Formation of pyrazines in hydroxyacetaldehyde and glycine nonenzymatic browning Maillard reaction: A computational study

By considering the formation of pyrazines (C4N2H6 and C4N2H4) as one of the possible final Maillard flavour compounds, Density Functional Theory computations at the standard state have been performed on the proposed mechanisms of glyoxal and glycine in the advanced stage of hydroxyacetaldehyde and glycine nonenzymatic browning reaction under different pH conditions. The results reveal that the basic condition is the most favourable for the production of pyrazines (Pzs), and the aqueous solution is more favourable than that of the gaseous state. The reactions at the isoelectric point of glycine and under neutral conditions are the second and third most favourable for the production of Pzs, respectively. The reaction under acidic conditions is the least feasible for the production of Pzs. Amino acetaldehyde is the most likely precursor of the pyrazine ring in the reaction. Presence of air or oxygen is necessary for the production of 2,3,5,6-tetrahydropyrazine (C4N2H4) from 3,6-dihydropyrazine (C4N2H6). Water is necessary with glyoxal and glycine species for the formation of Pzs and water is produced as a by-product during the formation of Pzs.