Inhibitory combinations of nisin, sodium chloride, and pH on Listeria monocytogenes ATCC 15313 in broth by an experimental design approach

The influence of pH (5.0–8.2), NaCl concentrations (0–6% w/v), and incubation time (0–24 h) on the inhibitory activity of nisin (0–100 I.U./ml) against Listeria monocytogenes (103 cfu/ml) was studied using the Doehlert experimental design and was confirmed by kinetic experiments. Predicted values were in agreement with experimental values. Experiments were carried out at 22°C in reconstituted TSB–YE1 broth with or without NaCl. Nisin had an immediate pH-dependent bactericidal effect, which increased with decreasing pH values. In modified TSB–YE1 broth without NaCl, the bactericidal efficacy of nisin (50 I.U./ml) was maximum at pH 6.6, with no L. monocytogenes survivors until 120 h at 22°C. Nisin (50 I.U./ml) action decreased in the presence of NaCl, with a minimal inhibitory effect between 2 and 4%. This partially protective effect was cancelled at higher levels of nisin.