A MACROSCOPIC MODEL FOR THE SINGLE-COMPONENT PROTEIN ADSORPTION-ISOTHERM

A usable, macroscopic model was developed to describe apparent protein adsorption equilibrium at hydrophobic solid-water interfaces. In part icular, the adsorbed mass of protein was expressed in terms of the fol lowing macroscopic properties: the partial molar area occupied by prot ein at the interface; the partial molar volume of protein in solution; the work of adhesion per unit area; the minimum surface area required by an adsorbing protein; and the apparent equilibrium concentration o f protein in solution. Adsorption at hydrophobic interfaces was consid ered to occur in the absence of specific electrostatic and biochemical interactions, according to a pseudo-equilibrium between protein in so lution and that adsorbed in some altered state. The work of adhesion b etween protein and surface was calculated assuming that the equilibriu m spreading pressure of protein could be used in estimation of protein interfacial energy. The Gibbs free energy of unfolding was used in th e estimation of protein flexibility, needed for the calculation of equ ilibrium spreading pressure with the selected equation of state. Good agreement was observed between the model and experimentally measured i sotherms for the milk proteins alpha-lactalbumin, beta-lactoglobulin, and bovine serum albumin at hydrophobic silica. (C) 1995 Academic Pres s, Inc.