SURFACE-PROPERTIES OF PROTEIN ALCOHOLIC SOLUTIONS .2. SURFACE DILATIONAL RHEOLOGY

Dynamic surface dilational properties of alcoholic solutions of protei ns (Bovine Serum Albumine (BSA) and beta-casein) were studied by the d amped longitudinal waves (0.1-1 Hz) method as a function of the ethano l content. At low ethanol contents (0-5%, v/v) the BSA solutions and t he beta-casein at 12%, v/v, exhibited viscoelastic behavior. At high e thanol content, the BSA solution surface displayed an elastic behavior . Absolute surface theological coefficients (high-frequency elasticity E(T0), low-frequency elasticity E(0), the constant rate of relaxation k(r), and the intrinsic surface viscosity eta(s)) of the surface at i ts quasiequilibrium were obtained from the frequency spectra of the wa ves' characteristics. We have introduced two models: one based on the adsorption-desorption of protein aggregates and another based on a con formational change surface reaction, which could fit our results. The decrease of E(T0), k(r), and eta(s) when ethanol content increases has been related to the decrease of surface coverage by protein. (C) 1994 Academic Press, Inc.