flavonoles

Flavonols are a class of flavonoids, a group of polyphenolic compounds abundant in plants. They are defined by a 3-hydroxyflavone skeleton with a double bond between C2 and C3 in the central heterocycle, and they commonly occur as glycosides in which sugars are attached to hydroxyl groups. The aglycone forms include several well-known compounds, and the most familiar flavonols in foods are quercetin, kaempferol and myricetin. Galangin is another example often cited as a simple flavonol skeleton.

Notable flavonol aglycones and their glycosides are widespread in the plant kingdom. Quercetin and kaempferol are frequently found as glycosides such as rutin (quercetin-3-O-rutinoside) and kaempferol-3-O-glucoside (astragalin). Glycosylation affects solubility, stability and bioavailability, while the aglycones are typically more readily absorbed in the gut.

Sources and distribution in foods are broad. Flavonols occur in fruits (apples, berries, grapes), vegetables (onions, leeks), and beverages (tea, red wine). They are also present in many herbs and cereals and contribute to the color and flavor profiles of plant-derived foods.

Biological activity is a major reason for interest in flavonols. They exhibit antioxidant properties and can modulate inflammation and cellular signaling in laboratory studies. Their health effects in humans depend on factors such as bioavailability, metabolism, and food matrix, and research continues to clarify their roles in nutrition and disease prevention.