Antioxidant activity of the natural flavonoids luteolin and catechin, which shows inconsistent comparative results in literature, was extensively evaluated as affected by the 1,4-pyrone moiety and 3-OH group. Catechin and luteolin were 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, their effect on lipid oxidation kinetics of canola and olive oil triacylglycerols as well as their oil-in-water (O/W) emulsions, in addition to oil stability indices (OSIs), was evaluated. In the DPPH● assay, catechin's 3-OH group led to lower IC50 values than luteolin's 1,4-pyrone moiety in acetone (3.4 µM compared with 9.4 µM), while there was no significant difference in methanol (IC50 = approximately 18.3 µM) or tetrahydrofuran (IC50 = approximately 27.2 µM). The FRAP test indicated a higher reducing power for catechin than for luteolin (689.4 µM compared with 573.1 µM). The antioxidants showed various 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.

中文翻译：

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木犀草素和儿茶素的结构-抗氧化活性关系

天然黄酮类化合物木犀草素和儿茶素的抗氧化活性在文献中显示出不一致的比较结果，被广泛评估为受 1,4-吡喃酮部分和 3-OH 基团的影响。儿茶素和木犀草素与合成抗氧化剂丁基化羟基甲苯相比，它们在极性质子和非质子溶剂中的 2,2-二苯基-1-苦基肼 (DPPH●) 清除活性和铁还原抗氧化能力 (FRAP)。此外，除了油稳定性指数 (OSI) 外，还评估了它们对油菜籽和橄榄油三酰甘油及其水包油 (O/W) 乳液脂质氧化动力学的影响。在 DPPH● 测定中，儿茶素的 3-OH 基团导致比木犀草素在丙酮中的 1,4-吡喃酮部分更低的 IC50 值（3.4 µM 与 9.4 µM 相比），而甲醇 (IC50 = 约 18.3 µM) 或四氢呋喃 (IC50 = 约 27.2 µM) 没有显着差异。FRAP 测试表明儿茶素的还原能力高于木犀草素（689.4 µM 与 573.1 µM 相比）。由于界面现象，抗氧化剂在油三酰甘油及其 O/W 乳液中表现出不同的性能。在 Rancimat 测试中发现儿茶素的 OSI 优于木犀草素（20.0 至 52.7 小时，而 3.5 至 4.2 小时）。