Olearia Phlogopappa : aspects of clonal cultivation and essential oil characterisation

The species Olearia phlogopappa was found to exhibit variation in both form and essential oil properties in populations around Tasmania. Six locations, Great Lake, Paradise Plains, Mount Wellington, Eaglehawk Neck, Elephant Pass and Buckland, were surveyed for a plant which yielded maximal quantities of organoleptically suitable essential oil from each site. Some preliminary morphological, dry matter and infra-red photographic studies were carried out which revealed a positive relationship between the rate of dry matter accumulation and height measurements. This, together with a small scale seasonal variation trial led to the development of multi-location trials. A rank order of clones was established on the basis of growth rate and oil yield. The major source of oil appeared to be the juvenile leaves in all cases. The effect of harvest was studied at two trial sites. A combination of a pruning trial and seasonal variation trials led to the recommendation that Olearia phlogopappa clones should be grown in a hedgerow and harvested in late summer. The plants can be cut to a height of approximately 30 cm, and the regenerative growth may be harvested a second time in August. In this way, the maximum oil yield may be obtained. The characterisation of the essential oil of each of six clones was carried out using a combination of gas chromatography/mass spectrometry, nuclear magnetic resonance spectroscopy, high performance liquid chromatography and Fourier transform infra-red techniques. The essential oil was pre-fractionated by means of a simple silica gel column. Through the use of this technique, fractions were obtained for further characterisation work. The separation occurred on the basis of polarity, so that hydrocarbons, oxygenated compounds and alcohols were obtained in separate fractions. This simplified the hplc purification and subsequent identification by nmr of several important components. Some 2D nmr experiments, in addition to standard \(^1\)H and \(^{13}\)C nmr techniques were used. The major components identified were as follows: α-pinene, β-pinene, cineole, linalool, α-terpineol, caryophyllene, germacrene-D, bicyclogermacrene, spathulenol, α-eudesmol, β-eudesmol, γ-eudesmol, liguloxide, caryophyllene oxide and kessane. In addition to the above components, there are some 50 minor components present in the oils, some of which contribute to the characteristic tomato, exotic fruity odour of these products. Changes in oil composition were suspected to be occurring during the steam distillation process, and these were investigated. The essential oil released from the plant material was compared to the release of volatiles from a solvent extract. The diversity of the clonal material was investigated concentrating on differences in several morphological features and growth rates. The seasonal variation of essential oil in the leaves was monitored and the greatest quantities of oil were found to be present in late summer, early autumn. The bulk of the oil is located in the current seasons growth, rather than in matured leaves. The quality of the oil was also observed to change through the monitoring of chemical composition. Organoleptically, the oils from the six clones under consideration were markedly different from one another. For instance, the desirable spicey, tomato-like properties were predominantly found only in one clone. This odour characteristic was also present in the other oils but was masked or over-ridden by other exotic fruity notes. In other cases, native bush, floral, or citrus notes were predominant in the oil. The major components of the oil were identified as germacrene-D, bicyclogermacrene and spathulenol. In some instances, (3-eudesmol or caryophyllene comprised the greatest part of the oil. However, the greatest contribution to the overall characteristic spicey odour was made by kessane and liguloxide. Minor components were not identified, but are also likely to be responsible for the complex aroma of the oil. This work makes a contribution to the body of knowledge relating to essential oils in endemic species. The uniqueness of Olearia oil is illustrated by its odour, and by its adaptability to a cropping situation. The commercial production of a natural essence such as this one heralds the inception of a potentially viable new industry