Metal ion complexation by products of the Maillard reaction

Potentiometric proton-liberation experiments were used to study the interaction between metal ions and a crude Maillard reaction product (MRP) of glucose-glutamate or a pure product of the Maillard reaction, the Amadori compound fructosyl glycine. The present study is the first to report values for stability constants for complex formation involving products of the Maillard reaction and metal ions. Proton displacement suggested binding of Zn2+, Cu2+, Mg2+ and Ca2+ by the glucose-glutamate MRP. The strength of binding occurred in the order Mg2+ > Cu2+ = Ca2+ > Zn2+. The order of binding affinity differs from that expected for a mononuclear binary system as predicted by the Irving-Williams series which might suggest the presence of two or more distinct ligands in the MRP. displacement suggested the formation of complexes of fructosyl glycine with zinc but not with calcium. The pKa value of fructosyl glycine was notably higher than that of glycine (3.25 vs 2.23, respectively), whereas the pKb value was reduced (8.93 vs 9.73, respectively). Such changes in protonation may help to explain the lower affinities for zinc exhibited by fructosyl glycine compared with glycine (glycine: log K1, 5.40; log K2,4.47; log K3, 2.73. Fructosyl glycine: log K1, 4.27, log K2, 3.83; log K3, 1.92). The results of the present study may explain some of the effects of Maillard reaction products on mineral homoeostasis in vivo. However, it is likely that the biokinetics and metabolism of such compounds also play a major role in mediating observed effects.