Poupard Pascal, Guyot Sylvain, Bernillon Stephane, Renard Catherine M G C
UR117, Recherches Cidricoles et Biotransformation des Fruits et Légumes, INRA, F-35653 Le Rheu, France.
J Chromatogr A. 2008 Feb 1;1179(2):168-81. doi: 10.1016/j.chroma.2007.11.083. Epub 2007 Dec 3.
The reactivity of the (-)-epicatechin structure towards caffeoylquinic acid o-quinones was studied in an apple juice model solution. The approach consisted in considering separately the reactivities of the two phenolic moieties of an (-)-epicatechin molecule: phloroglucinol and 4-methylcatechol were chosen to represent A- and B-rings, respectively. The oxidation products were characterised by RP-HPLC coupled with electrospray ionisation Mass spectrometry (MS). The reactivities of the A- and B-rings were clearly different on the basis of the oxidation products formed. Both A- and B-rings could be involved in covalent bond formation, but electron transfers only occurred with the B-ring. Most of the (-)-epicatechin oxidation products were linked by A/B-ring linkage ("head-to-tail" intermolecular coupling). After this first dimerisation step, intramolecular reactions seemed to be favoured. Therefore, the complexity of oxidation products in apple juice does not only result from an extensive polymerisation of native phenolic compounds, but also from a multiplicity of small molecules in different oxidation states and isomeric forms.
在苹果汁模型溶液中研究了（-）-表儿茶素结构对咖啡酰奎尼酸邻醌的反应活性。该方法包括分别考虑（-）-表儿茶素分子两个酚类部分的反应活性：分别选择间苯三酚和4-甲基邻苯二酚来代表A环和B环。氧化产物通过反相高效液相色谱（RP-HPLC）结合电喷雾电离质谱（MS）进行表征。根据形成的氧化产物，A环和B环的反应活性明显不同。A环和B环都可能参与共价键的形成，但电子转移仅发生在B环。大多数（-）-表儿茶素氧化产物通过A/B环连接（“头对尾”分子间偶联）。在这第一步二聚化步骤之后，分子内反应似乎更受青睐。因此，苹果汁中氧化产物的复杂性不仅源于天然酚类化合物的广泛聚合，还源于处于不同氧化态和异构体形式的多种小分子。
