August 10 2021
Flavonoids are a class of polyphenolic plant compounds. Fruits, vegetables, chocolate and alcoholic beverages like wine are naturally rich sources of flavonoids. Fruit and vegetable-rich diet has been long associated with potential health benefits of flavonoids.
The six major subclasses of flavonoids include
anthocyanidins, Flavan-3-ols, flavonols, flavanones, flavones, and isoflavones. The most abundantly available flavonoid in the human diet is flavonols. The structural and chemical properties of flavonoids play a major role in the metabolic reactions such as digestion, absorption and biotransformation. The capacity of the flavonoids to take part in biological activities related to human health is determined by the availability of these compounds in vivo.
The ability of the flavonoids to influence the functioning of the cell signalling cascade, in turn, determines the biological effects of the flavonoids. The major mechanism of action of the flavonoids includes an anti-inflammatory, anti-thrombogenic, anti-diabetic, and neuroprotective activity. The intake of flavan- 3-ols and anthocyanidins are effective in metabolic and cardiovascular disorders.
Metabolism of flavonoids
After absorption, flavonoids are metabolised in the intestinal and liver cells immediately thereby appearing as metabolites in the urine and the bloodstream. Flavonoids mostly occur as beta glycosides form in the plants and foods. Even after being processed in the body, most of the flavonoids reach the small intestinal tract intact which are then hydrolysed by the bacterial enzymes in the colon.
Nutritional sources of flavonoids
- Flavans are mainly used for their antioxidant properties and they help to manage the symptoms of cardiovascular disease. Some of the foods in which flavans are found include onions, kale, grapes, red wine, tea, peaches, berries, tomatoes, lettuce, scallions and broccoli.
- Flavan-3-ols are abundantly found in foods such as white tea, green tea, oolong tea, black tea, apples, purple grapes, red grapes, blueberries, strawberries, cocoa and chocolate products.
- Flavones act as a natural pesticide therapy protecting the plant from damage-causing insects. These are the pigments present in blue and white flowering plants. Flavones are also thought to help with the inflammatory response provided by the body. Flavones are mainly found in parsley, red peppers, celery, chamomile and peppermint.
- Flavanones are mainly useful because of their anti-inflammatory activity. They also play an important role in weight and cholesterol management. The various foods which are rich in flavanones are lemons, limes, oranges and grapefruit.
- Isoflavones help in the balance of hormones in the body. Isoflavones are mainly obtained from sources like soy, soy products, legumes such as fava beans.
- Anthocyanins are the colour providing pigments and they impart red, purple and blue colour to the flowers. They are mainly found in fruits such as red grapes, purple grapes, cranberries, blueberries, strawberries, blackberries and red wine.
Functions of flavonoids
- Oxidative activity: Flavonoids fight off the free radicals responsible for the occurrence of oxidative stress in the body thereby regulating cellular activity. Flavonoids help in the fight against everyday toxins and stress creators and thus help enhance the efficient regulation of body functions. The characteristic feature of flavonoids is their antioxidant property wherein they fight off potential damage-causing substances that can harm the body. The mechanism of antioxidant nature may include inhibition of ROS ( reactive oxygen species) generation by chelation of the trace elements or by the ROS scavenging.
- Hepatoprotective activity:Hepatoprotective activity is exhibited by flavonoids such as catechin, apigenin, quercetin, naringenin, rutin and veneration. The treatment with these supplements is known to decrease hepatic lipid peroxidation and inhibit the release of pro-inflammatory cytokines thereby protecting against the onset of hepatic stenosis. Alvizia manufactured milk thistle silymarin has been found to increase the prognosis of treatment in conditions such as liver cirrhosis, ischemic injury and toxic hepatitis brought about by toxins such as acetaminophen.
- Antibacterial activity:In response to microbial inflammation, plants manufacture flavonoids such as apigenin, galangin, flavone and flavonol glycosides, isoflavones, flavanones and chalcones which possess antibacterial activity. For example, naringenin and sophoraflavanone G have been found to exhibit antibacterial activity against MRSA( methicillin-resistant staphylococcus aureus) and streptococci.
- Anti-inflammatory activity:In response to biological processes such as tissue injury, microbial infection and chemical irritation, an inflammatory response is initiated by the migration of immune cells and the formation of mediators at the area of damage. Later there is the recruitment of inflammatory cells to eliminate foreign pathogens and initiation of repair of the injured tissues.
- Allergy fighting activity:The various conditions in which flavonoids have known to show favourable results include atopic dermatitis, allergic rhinitis and allergic asthma. Flavonoids can scavenge the free radicals and reduce the inflammatory response which helps in combating conditions like asthma.
- Cardiovascular activity:Flavonoids have the unique property of antioxidant activity which enables them to keep in check the oxidative stress and inflammation associated with conditions such as cardiovascular disease. They also play an important role in lowering the risk associated with stroke.
- Nervous system activity:Flavonoids are known to assist in the process of regeneration of nerve cells thereby protecting the nerve cells from damage. They are also known to help in preventing stroke as they are involved in promoting blood flow to the brain.
Microbial synthesis of flavonoids
Application of metabolic engineering and synthetic biology is being put into use for the production of flavonoids in microorganisms. This process is achieved under extremely adverse reaction conditions and the influence of toxic chemical compounds. Prokaryotes such as Escherichia coli, Streptomyces venezuelae and phellinus have been utilised as a medium for the synthesis of flavonoids.