Exploration of stabilization mechanism of polyol-in-oil-in-water quercetin-loaded Pickering double emulsions

The low solubility of quercetin considerably decreases its loading efficiency in traditional water and oil-based emulsion systems, which has limited their applications. To find a solution to this issue, in this investigation, polyol consisting of dipropylene glycol and glycerol as a solvent was used to increase quercetin solubility. It was further incorporated in polyol-in-oil-in-water Pickering double emulsions stabilized by SiO2. The characterization of these Pickering double emulsions was performed by analyses of their microscopic structures, particle sizes, rheology, and storage stability. The rise in the concentration of quercetin from 0 to 0.60 wt% decreased the droplet size of these emulsions and increased their viscoelasticity and storage stability. The microstructure of the emulsions showed the presence of some quercetin on the water-oil interface, suggesting that this bioactive compound might have recrystallized from the internal polyol phase during the preparation and then acted as a particle stabilizer in synergy with SiO2. To test and validate this hypothesis, we examined the Pickering stabilization properties of the recrystallization quercetin and its interaction with SiO2. We found that the recrystallized quercetin interacted with SiO2 through a hydrogen bond and co-stabilized the interface. Additionally, it also served as a thickener that was involved in the development of an intense entangled network structure that connected the droplets, which improved the emulsion stability. These results revealed an effective approach for the preparation of stable Pickering double emulsions with high quercetin loading.