GC-MS spectra of acetic and butyric acids present in the culture broth of C. tyrobutyricum ATCC 25755Tafter culturing for 40 h in P2 medium with 12C
-glucose (40.0 g/L) and [1,2,3-13C
] lactic acid (5.0 g/L). A) Mass spectra of butyric acid showing the presence of significant amounts of butyric acid with molecular weights higher than 88 (i.e.: 89, 90, 91 and 92) indicating the corporation of 13C. B) Mass spectra of acetic acid showing the absence of 13C in the acetic acid.