Mass spectrometric identification of nitrite-induced modifications in heated model peptides and the cured pork matrix

In contrast to N-nitrosamines, little is known about nitrite-induced protein modifications in cured meat products. Therefore, a combined mass spectrometry-based approach involving synthetic tryptic meat peptides and the analysis of cured pork sausages was used to identify these modifications. Model peptides were selected from gently extracted and digested sausage samples according to their abundance, tyrosine content, or position at the protein N-terminus and synthesized. Several deamination products of the peptide N-terminus were described for the first time in peptide model reactions with food-relevant nitrite concentrations, including α-chlorinated, α-phosphorylated and α,β-unsaturated peptides, which may have toxicological relevance due to their electrophilic properties. Tyrosine nitration was detected without an elevated nitrite concentration or the presence of additional oxidants. Furthermore, N-nitrosoproline was identified for the first time in a peptide, and a nitrosoprolyl peptide was also detected in sausages treated with nitrite, even without specific enrichment. Enhanced sensitivity was achieved using MRM³ mode.