Synthesis of oxidized guar gum by dry method and its application in reactive dye printing

The aim of this study was to prepare oxidized guar gum with a simple dry method, basing on guar gum, hydrogen peroxide and a small amount of solvent. To obtain a product with suitable viscosity for reactive dye printing, the effects of various factors such as the amount of oxidant and solvent, reaction temperature and time were studied with respect to the viscosity of reaction products. The product was characterized by Fourier transform infrared spectroscopy, size exclusion chromatography, scanning electron microscopy and differential scanning calorimetry. The hydrated rate of guar gum and oxidized guar gum was estimated through measuring the required time when their solutions (1%, w/v) reached the maximum viscosity. The effects of the salt concentration and pH on viscosity of the resultant product were studied. The mixed paste containing oxidized guar gum and carboxymethyl starch was prepared and its viscosity was determined by the viscometer. The rheological property of the mixed paste was appraised by the printing viscosity index. In addition, the applied effect of mixed paste in reactive dye printing was examined by assessing the fabric stiffness, color yield and sharp edge to the printed image in comparison with sodium alginate. And the results indicated that the mixed paste could partially replace sodium alginate as thickener in reactive dye printing. The study also showed that the method was low cost and eco-friendly and the product would have an extensive application in reactive dye printing.     

Rheology of hydroxyethyl guar gum derivatives

The rheological properties of aqueous solutions of hydroxyethyl guar gum, a synthetic derivative of guar gum, have been studied under continuous and oscillatory shear flow conditions. Data obtained from both experimental techniques were satisfactorily fitted according to Cross-type models. The effect of polymer concentration, molecular weight and temperature on the rheological behavior of hydroxyethyl guar gum systems have been investigated and discussed in terms of rheological parameters like the zero-shear viscosity η₀ and the characteristic times λ and λ′.     

Rheological properties of guar gum and hydroxyethyl guar gum in aqueous solution

The rheological properties of aqueous solutions of guar gum (GG) and hydroxyethyl guar gum (HEG) have been investigated. The flow properties of these polysaccharide solutions were studied at the shear rate in the range 1.5–1310s⁻¹ using a Rheotest-2 viscometer. The flow of these polysaccharide solutions was described by equation of state based on Cross model. The basic rheological parameters, like zero shear rate viscosity (η_o), elasticity modulus (G_o) and relaxation time (gl_o) were calculated using simple and established relations. Master viscosity curves indicated that the molecular weight distribution of native guar gum has been changed by hydroxyethylation under specified reaction conditions. The effect of concentration and temperature on η_o and λ_o has been studied, and the relations among these were established by simple equations.     

Relationship between the Rheological Properties of Thickener Solutions and Their Velocity through the Pharynx as Measured by the Ultrasonic Pulse Doppler Method

The dependence of the dynamic viscoelastic parameters of carboxymethylcellulose (CMC), xanthan gum, and guar gum solutions on the angular frequency (ω) was compared with that of their viscosity (μ) on the shear rate (γ). In addition, the effect of these rheological properties on the maximum velocity through the pharynx, V _max, as measured by the ultrasonic pulse Doppler method, was investigated. The CMC and guar gum solutions examined were taken as a dilute solution and a true polymer solution, respectively. The xanthan gum solution was taken as a weak gel above 0.5% and a true polymer solution below 0.2%. The maximum velocity, V _max, of the thickener solutions correlated well with μ, the dynamic viscosity η′, and the complex viscosity η^*, especially those measured at γ or ω of 20–30 s^?1 (or rad/s) and above, suggesting that μ, η′, and η^* are suitable indexes for care foods of the liquid type for dysphagic patients.     

白芨多糖胶-瓜尔胶复配溶液的流变性

考察了瓜尔胶溶液和白芨多糖胶-瓜尔胶复配溶液的流变特性。两组溶液呈现典型的假塑性,不同浓度下两组溶液表观黏度(ηa)随剪切速率(τ)的变化可以用Ostwald-Dewaele方程描述。白芨多糖胶和瓜尔胶复配产生协同增效作用,复配溶液的ηa大于单一组分的白芨多糖胶溶液或瓜尔胶溶液的ηa。复配溶液中白芨多糖胶与瓜尔胶的最佳配比是质量比为9∶1。     

Microwave initiated synthesis of polymethylmethacrylate grafted guar (GG-g-PMMA), characterizations and applications

Guar gum was grafted with polymethylmethacrylate (PMMA) by microwave initiated method. The synthesis was optimized for highest percentage grafting, by varying the microwave irradiation time and monomer (methyl methacrylate) concentration. The various grades of grafted product (GG-g-PMMA) were characterized through standard physicochemical characterization techniques (intrinsic viscosity measurement, elemental analysis, FTIR spectroscopy & SEM morphology study). Further, flocculation efficacy of this grafted polysaccharide was studied by standard 'Jar test' procedure in 0.5% kaolin suspension, to assess its application as flocculating agent for wastewater treatment and mineral ore beneficiation. Correlation between percentage grafting and intrinsic viscosity was also studied for the possibility of using it as a tool to control the intrinsic viscosity in the final product. This leads to the possibility of application of the grafted product as superior viscosifier than guar gum.     

The Physico-Chemical Properties of Dietary Fibre Determine Metabolic Responses,Short-Chain Fatty Acid Profiles and Gut Microbiota Composition in Rats Fed Low- and High-Fat Diets

The aim of this study was to investigate how physico-chemical properties of two dietary fibres, guar gum and pectin, affected weight gain, adiposity, lipid metabolism, short-chain fatty acid (SCFA) profiles and the gut microbiota in male Wistar rats fed either low- or high-fat diets for three weeks. Both pectin and guar gum reduced weight gain, adiposity, liver fat and blood glucose levels in rats fed a high-fat diet. Methoxylation degree of pectin (low, LM and high (HM)) and viscosity of guar gum (low, medium or high) resulted in different effects in the rats, where total blood and caecal amounts of SCFA were increased with guar gum (all viscosities) and with high methoxylated (HM) pectin. However, only guar gum with medium and high viscosity increased the levels of butyric acid in caecum and blood. Both pectin and guar gum reduced cholesterol, liver steatosis and blood glucose levels, but to varying extent depending on the degree of methoxylation and viscosity of the fibres. The medium viscosity guar gum was the most effective preparation for prevention of diet-induced hyperlipidaemia and liver steatosis. Caecal abundance of Akkermansia was increased with high-fat feeding and with HM pectin and guar gum of all viscosities tested. Moreover, guar gum had distinct bifidogenic effects independent of viscosity, increasing the caecal abundance of Bifidobacterium ten-fold. In conclusion, by tailoring the viscosity and possibly also the degree of methoxylation of dietary fibre, metabolic effects may be optimized, through a targeted modulation of the gut microbiota and its metabolites.     

Low viscosity hydrogel of guar gum: preparation and physicochemical characterization

Guar gum was cross-linked with glutaraldehyde and characterized by GPC, rheology, WADX, SEM and TGA. This guar gum is a galactomannan polysaccharide, that contains small amount of arabinose, glucose and uronic acid, besides galactose and mannose. The polymer has high molar mass, with Mw, Mn and Mv values of 2.0x10(6), 1.2x10(6) and 1.9x10(6)g/mol, respectively. The reticulation follows a slow process and lead to a viscosity increase of 40 times compared with the original gum solution. The final viscosity was similar to that of Hylan G-F 20, a hyaluronate derivative, commercially used in viscosupplementation treatment. The gel contains 95.6% of water and the amount of residual glutaraldehyde is much lower than the LD-50. Porous structure was detected by SEM and thermal stability was improved by the cross-linking. The low viscosity, the small amount of remained glutaraldehyde, and the thermal stability indicates that the guar hydrogel has potential to be applied as biomaterial with specific rheological requirements.     

Composition and effect of salt on rheological and gelation properties of Enterolobium contortisilliquum gum exudate.

The composition, structure and rheological properties and metal ions interaction with Enterolobium contortisilliquum gum were investigated. This gum contains galactose, arabinose, rhamnose and glucuronic acid as main monosaccharide components. 13C nuclear magnetic resonance spectroscopy revealed that the anomeric composition is similar to the Enterolobium cyclocarpum exudate, however no 4-O-methylglucuronic acid was detected for E. contortisilliquum. The rheological experiment resulted in a very similar flow behaviour to that found for E. cyclocarpum gum. The empirical stiffness parameter, B was determined (B=0.090) and suggested that the polysaccharide possesses semi-flexible chains. Cation affinity of the gum aqueous solution was determined by intrinsic viscosity measurements and gelation. The melting temperature of gels pointed to a charge/ionic radius ratio dependence for metal ions. Thermodynamic parameters (enthalpy and entropy) at the melting temperature were also calculated.     

A comparison between the hot and cold water soluble fractions of two locust bean gum samples

Locust bean gum extracted from two carob flours from eastern and western Mediterranean sources were fractionated on the basis of their solubility in water. Weight-average molecular weights determined by sedimentation equilibrium were about 300 000 for both the hot water and cold water soluble fractions, whereas a commercial sample of guar gum had a molecular weight of 700 000. Their values were lower than would be predicted from Mark-Houwink relationships where molecular weights were originally determined by light scattering.

The hot water soluble fraction from the eastern Mediterranean flour showed unexpected rheological behaviour. It had an extremely high Huggins' constant and a different relationship between the coil overlap parameter and the zero shear rate viscosity compared with previously reported results for galactomannans. Both effects may be explained by the anomalously low intrinsic viscosity of this fraction when determined by a Huggins' extrapolation. The use of the Kraemer extrapolation gave significantly higher intrinsic viscosities for this particular sample. Gels formed from the two hot water soluble fractions with κ-carrageenan had similar rheological properties.     

Enhancement of lectin-erythrocyte agglutination by gums

The erythroagglutinating activity of purified Vicia faba lectin was enhanced in the presence of gums; gum guar caused the highest enhancement. Circular dichroism probe demonstrated 40-57% beta-conformation and 4-23% alpha-conformation of the lectin at pH 7.2 depending upon the analytical methods used. The beta-conformations of untreated and modified V. faba lectins were increased in the presence of gums. The mixing of gum guar with lectin and with modified lectin, respectively, led to the highest values of beta-conformational change in the protein molecule, thereby increasing the number of receptor sites of the lectin molecule. The enhancement of the activity of V. faba lectin in the presence of gum guar might be due to the conformational change of the protein molecule.     

Characterization of extremely thermostable enzymatic breakers (alpha-1,6-galactosidase and beta-1,4-mannanase) from the hyperthermophilic bacterium Thermotoga neapolitana 5068 for hydrolysis of guar gum

An alpha-galactosidase and a beta-mannanase produced by the hyperthermophilic bacterium, Thermotoga neapolitana 5068 (TN5068), separately and together, were evaluated for their ability to hydrolyze guar gum in relation to viscosity reduction of guar-based hydraulic fracturing fluids used in oil and gas well stimulation. In such applications, premature guar gum hydrolysis at lower temperatures before the fracturing process is completed is undesirable, whereas thermostability and thermoactivity are advantageous. Hyperthermophilic enzymes presumably possess both characteristics. The purified alpha-galactosidase was found to have a temperature optimum of 100-105 degrees C with a half-life of 130 minutes at 90 degrees C and 3 min at 100 degrees C, while the purified beta-mannanase was found to have a temperature optimum of 91 degrees C and a half-life of 13h at this temperature and 35 min at 100 degrees C.These represent the most thermostable versions of these enzymes yet reported. At 25 degrees C, TN5068 culture supernatants, containing the two enzyme activities, reduced viscosity of a 0.7% (wt) guar gum solution by a factor of 1.4 after a 1.5-h incubation period and by a factor of 2.4 after 5 h. This is in contrast to a viscosity reduction of 100-fold after 1.5 h and 375-fold after 5 h for a commercial preparation of these enzymes from Aspergillus niger. In contrast, at 85 degrees C, the TN5068 enzymes reduced viscosity by 30-fold after 1.5 h and 100-fold after 5 h compared to a 2.5-fold reduction after 5 h for the control. The A. niger enzymes were less effective at 85 degrees C (1.6-fold reduction after 1.5 h and a 4.2-fold reduction after 5 h), presumably due to their thermal lability at this temperature. Furthermore, it was determined that the purified beta-mannanase alone can substantially reduce viscosity of guar solutions, while the alpha-galactosidase alone had limited viscosity reduction activity. However, the alpha-galactosidase appeared to minimize residual particulate matter when used in conjunction with the beta-mannanase. This could be the result of extensive hydrolysis of the alpha-1,6 linkages between mannose and galactose units in guar, allowing more extensive hydrolysis of the mannan chain by the beta-mannanase. The use of thermostable enzymatic breakers from hyperthermophiles in hydraulic fracturing could be used to improve well stimulation and oil and gas recovery. (c) 1996 John Wiley & Sons, Inc.     

Influence of Guar Gum on the In Vitro Starch Digestibility—Rheological and Microstructural Characteristics

The present study investigates the effect of guar gum on the digestibility of a waxy maize starch in vitro under simulated gastric and intestinal conditions. A detailed rheology and confocal scanning laser microscopy of the digesta were performed in order to study the possible mechanisms of interactions involved during in vitro hydrolysis of starch. No starch hydrolysis was observed under simulated gastric conditions, whereas more than 90% hydrolysis was observed at the end of digestion under simulated intestinal conditions. In the presence of guar gum, the starch hydrolysis was reduced by nearly 25% during the first 10 min and by 15% at the end of in vitro intestinal digestion. The rheological behavior of the digesta was significantly affected in the presence of the gum. The viscosity of digesta decreased during intestinal digestion; however, the extent of decrease was quite low in the presence of guar gum. The consistency index increased and flow behavior index of digesta decreased in the presence of gum after 1 min of intestinal digestion. All the samples (digested or undigested) displayed a pseudoplastic behavior as their apparent viscosity (η _a) decreased with an increase in shear rate. A negative correlation between the starch hydrolysis (%) and storage modulus for the starch sample without gum and a positive correlation for the starch sample with gum were found. Large granule remnants observed through confocal micrographs have shown that the solubilization of starch granule remnants during in vitro digestion is significantly reduced in the presence of gum.     

Comparison of the rheological and diffusion properties of some gelling agents and blends and their effects on shoot multiplication

The rheological and diffusion properties of blends of agar/guar gum, agar/Phytagel and Phytagel/guar gum were analysed and compared to those properties of agar or Phytagel applied alone at two different gelling concentrations. Moreover, their effects on the shoot multiplication of the apple scion Galaxy and two black locust clones (SF63, SF82) were studied, and their cost benefits over agar were calculated. Elastic hydrogel formation was demonstrated for each blend by rheological measurements, but the gel strength depended on the types and concentrations of the applied gelling agents and blends. Guar gum was able to speed the diffusion in the different blends, and diffusion was independent of gel strength. The rate of shoot multiplication increased (to 8.9 shoots per explant) and the percent of hyperhydrated shoots decreased (to 12%) when the blend of agar/guar gum was used for the shoot multiplication of apple. Similarly, the highest multiplication rates of black locust clones (between 3.9 and 4.1) were obtained on media solidified by blends containing guar gum. The best shoot performance with the lowest percent of hyperhydrated shoots (11–12% in SF63 and 2–23% in SF82) was achieved using agar alone or the agar/guar gum blend. The shoot multiplication was improved of both species and the production cost was reduced by 42% by using the agar/guar gum blend.     

Pressure cell assisted solution characterization of polysaccharides. 2. Locust bean gum and tara gum

Following the work carried out on guar gum in our first paper of a series, the "pressure cell" solubilization method was applied to two other less highly substituted galactomannans: locust bean gum (LBG) and tara gum. True molecular solution of the polymers was achieved using appropriate temperature, time, and pressure regimes. The technique of capillary viscometry was used to determine the intrinsic viscosity [eta] of the "pressure cell" treated and untreated samples. Molecular weight (M(w)) and radius of gyration (R(g)) were determined by light scattering. The data obtained for LBG and tara gum were compared statistically with reliable data found for guar gum in the literature. The variation in [eta] with M(w) followed the Mark-Houwink-Sakurada relationship, giving the exponent alpha = 0.74 +/- 0.01 for galactomannans consistent with random coil behavior. The characteristic ratio, C(infinity), and the chain persistence length, L(p), were both calculated for LBG and tara gum using the Burchard-Stockmayer-Fixman (BSF) method which is appropriate for flexible to semiflexible chains. A general value of 9 < C(infinity) < 16 and 3 < L(p) < 5 nm can now be estimated with statistical confidence for all galactomannans. According to our statistical analysis, the chain persistence length was found to be insensitive to the degree of galactose substitution.     

In vitro and in vivo evaluation of guar gum matrix tablets for oral controlled release of water-soluble diltiazem hydrochloride

The objective of the study was to develop guar gum matrix tablets for oral controlled release of water-soluble diltiazem hydrochloride. Matrix tablets of diltiazem hydrochloride, using various viscosity grades of guar gum in 2 proportions, were prepared by wet granulation method and subjected to in vitro drug release studies. Diltiazem hydrochloride matrix tablets containing either 30% wt/wt lowviscosity (LM1), 40% wt/wt medium-viscosity (MM2), or 50% wt/wt high-viscosity (HM2) guar gum showed controlled release. The drug release from all guar gum matrix tablets followed first-order kinetics via Fickian-diffusion. Further, the results of in vitro drug release studies in simulated gastrointestinal and colonic fluids showed that HM2 tablets provided controlled release comparable with marketed sustained release diltiazem hydrochloride tablets (D-SR tablets). Guar gum matrix tablets HM2 showed no change in physical appearance, drug content, or in dissolution pattern after storage at 40°C/relative humidity 75% for 6 months. When subjectd to in vivo pharmacokinetic evaluation in healthy volunteers, the HM2 tablets provided a slow and prolonged drug release when compared with D-SR tablets. Based on the results of in vitro and in vivo studies it was concluded that that guar gum matrix tablets provided oral controlled release of water-soluble diltiazem hydrochloride. Published: June 30, 2005     

Pressure cell assisted solution characterization of galactomannans. 3. Application of analytical ultracentrifugation techniques

The pressure heating cell approach previously applied to galactomannans in two earlier studies is now used to prepare samples for characterization using the analytical ultracentrifuge. Sedimentation velocity data were obtained for both guar gum and locust bean gum samples. These were compared to our earlier light scattering and intrinsic viscosity measurements on samples prepared using identical temperature and pressure profiles. A number of methods were then employed to obtain chain persistence lengths, including the Hearst-Stockmayer and Bohdanecky wormlike chain approaches. These results were compared to earlier results obtained using methods appropriate for excluded volume coil and rodlike chains, respectively.     

Rheological study of interactions between non-ionic surfactants and polysaccharide thickeners used in textile printing

The influence of four non-ionic surfactants (isododecyl and cetyl polyoxyethylene ethers) on aqueous polysaccharide solutions (sodium alginate, guar gum, and sodium carboxymethyl guar), applicable for textile printing pastes, were studied via rheological measurements.

Rheology of polysaccharide–surfactant solutions in aqueous matrices is primarily governed by polymer content, which imparts marked shear-thinning and viscoelastic character to the system. Such properties are modulated in moderate but sensible way by changes in surfactant concentration or type. Above 3% surfactants addition to non-substituted guar gum solutions results in a significant impact leading to phase separation and a particular strongly associated phase is formed due to hydrogen bonds between ethylene oxy units from the surfactant and primary hydroxyl groups in guar.

A satisfactory fitting of viscosity data is obtained with both the Cross equation and the Roberts–Barnes–Carew model. The experimental results of mechanical spectra can be described quite satisfactory with both the Friedrich–Braun and the generalized Maxwell models.     

A study of rheological and molecular weight properties of recycled polysaccharides used as thickeners in textile printing

Polysaccharide thickeners (alginate, carboxymethylated guar gum and carboxymethylated cellulose) used for the preparation of printing pastes, were recycled from printing paste residues and from wastewater concentrates, which were separated by ultrafiltration technique from wastewater after screen printing of cotton with reactive dyes. Concentrated aqueous polysaccharide solutions were studied via rheological measurements under steady and oscillatory shear conditions. Molecular weight averages and molecular weight distribution of thickeners were determined by size exclusion chromatography.A satisfactory fitting of viscosity data is obtained with the Cross equation and mechanical spectra are described with satisfactory approximation with the Friedrich–Braun model. The obtained parameters enable a quantitative interpretation of the changes in rheological properties. Moderate changes produced by thickener recycling on the shear-thinning and viscoelastic behaviour of polymers are a direct result of changes in molecular weight averages (MWA) and molecular weight distribution (MWD).     

Partial characterization of extracellular polysaccharides from cyanobacteria

Four cyanobacterial strains, Cyanothece sp., Oscillatoria sp., Nostoc sp. and Nostoc carneum were studied for physico-chemical characterization of extracellular polysaccharide (EPS) secreted during the controlled growth condition. Hydrolyzed EPSs showed the compositional involvement of four sugar moieties viz. mannose, glucose, xylose and ribose in varying combinations. Infrared spectra of EPSs showed a specific absorbance of O-H stretching at 3448-3400 cm(-1), asymmetrical-symmetrical C-H stretching at 2924 and 2854 cm(-1) and a bending vibration of C-H at 1400-1380 cm(-1). Absorbance at 1259 and 1140 cm(-1) with Cyanothece sp. EPS, indicated the presence of sulfur containing functional group. Thermal gravimetric analysis and differential scanning calorimetric analysis confirmed the polysaccharides thermal stability as high as around 250 degrees C. In the presence of 0.1 M NaCl aqueous solution, the intrinsic viscosity of polysaccharides from Oscillatoria sp. and Nostoc sp. decreased 1.6 fold, whereas, 3-5 fold reduction in intrinsic viscosity was observed with commercially available guar and xanthan gum.