Digestive behavior and gut microbiota responses of Glehnia littoralis polysaccharide–Iron complexes: Influence of polysaccharide molecular weight

Glehnia littoralis polysaccharides (GLPs) were fractionated by graded ethanol precipitation to yield fractions with different molecular weights, which were then coordinated with iron to construct GLPs–Iron complexes exhibiting distinct iron-binding ratios. Structural characterization confirmed that iron coordination occurred predominantly through hydroxyl and carboxyl groups without disrupting the polysaccharide backbone. In vitro digestion revealed that maximum gastric iron release decreased with increasing polysaccharide molecular weight (an approximately 1.96-fold difference between the lowest and highest fractions), while all complexes maintained low and stable intestinal release. In vitro fermentation demonstrated that native GLPs promoted the growth of Lactobacillus , while GLPs–Iron complexes, unlike free iron, were associated with an increased relative abundance of Bacteroides species involved in complex carbohydrate degradation. These results indicate polysaccharide–iron conjugation stabilizes iron and modulates microbial responses, highlighting a promising strategy for developing iron fortification systems with improved digestive stability and targeted microbiota interactions. • GLPs were fractionated and chelated with iron into stable, molecular weight–defined complexes. • Iron coordinated via hydroxyl and carboxyl groups without polysaccharide backbone disruption. • Iron release was molecular weight–dependent, with low-weight complexes showing higher gastric release. • GLPs promoted Lactobacillus, whereas GLPs–Iron complexes enriched beneficial Bacteroides.