T.B.J. Blijdenstein

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.

Suppression of depletion flocculation in oil-in-water emulsions: a kinetic effect of β-lactoglobulin

Abstract This paper reports on creaming and flocculation in 10% (w/w) oil-in-water emulsions, stabilised by β-lactoglobulin (β-lg) and flocculated by dextran. Dextran and an additional amount of β-lg were added at various concentrations after emulsion formation. A substantial effect of the β-lg concentration was observed. At higher β-lg concentrations, a larger dextran concentration was required to induce network formation. This effect was explained by a retardation of the flocculation process at larger β-lg concentrations, shown by diffusing wave spectroscopy (DWS). This retardation was caused by the unexpectedly high apparent viscosity at low shear-rates of mixed solutions of β-lg and dextran.

Microrheology: new methods to approach the functional properties of food

Three configurations have been developed to improve the understanding of structural element interactions in food material during deformation. The three configurations combine an inverted confocal scanning laser microscope (CSLM) and a cell that can apply to the sample a specific deformation: continuous shear, linear oscillatory shear and biaxial extension (compression). In the continuous shear and oscillatory shear configurations (OSCs), a zero-velocity plane is created in the sample by moving two plates in opposite direction, maintaining stable observation conditions of the structural behaviour under deformation. The OSC allows simultaneous application of CSLM and diffusing wave spectroscopy, a multiple light scattering technique. The third configuration (compression configuration) allows observation at a stagnation point during rheometric measurements. The configurations accept semi-liquid products (dressing, sauces, dairy products, etc.) for investigations in area such as aggregation, gelation, interactions at interface, coalescence, break-up.

Microrheology: Structural evolution under static and dynamic conditions by simultaneous analysis of confocal microscopy and diffusing wave spectroscopy

An oscillatory shear configuration was developed to improve understanding of structural evolution during deformation. It combines an inverted confocal scanning laser microscope (CSLM) and a special sample holder that can apply to the sample specific deformation: oscillatory shear or steady strain. In this configuration, a zero-velocity plane is created in the sample by moving two plates in opposite directions, thereby providing stable observation conditions of the structural behavior under deformation. The configuration also includes diffusion wave spectroscopy (DWS) to monitor the network properties via particle mobility under static and dynamic conditions. CSLM and DWS can be performed simultaneously and three-dimensional images can be obtained under static conditions. This configuration is mainly used to study mechanistic phenomena like particle interaction, aggregation, gelation and network disintegration, interactions at interfaces under static and dynamic conditions in semisolid food materials (desserts, dressings, sauces, dairy products) and in nonfood materials (mineral emulsions, etc.). Preliminary data obtained with this new oscillatory shear configuration are described that demonstrate their capabilities and the potential contribution to other areas of application also.