**3. Metabolism of flavonoids**

In the uptake of flavonoids, two major compartments must be considered. The first compartment contains tissues such as the small intestine, liver, and kidneys. The colon is the body's second compartment (**Figure 3**). Flavonoids that have been consumed and then released with bile will make their way to the colon. Although around 40% of the absorbed ()-catechin was released in rats, the role of biliary secretion in humans is unclear in the small intestine with bile [14]. Metabolism of flavonoids in tissues and in the colon is discussed below in detail.

#### **3.1 Metabolism in tissues**

Biotransformation enzymes operate on flavonoids in the first compartment, including the small intestine and liver. Flavonol biotransformation enzymes can also be found in the kidney. Flavonoids and their colonic metabolites have been found to have polar hydroxyl groups conjugated with sulfate, glucuronic acid, or glycine [15]. Furthermore, O-methylation of flavonoids and their colonic metabolites by the enzyme catechol-O-methyltransferase is significant in the inactivation of the catechol moiety, that is, the two contiguous (ortho) aromatic hydroxyl groups. The conjugation reactions are exceedingly efficient in humans, as indicated by the fact that flavonoids primarily appear as conjugates in plasma and urine and that flavonoid aglycones in plasma are difficult to detect since they are mainly below the analytical methods' detection limits. Differential (HPLC) tests demonstrate the existence of flavonoid conjugates in humans, including O-methylated couples, with and deprived of hydrolysis of the model with a combination of b-glucuronidases and sulfatases: flavonols, flavones, catechins, flavanones, and anthocyanins. Anthocyanins, on the other hand, take a diverse approach. The indication is mounting that anthocyanidin glycosides can tolerate deglycosylation events in humans, at least in part. LC-MS [16] has revealed the presence of peonidin-3-glucoside, as well as peonidin-3-sambubioside [17] and pelargonidin-3-glucoside in urine.

*Recent Advances in Flavonoid Metabolism: An Updated Review DOI: http://dx.doi.org/10.5772/intechopen.106243*

**Figure 3.** *Compartments involved in the metabolism of plant phenols.*
