Flavonoid

Flavonoids (or bioflavonoids; from the Latin word flavus, meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans.

In the 1930s, Albert Szent-Györgyi and other scientists discovered that Vitamin C alone was not as effective at preventing scurvy as the crude yellow extract from oranges, lemons or paprika.

Depending on the chemical structure, degree of oxidation, and unsaturation of the linking chain (C3), flavonoids can be classified into different groups, such as anthocyanidins, flavonols, flavanones, flavan-3-ols, flavanonols, flavones, and isoflavones.

Flavonoids secreted by the root of their host plant help Rhizobia in the infection stage of their symbiotic relationship with legumes like peas, beans, clover, and soy.

Flavonoids (specifically flavanoids such as the catechins) are "the most common group of polyphenolic compounds in the human diet and are found ubiquitously in plants".

The widespread distribution of flavonoids, their variety and their relatively low toxicity compared to other active plant compounds (for instance alkaloids) mean that many animals, including humans, ingest significant quantities in their diet.

[1] Foods with a high flavonoid content include parsley, onions, blueberries and strawberries, black tea, bananas, and citrus fruits.

[1][18][19][20] The U.S. FDA has warned numerous dietary supplement and food manufacturers, including Unilever, producer of Lipton tea in the U.S., about illegal advertising and misleading health claims regarding flavonoids, such as that they lower cholesterol or relieve pain.

[21][22] Flavonoids are poorly absorbed in the human body (less than 5%), then are quickly metabolized into smaller fragments with unknown properties, and rapidly excreted.

[1] Although no significant association has been found between flavan-3-ol intake and cardiovascular disease mortality, clinical trials have shown improved endothelial function and reduced blood pressure (with a few studies showing inconsistent results).

"[32][33] The FDA followed suit in 2023, stating that there is "supportive, but not conclusive" evidence that 200 mg per day of cocoa flavanols can reduce the risk of cardiovascular disease.

This is greater than the levels found in typical chocolate bars, which can also contribute to weight gain, potentially harming cardiovascular health.

[40] A colorimetric assay based upon the reaction of A-rings with the chromogen p-dimethylaminocinnamaldehyde (DMACA) has been developed for flavanoids in beer that can be compared with the vanillin procedure.

After proper mixing of the sample and the reagent, the mixture is incubated for ten minutes at ambient temperature and the absorbance of the solution is read at 440 nm.