Handbook of Meat Processing

446 Chapter 25

1980 ; Stuchly and Stuchly 1980 ; Schwan

1981 ; Foster and Schwan 1986 ; Pethig and

Kell 1987 ; Duck 1990 ; Foster and Schwan

1996 ; Gabriel 1996, 2006 ; Gabriel and

Gabriel 1996 ; Gabriel et al. 1996a, b, c ).

The γ - dispersion, also called orientation

polarization, is located at the GHz region,

and it is due to the polarization dipoles,

fundamentally free water molecules. The

β - dispersion or interfacial polarization is

mainly due to the Maxwell - Wagner effect.

This effect is produced due to interfacial phe-

nomena on heterogeneous materials (Feldman

et al. 2003 ). Other dispersions can be pro-

duced by proteins or other macromolecules

at frequencies between the β and γ diper-

sions, depending on the size and charge of

the molecules (Gabriel 2006 ). Another addi-

tional relaxation ( δ ) is located between the β

and γ dispersions. This relaxation is caused

by the rotation of amino acids, the rotation of

charged side groups of proteins, and the

relaxation of protein - bound water (Schwan

1981 ). The α - dispersion dominates between

millihertz and a few kilohertz, and is not yet

completely understood. Some hypotheses

remark the counter - ion effects near the mem-

The conductivity of most tissues rises
from a low value at low frequencies that
depend strongly on the volume fraction of
extracellular fl uid up to a plateau in the 10 –
100MHz frequency range, which mainly
corresponds to the conductivity of intra -
and extracellular ions. Conductivity then
rises dramatically, due to the dielectric relax-
ation of water (Rigaud et al. 1996 ) (Fig.
25.4 ).
This increase in conductivity is associated
with a decrease in permittivity, from very
high values at low frequencies in different
steps called dispersions. It is important to
highlight that these dispersions are not pro-
duced instantaneously and are characterized
by the correspondent relaxation phenomena
(Schwan 1988 ). In biological systems, there
are four main relaxation regions: α , β , δ and
γ (Fig. 25.3 ). Each of these steps character-
izes a type of relaxation that occurs in a spe-
cifi c frequency range and which allows the
identifi cation of different phenomena. The
dispersions of biological systems have been
widely studied by many authors (Grant et al.
1978 ; Schanne and P - Ceretti 1978 ; Pethig
1979 ; Stuchly 1979 ; Schwan and Foster

1,00E+08

e¢

s (S/m)

¶ (Hz)

1,00E+07

1,00E+06

1,00E+05

1,00E+04

1,00E+03

1,00E+02

1,00E+01

1,00E+00

1,00E–01

1,00E–02

1,00E

–01

1,00E

+01

1,00E

+03

3,00E

+05

1,00E

+07

1,00E

+09

1,00E

+11

1,00E

+13

Figure 25.4. Ideal representation of electric conductivity and dielectric constant spectra.