# Ultrasound-Assisted Extraction of \(\beta\)-Asarone from Sweet Flag (_Acorus calamus_) [PERSON]
## 3 Results and Discussions
### The Physical Effect of Sonication in UAE  
The extract of the ultrasound-assisted process was subjected to isolation, purification and characterization similar to the extract from conventional solvent extraction. The extraction product including \(\beta\)-asarone was found to be the same, confirming that the ultrasound process does not change any of the compound structure. Therefore, it is safe to deduce the qualitative characteristics of _A. calamus_ extract, including its biochemical activity is impervious to ultrasound irradiation in this study. The significant efficiency increase in the extraction is due to the physical effect of sonication. There have been many reports on the physical effect of ultrasonication during the extraction process [26; 39; 40; 41]. In this study, similar effects were observed from the SEM images. The dried _A. calamus_ rhizomes (Figure 7a) were ground to uniform sizes as shown in Figure 7b. The SEM images of the ground samples are shown in Figure 7c,d with their usual matrix characteristics such as fibers secretion, and oil sacs. The active compounds of the plants are available on the surface or exterior of the matrices, as well as enveloped in the oil sacs. During the solvent extraction process, the active compounds available on the plant matrices are extracted mostly via the washing mechanism, whilst the active compounds in the oil sacs are extracted by the process of diffusion. This is clearly visible in the SEM images of the _A. calamus_ residue after solvent extraction, as shown in Figure 8. The secretion or oil glands are now depleted and flattened. The diffusion process induced by the solvent has caused the sacs to be emptied. However, the plant structures are still well intact, without any significant rupture or damage. The SEM images of plant residue upon ultrasound-assisted extraction were also taken to compare the impact of sonication on the plant structure. By a quick look at the four images in Figure 9 and comparing them to the images in Figures 7 and 8, it can be clearly seen that the plant structures are heavily impacted by the process of sonication. Sonication results in acoustic cavitation, in which the formation and growth was by rectified diffusion, and the collapse of microbubbles. The process leads to high shear forces in the  
Figure 8: The SEM images of the _A. calamus_ residue after the solvent extraction process. Both images (**a**) and (**b**) shows the collapsed oil glands at different magnifications after the active compound is extracted. Image (**a**) was taken at \(3000\times\) magnification and image (**b**) at \(1000\times\) magnification. Figure 7: The (**a**) dried and (**b**) ground _A. calamus_ samples. (**c**,**d**) are the plant matrices with visible structures of fiber and oil glands at \(1000\times\) magnification. media. The implosion of microbubbles on a plant matrix results in micro jetting which generates effects such as particle breakdown or formation of pores [39]. Many of the cell walls are ruptured, therefore also breaking the sacs and cells. The strong agitation from microbubble oscillation and implosion could result in the fragmentation of the structures into smaller pieces, thus increasing the surface areas for contact with the solvent, thus improving the extraction efficiency. The damages of sonofragmentation effect can be seen in all four pictures; an example is in Figure 9a. Sonofragmentation effect can be seen resulting from bubble collapse, as well as the collision of the particles during ultrasound-induced streaming. The surface of the plant matrix had also been eroded by the physical action of ultrasound, as seen in Figure 9b. The visible impact of erosion is due to the release of solid structures into the solvent [26]. These are among the physical impacts of sonication that increase the extraction during the washing mechanism by decreasing the diffusion boundary, thus accelerating mass transfer to the solvent phase [42]. The effect of sonoporation can also be seen in Figure 9c.