During ultrafiltration (UF) of whey, membrane/solute interactions appear to have a considerable effect on the separation characteristics of the membrane. This is primarily caused by precipitation of poorly soluble salts and/or adsorption of whey proteins, taking place inside the membranes and affecting the pore size distribution. Evidence for location of precipitation and adsorption inside the membrane is obtained by measuring the amounts of salts precipitated (using radio labeling procedures) and protein adsorbed, and by comparing the protein adsorption with the adsorbed amounts on model surfaces having membrane-like characteristics. To quantify the influence of fouling in terms of pore narrowing, a characteristic pore size for UF membranes is defined, based on the retention of low-molecular-mass saccharides. Membrane morphology and surface properties appear to have a considerable influence on the amount and type of protein adsorbed, suggesting a potential for controlling membrane fouling by modification of membrane properties.
