Effect of degree of acetylation on gelation of konjac glucomannan

Effect of the degree of acetylation (DA) on the gelation behaviors on addition of sodium carbonate for native and acetylated konjac glucomannan (KGM) samples with a DA range from 1.38 to 10.1 wt % synthesized using acetic anhydride in the presence of pyridine as catalyst was studied by dynamic viscoelastic measurements. At a fixed alkaline concentration (CNa), both the critical gelation times (tcr) and the plateau values of storage moduli (G'sat) of the KGM gels increased with increasing DA, while at a fixed ratio of alkaline concentrations to values of DA (CNa/DA), similar tcr and values independent of DA were observed. On the whole, increasing KGM concentration or temperature shortened the gelation time and enhanced the elastic modulus for KGM gel. The effect of deacetylation rate related to the CNa/DA on the gelation kinetics of the KGM samples was discussed.     

Stereocontrolled Synthesis of an Octasaccharide Part of I-Active Glycolipids

The effects of glycerin and ethylene glycol on the elastic modulus and DSC thermograms of agarose and kappa-carrageenan gels were examined to clarify the relation between structure and properties. The elastic modulus of these gels as a function of the concentration of polyols increased up to a certain concentration and then decreased with increasing concentration of polyols. These polyols shifted the melting temperature of the gel to higher temperatures in kappa-carrageenan gels but to lower temperatures in agarose gels. The temperature dependence of elastic modulus was changed in opposite directions in agarose and kappa-carrageenan gels by the addition of polyols, and this is discussed on the basis of model consisting of junction zones which are connected by Langevin chains. It was suggested that the mean distance between junction zones became shorter in the presence of a small amount of polyols.     

Viscoelastic properties of f-actin, microtubules, f-actin/alpha-actinin, and f-actin/hexokinase determined in microliter volumes with a novel nondestructive method

A nondestructive method to determine viscoelastic properties of gels and fluids involves an oscillating glass fiber serving as a sensor for the viscosity of the surrounding fluid. Extremely small displacements (typically 1-100 nm) are caused by the glass rod oscillating at its resonance frequency. These displacements are analyzed using a phase-sensitive acoustic microscope. Alterations of the elastic modulus of a fluid or gel change the propagation speed of a longitudinal acoustic wave. The system allows to study quantities as small as 10 microliters with temporal resolution >1 Hz. For 2-100 microM f-actin gels a final viscosity of 1.3-9.4 mPa s and a final elastic modulus of 2.229-2.254 GPa (corresponding to 1493-1501 m/s sound velocity) have been determined. For 10- to 100-microM microtubule gels (native, without stabilization by taxol), a final viscosity of 1.5-124 mPa s and a final elastic modulus of 2.288-2. 547 GPa (approximately 1513-1596 m/s) have been determined. During polymerization the sound velocity in low-concentration actin solutions increased up to +1.3 m/s (approximately 1.69 kPa) and decreased up to -7 m/s (approximately 49 kPa) at high actin concentrations. On polymerization of tubulin a concentration-dependent decrease of sound velocity was observed, too (+48 to -12 m/s approximately 2.3-0.1 MPa, for 10- to 100-microM tubulin). This decrease was interpreted by a nematic phase transition of the actin filaments and microtubules with increasing concentration. 2 mM ATP (when compared to 0.2 mM ATP) increased polymerization rate, final viscosity and elastic modulus of f-actin (17 microM). The actin-binding glycolytic enzyme hexokinase also accelerated the polymerization rate and final viscosity but elastic modulus (2.26 GPa) was less than for f-actin polymerized in presence of 0.2 mM ATP (2.28 GPa).     

Effects of Potassium Chloride and Sodium Chloride on the Thermal Properties of Gellan Gum Gels

The exothermic and endothermic peaks in cooling and heating curves of differential scanning calorimetry (DSC) for gellan gum gels without and with potassium chloride and sodium chloride were analyzed. The gelling and melting temperatures shifted to higher temperatures with increasing gellan and salt concentration in the concentration range of gellan from 0.3 to 2.0% (w/w). The exothermic and endothermic enthalpy increased with increasing gellan and salt concentrations. Cooling DSC curves showed one exothermic peak for samples with salts and at low gellan concentration. Heating DSC curves showed many peaks for all samples except 0.3% (w/w) gellan gum gels. The sol-gel transition of samples was examined numerically by using a zipper model approach. The introduction of cations increases the number of junction zones or zippers and decreases the rotational freedom of parallel links. This makes the structure of junction zones more heat resistant, and increases the elastic modulus of the gel.     

Prediction on elastic properties of Nb-doped Ni systems

On the basis of first-principles simulation, the structure, formation enthalpy and mechanical properties (elastic constant, bulk and shear modulus and hardness) of five Nb-doped Ni systems are systematically studied. The calculated equilibrium volume increases with the Nb concentration increasing. The computational elastic constants and formation enthalpy indicate that all Nb-doped Ni systems are mechanically and thermodynamically stable in our research. The hardness of these systems was predicted after the bulk modulus and shear modulus had been accurately calculated. The results show that the hardness increases with the Nb concentration increasing when the Nb concentration was below 4.9%, beyond which the hardness will decrease; this is within the scope of our study.     

Rheology and gelation of water-insoluble dextran from Leuconostoc mesenteroides NRRL B-523

Dynamic oscillatory testing has been used to study the rheology of water-insoluble dextran. The rheological properties (storage and loss moduli) of dextran gel were measured and dextran was found to be neither a strong gel nor a weak gel, but an entanglement network at a concentration of 250 mg/ml. The extent of gelation, illustrated by the gel elastic modulus G′, is found to decrease with increasing concentration of calcium ions. This was confirmed by shift of crossover frequencies towards higher values on the dynamic spectra and lower yield stress τ values obtained from stress ramp experiments. Finally, a comparison between gelation of dextran and alginate (a similar biopolymer) was made for clear understanding of effect of calcium ions on the dextran gelation.     

Determination of the biological activity of heliomycin by a method of diffusion in agar]

A biological method for determination of geliomycin activity using agar diffusion is described. A nutrient medium containing Hottinger broth up to 35 mg per cent of amine nitrogen, 1.5 percent of agar-agar, tap water, pH 7.8 to 8.0 was used. Bacillus subtilis ATCC 6633 served as the test-culture. Geliomycin was dissolved in 0.1 N sodium hydroxide solution.     

Analysis of hantavirus genetic diversity in Argentina: S segment-derived phylogeny

Nucleotide sequences were determined for the complete S genome segments of the six distinct hantavirus genotypes from Argentina and for two cell culture-isolated Andes virus strains from Chile. Phylogenetic analysis indicates that, although divergent from each other, all Argentinian hantavirus genotypes group together and form a novel phylogenetic clade with the Andes virus. The previously characterized South American hantaviruses Laguna Negra virus and Rio Mamore virus make up another clade that originates from the same ancestral node as the Argentinian/Chilean viruses. Within the clade of Argentinian/Chilean viruses, three subclades can be defined, although the branching order is somewhat obscure. These are made of (i) "Lechiguanas-like" virus genotypes, (ii) Maciel virus and Pergamino virus genotypes, and (iii) strains of the Andes virus. Two hantavirus genotypes from Brazil, Araraquara and Castello dos Sonhos, were found to group with Maciel virus and Andes virus, respectively. The nucleocapsid protein amino acid sequence variability among the members of the Argentinian/Chilean clade does not exceed 5.8%. It is especially low (3.5%) among oryzomyine species-associated virus genotypes, suggesting recent divergence from the common ancestor. Interestingly, the Maciel and Pergamino viruses fit well with the rest of the clade although their hosts are akodontine rodents. Taken together, these data suggest that under conditions in which potential hosts display a high level of genetic diversity and are sympatric, host switching may play a prominent role in establishing hantavirus genetic diversity. However, cospeciation still remains the dominant factor in the evolution of hantaviruses.     

The Time Effect of Auxin and Calcium on Growth and Elastic Modulus in Hypocotyls

The relationship between Young's modulus and longitudinal growth has been studied on growing segments of etiolated sunflower hypocotyls. The modulus was determined by means of the resonance frequency method. IAA in a concentration of 2.8 10^?5 M produces a decrease in the modulus with a time lag of 4 minutes, while an increase in growth is observable only after 6 minutes. Addition of IAA results in a stronger decrease in the modulus if the segments are placed in a solution of 0.1 M mannitol rattier Hum in water. Through plasmometric measurements it has been found that the elastic extensibility is insignificant compared with the growth. After the addition of IAA, there occurs a marked elongation both in 0.1 M mannitol and in water, and at the same time a decrease in the elastic extensibility of the segments is observed. In the growing segments an increased modulus causes an in creased elastic extensibility, a matter which is directly contrary to the relationship found in a physical system with an applied external force. An explanation of this discrepancy has been given. With an excess of calcium the modulus increases, while the elongation decreases. Calcium deficiency implies both a decreased modulus and a decreased growth. With the addition of 10^?3 M Ca(NO₃)₂ to segments raised without calcium the modulus increases after only 10 minutes, while an increase in longitudinal elongation is observable after 30 minutes. With the addition of IAA to the calcium deficient segments the modulus decreases to the same extent as in an optimal supply o f calcium. The results are discussed with reference to other investigations about elasticity and growth. It has been concluded that plastic extensibility cannot he of great importance in longitudinal growth. Time studies of the auxin effect and I he interaction between auxin and calcium have confirmed the hypothesis that one of the primary actions of auxin consists in a loosening of the cell wall matrix. Calcium always increases Youngs modulus and gives the cell wall a more rigid structure. Furthermore, calcium in a certain concentration is necessary for longitudinal growth.     

A study of some factors influencing amylose gelation

Amylose fractions were prepared by aqueous leaching from pea, maize and patato starch granules. The fractions were characterised by iodine binding, β-amylolysis and viscometry. Amylose starts to form a gel rather than a precipitate on cooling aqueous solutions to room temperature at concentrations above the coil overlap concentration C¹. Amylose gels are almost purely elastic, with negligible viscous flow at room temperature. The rigidity modulus is strongly dependent on concentration, c, in that above 1·5% w/w the modulus increases as a function of c⁷. The modulus of a matured gel falls only slightly with increasing temperature; at temperatures below 100°C the gel could not be melted. The non-equilibrium nature of the system is shown by the dependence of rigidity on thermal history. The shear modulus is also dependent on amylose type; higher molecular weight amylose fractions produced less rigid gels at a given concentration.     

Rheological properties of ovalbumin hydrogels as affected by surfactants addition

The gel properties of ovalbumin mixtures with three different surfactants (sodium perfluorooctanoate, sodium octanoate and sodium dodecanoate) have been studied by rheological techniques. The gel elasticities were determined as a function of surfactant concentration and surfactant type. The fractal dimension of the formed structures was evaluated from plots of storage modulus against surfactant concentration. The role of electrostatic, hydrophobic and disulfide SS interactions in these systems has been demonstrated to be the predominant. The viscosity of these structures tends to increase with surfactant concentration, except for the fluorinated one. Unfolded ovalbumin molecules tend to form fibrillar structures that tend to increase with surfactant concentration, except for the fluorinated one. This fact has been related to the particular nature of this molecule.     

Rheology of protein gels synthesized through a combined enzymatic and heat treatment method

Whey protein gels prepared under acidic conditions (pH<4.6) remain largely unutilized because of their weak and brittle nature in contrast to the favorable elastic gels produced at neutral or basic conditions. However, such usage is important, as low pH food products are desirable due to their shelf stability and less stringent sterilization processes. In this study, we use a two-step process involving enzyme followed by heat treatment to produce whey protein gels at low pH (4.0). Dynamic rheological measurements reveal that the gel elastic modulus and yield stress increase substantially when heat treatment is supplemented with enzyme treatment. Both the elastic modulus and yield stress increase with increasing enzyme concentration or treatment time. In contrast, the dynamic yield strain decreases with enzyme concentration but increases with time of enzyme treatment. These results are explained in terms of the enzyme treatment time affecting the diffusion of the enzyme within the gel. This in turn leads to two types of gel microstructure at short and long enzyme treatment times, with the extent of enzyme diffusion modulating the structure at intermediate times.     

Recycling rice straw ash to produce low thermal conductivity and moisture-resistant geopolymer adobe bricks

Rice straw ash (RSA) geopolymer adobe bricks were produced using the geopolymerization reaction among the RSA, soil, and alkaline activator at the Biosystem Engineering Department, Faculty of Agriculture, Alexandria University, Egypt, to optimize adobe brick advantages. The bulk density, water absorption, compressive strength, and thermal conductivity of the new composite were measured at RSA contents of 0%, 5%, 10%, and 20% and sodium hydroxide contents of 2.5%, 5%, 7.5%, and 10% after curing the composite for 28 days. Results indicated that increasing RSA from 0% to 20% increased the compressive strength and decreased the bulk density, water absorption, and thermal conductivity. Further, increasing sodium hydroxide from 2.5% to 10% increased the bulk density and compressive strength and decreased the water absorption. Significant effects of RSA and sodium hydroxide percentages and their interaction on all the studied characters were reported. The best conditions to minimize bulk density, water absorption, thermal conductivity, and optimize compressive strength of the composite were at 10% sodium hydroxide and 20% RSA. The minimum bulk density, water absorption, and thermal conductivity were 1.463 g/cm³, 8.3%, and 0.46 W/(m·K), respectively, while the maximum CS was 2.1 MPa after 28 days. Using RSA geopolymer adobe bricks on building interior walls is recommended to decrease bricks' thermal conductivity, water absorption, and weight.     

Biomechanics of isolated tomato (Solanum lycopersicum L.) fruit cuticles: the role of the cutin matrix and polysaccharides

The mechanical characteristics of the cuticular membrane (CM), a complex composite biopolymer basically composed of a cutin matrix, waxes, and hydrolysable polysaccharides, have been described previously. The biomechanical behaviour and quantitative contribution of cutin and polysaccharides have been investigated here using as experimental material mature green and red ripe tomato fruits. Treatment of isolated CM with anhydrous hydrogen fluoride in pyridine allowed the selective elimination of polysaccharides attached to or incrusted into the cutin matrix. Cutin samples showed a drastic decrease in elastic modulus and stiffness (up to 92%) compared with CM, which clearly indicates that polysaccharides incorporated into the cutin matrix are responsible for the elastic modulus, stiffness, and the linear elastic behaviour of the whole cuticle. Reciprocally, the viscoelastic behaviour of CM (low elastic modulus and high strain values) can be assigned to the cutin. These results applied both to mature green and red ripe CM. Cutin elastic modulus, independently of the degree of temperature and hydration, was always significantly higher for the ripe than for the green samples while strain was lower; the amount of phenolics in the cutin network are the main candidates to explain the increased rigidity from mature green to red ripe cutin. The polysaccharide families isolated from CM were pectin, hemicellulose, and cellulose, the main polymers associated with the plant cell wall. The three types of polysaccharides were present in similar amounts in CM from mature green and red ripe tomatoes. Physical techniques such as X-ray diffraction and Raman spectroscopy indicated that the polysaccharide fibres were mainly randomly oriented. A tomato fruit CM scenario at the supramolecular level that could explain the observed CM biomechanical properties is presented and discussed.     

The material properties of bone-particle impregnated PMMA

The elastic Young's modulus and shear modulus of bone-particle impregnated polymethylmethacrylate (PMMA) has been measured experimentally at room temperature as a function of bone particle concentration. It was found that the moduli increased with increasing bone particle content. This increase was less than the stiffness increase predicted by higher-order composite theory [1, 2] under the assumption of perfect bonding between particles and matrix. It was concluded that a bond existed but that it was not a perfect bond.     

Viscoelastic behavior of cellulose acetate in a mixed solvent system

The effect of increasing water composition on the rheological and microstructural behavior of a ternary cellulose acetate (CA)/N,N-dimethylacetamide (DMA)/water system is examined. Addition of water to the CA/DMA system results in enhanced steady shear viscosity and dynamic viscoelastic properties and ultimately to phase-separated gel formation. The changes in dynamic rheological behavior of the system during gelation correlate well with the combined solubility parameter (delta) and, in particular, the Hansen hydrogen-bonding solubility parameter index (delta(h)) of the solvent system, suggesting hydrogen-bonding interactions may be the major route initiating the sol-gel process. For all gels studied, the elastic modulus and the critical stress to yield shifts to higher values with increasing CA concentration and/or water content. In addition, the elastic modulus exhibits a power-law behavior with water content, with the same power-law exponent observed for gels containing different CA concentrations. Addition of water leads to formation of a denser gel network, as evidenced from direct visualization of the gel microstructure through confocal microscopy.     

Responses of Ceriops Roxburghiana to NaCl Stress

Responses of Ceriops roxburghiana Arn. leaves to the sodium chloride, applied at different concentrations (ranging from 100 to 600 mM), has been evaluated. Total amino acid content decreased with increasing NaCl concentration, while the protein content increased significantly up to 400 mM concentration and decreased thereafter. Total sugar content decreased at concentrations beyond 400 mM. Proline and glycine betaine were accumulated with increasing NaCl concentration. Protease and ATPase activities were increased whereas proline oxidase activity were decreased with increasing salinity. Peroxidase and malate dehydrogenase (NADH-MDH) activities did not significantly differ under various NaCl concentrations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pretreatment of wheat straw for fermentation to methane

The effects of pretreating wheat straw with gamma-ray irradiation, ammonium hydroxide, and sodium hydroxide on methane yield, fermentation rate constant, and loss of feedstock constituents were evaluated using laboratory-scale batch fermentors. Results showed that methane yield increased as pretreatment alkali concentration increased, with the highest yield being 37% over untreated straw for the pretreatment consisting of sodium hydroxide dosage of 34 g OH(-)/kg volatile solids, at 90 degrees C for 1 h. Gamma-ray irradiation had no significant effect on methane yield. Alkaline pretreatment temperatures above 100 degrees C caused a decrease in methane yield. After more than 100 days of fermentation, all of the hemi-cellulose and more than 80% of the cellulose were degraded. The loss in cellulose and hemicellulose accounted for 100% of the volatile solids lost. No consistent effect of pretreatments on batch fermentation rates was noted. Semicontinuous fermentations of straw-manure mixtures confirmed the relative effectiveness of sodium and ammonium-hydroxide pretreatments.     

Investigations of the treatment of sawdust for rabbit feeding. 1. Effect of sodium hydroxide treatment

A total of one hundred and eighty-four New Zealand White rabbits were used in three separate experiments: to establish the concentration of sodium hydroxide solution needed to improve the nutritive quality of sawdust for rabbit feeding; to investigate whether there is any difference between the nutritive quality of hardwood- or softwood-sawdust when treated with optimum sodium hydroxide solution; and to study the extent to which NaOH-treated sawdust can be substituted for the conventional feeds in rabbit diets.Food consumption was significantly (P < 0.05) greater in rabbits given diets containing sawdust treated with 6% solutions of NaOH, than with sawdust treated with 0–3% solutions. Rabbits given sawdust treated with 4 or 5% NaOH showed significantly (P < 0.05) better rate of gain and efficiency of feed utilization than those given sawdust treated with 0 or 1% sodium hydroxide solutions, and also grew slightly, but non-significantly, faster than those fed on sawdust treated with 3 and 6% NaOH.Alkali treatment of sawdust increased carcass yield. Hardwood-responded better than softwood-sawdust to alkali treatment, and a higher concentration of alkali may be required for the latter. Rabbits may tolerate and efficiently utilize up to 15% of treated sawdust without any reduction in performance. Beyond this level, there was a significant (P < 0.05) decrease in the rate of gain, feed/gain ratio and carcass yield.     

60Co-γ射线辐照协同氢氧化钠预处理对油菜秸杆酶解产糖的影响

研究了辐照协同氢氧化钠预处理油菜秸秆对酶解产还原糖的影响。利用响应面法对氢氧化钠反应条件进行了优化,得出最优条件为氢氧化钠浓度为2．38％,反应温度为100℃,反应时间为0．5h。这一条件预期还原糖产量为524．93mg／g,通过实验验证,实际还原糖含量（528．51mg／g）能够很好地与预期相吻合。扫描电镜观察表明,辐照协同氢氧化钠预处理后秸秆表面积明显增大,出现很多蜂窝状孔洞结构,能够有效增大酶解可及表面积,从而提高酶解效率。