Chapter 4. Microwave-assisted Extraction

Abstract

For around thirty years Microwave Assisted Extraction (MAE) has been increasingly used for the extraction of natural compounds from plant matrices. MAE is based on the selective heating of polar molecules by microwave energy. This rapid and homogenous heating of a sample allows a short extraction time, and a reduction in solvent consumption and solvent waste; therefore, MAE is considered an environmental and human friendly method saving time, solvent, and energy. To perform an efficient MAE, some parameters such as solvent composition, solvent volume, solvent to feed ratio, time, power, matrix moisture, and particle size have to be controlled and optimized. Recent advances to go further in “green chemistry” have consisted of modifying MAE procedures such as MAE under vacuum or combining MAE with ultrasound. Moreover solvent free microwave extraction methods have been developed for volatile and non-volatile compound extraction and the use of alternative solvents such as water, ionic liquid, and deep eutectic solvents is spreading. Hence this chapter will present first the microwave heating principle and the influential parameters, then, microwave distillation, microwave assisted extraction for non-volatile compounds, and solvent free and extraction with alternative solvents will be presented. Pilot scale extraction for industrial application is also illustrated. Lastly, in the full concept of green chemistry the extraction of food by-products using NADEs is presented as a study case.