The effect of shear rate on the viscosity of solutions of guar gum and locust bean gum

The apparent viscosities of aqueous solutions of guar gum and locust bean gum have been measured over a range of shear rates from 14 to 1142 s^?1. Comparable measurements were also made on gum solutions to which glucose, sucrose or glucose syrup had been added. For all the solutions the variation of relative viscosity with shear rate fits a power law equation. Addition of sugar has no effect on the non-Newtonian behaviour of the gum solutions. The relative viscosity of the gum in the sugar solutions is lower than in water. The ratios of the relative viscosities closely correspond with the ratios of the intrinsic viscosities. This is interpreted in terms of a smaller extension of the gum molecule in the sugar solution.     

Rheological interactions between Lallemantia royleana seed extract and selected food hydrocolloids

BACKGROUND: Lallemantia royleana (Balangu) is a mucilaginous endemic plant which is grown in different regions of world. The flow behaviour of Balangu seed extract (BSE) and its mixture with xanthan, guar and locust bean gums at 1:3, 1:1 and 3:1 ratios, in addition to control samples (0% BSE), were evaluated. To describe the rheological properties of samples, the power law model was fitted on apparent viscosity–shear rate data. To evaluate the interaction between BSE and selected hydrocolloids in dilute solutions, the relative viscosity was also investigated. RESULTS: There was no significant difference between the consistency coefficient of guar and locust bean solutions and their blends substituted with 250 g kg^?1 BSE. The BSE–xanthan mixture at 1:3 and 1:1 ratios had consistency index equal to xanthan solution. BSE–locust bean gum at all ratios, BSE–xanthan at 1:3 ratio and BSE–guar gum at 1:1 and 3:1 ratios indicated relative viscosity lower than values calculated assuming no interaction. The intrinsic viscosity value of BSE was determined 3.50 dL g^?1. CONCLUSION: The apparent viscosities of BSE, selected hydrocolloids and their blends were the same at a shear rate of 293 s^?1 and the commercial gums can be substituted by 250 g kg^?1 and 500 g kg^?1 BSE. Copyright © 2011 Society of Chemical Industry     

Viscosity of solutions of xanthan/locust bean gum mixtures

Xanthan and locust bean gums are polysaccharides able to produce aqueous solutions with high viscosity and non‐Newtonian behaviour. When these solutions are mixed a dramatic increase on viscosity is observed, much greater than the combined viscosity of the separated polysaccharide solutions. In this work the influences of different variables on the viscosity of solutions of mixtures of xanthan/locust bean gum have been studied. Total polysaccharide concentration, xanthan and locust bean ratio on mixture and temperature at which the gum was dissolved (dissolution temperature) for both xanthan and locust bean gums have been considered. Under these different operational mixture conditions shear rate and time have also been considered to describe the rheological behaviour of the solutions studied. The high viscosity increase observed in these mixtures is due to the interaction between xanthan gum and locust bean gum molecules. This interaction takes place between the side chains of xanthan and the backbone of the locust bean gum. Both xanthan molecule conformation in solution – tertiary structure – and locust bean gum structure show great influence on the final viscosity of the solution mixtures. Xanthan conformation changes with temperature, going from ordered structures to disordered or chaotic ones. Locust bean gum composition changes with dissolution temperature, showing a dissolved galactose/mannose ratio reduction when temperature increases, ie the smooth regions – zones without galactose radicals – are predominantly dissolved. The highest viscosity was obtained for the solution mixture with a total polysaccharide concentration of 1.5 kg m⁻³ and a xanthan/locust ratio of 2:4 (w/w) and when xanthan gum and locust bean gum were dissolved at 40°C and 80°C, respectively. © 1999 Society of Chemical Industry     

The effect of shear rate on the viscosity of solutions of sodium carboxymethylcellulose and k-carrageenan

The apparent viscosities of aqueous solutions of sodium carboxymethylcellulose (NaCMC) and k-carrageenan have been measured over a range of shear rates from 14 to 1142 s^?1. Comparable measurements were also made on gum solutions to which glucose, sucrose, or glucose syrup had been added. For all the solutions the variation of relative viscosity with shear rate fits a power law equation. Addition of sugars to the most concentrated solutions of NaCMC has no effect on the non-Newtonian behaviour but addition of glucose syrup to the most dilute solutions of NaCMC decreased the non-Newtonian behaviour. However, the general pattern of behaviour showed close similarity with that of guar gum and locust bean gum. In the more concentrated glucose and sucrose solutions the non-Newtonian behaviour of k-carrageenan was increased appreciably. There was no comparable effect on k-carrageenan in glucose syrup solutions. This different behaviour of k-carrageenan is attributed to the development of solute-solute interactions.     

The effect of casein on the viscosity of solutions of hydrocolloids

The apparent viscosities of aqueous solutions of guar gum, locust bean gum, sodium carboxymethylcellulose and k-carrageenan have been measured over a range of shear rates from 14 to 1142 s^?1. Comparable measurements were made on solutions to which different quantities of casein (10-40 g litre^?1) had been added. For all the solutions a power law equation describes the variation of relative viscosity with shear rate. Addition of casein has no effect on the solutions of guar and locust bean gum, but does affect the rheology of solutions of sodium carboxymethylcellulose and k-carrageenan. The behaviour of k-carrageenan indicates a dependence on the polyanion:casein ratio, reaching a maximum at a concentration ratio of 1:4. The only significant solute-solute interactions in the hydrocolloid-casein solutions are electrostatic in nature.     

Relationship between sensory saltiness intensity and added oil in low-viscosity and high-viscosity polymer solutions

Generally, the foods we usually eat are not only aqueous solutions, but also viscous solutions and solids. Therefore, it is interesting for us to explore how taste components are perceived in a viscous polymer solution. The relationship between the sensory evaluation of saltiness intensity, amount of added oil, and apparent viscosity was clarified in low-viscosity and high-viscosity polymer solutions. The study was conducted using samples containing corn oil, sodium chloride, and [xanthan gum] or [xanthan gum + locust bean gum] as a thickener. Oil was added to the viscous polymer solutions regardless of whether they were low- or high-viscosity, and saltiness intensity was evaluated as compared with a reference solution. The low-viscous polymer solutions with [xanthan gum] were perceived to be saltier than the high-viscous polymer solutions with [xanthan gum + LBG] as the amount of oil increased. The shear stress value gradually increased as the amount of oil increased in both the low-viscosity and the high-viscosity polymer solutions, as derived from the fluid constitutive equation. There was a correlation between saltiness intensity and apparent viscosity in both high- and low-viscosity polymer solutions. A coefficient of determination (R²) of 0.918 was obtained between saltiness intensity and “apparent viscosity” for the samples using [xanthan gum] and that of 0.683 between saltiness intensity and “apparent viscosity” for the samples using [xanthan gum+LBG]. The low-viscosity polymer solutions showed a saltier intensity as the amount of oil increased and a greater correlation with apparent viscosity, as compared with the high-viscosity polymer solutions.     

Viscosity of guar gum and xanthan/guar gum mixture solutions

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⁻³), 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⁻³ 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. © 2000 Society of Chemical Industry     

Study of emulsions stabilized with Phaseolus vulgaris or Phaseolus coccineus with the addition of Arabic gum, locust bean gum and xanthan gum

The properties of o/w emulsions stabilized with 1%w/v common bean (Phaseolus vulgaris L.), V or scarlet runner bean (P. coccineus L.), Coc extracted by isoelectric precipitation or ultrafiltration, at pH 7.0 and 5.5, with the addition of Arabic gum, locust bean gum, xanthan gum and a mixture of xanthan gum–locust bean gum (0.1 %w/v and 0.25 %w/v) are studied. The stability of emulsions was evaluated on the basis of oil droplet size, creaming, viscosity and protein adsorption measurements. The addition of Arabic gum, caused an increase in D[4,3] values and a decrease in the amount of protein adsorbed at the interface. The addition of locust bean gum in some emulsions reduced the amount of protein adsorbed. The addition of xanthan and to a less extend of the polysaccharide mixture, promoted a decrease in D[4,3]. So, emulsion stability was affected by the polysaccharide nature. Differences were also observed with respect to the protein nature, the method of its preparation and emulsion's pH. All polysaccharides enhanced the emulsions viscosity with xanthan and xanthan–locust bean gum exhibiting the higher values. V isolates and isoelectricaly precipitated isolates of both V, Coc showed higher viscosity values. The stability was enhanced by the increase of the viscosity of the continuous phase and the creation of a network, which prevents the oil droplets from coalescence.     

Viscosity of locust bean (Ceratonia siliqua) gum solutions

Viscosity of locust bean (Ceratonia siliqua L) gum solutions has been studied. Shear rate, gum concentration and measuring and solubilisation temperatures were varied and the corresponding influences analysed. The gum solutions showed pseudoplastic behaviour. Apparent viscosity decreased with increasing measuring temperature. A maximum in the viscosity with increasing solubilisation temperature was observed, and it was assumed that this behaviour was related to differences in the molecular weight of the molecules dissolving at various temperatures, which produced a different galactose/mannose ratio in the solution. This effect was checked by a solubilisation study.     

Physicochemical, pasting and thermal properties of tuber starches as modified by guar gum and locust bean gum

This study was carried out in order to compare the functional characteristics of isolated starch from five tuber crops, yam, taro, sweet potato, yam bean and potato, as well as effect of guar gum (GG) and locust bean gum (LBG) on pasting and thermal properties of tuber starches. The results showed that total amylose content of five tested starches ranged from 17.85% to 30.36%. The results of pasting behaviour showed that potato starches exhibited the highest peak viscosity and yam starch presented a stable curve with little breakdown viscosity. Addition of GG and LBG resulted in a significant increase in peak, final viscosity, breakdown and setback viscosity for all tuber starches ( P  < 0.05), but a slight decrease in pasting temperature. The gelatinisation enthalpy (Δ H ) for starches with GG and LBG was slightly lower than those of the starches alone in yam and sweet potato, but not in taro and yam bean.     

Detection of adulteration of locust bean gum with guar gum by capillary electrophoresis and polarized light microscopy

Capillary electrophoresis (CE) and polarized light microscopy (PLM) were utilized in the detection of the adulteration of locust bean gum with guar gum. For CE analyses, standards of locust bean and guar gums were extracted with 30% CH₃CN, removing the residual proteins from the gum matrix. A 8.75 mM NaH₂PO₄-20.6 mM Na₂B₄O₇ buffer, pH 9, was used to separate these proteins and to identify marker proteins that were present in the guar gum. These markers did not co-migrate with components in the extracts of mechanically processed locust bean gum, and are used as indicators of adulteration. Using PLM with toluidine blue and iodine staining techniques, unadulterated locust bean gum samples were distinguished from mixed samples through the differential staining of components in locust bean versus guar and tara gums. These experiments in the use of CE and PLM provide orthogonal and complementary methods for the verification of 'true' positives and the elimination of 'false' positives.     

Functional Properties of Flax Seed Mucilage

Flax seed (Linwn usitatissimum L.) mucilage was prepared by extraction of seeds with water followed by evaporation, precipitation with ethanol and freeze drying of extract. Proximate composition, solubility, foamability and moisture sorption characteristics were determined. The mucilage contained less carbohydrates, more minerals and more protein than commercial locust bean and guar gums. Its solubility, however, was higher than locust bean and guar gums, and lower than gum arabic. Flax seed mucilage exhibited good foam stability properties in aqueous solutions at 1.0% (w/v). Very diluted solutions exhibited Newtonian-like behavior while shear thinning was shown at concentrations above 0.2% (w/v). The viscosity was maximum at a pH range 6.0–8.0 and it was reduced in solutions containing NaCl.     

Rheology of Mixed Systems of Sweet Potato Starch and Galactomannans

The effect of galactomannans (guar gum and locust bean gum) at different concentrations (0, 0.2, 0.4 and 0.6%, w/w) on rheological properties of sweet potato starch (SPS) was studied. The flow behaviors of SPS‐galactomannan mixtures were determined from the rheological parameters of power law and Casson models. The SPS‐galactomannan mixtures had high shear‐thinning fluid characteristics (n = 0.30‐0.36) exhibiting yield stress at 25°C. The presence of galactomannans resulted in the increase in consistency index (K), apparent viscosity (η_a,100) and Casson yield stress (σ_oc). In the temperature range of 25‐70°C, the mixtures followed the Arrhenius temperature relationship. Dynamic rheological tests at 25°C indicated that the SPS‐galactomannan mixtures had weak gel‐like behavior with storage moduli (G′) higher than loss moduli (G") over most of the frequency range (0.63‐62.8 rad/s) with frequency dependency. The magnitudes of dynamic moduli (G′, G" and η*) of the SPS‐galactomannan mixtures were higher than those of the control (0% gum), and increased with an increase in gum concentration. The tan δ (ratio of G"/G′) values (0.41‐0.46) of SPS‐guar gum mixtures were much lower than those (0.50‐0.63) of SPS‐locust bean gum mixtures, indicating that there was a more pronounced effect of guar gum on the elastic properties of SPS.     

Rheological study of xanthan and locust bean gum interaction in dilute solution

An oscillatory capillary rheometer was used to investigate visco-elastic properties of xanthan and locust bean gum (LBG) blends in dilute solution. Gums were evaluated for intrinsic viscosity and the elastic component. Molecular conformation of the complex of xanthan–LBG was assessed by the power law and the Huggins equations. A 60% xanthan–40% LBG blend exhibited the strongest attraction between xanthan and LBG molecules as evidenced by a greater intrinsic viscosity, the polymer miscibility coefficient α, the elastic component, and a positive Huggins coefficient K_m. The power-law model was successfully applied to predict the molecular conformation of xanthan and LBG alone in dilute solution and was exhibited as rod-like and random coil conformation. The power-law coefficient b increased as the LBG fraction increased in the blends, suggesting a more flexible xanthan–LBG complex dependent on LBG.     

Influence of mixing temperature on xanthan conformation and interaction of xanthan–guar gum in dilute aqueous solutions

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.     

A comparative study on viscosity behavior of water‐soluble chemically modified guar gum derivatives with different functional lateral groups

A comparative study was carried out on the viscosity behavior of three new water‐soluble chemically modified guar gum derivatives with different functional lateral groups, including O‐carboxymethyl‐O‐hydroxypropyl guar gum (CMHPG), with anionic character, O‐2‐hydroxy‐3‐(trimethylammonio)propyl guar gum (HTPG), with cationic character, and O‐carboxymethyl‐O‐2‐hydroxy‐3‐(trimethylammonio)propyl guar (CMHTPG), with amphoteric character. It was found that the shear rate, concentration, temperature, added salt and surfactant affected the viscosity properties of these new guar gum derivatives in aqueous solutions. Regardless of the functional lateral groups, all sample solutions behaved as non‐Newtonian shear‐thinning fluids, and their viscosity increased with the increase in their concentration but decreased with the increase in temperature. Aqueous CMHTPG solution had the strongest shear‐thinning property, and aqueous CMHPG solution investigated had the greatest viscous flow activation energy. In contrast to cationic HTPG or anionic CMHPG, amphoteric CMHTPG had an enhanced viscosity property in aqueous salt solutions, exhibiting an unusual anti‐polyelectrolyte viscosity behavior. The addition of sodium dodecylsulfate was found to result in a decrease in the viscosity of aqueous HTPG solution and an increase in the viscosity of aqueous CMHPG solution or CMHTPG solution. Copyright © 2005 Society of Chemical Industry     

Tribological properties of neutral polysaccharide solutions under simulated oral conditions

ABSTRACT:  Predictability of the perception of foods thickened by polysaccharides is only poor. Therefore, the effect of saliva on the lubrication properties of 2 types of neutral polysaccharides, cross-linked starch and locust bean gum, was studied. Despite the similar bulk rheological behavior of the 2 polysaccharides, the starch solution exhibited a significantly lower friction coefficient. Although starch viscosity was strongly decreased upon 10 s incubation with human saliva, a low friction coefficient was retained. The presence of remaining granules is held partly responsible for this. Addition of starch granules to locust bean gum also resulted in a decrease in the friction coefficient, but the effect was smaller compared to starch solutions digested by saliva. Smaller contact angles were measured for (digested) starch compared to locust bean gum solutions. This points to other parameters that assist in lubrication, such as the interaction of starch solution constituents with the rubbing surfaces. In addition, the importance of bulk viscosity for spreadability on surfaces was demonstrated. This study illustrates that the type of starch will determine not only the viscosity change but also the presence of intact granules upon digestion by saliva in the oral cavity; the combination of these 2 properties is regarded to be responsible for the poor predictability of sensory responses of starch containing foods.     

Rheological behaviour of pullulanase-treated guar galactomannan on co-gelation with xanthan

The present study involves the use of non-specific enzyme pullulanase (from Bacillus acidopullulyticus) to remove galactose residues from guar galactomannan to obtain modified guar galactomannan mimicking the functional properties of locust bean gum. The modified guar galactomannan blended with xanthan exhibited the rheological behaviour of elastic modulus (G′) greater than viscous modulus (G″) with a decrease in tan δ value similar to locust bean gum/xanthan blend. Also a twofold increase in the magnitude of elasticity compared to xanthan alone suggested the synergistic interaction with formation of three dimensional networks. The modified guar galactomannan with galactose content of 21% and M:G ratio 1:3.8, almost akin to locust bean gum, showed a better interaction with xanthan. Dynamic stress sweep study of modified guar galactomannan/xanthan blend with increased yield stress of 800 dynes/cm² also indicated the synergistic behaviour. Modified guar galactomannan also revealed the maximum synergistic interaction with xanthan at a mixing temperature of 60 °C than at 20 °C, 30 °C, 40 °C and 50 °C, respectively. Modification of guar galactomannan by pullulanase is an alternative route to produce galactose-depleted guar galactomannan with enhanced rheological functionalities on co-gelation with xanthan, as a cost effective replacement to locust bean gum.     

Steady shear flow properties of wild sage (Salvia macrosiphon) seed gum as a function of concentration and temperature

The steady shear flow properties of dispersions of a new potential hydrocolloid, sage seed gum (SSG), were determined as a function of concentration (0.5–2% w/w), and temperature (20–50 °C). SSG dispersions exhibited strong shear-thinning behavior at all conditions tested, which was even more pronounced than commercial hydrocolloids like xanthan, guar gum and locust bean gum. Different time-independent rheological models were used to fit the experimental data, although the Herschel–Bulkley model (H–B) was found the best model to describe steady shear flow behavior of SSG. An increase in gum concentration led to a large increase in yield stress and consistency coefficient values, whereas there was no definite trend with an increase in temperature. On the other hand, the above-mentioned increases in concentration and temperature did not yield a clear evolution of the shear-thinning characteristics of SSG dispersions. An Arrhenius-type model was also used to describe the effect of temperature. The activation energy (E_a) appeared in the range of 3949–16384 J/mol, as concentration increased from 0.5 to 2%, at a shear rate of 100 s⁻¹. The yield stress values estimated by viscoplastic rheological models were much higher than the data determined by stress ramp method. Apparent viscosity of SSG surpassed many commercial hydrocolloids such as guar gum, locust bean gum, Tara gum, fenugreek gum and konjac gum at the same conditions, which suggest it as a very good stabilizer in food formulations.