Advances in the Preparation, Structure, and Biological Activity of Polysaccharides from Nitraria L.: A Review

Nitraria L. species are drought- and salt-tolerant plants whose fruits, and in some studies leaves, have been investigated as sources of bioactive polysaccharides. However, the reported polysaccharide preparations and purified fractions are chemically heterogeneous and originate from different Nitraria species, geographic regions, plant organs, and extraction and fractionation procedures. This review critically summarizes current knowledge of the raw materials, extraction and purification methods, structural characteristics, and biological activities of Nitraria-derived polysaccharides. Particular attention is given to the relationship between extraction/fractionation procedures and the polysaccharide populations recovered, because extraction conditions may influence not only yield but also molecular weight, monosaccharide composition, branching, and other structural features. Reported fractions show substantial structural diversity in molecular-weight distribution, monosaccharide composition, and, where sufficiently characterized, glycosidic-linkage patterns and polysaccharide class, while differences in analytical procedures further limit direct cross-study comparisons. Biological studies have reported antioxidant, immunomodulatory, anti-inflammatory, antitumor, hypoglycaemic, anti-fatigue, anti-stress, hepatoprotective, hypolipidemic, analgesic, organ-protective, and gut-microbiota-modulating effects. Nevertheless, these findings were obtained using structurally distinct preparations and heterogeneous experimental systems, doses, administration routes, and endpoints; therefore, they should not be regarded as uniform properties of Nitraria polysaccharides as a whole. Current within-study comparisons suggest that fractionation and chemical modification may influence biological activity, but the available evidence remains insufficient to establish general structure–activity relationships. Future studies should prioritize standardized raw-material characterization, extraction and fractionation, detailed structural analysis, and biological evaluation of well-defined polysaccharide fractions to establish more reliable structure–activity relationships and support their rational development as functional-food ingredients and related bioactive products.