ABSTRACT
Ultrasound-assisted extraction (UAE) is an emerging extraction technique that has been widely used on different matrices by enhancing heat and mass transfer. It can break cell walls of microalgae to facilitate the diffusion of intracellular bioactive compounds. UAE has advantages over the classical methods in terms of reduction of solvent use, reduction of unit operations, reduction of extraction time, reduction in energy use, lower environmental impact and rapid return on investment. Sound waves that are at human hearing frequencies range from 16 Hz to under 20 kHz, while ultrasound waves have frequencies ranging from 20 kHz to 10 MHz, well above the human hearing range but below microwave frequencies. The mechanism of the extraction process of the ultrasound is due to the rarefaction and compression phenomena, as well as the critical molecular distance of the medium above which it starts to break down to generate bubbles in the liquid medium. The mechanisms of action assisting the extraction by ultrasound are: fragmentation by cavitation, erosion, sonocapillary effect, sonoporation, local shear stress and destruction and de-texturization of the materials used for extraction. The extraction of various bioactive compounds using UAE is discussed in this chapter.
