Dynamic Changes in Metabolite Profiles during the Processing of Wuyi Rock Tea

To investigate the changes in biochemical components during the processing of Wuyi rock tea, this study compared the flavor characteristics of Wuyi rock tea made from three major oolong tea varieties (‘Rougui’, ‘Shuixian’ and ‘Dahongpao’) and a major variety of Wuyi rock tea (‘Baijiguan’). Moreover, the metabolite composition of tea samples at different production stages was analyzed by non-targeted metabolomics based on ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) and headspace solid-phase microextraction-gas chromatography-single quadrupole mass spectrometry (HS-SPME-GC-SQMS) combined with chemometric analysis. The results indicated that the physicochemical properties of the raw materials (tea varieties) played a crucial role in the formation of the flavor of Wuyi rock tea. The tumbling and roasting stages during tea processing significantly drove the variations in the number and abundance of differential metabolites. L-lysine, L-tryptophan, indole, and methyl jasmonate, involved in plant stress responses, played a mediatory role in regulating the metabolites during the tumbling process. This stage significantly promoted the accumulation of bitter compounds such as chrysin, apigenin, and L-tryptophan, while markedly increasing the levels of sweet components such as L-threonine, N-acetyl-D-glucosamine, and L-fucose. A series of volatile compounds that contributed to the floral, fruity and green aroma characteristics of the tumbled samples were generated during this process, including (Z)-3-hexen-1-ol, (E)-nerolidol, phenylacetaldehyde, jasmine lactone, methyl jasmonate, and indole. High-temperature roasting significantly altered the contents of various taste components in tea samples, while causing a significant loss of aroma components such as cyclohexanol, phenylacetaldehyde, phenylacetic acid, and indole. These findings offer valuable insights into the mechanism behind the formation of the flavor of Wuyi rock tea and its processing control.