Effects of nanoparticle types and internal phase content on the properties of W/O emulsions based on dual stabilization mechanism

Abstract

In this study, water-in-oil (W/O) Pickering emulsions stabilized by different interfacial nanoparticles (ethyl cellulose-EC, whey protein isolate-WPI, Zein) and oleogel networks (glycerin monostearate) were constructed. The influence mechanism of different nanoparticles and oleogel networks under different internal phase fractions on the properties of emulsions was explored. Among different nanoparticles, EC nanoparticle had the smallest particle size (187.03 ± 2.23 nm) and highest contact angle (64.63 ± 2.94°), while Zein and WPI nanoparticles had bigger particle size (287.00 ± 5.54 nm and 213.77 ± 12.90 nm) and lower contact angle (59.71 ± 3.22° and 62.76 ± 1.47°). Microstructural observation revealed that the nanoparticles were located at the interface and in the water droplets, and the nanoparticles could aggregate into network structures. The oil phase had compact gel structures, which surrounded the water droplets. FTIR further proved that the interaction between interfacial particles and oleogel network was dominated by hydrogen bonding and hydrophobic interaction. Both nanoparticle type and water volume affected the rheological properties of the emulsions. Comparatively, EC-based emulsions had the highest shearing viscosity, creep recovery rate and storage modulus. The increase in water phase volume led to higher viscoelasticity, higher centrifugal stability and oil holding capacity of the emulsions. Upon heating, Zein-based emulsions presented the most significant phase separation and decrease in storage modulus. These findings suggested a dual stabilization mechanism for W/O emulsions, and both the nanoparticles and oleogel networks assisted in stabilizing the emulsions. The knowledge obtained in this study would be helpful in developing functional low-fat food and hydrophilic ingredient delivery systems.