Chemical profiles of primary and secondary essential oils of palmarosa (Cymbopogon martinii (Roxb.) Wats var. motia Burk.)
Introduction
Natural essential oils are extracted from different plant parts of aromatic crops. Essential oils which are also known by the names aromatic oils, fragrant oils, ethereal oils, steam-volatile oils are extensively used in fragrance, flavour and pharmaceutical industries and in aromatherapy. More than 250 types of essential oils (1,20,000 t world annual production) worth US$ 1.2 billion per annum are traded in the world market. A number of countries produce different kinds of essential oils. India ranks second in the world trade of essential oils. Essential oils are commonly extracted from aromatic crops through steam distillation. In this method, the aromatic crop biomass is loaded into a distillation tank and steam generated either in a boiler or in the distillation tank itself is allowed to pass through the crop biomass. The essential oil present in the biomass vapourises. Steam and essential oil vapours are passed through a condenser. The condensate (mixture of water and essential oil) is collected in a receiver. The essential oil is decanted, cleaned, made moisture free and traded. During the process of steam distillation, a part of the essential oil becomes dissolved in the condensate or distillation water. Unless recovered, the essential oil is lost as the distillation water is discarded. Since organoleptically important oxygenated compounds such as alcohols, esters, aldehydes, ketones, etc. are more soluble in condensate water, the aroma of the steam distilled essential oil is incomplete or is different from the natural aroma of the plant (Fleisher, 1990, Fleisher, 1991). Therefore, attempts were made to recover the dissolved essential oil from distillation water employing several techniques such as cohobation or re-distillation of condensate water (Gokhale, 1959), solvent extraction with diethyl ether (Bouzid et al., 1997), poroplast technique (Fleisher, 1990) and adsorption employing commercially available synthetic polymeric adsorbents (Bohra et al., 1994, Machale et al., 1997. The recovered oil is then added to the steam distilled oil to obtain a true replica of the natural essential oil (Fleisher, 1991). In the present investigation, a method employing hexane as an extractant is described for isolation of dissolved essential oil of an important aromatic crop palmarosa from the distillation water and the chemical profile of the steam distilled and recovered oils has been compared.
Section snippets
Efficiency of field distillation unit
Freshly harvested flowering biomass (500 g per sample) of palmarosa (Cymbopogon martinii) (Roxb.) Wats var. motia) was hydrodistilled in Clevenger (1928) trap for 3 h and the essential oil samples were collected. They were dried over anhydrous sodium sulphate to make them moisture free, weighed and the essential oil concentration (%) in the plant tissue samples were calculated:
Field distillation of aromatic crops
A plantation of palmarosa
Comparison of Clevenger and field distillation methods
Due to continuous re-distillation or cohobation of condensate water and more controlled distillation of crop biomass, the Clevenger distillations produced higher yields compared to field distillations (Table 1). The lower recoveries in field distillations were because of the following two major reasons:
- 1.
Incomplete recovery of essential oil from the crop biomass.
- 2.
Loss of dissolved essential oil in condensate or distillation water.
As a result, the field distillation efficiency ranged from 64.0 to
Conclusion
Steam distillation is not an efficient method for complete extraction of essential oils from aromatic crops. During steam distillation, a part of the essential oil becomes dissolved in the distillation water. In this investigation, a method has been described for recovering the dissolved essential oil from distillation water of palmarosa employing hexane as a solvent to trap the essential oil. Through this method 8% of total oil yield could be recovered from the distillation water. The
Acknowledgements
The authors are grateful to the Director, CIMAP, Lucknow and the Scientist-in-Charge, CIMAP, Field Station, Hyderabad for facilities.
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