Ultrasound assisted extraction (UAE)
In this method, the plant material is immersed in water or solvent and
then exposed to ultrasound. The ultrasonic waves have a frequency of 20
kHz–1 MH depending on plant species. In this method, the mechanical
vibration created by ultrasonic waves causes the walls and membranes of
plants to vibrate and rupture. As a result, essential oil droplets are
released. in other words, the cell walls are diffused, and once the
walls are broken, the essential droplets washed out [6, 72]. The
size of the plant material is an important factor in this method. The
smaller the size of the plant material, the more cells are exposed to
the waves [6]. Figure 11 shows Commonly used ultrasonic systems
[73].
Compared to traditional methods, the UAE is improving time and
temperature extraction and increases the range of solvent selection. It
also offers high quality products with higher efficiency. This method is
useful for compounds which sensitive to heat. The equipment is
relatively simple and inexpensive compared to other new techniques [6,
74]. For example, citrus flowers of lemon were extracted by UAE.
According to the result, the main component was Linalool with 11.3 %
efficiency [75].