Surfactant-free oil-in-water-in-oil emulsions stabilized solely by natural components-biopolymers and vegetable fat crys
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Surfactant-free oil-in-water-in-oil emulsions stabilized solely by natural componentsbiopolymers and vegetable fat crystals Ashok R. Patel1*# 1
Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Gent, Belgium Email: [email protected] # Current address: Sci-Five Consulting Services, Coupure 164F, 9000 Gent, Belgium ABSTRACT 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. INTRODUCTION In the last few years, research on emulsions with complex microstructures (such as double emulsions) have received a considerable interest especially from industrial scientists working in the field of colloid structuring. These complex emulsions have long been proposed to hold great potential for practical applications in a range of bio-related fields including pharmaceuticals (for controlled drug delivery),1, 2 foods (texturing, fat-reduction and delivery of bioactives)3-5 and cosmetics.6, 7 However, despite years of substantial academic research on these systems, their commercial applications have faced severe limitations owing to the requirement of a high concentration of synthetic surfactants for their stabilization.8, 9 Accordingly, there is currently a huge interest among academic and industrial researchers to find ways to create surfactant-free double emulsions. Some approaches that have been explored to minimize or completely eliminate the requirement of surfactants include: a) use of bio-polymer conjugates or complexes10-12 ; b) Pickering stabilization by colloidal particles13, 14 and c) structuring of one or more of the phases through aqueous phase gelation or oil phase solidification.15-17 However, most of these approaches have been explored selec
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