Analysis of protein oxidation markers alpha-aminoadipic and gamma-glutamic semialdehydes in food proteins using liquid chromatography (LC)-electrospray ionization (ESI)-multistage tandem mass spectrometry (MS).

To elucidate the formation of protein oxidation biomarkers alpha-aminoadipic semialdehyde (AAS) and gamma-glutamic semialdehyde (GGS) in food proteins was the main purpose of the present study. Food proteins, namely, myofibrillar proteins, alpha-lactalbumin, and soy proteins, as well as bovine serum albumin (BSA), were suspended in a piperazine-1,4-bis(2-ethanesulfonic acid) (PIPES) buffer and oxidized by Fe(3+) and H(2)O(2) while kept in an oven for 14 days at 37 degrees C. For the analysis of semialdehydes, a derivatization procedure with p-aminobenzoic acid (ABA) and NaCNBH(3) followed by liquid chromatography (LC)-electrospray ionization (ESI)-multistage tandem mass spectrometry (MS) was performed. For comparative purposes, the dinitrophenylhydrazine (DNPH) method was also employed as a routine method to assess carbonyl gain. Both semialdehydes were specifically and accurately detected by LC-MS in all oxidized proteins proving that GGS and AAS are formed as a consequence of the oxidation of lysine, proline, and arginine amino acid residues from BSA and other food proteins. Proteins from an animal source and, particularly, BSA were more susceptible to undergo oxidative reactions than soy proteins. The results from the present paper highlight the significance of using both semialdehydes as protein oxidation indicators in meat and dairy products. The analysis of GGS and AAS in real food systems would contribute to the understanding of the precise mechanisms involved in food protein oxidation and shed light on the fate of oxidizing amino acids during food processing and storage.