Whey protein adsorption onto steel surfaces—effect of temperature, flow rate, residence time and aggregation

Whey protein adsorption on stainless steel surfaces was investigated by in situ ellipsometry under well-defined flow conditions and protein solution residence times. The size distribution in solution of the protein aggregates formed under the same conditions was determined by dynamic light scattering. The adsorption was performed at 72 °C and 85 °C, which is below and above the unfolding temperature of β-lactoglobulin (75 °C). The effect of increasing the Reynolds number on the aggregation process was evident only for the longest protein solution residence time, when larger aggregates were produced. At the higher temperature, higher flow turbulence decreased the amount of protein adsorbed on the surface, which was attributed to shear-induced removal of protein from the surface. At both temperatures, longer protein solution residence times decreased both the adsorption kinetics and the amount of protein adsorbed. This could be related to the concentration of native protein available in solution. Based on the experimental results, a model of the formation of a protein monolayer and multilayers on solid surfaces was developed. The model takes into account the dependence of the adsorption process on both protein solution residence time and flow rate and predicts the evolution of adsorbed mass of protein per unit surface area with operating time. Surface-induced aggregation was identified as the main mechanism responsible for the formation of multilayers, based on experimental data. To reduce the amount of protein adsorbed/deposited on the surface an increase in protein solution residence time was found to be more effective than an increase in the Reynolds number.