PurposeTo provide new insights into how protein-surfactant competitive adsorbtion and corresponding surface tension reduction properties at the air-water and oil-water interface are impacted by the type of protein and the associated protein surface rheology.MethodInterfacial Rheology was utilized to obtain surface G’ and G” as a function of frequency. Force tensiometry was utilized to obtain changes in surface tension as a function of surfactant concentration. The impact on surface properties of two different proteins i.e. BSA and Lysozyme was investigated as a function of surfactant concentration i.e. polysorbates PS 20, PS 80 and Poloxomer (Kolliphor P188).ResultsSurface tension and interfacial tension measurements for BSA showed that in mixed BSA/polysorbate surfactant systems, BSA dominates the interfacial behavior at both the air-water and oil-water interfaces, until a high polysorbate concentration of 0.1 mg/ml. At these high polysorbate concentrations a mixed BSA-Polysorbate interfacial layer is formed as corroborated by the surface elasticity values being lower than that of pure BSA but higher than that of pure Polysorbate. For Kolliphor, it was observed that Kolliphor was unable to displace BSA at any concentration. This is corroborated by the high surface elasticity of the BSA which is maintained in the presence of Kolliphor. Surface and interfacial tension measurements for lysozyme show that for mixed lysozyme/polysorbate surfactant systems, the surface tension values are lower than that exhibited by either the lysozyme or the polysorbate surfactants. This potentially indicates the formation of a mixed layer of lysozyme and polysorbate. At the high polysorbate concentrations probed, the surface elasticity values are however closer to that of pure polysorbates, indicating that the mixed layer may be more heavily polysorbate dominated, especially at high polysorbate concentrations. For Kolliphor, the response was similar to that seen in the Kolliphor-BSA system in which the Kolliphor was not able to displace the protein i.e. Lysozyme.ConclusionsIn conclusion, it was seen that competitive adsorption between proteins and common excipient surfactants is dictated by the type of protein and its effective structuring/rigidity at the surface as reflected through surface elasticity and surface tan delta values. BSA was seen to exhibit a higher surface elasticity than lysozyme, and therefore has a more rigid structure and is more competitive at the interface.