Interfacial properties of fractal and spherical whey protein aggregates

Fractal and spherical aggregates of whey globular proteins are formed under conditions that coupled heating and shear flow in a plate heat-exchanger at high temperature and for short holding time. Their properties upon adsorption and spreading at the air-water interface have been studied at neutral pH and two subphase conditions. The surface activity of mixtures of aggregates and residual proteins is enhanced and the adsorption behaviour depends strongly on the denatured native-like monomers and the charge screening. After long hours of adsorption, they form a weakly dissipative viscoelastic network, with strong interactions. When spread at the air-water interface, protein aggregates dissociate and form monolayers whose properties are described by scaling laws in the semi-dilute regime. The scaling exponents found in charge-screening subphase conditions correspond to values for polymer in theta-conditions, whereas the values determined in long-range repulsion subphase conditions are intermediate between an ideal (theta-conditions) chain and a chain in good solvent.