Selective fortification of lysinoalanine, fructoselysine and N epsilon-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 degrees C for 1 h, in the presence of glucose at 65 degrees C for 68 h, or in the presence of glyoxylic acid at 37 degrees C 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, FL 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.