Protein–polysaccharide conjugation in food systems: Design principles, material and processing constraints, and functional outcomes

Protein-polysaccharide conjugation is increasingly used to improve protein functionality in food systems, yet reported outcomes remain inconsistent because performance depends on protein conformation, polysaccharide structure, reaction pathway, and processing severity. This review critically examines Maillard-type glycation, enzymatic coupling, chemical cross-linking, and process-intensified approaches from a process-structure-function perspective. Emphasis is placed on measurable indicators that distinguish useful modification from over-modification, including degree of grafting, free amino group loss, browning development, particle size, ζ-potential, solubility, interfacial behavior, digestibility, and advanced glycation products. Moderate conjugation can enhance hydration, solubility, emulsion stability, bioactive protection, film formation, and printability, whereas excessive modification may promote aggregation, browning, lysine blockage, impaired digestion, and sensory deterioration. The review proposes application-specific design considerations and highlights real-food constraints, scalability barriers, and safety issues that must be addressed to enable predictable and industrially relevant use of protein-polysaccharide conjugates.