The chemistry, distribution, and metabolic modifications of fruit flavonols

Fruits are considered as healthy foods because they provide a rich source of vitamins, antioxidants and other nutrients, including a range of essential bioactive flavonoid compounds. Flavonols, with diverse chemical properties and biological activities, are the most ubiquitous flavonoids that occur naturally in fruits and they are nutritionally important to animals and humans. Numerous investigations have emphasized that significant intake of dietary flavonols is associated with lower incidences of degenerative diseases. Here, we review current knowledge concerning the molecular structures, composition and distribution, regulation, and structural modification of fruit flavonols. In addition, we consider biotechnological approaches to enhance the levels of flavonols in plants or microorganism. An understanding of the factors determining production of flavonols in fruit crops will improve breeding programs and facilitate the production of fruits or bio-products with desirable contents of bioactive flavonols of benefit to humans.