Chemical constituents of lemongrass (Cymbopogon flexuosus Stapf) oils and their nematicidal activity against meloidogyne javanica
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Date
2007
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CCSHAU
Abstract
Laboratory studies were conducted to study the effects of steam distillation time and silica gel
column chromatography on the quality of essential oil of Lemongrass (Cymbopogon flexuosus).
Nematicidal activity of aqueous extracts of essential oil of Lemongrass (Cymbopogon flexuosus) was also
studied against the root knot nematode Meloidogyne javanica. For steam distillation studies, two
Lemongrass varieties viz., CKP 25 and OD 19 and six genotypes viz., NLG 84, NLG 118, HL 2, HL 3, HL
10 and HL 11 were taken and the essential oils of the freshly harvested grasses of these eight
varieties/genotypes were extracted by steam distillation using Clevenger apparatus. To obtain the optimum
time of steam distillation, two sets of Clevenger apparatus were used for each variety/ genotype. One of the
distillation units was labelled as “Full Time Distillation” and another distillation unit was labelled as
“Fractional Distillation”. The distillation unit labelled as “Full Time Distillation” was boiled for 4 hours
and all the essential oil that distils out from the grass in 4 hours was collected in one glass vial labelled as
“Full Time”. The second distillation unit labelled as “Fractional Distillation Unit” was also boiled for 4
hours but the oil fractions recovered at periodical interval of 1 hour were collected in four glass vials and
labelled as 0-1 h, 1-2 h, 2-3 h and 3-4 h. Among the various steam distilled oil fractions maximum oil
(74.2-82.6%) was recovered in the first hour. The citral-a (44.3-54.3%), citral-b (30.4-35.0%) and total
citral (75.1-89.3%) content in all the eight varieties/genotypes was higher in the 0-1 h distilled oil fractions
in comparison to “Full Time” distilled oil (the range of citral-a, citral-b and total citral being 43.0-50.7%,
27.5-31.7% and 70.5-82.4%, respectively). The higher citral content in the first hour distilled oil fraction
may be due to high volatility of citral-a and citral-b so that majority of these constituents distil out in the
first hour itself. Qualitative analysis of oils recovered from some hexane fractions (from 151–400 ml) in
silica gel column chromatography studies showed that citral-a (48.6-52.7%), citral-b (29.4-32.5%), and
total citral (77.9-81.9%) content was higher in comparison to their contents (44.8%, 29.1% and 73.9%,
respectively) in pure oil sample. This may be probably due to adsorption capacity of silica gel with citral-a
and citral-b for sometime in the earlier stage and thereafter due to desorption of these constituents in the
later stage, citral content increases in the oils recovered from later hexane fractions. Oils recovered from
various hexane fractions were found to be effective in controlling root knot nematode Meloidogyne
javanica. The mean percent mortality of aqueous extracts of essential oils recovered from various hexane
fractions was in the range of 66.3-77.9% as compared to 74.0-75.3% in the aqueous extract of Lemongrass
pure oil sample (variety CKP 25). Further, essential oils recovered from various hexane fractions were
found to exhibit nematicidal activity to varying extents probably due to different percentages of citral in
these oils. Keeping in view the steam distillation and column chromatographic studies, it can be inferred
that the first hour (0-1 h) distilled Lemongrass oil is of superior quality and hence, can be used in
preparations requiring high quality Lemongrass oil. Further, silica gel as an adsorbent can play a vital role
in improving the quality of essential oil of Lemongrasss.
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Keywords
Oils, Organic compounds, Fractionation, Distilling, Essential oils, Extraction, Planting, Silica, Genotypes