o-Quinone trapping by flavonols

The reactions between flavonols (quercetin, kaempferol, and morin) and the quinones of catechol and 4-methylcatechol were studied to investigate the ability of flavonols to trap o-quinones and, therefore, to contribute to the removal of these reactive carbonyls in foods. The reactions produced adducts, which were isolated and characterized using nuclear magnetic resonance and mass spectrometry. The reaction occurred between one of the oxygens of the quinone and the carbon at position 2 of the flavonol. As a result, the C-ring was opened, and an α,β-unsaturated ketone with phenolic substituents at positions 1 and 3 was produced. The reaction was accompanied by the dimerization of the flavonol if it contained an o-diphenol group. Both products (adduct and dimer) were determined in onions fried in the laboratory and commercially fried onions using LC-MS/MS. The extent of their formation depended on heating time and temperature, reaction pH, and the presence of antioxidants.