Modulation of microbiota composition and markers of gut health after in vitro dynamic colonic fermentation of plant sterol-enriched wholemeal rye bread

A human oral phase followed by a dynamic gastrointestinal digestion and colonic fermentation (simgi®) has been applied to wholemeal rye bread (WRB) and PS-enriched WRB (PS-WRB). The aim of this study was to evaluate the impact of these solid and high-fiber food matrices on the metabolism of PS, modulation of the microbiota and production of short-chain fatty acids (SCFA) and ammonium ion after a simulated chronic intake (5 days). In both breads, campesterol, campestanol, stigmasterol, β-sitosterol, sitostanol, Δ5-avenasterol, Δ5,24-stigmastadienol, Δ7-stigmastenol, and Δ7-avenasterol were identified, of which only β-sitosterol was metabolized to sitostenone after PS-WRB treatment. The presence of fiber in both breads exerted a prebiotic effect after fermentation by the increase in Firmicutes (Lactobacillus genus, maximum abundance of 89-99 %) and Actinobacteria (Bifidobacterium genus, maximum abundance of 30-31 %), reflected in an increase of SCFA content. The reduction of proteolytic activity confirmed by the decrease in ammonium ion contents is related to a reduction in the Proteobacteria phylum. Thus, PS-WRB could be considered as a healthy staple food choice since, besides the known hypocholesterolemic effect of PS, rye bread fiber preserves the beneficial microbiota and exerts a positive impact on markers of gut health.