Figure 3. SCFA production by each of the 17 strains. Liquid chromatography-electrospray ionization-tandem mass spectrometry (LC–ESI-MS/MS) analysis of short chain fatty acid metabolites was performed on 48 h cultures of peptone-yeast extract-Fildes solution supplemented with glucose at a concentration of 1% (w/v). Fatty acids in the culture supernatant were derivatized with 2-nitrophenylhydrazine and purified by liquid/liquid extraction.28 Short chain fatty acid peaks were identified by both their specific MS/MS ion-transitions and comparison of the retention times with those of known short chain fatty acids in a standard solution.