Chemical composition and biological potential of the volatile and non-volatile constituents of tarchonanthus camphoratus and tarchonanthus trilobus var galpinni of KwaZulu–Natal province.
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Date
2013
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University of Zululand
Abstract
The chemical composition and the biological activities of the volatile extracts (essential oils)
and non-volatile (solvent extracts) of the aerial parts Tarchonanthus camphoratus and
Tarchonanthus trilobus var galpinni collected from Sangoyana and Ubombo respectively, in
the Kwa-Zulu Natal province were investigated in this study. The essential oils were
separately extracted from the fresh leaves, dry leaves and dry stem by hydro-distillation and
their chemical constituents determined by Gas chromatography/mass spectrometry
(GC/MS). The essential oils investigated were of the dry leaf of T. camphoratus harvested in
2009 and of the fresh leaf, dry leaf and dry stem of both T. camphoratus leaf and T. trilobus
var galpinni harvested in 2010 and 2011. The compounds present in all the essential oils
were categorised as monoterpene hydrocarbons, sesquiterpene hydrocarbons, oxygenated
monoterpenes, oxygenated sesquiterpenes and others but they differed in the type and
percentage composition. Sesquiterpene hydrocarbons dominated all the essential oils with
β–caryophyllene and allo-aromadendrene present in all the essential oils either as minor or
major compounds. The oxygenated monoterpene 1,8-cineole, which is suspected to be
responsible for the camphor smell of T. camphoratus, was present in all the essential oils of
the leaves and stem of T. camphoratus. δ-Cadinene, a sesquiterpene hydrocarbon, featured
in all the essential oils except of the fresh and dry leaf of T. camphoratus harvested in 2011.
The chemical constituents in the non volatile extracts were determined by Pyrolysis-Gas
chromatography/mass spectrometry (Py-GC/MS). A variety of compounds categorised as
hydrocarbons, tetraterpenes, triterpenoids, phenols, fatty acids, fatty alcohols, steroids and
sterols among others were identified in the extracts. Phenols were identified in the
aqueous, methanol, dichloromethane leaf extracts and the methanol bark extract of T.
camphoratus and in the dichloromethane leaf and ethyl acetate leaf extracts of T. trilobus
var galpinni. Steroids were identified in the bark extracts of T. camphoratus and in the
methanol leaf extract of T. trilobus var galpinni. Hydrocarbons were identified in all the
solvent/non volatile extracts but were more dominant in the dichloromethane bark extracts
of both T. camphoratus and T. trilobus var galpinni. Triterpenoids were identified in the
dichloromethane leaf extracts, ethyl acetate bark extracts of both species, in the methanol
leaf of T. trilobus var galpinni and in the methanol bark extract of T. camphoratus. The
preliminary phytochemical screening of the extracts also revealed the presence of phenols,
flavonoids, saponins and tannins in some of the extracts. The volatile and non volatile
extracts were screened for their antibacterial activity, antioxidant activity and cytotoxic
activities and the volatile extracts were further screened for their insecticidal activities. The
extracts were screened for antibacterial activity against 4 Gram positive and 5 Gram
negative bacteria. The zones of inhibition of the fresh leaves, dry leaves and dry stem
essential oils of T. camphoratus ranged from 7.3 – 14.0, 7.3 – 16.7 and 13.5 – 20.4 mm
respectively and the zones of inhibition of the fresh leaf oil of T. trilobus var galpinni ranged
from 8.2 – 21.8 mm. The volatile extracts exhibited higher percent inhibition than the non
volatile extracts and the dry stem essential oil of T. camphoratus showed the highest
antibacterial activity of all the extracts. The non volatile extracts exhibited significant
antioxidant potential when tested by DPPH and ABTS•+ radical scavenging assays plus
reducing power assay but showed poor nitric oxide inhibition and iron chelating ability. The
volatile extracts generally showed poor antioxidant activity in all the antioxidant assays. The
essential oils of both the dry leaf of T. camphoratus and fresh leaf of T. trilobus var galpinni
showed the highest larval mortality of 100% which was observed at a concentration of 300
ppm after 24h whereas the lowest mortality after 24h was 20% at 25 ppm for T.
camphoratus and 20% at 50 ppm for T. trilobus var galpinni. Insecticidal activity of the
volatile extracts against stored product pests, S. zeamais and S. oryzae revealed a lack of
contact and fumigation toxicity by essential oils of both plant species. The essential oil of the
dry leaf of T. camphoratus, however, showed repellent activity of over 50% after 24h at all
the concentrations used on both S. zeamais and S. oryzae. Cytotoxic investigation of the
volatile and non volatile extracts revealed that the extracts generally had low toxicity.
This study is the first to provide the chemical profiles and biological activities of the volatile
and non volatile extracts of T. camphoratus and T. trilobus var galpinni from Kwa-Zulu Natal.
The volatile extracts could be considered as potential alternatives, whether alone or in
combination, to synthetic antibiotics, larvicides and repellents. The non volatile extracts on
the other hand, could be potential sources of antioxidants that could have great importance
as therapeutic agents.
Description
A thesis submitted to the Department of Chemistry, in the Faculty of Science and Agriculture in fulfilment of the requirements for the degree of Doctor of Philosophy, at the University of
Zululand, South Africa, 2013.
Keywords
Essential oils