Microwave assisted extraction (MAE), also known as microwave-assisted extraction, refers to the technique and method of extracting various chemical components from plants, minerals, animal tissues, etc. using appropriate solvents in a microwave reactor.
Microwave refers to electromagnetic waves with frequencies ranging from 300MHz to 300GHz, which utilize the effect of electromagnetic fields to effectively separate certain organic components in solid or semi-solid materials from the matrix and maintain the original compound state of the analyzed object.
The mechanism of microwave extraction can be analyzed from the following three aspects:
1) The microwave radiation process is the process in which high-frequency electromagnetic waves penetrate the extraction medium and reach the microtubule bundle and glandular cell system inside the material.
Due to the absorption of microwave energy, the temperature inside the cell will rapidly rise, causing the pressure inside the cell to exceed the capacity of the cell wall to expand;
As a result, the cell ruptured and its active ingredients freely flowed out, dissolving in the extraction medium at a lower temperature.
By further filtration and separation, the desired extract can be obtained.
2) The electromagnetic field generated by microwaves can accelerate the diffusion rate of molecules of the extracted components from the solid interior to the solid-liquid interface.
For example, when using water as a solvent, under the action of a microwave field, water molecules transition from a high-speed rotating state to an excited state, which is a high-energy unstable state.
At this point, water molecules may vaporize to enhance the driving force of the extracted components, or release their excess energy back to the ground state, and the released energy will be transferred to the molecules of other substances;
To accelerate its thermal motion and shorten the time for the molecules of the extracted components to diffuse from the solid interior to the solid-liquid interface;
The result increases the extraction rate several times and can lower the extraction temperature, maximizing the quality of the extract.
3) Due to the correlation between the frequency of microwaves and the frequency of molecular rotation, microwave energy is a non ionized radiation energy caused by ion migration and dipole rotation, resulting in molecular motion;
When it acts on a molecule, it can promote its rotational motion if the molecule has a certain polarity;
It can generate instantaneous polarization under the action of microwave field and perform polarity transformation motion at a speed of 2.45 billion times/s;
As a result, it generates vibrations, tears, friction and collisions between particles, and rapidly generates a large amount of thermal energy;
Causing cell rupture, causing cell fluid to overflow and diffuse into the solvent.
In microwave extraction, the difference in microwave absorption ability can selectively heat certain regions of the matrix material or certain components in the extraction system;
Thus, the extracted substance can be separated from the matrix or system and enter the extraction solvent with a smaller dielectric constant and relatively poor microwave absorption ability.
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