Advance in Ultrasound-Assisted Extraction of Edible Oils: A Review

Ultrasonic waves cause an increase in oil extraction efficiency through their mechanical effects, cavitation, and the energy generated by this phenomenon. Temperature, time, solvent to sample ratio, solvent type, and ultrasonic power are the most effective factors in the ultrasound-assisted extraction of oils. Temperature increase reduces the surface tension and vapor pressure of the solvent, leading to a rise in the solvent diffusion into the cell, and thus, the extraction efficiency increases. However, as the temperature approaches the solvent boiling point, its vapor pressure rises. Due to the smaller pressure difference between the interior and exterior of the cavitation bubbles, they collapse less intensively and cause the extraction efficiency to decrease. The increase in ultrasonic power has a similar effect on extraction efficiency. An elevation of the extraction time improves this parameter in the early minutes of extraction, by destroying the cell walls and making the oil diffuse out of the cell-matrix. An increase in the solvent to sample ratio up to an optimal level elevates the concentration gradient of the solvent towards the sample matrix by reducing the solution viscosity and brings about an improvement in the extraction efficiency. The application of the solvents with high vapor pressures results in a decrease in the cavitation energy because of the pressure difference between the cell interior and exterior. Therefore, such solvents do not have a positive effect on the extraction efficiency. Each of the aforementioned factors has its optimum level to enhance the ultrasound-assisted extraction efficiency.