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Abstract
Subcritical water extraction (SWE) was applied to extract essential oils from Trachyspermum ammi. Thymol as the main component of the extracted essential oils was quantified by reversed phase-high performance liquid chromatography with UV detection at 280 nm. The effects of various parameters on SWE such as temperature, pressure, water flow rate and mean particle size were screened by a fractional factorial design. The results showed that the temperature and water flow rate were significant (p<0.05), but the mean particle size and pressure were found to be insignificant. The response surface methodology (RSM), based on central composite design (CCD) was employed to obtain the optimum conditions of the significant parameters (temperature and water flow rate). The most suitable condition for extraction of essential oils was found to be at temperature 175oC, water flow rate 4 mL/min, mean particle size 1 mm and pressure 2 MPa. At these optimum extraction parameters, the maximum yield of thymol obtained experimentally (12.9634 mg/g dry sample) found to be close to its predicted value of 12.8921. The mathematical model developed was found to fit well with the experimental data. The SWE yield at optimized conditions was significant compared by hydrodistillation.