Volatile composition of Fu-brick tea and Pu-erh tea analyzed by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry

Dark tea is a special type of tea that requires microbial fermentation during the post-fermentation process, and its volatile composition is quite different from other tea kinds. The present study aimed at charactering the volatile composition of two typical Chinese dark teas (Fu-brick tea and Pu-erh tea). Volatile compounds from both teas were extracted and analyzed using simultaneous distillation extraction (SDE) combined with two-dimensional gas chromatography-time-of-flight-mass spectrometry (GC x GC-TOFMS). A total of 373 and 408 major aromatic components were tentatively identified in Fu-brick tea and Pu-erh tea, respectively. The relative quantification results showed that ketenes (24.87%), ketones (16.86%), aldehydes (14.36%) and olefine aldehydes (9.11%) were more abundant in Fu-brick teas, while in Pu-erh teas, ketenes accounted for 17.95%, followed by aldehydes (14.51%), ally esters and ketones (11.94% and 10.78%). Multivariate analysis indicated that obvious differences existed in the levels of some aromatic compounds between the two dark teas. Benzaldehyde and benzeneacetaldehyde in Fu-brick teas were considerably lower and accounted for approximately 55% of those in Pu-erh teas; whilst, nonanal and 2-hexenal in Fu-brick tea were twice as high as in Pu-erh tea. The application of pre-enrichment extraction with GC x GC-TOFMS analysis gives a thorough view of the aromatic constituents of dark teas.