This document discusses microwave-assisted extraction (MAE), an efficient method for deriving natural compounds from plants. MAE uses microwave energy to heat plant materials mixed with solvents, extracting compounds faster than conventional methods. It describes the principles of microwave heating, closed and open vessel extraction systems, factors affecting MAE like solvent, time, power and temperature, and its applications. MAE provides benefits of reduced extraction time, improved yields, and ability to extract thermolabile substances.

1. Microwave-assisted
Extraction (MAE)
Presented by: Naraino Majie Nabiilah
Date: 28th August 2014

2. Table of Content
• 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. INTRODUCTION
• MAE of anthraquinone in pure alcohol at
60°C for 30mins gave a recovery of 65%
which resulted from 3 days maceration in pure
ethanol at room temperature.
• The advantages that MAE has over Soxhlet
are:
– Reduction in extraction time
– Improved yield
– Better accuracy
– Suitable for thermolabile substances

5. 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. MICROWAVE THEORY
• 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.
• Microwaves are made up of two oscillating
perpendicular field’s i.e.
– Electric field
– Magnetic field

8. MICROWAVE THEORY
• 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.

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. EXTRACTION PRINCIPLE
• 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.

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.

12. Open and Closed-vessel system

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: propagate 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.

17. 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

18. Disadvantages of closed-vessel system
• High pressure used pose 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.

19. OPEN VESSEL
• Extraction is made at atmospheric pressure.
• The maximum possible temperature is
determined by the boiling point of the solvent
at that pressure.
• Losses of vapours are 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.

21. 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

22. Disadvantages of open-vessel system
• The ensuing method are 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. APPLICATION OF MAE

24. APPLICATION OF MAE

25. FACTORS AFFECTING MAE
• Solvent - appropriate solvent is very
important for obtaining optimal extraction
yields.

26. FACTORS AFFECTING MAE
• Extraction time - by increasing extraction
time, quantity of analytes is increased but
there is the risk of degradation.

27. FACTORS AFFECTING MAE
• Microwave power - the power must be
correctly 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 250Wfor open systems.

28. FACTORS AFFECTING MAE
• 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 100m – 2mm.
• Fine powders enhance extraction as they
provide a larger surface area.

29. 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.

30. 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.
• More research is needed to improve the design
and scale up of the novel extraction systems for
their better industrial applications.

31. 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=oFSe4HaPgg
o
– https://www.youtube.com/watch?v=3Em9qU4_2
YE

32. THANK YOU