Structural and physicochemical changes of galactomannan during germination of Gleditsia sinensis seeds

Galactomannan (GM) from Gleditsia sinensis (GSG) is a promising natural hydrocolloid due to its modifiability, biocompatibility and biodegradability, but its high molecular weight (M_w) and viscosity limit its dietary fiber applications. A reagent-free bioconversion strategy was developed by leveraging endogenous enzymes activated during seed germination. This study aimed to investigate the mechanism for germination under both constant- and variable-temperature conditions to modulate the structural and physicochemical properties of GSG through enzymatic depolymerization. The results revealed a cascade hydrolysis: GM was first broken down into low-M_w fragments, followed by the formation of mannooligosaccharides (MOS), and finally the release of mannose and galactose. The synergistic action of β-D-mannanase and α-D-galactosidase significantly reduced the M_w from 1.088 × 10⁶ to 0.041 × 10⁶ g/mol and increased solubility from 49.16 % to 98.60 %. Variable-temperature germination enhanced β-D-mannanase activity (peaking at 54.16 U/g) and accelerated degradation, particularly in later stages. A moderate increase in the mannose to galactose (M/G) ratio indicated selective cleavage of side chain. Crystallinity improved, while thermal stability slightly decreased. By precisely modulating germination time and temperature, tailored low-M_w GM with enhanced functionality was achieved without compromising viable yield (20-27 %), making them suitable for use in nutraceuticals, functional foods, and feed additives.