Reduction of N epsilon-(carboxymethyl) lysine by (-)-epicatechin and (-)-epigallocatechin gallate: The involvement of a possible trapping mechanism by catechin quinones

(-)-Epicatechin (EC) and (-)-epigallocatechin gallate (EGCG) (0.001-5%) were found to reduce N epsilon-(carboxymethyl) lysine (CML) concentrations by up to 0.80 +/- 0.11 mM and 0.85 +/- 0.07 mM, respectively, as quantified by HPLC-MS during heating at 80 degrees C and 100 degrees C in a glucose-lysine model system at pH 5, 7 and 8, which mimic different food processing conditions. With the addition of 1 mM EC, the free CML concentration in coconut milk was reduced to 5.7 +/- 0.1 mu g/mL (similar to 2.8x10(-2) mM), which was significantly lower than that in unheated coconut milk (6.1 +/- 0.2 mu g/mL (similar to 3.0x10(-2) mM), p < 0.05) indicating that the free CML may be eliminated by the addition of EC in coconut milk. Products of EC/EGCG quinones reacted with CML by a Michael addition or Schiff base addition in model systems were tentatively identified by UPLC-ESI-MS/MS.