Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 Meiling South Road, Hangzhou, Zhejiang 310008, People's Republic of China; Laboratory of Food Chemistry, Wageningen University, P.O. Box 17, 6700 AA Wageningen, the Netherlands.
Laboratory of Food Chemistry, Wageningen University, P.O. Box 17, 6700 AA Wageningen, the Netherlands.
Food Chem. 2023 Nov 1;425:136446. doi: 10.1016/j.foodchem.2023.136446. Epub 2023 May 24.
Auto-oxidation of flavan-3-ols leads to browning and consequently loss of product quality during storage of ready-to-drink (RTD) green tea. The mechanisms and products of auto-oxidation of galloylated catechins, the major flavan-3-ols in green tea, are still largely unknown. Therefore, we investigated auto-oxidation of epicatechin gallate (ECg) in aqueous model systems. Oxidation products tentatively identified based on MS included δ- or γ-type dehydrodicatechins (DhCs) as the main contributors to browning. Additionally, various colourless products were detected, including epicatechin (EC) and gallic acid (GA) from degalloylation, ether-linked ε-type DhCs, and 6 new coupling products of ECg and GA possessing a lactone interflavanic linkage. Supported by density function theory (DFT) calculations, we provide a mechanistic explanation on how presence of gallate moieties (D-ring) and GA affect the reaction pathway. Overall, presence of gallate moieties and GA resulted in a different product profile and less intense auto-oxidative browning of ECg compared to EC.
在即饮（RTD）绿茶的储存过程中，黄烷-3-醇的自动氧化会导致褐变，从而导致产品质量下降。儿茶素没食子酸酯（ECg）是绿茶中主要的黄烷-3-醇，其自动氧化的机制和产物在很大程度上仍不清楚。因此，我们研究了 ECg 在水相模型系统中的自动氧化。基于 MS 初步鉴定的氧化产物包括 δ-或 γ-型脱氢儿茶素（DhC），它们是褐变的主要贡献者。此外，还检测到各种无色产物，包括去酯化的表儿茶素（EC）和没食子酸（GA）、醚键连接的 ε-型 DhC 以及具有内酯型间黄烷键的 6 种 ECg 和 GA 的新偶联产物。通过密度泛函理论（DFT）计算，我们提供了一个关于儿茶素没食子酸酯中没食子酸酯部分（D 环）和 GA 的存在如何影响反应途径的机制解释。总的来说，与 EC 相比，儿茶素没食子酸酯中没食子酸酯部分和 GA 的存在导致了不同的产物谱和较弱的 ECg 自动氧化褐变。
