Fabrication and characterization of emulsions stabilized by tannic acid-wheat starch complexes

Soybean oil-based emulsions stabilized by tannic acid (TA) and wheat starch (WS) complexes were prepared via a simple high-intensity ultrasound emulsification technique. The effects of mass ratio of TA/WS (0.005-0.75) and WS concentration (0.25%, 0.5% and 1.0%) on TA/WS complexes and emulsions were investigated. As the mass ratio increased, TA and WS could gradually form soluble and insoluble complexes, and their hydrophobicity also improved. Consequently, the tendency of the particle size of emulsions to decrease first and then increase appeared with the increasing mass ratio, mainly due to the changes in the contents, size and hydrophobicity of the complex emulsifier. Additionally, the emulsifying capacity of TA/WS complexes improved with increasing concentration of complexes. Moreover, the creaming was inhibited at a high mass ratio or high complex concentration due to the formation of a thick interfacial network around oil droplets or obtention of smaller-sized droplets. Emulsion gel was formed due to TA cross-linked WS on the interface within different oil droplets, and the strength of the gel increased with the mass ratio due to increasing amounts of complexes being absorbed on the interface. When the mass ratio and WS concentration were no less than 0.05 and 0.5%, respectively, emulsions had better oxidative stability. The complexes also had high resistance against droplet coalescence. This study demonstrated that TA/WS complexes could be employed as an emulsifier to improve the oxidative stability of O/W emulsions and that easily oxidized, oil-soluble nutrients or medicines could be protected and delivered through these emulsion systems.