Antioxidant activity of olive phenols: mechanistic investigation and characterization of oxidation products by mass spectrometry
作者:Marjolaine Roche、Claire Dufour、Nathalie Mora、Olivier Dangles
DOI:10.1039/b416101g
日期:——
In this work, the antioxidant activity of olive phenols is first characterized by their stoichiometries ntot
(number of radicals trapped per antioxidant molecule) and their rate constants for the first H-atom abstraction k1 by the stable radical DPPH. It appears that oleuropein, hydroxytyrosol and caffeic acid have the largest k1 values, whereas dihydrocaffeic acid, an intestinal metabolite of caffeic acid, is the best antioxidant in terms of ntot. For phenols with a catechol moiety ntot is higher than two, implying an antioxidant effect of their primarily formed oxidation products. A HPLC–MS analysis of the main products formed in the AAPH-induced oxidation of olive phenols reveals the presence of dimers and trimers. With hydroxytyrosol and dihydrocaffeic acid, oligomerization can take place with the addition of water molecules.
The antioxidant activity of olive phenols is then evaluated by their ability to inhibit the AAPH-induced peroxidation of linoleic acid in SDS micelles. It is shown that olive phenols and quercetin act as retardants rather than chain breakers like α-tocopherol. From a detailed mechanistic investigation, it appears that the inhibition of lipid peroxidation by olive phenols can be satisfactorily interpreted by assuming that they essentially reduce the AAPH-derived initiating radicals. Overall, olive phenols prove to be efficient scavengers of hydrophilic peroxyl radicals with a long lasting antioxidant effect owing to the residual activity of some of their oxidation products.
在本研究中,首先通过它们的化学计量学ntot(每个抗氧化剂分子捕获的自由基数量)和稳定自由基DPPH的第一个H原子抽提反应速率常数k1,来表征橄榄多酚的抗氧化活性。结果显示,橄榄苦苷、羟基酪醇和咖啡酸具有最大的k1值,而咖啡酸的肠道代谢物二羟基咖啡酸在ntot方面是最优秀的抗氧化剂。对于含有邻苯二酚基团的多酚,ntot值高于二,这意味着它们初始形成的氧化产物具有抗氧化效果。通过高效液相色谱-质谱(HPLC-MS)分析,在AAPH诱导的橄榄多酚氧化过程中形成的主要产物显示出二聚体和三聚体的存在。在羟基酪醇和二羟基咖啡酸的情况下,聚合反应伴随着水分子的加入。
然后,通过它们抑制AAPH诱导SDS胶束中亚油酸过氧化的能力来评估橄榄多酚的抗氧化活性。结果表明,橄榄多酚和槲皮素作为延缓剂而非链断裂剂如α-生育酚。通过详细的机理研究,发现橄榄多酚抑制脂质过氧化的作用可以通过假设它们基本减少AAPH衍生出的引发自由基来满意地解释。总体而言,橄榄多酚证明是有效的亲水性过氧自由基清除剂,由于其氧化产物中一些残余的活性,具有持久的抗氧化效果。