2.6. Short-Chain Fatty Acid (SCFA) Extraction and Determination
SEPARATION
Short-chain fatty acids consisting of acetic, propionic, and butyric acids were extracted as the method previously described [A sample separation was performed by using gas chromatography. SCFA separation was carried out by a Bruker 450 GC Rtx-5MS Capillary column (Bruker, Billerica, MA, USA) (30 m × 0.25 mm × 0.25 µm). The column temperature was held at a temperature of 45 °C for 2 min and raised to 250 °C at a rate of 4.5 °C/min. Thereafter, an aliquot of sample at a volume of 1 μL was injected at a split ratio of 100. Helium gas was used as carrier at a flow rate of 1 mL/min. Regarding mass spectroscopy, the temperatures of the electron source and the quadrupole were held at 230 °C and 150 °C, respectively. The energy of electron ionization was set at 70 eV. An analysis was performed in full scan mode from 