Effect of surface and bulk solution properties on the adsorption of whey protein onto steel surfaces at high temperature

The adsorption of whey proteins on modified and unmodified 316 2R stainless steel surfaces was studied by in situ ellipsometry under well-defined flow conditions. The effects of bulk properties, e.g. temperature, pH, protein concentration and flow rate as well as surface modification by ion implantation, sputtering, chemical vapour deposition and silica sol–gel deposition, were investigated. The surface properties were characterized in terms of wettability and roughness. The results suggest a surface-induced aggregation process given that (1) the adsorbed amount at high temperature was significantly larger than expected for a monolayer, and (2) the adsorption was lower with a larger number of aggregates in solution. The surface modifications affected the initial adsorption rate, i.e. the rate of forming the monolayer, which in turn influenced the surface induced aggregation and eventually the total amount deposited. Therefore, once the surface was fully covered with protein, the rate of deposition, which is controlled by protein–protein interactions, was less affected by the surface modifications. This work evidenced the potential of surface modification regarding the reduction of protein adsorption on steel surfaces.