Quercetin oxidation leads to the formation of a metabolite, 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)benzofuranone, whose antioxidant potency was recently reported to be a 1000-fold higher than that of its precursor. The formation of similar metabolites (BZF) is limited to certain flavonols (FL), among which are myricetin, fisetin, and morin. Here we addressed the consequences of inducing the auto-oxidation of these flavonols in terms of their antioxidant properties (assessed in ROS-exposed Caco-2 cells). The mixtures that result from their oxidation (FLox) exhibited antioxidant activities 10-to-50-fold higher than those of their precursors. Such amplification was fully attributable to the presence of BZF in each FLox (established by HPLC-ESI-MS/MS and chemical subtraction techniques). An identical amplification was also found when the antioxidant activities of BZF, isolated from each FLox, and FL were compared. These findings warrant the search of these BZF in edible plants and their subsequent evaluation as a new type of functional food ingredients.