Release and metabolism of bound polyphenols from carrot dietary fiber and their potential activity in in vitro digestion and colonic fermentation

Dietary fiber is a carrier of abundant polyphenols and the potential benefits have attracted increasing attention. In this study, we performed in vitro simulated digestion in the oral, gastric and intestinal phases, and colonic fermentation with human fecal microbes, to explore the release and metabolism of bound polyphenols from carrot dietary fiber (CDF) and the potential activity. The results indicate that the bound polyphenols released by the fecal fermentation process (30.43%) from CDF were higher than in the digestion process (0.89%); 26 polyphenols and their catabolites were detected and the microbial pathways of primary polyphenols were proposed. The significant disintegration of the sheet-like structure of CDF after the in vitro fermentation was comparable to that of the digestion treatment. The released polyphenols exhibited antioxidant capacity and α-glucosidase inhibitory activity. The microbe community structure was regulated by the fecal-fermented CDF through decreasing the Firmicutes to Bacteroidetes ratio, improving the relative abundance (RA) of the beneficial microbiota and suppressing the RA of various harmful microbiota. Overall, this study suggests that the bound polyphenols might exert potential benefits in the gastrointestinal and colonic health of the CDF.