Oligosaccharide mapping analysis through UPLC-Orbitrap-HRMS and enzymatic hydrolysis from Polygonatum odoratum (Mill.) Druce

Polygonatum odoratum ( P. odoratum ) oligosaccharides (POO) are bioactive compounds with complex structures. Since the precise structure of POO remains undefined, their pharmacological development and clinical application have been hindered. This study developed a universal strategy to elucidate oligosaccharide structures of P. odoratum by combining Orbitrap high-resolution mass spectrometry (Orbitrap-HRMS) and enzymatic hydrolysis. Initially, monosaccharide constituents of free oligosaccharides (POO) and polysaccharides (POP) in P. odoratum were quantitatively analyzed. The accurate mass values, retention time, and sequence-specific fragment information facilitated initial characterization by comparing with the self-established oligosaccharide library based on these monosaccharides. Due to the limitations of MS in precisely identifying isomer structures, enzymatic hydrolysis was further employed to distinguish the glycosidic linkage and oligosaccharide type. Fructanase mixture, endo -1,4-β-mannanase, exo -1,3-β-D-glucanase, α-galactosidase and amyloglucosidase were used to identify hexose-based isomers, while α-L-arabinofuranosidase and endo -1,4-β-xylanase were used for pentose-based isomers. The study revealed that POO primarily consisted of fructooligosaccharides, and its isomers, such as 1-kestose, 6-kestose, and neokestose, were clarified. POP mainly comprised galactomannan, with the branching site at α-(1 → 6)-galactoside in POPO determined for the first time in P. odoratum . This strategy provides a straightforward methodology for analyzing plant oligosaccharides, establishing a structure analytical foundation for further pharmacological research and potential clinical applications.