To explore the characteristics of volatile compounds in Camellia nanchuanica black tea cultivated at various altitudes, a combination of headspace solid phase microextraction (HS-SPME) and GC/MS, along with multivariate analysis techniques, were employed to analyze the volatile metabolites in fresh leaves and the processed tea.The results revealed 574 substances out of 15 categories from the fresh leaves and a total of 575 substances of 16 categories in the congou black tea.And there was no significant difference in the total amount of volatile metabolites among fresh leaves picked at different altitudes.The aroma of processed black tea(processed by withering, fermentation, and drying)was significantly enriched compared to that of fresh leaves, with higher levels of esters, heterocycles, terpenes, aldehydes, and alcohols contributing to the flavor.Furthermore, the volatile substance of LA-CB (148.67 μg/g) was significantly higher than that of HA-CB(104.27 μg/g).Through orthogonal partial least squares discriminant analysis (OPLS-DA), 113 and 179 differential metabolites were identified from the fresh leaf group and black tea group, respectively.A differential metabolite flavor wheel was established by annotating the flavors of the different metabolites of the black tea group,showing that fruity sweetness was the main aroma characteristic of C.nanchuanica black tea from tea gardens of different altitudes, while the high level of volatile metabolites in LA-CB prolonged its aromatic smell.This result was consistent with sensory evaluation.Further analysis of the relative odor activity values of the metabolites suggested that substances such as 2-isopropyl-3-methoxypyrazine, 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone, benzyl mercaptan, 6-nonenal, and diethyl disulfide play a pivotal role in the formation of the unique aroma profile of C.nanchuanica black tea.Notably, 2-isopropyl-3-methoxypyrazine, with its distinct flavors of nuts, beans, and chocolate, was hypothesized to be a key component that distinguished the aroma characteristics of the processed black tea from its fresh leaves.This study offers theoretical insights into the discrimination of characteristic qualities of C.nanchuanica black tea at different altitudes, as well as the underlying factors contributing to the formation of its aroma quality.
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