Q exactive gc

Each sample (5 g) was chopped and put into a headspace vial with a 20 mL capacity and then placed in a robotic arm TriPlus RSH (CTC Analytics, Basel, Switzerland) autosampler incubation chamber and heated at 40 °C for 10 min for volatile compound enrichment. The extraction was performed using a headspace solid-phase microextraction (HS-SPME) extraction needle (50/30 μm DVB/CAR/PDMS Supelco, MA, USA) for 20 min. Using the GC-Orbitrap-MS system (Q Exactive GC, Thermo Fisher, MA, USA), the volatile chemicals were examined on a TG-5 column (0.25 × 0.25 × 0.32, 30 m, Fisher Scientific, MA, USA).
The GC-MS started out at 40 °C for 2 min and was then raised to 250 °C at a rate of 8 °C/min and held for 2 min, for a total running cycle of 32 min. The MS was run in positive electron impact ionization EI+ mode with a solvent delay for the first 0.5 min, scanning from ion mass fragments 35–475 m/z, an interscan delay of 0.1 s, and a resolution of 60,000 at FWHM (Full Width at Half Maximum). The carrier gas was helium of 99.996% purity (Shandong, China). The velocity of the helium gas was set at 1.2 mL/min.
For the retention times and retention index of volatile flavor compounds, we relied on computer matching with the reference of the MS library of NIST 14.0 (mass-spectral similarity match ≥ 80). By computing the percentages of GC peak regions, the compounds were given a numerical value.

GC-MS setup: GC-MS analysis was performed using a hybrid quadrupole-Orbitrap GC-MS/MS system (Q Exactive GC, ThermoFisher). The sample volume injected was 1 μL at a carrier gas flow rate of 1 mL/min of helium. The oven temperature was initially set to 50°C and held for 1 min, ramped up to 100°C at 10°C/min, and immediately ramped up to 200°C at 10°C/min and held for 1 min, then ramped up to 320°C at 10°C/min. The ion source temperature was set to 230°C. The scan range was 50.0 to 650.0 m/z, and the mass spectrum was acquired in electron ionization mode (70 eV).
The raw data from the GC-MS analysis were converted to ABF (Analysis Base File) format using analysis base file converter software, and peak detection, deconvolution, alignment, and filtering were performed to identify the metabolites based on the LUG database ((Untargeted database of GC–MS from Lumingbio)), removing all internal standards and false positive peaks. The raw data matrix of the sample information, retention times, and peak intensities was then exported to an Excel file for further analysis.

The GC-FID system used was 7890A GC (Agilent, Palo Alto, CA, USA) using a HP-5MS (30 m × 0.25 mm × 0.25 μm) column. The temperature gradient was set to 40°C, held for 2 min, increased linearly at 10°C/min until 320°C, and held for 5 min. The injections were 1 μL with a 1:20 split. The GC-HRMS system used was a QExactive GC (ThermoFisher, San Jose, CA, USA) set to acquire 30–550 m/z using a DB-5MS (30 m × 0.25 mm × 0.25 μm) column. The temperature gradient was set to 50°C, held for 2 min, increased linearly at 10°C/min until 300°C, and held for 3 min. The injections were 1 μL with a 1:10 split. The CI gas used was methane.