Gas Chromatographic Analysis of Essential Oil Constituents of Different Cultivars

There is wide variation in the chemical composition of pepper oil analysed by different research groups. These are due to use of oils from different varieties and geographic regions, variation in maturity of raw material, differences in the method of obtaining the oil, nonresolution of constituents in early gas chromatographic analyses using packed columns. The general composition of pepper oils is dependent to some extent upon the method of preparation. Steam distilled pepper oils usually contain about 70-80 per cent monoterpene hydrocarbons, 20-30 per cent sesquiterpene hydrocarbons and less than 4 per cent oxygenated constituents. Oils prepared by vacuum distillation of oleoresin extracts differ in containing less monoterpene hydrocarbons and more sesquiterpene hydrocarbons and oxygenated constituents. The low abundance of sesquiterpene hydrocarbons and oxygenated constituents in the steam distilled oils is probably a result of incomplete distillation and poor recovery of these high boiling constituents. Comparison between the oils obtained by these two methods should be judicious and confined to comparison of individual constituents in groups of mono- and sesquiterpene hydrocarbons.

Lewis et al. (1969) reported the composition of 17 cultivars of Kerala, India. The oil was isolated by steam distillation and the yield of the oil ranged from 2.4 to 3.8 per cent. The oil was analysed by packed column chromatography and compounds identified by retention time of authentic samples. In the oils, monoterpene hydrocarbons ranged from 69.4-85 per cent; sesquiterpene hydrocarbons 15-27.6 per cent and the rest oxygenated constituents. The major monoterpene hydrocarbons viz a-pinene ranged from 5.9-12.8 per cent, ^-pinene 10.6-35.5 per cent, limonene 22-31.1 per cent. The major sesquiterpene hydrocarbon, ^-caryophyllene ranged from 10.3-22.4 per cent. A Sri Lankan variety was also analysed by Lewis et al. and found that the oil contained a-pinene to the extent of 22.1 per cent, ^-pinene 11.1 per cent,sabinene 21.3 per cent, limonene 11.1 per cent and ^-caryophyllene 16.6 per cent.

Richard et al. (1971) also analysed the same 17 cultivars from Kerala, India. The volatile components were extracted with pentane-ether and injected into a packed column to separate the solvent and the aroma effluents introduced into a second connected capillary column through a Carle micro volume valve to separate the constituents. They found that in the pepper oil samples, the monoterpene hydrocarbons ranged from 49.5-73.3 per cent, the sesquiterpene hydrocarbons ranged from 19.8-45.1 per cent and oxygenated constituents ranged from 2-15.7 per cent.

Russel and Else (1973) analysed 12 samples of Lampong and 16 samples of Sarawak pepper grown in different regions of the two areas following the same procedure utilised by Richard et al. and carried out a statistical analysis. Significant differences could be established between the varieties.

Gopalakrishnan et al. (1993) analysed four new genotypes of pepper by a combination of GC-MS and Kovats indices on a methyl silicone capillary column. The four genotypes viz Panniyur-1, Panniyur-2, Panniyur-3 and Panniyur-4 (Culture-239) were developed at the Pepper Research Station of Kerala Agricultural University, Panniyur, Kerala State, India. The oils from the three Panniyur genotypes contained a-pinene in the range of 5.07-6.18, ^-pinene 9.16-11.08, sabinene 8.50-17.16 per cent, limonene 21.06-22.71 per cent and ^-caryophyllene 21.57-27.70. The oil from Panniyur-4 (culture 239) contained a-pinene 5.32 per cent, ^-pinene 6.40 per cent, sabinene 1.94 per cent, myrcene 8.40 per cent, p-cymene 9.70 per cent, limonene 16.74 per cent and caryophyllene 21.19 per cent. The capillary GC chromatogram is given in Fig. 3.1 and the composition of the oils in Table 3.1.

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