Natural biopolymer stabilized oil-in-water emulsions were formulated using beta-lactoglobulin (beta-lg), gum arabic (GA), and beta-lg:GA solutions as an alternative to synthetic surfactants. Emulsions using these biopolymers and their complexes were formulated varying the biopolymer total concentration, the protein-to-polysaccharide ratio, and the emulsification protocol. This work showed that whereas beta-lg enabled the formulation of emulsions at concentration as low as 0.5 (w/w)%, GA allowed to obtain emulsions at concentrations equal to or higher than 2.5 (w/w)%. In order to improve emulsion stability, beta-lg and GA were complexed through strong attractive electrostatic interactions. GA solution had to be added to previously prepared beta-lg emulsions in order to obtain stable emulsions. Interfacial tension and interfacial rheological measurements allowed a better understanding of the possible stabilizing mechanism. beta-lg and GA both induced a very effective decrease in interfacial tension and showed interfacial elastic behaviour. In the mixed system, beta-lg adsorbed at the interface and GA electrostatically bound to it, leading to the formation of a bi-layer stabilized emulsion. However, emulsion stability was not improved compared to beta-lg stabilized emulsion, probably due to depletion or bridging flocculation. (C) 2010 Elsevier Inc. All rights reserved.