Influence of phenolic compounds on the mechanisms of pyrazinium radical generation in the maillard reaction

The generation of pyrazinium radical cations during the early stages of the Maillard reaction has been previously demonstrated. In this study, the effect of food phenolic compounds [4-methylcatechol (4-MeC), (+)-catechin (CAT), and (-)-epigallocatechin-3-gallate (EGCG)] on the fate of these intermediates in Maillard model systems was investigated. Aqueous solutions containing either glyoxal + alanine (GO-A) or glycolaldehyde + alanine (GA-A) were treated with a concentration gradient of each phenolic compound, and quantitative analysis of the resulting pyrazinium radicals in these models was performed using electron paramagnetic resonance (EPR) spectroscopy. CAT and EGCG were observed to affect pyrazinium radical generation rates, in some cases either enhancing or suppressing formation depending on concentration, whereas the simple catechol (4-MeC) had no such effect. A mechanistic study was carried out by LC-MS, which suggested that under some conditions, CAT and EGCG react with imine intermediates via their A-rings, thus influencing the formation of the enaminol radical precursor and, ultimately, pyrazinium radicals. To the authors' knowledge, this is the first study demonstrating imine trapping by phenolic compounds under Maillard conditions and how such phenolic quenching reactions can alter pyrazinium radical formation.