A novel application of the vacuum distillation technology in extracting Origanum vulgare L. essential oils

摘要

Vacuum extraction technology is a dynamic extraction by using vacuum devices to reduce the pressure in the system to below normal pressure and maintain the solvent boiling at a lower temperature. In this study, an effective vacuum distillation-extraction (VDE) technology was developed to obtain volatile oil from oregano (Origanum vulgare L.). The process conditions, such as the pressure, the liquid-solid ratio and the distillation time were optimised using a single-factor experiment and the response surface methodology with a Box-Behnken design. A multivariate quadratic polynomial model was successfully established. It is shown that the model agrees well with the experimental results and the identified optimal process parameters were a liquid-solid ratio of 14:1, an extraction time of 253.8 min with a vapor pressure of 558 mbar. The optimal process conditions lead to the highest yield of 1.02%, which is an 8% increase compared with the conventional hydro-distillation (HD). The composition of the essential oils extracted by vacuum distillation-extraction under the optimal condition were analysed by Gas chromatography-mass spectrometry (GC-MS) and compared with those obtained from hydro-distillation. It was found that they differed in the contents of the dominant components contributing to the antimicrobial effects in oregano essential oil, such as thymol, carvacrol and terpineol, etc. Subsequent antibacterial experiments were also performed using S. aureus and E. coli. It is shown that the vacuum distillation extraction technology results in better antibacterial effects than the hydro-distillation.