Fundamental Food Microbiology, Third Edition - Fuad Fathir

CONTROL BY NOVEL PROCESSING TECHNOLOGIES 517
heat by dielectric and ionic mechanisms; water molecules, because of their dipolar
nature, are associated with dielectric heating. Heating of food is very rapid but not
uniform as compared with that in conventional heating. Destruction of microorganisms
(cells and spores) is accomplished by the heat mainly through denaturation of
proteins and nucleic acids. Microwave ovens are widely used now to cook and reheat
foods. This method has the potential of producing commercially pasteurized and
sterilized foods. However, because of the possible presence of cold spots in solid
and semisolid foods, the method cannot be used to assure safety and is thus currently
not regulated by the FDA (see Chapter 32). Many studies are now being conducted
to improve the uniform heating of the microwave oven.
B. Ohmic and Inductive Heating 3
In ohmic heating, electric currents are passed to heat food through an electrode
contacting the food. In contrast, in inductive heating, electric coils placed near a
food generate an oscillating electromagnetic field that sends electric currents to heat
the food. Of the two, ohmic heating has been studied well for it potential use in the
production of commercially pasteurized and sterilized food products. The destruction
of microbial cells and spores is achieved primarily by destabilizing proteins, nucleic
acids, membrane, and other vital functional components by heat. Food materials are
heated rapidly and uniformly from the generation of internal energy. This method
also produces cold spots in foods containing high fat and solids. Techniques are
being studied to minimize their occurrence.
C. Pulsed Electric Fields 3,4
Use of pulsed electric fields (PEF), a nonthermal method, involves application of
high-intensity electric pulses between two electrodes placed in a food for a very
short time to inactivate microorganisms. Various aspects of this method, including
applications in food, have been studied. A short review of the method is presented
in Section III of this chapter.
D. High-Pressure Processing 3
High-pressure processing (HPP) is a nonthermal method involving pressurization of
a packaged food in a water-filled closed chamber for a short duration to inactivate
microorganisms. A liquid food can be pressurized directly. In addition to antimicrobial
effect, it has many other food applications. The method has generated a great
interest and several foods have already been commercially produced. A review of
the current status of the method has been presented in Section IV of this chapter.
E. Pulsed Light Technology 3
This is a nonthermal method in which microorganisms on the surface of food (usually
in a transparent package) are inactivated by high-energy light pulses. Light pulses
in the wavelengths of 170 to 2600 nm are used for a very short duration (£0.01 s).
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