Antolovich Michael, Bedgood Danny R, Bishop Andrea G, Jardine Daniel, Prenzler Paul D, Robards Kevin
School of Science and Technology, Charles Sturt University, Locked Bag 588, Wagga Wagga 2678, Australia.
J Agric Food Chem. 2004 Feb 25;52(4):962-71. doi: 10.1021/jf0349883.
Two oxidation systems were examined for the oxidation of three groups of phenolic antioxidants; five cinnamic acids, two benzoic acids, and two phenols characteristic of olive fruits. Periodate oxidation, which is reported to produce products similar to polyphenol oxidase, was contrasted with the reactivity of the Fenton system, an inorganic source of hydroxyl radicals. Reaction products were identified as various quinones, dimers, and aldehydes, but the nature of the products differed between the two oxidation systems. Structure-activity effects were also observed for the different phenols. All cinnamic acids in this study reacted with the Fenton reagent to produce benzaldehydes as the main products, with the exception of 5-caffeoylquinic acid. In contrast, periodate oxidation gave no reaction with some of the cinnamic acids. Quinone formation was observed for the two compounds, caffeic acid and 5-caffeoylquinic acid, possessing o-hydroxy groups. Caffeic acid was unusual in that dimer formation was the main initial product of reaction. Benzoic acids were readily oxidized by both systems, but no identifiable products were isolated. Oleuropein was oxidized by both oxidants used in this study, resulting in quinones in each system, whereas little or no oxidation of tyrosol was observed. This highlights the importance of conjugation between the alkene double bond and the hydroxy group. The results question the validity of many existing methods of testing antioxidant activity.
研究了两种氧化体系对三类酚类抗氧化剂的氧化作用；这三类抗氧化剂包括五种肉桂酸、两种苯甲酸以及两种橄榄果实特有的酚类物质。据报道，高碘酸盐氧化产生的产物与多酚氧化酶产生的产物相似，该氧化体系与羟基自由基的无机来源——芬顿体系的反应活性形成对比。反应产物被鉴定为各种醌、二聚体和醛，但两种氧化体系产生的产物性质有所不同。不同酚类物质的结构 - 活性效应也被观察到。本研究中所有肉桂酸与芬顿试剂反应，以苯甲醛作为主要产物，但5 - 咖啡酰奎尼酸除外。相比之下，高碘酸盐氧化对某些肉桂酸没有反应。对于含有邻羟基的两种化合物——咖啡酸和5 - 咖啡酰奎尼酸，观察到了醌的形成。咖啡酸不同寻常之处在于二聚体形成是反应的主要初始产物。两种体系都能使苯甲酸容易被氧化，但未分离出可鉴定的产物。本研究中使用的两种氧化剂都能氧化橄榄苦苷，在每个体系中都生成了醌，而酪醇几乎没有被氧化或未被氧化。这突出了烯烃双键和羟基之间共轭作用的重要性。这些结果对许多现有的抗氧化活性测试方法的有效性提出了质疑。
