Panyong Congou black tea (PCT) is one of the most representative and historically famous Congou black teas in China and has been gaining more and more attention for its beneficial health properties. Currently, four grades of PCT are available, based on the raw leaf materials and consumer palatability. The chemical profiles distinguishing different grades of PCT are yet to be defined, nor has the relationship with grade been evaluated. In the present study, chemometric analysis showed that epigallocatechin (EGC), catechin (C), polyphenols, gallic acid (GA), and free amino acids are grade related bio-markers of PCT. These compounds are associated with the sweet and mellow aftertaste of PCT. A total of 34 volatile components were identified, of which the three component types with the highest relative percentages were alcohols (51.34–52.51%), ketones (27.31–30.28%), and aldehydes (12.70–13.18%). Additionally, our results revealed that sweet floral and fruity aromas were positively correlated with six volatile organic compounds (VOCs), 1-pentanol, propyl hexanoate, linalool, cyclohexanone, hexanal, and 2,5-dimethylpyrazine. Clear discrimination was achieved using orthogonal projections to latent structures discriminant analysis (OPLS-DA). The findings provide vital information on the characteristic flavor of each grade of PCT.

Rougui Tea (RGT) is a typical Wuyi Rock Tea (WRT) that is favored by consumers for its rich taste and varied aroma. The aroma of RGT is greatly affected by the process of green-making, but its mechanism is not clear. Therefore, in this study, fresh leaves of RGT in spring were picked, and green-making (including shaking and spreading) and spreading (unshaken) were, respectively, applied after sun withering. Then, they were analyzed by GC-TOF-MS, which showed that the abundance of volatile compounds with flowery and fruity aromas, such as nerolidol, jasmine lactone, jasmone, indole, hexyl hexanoate, (E)-3-hexenyl butyrate and 1-hexyl acetate, in green-making leaves, was significantly higher than that in spreading leaves. Transcriptomic and proteomic studies showed that long-term mechanical injury and dehydration could activate the upregulated expression of genes related to the formation pathways of the aroma, but the regulation of protein expression was not completely consistent. Mechanical injury in the process of green-making was more conducive to the positive regulation of the allene oxide synthase (AOS) branch of the α-linolenic acid metabolism pathway, followed by the mevalonate (MVA) pathway of terpenoid backbone biosynthesis, thus promoting the synthesis of jasmonic acid derivatives and sesquiterpene products. Protein interaction analysis revealed that the key proteins of the synthesis pathway of jasmonic acid derivatives were acyl-CoA oxidase (ACX), enoyl-CoA hydratase (MFP2), OPC-8:0 CoA ligase 1 (OPCL1) and so on. This study provides a theoretical basis for the further explanation of the formation mechanism of the aroma substances in WRT during the manufacturing process.

Flavonoids (especially anthocyanins and catechins) and amino acids represent a high abundance of health-promoting metabolites. Although we observed abscisic acid accumulation in purple leaves and low levels in albino tea leaves, the specific mechanism behind its impact on flavor compounds remains unclear. In this study, we treated tea leaves with exogenous abscisic acid and abscisic acid biosynthesis inhibitors (Flu), measured physiological indicators and conducted comprehensive transcriptomic and metabolomic analyses to elucidate the potential mechanisms underlying color change. Our results demonstrate that abscisic acid treatment induces purple coloration, while Flu treatment causes discoloration in tea leaves. Metabolomic analysis revealed higher levels of four anthocyanins and six catechins in the group treated with abscisic acid in comparison with the control group. Additionally, there was a notable increase in 15 amino acids in the Flu-treated group. Notably, the levels of flavonoids and amino acids showed an inverse relationship between the two treatments. Transcriptomic comparison between the treatments and the control group revealed upregulation of differentially expressed genes encoding dihydroflavonol reductase and uridine diphosphate-glycose flavonoid glycosyltransferase in the abscisic acid-treated group, leading to the accumulation of identified anthocyanins and catechins. In contrast, differentially expressed genes encoding nitrate reductase and nitrate transporter exhibited elevated expression in the group treated with Flu, consequently facilitating the accumulation of amino acids, specifically L-theanine and L-glutamine. Furthermore, our co-expression network analysis suggests that MYB and bHLH transcription factors may play crucial roles in regulating the expression of differentially expressed genes involved in the biosynthesis of flavonoids and amino acids. This study provides insights for targeted genetic engineering to enhance the nutritional and market value of tea, together with the potential application of purple and albino tea leaves as functional beverages. It also offers guidance for future breeding programs and production.

Diabetes remains a critical global public health challenge, posing a growing threat to human health and well-being. White tea is a lightly fermented tea and one of the six traditional tea categories in China. Owing to its rich content of bioactive compounds such as catechins and alkaloids, it has demonstrated potential anti-diabetic properties. However, its precise bioactive components, mechanisms of action, and relevant molecular targets require further investigation. In this study, an integrated approach combining polyphenol-targeted metabolomics, in vitro antioxidant assays, α-glucosidase inhibition tests, network pharmacology analysis, GEO database exploration, molecular docking, and molecular dynamics simulations was employed to identify the potential anti-diabetic compounds, targets, and mechanisms of white tea. The findings revealed that white tea is particularly abundant in 10 bioactive compounds, including epigallocatechin gallate, epicatechin gallate, and catechin, all of which exhibit significant anti-diabetic potential. These compounds were found to exert their effects by interacting with core molecular targets, namely cathepsin V (CTSV) and nucleotide-binding oligomerization domain-containing protein 1 (NOD1), and engaging in pathways related to signal transduction, apoptosis, and immune responses. This study establishes a strong theoretical basis for advancing white tea research and underscores new opportunities for applying natural products in diabetes therapy.