Metal Complexes and their Role in Wine Chemistry

To further understand the speciation of transition metals in wine, the stability constants of Cu(II), Fe(II) and Zn(II) complex species formed with a range of organic acids found in wine were investigated in both aqueous and 12.5% ethanol solution (25°C, I = 0.1 M KCl). When higher concentrations of metal complexes are formed at the wine pH of 3.25, which consequently results in a lower free metal ion concentration, decreased production of xanthylium ion pigments and decreased rates of caffeic acid oxidation are observed. In contrast, higher concentrations of metal complexes generally resulted in increased ascorbic acid oxidation. When higher concentrations of metal complexes are formed at the wine pH of 3.25, which consequently results in a lower free metal ion concentration, decreased production of xanthylium ion pigments and decreased rates of caffeic acid oxidation are observed. In contrast, higher concentrations of metal complexes generally resulted in increased ascorbic acid oxidation.

为进一步解析葡萄酒中过渡金属的形态分布（speciation），本研究针对葡萄酒中常见的多种有机酸与Cu(II)、Fe(II)及Zn(II)形成的配合物，分别在纯水体系及体积分数12.5%的乙醇溶液中（25℃，离子强度I=0.1 M KCl）测定了其稳定常数。当在葡萄酒pH 3.25的条件下生成更高浓度的金属配合物时，会随之降低游离金属离子浓度，此时可观察到黄鎓离子（xanthylium ion）色素的生成量减少，咖啡酸的氧化速率也有所减慢。与之相反，更高浓度的金属配合物通常会加速抗坏血酸的氧化。当在葡萄酒pH 3.25的条件下生成更高浓度的金属配合物时，会随之降低游离金属离子浓度，此时可观察到黄鎓离子色素的生成量减少，咖啡酸的氧化速率也有所减慢。与之相反，更高浓度的金属配合物通常会加速抗坏血酸的氧化。