β-Lactoglobulin, gum arabic, and xanthan gum for emulsifying sweet almond oil: Formulation and stabilization mechanisms of pharmaceutical emulsions

Emulsions are thermodynamically unstable systems generally stabilized by small surfactant molecules. To answer sustainable development concerns, it is possible to replace the latter by natural emulsifiers such as proteins and polysaccharides to formulate emulsions for the pharmaceutical field. In this work, we describe oil-in-water emulsions stabilized by natural biopolymers. In a first approach, we prepared emulsions with various binary mixtures of β-lactoglobulin (β-lg), gum arabic (GA) and xanthan gum (XG), and assessed their stability over a 6-month period by zeta potential and granulometry measurements in combination with Turbiscan and optical microscopy observations. The efficacy of the biopolymers to stabilize emulsions was in the order GA < β-lg:GA < β-lg < XG = β-lg:XG. In a second approach, we focused on the determination of the stabilization mechanisms induced by these biopolymers, by interfacial tension and rheological measurements. Different stabilization mechanisms could be highlighted: interfacial adsorption for β-lg and GA when used alone, thickening of the continuous phase by XG with possible interfacial adsorption, formation of an interfacial bi-layer by the β-lg:GA mixture, and combination of β-lg interfacial adsorption and XG thickening of the aqueous phase for the β-lg:XG mixture.