Abstract
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•A very important medicinal value of essential oils extracted from lemongrass.•Quantity and purity are improved by optimization of ultrasound pretreatment.•Time, power and temperature have a more or less significant effect on extraction yield.
The present study is conducted to investigate the effect(s) of ultrasonic pretreatment on the extraction of essential oils from dried leaves of lemongrass (Cymbopogon flexuosus) by hydro-distillation. The drying process was carried out within a forced convective dryer at 50 °C and a drying air velocity of 1 m/s. Using a response surface methodology (RSM) based on central composite design with the face centered, the obtained optimum conditions were as follows: an ultrasound pretreatment for 25 min within a power of 250 W, at 50 °C. Modeling showed that all factors (time, power and temperature) were found to be highly significant in the extraction process (p < 0.001), to significant in all 2-way interactions (p < 0.05) except in the Time × Temperature interaction. Then, a second-degree model with interactions was retained. The maximum amount of essential oils was obtained under optimized conditions (≈3.093 g/100 g d.m.). The major component of the extracted essential oils is citral, which represents 85% of the extracted mass and it is present in both cis-isomer (neral) and trans-isomer (geranial) (respectively at 38.89% and 45.86%).