On the Extraction of Essential Oils by Supercritical Carbon Dioxide and its Influence on the Mesomorphic Phase Structures
Abstract: A comparison of essential oils from leaves of Eucalyptus camaldulensis Dehn. obtained by hydrodistillation (HD) and supercritical carbon dioxide (SC-CO2) extraction is presented. Selected major components of the oils showed a predominance of higher molecular weight components in the SC-CO2 extracts than in those obtained by HD. Physico chemical properties such as molecular weight, vapour pressure of the components, steric factor as well as in oil composition. Discussions on environmental effects on the quality of the essential oils obtained on the same eucalyptus genotype treated by the same techniques are also presented. The monoterpenes 1,8-cineole, limonene and a-pinene, present in considerable amounts in eucalyptus leaf oils, as well as their mixtures and three eucalyptus oils from different genotypes, namely E. dives, E. polybractea and E. radiata, were also studied with regard to their solubility in dense CO2 (SC-CO2 and LCO2). In general, pure compounds showed a higher solubility in SC-CO2. The composition SC-CO2 at the highest pressure and temperature. Since polar lipids are always present in eucalyptus leaves from which the oil is extracted, the interaction between such lipids, water, SC-CO2 and essential oils is important to study. First, liquid crystalline properties and the extractability of monoolein/water systems by supercritical carbon dioxide are discussed. The most remarkable observation in this study was the loss of the native mesomorphic structure at high temperatures and the low recovery of monoolein in monoolein/water systems within the highest (18wt%) water content at temperatures between 35 and 65°C. These effects are explained by the SC-CO2, water and monoolein interactions which lead to different water and monoolein activities in the phase present. Further, two model systems composed of monoolein/water or soybean lecithin/water, cineole and SC-CO2 are presented for studying the phase behaviour. Generally, it is observed that the liquid crystalline structure remain also in presence of surplus of SC-CO2. Hence, it can be assumed that lipid structures in the plant tissues may remain also during SC-CO2 extraction and contribute to the matrix effects observed in extraction trials.
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