What are flavones? Types, sources and properties

Long before the structure of flavones was described, plants containing these compounds were used to produce natural dyes. Yellow reseda (Reseda luteola), for example, was used in Europe to dye fabrics yellow, and in 1833, luteolin, derived from it, was described. It is now known that luteolin belongs to the flavones, one of the groups of polyphenols found in plants. Other well-known members of this group include apigenin and diosmetin.

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Table of Contents:

What are flavones and how do they differ from other flavonoids?
What types of flavones are there, and what are their characteristics?
Where are flavones found, and which foods are good sources of them?
How are flavones absorbed by the body?
FAQ – Flavones, properties and natural sources

What are flavones and how do they differ from other flavonoids?

Flavones are a subgroup of flavonoids, which are polyphenolic compounds produced by plants. Their basic structure consists of two aromatic rings linked by a third ring containing an oxygen atom. Flavones are distinguished by a characteristic arrangement of atoms within the molecule, including the presence of a double bond between two carbon atoms and a group containing carbon and oxygen. Slight differences in the arrangement of additional chemical groups lead to the formation of many distinct substances.

Flavones are not the same as flavonols, flavanones or anthocyanins, although they all belong to the broad family of flavonoids. Flavonols, which include quercetin, have an additional hydroxyl group at the third carbon atom of the main skeleton. Flavanones, such as hesperetin, do not, however, possess the double bond characteristic of flavones in that part of the molecule. In plants, flavones may contribute to flower colouration, absorb some ultraviolet radiation and perform functions related to defence against environmental factors. Flavones also play a role in chemical signalling between plants and certain soil microorganisms, including nitrogen-fixing bacteria and mycorrhizal fungi.

What types of flavones are there, and what are their characteristics?

Among the best-known flavones are apigenin and luteolin. They have a similar structure, but differ in the number and arrangement of certain chemical groups within the molecule, which affects their properties. Other flavones, such as diosmetin, chrysoeriol and acacetin, also differ from them due to minor changes in their molecular structure. In plants, flavones may occur on their own or in combination with sugars. Such combinations are called glycosides. These include, amongst others, apiin, a derivative of apigenin, and orientin and isoorientin, derivatives of luteolin. The type of bond with the sugar can affect the stability of flavones and the way they break down during digestion.

Selected flavones and their natural plant sources

Flavone	Plants in which it is found
Apigenin	Parsley, celery, chamomile, thyme
Luteolina	Peppers, celery, oregano, sage
Diosmetin	Bergamot, lemon, orange
Chrysoeriol	Bergamot, orange, rosemary
Acacetin	Black locust, birch, kumquat
Baikalin	Baikal skullcap, thyme

Where are flavones found, and which foods are good sources of them?

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The flavone content in products may be reported as the amount of free aglycones or inclusive of their derivatives, which makes it difficult to compare analytical results directly. One of the richest dietary sources of apigenin is parsley. This compound is also found in celery, particularly in its leaves, and in chamomile flowers used to make infusions. Sources of luteolin include, amongst others, oregano, sage, peppermint, peppers and olives. Flavones are also found in certain citrus fruits and their juices, where derivatives of diosmetin and apigenin, amongst others, are present.

How are flavones absorbed by the body?

Flavones consumed in food do not enter the bloodstream entirely in their original, unaltered form. Some of their glycosides are broken down by intestinal enzymes, whilst others reach the large intestine, where they can be metabolised by the gut microbiota. Once absorbed, these compounds undergo further transformations in the cells of the intestine and liver, including conjugation with glucuronic acid or sulphate groups. This is why it is primarily metabolites of flavones that are detected in the blood, rather than large quantities of their free forms. In a study involving healthy adults who consumed parsley or chamomile tea, apigenin metabolites were detected in the urine and plasma. The time taken for them to appear and the amount excreted in the urine varied depending on the product and the chemical form of apigenin.

“Flavonoids are natural plant compounds found, amongst other things, in herbs, vegetables and citrus fruits. Among their best-known examples are apigenin and luteolin. Scientists are interested not only in their biological activity, but also in the way the body absorbs and metabolises these substances”. Anna Zięba – Dietitian

FAQ – Flavones, properties and natural sources

What are flavones and what properties do they have?

Flavones are a group of natural polyphenolic compounds belonging to the flavonoid family. In plants, they play a role in, amongst other things, protection against UV radiation, the formation of flower colour and responses to environmental factors. Their biological activity and metabolism in the human body are the subject of scientific research.

What are the most important types of flavones?

The best-studied flavones include apigenin, luteolin, diosmetin, chrysoeriol and acacetin. These compounds differ in their chemical structure, natural sources and metabolic pathways. In plants, they can occur both in free form and bound to sugar molecules.

Which foods contain the highest levels of flavones?

Well-known sources of flavones include parsley, celery, peppers, oregano, thyme, sage and mint. These compounds are also found in certain citrus fruits and in plants used to make herbal infusions. Their content depends on the species, variety and method of preparation of the product.

How do flavones differ from flavonoids?

Flavonoids are a broad group of plant compounds comprising, amongst others, flavones, flavonols, flavanones and anthocyanins. Flavones constitute one of its subgroups and have a characteristic chemical structure. For example, apigenin belongs to the flavones, whilst quercetin belongs to the flavonols.

What is apigenin and where is it found?

Apigenin is one of the best-studied flavones. It is found, amongst other things, in parsley, celery, thyme and chamomile. Researchers are analysing its chemical properties, biological activity and how it is absorbed and metabolised by the body.

What is luteolin and what are its natural sources?

Luteolin is a natural flavone found in many plants. It can be found, amongst others, in peppers, celery, oregano, sage and peppermint. It is being studied in relation to various cellular processes, but the results of laboratory studies should not automatically be equated with proven health benefits in humans.

Are flavones well absorbed by the body?

The bioavailability of flavones depends on their chemical structure, the form in which they occur in food, and individual digestive processes. Some compounds are converted by intestinal enzymes and the microbiota, and are then metabolised in the gut and liver. Human studies have confirmed the presence of apigenin metabolites in the blood and urine following the consumption of its natural sources.

Are flavones found in dietary supplements?

Yes. Certain flavones, including apigenin and luteolin, may be ingredients in dietary supplements and plant extracts. Individual products vary in their composition and active ingredient content. When choosing them, it is worth paying attention to the standardisation of the extract, the recommended dose and the information on the label. The mere presence of flavones in a product does not constitute grounds for attributing medicinal properties to it.

Sources:

Hostetler, G. L., Ralston, R. A., & Schwartz, S. J. (2017). Flavones: Food Sources, Bioavailability, Metabolism, and Bioactivity. Advances in nutrition (Bethesda, Md.), 8(3), 423–435. https://doi.org/10.3945/an.116.012948
Barreca, D., Mandalari, G., Calderaro, A., Smeriglio, A., Trombetta, D., Felice, M. R., & Gattuso, G. (2020). Citrus Flavones: An Update on Sources, Biological Functions, and Health Promoting Properties. Plants (Basel, Switzerland), 9(3), 288. https://doi.org/10.3390/plants9030288
Borges, G., Fong, R. Y., Ensunsa, J. L., Kimball, J., Medici, V., Ottaviani, J. I., & Crozier, A. (2022). Absorption, distribution, metabolism and excretion of apigenin and its glycosides in healthy male adults. Free radical biology & medicine, 185, 90–96. https://doi.org/10.1016/j.freeradbiomed.2022.04.007