Experimental and modeling studies on microwave-assisted extraction of thymol from seeds of Trachyspermum ammi (TA)

An efficient microwave-assisted extraction (MAE) technique has been developed to extract thymol from seeds of Trachyspermum ammi. The maximum percentage extraction of thymol reached 99% in 45 min under the optimal MAE conditions at 45 °C of extraction temperature and 1:30 (g of material/cm3 of solvent). The MAE showed obvious advantages in terms of short duration and high efficiency to extract thymol in comparison with conventional solvent extraction techniques. Scanning Electron Microscopy photographs of un-irradiated and irradiated seeds corroborate the enhancement observed in the rate and percentage extraction of thymol from T. ammi seeds. Experimental data at different conditions were fitted with a steady state model proposed by Wongkittipong et al. (2004) [21]. The effective diffusion coefficient for thymol varies from 0.6539 × 10−13 to 1.300 × 10−13 m2/s for microwave irradiated dry seeds. In case of microwave irradiated solvent-soaked seeds, effective diffusivity varies from 1.435 × 10−13 to 2.39 × 10−13 m2/s at different solvent-soaking times. Whereas for extraction in microwave reactor under controlled conditions effective diffusivity varies from 1.835 × 10−13 to 3.241 × 10−13 m2/s. The order of magnitude of effective diffusivity estimated in the present work agrees well with that of andrographolide from Andrographis paniculata.