Graduate School of Biomedical Sciences, Nagasaki University.
Chem Pharm Bull (Tokyo). 2020;68(12):1131-1142. doi: 10.1248/cpb.c20-00295.
Black tea accounts for 70-80% of world tea production, and the polyphenols therein are produced by enzymatic oxidation of four tea catechins during tea fermentation. However, only limited groups of dimeric oxidation products, such as theaflavins, theasinensins, and theacitrins, have been isolated from black tea and chemically characterized. This is largely because of the complexity and heterogeneity of the oxidation products. To determine structures and production mechanisms of uncharacterized black tea polyphenols, in vitro model fermentation experiments using pure catechins and polyphenol oxidase have been applied, and basic oxidation mechanisms have been established. Contemporary methods, such as LC-MS, are also effective to identify catechin oxidation products in black tea. Despite ongoing efforts, almost 60% of the solids in black tea infusion remain uncharacterized. These compounds include the so-called thearubigins, which are a heterogeneous mixture of uncharacterized catechin oxidation products with oligomeric structures. This review summarizes the current knowledge of the production mechanisms of representative black tea polyphenols and presents recent progress in characterization of thearubigins.
红茶占世界茶叶产量的 70-80%，其多酚类物质是在茶叶发酵过程中由四种茶儿茶素经酶促氧化产生的。然而，从红茶中分离和化学表征的二聚氧化产物仅限于有限的几类，如茶黄素、茶红素和茶褐素。这主要是因为氧化产物的复杂性和异质性。为了确定未表征的红茶多酚的结构和产生机制，已经应用了使用纯儿茶素和多酚氧化酶的体外模型发酵实验，并建立了基本的氧化机制。当代的方法，如 LC-MS，也可以有效地鉴定红茶中的儿茶素氧化产物。尽管在不断努力，但红茶浸提物中仍有近 60%的固体成分未被表征。这些化合物包括所谓的茶褐素，它是一种未表征的儿茶素氧化产物的混合物，具有寡聚结构。本综述总结了代表性红茶多酚产生机制的现有知识，并介绍了茶褐素表征的最新进展。
