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The storage process has a significant impact on tea quality. Few is known about effect of storage on quality of oolong tea. This study aimed to assess the effect of different storage times on the key chemical components of oolong tea by measuring changes in catechin, free amino acid, and alkaloid content. Variation in the main substances was determined by principal component analysis and heat map analysis. The results revealed notable effects of the storage process on the levels of theanine, epigallocatechin gallate (EGCG), and glutamine. These findings suggest that these compounds could serve as indicators for monitoring changes in oolong tea quality during storage. Additionally, the study observed an increase in the antibacterial ability of tea over time. Correlation analysis indicated that the antibacterial ability against Micrococcus tetragenus and Escherichia coli was influenced by metabolites such as aspartic acid, threonine, serine, gamma-aminobutyric acid, ornithine, alanine, arginine, and EGCG. Overall, this study presents an approach for identifying key metabolites to monitor tea quality effectively with relatively limited data., (© 2024. The Author(s).)

The plant hormone salicylic acid (SA) plays critical roles in plant innate immunity. Several SA derivatives and associated modification are identified, whereas the range and modes of action of SA‐related metabolites remain elusive. Here, the study discovered 2,4‐dihydroxybenzoic acid (2,4‐DHBA) and its glycosylated form as native SA derivatives in plants whose accumulation is largely induced by SA application and Ps. camelliae‐sinensis (Pcs) infection. CsSH1, a 4/5‐hydroxylase, catalyzes the hydroxylation of SA to 2,4‐DHBA, and UDP‐glucosyltransferase UGT95B17 catalyzes the formation of 2,4‐DHBA glucoside. Down‐regulation reduced the accumulation of 2,4‐DHBA glucosides and enhanced the sensitivity of tea plants to Pcs. Conversely, overexpression of UGT95B17 increased plant disease resistance. The exogenous application of 2,4‐DHBA and 2,5‐DHBA, as well as the accumulation of DHBA and plant resistance comparison, indicate that 2,4‐DHBA functions as a potentially bioactive molecule and is stored mainly as a glucose conjugate in tea plants, differs from the mechanism described in Arabidopsis. When 2,4‐DHBA is applied exogenously, UGT95B17‐silenced tea plants accumulated more 2,4‐DHBA than SA and showed induced resistance to Pcs infection. These results indicate that 2,4‐DHBA glucosylation positively regulates disease resistance and highlight the role of 2,4‐DHBA as potentially bioactive molecule in the establishment of basal resistance in tea plants. [ABSTRACT FROM AUTHOR]

Wuyi rock tea (WRT) is typically stored for weeks or months before consumption, and the roasted aroma changes into a floral aroma during the storage. However, little is known about the aroma change that occur during this period. The aroma in WRT during storage was extracted and identified using simultaneous distillation extraction coupled with gas chromatography mass spectrometry, in addition to calculating the odor activity value (OAV) and conducting aroma recombination experiments. The results revealed the emergence of floral aroma with increasing storage time. Alcohols, aldehydes, and aromatics were the main volatile types in WRT. According to partial least squares discriminant analysis, 20 volatiles were crucial variables contributing to the volatile differences in WRT with variations in storage time. The key volatiles causative for the overall aroma of WRT were determined based on their OAVs. In total, 25 volatiles with OAVs >1 were identified as aroma-active compounds. Notably, trans -β-ionone, 2-ethyl-3,5-dimethylpyrazine, linalool, octanal, nonanal, dehydro-β-ionone, and pentylfuran were substantial players in the overall aroma profile of WRT under storage. Based on the results of aroma combination experiments, the contribution of 18 volatiles with OAVs >2 to the overall aroma of WRT was confirmed. The findings augment our comprehension of aroma development in WRT throughout the storage. [Display omitted] • The flavor change of WRT during storage were analyzed by GC-MS, OAV and sensory evaluation. • Dynamic changes of aroma substances occurred in WRT during storage. • Content of aldehydes and heterocyclics increased during WRT storage. • Eighteen aroma-active volatiles were validated by aroma combination experiments. [ABSTRACT FROM AUTHOR]