Formation of pyrazines in dihydroxyacetone and glycine Maillard reaction: A computational study

Based on the electronic and Gibb's free energy changes, the possibility of the formation of 2,5-dimethyl pyrazine (25Pz) as one of the probable final products in dihydroxyacetone (DHA) and glycine Maillard reaction under different pH conditions is described. Mechanisms for the reaction have been proposed following the Hodge-scheme. Density functional computational calculations at the standard state have been performed on the proposed mechanisms of the reaction. Electronic and Gibb's free energy changes for the formation of different compounds have been estimated by following the total mass balance for different steps of the reaction. The possible order of feasibility for the production of 25Pz has been found as DHA + deprotonated glycine (DGly) gaseous > DHA + DGly aqueous > DHA + unprotonated glycine (UGly) gaseous > DHA + glycine zwitterion (GlyZ) gaseous > DHA + UGly aqueous > DHA + GlyZ aqueous > DHA + protonated glycine (PGly) aqueous > DHA + PGly gaseous phase reactions. Amino-acetone has been found to be the most likely precursor of the pyrazine ring. Oxidation plays an important role during the production of 25Pz. Water has been found as a by-product during the formation of 25Pz.