4. Results and discussion
4.1. Dielectric properties
Dielectric properties of beef meatball, mozzarella cheese, noodles,
and sauce are summarized in Tables 2–5, respectively.
Dielectric constant (e0
r) of beef meatballs (Table 2) increased
steadily as the temperature increased at the two RF frequencies
(27 and 40 MHz) until 100 C, while it decreased with increasing
temperature at the two microwave frequencies in particular
1800 MHz. Similar trends were observed in the dielectric properties
of salmon fillets (Wang et al., 2008b). Protein denaturation at
high temperature leads to a release of water and shrinkage, which
is believed to cause significant changes in the dielectric properties
of beef (Nelson and Datta, 2001). Three main types of proteins (actin,
collagen and myosin) in beef denature at different temperatures.
The denaturation is most likely accompanied by the
release of water and other components. The dielectric constant
for mozzarella cheese is summarized in Table 3. Values of e0
r increased
with temperature at the two RF frequencies but remained