The stability of triphasic oil-in-water Pickering emulsions can be improved by physical modification of hordein- and secalin-based submicron particles

Abstract

The main objective of this work was to study the capability of either non-modified or physically-modified β-hordein and γ-secalin particles as Pickering emulsion stabilizers. A comparison was performed with zein-based particles as a commercial source of prolamins. Protein dispersions in ethanol-water medium were subjected to different heat treatments and then characterized. A simple anti-solvent precipitation method in combination with sonication was applied to fabricate colloidal submicron particles. Analyses of the fluorescence intensity and thiol group content revealed heat-induced conformational changes of individual protein molecules but not protein aggregation. SEM micrographs confirmed the formation of spherical-shaped submicron and nano-particles. Ultrasound treatment relatively decreased the interfacial tension of prolamin-based particles. Contact angle results suggested the possible superiority of hordein and secalin particles to zein ones in Pickering stabilization. A predominant elastic gel-like behavior (i.e., G'>G″) along with different dependencies on the angular frequency was observed in dynamic frequency sweep test of Pickering emulsions. The shear thinning behavior of all samples was attributed to the deflocculation of oil droplets. The final emulsion characteristics were influenced by the particle type and the applied physical treatments. It was found that hordein-based particles have the ability to develop emulsion-foam (triphasic) structures with the physical stability at least 20 times higher than those prepared by zein-based particles. The results of this study may help in the design of Pickering systems using prolamin-based natural particles.