## 2 Materials and Methods
### Determination of Volatile Aroma Compounds by HS-SPME-GC-MS  
With reference to the modified approach of [PERSON] et al. (2018), the HS-SMPE-GC-MS method was used to determine the accumulation of volatile compounds in the flat peaches [43]. An amount of 4.5 g of lyophilized powder and 0.5 g of NaCl were loaded into a 20 mL headspace vial, then 2 uL of 330 ug/kg 3-octanol solution was added as the internal standard. Next, in a magnetic stirrer (HS-40, IKA, Germany), the capped headspace vial to which the sample to be measured was added was equilibrated at 45 \({}^{\circ}\)C and 300 r/min for 15 min using a magnetic rotor. The extraction SPME fibers, which were activated at 250 \({}^{\circ}\)C for 2 h, were selected from a divinylbenzene/carboxyl1/polydimethylsiloxane (DVB/CAR/PDMS, 50/30 \(\upmu\)m, StableFlex, Supelco, Bellefonte, PA, USA) extraction head. Finally, the extraction head was inserted into a headspace vial at 40 \({}^{\circ}\)C for 45 min at 300 rpm.  
The volatile compounds in the flat peaches were evaluated by the Agilent 7000D-GC-MS detector (Agilent Technologies Inc., Santa Clara, CA, USA) and separated by the HP-Innowax column (30 m \(\times\) 0.25 mm \(\times\) 0.25 \(\upmu\)m, Agilent Technologies Inc., Santa Clara, CA, USA). The extraction head was desorbed in the GC feeder for 7 min at 250 \({}^{\circ}\)C in non-split mode after the extraction operation. The column oven temperature was set to 230 \({}^{\circ}\)C in non-split injection mode. Helium was selected as the mobile phase and the ramp-up procedure was initiated at a constant flow rate of 1 mL/min, using 40 \({}^{\circ}\)C as the initial temperature, and held for 5 min. The temperature was then steeply increased to 86 \({}^{\circ}\)C at 4 \({}^{\circ}\)C/min and held for 5 min, then to 90 \({}^{\circ}\)C at 1.5 \({}^{\circ}\)C/min, to 180 \({}^{\circ}\)C at 5 \({}^{\circ}\)C/min and held for 3 min, and then steeply increased to 230 \({}^{\circ}\)C at 10 \({}^{\circ}\)C/min and held at 230 \({}^{\circ}\)C for 2 min before cooling back to 40 \({}^{\circ}\)C. Total ion chromatograms (TICs) were generated using an electron impact (EI) ionization mode with an ionization energy of 70 eV, mass spectrometry scan conditions set to a range of 35 to 350 m/z, a speed of 5 scans per second, and an ionization source temperature set to 270 \({}^{\circ}\)C.  
The chromatograms of the isolated compounds were compared using the NIST spectral library (NIST 14, National Institute of Standards and Technology, Gaithersburg, MD, USA) and combined with the mass spectral library of Wiley 6 for the preliminary identification of volatile compounds in the flat peaches. Only identified compounds with a threshold match of more than 85% were selected. To improve the accuracy of substance matching, the retention time (RT) was also compared with its associated retention index (RI). A semi-quantitative method was used to calculate the relative concentrations of the volatile compounds identified in the flat peaches, using the peak areas of the internal standards as a benchmark. Further confirmation of the discriminant substances for the extent to which the compounds contribute to the aroma of the fruits was performed by calculating the OAVs of discriminant substances in flat peach based on the OT of volatile compounds in water. The OT referenced in this study was derived from the literature on previous studies [44; 45; 46; 47].