Revealing the metabolic fate of bound phenolic compounds in dietary fiber from adzuki beans in vitro and their prebiotic properties in the colon.

The indigestible dietary fiber from adzuki beans acts as a natural delivery system for bound phenolics (BPs). However, their patterns of release along the gastrointestinal tract, as well as the specific ways they act on the gut microbiota, are still not fully clarified. In this study, insoluble dietary fiber (IDF) and soluble dietary fiber (SDF) were extracted from adzuki beans, and the content, composition, gastrointestinal release patterns, and microbiological modulatory effects of BPs were systematically analyzed. The BPs content in IDF and SDF was 60.97 ± 2.17 mg GAE/g DW and 7.35 ± 0.65 mg GAE/g DW, respectively. A total of 29 compounds were identified and these BPs exhibited minimal release throughout in vitro upper gastrointestinal simulation. Conversely, after 12 h of colonic fermentation,37.22% and 41.26% of BPs were released from IDF and SDF, respectively. As suggested by the biotransformation pathways, the gut microbiota converts macromolecular phenolic compounds primarily into protocatechuic acid and p-hydroxybenzoic acid. Furthermore, the BPs in adzuki bean dietary fiber promoted the proliferation of bacteria in the genus Bifidobacterium and reduced the abundance of those in the genus Dorea, and enhanced the production of short-chain fatty acids (SCFAs), thereby enhancing the prebiotic activity of adzuki bean dietary fiber. This provides a theoretical basis for further exploration of the role of adzuki bean dietary fiber as a functional nutritional factor in health promotion.