For ultrasound assisted extraction, extraction temperatures were maintained at 40 °C. It can be identified that similar extraction yield are obtained for extraction performed with the ultrasound reactor and for the US probe (18.1 ± 2.3% and 18.8 ± 2.2% respectively). Lower yields are obtained with the ultrasound bath (13.1 ± 0.1%). Those results may be explained by a low ultrasonic power delivered by the bath compared to the ultrasonic reactor and the probe. Compared to HRE, it can be noted that equivalent yields are achieved at 40 °C using ultrasound assisted extraction.
Microwave assisted extraction was performed at 70 °C and higher temperatures (boiling temperature, 125 °C and 150 °C). For these extractions (Fig. 3), increasing temperatures lead to an increase of the extraction yield, the highest yield (25.2%) being reached at 150 °C. It is a classical observation in extraction that extraction yields increase with increasing temperatures.
If the extraction yields gives an indication of a process performance, the composition of the extracts has to be studied to assess the selectivity of extraction.