3.7. Morphological analysis
The effect of ultrasound on the physical structure of the black-berry bagasse was evaluated through FESEM. As it can be observed in Fig. 4, ultrasonic vibration effectively changes the surface ofthe blackberry bagasse particles. Samples undergoing only SFE extraction present a much more homogeneous and clean surface(Fig. 4A), indicating that supercritical CO2 alone did not cause important morphological changes. In contrast, samples exposed to ultrasound exhibit an irregular surface, covered by particle fragments. Moreover, an effect of the ultrasound power can also be noticed by comparing Fig. 4B and C, with a greater amount of particles deposited under 400 W than at a 200 W power. The deposition of fragments on the surface is probably related to the removal of material from the internal parts of the cell wall, followed by its deposition on the surface during the extraction process. It should contribute to increase the accessibility of these particles to the solvent, which is in agreement with the relatively higher extractionyields in these samples. It is important to notice that the extraction process does not seem to cause fissures or rupture on the samplesurface, since it keeps its integrity under the particulate deposits