Gas chromatographic-mass spectral studies after methylation of metabolites produced by some anaerobic bacteria in spent media.

The gas chromatographic analysis of metabolites such as volatile fatty acids (VFAs) and non-volatile fatty acids (NVFAs) for identification of anaerobic bacteria is now widely performed. Cultures of anaerobes tested for NVFAs as methyl esters were found to contain several unidentified compounds not previously detected and/or reported with methylation procedures. Gas chromatographic-mass spectrometric studies demonstrated that these compounds correspond to the methyl esters of both saturated and unsaturated short-chain fatty acids, and also of 2-hydroxy and 2-oxo acids. The distribution of these acids among different species of anaerobes was determined and their amounts were measured. The effects of supplementing the culture medium with either glucose or amino acids on the production of these acids are described. The use of very polar stationary phases is suggested for a better separation of all NVFAs.