Structural changes of deposited casein micelles induced by membrane filtration

Abstract

Casein micelles undergo shape changes when subjected to frontal filtration forces. Grazing incidence small angle X-ray scattering (GISAXS) and atomic force microscopy (AFM) allow a quantification of such structural changes on filtration cakes deposited on smooth silicon micro-sieves. A trans-membrane pressure of deltap = 400 mbar across the micro-sieve leads to an immediate film formation after deposition of casein solution. We observe significant changes in the GISAXS pattern depending on how many layers are stacked on top of each other. Compared to a deposit formed by one layer, GISAXS on a deposit formed by three layers of casein micelles leads to less scattering in the vertical and more scattering in the horizontal direction. Simulations show that the experimental results can be interpreted by a structural transformation from an originally spherical micelle shape to an ellipsoidal-deformed shape. The results are supported by AFM measurements showing a reduced lateral size of casein micelles deposited on top of a membrane pore. The observed shape changes could be due to filtration forces acting on densely packed deposits confining the micelles into ellipsoidal shapes.

Effect of pH, transmembrane pressure and whey proteins on the properties of casein micelle deposit layers

“…They found that CMs arrange in a hexagonal lattice when forming deposit layers on membranes. In addition, experimental data from AFM and mGISAXS experiments indicate that CMs are subjected to an ellipsoidal shape change when CMs are exposed to elongational flow of the filtrate through the CM deposit towards the membrane pores [21]. This result is in good agreement with the studies on CM deposit compressibility [22] or the behavior of CMs under osmotic stress [13,14].…”

Effect of filtration forces on the structure of casein micelles

“…Grazing-incidence small-angle X-ray scattering (GISAXS) allows, for instance, for investigations on samples prepared on a solid support and hence for a direct comparison with those obtained from AFM measurements. GISAXS has been used to investigate changes of the natural conformation and size distribution of CM in films (Gebhardt et al, 2010 but more recently also in deposits on porous micro-sieves (Gebhardt et al, 2012). In all three studies the sizes estimated with GISAXS were in good accordance with those obtained by AFM.…”

Transmission behavior of pNIPAM microgel particles through porous membranes

“…8 however indicate that the microgel particles are quantitatively retained by the 3 kDa MWCO membrane. Some recent studies have shown that protein micelle undergo deformation during filtration [31,32], and therefore have attributes similar to microgel filtration.…”