08.05.2020 Views

2009_Book_FoodChemistry

food chemistry

food chemistry

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

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

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!