Detecting and Identifying Flavonoids

By Oliver TrevelyanReviewed by Emily Henderson, B.Sc.

Flavonoids are a group of organic chemicals that are thought to have beneficial effects on humans and may also have medicinal effects on some conditions.

Image Credit: Danijela Maksimovic/Shutterstock.com

The sources of flavonoids are plants so they are attractive to many because of their natural origins, however,  it is believed that some flavonoids may also have detrimental effects on humans. This dichotomy requires research to determine which flavonoids are present and whether they have beneficial or detrimental effects.

What is a Flavonoid

A flavonoid is a secondary metabolite of plants which means they are not required by the plant for growth, but they can help with plant defenses and may help the plant to survive. For example, they could be used to make the plant unpalatable to herbivores when the animal starts to eat the plant. They can also be used to attract pollinating insects or fight off infections.

Chemically a flavonoid has a base which is two phenylic rings and a heterocyclic ring with the chemical base C6 C3 C6. To date, over seven thousand flavanoid products have been identified. Flavonoids belong to several subgroups depending on the functional groups that are attached to the rings. Some of these subgroups are:-Anthocyanidins, Anthoxanthins, Flavanones, Flavanonols, Flavans and, Isoflavonoids. The different groups are classified by their chemical structures and active groups

Flavonoids are found in some plants which are commonly consumed by humans. Well-known foods that contain significant amounts of flavonoids are:- Parsley, onions, berries (particularly blueberries), tea, bananas, citrus fruits, sea buckthorns, buckwheat, Ginkgo Biloba, red wine, and dark chocolate with a high cocoa content. Some flavonoids are discovered by observing herbal medicines used by remote communities and extracting the target chemical from the plants used.

The relationship between these flavonoids and their impact on those consuming them is not always well understood and is the subject of research that requires the isolation and extraction of the chemicals and study of the effects of individual flavonoids. This is a complex matter as there are sometimes interactions between substances that make them more or less absorbable in the human gut. Many academic and commercial organizations are studying flavonoids but it is difficult to isolate the effect of the flavonoids from other phytochemicals.

Uses and functions of Flavonoids

Flavanoids have a myriad of potential uses. They could be used for medicine, pharmaceuticals, cosmetics, flavorings, pigments, and even recreational drugs. They can have antioxidative, anti-inflammatory, anticarcinogenic effects, and possibly even reduce antibiotic resistance in microbes.

Flavonoid dietary supplements are readily available online with claims of being able to improve cardiovascular health and many other health benefits. Consumers may assume that because flavonoids are natural derivatives they are all non-toxic. However, this may not always be the case and the links between health effects and consumption need to be studied.

Flavonoids are known to have effects that may be beneficial in tackling the pathology of many conditions. They are known to reduce inflammation and have a beneficial effect on cardiovascular disease and they can scavenge free radicals that damage DNA and are implicated in causing some cancers. Some flavonoids are thought to be beneficial in brain disorders and neurodegenerative diseases. Flavonoids have also been found to inhibit type 2 diabetes.

The potential uses of flavonoids are vast and they are also finding uses outside of the human body. The potential uses of Flavanoids are huge. There is currently a project studying the use of flavonoids from plants endemic to the island of Reunion to extract gold nanoparticles for use in innovative medical procedures.

Extraction and Isolation of  Flavanoids

Traditional extraction of flavonoids involves high-strength methanol and ethanol solvents and dipping percolation or reflux of the solvent flavonoid mix. Several other methods can be used such as supercritical fluid extraction, which can be used to boost extraction rates, and in lab conditions, microwave extraction can be used.

Enzymolysis which is slow can be used as conditions are benign and no thermal decomposition of the desired product will occur. Other low-temperature options are microporous resin adsorption and ultrafiltration membranes.

Many types of chromatography can also be used such as silica gel chromatography, polyamide chromatography, normal and reverse phase HPLC (High-Performance Liquid Chromatography). High-speed countercurrent chromatography can be used to produce high purity products quickly, and, it can be scaled up fairly easily.

Detection and identification of flavonoids can be carried out using spectrography. Flavonoids typically appear in two peaks, usually using wavelengths 250 – 280 nanometers and 300 – 400 nanometer but up to 520 – 540 nanometers. The Infrared spectrum can also be used to identify functional groups typically at wavelengths 1500 – 3650 nm.

Nuclear Magnetic Resonance Spectrography (NMR) is probably the most powerful method for determining the structure of molecules. NMR involves placing a sample in a magnetic field that excites the nuclei of molecules emitting radio waves that can be measured. For flavonoids DMSO-d6 (dimethylsulfoxide-d6) is an excellent solvent as almost all known flavonoids will dissolve in it, but, it has a high melting point so the collection of products can be difficult.

Mass spectrometry can also be used to identify Flavonoids. Mass spectrometry is very sensitive in identifying different flavonoids and can be combined with chromatography to get very accurate results.

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