Morinda citrifolia (noni) polysaccharides: Extraction methods, molecular structures, and biological activities

Morinda citrifolia L. (noni) has been traditionally consumed as both food and medicine, with its polysaccharides (NPs) increasingly recognized for their diverse bioactivities and potential applications in functional foods and therapeutics. This review provides a comprehensive and critical synthesis of recent advances in the extraction, purification, structural characterization, and biological functions of NPs. Current evidence shows that NPs are predominantly pectic polysaccharides, comprising homogalacturonan and rhamnogalacturonan-I regions, alongside minor hemicellulose-derived components such as (xylo)glucans. However, the extraction and purification of NPs still mostly rely on conventional approaches, which restrict the resolution of active fractions and hamper reproducibility. Despite their promising health benefits, such as antioxidant, anti-inflammatory, immunomodulatory, and gut microbiota-regulating activities, the underlying structure-activity relationships remain poorly understood due to methodological inconsistencies and limited mechanistic insights. This review highlights key knowledge gaps and methodological challenges in NPs research, and emphasizes the need for advanced analytical tools, mechanistic studies, and in vivo validations to unlock their full potential in food and pharmaceutical applications.