Antioxidant activity of the natural flavonoids luteolin and catechin, which shows inconsistent comparativeresults in literature, was extensively evaluated as affected by the 1,4-pyrone moiety and 3–OH group. Catechin and luteolinwere compared to the synthetic antioxidant-butylated hydroxytoluene for their 2,2-diphenyl-1-picrylhydrazyl (DPPH•)scavenging activity in polar protic and aprotic solvents and ferric reducing-antioxidant power (FRAP). Moreover, theireffect on lipid oxidation kinetics of canola and olive oil triacylglycerols as well as their oil-in-water (O/W) emulsions, inaddition to oil stability indices (OSIs), was evaluated. In the DPPH•assay, catechin’s 3–OH group led to lower IC50valuesthan luteolin’s 1,4-pyrone moiety in acetone (3.4μM compared with 9.4μM), while there was no significant difference inmethanol (IC50=approximately 18.3μM) or tetrahydrofuran (IC50=approximately 27.2μM). The FRAP test indicateda higher reducing power for catechin than for luteolin (689.4μM compared with 573.1μM). The antioxidants showedvarious performances in the oil triacylglycerols and their O/W emulsions due predominantly to the interfacial phenomena.A better OSI was found for catechin than for luteolin (20.0 to 52.7 hr compared with 3.5 to 4.2 hr) in Rancimat test.

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