Extraction experiments were carried out at atmospheric pressure in an electrically and mechanically modified domestic microwave oven, with temperature changes monitored by a gas thermometer. The rates of extraction were measured of six essential oil components of rosemary (Rosmarinus oficinalis L.) and detailed results are given for a-pinene and for 1,8-cineole. Major differences of behaviour were found according to whether the solvent employed was hexane, ethanol, or a mixture of 10 mol% hexane + 90 mol% ethanol. Simulated microwave extraction plots generated from the data of a series of thermostatted solvent extractions showed faster extraction rates than expected from the temperature changes. The rates of extractions were affected by the intensity of the microwave energy, the dielectric properties, size and composition of the workload, and the shape of the extracting vessel. Scanning electron micrographs showed that the kinetics and mechanism of the extractions were related to structural changes in the oil-containing glands.
The rates and extents of extraction have been measured for three major constituents of peppermint oil, namely l,&cineole, menthone and menthol, using the leaves of the black mint (Menthu X piperitu L.). The solvents used were hexane, ethanol and mixtures of composition 90mol% ethanol + 10mol% hexane and 90mol% hexane + 10mol% ethanol. The extractions were carried out isothermally at 25, 35 and 45°C as well as in an electrically and mechanically modified domestic microwave oven where the temperature increase vaned from c. 10 to 30°C. The rates of both isothermal and microwave extractions were sensitive to the solvent employed and decreased in the order 90mol% hexane > 90mol% ethanol > hexane > ethanol. The rates of microwave extraction were also affected by the microwave power output and the size of the sample load. The activation energies for the extractions were in the range 30-90kJ mol-', again dependent on the solvent used. Scanning electron microscopy on the spent leaves provided evidence of a link between the kinetics of extraction and structural changes on the glands.
The rates and extents of extraction into hexane, ethanol and two mixtures of hexane + ethanol (10.1 mol% hexane and 89.7 molo/o hexane) of six essential oil constituents of the leaves of rosemary (Rosmarinus officinalis L.) havc been measured. The data were fitted to a first order kinetic equation to yield rate constants ( k ) for the extraction of a-pinene, camphenc, P-pinene, limonene, 1,8-cineole and camphor. The values of k increased between threefold and fiftyfold in the mixed solvents compared to values obtaincd in the pure solvents. Experiments carried out over the temperature range 25-45°C yielded activation energies of over 100 kJ mol-' for every constituent, showing that the extraction of rosemary oil was a hindered process. Scanning electron micrographs showed that the kinetics and mechanism of the extractions are relatcd to structural changes in the oil-containing glands. The partition constants of most of the components were found to be 0.7 for hexane extraction.
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