Effects of Phenolic Compounds on the Mechanisms of Pyrazinium Radical Generation in the Maillard Reaction: Trapping of Reactive Imine Intermediates

Open Access
Author:
Bin, Qing
Area of Honors:
Food Science
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Ryan John Elias, Thesis Supervisor
  • Devin G Peterson, Thesis Supervisor
  • Donald B Thompson, Honors Advisor
Keywords:
  • Pyrazinium radical
  • glyoxal
  • glycolaldehyde
  • reactive imine-trapping
  • catechins
  • Maillard reaction
Abstract:
Previous studies have demonstrated the generation of pyrazinium radical cation in the Maillard reaction and its significant role as a precursor to the non-enzymatic Maillard browning. In this study, effects of polyphenol chemistry on the mechanisms of pyrazinium radical generation in the Maillard reaction were investigated. Aqueous models of glyxoal–alanine (GO–Ala), glycolaldehyde–alanine (GA–Ala), and glucose-alanine (Glu–Ala) were treated with a concentration gradient of phenolic compounds (epigallocatechin-3-gallate, catechin, and 4-methylcatechol, respectively), and quantitative analysis of the pyrazinium radicals in these models was performed using electron paramagnetic resonance (EPR) spectroscopy. Catechins were reported to alter pyrazinium radical generation with the A-ring determined as the main reactive site. Enhancement of radical formation was found in GO–Ala model, with the maximum enhancement reached at catechin concentration being 1/10 of GO concentration; suppression of radical formation was found in GA–Ala and Glu–Ala model. Studies on the mechanism of the effect of catechins on the radical formation by LC/MS revealed the reactive imine-trapping by catechins in these models, which was suggested to directly control the generation and quenching of radical precursor enaminol, thus affecting the radical yield. LC/MS/MS analysis provided the detection and identification of these imine adducts of EGCG. This is the first reported mechanism including the reactive imine-trapping by catechins and its linkage to radical formation in the Maillard systems.