Glycosidic Linkage Structures Influence Dietary Fiber Fermentability and Propionate Production by Human Colonic Microbiota In Vitro

Some dietary fibers can be produced by starch modification; however, information regarding the relationships between glycosidic linkages and dietary fiber fermentability or the production of short-chain fatty acids is limited. Thus, these relationships are investigated using an in vitro model of human colonic microbiota, which approximates the bacterial species richness and diversity in inoculated fecal samples. Six dietary fibers with various glycosidic linkage contents are prepared. Each dietary fiber (final concentration: 1.0 wt%) is administered in vitro to human microbiota models 18 h after fecal samples are inoculated. The contents of (1 -> 2) plus (1 -> 3) linkages and beta-linkages in the six dietary fibers negatively correlate with the fermentation speed and fermentation ratio of the indigestible parts of the dietary fibers (R-2= 0.8126 or 0.8306 andR(2)= 0.9106 or 0.9673, respectively) 24 h after administering each dietary fiber. Further, the concentrations of propionate produced in vitro by human microbiota positively correlate with the fermentation speed and fermentation ratio (R-2= 0.9149 and 0.9581, respectively). The in vitro assay reveals that (1 -> 2) plus (1 -> 3) linkages and beta-linkages in dietary fiber affect resistance to fermentation and propionate production by the human colonic microbiota.