Microwave assisted extraction in food processing

1. Microwave-assisted Extraction Process
COURSE TITLE: UNIT OPERATIONS IN FOOD ENGINEERING
By
Abhishek Bahadur(16BTFT066)
Harsh Srivastava(16BTFT068)
Rajat Gupta (16BTFT069)
Abdul Rehman (16BTFT070)
MadhoopPratap Tomar (16BTFT072)

2. Microwave assisted extraction:
An Introduction
• Microwave assisted extraction is an efficient
method which involves deriving natural
compoundsfrom the raw food samples.
• The technique allows organic compounds to
be extracted more rapidly with similar with
similar or better yield as compared to
conventionalextraction methods.

3. Introduction (in contd)
• Microwave energy consists of electromagnetic
waves and hence results from electric and
magnetic fields that are normal to each other.
• This type of non-ionizing energy promotes
molecular motion through migration of ions
and rotation of dipoles without altering
molecular structure; as a result, it generates
heat by friction.

4. Mechanism of Microwave assisted
extraction process
• Microwave energy can be converted into heat
via two different mechanisms, namely ̶
ionic conduction, and
dipole rotation.
• Both occur simultaneously in most
applications of microwave heating.

5. Ionic conduction
• Ionic conduction is the conductive migration of
dissolved ions in the applied electromagnetic
field that results in I2R losses (where I denotes
current intensity and R denotes resistance)
through resistance to ion flow.
• Whereas all ions in solution contribute to
conduction, losses through ion migration depend
on the size, charge, and conductivity of the
dissolved molecules

6. Dipole rotation
• Dipole rotation refers to the alignment, by
effect of the electric field, of molecules in a
sample having permanent or induced dipole
moments.
• As the electric field of microwave energy
increases, it aligns polarized molecules; as the
field decreases, thermally induced disorder is
restored.

7. Types of Microwave Extractors
Components of a Microwave-Assisted Extractor
Microwave systems for sample preparation in general
and extraction in particular can be of two different
types depending on the way microwave energy is
applied to the sample, namely:
(1) multimode systems, in which microwave radiation is
randomly dispersed in a cavity and the sample it
contains is evenly irradiated as a result; and
(2) single-mode or focused systems, in which microwave
radiation is focused on a restricted zone where the
sample is more strongly irradiated by microwave
energy than in multimode systems

8. Closed- and Open-Vessel Microwave-
Assisted Extractors
• In closed-vessel microwave-assisted devices,
which are usually of the multimode type, the
microwave treatment is conducted at a high
pressure.
• In open-vessel devices, which are generally of
the focused type, microwaves are applied at
atmospheric pressure and no overpressure is
produced as a result.

10. Advantages of Closed-vessel MAE
• They can reach higher temperatures because the boiling
points of the solvents used are raised by the increased
pressure inside the vessel and high temperatures decrease
the time needed for microwave treatment.
• Losses of volatile substances during microwave irradiation
are almost completely avoided by virtue of the absence of
vapor losses.
• They require less solvent as the absence of evaporation
dispenses with the need for continuous replenishment and
avoid the risk of contamination as a result.
• The fumes resulting from an acid microwave treatment
remain within the vessel, so no provision for handling
potentially hazardous fumes need be made.

11. Disadvantages of Closed-vessel MAE
• The high pressures used pose safety
(explosion) risks derived from the production
of hydrogen in acid treatments of metals and
alloys.
• The amount of sample that can be processed
is limited (usually less than 100 g) by
exception, the dynamic version commercially
available from CEM can treat approximately 1
kg of sample.

12. Advantages of Open-vessel MAE
• Increased safety resulting from operating at atmospheric
pressure with open vessels containing, for example, gas-
forming species.
• The ability to add reagents at any time during treatment,
which enables sequential acid attacks, if required.
• The ability to use vessels made of different materials
including PTFE, glass, and quartz.
• The ability to operate at high temperatures with quartz
material when using sulfuric acid near its boiling point to
destroy organic compounds.
• The ease with which excess solvent can be removed to
ensure complete dryness of the digest or extract.
• The ability to process large samples.

13. Usefulness of open-vessel systems
• Highly efficient transfer and precise control of the energy deposited
into the sample.
• Fully automatic operation.
• Digestion of samples of 10 g or moredespecially those with a high
carbon contentd produces large amounts of gas and vapors. In
open vessels, these are released by the reaction mixture and
continuously swept from the headspace above the sample. Thus, in
contrast to closed vessels, completion of gas-forming reactions is
favored as per Le Chatelier’s principle.
• Open-vessel operation is better suited to thermolabile species (eg,
organometals) because it uses low temperatures relative to closed-
vessel systems.
• Easy connection of the sample extraction step to other steps of the
analytical process.

14. Disadvantages of Open-vessel MAE
• The ensuing methods are usually less precise
than those developed with closed-vessel systems.
• Sample throughput is usually lower because most
open-vessel systems cannot process many
samples simultaneously.
• The operation times required to obtain results
similar to those of closed-vessel systems are
usually longer.
• Digestion is especially cumbersome with some
samples owing to the difficulty in reaching the
drastic conditions they require.

15. Types of Food Components Benefiting
From Microwave-Assisted Extraction
• The two major types of microwave-assisted treatment for
food samples are digestion and extraction (leaching).
• Both of which are widely used in food analysis.
• In continuous MAE, slurry samples can be circulated
through a dynamic manifold under microwave irradiation
(Terigar et al., 2010).
• Using this procedure with semisolid samples such as yogurt
could open up new prospects for the continuous treatment
of common food samples.
• Solvent-free microwave-assisted extraction treatment,
which is especially indicated for the removal of essential
oils from aromatic plants.

16. Reference
• Innovative Food Processing Technologies,
2016 Elsevier Ltd., Microwave-Assisted
Extraction of Food Components M.D. Luque
de Castro, L.S. Castillo-Peinado,University of
Cordoba, Cordoba, Spain