 60 kJ mol^?1. Cheddar, Colby, and the Mozzarellas did flow upon heating, and their E_a values were between 100 and 150 kJ mol^?1. Parmesan, the hardest cheese, flowed rapidly with heat and had an E_a > 180 kJ mol^?1. E_a provides an objective means of quantitating the flow of cheese, and together with elastic modulus and viscous modulus provides a picture of the behavior of cheese as it is heated.     

Separation and identification of hen egg protein isoforms using SDS–PAGE and 2D gel electrophoresis with MALDI-TOF mass spectrometry

Knowledge of the chemical composition and physicochemical properties of native egg white and yolk is necessary to interpret the functional and biological properties attributed to specific egg components. To date, many of the proteins located in this complex biological fluid remain uncharacterised, if not unknown. High-resolution techniques for proteome analysis, including SDS–PAGE and 2-dimensional (2D) gel electrophoresis, combined with mass spectrometry, were employed to separate and identify several protein components in hen’s egg. An advanced and sensitive glycoprotein staining kit was used to detect the presence of glycosylated proteins in the egg samples. Numerous spots were revealed when a mixture of egg white and yolk was subjected to 2D gel electrophoresis. Several of the already known egg proteins were identified. Isoforms of ovalbumin and conalbumin were visualised. The presence of FLJ 10305 and Fatso proteins in the proteome of Gallus domesticus was also confirmed.     

The effect of climate variations on glulam—an experimental study

Climate variations affect timber structures by causing moisture induced stresses which may lead to cracks in timber members. The paper presents experimentally determined moisture induced stresses that arise perpendicular to the grain of glulam specimens during exposure to 1-dimensional drying and wetting. Although to a certain extent reduced by creep effects, the determined tensile stresses can significantly exceed the characteristic tensile strength of glulam. Additional measurements of moduli of elasticity (E) and hygroexpansion coefficients (α) revealed that these parameters are strongly affected by the geometrical configuration (pith locations) of the specimens. By means of all the parameters determined here, it can be avoided that parameters have to be selected from different literature sources, which introduces large uncertainties into the numerical simulations.     

Effect of protein denaturation degree on texture and water state of cooked meat

We prepared cooked meat with varied denaturation degrees that were predicted based on 3D finite element heat transfer analysis and reaction kinetics. Using a meat sample with a clear denaturation distribution, we performed stress-relaxation measurements to obtain the elastic modulus and identified the state of water in the meat by using proton magnetic resonance imaging (¹H MRI) for quantification of a transverse relaxation time (T₂). Even after the complete denaturation of myosin, the elastic modulus did not exceed 14 kPa, which is not large compared with 6 kPa for unheated meat. However, when actin denaturation was initiated, the elastic modulus dramatically increased while the T₂ value at the meat surface remarkably decreased. The difference in the state of water between the surface and the core reflected the uneven denaturation distribution in the meat caused by heating. When actin denaturation was complete, the elastic modulus reached 60 kPa, which was the equilibrium value, and T₂ decreased and its distribution became more flat.     

Interpretation of mechanical spectra of carob fibre and oat wholemeal-enriched wheat dough using non-linear regression models

Oscillation and creep shear tests were applied to test the effect of fibre-rich additions - carob fibre (0-5%) and black oat wholemeal (0-20%) - on the rheological properties of wheat flour dough. Interpretation of changes in the values of the storage modulus (G′) and loss modulus (G″) and the tangent of the phase angle (tan δ) in the function of oscillation frequency (f) was performed on the basis of proposed 3-parameter non-linear regression models. The results of creep measurements were analysed using the 6-parameter Burgers model. Increase in the share of the fibre-rich additions caused the G′(f) and G″(f) curves to shift towards higher values, and steeper slope and stronger bending of the shapes of the curves, while the tan δ(f) curve tended to shift towards lower values. The application of carob fibre and oat wholemeal at rates of 2% and 10%, respectively, caused that the ratio of viscous to elastic properties of wheat flour dough was the least dependent on the shear rate (f). The result of creep tests showed an increase in the instantaneous and retarded moduli of elasticity and the Newtonian viscosity of wheat flour dough with increase in the share of the additions.     

Comparison of moisture-dependent orthotropic Young’s moduli of Chinese fir wood determined by ultrasonic wave method and static compression or tension tests

Wood with distinctively different properties in the longitudinal, radial and tangential directions exhibits a strong moisture-dependent material characteristic in the elastic range. The purpose of this study was to analyze the orthotropic elastic properties of Chinese fir wood [Cunninghamia lanceolata (Lamb.) Hook] determined at different moisture conditions using an ultrasonic wave propagation method. The results were compared with those obtained by the traditional static compression or tension tests. The results confirm that the stiffness coefficients obtained by the ultrasound without considering the complete stiffness matrix show significantly higher values than the compression or tension Young’s moduli in all the three anatomical directions at each specific MC. The differences between stiffness coefficients and Young’s moduli were significantly reduced by corrections with Poisson ratio. Only in tangential direction, the Young’s moduli with Poisson ratio correction are statistically equivalent to the Young’s moduli obtained by compression and tension.     

Moisture-dependent orthotropic elasticity and strength properties of Chinese fir wood

Elastic and strength properties are very important material characteristics in mechanical modelling. Due to the anisotropic and hygroscopic nature of wood, a characterization of wood mechanical behavior will require knowledge of its moisture-dependent properties in relation to the three principal axes of anisotropy. The influence of moisture content (MC) on the elastic and strength anisotropy of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook) wood was examined in the present study. Selected parameters, including the anisotropic Young’s moduli, shear moduli, Poisson’s ratios, yield and ultimate stress values in the longitudinal, radial and tangential directions, were determined in compression and tension tests at different moisture conditions. The results indicated that a distinct moisture dependency is exhibited for the elastic and strength behavior of Chinese fir wood. With the exception of some Poisson’s ratios, all investigated elastic and strength parameters were shown to decrease with increasing MC, whereby individual moduli and strength values were affected by the MC to different degrees. The two- and three-dimensional representation of the compliance matrix and the two-dimensional visualization of a yield surface give a valuable overview on the moisture-dependent elastic and strength anisotropy of Chinese fir wood.     

Study of Fundamental Factors Affecting Fabric Surface Protrusion Part II: The Effect of Yarn Bending Rigidity on the Fabric Surface Protrusion

Abstract

This paper reports the results of an investigation on the effects of yarn bending rigidity on fabric surface protrusion. The bending rigidity is regarded as the multiple of the elastic modulus E, and the moment of inertia of the cross-section of the yarn (EI). The study was based on an analytical model adopted from the elastic theory. The experimental results are found to be in reasonable agreement with the theoretical values.     

Viscoelastic properties of wheat gliadin and glutenin suspensions

Linear and non-linear rheological properties of wheat gliadin and glutenin suspensions were investigated at various concentrations. Linear dynamic viscoelastic properties for both gliadin and glutenin were strongly dependent on concentration. For gliadins, the storage moduli (G′), loss moduli (G″), and phase shifts dramatically changed within a narrow concentration range, indicating that gliadin suspension properties changed from viscous to viscoelastic. Glutenins exhibited viscoelastic solid behaviour at all measured concentrations. The non-linear shear viscoelastic properties of gliadin and glutenin also depended on concentration. Viscosities of gliadins displayed shear-thinning behaviour; viscosities for glutenins showed shear-thickening behaviour at low shear rates, and shear-thinning behaviour at higher shear rates. Our results indicate that gliadin’s structure in suspension changes over a small concentration range, and suggest that gliadin is important in adjusting and controlling gluten’s viscoelastic behaviour, and not only as a diluent of gluten’s functional properties.