N ε-(carboxymethyl)-L-lysine content in cheese, meat and fish products is affected by the presence of copper during elaboration process

Formation of dietary advanced glycation end products has been extensively studied, principally with the aim to decrease their intake. In this work, the relationship between copper potentially present during food elaboration and N ᵋ-(carboxymethyl)-L-lysine (CML) concentrations, has been examined for the first time. For CML determination, a reversed phase liquid chromatography-electrospray ionization-ion trap tandem mass spectrometry procedure, based on acid hydrolysis, ethyl chloroformate derivatization and quantification in MRM mode was set-up, yielding method quantification limit of 98 µg kg⁻¹; copper was determined by ICP-MS. For eleven commercial cheeses, CML and Cu were found in the ranges 3.70–8.58 µg g⁻¹ and 0.08–15.5 µg g⁻¹, respectively, suggesting an inverse relation between these two parameters. For beef, chicken, Mexican pork “carnitas” and salmon, the CML concentration was lower in the item cooked in Cu casserole while element concentration was increased, as compared to this same raw material prepared in Teflon™ (except for “carnitas”). Concentration-dependent effect of Cu, manifest by decreased CML formation, was confirmed evaluating conversion percentage of chemically protected lysine (ZLys) to ZCML in the absence and in the presence of different Cu concentrations (50.0% and 20.4% conversion for Cu:ZLys molar ratio 0:1 and 0.04:1, respectively). Consistent results obtained in the analysis of three different sample types point to the inhibitory effect of copper during CML formation; however, it should be stressed that Cu is only one parameter within a complex set of factors/conditions involved in glycation process. Although better understanding of the observed effect at molecular level is needed, the results obtained in this work strongly suggest beneficial effect of copper, inhibiting glycation process during food elaboration.