Selective fortification of lysinoalanine, fructoselysine and Nε-carboxymethyllysine in casein model systems

In the present study, a promising strategy to study nutritional effects of selected chemical reaction products formed in heat treated protein containing foods is addressed. In due course, a selective fortification of different marker compounds for lysine damage in casein-sugar mixtures was performed to provide model systems being applicable to investigate biological effects of the cross-link lysinoalanine (LAL), the MRPs fructoselysine (FL) and N-epsilon-carboxymethyllysine (CML) in a casein-linked preparation. The three different model proteins, casein-LAL, casein-FL and casein-CML were prepared by heating casein either in strong alkaline conditions at 105 degreesC for 1 h, in the presence of glucose at 65 degreesC for 68 h, or in the presence of glyoxylic acid at 37 degreesC for 19 h. Finally, the degree of lysine modification achieved was 39%, 75% and 55% for the casein-LAL, casein-FL and casein-CML, respectively. The calculation of lysine recovery and the respective analysis of each single modified casein (LAL-, FL- and CML-MP) for the selected fortified compound and each other compound vice versa proved that the individual procedure provides a specific fortification for LAL, R and CML, respectively. The modified proteins are suitable as reference model proteins to be investigated for specific biological and toxicological effects of casein-linked LAL, FL and CML.