Institute of Plasma Technology, Korea Institute of Fusion Energy, Gunsan, Republic of Korea.
Department of Food Science and Biotechnology, Daegu University, Gyeongsan, Republic of Korea.
Sci Rep. 2022 Sep 13;12(1):15396. doi: 10.1038/s41598-022-19806-0.
The efficient dimerization of (-)-Epigallocatechin gallate (EGCG), which is the major bioactive constituent isolated from the leaves of Camellia sinensis, was initially reported without changes in its stereochemistry using low-temperature plasma. The contribution of plasma during the dimerization of EGCG in a methanolic solution was quantified using a major factor, with the major factor demonstrated based on the contents of newly generated products, in this case the sum of oolonghomobisflavans A and B depending on the plasma treatment method. Samples were treated in three methods: plasma direct treatment, an indirect treatment using only reactive species, and an indirect treatment using effects other than those by reactive species. Ozone was identified as a major factor during the plasma treatment, and the operating ranges of the ozone concentration for regulated dimerization were evaluated. The mechanism by which EGCG synthesizes dimers A and B during the treatment process using low-temperature plasma was investigated using the derived major factor and prior literature. The ozone generated by the plasma reacted with methanol to form formaldehyde, and dimers A and B were synthesized by oligomers through a methylene-bridge by the formaldehyde. A plausible pathway of regulated dimerization was deduced based on these results, and the mechanism of EGCG dimerization by plasma is described using this pathway.
(-)-表没食子儿茶素没食子酸酯（EGCG）是从茶树叶子中分离出来的主要生物活性成分，最初报道了其在低温等离子体作用下立体化学不变的高效二聚化。使用主要因素定量评估了 EGCG 在甲醇溶液中二聚化过程中等离子体的贡献，主要因素是基于新生成产物的含量确定的，在这种情况下，根据等离子体处理方法，主要因素取决于乌龙同源二黄烷 A 和 B 的总和。样品通过三种方法进行处理：等离子体直接处理、仅使用反应性物质的间接处理和不使用反应性物质的其他影响的间接处理。臭氧被确定为等离子体处理过程中的主要因素，并评估了调节二聚所需的臭氧浓度的操作范围。使用推导的主要因素和先前的文献研究了使用低温等离子体处理过程中 EGCG 合成二聚体 A 和 B 的机制。等离子体产生的臭氧与甲醇反应生成甲醛，通过甲醛，二聚体 A 和 B 通过亚甲基桥由低聚物合成。基于这些结果推断出了一种受调控的二聚化的可能途径，并使用该途径描述了等离子体作用下 EGCG 的二聚化机制。
