Rheological properties of Cedrela odorata gum exudate aqueous dispersions (original) (raw)
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Food Biophysics, 2018
Bacterial cellulose as polysaccharide possessing outstanding chemical purity and a unique structure compared with wood cellulose, attracts great attention as a hydrocolloid system. It was shown, that at intense mechanical action on a neat bacterial cellulose film in presence of water, the gel-like dispersions are obtained. They retain stability in time (at least, up to several months) and temperature (at least, up to 60 • C) without macro-phase separation on aqueous and cellulose phases. The main indicator of the stability is constant viscosity values in time, as well as fulfilling the Arrhenius dependence for temperature dependence of viscosity. Flow curves of diluted dispersions (BC content less than 1.23%) show strong non-Newtonian behavior over the entire range of shear rates. It is similar with dispersions of micro-and nanocrystalline cellulose, but the absolute viscosity value is much higher in the case of BC due to more long fibrils forming more dense entanglements network than in other cases. Measuring the viscosity in increase and decrease shear rate modes indicate an existence of hysteresis loop, i.e., thixotropic behavior with time lag for recovering the structural network. MCC and NCC dispersions even at cellulose content more than 5% do not demonstrate such behavior. According to oscillatory measurements, viscoelastic behavior of dispersions corresponds to gel-like systems with almost total independence of moduli on frequency and essentially higher values of the storage modulus compared with the loss modulus.
Rheological properties and surface tension of Acacia tortuosa gum exudate aqueous dispersions
Carbohydrate Polymers, 2007
Steady shear flow properties of Acacia tortuosa gum aqueous dispersions at different concentrations (15-40% w/v) were studied at 20°C using a controlled shear rate Couette rheometer and Mooney-Ewart sensor systems. Flow curves showed shear thinning non-Newtonian behaviour with a tendency to a Newtonian plateau at high-shear rate. The results obtained fitted the Sisko model very well. The influence of temperature (5-40°C) on the flow curves was studied at given gum concentration (40% w/v). The infinite-shear rate Newtonian viscosity derived from the Sisko model fitted an Arrhenius-type equation. A controlled stress rheometer was used to conduct small amplitude oscillatory shear tests with the double cone geometry on A. tortuosa gum dispersion (40% w/v). It was clearly observed that the gum dispersion exhibited viscoelastic properties in a given temperature range (5-25°C). The elastic component was always higher than the viscous one. The frequency dependence of the dynamic moduli and the failure of the Cox-Merz rule supported the existence of a soft gel-like structure which weakened with temperature. The surface tension of A. tortuosa aqueous solutions was measured in a concentration range (0.01-1.5% w/v). The equilibrium value reached at (0.5% w/v) was (42.6 mN/m), which is significantly lower than the corresponding to A. senegal gum (46.9 mN/m). The rheological behaviour and surface tension of A. tortuosa gum suggest that it may compete with arabic gum in some industrial applications.
Rheological analysis of emulsion-filled gels based on high acyl gellan gum
Food Hydrocolloids, 2013
Emulsion-filled gels are widely used in cosmetic, food, and pharmaceutical industry. As rheological properties of these systems are strongly dependent on the properties of the gelled polymer network, rheological characteristics of gels containing high and low acyl gellan gum were analyzed. Under the processing conditions low acyl emulsions were unstable, thus in the present work the influence of oil and hydrocolloid concentrations on the viscoelastic behavior of emulsion-filled gels containing high acyl gellan gum was studied. Increasing gellan concentration (from 0.1 g/100 g to 0.5 g/100 g) produced stronger gels, while oil fraction (10 g/100 ge30 g/100 g) slightly affected the elastic behavior of the emulsions reinforcing the structure and the elastic characteristics of the gellan matrix. Sauter diameter (d 32) was measured for all emulsions and an average value of 12 mm was obtained. Rheological data (oscillatory and creeperecovery tests) were successfully modeled to interpret the structural characteristics of the gelled emulsions. The broadened BaumgaerteleSchausbergereWinter spectrum was used to represent the linear viscoelastic behavior of the continuous phase and the emulsified system, showing that the rheological behavior of the systems was controlled by the highly structured continuous phase rather than the contribution of filler lipid droplet in the emulsion. Relaxation spectra were validated using creeperecovery experiments. Regardless of hydrocolloid concentration, creep compliance of the gel emulsions decreased compared with their respective gels, showing that the inclusion of oil droplets produced a reinforcement of the structure and the gel strength of the matrix.
Journal of Texture Studies, 2010
Rheological studies of tragacanth and guar gums dispersions were carried out by means of steady shear (3 to 1000/s) and small amplitude oscillatory shear experiments (0.1 to 10 rad/s) for concentrations up to 8.9 g/L for tragacanth and 7.6 g/L for guar gum at 25C using stress controlled rheometer. The dispersions exhibited shear‐thinning characteristics. A simplified Cross model was adequate to fit the shear‐dependent viscosity behavior for both gums. Model parameters for guar gum were correlated with concentration employing power functions (with flow index constant) and for tragacanth gum the dependence was linear for flow index, power for time constant and exponential for zero‐shear rate viscosity. Mechanical spectra revealed that dispersions behave as dilute systems of coil polymers with trend to entangled systems at the highest concentrations. Loss and storage moduli were correlated with frequency and the resulting parameters were correlated with concentration. Cox–Merz rule hol...
Rheological Study of O/W Emulsions Containing Dried Whole Egg and Locust Bean Gum
Journal of Texture Studies, 1994
NaCl and 50% KCI, and Mineral salt: 65% NaC1, 25% KCl and 10% MgSO,) on the rheological properties of O/W emulsions containing locust bean gum was analyzed. Flow curves over the range 0. I to 100 sand transient flow curves at 0.2 s-', at 20 and 30C were obtained for 12 different emulsions, containing 30% ( d w ) of sunflower oil. The K and n power law parameters and the hysteresis loop area (HL) were evaluated from the flow curve. So were the Hahn parameters from time-dependent stress decay fitting. Rheological behaviour of emulsions was affected by the type of salt and the presence of sucrose. Changes in solvent properties of the continuous phase in the emulsions on the macromolecules present could be responsible for the different behaviour. The ageing effect on flow behaviour parameters and on the hysteresis loop area was also studied. Evolution of rheological parameters during emulsion storage suggests that increase of ionic strength and polar solutes concentration decrease the stabilizing properties of locust bean gum. Journal of Texture Studies 25 (1994) 3 3 4 3 . A / / Rights Reserved.
Small-deformation rheology of mesquite gum stabilized oil in water emulsions
Carbohydrate Polymers, 2006
The influence of the nature of the oil phase on the viscoelastic properties of emulsions stabilized with mesquite gum has been investigated. Mesquite gum-stabilized emulsions of D-limonene, n-decane, n-dodecane, n-tetradecane n-hexadecane and orange oil were analyzed, the observations showed that the nature of the oil used was determinant for the viscoelastic and gel formation ability of the emulsions. Orange oil-inwater emulsions stabilized with mesquite gum developed a gel-like structure with time, in contrast to the emulsions obtained with alkane oils and with D-limonene. This is rationalized in terms of a weak gel network of protein-polysaccharides molecules interconnecting spherical oil droplets. The gelling behavior of these systems has been described with a model derived from percolation theory. q
Food Biophysics, 2020
The interactions between sodium caseinate (NaCas) and basil seed gum (BSG) in the presence of calcium chloride (CaCl 2) were investigated. The phase behavior of the mixed aqueous dispersions and their gels revealed a homogeneous mixture, obtained at the higher concentrations of both CaCl 2 and BSG. The Herschel-Bulkley model sufficiently fitted the flow behavior of the mixture solution data. Apparent viscosity increased significantly (p < 0.05) by increasing the concentration of BSG, where the addition of CaCl 2 had no significant effect on the viscosity of the samples (p > 0.05). Furthermore, there was an increase in thixotropy due to the higher concentrations of BSG and CaCl 2. Based on the frequency sweep test, at the low frequencies, a more gel-like behavior was observed in the case of the higher concentrations of either BSG or CaCl 2. The rheological and SEM data suggested that the stronger structure of NaCas-BSG gel in the presence of the higher concentrations of CaCl 2 was related to the induction of complex formation between the two biopolymers.
LINEAR AND NONLINEAR VISCOELASTIC BEHAVIOR OF OIL-IN-WATER EMULSIONS STABILIZED WITH POLYSACCHARIDES
Journal of Texture Studies, 2002
The rheological behavior and stability of oil-in-water emulsions stabilized by different thickening agents were analyzed. Food emulsions were prepared with commercial sunflower oil (40% w/w oil-in-water) and stabilized with 1% emulsifier. The tested thickeners were: (1) 1% w/w xanthan gum (XG), (2) 5% w/w potato starch (PS), (3) 5% PS + 0.5% XG, (4) 1% w/w guar gum (GG), and (5) 0.5% XG + 0.5% GG. Mean droplet size and droplet size distribution (DSD) of emulsions were determined by static light scattering. Steady flow (viscosity versus shear rate), transient flow (viscosity versus time) and oscillatory shear tests (linear viscoelasticity) were performed. The addition of thickening agents improved the stability of the emulsions, the effect was less marked in systems containing only GG. DSD was not significantly modified in emulsions containing starch or hydrocolloids. Microscopic observations showed that all the tested emulsions were flocculated due to the presence of hydrocolloids. The observed shear thinning behavior was attributed to the molecular structure of the polysaccharides and to the flocculation/deflocculation process; viscosity data were satisfactorily fitted to the Cross model. Frequency sweeps showed that emulsions with PS or XG have a weak gel structural network (G’ > G); those with GG correspond to a polymeric solution where G’ and G″ curves intersect within the range of tested frequencies. The viscoelastic linear behavior was described according to the Maxwell generalized model. The discrete relaxation spectrum and relaxation times were estimated from the experimental values of G’ and G″ for emulsions with PS, PS + XG, and XG. Nonlinear viscoelasticity was also studied from stress relaxation curves at different shear strains. The damping function was calculated and the Soskey-Winter parameters were determined. Transient flow viscosities at different shear rates were comparable to the values estimated from stress relaxation measurements.
Biochemical Engineering Journal, 2011
Start-up at the inception of shear and flow interrupted experiments were carried out to illustrate the transient flow properties and thixotropic recovery of low-acyl gellan gum fluid gels prepared by a lowenergy mechanical treatment. Small amplitude oscillatory shear tests were conducted to illustrate the rheological response under non-destructive conditions. Confocal laser scanning microscopy revealed the occurrence of a dispersion of gel-like domains in a continuous phase. Rheological methods were used to check that the samples characterised were free of thermo-mechanical history effects prior starting the transient flow tests. Start-up shear flow experiments at 10 s −1 resulted in a nearly instantaneous sharp rise of viscosity until a peak value was reached before it dropped following a sum of two first-order kinetic equations. The kinetic coefficients as well as the relative fall in viscosity were found to increase with gellan concentration. The equilibrium modulus as well as the peak and steady-state viscosities scaled with the gellan concentration following a power law equation with a characteristic exponent of about 2.0. Conversely, the degree of thixotropic recovery after a rest time of 10 s went down as gellan concentration increased, emphasising the need to balance both effects when formulating gellan fluid gels as stabilisers. The results obtained do a better job of highlighting the importance of peak viscosity than steady-state viscosity when data for pump selection and calculation are required.
Macromol
The effects of treating two biopolymers (Trigonella foenum—graceum galactomannan and xanthan gum mixtures) with microwaves and ultrasound on the rheological aspects of O/W emulsions were investigated. The data obtained from steady shear flow were fitted with various models and the best were chosen due to the values of R2 and RMSE. The oscillatory shear rheology data demonstrated that the emulsions not treated with microwaves or ultrasound had viscous-like behavior and treated samples demonstrated weak gel behavior. The values obtained for various rheological parameters (especially apparent viscosity, storage modulus and loss modulus) indicated that fenugreek galactomannan had more impact on the rheological aspects of emulsions in comparison with xanthan gum. In addition, the synergistic interaction between two biopolymers, particularly in samples treated with ultrasound, resulted in better rheological aspects which could be affiliated with the strong bonds between the hydrocolloids....