Rheological Behavior of Food Emulsions Mixed with Saliva: Effect of Oil Content, Salivary Protein Content, and Saliva Type

In this paper, we studied the effect of saliva on the rheological properties of ß-lactoglobulin- and lysozyme-stabilized emulsions, prepared at pH¿=¿6.7 in relation to variation of emulsions- and saliva-related parameters. The effect of oil¿volume fraction (2.5% w/w to 10% w/w), salivary protein concentration (0.1 to 0.8 mg ml¿1), and the use of both stimulated and unstimulated saliva was investigated. Viscosity and storage modulus were measured before (¿ emul and G¿emul, respectively) and after addition of saliva (¿ mix and G¿mix). To better estimate the changes due to saliva-induced flocculation of the emulsions, the ratios ¿ mix/¿ emul, G¿mix/G¿emul were calculated. In addition, tan ¿ (=the ratio of the loss and storage moduli) was investigated to evaluate the viscoelastic behavior of the emulsion/saliva mixtures. Increasing the oil¿volume fraction and salivary protein concentration resulted in an increase in ¿ mix/¿ emul and G¿mix/G¿emul, while a decrease in tan ¿ of the emulsion/saliva mixtures is occurring. When compared with unstimulated saliva, mixing ß-lactoglobulin-stabilized emulsions with stimulated saliva led to a reduction in ¿ mix/¿ emul and G¿mix/G¿emul, and an augment of tan ¿ at all measured deformations. In case of lysozyme-stabilized emulsions, the use of stimulated saliva increased G¿mix/G¿emul for ¿

Structural response to O*-O' and magnetic transitions in orthorhombic perovskites

We present a temperature dependent single crystal x-ray diffraction study of twinned orthorhombic perovskites La1-xCaxMnO3, for x=0.16 and x=0.25. These data show the evolution of the crystal structure from the ferromagnetic insulating state to the ferromagnetic metallic state. The data are modelled in space group Pnma with twin relations based on a distribution of the b axis over three perpendicular cubic axes. The twin model allows full structure determination in the presence of up to six twin fractions using the single crystal x-ray diffraction data.Comment: 13 pages, including 13 figures and 2 table

Strong-correlation effects in Born effective charges

Large values of Born effective charges are generally considered as reliable indicators of the genuine tendency of an insulator towards ferroelectric instability. However, these quantities can be very much influenced by strong electron correlation and metallic behavior, which are not exclusive properties of ferroelectric materials. In this paper we compare the Born effective charges of some prototypical ferroelectrics with those of magnetic, non-ferroelectric compounds using a novel, self-interaction free methodology that improves on the local-density approximation description of the electronic properties. We show that the inclusion of strong-correlation effects systermatically reduces the size of the Born effective charges and the electron localization lengths. Furthermore we give an interpretation of the Born effective charges in terms of band energy structure and orbital occupations which can be used as a guideline to rationalize their values in the general case.Comment: 10 pages, 4 postscript figure

A self-interaction corrected pseudopotential scheme for magnetic and strongly-correlated systems

Local-spin-density functional calculations may be affected by severe errors when applied to the study of magnetic and strongly-correlated materials. Some of these faults can be traced back to the presence of the spurious self-interaction in the density functional. Since the application of a fully self-consistent self-interaction correction is highly demanding even for moderately large systems, we pursue a strategy of approximating the self-interaction corrected potential with a non-local, pseudopotential-like projector, first generated within the isolated atom and then updated during the self-consistent cycle in the crystal. This scheme, whose implementation is totally uncomplicated and particularly suited for the pseudopotental formalism, dramatically improves the LSDA results for a variety of compounds with a minimal increase of computing cost.Comment: 18 pages, 14 figure

Flow-induced coalescence in protein-stabilized highly concentrated emulsions: Role of shear-resisting connections between the droplets

This work focuses on flow-induced coalescence in highly concentrated emulsions stabilized by bovine ß-lactoglobulin. In these systems, flow-induced coalescence results in separation of oil. The amount of oil separated increases with the intensity of the flow treatment and reaches a plateau value above a certain intensity of the flow treatment. In this work, the flow treatment was chosen to be sufficiently intense to reach this plateau value. The oil separation increased roughly linearly with the volume fraction of emulsion droplets, starting at a critical volume fraction of approximately 0.90. Furthermore, at constant volume fraction, the oil separation increased with the time lapse during which the emulsion had been at this volume fraction. It reached a maximum value, which did not depend on the electrolyte concentration but was higher for calcium ions than for sodium ions. The rate at which the oil separation reached this maximum value increased with the electrolyte concentration. These observations are explained on the basis of a previously developed mechanism of flow-induced coalescence, in which the sensitivity to flow-induced coalescence is related to a slip¿stick transition between the surfaces of the thin films between emulsion droplets, caused by shear connections. It is shown that the same mechanism of coalescence is also relevant at volume fractions below 0.5 for systems in which the emulsion droplets are aggregate

Effect of fat hardness on large deformation rheology of emulsion-filled gels

The aim of this work was to investigate the impact on the texture properties of emulsion-filled gels when saturated solid fat is replaced by unsaturated liquid oil. Whey protein aggregate, gelatin and micellar casein, were chosen to form different types of gel matrices and the fat hardness was varied by selection of the fat type and variation of the temperature. As emulsifier, either whey protein aggregates, whey protein or sodium caseinate was used. Texture properties of the filled gels were investigated by uniaxial compression. The fracture properties were affected by the presence of emulsion droplets, however the effect of fat hardness was small. The presence of emulsion droplets (either liquid or solid) increases the gel stiffness as compared to the emulsion-free gel, indicating that the droplets are an active part of the gel. An increase in solid fat content led to a moderate increase in gel stiffness for whey protein aggregate gels, which was in agreement with predictions according to the Palierne model for the effect of fat hardness on the stiffness of the filled gels. For the gelatin and micellar casein gels, the magnitude by which the gel stiffness increased as a function of the solid fat content was much larger than expected on the basis of this model. Microscopical observation suggested that this was caused by an inhomogeneous distribution of the fat droplets, due to droplet aggregation or/and concentration of the droplets in gel strands, which increases the effective volume fraction of the droplets in the matrix

Colloidal destabilisation mechanisms in protein-stabilised emulsions

Over the past decade important new insights have been gained into the functionality of proteins as emulsion and foam stabilisers. This paper reviews important new findings in the fields of emulsion stabilisation by polysaccharide thickeners, coalescence in highly concentrated and dilute aggregated emulsions and emulsion droplet–air interaction. These new findings will be discussed in terms of recent improved understanding of the surface rheological behaviour and thin film behaviour of proteins. These insights may lead to an improved use of the special properties that proteins have as emulsion stabilisers compared to other stabilisers, such as low-molecular-weight surfactants or polyelectrolytes

Effect of fat hardness on large deformation rheology of emulsion-filled gels

The aim of this work was to investigate the impact on the texture properties of emulsion-filled gels when saturated solid fat is replaced by unsaturated liquid oil. Whey protein aggregate, gelatin and micellar casein, were chosen to form different types of gel matrices and the fat hardness was varied by selection of the fat type and variation of the temperature. As emulsifier, either whey protein aggregates, whey protein or sodium caseinate was used. Texture properties of the filled gels were investigated by uniaxial compression. The fracture properties were affected by the presence of emulsion droplets, however the effect of fat hardness was small. The presence of emulsion droplets (either liquid or solid) increases the gel stiffness as compared to the emulsion-free gel, indicating that the droplets are an active part of the gel. An increase in solid fat content led to a moderate increase in gel stiffness for whey protein aggregate gels, which was in agreement with predictions according to the Palierne model for the effect of fat hardness on the stiffness of the filled gels. For the gelatin and micellar casein gels, the magnitude by which the gel stiffness increased as a function of the solid fat content was much larger than expected on the basis of this model. Microscopical observation suggested that this was caused by an inhomogeneous distribution of the fat droplets, due to droplet aggregation or/and concentration of the droplets in gel strands, which increases the effective volume fraction of the droplets in the matrix

Colloidal destabilisation mechanisms in protein-stabilised emulsions

Over the past decade important new insights have been gained into the functionality of proteins as emulsion and foam stabilisers. This paper reviews important new findings in the fields of emulsion stabilisation by polysaccharide thickeners, coalescence in highly concentrated and dilute aggregated emulsions and emulsion droplet–air interaction. These new findings will be discussed in terms of recent improved understanding of the surface rheological behaviour and thin film behaviour of proteins. These insights may lead to an improved use of the special properties that proteins have as emulsion stabilisers compared to other stabilisers, such as low-molecular-weight surfactants or polyelectrolytes