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

dielectric constant and dielectric loss in peanuts are relatively low compared to other
foods on a dielectric properties map (Ryynanen, 1995), although this would be
expected because of the high content of oil in the peanuts.
In Set 2, 11 % moisture content peanuts absorbed more energy than the 5 %
moisture content peanuts in each replicate, but the remaining treatments were not
different (data not shown). In peanuts, water dominates the effect on dielectric
properties (Trabelsi and Nelson, 2004). In fact, in many materials, the change in
dielectric constant and dielectric loss with moisture content is so pronounced, it has
been used to develop methods of measuring moisture content using microwave
technology (Engelder and Buffler 1991). These differences in energy absorption
with moisture content agree with the literature (Trabelsi and Nelson, 2004), as a
significant decrease in dielectric constant and dielectric loss was seen in shelled
peanuts as moisture content decreased from 18 to 7%.
Peanut Temperature. As microwave energy is absorbed by the peanuts, the
rate of temperature increase will depend on the power (P), mass (M), and specific
heat (Cp), as in the following equation (Metaxas and Meredith, 1983):
P = M Cp (T-T0) / t
During microwave heating, both internal (Table 2) and surface temperatures of the
peanuts were monitored. A comparison of internal and surface temperature profiles
for select treatments can be seen in Fig. 2 and 3. The average internal temperature
profiles of the treatments (Table 2) from both sets were significantly different from
each other (p < 0.0001). In Set 1, peanuts from treatment 11NF had the highest
internal temperatures, followed by 8NF.
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