Abstract:
The extraction of asiaticoside of which shows many healing effects from Centella asiatica (Linn.) Urban by the conventional method was found the low efficiency in terms of the amount of asiaticoside and the extraction time;and the hazardous solvent used. Thus, the use of ultrasound to enhance the extraction efficiency of asiaticoside is proposed and studied in this present research. To investigate the factors affecting the extraction process, series of experiments were carried out at various conditions i.e. the irradiation time between 0.5-90 minutes, the three different kinds and concentration of solvent (ethanol, methanol and acetone with the concentration between 20-100%), the particle sizes between 0.15-0.85 mm, the ratio of solid to solvent between 1-15 g/100 ml and the intensity of ultrasound between 9-100 W/cm2. Two types of the ultrasonic sources have been used i.e. an ultrasonic probe (20 kHz) and an ultrasonic bath (47 kHz). The amounts of asiaticoside obtained from the cases with ultrasound have been compared to the cases without ultrasound to investigate the most suitable operating conditions. From the experimental results, it is shown that in case of the ultrasonic probe, within the same extraction time (i.e.1 minute) the use of ultrasound can enhance the yield of the extraction up to 3 times compared with the case without ultrasound. When the same amount of asiaticoside extracted is compared (i.e. 1.2 g asiaticoside/100 g dried particle solids), the extraction time used is only one minute in the case with ultrasound compared to 90 minutes used in the case without ultrasound. Similarly, for the case of the ultrasonic bath, it is found that the amount of asiaticoside extracted can be increased by 1.5 times in the case of ultrasonic irradiation compared to the case without the irradiation under the same extraction time (i.e. 10 minutes). When the same amount of asiaticoside extracted is compared (i.e. 1 g asiaticoside/100 g dried particle solids), the extraction time is reduced to 1/4 of the time used in the case without an ultrasonic irradiation. The results concerning with the factors affecting the extraction process obtained from the use of the ultrasonic probe have the similar trends. The suitable operating conditions are found as the following: the 40% ethanol solvent (V/V), a particle size of 0.25-0.425 mm, a ratio of solid to solvent of 1 g/100 ml, an ultrasonic intensity of 35 W/cm2 within 2 min of the extraction time. The effect of ultrasonic on the chemical composition of asiaticoside is unfound under the experiment conditions. Under an appropriated operating condition, the use of ultrasound in the extraction is found economically attractive.