Flavonoids as a Potent Anti-Oxidant in Nutrition: A Mini-Review

Flavonoids are an important class of phytochemicals products found in most of herbs, fruits, vegetables and certain beverages [1,2]. Flavonoids belong to a class of plant secondary metabolites having a polyphenolic structure. They have the general structure of a 15-carbon skeleton, which consists of two phenyl rings and heterocyclic ring [3]. Also they are responsible for the beamy colors in fruits and vegetables [2,4]. Flavonoids are the largest group of plant secondary products, with more than 6,000 types [1]. Some of the best-known flavonoids are quercetin and kaempferol. They can be classified into three classes including:

1) Flavonoids or bioflavonoids,

2) Isoflavonoids, and

3) Neoflavonoids [1,5].

Due to the widespread distribution of flavonoids, high diversity and their relatively low toxicity compared to other active plant compounds such as alkaloids leads to ingest considerable quantities by animals and humans, in their diet [3,4].

Biological activities and benefits of flavonoids

Flavonoids have been presented positive effects on human and animal health, disease therapy and chemoprevention [4-6]. Flavo noids are related to a broad spectrum of health-promoting effects and are an essential component in a variety of functional food, pharmaceutical, medicinal and cosmetic applications [7-9]. This is because of their antioxidative, anti-inflammatory, anti-mutagenic and anti-carcinogenic properties associated with their potential to modulate key cellular enzyme functions. They are also known to be powerful inhibitors for several enzymes, such as Xanthine Oxidase (XO), Cyclo-Oxygenase (COX), lipoxygenase and phosphoinositide 3-kinase [5,8,10]. Flavonoid naturally secondary metabolite exist in plant origin compounds show important anti-oxidative effect that participate to elimination of oxygen-derived free radical [10-12] improve blood pressure and vascular function [1,8], as well as control of PHS and cardiac disorders in animals [7].

The bioavailability of flavonoids

The bioavailability of flavonoids is generally low due to limited absorption, extensive metabolism, and rapid excretion [4,5,13]. Thought is flavones are to be the most bioavailable of all flavonoid subclasses, while anthocyanins and galloylated catechins are very poorly absorbed [3,5,9]. The wide difference in structures within subclasses, it is difficult to generalize the absorbability and bioavailability of flavonoids [5,14].

Antioxidant activity

Flavonoids are effective scavengers of free radicals [7,14,15]. However, it is well demonstrated that even with very high flavonoid intakes, plasma and intracellular flavonoid concentrations in humans are more lower than concentrations of other antioxidants, such as ascorbate (vitamin C), uric acid, and glutathione [11,14,15]. Moreover, most circulating flavonoids are actually flavonoid metabolites, some of which have lower antioxidant activity than the others [5,14,16].

It is clearly demonstrated that the presence of different bioactive compounds such as flavonoids is responsible for the pharmacological effects of some medicinal plants. Flavonoids have received much attention in the literature over the past years. But the study of flavonoids is difficult because of the heterogeneity of the different molecular structures in different type of flavonoids and the scarcity of data on their bioavailability. Therefore, further studies are needed so that the usefulness of flavonoids in the diet could be improved for better animal health.

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