Identification and Comparison of Aroma-Active Compounds in Different Chinese Dark Teas

To investigate the influence of manufacturing process on the flavor of Chinese dark tea, the volatile profiles of five varieties (Fuzhuan, Pu-erh, Liubao, Bailiang, and Tianjian) were analyzed using gas chromatography–mass spectrometry/olfactometry (GC-MS/O). A total of 178 volatile compounds were identified by GC-MS, among which linalool and its oxides were the most abundant aroma-active components, particularly in Pu-erh tea, which underwent the longest fermentation. GC-O analysis revealed 11 compounds with relative odor activity values (ROAVs) greater than 1, including β-gulonic aldehyde, (E,Z)-2,6-nonadienal, β-isopropenyl, (Z)-4-hexenal, 3-methylbutanal, (E,Z)-2,4-decadienal, (E,E)-2,4-decadienal, hexanal, linalool, and (R/Z)-linalool oxide. These were considered the key aroma-active compounds contributing to the overall aroma of dark tea. Principal component analysis further indicated that the distinctive woody and aged notes of Pu-erh tea were associated with linalool, (E/Z)-linalool oxide, 1,2,3-trimethylbenzene, β-gulonic aldehyde, benzaldehyde, and citronellol. In contrast, α/β-ionone and a series of fatty acid derivatives such as (E,Z)-2,6-nonadienal, (Z)-4-heptenal, (E,Z)-2,4-dodecadienal, (E,E)-2,4-dodecadienal, and hexanal were mainly responsible for sweet, grassy, and herbal notes. These substances are particularly prominent in Fuzhuan and Bailiang teas. Our findings demonstrate that processing techniques significantly affect the aroma quality of dark tea, providing a valuable reference for variety discrimination and process optimization.