Inulin: functional ingredients in food industry, extraction, and health applications—a comprehensive review

Inulin is a naturally occurring water-soluble fructan-type polysaccharide composed primarily of β (2→1)-linked D-fructose units, typically terminated by a glucose residue. Inulin is widely used as a functional ingredient due to its technological and health-promoting benefits. This review provides a comprehensive, up-to-date evaluation of inulin, focusing on its structural characteristics, physicochemical properties, extraction techniques, and applications in food. Conventional and emerging green extraction methods, such as microwave-assisted, ultrasound-assisted, and enzyme-assisted methods, are compared with respect to efficiency, yield, and sustainability. The functionality of inulin as a fat replacer, sugar substitute, and texturizing agent is critically examined, particularly with respect to its degree of polymerization. In addition, the prebiotic and immunomodulatory effects of inulin are addressed, emphasizing its role in modulating gut microbiota and associated health outcomes. Advanced analytical techniques, such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), are also discussed to determine the structure-function relationships of inulin. This review summarizes recent advances and identifies key research gaps to support the effective, targeted use of inulin in functional foods and health applications.