Tan Junfeng, de Bruijn Wouter J C, van Zadelhoff Annemiek, Lin Zhi, Vincken Jean-Paul
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.
J Agric Food Chem. 2020 Nov 25;68(47):13879-13887. doi: 10.1021/acs.jafc.0c05716. Epub 2020 Nov 10.
Green tea catechins are well known for their health benefits. However, these compounds can easily be oxidized, resulting in brown color formation, even in the absence of active oxidative enzymes. Browning of catechin-rich beverages, such as green tea, during their shelf life is undesired. The mechanisms of auto-oxidation of catechins and the brown products formed are still largely unknown. Therefore, we studied auto-oxidative browning of epicatechin (EC) and epigallocatechin (EGC) in model systems. Products of EC and EGC auto-oxidation were analyzed by reversed-phase ultra-high-performance liquid chromatography with photodiode array detection coupled to mass spectrometry (RP-UHPLC-PDA-MS). In the EC model system, 11 δ-type dehydrodicatechins (DhCs) and 18 δ-type dehydrotricatechins (DhCs) that were related to browning could be tentatively identified by their MS signature fragments. In the EGC model system, auto-oxidation led to the formation of 13 dihydro-indene-carboxylic acid derivatives and 2 theaflagallins that were related to browning. Based on the products formed, we propose mechanisms for the auto-oxidative browning of EC and EGC. Furthermore, our results indicate that dimers and oligomers that possess a combination of an extended conjugated system, fused rings, and carbonyl groups are responsible for the brown color formation in the absence of oxidative enzymes.
绿茶儿茶素因其对健康有益而闻名。然而，即使在没有活性氧化酶的情况下，这些化合物也很容易被氧化，导致形成褐色。富含儿茶素的饮料，如绿茶，在保质期内出现褐变是不理想的。儿茶素的自动氧化机制以及形成的褐色产物在很大程度上仍然未知。因此，我们在模型系统中研究了表儿茶素（EC）和表没食子儿茶素（EGC）的自动氧化褐变。通过反相超高效液相色谱-光电二极管阵列检测-质谱联用（RP-UHPLC-PDA-MS）分析了EC和EGC自动氧化的产物。在EC模型系统中，可通过其质谱特征碎片初步鉴定出11种与褐变相关的δ型脱氢二聚儿茶素（DhCs）和18种δ型脱氢三聚儿茶素（DhCs）。在EGC模型系统中，自动氧化导致形成13种与褐变相关的二氢茚羧酸衍生物和2种茶黄素。基于形成的产物，我们提出了EC和EGC自动氧化褐变的机制。此外，我们的结果表明，在没有氧化酶的情况下，具有扩展共轭体系、稠环和羰基组合的二聚体和寡聚体是导致褐色形成的原因。
