Relative ordered structure evaluation of water-extracted polysaccharides from Morchella sextelata: Geographical...

Polysaccharides derived from Morchella fruiting bodies exhibit multiple pharmacological activities, which are closely associated with their structural features. In this study, polysaccharides were extracted by hot water from Morchella sextelata cultivated in five geographical origins (Sichuan, Yunnan, Shaanxi, Guizhou and Fujian Provinces) across China. Structural characteristics of homogeneous components were analyzed using Fourier transform infrared spectroscopy, monosaccharide composition, methylation analysis and ¹H nuclear magnetic resonance spectra, with structural features further elucidated by chemometrics. It was found that polysaccharides from five geographic origins were consistently separated into three conserved subtypes: glucans, heteroglucans and galactomannans. The main observed difference lay not in these fundamental categories, but in the relative distribution and fine structural proportions (e.g., molar ratios, branching density) among origins. Specifically, glucans featured a → 4)-α-Glcp-(1 → linked backbone branched at O-6 position. Heteroglucan exhibited a composite backbone architecture primarily comprising →4)-α-Glcp-(1→, →2)-α-Manp-(1→, →6)-α-Galp-(1→, →4,6)-α-Glcp-(1 → and →2,6)-α-Manp-(1 → residues. The galactomannan was primarily constituted by →2)-α-Manp-(1 → and →6)-α-Galp-(1 → residues, with specific side chains. These polysaccharides can be classified into distinct subtypes based on their monosaccharide composition and glycosidic linkage patterns. This classification has demonstrated the validity of the "relative ordered structure" theory for water-extracted polysaccharides from M. sextelata and simplified the inherent complexity of polysaccharide structures, thereby significantly advancing our understanding of their regularity governing.