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• The most remarkable changes in volatiles of WRT occurred during roasting. • Flavanols were promptly oxidized and converted to heterogeneous oxidation products. • Flavonols, phenolic acids, and xanthine alkaloids remained stable during processing. • Central vacuole of tea leaf cells shrunk remarkably during withering. Wuyi Rock tea (WRT), a top-ranking oolong tea, possesses characteristic woody, floral, nutty flavor. WRT flavor is mainly formed during the manufacturing process. However, details regarding its formation process are not fully understood yet. In this study, the dynamics of volatile and phenolic components over the whole manufacturing process of WRT were investigated. During withering, despite minor changes in volatile and phenolic components, the central vacuole shrunk remarkably, which reduced the cell mechanical performance and facilitated the subsequent enzymatic fermentation. During fermentation, approximately 78% of flavan-3-ols in fresh tea leaves were oxidized and converted to a diverse mixture of highly heterogeneous oxidation products, such as theaflavins, whereas flavonols, phenolic acids, and xanthine alkaloids remained stable throughout the manufacturing process. Aldehydes, ketones, and heterocyclic compounds, imparting woody, floral, and nutty scent, were mainly formed during the roasting steps. This detailed information can expand our understanding on the formation of WRT flavor. [ABSTRACT FROM AUTHOR]

• Sensory analysis showed roasting reduced the perceived bitterness of WRT. • Phenolics, purine alkaloids and bitter amino acids decreased after roasting. • Human bitter taste receptors, TAS2R39 and TAS2R14, were robustly activated by WRT. • Roasting reduced the activation of WRT upon TAS2R39 and TAS2R14. The influence of roasting on tea bitterness remains unclear. With Wuyi Rock tea (WRT) as an example, this study investigated the impact of roasting on WRT's bitterness, utilizing an integrated approach involving sensory evaluation, bitter compound profiling, and cell-based calcium imaging. Sensory analysis revealed that roasting effectively reduced the perceived bitterness of WRT. This reduction was supported by decreases in various bitter compounds, including 19 flavanols, 11 flavonols, 12 phenolic acids, 2 purine alkaloids, and 9 bitter amino acids, which diminished by 16%, 26%, 19%, 2%, and 70%, respectively. Furthermore, we established two heterogeneous bitter receptor expression systems: TAS2R39/Gα15-HEK293T and TAS2R14/Gα15-HEK293T cell lines. These systems quantitatively confirmed the reduction in bitterness, demonstrating 51% and 62% decreases in intracellular calcium mobilization within the transfected cells, respectively. These findings provide compelling evidence for the bitterness-ameliorating effect of roasting, expanding our knowledge of the role of roasting in shaping the flavor of tea. [ABSTRACT FROM AUTHOR]