N-Carboxymethyllysines

Both thee-N-monocarboxymethyl and the e-N-dicarboxymethyl derivatives of lysine are formed by reaction of proteins with iodoacetate at alkaline pH values at which lysyl residues are at least partially un-protonated ( 3.8.2). Both derivatives are stable to acid hydrolysis under the usual conditions. 

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Al-Abed Y and Bucala R (1995) N-carboxymethyllysine formation by direct addition of glyoxal to lysine during the Maillard reaction. Bioorg Med Chem Lett 5, 2161-2162. 

Liardon R, De Weck-Gaudard D, Philippossian G and Finot P-A (1987) Identification of N-carboxymethyllysine a new Maillard reaction product, in rat urine. J Agr Food Chem 35, 427-431. 

In heat treated or stored food products several amino acids are not fully available because of derivatization or crosslinking reactions. Since 30 years furosine is known as a useful indicator of early Maillard reaction which is applied in food science, nutrition and medical biochemistry. Recently more sensitive analytical methods for furosine determination are available which have again increased the attractivity of this important indicator. Lately, N -carboxymethyllysine (CML) became available as another marker of special interest, because CML is a more useful indicator of the advanced heat damage by Maillard reaction than furosine. In addition, CML has the advantage to indicate reactions of lysine with ascorbic acid or ketoses such as fructose. Indicators for protein oxidation of sulfur amino acids are methionine sulfoxide and cysteic acid. An established marker for cross-linking reactions is lysinoalanine, which also indicates protein damages due to processing under alkaline conditions. Other markers formed as a consequence of alkaline treatment are D-amino acids. 

As an alternative method for the above mentioned food items we proved the formation of N -carboxymethyllysine (CML) in a model system of several sugars and lysine (24) or casein, respectively. CML, an oxidative decomposition product of e-fructoselysine was identified for the first time in 1985 (25) in biological material and later also in food items (26, 27). This new compound can be detected... 

Figure 5. Formation of N -Carboxymethyllysine (CML) in a model system with lysine monohydrochloride and various reducing sugars after heating at 98°C (recalculated from Ruttkat and Erbersdobler, 1995).

N -Carboxymethyllysine It s Origin in Selected Foods 3 RESULTS AND DISCUSSION... 

V. Somoza, E. Wenzel, C. WeiB, 1. Clawin-Radecker, N. GriibeL and H. F. Erbersdobler, Dose-dependent utilisation of casein-linked lysinoalanine, A(epsi-lon)-ihictoselysine and W(epsilon)-carboxymethyllysine in rats. Mol. Nutr. Food Res., 50 (2006) 833-841. 

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