Controlled biosynthesis of curdlan oligosaccharides with tunable degree of polymerization and their prebiotic effects...

Curdlan oligosaccharides (GOS) possess unique physiological and biochemical activities. In this study, an enzyme-assisted coupled fermentation system was developed to efficiently produce GOS with a controllable degree of polymerization (DP) by adjusting the supplemental concentration of endo-β-1,3-glucanase (BGN). By adding 5-15% BGN, GOS with molecular weights (Mw) ranging from 5104 Da to 1269 Da and DP distributions of 12-42, 11-32, 9-18, 7-16, and 5-11 were prepared. Notably, 10% BGN supplementation increased the oligosaccharide yield from 6.18 g/L at the shake-flask level to 9.63 g/L in batch fermentation, demonstrating the scalability and stability of the system. To preliminarily evaluate the microbial utilization of GOS with different DP ranges, LGOS (5-11) and HGOS (11-32) were subjected to in vitro fecal fermentation. GOS modulated gut microbial composition and diversity, promoting short-chain fatty acid (SCFA) production; notably, LGOS induced stronger early-stage effects, whereas HGOS exerted more gradual effects observed at later fermentation stages (12-24 h). Structural analysis further revealed progressive depolymerization of GOS during fermentation, confirming microbial utilization. This study provides a scalable and effective strategy for producing GOS with specific DPs and elucidates their differential impacts on gut microbiota modulation, offering new insights into their potential as functional prebiotics.