Structural characterization of acetylated mannan from Typha angustifolia pollen and the impact of acetylation on its growth-promoting effect toward Lactobacillus johnsonii.

Acetylated mannan (PTPS-W-2) was isolated from Typha angustifolia Pollen through hot-water extraction followed by ion-exchange and size-exclusion chromatography. Structural characterization indicated that PTPS-W-2 is a homogeneous polysaccharide with an average molecular weight of approximately 42 kDa, composed exclusively of mannose residues. The backbone consists predominantly of →4-β-Manp-(1→4)-β-Manp-(1→ linkages, with partial O-acetyl substitution at the C-2 and C-3 positions. Notably, this represents the first report of isolating a plant-derived acetylated mannan with a high degree of purity and structural homogeneity. In vivo administration for two weeks demonstrated that PTPS-W-2 selectively modulated the gut microbiota community by significantly enriching Lactobacillus johnsonii and enhancing intestinal phenyllactic acid production, which was further confirmed using an in vitro monoculture fermentation model. Notably, deacetylated PTPS-W-2 exhibited a markedly weaker growth-promoting effect on L. johnsonii. Comparative physicochemical analyses further showed that deacetylation markedly reduced the aqueous solubility of the mannan. These findings suggest that acetylation-associated structural and physicochemical features, particularly those related to hydration and substrate accessibility, may contribute to the microbial responsiveness of PTPS-W-2. Overall, this study highlights the potential importance of acetylation-associated structural features in shaping the physicochemical properties and microbiota-modulating behavior of plant-derived mannans, providing new insights into their structure-property-function relationships.