Extraction and characterisation of the essential oil from Centella Asiatica (Pennywort) growing in South Africa
Date
2014
Authors
Florczak, Melissa Claudia
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Abstract
Aromatic plants and oils have been used for thousands of years in perfumes, and cosmetics and for their culinary and medicinal purposes. The essential oil from Centella Asiatica growing specifically in South Africa has many therapeutic uses and is used to treat various diseases. Different extraction methods were used on the leaves of Centella Asiatica and the composition of each sample of oil obtained was analysed to see how the composition of each sample is affected. The methods of extracting were optimised specifically for Centella Asiatica. The different extraction methods used were steam distillation, water distillation, solvent extraction and soxhlet extraction. Steam and water distillation were preformed with three different apparatus to compare the efficiency of the extraction and the affect on composition of the oil. It was found that steam distillation using the apparatus described by the British Pharmacopedia Volume IV was the most sufficient apparatus to use to obtain the greatest yield of oil. Soxhlet extraction was found to be the worst extraction method for volatile compounds
The optimised parameters for extraction of essential oils from Centella Asiatica using this apparatus were 100 g of leaves at a distillation rate of 2/3 ml min-1 for 75 minutes using 0.4 ml of xylene initially. It was also necessary to perform a 30 minute initial distillation with no plant matter. Steam distillation with this apparatus was found to yield the best quality oil.
The major constituents that were found in all the methods were α-carophyllene, carophyllene and germacrene D. There were some similarities found in the compositions of the essential oil between extraction methods in terms of the constituents found. However the abundance of those constituents varied between extractions. Each constituent has a different therapeutic effect. Therefore if an extraction method were to be chosen to extract a some specific constituent like germacrene D and α-carophyllene, steam distillation with the apparatus described by the British Pharmacopedia should be used. However if an extraction method were to be used to extract carophyllene, water distillation should be used.
The essential oil extracted using steam distillation yielded a greater amount sesquiterpenoid hydrocarbons. However monoterpenoid hydrocarbons were present in greater amount in the essential oil extracted using water distillation.
In the essential oil extracted from Centella Asiatica, 43 constituents were identified from steam distillation extraction representing 98.60% of the composition of oil and 54 constituents representing 98.29% from water distillation extraction.
It was found that from steam distillation using fresh leaves compared to dry leaves extraction a greater number of constituents were identified. Salting out was also used for extraction and compared to water distillation and it was found that the salting-out extractions yielded a greater amount of oxygenated polar compounds.
A commercial oil of Centella was also analysed and compared to the natural oil. It was found that the commercial oil was a synthetic oil and its composition was completely different from the natural oil and therefore synthetic oils cannot be used therapeutically for substitutes for natural essential oils.
Centella Asiatica prefers to grow in damp environments, therefore they are extremely prone to pollution. This was found to also affect the chemical composition of the oil obtained since the soil quality of where the plants were growing was important. This was investigated by spiking the soil of some Centella asiatica plants with chromium(VI), mercury(II) and lead(II). It was found that Centella Asiatica can store heavy metals in the leaves. Since it is a medical plant with many therapeutic uses, this is causes great concern about heavy metal contamination of herbal raw materials of Centella Asiatica. This also highlights the importance of good quality control on Centella Asiatica, so that heavy metals are not ingested. The people in the rural areas who use it as a raw plant for herbal preparations could be at risk of ingesting heavy metals if grown in a polluted area.
Description
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the Degree of Master of Science.
Johannesburg, 2014.