Intrinsic viscosity and viscoelastic properties of xanthan/guar mixtures in dilute solutions: Effect of salt concentration on the polymer interactions (original) (raw)
Related papers
Food Research International, 2006
Dynamic viscoelastic and intrinsic viscosity properties of xanthan, guar, and xanthan-guar blends in dilute aqueous solutions were investigated by using an oscillating capillary rheometer. Influence of mixing temperature on xanthan conformation and interaction with guar is discussed. Synergistic interaction occurred at mixing temperatures of 25 and 80°C, but a stronger synergistic interaction was observed at mixing temperature 80°C. The viscous component for all gum solutions was greater than that of the elastic component, which indicated a liquid-like behavior in the dilute regime for the polysaccharide solutions. For both mixing temperatures, the relative viscosities and elasticities of xanthan and guar blends were higher than the relative viscosities and elasticities calculated for blends assuming no interaction. The intrinsic viscosities of xanthan and xanthan-guar blends were higher at 80°C than at 25°C. The intrinsic viscosities of xanthan and guar blends were lower than those calculated from the weight averages of the two, and significantly decreased as the xanthan fraction decreased, indicating that xanthan was crucial in controlling the blend viscosity, and that the molecular binding occurred between xanthan and guar.
Journal of Food Science, 2007
An oscillating capillary rheometer was used to investigate the effects of xanthan deacetylation on the viscoelastic properties and intrinsic viscosity of xanthan and guar mixtures in dilute aqueous solutions. Deacetylated xanthan exhibited a stronger synergistic interaction with guar than native xanthan did due to the destabilized helical structure and increased chain flexibility of the deacetylated xanthan. No gels were observed for all xanthan-guar mixtures. Native xanthan-guar mixtures exhibited a liquid-like behavior, whereas deacetylated xanthan-guar mixtures exhibited a gel-like behavior. The relative viscosity and elasticity of deacetylated xanthan-guar mixtures were much stronger than those for native xanthan-guar mixtures. The intrinsic viscosities of deacetylated xanthan-guar mixtures were higher than the calculated values assuming no interaction, whereas the intrinsic viscosities of native xanthan-guar mixtures were lower than the calculated values assuming no interaction, demonstrating that intermolecular binding occurred between the disordered segments of xanthan and guar gum in dilute aqueous solutions.
Viscosity of guar gum and xanthan/guar gum mixture solutions
Journal of the Science of Food and Agriculture, 2000
The viscosity of diluted guar gum solutions and the viscosity of xanthan and guar gum mixture solutions have been studied. Guar gum solutions showed pseudoplastic behaviour. Apparent viscosity increased with gum concentration and decreased with the temperature at which viscosity was measured. A maximum in the plot of viscosity versus increasing dissolution temperature was observed at 60°C. This behaviour was related to differences in molecular structure of the polymers solved at different temperatures. Mixtures of xanthan and guar gum showed a higher combined viscosity than that occurring in each separate gum. This synergistic interaction was affected by the gum ratio in the mixture and dissolution temperature of both gums. The effect of polysaccharide concentration (1.0, 1.5 and 2.0 kg m À3), xanthan/guar gum ratio (1/5, 4/2, 3/3, 4/2 and 5/1) and dissolution temperature (25, 40, 60 and 80°C for both gums) on the viscosity of solutions of mixtures were studied. The highest viscosities were observed when 2.0 kg m À3 gum concentration was used together with a ratio of xanthan/ guar gum of 3/3 (w/w) and dissolution temperature of 40 and 80°C for xanthan and guar gum, respectively.
Role of conformation and acetylation of xanthan on xanthan-guar interaction
Carbohydrate Polymers, 1992
The synergistic effect obtained by mixing xanthan and guar solutions were examined by low shear viscosity measurements in relation to the temperature. Native and deacetylated xanthan samples were used in mixtures in which the total polymer concentrations were 1 g/litre and 0.5 g/litre. Gelation was observed for temperatures lower than 15 °C for the native xanthan-guar system (weight ratio 1/1) in 10 -2 M NaC1 and at 22-24°C for the same system in water; in this last case, it is known that the xanthan is in the disordered conformation. For a mixture of deacetylated xanthan-guar, gelation was observed at a temperature below 26°C in water. The results confirm that there is a stronger interaction between deacetylated xanthan and guar than native xanthan and guar because of enhanced xanthan-guar gum backbone association in the former case.
Influence of the Ionic Strength in the Intrinsic Viscosity of Xanthan Gum. An Experimental Review
2015
This study involves the influence of ionic strength in intrinsic viscosity of xanthan gum. The best concentration of monovalent and bivalent cations chloride salts is evaluated. The salt concentration is 0.001 M for monovalent cations and 3 x 10-5 M for bivalent cations and the hydrodynamic radius is maximum for these concentrations. The minimal concentration is in the range of 0.01 to 0.1 M for different cations.
Carbohydrate polymers, 2018
The influence of concentration on the shear and extensional rheology properties of aqueous solutions of xanthan and guar gums was studied in this work. Shear rheology involved small amplitude oscillatory shear (SAOS), flow curves and transient flow, while the extensional rheology was analyzed using hyperbolic contraction flow. In addition, the mechanical properties during solutions manufacture were monitored in situ through the evolution of torque with processing time by mixing rheometry. The results showed that the hydrocolloids exert a great influence on the process rheokinetics and on the resulting rheological response. SAOS tests showed that the xanthan gum solutions behaved as weak gels, whereas guar gum solutions suggest the presence of entanglement and the formation of a viscoelastic, gel-like structure. All the systems exhibited shear-thinning behaviour. Guar gum solutions obeyed the Cox-Merz rule, with some divergence at high rates for the more concentrated solutions, while...
The effect of calcium salts on the viscosity and adsorption behavior of xanthan
Carbohydrate Polymers, 2011
The effect of CaCl 2 , Ca(NO 3 ) 2 , CaSO 4 , CaCO 3 and Ca 3 (PO 4 ) 2 on the flow behavior of xanthan gum solutions was investigated. Regardless the concentration and type of calcium salt used, xanthan solutions presented pseudoplastic behavior. The soluble salts (CaCl 2 and Ca(NO 3 ) 2 ) induced the disordered state in the xanthan chains at concentration of 1.0 g/L or 10 g/L, decreasing the flow consistency index (K) values. At 100 g/L soluble salts K values were similar to those found for pure xanthan solutions, whereas at the same concentration of insoluble particles the K values increased 20%. The adsorption of xanthan gum onto Si/SiO 2 surfaces in the presence of calcium salts was investigated by ellipsometry and atomic force microscopy (AFM). The adsorbed layer of xanthan onto Si/SiO 2 consisted of two regions: (i) a thin acid resistant sublayer, where xanthan chains were like highly entangled fibers and (ii) a thick upperlayer, whose morphology was calcium salt dependent.
Synergistic gelation of xanthan gum with locust bean gum: A rheological investigation
1997
Many industrial products often include in their formulation more than one polysaccharide to achieve the desired properties during and after processing. Many such mixed systems behave as would be expected from the known properties of the individual polymers. In others, however, their properties are superior to those of either component alone, or may be qualitatively different. In many polysaccharide systems, the combination of a gelling polymer with a nongelling one gives rise to strong synergistic effects, as a consequence of interaction among different chain polymers and formation of mixed junction zones.
Journal of Food Process Engineering, 2011
The viscosity of the binary and ternary systems of tragacanth (T), guar (G) and methylcellulose (MC) was obtained by means of a rotational viscometer in the range of concentration from 1 to 10 g/L at 25, 35, 45 and 55C. The modeling was based on polymer concentration, temperature and shear rate. The viscometric parameters, flow and consistency indices were evaluated as a function of the cited variables, obtaining the corresponding correlations. Interactions between polymers are hypothesized because of its structure and molecular weight. An interaction parameter Dh ij was calculated for modeling. As expected, in all the cases, the apparent viscosity decreases with temperature and it was introduced in the proposed models for T-G and G-MC systems. Synergistic effects were found for T-G in all the cases and G-MC when G concentration was higher than MC concentration. These results could suggest that interactions between MC and G molecules are generated.j fpe_371 475..490 PRACTICAL APPLICATIONS Hydrocolloids are additives used as stabilizers with multiple applications on different industries. In food industry, the interest to find new textures and sensorial properties has led to research on new sources, derivatives or mixtures. In the last case, new ingredients, developed from well-characterized and widely used hydrocolloids have been the subject of recent patents. Additionally, rheological measurements are frequently used to process control and, therefore, it is the main reason to employ correlations of flow properties involving process variables in order to predict the rheological behavior.