Surfactant-free oil-in-water-in-oil emulsions stabilized solely by natural components-biopolymers and vegetable fat crystals

Surfactant-free oil-in-water-in-oil (O/W/O) emulsions were successfully prepared through a facile approach using natural ingredients (biopolymers and crystalline fat particles) as stabilizers. Microstructure (PLM, cryo-SEM and confocal microscopy) and diffusive NMR studies revealed that emulsions with ultra-high loading of internal oil droplet phase with high storage stability could be easily prepared in absence of low-molecular weight synthetic surfactants. The internal oil droplets were stabilized by the presence of interfacial layers of gelled biopolymers while the encased water droplets were stabilized by a combination of interfacial crystal accumulation (Pickering stabilization) and network stabilization created by bulk crystallization of fat particles. Small (oscillatory shear rheology) and large (force-displacement measurements) deformation studies were used to gain important insights into the ‘structure-properties’ links. Furthermore, on monitoring the stability of these emulsions in terms of droplet size changes and diffusion of the internal oil phase (over a period of 3 months), they showed exceptional stability with absence of any droplet coalescence and minimal oil diffusion to the external phase. Such complex colloids stabilized by natural ingredients could find important industrial applications in development of novel products in bio-related fields of pharmaceuticals, cosmetics and foods.