Structure and conformation characterization of galactomannan from seeds of Cassia obtusifolia

The fine structure and conformational properties of neutral polysaccharide isolated from the whole seeds of Cassia obtusifolia (CP-30) were systematically investigated for the first time, by 1D and 2D NMR, size exclusion chromatography coupled with multiple detectors (SEC-MALS), dynamic light scattering (DLS), and static light scattering (SLS). The structure of CP-30 was elucidated to be a galactomannan, consisting of 1,4-linked-Manp backbone with side chains (T-Galp) attached to O-6 of 1,4-linked-Manp. DLS and SLS results showed that 0.6 M NaNO3 was a good solvent for CP-30. The structure sensitive parameter ρ (1.33–1.80), the Mark-Houwink exponent α (0.59), and the conformational parameter ν (0.51 from z vs Mw, and 0.52 from Rh vs Mw) suggested a random coil conformation of CP-30 in solution. The molar mass per unit of contour length (356.6 nm−1), persistent length (5.3 nm), and characteristic ratio (24.0) obtained by the wormlike cylinder model further indicated a dense random coil conformation of CP-30. By scanning electron microscopy, the linear chain shape of CP-30 in water was observed. The present research provided systematic information on structural and conformational properties of CP-30, which was important for elucidating the physicochemical characteristics of cassia polysaccharide and meaningful for its further application in food and medicinal industry.