Rheokinetic Analysis of Protein Films at the Air−Aqueous Phase Interface. 1. Bovine Serum Albumin Adsorption on Ethanol Aqueous Solutions

Abstract

In this paper surface dynamic properties (surface tension and surface dilational properties) of bovine serum albumin (BSA) films adsorbed on the air-aqueous sucrose solution interface are presented, as a function of adsorption time. The experiments were performed using a superficial, sinusoidal oscillatory rheometer (ring trough), at constant temperature (20 °C). The surface rheological parameters (i.e. surface dilational modulus, elastic and viscous component, and loss tangent angle) and the surface tension were measured as a function of sucrose concentration (0, 0.25, 0.5, and 1 M) and on a mixture of ethanol (1.0 M) and sucrose (0.5 M) in the aqueous phase. The films displayed a viscoelastic behavior, which was practically elastic. At low sucrose concentration (<0.5 M) the surface rheological properties were similar to those on water, whereas at the highest sucrose concentration (1 M) these properties decreased significantly. The transient surface dynamic properties also depend on sucrose concentration in the aqueous phase. A first-order kinetic model is a satisfactory mathematical description of the BSA adsorption and unfolding at the interface. These phenomena have been related to the protein unfolding and/or protein-protein interactions in the presence of solutes (ethanol or sucrose) in the aqueous phase.