Kinetics of Colloidal Deposition and Release of Polystyrene Latex Particles in the Presence of Adsorbed beta-Lactoglobulin Studied Using a Flow Cell
The effect of adsorbed whey protein, beta-lactoglobulin, has been investigated on the attachment of polystyrene latex particles to an indium tin oxide (ITO) surface and the subsequent release in anionic surfactant SDS solution and distilled-deionized water at pH 6.0. Experiments were carried out using a wall-jet flow cell and particle attachment was measured in situ using the technique of evanescent wave microscopy. The deposition rate of particles increased as predicted up to a shear rate of approximately 1000 s-1, for deposition at a diffusion-limited rate. There was a reduction in the rate at higher shear rates indicating a decrease in sticking efficiency. As the shear rate increased, the ITO surface became saturated more quickly due predominantly to blocking of the surface by deposited particles. The presence of adsorbed beta-lactoglobulin on the ITO surface caused a large reduction in the subsequent deposition rate of protein-coated particles. This was due to an increase in electrostatic repulsion. Differences were found in both the extent of removal and in the release (cleaning) kinetics of particles in SDS and in distilled-deionized water for the different particle-protein-ITO surface conditions investigated. Release of particles was also independent of the shear rate. Results were interpreted by considering the roles of protein replacement and elution which occurs in SDS solutions; >90% removal of protein-coated particles from a coated ITO surface was observed in SDS when both processes play a role. This compared to 55% removal in distilled-deionized water where they were considered negligible. Copyright 1997Academic Press
Joscelyne
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Food Engineering, Lund University, Lund, S-221 00, Sweden
Tr&auml;g&aring;rdh
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