Pigments and Colors:Extraction and Purification- Extraction of naturally occurring pigments like anthocyanins, tannins etc from their sources and purification methods

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

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Why we needto extract ?

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4. 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.
KPR. DOS&R in ORGANIC CHEMISTRY TUT

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6. 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.
KPR. DOS&R in ORGANIC CHEMISTRY TUT

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FLOW CHART

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PAPER or THINLAYER CHROMATOGRAPHY

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