Unlocking the prebiotic potential of shiitake stipes insoluble dietary Fiber-bound Phenolics: Structural modulation, antioxidant release, and gut microbiota regulation via untargeted metabolomics

Shiitake stipes, a major by-product of mushroom cultivation, are a rich source of insoluble dietary fiber (IDF) covalently bound to phenolic compounds. This study investigated the functional relationship between bound phenolics (BP) and IDF by comparing native BP-IDF with phenolics-removed IDF (RP-IDF). The removal of BP was associated with marked changes in fiber morphology and significantly reduced water/oil-holding capacities, swelling power and antioxidant activity, suggesting that BP may contribute to the structural and functional properties of the IDF matrix. BP-IDF achieved a colon-specific release profile, whereby 82% of its phenolic compounds remained undigested in the upper gastrointestinal tract and arrived at the colon. The BP-IDF complex was associated with increased relative abundances of beneficial genera such as Megamonas and Segatella , together with reduced abundance of Escherichia-Shigella . Untargeted metabolomics further suggested that BP-IDF altered the fermentation metabolite profile, particularly tryptophan metabolism-related pathways and metabolites. Together, these findings provide preliminary evidence that the native BP-IDF complex may exert prebiotic effects through coordinated structural protection, phenolic release, microbiota modulation, and fermentation-related metabolic changes. These results clarify the prebiotic mechanism of BP in mushroom by-products, supporting their use as functional food ingredients.