Carbonyl compounds can be formed as a result of oxidative degradation
of the side chains of lysine, proline, arginine and histidine residues.
The changes in the concentrations of protein carbonyls during frozen
storage of pork patties are illustrated in Fig. 3a. The concentration of
protein carbonyls increased (P≤ 0.05) in all groups during frozen storage
demonstrating that muscle proteins in the frozen stored patties were
susceptible to protein oxidation. The duration of frozen storage had a
strong impact on the extent of protein oxidation. In the CONT and
TP100 groups, the initial concentrations of protein carbonyls increased (P ≤ 0.05) with the frozen storage to reach on 180 days of storage a
value which was more than twofold the initial value. This carbonyl profile
is in line with those previously found in frozen chicken and turkey meat
(Soyer et al., 2010). Analogous increases in protein carbonyls have been
found in fish after 8 months of frozen storage, with protein carbonyls
reaching the value of 7.7 nmoles/mg after 13 months (Baron et al., 2007).