Kinetic investigation of the trapping of Nε-(carboxymethyl)lysine by 4-methylbenzoquinone: A new mechanism to control Nε-(carboxymethyl)lysine levels in foods

- o-Benzoquinones trap CML under neutral and alkaline conditions.
- Reaction between 4MBQ and CML generates coloured CML-quinone adducts.
- Reaction between 4MBQ and CML involves the formation of colourless CML-phenol species.

o-Benzoquinones, formed during oxidation of polyphenols, react with amines through a Michael addition. In the present study, the ability of 4-methylbenzoquinone (4MBQ) to trap Nε-(carboxymethyl)lysine (CML) through a Michael addition with the amine groups on CML was investigated at different pH values. Apparent second order rate constants (k2) for the reaction of 4MBQ with CML were determined by stopped-flow spectrophotometry at 25 °C to be ∼0.0 M−1 s−1 at pH 5, 9.5 M−1 s−1 at pH 7, and 164.5 M−1 s−1 at pH 8 based on the loss of 4MBQ at 401 nm. The reaction between 4MBQ and CML generated coloured CML-quinone compounds via colourless CML-phenol species as identified by LC-ESI-MS/MS. These data provide evidence that CML formed during food production can be trapped by o-benzoquinones, which is a new mechanism by which polyphenols may be used to control CML levels in foods.