Nutrition Division, R&D Central Research Laboratories, 1-3 Takaramachi, Taiyo Kagaku Co. Ltd, Yokkaichi, Mie 510-0844, Japan.
Int J Food Sci Nutr. 2010 Mar;61(2):109-24. doi: 10.3109/09637480903292601.
Commercially available tea infusions are the major source of catechins for preparing bottled tea beverages and tea supplements available in the market today. In the present study, we analyzed five tea infusions to measure the total antioxidant capacity (TAC) by oxygen radical absorbance capacity (ORAC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity (DRSC) assays, total polyphenol content by the colorimetric method and individual catechin content by high-performance liquid chromatography. Four major tea catechins were also analyzed for their TAC to reveal differential antioxidant behavior of the tea infusions, resulting in the ORAC and DRSC methods. The correlation coefficients between DRSC and the total polyphenol or total catechin content of the tea infusions were 1.0 and 0.99. However, the values fall to 0.73 and 0.69, respectively, while the ORAC activity was correlated with total polyphenol and total catechin content. Determining the TAC of individual tea catechins showed that ORAC of epicatechin was seven-fold higher than that of epigallocatechin gallate; on the contrary, epigallocatechin gallate showed significantly (P < 0.05) stronger DRSC activity than epicatechin. By evaluating the structure-activity relationship, this study further revealed that OH substitution at the 3' position in pyrogallol moieties contributes to the lower ORAC value of epigallocatechin and epigallocatechin gallate comparing with their non-3'-OH counterparts, such as epicatechin and epicatechin gallate, respectively. Also, numbers of OH substitutions were poorly correlated with the observed ORAC value unlike the DRSC. Overall, results of this study enabled us to hypothesize that substances having a lower TAC value in the ORAC assay compared with that in DPPH assays may pertain to a pro-oxidant effect by generating reactive oxygen species in an aqueous buffer, at a physiological pH. We also propose that substances exhibiting lower TAC value in the ORAC assay compared with that in the DPPH assay are powerful pro-oxidants compared with the substances showing a higher TAC value in the ORAC assay than that in the DPPH assay.
市售茶包是现今市售瓶装茶饮料和茶补充剂中儿茶素的主要来源。在本研究中，我们分析了五种茶包，通过氧自由基吸收能力 (ORAC) 和 2,2-二苯基-1-苦基肼基 (DPPH) 自由基清除能力 (DRSC) 测定法来测定总抗氧化能力 (TAC)，通过比色法测定总多酚含量，通过高效液相色谱法测定各儿茶素含量。还分析了四种主要的茶儿茶素来揭示茶包的 TAC 的差异抗氧化行为，从而产生 ORAC 和 DRSC 方法。DRSC 与茶包中总多酚或总儿茶素含量之间的相关系数分别为 1.0 和 0.99。然而，当 ORAC 活性与总多酚和总儿茶素含量相关时，这些值分别降至 0.73 和 0.69。确定单个儿茶素的 TAC 表明，表儿茶素的 ORAC 是表没食子儿茶素没食子酸酯的七倍；相反，表没食子儿茶素没食子酸酯的 DRSC 活性明显（P < 0.05）强于表儿茶素。通过评估结构-活性关系，本研究进一步表明，在没食子酸基团中的 3' 位的 OH 取代使得表没食子儿茶素和表没食子儿茶素没食子酸酯的 ORAC 值低于其非 3'-OH 对应物，例如表儿茶素和表儿茶素没食子酸酯。此外，OH 取代数与观察到的 ORAC 值的相关性较差，而与 DRSC 相反。总的来说，本研究的结果使我们假设，在 ORAC 测定中与 DPPH 测定相比 TAC 值较低的物质可能通过在生理 pH 下在水性缓冲液中产生活性氧而具有促氧化作用。我们还提出，在 ORAC 测定中与 DPPH 测定相比 TAC 值较低的物质与在 ORAC 测定中 TAC 值高于 DPPH 测定的物质相比，是更强的促氧化剂。
