3. Results
3.1. Dielectric properties of vegetable powders at different
frequencies
The dielectric properties of vegetable powders at room temperature
(22 ± 3 C) with applied frequency are shown in Fig. 4. It
shows that vegetable powders have the different values of dielectric
constant and dielectric loss factor, and the values decreased as
the frequency increased from 1 to 30 MHz. The dielectric constant
values follow the order chili powder > potato starch > tapioca
flour > Broccoli powder > onion powder. As seen in Fig. 4, the
highest values of dielectric constant and loss factor were 6.85 and
0.39, respectively, for chili powder. It is widely known that MC is
the one of the most important parameters affecting the dielectric
properties of foods. The decreasing order in ε
́
and εʺ of different
food powders generally agrees with their MC, except for chili
powder and potato starch, as potato starch has a higher MC (12.9%
w.b) than chili powder (7.8%) but smaller ε
́
and εʺ (Fig. 4). This could
be explained by the fact that the dielectric properties are not only
affected by MC, also by bulk density and particle size of the product
(Nelson, 1996). Additionally, the lowest dielectric constant values
were 3.11 for broccoli (MC: 3.9%) and 2.93 for onion powder (MC:
1.4%), respectively. The dielectric loss factors follow the similar
order as dielectric constant, but are very low for all the samples due
to the low moisture content. The εʺ for broccoli powder and onion
powder was not shown in the figure because the values were too
low and the instrument could not give stable values