The sulfhydryl (SH) groups of MP are susceptible to hydroxyl radicals
and are converted into disulfides, such as intra- and intermolecular
S–S linkages. The SH contents decreased across the entire NaNO2 concentration
range (Fig. 1 C). The lost SH groups were mostly converted
to S–S bonds, which markedly increased in sausages (Fig. 1 D). The decrease
in SH groups and increase in S–S bonds with length of display
time can be explained by protein oxidation during storage (Feng et al.,
2015). Conversion of nitrite to nitric oxide could also promote oxidation
of sulfhydryls to disulfides (Heinecke et al., 2013).