Handbook of Meat Processing

Curing 139

and other oxidizing agents such as nitrite can

oxidize the Fe 2+ to Fe 3+. The metmyoglobin

(MetMb) that is formed is brown.

The “ original ” myoglobin (Mb), the oxi-

myoglobin (MbO 2 ), and the metmyoglobin

occur together in meat. In the muscle of a live

animal there is very little metmyoglobin, but

it increases postmortem with the disappear-

ance of oxygen, except when meat is packed

with high oxygen. In MAP - packs with

about 70% oxygen, the color is bright red.

Oximyoglobin is not heat or light stable, and

Nitrite and the Color of

Meat Products

For consumers, the red color of cured meat
products is one of the important effects of
nitrite in meat products. The red color devel-
ops in a number of complicated reaction
steps until NO - myoglobin (Fe 2+ ) is formed.
Myoglobin exists in muscle in three states,
in which the cofactor heme, a porphyrin ring
with an iron ion in its center, binds different
ligands or in which the iron exists in the Fe 2+
or Fe 3+ state. In the native myoglobin, the
porphyrin moiety (Fig. 6.14 ) is supported in
the ligand binding by amino acids of neigh-
boring protein.
In its “ original ” state, myoglobin with
Fe 2+ in the porphyrin cofactor does not bind
any ligand except water molecules. In the
presence of oxygen, the porphyrin can bind
an O 2 molecule, and it becomes bright red.
The iron ion is in the Fe 2+ state. But oxygen

Figure 6.13. Chemical reactions leading to possible nitrosamine formation; M/M + are transition metal ions (like
Fe 2+ /Fe 3+ and others).

Table 6.10. NO - dimethylamine in foods ( μ g/
kg); adapted from Deierling et al. (1997)

Food N > 0.5 Content

min max

Beer 195 3 0.5 1.2

Pizza 57 6 0.5 8.7

Meat products 17 0 0 0

Milk products 6 0 0 0

COO–

CH 2

CH 2

COO–

CH 2

CH 2

CH 3

CH 3

CH 2

CH 3

CH

H 3 C

H 2 C

HC

CCC

H

C C

CCN

Fe

C C

N

C

C

C C

H

Haem

C

H

C

H

C

NNC

C

C

C

Figure 6.14. Haem/Fe - protoporphyrin (IX), cofactor

of myo - and hemoglobin.