Fabrication, characterization, and application of pea protein isolate-polyphenol-iron complexes with antioxidant and antibacterial activity

Plant proteins are becoming increasingly popular as functional ingredients in foods because of their health, sustainability, and environmental benefits. The functional performance of plant proteins can often be improved by combining them with other food ingredients. For instance, they can be combined with polyphenols and metal ions to form surface active protein-polyphenol-iron complexes with biological activity. In this study, ternary complexes of pea protein isolate (PPI), epigallocatechin-3-gallate (EGCG) and iron (Fe³⁺) was prepared using a simple molecular self-assembly method. The formation mechanism, characteristics, and functional properties of these complexes were then characterized. Our results showed that PPI, EGCG, and Fe³⁺ could spontaneously combine to form nano-sheet networks held together by hydrogen bonds, phenolic hydroxyl coordination bonds, and electrostatic interactions. The addition of Fe³⁺ increased the fraction of disordered secondary structures, reduced the thermal denaturation temperature, reduced the surface hydrophobicity, increased the particle size, and altered the surface potential of the proteins in a dose dependent manner. Optimizing the EGCG-to-Fe³⁺ ratio in the complexes (1:2 w/w) led to the formation of protein composites with improved surface, antioxidant, and antibacterial activities. This study provided valuable insights into the interaction mechanisms of proteins, polyphenols, and metal ions in ternary complexes. These complexes may be used as multifunctional ingredients in plant-based foods because of their beneficial antioxidant, antimicrobial, nutritional, and emulsification properties.