2.4.4. Determination of SCFA Content during Fermentation

The supernatant of the fermentation broth was passed through a 0.22 μm filter membrane, and then the composition and content of the SCFAs were determined using gas chromatography [19]. The chromatographic analysis was carried out on an Agilent 6890N gas chromatograph (Agilent Technologies, Santa Clara, CA, USA) and an HP-INNOWAX column (0.32 mm × 30 m, 0.25 μm Agilent Technologies, Santa Clara, CA, USA). The GC conditions were an FID detector with N₂ carrier gas. The flow rate of N₂ was 19.0 mL/min, and the split ratio was 1:10. The airflow rate was 300 mL/min, and the H2 flow rate was 30 mL/min. The temperature of the detector and the injector was 240 °C. The heating procedure was conducted from 100 °C (0.5 min) to 180 °C (4 °C/min). The sample injection volume was 1 µL, and the determination time was 20.5 min. Data were analyzed using HP Chem workstation software (A.09, Agilent). The content of SCFAs was calculated with a standard curve as shown in Table S2.