2009_Book_FoodChemistry

612 12 Meat
household as meat tenderizers. Analytical determination
of proteinases is relatively difficult.
A possible assay may be based on disc gel electrophoresis
of meat extracts, prepared in the presence
of urea and SDS. The band intensities of
the lower molecular weight collagen fragments
increase in proteinase-treated meat.
12.10.1.5 Anabolic Steroids
Anabolic compounds present in animal feed as
an additive increase muscle tissue growth. Owing
to a potential health hazard, some of these compounds
are banned in many countries. Their detection
can be achieved by the mouse uterus test
or by a radioimmunoassay. Special receptor proteins
which have the property of binding strongly
to estrogens are isolated from rabbit or cattle
uterus. The hormone-receptor complex is in equilibrium
with its components:
Receptor + estrogen ⇌ Receptor-estrogen
complex (12.30)
The nonlabelled estrogens bound to receptor in
the test sample will be competitively displaced
by the addition of 17-β-estradiol labelled with tritium
for radiochemical assay.
To reach equilibrium, a suitable amount of receptor
protein and a constant amount of labelled
estradiol are incubated together with the test sample.
The amount of the radioactive 3 H-estradiol
receptor complex will decrease in the presence
of competitive estrogens from the meat extract.
The binding affinity of the estrogen receptor depends
on the type of estrogen present (Fig. 12.42).
Hence, detection limits differ and range from 0.3
to 50 ppb (mg per metric ton).
Anabolic compounds can be further separated by
gas–liquid chromatography after derivatization
of the polar functional groups, and identified
by mass spectrometry. This method allows
the determination of weak or nonestrogenic
components too, but in the past it suffered from
high losses in sample preparation and could not
compete with radioimmunoassay in sensitivity.
In the meantime disadvantages of the method
have been eliminated.
12.10.1.6 Antibiotics
Antibiotics are used as part of therapy to treat animal
diseases and, sometimes in low concentrations,
as constitutents of animal feed to increase
feed utilization and to accelerate animal growth.
Detection of antibiotics is usually achieved by the
inhibition of the growth of bacteria (“inhibitor
test”). Bacillus subtilis, strain BGA, is one of the
recommended test organisms.
Chemical methods must be used in order to identify
and quantify the antibiotics and other veterinary
medical residues. The principal method
is chromatographic separation coupled with mass
spectrometry. The tetracyclines, which are common
antibiotics, can be determined relatively easily
by fluorometric measurement of adequately
prepared and purified meat extracts.
12.10.2 Processed Meats
Fig. 12.42. Relative binding affinity of estrogen compounds
to estrogen receptor. 50% binding achieved
by: 0.034 ng diethylstilbestrol (DES), 0.33 ng 17-βestradiol
(EST), 0.6 ng hexestrol (HEX), 1.2 ng zeranol
(ZER), 2.9 ng dienestrol (DIEN). (according to Ingerowski
and Stan, 1978)
Besides the estimation of the animal species and
the control of additives, the analysis of processed
meats is associated with verifying composition.
Here the emphasis is on the content of extraneous
added water, carbohydrate-containing thickeners
and binders, nonmeat protein additives and
fat. In addition, the determination of nitrites,
nitrates, nitrosamines and, for enhancing the