Dextrans differing in molecular weight and α-(1 → 3) branching exhibit distinct fermentation dynamics by human gut microbiota in vitro

Dextran is a structurally diverse, soluble α-glucan produced by lactic acid bacteria, but how differences in its structure influence fermentability and microbiota modulation relative to other soluble fibers remains unclear. We characterized two novel dextrans, VIII40 from Weissella confusa VIII40 (7436 kDa; 3% α-(1→3) branching) and DSM22752 from Periweissella beninensis DSM 22752 (216 kDa; 29% α-(1→3) branching), and compared their in vitro fecal fermentation outcomes with linear dextrans (200 and 2000 kDa; <5% α-(1→3) branching), inulin, psyllium husk, and non-fermentable HPMC. VIII40 exhibited higher apparent viscosity and more elastic behavior than DSM22752. All tested dextrans were fermentable, but the extent and dynamics of fermentation depended on structure: VIII40 was closest to inulin, whereas DSM22752 behaved more like partially fermentable psyllium husk. Both novel dextrans produced high levels of butyrate. The highly branched DSM22752 dextran was not bifidogenic, whereas the predominantly linear dextrans showed similar bifidogenic effects despite large differences in molecular weight. Both novel dextrans increased Bacteroides, Parabacteroides , and Phascolarctobacterium , whereas VIII40 additionally enriched Blautia and shifted the community away from proteolytic fermentation. Together, these findings support the further development of structure-defined dextrans as alternative soluble fiber ingredients for fiber-enriched foods.