College of Horticulture, Fujian Agriculture and Forestry University, Fuzhou 350002, China; FAFU-UCR Joint Center for Horticultural Biology and Metabolomics, Fujian Provincial Key Laboratory of Haixia Applied Plant Systems Biology, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
College of Horticulture, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
Food Res Int. 2020 Feb;128:108778. doi: 10.1016/j.foodres.2019.108778. Epub 2019 Nov 8.
Oolong tea is a partially fermented tea with distinct tastes and aromas. However, the dynamic biochemical changes during oolong tea processing are not well understood. In this study, we performed metabolomics-based profiling of non-volatile and volatile constituents of oolong tea during its entire processing procedures by UPLC-QTOF MS and GC-TOF MS. A step-wise change of tea metabolome was observed, where catechins and oxidized products, flavonol glycosides and amino acids were identified as key discriminate metabolites. The ZuoQing process comprising alternating YaoQing and TanQing steps was deemed most critical for key metabolic transformation. Extensive YaoQing facilitated the oxidative polymerizations of catechins into theaflavins and proanthocyanidins, lowering the astringency in raw tea. Two direct terpene precursors farnesyl pyrophosphate and geranyl pyrophosphate accumulated to high levels during ZuoQing, which provided more substrates for the synthesis of downstream volatile terpenes. Moreover, both YaoQing and prolonged TanQing facilitated the formation of terpenes as well as fatty acid and benzenoid-derived volatiles, which contributed to the fruity and floral fragrances in oolong tea. The fixation step not only converted amino acids into aromatic compounds, but also lowered the amounts of flavonol glycosides, potentially improving the flavor quality of the final tea product. This study provides a comprehensive profile of flavor-related metabolic changes during oolong tea processing and will contribute to better quality control and flavor improvement of oolong tea.
乌龙茶是一种部分发酵的茶，具有独特的口感和香气。然而，乌龙茶加工过程中的动态生化变化尚不清楚。在这项研究中，我们通过 UPLC-QTOF MS 和 GC-TOF MS 对乌龙茶在整个加工过程中的非挥发性和挥发性成分进行了基于代谢组学的分析。观察到茶代谢组的逐步变化，其中儿茶素和氧化产物、黄酮醇糖苷和氨基酸被鉴定为关键区分代谢物。包含交替摇青和杀青步骤的做青过程被认为对关键代谢转化最为关键。广泛的摇青促进了儿茶素氧化聚合为茶黄素和原花青素，降低了生茶的涩味。在做青过程中，两种直接的萜烯前体法尼基焦磷酸和香叶基焦磷酸积累到高水平，为下游挥发性萜烯的合成提供了更多的底物。此外，摇青和长时间的杀青都有利于萜烯以及脂肪酸和苯丙素衍生的挥发性化合物的形成，这有助于乌龙茶的果香和花香。固定步骤不仅将氨基酸转化为芳香化合物，还降低了黄酮醇糖苷的含量，可能改善了最终茶产品的风味质量。本研究提供了乌龙茶加工过程中与风味相关的代谢变化的综合概况，将有助于更好地控制和改善乌龙茶的品质和风味。
