Department of Viticulture and Enology, University of California , Davis, California 95616, United States.
J Agric Food Chem. 2012 Aug 29;60(34):8484-91. doi: 10.1021/jf302017j. Epub 2012 Aug 20.
Quinones are key reactive electrophilic oxidation intermediates in wine. To address this question, the model 4-methyl-1,2-benzoquinone was prepared to study how it reacts with wine nucleophiles. Those investigated included the varietal volatile thiols 4-methyl-4-sulfanylpentan-2-one (4MSP), 3-sulfanylhexan-1-ol (3SH), and 2-furanmethanethiol (2FMT); hydrogen sulfide (H2S); glutathione (GSH); sulfur dioxide; ascorbic acid (AA); and the amino acids methionine (Met) and phenylalanine (Phe) in the first kinetic study of these reactions. Products were observed in fair to quantitative yields, but yields were negligible for the amino acids. The reaction rates of 4-methyl-1,2-benzoquinone toward the nucleophiles were quantified by UV-vis spectrometry monitoring the loss of the quinone chromophore. The observed reaction rates spanned three orders of magnitude, from the unreactive amino acids (Met and Phe) (KNu = 0.0002 s(-1)) to the most reactive nucleophile, hydrogen sulfide (KH2S = 0.4188 s(-1)). Analysis of the kinetic data showed three categories. The first group consisted of the amino acids (Met and Phe) having rates of essentially zero. Next, phloroglucinol has a low rate (KPhl = 0.0064 s(-1)). The next group of compounds includes the volatile thiols having increasing reactions rates K as steric inhibition declined (K4MSP = 0.0060 s(-1), K3SH = 0.0578 s(-1), and K2FMT = 0.0837 s(-1)). These volatile thiols (4MSP, 3SH, 2FMT), important for varietal aromas, showed lower K values than those of the third group, the wine antioxidant compounds (SO2, GSH, AA) and H2S (KNu = 0.3343-0.4188 s(-1)). The characterization of the reaction products between the nucleophiles and 4-methyl-1,2-benzoquinone was performed by using HPLC with high-resolution MS analysis. This study presents the first evidence that the antioxidant compounds, H2S, and wine flavanols could react preferentially with oxidation-induced quinones under specific conditions, providing insight into a mechanism for their protective effect.
醌类物质是葡萄酒中关键的反应性亲电氧化中间体。为了解决这个问题，制备了模型化合物 4-甲基-1,2-苯醌，以研究其与葡萄酒亲核试剂的反应。研究的亲核试剂包括品种挥发性硫醇 4-甲基-4-巯基戊-2-酮（4MSP）、3-巯基己-1-醇（3SH）和 2-呋喃甲硫醇（2FMT）；硫化氢（H2S）；谷胱甘肽（GSH）；二氧化硫；抗坏血酸（AA）；以及在这些反应的首次动力学研究中，甲硫氨酸（Met）和苯丙氨酸（Phe）这两种氨基酸。观察到产物的产率相当高，但氨基酸的产率可以忽略不计。通过紫外-可见光谱监测醌类物质的发色团的损失，定量测定了 4-甲基-1,2-苯醌与亲核试剂的反应速率。观察到的反应速率跨越了三个数量级，从反应性差的氨基酸（Met 和 Phe）（KNu = 0.0002 s(-1))到最活泼的亲核试剂硫化氢（KH2S = 0.4188 s(-1))。对动力学数据的分析表明，有三个类别。第一组由反应速率几乎为零的氨基酸（Met 和 Phe）组成。其次，间苯三酚的反应速率较低（KPhl = 0.0064 s(-1))。接下来的一组化合物包括挥发性硫醇，随着空间位阻的降低，反应速率 K 增加（K4MSP = 0.0060 s(-1), K3SH = 0.0578 s(-1), K2FMT = 0.0837 s(-1))。这些挥发性硫醇（4MSP、3SH、2FMT）是品种香气的重要组成部分，其 K 值低于第三组化合物（葡萄酒抗氧化剂化合物 SO2、GSH、AA 和 H2S）（KNu = 0.3343-0.4188 s(-1))。通过使用高效液相色谱法和高分辨率 MS 分析，对亲核试剂与 4-甲基-1,2-苯醌之间的反应产物进行了表征。这项研究首次证明，抗氧化剂化合物、H2S 和葡萄酒黄烷醇可以在特定条件下优先与氧化诱导的醌类物质反应，为它们的保护作用提供了一种机制。
