Surface tension of bovine serum albumin and tween 20 at the air‐aqueous interface

Abstract

AbstractInterfacial properties (surface tension, σ, and critical micelle concentration, CMC) of aqueous solutions of Tween 20 (polyoxyethylene sorbitan monolaurate) and/or bovine serum albumin (BSA) were evaluated. Temperature, Tween 20 concentration in the aqueous phase, BSA/Tween 20 ratio, and aqueous phase composition [water, ethanol (0.5, 1.0, and 2.5 M), and sucrose (0.5 M)] were the variables studied. The CMC of Tween 20 was determined by surface tension measurements (Wilhelmy plate method). The existence of BSA‐Tween 20 interactions was deduced from surface tension measurements. The results show that the effect of temperature on CMC depends on the aqueous phase composition, but the σ value at CMC, σCMC, does decrease as temperature is increased. The CMC and σCMC values also depend on the aqueous phase composition. In aqueous ethanol solutions, the CMC increases, but σCMC decreases. However, in sucrose aqueous solutions, the CMC decreases, but there is no significant effect on σCMC. The BSA‐Tween 20 interactions at the interface depend on both Tween 20 concentration (C) and solute in the bulk phase. In water and aqueous solutions of ethanol and sucrose, σ values decrease in the presence of protein at C<CMC but are practically independent of C at C>CMC. This is an indication that the interfacial characteristics of the mixed film are determined by either the protein or the lipid at the higher and lower protein/lipid ratio, respectively. In the intermediate region, the existence of BSA‐Tween 20 interactions dominates the interfacial characteristics of mixed films.