Mengcong Zhang

Wuyi Rock Tea (WRT) is cherished for its exceptional “rock flavor” and its quality shows obvious regional differences. However, the flavor characteristics of Primary Wuyi Rock Teas (PWRTs) from different production areas remain unclear. Here, the Camellia sinensis var. sinensis cv. ‘Rougui’ and ‘Shuixian’, two quintessential cultivars for making WRT, planted in Zhengyan, Banyan, at high elevations, and Waishan production areas were used to make PWRTs. We conducted a comprehensive comparison of the sensory attributes, volatile organic compounds (VOCs), and macro-compositions of PWRTs of ‘Rougui’ and ‘Shuixian’ cultivars from different producing areas. Sensory evaluation indicated that both ‘Rougui’ and ‘Shuixian’ PWRTs from Zhengyan exhibited the best flavor qualities, followed by those from Banyan, at high altitudes, and Waishan production areas. The results of the determination and analysis of VOCs showed 680 VOCs in ‘Rougui’ and ‘Shuixian’ PWRTs, and that the different production areas mainly influenced the quantitative pattern of VOCs and rarely the qualitative composition. Integrated multivariate statistical analysis methods revealed that benzyl alcohol, hotrienol, butanoic acid, 2-methyl-, hexyl ester, benzene, (2-nitroethyl)-, and geranyl isobutyrate may be the key VOCs affecting the aroma differences in PWRTs from different production areas. In addition, water-extractable substances, tea polyphenols, caffeine, and free amino acids may be the important macro-compositions that distinguish PWRTs from different production areas. The metabolite basis for differences in the flavor qualities of PWRTs across production areas was elucidated, which may be helpful for the production of high-quality WRT.

The enzymatic reaction stage (ECS) of oolong tea processing plays an important role in the formation of the flavor quality of the oolong tea. To investigate the dynamic changes in the volatile and non-volatile components in the leaves of oolong tea during the ECS, metabolomic studies were carried out using the leaf samples collected at different stages of the ECS of Aijiao oolong tea. Out of the identified 306 non-volatile metabolites and 85 volatile metabolites, 159 non-volatile metabolites and 42 volatile metabolites were screened out as key differential metabolites for dynamic changes during the ECS. A multivariate statistical analysis on the key differential metabolites showed that the accumulations of most metabolites exhibited dynamic changes, while some amino acids, nucleosides, and organic acids accumulated significantly after turning-over treatment. The evolution characteristics of 27 key precursors or transformed VOCs during the ECS of Aijiao oolong tea were clarified, and it was found that the synthesis of aroma substances was mainly concentrated in lipids as precursors and glycosides as precursor pathways. The results revealed the dynamic changes in the flavor metabolites in the ECS during the processing of Aijiao oolong tea, which provided valuable information for the formation of the characteristic flavor of Aijiao oolong tea.

Understory planting affects the growth environment of tea plants, regulating the tea plant growth and the formation of secondary metabolites, which in turn affects the flavor of Xiaobai white tea. The present research adopted biochemical composition determination, widely targeted volatilities (WTV) analysis, multivariate statistical analysis, and odor activity value (OAV) analysis to analyze the characteristics in the macro-composition and volatile compounds of understory white tea. The sensory evaluation results indicated that understory Xiaobai white tea (LWTs) was stronger than ordinary Xiaobai white tea (PWTs) in terms of the taste of smoothness, sweetness, and thickness as well as the aromas of the flower and sweet. Understory planting reduced light intensity and air temperature, increased air humidity, organic matter, total nitrogen, and available nitrogen contents, which improved the growth environment of tea plants. The phytochemical analysis showed that the water-extractable substances, caffeine, flavonoids, and soluble sugar contents of understory tea fresh-leaf (LF) were higher than those of ordinary fresh-leaf (PF). The phytochemical analysis showed that the free amino acids, theaflavins, thearubigins, water-extractable substances, and tea polyphenols contents of LWTs were significantly higher than those of PWTs, which may explain the higher smoothness, sweetness, and thickness scores of LWTs than those of PWTs. The 2-heptanol, 2-decane, damasone, and cedar alcohol contents were significantly higher in LWTs than in PWTs, which may result in stronger flowery and sweet aromas in LWTs than in PWTs. These results provide a firm experimental basis for the observed differences in the flavor of LWTs and PWTs.