Food protein-polysaccharide polyelectrolyte complexes (PECs) for electrochemical systems: Structure-property relationships, rational design, and emerging applications

Protein-polysaccharide complexes (PPCs) comprise a broad class of assemblies stabilized by non-covalent interactions, whereas protein-polysaccharide polyelectrolyte complexes (PECs) arise predominantly from electrostatic association between oppositely charged biopolymers. This review critically examines how the physicochemical and structural characteristics of food-derived protein-polysaccharide PECs govern functions relevant to electrochemical systems, including ionic transport, interfacial interactions, structural stability and analyte recognition. Their limited electronic conductivity motivates functionalization with conductive components to establish complementary ionic and electronic transport pathways. We highlight the importance of structure-interaction-property-function relationships and control over charge characteristics, intermolecular interactions, hydration, and structural organization for rational protein-polysaccharide PEC design. Protein-polysaccharide PECs can be engineered into films, hydrogels, interfacial layers, or membranes for emerging electrochemical applications. However, direct electrochemical evidence for protein-polysaccharide PECs remains limited, highlighting the need for systematic studies linking molecular and structural attributes to quantitative electrochemical performance.