*3.6. Morphological Analysis*

SEM analysis was used to reveal the change in the plant material after application of di fferent extraction techniques. The untreated flowers showed closed cells and rough surfaces (Figure 4a).

**Figure 4.** SEM (scanning electron microscopy) micrographs of black locust flowers: (**a**) without treatment; (**b**) after maceration; (**c**) after Soxhlet extraction, and (**d**) after the UAE (Ultrasound-assisted extraction).

In the samples subjected to the extraction, the physical modification of cell walls with different degradation degrees can be noticed. The SEM micrographs of the sample after maceration (Figure 4b) were not considerably different from those of untreated samples, but only puny damage was observed on the external surface of the flower. In Soxhlet extraction (Figure 4c), the profuse rupture of the cellular matrix and small broken pieces were dispersed due to the treatment with high temperature. The surface of the flower was greatly destroyed after treatment with the UAE (Figure 4d). This indicates that ultrasound treatment affects the structure of the cell due to the high, localized pressures induced by cavities [38,39], which should result in the instantaneous release of the soluble compounds into the solvent. Unlike this mechanism of UAE, the maceration depends on the permeation and solubilization in order to bring the compound out of the cell [31,40].
