Comparison of interfacial interactions between bovine serum albumin with water- and oil-soluble surfactants: An interfacial rheological study

The interfacial interactions between bovine serum albumin (BSA) with a water-soluble surfactant polyoxyethylene sorbitan monooleate (Tween 80) and an oil-soluble surfactant sorbitan monooleate (Span 80), respectively, were studied using the interfacial dilatational rheological experiments. The BSA molecules were irreversibly adsorbed at interface and formed a network with high dilatational modulus. The increasing interfacial pressure induced the transformation of BSA molecules from a compact globular to an unfolded flexible conformation, which enhanced the relaxation process. Tween 80 formed hydrophilic complexes with BSA in the aqueous phase, significantly slowing down the dynamic adsorption. In addition, Tween 80 played a dominant role at the interface due to its higher interfacial activity, thus inhibiting the interfacial performance of BSA. As BSA and Span 80 diffused towards the interface from different phases, they adsorbed rapidly at the interface and formed a mixed adsorption layer, thus exhibiting synergistic effects in decreasing the interfacial tension. However, the alternate arrangement of BSA and Span 80 at the interface disrupted the inter-protein interactions, resulting in a significant decrease in the dilatational modulus of the interfacial film. The obtained results showed that Span 80 from the oil phase and Tween 80 from the aqueous phase interacted with the protein in different ways, and thus presented distinct dynamic adsorption processes and interfacial performance. The present work provided a theoretical foundation for their practical application in food, cosmetic, and pharmaceutical industries.