The formation of carbonyl compounds

The formation of carbonyl compounds has been widely accepted as a
marker of protein oxidation (Vossen & De Smet, 2015). The addition of
NaNO2 showed a clear antioxidant effect against protein oxidation as it
produced a significantly lower level of carbonyl derivatives in MP treated
with NaNO2 compared to the control. MP of sausages with high
NaNO2 concentrations (100, 200 and 400 mg/kg) contained markedly
lower carbonyls, demonstrating that NaNO2 can prevent such oxidative
changes. The decrease of carbonyls with the addition of 180 mg/kg
NaNO2 in other studies is in accordance with present study (Vossen &
De Smet, 2015). During oxidation, the lysine residues can be converted
into carbonyls through deamination (Stadtman, 2006). The increase of
free amine contents with the increase of NaNO2 indicating that NaNO2
prevented the replacement of free amines of lysine residues with a
carbonyl moiety. This effect of NaNO2 was also supported by the significantly
negative relationship between free amines and carbonyls. The
active carbonyl–NH2 interactions contributed to the loss of carbonyls,
which might explain the decrease in carbonyl content with storage
time (Estévez, 2011; Xiong et al., 2009). Some di-carbonyl compounds
derived from lipid oxidation, notably malondialdehyde,