chemistry of food

1. DOS&R IN ORGANIC CHEMISTRY
TUMKUR UNIVERSITY
Pigments and colours
By
PRUTHVIRAJ K
Faculty
DOS&R in Organic Chemistry
KPR. DOS&R in ORGANIC CHEMISTRY TUT

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Food colourants
• Substances which add or restore colour in a food, that
includes natural/synthetic constituents which are
normally not consumed as foods as such (FSSAI, 2011).
Food colours can be classified into three groups; natural
food colourants, which refer to ones that are synthesized
naturally; nature-identical colorants, which although
synthesized in industries, mime the natural ones and
finally the artificial/synthetic colourants
 To restore the original food appearance.
 To intensify colours that are normally found in food and
the consumer will associate this improved colour with food
quality.
 To protect the flavour and light susceptible vitamins.
 To preserve the identity or character by which food is
recognized

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Classification of food colourants
• Synthetic colours: These do not occur in nature and are produced by
chemical synthesis. Seven synthetic colourants, belonging to four distinct
chemical classes, are permitted by the FDA for use in foods and in orally
ingested drugs and cosmetics: FD&C Red No. 40, FD&C Red No. 3, FD&C
Yellow No. 5, FD&C Yellow No. 6, FD&C Blue No. 1, FD&C Blue No. 2 and FD&C
Green No. 3. Citrus Red No. 2 is permitted only for colouring skins of oranges
and Orange B for surfaces of casings of frankfurters and sausages. They share
the common property of water solubility, being conferred by the presence of
one or more sulphonic or carboxylic acid groups (Parkinson and Brown,
1981)
• Nature-identical Colours: These colours are also manufactured by chemical
synthesis, but do not require FDA certification and are considered chemically
and functionally indistinguishable from the same colourant found in nature
• Natural Colours: Natural food colour is any dye, pigment or any other
substance extracted using conventional methods, from vegetable, animal,
mineral or other sources capable of colouring food drug, cosmetics or any part
of the human body; colours come from a variety of sources such as seeds,
fruits, vegetables, algae and insect.

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Carotenoids
• Carotenoids group
are
for yellow, orange and red
of phytochemicals
colours
important role in the prevention
responsible
of foods and having an
of
good health. In addition
human diseases
to
maintaining
antioxidants some carotenoids also contribute
and
being potent
to
A. Although
bioavailability, metabolism
dietary
has been
and
vitamin
studied
biological
extensively,
functions
the chemistry of carotenoids
their
are only now
(Rao and
beginning to
Rao,
be
2007).
investigated
ß-Carotene, ß-apo-8-carotenal and canthaxanthin:
These are most commercially
the
important of carotenoids.
occurring
carotene.
isomer
Carotene
of the naturally
is the pigment
the
Beta-Carotene is
carotenoid,
responsible for the of butter, cheese, carrots,
largely
alfalfa
grains.
colour
The colourant is synthetically extracted
and cereal
with acetone, which all-trans form. Both the
results in the
sources of
synthetic and natural
colour additives
ß-carotene are permitted
(Marmion, 1991)

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Betalains
Betalains are a group of red and
colour water soluble pigments found in red beet,
yellow
cactus fruits and in some flowers. They are stable to pH
range 4-6 but degraded by thermal
sensitivity of betalains to different factors suggests
their application as food colourants is limited. Based
processing. The
that
on
these properties, betalains can be used in foods with a
short shelf-life, produced by a minimum heat treatment, and packaged and
marketed in a dry state under reduced levels of light, oxygen, and humidity
Chlorophyll
Chlorophylls have been the least
pigments. Chlorophylls (E 140) are vegetable pigments
studied of the food
that
occur naturally in plants and confer colour
. Among the five
different chlorophylls that exist, only two (a and b) are used
is difficult to stabilize, being this the
in the food industry as colourants. Their complex structure
main drawback of their
which has studied mechanisms of
retaining
use in the industry,
or replacing the magnesium ion within the
structure. The used commercial colourants of chlorophylls
are extracted from alfalfa, and have been employed in dairy
products, soups, drinks and sugar confections

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Anthoxanthins
is a pigment and is similar to
it exists in less oxidized state as the
the central group is uncharged. It is actually a
Anthoxanthin
anthocyanin, but
oxygen on
composite of compounds known as flavones, flavonols and
flavanones. Anthoxanthins are white, pale yellowish, water
soluble pigments found in a plant’s cell sap. They contribute
the cream and white colour of cauliflower, onions,
potatoes and turnips. Short cooking is desired.
white
With
prolonged heat, the pigment turns into a brownish grey colour.
Lycopene
Lycopene is the pigment principally responsible for
the characteristic deep red colour of ripe tomato fruits and
tomato products; it is also found in watermelon, papaya,
pink grapefruit and pink guava. Processed tomato products
are more available dietary sources of lycopene than fresh
tomatoes. Lycopene is a member of the carotenoid family; it
is a natural fat-soluble pigment found in certain plants and
microorganisms, where it serves as an accessory lightgathering pigment and to
protect these organisms against the toxic effects of oxygen and light.

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14. Carotenoids
• Carotenoids are insoluble red, orange, or yellow & function as
accessory pigments in plants: carotene (an orange pigment found in
carrots), lutein (a yellow pigment found in fruits and vegetables), and
lycopene(a red pigment in potatoes).antioxidants
• Carotenoids are lipophilic pigments that are not soluble in water.
They are therefore not located in the vacuoles but in the mebrane
structures of plastids (chloroplasts & exclusively in the chromoplasts
of flower petals). Common pigment in the many yellow flowers of the
Asteraceae (also known as DYCs = damn yellow composites)
KPR. DOS&R in ORGANIC CHEMISTRY TUT

15. • The xanthopylls found in the bodies of animals are ultimately derived from
plant sources in the diet. For example, the yellow color of chicken egg yolks,
fat, and skin comes from ingested xanthophylls (primarily lutein, which is
often added to chicken feed for this purpose)
• Astaxanthin belongs to the xanthophyllbsubgroup of the carotenoids.
Astaxanthin isbfound in microalgae, yeast, salmon, trout,
krill,bshrimp,bcrayfish, crustaceans, and the feathersbof some birds. It
provides the red color of salmon meat and cooked shellfish.
• Astaxanthin, unlike some carotenoids, is not converted to vitamin A
(retinol) in the human body. While too much vitamin A is toxic, astaxanthin
has low toxicity. It is one of the most desirable antioxidants. The primary
natural source is the green alga Haematococcus pluvialis. Under high light
& salt stress, it accumulates high levels of astaxanthin (up to 40 g of
astaxanthin in one kg algae = 4 % dry weight
• The U.S. Food and Drug Administration (FDA) has approved astaxanthin as a
food coloring (or color additive) for specific uses in animal and fish foods
only. The European Commission considers it a natural food dye # E161.
•
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19. Anthocyanins
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31. Tannins
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Extraction
With solvents- extracted with nonpolar solvents. If the tissue is previously dried,
then water-immiscible solvents are used such as petroleum or ethyl ether; with
the fresh materials acetone or ethanol are used, which have two functions,
extracting and dehydrating solvents. Solvents used in extraction must be pure
(without oxygen, acids, halogens) to avoid degradation. Up to now, no solvent is
optimal for the extraction of all carotenoids: carbon disulfide is the best solvent,
but volatility, flammability, toxicity, and degradation limit its use. Chloride solvents
are good, but they show high toxicity; free peroxide ether, despite its efficiency, is
not used because of its flammability and volatility; other solvents such as hexane,
heptane, and isooctane are not so good for extraction, but their other
characteristics are favorable. On the other hand, it must be considered which
compounds will be extracted: polar solvents (such as acetone, methanol, ethanol)
are good with xanthophylls but not with carotenes. As a general rule, the
extraction process consists of the removal of hydrophobic carotenoids from an
hydrophilic medium. The use of nonpolar solvents is not recommended because of
penetration through the hydrophilic mass that surrounds pigments is limited,
while slightly polar solvents dissolve poorly carotene in dried samples and
solubility diminish in fresh samples. Thus, it was postulated that complete
extraction can be reached by using samples with low moisture, and slightly polar
plus nonpolar solvents.

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Extraction
Enzymatic and/or aqueous extraction. Food industries have used enzymatic
methods to obtain a diversity of products: maize starch, gluten and starch of
wheat, gelatin, deboned meat, among others. The main advantages of these
procedures are specificity, moderated temperature and pH, treatments are mild,
secondary products are scarce, and the final product is almost not affected. In
enzymatic processing, enzymes with mixed activities are used because of cell wall
complexity.
Aqueous extraction has been proposed since 1950 as an alternative to organic
solvent. This technology was implemented because of safety and the cheapness of
the process, which is based on oil-water insolubility and phases are separated by
differences in density.
Saponification xanthophylls are usually esterified,279 which produces additional
analyses complications, for example, a pigment with two hydroxyl groups can be
without one or two positions esterified, which requires both separation and
identification. Thus, saponification obtains less complex mixtures when only
nonesterified pigments appear. Another advantage of saponification is chlorophyll
destruction in the saponified samples.