Structure of casein micelles in filtered deposits investigated directly above the membrane

Casein micelles (CMs) are used as raw material for processed food as well as in a number of technical applications such as blend fabrics, glues and coatings. A fast and cost-effective way of their preparation from skimmed milk is the micro-filtration of milk. During the micro-filtration a porous membrane enables the separation of CMs from smaller milk ingredients such as whey proteins, lactose and salts. This process is the most challenging one among all membrane processes because smaller proteins are meant to pass the membrane while deposited CMs form an additional mass transfer barrier. It is therefore of paramount interest to understand structural details of deposited layers in order to enable a more targeted process design. Recent X-ray scattering experiments showed that CMs deform when subjected to osmotic stress 1,2 or shearing forces 3 . These experimental results support the hypothesis that casein micelles behave as soft objects that structurally respond to changes in their environment.