Bacterial samples were prepared by measuring the absorbance
of the incubated bacterial suspension at OD600 nm. At an absorbance
reading of 0.132 (equivalent to 0.5 McFarland units) an
aliquot of 100mL of bacterial suspension (1–1.5 107 CFU) was
added to a 20 ml clear vial containing 9 ml LEB with 50mg ml1
cycloheximide, 40mg ml1 nalidixic acid, 15mg ml1 acriflavine
HCl, 100mg ml1 2-nitrophenyl-b-D-glucoside and 20mg ml1
2-[(3-fluorophenyl) carbamoylamino]acetic acid. Then, 0.9 ml
whole cow's milk was added to the inoculated LEB. Preparation
of all bacterial samples followed this procedure. All samples were
incubated overnight at 37 C and then subjected to volatile
profiling via HS-SPME GC–MS. Uninoculated LEB with selective
agents, whole cow's milk plus added substrates was tested every
day of sampling.