Handbook of Meat Processing

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.