Rheology and Microstructure of Interfaces Stabilized by Mixed Proteins and Surfactants: A Computer Simulation Study

Introduction ........................................................................................................ 401 The Model ........................................................................................................... 402 Brownian Dynamics Simulation...................................................................... 403 One-Component Monolayers........................................................................... 405 Two-Component Monolayers .......................................................................... 407 Conclusions......................................................................................................... 410 Acknowledgments ............................................................................................. 411 References ........................................................................................................... 411 The adsorption of proteins and small-molecule surfactants at air-water and oil-water interfaces is crucial to the formation and stabilization of emulsions and foams. Complex interfaces that consist of mixtures of adsorbing species are of particular relevance in food systems (Dickinson and McClements, 1995). Proteins and low-molecular-weight (LMW) surfactants have very different individual adsorption behavior and, most interestingly, they present complex interfacial structures when adsorbed from mixed bulk solutions (Pugnaloni et al., 2004a). In particular, it has been shown by atomic force microscopy (AFM) (Mackie et al., 1999) and Brewster angle microscopy (Rodrı ´ guez Patino et al., 1999) that competitive adsorption of protein plus surfactant mixtures occurs in a heterogeneous fashion, with the surfactant forming segregated domains in a quasi-two-dimensional protein matrix, at least over periods of time of a few days.