Human intestinal hydrolysis of phenol glycosides – a study with quercetin and p-nitrophenol glycosides using ileostomy fluid

In order to study the influence of sugar moiety, aglycon structure and microflora concentration on the human ileal hydrolysis of phenol glycosides, various quercetin and p-nitrophenol glycosides were incubated under anaerobic conditions (37°C for 0, 0.5, 1, 2, 4, 6, 8, 10 and 24 h) with ileostomy fluids from three different donors. The glycosides, i.e. β-D-glucopyranosides, β-D-galactopyranosides, α-L-arabinofuranosides, β-D-xylopyranosides and a-L-rhamnopyranosides as well as the liberated aglycones were identified by HPLC-DAD and HPLC-ESI-MS/MS. Among the quercetin glycosides under study, the 3-O-β -D-glucopyranoside showed with 0.22 μmol/h the highest hydrolysis rate, followed by the 3-O-β -D-galactopyranoside, the 3-O-β-D-xylopyranoside and the 3-O-a-L-arabinofuranoside (0.04 and each 0.03 μmol/h, respectively). Quercetin 3-O-α-L-rhamnopyranoside was found to be stable for the entire incubation period. Using quercetin 3-O-β-D-glucopyranoside as a representative example, linear hydrolysis rate was observed from 75 to 2500 μL ileostomy fluid corresponding to its microflora content (log 0.68 up to 21.9 colony forming units). Studies performed in the presence of antibiotics did not reveal any hydrolysis. The p-nitrophenol glycosides were hydrolyzed faster than the corresponding quercetin glycosides. The hydrolysis rate decreased from the β-D-glucopyranoside (0.41 μmol/h), to the β-D-galactopyranoside (0.21 μmol/h), the β-D-xylopyranoside (0.12 μmol/h), the α-L-arabinofuranoside (0.09 μmol/h) to the α-L-rhamnopyranoside (0.06 μmol/h). These results demonstrate that the human ileal hydrolysis of phenol glycosides depends on the sugar and the aglycon structure as well as the microflora.