Physicochemical properties and structural characterization of a galactomannan from Sophora alopecuroides L. seeds

• Neutral F25 from Sophora alopecuroides L. seeds was characterized for the first time.
• The macromolecular solution behavior of F25 was revealed in different manners.
• The proposed structure of F25 was clarified and confirmed as a galactomannan.
• 3D molecular modeling of F25 was preliminarily established.

A water-soluble neutral polysaccharide (F25) was fractionated from crude polysaccharides of Sophora alopecuroides L. seeds. Its physicochemical properties and structural characterization were investigated. The I2-KI and Congo red reactions showed F25 possessed many branches without triple-helical conformation, which coincided with methylation and NMR analyses, i.e., F25 was a galactomannan with 1,4-linked β-d-Manp backbone distributed randomly (M/G 1.48–1.84) by major T-α-d-Galp (86.82%) or minor 1,4-linked α-d-Galp (13.18%) at O-6. Compared with [η] of deionized water (2.98 dL/g), it was indicated that NaCl (2.89–2.90 dL/g) and NaOH (2.27–2.28 dL/g) could affect intrinsic interactions and conformation of F25 in solution, leading to molecular non-entanglements and intramolecular associations. This was demonstrated by 3D molecular modeling. Furthermore, the amorphous nature of F25 was revealed with higher crystallinity (25.7%) and crystallite size (7.6 nm) compared to other polysaccharides. In this study, the possible relationships between molecular structure and physicochemical properties were obtained for F25, which could be potentially applied in food and pharmaceutical industries.