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Shaken black tea (SBT) is a new type of black tea that combines the traditional black tea processing technology with the shaking process of oolong tea. In this study, non-targeted metabolomics analysis based on ultra-high-pressure liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS) was applied to comprehensively analyze the non-volatile metabolites of SBT during the manufacturing process. Using multivariate statistical analysis, 93 compounds were screened as differential compounds. During the whole process of SBT, amino acids, dipeptides, theaflavins and lipids contents showed significant increases, while that of catechins and procyanidin C1 significantly decreased. Compared with fresh leaves, the content of proteinaceous amino acids (PAAs) in the dried black tea increased 1.61-fold, and total catechins decreased to 7.25%. The results of hierarchical clustering analysis (HCA) showed that fermentation is the key process that causes the variations of these metabolites, followed by drying and shaking. The biosynthesis metabolism of amino acids, flavonoids and linoleic acid are abundant, mainly due to the stress response of fresh tea leaves to dehydration and mechanical damage during shaking processing. It is beneficial to explore the quality formation during the production of SBT through comprehensive analysis of the changes in metabolites. • Fermentation led to significant changes in metabolites, followed by drying, shaking. • Shaking process promoted the accumulation of amino acids, dipeptides and theaflavins. • Remarkable increase of dipeptides is mainly in the fermentation and drying process. • Variation of taste compounds, amino acids, flavonoids, and dipeptides, were studied. • Metabolic pathway of key compounds like amino acids, flavonoids, lipids, were revealed. [ABSTRACT FROM AUTHOR]

Yellowing is the key process used to produce the unique yellow tea, but the effect of the yellowing process on tea quality and chemical composition remains unclear. Here, electronic eye and tongue and metabolomics were applied to investigate dynamic changes in tea leaves during the yellowing process for the first time. During the first 18 h of yellowing, the colour of tea leaves was observed becoming yellowish. Compounds related to umami and sweetness (amino acids, catechins, sucrose, phenolic acids, etc.) are at high levels. However, after 24 h of yellowing, the colour of tea becomes darker, with richness of tea infusion decreasing significantly. The levels of most catechins, amino acids, phenolic acids, and glycosidically bound volatiles (GBVs) decreased significantly, whereas betaine, piperidine, theasinensin B, and lysophosphatidylcholines (LPCs) increased significantly. Meanwhile, according to partial least-squares (PLS) analysis, most amino acids and sucrose were positively correlated with umami and sweetness; most catechins and phenolic acids had positively correlated with bitterness and astringency; phaeophorbides were positively correlated with red value (+a*) of tea leaves' colour. This work provides a comprehensive, novel knowledge on the quality and chemical changes of yellow tea during the yellowing process. • Metabolomics and electronic multi-sensors were used for yellow tea study. • A dynamic view was acquired by the determination of quality and metabolites. • Yellow tea quality is optimal after 18 h under 40 °C. • The decline in amino acids and catechins is responsible for taste deterioration. [ABSTRACT FROM AUTHOR]