2009_Book_FoodChemistry

608 12 Meat
drolysate is used as the amino acid source and
other important precursors of meat aromas like
thiamine and monosaccharide phosphates are applied
in the form of yeast autolysates.
Fats or oils are added to produce the carbonyl
compounds which contribute to the animal
species specific note of meat aroma.
12.9.4 Aroma Defects
If cooked meat is stored for a short time, e. g.,
48 h at ca. 4 ◦ C, an aroma defect develops, which
becomes unpleasantly noticeable especially after
heating and is characterized by the terms metallic,
green, musty and pungent. This aroma defect,
also called warmed over flavor (WOF), is caused
by lipid peroxidation (cf. 12.6.2.1). The indicator
of this aroma defect is hexanal, which increases
as shown in Table 12.27.
Other changes which contribute to the aroma defect
are the increase in metallic/musty smelling
epoxydecenal, which, like hexanal, is formed in
the peroxidiation of linoleic acid (cf. 3.7.2.1.9),
and the decrease in HD3F. The latter is probably
due to the reaction of its enolic OH group with
peroxy radicals.
The WOF appears in chicken much faster
because its linoleic acid content is about 10 times
higher than that in beef. Apart from the changes
in concentration of the odorants listed in Table
12.27, the degradation of 2,4-decadienal,
which is typical of an advanced lipid peroxidation
(cf. 3.7.2.1.9), has an additional negative effect
on the aroma.
The WOF is inhibited by additives which bind
Fe ions, e. g., polyphosphates, phytin, and EDTA.
In comparison, antioxidants are almost ineffective.
Therefore, it is assumed that a site specific
mechanism is involved in the formation of WOF.
The Fe ions liberated in the cooking process are
bound by the phospholipids via the negatively
charged phosphate residues and, consequently,
adjoin the unsaturated acyl residues of these
lipids. Radicals from the Fenton reaction of Fe
ions with hydroperoxides (cf. 3.7.2.1.8) attack
only the unsaturated acyl residues, starting their
peroxidation. This hypothesis can also explain
the observation that multivalent ions (Ca 3⊕ ,
Al 3⊕ ) inhibit WOF as they probably displace the
Fe ions from the phospholipids.
12.10 Meat Analysis
12.10.1 Meat
The determination of the kind of animal, the origin
of meat, differentiation of fresh meat from
that kept frozen and then thawed, and the control
of veterinary medicines is of interest. The latter
include antibiotics (penicillin, streptomycin,
tetracyclines, etc.) used to treat dairy cattle infected
with mastitis, and other chemicals, including
diethyl stilbestrol, used for cattle to increase
the efficiency of conversion of feed into meat.
Table 12.27. Changes in the concentrations of important
aroma substances on cold storage and reheating of
roasted beef
Concentration
(µg/kg)
Compound I a II b
Hexanal 269 2329
trans-4,5-Epoxy-(E)-2-decenal 1.5 10.7
4-Hydroxy-2,5-dimethyl-3(2H)
-furanone (HD3F) 1108 665
a I: hamburgers were fried for 7 min.
b II: as in I, then storage at 4 ◦ C for 48 h and heated
at 70 ◦ C for 45 min until a core temperature of 60–
65 ◦ C is reached.
12.10.1.1 Animal Origin
The animal origin of the meat can be determined
by immunochemical and/or electrophoretic methods
of analysis as well as by PCR. The PCR
method is described in 2.6.4.2.2. Electrophoretic
protein analysis will be discussed here. The sexual
origin of a meat sample can also be of interest,
as discussed here for beef.
12.10.1.1.1 Electrophoresis
To determine the animal or plant origin of the
food, electrophoretic procedures have often