A comparative study of solvent extraction, Soxhlet extraction, steam distillation, headspace analysis and headspace solid phase microextraction for the extraction of volatile terpenoid compounds in the curry leaf plant (Murraya koenigii).

Abstract

A comparative study was undertaken of different extraction methods for the isolation of volatile organic compounds from Murraya koenigii (curry leaf plant). The techniques studied included the traditional methods of extraction, namely, Soxhlet and solvent extraction as well as steam distillation. The solvent–free extraction techniques of headspace analysis and headspace solid phase micro-extraction (HS-SPME) were also investigated. In the evaluation of SPME, two different fibre coatings, poly(dimethylsiloxane) and poly(acrylate), were compared. Preliminary work to determine the effect of extraction parameters, such as extraction time, was carried out. The volatile oils in the fresh leaves of Murraya koenigii were isolated by the above-mentioned extraction methods and analysed by gas chromatography-mass spectrometry. The main aroma contributing compounds were identified by comparison of their retention times with those of standards and their mass spectra with those of known compounds contained in the National Institute of Science and Technology Standard Reference Database 1A (NIST 98). The essential oil contained mainly terpenes: monoterpene and sesquiterpene hydrocarbons. The constituents were identified and only the five selected analytes of interest, a-pinene, β-pinene, a-phellandrene, β-caryophyllene and a-caryophyllene were quantified in three of the methods, namely solvent extraction, soxhlet extraction and steam distillation. From the quantitative determination of the compounds of interest, steam distillation favoured the extraction of β-caryophyllene. The solvent and Soxhlet extractions showed no significant differences between the quantities obtained for a- and β- caryophyllene. The steam distillation and Soxhlet methods showed similar quantities of a-caryophyllene extracted. The extraction of the monoterpenes, a-pinene, β-pinene, and a-phellandrene, was favoured by the Soxhlet method of extraction. Quantification was difficult with HS-SPME and headspace analysis. Headspace analysis proved effective in the detection of the very volatile analytes. Headspace-SPME combined with GC-MS was found to be suitable for the identification of both monoterpenes and sesquiterpenes of M. koenigii. From this study, solvent extraction and Soxhlet extraction were found to be superior to the other methods studied for the characterisation and quantitation of the volatile organic compounds in essential oils of Murraya koenigii.