RHEOKINETIC ANALYSIS OF PROTEIN FILMS AT THE AIR-AQUEOUS SUBPHASE INTERFACE .2. BOVINE SERUM-ALBUMIN ADSORPTION FROM SUCROSE AQUEOUS-SOLUTIONS

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 functi on of adsorption time. The experiments were performed using a superfic ial, sinusoidal oscillatory rheometer (ring trough), at constant tempe rature (20 degrees C). The surface rheological parameters (i.e. surfac e 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 hi) in the aqueous phase. The films displayed a v iscoelastic behavior, which was practically elastic. At low sucrose co ncentration (< 0.5 hi) 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 dynam ic properties also depend on sucrose concentration in the aqueous phas e. A first-order kinetic model is a satisfactory mathematical descript ion of the BSA adsorption and unfolding at the interface. These phenom ena have been related to the protein unfolding and/or protein-protein interactions in the presence of solutes (ethanol or sucrose) in the aq ueous phase.