Comprehensive review on Allium polysaccharides: Structural diversity, structure-activity relationships, biological...

The genus Allium, encompassing garlic (A. sativum), onion (A. cepa), leek (A. ampeloprasum), chive (A. schoenoprasum), and allied species, represents one of the most pharmacologically significant plant groups in human diet and traditional medicine. Polysaccharides constitute the primary non-volatile bioactive fraction of Allium plants, predominantly comprising inulin-type fructans, fructooligosaccharides, pectic polysaccharides, and minor galactan-rich fractions. Structurally, these polymers are defined by β-(2 → 1)- and β-(2 → 6)-linked fructosyl backbones, internal α-glucosyl insertions, and variable degrees of polymerization, collectively generating remarkable molecular heterogeneity. Accumulating evidence from in vitro and in vivo studies demonstrates that Allium polysaccharides (APS) exert pleiotropic bioactivities, including antioxidant, anti-inflammatory, immunomodulatory, antitumor, and antibacterial effects, through diverse molecular mechanisms encompassing Keap1/Nrf2/ARE, TLR4/NF-κB/MAPK, NLRP3 inflammasome, gut microbiota, and intestinal barrier pathways. Critically, these activities are governed by an integrated structure-activity relationship framework in which molecular weight, glycosidic linkage topology, branching pattern, uronic acid content, and extraction methodology collectively determine biological potency. Despite substantial preclinical progress, robust clinical validation, standardized structural characterization, and mechanistic dissection at the receptor level remain limited. This review systematically integrates current knowledge on the structural chemistry and delineates the SAR principles underlying their functional diversity, bioactivity of APS, and identifies priority areas for future translational research.