Comparative study of volatile compounds from genus Ocimum

American Journal of Applied Sciences, March, 2009 by S. Raseetha Vani, S.F. Cheng, C.H. Chuah

Biological pathway: Methyl chavicol and methyl eugenol, which are found abundantly in Ocimum Basilicum and Ocimum Sanctum, respectively, are volatile essential oil used extensively in various application including perfumes (8), (10), food seasoning and flavouring (6), aromatheraphy (14) and medicinal application (8), (14). Methyl chavicol stimulates liver regeneration, shows hypothermic and DNA binding activities. Methyl eugenol also shows DNA binding activities, spasmolytic and gives muscle relaxant effects (6).

Since both methyl chavicol and methyl eugenol have high economic value, researches have tried to understand the biosynthetic pathway that produces this compound in the plant, which however, still remains fully unexplored. Chavicol O-methyltransferase (CVOMT) identified in crude protein extracts of sweet basil (26), is responsible for the conversion of chavicol to methyl chavicol. Analysis shows that eugenol is being transformed into methyl eugenol by eugenol O-methyltransferase (EOMT). Both CVOMT and EOMT, which are enzymes, use S-denosylmethionine (SAM) as the methyl donor (26-30). But the enzyme involved in basil is different from those involved in Clarkia breweri plant, which uses (iso)eugenol O-methyltransferase (IEMT) (29), (30).

CVOMT methylates the 4-hydroxyl group of chavicol to produce methyl chavicol. EOMT methylates the 4-hydroxyl group of eugenol to methyl eugenol.

Chavicol was not present at any of the months being identified because it has all been converted to methyl chavicol. Methyl chavicol was found to characterize Ocimum Basilicum in abundance except in June 2003. This finding is consistent to previous publication (22), (24), (25). Ocimum Basilicum species, on various chemotypes being studied, which originates from Yemen and Thailand, also contain methyl chavicol as the major compound (31). Meanwhile, eugenol is not detected during several months, except June 2008, due to same prior discussed biosynthesis pathway. At present, the enzymatic activity involved in the biochemical translation is still being studied in detail (29).

CONCLUSION

The application of GC-MS for the analysis of essential oil allowed the detection of significant differences in the proportions of volatile compounds from Ocimum Basilicum and Ocimum Sanctum tested in relation to many factors that contribute to the fragrances present. From our study, Ocimum Basilicum should be harvested in April for methyl chavicol and Ocimum Sanctum in the month of October, for methyl eugenol under the climatic conditions in Malaysia. At the same time, present study indicates that Ocimum Basilicum are rich in methyl chavicol and Ocimum Sanctum belongs to methyl eugenol rich type.

ACKNOWLEDGEMENT

The authors would like to thank the Malaysian Metereology Department for providing the climate data.

REFERENCES

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