Adsorption of Whey Protein and Sodium Caseinate on Colloidal Cr2O3 as a Model for the Prefouling of Steel

Abstract

The adsorption of whey protein (β-lactoglobulin/α-lactalbumin) and NaCas (αs1/αs2/β/κ-caseins) onto colloidal Cr2O3 was examined at 20 °C as a model for the prefouling of steel . The role of electrostatic interactions in formation of a monolayer of adsorbed protein was studied by characterizing the adsorption as function of pH. From zeta potential measurements NaCas and whey proteins were found to have their isoelectric point around pH 5 and colloidal Cr2O3 an isoelectric point of pH 3, similar to stainless steel. Expecting maximum adsorption in a pH range where surface charges have opposite signs, we assessed whey protein and NaCas adsorption onto Cr2O3 in the pH range 3 to 7. Colloidal stability analysis indicated protein adsorption through its stabilizing effect on the Cr2O3 dispersions. Stabilization by adsorbed NaCas was not found to be pH dependent Whey proteins were found to stabilize Cr2O3 marginally less at low pH than at neutral pH. Similarly, adsorption isotherms constructed via UV-Vis spectroscopy, revealed that adsorption of NaCas onto Cr2O3 was pH-independent and whey protein adsorbed less at low pH than at neutral pH. From these findings, we conclude that electrostatic interactions are not the primary factor in monolayer adsorption of milk proteins. These findings contribute to the understanding required for the development of better strategies to mitigate protein fouling in the food industry.