Increasing the geranoil content of palmarosa oil by chemical methods
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Date
1997
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Department of Soil Science and Agricultural Chemistry, Horticulture College, Vellanikkara
Abstract
Palmarosa, Cymbopogon martinii (Stampf) var. motia is an important essential oil
crop grown commercially in various states of peninsular India. Palmarosa oil finds
extensive use in flavouring, cosmetics and toiletry. The oil is valued for the principal
constituent geraniol, present in the oil to the extent of 75-82%. Besides being a high
grade perfume, geraniol is the starting material for a number of synthetic aroma
chemicals. Next to geraniol, the most abundant chemical component of the oil is
geranyl esters, predominantly geranyl acetate. Most oils contain about 2 - 12%
geranyl acetate. Several factors like the genotype, season, harvest stage, method of
oil extraction etc. influence the ratio of geraniol to geranyl acetate in the oil and it is
found that a reciprocal relationship exists between the geraniol and geranyl acetate
content of the oil. At most times, the geraniol content of palmarosa oil produced by
cultivators fall short of requirements of the user industry. The availability of an
inexpensive and efficient method of hydrolytic conversion of geranyl acetate to geraniol
will facilitate the farmer to undertake an on-farm quality upgradation of his product
which will fetch him better price. A laboratory investigation was carried out at the
Aromatic and Medicinal Plants Research Station, Odakkali, Kerala during 1994-96 to
develop a method for upgrading the quality of palmarosa oil by the conversion of
geranyl acetate in the oil to geraniol.
Four treatments were tried for the hydrolysis of geranyl acetate, with essential
oil of palmarosa type ODP-3 as the test material viz., methanolic sodium hydroxide,
methanolic sodium carbonate, ammonia and aqueous sodium hydroxide.
Mixing of essential oil with 5% methanolic NaOH reagent in the ratio of 1 : 4 and
keeping undisturbed at ambient conditions for 30 min were the optimum conditions for
the complete hydrolysis of geranyl acetate in the oil. The product of reaction analysed
90.5% geraniol and the process yielded geraniol to the extent of 78.74% of the oil
taken for processing. However, treatment of the oil with methanolic sodium carbonate
or ammonia did not result in hydrolysis of geranyl acetate.
In the case of aqueous sodium hydroxide method of hydrolysis, refluxing the
essential oil with an equal volume of 20% aqueous NaOH solution for 30 min was
optimum for the complete hydrolysis of geranyl acetate in the oil. The product
contained 89.35% geraniol and the quantity of geraniol yielded by the process was
estimated at 86.67% of the oil taken for processing.
Comparison of the methods of hydrolysis studied -revealed that in terms of
geraniol content of the product, geraniol yield from the process and time: required for
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the reaction, the aqueous sodium hydroxide method was found to be the best. The
efficiency of the method for quality upqradation was tested on essential oils of different
Cymbopogon types viz., ODP-1, ODP-3, C-3, OD-455 and Jamrosa. All the oils
were characterised by low level of geraniol and high level of geranyl acetate and none
of them conformed with ISI specifications for palmarosa oil. In case of all the oils, the
treatment resulted in complete conversion of gerariyl acetate to geraniol with
commensurate increase in the level of geraniol, bringing about a vast increase in
their quality. By the process, oils of ODP-3 and Jamrosa were upgraded to meet the
specifications for palmarosa oil.
Verification of the sodium hydroxide hydrolysis method on pilot plant scale
showed that it can be employed on large scale for the quality improvement of
. palmarosa oils which contain appreciable amount of geranyl acetate.
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170961