不同pH条件下TSs的形成机理及其与TFs的竞争性形成研究

采用液态发酵的方式,结合不同的pH条件,通过酶促氧化儿茶素生成相应聚酯型儿茶素（Theasinensins, TSs）或茶黄素（Theaflavins, TFs）的单体物质来深入探讨TSs的形成机理及其与TFs的竞争性形成。结果表明,酸性条件下,TSs的单体物质能够持续生成,而且一直积累;中性和碱性条件下生成的TSs单体物质达到最大值的时间很短,稳定性较差。不同pH条件下,由于自身氧化还原电位值的高低,各个儿茶素单体之间被氧化而消耗的速率有所差别,而且基于生成TSs和TFs需要共同的儿茶素底物,因此两者的形成具有竞争性。pH=6和中性条件下EGCG和EGC转化形成TSs单体的量高于形成TFs的量,而pH=5水平下则相反。

Formation Mechanism of TSs and Competitive Formation Between TSs and TFs under Various pH

To illustrate the formation mechanism of theasinensins (TSs) and the competitive formation between TSs and theaflavins (TFs), catechins((EGCG, EGC, EC and ECG) were oxidized to form TSs monomers or TFs monomers by enzymatic oxidation and the experiments were performed by liquid fermentation under dif ferent pH values. The results showed that the TSs monomers were synthesized and accumulated continuously under acidic conditions, while the peaks of TSs monomers appeared in a short time but showed poor stability under neutral or alkaline conditions. Due to the magnitudes of the oxidation reduction potential (ORP) are variable for catechin s, the enzymatic oxidative rates of catechins are different under different pH conditions. For the reason that there was a competition between the formation of TSs and TFs:the content of TSs monomers transformed by EGCG and EGC was higher than TFs monomers under the neutral condition or pH=6, however, conversely under the condition pH=5.