Handbook of Meat Processing

Physical Sensors for Quality Control during Processing 445

caused by light refraction (von Hippel 1954 ;

Kent 2003 ). Atomic or ionic polarization

appears when atoms or ions are displaced in

a molecule. These displacements are typi-

cally associated with changes in chemical

bounds into the molecule, producing resul-

tant dipolar moments. A distortion of the

molecule ’ s natural vibration is produced,

and, therefore, this polarization is also called

vibrational (Kao 2004 ). This phenomenon is

mainly produced at the infrared region.

On the other hand, relaxation phenomena

are produced at microwave and radio fre-

quencies, and characterize, with the conduc-

tivity, the dielectric behavior of practically

all tissues at these frequencies. In meat prod-

ucts, these relaxation phenomena are the

result of the interaction between electromag-

netic radiation and tissue constituents (at the

cellular and molecular levels).

Dielectric Mechanisms in

Cellular Systems

There are different mechanisms affecting the
dielectric behavior of cellular food systems.
These mechanisms are divided into two
classes: resonance and relaxation processes.
Resonance phenomena happen when the
applied electric fi eld has a frequency that
matches the natural oscillation frequency of
the material. It includes electronic polariza-
tion and atomic polarization, which are pro-
duced at the highest microwave frequencies
and above them (Fig. 25.3 ). Electronic polar-
ization results from the displacement of the
electronic cloud with respect to the nucleus,
whether in single atoms or in molecules
(Grimnes and Gr ø ttem - Martinsen 2008 ). The
effects of this particular polarization can be
observed in the visible part of the spectrum,

H O +

CC

R O-

H 2 N+ +

Figure 25.3. Ideal representation of dielectric constant spectrum in biological systems. The four relaxation
regions that can be presented in these systems are also represented: α , β , δ and γ. (Adapted from Castro -
Gir á ldez et al. 2008 .)