Identification of modified lysozyme peptides upon photo-oxidation by LC-TOF-MS.

Protein oxidation can have major implications on the quality and safety of foods, but the majority of methods to evaluate oxidative damage lack specificity. Therefore, this study aimed to identify specific markers for protein oxidation. A well-characterized protein, lysozyme, was modified by photo-oxidation and subsequently hydrolyzed prior to peptide analysis by LC-TOF-MS. A semiquantitative analysis of the peptides indicated that from the seven peptides containing sensitive amino acids, two peptides (HGLDNYR and WWCNDGR) were highly affected upon photo-oxidation and have the potential to serve as markers for protein oxidation. Site-specific modifications enabled the description of the degradation pathway of several lysozyme peptides but also indicated that the surrounding amino acids and the 3D structure of the protein have an impact on the induced modifications. It is therefore advisable to evaluate protein oxidation on the intact protein.