The pure cultures were initially propagated on Lactobacillus MRS broth (BDH, Montréal, Canada) pH 5.5–5.7, and frozen at −70°C in 1 ml sterile cryogenic vials (Nalgene) containing 0.2 ml of the MRS-grown cells, 0.4 ml of 10% glycerol (BDH) and 0.4 ml 20% non-fat milk. Fresh inocula of these pure cultures were prepared by adding a 1 ml thawed cell suspension to 99 ml of MRS broth, and incubating at 30°C for 16 h. The commercial freeze-dried mixed cultures were rehydrated in either a 2% salt solution or the PTM medium composed of 15 g/l peptone, 10 g/l tryptone and 5 g/l meat extract. The freeze-dried culture was added to the rehydration medium in a 1:4 ratio and incubated for 10 min at 23°C. Unless otherwise stated, the PTM-rehydrated suspension was used to inoculate MRS broth, which was subsequently incubated as for the pure cultures.