Dietary flavonols and O-glycosides

Flavonols are the most widespread subgroup of the flavonoids. Quercetin, kaempferol, myricetin, and isorhamnetin are the major dietary flavonol aglycones, which most commonly occur as O-glycosides in dietary sources including fruits, vegetables, tea, and wine. The role of flavonols and O-glycosides in human nutrition has gained increased interest due to their associated health beneficial effects for a number of chronic diseases, including cardiovascular diseases, diabetes, and cancer. However, the potential bioactivity of flavonols and O-glycosides will depend on their bioavailability. Following digestion, flavonol glycosides are cleaved to their aglycones, which may be metabolized in the enterocytes and further in the liver, forming glucuronidated, sulfated, and/or methylated metabolites, or they may be passively permeate the intestinal epithelial barrier. Flavonols that reach the colon may be degraded by the colonic microbiota to different metabolites, which may also contribute to the observed biological effects. In this chapter, the recent findings on the bioavailability, metabolism, bioactivity, and benefits of dietary flavonols and O-glycosides are highlighted. In addition, the recent information on food applications, safety issues, marketed products, and patents are also presented.