Identification of volatiles derived from Citrobacter freundii fermentation of a trypticase soy broth

Twenty-two compounds emanated as volatiles from an 8-day fermentation of trypticase soy broth by Citrobacter freundii, American Type Culture Collection (ATCC 8090), were identified by dynamic headspace analysis techniques. Compound identifications were made on the basis of a comparison of Kovats indices and GC/MS spectra for unknowns and authentic samples. Of the compounds identified, nine were pyrazines, four were alcohols, two were aldehydes, two were ketones, two were esters, two were sulfides, and one was phenol. In decreasing order, the five most abundant compounds in the volatiles were 3-methyl-1-butanol (91.1%), phenol (5.00%), 2,5-dimethylpyrazine and phenethyl alcohol (each 1.18%), and 2-methyl-1-propanol (0.38%). Low molecular weight amines (ammonia, methyl- and ethylamine) were not detected in the volatiles. Pyrazines identified in the bacteria-produced supernatant (BPS) were generated almost exclusively by heating (autoclaving) the broth; their formation did not seem to be influenced by bacterial action. Laboratory bioassay of 4- and 8-day BPS derived from C. freundii against mixed sexes of adult Mexican fruit flies, Anastrepha ludens, showed the supernatants were comparable in attractancy to a 30% NuLure solution.