Escudero A, Hernández-Orte P, Cacho J, Ferreira V
Department of Analytical Chemistry, Faculty of Sciences, University of Zaragoza, 50.009 Zaragoza, Spain.
J Agric Food Chem. 2000 Sep;48(9):4268-72. doi: 10.1021/jf991177j.
A young white wine that had undergone spontaneous oxidation and showed a strong off-flavor reminiscent of cooked vegetables was demixed by salting out to obtain an ethanolic extract that retained the off-flavor of the wine, as was demonstrated by sensory analysis. This extract, together with a second one obtained from a non-oxidized wine sample, were chromatographed into a reversed-phase HPLC column using a water/ethanol gradient. The column effluents were collected in 14 different fractions that were evaluated for smell. Four fractions were found to differ between oxidized and non-oxidized wine, but only one showed a clear cooked vegetables off-flavor and, when added to a non-oxidized wine, made it significantly more similar to the oxidized wine. The fraction was analyzed by GC-MS-olfactometry, which made it possible to identify methional as the single important odorant of the fraction. The odor threshold of methional in a synthetic wine was found to be 0.5 microg L(-)(1). The analytical determination of methional through GC-FPD in several oxidized and non-oxidized wines showed that, in the former, methional can reach more than 200 Odor Units, whereas in the non-oxidized samples, it was not possible to detect methional. The methional concentration was found to increase in wines spiked with both methionol or methionine, which suggests that it can be formed from direct peroxidation of methionol or via Strecker degradation of methionine mediated, probably, by o-quinones formed during wine oxidation.
一款年轻的白葡萄酒发生了自然氧化，呈现出强烈的异味，类似煮熟蔬菜的味道。通过盐析将其分离，得到一种乙醇提取物，感官分析表明该提取物保留了葡萄酒的异味。将此提取物与从未氧化葡萄酒样品中获得的另一种提取物一起，使用水/乙醇梯度在反相高效液相色谱柱上进行色谱分析。柱流出物收集在14个不同的馏分中，并对其气味进行评估。发现有四个馏分在氧化葡萄酒和未氧化葡萄酒之间存在差异，但只有一个馏分呈现出明显的煮熟蔬菜异味，当将其添加到未氧化葡萄酒中时，会使其显著更接近氧化葡萄酒。通过气相色谱-质谱-嗅觉测量法对该馏分进行分析，从而能够鉴定出甲硫醛是该馏分唯一重要的气味物质。发现在合成葡萄酒中甲硫醛的气味阈值为0.5微克/升。通过气相色谱-火焰光度检测法对几种氧化和未氧化葡萄酒中甲硫醛的分析测定表明，在氧化葡萄酒中，甲硫醛含量可超过200气味单位，而在未氧化样品中则无法检测到甲硫醛。发现添加了甲硫醇或甲硫氨酸的葡萄酒中甲硫醛浓度会增加，这表明它可能由甲硫醇的直接过氧化作用形成，或者可能通过葡萄酒氧化过程中形成的邻醌介导的甲硫氨酸的斯特雷克降解形成。
