Ovalbumin-peanut protein isolate emulsion gels for enhanced co-delivery of curcumin and quercetin

Hydrophobic phytochemicals often show limited solubility and low bioaccessibility during digestion, which restricts their use in functional food systems. In this study, a protein-based emulsion gel was developed by embedding a curcumin-quercetin supramolecular co-assembly within a composite network formed from ovalbumin and peanut protein isolate. The curcumin-quercetin co-assembly at a 5:5 ratio showed the strongest synergistic antioxidant activity, with a combination index of 0.598. Density functional theory calculations and independent gradient model analysis based on Hirshfeld partition indicated that π-π stacking and C-H···π interactions stabilized the co-assembled structure, modulated frontier orbital energy levels, reduced the energy gap, and increased electrophilicity, thereby enhancing radical-scavenging activity. The ovalbumin-peanut protein isolate composite at a 5:5 ratio formed a well-developed gel network and generated nanoscale embedded structures of approximately 779 nm through electrostatic and hydrophobic interactions. Incorporation of 1% curcumin-quercetin co-assembly resulted in encapsulation efficiencies above 97% for both phytochemicals. It also increased the storage modulus by 77.5% and improved water-holding capacity to 82.15%. Low-field nuclear magnetic resonance analysis showed a higher proportion of bound water, while the thermal transition temperature increased from 81.83 to 91.21 °C. These results indicate that the co-assemblies served as active crosslinking domains within the protein network through hydrogen bonding and hydrophobic interactions. During simulated digestion, the integrated co-assembly gel system delayed lipid digestion, with a free fatty acid release of approximately 58.55%, and increased the bioaccessibility of curcumin and quercetin to 58.96% and 63.17%, respectively. This study reveals how molecular co-assembly and protein gel structuring jointly improve the stability and delivery performance of hydrophobic phytochemicals, providing a basis for designing nutrient-dense functional food delivery systems.