Importance in all parts of the plant i.e. stem,

Importance of Flavonoids and Iso flavonoids in human

consist of large groups of polyphenolic compounds having a benzo-?-pyrone
structure and are present largely in all parts of the plant i.e. stem, leaves,
roots, fruit, vegetables and flower. They are synthesized by the phenyl
propanoid pathways 1.

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are the hydroxylated phenolic compounds and synthesized by the plants in response
to microbial infections. Their activities are structure dependent. The chemical
nature of Flavonoids depends upon their Structural class, Degree of hydroxylation,
Substitution, Conjugation, Degree of polymerization 2.

a dietary substance, flavonoids are thought to be considered a health promoting
substances due to their high capacity of antioxidants. Studies on the
flavonoids by the UV spectrophotometry have revealed the most flavones and
flavanols  exhibits two majors absorption
bands Band I (320-385nm) represents the B absorption band while Band II
(250-285nm) correspond to a ring absorption. Functional groups attached to the
flavonoids skeleton may cause in shift absorption 3-4

Natural source of Flavonoids:

are the large groups of natural substances with variable structure present
almost in all growing parts of the plant. These are the major secondary
metabolites in the plant structure. Besides in the relevance in plants; these
are also important in the human health due to their pharmacological activity.
Flavones are found in citrus fruits. These are the major coloring component in
the flowering plants. Basically, flavonoids in food are responsible for color,
taste, prevention of fat oxidation and protection of vitamins and enzymes.
Large amount of polyphenolic compounds are found in the coffee, tea and red
wine 5.

Flavonoids level in Plants:

 Flavonoids found highest amount in human food
as soy isoflavones , flavanols and isoflavanones. The level of individual and
total flavonoids in food is influenced by the species, environmental such as

·       Light

·       Ripeness

·       Post
harvesting treatments

level of flavonoids is different in different parts of plants. However the
processing and preparation of food may decrease the flavonoid level depending
upon the method 6.

Dietary intake of Flavonoids:

flavonoids family of the plant family comprises the most widely distributed
group of the secondary metabolites ingested by the humans. Accurate estimation
of the total dietary intake of flavonoids is difficult, due to their wide
varieties and extensive distribution. Although the dietary data on flavonoids
and dihydrochalcones are yet available, these compounds may make a significant
contribution to the daily intake of flavonoids. Flavonoids are stable to heat,
but easily lost due cooking and frying 7.

Flavonoids and Human Health:

are the naturally occurring polyphenolic antioxidant present in the human food.

contribute to antioxidant properties green vegetables, fruits, olive oils,
teas, red wine

beans oil and chocolate. Some flavonoids have been reported to possess a
biological activities including

·       Anti-inflammatory

·       Anti-allergic

·       Anti-viral

·       Anti-proliferative

·       Anti-carcinogenic

addition to having an effects on mammalian metabolism. Flavonoids have received
a considerable attention because of their beneficial effects as antioxidants in
prevention of human diseases such as;

·       Cardiovascular

·       Pathological
diseases of:

·       Gastric

·       Duodenal

·       Allergies

·       Vascular

·       Bacterial

Flavonoids have so far been found to exhibit a wide spectrum of pharmacological

including Oxidative activity, Anti-allergic activity, Anti-inflammatory,
Anti-diabetic, Hepatic and gastro protection activity, Anti-viral activity and
Anti-neoplastic activity 8-9

General benefits of Consumption of Flavonoids and Isoflavonoids:

phenolic compounds, particularly flavonoids, are thought to be considered to
play important role in human health. In vitro and animal studies have
demonstrated that flavonoids have antioxidant and ant mutagenic activities and
may reduce the risk of cardiovascular diseases and strokes. Isoflvonoids such
as phytoestrogens, have a wide range of hormonal and non-hormonal activities in
animals and in vitro, suggesting potential human health benefits of diets rich
in these compounds. Flavonoids may act as antioxidant to inhibit free radical
mediated cytotoxicity and lipid peroxidation, as anti-proliferative agent to
inhibit tumor 10.

may confer protection against chronic diseases such as atherosclerosis and
cancer. Research showed that habit of tea drinking prevent cardiovascular
diseases and also include the capillary strengthening property, an antioxidant
property responsible for radio protective effect and anti-microbial property

have shown many biological properties that may account for cancer chemo prevention.
In recent years, considerable attention has been paid to their abilities to
inhibit the cell cycle, cell proliferation and oxidative stress and to induce
detoxification enzymes, apoptosis and active the immune system. Multiple mechanisms
have been identified for anti-neoplastic effect of flavonoids including 12:

·       Oxidant

·       Anti-inflammatory

·       Anti-proliferating

·       Inhibition
of bio activating enzymes

·       Induction
of detoxifying enzyme

Flavonoids as Natural Products:

consist of large number of polyphenolic groups have the benzo-pyrone type

widely spread all over the plants parts .i.e. leaves, stem, flower, roots and
shoots. Mainly, these are present in the plants in the form of anti-oxidants.

Flavonoids are
synthesized by phenyl propanoid pathways. Flavonoids imparts the color to the
plant, these are the secondary metabolites. Flavonoids class is divided into
main six subgroups:  chalcones,
flavanols, flavones, flavandiols, proanthocyanidines and condensed tannins. The
compounds that are formed is depend upon Substitutions of the basic flavonoid
ring A, B and C. The second most important class of flavonoids is the phenolic
acids: divided into two basic categories hydrpxybenzoic acid and
hydroxycinnamic acid. The most common hydrpxybenzoic acids are as follows:

Gallic acid

Salicyclic acid

Vanilic acid


Protocatechuic acid

While the well knows
hydroxycinnamic acids are as follows:


Caffic acid

Sinapic acid

Feruic acid

Flavonols is the most
important Flavonoid and used as a medicine against the stress that’s why
Flavonoids have wide application in physiological activities 19.

Biotransformation of Flavonoids:

are the important secondary metabolites which are synthesized in plants in
Shikmic acid pathways. There are the several methods to extract the phenolic
compounds from the plant .i.e. Physical, physiochemical and chemical techniques
such as cold pressing, supercritical fluid extraction, solvent extraction,
ultrasound-assisted extraction and microwave-assisted extraction. The basic
disadvantage of all these techniques is low yield which is the basic problem
for a chemist. The phenolic compounds are bound to the cell wall of the plant
through the –OH group (O-glycosides)
or C-C bond (C-glycosides). We can maximize the yield of these phenolic
compounds by the breaking of the –OH bond prior to use of conventional
techniques. The –OH bond break through the enzymes or microbes, because the
pretreatments with the chemicals can leads to the unwanted products. The chemical
also have a toxic impact on our environment. Through the process of
fermentation of the phenolic compounds by Microbes, microbial metabolites are
released by the process of glycosylation, deglycosylation, methylation and
sulphate conjugation.

Glycosylation and Deglycosylation
of Flavonoids:

Glycosylation is the
reaction of the biosynthesis of the Phenolic compounds in which the glycosyl
donor is attached to the aglycone in the presence of the enzyme. These
reactions can enhance the stabilization, detoxification and solubilization of
the substrate.  Deglycosylation is in
contrast to the glycosylation, deglycosylation is also done in the presence of
the microbes.

Ring cleavage and Methylation of the Flavonoids:

flavonoids undergoes the ring opening reaction in which their C-ring is split
into the Chalcones along with the hydroxylation at different C-positions are
produced. The ring fission of the heterocyclic phenolic compounds occurs in the
presence of Aspergillus spp, Pencillium spp and Rhizopus spp. O-methylated
flavonoids are known as Xenobiotic transformation metabolites, is a common
hepatic metabolite. The fermentation of the 7-hydroxyflavanone with Pencillium chermesinum at 25o
C for six days resulted in two methylated products: 7-methoxyflavanone and
3,4-dihydroxy-7-methoxyflavanone 13.



 Source of phenolic compound






Microbial Metabolites













Schematic Diagram of microbial conversion of phenolic compounds