**7. Metabolism of quercetin and rutin**

Quercetin is poorly absorbed in the stomach, but its primary site for absorption is the small intestine. Naturally, quercetin inbound to sugars and the sugar moiety is removed during absorption into the enterocytes by the lactase phloridzin hydrolase enzyme. After absorption quercetin is biotransformed to glucuronide conjugate through UDP-glucuronosyl transferases (UGTs), sulfate conjugates by sulfotransferases, and methylation through catechol-O-methyl transferase [37]. Hepatic and intestinal cells play a key role in metabolism (**Figure 4**).

A similar mechanism occurs in the gut where quercetin glucosides are absorbed and deglycosylated to quercetin aglycone with the assistance of enzymes present in the gut microbiota.

Rutin, consisting of quercetin moiety, is unabsorbed in the intestine but undergoes deglycosylation by β-glucosidases and α-rhamnosidases by the gut microbiota [38] followed by catabolic reactions to results in low-molecular-weight phenolic species (**Figure 5**).
