Free Radical Formation from Secondary Amines in the Maillard Reaction

ESR spectroscopy has been used to study the formation of free radicals in the Maillard browning reaction, from the reaction between glycolaldehyde or glyceraldehyde and N,N ‘-dialkylethylenediamines (alkyl = methyl, ethyl, iso -propyl, tert -butyl) in either aqueous buffer or in methanol. Two series of cyclic cation radicals are formed. The first is a 1:1 sugar:amine product in which the nitrogen atoms in 1 ethylenediamine molecule are bridged by a sugar molecule. The second, and more stable, is a 2:2 product in which a substituted dihydropyrazine cation radical is formed by the bridging of two amines with two sugars. In addition, nitroxide radicals are also observed when methanol is used as the solvent. A mechanism for the formation of these radicals in the early stages of the Maillard reaction is proposed.