Abstract:

In order to explore the application feasibility of ultrasonic technique to the extraction of gynosaponins from Gynostemma pentaphyllum, one-factor-at-a-time experiments were conducted to investigate three factors (i.e., material/liquid ratio, temperature and extraction duration) influencing conventional water bath extraction and ultrasonic-enhanced extraction, and to compare efficiency of water bath extraction and ultrasonic-enhanced extraction at different frequencies (40 and 28 kHz) as well. Furthermore, the 28-kHz-frequency ultrasonic-enhanced extraction was optimized by orthogonal array design. Compared with the water bath extraction, the ultrasonic treatment at 40 kHz did not present marked enhancement effect on the extraction of gynosaponins, while the enhancement effect was obvious when ultrasonic frequency was decreased to 28 kHz. The optimal conditions for the 28-kHz-frequency ultrasonic-enhanced extraction were as follows: material/liquid ratio 1:30, temperature 70 ℃, and duration 60 min. The optimized extraction technique yielded 7.5934% of gynosaponins, and it also had good reproducibility and high reliability.

Key words: ultrasonic, Gynostemma pentaphyllum, gynosaponins, extraction, technique