Comparative evaluation of atmospheric and vacuum microwave-assisted extraction of bioactive compounds from fresh and dried Centella asiatica L. leaves

Microwave-assisted extraction (MAE) involves extraction under higher-temperature and oxygen-rich environment, which may cause degradation of bioactive compounds being extracted. Reducing the extraction temperature by reducing the system pressure is thus of interest. Nevertheless, information is lacking on the kinetics of vacuum microwave-assisted extraction (VMAE) at various pressures. Detailed temperature evolution of a material-solvent mixture during VMAE is also not available. This study investigated the extraction kinetics of triterpene saponins and phenolics from both fresh and dried Centella leaves during MAE and VMAE at various pressures. In the case of fresh leaves, the maximum contents of triterpene saponins were reached when VMAE was performed at 60 kPa, whereas the maximum total phenolics content (TPC) was achieved when the extraction was performed at atmospheric condition. In the case of dried leaves, the maximum triterpene saponins contents as well as TPC were achieved when extraction was performed at atmospheric condition.