Wine oxidation changes the chemistry, sensory profile and color of wines. In wine oxidation, phenolics are oxidized to quinones and these reactive compounds can be quenched by sacrificial nucleophiles, such as the A-ring on flavanoids, preventing oxidative damage from the loss of desirable flavor molecules. The "catechol" B-ring on flavanoids, in contrast, can be oxidized by quinones through electron transfer reactions that lead to flavanoid quinones, precursors of browning products. Here we compared the rate of flavanoids reacting by either nucleophilic quinone quenching, or by electron transfer to generate flavanoid quinones. Our approach is based on mathematical modeling of reaction data to derive the rate constants of reactions of A-ring quenching vs B-ring electron transfer with caffeic acid quinone, by fitting the predicted loss of precursors and the appearance of products (or derivatives) with experimental data collected by LC/MS. The rate constant of the electron transfer reaction of caffeic acid quinone towards 4-methyl-catechol was fast (k4MC = 3.43E-2 mLmol-1sec-1) but nucleophilic reactions with afzelechin (kAfz = 2.53E-3 mLmol-1sec-1) or malvidin-3-glucoside (kMal = 5.34E-3 mLmol-1sec-1), were much slower. No reaction was detected between caffeic acid quinone and isorhamnetin. Additionally, the electron transfer reaction rate of catechin and caffeic acid quinone was much faster at pH 7 (1.22E-02 mLmol-1sec-1) vs pH 3.5 (1.79E-03 mLmol-1sec-1). These results help explain why the reaction of catechin and caffeic acid quinone favors the formation of browning products, and more so at higher pH values. Furthermore, bisulfite reacted with quinones faster than the electron transfer reactions, preventing the browning observed in the reaction of catechin with caffeic acid quinone in the absence of bisulfite.

中文翻译：

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黄烷醇通过电子转移反应优先与醌反应，刺激而不是阻止葡萄酒褐变

葡萄酒氧化会改变葡萄酒的化学成分、感官特征和颜色。在葡萄酒氧化中，酚类物质被氧化成醌类，这些反应性化合物可以被牺牲性亲核试剂淬灭，例如类黄酮上的 A 环，防止因失去所需风味分子而造成氧化损伤。相比之下，黄酮类化合物上的“儿茶酚”B 环可以被醌类通过电子转移反应氧化，从而生成黄酮类醌类化合物，即褐变产物的前体。在这里，我们比较了通过亲核醌淬灭或通过电子转移生成黄酮醌的黄酮类化合物的反应速率。我们的方法基于反应数据的数学建模，以推导出 A 环猝灭与 B 环电子转移与咖啡酸醌的反应速率常数，通过将预测的前体损失和产物（或衍生物）的外观与 LC/MS 收集的实验数据进行拟合。咖啡酸醌对 4-甲基-邻苯二酚的电子转移反应的速率常数很快 (k4MC = 3.43E-2 mLmol-1sec-1) 但与 afzelechin 的亲核反应 (kAfz = 2.53E-3 mLmol-1sec-1) ) 或malvidin-3-glucoside (kMal = 5.34E-3 mLmol-1sec-1)，速度要慢得多。咖啡酸醌与异鼠李素之间未检测到反应。此外，儿茶素和咖啡酸醌的电子转移反应速率在 pH 7 (1.22E-02 mLmol-1sec-1) 比 pH 3.5 (1.79E-03 mLmol-1sec-1) 时要快得多。这些结果有助于解释为什么儿茶素和咖啡酸醌的反应有利于形成褐变产物，在较高的 pH 值下更是如此。此外，