Cooking, simulated digestion, and in vitro colonic fermenta-tion of Nigerian wholegrains affect phenolic acids metabolism and gut microbiota composition

Wholegrains contain both fibre and phenolic acids (PAs), and their gastrointestinal modifications are critical for their bioavailability and bioactivity. We evaluated the modifications on the PAs profile and gut microbiota composition in selected Nigerian wholegrains, following cooking and gastrointestinal digestion. Red fonio (RF), red millet (RM), red sorghum (RS) and white corn (WC) were cooked, digested and fermented in vitro. A total of 26 PAs derivatives were quantified in soluble and bound fractions by Ultraperformance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS) analysis. DNA samples were analysed by 16S rRNA gene-based next-generation sequencing to determine the gut microbiota composition. Results show that cook-ing and digestion significantly affected the levels of PAs in all grains (p<0.05), when compared to raw grains. Colonic fermentation over a 24 h period show total soluble PA in RS and WC peaking at 4-6 h, and RM and RF peaking at 24h. The sequencing of samples showed Enterobacteriaceae as the most abundant genus at 24 h in all grains studied. 3-hydroxybenzaldehyde correlated posi-tively abundance of Dorea and the proportion of the mucus degrader Akkermansia (p<0.05), whereas hydroferulic and isoferulic acid levels had a negative correlation with the Oscillospira and Ruminococcaceae members (p<0.05) respectively. Our data indicate that cooking, digestion and colonic fermentation affected the release of bound phenolic acids from wholegrains, and con-sequently their metabolic conversion. Thus, phenolic acid fermentation in the gut can lead to rele-vant improvements in the intestinal microbial ecosystem. This in vitro study lays the foundations for the design of an in vivo human intervention study that can confirm the promising trends herein observed