Understanding the molecular responses of tea leaves to mechanical stress is crucial for elucidating the mechanisms of post-harvest quality formation during oolong tea processing. This study employed an integrated multi-omics strategy to characterize the changes and interactions among metabolomic (MB), transcriptomic (TX), and proteomic (PT) profiles in mechanically stressed tea leaves. Mechanical stress initially activated damage-associated molecular patterns (DAMPs), including Ca²⁺ signaling, jasmonic acid signaling, and glutathione metabolism pathways. These processes subsequently induced quality-related metabolic pathways (QRMPs), particularly α-linolenic acid and phenylalanine metabolism. Up-regulated expression of LOX, ADH1, and PAR genes, together with the increased abundance of their encoded proteins, respectively promoted the accumulation of jasmine lactone, benzyl alcohol, and 2-phenylethanol. These findings indicate that mechanical stress influences the metabolite biosynthesis in tea leaves through coordinated molecular responses. This study provides new insights into the molecular mechanisms underlying tea leaf responses to mechanical stress and a foundation for future investigations into how early molecular events may contribute to post-harvest metabolic changes during oolong tea processing.

This study was undertaken in order to investigate the effects of different drying temperatures (60, 70, 80, 90 and 100 ℃) on the quality of pressed white tea cake made from withered leaves. Various quality components of white tea cake such as aroma, sugar components, polyphenols and amino acids were analyzed using targeted metabolomics based on headspace solid-phase microextraction combined with gas chromatography-time-of-flight mass spectrometry (HS-SPME-GC-TOF-MS). The results showed that the sensory quality score of white tea cake increased first and then decreased with increasing drying temperature, reaching its maximum (90.2) at 80 ℃. The total catechin content of white tea cake dried at 80 and 90 ℃ was significantly lower than that of white tea cake dried at 60, 70 and 100 ℃ (P < 0.05). The contents of total amino acids and refreshing taste amino acids in white tea cake dried at 80 ℃ were significantly higher than those in white tea cake dried at 70 ℃ (P < 0.05). The sugar contents of white tea cake dried at 70 and 80 ℃ were significantly higher than those of white tea cake dried at low temperature (60 ℃) and high temperature (90 and 100 ℃) (P < 0.05). The main volatile substances of white tea cake were generally consistent across all drying temperatures, in which alcohols accounted for a large proportion. The contents of ester aroma substances such as methyl tridecanoate, methyl octanoate, methyl nonanoate and acetic acid lactone in white tea cake dried at 80 ℃ were significantly higher than those in white tea cake dried at 90 and 100 ℃ (P < 0.05). In general, drying at 80 ℃ can improve the refreshing taste and sweetness of pressed white tea cake and the content of pleasant aroma substances, thereby conducing to the quality formation. The appropriate drying temperature for pressed white tea cake, therefore, is 80 ℃. The results can provide reference for the processing technology of white tea cake pressed by withered leaves.

Shaking is one of the key processes contributing to the quality formation of oolong tea. As an abiotic stress factor, mechanical stress leads to a series of physiological and biochemical changes in plants through various biological effects, which has been widely used in the processing of scented black tea, scented white tea, scented green tea and other tea types to improve their quality. In order to ascertain the physiological changes of green tea leaves in response to mechanical stress, postharvest fresh shoots with 3–4 leaves from the tea cultivar ‘Tieguanyin’ were evaluated for changes in water content, photosystem Ⅱ (PS Ⅱ) parameters, antioxidant enzyme activities and subcellular structure under natural spreading or continuous vibration stress treatment after withering. Compared with naturally spread leaves and withered leaves, the water content in the leaves subjected to vibration stress was not significantly different within the first 30 min of vibration (P > 0.05) but was significantly lower at 60 min (P < 0.05). The green-grassy odor became stronger with increasing vibration time, the refreshing aroma became weaker, and the clear compact lamellar structures of the chloroplast and the thylakoid were gradually loosened, deformed, shrunk, and disrupted. The number of starch granules increased significantly at 5 min, and the number of osmiophilic granules increased significantly at 15 min, resulting in the formation of aggregates. The actual photosynthetic efficiency Y (Ⅱ) and photochemical quenching coefficient (qP) of PS Ⅱ generally showed a decreasing trend with increasing vibration time, and the electron transfer rate (ETR) declined initially and then rose. The Y (Ⅱ) and ETR at 5 and 10 min of vibration were significantly lower than those observed in naturally spread leaves (P < 0.05). The quantum yield Y (NO) of non-regulated energy dissipation increased with the prolongation of vibration stress treatment time, and was significantly higher than that of naturally spread leaves at 30 min (P < 0.05). The relative conductivity of tea leaves under vibration stress for 10 min was significantly higher than that of naturally spread leaves (P < 0.05). The activities of ascorbate peroxidase, dehydroascorbate reductase and glutathione reductase in tea leaves under vibration stress for 5 and 10 min were higher than those in naturally spread leaves. Vibration treatment (for up to 30 min) did not show significant variations in water content, but enhanced the green-grassy odor. Continuous vibration treatment caused cell injuries by increasing the cell membrane permeability, thereby facilitating the release of intracellular contents and increasing cell conductivity. At the subcellular level, vibration treatment promoted thylakoid degradation and severely damaged chloroplasts, thus destroying PS Ⅱ stability. Meanwhile, it protected tea leaf cells against mechanical stress-induced damage by elevating the activities of defense enzymes. Taken together, this study lays a foundation for the regulating of shaking during the processing of oolong tea.