2009_Book_FoodChemistry

12.10 Meat Analysis 613
pinkish-red color of processed meat, L-ascorbic
acid is of importance in pickle-cured meat
products. Other analytical problems involve the
detection of condensed phosphates, citric acid
and glucono-δ-lactone, as well as the detection
of polycyclic aromatic compounds in smoked
meats, of mycotoxins in products with desirable
or undesirable growth of molds and of chlorine
compounds in seasonings.
12.10.2.1 Main Ingredients
The first insight into the composition of processed
meat, i. e. whether it contains an excess of fat or
carbohydrate, which would lower the protein content
and thus lower the value of the processed
meat, is obtained by proximate analysis of the
product’s main ingredients: moisture, raw protein,
fat and ash content. If their sum is less than
100 ± 0.5% of the sample weight, then the presence
of carbohydrate binders should be verified.
A positive finding should be further investigated
since incorporation of liver into processed meat
may provide glycogen. Hence, thorough carbohydrate
analysis is required.
12.10.2.2 Added Water
Moisture content is related to protein content and
is relatively constant. Feder’s method of analysis
of water added to chopped or ground meat or
to emulsion-type sausages is based on these findings.
The method uses the empirical equation:
Water added (%)=Moisture (%)
− Protein (%) × F (12.31)
F for beef and pork = 4.0;
F for poultry leg = 3.9 and breast = 3.6
This indirect method for assessing the amount
of added water has been repeatedly criticized.
In spite of this, no better method has yet been
developed. Moreover, the calculated water content
is never used alone to evaluate a meat product.
Other significant data, such as muscle protein
content and the proportion of fat to protein, are
also included.
12.10.2.3 Lean Meat Free of Connective
Tissue
A measure of meat quality is expressed as the
amount of lean meat free of connective tissue,
which corresponds to meat proteins devoid of
connective tissue protein (MPDCP). To obtain
this value, the meat sample is analyzed for
connective tissue proteins (CP), added extraneous
protein (EP) and nonprotein-nitrogen
(NPN), e. g., glutamate, purine and pyrimidine
derivatives, urea. These values are then deducted
from the value for total protein (TP):
MPDPC = TP − (CP + EP + NPN) (12.32)
Another method still being tested is based on
drastic treatment (heating to 130 ◦ CatpH9)of
a meat sample. Under these conditions, extraneous
proteins, collagen and blood plasma proteins
solubilize, while the residual protein is calculated
as MPDCP using a constant factor.
12.10.2.3.1 Connective Tissue Protein
The amino acid 4-hydroxyproline is a marker
compound for connective tissue. It occurs only
in connective tissue protein. The amount of
4-hydroxyproline is determined in the acidhydrolysate
of the sample or the isolated protein
using an amino acid analyzer, or color-imetrically
using a specific color reaction. The latter, accepted
widely in practice, is a direct photometric
procedure based on the oxidation of hydroxyproline
in alkaline solution by H 2 O 2 or N-chlorop-toluenesulfonamide
(chloramine-T). The oxidation
yields a pyrrole derivative which is then
condensed with p-dimethylaminobenzaldehyde
to form a red pigment. The connective tissue
content of meat is calculated by multiplying the
hydroxyproline value by a factor of 8, which corresponds
to an average of 12.4% hydroxyproline
content of connective tissue.
12.10.2.3.2 Added Protein
In order to extend or improve the water holding
capacity of processed meat, the product may