Quantification of Short-Chain Fatty Acids by GC-FID

The production of short-chain fatty acids (SCFAs; butyrate, acetate, and propionate) in fermentation samples from all sub-reactors was determined using Gas Chromatography coupled to Flame Ionization Detector (GC-FID) (Shimadzu GC-2030) as previously described [10 (link)]. In brief, supernatants collected from fermentation samples were centrifuged (14,000 g, 30 min, 4 °C) and filter sterilized (0.22 µm). 2-ethyl butyric acid was used as an internal standard and added to each sample at a concentration of 0.5 mM. Around 100 µL of each sample was injected in a capillary column Stabilwax-DA (60 m × 0.25 µm; Restek) with a run time of 20 min. The peaks were identified and quantified with standards from MilliporeSigma (Oakville, ON, Canada). Results were expressed as the concentration of SCFAs in mM. All samples were analyzed in duplicates (two technical measures).