However, cellular uptake of aglycones has been suggested to occur in their native form by passive diffusion. Absorbed polyphenols can directly undergo phase II metabolism as phenolic structures are generally unfavorable substrates to the cytochrome P450s (phase I metabolism). At nutritional doses, almost all polyphenols are conjugated to form O- glucuronides, sulfate esters and O-methyl ethers, by glucuronidation, sulfation and methylation, in the gut mucosa and later in the liver or kidney. Glucuronidation and sulfation of polyphenols may facilitate their rapid urinary and biliary excretion by increasing their hydrophilicity, and also may limit their potential toxicity. .
