## 2 Material and Methods
### GC-O and GC-MS Analysis  
An Agilent 7890A GC (Agilent Technologies, Palo Alto, CA, USA) equipped with an FID and a sniffing port (Sniffer 9000, Brechbuhler, Switzerland) was used for GC-O analysis. An Agilent capillary column HP-SMS (30 m \(\times\) 0.25 mm i.d., 0.25 \(\upmu\)m film thickness; Agilent Technologies, Palo Alto, CA, USA) was used for the separation of target compounds. The conditions of the GC were set as follows: initial temperature 50 \({}^{\circ}\)C (3 min), increased to 180 \({}^{\circ}\)C at a rate of 3 \({}^{\circ}\)C min\({}^{-1}\) and maintained for 5 min, and then increased to 250 \({}^{\circ}\)C at a rate of 10 \({}^{\circ}\)C min\({}^{-1}\), and maintained for 5 min; the temperature of the injection port, the injection mode and the flow velocity of carrier gas (constant-flow mode; He > 99.999%) were 250 \({}^{\circ}\)C, splitless, and 1.0 mL min\({}^{-1}\), respectively. The conditions of olfactometry were set as follows: the flow of humidified air was 60 mL min\({}^{-1}\) and the temperature of the transfer line was 250 \({}^{\circ}\)C. A \"Y\" glass was used between the FID detector and the sniff port to split the GC effluent into 1:1.  
In total, 6 assessors (4 males and 2 females, average age 32, non-smoking history, odor cosmetics were not used during the experiments) were selected from Yunnan Tasty Deepure Biological Tea Group Co., Ltd. (Pu'er, Yunnan, China) and Pu'er Institute of Pu-erh Tea among 17 experienced tea experts in accordance with the International Standard method [20] to perform GC-O analysis. Before the experiment, all selected assessors were trained for more than 20 h over a period of 30 d using 13 odor-active standards [\(\alpha\)-terpineol, linalool, (\(E\))-nerolidol, (3\(Z\))-3-hexenyl 2-methylbutanoate, hexanal, 2-hexenal, methyl salicate, phenylethyl alcohol, \(\alpha\)-ionone, \(\beta\)-ionone, geraniol, (\(E\))-\(\beta\)-damascenone and 1-octen-3-ol], which were detected in SBT, until all the assessors could quickly describe the aroma characteristics and aroma intensities of all selected odor compounds at their different diluted concentrations. The detection frequency method was used to analyze the aroma characteristics and aroma intensities of each effluent in GC-O analysis. A 9-point scale from 1 to 9, wherein \"1\", \"5\", and \"9\" indicated the weakodor, moderate odor, and extreme odor intensity, respectively, was used to quantify odor intensities of the effluents. During the experiments, the odor characteristics and odor intensities of the effluents were recorded and scored, respectively. Finally, the odor intensity value of each detected odor-active compound was averaged for all the scores that were detected by six assessors (three times by each assessor). After GC-O analysis, all the samples were analyzed by using GC-MS under the same capillary column, and the perceived scents were identified by the retention indices (calculated by using n-alkanes from C\({}_{8}\) to C\({}_{32}\)) between the GC-O and the GC-MS, the mass spectra database (NIST11.L) of GC-MS, the odor characteristic of each odor-active compound, and corresponding standard of each odor-active compound.  
The conditions of GC-MS were listed as follows: an Agilent 7890A GC equipped with 5975C mass selective detector quadrupole MS instrument (Agilent Technologies, Palo Alto, CA, USA) was used to identify the perceived odor-active compounds. The conditions of GC (injector temperature, oven temperature program, the kind of carrier gas, and the flow rate of carrier gas) and the model capillary column were the same as described under GC-O analysis. The electron-impact (EI), interface temperature, ion source temperature, quadrupole temperature, mass scan range, and solvent delay time were 70 eV, 280 \({}^{\circ}\)C, 230 \({}^{\circ}\)C, 150 \({}^{\circ}\)C, 35-450 aum, and 3.0 min, respectively.