Independent fermentation and metabolism of dietary polyphenols associated with a plant cell wall model

Ingested polyphenols from plant-based foods are in part carried to the large intestine and metabolised by resident microbiota. This work investigated the release and microbial transformation of polyphenols adsorbed individually or in combination to apple cell walls (ACW) and pure (bacterial) cellulose (BC). BC and ACW, representing poorly- and highly-fermentable fibre models respectively, were used to investigate influences of interactions with polyphenols (cyanidin-3-glucoside, (±)-catechin, ferulic acid), on the release and microbial metabolism of polyphenols during in vitro digestion and fermentation. Bound polyphenols were partially released (20-70%) during simulated digestion, depending on polyphenol molecular structure. All remaining bound polyphenols were completely released and metabolised after 6-9 h by porcine large intestine microbiota, with formation of a number of intermediates and end-products. The same pathways of polyphenol microbial metabolism were observed in the presence and absence of ACW/BC, suggesting that microbial metabolism of polyphenols and carbohydrate substrates seems likely independent. Some polyphenol metabolism products were produced faster in the presence of carbohydrate fermentation, particularly of ACW. Microbial metabolism pathways of model polyphenols by a porcine faecal inoculum are not affected by being associated with BC or ACW, but the rate of metabolism is modestly enhanced with concurrent carbohydrate fermentation. The metabolic pathways of polyphenol degradation are not influenced by the presence of plant cell walls during in vitro fermentation, but co-fermentation of cell walls may lead to faster microbial metabolism of polyphenols.