*2.8. Analyses of SCFAs*

SCFA contents, including acetic, propionic, butyric, valeric, isobutyric, and isovaleric acids in the fermentation fluids, were analyzed by using gas chromatography (GC; Shimadzu G2010Plus, Kyoto, Japan) on a DB-FFAP chromatographic capillary column (30 m × 0.530 mm × 1.00 μm; Agilent, Santa Clara, CA, USA), with calculated standard curves based on the method described in Tian et al. [26], with minor modifications. A total of 200 μL of the fermentation samples was mixed with 200 μL of 0.3 mg/mL 2-ethylbutyric acid and 50 μL of 0.15 M oxalic acid. The mixture was filtered at 0.22 μm into a vial for analysis.
