Non-targeted metabolomics analysis reveals dynamic changes of volatile and non-volatile metabolites during oolong tea manufacture. (February 2020)

• Record Type: Journal Article
• Authors: Chen, Si; Liu, Huihui; Zhao, Xiaoman; Li, Xinlei; Shan, Wenna; Wang, Xiaxia; Wang, Shanshan; Yu, Wenquan; Yang, Zhenbiao; Yu, Xiaomin
• Is Part Of: Food research international. Volume 128(2020)
• Publication Date: 2020-02
• Subjects: Oolong tea -- Tea processing -- Metabolomics -- UPLC-QTOF MS -- GC-TOF MS -- Tastes -- Aromas; Food -- Analysis -- Periodicals; Food industry and trade -- Periodicals; Food industry and trade -- Canada -- Periodicals; Food Technology -- Periodicals; Food -- Periodicals; Food-Processing Industry -- Periodicals; Aliments -- Industrie et commerce -- Périodiques; Aliments -- Industrie et commerce -- Canada -- Périodiques; Aliments -- Recherche -- Périodiques; Food industry and trade; Canada; Periodicals; Electronic journals; 664.005
• DOI: 10.1016/j.foodres.2019.108778
• Languages: English
• ISSNs: 0963-9969

Abstract

Graphical abstract: Highlights: Metabolomics was used to analyze flavor metabolites during oolong tea processing. A stepwise changing pattern in volatile/non-volatile metabolites was shown. The turnover stage promotes the formation of characteristic flavors in oolong tea. Prolonged indoor withering contributes to aroma accumulation in oolong tea. Abstract: 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.