448 Chapter 25
Chemical, physical, and structural transfor-
mations produce changes in the electrical
properties of the muscle tissue, and the
impedance variation permits the control of
some quality aspects, such as types of fresh
pork meat (freshness, tenderness, fat content)
or the detection of frozen meat, and safety
aspects, such as a microbial detection or
chemical contaminations. As was explained
in the beginning of this chapter, the dielectric
dispersions measured in the impedance of
meat with capacitor equipment (Fig. 25.6 ) are
produced at different ranges of the frequency
of the electric fi eld imposed on a meat sample.
At high frequency, the dispersion produced
is in the dipolar mechanisms (such as water
molecules), which consist of the orientation
of the molecules, spin rotation, and transport
of charges in the way of the fi eld, increasing
the conductivity of the media. Next affected
is the ionic motion of the charged molecules
(anions and cations). At medium frequency,
the dispersion produced is the Maxwell -
Wagner effect, which depends on the varia-
was developed in the sixties and mainly con-
cerned the follow - up of variations in the
composition of the human body (Charnet
et al. 1999 ). Bioimpedance was used for the
fi rst time in the control of meat products and
processes in the eighties (Damez and Clerjon
2008 ).
The principle of the impedancemetry is
based on the ability of a medium to pass
an alternating electrical current. When the
impedance is not depending on the frequency,
the system works as a resistive media; other-
wise, as in the biological tissue and colloidal
systems, the impedance has resistive, capaci-
tive, and inductive components (Damez and
Clerjon 2008 ). Meat tissue is composed of
cells with an internal liquid phase (cyto-
plasm), surrounded by the external liquid
phase with a different composition than the
internal liquid phase, because the cell mem-
brane is between both phases (Chenoll et al.
2007 ). Cell membrane is a dielectric material,
working at a low frequency as an isolator,
behaving like a capacitor (Damez et al. 2007 ).
Ionic conductivity
kHz-GHz
electron flow
direction
cations anions
E
–+
γ-dispersion
Dipolar mechanisms
0.1–100 GHz
β-dispersion
Maxwell-Wagner effects
0.001–100 MHz
α-dispersion
Counterion effects
1Hz-1kHz
Figure 25.6. Basic capacitor equipment and different dispersion in the dielectric properties of meat.