Sensory evaluation, quantitative chemical analysis, and untargeted metabolomics based on ultra-high performance liquid chromatography-quadrupole exactive orbitrap-mass spectrometry (UPLC-Q-Exactive-MS) were applied to investigate the pattern of changes in the major non-volatile components of Liupao tea during the aging process. Tea samples were collected before aging and after 1 to 6 months of aging. The results showed that as aging progressed, the tea infusion gradually turned a deeper and brighter red; the aroma evolved toward a sweeter and more aged profile, and the taste became progressively mellower, with a significant improvement in overall sensory quality. Quantitative chemical analysis revealed that the levels of tea polyphenols, free amino acids, caffeine, and flavonoids decreased with aging time, while that of theabrownins significantly increased (P < 0.001). Metabolomic profiling identified a total of 164 non-volatile compounds, among which 48 were classified as key differential metabolites based on variable importance in projection (VIP) values and statistical significance (P < 0.05). Among these, 9 metabolites such as xanthine were significantly up-regulated after 6 months of aging, while 39 metabolites such as 5-methyluridine were significantly down-regulated. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that metabolic pathways related to caffeine, purines, and pyrimidines played crucial roles in regulating the relative abundance of these key differential metabolites, thereby contributing to the development of the flavor quality of Liupao tea.

Stir bar sorptive extraction (SBSE) combined with gas chromatography-mass spectrometry (GC-MS) was used to detect the volatile composition of 20 Anjibaicha samples, and gas chromatography-olfactometry-mass spectrometry (GC-O-MS) combined with relative odor activity value (ROAV) was utilized to identify its key aroma-active compounds. Results showed that 109 volatile compounds were detected in the tea samples. Among them, geraniol, diisobutyl phthalate, phytol, methyl salicylate, cis-jasmone, linolenic acid, and linalool were the most abundant components. It was found that the contents of volatile components in different grades of Anjibaicha varied greatly. Moreover, a total of 34 common characteristic peaks were selected to establish a fingerprint of the volatile components of Anjibaicha. Sixteen compounds were identified as key aroma-active compounds of Anjibaicha, including trans-β-ionone, geraniol, linalool, hexanal, heptanal, (E)-2-heptenal, α-ionone, and (Z)-3-hexenyl hexanoate.

Green tea was made from one bud with two leaves from the tea cultivar Longjing 43 by stir frying, roasting, steaming or sun drying. Stir bar sorptive extraction (SBSE) combined with gas chromatography-olfactometry-mass spectrometry (GC-O-MS) was applied to analyze the influence of different manufacturing processes on the key aromaactive compounds of green tea. The results showed that 31, 27, 25 and 30 key aroma-active compounds were respectively identified from stir-fried green tea, roasted green tea, steamed green tea and sun-dried green tea, which all had floral, fruity and green flavors. Totally, 13 key aroma-active compounds were common to these 4 types of green tea, including β-ionone, naphthalene, linalool, linalool oxide I, geraniol, 1-octene-3-ol, 2-heptanone, heptanal, hexanal, (Z)-3-hexenyl acetate, (E,E)-2,4-decadienal, α-ionone, and phenylethyl alcohol. It was found that β-ocimene and (Z)-hex-3-enyl 2-methylbutyrate contributed greatly to the aroma characteristics of stir-fried green tea; 2-pentylfuran, phenylacetaldehyde and α-terpineol contributed greatly to the aroma characteristics of roasted green tea; and geranylacetone, γ-terpinene and α-citral contributed greatly to the aroma characteristics of sun-dried green tea. The results obtained from this study will help to understand the formation mechanism of green tea aroma quality and to develop directional processing and regulation technologies for green tea aroma quality.

In this study, the volatile components and key aroma-active compounds of 13 representative Huiming tea samples were analyzed using stir bar sorptive extraction (SBSE) combined with gas chromatography-olfactometry-mass spectrometry (GC-O-MS). Results showed that a total of 120 volatile components were identified, mainly including 26 alcohols, 26 esters, and 14 ketones. Among them, the contents of the aroma compounds geraniol, 2,2,4-trimethyl-3-hydroxypentyl isobutyrate, indole, (Z)-jasmone, and 1-octen-3-ol were the highest. Moreover, a total of 42 key aroma-active compounds were identified by GC-O analysis, including 2-ethyl-3,5-dimethylpyrazine, 6-methyl-5-heptene-2-one, linalool, (Z)-3-hexenyl butanoate, 3,5-octadiene-2-one, and (E)-β-ionone, which played an important role in the formation of the fresh and floral aromas of Huiming tea. The results of this study will contribute to revealing the chemical basis of the aroma quality of Huiming tea, and provide a theoretical basis for improving the aroma quality of Huiming tea.

To elucidate the chemical material basis of the flavor quality of Chongjue Luohan tea, four representative tea samples (Zifu, Ankang, Ping’an and Jufu teas) were analyzed by sensory evaluation and metabolomics based on ultra-high performance liquid chromatography-quadrupole-mass spectrometry (UPLC-Q-MS). The results showed that Luohan tea contained higher levels of tea polyphenols, ranging from 13.7% to 18.1%, than traditional black tea (9.6%). In addition, a total of 206 secondary metabolites were identified in Luohan tea, including flavonoids (71), amino acids and their derivatives (31), organic acids (24), nucleotides and their derivatives (19), phenolic acids (16), alkaloids (12), and saccharides and their derivatives (7). Multivariate statistical analysis pinpointed 46 differential metabolites. Notably, Zifu and Ankang tea samples contained higher levels of bitter and astringent components, such as flavanols, proanthocyanidins and flavanol glycosides, whereas Ping’an and Jufu tea samples were richer in umami and sweet components, such as L-asparagine and L-theanine. The results of this study provide a reference for research to develop new types of Luohan tea.