Abstract: In order to understand the contribution of stems and leaves to the quality of Keemun black tea, this study analyzed the differences in aroma, taste quality and metabolites among black tea manufactured from tender leaves, tender stems, single buds and intact buds with leaves (mainly one bud with two leaves) from the tea variety ‘Fuzao 2’ by gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), sensory evaluation, and preference evaluation. The results showed that all four black teas were sweet aroma type, and the bud-leaf tea had a strong sweet aroma. The single-bud tea had a fresh and brisk taste. The tender-stem tea scored highest in preference evaluation. Metabolite analysis showed the content of catechins was the highest in the single-bud black tea and the lowest in the tender-stem black tea, while free amino acids were significantly enriched in the tender-stem black tea, reaching up to 80 mg/g. The contents of quercetin and rutin were higher in the stem black tea, while the contents of kaempferol-3-O-glucoside and kaempferol-3-O-rutinoside were the highest in the leaf black tea. The ratio of thearubigins to theaflavins was 11.6, 9.4, 14.6, and 8.2 in black tea made from intact buds with leaves, buds, leaves, and tender stems, respectively. The total amount of volatile compounds in the tender-stem black tea (32.37 μg/g) was significantly lower than that in the bud (100.01 μg/g), leaf (95.67 μg/g), and bud-leaf black tea (92.42 μg/g). The contents of benzaldehyde, benzeneacetaldehyde and indole were higher in the tender stem black tea, while the contents of β-ionone, α-ionone and linalool oxide in the leaf black tea were higher than those in the other three black teas. This study shows that high contents of theanine in tender stems and glycoside aroma precursors in tea leaves contribute primarily to the formation of the quality of Keemun black tea.

Key words: Keemun black tea; sensory evaluation; flavor compounds; volatile compounds; glycosisde compounds