Release of bound polyphenols from wheat bran soluble dietary fiber during simulated gastrointestinal digestion and colonic fermentation in vitro

Dietary fiber can act as a carrier of bound phenolics in the distal tracts of the gut, where potential microbial processing occurs, but specific mechanism is unclear. This study aimed to evaluate the release characteristic and activity of bound polyphenols from wheat bran soluble dietary fiber (SDF) during simulated gastrointestinal digestion and colonic fermentation in vitro. The result suggested that the bioaccessibility of bound polyphenols in colonic fermentation was 7.42 times that in gastrointestinal digestion stage. Gallic acid, p-hydroxybenzoic acid and vanillic acid were the most abundant polyphenol metabolites after the fermentation for 6 h. The released phenolics exhibited strong radical scavenging activity (DPPH, 99.22 ± 2.05 µmol TE/100 g DW; ABTS, 330.27 ± 3.56 µmol TE/100 g DW). Fecal fermentation of SDF significantly reduced the value of F/B and stimulated the growth of beneficial bacteria, such as Bacteroides, Akkermansia, and Faecalibacterium. Therefore, bound polyphenols may maintain gut health through their prebiotic activity.