Improving antioxidant ability of functional emulsifiers by conjugating polyphenols to sodium caseinate

Abstract

Sodium caseinate (NaCas), a commonly used food emulsifier, is prone to oxidation, resulting in decreased emulsion quality and stability. This study aims to understand the effect of polyphenol structures on protein's antioxidant activity and develop protein-polyphenol complexes (PPCs) with better physical and oxidation stabilities. NaCas' antioxidant abilities with or without polyphenols were examined by DPPH, FRAP, and β-carotene blenching test. The binding mechanism between protein and polyphenols was also investigated using multispectral technology and molecular docking. The results show that the addition of kaempferol, phloretin, catechin, resveratrol, and hydroxytyrosol improved NaCas' free radicals scavenging ability, reducing power and lipid protection effect. In contrast, adding apigenin, coumarin, p-hydroxybenzoic acid, and p-coumaric acid caused unsatisfactory results. The number and location of free phenolic hydroxyl groups, the binding affinity between protein and polyphenol, and protein conformation are the criteria dictating the antioxidant properties of PPCs. Finally, four novel antioxidant emulsifiers were obtained, including NaCas-catechin, NaCas-resveratrol, NaCas-phloretin, and NaCas-hydroxytyrosol complexes. Our results explored the potential application of nano-delivering functional oil using PPCs as antioxidant emulsifiers.