The document discusses plant pigments, which are colored compounds found in plants, including chlorophylls, carotenoids, anthocyanins, and flavonoids, each playing important roles in plant nutrition and health. It highlights their chemical properties, effects of cooking on their color, and their nutritional benefits, including antioxidants and potential health advantages. The document also addresses how environmental factors such as pH and metal ions can influence the color and stability of these pigments in food preparation.

1. Plant Pigments
Dr. Gitanjali, Assist Prof. Cum Scientist
Department of Food & Nutrition
College of Community Science
RPCAU, Pusa, Samastipur

2. Plant pigments
•Plant compounds that are perceived by humans to have color are
referred to as PIGMENTS.
•Pigments are molecule that absorb specific wavelength of light and
reflects all others.
•Pigments are coloured and extracted from plant material, but
other sources such as insects, algae, cyanobacteria and fungi are
also used.
• Extracted pigments can be concentrated using either water or
lower alcohols for water-soluble pigments and organic solvents for
lipophilic pigment.

3. Plant pigments
• Pigment refers to normal constituents of cells (or) tissues
that impart color
• A pigment may have properties beyond that of a colorant
for example:
 As energy receptors
 Carriers of oxygen (or)
Protect against radiation

4. Plant pigments indigenous to food
The chief pigments of fruits and vegetables can be
classified into:
 Chlorophylls
 Carotenoids
 Anthoxanthins and
 Anthocyanins

5. Chlorophyll
 The name “CHLOROPHYLL” was originally intended
to describe those green pigments of the higher plants
 Chlorophylls are of great importance in plant foods
because of their role in photosynthesis and
 The formation of carbohydrates from CO2 & H2O
Pigment

6. Chloroplast
 Green pigments – Chloroplast
Two chlorophylls have been isolated ,
• chlorophyll a and
• chlorophyll b;
• and they occur in plants in the ratio of
approximately 3a:1b.
 Chemically, they are very similar.
They belong to that group of important biological
pigments,
• The porphyrins

7. Cont:
•They are fairly large molecules composed of
• Four pyrrole rings held together by methane
carbons (-CH=) to form a large flat molecule.
•In chlorophyll, Magnesium atom is held by a
nitrogen on two of the rings by ordinary covalent
bonds.
•The other two nitrogen's share two electrons
with the magnesium to form a coordinate
covalent bond.

8. Effect of cooking on Chlorophyll
 The complex structure of proteins makes chlorophyll very
susceptible to chemical changes in cooking and consequently
the pleasant green color is difficult to retain.
 When a green vegetable is put in boiling water, the green
colour becomes brighter. This is due to the greater translucency
of plant tissue due to explosion of intercellular air collapse of
the intercellular space.
 As cooking continues compartmentalization within the cell is
disrupted, cell constituents including organic acids diffuse from
the vacuoles throughout the cell and into the cooking water.

9. Solubility of Chlorophyll
• Removal of the phytyl group from the molecule of
chlorophyll is catalyzed by the enzyme chlorophyllase
found in some vegetables.
Hydrolysis of the ester linkage yields a compound
chlorophyllide which is water soluble.
•A limited amount of chlorophyllide produced during
the storage of certain green vegetables
prior to cooking accounts for
the lighter green tint

10. Heating of chlorophyll in the presence of organic acid
•Magnesium present in the structure of chlorophyll is
rather easily disrupted by the hydrogen molecule .
• A pale-greenish grey compound known as pheophytin-a
or
• An olive green pheophytin-b results.
• No longer masked by the intense green chlorophyll,
the yellow and orange pigments in green plant tissue
show along with the green.
•This combination together with pheophytins give the
vegetable a muddy olive green colour.

11. Flavonoids
 Widely distributed in the plant foods
 These are water soluble pigments present in vacuoles.
 these are present in juices of the plants
 Chemically, flavonoids contain two benzene rings with a 3C bridge.
 The C bridge is condensed through an oxygen atom into an
intermediate ring.
 Benzene rings hold the OH groups.
 Flavonoids are among the best-characterized plant secondary metabolites
in terms of coloration mechanism, biochemistry, genetics and molecular
biology
Flavonoids are classified as:
• Anthocyanins (red, blue, purple)
• Anthoxanthins (yellow)
• The catechins leuco anthocyanins
• The highlighted ones change to brownish pigments. They are also known as
food Tannins.

12. Subclasses of Flavonoids
1. Flavonols
2. Flavones
3. Isoflavones
4. Flavanones
5. Catechins
• Anthocyanins
C6–C3–C6 Compounds

13. Structure of Flavonoids
Flavonols & flavones
are very pale-yellow
& are invisible to the
human eye
As they absorb UV,
which insects
recognize, they give
color and patterns to
flowers to attract
insects

14. Anthocyanins
Water soluble plant pigments
Color varies from deep red to purple to blue
 present in fruits, vegetable and flowers
Phyto-protective and pollination attractants
Natural food colors
 Anthocynins are members of flavanoids
 Phenolic phytochemicals
Anthocyanins are highly prone to undergo
degradation and oxidation.

15. Anthocyanins
• They are found in the vacuoles of the plant cells
• They occur in plant cells as glycosides.
•Examples of anthocyanins are cherries, red apples, various berries,
blue grapes, pomegranates, skin of radish & leaves of red cabbage
•The colour results from the structure of anthocyanidins which is
combined with monosaccharide units
• The carbohydrates are commonly bounded by
 Glucose
 Galactose
 Rhamnose
 Pentose
In cookery and processing these pigments have the tendency to
leach out in the cooking water, but they are not lost if the cell
walls remain intact

16. Content of Anthocyanins in Food and Beverages

17. Effect of pH (Anthocyanins)
• As pH changes
 The colour of the anthocyanins changes from
crimson(pH3) to bright green (pH14)
•Addition of alkali
 Gives the pigment a bluish green shade
 This shade is probably caused by the presence of
anthoxanthins with anthocyanins
•On the addition of alkali
 The anthoxanthins turn yellow, while
 The anthocyanins turn blue with a mixture of 2
colors appear green
 Such a colour can be seen in a red cabbage

18. Effect of Metal (Anthocyanins)
 Special enamel linings of cans are used when canning
anthocyanin containing fruits and vegetables.
 Unusual colors ranging from green to stale blue, develop when
anthocyanins contain iron, aluminum, tin and copper ions.
The ascorbic acid with copper or iron accelerates the oxidation
and undesirable colors changes of anthocyanin compounds.
 The metal iron precipitates the pigment.
 Iron reacts with anthocyanins to form intense black coloration.

19. Effect of the method of cooking
Anthocyanins are water soluble sap pigments which can be leached
from a vegetable by cooking water.
• The pigment will change into a dull unappetizing blue.
• With tap water, the pigments change to an unattractive blue or
grey color.

20. Anthoxanthins
• Colorless or pale yellow pigments, closely related to
anthocyanins.
• They are also water soluble and present in vacuoles of plant cells
• Widely distributed
• Examples : cauliflower, onions etc.
• In green leafy vegetables, the color is masked by chlorophyll.
•Anthoxanthins are glycosides, which on boiling with acids yield
monosaccharide and a flavone or a flavone derivative such as
flavonal, flavanonal, or isoflavone.

21. Changes during cooking /processing
 Effect of pH
• The color of the vegetable turns white with little acid added during
cooking.
• If the water is slightly alkaline, a distinct yellow color results.
 Effect of metal
• They cause the cooking water to turn yellow when cooked in
aluminium pans.
• Because the flavones scavenge aluminium and form a flavone
aluminium chelate.
 Pears and potatoes sometimes develop a pinkish color in their cut
surfaces
• on standing for a while after being peeled or sliced.
• This color change is due to the conversion of the pro- anthocyanin to
the pigmented and closely related compound cyanindin.

22. Tannins
• Dark colors in foods and astringency tastes are ascribed to
tannins. They are comprised of
 Catchins
 Leucoanthocyanins
 some hydroxy acids.
• All of them give colors with metal ions.
• Cathechins and lecoanthocyanins are present in the tissues of
woody plants such as apples, peaches, grapes, almonds, pears.
• Present in cereals and millets.
• Tea and cocoa contain catechin and epicatechin.
• Tannins are readily dispersed in hot water to form colloidal
solutions.
• When a fruit is pressed, as apples in the preparation of cider or
grapes in making juice or wine tannins flow out in the juice.

23. Tannins
• They have low nutritional value and are responsible for decreases in food
intake, growth rate and protein digestibility.
• Tannin-containing plant extracts are used against diarrhoea, diuretics, against
stomach and duodenal tumours, and as anti inflammatory, antiseptic, and anti
carcinogenic properties.
• In the food industry , used to clarify wine, beer and fruit juices.
• The growth of many fungi, yeasts, bacteria and viruses is inhibited by tannins.
• The antimicrobial property of tannic acid can also be used in food processing to
increase the shelf-life of certain foods.
•Tannins have also been reported to exert other physiological effects, such as
to accelerate blood clotting, reduce blood pressure, decrease the serum lipid
level, produce liver necrosis and modulate immuno responses.

24. Tannins
 In the extraction such as brewing of tea or coffee some of the tannins are
extracted.
 When tea or coffee are brewed with hard water, a brown precipitate forms on
the surface of the liquid.
 As the beverage cools, it appears throughout the liquid. Instead of a clear,
sparkling infusion, the tea or coffee is distinctly muddy.
 The precipitate clings to the side of the cup and the color is very noticeable.
These transformations are caused by the reactions of the tannins in the tea
and coffee with Ca and Mg ions of water.
 If iron is present, very dark complexes are formed.
 The change in color which occurs when lemon juice is stirred into black tea is
also the result of a change in the tannins present.

25. Carotenoids
 Carotenoids are lipid-soluble, yellow–orange–red pigments
found in all higher plants and in some animals.
 Animals cannot synthesize carotenoids.
 Carotenoids can be divided into carotenes containing only
carbon and hydrogen, and xanthophylls made up of carbon,
hydrogen and oxygen.
 Carotenoids are also used for nutritional purposes as
provitamin A agents or as dietary supplements.
 Acts as anti oxidants

26. Sources

27. Betalins
• Betalins are red or yellow water-soluble pigments
color in flowers or fruits of the families of
Caryophyllales (including cactus, amaranthus and red
beets).
• Advantage of betalins color is that it does not depend
on the pH and is more stable than that from
anthocyanins.
• Beets contain pigments that are closely related to
anthocyanins.
• Betalains are classified into red (crimson) betacyanins
and yellow betaxanthins.
 Betacyanins (beet color)
 Betanidin and betanin.
 Betaxanthins (yellow pigment)
Betacyanins Betaxanthins

28. Betalins
• Although these pigments are held tightly within cells in the raw
vegetable.
• They diffuse rather rapidly into the cooking water resulting in the
highly pigmented water associated with boiling beets.
•This problem is aggravated by cutting beet into small pieces and
cooking leading to dull coloration in the boiled product.
 Effect of pH
 Betacyanins turn into a reddish color in an acidic medium.
 In neutral or alkaline pH a browinish blue pigment results.

29. Betalins