Inulin structure–function relationships across the food–health continuum: the central role of degree of polymerization

Inulin is a fructan-derived dietary fiber and functional food hydrocolloid whose physicochemical, technological, and biological properties are strongly governed by degree of polymerization (DP). DP links molecular structure with extraction behavior, solubility, hydration, rheology, fermentation kinetics, and biological functionality. Emerging enzyme-, microwave-, and ultrasound-assisted extraction methods improve recovery efficiency and molecular integrity, although maintaining controlled DP distributions remains challenging. Short-chain inulin generally exhibits greater solubility and rapid proximal colonic fermentation, whereas long-chain fractions show stronger gel-forming and water-retaining properties and slower distal fermentation. These differences influence inulin performance as a texture modifier, fat replacer, dietary fiber, and prebiotic ingredient. This review critically integrates advances in inulin biosynthesis, extraction, fractionation, DP-dependent structure–function relationships, gut microbiota interactions, and food–health applications, while highlighting challenges in DP characterization, structural standardization, processing-induced changes, scale-up, and translation into functionally defined ingredients.