SURFACE DILATIONAL PROPERTIES OF PROTEIN AND LIPID FILMS AT THE AIR-WATER-INTERFACE

The surface dilational properties (i.e. surface dilational modulus, el astic and viscous components, and loss angle tangent) and surface tens ion of mixed emulsifiers (bovine serum albumin (BSA), monostearin, and monoolein) were determined using a modified Langmuir trough. The surf ace dynamic properties were measured at 20 degrees C, as a function of time, interfacial composition (BSA-monostearin and BSA-monoolein mixt ures), subphase composition (aqueous solutions of ethanol and sucrose) , and compression-expansion frequency. The films displayed a viscoelas tic behavior and were frequency-dependent. The surface dilational modu lus increased as the concentration of monostearin spread on the interf ace increased, but it decreased as the concentration of monoolein spre ad on the interface increased. In the presence of ethanol or sucrose i n the interface at 1.0 M, the surface rheological parameters decreased . These phenomena have been related to protein-lipid interactions at t he interface as a function of the aqueous phase composition.