Enhancing Pickering emulsion stabilization of insoluble rice bran natural complexes: Structure-dependent interfacial...

Rice bran is an abundant agricultural by-product rich in proteins, polysaccharides, and polyphenols, exhibiting potential for Pickering emulsion stabilizers. However, these nutrients predominantly exist as insoluble rice bran natural complexes (IRBNC), which are underutilized due to their compact structure, limited wettability, and poor interfacial activity. To overcome these limitations and optimize the interfacial properties of IRBNC for enhanced emulsification, three catechin monomers with varying numbers of phenolic hydroxyl groups and galloyl moieties-epicatechin (EC), epigallocatechin (EGC), and epicatechin gallate (ECG) were selected as structural models to modify IRBNC. Appropriate concentrations of EC (25 mg/g), EGC (50 mg/g), and ECG (25 mg/g) decreased the ordered structure of proteins in IRBNC, shifted particle wettability from highly hydrophobic (127.015°) to amphiphilic (ranging from 86.976° to 95.695°), loosened the compact layered microstructure, thereby improving interfacial activity (equilibrium interfacial tension: 20.43 to 16.19 mN/m). Consequently, Pickering emulsion stabilized by IRBNC modified with appropriate concentrations of EC, EGC, and ECG exhibited smaller average droplet size (from 59.94 μm to 46.32 μm) and lower creaming index values (from 23.9% to 14.5%) compared with unmodified IRBNC. Moreover, appropriate catechin modification inhibited the formation of lipid oxidation products in IRBNC-stabilized Pickering emulsions during storage. Notably, modification efficiencies followed a structure-dependent trend (ECG > EGC > EC), with ECG exhibiting the strongest effect due to its galloyl substitution and higher phenolic hydroxyl density. Overall, appropriate catechin modification, particularly with ECG, represents an effective strategy to tailor the structural and interfacial properties of IRBNC for enhanced Pickering emulsion stabilization.