The yellowing process is the crucial step to form the characteristic sensory and chemical properties of yellow tea. To investigate the chemical changes and the associations with sensory traits during yellowing, yellow teas with different yellowing times (0–13 h) were prepared for sensory evaluation and chemical analysis. The intensities of umami and green-tea aroma were reduced whereas sweet taste, mellow taste and sweet aroma were increased under long-term yellowing treatment. A total of 230 chemical constituents were determined, among which 25 non-volatiles and 42 volatiles were the key chemical contributors to sensory traits based on orthogonal partial least squares discrimination analysis (OPLS-DA), multiple factor analysis (MFA) and multidimensional alignment (MDA) analysis. The decrease in catechins, flavonol glycosides and caffeine and the increase in certain amino acids contributed to the elevated sweet taste and mellow taste. The sweet, woody and herbal odorants and the fermented and fatty odorants were the key contributors to the characteristic sensory feature of yellow tea with sweet aroma and over-oxidation aroma, including 7 ketones, 5 alcohols, 1 aldehyde, 5 acids, 4 esters, 5 hydrocarbons, 1 phenolic compound and 1 sulfocompound. This study reveals the sensory trait-related chemical changes in the yellowing process of tea, which provides a theoretical basis for the optimization of the yellowing process and quality control of yellow tea.

UV-B radiation is an inevitable abiotic stress, which could induce a series of changes in metabolites and related metabolisms in plants. UV-B-induced metabolic changes in leaves of Camellia sinensis affect the tea quality. This review summarizes the recent investigations into UV-B radiation-induced changes in tea metabolites and their related gene expression, involving in flavonoids, amino acids, and volatile compounds. UV-B radiation induces flavonoid accumulation by increasing expression of key genes in general phenylpropanoid pathway and flavonoid pathway. The UV-B radiation-induced gene expressions in flavonoid biosynthesis pathway also are affected by transcription factors and endogenous phytohormones signaling pathway. Changes of individual amino acids under UV-B radiation exhibit significant variation among different plants, and their responses to UV-B radiation dose are different. These regulations involve in modulation of gene expressions related to GABA shunt and tricarboxylic acid cycle (TCA). Volatile compounds in Camellia sinensis under UV-B radiation are regulated by both metabolites biosynthesis and volatile glycosidic-precursors hydrolysis. In a word, UV-B radiation influences metabolisms in tea in a rather complex way. More researches on UV-B-induced transcriptional regulation, endogenous-phytohormone signal regulation, metabolisms diversions regulation, etc. are needed in the future.