关键词: 脱氢聚酯型儿茶素A, 茶黄素-3-没食子酸酯, 歧化途径, 苯骈化途径

Abstract: The aim of this study was to explore several major oxidation pathways of epigallocatechin gallate (EGCG) and the competition mechanism between the disproportionation pathway and the benzene pathway. Dehydrotheasinensin A (DTSA) and theaflavin-3-gallate (TF) were obtained by enzymatic oxidation of mixtures of different proportions of EGCG and epicatechin (EC). The results showed that several products including DTSA and GA were formed from the hydrolysis of EGCG by polyphenol oxidase (POD), while theaflavin-3-gallate (TF-3-G) was formed and the consumption rate of EGCG was increased by 3.86%–4.95% when epicatechin (EC) was added to the reaction solution. The formation rate of DTSA was not significantly changed during the early reaction stage but it was lower in EGCG + EC systems than in the single system during the later stage with a maximum difference of up to 10.84%. The formation of TF-3-G was significantly higher (up to 11.16%) at 5 mmol/L EC than at 2.5 mmol/L EC concentration. The enzymatic oxidation process of EGCG + EC could be divided into four stages: initial stage, dimer formation, change of the main pathways and dimer consumption. At the initial stage, the disproportionation and the benzene pathways were both dominant and their proportions were higher than 85%. At the second stage, the proportion of the benzene pathway was increased with the addition of EC while the proportion of EGCG transformed into DTSA was significantly reduced and the disproportionation pathway was weakened. As the reaction processed, a number of oxidation polymerization pathways gradually appeared in the system and the proportions of other substances were increased. At the third stage, DTSA began to be consumed and TF-3-G was slowly increased. The disproportionation pathway was dominant during the whole process of EGCG enzymatic oxidation.

Key words: dehydrotheasinensin A (DTSA), theaflavin-3-gallate (TF-3-G), disproportionation pathway, benzene pathway