Polymerized whey protein-SDS interactions at their high concentrations

Abstract

Protein-surfactant interactions have been an ongoing topic of interest for many decades. Applications involving complexes of proteins and surfactants are relevant in food, pharmaceuticals, hygiene, molecular characterization, and other fields. In this study, the interactions of polymerized whey proteins (PWP) and sodium dodecyl sulfate (SDS) at high concentrations are investigated. Different characterization techniques are used, including electrical conductivity, turbidity, isothermal titration calorimetry, dynamic light scattering, dilute solution viscometry, rheology, and surface hydrophobicity to elucidate information on the modes and extent of interactions. Results indicate that PWP-SDS interactions produce highly extended, worm like micelles, with SDS decorating PWP chains and covering non-polar residues. PWP can host SDS up to quite high surfactant to protein ratios (SPR), producing solutions that are highly viscous with shear thickening properties, yet with no networking or gelation. Interestingly, dilution of high viscosity PWP-SDS solutions leads to even smaller size of PWP-SDS molecular complex as compared with PWP without SDS. The current study extends the vision of protein surfactant interactions by examining concentration range beyond that found in literature. The results reveal insights that can help expand studies on other systems and find applications in various fields including coatings, cosmetics, food ingredients, drug transport, and disease treatment.