Analytical data for Acacia senegal var. senegal gum samples collected between 1993 and 1995 from Sudan

Over 1500 authentic and commercial A. senegal var. senegal gum samples were analysed to evaluate existing quality control parameters and to assess the potential of new parameters such as pH, viscosity, viscosity average molecular weight (M_V) equivalent weight and total uronic acid content as additional qualifying indices. The data obtained indicate the following mean values: moisture (10.75%), ash (3.77%), nitrogen (0.328%), specific rotation (−31.3°), pH (4.66), equivalent weight (1436) and total uronic acid content (13.71%). The results also indicate wide variations in intrinsic viscosity and viscosity average molecular weight (mean values 16.4 ml g⁻¹ and 9.0×10⁵, respectively. Accordingly these parameters, therefore, cannot be recommended as qualifying indices.     

Effect of hydrocolloid type and concentration on flow behaviour and sensory properties of milk beverages model systems

Formulation of low-calorie flavoured milk beverages involves the use of hydrocolloids to obtain an acceptable mouthfeel. Sodium alginate and κ-carrageenan are the most commonly used. In this paper, the rheological behaviour of model solutions containing either of these two hydrocolloids, with or without the addition of sucrose, in water or milk, has been studied. All solutions fitted well to the Ostwald de Waele model. The analyses of variance showed that in κ-carrageenan solutions, the effect of the medium–hydrocolloid interaction on both flow index (n) and apparent viscosity at 1 s⁻¹ (η₁) was significant. Milk-based solutions were more pseudoplastic and more viscous than the aqueous solutions, due to the well known κ-carrageenan–casein molecular interaction. In alginate solutions, the medium–hydrocolloid interaction was also significant but the differences in both n and η₁ values were of less entity. Sensory viscosity differences of more viscous chocolate milk model systems were well explained by apparent viscosity values at low shear rate (10 s⁻¹), while for less viscous samples apparent viscosity at higher shear rate (300 s⁻¹) values were appropriate. At similar viscosity, κ-carrageenan systems showed better flavour-releasing properties than alginate.     

On solid-like rheological behaviors of globular protein solutions

Dynamic viscoelastic and steady flow properties of β-lactoglobulin, bovine serum albumin, ovalbumin, and α-lactalbumin aqueous solutions were investigated at 20°C. When a sinusoidal strain in the linear viscoelastic region was applied, the solutions of the globular proteins except for α-lactalbumin showed typical solid-like rheological behavior: the storage modulus G′ was always larger than the loss modulus G″ in the entire frequency range examined (0.1–100 rad/s). Under a steady shear flow, strong shear thinning behavior was observed with increasing shear rate from 0.001 to 800 s⁻¹, for the globular proteins except for α-lactalbumin. The values of the steady shear viscosity η were lower than those of the dynamic shear viscosity η* at a comparable time scale of observation, violating the Cox–Merz rule, and thus suggesting that a solid-like structure in a globular protein solution was susceptible to a steady shear strain. During isothermal gelation of the protein colloids at 70°C, no crossover between G′ and G″ was observed so that the gelation point was judged by an abrupt increase in the modulus or a sudden decrease in tanδ.     

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.     

Fractionation and physicochemical characterization of peach gum polysaccharides

One kind of Chinese peach gum was fractionated by different solvent extraction (water followed by alkaline solutions). Chemical analysis showed peach gum polysaccharides were acidic arabinogalactans, mainly composed of arabinose (∼50%), galactose (∼37%) and uronic acid (13–14%), with the molecular weight of ∼4.60 × 10⁶ g/mol according to high performance size exclusion chromatography (HPSEC) analysis. Peach gum solution exhibited typical shear thinning flow behavior properties, K (consistency index) values increased while n (flow index) values decreased with the increasing of concentration. Dynamic sweep tests showed that moduli of peach gum solutions were highly dependent on frequency, concentration and temperature. Water extractable fraction was able to form gel network when concentration was higher than 4%. Alkaline extracted peach gum gave weaker rheological responses, such as lower viscosity at same concentration when compared to the water extractable fraction. Two alkaline extractable fractions exhibited similar intrinsic viscosities of 21.18 dl/g (0.1 M NaOH extractable, AE01) and 21.76 dl/g (0.5 M NaOH extractable, AE05), respectively, while water extractable fraction (WE) formed aggregate in water at low concentration. All fractions extracted from peach gum exudates showed better emulsion capacity and stability than gum arabic and fenugreek, which could be used in food industry to replace or partially replace gum arabic.     

Rheological behaviour of tamarind seed gum in aqueous solutions

Tamarind seed gum as seed polysaccharide from Tamarindus indica L. has been characterized for physicochemical and rheological properties in the present work. The structural analysis determined the presence of glucose:xylose:galactose in a molar ratio of 2.61:1.43:1.The Huggins and Kraemer plots obtained by capillary viscometry gave an intrinsic viscosity of 4.7 dl g⁻¹ and the viscosity average molecular mass was calculated to be 9.18 × 10⁵ g mol⁻¹ using the Mark-Houwink relationship. The steady shear and dynamic viscoelasticity properties of tamarind seed gum in aqueous solutions at different concentrations were investigated at 20 °C using a Haake Rheometer RS75. The tamarind seed gum solutions clearly exhibited shear-thinning flow behaviour at high shear rate and Newtonian region occurred at low shear rate range, however, at higher concentrations, pronounced shear thinning was observed. The value of zero shear viscosity (η₀) was estimated by fitting Cross and Carreau models. The specific viscosity at zero shear rate (η_sp0) was plotted against the coil overlap parameter (C[η]) and the slopes of the lines in the dilute and semi-dilute regions were found to be ∼2.2 and 4.3, respectively. The value of the critical concentration (C^∗) was about 4.23/[η]. While, the mechanical spectra in the linear viscoelastic region of tamarind seed gum solutions showed the typical shape for macromolecular solutions. Plots of η versus γ and η^∗ versus ω were superimposable and hence obey the Cox-Merz rule.     

Effects of pulsed electric fields (PEF) treatment on physicochemical properties of potato starch

Potato starch–water suspensions (8.0%, w/w) were subjected to pulsed electric fields (PEF) treatment at 30 kV·cm^− 1, 40 kV·cm^− 1 and 50 kV·cm^− 1, respectively. The physicochemical properties of PEF-treated potato starch samples were investigated using scanning electron microscopy (SEM), laser scattering technique, X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and the Brabender rheological method, with native potato starch as reference. It has been concluded from SEM analysis that dissociation and damage of PEF-treated potato starch granules appeared. Some granules aggregated with each other and showed gel-like structures. It was revealed from particle size analysis that there was an obvious increase of the granule size after PEF treatment. This has been attributed to the aggregation among granules. It was also demonstrated from other analysis that relative crystallinity, gelatinization temperatures, gelatinization enthalpy, peak viscosity as well as breakdown viscosity of modified samples all decreased with increasing electric field strength.

Industrial relevance

In this study, the effect of PEF treatment (up to 50 kV·cm^− 1) on physicochemical properties of potato starch has been investigated. The results from SEM images showed that dissociation, denaturation and damage of potato starch granules had been induced by the PEF treatments. Some of granule fragments showed gel-like structures, and congregated with each other or with other starch granules. Laser scattering measurements of particle size revealed that an obvious increase of granule size under electric field strength of 50 kV·cm^− 1, which was attributed to the aggregation of the starch granules. The X-ray diffraction pattern showed an obvious loss of crystalline structure after the PEF treatment at 50 kV·cm^− 1, which induced a trend of transformation from crystal to non-crystal in potato starch granules. DSC analysis showed a decrease in gelatinization temperatures (T_o and T_p) and gelatinization enthalpy (ΔH_gel) with increasing electric field strength. Brabender rheological method has been used to show that the peak viscosity and breakdown viscosity decrease with increasing electric field strength of PEF treatment. All the results reveal that the PEF treatment can lead to an intragranular molecular rearrangement of potato starch granules, which induces changes of various physicochemical properties of the treated starch thus may endow it some new characteristics and functions. This phenomena may warrant further more detailed study.     

Study of xanthan gum/waxy corn starch interaction in solution by viscometry

The objective of the study was to investigate the molecular interactions of xanthan gum and waxy corn starch in a ternary system. Solutions of xanthan gum/(waxy corn starch) blends dissolved in a mixed solvent of 90% DMSO/10% H₂O (v/v) were studied by means of viscometry as a function of total polymer concentration and composition. The classical Huggins equation, η_sp/C=[η]+bC, which expresses the specific viscosity (η_sp) of a polymer as a function of the concentration C, was found to be suitable for all blends in the dilute system. The intrinsic viscosity ([η]) and Huggins parameter b of the blends increased with the increase of xanthan fraction in the blends. Meanwhile, the addition of xanthan gum also dramatically lowered the overlap concentration (C*) of the blends. The results indicate that xanthan gum is a good thickener, and xanthan gum and waxy corn starch are attracted to each other in the solution under study.     

Solution viscosity and structural modification of pumpkin biopectin

Solutions of ‘biopectin’ obtained from pumpkin pulp by digestion with the multi-enzyme culture supernatant from Bacillus polymyxa (strain 88A) were prepared in 0.10 M NaCl and characterised by rotational viscosity measurements at 20 °C. The resulting double-logarithmic plot of specific viscosity versus the product of concentration (c) and intrinsic viscosity ([η], from combined Huggins and Kraemer extrapolation to c=0) showed a sharp increase in slope at c[η]≈1 in comparison with the normal value of c[η]≈4 for disordered coils, suggesting a branched structure, possibly arising from Ca²⁺-mediated association of constituent chains.Pumpkin biopectin is non-gelling, in marked contrast to the pectin obtained from the same source by conventional extraction with acid, although the yield is more than doubled. Attempts to induce gelation (with 70 wt% solids at low pH or with stoichiometric Ca²⁺ at neutral pH) by removing the high content of divalent cations naturally present in the biopectin and by chemical deacetylation under acidic conditions (pH 1.2; 4 days; 40 °C) proved unsuccessful. Further research using enzymic deacetylation is suggested.     

Investigation of molecular weight distribution of LBG galactomannan for flours prepared from individual seeds, mixtures, and commercial samples

The molecular weight distribution has been determined for the galactomannan solubilized from three types of locust bean gum (LBG) flours: single carob seeds, mixtures, and a range of commercial products. To prepare crude endosperm flours from carob seeds with minimal galactomannan degradation, a new extraction and milling method was developed. The method consists of applying a brief thermal shock to the seeds, followed by an extended 3-day swelling period, and manual separation of endosperms; particle size reduction to a flour is accomplished on hydrated endosperms using a centrifugal mill. This method was optimized so that redissolved LBG flours produced solutions with the highest possible viscosity and the least amount of galactomannan degradation as determined by SEC. For the three samples types, the molecular weight distribution, w(M), was found to be unimodal, appearing as a sharply defined main peak (M_p≈1.1×10⁶ g/mol) with a small high molecular weight tail (up to 2.0×10⁶ g/mol) and broad low molecular weight tail (down to 0.01×10⁶ g/mol); polydispersities (M_w/M_n) were estimated to be 1.5–1.8. Variations in M_w and [η] for galactomannans extracted from individual seeds originating from the same carob tree were minimal and nearly indistinguishable from a bulk mixture (6 seeds, M_w=0.96–1.1×10⁶ g/mol, [η]=14.2–15.1 dl/g). There was a higher variability in these molecular parameters for galactomannans solubilized from commercial LBG flours, which generally exhibited lower M_w and [η], broader distributions, and reduced solubilities (M_w=0.86–1.0×10⁶ g/mol, [η]=12.4–13.6 dl/g). These side-effects were attributed to damage caused by industrial scale seed processing. The near constancy of M_p for the three sample types suggests that the average molecular size of LBG galactomannan varies only slightly due to natural or biological causes.     

Neutron reflectivity study of the competitive adsorption of β-casein and water—soluble surfactant at the planar air-water interface

Application of the technique of specular neutron reflection to the study of adsorbed layer structure is illustrated for the case of β-casein at the air—water interface in the presence and absence of nonionic water—soluble surfactant C₁₂E₆. Guinier analysis of reflectivity data for a 5 × 10⁻³ wt% solution of pure β-casein in air-contrast-matched water (8 vol% D₂O) at pH 7.0 gives a time-independent adsorbed amount of 2.05 ± 0.10 mg/m2 and an adsorbed layer thickness of 1.65 ± 0.07 nm; these values are found to increase quite substantially as the pH is reduced towards the protein's isoelectric point. In the presence of surfactant the loss of reflectivity is a direct measure of protein displacement from the interface because the hydrogenated surfactant is almost contrast matched to the aqueous phase. At a C₁₂E₆ concentration in the range 2–2.5 × 10⁻⁴ wt% (surfactant: protein molar ratio, R ≈ 2.2), there is roughly half the protein lost from the interface but little change in adsorbed layer thickness as inferred from the slopes of the Guinier plots. Protein is effectively completely removed from the surface for R 10. These results are in semi-quantitative agreement with complementary competitive adsorption data for β-casein in soya oil-in-water emulsions.     

Rheological properties of cereal starch gels and Mesona Blumes gum mixtures

The effect of Mesona Blumes gum (MBG) was examined on steady and dynamic shear of MBG/rice starch and MBG/wheat starch gels. In addition, stress relaxation and creep tests were performed for two types of cereal starch gels. The flow curves of both MBG/starch gels exhibited pseudoplastic behavior at shear rates between 0.01 and 10 s⁻¹, and the data were fitted into the power law model (R² = 0.91–0.98). Dynamic mechanical spectrum showed that all gels were strong gels in frequency between 0.1 and 10 Hz. Stress relaxation data at different strains indicated a strain‐softening phenomenon for both gels. Data were fitted into Maxwell model (R² = 0.91–0.98). Creep curves were conducted at the shear stress 6.4 Pa within linear viscoelastic region of both MBG/starch gels. Data were fitted into Burgers model (R² = 0.91–0.98). Apparent viscosity η, storage moduli G′, equilibrium stress relaxation modulus G_e and zero apparent viscosity η₀ of MBG/rice starch gels decreased in the following order: 6/0>6/0.5>6/0.35>6/0.1 (starch/gum w/w). Whereas η, G′, G_e, and η₀ of MBG/wheat starch gels increased gradually along side the increase of MBG contents. The stress relaxation time λ of MBG/rice starch gels increased in the following order: 6/0<6/0.5<6/0.35<6/0.1 (starch/gum w/w) while λ of MBG/wheat starch gels decreased gradually with the increase of MBG level. The influence of MBG on two examined cereal starch is totally opposite.     

Enhancement effect on apparent viscosity of aqueous tragacanth gum dispersions promoted by sugars

Flow curves of aqueous dispersions of tragacanth gum (T) with sucrose and glucose at different temperatures were determined using a controlled‐stress rheometer. The effect of sodium chloride without or with sucrose (at the highest content) on the rheology of T dispersions was evaluated. The presence of sucrose and glucose promoted a noticeable enhancement impact on the apparent viscosity of aqueous T dispersions, which depended on sugar type/content, shear rate and temperature. In all cases, the glucose addition led to the largest enhanced viscosities at low shear rates (<10 s^?1) and temperature. The joint action of sugar and salt exhibited a notable effect on apparent viscosity at low shear rates, softening the strong shear‐thinning behaviour of T samples. Flow curves of T in the presence of sugars were satisfactorily described by the Cross‐Williamson model, being semi‐empirical correlations of the model parameters with ingredients content and temperature stablished.     

Steady and dynamic shear rheological properties of extrusion modified fenugreek gum solutions

This study investigated the rheological properties of extrusion modified fenugreek gum solutions (0.5, 1.0, 1.5, and 2.0%, w/v) under steady and dynamic shear conditions. Fenugreek gum was extruded in a twin-screw extruder without an exit die to minimize a decrease in molecular weight of fenugreek gum during extrusion process. Both of the steady and dynamic shear rheological tests revealed that extrusion process did not substantially influence the steady and dynamic shear properties of the gum. The power law model was applied to describe the flow behavior of the extruded gum solutions. The extrusion modified fenugreek gum solutions exhibited a shearthinning flow behavior at 25°C, and the values of consistency index (K) and apparent viscosity (η_a,100) increased with an increase in the gum concentration. The magnitudes of storage modulus (G′) and loss modulus (G″) for the extrusion modified fenugreek gum solutions increased with increasing frequency (ω) and with increasing gum concentration.     

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     

The chemical composition and some physical properties of a water-soluble gum from Prosopis africana seeds

A water‐soluble gum was extracted from the endocarp capsule of the seed coat of Prosopis africana. The gum yield varied substantially with the method of dehulling. Maximum yield was obtained after boiling in 0.1 m Na₂CO₃ for 4 h. The effects of two different gum concentrations on the rheological properties of gum solutions were examined. The gum formed viscous solutions at low concentrations and exhibited stable viscosity in the pH range 6.0–8.0. Chemical analyses showed that the purified gum had a composition of 2.4% fat, 1.04% protein, 21.5% crude fibre and a gelation concentration of at least 10%. Galactose and mannose were the major polysaccharides identified. Large reductions in viscosity were observed with the addition of various concentrations of Na⁺ salts. The activation energies of flow for 2 and 3% gum solutions were in the range of 19.2–22.8 kJ mol^?1 and were characteristic of systems with little intra‐ and intermolecular interactions.     

Effect of ultrasonic treatment on the rheological properties and particle size of gum tragacanth dispersions from different species

Dispersions of different species of gum tragacanth were sonicated at a frequency of 24 kHz with a total nominal output power of 200 W for different time intervals (0, 7, 15, 45 and 90 s). Various species behave differently under sonication, which is related to structural differences in these species. In the case of Astragaslus compactus and A. rahensus dispersions, as the sonication time increased, the viscosity and particle size of the dispersions decreased, just as in gum Arabic solutions. However, A. gossypinus gum behaved differently compared to the other species. At early stages of sonication (up to 15 s), the viscosity of the dispersions increased sharply and reached its maximum value (106.04 mPa s) as the particle size increased slightly to 275.69 μm. Continuing sonication led to a decrease in the viscosity of the dispersions, though the particle size did not show any changes. This behaviour is thought to be due to the rupture and aggregation of particles.     

Zeta potentials of gum arabic stabilised oil in water emulsions

The electrostatic contribution to the mechanism by which gum arabic stabilises oil in water has been investigated using laser Doppler electrophoresis. Electrophoretic mobilities of -limonene emulsion droplets measured in 10⁻³, 10⁻² and 10⁻¹ M NaCl over a pH range from 1 to 10, and 10⁻³–10⁻¹ M CaCl₂ in doubly distilled water, yielded relatively low potentials (less than 28 mV in magnitude). The interpreted zeta potentials are less than those required for electrostatic stabilisation alone. This data supports the postulated steric stabilisation mechanism with a finite electrostatic contribution. A model which suggests the arabino galacto proteins are adsorbed—via the proteins—to the interface with the polysaccharide moieties protruding into solution to give rise to a steric stabilising layer is supported by the data. No charge reversal is observed for the Ca solutions in contrast to the pH data indicating that some of the charge groups are inaccessible to the Ca ions.     

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.     

Steady shear flow behavior of gum extracted from Ocimum basilicum L. seed: Effect of concentration and temperature

Steady shear flow behavior of basil seed gum (BSG) was investigated between 0.5% and 2% (wt/wt) concentration and temperatures of 5-85 °C. BSG showed shear thinning behavior at all concentrations and temperatures. The Herschel-Bulkley model was employed to characterize flow behavior of BSG solutions at 0.1-1000 s⁻¹ shear rate. The pseudoplasticity of BSG increased markedly with concentration. Flow behavior of 1% BSG indicated a higher viscosity of this gum at low shear rates compared to xanthan, konjac and guar gum at similar concentration. The activation energy of BSG quantified using an Arrhenius equation increased from 4.9 × 10³ to 8.0 × 10³ J mol⁻¹ as concentration changed from 0.5% to 2% wt/wt. This indicated a heat-resistant nature of BSG. Increasing the apparent viscosity of BSG as temperature increase from 60 °C showed a sol-gel behavior of BSG based on dynamic oscillatory measurements. The static yield stress was obvious between shear rates 0.001-0.1 s⁻¹ (9.98 Pa for 1% BSG at 20 °C). The existence of the yield stress, high viscosity at low shear rates and pseudoplastic behavior of BSG make it a good stabilizer in some food formulations such as mayonnaise and salad dressing.