Asclepias syriaca L., the common milkweed, is a new industrial crop. The seed contains about 20-30 wt % of a highly unsaturated oil having unusual fatty acids. Exploring value-added products from the oil, milkweed triglycerides have been oxidized by in situ performic acid to the polyoxirane and polyhydroxy triglycerides (PHTG). The rheological properties of milkweed PHTG were characterized in various shear flows. Milkweed PHTG displayed nonlinear viscoelastic behavior at applied strains greater than 1%. Milkweed PHTG was found to obey time-strain separability. A nonlinear Wagner constitutive model was used successfully to qualitatively predict the behavior of milkweed PHTG in both start-up and cessation of steady-state shear flow. 相似文献
Flour and doughs represent rheologically complex materials whose properties are dependent on many factors including processing conditions. To avoid some of the problems associated with the rheological characterization of dough, we have initiated a study focused on the rheological properties of one of the major components of dough, vital wheat gluten. Suspensions of vital wheat gluten were prepared with concentrations of 225–325 mg/mL.The moduli of the gluten suspensions was 0.2 Pa at 225 mg/mL to 37 Pa at 325 mg/mL. At <250 mg/mL, the gluten suspensions exhibited fluidlike behavior. The crossover frequency, (G′[ω] = G″[ω]) shifted slightly from 0.5 rad/sec at 225 mg/mL to 0.9 rad/sec at 250 mg/mL. At >300 mg/mL, the gluten suspensions exhibited solidlike behavior. The crossover frequencies were independent of concentration and equal to 100 rad/sec. At <250 mg/mL, the high‐frequency behavior of moduli were proportional to ω3/4, as expected for a semiflexible coil. At >300 mg/mL, the high‐frequency behavior of moduli were proportional to ω1/2, indicating a flexible coil. These results suggest vital wheat gluten suspensions undergo a structural change between 250 and 300 mg/mL. 相似文献
1.?The objectives were to quantify the presence of neurogenic inflammation in 4 regions of the upper digestive tract of anaesthetised ducks (post-pharynx, pseudo-crop, transition between the pseudo-crop and the proventriculus, and proventriculus) after application of HCl stimulation of up to 4?M in the pseudo-crop.
2.?The second objective was to quantify the presence of neurogenic inflammation in the same digestive tract regions as mentioned above during 4 feeding periods of foie gras production (rearing, preparation to force-feeding, and second and last meals of the force-feeding period).
3.?Extravasation increased above a HCl stimulation threshold of 2?M. Furthermore, more extravasation was observed in the proventriculus compared to the other regions (P?
4.?Highest extravasation responses were observed in the proventriculus and the pseudo-crop at the end of the preparation period, and in the proventriculus after the second forced meal, compared with the rearing period (P?
5.?Such a kinetic could be indicative of a relative mildness of the irritant components associated with this feeding practice. 相似文献
Cocoa is a major crop and income source for most farmers and rural households in the Centre, South and South-West regions of Cameroon, where cocoa is generally produced in agroforestry systems. In this country, cocoa-based agroforestry systems (CBAFS) are undergoing multiple changes alongside the rapid changes underway in the natural, economic and socio-political conditions. This study—carried out in the Akongo subregion in central Cameroon—was designed to gain insight into the CBAFS trends and dynamics in the light of those multiple changes. This semi-structured socioeconomic survey involved interviews and direct observations at plot, farm, household and village scales. Overall, forty cocoa growers from ten villages were interviewed and then fifteen cocoa plots were characterized on the basis of the survey findings. They revealed that cocoa was the major crop in this study area, with cocoa plantations occupying three quarters of the total farming area. Three types of CBAFS were identified, which differed according to their vegetation structure, management practices and age of the plantations. Dynamics affecting the structural characteristics and the spatial extension of these systems emerged and were intimately linked to the dynamics of the cocoa farmer population in relation to their context.
Cellulosic fiber gel substances were prepared from maize hulls by chemically and physically treating the pericarp cell‐wall substrate in a multistage process to disintegrate morphological cellular structure. Thermal alkaline degradation was used with impact shear in the first stage, followed by alkaline peroxidation and shear in the second stage. The degradation products were removed in the liquid supernatants at each stage. The maize fiber gels are characterized by high viscosities and hydration capacities. After drying, they can be reconstituted to the original gel form by using shear forces. The fiber gels were also dried together with hydrophilic materials to more easily reconstitute the gel form. The alkaline‐extracted hemicellulose effluents from the fiber gel preparation, including the second stage peroxidized extract, were purified and used as hydrophilic material. Oat flour hydrolyzate, an amylodextrin, also was used as a hydrophilic material. The physical properties of the gels were characterized by scanning electron microscopy and rheological evaluations. 相似文献
Nutrim is a newly developed food product containing dietary soluble fiber β‐glucan. The microstructural heterogeneities of Nutrim‐10 suspensions were investigated by monitoring the thermally driven displacements of well‐dispersed microspheres through video fluorescence microscopy. By comparing the distribution of the time‐dependent mean‐square displacement (MSD) of polystyrene microspheres embedded in three concentrations of Nutrim‐10 suspensions, we found that the degree of heterogeneity of suspensions increased dramatically within a narrow range of Nutrim‐10 concentrations. The ensemble‐averaged MSD of 5.5% Nutrim‐10 suspension exhibited a power‐law behavior scaling linearly with time, which was similar to the behavior for a homogeneous aqueous glycerol solution. But the MSD distribution was wider and more asymmetric than for glycerol. Increasing Nutrim‐10 concentration rendered the MSD distribution much more asymmetric and skewed. This study provided a quantitative method to characterize the organization of Nutrim‐10 in suspension. 相似文献
The solution rheological behaviors of OATRIM-10 and cooked oat bran were investigated. The rheological properties of the materials were investigated using both thixotropic loop and small-amplitude oscillatory shear experiments. The cooked oat bran exhibited shear-thinning behavior during a thixotropic loop experiment over a shear rate range of 0–250/sec. The shear-thinning behavior was reproduced during the measurement of a second thixotropic loop. In contrast, OATRIM-10 exhibited an unexpected region of shear-thickening behavior at 20–80/sec. The shear-thickening and subsequent shear-thinning regions for OATRIM-10 could be described by a transient network model indicating that the shear-thickening behavior is caused by a shear-induced entangled network that is partially disentangled at higher shear rates. Subsequent thixotropic loop experiments displayed the shear-thickening region for OATRIM-10, indicating that the network structure can be reformed during the imposition of a shear field. Small-amplitude oscillatory shear data for cooked oat bran can be described reasonably well using a generalized linear viscoelastic (GLV) model. The oscillatory shear data obtained for OATRIM-10 could not be described by the GLV model. OATRIM-10 exhibited a distinctive plateau centered at 10/sec, and the low frequency response of storage modulus G′ decreased with a much larger slope in frequency than was predicted by the GLV model. 相似文献
Cake shortening contents were replaced with Nutrim oat bran (OB) and flaxseed powder, and the effects of these substitutions on the physical and rheological properties of cakes were investigated. Cakes with shortening replaced up to 40% by weight possessed a volume similar to that of the control cake produced with shortening. Replacement using Nutrim OB and flaxseed powder revealed significant color changes in both the cake crust and crumb. At high levels of substitution, the cake crust became lighter, while the crumb darkened. At >40% by weight substitution with either Nutrim OB or flaxseed, the cakes displayed increased hardness; however, cohesiveness and springiness increased gradually with increasing substitution. Increased substitution with Nutrim OB caused an increase in the measured shear viscosity and oscillatory storage and loss moduli of the cakes. Increased substitution with flaxseed caused decreases in these rheological parameters. Additional rheological experiments were performed to elucidate changes in the formulations during the baking process and indicated an increase in the elasticity of the baked batter with decreasing shortening. 相似文献
The entanglement molecular weights of waxy maize (WM) and normal maize (NM) starches were calculated from solution rheological data. The viscoelastic behavior of both WM and NM starches were measured at several different concentrations and then shifted to produce a master curve for each of the materials. The theory of Doi and Edwards was used to calculate the plateau moduli from which values for the entanglement molecular weights for WM and NM starches were calculated. The entanglement molecular weights were 100 ± 15 kg/mol for WM starch and 96 ± 8 kg/mol for NM starch. These two values were within experimental error of one another and represent the entanglement molecular weight of amylopectin, the major component of WM and NM starches. The entanglement degrees of polymerization for WM and NM starch, using a value of 162 g/mol for the monomer molecular weight of amylopectin, were 617 ± 92 and 592 ± 49, respectively. The values for the entanglement molecular weight and the entanglement degrees of polymerization for WM and NM starch were markedly higher than those quoted for many commercial polymers. This finding indicates that molecular weights of >1 million are required to produce starch-based materials with consistent physical properties. 相似文献
