Surface Interaction between a Protein Monolayer and Surfactants and Its Correlation with Skin Irritation by Surfactants

Abstract

The behavior of a zein film deposited on the surface of a dilute surfactant solution was studied with the Langmuir balance technique. The aim was to determine directly surface interactions between protein molecules and surfactant monomers, as a model of skin irritation by surfactants. First, to characterize the system, the surface pressure–area isotherm of zein deposited on pure water is determined and the possible zein conformations at the interface are discussed. Second, to reveal directly zein–surfactant interactions, the zein film deposited on three types of surfactant solutions was allowed to relax at constant pressure. Two kinds of behaviors were observed: (1) Irritating surfactants such as sodium dodecyl sulfate and sodium dodecyl ether sulfate show an increase in surface area with time, which can be related to an expansion of the zein film due to protein–surfactant interactions. (2) On the contrary, solutions of nonirritating surfactants such as alkylpolyglucosides show the same behavior as pure water: the film is slightly contracted. The results are in agreement with the zein solubilization by surfactants as determined by the zein test, which reflects perfectly the epidermic alteration potential of the surfactant. The method developed has the advantage of use of dilute surfactant solutions, in which the protein is not soluble. Difficulties related to the determination of the protein concentration in solution can thus be avoided.