Fig. 4

Detected relative amounts of leucine and phenylalanine fermentation products in stationary phase. a White bars: isocaproate, grey bars: isovalerate. Determined in non-derivatized samples after ether extraction by GC/MS, peak areas were determined using MetaboliteDetector software and were normalized on the relative proportion of the specific quantification ion and the internal standard o-cresol added prior to extraction. b White bar, 3-phenylpropanoate, grey bar, phenylacetate. Determined in derivatized samples after drying by GC/MS. Peak areas were determined using MetaboliteDetector software and were normalized on ribitol and the relative proportion of the specific quantification ion added as internal standard prior to drying procedure. We cannot exclude differences of the two compounds during extraction, drying or derivatization procedures