New Crops Potential of Queensland-grown Geranium (Pelargonium hybrid) for Essential Oil
Summary of PhD thesis
The University of Queensland Gatton
Essential oil production from a purpose-bred Australian geranium (Pelargonium hybrid) growing at Perseverance Creek in Queensland, Australia, was investigated with a view to determining its suitability as a new crop product.
Climatic, agronomic and environmental factors were monitored. Growth studies indicated geraniums were well adapted to the site and its environment. Soils from the site were low in pH but suitable for geranium growing. The plants were not affected by low nitrogen, low boron or marginal sulphur levels in the soil.
The effect of cutting the geranium plants at various heights was significant in terms of oil yield whereas the effects of pre-drying the leaves or packing the still at differing densities were not. Studies of the harvested leaves found the oil was concentrated in the youngest leaves, near the growing tip. Mechanical harvesters would need to trim the geranium plant to maximumise oil yield.
Geranium essential oils were extracted from leaf material collected in a series of experiments over time, designed to investigate the effects of seasonal conditions on oil yield and composition. Analysis of essential oils was by gas chromatography, gas chromatography with mass spectrometry using non-polar BPX-5 and chiral b -cyclodextrin columns.
Queensland-grown geranium oil contained citronellol (28.9%), citronellyl formate (14.2%), geraniol (10.2%), 6,9-guaiadiene (6.8%), isomenthone (6.7%), geranyl formate (5.7%), linalool (3.7%), germacrene D (2.2%), geranyl tiglate (1.6%), geranyl propanoate (1.2%), furopelargone B (1.2%), cis-rose oxide (1.1%), b -bourbonene (1.1%), b -caryophyllene (1.1%), phenyl ethyl tiglate (0.8%) and citronellyl tiglate (0.8%). It is therefore of the 'Bourbon' type and is similar to Chinese geranium oil.
This oil is therefore considered a valuable and extremely desirable product.
The concentrations of most compounds detected in the Queensland-grown oil varied with season. The ratio of the concentrations of the two important alcohols, citronellol and geranoil (the citronellol:geraniol ratio, C:G) was found to be a sensitive indicator of compositional changes in the oil. Changes in C:G were linked to variablility in the prevailing weather conditions and have been proposed as an indicator of physiological stress experienced by the plants.
Distillation studies of geranium using copper, stainless steel, mild steel, aluminium or borax glass-lined vessels indicated that the resulting oil yields were not affected by the nature of the material lining the distillation vessel. However, the aroma of the resulting oil was affected, with the product from copper, stainless steel or glass-lined vessels having a more pleasant aroma than that of the oil extracted using an aluminium-lined vessel.
In terms of oil quality, oils extracted using copper, stainless steel or glass-lined vessels were significantly higher in linalool and 2-phenyl ethyl tiglate and significantly lower in geranial than oils extracted using mild steel or aluminium-lined vessels. The most variability in component levels was evident amongst the water soluble compounds, such as the aldehydes and some sesquiterpenes.
Hydro-distilled geranium oils contained a wide range of esters. GC-MS identified these esters emerging as a series, with citronellyl esters eluting regularly before neryl and geranyl esters. Iso-esters (comprising 1.2% of the oil) were of the (n-1)-substituted type and they eluted before their straight chain namesakes. Successive ester series were spaced 90-120 retention index units apart.
Australian-grown geranium oil was high in esters (comprising 30% of the oil) with the most prevalent being formates (19.7%) and tiglates (3.9%). It was low in acetates (0.8%).
The new concepts of chiral excess (CE) and total excess (TE) were developed to allow the chirality of geranium essential oils to be expressed as a single number so that 18 commercial geranium oils from a wide range of geographical origins and 24 geranium oils collected over several seasons from the Queensland study site, were able to be distinguished.
Australian geranium oils had high TE values. TE values were able to differentiate oils from different growing areas. TE values in oil from Australian-selected geranium varied with season, being higher in August than it was in April or November.
In terms of the new crop potential of Queensland-grown geranium, the production, harvesting and extraction of the crop and the quality characterisation of the essential oil are now sufficiently well documented to indicate that geranium warrants carefully controlled commercialisation.
Doimo, L., Fletcher, R.J. and D'Arcy, B. (1996) Composition of Queensland-grown rose geranium essential oil. Proceedings, Fourth Annual Research Conference, The University of Queensland Gatton, October, 1996, 62.
Doimo, L., Fletcher, R.J. and D'Arcy, B.R. (1999) Chiral excess: measuring the chirality of geographically and seasonally different geranium oils. Journal of Essential Oil Research 11: 291-299.
Doimo, L., Fletcher, R.J. and D'Arcy, B.R. (1999) Comparison in the g-lactone content of oils and extracts from white cypress pine (Callitris glaucophylla Thompson and Johnson). Journal of Essential Oil Research 11: 415-422.
Doimo, L., Fletcher, R.J. and D'Arcy, B.R. (1999) Esters in Australian geranium oil (Pelargonium Hybrid). Journal of Essential Oil Research 11: 611-614.
Doimo, L., Fletcher, R.J. and D'Arcy, B.R. Is geranium (Pelargonium hybrid) oil composition affected by the metal comprising the distillation vessel? (To be resubmitted to J. Ess. Oils Res.)
Doimo, L., Fletcher, R.J., D'Arcy, B.R. and Bird, L. (1999) A new essential oil from Eucalyptus dura L.A.S. Johnson and K.D. Hill. Journal of Essential Oil Research 11: 149-150.
Doimo, L., Fletcher, R.J., D'Arcy, B.R. and Michael, G.D. (1996) Queensland-grown Pelargonium graveolens leaf essential oil: a GC-MS study. In "New Crops, New Products. New Opportunities for Australian agriculture." Proceedings, First Australian New Crops Conference, The University of Queensland Gatton, July, 1996. (Imrie, B.C., Bray, R.A., Wood, I.M. and Fletcher, R.J., Eds.). RIRDC Research paper 97/21, 2: 247-58.
Doimo, L., Fletcher, R.J., D'Arcy, B.R. and Southwell, I.A. (1999) A new chemovar of Gympie Messmate (Eucalyptus cloeziana F. Muell.) containing alpha-pinene and Tasmanone. Journal of Essential Oil Research 11: 77-78.
Doimo, L., Fletcher, R.J., D'Arcy, B.R., Bartley, J.P. and Michael, G.D. Essential oil composition from some weedy Australian Asteraceae. (To be resubmitted to J. Ess. Oils Res.)
Doimo, L., Mackay, D.C., Rintoul, G.B., D'Arcy, B.R. and Fletcher, R.J. (1999) Citronellol: geraniol ratios and temperature in geranium (Pelargonium hybrid). The Journal of Horticultural Science and Biotechnology 74: 528-530.
Contact: Dr Rob Fletcher, School of Agriculture and Horticulture, The University of Queensland Gatton, 4343; Telephone: 07 5460 1311 or 07 5460 1301; Facsimile: 07 5460 1112; International facsimile: 61 7 5460 1112; Email:email@example.com
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Latest update 30 October 2000 by:RF