Interfacial behavior and emulsion stability of lipid delivery system regulated by two-dimensional facial amphiphiles bile salts

Bile salts as two-dimension facial amphiphile effectively emulsify lipids at low concentrations to promote gut digestion. Hence, we select various bile salts sodium cholate (NaC), sodium glycocholate (NaGC) and sodium taurocholate (NaTC) to study the interfacial tension and rheological dilational modulus to illustrate the interfacial adsorption mechanism and interface film strength, which is closely related to emulsion stability. Unlike linear surfactant molecules, the interfacial behavior of bile salts contains into two stages. At the low concentration for the first stage, the rigid facial molecules adsorb at the lipid-water interface with the hydrophilic concave and hydrophobic convex surface. And the interfacial relaxation is mainly dominated by intermolecular interaction and diffusion exchange, resulting in that the adsorption layer is especially an elastic film. During the second stage, aggregates are gradually generated at the interface as the concentration increases, and the interfacial relaxation is mainly dominated by the rapid diffusion exchange between the adsorption film and the sublayer, leading to the faster formation of the adsorption film. The mechanism of facial amphiphile adsorbed at lipid-water interface indicates soft molecular membrane established at interfaces on account of intermolecular interaction, revealing that higher interfacial strength benefits emulsion stability. We also found that NaTC with excellent adsorption capacity can stabilize edible oil for 8 h to facilitate lipid digestion. Compared with linear surfactant, bile salts with great biocompatibility can form two-dimension adsorption layer to emulsify and stabilize lipids, which can be widely used in lipid delivery system.