## 2 Materials and Methods
### Detection and Analysis of Volatile Compounds by GC-MS  
Headspace solid-phase microextraction (SPME, Agilent, Palo Alto, CA, USA) combined with GC-MS (8890-7000D, Agilent) was used to identify metabolites in the analytical samples. Each dry tea sample was quickly removed from an ultra-low temperature refrigerator at \(-80\)\({}^{\circ}\)C and thoroughly ground into powder using a ball mill (MM400, Retsch, Haan, Germany) under the protection of liquid nitrogen. Then, 500 mg of dry tea sample was weighed and placed in a 20 mL headspace bottle (Agilent) and 1 mL of saturated NaCl solution and 10 \(\upmu\)L 3-Hexanone isotope (3-Hexanone-2,2,4,4-d4, CAS: 24588-54-3) were quickly added as the internal standard solution. Finally, the bottle cap was tightened and 3 replicates for each sample were weighed. We used CTC Analytics AG equipment (PAL RSI 120, Basel, Switzerland). Under constant temperature conditions of 60 \({}^{\circ}\)C, the sample was shaken for 5 min, and a 120 \(\upmu\)m DVB/CWR/PDMS extraction head was inserted into the headspace bottle of the sample. It was extracted in the headspace for 15 min, analysed at 250 \({}^{\circ}\)C for 5 min, and then GC-MS separation and identification were performed. Before sampling, the extraction head was aged for 5 min at 250 \({}^{\circ}\)C in a Fibre Conditioning Station(note: a new extraction head should be aged at 250 \({}^{\circ}\)C in a Fibre Conditioning Station for 2 h before extraction). Additionally, it used SPME Arrow, which had a sensitivity of up to 10 times that of traditional SPME fibre heads.  
The identification and the quantification of the volatile components were conducted using an Agilent Model 8890 GC and a 7000 D mass spectrometer (Agilent) equipped with a 30 m \(\times\) 0.25 mm \(\times\) 0.25 \(\upmu\)m DB-5 MS (5% phenyl-polymethylsiloxane) capillary column. The carrier gas was helium (99.999% purity) at a flow rate of 1.2 mL/min. The injector temperature was maintained at 250 \({}^{\circ}\)C, and the detector was 280 \({}^{\circ}\)C. The oven temperature was programmed from 40 \({}^{\circ}\)C (3.5 min) to 100 \({}^{\circ}\)C increasing at 10 \({}^{\circ}\)C/min, and then to 180 \({}^{\circ}\)C at 7 \({}^{\circ}\)C/min, and finally, to 280 \({}^{\circ}\)C at 25 \({}^{\circ}\)C/min and kept for 5 min.  
The MS operating parameters were as follows: electron impact (EI) ionisation mode, 70 eV; ion source temperature, 230 \({}^{\circ}\)C; quadrupole mass detector, 150 \({}^{\circ}\)C; and transfer line temperatures, 280 \({}^{\circ}\)C. The selected ion monitoring (SIM) mode between \(m/z\) 30 and 500 was used for the identification and quantification of analysis based on self-built databases (Metware Biotechnology Co., Ltd., Woburn, MA, USA).  
During the analysis process, the fingerprint MS of the sample was matched and compared with the reference MS in the database for scoring and qualitative analysis, and the retention index information was referenced to increase the accuracy of qualitative analysis. MassHunter tool (Agilent) was used to process mass spectrometry files and select quantitative ions for integration and calibration processing. The retention index (RI) range was defined between (RI target\(-\) threshold) and (RI target\(+\) threshold), and the threshold was set as 60. All the detected volatiles within the RI range were selected as candidates [4].