Dynamic adsorption and dilatational properties of BSA at oil/water interface: Role of conformational flexibility

The influence of protein concentration (c) and/or disulfide bond (S–S) cleavage with β-mercaptoethanol (2-ME) on interfacial adsorption dynamics, including diffusion, penetration and structural rearrangement at the interface, as well as dynamic dilatational properties of bovine serum albumin (BSA) was systematically investigated using drop shape analysis. The results indicated that for native BSA increasing the c from 0.01 to 0.5% (w/v) progressively improved the rate of diffusion and the ‘equilibrium’ surface pressure (π), while a further increase in c (to 1.0%, w/v) contrarily impaired these characteristics; increasing the c progressively improved the penetration and structural rearrangement at the interface. In contrast, the surface dilatational modulus (E) development was less dependent on the c than that for the π. On the other hand, the S–S cleavage with 2-ME at any test c value progressively improved the diffusion and penetration, as well as ‘equilibrium’ π, while the structural rearrangement was highly dependent on the c. At c < 0.5% (w/v), increasing the 2-ME concentration progressively improved the rearrangement, while at c values of 0.5% or above, a contrary trend was observed. The S–S cleavage generally improved the E or its elasticity development over the whole adsorption, regardless of the c. The E-π plots indicated that besides the adsorption, the lateral macromolecular interactions at the interface could be affected by variation in c and/or 2-ME concentration. The relationships between the conformational flexibility and interfacial characteristics of BSA, as well as between its interfacial and emulsifying properties have been well established.