Microwave-pretreatment hydrodistillation extraction of eucalyptol from Eucalyptus citriodora and optimization by response surface methodology

This study aimed to optimize the process of extracting essential oil from Eucalyptus citriodora leaves using either conventional hydrodistillation (CHD) or microwave-pretreatment hydrodistillation (MPHD), and to compare the two methods. The response surface methodology was utilized to optimize two techniques. The essential oil yield was quantified in terms of eucalyptol, and the highest yields of eucalyptol in CHD and MPHD were 2.72% and 3.50%, respectively. For CHD, the optimum conditions for extraction of eucalyptol from E. citriodora leaves were 700 mL/100 g solvent-to-solid ratio and a 4 h extraction time with a 2.64 mg/100 g eucalyptol predicted yield. For MPHD, the optimum conditions were the solvent-to-solid ratio of 555 mL/100 g, extraction time of 4 h, irradiation time of 30 s, and power of 466 W, giving a 2.24 mg/100 g eucalyptol predicted yield. The validation study verified the efficacy of the optimized models. Gas chromatography-mass spectrometry (GC-MS) showed eucalyptol as the most abundant chemical constituent of both the CHD and MPHD distillates. In conclusion, MPHD had a lower solvent requirement, consuming less water for a slightly lower yield than CHD. In terms of efficiency, both techniques worked almost equally well for extracting eucalyptol from E. citriodora leaves, but MPHD was more environmentally sustainable in terms of water consumption.