Studies on microwave steam distillation process for extraction of lemongrass essential oil

Abstract

Essential oils are concentrated aromatic oily liquids distilled from different parts of aromatic plants. Conventionally steam distillation has been widely used for extraction. Modern technologies have been continuously developed to conquer the inadequacies of conventional methods. Microwave steam distillation is based on the interaction between water in the plant material and microwaves generated by the energy source. In this process, the steam generated outside accelerates evaporating and carrying of the essential oil, from the plant material, towards the condenser. In this study a microwave steam distillation system for extracting lemongrass essential oil was developed which composed of a microwave reactor, steam generator, cartridge, extraction unit, supporting stand, energy meter and temperature sensor and controller. In order to evaluate the developed system towards extraction of lemongrass essential oil, the effect of process parameters which would influence the essential oil yield, energy consumption and temperature of extraction such as bulk densities of 0.375, 0.675 and 0.875 g cm-3, microwave powers of 280, 420 and 560 W and soaking times of 30, 40 and 50 min were studied. The physical quality characteristics such as specific gravity, refractive index, solubility and colour of essential oil were analysed. The optimised operating conditions of bulk density, microwave power and time of extraction for lemongrass essential oil in microwave steam distillation were found to be of 0.375 g cm-3, 420 W and 30 min respectively. Scanning Electron Micrographs of lemongrass provided evidences to sudden rupture of essential oil glands with microwave steam distillation process. Gas Chromatographs of essential oil extracted through microwave steam distillation process showed higher percentage of Citral than that of steam distillation process. From the study it was concluded that microwave steam distillation could be considered as an extraction technique that results in the rapid production of high quality essential oil at shorter extraction period with minimum energy consumption.