Co-delivery of insulin and quercetin in W/O/W double emulsions stabilized by different hydrophilic emulsifiers

Insulin (hydrophilic) and quercetin (hydrophobic) have broad biological benefits; however, their rapid hydrolysis (via protease degradation) during digestion hinders their stability and delivery for absorption before degrading. In this study, we encapsulated insulin and quercetin using a self-assembled water-in-oil-in-water (W/O/W) double emulsion. We prepared the co-delivery emulsion by two-step emulsification and investigated the effects of the type of hydrophilic emulsifier for the outer water phase on the physicochemical properties, stability, and digestive properties. The black-bean-protein-stabilized W/O/W double emulsion had a higher absolute zeta potential value (52.80 mV), higher encapsulation efficiency (insulin: 95.7%, quercetin: 93.4%), lower viscosity, better emulsifying properties (EAI: 122.26 m²/g, ESI: 224 min), and lower levels of hydroperoxides (0.86 mmol/L) and TBARS (25.80 μmol/L) than emulsions stabilized by other hydrophilic emulsifiers. The emulsion yielded a 2.60- and 4.56-fold increase in the bioaccessibility of insulin and quercetin, respectively, while increasing their chemical stability and solubility under simulated gastrointestinal conditions.