450 Chapter 25
application is to detect the fraudulent addi-
tion of water in meat products (Kent et al.
2000, 2001, 2002 ). It was also employed to
measure water activity in proteic gels (Clerjon
et al. 2003 ). A microwave sensor for control-
ling meat and fi sh freshness was developed,
based on the change in dielectric properties
due to the reduction of muscle anisotropy
during meat and fi sh aging (Clerjon and
Damez 2007 ). It is also possible to predict the
fat content in fi sh or minced meat (Kent
1990 ; Kent et al. 1993 ; Boggaard et al. 2003 ).
A nondestructive meter for measuring fat in
fi sh (Kent 1990 ), fat in meat (Kent et al.
1993 ), and fi sh freshness (Boggaard et al.
2003 ; Tejada et al. 2007 ) is already on
the market (Distell Company ® , West
Lothian, Scotland). A Guided Microwave
Spectometer ® (Thermo Electron Corporation,
U.S.) has been developed for on - line mea-
surements of moisture and fat content in
ground meat. There exists also an on - line
sensor for measuring the fat - to - lean ratio in
pork middles (Keam Holden Ltd., New
Zealand).Near Infrared Spectroscopy
Near infrared (NIR) spectroscopy is a tech-
nique that uses a portion of the electromag-
netic spectrum, from 780 to 2500nm (Datta
and Almeida 2005 ). NIR spectra are com-
posed of overlapping absorptions, corre-
sponding to overtones, and combinations of
vibrations involving C - H, O - H, and N - H
chemical bonds (Osborne 2000 ). This tech-
nique provides information about the molec-
ular bonds and chemical constituents of the
sample (Belton 1997 ), and allows a complete
picture of the organic composition of the ana-
lyzed material (Van Kempen 2001 ). It can be
considered one of the most powerful analyti-
cal techniques to analyze fi nal meat quality
(Van Kempen 2001 ). On the other hand,
although this technique gives information on
the molecular level, some research also
showed the utility of determining macro-Meat Qualitymeter ® from Tecpro (U.S.),
which analyzes some chemical and physical
pro perties as an ATP content using low - fre-
quencies or RFM1000 from Process - sensor
Corporation, which uses high frequencies to
analyze chemical properties as moisture.
On the safety side, bioimpedance spec-
troscopy has been used to determine micro-
bial levels in meat. Kim et al. (2008)
developed an interdigitated microelectrode
sensor that works at low frequencies to detect
salmonella enteritidis in pork meat. Ong et
al. (2002) developed an electrical conductiv-
ity sensor that works at low frequencies to
control E. Coli , Pseudomonas putida, and
Bacilus subtilis. Radke and Alocilja (2005)
developed a conductivity sensor to control E.
Coli counts in pork meat pieces, with the new
methodology previously published (Radke
and Alocilja 2003 ).
Microwave Spectrometry
Microwaves include waves with wavelengths
from 3m to 3mm. The corresponding
frequency range extends from 100MHz
to 1mmGHz (Kent 2001 ). In the electromag-
netic spectrum, microwaves are located
between radio waves at low frequencies and
infrared at higher frequencies (Fig. 25.1 ).
The interaction of microwaves and meat
products produces the so - called γ - dispersion
(Fig. 25.3 ), which is closely related to the
water content and its state (Kent and Jason
1975 ). But the dielectric spectrum at these
frequencies also depends on food composi-
tion, which obviously infl uences the water
state. Moreover, the presence of ions pro-
duces ionic conductivity, which affects the
loss factor spectrum (Fig. 25.4 ), and also the
electrical charges of proteins; the presence of
free amino acids or the pH variations are
some of the factors that can affect the dielec-
tric spectrum at these frequencies (Gabriel
2006 ).
The application of this technique to food
quality control has been widely studied. One