Xanthan Gum In Aqueous Solution Research Articles

Xanthan gum and Tara gum galactomannans have a synergistic effect on gelation properties

Rheology is essential for assessing the applicability of bio-based and renewable polymers because it provides crucial information about their mechanical properties, flow behavior, and processing characteristics. So, gels formed by carbohydrate polymer mixtures have specific rheological properties that can be used in the food industry to improve processes, develop new products, or replace ingredients. The aim of the research was to characterize the interactions and synergy of the aqueous mixture of Xanthan gum (XG) and Tara gum (TG). Commercial TG was previously purified, and aqueous mixtures were prepared using varying concentrations of XG and TG. Rheological properties were determined using a rotational rheometer. An equation was proposed to quantify the degree of solid behavior of the formed gel as a function of its mechanical properties. Pure TG or XG in aqueous solution exhibited pseudoplastic behavior. At a 0.4% w/w concentration, the XG solution displayed a “weak gel” behavior. The concentrations of XG and TG in the aqueous mixture of the gums had a significant effect on the gel strength, presenting a region of maximum value, limited between the concentrations of 0.4–0.5% TG and 0.2–0.3% XG. The greatest strength of the gel was obtained at intermediate concentrations of gum; however, the value of the strain limit displayed a linear increase with TG concentration, confirming the synergistic effect on the solid-like behavior and strength of the gel.

Effect of xanthan gum co-extruded with OSA starch on its solubility and rheological properties

Xanthan gum (XG) was modified by the twin-screw extrusion process in the presence of Octenyl succinate anhydrate (OSA) starch in this study. The impact of OSA starch level on the rheological properties of XG was investigated. The extrusion process significantly improved the dispersibility, pseudoplasticity and elastic modulus of XG. The solubility and viscosity of the extruded XG in aqueous solution (1.0%, w/w) were increased from 67.04% and 0.2302 Pa⋅s to 95.20% and 1.1676 Pa⋅s, respectively, and reached the maximum of 96.63% and 1.7060 Pa⋅s when OSA starch level was 10%. Extruded samples were more sensitive to temperature and salt ion. Meanwhile, the co-extrusion process significantly changed the rheological properties of XG in the solutions at different pH values and sugar concentrations. The analysis of FTIR and SEM observation revealed that the molecular chains of XG and OSA starch were entangled through hydrogen bonding after the extrusion processing, leading to the formation of a denser network structure. In general, the extruded XG exhibited a strong gelatinous property with a high pseudoplasticity, while its features of high viscosity and dispersibility have a great potential for the application in food industry, especially in dysphagia products.

Impact of octenyl succinic anhydride (OSA) modified starch on the particle size distribution and rheological properties of xanthan gum in aqueous solutions

Abstract Effects of addition of octenyl succinate anhydride (OSA) starch on the structural, rheological and thermo-rheological properties of aqueous solutions of 0.5 (w/v %) xanthan gum were evaluated. Analysis by dynamic light scattering revealed the absence of complex formation in the mixed solution. However, it was noticed that an increase in the concentration of OSA starch (COSA) leads simultaneously to an increase of the number of micelles and their self-assembly within the network formed by the xanthan macromolecules. This same mechanism was observed during the evaluation of the rheological properties. For systems containing 0.5 (w/v %) of xanthan and for which COSA ≤ 4 (w/v %), a thermoreversible behavior was found similar to that of xanthan in solution. Furthermore, for COSA ≥ 5 (w/v %), the rheological behavior remained indifferent to the increase in temperature but, scored a spectacular rise in storage modulus when the cooling temperature begins near 70 °C.

Aggregating thermodynamic behavior of amphiphilic modified Xanthan gum in aqueous solution and oil-flooding properties for enhanced oil recovery

Novel chloride-substituted octylphenoxy polyoxyethylene (COP20, polymerization degree: 20) was synthesized. Xanthan gum (XG) was then modified by using COP20 to produce XGP20. XGP20 could be expected to be applied in polymer flooding. Compared with XG, the XGP20 solutions exhibited lower interfacial tensions in additional to higher apparent viscosities and salt-thickening effect. Its critical micelle concentrations (CMC) were 0.3 g/L in water and 5 g/L NaCl at 30 °C, and the interface tension was 0.46 mN/m in the saline solution. Large associating structures formed in the XGP20 saline solution. The thermodynamic data of micellization revealed that the micelle formations were spontaneous from 30 to 50 °C. Both standard enthalpy and entropy increased clearly with temperature. Compared with XG, the resistance and residual resistance factors were evidently higher in 5.177 g/L salt for XGP20. Nuclear magnetic resonance images showed that the sweep efficiency of water was enhanced significantly after XGP20 polymer flooding.

Yield stress measurement of a thixotropic colloid

Yield stress measurements have long been considered to be inconsistent and difficult, especially for a thixotropic colloid, since the thixotropic behavior gives rise to time-dependent rheological properties. In this paper, we attempted measuring the yield stress of aqueous xanthan gum (XG) solutions in different XG concentration. Our rheological measurements showed that XG in aqueous solutions, which can be characterized as weak gels, were thixotropic for 0.4, 0.6, 0.8, and 1 wt% XG concentrations. To ensure the accuracy of our rheological measurement data, detailed wall slip and stress relaxation time were first investigated prior to the actual yield stress measurement. A standard sample loading procedure was used to ensure the consistency of the loaded sample. Various methods were employed such as steady shear, oscillatory shear, rheological model fitting, and creep test to determine the yield stress of aqueous XG solutions. A sigmoidal model was also proposed to obtain a yield stress from our steady shear measurement unambiguously. In our steady shear measurements, a resistance to an avalanche of flow is observed and it is likely due to a conformational change of XG polymers under shear. As compared to other measurement methods, it was found that the most reliable way to obtain a yield stress is via small amplitude oscillatory shear measurements, in which a yield stress can be obtained conveniently at the maximum storage modulus, and it is well matched with our steady shear and creep test results.

Effect of Protonation State and N-Acetylation of Chitosan on Its Interaction with Xanthan Gum: A Molecular Dynamics Simulation Study.

Hydrophilic matrices composed of chitosan (CS) and xanthan gum (XG) complexes are of pharmaceutical interest in relation to drug delivery due to their ability to control the release of active ingredients. Molecular dynamics simulations (MDs) have been performed in order to obtain information pertaining to the effect of the state of protonation and degree of N-acetylation (DA) on the molecular conformation of chitosan and its ability to interact with xanthan gum in aqueous solutions. The conformational flexibility of CS was found to be highly dependent on its state of protonation. Upon complexation with XG, a substantial restriction in free rotation around the glycosidic bond was noticed in protonated CS dimers regardless of their DA, whereas deprotonated molecules preserved their free mobility. Calculated values for the free energy of binding between CS and XG revealed the dominant contribution of electrostatic forces on the formation of complexes and that the most stable complexes were formed when CS was at least half-protonated and the DA was ≤50%. The results obtained provide an insight into the main factors governing the interaction between CS and XG, such that they can be manipulated accordingly to produce complexes with the desired controlled-release effect.

Radiation induced degradation of xanthan gum in aqueous solution

In our previous study, we have investigated the effect of gamma rays on xanthan gum in the solid state and it was determined that dose rate was an important factor effecting the radiation degradation of xanthan gum. In the present study, in order to provide a better understanding of how ionizing radiation effect xanthan gum, we have investigated the effects of ionizing radiation on aqueous solutions of xanthan at various concentrations (0.5–4%). Xanthan solutions were irradiated with gamma rays in air, at ambient temperature, at different dose rates (0.1–3.3–7.0kGy/h) and doses (2.5–50kGy). Change in their molecular weights was followed by size exclusion chromatography (SEC). Chain scission yield (G(S)), and degradation rate constants (k) were calculated. It was determined that, solution concentration was a factor effecting the degradation chemical yield and degradation rate of xanthan gum. Chain scission reactions were more effective for lower solution concentrations.

Some properties of xanthan gum in aqueous solutions: effect of temperature and pH

The properties of xanthan gum (XG) aqueous solutions were investigated by using viscometric, electrokinetic and surface tension measurements. The effects of polymer concentration, temperature and pH on the viscosity of the XG solutions were evaluated and discussed. Zeta potential data determined for XG solutions in water in the temperature range of 15–45 °C corroborated with the results obtained from the viscometric investigations suggest the occurence of conformational changes above 36 °C. The activation energy of flow and that associated with the electrophoretic migration of the charged particles were estimated for XG solutions in water. In acid medium, xanthan gum determines a slight decrease of the surface tension of pure water at all investigated temperatures.

Effect of Xanthan gum Solution on the Preservation of Acerola (Malpighia glabra L.)

Abstract Nowadays, storing fresh fruit and vegetable by edible film was the best method. There are a lot of chemical which can coat the surface of fruit to increase the preservation time. Among the chemicals was xanthan gum which was known as an additive and applied widely in food technology but it can use currently in the post harvest technology as an edible film. Coating of acerola fruit with xanthan gum has been found to delay the ripening process. Xanthan gum in aqueous solutions of 0.4, 0.6, 0.8, 1.0, 1.2 and 1.4% (w/v) was applied as an edible coating of unripe acerola which were stored at 30°C and 70-80% RH for 6 days. Fruits were coated with 1.4% xanthan gum delayed the ripening process by slowing down the rate of respiration, in terms of percentage weight loss, soluble solids concentration (°Bx), total acidity and color of acerola fruit during storage as compared to the uncoated control and fruit treated with other xanthan gum concentration. The result suggest that using 1.4% xanthan gum as edible coating may form a protective barrier on the surface of acerola, the ripening process of acerola can be delayed and prevented oxygen penetration. It can be prolong the preservation during 6 days at 30°C without any negative effects on quality of fruit. The appearance of acerola does not have blemishes and which is fresh, shiny and bright colored.

Rheological and kinetic study of the ultrasonic degradation of xanthan gum in aqueous solution: Effects of pyruvate group

The influence of the pyruvate group on the efficiency of ultrasonic degradation of xanthan gum in aqueous solution has been studied. Blends of natural and pyruvate-free xanthan gums were ultrasonicated at 20°C for up to 30min and evaluated for molecular-weight degradation by viscometry. Solutions of pure pyruvate-free xanthan exhibited the highest stability to degradation among all blend ratios studied. Removing the pyruvate group is believed to enable the molecular chains to adopt a more compact conformation, which renders the polymer less susceptible to ultrasonication. In addition, the effects of salt on ultrasonic degradation efficiency were studied by using 0.1, 10−2, or 10−4M of NaCl or Na2SO4 in solution prior to ultrasonication. A degradation kinetics model was developed to quantify the degradation behavior. The absence of pyruvate groups renders the xanthan gum less sensitive to the influence of salt, and hence decreases the ultrasonic degradation efficiency.

Rheological and kinetic study of the ultrasonic degradation of xanthan gum in aqueous solutions

The effectiveness of ultrasound to degrade the molecular weight of xanthan gum in aqueous solutions was investigated for sonication times up to 60min at 20°C and for polymer concentrations up to 0.1g/dl. The Huggins equation was found to be applicable to the intrinsic viscosity of xanthan gum prior to sonication, while a truncated form was found to be adequate for estimating the intrinsic viscosity of the degraded xanthan. To better understand the influence of salting-in and salting-out salts (classified on the basis of the Hofmeister series) on degradation, xanthan-gum solutions were pre-mixed with 0.1, 10−2, 10−3, or 10−4M NaCl or Na2SO4, prior to ultrasonication. A kinetic model was developed and successfully applied to quantify and predict the degradation rates and efficiency. The various reaction rate constants and reaction orders were found to correlate with the different salt species and concentrations used, suggesting that salting-in and salting-out salts could increase or inhibit ultrasonic degradation by adjusting the molecular conformation of the xanthan.

Effects of Montmorillonite and Acrylic Acid on the Superabsorbent Polymer Based on Xanthan

Superabsorbent polymers, which have been used for many applicaions, are an important class of polymers. Superabsorbent polymer based on organic montmorillonite (MMT) and xanthan gum(XG) were prepared by by free-radical graft polymerization of aceylic acid on XG in aqueous solution as a free radical initiator, and then organic montmorillonite (OMMT) was introduced as filler into superabsorbent. The effects of montmorillonite and xanthan on the swelling behaviour of the superabsorbent polymer had been studied in detail. Under the optimal synthesis condition, where the temperature was 65°C, the ratio between the AA monomers and XG was m (XG) : m(AA) = 4 : 1, the weight rate of the initiator and the cross-linker were 1.2% and 0.07%, and the neutralization degree of AA was 70%, the product attained the best water absorbency of 882 g/g in distilled water and 107 g/g in 0.9 wt.% NaCl solution.

Effect of Irradiation on the Molecular Weight, Structure and Apparent Viscosity of Xanthan Gum in Aqueous Solution

Xanthan gum samples were irradiated in aqueous solution at different doses (0-120 kGy) of 60Co γ-rays. The changes of molecular weight and structures of irradiated xanthan gum samples were investigated and characterized by using gel permeation chromatography(GPC), X-ray diffraction (XRD), fourier-transform infrared spectra (FTIR), ultraviolet–visible spectral (UV–vis) analysis and rheometer. Results showed the molecular weight decreased gradually with increasing irradiation dose. The radiation chemical yields G(d) of xanthan gum was 26.55. FTIR spectra and XRD indicated that γ-irradiation introduced no significant changes into the structure and crystal texture, but UV spectra showed a distinct absorption peak at about 265 nm, increasing with irradiation dose, which was attributed to the formation of carbonyl groups or double bond. Apparent viscosity of xanthan gum solution decreased with increasing irradiation dose and remain basically constant with the prolonging of shear time after irradiation.

Micellar properties of OSA starch and interaction with xanthan gum in aqueous solution

Octenyl succinate (OSA) modified starches are used, as emulsifiers and stabilizers, in many food, cosmetics and pharmaceutical products. The aim of this study was to determine critical micellar concentration (CMC) of two different octenyl succinate modified waxy corn starches at 25 °C, and to examine possibility of their interactions with xanthan gum in aqueous solution. The CMC was determined by viscometry, conductometry, surface tension and dye solubilization. The CMC values for two OSA starches (OS1 and OS2) varied from 0.050 to 0.088 g/100 cm 3 and from 0.041 to 0.081 g/100 cm 3 respectively, depending on applied technique. The same techniques were used for investigation of the interactions between OSA starch and xanthan gum. The addition of xanthan gum decreases the specific viscosity and increases surface tension and the CMC values compared to the single OSA starch solutions.

Interactions of anionic polysaccharides with carbon nanotubes

Agarose, i-, k-, and l-carrageenans, and xanthan gum in aqueous solutions interacted with single-walled carbon nanotubes (SWCNTs) as proven by their wetting in solution and by the microRaman spectroscopy, rheological studies, and differential scanning calorimetry. The investigations provided evidence that the effect of complexation of polysaccharides was independent of the possibility of the formation of helical complexes. Complexation involved, to a certain extent, interactions between hydrophobic surface of nanotubes and hydrophobic sides of the saccharide units of polysaccharides. However, clathration of nanotubes in the polysaccharide matrices was also essential. Formation of the clathrate cages involved intra- and intermolecular hydrogen bonds within polysaccharides.

E.s.r. study of the conformational transition of spin-labelled xanthan gum in aqueous solution

The order to disorder transition of xanthan molecules in aqueous solutions has been studied using e.s.r. spectroscopy. Nitroxide spin-label was covalently attached to carboxyl groups on the xanthan side chains. The e.s.r. spectra obtained for aqueous spin-labelled xanthan solutions at varying ionic strengths contained both isotropic and anisotropic components at room temperature. The anisotropic component was attributed to the association of the side chains with the xanthan cellulosic backbone and was found to be present in greater proportions at increasing ionic strength. The spectra gradually changed with rising temperature and the proportion of anisotropic component decreased. This spectral change reflected the disruption of the side chain association with the backbone during the conformational change. Hysteresis effects were observed following sequential heating and cooling cycles suggesting that chain aggregation occurred.

Properties of xanthan gum in aqueous solutions: Role of the conformational transition

Xanthan is shown to exist in native (I) and denatured (II) forms, both of which are ordered by the criterion of optical activity, and both of which undergo a temperature-driven, conformational transition to a common, disordered form (III). Changes in optical activity and conductivity are identical for the transformations I → III and II → III. The denatured, ordered form II displays a considerably larger viscosity increment than the native, ordered form I under given conditions of added salt at temperatures below the transition temperature (Tm). Light-scattering measurements yield the same molecular weight for forms I and II; consequently, the observed difference in viscosity increment appears to reflect inherent differences in the chain extension and conformation of forms I and II. Measured persistence lengths for forms I and II are consistent with earlier reports of the persistence length of single-stranded, ordered xanthan in solution. In the present viscosity studies, the absence of any dependence of measured properties of the native form I and the denatured form II on the thermal and concentration history strongly suggests that forms I and II are not aggregated species. Similar comparisons of the chain extension of disordered form III with the ordered forms I and II are more difficult, owing to the absence of conditions under which ordered and disordered forms are simultaneously stable. It is possible, nevertheless, to conclude that the viscosity increment of form II exceeds that of form III, whereas those of forms I and III are similar. Measurements of the molecular weight of form III, needed to convert this observation reliably into information about chain extension, are lacking. These observations are interpreted in terms of a model for xanthan in which the native, single-stranded, ordered form I is stabilized by side chain-backbone interactions that are shown, by experiments reported here, to be strong. These strong interactions are disrupted upon temperature-induced conversion into the disordered form III above the Tm. On subsequent cooling, there is established an alternative pattern of side chain-backbone interactions, presumably dictated by kinetic rather than thermodynamic factors, which stabilizes a more-extended backbone conformation in the denatured, ordered form II. The assumption is made that these strong, side chain-backbone interactions can bridge some backbone breaks which can appear during partial degradation of forms I and II.

Xanthan Gum—A Lyotropic, Liquid Crystalline Polymer and its Properties as a Suspending Agent

Abstract A variety of polysaccharides have been used in drilling fluids,1–4 and some of these polymers have been studied in tertiary recovery. Of particular interest in both these areas has been xanthan gum, the extracellular polysaccharide produced by Xanthomonas campestris, because of its relatively stable viscosity properties as a function of salt concentration, pH, temperature, and shear degradation. Indeed, no synthetic polymer or any other commercially available, naturally occurring polymer, or polymer derivative has been able to duplicate the solution behavior of xanthan gum. During a study of xanthan gum's ability to suspend barium sulfate, it appeared that xanthan gum in aqueous solution at relatively low concentrations could have lyotropic liquid crystalline behavior. Behavior of this type has been noted for other biopolymers5 and recently has been demonstrated for various cellulose derivatives.6–10 An anisotropically ordered polymer solution would be extremely difficult to reproduce synthetically but could explain most of the unique properties of xanthan solutions. To test the possibility that xanthan gum could have liquid crystalline order, a variety of xanthan solutions of various polymer concentrations in the presence and absence of various salts were studied under a polarized light microscope (100X). With solutions from 2 to 10% (wt/vol) xanthan gum in distilled water at room temperature, birefringent, ordered domains were observed at 10% concentration, with a decrease in birefringence as the polymer concentration decreased. At 2% concentration, no birefringence was observed, indicating the apparent area of change from an isotropic to an anisotropic phase. This point appears to occur at 2.9% by optical determination. In fact, this value could be considerably lower as revealed by other techniques for anisotropic xanthan solutions.8–10 For the 10% solution of xanthan gum, heating in a roller oven at 150°F (66°C) for 2 hours did not diminish the birefringence. Similarly, when a 10% xanthan gum solution was prepared in 10% KCI and in 33% CaCl2 solutions, birefringence was not decreased.