Plant flavonoids represent an important group of secondary metabolites and around 6500 varieties of flavonoids have been reported so far. These are the polyphenolic compounds that are found in almost all plant species. Extensive biological roles of flavonoids have been reported which include antiviral, anti-hepatotoxic, therapeutic, antibacterial, and other roles in nature. The presence of flavonoids in leaves enhances the physiological survival of plants by shielding them from parasitic diseases and UV radiations. Moreover, flavonoids also play role in photosensitisation, photosynthesis, respiration, sex-determination and morphogenesis. Plant flavonoids are generally found in low, variable concentrations and hence, it is challenging to find their consistent supply. Therefore, numerous biotechnological approaches have been explored for the enhanced production of these biologically and pharmacologically beneficial compounds. Flavonoids, mainly flavone-3-ols and proanthocyanins, have been related with decreased risk of cardiovascular disease by increasing the discharge of endothelial nitric oxide and preventing narrowing of the blood vessels. It has been reported that the free radical scavenging properties of these compounds may help lessen the risk of cancer. Flavonoids are also able to chelate (bind) metals, stimulate the immune system and reduce allergic responses and protect against bacteria and viruses. The present review highlights flavonoids as nutraceuticals and pharmaceuticals.
