Adsorption of single component and binary mixtures of protein and surfactants at the oil-water interface

The dynamic interfacial tensions of non-ionic Triton X-100 surfactants, chicken-egg-white lysozyme proteins, and binary mixtures of Triton X-100-lysozyme at the dodecane-water interface were measured using a capillary wave technique. Consistent with results reported in the literature, the adsorption of Triton X-100 was found to be diffusion-controlled. The adsorption of lysozyme is well represented by a series of two first-order relaxation processes, which, respectively, had been identified in the literature as related to the adsorption/penetration of protein onto the interface and rearrangement/unfolding to its equilibrium in the interface. Our data show that the second process is the slower of the two. For Triton X-100-lysozyme binary mixtures, we found that the presence of nonionic Triton surfactants has little or no effect on the first process. In contrast, the Triton surfactants play a significant role in impeding the rearrangement/unfolding of the protein molecules in the interface. (C) 1999 Elsevier Science B.V. All rights reserved.