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The oxidation of wine constituents: An investigation on the effects of oxygen additions, and the role of phenolics, iron and hydroxyl radicals.

机译：葡萄酒成分的氧化：研究添加氧气的影响以及酚类，铁和羟基自由基的作用。

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The following studies were intended to contribute both practical and fundamental information on the process of wine oxidation, and the chemical mechanisms in which key contributing substances such as oxygen (reactive oxygen species), phenolics, and metals intervene. At first, studies on the effects of adding small amounts of oxygen in commercial red wines were performed and novel dissolved oxygen distribution patterns were precisely recorded. At the same time, minimal changes on the wine's phenolic profile were observed, suggesting that these reactions might depend on the presence and concentration of other important substances. Additionally, the presence of wine free radical signals, measured with electron paramagnetic resonance (EPR) spectroscopy, was evaluated. In agreement with the literature, free radical signals were observed only when wine samples were concentrated, or when purified wine phenolic fractions were measured. Nevertheless, it was noted that these signals were enhanced in oxygen rich environments and suppressed under nitrogen rich ones. All of this, led us to advance a theory of oxidation in which oxygen, phenolics, and metal ions are essential in forming a strong free radical, namely hydroxyl radical ( ˙OH), in a "Fenton" reaction, that would be capable of oxidizing most hydroxyl-substituted compounds, thus generating a wide variety of carbonyl compounds, and possibly having an impact in wine color chemistry and flavor. To verify this theory, the ˙OH oxidation of glycerol and ethanol was studied in model solutions and wines. In spite of the strong protective effect displayed by ethanol against this type of wine oxidation, significant amounts of the two main oxidation product of glycerol, namely glyceraldehyde and dihydroxyacetone, were observed. In addition to that, a moderate increase in color was measured when these carbonyl compounds where present in large amounts. The polymers formed, and the reactions mechanism of flavanols, (+)-catechin and (-)-epicatechin, and malvidin-3-glucoside linked by glyceraldehyde were characterized using electrospray tandem mass spectrometry. Therefore, it was shown that ˙OH is the likely compound responsible for the oxidation of glycerol and ethanol in wine, and it was suggested that other hydroxyl-substituted wine substances such as sugars and organic acids probably undergo the same kind of oxidation reactions.
机译：以下研究旨在提供有关葡萄酒氧化过程的实用信息和基础信息，以及有关诸如氧气（活性氧物质），酚类和金属等关键贡献物质介入的化学机理的信息。首先，进行了关于在商业红酒中添加少量氧气的影响的研究，并精确记录了新的溶解氧分布模式。同时，观察到葡萄酒中酚类的变化很小，这表明这些反应可能取决于其他重要物质的存在和浓度。此外，评估了通过电子顺磁共振（EPR）光谱测量的葡萄酒自由基信号的存在。与文献一致的是，仅在浓缩葡萄酒样品或测量纯净的葡萄酒酚类成分时才观察到自由基信号。然而，应注意的是，这些信号在富氧环境中得到增强，而在富氮环境中被抑制。所有这些使我们提出了一种氧化理论，其中氧，酚和金属离子对于在“芬顿”反应中形成强自由基即羟基自由基（＆OH）至关重要。会氧化大多数羟基取代的化合物，从而生成各种各样的羰基化合物，并可能对葡萄酒的颜色化学和风味产生影响。为了验证该理论，在模型溶液和葡萄酒中研究了甘油和乙醇的OH氧化。尽管乙醇显示出对这种类型的葡萄酒氧化的强保护作用，但是仍观察到大量的甘油的两种主要氧化产物，即甘油醛和二羟基丙酮。除此之外，当这些羰基化合物大量存在时，测得颜色适度增加。使用电喷雾串联质谱法表征了形成的聚合物，以及黄烷醇，（+）-儿茶素和（-）-表儿茶素以及通过甘油醛连接的Malvidin-3-葡萄糖苷的反应机理。因此，表明OH可能是导致葡萄酒中甘油和乙醇氧化的化合物，并且表明其他羟基取代的葡萄酒物质如糖和有机酸可能经历相同类型的氧化反应。

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