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Flavonoid

life science Maturity 5-7 Next article →

Flavonoids are a massive group of plant compounds called polyphenolic secondary metabolites. The name comes from the Latin word "flavus," which means yellow. These substances are found in many different types of plants across the world. They are essential for plant survival and biological processes.

Flavonoids Biochemistry
Flavonoids Biochemistry

While humans consume many flavonoids through food, they are not classified as nutrients. This is because they do not provide calories or influence growth and development. They also do not have established effects on preventing human diseases. Scientists study them to understand how plants interact with their environments.

To understand their chemistry, we must look at their unique molecular structure. Every flavonoid is built upon a 15-carbon skeleton. This structure consists of two phenyl rings, known as rings A and B. These are connected by a middle heterocyclic ring, called ring C, which contains an oxygen atom.

Flavylium cation
Flavylium cation

Because of this specific arrangement, scientists often use the abbreviation C6-C3-C6. This shorthand describes the two six-carbon rings connected by a three-carbon chain. The exact shape and properties change based on how these carbons are arranged. This chemical variety allows for thousands of different flavonoid compounds to exist.

Flavonoids perform several vital roles to help plants live and thrive. They act as important pigments that create colors in flower petals. These colors, such as red, blue, or yellow, attract pollinating insects.

Dish of blueberries
Dish of blueberries

They also provide antioxidant protection against ultraviolet light from the sun. This helps protect the plant's cells from damage. Additionally, flavonoids can act as chemical messengers to regulate cell growth. They even help plants defend themselves against pathogens and environmental stresses. Some flavonoids can even inhibit the growth of organisms that cause diseases.

One fascinating process involves the relationship between plants and soil bacteria. Certain flavonoids are secreted from the roots of host plants, such as legumes. Legumes include common plants like peas, beans, clover, and soy.

Parsley100
Parsley100

When bacteria called Rhizobia live in the soil, they can sense these flavonoids. This chemical signal triggers the bacteria to secrete something called Nod factors. The host plant then recognizes these factors and begins a symbiotic relationship. This process can lead to the formation of root nodules on the plant. This interaction is a key part of how nitrogen is fixed in the soil.

Chemists classify flavonoids into several distinct subgroups based on their structures. One group is the anthocyanidins, which use a flavylium ion skeleton.

Flavylium cation
Flavylium cation

Another major group is the anthoxanthins, which include flavones and flavonols.

Flavone skeleton colored
Flavone skeleton colored

There are also flavanones and flavanonols, which have different functional groups.

Flavanone skeleton colored
Flavanone skeleton colored

Another important category is the isoflavonoids, which are derived from a different chemical structure. Finally, there are neoflavonoids, which come from a 4-phenylcoumarin structure. These different shapes determine how each compound behaves in nature.

The study of these compounds has a notable history in science. In the 1930s, Albert Szent-Györgyi and other researchers made an important observation. They found that vitamin C alone was not as effective at preventing scurvy as extracts from oranges or lemons. They believed other substances in the fruit were providing extra help. They called these substances "citrin" or "vitamin P."

Grapefruit Schnitt 2008-3-3
Grapefruit Schnitt 2008-3-3

Later research showed that these substances, like hesperidin, did not meet the official criteria to be called vitamins. Therefore, the term "vitamin P" is now considered obsolete in science.

Humans consume a wide variety of flavonoids through many different foods. You can find them in blackberries, black currants, and red cabbage. They are also abundant in citrus fruits, blueberries, and dark chocolate.

Dish of blueberries
Dish of blueberries

In the United States, the average adult consumes about 190 mg of flavonoids per day. Most of this intake comes from flavan-3-ols, often found in tea or cocoa. In the European Union, the average intake is about 140 mg per day.

Flavonoid intake of adults (18 to 64 years) in the European Union
Flavonoid intake of adults (18 to 64 years) in the European Union

Despite this, the body absorbs less than 5% of these compounds. They are quickly metabolized in the liver and excreted from the body.

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🖼️ Images & Media (15)
File:Flavonoids Biochemistry.png
Flavonoids Biochemistry.png
File:Flavylium cation.svg
Flavylium cation.svg
File:Flavone skeleton colored.svg
Flavone skeleton colored.svg
File:Flavonol skeleton colored.svg
Flavonol skeleton colored.svg
File:Flavanone skeleton colored.svg
Flavanone skeleton colored.svg
File:Flavanonol skeleton colored.svg
Flavanonol skeleton colored.svg
File:Flavan acsv.svg
Flavan acsv.svg
File:Flavan-3-ol.svg
Flavan-3-ol.svg
File:Flavan-4-ol.svg
Flavan-4-ol.svg
File:Flavan-3,4-diol.svg
Flavan-3,4-diol.svg
File:Parsley100.jpg
Parsley100.jpg
File:Dish of blueberries.jpg
Dish of blueberries.jpg

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