Extraction of Thymus pallecens de Noé essential oil by microwave steam distillation and steam distillation processes: Kinetics, optimization, chemical composition and insecticidal activity

S. Bertouche, N. Sabba, N. Sahraoui, Y. Nait Bachir


The essential oil of Thymus pallescens de Noé  has been isolated using an extraction process developed in our laboratory: steam distillation assisted by microwaves also called microwave steam distillation (MSD). This process is a combination of traditional techniques, namely, a steam distillation (SD) and an innovative technology, a microwave heating. Kinetic study of extraction, analysis of essential oils by gas chromatography and mass spectrometry, optimization of operating conditions using response surface methodology (RSM) were studied. The selected operating parameters are the steam flow rate and the microwave heating power. Yield obtained by microwave steam distillation is comparable to that obtained by the conventional steam distillation, while the extraction time is greatly reduced: 6 min for MSD extraction against 15 min for the SD. The best performance was obtained with a power of 600Wand steam flow rate of 10 g•min-1. The essential oils of T. pallescens isolated either by MSD or by SD are rather similar in their composition. The same number of components is found in the essential oils with equivalent relative amounts for both extraction methods. The contact and fumigation toxicities of these oils were tested against the insect Rhyzopertha dominica using the filter paper method. The toxicity tests showed that insect mortality increased with the concentration used (0.39%, 0.78%, 1.56% and 3.12%V). The results suggest that the oil T. pallescens has important insecticidal properties and may be useful as a natural cereal protection agent against Rhyzopertha dominica to replace synthetic insecticides

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