• Flavonoids are a group of polyphenolic compounds, diverse in
chemical structure and characteristics, found ubiquitously in
• Flavonoids (or biofiavonoids) (from the Latin
word flavus meaning yellow, their color in nature) are a class
of plant secondary metabolites.
• Over 4,000 different flavonoids have been identified within the
major flavonoid classes which include flavonols, flavones,
flavanones, eatechins, anthocyanidins, isoflavones,
dihydroflavonols, and chalcones.
• Flavonoids constitute one of the most characteristic classes of
compounds in higher plants.
• Flavonoids are found in higher vascular plants, particularly in
the flower, leaves and bark. They are especially abundant in
fruits, grains and nuts, particularly in the skins.
Many flavonoids are easily recognized as flower pigments in most
angiospcrm families (flowering plants).
However, their occurrence is not restricted to flowers but include all
p sof hcplann
• Beverages consisting of plant exkacts (beer, tea, wine, knit
juice) are the principle soume of dietary fiavonoid intake.
• Flavonoids (particularly glycosides) can be degraded by enzyme
action when collected plant material is fresh or non-dried.
• lt is thus advisable to use dry, lyophilized, or frozen samples.
• When diy plant material is used, it is genemlly ground into a powder.
• For extraction, the solvent is chosen as a function of the type of
• flavonoid required and hence polarity is an important considemtion
• Less polar flavonoids (e.g., isoflavones, flavanones, methylated
flavours, and flavonols) are extracted with chloroform,
• dichloromcthane, diethyl ether, or ethyl acetate,
• While flavonoid glycosides and more polar aglycones are extracted
with alcohols or alcohol—water mixtures.
• Glycosides have increased water solubility and aqueous alcoholic
solutions are suitable.
• Sblnoda test: To the ethanolic extract + added four pieces of magnesium
fillings (ribbon) + few drops of concentrated HCI. A pink or red colour
indicates the presence of flavonoid.
- orangc to red indicated flavones,
— red to pink indicated flavonoids,
- pink to magenta indicated flavononcs.
hydroxide. This gives a yellow color. A change in color from yellow to
colorless on addition of dilute HCI is an indication for the presence of
• p-Dlnietbyfnmlnoclnnainaldehyde test: A colorimetric assay based upon
the reaction of A-rings with the chromogen p-
dimcthylaminocinnamaldehyde (DMACA) has been developed for
flavanoids in beverages that can be compared with the vanillin procedure.
General method of determination of
• The no. of OH group is estimated by the usual methods =>
Flavone does not contain any —OH group.
• On fusion with alkali, flavones are degraded to a phenol and
aromatic acids. Ex:-
Determination of structure of
• Same iiianner as that of flavone
• The lxOl formula is C„H 1,) O,
• It contains one hydroxyl group as indicated by
• On boil wltli ethanolic solutlon of KOH,
Flavonol yields, O- Hydroxy benzoylinetlianol
and benzoic acid indicates that Flavonol is 3-
• Flnally the structure of flavonols are conflnned
by its synthesis -Roblnsons method
• Widely distributed pigments occurs as rhamnosides (quercitine) in
the bark of Quercus tinctoria.
• Mol formula is CASHJ oO7
• It was found to contain four hydroxyl groups as it forms penia-
acetyl and pentamethyl group.
• On fusion with KOH, it gives Phloroglucinol + protocatechuic acid-
it indicates that quercetine is 5,7,3’,4’ — tenahydroxy flavonol .
• The structure was further supported by the fact that on boiling
with alcoholic potash pentamethyl quercetin gives 6-OH,
m,2,4-trimethyl acetophenone and veratric acid.
The structwe was further supported by iG synlesis from
Kostaneck'e Synthesis using ,2,4 dimc1oxy,6-hydroxy
acetophenonc and 3,4-dimethoxy benzaldehyde as starting