Black tea (BT) is rich in dietary antioxidants, but its antioxidant composition has not been fully understood. To identify the true antioxidants occurring in BT, we established an approach based on 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay coupled with ultra-high performance liquid chromatography-high resolution mass spectrometry (DPPH-UHPLC-HRMS). The employment of HRMS enable us to detect trace antioxidants, resolve co-eluted antioxidants, and characterize chemical structures of unknown antioxidants. In total, 56 phenolic compounds were screened as potential antioxidants from 106 compounds identified in BT. Catechol and pyrogallol were revealed as the key substructures in enhancing the antioxidant abilities of phenolic compounds. During BT brewing, high temperature with extended time promote antioxidant leaching but may induce the degradation of esterified and glycosylated compounds such as theaflavin-3-gallate and rutin. In conclusion, this work identified the true antioxidant constituents of BT, their structural characteristics, and their dynamic changes under various brewing conditions.

中文翻译：

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通过将体外清除自由基的方法与UHPLC-HRMS分析相结合，揭示了红茶的抗氧化特性。

红茶（BT）富含饮食中的抗氧化剂，但其抗氧化剂成分尚未得到充分了解。为了鉴定在BT中存在的真正抗氧化剂，我们建立了一种基于2,2-二苯基-1-picylhydrazyl自由基清除试验结合超高效液相色谱-高分辨率质谱（DPPH-UHPLC-HRMS）的方法。HRMS的使用使我们能够检测痕量的抗氧化剂，分解共洗脱的抗氧化剂并表征未知抗氧化剂的化学结构。总共从BT中鉴定的106种化合物中筛选出56种酚类化合物作为潜在的抗氧化剂。儿茶酚和邻苯三酚是增强酚类化合物抗氧化能力的关键亚结构。在BT酿造过程中，高温和延长时间会促进抗氧化剂的浸出，但可能导致酯化和糖基化的化合物（如茶黄素-3-没食子酸酯和芦丁）降解。总之，这项工作确定了BT的真正抗氧化剂成分，其结构特征以及它们在各种酿造条件下的动态变化。