EGCG-egg yolk proteins complexes-stabilized HIPPEs for enhanced delivery of lipophilic bioactives: Insight into structure and function relationship

Non-covalent complexes of proteins and polyphenols provide interfacial properties and antioxidant protection for delivering lipophilic bioactives. In this study, low-density lipoprotein and high-density lipoprotein (3:7, w/w) extracted from egg yolk were combined with epigallocatechin gallate (EGCG, 0, 10, 20, 40 μg/mL) and subjected to ultrasound treatment (20 kHz, 75 W, 10 min) to form protein-EGCG complexes. The structural and interfacial properties of these complexes were systematically characterized and subsequently applied to stabilize high-internal-phase Pickering emulsions (HIPPEs) loaded with phytosterol esters (PEs). Spectroscopic and rheological analyses confirmed that EGCG induced partial protein unfolding via hydrogen bonding and hydrophobic interactions, enhancing interfacial adsorption. HIPPEs containing 10 or 20 μg/mL EGCG exhibited optimal properties, including reduced droplet size, improved interfacial viscoelasticity, a high zeta potential (31.5 mV), and increased bioaccessibility of PEs during digestion. In contrast, 40 μg/mL EGCG caused protein aggregation and double-emulsion formation, impairing emulsion stability and digestion. These findings reveal a concentration-dependent dual role of EGCG and identify an optimal range for balancing emulsion stability and nutrient release. The study provides a strategy for designing functional emulsions for lipophilic bioactives in food applications.