An automatic thermal desorption-gas chromatography-mass spectrometry (ATD-GC-MS) method was developed, optimized and applied in combination with chemometrics for the detection of the aroma components of three different grades (superfine, grade A and grade B) of Rougui oolong tea. In automatic thermal desorption, the operating parameters adsorption temperature, adsorption time and cold trap temperature were optimized by single factor experiments and response surface methodology. The optimal parameters were determined as follows: adsorption temperature of 55 ℃, adsorption time of 37 min and cold trap temperature of -29 ℃. A total of 173 aroma components were identified, 90 of which were common to all the three grades. In addition, a partial least squares discriminant analysis (PLS-DA) model to distinguish the different grades of Rougui oolong tea was established based on the peak areas of the aroma components of Rougui oolong tea. and the distribution of 47 characteristic aroma components in the three different grades of Rougui oolong tea was discussed by hierarchical cluster analysis. The results of this study could provide a theoretical basis for the identification of the aroma quality and grade of Rougui oolong tea.

Automatic thermal desorption-gas chromatography-mass spectrometry (ATD-GC-MS) was used to capture and detect environmental volatile components in Tieguanyin tea at the key stages of the fine manipulation process, and short time series expression miner (STEM) and partial least squares-discriminant analysis (PLS-DA) were used to analyze the volatile components. The results showed that a total of 122 volatile components belonging to eight chemical classes, i.e., alcohols, esters, olefins, alkanes, aldehydes, aromatic hydrocarbons, ketones and other compounds were identified, esters being the major ones. The STEM results showed that the detected volatile components could be divided into 19 trends, and there was significant enrichment in two trend models. Among them, the levels of 2-butanol, ethyl acetate, isovaleraldehyde, 3-methyl-1-butanol, 1-hexanol, 2-heptanol, methyl hexanoate, 6-methyl-5-hepten-2-one, and octyl isobutyrate, which have a special aroma, increased significantly with increasing number of fine manipulation cycles. PLS-DA could effectively distinguish between tossing and sun withering, and seven characteristic volatile components (variable importance in the projection (VIP) > 1) were common to the two stages including (Z)-4-hexen-1-yl acetate, (E)-butanoic acid, 3-hexenyl ester, (E)-3-hexen-1-ol, 2-hexenal, 3-methyl-butanenitrile, (E)-4,8-dimethylnona-1,3,7-triene and (Z)-3,7-dimethyl-1,3,6-octatriene. The proportion and composition of environmental volatile components in Tieguanyin tea changed during the fine manipulation process. Most of the volatile components showed obvious and regular changes. The seven shared volatile components could be considered as aroma indexes for judging intelligent fine manipulation.