Abstract
Long term stabilization of water-in-oil (W/O) emulsions remains a particularly challenging problem in colloid science. Recent studies have shown that polyphenols act as Pickering stabilizers at the water-oil interface. In this work we propose a novel way to stabilize water droplets via interfacial complex formation. It was observed that polyphenol crystals (curcumin or quercetin) absorb at the interface and provide stabilization of water droplets for several days; however formation of a polyphenol- whey protein (WPI) complex at the water-oil interface revealed a pronounced improvement in the stabilization. The mechanism of complex formation was tested by subjecting the systems to different environmental conditions, such as ionic strength and temperature. The evidence suggests that the complex is probably stabilized by electrostatic attraction between the oppositely-charged polyphenol particles and protein at the interface, although hydrogen bonding between the two components may also contribute. The resulting stable water droplets have a Sauter mean diameter (D3,2) of approximately ∼22 and ∼27 μm for curcumin and quercetin systems, respectively. Emulsions were more stable at pH 3 than at pH 7, due to either weaker complex formation at pH 7 and/or chemical degradation of the polyphenols at this more alkaline pH. Interfacial shear viscosity measurements confirmed that there was strong interfacial complex formation with aqueous WPI concentrations of ∼0.5 wt.%.
Highlights
IntroductionIn many water-in-oil (W/O) emulsion systems (e.g., in food, pharmaceuticals, cosmetics, agriculture etc.), adsorbed solid
In many water-in-oil (W/O) emulsion systems, adsorbed solid⇑ Corresponding author.particles can provide kinetic stability to the dispersed phase [1]
At pH 3, there is the possibility of electrostatic attraction between the negatively-charged quercetin crystals wetted by water from the oil side of the interface and the positively-charged Whey protein isolate (WPI) adsorbing from the aqueous side of the interface
Summary
In many water-in-oil (W/O) emulsion systems (e.g., in food, pharmaceuticals, cosmetics, agriculture etc.), adsorbed solid. Particles can provide kinetic stability to the dispersed phase [1]. Such solid particles are known as ‘Pickering’ particles and create a steric barrier between adjacent water droplets, thereby hindering coalescence [1]. The use of Pickering particles as stabilizers for W/O emulsions is gaining significant attention owing to their ability to adsorb irreversibly at the interface and the lack of alternative, clean-label W/O emulsifiers [2,3].
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