Formation and lipid oxidative characteristics of oil-in-water emulsions stabilized by tea residue Protein–EGCG composite nanoparticles

Food-grade particles derived from food-processing by-products can combine interfacial stabilization with antioxidant functionality. In this study, water-insoluble tea residue protein (TRP) and epigallocatechin gallate (EGCG) were used to prepare composite nanoparticles (TRPENPs) for stabilizing oil-in-water (O/W) emulsions. Spectroscopic and thermodynamic analyses supported spontaneous TRP–EGCG association and the accompanying protein conformational changes. As a central functional result, TRP achieved an EAI of 23.86 ± 0.14 m²/g, statistically comparable to β-lactoglobulin (23.92 ± 0.09 m²/g; P > 0.05). At a TRP:EGCG mass ratio of 1:0.08, the nanoparticle suspension showed DPPH and ABTS radical-scavenging activities of 78.73% and 84.24%, respectively; separately, the pH 7 emulsion at an oil-to-water ratio of 4:6 showed values of 75.29% and 73.93%. Among the one-factor conditions tested, a TRPENP concentration of 15 g/L and an oil-to-water ratio of 4:6 provided favorable physical stability. The selected emulsion exhibited shear-thinning behavior and G′ values greater than G″. During accelerated oxidation at 55 °C for 10 days, the pH 7 TRPENP emulsion had lower peroxide value and TBARS levels than the TRP-only emulsion, polysorbate 80 emulsion, and flaxseed oil controls. These findings indicate that TRP–EGCG particles provide physical stabilization and antioxidant protection in flaxseed-oil emulsions. The system therefore offers a potential route for the value-added use of tea residue protein in antioxidant emulsion formulations.