Abstract SCHIRACK, ANDRIANA VAIS. The Effect of Microwave ...

the material to absorb electromagnetic radiation and convert it into heat. The
magnetic field interactions in food are negligible, due to only trace amounts of
magnetic materials present such as nickel, cobalt, or iron. As a result, only the
electric field has an effect (Ryynanen, 1995; Mudgett, 1989). The overall heating
rate in microwave processing is dependent on dielectric constant and dielectric loss,
specific heat, and density. Microwave energy inactivates microorganisms by thermal
denaturation of proteins and nucleic acids, just like conventional thermal processing,
and depends on the same time/temperature relationships (Mudgett, 1989).
The transmission properties of the electromagnetic waves are related to the
dielectric and thermal properties of the food, and also determine the distribution of
energy (Ryynanen, 1995). Packaging also has an effect, as microwaves are
transmitted through ceramic, plastics, paper, and glass, but metals such as
aluminum foil reflect microwaves (Giese, 1992). Energy reflected from the surface
causes standing wave patterns of nodes and antinodes, which result in uneven
energy distribution at product surfaces and hot and cold spots within the product
(Mudgett, 1989).
The microwave penetration depth and overall heating rate will be determined
by the specific heat, density, surface to volume ratio, thermal conductivity,
evaporative cooling of the food, as well as the shape of the food. The sphere and
cylinder are the best shapes for microwave heating, because microwaves can
penetrate the food from all sides. In general, foods which have a high surface-to-
volume ratio will cook more rapidly (Giese, 1992). Products heated in a continuous
microwave with slab geometry, such as trays of peanuts in microwave blanching,
31