Structural and physicochemical characterization of plant-derived galactomannans: revealing promising substrates for...

A structurally distinct galactomannan (SJ-GM) isolated from the seeds of the economically dominant Sophora japonica Linn., was characterized and comparatively evaluated with galactomannans (GMs) derived from guar gum (GG-GM) and Gleditsia sinensis (GS-GM). Monosaccharide composition analysis and nuclear magnetic resonance (NMR) spectroscopy revealed that SJ-GM had the highest mannose to galactose (M/G) ratio, indicating fewer galactose side chains and a more linear molecular structure. Rheological analysis demonstrated that SJ-GM exhibited moderate viscosity, which is beneficial for establishing controlled-hydrolysis conditions. X-ray diffraction (XRD) patterns displayed broad halos without distinct Bragg reflections, confirming the predominantly amorphous nature of all three GMs. Furthermore, SJ-GM exhibited a relatively narrow molecular-weight distribution and a lower polydispersity index, both of which facilitated improved hydrolysis efficiency. The effects of autohydrolysis on the conversion of the three GMs into mannooligosaccharides (MOS) were comparatively evaluated. At 180 °C for 100 min, crude SJ-GM (C-SJ-GM, purity 64.45 %) achieved the highest MOS yield (44.3 %), exceeding those of GS-GM (40.1 %) and GG-GM (37.9 %). Despite its lower purity compared with refined GM, C-SJ-GM maintained comparable structural characteristics and delivered high MOS yields without the need for a dedicated pre-purification step before autohydrolysis, highlighting its economic potential as a cost-effective substrate for industrial-scale MOS production.