Xylan-rich Insoluble Passion Fruit Peel Fiber Shows Distinct Gut Microbiota Responses Despite Lower SCFA Production

Fermentable dietary fibers (DFs) are commonly evaluated by their short-chain fatty acid (SCFA) production, which tends to emphasize rapidly fermented soluble DFs and may underestimate the microbiota-shaping role of insoluble plant cell wall components. Here, we characterized polysaccharides from the insoluble DF fraction (PFI) of yellow passion fruit peel and compared its microbiota fermentation profile in vitro with the soluble fraction (PFS) and fructooligosaccharides. PFS, previously characterized as a high-methoxyl homogalacturonan, was rapidly fermented and generated higher total SCFA concentrations (74.9 mM) than PFI (45.0 mM). In contrast, PFI, was characterized as a complex matrix of polysaccharides potentially differing in microbiota accessibility and fermentability, including an insoluble cellulosic residue, linear (1→4)-β-D-xylan, arabinan/arabinogalactan, fucogalactoxyloglucan, mannan and glucuronoxylan. PFI showed slower fermentation and lower total SCFA production, however induced unique beta-diversity shifts distinct from soluble DF treatments. PFI was also the only fraction to increase the abundance of taxa associated with complex plant polysaccharide degradation and previously linked to host health outcomes such as Ruminococcus and [Eubacterium] siraeum. These findings reinforce the idea that same-source soluble and insoluble fractions exert divergent microbiota effects, and suggest that the microbiota-modulating potential of insoluble DFs cannot be inferred from total SCFA output alone. Acknowledgments: CAPES, CNPq.