Food Biochemistry and Food Processing

320 Part III: Muscle Foods

be stable during frozen storage and is responsible
for rancidity development in chicken, especially in
the muscle Gastrocnemius(Grosman et al. 1988).

Antioxidative Enzymes

Antioxidative enzymes and their regulation in the
muscle constitute a defense system against oxida-
tive susceptibility (i.e., an increased concentration
of polyunsaturated fatty acids) and physical stress
(Young et al. 2003). Glutathione peroxidase con-
tains a covalently bound selenium atom that is
essential for its activity. This enzyme catalyzes the
dismutation of alkyl hydroperoxides by reducing
agents like phenols. Its activity has been reported to
be lower in oxidative muscles than in glycolytic
muscles (Daun et al. 2001). Superoxide dismutase is
a copper metalloenzyme, and catalase is an iron
metalloenyzme. Both enzymes catalyze the dismu-
tation of hydrogen peroxide to less harmful hydrox-

ides. These enzymes influence the shelf life of the

meat and protect against the prooxidative effects of

chloride during further processing.

PROTEOLYSIS

Proteolysis constitutes an important group of reac-

tions during the processing of meat and meat prod-

ucts. In fact, proteolysis has a high impact on texture,

and thus meat tenderness, because it contributes to

the breakdown of the myofibrillar proteins responsi-

ble for muscle network, but proteolysis also gener-

ates peptides and free amino acids that have a direct

influence on taste and also act as substrates for fur-

ther reactions contributing to aroma (Toldrá 1998,

2002). In general, proteolysis has several consecu-

tive stages (see Fig. 14.3) as follows: (1) action of

calpains and cathepsins on major myofibrillar pro-

teins, generating protein fragments and intermediate

size polypeptides; (2) these generated fragments and

Figure 14.3.General scheme of proteolysis during the processing of meat and meat products.