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• RGT and SXT exhibit distinctive different sensory and volatile profiles. • A total of 12 odor-active compounds (OACs) with OAV > 1 are identified as key OACs. • Eight OACs are commonly shared between RGT and SXT, but with different contents. • The unique key OACs of RGT are (E) -linalool oxide and (Z) -jasmone. • The unique key OACs of SXT are β-cyclocitral and α-ionone. The distinctive fragrance of Wuyi Rock Tea (WRT) has garnered high attention in recent years. Herein, we conducted a comprehensive comparison of the sensory attributes and odor-active compounds (OACs) between two quintessential WRTs, namely Rougui (RGT) and Shuixian (SXT). Sensory analysis revealed that RGT exhibited a more pronounced fruity aroma, while SXT had a more complex and intricate sensory profile. By using gas chromatography-olfactory mass spectrometry (GC-O-MS) and two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOF-MS) analyses, 26 OACs were identified. Among them, 12 compounds with odor activity values > 1 were recognized as key OACs. Noteworthily, eight compounds, including 6-methyl-5-hepten-2-one, 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, linalool, methyl salicylate, geraniol, (E) -β-ionone, and (E) -nerolidol, were shared by both teas. The unique compounds for RGT were (E) -linalool oxide and (Z) -jasmone, while those for SXT were β-cyclocitral and α-ionone. These findings offer valuable insights for better understanding the flavor differences between the two most important types of WRT. [ABSTRACT FROM AUTHOR]

• Green tea phenolic profile was changed massively by tyrosinase incubation. • Pre- & post-oxidation of green tea phenolics had similar anti-obesity effect. • Pre- & post-oxidation of green tea phenolics had similar effect on gut microbiota. • Anti-obesity effect of tea was associated with the alteration in gut microbiota. Green and black teas are regarded to possess therapeutic potential for the treatment of obesity, however it is not clear which tea performs better in body weight control. In this study, aiming to eliminate cultivar variation, green tea phenolics (GTP) were oxidized by tyrosinase to obtain oxidized tea phenolics (OTP). Thereafter, their anti-obesity effect on high-fat diet induced obese mice were compared. The results showed that despite their distinctive phenolic profiles, GTP and OTP exerted similar anti-obesity properties after 12 weeks of dietary intervention. Furthermore, cecal microbiota profiling exhibited comparable modulatory effects of GTP and OTP on multiple bacterial taxa, including Parabacteroides distasonis , Bifidobacterium , Prevotella , and Akkermansia muciniphila , which were strongly associated with obesity related indexes. Putative bacterial function profiling implicated that both GTP and OTP might regulate the lipid metabolism similarly. Collectively, the oxidation of GTP did not influence the anti-obesity and gut microbiota modulatory effects to any large extent. [ABSTRACT FROM AUTHOR]

• 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]

• A novel approach to flavor tea while retaining antioxidant activity was addressed. • The fermented tea with W. cocos imparted a jasmine-like & citrus-like flavor. • Methy anthranilate, linalool & 2-phenylethanol were identified as key odorants. • Upscaling to bioreactor (2 L) was succesfully applied. • 80% of antioxidant activity of green tea was preserved after fermentation. In response to the increasing interest of western consumers in high antioxidant activity of green tea but their low acceptance of its green odor, we employed a new starter culture, Wolfiporia cocos to tune flavor of green tea infusion. After submerged fermentation for 17 h, W. cocos changed the characteristic green odor to an attractive floral, jasmine-like, and slightly citrus-like flavor while preserving most of in vitro antioxidant activity. By application of mSBSE-GC-MS-O combined with sensorial tests, the formed pleasant aroma was mainly attributed to methyl anthranilate (OAV 802), linalool (OAV 190), 2-phenylethanol (OAV 165), and geraniol (OAV 118). Concurrently, the catechin profile determined by UHPLC-MS showed diverse reduction rates (10–50%) for the individual catechins after fermentation. Nevertheless, up to 80% of in vitro antioxidant activity in DPPH assay was preserved. Overall, our findings provide an innovative approach to naturally flavor green tea while retaining the antioxidant activity. [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]