Enzyme-modified guar gum/xanthan gelation: An analysis based on cascade model

The gel properties of a mixture of enzymatically-modified guar gum (EMG) and xanthan (XG) were investigated. The guar gum sample treated with α-galactosidase to remove galactose residues had a mannose/galactose ratio of 3.02, and was capable of forming a synergistic gel with xanthan. The concentration-dependent and temperature-dependent modulus data for the EMG/XG gel were analyzed by the two-component cascade model which assumed a heterotypic association between segments of EMG and XG. The optimal functionalities (number of cross-linking sites per chain), f_EMG and f_XG, were found to be 300 and 30, respectively. The former is equal to the number of segment size with more than six unsubstituted mannose residues in a galactomannan backbone, while the latter corresponds to a cross-link density of one per 37 repeating units in a xanthan molecule. The cascade analysis of the composition dependence of critical gelling concentration was performed by introducing the effect of the homotypic association of XG or EMG, which became significant in the gel point measurement. The enthalpy change per cross-link for the heterotypic association was found to be two times higher than that for the homotypic association.     

Experimental Analysis of Structural Change and Rheological Behavior of Macromolecular Solutions with Guar and Xanthan Gums in Crossflow Microfiltration Processing

The present paper reports on the structural change and rheological behavior of mixtures of macromolecular suspensions (guar and xanthan gums) in crossflow microfiltration processing. Mixtures in suspension of guar and xanthan gums at low concentrations (1,000 ppm) and different proportions were processed by microfiltration with membrane of nominal pore size of 0.4 μm. The rheological behavior of the mixtures was investigated in rotational viscometers at two different temperatures, 25 and 40 °C, at the beginning and at the end of each experiment. The shear stress (τ) in function of the shear rate (γ) was fitted and analyzed with the power-law model. All the mixtures showed flow behavior index values (n) lower than 1, characterizing non-Newtonian fluids (pseudoplastic). The samples of both mixtures and permeates were also analyzed by absorbency spectroscopy in infrared radiation. The absorbency analysis showed that there is good synergism between xanthan and guar gums without structure modifications or gel formation in the concentration process by microfiltration.     

Improving effect of xanthan and locust bean gums on the freeze-thaw stability of white sauces made with different native starches

The effect of adding xanthan gum and locust bean gum at low concentrations (0.15% w/w) on the freeze/thaw stability of white sauces prepared with native starches from four different sources (corn, waxy corn, potato, and rice) was investigated. Linear viscoelastic properties were taken as structural indicators and these and syneresis as indicators of the freeze/thaw stability of the sauces. The pasting properties of the starch in the sauce system were also studied. Both hydrocolloids reduced the structural changes occurring after thawing, xanthan gum being more effective than locust bean gum. In corn and potato sauces, the most affected by the freeze/thaw cycle, the appearance of syneresis and the increase in viscoelastic functions were significantly reduced by both hydrocolloids. In general, the addition of hydrocolloids affected peak, hot peak and cold peak viscosities and reduced relative total setback. The results regarding the possible effects of hydrocolloid addition to white sauce systems are discussed in molecular terms.     

Dynamic Rheology of Rice Starch‐Galactomannan Mixtures in the Aging Process

The effect of galactomananns (guar gum and locust bean gum) at different concentrations (0, 0.2, 0.4, 0.6 and 0.8%, w/w) on the dynamic rheological properties of aqueous rice starch dispersions (5%, w/w) was investigated by small‐deformation oscillatory measurements during aging. Magnitudes of storage (G′) and loss (G′′) moduli measured at 4°C before aging increased with the increase in gum concentration in the range of 0.2–0.8%. G′ and G′′ values of rice starch‐locust bean gum (LBG) mixtures, in general, were higher than those of rice starch‐guar gum mixtures. G′ values of rice starch‐guar gum mixtures as a function of aging time (10 h) at 4°C increased rapidly at initial stage and then reached a plateau region at long aging times. However, G′ values of rice starch‐LBG mixtures increased steadily without showing a plateau region. Increasing the guar gum concentration resulted in an increase in plateau values. The rate constant (K) for structure development during aging was described by first‐order kinetics. K values in rice starch‐guar gum mixtures increased with the increase in guar gum concentration. G′ values of rice starch‐galactomannan mixtures after aging were greater than those before aging.     

Concentrated O/W emulsions formulated by binary and ternary mixtures of sodium caseinate,xanthan and guar gums: rheological properties,microstructure, and stability

Food Science and Biotechnology - The effects of xanthan gum (XG) (0, 0.3, 0.6 wt%), guar gum (GG) (0, 0.3, 0.6 wt%) and XG:GG mixtures (0.3–0.3, 0.3–0.6, 0.6–0.3 and 0.6–0.6...     

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.     

Rheological properties of whey protein isolate stabilized emulsions with pectin and guar gum

Dynamic oscillatory and steady-shear rheological tests were carried out to evaluate the rheological properties of whey protein isolate (WPI) stabilized emulsions with and without hydrocolloids (pectin and guar gum) at pH 7.0. Viscosity and also consistency index of emulsions increased with hydrocolloid concentration. At γ = 20 s⁻¹, the value of viscosity of the emulsion with 0.5% (w/v) pectin was about fivefold higher than that of the emulsion without pectin. Flow curves were analyzed using power law model through a fitting procedure. Flow behaviour index of all emulsions except for containing 0.5% (w/v) guar gum was approximately in the range of 0.9–1.0, which corresponds to near-Newtonian behaviour. The shear thinning behaviour of emulsions containing 0.5% (w/w) guar gum was confirmed by flow behaviour index, n, of 0.396. Both storage (G′) and loss modulus (G″) increased with an increase in frequency. Emulsions behaved like a liquid with G″ > G′ at lower frequencies; and like an elastic solid with G′ > G″ at higher frequencies. Effect of guar gum was more pronounced on dynamic properties. Phase angle values decreased from 89 to <10° with increasing frequency and indicated the viscoelasticity of WPI-stabilized emulsions with and without pectin/guar gum.     

Influence of type,concentration and flow behaviour of hydrocolloid solutions on aroma perception

The effects of the addition of two hydrocolloids—locust bean (LBG) and xanthan gums—at two concentrations (0.2 and 0.5%, w/v) on the intensity of the aroma of limonene and of isopentyl acetate solutions was studied using the pairwise ranking test. Previously, the rheological behaviour of the studied gums was analysed, finding that while LBG solutions were slightly pseudoplastic at the lower concentration and more so at the higher one, the xanthan solutions were clearly pseudoplastic at both concentrations. Addition of 0.2% LBG did not alter the limonene aroma intensity perceived, but on adding 0.5% LBG, above the coil overlap concentration (c*), the decrease in aroma intensity was significant. Addition of xanthan gum at any concentration did not modify the limonene aroma intensity perceived by judges, which can be attributed to the low value of c* for solutions of this gum. No difference in isopentyl acetate aroma was found among samples.     

Effect of processing treatments and storage conditions on stability of fruit juice based beverages enriched with dietary fibers alone and in mixture with xanthan gum

The present work aims to study the synergistic effect between xanthan gum (X) with a range of hydrocolloids such as barley β-glucan (Bg), guar gum (G), and konjac-mannan (K) on the viscosity of heat-treated fruit juice based beverages. The protective effect of X on the stability of Bg, G, and K in a fruit juice based beverage during processing and storage (0–16 weeks at 4 °C or 20 °C) was also evaluated. The results showed that pasteurization stabilized viscosity and turbidity of beverages enriched in Bg and BgX. However, the viscosity of pasteurized beverages enriched in K and G varied with storage time. In general, addition of X showed a complete protective effect against degradation at 4 °C for K (KX) whereas it provides no protection at all for G (GX). Viscosity and turbidity of beverages prepared with Bg and BgX increased significantly while those with G and K decreased slightly over time. Viscosity and turbidity changes are rapid when beverages are stored at 20 °C. We clearly evidenced that processing and storage treatments along with proper formulation are crucial to ensure technological stability of dietary fibers and X proved to be efficient to stabilize other fibers.     

Viscosity of galactomannans during high temperature processing: influence of degradation and solubilisation

The rheological properties of guar gum (GG) and locust bean gum (LBG), in response to high temperature treatments, were measured using a rheometer equipped with a high pressure cell. This has allowed the viscosity to be assessed at temperatures above 100°C and as the polymer suspension is heated from 20 to 121°C and then cooled back to ambient temperature to simulate a food sterilisation cycle. Activation energies for depolymerisation estimated from viscosity changes with time at a series of constant temperatures were estimated as 63 kJ/mol for GG and 98, 104, 110 kJ/mol for three different samples of LBG. A model was developed to interpret the viscosity change through the simulated sterilisation cycle. This took into account the degradation of the polysaccharide and the change in viscosity due to thermal motion. Estimations of molecular weight changes during the heating process suggest that GG is more susceptible to thermal degradation than LBG. It is suggested that this is due to the greater ability of the latter to associate in solution.     

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.     

Role of initial apparent viscosity and moisture content on post irradiation rheological properties of guar gum

Guar gum is a polygalactomannan used in various industries. Previous studies on radiation processing of guar gum showed a decrease in its viscosity during irradiation. Present work reports rheological properties and magnitude of depolymerization as affected by initial apparent viscosity (AV) and moisture contents of guar gum during irradiation processing. Rate of degradation was found to be dependent on the initial moisture content of guar gum during irradiation. D₅₀ values for oven dried gum was 490 Gy and it increased to 1250, 2600 and 2420 Gy in samples having 10%, 25% and 30% initial moisture respectively. EPR spectroscopy showed disappearance of anisotropic signals with increasing moisture content indicating crosslinking of polymer. FTIR spectroscopy results suggested that there were no major chemical functional group transformations during irradiation.     

Rheological and structural characterization of gels from whey protein hydrolysates/locust bean gum mixed systems

The gelling ability of whey proteins can be changed by limited hydrolysis and by the addition of other components such as polysaccharides. In this work the effect of the concentration of locust bean gum (LBG) on the heat-set gelation of aqueous whey protein hydrolysates (10% w/w) from pepsin and trypsin was assessed at pH 7.0. Whey protein concentrate (WPC) mild hydrolysis (up to 2.5% in the case of pepsin and 1.0% in the case of trypsin) ameliorates the gelling ability. The WPC synergism with LBG is affected by the protein hydrolysis. For a WPC concentration of 10% (w/w), no maximum value was found in the G′ dependence on LBG content in the case of the hydrolysates, unlike the intact WPC. However, for higher protein concentrations, the behaviour of gels from whey proteins or whey protein hydrolysates towards the presence of LBG becomes very similar. In this case, a small amount of LBG in the presence of salt leads to a big enhancement in the gel strength. Further increases in the LBG concentration led to a decrease in the gel strength.     

Steady and Dynamic Shear Rheology of Rice Starch‐Galactomannan Mixtures

Rheological properties of rice starch‐galactomannan mixtures (5%, w/w) at different concentrations (0, 0.2, 0.4, 0.6 and 0.8%, w/w) of guar gum and locust bean gum (LBG) were investigated in steady and dynamic shear. Rice starch‐galactomannan mixtures showed high shear‐thinning flow behaviors with high Casson yield stress. Consistency index (K), apparent viscosity (η_a,100) and yield stress (σ_oc) increased with the increase in gum concentration. Over the temperature range of 20–65°C, the effect of temperature on apparent viscosity (η_a,100) was described by the Arrhenius equation. The activation energy values (E_a = 4.82–9.48 kJ/mol) of rice starch‐galactomannan mixtures (0.2–0.8% gum concentration) were much lower than that (E_a = 12.8 kJ/mol) of rice starch dispersion with no added gum. E_a values of rice starch‐LBG mixtures were lower in comparison to rice starch‐guar gum mixtures. Storage (G′) and loss (G′′) moduli of rice starch‐galactomannan mixtures increased with the increase in frequency (ω), while complex viscosity (η*) decreased. The magnitudes of G′ and G′′ increased with the increase in gum concentration. Dynamic rheological data of ln (G′, G′′) versus ln frequency (ω) of rice starch‐galactomannan mixtures have positive slopes with G′ greater than G′′ over most of the frequency range, indicating that their dynamic rheological behavior seems to be a weak gel‐like behavior.     

Impact of chemical composition of xanthan and acacia gums on the emulsification and stability of oil-in-water emulsions

Xanthan gum (GX) and acacia gum (GA) are widely employed in food industry, indeed xanthan gum is used for its thickening properties of aqueous solutions and acacia gum for its emulsifying ability. The present work aims to study the effect of GX–GA mixtures on the stability of oil-in-water (o/w) emulsions; attention is particularly focused on the impact of the chemical structure of each gum. Emulsion stability has been evaluated by monitoring the evolution of droplet size and viscometric properties over time when submitted to accelerated ageing conditions. On the one hand results show that the higher the ArabinoGalactanProtein (AGP) content the more stable the emulsion as observed when GA is used alone. On the other hand, we proved, unexpectedly, that the most viscous aqueous phase does not exhibit the best emulsion stability. Besides, we clearly evidenced the presence of specific interactions between GX and GA in both emulsion and aqueous solution, these interactions being governed by the gums chemical composition.     

稳定剂对软冰淇淋品质的影响

对软冰淇淋浆料的粘度及软冰淇淋的硬度、膨胀率、抗融性等指标进行测试来观察黄原胶、刺槐豆胶和卡拉胶对软冰淇淋品质的影响.结果表明：在没有乳化剂存在的前提下,刺槐豆胶的抗融性最好,卡拉胶次之,黄原胶较差,但刺槐豆胶对软冰淇淋膨胀率的影响不稳定,当添加量为0.2%～0.4%时能显著提高软冰淇淋的膨胀率,其他用量时膨胀率则反而降低,黄原胶可提高产品的膨胀率,卡拉胶则降低膨胀率;在粘度方面,三者均有增稠作用,作用大小依次为黄原胶、刺槐豆胶和卡拉胶;三者均有降低产品硬度的趋势,刺槐豆胶的降低程度大于卡拉胶和黄原胶.     

The physiological and rheological effects of foods supplemented with guar gum

The high molecular weight polysaccharide Guar gum has a plethora of uses in the food, pharmaceutical and paint industries. This polysaccharide is also employed as a dietary fibre, but the quantity used in food is limited due to its viscous properties. Guar gum may be modified enzymatically or chemically to reduce its molecular weight and by extension its viscosity. This modification though is believed to reduce its physiological efficacy, for example the attenuation of postprandial glycemia. However, a number of studies have shown the viscosity effects alone of this fibre in vitro and in vivo is not always correlated with blunted glycemia. The absolute mechanisms behind the benefits seen with guar gum consumption are not known and studies have shown factors such as food composition, food matrix and food and fibre processing conditions may all play a significant role.     

Rheological properties of xanthan gum-gelatine spray-dried mixtures. Application in a custard-like formulation

 The effect of a spray-drying process on the rheological and textural properties of xanthan gum-gelatine dispersions was studied. Remarkable differences were found between co-dried samples and dispersion samples. Apparent viscosity and extrusion values were higher and shear-thinning behavior more pronounced than in non-dried samples. Also, stronger thickening and stabilizing properties were noticed. With regard to viscoelastic properties, an increase in the elastic component was observed. The new product was used in a standard confectioner's custard formulation and its properties were studied. When these samples were compared with a traditional custard made with starch, although enhanced rheological properties were recorded a similar visual appearance between samples was observed. Received: 27 March 2000     

Impact of xanthan gum,sucrose and fructose on the viscoelastic properties of agarose hydrogels

Mixed carbohydrate systems are of special interest for the food and non-food industry as they offer a versatile range of unique and novel functional properties. However, intense research is required to understand the complex processes occurring in such systems on a molecular level and to be able to modify them aim-oriented. In food, characteristic properties are based on the physicochemical functions of the biopolymers added. Thus, small deformation tests and moisture analysis have been applied to study the impact of xanthan gum and two types of sugar on the viscoelastic properties, the sol–gel transition and the water holding capacity of 1% agarose hydrogels. Agarose gels are very elastic, turbid and prone to synaeresis, which impinges on their mouth feeling. Additions of xanthan gum revealed less elastic gels with an unaffected water holding capacity. Progressive addition of two different types of up to 40% of sugar yield an increase of the elasticity of agarose gels, whereby sugar concentrations of 60% partially result in a structural breakdown and thus a significant lower network structure but better water holding. In ternary systems, the effect of the sugar concentration and sugar type used is diminished by xanthan gum. The gelation mechanism of agarose gels with a distinct amount of co-solutes is presumably mainly affected by the water shortage evolved from the competition for it of all solutes present.