Bradshaw Mark P, Cheynier Veronique, Scollary Geoffrey R, Prenzler Paul D
National Wine and Grape Industry Centre, Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW 2678, Australia.
J Agric Food Chem. 2003 Jul 2;51(14):4126-32. doi: 10.1021/jf034139f.
An examination of the ascorbic acid-induced oxidation of (+)-catechin was carried out. Using varying concentrations of ascorbic acid in a model white winebase, it was observed that there are at least two distinct steps in its oxidation process. The first step involves the formation of species that absorb in the visible region of the spectrum, while the second step generates species of less or no absorbance in the visible region. The first step reaches an absorbance maximum when ascorbic acid is completely oxidized. In winebase solutions containing both ascorbic acid and (+)-catechin, the lag period prior to the onset of (+)-catechin oxidation was dependent on the concentration of ascorbic acid. It was also observed that the end of the lag period corresponds to the complete oxidation of ascorbic acid. Xanthylium cations were identified as a species responsible for the increase in absorbance at 440 nm post lag period. The implication of the results, for establishing a chemical basis to the ascorbic acid crossover from antioxidant to pro-oxidant, is discussed.
对抗坏血酸诱导的（+）-儿茶素氧化进行了研究。在模拟白葡萄酒基质中使用不同浓度的抗坏血酸，观察到其氧化过程至少有两个不同的步骤。第一步涉及形成在光谱可见区域有吸收的物质，而第二步产生在可见区域吸收较少或无吸收的物质。当抗坏血酸完全氧化时，第一步达到最大吸光度。在同时含有抗坏血酸和（+）-儿茶素的葡萄酒基质溶液中，（+）-儿茶素氧化开始前的延迟期取决于抗坏血酸的浓度。还观察到延迟期的结束对应于抗坏血酸的完全氧化。黄嘌呤阳离子被确定为延迟期后在440nm处吸光度增加的物质。讨论了这些结果对于建立抗坏血酸从抗氧化剂转变为促氧化剂的化学基础的意义。
