2. Contents
Introduction
Microwave theory
Extraction principle
Instruments
Closed vessel
Open vessel
Application of MAE
Factors affecting MAE
Conclusion
3. INTRODUCTION
Microwave-assisted extraction is an efficient method which
involves deriving natural compounds from raw plants.
Microwave extraction allows organic compounds to be extracted
more rapidly, with similar or better yield as compared to
conventional extraction methods.
4. MAE of anthraquinone in pure alcohol at 60°C for 30 minutes
gives a recovery of 65% which results from 3 days maceration in
pure ethanol at room temperature.
The advantages that MAE has over other techniques such as
Soxhlet are:
Reduction in extraction time
Improved yield
Better accuracy
Suitable for thermolabile substances
INTRODUCTION
6. MICROWAVE THEORY
Microwaves are non-ionizing electromagnetic waves of
frequency between 300MHz to 300 GHz and positioned between
the X-ray and infrared rays in the electromagnetic spectrum.
Microwaves serves two major purposes:
Communication
Energy vectors
7. The energy vector application is the direct action of waves on
materials that has the ability to convert a part of the absorbed
electromagnetic energy to heat energy.
As any other EM wave we have two parts of Microwaves
Electric field
Magnetic field
MICROWAVE THEORY
8. In MAE, heating occurs in a targeted and selective manner with
practically no heat being lost to the environment as the heating
occurs in a closed system.
This unique heating mechanism significantly reduces the
extraction time (usually less than 30min) as compared to
Soxhlet.
MICROWAVE THEORY
9. EXTRACTION PRINCIPLE
Dried plants contain a minute microscopic trace of moisture
which serves as target for microwave heating.
High temperature and pressure is generated inside the oven.
High temperature causes dehydration of cellulose which
accounts for its reduction of mechanical strength.
10. The MAE process is as follows:
Microwave radiation
Moisture get heated up
Moisture evaporates
Generation of tremendous pressure on cell wall
Swelling of plant cell
Rupture of the cell
Leaching out of phyto-constituents
This phenomenon can be intensified if the plant matrix is
impregnated with solvents with higher heating efficiency under
microwave.
EXTRACTION PRINCIPLE
11. INSTRUMENTS
There are two types of commercially available MAE systems:
Closed extraction vessels
Focused microwave ovens
The former performs extraction under controlled pressure and
temperature.
In the latter, only a part of the extraction vessel containing the
sample is irradiated with microwave.
13. INSTRUMENTS
Both systems are available as multi-mode and single-mode.
A multi-mode system allows evenly radiation of sample by
random dispersion of microwaves.
Single-mode (aka focused system) allows focused radiation on a
restricted zone by a much stronger electric field.
14. INSTRUMENTS
Both multi-mode and focused system comprises of the following
four components:
Microwave generator: magnetron which generates
microwave energy
Wave guide: propagates microwave to microwave cavity
The applicator: where the sample is placed
Circulator : allow microwave to move in forward direction
15. CLOSED VESSEL
With closed vessel extraction, pressurised microwave assisted
extraction is performed under pressure (with or without
regulation).
The pressure allows temperatures above boiling points of the
solvents to be reached enhancing speed and efficiency.
To avoid overpressure, power, temperature and pressure can be
controlled.
When dealing with thermolabile compounds, high temperature
causes degradation of analytes. Therefore, the open system is
chosen.
16. Advantages of closed-vessel system
Decreased in extraction time
Loss of volatile substances is avoided
Less solvent is required because no evaporation occurs
No hazardous fumes during acid microwave since it is a
closed vessel
17. Disadvantages of closed-vessel system
High pressure used poses safety risks
The usual constituent material of the vessel does not allow high
solution temperatures
Addition of reagents is impossible since it is a single step procedure
Vessel must be cooled down before it can be opened to prevent loss of
volatile constituents.
18. OPEN VESSEL
Extraction is made at atmospheric pressure.
The maximum possible temperature is determined by the boiling point of
the solvent at that pressure.
Loss of vapours is prevented by the presence of a cooling system on the
top of the extraction vessel that causes condensation of solvent vapours.
Heating is homogenous and efficient.
19. Advantages of open-vessel system
Increased safety
Addition of reagent is possible
Vessels made of various material can be used
Excess solvent can be removed easily
Ability to process large samples
No requirement for cooling down or depressurisation
Low cost of equipment
Suitable for thermolabile products
20. Disadvantages of open-vessel system
This method is less precise than in close-vessel system
The sample throughput is lower as open system cannot process
many samples simultaneously
Require longer time to achieve same results as for closed system
23. Solvent - Appropriate solvent is very important for obtaining
optimal extraction yields.
FACTORS AFFECTING MAE
24. Extraction time - By increasing extraction time, quantity of
analytes is increased but there is the risk of degradation.
FACTORS AFFECTING MAE
25. Microwave power - Power must be chosen to minimise the
time needed for extraction.
However, increased power may cause solvent loss by
evaporation.
Maximum power used ranges between 600W and 1000W
for closed systems and around 250W for open systems.
FACTORS AFFECTING MAE
26. Matrix characteristics - the plant particle size and the status in
which it is presented for MAE can affect the recoveries of
compounds.
The particle sizes of the extracted materials are generally in the
range of 100m – 2mm.
Fine powders enhance extraction as they provide a larger
surface area.
FACTORS AFFECTING MAE
27. FACTORS AFFECTING MAE
Temperature - temperature should be sufficient to ensure
good solubility of compounds and a good penetration of
solvent in the plant matrix to enhance extraction yield.
However, it should not be too high enough to degrade the
target compounds.
28. CONCLUSION
Chemical analysis of extracts from plant material plays a central
role in development and modernization of herbal medicine.
MAE has proven to be effective in all aspects compared to
traditional extraction techniques like Maceration/Percolation.
More research is needed to improve the design and scale up of the
novel extraction systems for their better industrial applications.
29. REFERENCES
S. Hemalatha, 2007, Microwave Assisted Extraction – An
innovative and promising Extraction Tool for Medical,
Pharmacognosy Reviews, Vol 1-Issue 1
Farid Chemat, Giancarlo Cravotto, 2012, Microwave-
assisted Extraction for Bioactive Compounds: Theory and
Practice, Ebook
Mauricio A. Rostagno, Juliana M. Prado, 2013, Natural
Product Extraction: Principles and Applications, Ebook
YouTube videos:
https://www.youtube.com/watch?v=oFSe4HaPggo
https://www.youtube.com/watch?v=3Em9qU4_2YE