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The constituents of medicinal plants - Pengelly A.

Pengelly A. The constituents of medicinal plants - London, 2001. - 109 p.
Download (direct link): theconstituents2001.djvu
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Alcohols rank with phenols as the most potent antimicrobial essential oil compounds, however they do not contain the irritant properties of the latter.
Tea tree oil
Derived from leaves of Melaleuca alternifolia and M. linariifolia (Myrtaceae), native to the east coast of New South Wales. To meet the Australian Standard for tea tree oil the terpinen-4-ol content must be at least 30% while that of the oxidised terpene 1,8 cineole must not exceed
&
A
mentho
terpinen-4-ol
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I
15% [Williams et al 19881. The chemotypes of tea tree oil from natural stands depends is genetically determined, so that all commercial plantations are started from seed known to be of the right chemotype. Other terpene constituents of tea tree oil are the alcohol a-terpineol, hydrocarbons a- and р-pinene, p-cymene and y-terpinene, and sesquiterpenes including the unique compound viridflorene [Penoel 1990].Terpinen-4-ol is also a major ingredient in marjoram - Marjorcina hortensis (Lamiaceae).
While tea-tree oil is not the most powerful antimicrobial available, it is considered by some to be the ideal skin disinfectant due to its activity against a wide range of micro-organisms (both gram-t- and gram- bacteria as well as fungi), its low incidence of irritation, and ease of penetration [Altman 1988]. Tea tree oil can be applied to all afflictions of the skin and orifices. The broad antimicrobial activity makes it useful for vaginal irritations since these can result from a variety of pathogenic organisms including yeasts and bacteria [Williams & Home 1995]. However its action is not restricted to that of an antiseptic, it is revered by aromatherapists for its general harmonizing attributes and immune stimulant effects [Penoel 1990].
Peppermint oil
Derived from the dried leaves and flowering tops of Mentha piperita (Lamiaceae).
The oil consists of about 50% menthol. The taste and odour of peppermint oil are also influenced by some of its minor components, notably the menthol esters jasmone and menthofuran. The latter compound has a disagreeable odour and is mainly concentrated in young peppermint plants [Samuelsson 1992]. Peppermint is one of the best carminatives and the oil is sometimes administered in capsules for irritable bowel syndrome. Animal studies using peppermint oil demonstrated a significant spasmolytic effect, thought to be linked to the menthol content [Taddei et al 1988]. Menthol is an ingredient in
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several pharmaceutical preparations and inhalants for congestion of the respiratory tract.
Other terpene alcohols
Geraniol, citronellol from rose oil, Rosa gallica (Rosaceae) and scented geraniums Pelargonium spp. (Geraniaceae). Nerol is a steroisomer of geraniol.
Borneol is found in Rosemary oil - Rosmarinus officinalis (Lamiaceae)
Linalol from lavender oil - Lavandula spp. (Lamiaceae) and ylang ylang - Cananga odorata (Annonaceae). Santalol from heartwood of sandalwood - Santalum album, S. spicatum (Santalaceae)
Aldehydes
Aldehydes such as those found in citrus oils correspond to their respective alcohol - note that their names end in “al", hence: geraniol, citronellol (alcohols); geranial, citronellal (aldehydes)
Citrus oils
Essential .oils are present in leaves, flowers and fruits of plants in the citrus, however the main medicinal oils are found in the fruit peel. The best quality oils come from the bitter orange - Citrus aurantium (Rutaceae) and the lemon
- Citrus limon. Although the hydrocarbon limonene is the major constituent, the aroma of the oils is determined by the presence of aldehydes, namely the isomers geranial and neral - together known as citral, and citronellal. Citral features as the dominant constituent in other citrus flavoured oils such as those from lemon grass (Cymbopogon citratus), lemon balm (Melissa officinalis), lemon verbena (Alloysia triphylla) and the Australian sweet verbena tree - Backhousia citriodora, which consists almost entirely of citral. The lemon scented gum -Eucalyptus citriodora (Myrtaceae) - consists mainly of citronellal with a small amount of the alcohol citronellol,
geranial
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3
while lemon scented tea tree (Leptospermum citratum) contains both citral and citronellal.
Properties of aldehydes
Apart from its pleasant aroma, citral is valued for its sedative, antiviral and antimicrobial properties. Citral rich oils derived from lemongrass and lemon scented tea tree were shown to inhibit Candida albicans at more than four times the rate (zone of inhibition) of tea tree oil [Williams & Home 19951. However many aldehydes are irritants, causing skin sensitivity in some people thereby restricting their use in topical applications. Citral and other aldehydes are also thought to have antitumor properties, though the few clinical trials carried out on them are inconclusive [Tisserand & Balacs 1988/89).
Cyclic aldehydes
These are also known as aromatic aldehydes - they are derived from phenylpropanoids and have no terpene structure. They have characteristically sweet, pleasant odours and are found in some of our most well known herbs and spices such as cinnamon and nutmeg.
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