Biotransformation of Rutin in In Vitro Porcine Ileal and Colonic Fermentation Models

Abstract

Quercetin, a polyphenol antioxidant, is widely distributed in food in the form of glycoside rutin, which is not readily absorbed in the gastrointestinal tract. The microbiota of the colon is known to biotransform rutin, generating quercetin aglycones that can be absorbed. We investigated the role of the ileal and colonic microbiota in rutin biotransformation using established in vitro fermentation models. Overall, a higher rate of rutin biotransformation was observed during colonic fermentation compared with ileal fermentation. The colonic microbiome showed higher potential for rutin conversion to quercetin through an increased abundance of α-rhamnosidase- and β-glucosidase-encoding genes compared to the ileal microbiome. Nonetheless, rutin metabolism occurred rapidly during ileal fermentation (∼20% rutin disappearance after 1 h). The appearance of quercetin varied depending on the ileal inoculum and correlated with an increased abundance of Firmicutes, suggesting that quercetin absorption could be improved via modulation of the ileal microbiota.

Keywords: colon fermentation; fecal microbiome; ileal fermentation; ileal microbiome; polyphenol biotransformation.

Figure 1

Overview of the study.

Figure 2

Rutin biotransformation in ileal and colonic fermentation in vitro. Graphs show the mean ± standard error (error bars are smaller than the symbol size) of rutin disappearance over time during in vitro ileal (a) and colonic (b) fermentations. The graphs also show the mean ± standard error (error bars are smaller than the symbol size) concentration of quercetin present at each time point during in vitro ileal (c) and colonic (d) fermentations. The fermentation inocula were prepared using ileal digesta (for ileal fermentations) and feces (for colon fermentations) from pigs fed diets containing cellulose (6%), pectin (3 or 6%), or fructooligosaccharides (FOS; 3 or 6%) as the sole fiber source (n = 5 fermentations per diet, except for pectin (3%) colon fermentations, n = 3). The raw data were square-root transformed (Sqrt) to fulfill the model assumptions. quadratic. quintic. quartic.

Figure 3

Differences between fecal and ileal microbiomes with regards to rutin biotransformation. Principal coordinates analysis (PCoA) plot and Adonis variance analysis (999 permutations) of (a) microbial genera and (b) KEGG (L4) pathway profiles of porcine fecal and ileal digesta samples based on Bray–Curtis distance. Pigs were fed diets containing cellulose (6%), pectin (3 or 6%), or fructooligosaccharides (FOS, 3 or 6%) as the sole fiber source. (c) Hydrolytic pathway from rutin to quercetin via isoquercitrin by two enzymes. (d) Relative abundance of KEGG orthology associated with the conversion of rutin to quercetin. ****P < 0.0001.

Figure 4

Correlation matrix heatmaps of microbiota and rutin biotransformation. The color represents Spearman’s correlation coefficient between the mean relative abundance of microbial taxa in fecal/ileal samples of pigs, and the average level of phenolic compounds in the in vitro fermentations for each diet. Rutin disappearance refers to the total rutin disappearance over the in vitro fermentation duration. Quercetin and 3HPPA appearances refer to the concentrations of quercetin and 3HPPA at the final in vitro fermentation time point. The statistical significance of the correlation is denoted (^#P < 0.1 and *P < 0.05).