1. Microwave In Food
Technology
By
Nivedha Mohanan
B.Tech Food Tech
Amity University
Jaipur
2.
3. Microwaves: Properties
General
•Electromagnetic waves of radiant energy
•Wavelength: 0.025-0.75(m)
•Frequency: 20,000-400(MHz)
Specific to Food Applications:
•Frequency Approved for Food Application: 2450MHz & 915MHz
•Reflected by metals, pass through the air, absorbed by several food
constituents
4. • Absorbed material heated up to the extent of absorption. Microwave
loses heat in the process.
• Loss factor and loss tangent used to define the loss of Microwave
energy.
• Materials that are highly absorbent of microwaves are called ‘highly
lossy’ materials.
• Loss Factor is also a measure of the degree of the penetration of the
microwave. The greater the loss, the more the heat produced and
lesser the penetration.
• According to these properties the microwave frequency is chosen.
5. Mechanism of Microwave Heating
• Microwave reverses its directions corresponding to frequencies of either
915MHz or 2450MHz.
• Food and certain other materials acts as dipoles. Ex: Water.
• When microwaves pass through the food, water and other polar molecules
try to along themselves with the electric field which changes at least 915
times a second.
• This leads to intermolecular friction, which in turn causes heating.
• As different components of food have different heating factors, it takes
simultaneous conduction(solids) and convection(liquids) to equalize the
distribution.
• The conduction and convection are the secondary effects while
intermolecular frictional heat is the primary effect.
6.
7. Microwave & Conventional Heating:
The Differences
Conventional
•A direct flame, heated air, etc used in the conventional heating.
•Food molecules largely react from the surface inwards, producing a heating
gradient.
•This can lead to difference in the burning of food surface and interiors.
Microwave
•Microwaves penetrate up to a few centimetres of the food which heats the
food uniformly.
•Heat is passed in from surface by conduction but is generated quickly and
uniformly throughout the mass.
•Hence the moisture is boiled away internally.
8. • Microwave heating thus leads to no crusting and surface browning.
• This is a limitation when a crust on the surface is desired. For ex,
bread baking.
• In such a case, the microwave heating is accompanied by or followed
or preceded by a conventional heating methods.
9. Microwave Generators and Equipment
• Most commonly used microwave generator is Magnetron.
• It is a kind of electron tube within a magnetic field which propagates high
frequency radiant energy.
• Power output is measured in kwatts. Larger the power, better the heating.
• Also, the weight of the food also determines the heating time of the food.
• Simple Microwave oven is a metal cabinet into which the Magnetron is
attached.
• Food is attacked by the oven and thus the food gets heated from all forces.
10.
11. • Complex microwave tunnel oven are equipped with an endless
moving belt of low loss material on which food is conveyed past
magnetrons.
• Open at inlet and exit for transfer of food.
• Trapping of microwaves is done by providing heat absorbing food
which absorb any stray radiation.
• Possible to heat liquid resources. Liquid maybe pumped through low
loss coil of glass or kept near to microwave.
12.
13. Microwave Food Applications
• Baking
Internal heating quickly achieves desired temperature throughout the
product. Often combined with external heating.
• Concentrating
Permits concentration of heat sensitive solution and slurries at
relatively low temperatures in relatively low time.
• Cooking
Microwaves cook large pieces without high temperature gradient
between the surface and interior. Suited for continuously cooking of
file.
14. • Curing
Effective for glue line curing of laminates without direct heating of the
laminates themselves.
• Drying
Microwaves selectively heat water with little direct heating of the
solids.
• Enzyme Inactivation
Rapid uniform heating to inactivating control can control and terminate
at enzymatic reactions.
• Finish Drying
Used to remove excess traces of water after using conventional heating
without overheating the system.
15. References
• All the data or text input is derived from the Food Science belonging
to Food Science Text Series.
