M. Berjano

Flow behaviour and stability of light mayonnaise containing a mixture of egg yolk and sucrose stearate as emulsifiers

Abstract In this paper the influences of sucrose stearate concentration, fraction of dispersed phase and processing parameters on the stability of oil-in-water emulsions with a chemical composition similar to commercial light mayonnaise, but using a mixture of egg yolk and a sucrose stearate, with high hydrophilic—lipophilic balance, have been studied. Emulsions have been characterized by carrying out steady flow tests and droplet size distribution measurements as a function of ageing. From the experimental results obtained we may conclude that the stability of the emulsions is improved by increasing energy input and oil and sucrose stearate concentrations, using processing temperatures ~50°C. All these factors yield higher values of steady-state viscosity. The emulsions studied show both linear viscoelastic functions and droplet size distribution values quantitatively similar to those reported for other commercial mayonnaises. Moreover, a significant flocculation process takes place up to around six days after manufacture. Nevertheless, the application of a steady shear on the samples produces marked structural destruction.

Linear viscoelastic behavior of commercial and model mayonnaise

Oscillatory shear experiments in the linear viscoelastic domain were carried out on four commercial brands of mayonnaise and three samples of model mayonnaise with different oil contents (75, 77.5, and 80% w/w), at temperatures between 10 and 40 °C. A power‐law relationship between complex viscosity and frequency was found for all the samples. The power‐law indexes were compared with those obtained from stress relaxation tests carried out on commercial mayonnaise. No significant differences between them were found. Shear strain in the nonlinear viscoelastic region, above a certain threshold value, produced an irreversible structural breakdown of the emulsion. This was dependent not only on the magnitude of the strain but also on the elapsed time since the deformation started.

Transient flow of o/w sucrose palmitate emulsions

Abstract This paper deals with the characterisation and modelling of the nonlinear viscoelasticity properties of concentrated oil-in-water emulsions containing sunflower oil (60–80 wt%), water and a hydrophilic sucrose palmitate (1–5 wt%). With this aim, transient shear flow and nonlinear stress relaxation tests were carried out. Oscillatory shear measurements were also performed to calculate the linear relaxation modulus of the emulsions studied. The transient flow behaviour of all the emulsions studied is qualitatively similar, showing always a stress overshoot followed by a stress decay which tends to a steady-state value. However, at a critical shear rate, which depends on temperature and disperse phase concentration, a stress undershoot may be found. This behaviour has been attributed to optically observed shear-induced microstructural changes. A factorable nonlinear viscoelastic constitutive equation, the Wagner model with Soskey–Winter’s damping function, predicts the transient flow of these emulsions, in a range of shear rates, fairly well. However, a lack of concordance is found as shear rate increases, fact that has been explained on the basis of wall-slip phenomena and shear-induced microstructural changes.

Temperature dependence of viscosity for sucrose laurate/water micellar systems

The viscous behavior of sucrose laurate aqueous systems of high hydrophilic-lipophilic balance up to a 50% (wt) surfactant concentration at temperatures between 5°C and 60°C has been studied. Systems up to a 45% (wt) surfactant concentration show Newtonian behavior. The influence of temperature was studied using the activated diffusive relaxation model described by Goodwin. A maximum specific viscosity that appears at lower temperature as sucrose laurate concentration increases can be observed. These results are related to the micellar growth of the sucrose laurate aggregates as temperature rises. More concentrated systems show complex viscous response. Thus, a limit viscosity at low shear rates and a shear-thinning behavior after a critical shear rate are observed. Limit viscosity decreases and critical shear rate increases as temperature rises. This behavior is related to the threshold micelle concentration for entanglement of rod-like micelles.

Flow behavior of sucrose stearate/water systems

The aim of this work was to carry out a rheological study of aqueous systems containing a nonionic surfactant derived from sugar. The compositions studied ranged from the micellar region up to the occurrence of fully developed liquid crystals. This study was carried out at 50°C.Systems up to 2% (wt) sucrose stearate exhibited a power-law decrease in the steady-state apparent viscosity with shear rate. At higher sucrose stearate concentrations, the flow curves exhibited two well-defined regions depending on shear rate, so that the apparent viscosities fitted the Carreau model A [Carreau, P.J., D. De Kee and M. Daroux,Can. J. Chem. Eng. 57:135 (1979)]. The existence of three composition ranges is proposed. An increasingly stronger micellar structure, as surfactant concentration rises, extends up to 10% (wt) sucrose stearate. Between 15% and 35% (wt) sucrose stearate, the results obtained are consistent with the occurrence of a lamellar liquid-crystal dispersion in an isotropic micellar solution. The liquid crystalline content in the dispersion steadily increases with surfactant concentration up to reaching a fully developed lamellar liquid crystal at 40% (wt) sucrose stearate.

Influence of surfactant concentration and temperature on the flow behaviour of sucrose oleate aqueous systems

Abstract This paper deals with the flow behaviour of aqueous systems of a sucrose oleate with a high hydrophilic—lipophilic balance (HLB, 15). Influences of temperature (10–45°C) and surfactant concentration (10–45 wt.%) have been studied. The flow curves show both a limiting viscosity at low shear rates and a shear-thinning region after a critical shear rate that depends on temperature and sucrose oleate concentration. Experimental flow curves have been shifted on a master curve using the time—temperature superposition method. This master curve includes all the experimental flow curves obtained with the systems having a sucrose oleate concentration between 10 and 30 wt.%. The shift factor shows a complex dependence on temperature, having two different Arrhenius-like regions with two different activation energies. These results can be explained on the basis of the existence of a micellar phase at low concentrations and temperatures and then a lamellar phase, completely developed for concentrations higher than 35 wt.% surfactant.

Influence of the Type of Emulsifier on the Rheokinetics of the Emulsification Process

The consecutive disruption of oil droplets and their coalescence are the two critical steps during emulsification, both of which are favoured by an intense agitation. The role of a suitable surfactant is of paramount importance as it first lowers the interfacial tension favouring the disruption of droplets, and then prevents coalescence by increasing the repulsive potential between droplets.