Effect of Epigallocatechin-3-Gallate Modification on the Structure, Hydrophilicity and Pickering Emulsion Stability of Rice Bran Protein-Polysaccharide-Phenol Natural Complex

To improve the application of insoluble protein-polysaccharide-phenol natural complex particles as Pickering emulsion stabilizers within the food industry, insoluble rice bran protein-polysaccharide-phenol natural complex (IRBPPP) was modified using epigallocatechin-3-gallate (EGCG) under alkaline conditions. The addition of EGCG increased the bound phenol content and soluble protein content of IRBPPP, and decreased the free amino content, ζ-potential, surface hydrophobicity, and contact angle of IRBPPP. The addition of moderate EGCG (12.5-25 mg/g) enhanced the protein flexibility in IRBPPP (α-helix/β-sheet decreased from 23.56% to 18.74%) and induced the transition from highly hydrophilic particles to near-neutral particles (contact angle decreased from 139.8° to 87.3°), which enhanced the Pickering emulsion stability. Conversely, the addition of excessive EGCG (100 mg/g) reduced the stability of IRBPPP-EGCG-stabilized Pickering emulsion compared to the addition of moderate EGCG. Overall, the EGCG modification altered the Pickering emulsion stability by modulating protein flexibility, particle morphology, and hydrophilicity of IRBPPP.