Identification and quantitative evaluation of the lysine-arginine crosslinks GODIC, MODIC, DODIC, and glucosepan in foods

The presence of the various protein crosslinks GOLD 2, MOLD 3, GODIC 4, MOD IC 5, DODIC 6, and glucosepan 7 in foods has been established for the first time by liquid chromatography - mass spectrometry (LC-MS) with electrospra y ionization (ESI). In compounds 2 and 3 two lysine moieties, in 4-7 a lysi ne and an arginine side chain are joined by the crosslink. Unequivocal iden tification of 2-7 was achieved with independently synthesized reference mat erial. The quantitative results for the investigated foodstuffs show MODIC 5 to be thr most important Maillard crosslink. The concentrations of 5 and GODIC 4 are 5-10 fold higher than those of the corresponding imidazolium co mpounds 3 and 2, establishing 5 and 4 as the major food protein crosslinks derived from methylglyoxal and glyoxal, respectively. The maximum value of 151 mg MODIC 5/kg protein (equivalent to 0.42 mmol/kg protein) was found in a butter biscuit sample which also shows the highest overall Maillard cros slink content with 0.71 mmol 47/kg protein. These first quantitative result s suggest that compounds 4-7 can be jointly responsible for protein polymer ization in the course of food processing.